Clinical isolates of Streptococcus pneumoniae that exhibit tolerance of vancomycin

The ability of Streptococcus pneumoniae to escape lysis and killing by vanc omycin, a property termed "tolerance," has recently been noted in a laborat ory strain of the species. Vancomycin tolerance in clinical isolates repres ents a potential new health risk. We determined the prevalence of vancomyci n and penicillin tolerance among 116 clinical isolates of pneumococci by mo nitoring lysis and viability after exposure to the respective antibiotic fo r 4 hours. Eight percent of the strains were tolerant to penicillin and 3% were tolerant to vancomycin. The 3 vancomycin-tolerant isolates also had a high ratio of minimum bactericidal concentration to minimum inhibitory conc entration, in contrast to nontolerant strains. They were of serotype 9V and had reduced susceptibility to penicillin. Only 1 was also tolerant to peni cillin. Growth rate and ability to divide were not affected in the 3 vancom ycin-tolerant strains, and they all lysed with deoxycholate, which indicate s autolysin production. Vancomycin tolerance among clinical isolates of pne umococci will necessitate tracking to determine the magnitude of the evolvi ng health risk, since tolerance may contribute to treatment failure (in par ticular, cases of meningitis, in which bactericidal activity is critical fo r eradication) and since it may also be a favored background for acquisitio n of resistance of vancomycin.