MENINGITIS CAUSED BY NEISSERIA MENINGITIDIS C RELATIVELY RESISTANT TO PENICILLIN AND AMPICILLIN

To The Editors: Several communications from European countries have described isolates of Neisseria meningitidis with decreased susceptibility to penicillin and ampicillin,1, 2 and more recently North American publications3, 4 have reported strains of N. meningitidis relatively resistant to penicillin detected in the United States. Because information on resistance of N. meningitidis to penicillin is scarce in the Americas, we considered it relevant from the epidemiologic point of view5, 6 to alert physicians about its occurrence in Uruguay. The minimal inhibitory concentration (MIC) was determined for 84 invasive isolates by E-test® (AB Biodisk, Solna, Sweden) for penicillin, ampicillin, ceftriaxone, cefotaxime and rifampin. The tests were performed on Mueller-Hinton-enriched chocolate agar plates with incubation for 24 h in a candle jar at 35°C. All the results were read according to the break points established by the National Committee for Clinical Laboratory Standards for Neisseria gonorrhoea. For penicillin and ampicillin the break points were the following: susceptibility <0.06 μg/ml, relative resistance >0.06 to 1 μg/ml and resistance >1 μg/ml. Since 1989 we have been receiving invasive isolates of N. meningitidis at the Central Public Health Laboratory, Montevideo, Uruguay. In 1993 we detected for the first time eight isolates of N. meningitidis serogroup C with moderate resistance to penicillin and ampicillin (38%). Thereafter N. meningitidis C became the most frequent serogroup and the intermediate resistance increased to 91%, the increase persisting during 1995. None of the 84 isolates was a beta-lactamase producer or resistant to the tested cephalosporins and rifampin. Genetic studies are under way to trace the origin of these isolates. Alicia Pisano, M.Sc.; Gabriel Perez, M.Sc.; Maria Hortal, M.D.; Pablo Giordano, M.D. Central Public Health Laboratory (AP, GP, MH) Pasteur Hospital (PG) Montevideo, Uruguay