Organ- and host-specific clonal groups of Staphylococcus aureus from human infections and bovine mastitis revealed by the clumping factor A gene.

Staphylococcus aureus has become a major concern in public health because of the rapid evolution of resistant and host/organ specialized lineages adapted to humans and major food animals. However, the mechanism(s) of host and organ specializations in S. aureus is presently ill defined. The objective of our study was to investigate whether coding intragenic repeat-containing markers would be capable of detecting and grouping adaptive clones, tracing their sources, or studying the basis for their specializations in different microenvironments. We have analyzed the number of copies as well as the nucleotide sequences in the hypervariable R-domain of the clumping factor A gene in 95 isolates from different organs in human patients and from bovine mastitis, using polymerase chain reaction, sequencing, multiple sequence alignment, and phylogenetic relationships. The results showed that isolates of the same human organ were polymorphic for clfA, whereas those of the mammary were clonal. Twenty of the 23 sputum isolates had lower copy numbers of 43-48, while 21 of the 24 skin isolates had 55-63 copies. Twenty-four repeat types were identified with the index of discrimination of 0.9. Repeat types and overall sequence pattern groups were highly consistent. In addition, sequence alignments and phylogenetic analysis placed the isolates from different hosts and organs into respective clusters. Thus, clfA is useful in detecting the clonal lineage of mastitis, and tracing and grouping organ-specific strains, and might be a potential tool for studying host specialization and selection.