Hospital water systems occupy a unique ecological niche that differs substantially from both the municipal supply feeding them and the clinical environments surrounding them. Within premise plumbing—the network of pipes, storage tanks, and fixtures inside a building—water can stagnate, warm, and lose residual disinfectant, creating conditions in which microbial biofilms establish and persist. The bacteria recovered in this study from three hospitals in Babil Governorate are consistent with that ecological picture: genera such as Pseudomonas, Acinetobacter, Aeromonas, and Sphingomonas are well recognized as inhabitants of engineered water systems, where they survive on trace nutrients, resist desiccation poorly or well depending on the species, and in some cases tolerate disinfectant exposure better than many other organisms. Their detection in tap water does not automatically imply a transmission event, but it does indicate that the water reaching hospital taps is not microbiologically inert.

The heterotrophic plate count reported for the Turkish Hospital sample, 3.43 × 10⁴ colony-forming units per milliliter, provides a useful quantitative anchor for interpreting the findings. Heterotrophic plate counts measure the bacteria capable of growing on non-specific media under defined incubation conditions, and they serve as a general indicator of microbial load rather than a direct measure of pathogen risk. Drinking water intended for consumption is generally expected to maintain very low heterotrophic counts, and elevated values in a hospital setting suggest either regrowth within the plumbing network, insufficient disinfectant residual, or contamination at outlets. Because the study sampled three hospitals and found the highest load in one of them, the data also hint at variability between facilities, which could reflect differences in building age, pipe materials, water storage practices, maintenance schedules, or the frequency of outlet use. Such variability is a common feature of premise plumbing studies and reinforces the argument that water quality monitoring should be facility-specific rather than assumed uniform across a city or region.

The identification method used in the study, the VITEK 2 Compact system, relies on phenotypic characterization: it profiles biochemical and enzymatic reactions of an isolate and matches the pattern against a database. This approach is well established in clinical laboratories and offers rapid, standardized identification, but it has known limitations when applied to environmental isolates. Environmental bacteria are underrepresented in identification databases relative to clinical strains, and closely related species can produce ambiguous biochemical profiles. This is particularly relevant for genera like Pseudomonas, which contains dozens of species with overlapping phenotypes, and for organisms such as Granulicatella, which are nutritionally fastidious and can display variable morphology. The authors’ caution in describing their resistance estimates as descriptive is therefore well founded. Molecular methods such as 16S ribosomal RNA gene sequencing or whole-genome sequencing would provide independent confirmation of species identity and, in the case of genome sequencing, could reveal the presence of resistance genes directly rather than inferring resistance from growth in the presence of antibiotics.

The resistance pattern observed in the single Gram-positive isolate, Granulicatella elegans, which resisted ten of fourteen tested agents, deserves careful consideration. Granulicatella species, formerly grouped with the nutritionally variant streptococci, are best known as causes of infective endocarditis and are normally discussed in the context of oral and upper respiratory flora rather than water systems. Their detection in tap water raises interesting questions about the origin of the isolate. It is possible that the organism entered the water through human shedding, aerosolization from sinks and drains, or backflow events, or that it persists in biofilms within the plumbing. Nutritionally variant streptococci are notoriously difficult to culture and identify, and their antimicrobial susceptibility can be atypical, with reported tolerance to penicillin and other agents. A single isolate, however, cannot establish whether this resistance level is characteristic of water-associated Granulicatella populations or an idiosyncratic finding. Repeated sampling over time and across multiple outlets would be needed to determine whether such organisms are persistent residents of the hospital plumbing or transient contaminants.

The relative susceptibility of the Gram-negative isolates is also noteworthy. In many studies of hospital water systems, Gram-negative non-fermenters such as Pseudomonas aeruginosa and Acinetobacter baumannii are the organisms of greatest concern because of their capacity to cause nosocomial infections and their propensity to acquire multidrug resistance. In this study, the Gram-negative species recovered were largely susceptible to the agents tested, with sporadic resistance confined to Pseudomonas stutzeri and Moraxella lacunata. This pattern may reflect genuine susceptibility in the environmental population, or it may reflect the small number of isolates examined—eleven in total, with several species represented by only one strain. With such limited sampling, the absence of widespread resistance cannot be taken as evidence that resistance is rare in these water systems. Statistical power in descriptive microbiological surveys of this kind is inherently low, and rare but clinically important resistant strains could easily be missed by sampling a small number of sites on a limited number of occasions.

The presence of Francisella tularensis among the identified species is perhaps the most striking element of the findings and warrants careful interpretation. F. tularensis is the agent of tularemia, a zoonotic disease with multiple transmission routes including water, and its detection in any clinical or environmental sample carries significant public health implications. However, the identification of this organism by an automated phenotypic platform alone should be regarded as provisional. Automated systems can misidentify fastidious or slow-growing organisms, and Francisella species are notoriously demanding in culture, requiring enriched media and sometimes specialized conditions. Environmental Francisella-like organisms also exist and can produce confusing profiles. Confirmation of such a finding would typically require molecular methods targeting specific genetic markers, and in a research context, culture confirmation in a reference laboratory with appropriate biosafety facilities. Until such confirmation is available, the report of F. tularensis in hospital tap water should be treated as a signal requiring verification rather than a definitive identification. This distinction matters both for public health response and for the scientific record, since confirmed detection of a Tier 1 select agent in a hospital water supply would trigger very different investigations than the detection of a common water bacterium.

