PNEUMOCOCCI DETECTED IN SALIVA BY lytA-PCR WHEN PRESENT ARE AT VERY LOW DENSITY AND IN MOST CASES MAY BE NON-PNEUMOCOCCAL STREPTOCOCCI CONTAINING PNEUMOCOCCAL GENE HOMOLOGUES
The presence of pneumococci (Sp), detected by PCR, in a high proportion of saliva samples from healthy children has previously been reported. Having obtained similar results, we analysed paired nasal swab and saliva samples from children, in which both samples were lytA PCR positive (Ct<35), using molecular serotyping by microarray.
The products of standard culture on selective agar plates from the 49 sample pairs, obtained from healthy children aged 6 months to 5 years attending pre-school nursery in Coimbra, Portugal, were subjected to molecular serotyping analysis by microarray as previously described.
Among the 49 nasal samples, 45 had evidence of Sp by microarray, 4 only related non-Sp and one no evidence of Sp or related species. In 28 there was evidence of single Sp serotypes and in 9 of multiple serotypes. By contrast only 3/49 saliva samples had evidence of Sp by microarray, in each case matching the Sp detected in the nasal sample from the same child but in all 3 at low abundance within a complex mix of other species.
These results suggest that the common finding of qPCR results suggestive of the presence of Sp in saliva samples in young children may, in reality, reflect the presence of genetically related streptococci from the oral flora, usually in complex mixtures. While our findings do not definitively rule out the presence of small numbers of viable pneumococci whose presence is masked by the rich oral microbial flora, nevertheless, they suggest that transmission of Sp via saliva may be less important than via nasal secretions in this age group.
Work supported by an investigator-led project grant from Pfizer.