Tolerance to vancomycin in a multiresistant, Colombian isolate of Streptococcus pneumoniae

The present study was set up to determine vancomycin tolerance in Colombian, multiresistant, invasive, paediatric isolates of Streptococcus pneumoniae. A total of seven clinical isolates of penicillin-resistant S. pneumoniae, serotype 14, corresponding to the Spain^9v-3 clone, were studied. Isolates were grown in Todd Hewitt broth at 37°C. Growth (A₅₉₅) and cell viability (cfu/mL) were monitored hourly for 4 h after addition of vancomycin at 10× MIC. S. pneumoniae R6 was used as a control for growth. For R6, the mean decrease in A₅₉₅ and cell viability (log₁₀ cfu/mL) after 4 h of vancomycin treatment (in 10 independent experiments) was 95.1 % and 4.2 log₁₀, respectively. Six out of seven isolates exhibited similar behaviour. In contrast, for S. pneumoniae E239, the mean decrease in A₅₉₅ and cell viability was 48.5% and 2.2 log₁₀ after 4 h of vancomycin exposure, which suggested the presence of tolerance to vancomycin. The emergence of vancomycin-tolerant strains is of great concern in Colombia, owing to the alarming increase in resistance to penicillin.