Understanding the effect of exposure of human pathogens to polluted surface water: Salmonella as a model organism

Abstract

Unplanned urbanization often results in the surface waters getting contaminated with industrial and faecal pollutants. The wide spectrum of industrial pollutants put pressure on the faecal organisms during their survival in these polluted waterbodies. Although such pressure is commonly known to result in shorter survival of these organisms which can be pathogenic to humans, its effect on the virulence indicators is not fully understood. This study attempts to detect the presence and responses of Salmonella in waterbodies contaminated with industrial pollutants. A lake (Hatirjheel) receiving low level of industrial pollutants and a river (Buriganga) receivng high level of industrial pollutants within Dhaka city were selected for sampling. A total of 40 water samples were aseptically collected from Hatirjheel Lake and 20 samples from Buriganga River within a duration of three months. Then they were processed for isolation of cultureable Salmonella, before checking for Salmonella specific virulence gene invA. After that, randomly selected 5 strains from each were checked for their susceptibility to an array of eight antibiotics. Further, randomly selected three strains from each lake were tested for survival potential under starvation stress. Across the study period, 40% of the sample collected from the lake and 70% of the sample collected from the river yielded culturable Salmonella all of which contained invA gene. The antibiogram revealed that isolates from Buriganga showed complete resistance to ampicillin, co-trimoxazole and cefepime while the Hatirjheel isolates showed complete resistance to only ampicillin and cefepime. The survival patterns between the lake and river showed slight difference but both showed a gradual decrease in culturable count over the time. The study reveals that both Buriganga River and Hatirjheel Lake can be endemically contaminated with potentially pathogenic Salmonella and that there is an indication that the pollution level might have some influence on antibiotic resistance of Salmonella. To the best of our knowledge, this is the first study on focusing on Salmonella in the surface waters of Dhaka city.