Prevalence of Staphylococcus aureus protein A (spa) mutants in the community and hospitals in Oxfordshire

• Published in: BMC microbiology Vol. 14; no. 1; p. 63
• Main Authors: Votintseva, Antonina A, Fung, Rowena, Miller, Ruth R, Knox, Kyle, Godwin, Heather, Wyllie, David H, Bowden, Rory, Crook, Derrick W, Walker, A Sarah
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 12.03.2014; BioMed Central
• Subjects: Bacteriology; DNA Primers - genetics; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; Genetic aspects; Health aspects; Hospital patients; Hospitals; Humans; Immune response; Laboratories; Livestock; Medical research; Molecular Sequence Data; Molecular Typing - methods; Mutation; Physiological aspects; Prevalence; Sensitivity and Specificity; Sequence Analysis, DNA; Staphylococcal Infections - diagnosis; Staphylococcal Infections - microbiology; Staphylococcal Protein A - genetics; Staphylococcus aureus; Staphylococcus aureus - classification; Staphylococcus aureus - genetics; Staphylococcus aureus - isolation & purification; Studies; United Kingdom; United Kingdom
• ISSN: 1471-2180; 1471-2180
• DOI: 10.1186/1471-2180-14-63

Staphylococcal protein A (spa) is an important virulence factor which enables Staphylococcus aureus to evade host immune responses. Genotypes known as "spa-types", based on highly variable Xr region sequences of the spa-gene, are frequently used to classify strains. A weakness of current spa-typing primers is that rearrangements in the IgG-binding region of the gene cause 1-2% of strains to be designated as "non-typeable". We developed an improved primer which enabled sequencing of all strains, containing any type of genetic rearrangement, in a large study among community carriers and hospital inpatients in Oxfordshire, UK (6110 isolates). We identified eight novel spa-gene variants, plus one previously described. Three of these rearrangements would be designated "non-typeable" using current spa-typing methods; they occurred in 1.8% (72/3905) asymptomatically carried and 0.6% (14/2205) inpatient S. aureus strains. Some individuals were simultaneously colonized by both formerly non-typeable and typeable strains; previously such patients would have been identified as carrying only currently typeable strains, underestimating mixed carriage prevalence and diversity. Formerly non-typeable strains were found in more spa-types associated with multilocus sequence type ST398 (35%), common among livestock, compared to other groups with any non-typeable strains (1-4%), suggesting particular spa-types may have been under-represented in previous human studies. This improved method allows us to spa-type previously non-typeable strains with rearrangements in the spa-gene and to resolve cases of mixed colonization with deletions in one or more strains, thus accounting for hidden diversity of S. aureus in both community and hospital environments.