Hospital Drains in Iraq Harbor Drug-Resistant, Toxin-Armed Pseudomonas aeruginosa

Hospital wastewater has long been viewed as a passive byproduct of clinical care, a murky stream of discarded drugs, disinfectants, and microbial debris flowing toward treatment plants. A new study from Babylon city, Iraq, suggests it should be viewed instead as an active reservoir of some of the most dangerous bacteria in modern medicine. Researchers who sampled 155 hospital wastewater specimens between December 2025 and June 2026 recovered 119 isolates of Pseudomonas aeruginosa, an opportunistic pathogen notorious for its arsenal of tissue-destroying toxins and its stubborn resistance to antibiotics. More than eight in ten of those isolates were multidrug-resistant, and virtually all carried at least one virulence gene linked to severe human infection. The findings, published in Molecular Biology Reports, add weight to a growing body of evidence that hospital effluents are not merely conduits for resistance genes but incubators where virulence and drug tolerance travel together into the wider environment.

The team, led by Farah H. Omer of the University of Mosul and including investigators from the University of Babylon, the University of Anbar, and Ahvaz Jundishapur University of Medical Sciences in Iran, set out to answer a deceptively simple question: what is actually swimming in the water leaving hospitals in a mid-sized Iraqi city? To find out, they passed wastewater samples through cellulose ester membrane filters, a technique that traps bacteria on the filter surface while the liquid passes through. The trapped organisms were then cultured on cetrimide agar, a selective medium that favors Pseudomonas species and produces characteristic green pigmented colonies of P. aeruginosa. Suspected colonies were identified with a VITEK2 automated system, a workhorse of clinical microbiology laboratories, and every isolate was confirmed by polymerase chain reaction targeting the ecfX gene, a species-specific genetic marker that leaves little room for misidentification.

With the isolates confirmed, the researchers turned to antibiotic susceptibility testing using the disc diffusion method, following standards set by the Clinical and Laboratory Standards Institute. The results were sobering. Resistance to aztreonam, a monobactam antibiotic often used against gram-negative infections, reached 65.5 percent of isolates, while 58.8 percent resisted ceftazidime, a third-generation cephalosporin that is a mainstay of treatment for Pseudomonas infections. Ceftazidime resistance in this species is known to be multigenic and complex, involving combinations of reduced permeability, efflux pumps, and hydrolytic enzymes, which makes its high prevalence in wastewater isolates particularly concerning. Against this grim backdrop, one drug stood out: colistin, an older polymyxin antibiotic that has been revived as a last-resort agent, inhibited 89.9 percent of the isolates, making it by far the most effective compound tested.

The most alarming statistic, however, was the burden of multidrug resistance. Using standard definitions, the team classified 82.4 percent of the isolates, 98 of the 119 recovered, as multidrug-resistant, meaning they were nonsusceptible to at least one agent in three or more antimicrobial categories. That proportion rivals or exceeds what is often reported from clinical settings, where selective pressure from therapeutic antibiotic use is intense. Its presence in wastewater implies that the hospital drain is functioning as a selective reactor: bacteria exposed to a cocktail of residual antibiotics, disinfectants, and heavy metals are winnowed down to the hardiest strains, which then multiply and disperse. Environmental microbiologists have documented similar patterns in hospital effluents in the Czech Republic, South Africa, and elsewhere, but the Iraqi data underscore how widespread the phenomenon has become and how little containment typically occurs between the hospital sink and the municipal sewer.

Resistance alone does not make a bacterium dangerous; it must also carry the tools to cause disease. The researchers therefore screened every isolate by PCR for fourteen virulence genes spanning the major weapon systems of P. aeruginosa. The results read like a catalogue of the pathogen’s most feared capabilities. The toxA gene, which encodes exotoxin A, a potent inhibitor of protein synthesis that damages host cells, was present in 100 percent of the isolates. The lasB gene, which encodes elastase B, an enzyme that degrades elastin and other tissue proteins and helps the bacterium invade and spread, was found in 65.5 percent. The exoT gene, part of the type III secretion system that injects toxic effectors directly into host cells, appeared at the same frequency of 65.5 percent. Every one of these genes contributes to the tissue destruction and immune evasion that make P. aeruginosa infections so difficult to treat in burn wounds, lungs, and catheterized patients.

