In vitro activity of β-lactams, macrolides, telithromycin, and fluoroquinolones against clinical isolates of Streptococcus pneumoniae: correlation between drug resistance and genetic characteristics

The in vitro activity of antimicrobial agents against Streptococcus pneumoniae was determined using 16 strains of penicillin-susceptible S. pneumoniae (PSSP) and 26 strains of penicillin intermediately resistant S. pneumoniae (PISP) + penicillin-resistant S. pneumoniae (PRSP) in Japan. The minimum inhibitory concentrations (MICs) of potent antibiotics, including eight beta-lactams (benzylpenicillin, ampicillin, cefotiam, cefepime, cefditoren, faropenem, panipenem, and biapenem), three macrolides (erythromycin, clarithromycin, and azithromycin), telithromycin, and three fluoroquinolones (ciprofloxacin, levofloxacin, and gatifloxacin), were determined. Twenty-three strains exhibited genetic variations at pbp1a + pbp2x + pbp2b, which are genetic-PRSP (g-PRSP). g-PISP strains accounted for 62.5% (10/16) of the PSSP strains. The existence of an abnormal pbp gene conferred not only penicillin resistance but resistance to cephems; however, panipenem and biapenem had potent in vitro efficacy against alterations. Regarding the macrolide resistance mechanisms (mefA or ermB): 16 isolates had only mefA, 18 isolates had ermB, and 2 isolates had both mefA and ermB. There was no correlation between the existence of an abnormal pbp gene and the existence of the mefA gene or the ermB gene.