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Pseudomonas Colonisation: No Quick Fix

We underestimate the tenacity of our waterborne pathogens.  They endure.  A recent paper by William Stribling and team from the Multi-Drug-Resistant Organism Repository and Surveillance Network in the US illustrates just how persistent Pseudomonas aeruginosa can be in an in-premise water system.

The authors note that the “hallmark of Pseudomonas aeruginosa lies in its remarkable propensity for developing resistances through chromosomal mutations”, and indeed this makes the development of drug resistance and environmental tolerance, its “Signature”.  Pseudomonas aeruginosa has a huge arsenal of weapons to call upon in times of need, and its ability to readily form biofilm is a key factor supporting its persistence in both patients and with environmental contamination within taps and drains.  Eradication is close to impossible.

The paper is a Grimms Fairy Tale of routine genome-based surveillance of multi-drug-resistant clinical isolates across US Military Hospitals, which identified an epidemic cluster of P. aeruginosa in a single hospital in 2020.  The detective work commenced with molecular techniques identifying a protracted outbreak clone with cases arising from all hospital floors and from a date aligned to the new hospital facility was opening.  Sharing this important and unique dataset enables “lessons learnt”.  The molecular biology within this paper is extraordinary, and hats off to those who get into the details of SNPS and phylotypic evolutionary pathways, however there are clear points which every Hospital Water Safety Group should note and challenge themselves as to whether they can implement and improve at their facility.

What is in your surveillance playbook?  This study undertook Whole Genome Sequencing (WGS) on 5129 Pseudomonas aeruginosa patient isolates collected from 71 healthcare facilities between 2011 and 2020.  In total, 547 different sequence types (ST) were found, however a 425-bed military medical center came under the spotlight when 253 x ST 621 Pseudomonas aeruginosa isolates were found within 82 patients.  The data were reported from respiratory samples (42%), Urine (39%), Wound (7%), Surveillance (6%), Tissue (3%) and Blood Culture (2%).  The 82 patients were from 26 wards (including ER, ICU, Step-down HDU and ward level), across all floors and from two separate buildings.  On average there were 11.5 new patient cases per year.  Would your surveillance system pick up this outbreak?

Risk Recognition of New Build Programs.  Clinical isolates were collected from 2011 timepoint onwards, but the genetic diversity of the clinical isolates suggested an earlier origin and inferred using “Most Recent Common Ancestor” as 1999 +/- 3 years.  This aligned with the hospital facility opening in 1996.  Despite the early predicted origin, it was only after the facility expansion and new build program that Pseudomonas aeruginosa isolates underwent significant genetic diversity, and in 2012 saw the emergence of a new subclone.  Was it the new environment and environmental pressures which triggered this event?  Should enhanced molecular surveillance alongside new build and major refurbishment programs be adopted for such resilient waterborne pathogens and these risks recognised on risk registers?

Environmental Reservoirs Sustain Waterborne Pathogen Transmission Events.  The data evidenced that a new patient was infected with a near identical strain from a preceding patient within the same ward despite no overlap in time (approximately 1 year gap between events).  A targeted environmental sampling program was undertaken between 2011 and 2012 which included 159 swabs from 55 locations on 8 wards (including the ER).  Sink drains located in patient rooms were found to be positive for ST 621 isolates in 7/8 wards.  Within the same time period, 56 clinical isolates from 13 patients were identified, and revealing 11 new cases indicating transmission was actively occurring.  How does your WSG manage persistence of Pseudomonas in environmental reservoirs and how do you verify success of any remedial measures?

With traditional surveillance approaches, outbreaks comparable to that described in this extraordinary study would likely avoid detection – it would fly under the radar, you won’t spot it.  Prospective WGS programs are evidenced as reporting large numbers of previously unrecognised outbreaks (Parcell et al., 2018 & 2021; Wendel et al., 2022).  The data indicates the origin of Pseudomonas aeruginosa colonisation at around the time of building opening, follows the evolution and spread of the organism and the new subclone emergence following building work expansion.  The data also tracts the notable feature and evolution of Antibiotic Resistance over time – firstly resistance to Cephalosporin, then Carbapenem and finally Colistin.  Persistence for more than 20 years, with patient room drains as a noted environmental reservoir supporting transmission.

