Molecular Epidemiology of the Integron-Located VEB-1 Extended-Spectrum β-Lactamase in Nosocomial Enterobacterial Isolates in Bangkok, Thailand

Over a 2½-month period in 1999, 37 ceftazidime-resistant nonrepetitive enterobacterial isolates were collected from 37 patients in a Bangkok hospital, Thailand. Eighty-one percent of these strains expressed a clavulanic acid-inhibited extended-cephalosporin resistance profile. An identical extended-spectrum β-lactamase (ESBL), VEB-1, was found in 16 unrelated enterobacterial isolates (Escherichia coli, n = 10; Enterobacter cloacae, n = 2; Enterobacter sakazakii, n = 1; and Klebsiella pneumoniae, n = 3) and in two clonally related E. cloacae isolates. The bla(VEB-1) gene was located on mostly self-conjugative plasmids (ca. 24 to 200 kb) that conferred additional non-β-lactam antibiotic resistance patterns. Additionally, the bla(VEB-1) gene cassette was part of class 1 integrons varying in size and structure. The bla(VEB-1)-containing integrons were mostly associated with bla(OXA-10)-like and arr-2-like gene cassettes, the latter conferring resistance to rifampin. These data indicated the spread of bla(VEB-1) in Bangkok due to frequent transfer of different plasmids and class 1 integrons and rarely to clonally related strains. Plasmid- and integron-mediated resistance to rifampin was also found in enterobacterial isolates.