Advertisement

Pseudomonas aeruginosa in CF and non-CF homes is found predominantly in drains

Open ArchivePublished:November 28, 2014DOI:https://doi.org/10.1016/j.jcf.2014.10.008

      Abstract

      Background

      For patients with cystic fibrosis (CF) Pseudomonas aeruginosa infection is a major contributor to progressive lung disease. While colonizing strains are thought to be primarily environmental, which environments are important in lung colonization is unclear.

      Methods

      We took 11,674 samples from a broad range of sites over 3–8 visits to homes with (7) and without (8) CF patients.

      Results

      Twenty-eight percent of sampled drains yielded P. aeruginosa at least once, and a general mixed linear model estimated that 6.3% of samples from drains yield P. aeruginosa. This is more than eight times the estimated recovery from any other type of household environment.

      Conclusions

      These findings implicate drains as important potential sources of P. aeruginosa infection. They suggest that maximizing P. aeruginosa control efforts for drains would reduce exposure with minimal extra burden to CF patients and families.

      Keywords

      Pseudomonas aeruginosa infection is a leading cause of morbidity in cystic fibrosis (CF) patients. P. aeruginosa can be transmitted between siblings [
      • Renders N.H.M.
      • Sijmons M.A.F.
      • vanBelkum A.
      • Overbeek S.E.
      • Mouton J.W.
      • Verbrugh H.A.
      Exchange of Pseudomonas aeruginosa strains among cystic fibrosis siblings.
      ,
      • Tubbs D.
      • Lenney W.
      • Alcock P.
      • Campbell C.A.
      • Gray J.
      • Pantin C.
      Pseudomonas aeruginosa in cystic fibrosis: cross-infection and the need for segregation.
      ] and patient-to-patient transmission can occur in clinical settings and in camps for CF children [
      • Cheng K.
      • Smyth R.L.
      • Govan J.R.W.
      • Doherty C.
      • Winstanley C.
      • Denning N.
      • et al.
      Spread of beta-lactam-resistant Pseudomonas aeruginosa in a cystic fibrosis clinic.
      ,
      • Denton M.
      • Kerr K.
      • Mooney L.
      • Keer V.
      • Rajgopal A.
      • Brownlee K.
      • et al.
      Transmission of colistin-resistant Pseudomonas aeruginosa between patients attending a pediatric cystic fibrosis center.
      ,
      • McCallum S.J.
      • Gallagher M.J.
      • Corkill J.E.
      • Hart C.A.
      • Ledson M.J.
      • Walshaw M.J.
      Spread of an epidemic Pseudomonas aeruginosa strain from a patient with cystic fibrosis (CF) to non-CF relatives.
      ,
      • Jones A.M.
      • Govan J.R.W.
      • Doherty C.J.
      • Dodd M.E.
      • Isalska B.J.
      • Stanbridge T.N.
      • et al.
      Identification of airborne dissemination of epidemic multiresistant strains of Pseudomonas aeruginosa at a CF centre during a cross infection outbreak.
      ,
      • Scott F.W.
      • Pitt T.L.
      Identification and characterization of transmissible Pseudomonas aeruginosa strains in cystic fibrosis patients in England and Wales.
      ,
      • Ojeniyi B.
      • Frederiksen B.
      • Hoiby N.
      Pseudomonas aeruginosa cross-infection among patients with cystic fibrosis during a winter camp.
      ]. However, initial infections are frequently found to be genetically more similar to isolates collected from environmental sources compared to those from chronically infected CF patients [
      • Burns J.L.
      • Gibson R.L.
      • McNamara S.
      • Yim D.
      • Emerson J.
      • Rosenfeld M.
      • et al.
      Longitudinal assessment of Pseudomonas aeruginosa in young children with cystic fibrosis.
      ,
      • Rau M.H.
      • Marvig R.L.
      • Ehrlich G.D.
      • Molin S.
      • Jelsbak L.
      Deletion and acquisition of genomic content during early stage adaptation of Pseudomonas aeruginosa to a human host environment.
      ,
      • Jelsbak L.
      • Johansen H.K.
      • Frost A.L.
      • Thogersen R.
      • Thomsen L.E.
      • Ciofu O.
      • et al.
      Molecular epidemiology and dynamics of Pseudomonas aeruginosa populations in lungs of cystic fibrosis patients.
      ,
      • Workentine M.
      • Surette M.G.
      Complex Pseudomonas population structure in cystic fibrosis airway infections.
      ]. This indicates that the source of these initial infections is likely somewhere in patients' everyday environments. In this study we examine sites within the human home, an important component of patients' environments, with respect to rate of recovery of this important pathogen.
      P. aeruginosa is often referred to as “global” or “ubiquitous” [
      • Kapatral V.
      • Bina X.W.
      • Chakrabarty A.M.
      Succinyl coenzyme A synthetase of Pseudomonas aeruginosa with a broad specificity for nucleoside triphosphate (NTP) synthesis modulates specificity for NTP synthesis by the 12-kilodalton form of nucleoside diphosphate kinase.
      ,
      • Goldberg J.B.
      Pseudomonas: global bacteria.
      ,
      • Stover C.K.
      • Pham X.Q.
      • Erwin A.L.
      • Mizoguchi S.D.
      • Warrener P.
      • Hickey M.J.
      • et al.
      Complete genome sequence of Pseudomonas aeruginosa PAO1, an opportunistic pathogen.
      ]. However, few studies have examined it systematically in environments or at a scale relevant to young CF patients. Ojima et al. [
      • Ojima M.
      • Toshima Y.
      • Koya E.
      • Ara K.
      • Kawai S.
      • Ueda N.
      Bacterial contamination of Japanese households and related concern about sanitation.
      ] Regnath et al. [
      • Regnath T.
      • Kreutzberger M.
      • Illing S.
      • Oehme R.
      • Liesenfeld O.
      Prevalence of Pseudomonas aeruginosa in households of patients with cystic fibrosis.
      ] and Schelstraete et al. [
      • Schelstraete P.
      • Van Daele S.
      • De Boeck K.
      • Proesmans M.
      • Lebecque P.
      • Leclercq-Foucart J.
      • et al.
      Pseudomonas aeruginosa in the home environment of newly infected cystic fibrosis patients.
      ] focused on the interior (primarily bathrooms/washrooms and kitchens) of CF patient homes. In an earlier study, we examined a large number of outdoor and indoor sites, but only in homes without CF patients [
      • Remold S.
      • Brown C.
      • Farris J.
      • Hundley T.
      • Perpich J.
      • Purdy M.
      Differential habitat use and niche partitioning by Pseudomonas species in human homes.
      ]. Mortensen et al. [
      • Mortensen J.E.
      • Fisher M.C.
      • Lipuma J.J.
      Recovery of Pseudomonas cepacia and other Pseudomonas species from the environment.
      ] examined homes both with and without a resident with CF, but focused on a limited set of kitchen, bathroom and laundry related sites.
      Here we present an analysis of P. aeruginosa recovery from a broad range and large number of types of sites in human homes. The study was part of a 4.5-year larger effort to examine bacteria from the genus Pseudomonas. We compare recovery of P. aeruginosa in homes with and without a patient with CF in residence, and we test for seasonal variability in recovery and in persistence in household sites over multiple samplings. We identify sites from which P. aeruginosa are most frequently recovered; we anticipate that these are potential environmental sources of P. aeruginosa infection whose identification may inform strategies to minimize patient exposure to household P. aeruginosa.

