Study on antibacterial activity of 20 antimicrobial agents against S. pneumoniae in vitro

Objective: To investigate the antibacterial activity of 20 antimicrobial agents in vitro against 60 strains S. pneumoniae isolated from clinical samples. Methods: Minimum inhibitory concentration (MIC) of 20 antimicrobial agents against S. pneumoniae was performed by broth diffusion method. Results: Among 60 strains S. pneumoniae, there were 42 strains (71.7%) penicillin-susceptible S. pneumoniae (PSSP), 18 strains (28.3%) penicillin non-susceptible S. pneumoniae (PNSSP), among of them, 2 strains (3.3%) were penicillin-resistant S. pneumoniae (PRSP). For PSSP, ceftriaxone, cefotaxime, gatifloxacin, moxifloxacin, levofloxacin and amoxicillin-clavulanic acid were the most sensitive antimicrobial agents, and the sensitive rates were all 100%. In contrast, erythromycin, roxithromycin, clarithromycin, azithromycin were the most resistant antimicrobial agents, and the resistant rates were 83.3%, 83.3%, 74.7% and 74.7%, respectively. For PNSSP, the most sensitive antimicrobial agents were amoxicillin-clavulanic acid, moxifloxacin, cefotaxime, gatifloxacin and levofloxacin, and the sensitive rates were 100%, 100%, 88.8%, 94.4% and 94.4%, respectively. The most resistant antimicrobial agents were erythromycin, clarithromycin, azithromycin, and the resistant rates were all 66.7%. Moxifloxacin and amoxicillin-clavulanic acid had the strongest antibacterial activity according to the accumulative inhibition percentage curves. Conclusion: A high frequency of resistance to macrolides including erythromycin, clarithromycin, roxithromcin, azithromycin and trimethoprim-sulfamethoxazole and fosfomycin was found. Levofloxacin, moxifloxacin, gatifloxacin, amoxicillin-clavulanic acid, cefotaxime and ceftriaxone were susceptible to S. pneumoniae, which could be the first choice for high resistant S. pneumoniae in clinic.