Vol.58 No.4 July 2010
Laboratory-derived Streptococcus pneumoniae and Haemophilus influenzae strains resistant to ceftriaxone and other β-lactam antibiotics
1)School of Nursing, Toho University School of Medicine, 4-16-20 Omori-nishi, Ota-ku, Tokyo, Japan
2)Chemotherapy Division, Mitsubishi Chemical Medience Corporation
3)Kitasato Institute for Life Science, Kitasato University
Abstract
Laboratory-derived resistant strains were obtained by serial passage of Streptococcus pneumoniae and Haemophilus influenzae ATCC strains and clinical isolates on agar containing increasing concentrations of ceftriaxone(CTRX) and other β-lactam antibiotics.
Ten strains of S. pneumoniae and 10 strains of H. influenzae were subcultured 10 times on agar media containing β-lactam antibiotics at gradually higher concentrations. CTRX MICs and antibiotics used for acquired strain resistance before and after exposure to antibiotics were determined. PBPs gene mutations before and after antibiotic exposure was estimated. An increase of 4 times or more in MIC was observed in 10 strains of S. pneumoniae-strains numbered 4 each for amoxicillin and cefotiam, 3 each for cefotaxime, CTRX, and cefditoren and 2 for panipenem. An increase in MIC of 8 times or more was observed in 10 strains of H. influenzae-strains numbered 7 for CTX, 6 for CDTR, 4 for CTM, 2 for meropenem, 1 each for CTRX and amoxicillin/clavulanic acid. The increase in CTRX MICs was low for strains for which MICs of each antibiotic increased.
No differences were seen in the PBPs gene before and after exposure to antibiotics, except for part of strains, suggesting that other resistance mechanisms of participate in resistance.
Key word
Streptococcus pneumoniae, Haemophilus influenzae, β-lactams, resistance, gene mutation
Received
March 31, 2010
Accepted
June 14, 2010
Jpn. J. Chemother. 58 (4): 451-459, 2010