      1. Materials and methods

      1.1 Sampling

      We analyzed frequency of recovery of P. aeruginosa. We took 11,674 samples using saline-moistened sterile swabs from 123 types of sites in and around the home and from the people and pets residing there. The collection of sites sampled (Supplemental Table 1) was designed to be diverse, but did not include all types of sites from which Pseudomonas have been reported to be recovered (e.g. washing machines, air samples or tap water samples). None of the homes contained Jacuzzis or hydrotherapy pools, types of sites from which P. aeruginosa has not only been detected, but from which colonization of patients has been documented [
      • Govan J.
      • Nelson J.
      Microbiology of lung infection in cystic fibrosis.
      ]. Swabs were streaked onto Pseudomonas isolation agar (PIA). We prepared this media according to the formulation in the Product Information of the REML Pseudomonas Isolation Agar (R454391). This is a modification of Kings A media [
      • King E.O.
      • Ward M.K.
      • Raney D.E.
      Two simple media for the demonstration of pyocyanin and fluorescin.
      ] in that 25 mg/L of the broad spectrum antibiotic Irgasan is added.
      Sampling took place in 15 households in the Louisville, KY (USA) metropolitan area between October 2007 and March 2012, between 3 and 8 times per household, on average every 4.6 months. Seven households included a child with CF and 8 had no CF patients. All households with a CF patient were recruited through the Pediatric CF Center at the University of Louisville. Federal and institutional guidelines and policies, including informed consent and assent, where appropriate, were approved by the Institutional Review Board. Sampling of animal subjects was approved by the Institutional Animal Care and Use Committee. Five of the seven patients had positive P. aeruginosa cultures from upper respiratory sites at least once during the course of the study.
      P. aeruginosa were identified by comparing at least 500 bp 16 s rDNA sequences of all isolates obtained with two databases: Bioinfo 1200 nucleotide and EzTaxon [
      • Chun J.
      • Lee J.-H.
      • Jung Y.
      • Kim M.
      • Kim S.
      • Kim B.K.
      • et al.
      EzTaxon: a web-based tool for the identification of prokaryotes based on 16S ribosomal RNA gene sequences.
      ,
      • Croce O.
      • Chevenet F.
      • Christen R.
      A new web server for the rapid identification of microorganisms.
      ], and were confirmed using primers that selectively amplify P. aeruginosa [
      • Spilker T.
      • Coenye T.
      • Vandamme P.
      • LiPuma J.J.
      PCR-based assay for differentiation of Pseudomonas aeruginosa from other Pseudomonas species recovered from cystic fibrosis patients.
      ]. This sequence-based approach was chosen to avoid possible misidentification that might arise were environmental strains to differ phenotypically from the mostly clinical strains that were used to establish and validate the more rapid detection techniques.

