Extended Spectrum Beta-Lactamase (ESBL) Enterobacteriaceae are becoming widespread enzymes in food-producing animals worldwide. Escherichia coli and Klebseilla pneumoniae are two of the most significant pathogens causing mastitis. Our study focused on the characterization of the genetic support of ESBL/pAmpC and antibiotic resistance mechanisms in cefotaxime-resistant (CTXR) and susceptible (CTXS) Enterobacteriaceae isolates, recovered from bovine mastitis in Tunisia, as well as the analyses of their clonal lineage and virulence-associated genes. The study was carried out on 17 ESBL/pAmpC E. coli and K. pneumoniae and 50 CTXS E. coli. Detection of resistance genes and clonal diversity was performed by PCR amplification and sequencing. The following β-lactamase genes were detected: blaCTX-M-15 (n = 6), blaCTX-M-15 + blaOXA-1 (2), bla CTX-M-15 + blaOXA-1 + blaTEM-1b (2), blaCTX-M-15 + blaTEM-1b (4), blaCMY-2 (3). The MLST showed the following STs: ST405 (n = 4 strains); ST58 (n = 3); ST155 (n = 3); ST471 (n = 2); and ST101 (n = 2). ST399 (n = 1) and ST617 (n = 1) were identified in p(AmpC) E. coli producer strains. The phylogroups A and B1 were the most detected ones, followed by the pathogenic phylogroup B2 that harbored the shigatoxin genes stx1/stx2, associated with the cnf, fimA, and aer virulence factors. The qnrA/qnrB, aac(6′)-Ib-cr genes and integrons class 1 with different gene cassettes were detected amongst these CTXR/S isolated strains. The presence of different genetic lineages, associated with resistance and virulence genes in pathogenic bacteria in dairy farms, may complicate antibiotic therapies and pose a potential risk to public health.
Keywords: ESBL; Tunisia; clonal lineages; integrons; mastitis; p(AmpC); pathogenic bacteria; virulence.