Distribution of Streptococcal Groups in Clinical Specimens with Evaluation of Bacitracin Screening

Abstract

During a 2-year period, 4,968 strains of beta-hemolytic streptococci were examined for the clinical source distribution and bacitracin sensitivity of each group. In the upper respiratory tract, groups A (51.7%) and C (20.4%) accounted for most of the isolates, and in wounds and exudates group A (79.1%) made up most of the isolates. Group B (71.2%) was the major component of isolates from the genitorinary tract and, while composing 29.3% of the lower respiratory tract isolates, competed with group A (18.8%) and the nongroupables (22.8%) for supremacy. Bacitracin screening showed that 0.5% of group A streptococci were resistant, and sensitive non-group A isolates were group B (2.6%), group C (6.0%), group G (8.0%), and the nongroupables (2.2%). It was found that those groups which were most predominant in wounds and the upper respiratory tract gave the highest rate of false positives with bacitracin, whereas the predominant group of the genitourinary tract gave the lowest rate of false positives.

Rapid recognition of group B streptococci by pigment production and counterimmunoelectrophoresis

“…The incidence of false negatives (group B streptococci not forming a pigment) was 15% in Fallon's study by his technique (6) and 3% in our study with the stab cultures. This compares favorably with the bacitracin tests for identification of group A streptococci, since it has been shown that 0.5% of group A are resistant to bacitracin (false negatives), whereas 2.6% of group B, 6% of group C, 8% of group G, and 2.2% of the nongroupables are sensitive to bacitracin (false positives) (11). Similarly, a positive hippurate test can be obtained with streptococci other than group B (false positives) (5).…”

Presumptive identification of group A, B, and D streptococci on agar plate media

“…The most persistent source of error in our battery of tests resulted from the susceptibility of beta-hemolytic non-group A, B, or D streptococci to bacitracin. Approximately 8% of these streptococci are susceptible to bacitracin (7,10). Because these strains are frequently mistaken for group A streptococci, the procedures for identifying these streptococci need to be improved.…”

Laboratory identification and epidemiology of streptococcal hospital isolates

“…In 1942, Rantz and Kirby (29) published one of the first reports demonstrating the importance of non-group A streptococci in extrarespiratory infections. There followed a limited number of publications on this subject citing single or small collections of infections due to non-group A or D streptococci (21,22,26,34). In the 1960s there was an increasing awareness of the emergence of group B infections (10,17,23), but it was not until Reinarz and Sanford in 1965 (30) and Feingold et al in 1966 (14) again demonstrated the importance of various serological groups of streptococci as causative agents of extrarespiratory infections that sustained interest developed.…”