      1.2 Statistical analysis

      Data were analyzed using generalized linear mixed models (PROC GLIMMIX, SAS/STAT 9.3 [
      • SAS Institute I
      SAS/STAT® 9.3 User's Guide.
      ) and also with Fisher's exact tests when recovery rates were too low to allow convergence of the mixed models. Sampled sites were binned into “environment types” (Supplemental Table 1), and sampling dates were binned into “sampling periods” (which season of which year, with seasons defined as: winter, December–February; spring, March–May; summer, June–August; fall, September–November). Using a general linear mixed model, we modeled presence/absence of P. aeruginosa as the binary response variable, environment type, sampling period and house type (whether a CF patient resides in the home or not) as fixed predictor variables, house nested in house type and its interaction with environment and sampling period as random factors, and we accommodated repeated samplings of individual sampled sites at different sampling periods using an autoregressive order 1 R-side covariance structure. We used least squares means estimates to calculate the probability of recovery for each environment and season with 95% confidence intervals.

      2. Results

      2.1 Recovery from Humans and Pets

      We sampled mouth, throat, and nose, of all humans and pets, and asked all human subjects to cough onto PIA plates. We sampled skin sites and obtained fecal and genital samples from humans and fecal samples from pets (Supplemental Table 1). With the exception of samples taken from upper-respiratory sites from CF patients, rates of recovery from humans were very low (Table 1). Of the 863 samples taken from pets in this study (3 birds, 7 cats, 13 dogs), none yielded P. aeruginosa.
      Table 1P. aeruginosa recovery from humans by CF status and sample site type.
      CF patient
      Whether person had been diagnosed with CF.
      CF home
      Whether person lived in a home with a person with CF.
      Fecal/genital
      Types of sites from which samples were taken. Numbers outside parentheses give fraction of persons from whom P. aeruginosa was ever recovered; numbers within parentheses give fraction of samples from which P. aeruginosa was recovered.
      Skin
      Types of sites from which samples were taken. Numbers outside parentheses give fraction of persons from whom P. aeruginosa was ever recovered; numbers within parentheses give fraction of samples from which P. aeruginosa was recovered.
      Upper respiratory
      Types of sites from which samples were taken. Numbers outside parentheses give fraction of persons from whom P. aeruginosa was ever recovered; numbers within parentheses give fraction of samples from which P. aeruginosa was recovered.
      NoNo0/16 (0/73)1/27 (1/148)1/27 (3/148)
      NoYes1/10 (1/43)1/23 (1/151)0/23 (0/151)
      YesYes1/5 (1/19)0/7 (0/48)5/7 (14/48)
      a Whether person had been diagnosed with CF.
      b Whether person lived in a home with a person with CF.
      c Types of sites from which samples were taken. Numbers outside parentheses give fraction of persons from whom P. aeruginosa was ever recovered; numbers within parentheses give fraction of samples from which P. aeruginosa was recovered.

      2.2 CF and non-CF houses do not differ except in recovery from patients

      Very low recovery rates precluded using generalized mixed linear models in analysis of recovery from humans. We therefore considered whether P. aeruginosa was ever recovered from a particular person's fecal/genital samples, skin samples, or upper respiratory samples (Table 1). Fisher's exact tests reveal no differences in recovery from non-patients sharing a home vs. not sharing a home with a CF patient. Though upper respiratory samples from CF patients yielded more P. aeruginosa than upper respiratory samples from non-patients, CF patients and non-patients, even from the same households, did not differ in rates of recovery from skin or fecal/genital samples (Table 1). Furthermore, in all analyses of P. aeruginosa recovery from environmental sites (see below), general linear mixed models detected no differences in rates of recovery of environmental samples between houses with and without a patient with CF (p = 0.65, model of all sampling for free-living P. aeruginosa; p = 0.83 and 0.13, sub-models considering only indoor samplings or only drain sampling respectively).

      2.3 Recovery is highest from drains

      Overall rates of recovery of P. aeruginosa were quite low: from 6494 environmental samples taken, 93 P. aeruginosa were recovered. A general linear mixed model found significantly more P. aeruginosa in drains than in all other environment types (Fig. 1). In all, 28% of the drains sampled yielded P. aeruginosa at least once, and a general mixed linear model estimated the probability of recovering P. aeruginosa from a drain at any single time to be 6.3% (these numbers differ in part because most drains did not yield P. aeruginosa at all samplings). Furthermore, all but two households contained at least one drain that yielded P. aeruginosa. Both of these households included a family member with CF. Different types of drains did not differ in recovery rates, according to a sub-model comparing kitchen sink, bathroom sink and bathtub drains (sub-model excludes fall 2010 drain samplings, in which no P. aeruginosa were recovered, because their inclusion causes the model to fail to converge; p = 0.29).
      Figure thumbnail gr1
      Fig. 1Probability and 95% CI of P. aeruginosa recovery as calculated from mixed general linear model with P. aeruginosa recovery as the response variable, environment type, house type and sampling period as fixed predictor variables, house nested within house type and its interactions with environment type and sampling period as random factors, and repeated measures of particular sites across sampling periods modeled with an autoregressive order 1 function. Assignment of 94 types of sites to environment types given in Suppl. Table 1. Each letter that appears multiple times designates pairs of environment types that did not differ significantly; those that differed significantly (p < 0.05 after Tukey correction for multiple comparisons) do not share letters.
      Recovery from garbage and compost was higher than for the remaining types of sites but was almost an order of magnitude lower than for drains. Recovery from all other environment types was extremely low, including from water samples (e.g. toilets, pet water bowls, humidifiers; 0.0015) and samples taken by inserting swabs into houseplant and outdoor soils (0.0005) (Fig. 1).

