Detection of linezolid and vancomycin resistant Enterococcus isolates collected from healthy chicken caecum.

AIM: The poultry industry represents an important economic sector in Tunisia. This study aims to determine the antimicrobial resistance phenotypes and genotypes and virulence factors of enterococci collected from chicken caecum in Tunisia.

METHODS AND RESULTS: Forty-nine composite chicken caecum samples were recovered in 49 different Tunisian farms (december 2019 to march 2020). Each composite sample corresponds to six individual caecum from each farm. Composite samples were plated on Slanetz-Bartley agar both supplemented (SB-Van) and not supplemented (SB) with vancomycin and isolates were identified by MALDI-TOF. Antibiotic resistance and virulence genes were tested by PCR and sequencing and multilocus-sequence-typing of selected enterococci was performed. One hundred sixty seven enterococci of 6 different species were recovered. Acquired linezolid-resistance was detected in 6 enterococci of 4/49 samples (8.1%): A) four optrA-carrying E. faecalis isolates assigned to ST792, ST478 and ST968 lineages; B) two poxtA-carrying E. faecium assigned to ST2315 and new ST2330. Plasmid typing highlighted the presence of the rep10, rep14, rep7, rep8 and pLG1 in these strains. One vancomycin-resistant E. faecium isolate (typed as ST1091) with vanA gene (included in Tn1546) was detected in SB-Van plates. The gelE, agg, esp and hyl virulence genes were found in linezolid- and vancomycin-resistant enterococci. High resistance rates were identified in the enterococci recovered in SB plates: tetracycline (74.8%, tet(M) and tet(L) genes), erythromycin (65.9%, erm(B)) and gentamicin (37.1%, aac(6')-Ie-aph(2″)-Ia).

CONCLUSION: The detection of emerging mechanisms of resistance related to linezolid and vancomycin in fecal enterococci of poultry farms has public health implications and further surveillance should be carried out to control their dissemination by the food chain.