Detection of linezolid and vancomycin resistant Enterococcus strains isolated from avian cecum in Tunisia
Ben Yahia Houssem1,2, Abdellaoui Chaima1, Sara García-Vela3,4, Gharsa Haythem1,2, Ben Sallem Rym1,2, Carmen Torres3, Ben Slama Karim1,2

1 Institut Supérieur des Sciences Biologiques Appliquées de Tunis, Université de Tunis El Manar, 2092 Tunis, Tunisie
2 Laboratoire des Microorganismes et Biomolécules Actives, Faculté des Sciences de Tunis, Université Tunis El Manar, 2092 Tunis, Tunisie
3 Area de Bioquímica y Biología Molecular, Universidad de La Rioja, 26006 Logroño, Spain
4 Food Science Department, Laval University, Quebec, Canada

Background: Enterococcus has become a potentially high risk zoonotic opportunistic pathogen that can cause critical public health problems. The ability of these bacteria to acquire antibiotic resistance genes poses a major global threat. The aim of this investigation was to detect and characterize vancomycin and linezolid resistance acquired by enterococci isolated from avian cecum samples in Tunisia.

Materials/Methods: Cæcum chicken samples (n=294) were collected from 49 different Tunisian farms during December 2019 to March 2020. Six caeca per each farm were collected and then mixed in sterile spittoons, constituting a composite sample. More than one colony per sample was taken. A total of 167 isolates were recovered on Slanetz– Bartley agar supplemented or not with vancomycin. All the isolates were identified by MALDI-TOF. Phenotypic antimicrobial susceptibility testing, resistance genotyping and molecular typing by pulsed-field gel electrophoresis (PFGE) were performed.

Results: The identification results showed the predominance E. faecium (n=112), followed by E. faecalis (n=34), E. durans (n=08), E. hirae (n=10), E. gallinarum (n=2) and E. avium (n=1). Linezolid-resistance was detected in 5 Enterococcus isolates. After PCR and sequencing, our results showed that 4 E. faecalis harbored the optrA gene and one E. faecium harbored the poxtA gene. Acquired-vancomycin-resistance was detected in 2 E. faecalis isolates. This resistance was mediated by the vanA gene. High rates of resistance to tetracycline, erythromycin and chloramphenicol were also observed. After molecular characterization of the collected Enterococcus isolates, our results highlighted that the tet(M), tet(L), erm(B), msr and fexA genes were detected in most tetracycline, erythromycin and chloramphenicol resistant enterococci. The molecular typing of linezolid- and vancomycin-resistant isolates, performed by PFGE, showed a high genetic diversity.

Conclusion: This investigation provides insights that avian sector can be a reservoir of vancomycin and linezolid resistant enterococci and could be a potential vector of MDR enterococci transmission. Consequently, the implementation of specific control systems in regional and national surveillance of antibiotic resistant bacteria is becoming mandatory.