Is lactate an undiscovered pneumococcal virulence factor?

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Authors : Abdirahman Hassan


Streptococcus pneumoniae is Gram-positive alpha haemolytic bacteria that commonly found in the nosphrynax of elderly people and young children; it causes approximately 2 million deaths mostly children under age of 5 year and people over 60 years of age. Most important diseases caused by S. pneumoniae are including pneumonaie, meningitis and bacteraemia. The pathogens can be transmitted through contact. Streptococcuspneumoniae obtains its energy mainly carbohydrates through fermentation process. However, in some situations where there are limited sugars or in the presence of galactose the homolactic fermentation is shifted to mixed fermentation in which in addition to lactate, ethanol, formate and acetate are formed. In this study, the role of lactate (lactic acid) and formate (formic acid) in bacterial competition and cytotoxicy was investigated. We hypothesised that lactic acid and formic acid are able to contribute to the virulence of streptococcus pneumoniae. Bacteria were grown on either BHI or BAB. The killing assay was done by exposing various acids on S.pneumoniae as control then lactic acid producing bacteria and non-acid producing bacteria was tested with these acids. Growth assay experiment was done followed by cytotoxicity test using A549 epithelial cells incubated for 24h. The effect of lactic acid for killing assay was significant. Similar effect was seen when lactic acid was exposed to A549 cells. However, a hydrochloric acid was unable to inhibit the growth of bacteria. This study concludes that lactic acid produced by Streptococcus pneumoniae is a potential virulence factor and may contribute to Streptococcus invasive disease.

Keywords: Streptococcal, pneumonia, Gram-positive immunocompromised, microorganisms BAB, Lactate, fermentation


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