Three cefotaximases, CTX-M-9, CTX-M-13, and CTX-M-14, among Enterobacteriaceae in the People's Republic of China

Abstract

Of 15 extended-spectrum beta-lactamase (ESBL)-producing isolates of the family Enterobacteriaceae collected from the First Municipal People's Hospital of Guangzhou, in the southern part of the People's Republic of China, 9 were found to produce CTX-M ESBLs, 3 produced SHV-12, and 3 produced both CTX-M and SHV-12. Eleven isolates produced either TEM-1B or SHV-11, in addition to an ESBL. Nucleotide sequence analysis of the 12 isolates carrying bla(CTX-M) genes revealed that they harbored three different bla(CTX-M) genes, bla(CTX-M-9) (5 isolates), bla(CTX-M-13) (1 isolate), and bla(CTX-M-14) (6 isolates). These genes have 98% nucleotide homology with bla(Toho-2). The bla(CTX-M) genes were carried on plasmids that ranged in size from 35 to 150 kb. Plasmid fingerprints and pulsed-field gel electrophoresis showed the dissemination of the bla(CTX-M) genes through transfer of different antibiotic resistance plasmids to different bacteria, suggesting that these resistance determinants are highly mobile. Insertion sequence ISEcp1, found on the upstream region of these genes, may be involved in the translocation of the bla(CTX-M) genes. This is the first report of the occurrence of SHV-12 and CTX-M ESBLs in China. The presence of strains with these ESBLs shows both the evolution of bla(CTX-M) genes and their dissemination among at least three species of the family Enterobacteriaceae, Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae, isolated within a single hospital. The predominance of CTX-M type enzymes seen in this area of China appears to be similar to that seen in South America but is different from those seen in Europe and North America, suggesting different evolutionary routes and selective pressures. A more comprehensive survey of the ESBL types from China is urgently needed.

FIG. 1.

Nucleotide sequence alignment of the open reading frames of CTX-M-9 ; this study), CTX-M-13 (this study), CTX-M-14 (this study), and Toho-2 (29). Dots indicate identical nucleotides. Hyphens show nucleotide deletions. Amino acids in parentheses indicate substitutions compared with the sequence of CTX-M-9. The numbering is according to Ambler et al. (1). The asterisk at the end indicates the stop codon.

FIG. 1.

Nucleotide sequence alignment of the open reading frames of CTX-M-9 ; this study), CTX-M-13 (this study), CTX-M-14 (this study), and Toho-2 (29). Dots indicate identical nucleotides. Hyphens show nucleotide deletions. Amino acids in parentheses indicate substitutions compared with the sequence of CTX-M-9. The numbering is according to Ambler et al. (1). The asterisk at the end indicates the stop codon.

FIG. 2.

(a) Plasmid DNA profiles of the clinical isolates carrying bla_CTX-M genes and their transconjugants; (b) Southern blots hybridized with a bla_CTX-M-specific probe. Lanes A, V517 plasmid size marker; lanes B and C, E. coli strain 8 and its transconjugant (bla_CTX-M-14), respectively; lanes D and E, E. coli strain 7 and its transconjugant (bla_CTX-M-14), respectively; lanes F and G, K. pneumoniae strain 1 and its transconjugant (bla_CTX-M-13), respectively; lanes H and I, K. pneumoniae strain 2 and its transconjugant (bla_CTX-M-14), respectively; lanes J and K, E. coli strains 5 and 6, respectively (bla_CTX-M-14); lanes L, E. cloacae strain 3 (bla_CTX-M-14); lanes M and N, E. cloacae strain 1 and its transconjugant (bla_CTX-M-9), respectively.