First report on the occurrence of SHV-12 extended-spectrum beta-lactamase-producing Enterobacteriaceae in the Philippines.

BACKGROUND AND PURPOSE: Soon after the introduction of extended-spectrum beta-lactam antibiotics to treat infections caused by Gram-negative bacteria that were resistant to the existing beta-lactams, resistant strains quickly emerged. This study investigated the antimicrobial susceptibility patterns, conjugative transferability, and molecular characterization of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in the Philippines.

METHODS: ESBL-producing Enterobacteriaceae were collected from patients at the Philippine General Hospital from June 2000 to August 2001. The antimicrobial susceptibility patterns were determined using the standard disk diffusion assay. ESBL production was confirmed using the double-disk synergy assay and the E-test, while the ESBLs were characterized for type using polymerase chain reaction, sequencing, and isoelectric focusing. Conjugation studies were conducted in vitro on solid medium.

RESULTS: All of the ESBL-producing isolates were also resistant to most other classes of antimicrobials studied. The ESBL genes on conjugative and non-conjugative plasmids were bla(SHV-12). Fifteen isolates also carried bla(TEM-1). None of the isolates were positive for the CTX-M type of ESBL. Plasmids from cefoxitin-resistant isolates did not produce amplified products using CMY primers for the AmpC gene.

CONCLUSIONS: SHV-12 is the dominating ESBL among the Enterobacteriaceae studied. The gene bla(SHV-12) is carried together with genes for multiple resistance to other classes of antimicrobials in conjugative and nonconjugative plasmids.