RESUMEN
Quinolone-resistant Salmonella Infantis (n = 64) isolated from human stool samples, food and poultry during the years 2006-2011 were analysed for their resistance phenotypes, macrorestriction patterns and molecular mechanisms of decreased susceptibility to fluoroquinolones. Minimum inhibitory concentrations (MICs) of nalidixic acid (NAL) and ciprofloxacin (CIP) were determined by the agar dilution procedure, and the susceptibility to additional antimicrobial agents was determined by the disc diffusion method. To assess the influence of enhanced efflux activity, MICs were determined in the presence and absence of the inhibitor PAßN. The results of pulsed-field gel electrophoresis (PFGE) typing revealed that quinolone-resistant S. Infantis in Serbia had similar or indistinguishable PFGE profiles, suggesting a clonal spread. All S. Infantis showed combined resistance to NAL and tetracycline, whereas multiple drug resistance to three or more antibiotic classes was rare (2 isolates of human origin). The MICs ranged between 512 and 1024 µg/mL for NAL and 0.125-2 µg/mL for CIP. A single-point mutation in the gene gyrA leading to a Ser83âTyr exchange was detected in all isolates, and a second exchange (Ser80âArg) in the gene parC was only present in eight S. Infantis isolates exhibiting slightly higher MICs of CIP (2 µg/mL). The inhibitor PAßN decreased the MIC values of CIP by two dilution steps and of NAL by at minimum 3-6 dilution steps, indicating that enhanced efflux plays an important role in quinolone resistance in these isolates. The plasmid-mediated genes qnr, aac(6')-lb-cr and qepA were not detected by PCR assays.
Asunto(s)
Girasa de ADN/metabolismo , Topoisomerasa de ADN IV/metabolismo , Infecciones por Salmonella/microbiología , Salmonella enterica/genética , Girasa de ADN/genética , Topoisomerasa de ADN IV/genética , ADN-Topoisomerasas/genética , ADN-Topoisomerasas/metabolismo , Farmacorresistencia Bacteriana , Regulación Bacteriana de la Expresión Génica/fisiología , Humanos , Infecciones por Salmonella/epidemiología , Serbia/epidemiología , TranscriptomaRESUMEN
Molecular typing and resistotyping coupled with gyrA single nucleotide polymorphism (SNP) of 60 Salmonella Enteritidis (SE) isolates originated from poultry, food, and humans in Serbia is described. Molecular fingerprinting was performed by randomly amplified polymorphic DNA (RAPD) using four primers, and the diversity index (D) was 0.688. In combination with resistotyping and gyrA SNP, D increased to 0.828. A total of 23 genetic groups were obtained. When four RAPD primers were combined, epidemic isolates from a fast-food restaurant outbreak were clustered in a distinctive genetic group. Among 60 SE strains, three had multiple resistances to three or more antibiotics. Nine strains were resistant to nalidixic acid (NAL; a non-fluorinated quinolone). The mutations in quinolone resistance-determining region (QRDR) found in NAL-resistant strains were attributed to Asp(87) â Asn in six strains, Asp(87) â Gly in one strain, and Ser(83) â Phe in one strain. One NAL-resistant strain had no mutations in QRDR, suggesting another mechanism of resistance.