Resistance to antimicrobial agents in human Salmonella isolated in Bulgaria, 1999–2004

Abstract number: 1134_03_237

Asseva G., Petrov P., Ivanov I., Kantardjiev T.

Objective:  

To analyse the distribution of resistant Salmonella and resistance mechanisms among most frequently encountered serovars in Bulgaria: S. enteritidis, S. typhimurium, S. corvallis.

Methods:  

Culture, biochemical tests and serotyping for identification of strains.Screening for resistance to 14 antimicrobial agents: Cefotaxime, Cefoxitin, Carbenicillin, Ceftazidime, Cefuroxime, Cephalothin, Ampicillin, Amoxicillin/Clavulanic acid, Gentamicin, Tetracycline, Chloramphenicol, Ciprofloxacin, Nalidixic acid, Trimethoprim/Sulfamethoxazole with the standard Bauer-Kirby disk-diffusion method. Double disk synergy method (Jarlier et al.) was applied to determine ESBLs production. Transfer of bla-CTX-M and bla-TEM genes has been studied with experimental conjugation. For PCR detection of bla-CTX-M and bla-TEM genes specific primers have been used.

Results:  

For a study period 200 Salmonella strains out of 2123 were resistant to one and more antimicrobial agents;23 resistant strains were isolated from 163 confirmed cases during outbreaks and 177 of resistant strains were causing sporadic cases of human illness or carrier state. 104 ESBLs producers have been detected:5 S. enteritidis,1 S. typhimurium, 1 S. isangi and 97 S. Corvallis with types of extended-spectrum beta-lactamases CTX-M3,TEM and SHV. All ESBLs producing strains were multiresistant to 9,10 and 11 antimicrobial agents.Bla-CTX-M3 and bla-TEM genes were successfully transferred into a recipient E. coli C1A strain simultaneously with genes coding for resistance to aminoglycosides and sulfonamides (for bla-CTX-M3)and genes coding for resistance to aminoglycosides and chloramphenicol (for bla-TEM.PCR amplification revealed bla-CTX-M3 gene in S.Enteritidis and bla-TEM in S.corvallis.Before 1999 all S. Enteritidis were susceptible to all antimicrobial agents tested. In this study salmonellae have revealed resistance to at least one antimicrobial agent, most frequently to Nalidixic acid and Trimethoprim/sulfamethoxazole.Resistance to Nalidixic acid combined with retained susceptibility to ciprofloxacin in S. enteritidis is suggestive for mutations in the chromosomal gyrA.Resistance to ampicillin in S.Enteritidis could be explained with widely distributed plasmids in European countries including Bulgaria.Selection of multiresistant bla-TEM producing S.Corvallis is probably unique for our country.

Conclusions:  

Diversity of resistance genes are widely distributed among the leading causative agents of human salmonelloses in Bulgaria.