Identification of fluoroquinolone-resistant extended-spectrum β-lactamase (CTX-M-8)-producing Escherichia coli ST224, ST2179 and ST2308 in buffalo (Bubalus bubalis).

D2 differed from one another by fewer than five single nucleotide differences, but only the WM98 sequence was not interrupted by large insertions or deletions (positions of insertions/deletions are indicated in Figure 1). AB307-0294 (GenBank accession number CP001172) was also identical over most of this span, but contained patches that differed and lacked a large span. The AB0057 sequence (GenBank accession number CP001182), for which the ampC gene was previously corrected, differed at 33 more positions (single base substitutions or additions or deletions; mainly the absence of an A or a T in a run of As or Ts) and many of these differences may be errors caused by the sequencing technology used. Contigs containing ampC and its surrounds were retrieved from the whole genome sequence of G7 reported previously 6 and joined using the manually determined sequence described above. Comparison with the WM98 sequence revealed a segment of 31.8 kb, defined as between the first and last base differences surrounding the ISAba1-ampC in G7, which differed from the corresponding region in WM98 by 2.2% (Figure 1). This indicates that this segment has been replaced by a segment imported from another A. baumannii strain that included an ISAba1 upstream of the ampC gene. Hence, it appears that a DNA segment that included an ISAba1-activated ampC gene was introduced into an isolate belonging to the GC1 clonal complex, possibly by conjugation , and that homologous recombination incorporated it into the chromosome displacing the resident copy. Examination of the regions on either side of the 31.8 kb diverged segment revealed the presence of two smaller replaced patches of 4.7 and 2.8 kb in G7, which differed from the corresponding regions in WM98 by 4.5% and 2.1%, respectively (Figure 1). Outside these patches, WM98 and G7 differed by only 3 bp. This is the first study providing evidence for horizontal transfer of a DNA segment that contains an ISAba1-activated ampC gene between two A. baumannii strains. The findings highlight the significance of the horizontal transfer of chromosomal DNA segments in the generation of cephalosporin resistance in A. baumannii. 3 Hamidian M, Hall RM. Tn6168, a transposon carrying an ISAba1-activated ampC gene and conferring cephalosporin resistance in Acinetobacter baumannii. 4 Hamidian M, Hall RM. ISAba1 targets a specific position upstream of the intrinsic ampC gene of Acinetobacter baumannii leading to cephalosporin resistance. ISAba125-activated ampC gene between Acinetobacter baumannii strains leading to cephalosporin resistance. A …