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Occurrence of mucoid M-18 Streptococcus pyogenes in a central Ohio pediatric population
M J Marcon1, M M Hribar, D M Hosier
1Department of Laboratory Medicine, Children's Hospital, Columbus, Ohio 43205.
Abstract:
During a 1-year period from October 1986 through September 1987, we recovered 116 mucoid, hemolytic Streptococcus pyogenes isolates from clinical specimens collected from patients seen at our pediatric institution. A total of 102 isolates were from throat cultures (101 for pharyngitis, 1 for acute rheumatic fever), 13 were from other superficial body sites, and 1 was from pleural fluid. All of 40 mucoid isolates tested to date were determined to be M-type 18 strains. A direct latex agglutination test for group A carbohydrate antigen in throat swab specimens was equally sensitive in detecting M-18 mucoid and nonmucoid strains (45 of 77 [58%] and 795 of 1,186 [67%], respectively; not significant, P greater than 0.05). Antimicrobial susceptibility tests performed with 40 mucoid and 40 nonmucoid isolates against penicillin and nine other antimicrobial agents showed all strains to be susceptible, with no difference in MICs. All isolates tested were also considered fully susceptible to the bactericidal activity of penicillin. Further studies are needed to establish the relative virulence of M-18 strains and their possible association with the resurgence of acute rheumatic fever in central Ohio and other areas of the United States.
Insights
Mucoid Streptococcus pyogenes, specifically M-type 18 strains, were identified in clinical samples. These strains showed susceptibility to penicillin and other antimicrobials, but further research is needed to assess their virulence and link to acute rheumatic fever.
Area of Science:
- Microbiology
- Infectious Diseases
- Clinical Medicine
Background:
- Streptococcus pyogenes (group A Streptococcus) is a significant human pathogen.
- Mucoid variants of S. pyogenes, particularly M-type 18, have been increasingly observed.
- The resurgence of acute rheumatic fever (ARF) necessitates understanding the epidemiology and virulence of circulating S. pyogenes strains.
Purpose of the Study:
- To characterize mucoid, hemolytic Streptococcus pyogenes isolates recovered from clinical specimens.
- To evaluate the diagnostic sensitivity of a latex agglutination test for group A carbohydrate antigen in detecting M-18 strains.
- To assess the antimicrobial susceptibility and penicillin bactericidal activity of these mucoid isolates.
Main Methods:
- Collection and identification of 116 mucoid, hemolytic S. pyogenes isolates from clinical specimens over a 1-year period.
- Serotyping of mucoid isolates to determine M-type.
- Evaluation of a direct latex agglutination test for group A carbohydrate antigen using throat swab specimens.
- Antimicrobial susceptibility testing (MICs) and assessment of penicillin bactericidal activity against mucoid and nonmucoid S. pyogenes isolates.
Main Results:
- 116 mucoid, hemolytic S. pyogenes isolates were recovered, predominantly from throat cultures.
- All 40 mucoid isolates tested were identified as M-type 18 strains.
- The latex agglutination test showed similar sensitivity for mucoid (M-18) and nonmucoid strains.
- All tested mucoid and nonmucoid strains were susceptible to penicillin and other tested antimicrobial agents, with no significant differences in MICs or penicillin bactericidal activity.
Conclusions:
- Mucoid M-type 18 Streptococcus pyogenes strains were prevalent in clinical isolates during the study period.
- Current diagnostic methods and antimicrobial susceptibility profiles do not distinguish these mucoid strains from nonmucoid ones.
- Further investigation is required to determine the virulence of M-18 strains and their potential role in the resurgence of acute rheumatic fever.