      2.4 Temporal patterns in recovery

      We examined the patterns of recovery across samplings (which were spaced an average of 4.6 months apart) at individual sites. We found that recovery of P. aeruginosa at one sampling was significantly correlated with recovery in the previous sampling (p < 0.0001, autoregressive order 1 covariance structure in generalized linear mixed model), and this significant correlation held when considering only drain sites. This relationship could not be tested for non-drain samples due to failure of model convergence. We considered the subset of drains (50) that were sampled 8 times, looking at the number of samplings at which each drain site yielded P. aeruginosa relative to an expected distribution assuming no correlations in recovery, using a randomization test. We found that there were significantly fewer sites than expected with only one recovery (p = 0.038, and an overrepresentation of sites with four (p = 0.007) and 8 (p < 0.001). Among the 1358 non-drain sites, 21 yielded P. aeruginosa only once, and two bath toys (from different houses) yielded P. aeruginosa twice each.
      When considering all environment types, seasons differed in recovery (p = 0.04, linear contrast of sampling periods). This was driven by significantly higher recovery in the fall than in the winter. A sub-model considering only indoor samples (excludes samples taken from water, because failure to recover any P. aeruginosa from indoor water samples causes failure of the model to converge) found marginally significant differences among seasons (p = 0.08) driven by higher recovery in fall than in winter and spring. Although there was a trend toward higher recovery from drains in fall, this trend was not statistically significant (p = 0.18, drain sampling sub-model).

