A Comprehensive Study on Antibiotic Resistance among Coagulase-Negative Staphylococci (CoNS) Strains Isolated from Ready-to-Eat Food Served in Bars and Restaurants

Abstract

The present study aimed to characterize and assess the diversity of CoNS strains as potential vectors for the spread of resistance to antimicrobial agents from RTE foods served in bars and restaurants. Eighty-five CoNS strains, obtained from 198 RTE food samples, were investigated. Sixty-seven CoNS isolates (78.8%) were resistant to at least one antibiotic tested, and 37 (43.5%) were multidrug resistant (MDR-CoNS). Moreover, CoNS strains contained genes conferring resistance to antibiotics critically important in medicine, i.e., β-lactams [mecA (29.4%); blaZ (84.7%)], aminoglycosides [aac(6')-Ie-aph(2″)-Ia (45.9%); aph(2″)-Ic (3.5%)], macrolides, lincosamides and streptogramin B-MLS_B [msrA/B (68.2%); ermB (40%) and mphC (4.7%)], tetracyclines [tetK (31.8%); tetM (16.5%) and/or tetL (2.35%)]. We also found the fusB/C/D genes responsible for the acquired low-level fusidic acid resistance (17.6%) and streptogramin resistance determinant vgaA in 30.6% of isolates. In three linezolid resistant strains (2 S. epidermidis and 1 S. warneri), mutation was detected, as demonstrated by L101V and V188I changes in the L3 protein amino acid sequences. The high frequency in RTE food of MDR-CoNS including methicillin-resistant (MR-CoNS) strains constitutes a direct risk to public health as they increase the gene pool from which pathogenic bacteria can pick up resistance traits.

Keywords: antimicrobial resistance; coagulase-negative staphylococci (CoNS); methicillin resistant coagulase-negative staphylococci (MR-CoNS); multidrug resistant coagulase-negative staphylococci (MDR-CoNS); ready-to-eat food.

Figure 1

Antibiotic resistance profile of MR-CoNS isolates. Phylogenetic tree was obtained from the analysis of the partial gene sequence of tuf from isolates. Phylogenetic tree was created from DNA sequences using the neighbor-joining method with Kimura 2-parameter distance correction model with 1000 bootstrap replications using the MEGA X software. Abbreviations: green circles—resistant; circles without filling—medium sensitive, shape completely omitted-sensitive. P—penicillin, QD—quinupristin/dalfopristin, E—erythromycin, FOX—cefoxitin, DA—clindamycin, RD—rifampicin, FD—fusidic acid, CN—gentamycin, NOR—norfloxacin, F—nitrofurantoin, LZD—linezolid, TE—tetracycline, C—chloramphenicol, CIP—ciprofloxacin, SXT—trimethoprim/sulfamethoxazole. Strains antibiogram visualized using iTOL.

Figure 2

Correlation matrix of genotypic and phenotypic antibiotic resistance of all (n = 85) CoNS isolates. Green is positive correlation and purple is negative correlation. The strength of the color and size indicate the numerical value of correlation coefficient. Abbreviations: P—penicillin, QD—quinupristin/dalfopristin, E—erythromycin, FOX—cefoxitin, DA—clindamycin, RD—rifampicin, FD—fusidic acid, CN—gentamycin, NOR—norfloxacin, F—nitrofurantoin, LZD—linezolid, TE—tetracycline, C—chloramphenicol.