Heterotrophic bacteria in drinking water: evaluating antibiotic resistance and the presence of virulence genes.

Heterotrophic bacteria, impacting those with infections or compromised immunity, pose heightened health risks when resistant to antibiotics. This study investigates heterotrophic plate count bacteria in water from North West-C (NWC) and North West-G (NWG) facilities, revealing prevalent ß-hemolysis (NWC 82.5%, NWG 86.7%), enzyme production (98%), and antibiotic resistance, especially in NWC. NWG exhibits variations in hemolysin (P = 0.013), lipase (P = 0.009), and DNase activity (P = 0.006). Antibiotics, including ciprofloxacin, persist throughout treatment, with high resistance to ß-lactams and trimethoprim (47%-100%), predominantly in NWC. Multiple antibiotic resistance index indicates that 90% of values exceed 0.20, signifying isolates from high antibiotic usage sources. Whole genome sequencing reveals diverse antibiotic resistance genes in heterotrophic strains, emphasizing their prevalence and health risks in water.IMPORTANCEThis study's findings are a stark reminder of a significant health concern: our water sources harbor antibiotic-resistant heterotrophic bacteria, which can potentially cause illness, especially in individuals with weakened immune systems or underlying infections. Antibiotic resistance among these bacteria is deeply concerning, as it threatens the effectiveness of antibiotics, critical for treating various infections. Moreover, detecting virulence factors in a notable proportion of these bacteria highlights their elevated risk to public health. This research underscores the immediate need for enhanced water treatment processes, rigorous water quality monitoring, and the development of strategies to combat antibiotic resistance in the environment. Safeguarding the safety of our drinking water is imperative to protect public health and mitigate the spread of antibiotic-resistant infections, making these findings a compelling call to action for policymakers and public health authorities alike.

Predicting heterotrophic plate count exceedance in tap water: A binary classification model supervised by culture-independent data.

Culture-independent data can be utilized to identify heterotrophic plate count (HPC) exceedances in drinking water. Although HPC represents less than 1% of the bacterial community and exhibits time lags of several days, HPC data are widely used to assess the microbiological quality of drinking water and are incorporated into drinking water standards. The present study confirmed the nonlinear relationships between HPC, intact cell count (ICC), and adenosine triphosphate (ATP) in tap water samples (stagnant and flushed). By using a combination of ICC, ATP, and free chlorine data as inputs, we show that HPC exceedance can be classified using a 2-layer feed-forward artificial neural network (ANN). Despite the nonlinearity of HPC, the best binary classification model showed accuracies of 95%, sensitivity of 91%, and specificity of 96%. ICC and chlorine concentrations were the most important features for classifiers. The main limitations, such as sample size and class imbalance, were also discussed. The present model provides the ability to convert data from emerging measurement techniques into established and well-understood measures, overcoming culture dependence and offering near real-time data to help ensure the biostability and safety of drinking water.

Heterotrophic Plate Count Can Predict the Presence of Legionella spp. in Cooling Towers.

Legionella pneumophila (Lp) colonizes aquatic environments and is a potential pathogen to humans, causing outbreaks of Legionnaire's disease. It is mainly associated with contaminated cooling towers (CTs). Several regulations, including Spanish legislation (Sl), have introduced the analysis of heterotrophic plate count (HPC) bacteria and Legionella spp. (Lsp) in management plans to prevent and control Legionella outbreaks from CTs. The 2003 Sl for CTs (RD 865/2003) considered that concentrations of HPC bacteria ≤10,000 cfu/mL and of Lsp ≤100 cfu/L are safe; therefore, no action is required, whereas management actions should be implemented above these standards. We have investigated to what extent the proposed standard for HPC bacteria is useful to predict the presence of Lsp in cooling waters. For this, we analyzed Lsp and HPC concentrations, water temperature, and the levels of chlorine in 1376 water samples from 17 CTs. The results showed that in the 1138 water samples negative for Legionella spp. (LN), the HPC geometric mean was significantly lower (83 cfu/mL, p < 0.05) than in the positive Lsp. samples (135 cfu/mL). Of the 238 (17.3%) LP samples, 88.4% (210/238) were associated with values of HPC ≤10,000 cfu/mL and most of them showed HPC concentrations ≤100 (53.7%). In addition, a relatively low percentage of LP (28/238, 11.6%) samples were associated with HPC bacteria concentrations >10,000 cfu/mL, indicating that this standard does not predict the colonization risk for Legionella in the CTs studied. The present study has demonstrated that a threshold concentration ≤100 cfu/mL of HPC bacteria could better predict the higher concentration of Legionella in CTs, which will aid in preventing possible outbreaks.

