Abstract
Streptococcus pyogenes an adapted human pathogen asymptomatically colonizes the nasopharynx, among other polymicrobial communities. However, information on the events leading to the colonization and expression of virulence markers subject to interspecies and host-bacteria interactions are limited. The interference of acyl homoserine lactones (AHLs) with the hemolytic activity and viability of S. pyogenes M6 S165 was examined. AHLs, with fatty acid side chains ≥12 carbon atoms, inhibited hemolytic activity by downregulating the expression of the sag operon involved in the production of streptolysin S. Inhibitory AHLs upregulated the expression of transcriptional regulator LuxR. Electrophoretic mobility shift assays revealed the interaction of LuxR with the region upstream of sagA. AHL-mediated bactericidal activity observed at higher concentrations (mM range) was an energy-dependent process, constrained by the requirement of glucose and iron. Ferrichrome transporter FtsABCD facilitated transport of AHLs across the streptococcal membrane. The study demonstrates a previously unreported role for AHLs in S. pyogenes virulence.
Highlights
The present study investigated the effect of AHLs on the hemolytic activity of S. pyogenes M6 S165
S. pyogenes M6 S165 was cultured in the presence of different AHLs, which varied in the number of carbon atoms in their fatty acid side chain, and assayed for hemolytic activity
To determine if the inhibitory AHLs inactivated the streptolysin S (SLS) secreted in the growth media, the supernatant from the growth of S. pyogenes M6 S165 was mixed with different AHLs (20 μM) and assayed for hemolytic activity
Summary
A decrease in the sagA transcripts was detected only in S. pyogenes M6 S165 cultured with the inhibitory AHLs. The transcript levels of the slo gene encoding streptolysin O remained unaffected (Fig. 2B), thereby indicating that the inhibition of the hemolytic activity due to the oxo-AHLs is the result of a decrease in SLS. The effect of AHLs on the hemolytic activity of S. pyogenes M1 strain was examined and no decrease was recorded in the presence of oxo-C12-HSL (10 μM) (Fig. 4A).
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