      3. Discussion

      The central finding of this study is that rather than being consistent with P. aeruginosa being ubiquitous we found that those P. aeruginosa not isolated from upper respiratory samples of CF patients were primarily recovered from drains. Indeed, a number of sites commonly named as important sources of P. aeruginosa yielded little or no recovery, including soil and water, surfaces such as counters and produce, non-upper respiratory sites from CF patients, and pets.
      Soils and water sources yielded very few isolates. We note that the low recovery of P. aeruginosa from soil is not due to a failure to detect Pseudomonas with our sampling technique; in a previous study in which we used the same sampling technique, we recovered strains of Pseudomonas from 49% of soil samples [
      • Remold S.
      • Brown C.
      • Farris J.
      • Hundley T.
      • Perpich J.
      • Purdy M.
      Differential habitat use and niche partitioning by Pseudomonas species in human homes.
      ], and among the soil samples taken in this effort, 44% yielded some Pseudomonas (data not shown). A caveat that we cannot rule out is that the soil microhabitat preferences specific to P. aeruginosa result in low recovery using our sampling approach.
      The surfaces of food sources, particularly fresh produce, have been cited as potential sources for P. aeruginosa,[
      • Mortensen J.E.
      • Fisher M.C.
      • Lipuma J.J.
      Recovery of Pseudomonas cepacia and other Pseudomonas species from the environment.
      ,
      • Schwaiger K.
      • Helmke K.
      • Holzel C.S.
      • Bauer J.
      Antibiotic resistance in bacteria isolated from vegetables with regards to the marketing stage (farm vs. supermarket).
      ,
      • Allydice-Francis K.
      • Brown P.D.
      Diversity of antimicrobial resistance and virulence determinants in Pseudomonas aeruginosa associated with fresh vegetables.
      ], but we did not recover P. aeruginosa from our sampling of 159 samples taken from 17 types of ground vegetables and 17 refrigerator vegetable drawers. Although it is possible that the observed low recovery of Pseudomonas from non-drain surfaces may be due to a failure of swabbing to detect biofilm Pseudomonas, studies of biofilms of Listeria monocytogenes and Salmonella enteritidis indicate swabbing yields good recovery of biofilm bacteria [
      • Lahou E.
      • Uyttendaele M.
      Evaluation of three swabbing devices for detection of Listeria monocytogenes on different types of food contact surfaces.
      ,
      • Miwa N.
      • Konuma H.
      • Kumagai S.
      Survival of Salmonella Enteritidis on four types of stainless steel surface under a dry condition and recovery by swabbing.
      ].
      Notably, we recovered almost no P. aeruginosa from vertebrate sites that were not upper respiratory sites. We recovered only two P. aeruginosa from human skin samples (both from non-patients), and only two instances of recovery of this species from a fecal sample (one from a patient). Our rate of fecal recovery from patients (1 out of 5) is thus lower than that of Agnarsson et al. [
      • Agnarsson U.
      • Glass S.
      • Govan J.
      Fecal isolation of Pseudomonas aeruginosa from patients with cystic fibrosis.
      ] who found that 80% of colonized patients had P. aeruginosa in their stool, but this difference may be driven by small sample size. Importantly, we also recovered no P. aeruginosa from household pets (863 samples from 23 pets), suggesting that healthy pets do not commonly act as a reservoir for P. aeruginosa.
      While the exact source of the P. aeruginosa in the household drains is unknown, it is possible that tap water could be a potential source: one study found P. aeruginosa in the tap water of nearly 11% households sampled [
      • von Baum H.
      • Bommer M.
      • Forke A.
      • Holz J.
      • Frenz P.
      • Wellinghausen N.
      Is domestic tap water a risk for infections in neutropenic patients?.
      ], and a number of studies have connected intensive care unit taps to hospital infections (reviewed in [
      • Trautmann M.
      • Lepper P.M.
      • Haller M.
      Ecology of Pseudomonas aeruginosa in the intensive care unit and the evolving role of water outlets as a reservoir of the organism.
      ]). Because the running water samples in our study were taken by wetting swabs immediately after opening the tap, failure to detect P. aeruginosa in these samples suggests there is little P. aeruginosa in the kitchen water pipes, but our study was not designed for comparison with studies of tap water in which a much larger volume of water is collected after a period of flushing the pipes.
      Our sampling design sheds some light on the extent to which P. aeruginosa is a permanent vs. a transient resident in household sites. Our repeated sampling through time showed that a greater proportion of drains will at some point yield P. aeruginosa than would be expected based on a single sampling (28% vs. an estimate of 6.3%). There was also significantly higher recovery in fall relative to other seasons. Together these results suggest there is temporal variability in whether or not P. aeruginosa is present at a site, or whether or not its population size is above the limit of detection of our sampling technique. On the other hand, we detected a significant association between recovery in a current sampling with the results of the previous one, suggesting that P. aeruginosa's association with a particular site can be long term, rather than transient. This association reflects a higher than expected rate of repeatedly recovering P. aeruginosa from drains.
      We note that detecting P. aeruginosa almost exclusively in drains implicates but does not establish drains as a source of patient infection. The latter would be aided by two things: establishing genetic similarity between strains from patients and drains, and establishing directionality of movement of strains. We used 12 of the 15 variable tandem repeat primers developed by Vu-Thien et al. [
      • Vu-Thien H.
      • Corbineau G.
      • Hormigos K.
      • Fauroux B.
      • Corvol H.
      • Clement A.
      • et al.
      Multiple-locus variable-number tandem-repeat analysis for longitudinal survey of sources of Pseudomonas aeruginosa infection in cystic fibrosis patients.