Calidad microbiológica del agua para hemodiálisis

RESUMEN Introducción: El elevado costo del tratamiento sustitutivo de la enfermedad renal crónica representa un reto para los sistemas de salud y la exigencia de la calidad del agua de la hemodiálisis aumenta con el transcurso de la historia de la hemodiálisis. Objetivo: identificar los indicadores microbiológicos del agua para hemodiálisis ambulatoria. Métodos: Estudio descriptivo de resultados microbiológicos de 150 muestras de agua de la planta de hemodiálisis ambulatoria del Instituto de Nefrología "Dr. Abelardo Buch López" en el periodo de enero de 2019 a abril de 2020. Las muestras se analizaron en el laboratorio de microbiología de agua del Instituto de Higiene, Epidemiología y Microbiología, La Habana, mediante métodos descritos en el texto. Se utilizó estadística descriptiva. Resultados: De las muestras de agua analizadas 92 % (n=138) fueron microbiológicamente satisfactorias, 8 % (n=12) que no cumplieron los requisitos se registraron en los primeros seis meses del año 2019. En la totalidad de los informes de positividad o alerta, se procedió a la limpieza y desinfección del sistema de tratamiento. No se comprobó presencia de Pseudomonas aeruginosa en las muestras. No hubo incidencia de infecciones asociadas con el tratamiento de hemodiálisis. La determinación de endotoxinas no se realizó en el período. Conclusiones: La mayoría de los informes microbiológicos recibidos en el período de estudio cumplieron las normas establecidas. La vigilancia de la calidad del agua para hemodiálisis permite la ejecución de acciones preventivas, lo cual es determinante en el proceso de diálisis y para la calidad de vida de los pacientes.

ABSTRACT Introduction: The high cost of replacement therapy for chronic kidney disease poses a challenge to the health systems, and a better quality of the water for hemodialysis is required over time. Objective: To identify the microbiological indicators of the water for outpatient hemodialysis Methods: A descriptive study based on the microbiological results of 150 samples of water from the outpatient hemodialysis water station at the Institute of Nephrology "Dr. Abelardo Buch López", from January 2019 to April 2020. Samples were analyzed in the water microbiology laboratory at the Institute of Hygiene, Epidemiology and Microbiology, Havana by methods described in the text. Descriptive statistics was used. Results: Of the water simples analyzed, 92% (n=138) were microbiologically satisfactory, 8% (n=12) did not meet the requirements and were registered in the first half of 2019. In the event of a positivity or alert report, the treatment system was all cleaned and disinfected in each case. Pseudomonas aeruginosa was not identified in the samples. No infection was associated with the hemodialysis treatment. Endotoxin determination was not performed in this period. Conclusions: Most of the microbiological reports received during the study period met the established standards. Monitoring the quality of water for hemodialysis allows the implementation of preventive measures that are critical for the dialysis process and the quality of life of the patients.

The Optimum Duration of Flushing Dental Unit Waterlines for Microbial Removal

ABSTRACT@#This study aims to evaluate the optimum duration of flushing dental unit waterlines (DUWLs) in Universiti Sains Islam Malaysia (USIM) dental polyclinics for removal of heterotrophic bacteria. Water samples were obtained from triple air syringes at each dental chair from oral surgery clinic, outpatient clinic and polyclinic 17 at Faculty of Dentistry, USIM after 16 and 64 hours of not operating the dental units as baseline samples. This is followed by sampling after continuous flushing at 30 seconds, 1 minute, 2 minutes and 3 minutes of flushing duration. The levels of heterotrophic plate count (HPC) for each flushing duration were determined by quantification of colony forming units (CFUs) after cultivation of samples on plate count agar (PCA), R2A agar and 5% sheep blood agar (SBA). Statistically, there was no significant reduction in CFUs of HPC for all flushing duration compared to baseline (P > 0.05) with the most notable HPC reducing level after 1 minute and 3 minutes of flushing DUWLs. However, HPC level at USIM dental clinics is still exceeding the recommendation by Centers for Disease Control and Prevention (CDC) which should be less than 500 CFU/mL. The existing method of controlling DUWLs contamination in USIM dental clinics is only by flushing DUWLs 1 minute every morning prior to dental treatment as recommended by Malaysian Dental Council (MDC) without the use of chemical germicides. Thus, the flushing method alone is not reliable to reduce the number of microorganisms in the DUWLs.

