Polyphasic characterization of antibiotic resistant and virulent enterococci isolated from feed and stored-product insects

Feed and stored-product insects from livestock facilities and feed mills were collected and cultured for Enterococcus spp. A total of 362 enterococcal isolates isolated from 89 feed samples and 228 stored-product insects were identified to the species level using multiplex PCR. These isolates represented Enterococcus casseliflavus (53%), E. gallinarum (20%), E. faecium (16%), E. hirae (5%) and E. faecalis (5%). Enterococci were phenotypically resistant to tetracycline (48%), erythromycin (14%), streptomycin (17%), kanamycin (12%), ciproflaxacin (11%) ampicillin (3%) and chloramphenicol (1%). Tetracycline resistance in enterococci was encoded by tet(M) (49%), tet(O) (15%), and tet(K) (1%). Enterococci carried virulence genes including gelatinase gene (gelE; 22%), an aggregation substance gene (asa1; 7%), an enterococcus surface protein gene (esp; 2%), and cytolysin gene; (2%). The isolates with cylA gene and gelE genes were hemolytic and gelatinolytic, respectively. The erythromycin resistance encoded by ermB was detected in 8.5% of isolates. The conjugative transposon Tn916/Tn1545 family was detected in 10.5% of enterococcal isolates. Phenotypic and genotypic analysis of these isolates for antibiotic resistance and virulence factors demonstrated that the feed and stored-product insects collected from livestock facilities and feed mills carried antibiotic-resistant and potentially virulent enterococci and may spread the antibiotic resistance and virulent genes to pathogens of clinical importance by horizontal gene transfer.