Evaluation the Impact of Chlorination on the Development of Chlorine and Antibiotic-Resistant Bacterial Isolates in Public Swimming Pools

Water is necessary for human daily activities and acts as a vehicle for the transmission of several waterborne diseases. This study was designed to investigate the bacteriological safety of water in swimming pools in Sulaymaniyah city-Iraq. For this purpose, during summer time (August to September 2021), sixty-seven water samples were collected from eight indoor public swimming pools. The physicochemical parameters were measured and the bacteriological assessment was done using the Most Probable Number test. The diversity of microbial communities was then assessed using the Vitek 2 compact and the 16S rRNA gene. In addition, the chlorine resistance test and biofilm formation were quantified using the microdilution technique and crystal violet staining method, respectively. Moreover, the Kirby- Bauer disk diffusion technique was used to test antimicrobial susceptibility.
Variable results of the physicochemical analysis were recorded for each of the temperatures (25.81±1.16 to 28.69±1.03 °C), pH (7.02±0.24 to 7.46±0.31), and free chlorine (0.12±0.05 to 1.38±1.24 mg L-1). MPN negative results revealed that non-lactose fermenting bacteria were detected in 80% of the water samples, including Enterobacter cloacae 34/59 (57.63%), and Pseudomonas spp. 10/59 (16.95%), and other important opportunistic pathogens 15/59 (25.42%). The contamination rate was strongly correlated with the sources of water used for the swimming pool and the free chlorine concentrations in the pools. Chlorine resistance test results revealed variations for all isolated bacteria ranging from 1.25 to 5 mg L-1. Moreover, a negative linear correlation was found between chlorine concentrations, and both bacterial growth and biofilm formation. Most significantly, there was a strong positive correlation (r=0.90 to 0.98) between the degree of biofilm formation and bacterial growth. Moreover, different antibiogram profiles were recorded for the 15 antibiotics used in this study.
It can be concluded that most of the studied swimming pools are heavily contaminated by chlorine and antibiotic-resistant waterborne pathogens.