The wider virulence screen painted a picture of genetically well-armed populations. Genes encoding phospholipases C (plcH and plcN), which disrupt host cell membranes; exoenzymes S, T, U, and Y, the type III secreted effectors with distinct cytotoxic and immunomodulatory roles; alkaline protease (apr); the quorum-sensing and phenazine biosynthesis genes phzI and phzII, which govern pigment production and intercellular signaling; and the alginate biosynthesis genes algD and algU, which underpin the mucoid, antibiotic-impermeable biofilm phenotype, were all detected across the collection. The simultaneous presence of exoS and exoU alleles, which are usually considered largely mutually exclusive in clinical strains, has been noted before in environmental isolates and hints that wastewater populations may recombine and shuffle virulence determinants in ways that clinical populations do not.

Perhaps the most intriguing analytical step was the search for statistical relationships between virulence genes and antibiotic susceptibility. The team reported significant positive correlations between several gene pairs and specific drugs: algU with ciprofloxacin; phzII with piperacillin; phzI with imipenem, ceftazidime, and amikacin; plcN with imipenem; plcH with amikacin, piperacillin, and piperacillin-tazobactam; exoY with piperacillin; exoT with ceftazidime; and exoS with colistin. Correlation does not establish causation, and the authors did not claim direct genetic linkage between these loci and resistance mechanisms. But such associations are consistent with a scenario in which virulence and resistance traits are being co-selected in the same bacterial lineages, whether through shared mobile genetic elements, biofilm lifestyles that favor both traits, or the linkage of virulence determinants with efflux systems that pump out antibiotics. If hospital effluent consistently selects for strains that are both drug-tolerant and toxin-armed, the public health stakes rise considerably.

The study was approved by the Ethics Committee of the University of Babylon in November 2025 and involved no human or animal samples, sidestepping many of the logistical hurdles of clinical surveillance while capturing something clinical surveillance often misses: the environmental fate of pathogens after they leave the ward. Previous work in Iraq has documented cephalosporin resistance in clinical P. aeruginosa from Basra and the presence of resistance genes in water samples from Baghdad, and studies from Iran, China, Mexico, and Bangladesh have traced resistant and virulent strains in drinking water, groundwater, soil, and food. The Babylon data fit into this global mosaic and suggest that in regions where wastewater treatment is limited or absent, hospital effluents may serve as a continuous, largely unmonitored source of high-risk bacteria entering rivers, irrigation systems, and communities.

The authors’ conclusion is blunt: hospital effluents are critical sources of multidrug-resistant and virulent P. aeruginosa, and there is an urgent demand to improve wastewater management. That demand carries technical implications. Effective interventions could include on-site pretreatment of hospital effluent before discharge, enhanced monitoring of resistance and virulence markers in sewer networks, and stewardship programs that reduce the quantity of antibiotics entering the drain in the first place. The near-universal presence of toxA and the high frequency of lasB and exoT in these environmental isolates suggest that virulence screening, not just resistance testing, should inform risk assessments of hospital wastewater. As antimicrobial resistance continues to erode the clinical arsenal, with colistin remaining one of the few reliably effective agents, the drains of the world’s hospitals have become more than plumbing. They are, according to this study, active evolutionary arenas where the next generation of dangerous pathogens may be assembling, one selective pressure at a time.

Subject of Research: Virulence genes and antibiotic resistance in Pseudomonas aeruginosa from Iraqi hospital wastewater

Article Title: Virulence arsenal and antibiotic resistance backgrounds in Pseudomonas aeruginosa isolates from hospital wastewater samples from Iraq

Article References: Omer, F. H., Al-Khafaji, N. S. K., Shakir, B., Almjalawi, A., Al-Alaq, F. T., Al-Dahmoshi, H. O. M., Al-Ouqaili, M. T. S., Ahmad, F., & Saki, M. (2026). Virulence arsenal and antibiotic resistance backgrounds in Pseudomonas aeruginosa isolates from hospital wastewater samples from Iraq. Molecular Biology Reports, 53(1), Article 1654. https://doi.org/10.1007/s11033-026-12865-w

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12865-w

Keywords: Pseudomonas aeruginosa, hospital wastewater, antimicrobial resistance, multidrug resistance, virulence genes, toxA, lasB, Iraq, colistin, PCR, public health, wastewater management