Characterization of Neisseria meningitidis serogroup C by multilocus enzyme electrophoresis and ribosomal DNA restriction profiles (ribotyping).

We compared multilocus enzyme electrophoresis (MEE) and ribosomal DNA fingerprinting (ribotyping) for subtyping 44 strains of Neisseria meningitidis serogroup C that were isolated in Los Angeles County, California, between December 1985 and July 1986. The isolates were divided into six enzyme types (ETs) by MEE, but 36 of the isolates were clustered in one ET, 3. The same isolates were divided into 17 ribotypes by use of restriction endonucleases ClaI, EcoRI, and XhoI. Twenty of the 36 ET 3 isolates were divided into 17 ribotypes by use of restriction endonucleases ClaI, EcoRI, and XhoI. Twenty of the 36 ET 3 isolates were grouped in a single ribotype, J. The rate of infection with ribotype J strains was higher in the southern part of the study area than in the northern part. Isolates from each of eight pairs (each isolate pair was cultured from the same patient from the same or different sites) were found identical by MEE, but ribotyping revealed a difference in one pair. In this study, ribotyping showed a greater discriminating capacity than MEE for subtyping N. meningitidis serogroup C, but the epidemiologic relevance of this increased sensitivity needs further assessment.

Changes in antimicrobial resistance of Salmonella isolated from humans in the United States.

Changes were examined that occurred in the antimicrobial susceptibility between 1979-1980 and 1984-1985 of Salmonella organisms isolated from humans who resided in a random sample of counties in the United States. Resistance to one or more antimicrobials rose significantly from 16% (82 of 511 isolates) in 1979-1980 to 24% (117 of 485 isolates) in 1984-1985. In addition, statistically significant increases occurred in the proportion of organisms resistant to only one antimicrobial (from 4% to 9%), the rate of resistance of Salmonella typhimurium (from 14% to 26%), and the rate of resistance to tetracycline. For one commonly occurring serotype, Salmonella heidelberg, the proportion of resistant strains fell significantly from 67% in 1979-1980 to 35% in 1984-1985. When epidemiologic characteristics of patients were examined, previous use of antimicrobials for treatment of other illnesses was a significant risk factor for acquiring clinically important infections with antimicrobial-resistant Salmonella. Changes detected in the antimicrobial resistance of Salmonella during this time will ultimately affect the efficacy of antimicrobial therapy in treating human disease.