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Antimicrobial resistance of Salmonella Typhimurium strains isolated from stool samples

Salmonella enterica is a major pathogen in humans as well as in animals and comprises more than 2500 serovars. The antimicrobial resistance rate varies with different serovars and different antibiotics. Salmonella Typhimurium (S.Typhimurium), one of the most common serovars associated with clinically reported salmonellosis in humans, is relatively more resistance to antimicrobial agents than are other serotypes. In the study period, out of 1019 Salmonella prior isolates, 53 (5, 2 %) strains were S.Typhimurium. Sensitivity to antibiotics was tested in 46 of S.Typhimurium isolates. Resistance against at least one or more antibiotics, was found in 29 (63%) of the strains. Resistance was most common against ampicillin (54%), tetracycline (24 %), chloramphenicol (22%), cotrimoxazole (8, 7%) and amoxicillin/clavulanic acid 2%. Multiple resistance against four or three antimicrobial agents was found in 14 (30, 4%) isolates. The tested isolates were sensitive to third- generation cephalosporins. Production of Extended-spectrum β-lactamases were phenotypically confirmed by performing the double-disk synergy test, and the E test ESBL in 2 S.Typhimurium isolates. Resistance to nalidixic acid (which may indicate the occurrence of resistance to fluoroquinolones) was established in 2 isolated strains. According to the EUCAST minimal inhibitory concentration (MIC) breakpoints all isolated strains were sensitive to ciprofloxacin.Through the five-year period we noticed decrease in the total number of Salmonella enterica isolates. Multiple resistance strains against four or three antimicrobial agents was found in 30, 4% S.Typhimurium isolates and the values of MIC of ciprofloxacin showed a tendency to increase. Failure to identify drug-resistant salmonellae may affect the choice of appropriate alternative antibiotics in the treatment of patients with invasive salmonellosis.

Salmonella typhimurium; antimicrobial resistance; multiple resistance

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