Emergence of rifampin-resistant Rhodococcus equi with several types of mutations in the rpoB gene among AIDS patients in northern Thailand

Abstract

The antimicrobial susceptibilities of 30 Rhodococcus equi isolates obtained from 30 patients between 1993 and 2001 in northern Thailand were investigated. The MICs showed a tendency toward resistance to various antibiotics but sensitivity to imipenem, minocycline, vancomycin, and teicoplanin (MICs, </=0.5 micro g/ml) and relative sensitivity to meropenem, clarithromycin, and ciprofloxacin (MICs, </=2 micro g/ml). Of the 30 isolates, 26 were susceptible (MICs, </=1 micro g/ml), 1 showed low-level resistance (MIC, 8 micro g/ml), and 3 showed high-level resistance (MICs, >/=64 micro g/ml) to rifampin. PCR amplification and DNA sequencing of the rpoB gene and molecular typing by pulsed-field gel electrophoresis (PFGE) were performed for eight R. equi isolates from eight AIDS patients with pneumonia or lung abscess caused by R. equi between 1998 and 2001, including one low- and three high-level rifampin-resistant isolates. As a result, two high-level rifampin-resistant strains with PFGE pattern A had a Ser531Trp (Escherichia coli numbering) mutation, and one high-level rifampin-resistant strain with PFGE pattern B had a His526Tyr mutation, whereas one low-level rifampin-resistant strain with PFGE pattern C had a Ser509Pro mutation. Four rifampin-susceptible strains with PFGE patterns D and E showed an absence of mutation in the rpoB region. Our results indicate the presence of several types of rifampin-resistant R. equi strains among AIDS patients in northern Thailand.

FIG. 1.

PFGE patterns of PshBI-digested DNAs from R. equi isolates from eight AIDS patients with pneumonia or lung abscess caused by R. equi between 1998 and 2001. The PFGE patterns in two high-level rifampin-resistant strains were the closely related patterns A1 and A2 (lanes 1 and 3), but another high-level rifampin-resistant strain showed a different pattern, B (lane 2). One low-level rifampin-resistant strain showed pattern C (lane 4). The PFGE patterns of two rifampin-susceptible strains were identical (pattern D; lanes 5 and 6), and another two rifampin-susceptible strains showed the possibly related patterns E1 and E2 (lanes 7 and 8).