The broader context of antimicrobial resistance in water environments adds depth to these findings. Water systems, particularly those connected to healthcare facilities, are increasingly recognized as reservoirs and mixing vessels for resistance determinants. Biofilms that line pipes provide a protected environment where bacteria can exchange genetic material, and the selective pressure exerted by residual disinfectants and by antibiotics entering the water through excretion and disposal can favor resistant strains. Environmental Pseudomonas species are particularly noted for their capacity to acquire resistance genes from other bacteria, including enteric organisms shed into the environment. The sporadic resistance observed in P. stutzeri in this study fits within that framework: even when environmental isolates remain susceptible to most agents, individual strains can carry resistance traits that may spread under appropriate selective conditions. Monitoring such systems over time can therefore serve as an early indicator of resistance emergence in the local environment.

The clinical relevance of water-associated opportunistic pathogens depends heavily on the route of exposure and the vulnerability of the population. In a hospital, tap water contacts patients in numerous ways: drinking, ice preparation, bathing, wound care, dental procedures, rinsing of medical equipment, and humidification. Immunocompromised patients, those with indwelling devices, and those with extensive wounds are at elevated risk from organisms that would pose little threat to healthy individuals. Species such as Sphingomonas paucimobilis, which is infrequently pathogenic but has been implicated in catheter-related infections and other nosocomial cases, and Aeromonas species, which cause wound and gastrointestinal infections, illustrate the range of clinical possibilities. The presence of such organisms in tap water does not prove that infections occur, but it establishes the potential for exposure and provides a baseline against which clinical isolates can later be compared. In outbreak investigations, having prior characterization of water-associated flora can be decisive in tracing the source of an infection cluster.

Infection control implications follow directly from these considerations. Hospitals in many countries have adopted water safety plans that include regular microbiological monitoring, point-of-use filtration for high-risk wards, thermal or chemical disinfection of plumbing systems, and protocols for flushing outlets that have been unused. The findings from Babil Governorate support the view that such measures are relevant beyond high-income settings. The authors’ call for routine microbiological monitoring and improved water safety protocols aligns with international guidance on water safety in healthcare facilities, which emphasizes that water quality cannot be assumed from the quality of the municipal supply alone. Local assessment, documentation, and corrective action form the backbone of effective water management in hospitals.

From a research perspective, this study contributes baseline data from a region where such information has been scarce. Baseline data are valuable precisely because they enable comparison: future studies in the same hospitals, or in similar settings across Iraq and neighboring countries, can evaluate whether the bacterial communities and resistance profiles change over time, whether interventions such as plumbing renovation or disinfection protocols alter the flora, and whether clinical infections in these facilities can be linked to water sources. Expanding the scope of future work to include molecular identification, quantification of resistance genes, biofilm sampling from within pipes, and correlation with clinical surveillance would substantially strengthen the evidence base. Sampling across seasons would also be informative, since water temperature, stagnation patterns, and hospital occupancy can vary throughout the year and influence microbial dynamics within plumbing systems.

The study also highlights a methodological point with implications for laboratory practice. Automated phenotypic identification systems are indispensable in routine clinical microbiology, but their application to environmental samples requires awareness of their limits. Environmental isolates may fall outside the calibration of the databases, and species-level assignments for uncommon organisms should ideally be corroborated. For hospital infection control teams interpreting such results, the practical message is that a species name generated by an automated system is a strong hypothesis rather than an absolute conclusion, and that unusual or high-consequence identifications merit confirmatory testing. This is especially true when the identified organism has implications for public health reporting or for infection control decisions.

Finally, the findings sit within a growing international literature on the microbiology of hospital water. Studies from Europe, the Americas, and Asia have repeatedly documented that premise plumbing in healthcare facilities harbors diverse bacterial communities, including opportunistic pathogens and resistant strains, and that these communities differ between buildings and even between outlets within the same building. The Iraqi data add a regional perspective to this picture and suggest that the phenomena observed elsewhere—regrowth in plumbing, biofilm-associated persistence, and sporadic resistance—are also present in hospitals of the region. As climate, infrastructure, and water management practices vary widely across settings, region-specific data of this kind are essential for designing realistic and effective water safety interventions. The work thus serves both as a local alert and as a contribution to the global understanding of hospital water systems as reservoirs of opportunistic and potentially resistant bacteria.

Subject of Research: Isolation and identification of antibiotic-resistant bacteria in hospital tap water

Article Title: Isolation and identification of antibiotic-resistant bacteria in hospital tap water

Article References: Isolation and identification of antibiotic-resistant bacteria in hospital tap water. (n.d.). https://doi.org/10.3389/frabi.2026.1901158

Image Credits: AI Generated

DOI: 10.3389/frabi.2026.1901158

Keywords: Isolation, identification, antibiotic-resistant, bacteria, hospital, water, scientific research