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Major outbreak of toxic shock-like syndrome caused by Streptococcus mitis
Hong-Zhou Lu1, Xin-Hua Weng, Bai Zhu
1Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Abstract:
Severe illness caused by viridans streptococci rarely occurs in immunocompetent hosts. Between December 1990 and May 1991, thousands of patients in the YangZi River Delta area of Jiangsu Province, China, suffered from scarlet fever-like pharyngitis. Fewer cases occurred in subsequent years with the same seasonality. Approximately half of the cases developed complications characteristic of streptococcal toxic shock-like syndrome (TSLS). Throat cultures yielded predominant growth of alpha-hemolytic streptococci. All cases admitted to Haian People's Hospital were investigated. Clinical specimens were collected, medical records were reviewed, and bacterial isolates were identified phenotypically and analyzed by 16S rRNA gene sequencing and pulsed-field gel electrophoresis (PFGE). Proteins were purified from culture supernatants by extraction, ammonium sulfate precipitation, and fast-protein liquid chromatography. Biological activities of protein components were determined by subcutaneous inoculation into rabbits. A total of 178 cases of non-beta-hemolytic streptococcal scarlet fever-like pharyngitis were studied. In 88 (79.3%) of 111 patients, oropharyngeal swab cultures grew morphologically identical alpha-hemolytic streptococci. A protein in culture supernatants was pyrogenic in rabbits, was mitogenic for splenocytes, and enhanced rabbit susceptibility to endotoxin challenge. The N-terminal amino acid sequence of this 34-kDa protein showed no homology with known Streptococcus pyrogenic exotoxins. The organism was identified as Streptococcus mitis based on biochemical and 16S rRNA sequence analyses. Representative outbreak isolates from 1990 to 1995 displayed identical PFGE patterns. This TSLS outbreak in southeastern China was caused by a toxigenic clone of S. mitis. An apparently novel toxin may explain the unusual virulence of this organism.
Insights
A rare outbreak of scarlet fever-like pharyngitis in China was caused by a toxigenic clone of Streptococcus mitis. This organism produced a novel pyrogenic toxin, leading to severe illness and toxic shock-like syndrome (TSLS) in immunocompetent individuals.
Area of Science:
- Microbiology
- Infectious Diseases
- Toxicology
Background:
- Viridans streptococci rarely cause severe illness in immunocompetent hosts.
- An unusual outbreak of scarlet fever-like pharyngitis occurred in China between 1990-1991, with recurrent seasonality.
- Many cases developed streptococcal toxic shock-like syndrome (TSLS).
Purpose of the Study:
- To investigate the etiology of the TSLS outbreak.
- To identify the causative agent and its virulence factors.
- To characterize the novel toxin responsible for the severe illness.
Main Methods:
- Phenotypic identification, 16S rRNA gene sequencing, and pulsed-field gel electrophoresis (PFGE) of bacterial isolates.
- Purification and characterization of proteins from bacterial culture supernatants.
- In vivo (rabbit pyrogenicity, endotoxin challenge) and in vitro (splenocyte mitogenicity) assays to determine protein biological activities.
Main Results:
- Alpha-hemolytic streptococci, identified as Streptococcus mitis, were predominant in patient throat cultures.
- A 34-kDa protein from culture supernatants demonstrated pyrogenic activity, mitogenicity, and enhanced endotoxin susceptibility in rabbits.
- This protein showed no homology to known streptococcal pyrogenic exotoxins, suggesting a novel toxin.
- PFGE analysis revealed identical patterns among outbreak isolates from 1990-1995, indicating a single toxigenic clone.
Conclusions:
- The TSLS outbreak was caused by a specific toxigenic clone of Streptococcus mitis.
- A novel pyrogenic toxin produced by this S. mitis clone likely explains the unusual virulence and severe disease presentation.
- This finding highlights the potential for previously innocuous bacteria to emerge as significant pathogens under certain conditions.