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During a study on the epidemiology of Staphylococcus aureus colonization in newborns, mothers, and hospital staff, S. aureus was isolated from 536 of 1,945 specimens. Ninety-three isolates of S. aureus from the three groups of individuals were included in a study to evaluate the potential of DNA fingerprinting for strain differentiation. The 93 isolates were also phage typed and their plasmid profiles were analyzed. Cleavage of DNA with BamHI resulted in 13 different DNA restriction endonuclease band patterns (DNA REBPs), one of which consisted of eight isolates whose DNA was not cleaved with BamHI. The DNAs from these eight isolates were easily cleaved with HindIII. The different DNA REBPs were stable both during in vitro and in vivo growth and allowed strain differentiation within phage groups or types. We could not show any strong association between DNA REBP classes, phage types or groups, and plasmid profiles. Of the 93 isolates, 27 (29.0%) could not be phage typed and 12 (12.9%) lacked plasmids. We therefore conclude that DNA fingerprinting is a powerful tool, in addition to phage typing and plasmid profile analysis, for strain differentiation of S. aureus.

We tested two sets of primers derived from the dhps gene of Neisseria meningitidis for the amplification of meningococcal DNA by PCR. Both the NM1-NM6 primers and the NM3-NM6 primers amplified dhps DNA from all of the meningococci included in the study, resulting, in most cases, in amplicons of 0.70 and 0.23 kb, respectively. Also, dhps DNAs of N. gonorrhoeae and some commensals were amplified but Haemophilus influenzae, Streptococcus pneumoniae, and Escherichia coli DNAs were not. By PCR amplicon restriction endonuclease analysis (AREA) of the larger amplicon, we could differentiate between individual strains of N. meningitidis. Following two cases of meningococcal disease, we used PCR AREA to identify healthy contacts carrying the disease-causing strain. We conclude that PCR AREA is a useful method for meningococcal strain differentiation and that it has potential as a method for studying the spread of a disease-causing strain in an affected population. The method is quicker and easier to perform and interpret than chromosomal DNA fingerprinting.

Plasmid profile analysis, restriction endonuclease analysis, and multilocus enzyme electrophoresis were used in conjunction with serotyping, bacteriophage typing, and biochemical fingerprinting to trace epidemiologically related isolates of Salmonella typhimurium from an outbreak caused by contaminated chocolate products in Norway and Finland. To evaluate the efficiency of the epidemiological marker methods, isolates from the outbreak were compared with five groups of control isolates not known to be associated with the outbreak. Both plasmid profile analysis and phage typing provided further discrimination over that produced by serotyping and biochemical fingerprinting. Plasmid profile analysis and phage typing were equally reliable in differentiating the outbreak isolates from the epidemiologically unrelated controls and were significantly more effective than multilocus enzyme electrophoresis and restriction enzyme analysis of total DNA. The greatest differentiation was achieved when plasmid profile analysis and phage typing were combined to complement serotyping and biochemical fingerprinting. However, none of the methods employed, including restriction enzyme analysis of plasmid DNA, were able to distinguish the outbreak isolates from five isolates recovered in Norway and Finland over a period of years from dead passerine birds and a calf.

By cloning studies and complementation experiments, the sulfonamide resistance gene of a serogroup B and serotype 15 (B:15) strain of Neisseria meningitidis was localized to a 1.2-kb chromosomal SspI fragment expressing a drug-resistant dihydropteroate synthase. The fragment hybridized to DNA from both resistant and susceptible strains, suggesting that the resistance gene is a variant of the normal gene for dihydropteroate synthase.

Rapid diagnosis of meningococcal disease followed by early treatment is essential. However, culture of blood or cerebrospinal fluid (CSF) may be unsuccessful because antibiotic treatment is often started before adequate specimens are collected, and because bacteria may die during transportation to the laboratory. We have used the polymerase chain reaction (PCR) to detect meningococcal DNA in a culture-negative CSF of a 15-year-old girl with meningococcal disease. Two oligonucleotides flanking the dihydropteroate synthase gene (dhps) of Neisseria meningitidiswere used as primers. The PCR reaction is a rapid technique for the early detection of meningococcal meningitis, and also when culture is negative.

Chromosomal DNA fingerprinting indicated that Norwegian Taylorella equigenitalis strains are genetically homogeneous and similar to some Swedish isolates but different from other European strains. As contagious equine metritis is rarely a serious disease in Norwegian horses, we conclude that the dominant T. equigenitalis strain in Norway is a genetically homogeneous clone of low virulence.