      ] to determine the haplotypes of a subset of our P. aeruginosa isolates and found that the upper respiratory strains from our five P. aeruginosa colonized patients were not identical to any strains from their houses (unpublished data). We note however that our sampling was not designed to identify sources of individual infections because the patients were not newly colonized. Upper respiratory and drain strains collected in our study could therefore differ because of founder effects, changes in the rapidly evolving tandem repeat regions used for this genotyping, or because of ecological turnover in the drains occurring since the colonization event. The hypothesis of rapid differentiation of drain and upper respiratory strains is consistent with the results of Schelstraete et al. [
      • Schelstraete P.
      • Van Daele S.
      • De Boeck K.
      • Proesmans M.
      • Lebecque P.
      • Leclercq-Foucart J.
      • et al.
      Pseudomonas aeruginosa in the home environment of newly infected cystic fibrosis patients.
      ], who looked for associations between strains found in patients and in their homes immediately after a first colonization event: they were able to find identical genotypes in the patients and their homes, but only for 9 of 50 patients.
      The directionality of movement (drain to human vs human to drain) cannot be established based on genetic similarity and must be addressed separately. Importantly, we find no differences in recovery rates between homes with and without a CF patient, indicating that predominant P. aeruginosa recovery from drains is not driven by spread from patients to drains, but rather, that drains in patients homes likely harbor this bacterium before the patient becomes infected. This result is consistent with that of Mortensen et al. [
      • Mortensen J.E.
      • Fisher M.C.
      • Lipuma J.J.
      Recovery of Pseudomonas cepacia and other Pseudomonas species from the environment.
      ] who also found no differences in recovery between CF and non-CF homes and with Panagea and colleagues [
      • Panagea S.
      • Winstanley C.
      • Walshaw M.J.
      • Ledson M.J.
      • Hart C.A.
      Environmental contamination with an epidemic strain of Pseudomonas aeruginosa in a Liverpool cystic fibrosis centre, and study of its survival on dry surfaces.
      ] who found only limited, transient spread of P. aeruginosa from patients to nearby environmental sites. Our finding that P. aeruginosa is found predominantly in drains is also consistent with other studies that evaluated household sites [
      • Ojima M.
      • Toshima Y.
      • Koya E.
      • Ara K.
      • Kawai S.
      • Ueda N.
      Bacterial contamination of Japanese households and related concern about sanitation.
      ,
      • Regnath T.
      • Kreutzberger M.
      • Illing S.
      • Oehme R.
      • Liesenfeld O.
      Prevalence of Pseudomonas aeruginosa in households of patients with cystic fibrosis.
      ] and with our results in a previous study of 20 homes, all without CF patients [
      • Remold S.
      • Brown C.
      • Farris J.
      • Hundley T.
      • Perpich J.
      • Purdy M.
      Differential habitat use and niche partitioning by Pseudomonas species in human homes.
      ]. Taken together, the results of our study and the others strongly implicate drains as a potentially important reservoir for P. aeruginosa infection of CF patients.
      Our results are consistent with the recent update to the Infection Prevention and Control Guideline for Cystic Fibrosis [
      • Saiman L.
      • Siegel J.D.
      • LiPuma J.J.
      • Brown R.F.
      • EARNMSNP-BCCS
      • Bryson E.A.
      • MJLMSW
      • Chambers M.J.
      • et al.
      Infection prevention and control guideline for cystic fibrosis: 2013 update.
      ] that, in light of the studies cited above, suggest that focusing cleaning in homes of patients with CF on bathroom drains could contribute to minimizing exposure to P. aeruginosa. We note however that the strains that we recovered from drains came from kitchen sink drains as well as bathroom drains. Unfortunately, clear recommendations regarding which approaches should be implemented to provide the most effective routine cleaning or sanitizing of drains are as yet unavailable. Chlorine at concentrations as low as 100 ppm can effectively kill Pseudomonas [
      • Rutala W.A.
      • Cole E.C.
      • Thomann C.A.
      • Weber D.J.
      Stability and bactericidal activity of chlorine solutions.
      ], and hypochlorite (bleach) has been shown to decrease bacterial contamination in household settings [
      • Rusin P.
      • Orosz-Coughlin P.
      • Gerba C.
      Reduction of faecal coliform, coliform and heterotrophic plate count bacteria in the household kitchen and bathroom by disinfection with hypochlorite cleaners.
      ,
      • Kagan L.J.
      • Aiello A.E.
      • Larson E.
      The role of the home environment in the transmission of infectious diseases.
      ,
      • Barnes C.S.
      • Kennedy K.
      • Gard L.
      • Forrest E.
      • Johnson L.
      • Pacheco F.
      • et al.
      The impact of home cleaning on quality of life for homes with asthmatic children.
      ]. However the effect may be short term; one study showed that after 3–6 hours bacterial counts begin to rise again in many household sites, including in sink drain U-tubes [
      • Scott E.
      • Bloomfield S.F.
      • Barlow C.G.
      Evaluation of disinfectants in the domestic environment under ‘in use’ conditions.
      ]. Furthermore, eradication of epidemic strains of P. aeruginosa in hospital settings has in some cases only been achieved by complete replacement of sink drains [
      • Hota S.
      • Hirji Z.
      • Stockton K.
      • Lemieux C.
      • Helen Dedier M.
      • Wolfaardt G.
      • et al.
      Outbreak of multidrug‐resistant Pseudomonas aeruginosa colonization and infection secondary to imperfect intensive care unit room design.
      ,
      • Gillespie T.
      • Johnson P.
      • Notman A.
      • Coia J.
      • Hanson M.
      Eradication of a resistant Pseudomonas aeruginosa strain after a cluster of infections in a hematology/oncology unit.
      ], presumably due to higher resistance of P. aeruginosa in biofilms to disinfectants [
      • Buckingham-Meyer K.
      • Goeres D.M.
      • Hamilton M.A.
      Comparative evaluation of biofilm disinfectant efficacy tests.
      ].
      Clearly further research focusing on correlations among cleaning regimes, cleaning agents, drain materials and P. aeruginosa recovery and infection rates are called for. The identification of appropriate regimens for cleaning and sanitizing drains will reduce opportunities for infection, and the knowledge that such regimens are targeting the majority of the household P. aeruginosa may be helpful for families as they weigh the benefits and risks associated with interacting with household microbes from different types of sites.