Dental Unit Waterlines in Quito and Caracas Contaminated with Nontuberculous Mycobacteria: A Potential Health Risk in Dental Practice.

Three cases of severe odontogenic infections due to nontuberculous mycobacteria (NTM) in Venezuela that were directly associated with dental procedures and the finding of dental unit waterlines (DUWLs) in dental offices that were colonized with mycobacteria species was the reason for assessing the water quality of DUWLs in dental offices in two capital cities in South America, namely, Quito and Caracas. The main water supplies and the water from 143 DUWLs in both cities were sampled and especially checked for contamination with NTM. To measure the overall bacteriological quality of the water also the presence of heterotrophic bacteria, coliform bacteria, and Pseudomonas was determined. Results showed that respectively 3% and 56% of the DUWLs in Quito and Caracas yielded NTM species (up to 1000 colony-forming units (CFU)/mL). Furthermore, high and unacceptable total viable counts of heterotrophic bacteria and/or coliform bacteria and Pseudomonas were detected in 73% of the samples. We conclude that, in both cities, the water in the majority of DUWLs was contaminated with NTM and other potential pathogens, presenting a risk to human health. The detection of NTM in DUWL water with acceptable heterotrophic bacteria counts shows the need to include NTM in water quality testing. Mycobacteria are more resistant to disinfection procedures than other types of vegetative bacteria, and most testing protocols for DUWLs do not assess mycobacteria and thus do not guarantee risk-free water.

Response of the Bacterial Community and Antibiotic Resistance in Overnight Stagnant Water from a Municipal Pipeline.

Although drinking water safety has raised considerable concern, to date, the hidden health risks in newly released overnight water from a municipal pipeline have seldom received attention. In this study, bacterial community composition and the response of antibiotic-resistant bacteria (ARB) to ciprofloxacin, azithromycin, tetracycline, penicillin, and cephalosporin in overnight stagnant water were analyzed. With increases in heterotrophic bacteria plate count (HPC) during water stagnation, the numbers of ARB and the ARB/HPC ratios for the five antibiotics in resident water were observed to increase, which illustrated that the prevalence of ARB rose in the pipe network water during stagnation time (ST). Furthermore, during water stagnation for 12 h, an increase in bacteria related to fermentation was also observed. When the ST rose to 48 h, the fermentation bacteria become non-significant, and this was related to the exchange of pipe network water during daytime stagnation within the 48-h period. The antibiotic resistance index (ARI) showed that tetracycline had the highest resistance level in fresh water, and then decreased during water stagnation. When ST increased to 12 h, all ARI values of the five antibiotics were low, which was associated with changes in parameters during water retention and reduced resistance during short-term stagnation. When the ST increased to 24 and 48 h, the resistance to most antibiotics (except for tetracycline) increased, which showed that increasing antibiotic resistance is caused by the formation of biofilms in the pipeline during water stagnation.

Point-of-use filters for prevention of health care-acquired Legionnaires' disease: Field evaluation of a new filter product and literature review.

BACKGROUND: The Centers for Medicare & Medicaid Services requires that health care facilities assess their building water systems and minimize the risk of growth and spread of Legionella and other waterborne pathogens. Increasingly, point-of-use (POU) filters are being used to prevent exposure to these pathogens. This study provides efficacy and performance specifications (membrane size, pore size, and use restrictions), which will aid in selecting POU filters. METHODS: New faucet and shower filters rated for 62 days of use were evaluated at an acute care facility in Southwestern Ontario, Canada. Five faucets and 5 showers served as controls or were equipped with filters. Hot water samples were collected weekly for 12 weeks and cultured for Legionella, heterotrophic plate count, and Pseudomonas. Literature searches for articles on POU filters used in health care settings were performed using PubMed and Google Scholar. Filter specifications from 5 manufacturers were also compared. RESULTS: The 62-day POU filters installed on both faucets and showers eliminated Legionella and reduced heterotrophic plate count concentrations for 12 weeks. No Pseudomonas was recovered during this study. Twenty peer-reviewed studies are summarized, and 21 features of 53 POU filters have been compiled. CONCLUSIONS: The information provides infection preventionists and facility engineers with information to verify claims from manufacturers and compare differences among POU products, including validated efficacy, filter design, and operational specifications.

