E test for studying in vitro activity of seven antimicrobial agents against penicillin-susceptible and penicillin-resistant pneumococci

Objective To evaluate the comparative activity of seven oral antimicrobial agents against 100 strains of Streptococcus pneumoniae (S, pneumoniae). Methods Total 100 strains of S. pneumoniae were collected from general hospitals in Beijing from June 1996 to June 1997. E test method was used to detect the minimum inhibitory concentration (MIC) values of the following seven drugs against S. pneumoniae: penicillin, amoxicillin/clavulanate, cefaclor, cefuroxime, ceftriaxone, azithromycin and ofloxacin. The breakpoint of susceptibility categories was defined according to NCCLS. Results 74% of isolates were susceptible (S, MIC 0.06 mg/L) to penicillin, and 5% were penicillin resistant (R, MIC 2 mg/L). The intermediately resistant (I, MIC 0.1 - 1 mg/L) rate to penicillin was 21%. The total rates of R or I were 26% for penicillin, 6% for both amoxicillin/clavulanate and ceftriaxone, 9% for cefuroxime, 66% and 68% for azithromycin and ofloxacin respectively. Overall 94%, 94% and 91% of the pneumococcal isolates were susceptible to amoxicillin/clavulanate, ceftriaxone and cefuroxime respectively. S. pneumoniae was highly resistant to azithromycin tested as a representative of macrolides (MIC50 and MIC90 both > 256 mg/L, R rate 66%), and had a highly intermediately resistant rate to ofloxacin (I rate 62%). Conclusions Our data suggest that in vitro activity of oral amoxicillin/clavulanate was as good as ceftriaxone and cefuroxime. It can be considered as an alternative compound in the treatment of community acquired pneumoniae and other respiratory tract infections caused by multiresistant S. pneumoniae.