We cannot continue doing more of the same monitoring, control measures and remediation – it doesn’t work.  Removal of water reservoirs is needed as decontamination of drains is ineffective due to

  • limited penetration of chemicals
  • lack of access for any physical cleaning
  • rapid recolonization from patient fluids and retrograde contamination from wastewater system
  • transmission via splash and drain aerosolisation
  • tolerance to heat and chemicals by waterborne pathogens

Recently IPC Journal Club’s Dr Phil Norville presented a summary of Saied Ali’s excellent review paper on drain disinfection, both of which are helpful for Water Safety Groups in determining the limitations and potential unintended consequences of repeated drain disinfection (Tackling CPE drain contamination: a scoping review; https://ipcpartners.org/blog/disinfection-strategies-for-cpe-in-hospital-water-systems/).

To be effective and future proof our hospitals from waterborne infections there needs to be investment in surveillance and embrace patient surveillance utilising molecular techniques, remove water sources and adopt alternative methods where possible (remembering the WHO Gold Standard for hand hygiene is alcohol based hand rub, not hand washing), tightly control any remaining water sources, reservoirs and wastewater interfaces with the recognition that they bring a high level of risk to the patient.  As Stribling and his team conclude, “Threat is only a prescription and a few mutations away”. We hope you enjoy reading this paper and take away the “Lessons Learnt”.  If you would like to discuss any further aspects or application in your hospital facility, please do not hesitate to contact us.

References

  • Stribling W, Hall LR, Powell A, Harless C, Martin MJ, Corey BW, Snesrud E, Ong A, Maybank R, Stam J, Bartlett KV, Jones BT, Preston LN, Lane KF, Thompson B, Young LM, Kwak YI, Barsoumian AE, Markelz AE, Kiley JL, Cybulski RJ, Bennett JW, Mc Gann PT, Lebreton F. Detecting, mapping, and suppressing the spread of a decade-long Pseudomonas aeruginosa nosocomial outbreak with genomics. Elife. 2025 Oct 29;13:RP93181. doi: 10.7554/eLife.93181. PMID: 41159557; PMCID: PMC12571482.  https://pmc.ncbi.nlm.nih.gov/articles/PMC12571482/
  • Parcell BJ, Oravcova K, Pinheiro M, Holden MTG, Phillips G, Turton JF, Gillespie SH. Pseudomonas aeruginosa intensive care unit outbreak: winnowing of transmissions with molecular and genomic typing. J Hosp Infect. 2018 Mar;98(3):282-288. doi: 10.1016/j.jhin.2017.12.005. Epub 2017 Dec 8. PMID: 29229490; PMCID: PMC5840502.
  • Parcell BJ, Gillespie SH, Pettigrew KA, Holden MTG. Clinical perspectives in integrating whole-genome sequencing into the investigation of healthcare and public health outbreaks – hype or help? J Hosp Infect. 2021 Mar;109:1-9. doi: 10.1016/j.jhin.2020.11.001. Epub 2020 Nov 9. PMID: 33181280; PMCID: PMC7927979.
  • Wendel AF, Malecki M, Mattner F, Xanthopoulou K, Wille J, Seifert H, Higgins PG. Genomic-based transmission analysis of carbapenem-resistant Pseudomonas aeruginosa at a tertiary care centre in Cologne (Germany) from 2015 to 2020. JAC Antimicrob Resist. 2022 May 20;4(3):dlac057. doi: 10.1093/jacamr/dlac057. PMID: 35611260; PMCID: PMC9122648.
  • Ali S, Burke LP, Fitzpatrick F, Fitzgerald-Hughes D. A Scoping Review of Disinfection Strategies for Carbapenemase-Producing Enterobacterales (CPE) in Hospital Water Systems. J Hosp Infect. 2025 Nov 1:S0195-6701(25)00340-8. doi: 10.1016/j.jhin.2025.10.021. Epub ahead of print. PMID: 41183683.