DNA from group A streptococci of various M and T types was cleaved with endonucleases to produce a DNA fingerprint. Comparison of DNA fingerprints proved to be a very useful tool for studying the epidemiology of isolates from various outbreaks of streptococcal disease. Patterns of DNA fragments from HindIII digests of samples of total DNA were conserved among strains of the same M serotype yet were easily distinguished from those of different M serotypes. Different M types were associated with specific restriction enzyme profiles. DNA fingerprints of strains of the same M type were stable enough to establish a clonal relationship between strains obtained from an isolated outbreak of disease or strains endogenous to people geographically isolated by continent. Strains of the same serotype from different continents had very similar, but distinguishable, restriction profiles. Those strains unable to be typed with standard typing sera were also amenable to comparison because they yielded unique fingerprints.

A collection of Streptococcus zooepidemicus strains from human and animal infections was examined for DNA banding patterns after nuclease digestion and agarose gel electrophoresis. The large variety of DNA fingerprints found revealed the complexity of the species but showed that isolates from clusters of outbreaks had identical prints. The results confirmed the specificity of bacteriocin and bacteriophage typing of S. zooepidemicus; the technique also gave useful profiles on untypable strains. Strains with common bacteriocin and biotyping patterns from sporadic infections could be differentiated by their DNA fingerprints. In several outbreaks and incidents, more than one strain of S. zooepidemicus were encountered, and the importance of carefully interpreting typing data is stressed. Chromosomal DNA fingerprinting is a very efficient technique for demonstrating differences between strains of S. zooepidemicus, and its use is recommended for future epidemiological studies of this infectious agent.

In a study of intergroup reactions, four virulent Group A streptococcal phages were found to form plaques in high titer on lawns prepared from a number of Group C streptococcal strains. Whether the phages were propagated on the homologous (Group A) strain or a heterologous (Group C) strain did not appear to influence consistently the plaque-forming efficiency on lawns prepared from a homologous (Group A) or a heterologous (Group C) strain or to alter significantly the percent of Group C strains which showed plaque formation. Considerable variability was found in the ability of temperate phages to lyse strains of a heterologous group. A single Group C indicator strain was lysed by a high percentage of freshly induced temperate Group A phages. A single temperate Group C phage lysed a significant proportion of Group A strains when freshly induced or when propagated on a Group A strain. Intragroup transduction of streptomycin resistance was demonstrated between Group C strains. Intergroup transduction of streptomycin resistance and also bacitracin resistance was achieved between Group C and Group A streptococci. These observations provide evidence that Group A streptococci can serve as recipients in intergroup transmission of genetic information. Ultraviolet irradiation of the transducing lysate and lowering the propagation temperature of the transducing lysate increased the frequency of transduction in both the intragroup and intergroup transduction systems.

We assembled an international collection of strains from sporadic and epidemic human infection with Streptococcus zooepidemicus (Lancefield group C) for laboratory study. Cultural and physiological characteristics of the isolates were determined, including biotyping with the API 20 STREP test kit and susceptibility testing with penicillin, erythromycin and tetracycline. The strains were examined for bacteriocin production and sensitivity and typed with a specially developed group-C streptococcal bacteriophage system incorporating a panel of 14 phages. Results of these tests gave useful discrimination between many of the strains: differences were shown between each of the major outbreak strains, including those complicated by post-streptococcal glomerulonephritis. Serious group C streptococcal infection may be caused by S. zooepidemicus and isolates should be identified to species level; the application of a typing scheme such as this may help to distinguish epidemiological patterns of infection.