Microbiological Quality and Antimicrobial Resistance of Drinking and Reused Water Sources at Islamic University, Kushtia, Bangladesh

Access to safe water remains a major public health concern worldwide, particularly in lower-middle-income countries such as Bangladesh. To date, no comprehensive study has evaluated the microbiological safety and antimicrobial resistance patterns of drinking water and reused dishwashing water within the campus environment of Islamic University (IU), Kushtia. This study assessed the bacteriological quality of multiple water sources with emphasis on total viable bacterial count (TVBC) and the indicator organism Escherichia coli . A total of 28 samples were collected from student halls and nearby eateries. Microorganisms were characterized using integrated cultural, biochemical, and molecular approaches, revealing the presence of E. coli along with Erwinia , Acinetobacter , Pseudomonas , and Lactobacillus spp. Representative isolates were further confirmed by 16S rRNA gene sequencing and phylogenetic analysis, strengthening taxonomic identification. Antimicrobial susceptibility testing and multiple antibiotic resistance index (MARI) analysis were performed for all isolates. Statistical analysis of log₁₀-transformed TVBC data using one-way ANOVA showed a significant difference among water sources (p < 0.001), with reused water exhibiting the highest bacterial load. The mean TVBC values for reused water, tube-well water, water pump, and tap water were 1.11×10⁵±726, 3.81×10²±25.44, 3.17×10²±36.38, and 2.21×10⁴±658 CFU/ml, respectively. Notably, E. coli isolates showed high susceptibility to imipenem (100%), nitrofurantoin (100%), and gentamicin (85.71%), while resistance was observed against ciprofloxacin (71.42%), doxycycline (57.14%), and ceftriaxone (42.85%). MARI values > 0.20 indicated exposure to high-risk contamination sources with frequent antibiotic pressure. Overall, elevated TVBC and MARI values identify reused water as a high-risk source, unsuitable for utensil cleaning according to WHO guidelines, posing potential cross-contamination risks.