Sensitivity of Staphylococcus aureus and Streptococcus pyogenes isolated from skin infections in 1992 to antimicrobial agents

We studied the efficacy of antimicrobial agents against Staphylococcus aureus (S. aureus) and Streptococcus pyogenes (S. pyogenes) isolated from skin infections in 1992. For S. aureus, we measured the minimum inhibitory concentrations (MICs) of the following 10 drugs: methicillin (DMPPC), cefaclor (CCL), gentamicin (GM), erythromycin (EM), clindamycin (CLDM), minocycline (MINO), vancomycin (VAN), fusidic acid (FA), ofloxacin (OFLX) and nadifloxacin (NDFX); for S. pyogenes, we determined the MICs of the following 9 drugs: ampicillin (ABPC), amoxicillin (AMPC), cefpodoxime proxetil (CPDX- PR), erythromycin (EM), clindamycin (CLDM), minocycline (MINO), norfloxacin (NFLX), ofloxacin (OFLX) and nadifloxacin (NDFX). These drugs are frequently used to treat skin infections, either systemically or topically. NDFX is a new synthetic fluoroquinolone, recently developed for use as a topical acne medication in Japan. It is used NDFX for acne, but not for skin infections. There were no strains of S. aureus resistant to NDFX, VAN or FA. The resistance (≥12.5 μg/ml) of S. aureus was highest to GM and lowest to OFLX. Four strains of methicillin-resistant (≥12.5 μg/ml) S. aureus (MRSA) were found. In contrast, no resistant strains of S. pyogenes were found except to MINO. Only two strains of S. pyogenes were susceptible to MINO. The sensitivity of S. pyogenes to ABPC, AMPC, CPDX-PR, EM and CLDM was very good. All the strains were susceptible at a MIC below ≥0.05 μg/ml. However, the S. pyogenes strains were not very sensitive to the new quinolones, especially NFLX. We concluded that penicillins, cephalosporins and macrolides are still effective against streptococcal infections. In contrast, we found S. aureus to be resistant to several kinds of antimicrobial agents. Accordingly, we need to check the sensitivity of S. aureus, before using antimicrobial agents for staphylococcal infections. Roughly speaking, the drugs that are strongly effective against S. aureus are not effective against S. pyogenes. For example, the efficacy of MINO against S. aureus was very good, but almost all S. pyogenes strains were resistant to it. The pattern is much the same for the new quinolones.