Diagnosis of invasive group a streptococcal infections by using immunohistochemical and molecular assays

Area of Science:

• Medical Microbiology
• Pathology
• Infectious Diseases

Background:

• Invasive group A streptococcus (GAS) infections are a significant cause of mortality in the US.
• Current diagnostic methods, like bacterial cultures, have limitations, including failure to obtain samples or inhibition of growth by antibiotics.
• There is a need for alternative diagnostic approaches for GAS infections, particularly in formalin-fixed, paraffin-embedded tissues.

Purpose of the Study:

• To evaluate the utility of an immunohistochemical (IHC) assay for diagnosing invasive group A streptococcus (GAS) infections.
• To compare IHC results with traditional culture methods and molecular confirmation using PCR.
• To assess the diagnostic performance of IHC and PCR in formalin-fixed, paraffin-embedded tissue samples.

Main Methods:

• An immunohistochemical assay was applied to formalin-fixed tissue samples from 122 patients with suspected GAS infection.
• Bacterial cultures were performed, and when positive, Streptococcus pyogenes was identified.
• A heminested polymerase chain reaction (PCR) assay targeting the sepB gene of S. pyogenes was used to confirm IHC findings in paraffin-embedded samples.

Main Results:

• Immunohistochemical staining, indicating GAS presence, was observed in 27 out of 122 cases.
• Streptococcus pyogenes was isolated by culture in 18 cases.
• In 8 cases where cultures were negative or not performed, IHC results were confirmed by PCR amplification of the S. pyogenes sepB gene.

Conclusions:

• Immunohistochemical analysis is a valuable tool for diagnosing invasive GAS infections, especially when bacterial cultures are inconclusive or unavailable.
• Combining IHC with PCR offers a reliable method for detecting GAS in formalin-fixed, paraffin-embedded tissue samples.
• These methods can improve the timely diagnosis and management of invasive streptococcal infections.