Enterococci isolated from plant-derived food - analysis of antibiotic resistance and the occurrence of resistance genes

Abstract This study analyzed phenotypic and molecular resistance to tetracyclines, macrolides, glycopeptides, aminoglycosides in Enterococcus strains isolated from plant-derived food. The study involved examining 270 food samples and 72 obtained Enterococcus sp. strains were isolated and identified as E. faecium, E. faecalis and E. casseliflavus. Most of them (55.6%) were resistant to streptomycin, followed by those resistant to rifampicin (51.4%), tigecycline (37.5%), erythromycin (36.1%) and fosfomycin (27.8%). More than half of the strains under analysis showed the high-level aminoglycoside resistance (HLAR) phenotype (55.6%). Resistance to aminoglycosides was associated mainly with the presence of the ant(6')-Ia gene (54.2%), followed by the aph(3')-IIIa gene (30.5%), and – to a small extent – with the presence of the aac(6')-Ie-aph(2'')-la gene (8.3%). Resistance to tetracycline was caused mainly by the tetM (40.3%) and tetL (22.2%) genes and to macrolides - by ermB (33.3%) and ermA (11.1%). A conjugative transposon of the Tn916/Tn1545 family was present in nearly half (45.8%) of the isolates. The findings show that there is a need to monitor plant-derived food for the presence of antibiotic-resistant Enterococcus strains, because it can be a potential reservoir of genes encoding resistance to clinically important antibiotics.