beta-lactamase-producing activity and antimicrobial susceptibility of major pathogenic bacteria isolated from clinical samples. Japan beta-lactamase Research Group

beta-Lactamase production and susceptibility to an assortment of antimicrobial agents were examined in 9,483 strains of organisms isolated from clinical materials obtained from inpatients and outpatients at 104 institutions throughout Japan from December 1999 to February 2000. The organisms were Staphylococcus aureus, 1,369 strains, including 847 methicillin-resistant (MRSA) strains; Enterococcus faecalis, 735 strains; Enterococcus faecium, 302 strains; Moraxella (Branhamella) catarrhalis, 730 strains; Haemophilus influenzae, 1,142 strains; Escherichia coli, 1,276 strains; Klebsiella pneumoniae, 1,058 strains; Enterobacter cloacae, 772 strains; Serratia marcescens, 847 strains; and Pseudomonas aeruginosa, 1,252 strains. The 23 antimicrobial agents used were ampicillin, sulbactam/ampicillin, clavulanic acid/amoxicillin, oxacillin, piperacillin, cefazolin, cefotiam, cefmetazole, cefoperazone, sulbactam/cefoperazone, cefotaxime, ceftazidime, cefepime, cefpodoxime, imipenem, gentamicin, arbekacin, clarithromycin, minocycline, chloramphenicol, vancomycin, teicoplanin, and levofloxacin. Antimicrobial agents appropriate for each organism were used. Among S. aureus strains, 61.9% were MRSA, and 62.3% were positive for beta-lactamase. Among the MRSA strains, none was resistant to vancomycin or teicoplanin, and only 3% were resistant to arbekacin. There was no vancomycin resistance in the Enterococcus strains. Only 0.1% of E. faecalis strains were ampicillin-resistant. Among the M. catarrhalis strains, 97.5% produced beta-lactamase, while among the H. influenzae strains, 8.5% produced beta-lactamase and 14.5% were beta-lactamase-negative and ampicillin-resistant (BLNAR). Among the Enterobacteriaceae and P. aeruginosa strains, there were 20 (E. coli; 7/1,276, K. pneumoniae; 13/1,058) that produced extended-spectrum beta-lactamases (ESBLs), and 11 that produced class B beta-lactamases. Multiple drug resistance was advanced in every species, and organisms resistant to 7 or more common antimicrobial agents were isolated. The best combination of antimicrobial agent and beta-lactamase inhibitor was sulbactam/cefoperazone. Sulbactam/cefoperazone, cefepime, and imipenem still have excellent antimicrobial activity. Rates of resistance to each antimicrobial agent differed more among institutions than among geographical regions.