Penicillin-resistant Variants of Pneumococci

Abstract

All of the 74 strains of pneumococci isolated from human infections from 1963 to 1964 proved to be uniformly and highly susceptible to penicillin. Of these strains, 15 were identified by capsule-swelling reactions and were submitted to serial transfer in the presence of increasing concentrations of penicillin. Highly penicillinresistant mutants were selected from 14 of the 15 strains, whereas one strain was moderately resistant. Of these mutants, 11 could still react with specific antiserum, and all of the mutants could be identified by fermentation reactions and optochin inhibition. The in vitro development of penicillin resistance in these mutants did not result in a change in cell-wall composition sufficient to diminish bile solubility. The possibility of encountering rising penicillin resistance among pneumococci, as well as the possibility that such mutants may react atypically, should be kept in mind.

The protection of small amounts of splenic tissue against intravenous pneumococcal challenge following subtotal splenectomy

“…Most individuals who developed these pneumococcal infections had been treated with prophylactic penicillin and other antibiotics or had received multiple antibiotics in the past, suggesting that they either became colonized with organisms resistant to antibiotics because sensitive bacteria were eradicated, or the antibiotics were related to the development of new resistant strains. The latter hypothesis is supported by the observation that pneumococci grown in vitro in the presence of subinhibitory concentrations of penicillin will acquire resistance to this antibiotic [25]. Polyvalent pneumococcal vaccine does not protect against all pneumococcal serotypes or other encapsulated bacteria to which the patient is susceptible.…”