Sir.—We wish to comment on the interesting report by Klugman et al1 concerning the so-called multiply resistant, penicillin-susceptible (MRPS) isolates of Streptococcus pneumoniae from both carriers and diseased patients.
First, it is uncertain that 7.9% of 254 healthy white children at different day-care centers were colonized with true MRPS S pneumoniae. The authors found 20 strains (7.9%) sensitive to penicillin by the methicillin disk diffusion method that were resistant to several other agents. However, the definitive test using antimicrobial dilutions in agar was done with only 15 strains, three of which were relatively resistant (minimal inhibitory concentrations [MICs], 0.12 to 1.0 mg/L).
Thus, the methicillin disk test classified 20% of the strains as falsely susceptible (acknowledged by the authors but not properly discussed). In accordance with this finding, the correct figure should be 12 confirmed MRPS strains, representing 4.7% of the population analyzed. Moreover, since the results for
CONDE-GLEZ CJ, CALDERON E. Unusual Multiply Resistant Pneumococci. Am J Dis Child. 1988;142(3):253-254. doi:10.1001/archpedi.1988.02150030019008