Variations in bacterial strains can trigger varying immune responses, study states

A new study published in PLOS Pathogens revealed the role of genetic variations between different strains of the same bacterial species in inducing variations in immune system responses. Former studies have shown that susceptibility to infection with the same species of disease causing bacteria may vary among people.

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The researchers at Rockefeller University, New York have examined different strains of two major species of pathogenic bacteria, Staphylococcus aureus and Streptococcus pyogenes, and have analyzed the response of immune system T and B cells in donated human blood samples once exposed to different strains of each species.

The study findings obtained from an individual blood sample showed widely varied responses by T and B cells of the adaptive immune system, which is responsible for creating "memory" of specific pathogens to avoid future infection. Results of blood samples from 10 additional donors showed similar responses to different strains.

Furthermore, the researchers formed mutant bacteria with deactivated "accessory" genes–genes that account for between-strain differences–leaving the "core" genome of the species intact. As a result, the mutant strains induced a dampened T cell response, which suggested that changes in "accessory" genes were accountable for the varied immune responses seen for unmutated strains.

These findings imply that differences in bacterial "accessory" genes might help to describe the clinical variation found typically among the patients infected with same bacterial species.

Former research has often described "signature" immune responses to various bacteria using only a single strain for each species. However, based on the conclusions of the current study, the scientists proposed that immune response signatures should instead be classified according to the specific strain or the species' common "core genome." Such a shift could assist the development of strategies for predicting the outcomes of the disease in patients.

According to the study authors, the current practice can only identify the bacterial species in infected patients. The results of the study may increase the likeliness that describing the specific infecting strain becomes a necessary part of patient evaluation and treatment.

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