Abstract
The optimal incubation conditions for isolation of group A streptococci from throat cultures are controversial. Therefore, we compared the effects of aerobic and anaerobic incubations after 24 and 48 h on the recovery of group A streptococci. Throat swabs submitted to the clinical laboratory were inoculated onto duplicate 5% sheep blood agar plates, incubated aerobically or anaerobically (GasPak jar) at 35 degrees C, and examined semiquantitatively after 24 and 48 h. Group A streptococci were identified by the fluorescent-antibody technique. Of 1,040 specimens, 506 (48.6%) grew beta-hemolytic streptococci, including 200 (19.2%) group A streptococci. Group A streptococci were recovered significantly more often with anaerobic incubation than with aerobic incubation after 24 h (182 versus 138; P less than 0.001) and after 48 h (193 versus 174; P less than 0.05). Non-group A beta-hemolytic streptococci also were recovered significantly more often with anaerobic incubation after 24 and 48 h (P less than 0.001). Colony counts were not affected by the incubation atmosphere. We conclude that incubation of throat cultures in an anaerobic atmosphere is superior to incubation in air for detection of group A streptococci. The greater sensitivity of anaerobic incubation, however, may not justify the extra laboratory effort and cost required to differentiate group A streptococci from the non-group A streptococci detected as a result of anaerobic incubation. Throat cultures should be examined after 24 and 48 h, especially if plates are incubated aerobically.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Breese B. B. Beta-hemolytic streptococcus: its bacteriologic culture and character. Am J Dis Child. 1978 May;132(5):502–508. doi: 10.1001/archpedi.1978.02120300062013. [DOI] [PubMed] [Google Scholar]
- COOK G. T., JEBB W. H. H. Isolation of beta-haemolytic streptococci from nose and throat swabs by aerobic and anaerobic incubation. Mon Bull Minist Health Public Health Lab Serv. 1952 Jan;11:18–21. [PubMed] [Google Scholar]
- Dykstra M. A., McLaughlin J. C., Bartlett R. C. Comparison of media and techniques for detection of group A streptococci in throat swab specimens. J Clin Microbiol. 1979 Feb;9(2):236–238. doi: 10.1128/jcm.9.2.236-238.1979. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ederer G. M., Chapman S. S. Simplified fluorescent-antibody staining method for primary plate isolates of group A streptococci. Appl Microbiol. 1972 Jul;24(1):160–161. doi: 10.1128/am.24.1.160-161.1972. [DOI] [PMC free article] [PubMed] [Google Scholar]
- McGonagle L. A. Evaluation of a screening procedure for the isolation of beta-hemolytic streptococci. Health Lab Sci. 1974 Apr;11(2):61–64. [PubMed] [Google Scholar]
- Murray P. R., Wold A. D., Schreck C. A., Washington JA I. I. Effects of selective media and atmosphere of incubation on the isolation of group A streptococci. J Clin Microbiol. 1976 Jul;4(1):54–56. doi: 10.1128/jcm.4.1.54-56.1976. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Pien F. D., Ow C. L., Isaacson N. S., Goto N. T., Rudoy R. C. Evaluation of anaerobic incubation for recovery of group A streptococci from throat cultures. J Clin Microbiol. 1979 Sep;10(3):392–393. doi: 10.1128/jcm.10.3.392-393.1979. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sanders E. Bacterial interference. I. Its occurrence among the respiratory tract flora and characterization of inhibition of group A streptococci by viridans streptococci. J Infect Dis. 1969 Dec;120(6):698–707. doi: 10.1093/infdis/120.6.698. [DOI] [PubMed] [Google Scholar]