      Acknowledgments

      We thank our volunteer families for allowing us into their homes and lab members who participated in sampling and identifications. We thank Margaret Carreiro, Sarah Emery, Jim Graham, Mike Perlin and two anonymous reviewers for helpful comments and Sarah Allen and Eileen Remold-O'Donnell for help with manuscript preparation. This work was supported by the National Science Foundation , DEB-0950361 .

      Appendix A. Supplementary data

      References

        • Renders N.H.M.
        • Sijmons M.A.F.
        • vanBelkum A.
        • Overbeek S.E.
        • Mouton J.W.
        • Verbrugh H.A.
        Exchange of Pseudomonas aeruginosa strains among cystic fibrosis siblings.
        Res Microbiol. 1997; 148: 447-454
        • Tubbs D.
        • Lenney W.
        • Alcock P.
        • Campbell C.A.
        • Gray J.
        • Pantin C.
        Pseudomonas aeruginosa in cystic fibrosis: cross-infection and the need for segregation.
        Respir Med. 2001; 95: 147-152
        • Cheng K.
        • Smyth R.L.
        • Govan J.R.W.
        • Doherty C.
        • Winstanley C.
        • Denning N.
        • et al.
        Spread of beta-lactam-resistant Pseudomonas aeruginosa in a cystic fibrosis clinic.
        Lancet. 1996; 348: 639-642
        • Denton M.
        • Kerr K.
        • Mooney L.
        • Keer V.
        • Rajgopal A.
        • Brownlee K.
        • et al.
        Transmission of colistin-resistant Pseudomonas aeruginosa between patients attending a pediatric cystic fibrosis center.
        Pediatr Pulmonol. 2002; 34: 257-261
        • McCallum S.J.
        • Gallagher M.J.
        • Corkill J.E.
        • Hart C.A.
        • Ledson M.J.
        • Walshaw M.J.
        Spread of an epidemic Pseudomonas aeruginosa strain from a patient with cystic fibrosis (CF) to non-CF relatives.
        Thorax. 2002; 57: 559-560
        • Jones A.M.
        • Govan J.R.W.
        • Doherty C.J.
        • Dodd M.E.
        • Isalska B.J.
        • Stanbridge T.N.
        • et al.
        Identification of airborne dissemination of epidemic multiresistant strains of Pseudomonas aeruginosa at a CF centre during a cross infection outbreak.
        Thorax. 2003; 58: 525-527
        • Scott F.W.
        • Pitt T.L.
        Identification and characterization of transmissible Pseudomonas aeruginosa strains in cystic fibrosis patients in England and Wales.
        J Med Microbiol. 2004; 53: 609-615
        • Ojeniyi B.
        • Frederiksen B.
        • Hoiby N.
        Pseudomonas aeruginosa cross-infection among patients with cystic fibrosis during a winter camp.
        Pediatr Pulmonol. 2000; 29: 177-181
        • Burns J.L.
        • Gibson R.L.
        • McNamara S.
        • Yim D.
        • Emerson J.
        • Rosenfeld M.
        • et al.
        Longitudinal assessment of Pseudomonas aeruginosa in young children with cystic fibrosis.
        J Infect Dis. 2001; 183: 444-452
        • Rau M.H.
        • Marvig R.L.
        • Ehrlich G.D.
        • Molin S.
        • Jelsbak L.
        Deletion and acquisition of genomic content during early stage adaptation of Pseudomonas aeruginosa to a human host environment.
        Environ Microbiol. 2012; 14: 2200-2211
        • Jelsbak L.
        • Johansen H.K.
        • Frost A.L.
        • Thogersen R.
        • Thomsen L.E.
        • Ciofu O.
        • et al.
        Molecular epidemiology and dynamics of Pseudomonas aeruginosa populations in lungs of cystic fibrosis patients.
        Infect Immun. 2007; 75: 2214-2224
        • Workentine M.
        • Surette M.G.
        Complex Pseudomonas population structure in cystic fibrosis airway infections.
        Am J Respir Crit Care Med. 2011; 183: 1581-1583
        • Kapatral V.
        • Bina X.W.
        • Chakrabarty A.M.
        Succinyl coenzyme A synthetase of Pseudomonas aeruginosa with a broad specificity for nucleoside triphosphate (NTP) synthesis modulates specificity for NTP synthesis by the 12-kilodalton form of nucleoside diphosphate kinase.
        J Bacteriol. 2000; 182: 1333-1339
        • Goldberg J.B.
        Pseudomonas: global bacteria.
        Trends Microbiol. 2000; 8: 55-57
        • Stover C.K.
        • Pham X.Q.
        • Erwin A.L.
        • Mizoguchi S.D.
        • Warrener P.
        • Hickey M.J.
        • et al.
        Complete genome sequence of Pseudomonas aeruginosa PAO1, an opportunistic pathogen.
        Nature. 2000; 406: 959-964
        • Ojima M.
        • Toshima Y.
        • Koya E.
        • Ara K.
        • Kawai S.
        • Ueda N.
        Bacterial contamination of Japanese households and related concern about sanitation.
        Int J Environ Health Res. 2002; 12: 41-52
        • Regnath T.
        • Kreutzberger M.
        • Illing S.
        • Oehme R.
        • Liesenfeld O.
        Prevalence of Pseudomonas aeruginosa in households of patients with cystic fibrosis.
        Int J Hyg Environ Health. 2004; 207: 585-588
        • Schelstraete P.
        • Van Daele S.
        • De Boeck K.
        • Proesmans M.
        • Lebecque P.
        • Leclercq-Foucart J.
        • et al.
        Pseudomonas aeruginosa in the home environment of newly infected cystic fibrosis patients.
        Eur Respir J. 2008; 31: 822-829
        • Remold S.
        • Brown C.
        • Farris J.
        • Hundley T.
        • Perpich J.
        • Purdy M.
        Differential habitat use and niche partitioning by Pseudomonas species in human homes.
        Microb Ecol. 2011; 62: 505-517
        • Mortensen J.E.
        • Fisher M.C.
        • Lipuma J.J.
        Recovery of Pseudomonas cepacia and other Pseudomonas species from the environment.
        Infect Control Hosp Epidemiol. 1995; 16: 30-32
        • Govan J.
        • Nelson J.
