Isolation and identification of pathogenic bacteria of the genus Escherichia and Salmonella in the water environment tested positive for antibiotic residues in the city of Ndjamena, Cha

Abstract

Objective: The water environment is facing increasing contamination by antibiotic residues, favoring the development of pathogenic bacteria, in particular Escherichia and Salmonella. This study aims to determine the presence of pathogenic bacteria of the genus Escherichia and Salmonella in the water environment containing antibiotic residues in the city of Ndjamena, Chad. Methodology and results: Information gathered from questionnaires and the results of preliminary positive tests (premiTest) were used to identify the sample. A total of 27 wastewater samples from retention basins, hospital drainage channels, abattoir water and the Chari and Logone rivers were tested positive for antibiotic residues and retained for isolation of Escherichia and Salmonella bacteria. Cultures on specific media (EMB for Escherichiaand SS for Salmonella) were carried out in accordance with reference methods. A total of 36 isolates were obtained, including 15 of the Escherichia genus with a prevalence of 55.6% and 20 of the Salmonella genus with a prevalence of 74%. Analyzing the data by commune, a 100% prevalence of Salmonella was observed in the 2nd, 3rd, 6th and 10th arrondissements, and 80% and 57.1% respectively in the 8th and 7th arrondissements. Escherichia isolates were 100% prevalent in the 8th and 10th arrondissements, and 75% and 66.6% respectively in the 1st and 10th arrondissements. At neighborhood level, 100% Salmonella prevalence was observed in Ardepdjoumal, Diguel, Diguel Est, Gardolet, Clemat, Ndjari and Walia, while 100% E. coli prevalence was found in Dembé, Diguel, Diguel Est, Clemat, Ndjari, Walia, Gueli and Zafaye. These prevalences varied significantly at the 5% level (p-value = 0.004224 for Salmonella and p-value = 0.01921 for Escherichia) between the different districts and neighborhoods of the city of Ndjamena. Conclusion and application of results: This study revealed variability in the presence of Salmonella and E. coli in water samples from the various districts and neighborhoods of N’Djamena, with prevalences ranging from 0 to 100%. These high prevalences are explained by poor waste management in communes, health and veterinary establishments, highlighting for the first time the level of contamination of the water environment by these pathogenic bacteria. It is essential that the Ministries of Public Health and Livestock exert pressure to prohibât the discharge of drug residues into wastewater, in order to prevent drug résistance mechanisms in Chad.