Experimental Assessment of Antibiotic Resistance Patterns in Bacteria Isolated from Wastewater Treatment Plants

Wastewater treatment plants (WWTPs) are recognized hotspots for the proliferation and dissemination of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). As effluent discharge may introduce ARB into natural water ecosystems, assessing resistance patterns in these environments is critical to public and environmental health. This study aims to experimentally assess antibiotic resistance patterns in bacterial isolates from different stages of WWTP processes (influent, activated sludge, effluent), evaluating variations in resistance prevalence and identifying critical control points. Bacterial samples were collected across influent, biological treatment (activated sludge), and effluent from three municipal WWTPs. Standard microbiological culturing techniques were used to isolate representative bacteria (e.g., Escherichia coli, Pseudomonas spp., Enterococcus spp.). Isolates were subjected to antibiotic susceptibility testing against a panel of antibiotics (e.g., ampicillin, ciprofloxacin, tetracycline, vancomycin) using disk diffusion and minimal inhibitory concentration (MIC) assays, following CLSI guidelines. Resistance profiles were analyzed by stage and WWTP. Statistical analyses included chi-square tests and ANOVA to compare resistance rates across treatment stages. A total of 450 isolates were tested. Resistance prevalence significantly declined from influent to effluent for most antibiotics. For example, figure 1 shows a bar chart of percent resistance by sample stage: ampicillin resistance dropped from 75 % (influent) to 30 % (effluent); ciprofloxacin from 60 % to 25 %. figure 2 presents a line graph showing cumulative multi-drug resistance (MDR) rates decreasing across treatment stages. However, some isolates from effluent remained resistant to multiple antibiotics, including tetracycline and vancomycin. Findings highlight that conventional WWTP processes reduce—but do not eliminate—ARB. Results support the need for targeted disinfection or advanced tertiary treatments to minimize environmental release of resistance. Data provide a baseline for policymakers and engineers to strengthen wastewater treatment standards and safeguard public health.