        Microbiology of lung infection in cystic fibrosis.
        Br Med Bull. 1992; 48: 912-930
        • King E.O.
        • Ward M.K.
        • Raney D.E.
        Two simple media for the demonstration of pyocyanin and fluorescin.
        J Lab Clin Med. 1954; 44: 301-307
        • Chun J.
        • Lee J.-H.
        • Jung Y.
        • Kim M.
        • Kim S.
        • Kim B.K.
        • et al.
        EzTaxon: a web-based tool for the identification of prokaryotes based on 16S ribosomal RNA gene sequences.
        Int J Syst Evol Microbiol. 2007; 57: 2259-2261
        • Croce O.
        • Chevenet F.
        • Christen R.
        A new web server for the rapid identification of microorganisms.
        J Microbiol Biochem Technol. 2010; 2: 084-088
        • Spilker T.
        • Coenye T.
        • Vandamme P.
        • LiPuma J.J.
        PCR-based assay for differentiation of Pseudomonas aeruginosa from other Pseudomonas species recovered from cystic fibrosis patients.
        J Clin Microbiol. 2004; 42: 2074-2079
        • SAS Institute I
        SAS/STAT® 9.3 User's Guide.
        SAS Institute, Inc., Cary, NC2011
        • Schwaiger K.
        • Helmke K.
        • Holzel C.S.
        • Bauer J.
        Antibiotic resistance in bacteria isolated from vegetables with regards to the marketing stage (farm vs. supermarket).
        Int J Food Microbiol. 2011; 148: 191-196
        • Allydice-Francis K.
        • Brown P.D.
        Diversity of antimicrobial resistance and virulence determinants in Pseudomonas aeruginosa associated with fresh vegetables.
        Int J Microbiol. 2012; 2012 ([Article ID 426241])
        • Lahou E.
        • Uyttendaele M.
        Evaluation of three swabbing devices for detection of Listeria monocytogenes on different types of food contact surfaces.
        Int J Environ Res Public Health. 2014; 11: 804-814
        • Miwa N.
        • Konuma H.
        • Kumagai S.
        Survival of Salmonella Enteritidis on four types of stainless steel surface under a dry condition and recovery by swabbing.
        Food Hyg Saf Sci. 2013; 54: 219-223
        • Agnarsson U.
        • Glass S.
        • Govan J.
        Fecal isolation of Pseudomonas aeruginosa from patients with cystic fibrosis.
        J Clin Microbiol. 1989; 27: 96-98
        • von Baum H.
        • Bommer M.
        • Forke A.
        • Holz J.
        • Frenz P.
        • Wellinghausen N.
        Is domestic tap water a risk for infections in neutropenic patients?.
        Infection. 2010; 38: 181-186
        • Trautmann M.
        • Lepper P.M.
        • Haller M.
        Ecology of Pseudomonas aeruginosa in the intensive care unit and the evolving role of water outlets as a reservoir of the organism.
        Am J Infect Control. 2005; 33: S41-S49
        • Panagea S.
        • Winstanley C.
        • Walshaw M.J.
        • Ledson M.J.
        • Hart C.A.
        Environmental contamination with an epidemic strain of Pseudomonas aeruginosa in a Liverpool cystic fibrosis centre, and study of its survival on dry surfaces.
        J Hosp Infect. 2005; 59: 102-107
        • Vu-Thien H.
        • Corbineau G.
        • Hormigos K.
        • Fauroux B.
        • Corvol H.
        • Clement A.
        • et al.
        Multiple-locus variable-number tandem-repeat analysis for longitudinal survey of sources of Pseudomonas aeruginosa infection in cystic fibrosis patients.
        J Clin Microbiol. 2007; 45: 3175-3183
        • Saiman L.
        • Siegel J.D.
        • LiPuma J.J.
        • Brown R.F.
        • EARNMSNP-BCCS
        • Bryson E.A.
        • MJLMSW
        • Chambers M.J.
        • et al.
        Infection prevention and control guideline for cystic fibrosis: 2013 update.
        Infect Control Hosp Epidemiol. 2014; 35: S1-S67
        • Rutala W.A.
        • Cole E.C.
        • Thomann C.A.
        • Weber D.J.
        Stability and bactericidal activity of chlorine solutions.
        Infect Control Hosp Epidemiol. 1998; 19: 323-327
        • Rusin P.
        • Orosz-Coughlin P.
        • Gerba C.
        Reduction of faecal coliform, coliform and heterotrophic plate count bacteria in the household kitchen and bathroom by disinfection with hypochlorite cleaners.
        J Appl Microbiol. 1998; 85: 819-828
        • Kagan L.J.
        • Aiello A.E.
        • Larson E.
        The role of the home environment in the transmission of infectious diseases.
        J Community Health. 2002; 27: 247-267
        • Barnes C.S.
        • Kennedy K.
        • Gard L.
        • Forrest E.
        • Johnson L.
        • Pacheco F.
        • et al.
        The impact of home cleaning on quality of life for homes with asthmatic children.
        Allergy and Asthma Proceedings. 2008; 29: 197-204
        • Scott E.
        • Bloomfield S.F.
        • Barlow C.G.
        Evaluation of disinfectants in the domestic environment under ‘in use’ conditions.
        J Hyg. 1984; 92: 193-203
        • Hota S.
        • Hirji Z.
        • Stockton K.
        • Lemieux C.
        • Helen Dedier M.
        • Wolfaardt G.
        • et al.
        Outbreak of multidrug‐resistant Pseudomonas aeruginosa colonization and infection secondary to imperfect intensive care unit room design.
        Infect Control Hosp Epidemiol. 2009; 30: 25-33
        • Gillespie T.
        • Johnson P.
        • Notman A.
        • Coia J.
        • Hanson M.
        Eradication of a resistant Pseudomonas aeruginosa strain after a cluster of infections in a hematology/oncology unit.
        Clin Microbiol Infect. 2000; 6: 125-130
        • Buckingham-Meyer K.
        • Goeres D.M.
        • Hamilton M.A.
        Comparative evaluation of biofilm disinfectant efficacy tests.
        J Microbiol Methods. 2007; 70: 236-244