Evaluation of disinfection processes for water heater devices used for extracorporeal life support.

The Maquet Heater Unit 35 (HU35) is widely used to maintain patient body temperature during extracorporeal life support. Water is used as a medium for heat transfer though it also provides a medium for the growth of pathogens. Thus, the use of a heating unit presents a risk for transmission of water-borne pathogens in critically ill patients. Recently, a Mycobacterium chimaera outbreak in cardiac surgery has been linked to the production of bioaerosols by heater-cooler devices. Consequently, manufacturers have revised cleaning recommendations, with significant impact on staff, budget and environment. Heterotrophic plate counts (HPC) and non-tuberculous mycobacterium growth were assessed following three disinfection processes over a 16-month period. It was found that water quality was acceptable in HU35s when disinfecting with a lower concentration of Chloramine-T than currently recommended, provided exposure of the device to potential pathogens was minimised by the use of a 0.2 µm water filter.

High heterotrophic counts in potable water and antimicrobial resistance among indicator organisms in two peri-urban communities of Karachi, Pakistan.

OBJECTIVE: Fecal contamination of potable water leads to unsafe water supply. Although many urban areas of large metropolitan cities receive safe water, peri-urban areas are often not monitored by public health authorities and water supply and quality remain unknown. We assessed microbiological quality and rates of antimicrobial resistance in viable indicator bacteria in two peri-urban communities of Karachi, Pakistan. Water samples were collected over 5 months (October 2015 to February 2016) from these peri-urban communities and samples were processed for microbiological quality as per Standing Committee of Analysts, United Kingdom and World Health Organization guidelines and criteria for drinking water. RESULTS: Both communities received unimproved water. Potable water samples collected from 100 households showed that 96% of samples were unsafe for consumption. Extended spectrum beta lactamases production was found in 29.2% of fecal indicator organisms (coliforms). Use of unimproved water sources and unsafe potable water quality in peri-urban Karachi deserve immediate attention and upgrade. The study is instrumental in attracting the attention of authorities to the state of water resources in peri-urban communities in Karachi with a view to influence improvement of services and effects on human health.

A Study on the Microbiological Status of Mineral Drinking Water.

INTRODUCTION: Water-borne diseases constitute a major health burden in Bangladesh. The objective of this study was to assess the overall quality of mineral water samples that obtained from different shops of Dhaka city. MATERIAL AND METHODS: To achieve the above-mentioned objective, methods of heterotrophic plate count (HPC) and total coliform count (TCC) were applied. Moreover, isolated colony from mineral water samples were characterized by using biochemical and antimicrobial susceptibility tests. RESULTS: Different water samples showed different HPC ranged from 1.0×10 to 8.00×102. Antimicrobial sensitivity test of some selected bacteria viz S. intermedius, S. aureus, S. felis and S. Saccharolyticus were performed. It was observed that Staphylococcus spp. isolates were susceptible to erythromycin, tetracycline, norfloxacin and ciprofloxacin. Furthermore, a few Staphylococcus spp. isolates were intermediate resistant to penicillin and oxacillin. However, most of the Staphylococcus spp. isolates were resistant to cefixime. CONCLUSION: The results indicate that mineral water serves as a reservoir of various bacteria and that people in Dhaka city, who are the consumers of these water, might get diseases. This study emphasizes the need for elaborated microbiological examinations of mineral drinking water commonly used in Dhaka city.

The microbial contamination and the presence of ß-lactamase producing Gram-negative bacteria in the water and on the surfaces of public recreation water facilities.

The microbiological quality of bathing water and the surfaces of the surrounding pool platforms of two pools was estimated. ESBL- and MBL-producing Gram-negative bacteria isolated from water and surface samples were also studied. The water samples were satisfactory in 31 (86.1 %) out of 36 cases. Pseudomonas aeruginosa as well as Escherichia coli were identified in only 2 (5.5 %) cases. There were no correlations between the HPC and number of enterobacteria in the pool water and those found in the surface samples. Isolated strains were resistant to ticarcillin with clavulanic acid in 52.3 % of cases; all of them were susceptible to ciprofloxacin. The sequences for blaCTX-M were found in 21.6 % of strains, mostly from the groups blaCTX-M9 and blaCTX-M25, whilst the genes for chosen carbapenemases were noted in 15 (17.0 %) of strains. It is necessary to implement new approaches to monitoring resistant bacteria, not only clinical ones but also those found in other public environments.

