Antimicrobial resistance and presence of class 1 integrons in salmonella serovars isolated from clinical cases of animals and humans in North Dakota and Uganda.

Abstract

Back ground: Salmonellae are one of the leading causes of food borne illness worldwide and have been used as indicator organisms for studying antimicrobial resistance (AMR) trends. In the United States, Salmonella are among organisms currently under public health surveillance for AMR. Objectives: The objective of this study was to characterise AMR patterns of Salmonella isolates from animals and humans in North Dakota (ND), and Kampala, Uganda and determine the association between the observed AMR and presence of class 1 and 2 integrons. Methods: Salmonella isolates were collected from the Veterinary Diagnostic Laboratory (VDL) at North Dakota State University and the North Dakota Department of Health, from 2003 to2008. Additional samples were also retrieved from archives at the Microbiology Department, Faculty of Veterinary Medicine at Makerere University in Kampala, Uganda. AMR profiles were determined using a panel of 15 antimicrobials. Screening for the class 1 and 2 integrons was done using PCR with primers specific for the int1 and int2. Results: Out of 359 Salmonella isolates tested 36.2% were resistant to at least 2 antimicrobials. The highest resistance frequency was seen against Tetracycline (39.6%) and Streptomycin (34.7 %). A total of 20.7% (57/276) of the ND samples tested positive for presence of class 1 integrons and was significantly associated (p<0.05) with AMR to Ampicillin, Kanamycin, Tetracycline and Sulfisoxazole. Of all Ugandan Salmonella isolates tested (94.4% 68/72) were resistant to ≥2 antimicrobials with highest resistance observed against Sulfisoxazole and TrimethoprimSulphamethoxazole. Presence of class 1 integron was significantly associated (p<0.05) with AMR to Tetracycline and Amoxicillin. DNA sequencing of the class 1 integron variable regions identified several resistance genes including aadA1, dfrA7, and dfrA5 genes. Conclusion: These results signal serious implications for treatment of salmonellosis in both public and animal health.