Ready-to-eat dairy products as a source of multidrug-resistant Enterococcus strains: Phenotypic and genotypic characteristics

摘要

The enterococci are ubiquitous bacteria able to colonizethe human and animal gastrointestinal tracts andfresh and fermented food products. Their highly plasticgenome allows Enterococcus spp. to gain resistance tomultiple antibiotics, making infections with these organismsdifficult to treat. Food-borne enterococci couldbe carriers of antibiotic resistance determinants. Thegoal of this work was to study the characteristics of Enterococcusspp. in fermented milk products from Polandand their antibiotic resistance gene profiles. A total of189 strains were isolated from 182 dairy products outof 320 samples tested. The predominant species wereEnterococcus faecium (53.4%) and Enterococcus faecalis(34.4%). Isolates were resistant to streptomycin(29.1%), erythromycin (14.3%), tetracycline (11.6%),rifampicin (8.7%), and tigecycline (8.1%). We also detected2 vancomycin-resistant and 3 linezolid-resistantstrains; however, no vanA or vanB genes were identified.A total of 57 high-level aminoglycoside resistancestrains (30.2%) were identified, most of which have theant(6′)-Ia gene, followed by the aac(6′)-Ie-aph(2″)-Iaand aph(3″)-IIIa genes. Resistance to tetracycline wasmost often conferred by tetM and tetL genes. Macrolideresistance was most frequently encoded by ermBand ermA genes. Conjugative mobile genetic element(transposon Tn916–Tn1545) was identified in 15.3% ofthe strains, including 96.3% of strains harboring thetetM gene. This study found that enterococci are widelypresent in retail ready-to-eat dairy products in Poland.Many isolated strains are antibiotic resistant andcarry transferable resistance genes, which represent apotential source of transmission of multidrug-resistantbacteria to humans.