Characterization of bacterial community dynamics in a full-scale drinking water treatment plant.

Understanding the spatial and temporal dynamics of microbial communities in drinking water systems is vital to securing the microbial safety of drinking water. The objective of this study was to comprehensively characterize the dynamics of microbial biomass and bacterial communities at each step of a full-scale drinking water treatment plant in Beijing, China. Both bulk water and biofilm samples on granular activated carbon (GAC) were collected over 9months. The proportion of cultivable cells decreased during the treatment processes, and this proportion was higher in warm season than cool season, suggesting that treatment processes and water temperature probably had considerable impact on the R2A cultivability of total bacteria. 16s rRNA gene based 454 pyrosequencing analysis of the bacterial community revealed that Proteobacteria predominated in all samples. The GAC biofilm harbored a distinct population with a much higher relative abundance of Acidobacteria than water samples. Principle coordinate analysis and one-way analysis of similarity indicated that the dynamics of the microbial communities in bulk water and biofilm samples were better explained by the treatment processes rather than by sampling time, and distinctive changes of the microbial communities in water occurred after GAC filtration. Furthermore, 20 distinct OTUs contributing most to the dissimilarity among samples of different sampling locations and 6 persistent OTUs present in the entire treatment process flow were identified. Overall, our findings demonstrate the significant effects that treatment processes have on the microbial biomass and community fluctuation and provide implications for further targeted investigation on particular bacteria populations.

Seasonal distribution and prevalence of diarrheagenic Escherichia coli in different aquatic environments in Taiwan.

Diarrheagenic Escherichia coli (DEC) are the most common agents of diarrhea. Waterborne DEC could pose a potential health risk to human through agricultural, household, recreational, and industrial use. There are few published reports on the detection of DEC and its seasonal distribution in aquatic environments. The presence of DEC in different types of aquatic environments was investigated in this study. Water samples were collected from major rivers, water reservoirs, and recreational hot springs throughout Taiwan. Moreover, an intensive water sampling plan was carried out along Puzih River. The detection of DEC target genes was used to determine the presence of enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), and Shiga toxin-producing E. coli (STEC). Among the 383 water samples analyzed, DEC was found in 122 (31.8%) samples. The detection rate varied by genotype, raging from 3.6% for STEC to 17.2% for EPEC. The DEC detection rate was higher from river waters than reservoirs and hot springs. In addition, DEC was detected at a higher rate in spring and summer. The presence of EPEC was significantly associated with total coliform levels among hot spring samples. Moreover, the presence of ETEC in river water samples was associated with heterotrophic plate counts. Water with EPEC differed significantly in pH from Puzih River samples. These results suggest that seasonal characteristics may affect the presence of DEC in different aquatic environments, and water quality indicators may be indicative of the presence of DEC.

Evaluation of heterotrophic plate and chromogenic agar colony counting in water quality laboratories.

The enumeration of bacteria using plate-based counts is a core technique used by food and water microbiology testing laboratories. However, manual counting of bacterial colonies is both time and labour intensive, can vary between operators and also requires manual entry of results into laboratory information management systems, which can be a source of data entry error. An alternative is to use automated digital colony counters, but there is a lack of peer-reviewed validation data to allow incorporation into standards. We compared the performance of digital counting technology (ProtoCOL3) against manual counting using criteria defined in internationally recognized standard methods. Digital colony counting provided a robust, standardized system suitable for adoption in a commercial testing environment. The digital technology has several advantages:•Improved measurement of uncertainty by using a standard and consistent counting methodology with less operator error.•Efficiency for labour and time (reduced cost).•Elimination of manual entry of data onto LIMS.•Faster result reporting to customers.

Effect of different heterotrophic plate count methods on the estimation of the composition of the culturable microbial community.

