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Streptococcus pyogenes are Gram-positive opportunistic pathogens residing in the human nasopharynx and skin. Changes in environmental conditions, such as pH, temperature and availability of essential ions, can stimulate the expression of S. pyogenes virulence factors. One such factor could be the availability of an extracellular pool of polyamines. Polyamines are synthesized from amino acids, and are universally present in the environment. Polyamines have been implicated in the ecology of pathogenesis by modulating quorum sensing, host adaptation and virulence. Polyamines mediate pathogenesis and help the pathogen resist environmental stress. In this study, we investigated the ability of the polyamine, spermidine, to promote acid stress survival of S. pyogenes. S. pyogenes does not synthesize spermidine, but the extracellular pool of spermidine constituted by the host and microbiome could be utilized as a signalling molecule. We report that spermidine promotes acid stress resistance in S. pyogenes . Moreover, spermidine affects the morphology of S. pyogenes by decreasing the cell size and increasing the dltA gene expression. Along with dltA, spermidine upregulated the gene expression of cell wall-modifying genes such as mur, pgdA, pepO and srtA, which might help the bacteria to resist acidic stress.

Biofilm research is growing rapidly due to the widespread existence of biofilms in pathogens and their resistance to a variety of antimicrobial therapies. World Health Organization in 2017 categorised pathogens into three categories based on their AMR [Antimicrobial resistance] and severity of infection viz. critical, high and medium. Acinetobacter baumannii, Pseudomonas aeruginosa and organisms belonging to Enterobacteriaceae family are top priority pathogens- ‘critical’, amongst which the majority of them are reported to cause the infection due to biofilm formation. As antibiotic resistance has increased tremendously in the last few years, the current research is concentrated on the development of effective approaches to inhibit biofilm formation by bacteria. Anti-biofilm activity is mediated by a spectrum of molecules obtained from plants, mammals, fungi, microbes, and marine sponges. The chapter gives a comprehensive idea about natural bioactives from plant and other sources that act as anti-biofilm agents. Clinical validation of these bioactives will aid the medical field with alternate preventive and treatment methods against pathogenic biofilms.

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