Chromosomal blaCTX-M-15 associated with ISEcp1 in Proteus mirabilis and Morganella morganii isolated at the Military Hospital of Tunis, Tunisia

This study investigated the genetic environment of bla CTX-M genes and associated resistance genes in seven Proteus mirabilis and six Morganella morganii extended spectrum β-lactamase (ESBL)-positive isolates. The isolates were recovered from hospitalized patients with respiratory or urinary tract infections at the Military Hospital of Tunis, Tunisia. Twenty-one of the 200 strains exhibited non-susceptibility to third generation cephalosporins and, among these strains, the double-disk synergy test confirmed the ESBL phenotype in 13 isolates. These ESBL producers were co-resistant to chloramphenicol, tetracycline and oflaxacin but remained susceptible to ertapenem (MIC<0.25 mg l−1). The presence and nature of bla CTX-M-15, bla CTX-M-8, bla TEM-24, bla TEM-1 and bla TEM-2 genes was determined by PCR and sequencing. Chromosomal localization of the bla CTX-M-15 gene was confirmed in all strains, with the exception of M. morganii isolate M-17991, by Southern-blot analysis performed either on chromosomal or plasmid DNA. M. morganii M-12012 and M. morganii M-6019 showed the same PFGE pattern, whereas the remaining CTX-M-15-producing isolates were unrelated. The presence of ISEcp1 was ascertained in CTX-M-15-producing isolates. A class 1 integron with different gene cassettes (dfrA1, orfC and aadB) was found in five P. mirabilis and six M. morganii isolates.