Search

ABSTRACTWe characterized 32 levofloxacin-nonsusceptible Streptococcus pneumoniae(LNSP) isolates obtained from a broad geographic region of North America over a 5-year period by using capsular serotypes, antimicrobial susceptibility profiles, BOX-PCR, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). Sixteen international clones identified by the Pneumococcal Molecular Epidemiology Network also were included for comparison. Fifteen serotypes were represented, with serogroups 6, 9, 14, 19, and 23 accounting for 63% of isolates. Among isolates whose quinolone resistance-determining regions were sequenced, all contained gyrAand parCpoint mutations. Sixty-three percent were penicillin susceptible, and 84% were erythromycin susceptible. BOX-PCR analysis identified 39 different band patterns among 32 LNSP and 16 international clones and grouped 16 isolates, including 2 international clones, into seven unrelated groups of 2 to 4 isolates each. PFGE analysis identified 35 different band patterns among 32 LNSP and 16 international clones and grouped 21 isolates, including 3 international clones, into eight unrelated groups of 2 to 6 isolates each. MLST performed on 10 isolates identified five allelic profiles and separated 9 isolates into four groups of 2 to 3 isolates each. Overall, each typing method indicated that the LNSP were heterogeneous and that resistance to fluoroquinolones was not closely associated with a particular serotype or with coresistance to other antimicrobial classes and suggests that LNSP have likely arisen through independent mutational events as a result of selective pressure. However, seven LNSP were found to be related to three international clones by PFGE.

ABSTRACTWe studied 198 macrolide-resistant S. pneumoniaeisolates obtained from adults and children to evaluate whether 2-µg clindamycin disks can distinguish between isolates manifestingermB- versus mefE-mediated resistance to clarithromycin and to determine the relative frequency with which each resistance mechanism occurred in these populations. ThemefEgene was predominant among 109 isolates from children, occurring in 73.4% versus 50.6% of 89 isolates from adults. Three isolates (1.5%) did not amplify either gene. Among 125mefE+isolates, the MIC of clarithromycin at which 90% of the isolates tested were inhibited, determined by Etest, was 32 µg/ml versus >256 µg/ml in 70 ermB+isolates. All ermB+isolates were highly resistant to clindamycin (MICs >256 µg/ml), whereas all mefE+isolates were susceptible to clindamycin using the 2-µg disk. Testing S. pneumoniaefrom the respiratory tract for susceptibility to clindamycin by agar disk diffusion is an easy and inexpensive method to estimate the frequency of resistance mediated by ermBin specific patient populations. Macrolide resistance mediated by ermBis usually of greater magnitude than that due to mefE. Clinical studies are needed to determine the significance of high- versus low-level macrolide resistance in S. pneumoniae.