Heterotrophic plate counts (HPC) are routinely determined within the scope of water quality assessment. However, variable HPC methods with different cultivation parameters (i.e., temperature and media type) are applied, which could lead to significant effects in the outcome of the analysis. Therefore the effect of different HPC methods, according to DIN EN ISO 6222 and EPA, on the culturable microbial community composition was investigated by 16S rRNA gene sequence analysis and statistical evaluation was performed. The culturable community composition revealed significant effects assigned to temperature (p < 0.01), while for media type no statistical significance was observed. However, the abundance of certain detected bacteria was affected. Lower temperature (22 °C) showed the abundance of naturally occurring Pseudomonadaceae and Aeromonadaceae, whereas at high temperature (37 °C) numerous Enterobacteriaceae, Citrobacter spp. and Bacilli were identified. The highest biodiversity was detected at lower temperature, especially on R2A medium. These results indicate that different temperatures (low and high) should be included into HPC measurement and selection of media should, ideally, be adjusted to the monitored water source. Accordingly, it can be inferred that the HPC method is more suitable for continuous monitoring of the same water source than for single assessments of a water sample.

Pseudomonas aeruginosa and Heterotrophic Bacteria Count in Bottled Waters in Iran.

BACKGROUND: Nowadays, due to increased public awareness about water pollution and water borne diseases as well as water network deficiencies, bottled water consumers have increased dramatically worldwide, including Iran. Pseudomonas aeruginosa is an opportunistic human pathogen capable of causing widespread infections in burn and immune-compromised patients. The aim of this study was to investigate, P. aeruginosa in bottled waters selling in Iranian markets. METHODS: One hundred and twenty samples of five unknown (not famous) domestic bottled water brands were purchased from Tehran retailers during 2013. The samples were evaluated for the presence of P. aeruginosa. In addition, heterotrophic plate counts were determined by incubation at 37 °C for 24 h. RESULTS: P. aeruginosa was detected in 36.7% (44 samples) of all samples examined. In addition, heterotrophic bacteria in 32.5% (39 samples) of the samples were higher than 100 CFU/mL, while in 7.5% (9 samples) of the samples HPC relied between 20 and 100 CFU/ml. CONCLUSION: In contrast to public believe, bottled waters are not free of microorganisms, and it is suggested that authorities should provide stricter monitoring and control plan for water resources and plants. Concerning HPC and P. aeruginosa brands B and D were not suitable for drinking.

Field evaluation of a new point-of-use faucet filter for preventing exposure to Legionella and other waterborne pathogens in health care facilities.

BACKGROUND: Opportunistic waterborne pathogens (eg, Legionella, Pseudomonas) may persist in water distribution systems despite municipal chlorination and secondary disinfection and can cause health care-acquired infections. Point-of-use (POU) filtration can limit exposure to pathogens; however, their short maximum lifetime and membrane clogging have limited their use. METHODS: A new faucet filter rated at 62 days was evaluated at a cancer center in Northwestern Pennsylvania. Five sinks were equipped with filters, and 5 sinks served as controls. Hot water was collected weekly for 17 weeks and cultured for Legionella, Pseudomonas, and total bacteria. RESULTS: Legionella was removed from all filtered samples for 12 weeks. One colony was recovered from 1 site at 13 weeks; however, subsequent tests were negative through 17 weeks of testing. Total bacteria were excluded for the first 2 weeks, followed by an average of 1.86 log reduction in total bacteria compared with controls. No Pseudomonas was recovered from filtered or control faucets. CONCLUSION: This next generation faucet filter eliminated Legionella beyond the 62 day manufacturers' recommended maximum duration of use. These new POU filters will require fewer change-outs than standard filters and could be a cost-effective method for preventing exposure to Legionella and other opportunistic waterborne pathogens in hospitals with high-risk patients.

Microbial quality of drinking water from microfiltered water dispensers.

A comparison was made between the microbial quality of drinking water obtained from Microfiltered Water Dispensers (MWDs) and that of municipal tap water. A total of 233 water samples were analyzed. Escherichia coli (EC), enterococci (ENT), total coliforms (TC), Staphylococcus aureus, Pseudomonas aeruginosa and heterotrophic plate count (HPC) at 22 °C and 37 °C were enumerated. In addition, information was collected about the principal structural and functional characteristics of each MWD in order to study the various factors that might influence the microbial quality of the water. EC and ENT were not detected in any of the samples. TC were never detected in the tap water but were found in 5 samples taken from 5 different MWDs. S. aureus was found in a single sample of microfiltered water. P. aeruginosa was found more frequently and at higher concentrations in the samples collected from MWDs. The mean HPCs at 22 °C and 37 °C were significantly higher in microfiltered water samples compared to those of the tap water. In conclusion, the use of MWDs may increase the number of bacteria originally present in tap water. It is therefore important to monitor the quality of the dispensed water over time, especially if it is destined for vulnerable users.