Potential Risk Assessment of Drinking Water Source Exposed to Contamination Using Microbial Indicators and Multiple Antibiotic Resistance Index

In this study, drinking water sources including drilled wells (DW), water tankers (WT), stabilized water tanks (SWT), and plastic bottles (PB) as sequential sample were assessed at Dhamar City, Yemen to investigate the microbial contamination and the potential risk of contamination using microbial indicators and multiple antibiotic resistance index. The sequential sample involving, 5 drilled wells, 10 water tankers, 20 water tanks, and 100 plastic bottles. The study encompassed five sequential samples. Each water sample was collected in triplicate and analyzed for E.coli as a microbial indicator and antibiotic susceptibility testing. Results indicated that all the water samples were contaminated by E.coli and total coliform exceeded the acceptable levels recommended by WHO of microbial quality of drinking water. E.coli isolates (240) showed high resistance to the tested antibiotics comprising 79.82% to ampicillin, 78.32% to gentamicin, 67.5% to ceftriaxone, 19.98% to ciprofloxacin, 18.32% to amoxiclav, and 33.34% were resistant to tetracycline. The multiple antibiotic resistance index of E. coli that showed resistant to three antibiotics ranged from 0.19 to 0.24 for all the tested samples and exceeded the threshold value of 0.2 for all samples except sequential sample 4, indicating a high risk of contamination for drinking water effected by anthropogenic activities related to urbanization, accumulation of microbial contamination during the various transferring processes of water from the source into households, as well as  misuse and greater exposure to antibiotics in humans and poultry farms, which may pose a high ecological risk to the waters.