Identification, cloning, and expression of the CAMP factor gene (cfa) of Group A streptococci

The CAMP reaction is a synergistic lysis of erythrocytes by the interaction of an extracellular protein (CAMP factor) produced by some streptococcal s pecies with the Staphylococcus aureus sphingomyelinase C (beta-toxin), Grou p A streptococci (GAS [Streptococcus pyogenes]) have been long considered C AMP negative, and this reaction commonly has been used to distinguish GAS f rom Streptococcus agalactiae. We here provide evidence that GAS possess thi s gene and produce an extracellular CAMP factor capable of participating in a positive CAMP reaction. The S. pyogenes CAMP factor is specified by a 77 4-bp open reading frame homologous to the CAMP factor genes from S. agalact iae and Streptococcus uberis, This gene, designated cfa, was isolated on a 1,256-bp fragment and cloned in Escherichia coli. Recombinant clones off, c oli expressing cfa secreted an active CAMP factor. The deduced 28.5-kDa pro tein encoded by cfa consists of 257 amino acids, with a predicted 28-amino- acid signal peptide. The cfa gene is widely spread among GAS: 82 of 100 cli nical GAS isolates produced a positive CAMP reaction. Of the CAMP-negative strains, 17 of the 18 GAS strains contained the cfa gene. Additionally, CAM P activity was detected in streptococci from serogroups C, M, P, R, and U. The cfa gene was cloned and actively expressed in Escherichia coli and gene fusions were made, placing the beta-galactosidase gene (lacZ) under contro l of the cfa promoter. These cfa promoter-lacZ fusions were introduced into S. pyogenes via a bacteriophage-derived site-specific integration vector w here they showed that the cfa gene has a strong promoter that may be subjec t to as-yet-unidentified regulatory factors. The results presented here, al ong with previous reports, indicate that the CAMP factor gene is fairly wid espread among streptococci, being present at least in groups A, B, C, G, M, P, R, and U.