Antimicrobial Resistance Patterns of Salmonella Strains Isolated from Beef in Namibia

Aim: The aim of the study was to determine the antimicrobial resistance profiles of Salmonella strains isolated from beef in Namibia.

Methodology: To assess the antimicrobial resistance of Salmonella, a total of 81 strains isolated from 9508 routine beef samples from January 2008 to December 2009 were used. Isolation of Salmonella was done using a standard isolation procedure where the serotyping was done according to the White Kauffmann Le Minor scheme. Salmonella isolates were from carcass swabs (n = 45), meat juice (n = 19) and meat cuts (n = 17). Antimicrobial susceptibility testing on the serotyped Salmonella strains was carried out against 16 different antimicrobials using the Kirby-Bauer disc diffusion method on Mueller-Hinton agar.

Results: Twenty one of 81 isolates (25.93%) from beef samples belonging to 15 different Salmonellaserovars showed antimicrobial resistance to one or more of the 16 antimicrobials tested and 13 (16.05%) exhibited resistance to two or more antimicrobials. Two S. Chester isolates and one S. Schwarzengrund isolate exhibited resistance to two or more antimicrobial classes. The resistance was most commonly observed to sulfisoxazole (23.46%), trimethoprim-sulfamethoxazole (13.58%), tetracycline (3.7%), amoxicillin-clavulanic acid (1.23%), cephalothin (1.23%) and chloramphenicol (1.23%). Most of the Salmonella isolates that showed resistance to two or more antimicrobials had a common resistance pattern to both sulfisoxazole and trimethoprim-sulfamethoxazole.

Conclusions: The present study revealed low antimicrobial resistance in Salmonella strains isolated from beef in Namibia. This suggests that there could still be a public health risk if such strains may reach the consumers.