Enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) fingerprinting reveals intra-serotype variations among circulating Listeria monocytogenes strains

Abstract

Forty-five presumptive Listeria monocytogenes isolates were confirmed by multiplexpolymerase chain reaction (PCR) and characterized for antimicrobial susceptibility and tolerance to commonly used disinfectants. Isolates were also serotyped by PCR and characterized by enterobacterial repetitive intergenic consensus ERIC-PCR fingerprinting. All of the isolates showed PCR products of 938 bp (genus) and of 750 bp (species). Antimicrobial susceptibility was 100% for ampicillin, amoxicillin/ clavulanic acid, vancomycin and chloramphenicol, whereas for trimethoprim/ sulfamethoxazole it was 98, azithromycin 96, erythromycin 91, tetracycline 82, penicillin 97.8 (2.2% no susceptible), ciprofloxacin 84.4, rifampin 64.4, meropenem 71.1 and clindamycin 22.2%, respectively. All the isolates were resistant to cephalosporins. 71% of the isolates showed a MIC ≤ 200 ppm/10 to15 min for sodium hypochlorite and 98% a MIC ≤ 1.5%/2 to15 min for Tego-51. 58% of isolates were serotyped as 4b/4d/4e, 16% as ½b/3b, 7% as ½a/3a, and 4% as ½c/3c. ERIC-PCR showed 28 polymorphic bands ranging from 100 to 2810 bp that did not cluster according to any phenotype. ERIC-PCR fingerprinting revealed intra-serotypic variations and proved that different L. monocytogenes strains were circulating in the country during the isolation period.   Key words: Listeria monocytogenes, molecular serotyping, antimicrobial susceptibility, disinfectant tolerance, enterobacterial repetitive intergenic consensus- polymerase chain reaction (ERIC-PCR).