Meningococci isolated in primary cultures from nasopharyngeal carriers occasionally consisted of mixtures of smooth (S) and rough (R) strains. The R strains were separated from the S strains and their morphological and serological characteristics were studied. Some of these R strains reverted spontaneously to S strains which subsequently produced group-specific polysaccharide. Several R strains, grown in the presence of deoxyribonucleic acid from either an R strain of known parentage or an S strain, formed recombinants with serological group specificity.
The minimal inhibitory concentrations of 49 antimicrobial agents for 37 to 40 meningococcal strains freshly isolated from the nasopharynx of healthy carriers were determined. Coumermycin A1 and rifampin were the most effective agents tested. The geometric mean values of the minimal inhibitory concentrations for coumermycin A1 and rifampin were 0.0001 and 0.02,qg/ml, respectively. Sulfadiazine was effective during World War II both as a chemotherapeutic agent in meningococcal disease and as a chemoprophylactic agent in the elimination of meningococci from the nasopharynx of healthy carriers (2, 7, 13). Vollum and Griffiths (16) reported the successful prevention of meningitis in Nigeria by the administration of four 1-g doses of sulfonamide snuff over a period of 2 days. Although penicillin has replaced sulfadiazine in the treatment of meningococcal disease (14), sulfadiazine remains the most widely used antimicrobial agent against nasopharyngeal carriers of meningococci. Since Millar et al. (12) reported, in 1963, the prevalence of sulfadiazine-resistant meningococci among Naval personnel at the San Diego Naval Training Center, there has been no known effective antibacterial agent for controlling the spread of sulfadiazine-resistant meningococci. The prevalence of carriers of sulfadiazine-resistant meningococci among Naval personnel was discussed by Devine et al. (3) in 1969. Eickhoff and Finland (5), in 1965, reported on the spectrum of susceptibility in vitro of meningococci to sulfadiazine and several other commonly used antibiotics available at that time. Dowd et al. (4) reported the failure of oxytetracycline, erythromycin, penicillin G, and ampicillin to eliminate the meningococcal carrier state. Erythromycin estolate, doxycycline, and sulfadiazine plus pyrimethamine failed to eliminate sulfadiazine-resistant meningococci from the nasopharynx of carriers (3). The incidence of meningococcal disease among military recruits is much higher than among similar age groups of civilians (14). A prophylactic drug for control of epidemics is needed. Conse-' This investigation made in connection with Research Project M4305.
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