S. pneumoniae interacts with other nasopharyngeal bacteria

By Joanna Lyford, Senior medwireNews Reporter

Streptococcus pneumoniae bacteria are able to detect and respond to other bacterial species in the same host niche, researchers report in Open Biology.

This ability may help the bacteria to adapt to their environment, say the researchers who suggest that communication among bacterial species could potentially be harnessed for therapeutic intervention.

Noting that S. pneumoniae usually colonises the human nasopharynx harmlessly, and that this niche is simultaneously populated by other bacterial species, Lucy Hathaway (University of Bern, Switzerland) and colleagues looked for a role and pathway of interspecies communication.

They developed mutant strains of pneumococcal isolates that had inactive versions of aliB-like ORF 1 and/or aliB-like ORF 2, genes that are found only in non-encapsulated strains of the bacteria and encode substrate-binding proteins. Non-encapsulated S. pneumoniae accounts for 10% to 15% of strains isolated from the human nasopharynx, they explain.

By culturing the mutant strains with nasopharyngeal washings containing many other bacterial strains, the team identified ligands of the two proteins.

AliB-like ORF 1 had just one ligand, a sequence that matches a ribosomal subunit protein of Enterobacteriaceae, including Salmonella enterica, E. coli, Serratia symbiotica and Klebsiella pneumoniae. This protein is thought to facilitate competence for genetic transformation.

Meanwhile, AliB-like ORF 2 had two peptide ligands that matched subunit proteins of the human commensal Prevotella salivae and P. tannerae strains, which are common in healthy human nasopharyngeal microbiota.

Further analysis revealed ligand binding to be highly specific and, in the case of AliB-like ORF 2, to promote bacterial colonisation in vivo. In a mouse model of S. pneumoniae infection, bacterial colonisation 24 to 48 hours after inoculation was significantly lower with mutant strains lacking AliB-like ORF 1 and 2 than with wild-type strains.

The researchers conclude that S. pneumoniae is able to recognise and respond to peptides matching other bacterial species.

“We therefore propose that sensing of short peptides is a newly described mechanism which could be employed by bacteria to sense neighbouring species in the microbiota and adapt accordingly”, they write. “Manipulation of this communication could be a new target in the control of bacterial colonization and infections.”

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