Two newly discovered immune modulators, chemotaxis inhibitory protein of Staphylococcus aureus (CHIPS)and staphylococcal complement inhibitor (SCIN), cluster on the conserved 3 end of ␤-hemolysin (hlb)-converting bacteriophages (␤C-s). Since these ␤C-s also carry the genes for the immune evasion molecules staphylokinase (sak) and enterotoxin A (sea), this 8-kb region at the 3 end of ␤C-represents an innate immune evasion cluster (IEC). By PCR and Southern analyses of 85 clinical Staphylococcus aureus strains and 5 classical laboratory strains, we show that 90% of S. aureus strains carry a ␤C-with an IEC. Seven IEC variants were discovered, carrying different combinations of chp, sak, or sea (or sep), always in the same 5-to-3 orientation and on the 3 end of a ␤C-. From most IEC variants we could isolate active bacteriophages by mitomycin C treatment, of which lysogens were generated in S. aureus R5 (broad phage host). All IEC-carrying bacteriophages integrated into hlb, as was measured by Southern blotting of R5 lysogens. Large quantities of the different bacteriophages were obtained by mitomycin C treatment of the lysogens, and bacteriophages were collected and used to reinfect all lysogenic R5 strains. In total, five lytic families were found. Furthermore, phage DNA was isolated and digested with EcoR1, revealing that one IEC variant can be found on different ␤I-s. In conclusion, the four human-specific innate immune modulators SCIN, CHIPS, SAK, and SEA form an IEC that is easily transferred among S. aureus strains by a diverse group of ␤-hemolysin-converting bacteriophages.Recently, we described two new innate immune modulators of Staphylococcus aureus: staphylococcal complement inhibitor (SCIN) and chemotaxis inhibitory protein of S. aureus (CHIPS). SCIN is a C3 convertase inhibitor, blocking the formation of C3b on the surface of the bacterium and the ability of human neutrophils to phagocytose S. aureus (25). CHIPS is a bacterial chemokine receptor modulator that specifically binds two chemokine receptors. CHIPS attenuates the response of the C5a receptor (C5aR) as well as the formylated peptide receptor of human neutrophils. This results in inhibition of neutrophil chemotaxis and activation in response to C5a and formylated peptides (6,10,20,21). Both SCIN and CHIPS are important virulence factors that protect S. aureus from innate immune defense systems.The SCIN (scn) and CHIPS (chp) genes are found in 6/7 and 3/7 sequenced S. aureus strains, respectively. Analyses of these sequenced genomes showed that both scn and chp are carried by ␤-hemolysin (hlb)-converting bacteriophages (␤C-s), formerly known as double-and triple-converting phages. Doubleconverting bacteriophages were earlier described to negatively convert ␤-hemolysin expression but simultaneously introduce the staphylokinase (SAK) gene. Triple conversion leads to ␤-hemolysin-negative and SAK-and staphylococcal enterotoxin A (SEA)-positive strains. 13 and 42 are examples of, respectively, double-and triple-converting bacteriophages. Both 13 and ...

The complement system is pivotal in host defense but also contributes to tissue injury in several diseases. The assembly of C3 convertases (C4b2a and C3bBb) is a prerequisite for complement activation. The convertases catalyze C3b deposition on activator surfaces. Here we describe the identification of staphylococcal complement inhibitor, an excreted 9.8-kilodalton protein that blocks human complement by specific interaction with C4b2a and C3bBb. Staphylococcal complement inhibitor bound and stabilized C3 convertases, interfering with additional C3b deposition through the classical, lectin and alternative complement pathways. This led to a substantial decrease in phagocytosis and killing of Staphylococcus aureus by human neutrophils. As a highly active and small soluble protein that acts exclusively on surfaces, staphylococcal complement inhibitor may represent a promising anti-inflammatory molecule.

Leukocyte migration is a key event both in host defense against invading pathogens as well as in inflammation. Bacteria generate chemoattractants primarily by excretion (formylated peptides), complement activation (C5a), and subsequently through activation of leukocytes (e.g., leukotriene B4, platelet-activating factor, and interleukin 8). Here we describe a new protein secreted by Staphylococcus aureus that specifically impairs the response of neutrophils and monocytes to formylated peptides and C5a. This chemotaxis inhibitory protein of S. aureus (CHIPS) is a 14.1-kD protein encoded on a bacteriophage and is found in >60% of clinical isolates. CHIPS reduces the neutrophil recruitment toward C5a in a mouse peritonitis model, even though its activity is much more potent on human than on mouse cells. These findings suggest a new immune escape mechanism of S. aureus and put forward CHIPS as a potential new antiinflammatory therapeutic compound.

Enterococcus faecium, an ubiquous colonizer of humans and animals, has evolved in the last 15 years from an avirulent commensal to the third most frequently isolated nosocomial pathogen among intensive care unit patients in the United States. E. faecium combines multidrug resistance with the potential of horizontal resistance gene transfer to even more pathogenic bacteria. Little is known about the evolution and virulence of E. faecium, and genomic studies are hampered by the absence of a completely annotated genome sequence. To further unravel its evolution, we used a mixed whole-genome microarray and hybridized 97 E. faecium isolates from different backgrounds (hospital outbreaks (n = 18), documented infections (n = 34) and asymptomatic carriage of hospitalized patients (n = 15), and healthy persons (n = 15) and animals (n = 21)). Supported by Bayesian posterior probabilities (PP = 1.0), a specific clade containing all outbreak-associated strains and 63% of clinical isolates was identified. Sequencing of 146 of 437 clade-specific inserts revealed mobile elements (n = 74), including insertion sequence (IS) elements (n = 42), phage genes (n = 6) and plasmid sequences (n = 26), hypothetical (n = 58) and membrane proteins (n = 10), and antibiotic resistance (n = 9) and regulatory genes (n = 11), mainly located on two contigs of the unfinished E. faecium DO genome. Split decomposition analysis, varying guanine cytosine content, and aberrant codon adaptation indices all supported acquisition of these genes through horizontal gene transfer with IS16 as the predicted most prominent insert (98% sensitive, 100% specific). These findings suggest that acquisition of IS elements has facilitated niche adaptation of a distinct E. faecium subpopulation by increasing its genome plasticity. Increased genome plasticity was supported by higher diversity indices (ratio of average genetic similarities of pulsed-field gel electrophoresis and multi locus sequence typing) for clade-specific isolates. Interestingly, the previously described multi locus sequence typing–based clonal complex 17 largely overlapped with this clade. The present data imply that the global emergence of E. faecium, as observed since 1990, represents the evolution of a subspecies with a presumably better adaptation than other E. faecium isolates to the constraints of a hospital environment.

Antibodies to TSST-1 have a neutralizing capacity, and median levels of antibodies to TSST-1, SEA, ClfA, and ClfB are higher in persistent carriers than in noncarriers. These antibodies might be associated with the differences in the risk and outcome of S. aureus infections between nasal carriers and noncarriers.