A Study of the Identification of Medically Important Streptococci

Summary: 1. The type of animal blood used in preparing blood agar plates did not significantly affect the demonstration of hemolysis by any streptococcal species except for S.faecalis. S.faecalis more consistently displayed an alpha reaction on sheep blood agar while expressing a beta reaction on horse and rabbit blood agars. 2. A recommended scheme for identifying streptococci, adaptable to most any clinical laboratory, was developed and is outlined in Table 13. 3. S.agalactiae (group B) was the most frequent beta hemolytic streptococcal isolant. Significantly, it was the only species over-all to be recovered from every clinical source. The CAMP test proved to be the best method for the presumptive identification of the group B streptococci. 4. The alpha streptococci were isolated in substantial numbers from a variety of infectious situations suggesting that their role in infection may be greater than previously believed. 5. S.avium accounted for a greater percentage of group D isolations than previously reported in other studies of a similar nature. 6. The bile-esculin test was supported as the best nonserological method for distinguishing the group D streptococci. Arginine hydrolysis was shown to be the best method for distinguishing between the enterococci and the nonenterococci. The test commonly used for this purpose, growth in 6.5% NaCl, resulted in the misidentification of S.avium as an enterococcal species. 7. Urinary tract isolants from every division (notably S.agalactiae, S.mutans. and S.faecalis) exhibited patterns of overall greater antibiotic resistance than those strains isolated from other sources. 8. Among the group D species, S.faecalis displayed the greatest antibiotic resistance followed by S.avium, S.faecium, and S.bovis. S.avium, a nonenterococcus. showed greater drug resistance than S.faecium, an enterococcus. S.bovis was the least resistant with susceptibility patterns more closely related to the alpha streptococci