The repressor CodY is reported to inhibit metabolic genes mainly involved in nitrogen metabolism. We analyzed codY mutants from three unrelated Staphylococcus aureus strains (Newman, UAMS-1, and RN1HG). The mutants grew more slowly than their parent strains in a chemically defined medium. However, only codY mutants were able to grow in medium lacking threonine. An excess of isoleucine resulted in growth inhibition in the wild type but not in the codY mutants, indicating that isoleucine plays a role in CodY-dependent repression. Prototypic CodY-repressed genes including the virulence regulator agr are repressed after up-shift with isoleucine. The CodY-dependent repression of agr is consistent with the concomitant influence of CodY on typical agr-regulated genes such as cap, spa, fnbA, and coa. However, some of these virulence genes (e.g., cap, fnbA, and spa) were also regulated by CodY in an agr-negative background. Microarray analysis revealed that the large majority of CodY-repressed genes were involved in amino acid metabolism; CodY-activated genes were mainly involved in nucleotide metabolism or virulence. In summary, CodY in S. aureus not only acts as a repressor for genes involved in nitrogen metabolism but also contributes to virulence gene regulation by supporting as well as substituting for agr function.Staphylococcus aureus asymptomatically colonizes the nares of healthy individuals but also causes a variety of infections in humans. Regulatory loci are necessary for the adaptation of the organism to the different nutrient limitations and stress conditions encountered in vivo. This allows the pathogen to survive and/or multiply in different compartments during colonization and infection processes. However, knowledge of the environmental conditions encountered in vivo is still incomplete, and the interaction of regulatory circuits leading to metabolic adaptation and differential expression of virulence factors remains poorly understood. The in vitro expression of most virulence factors is tightly related to the growth phase. For instance protein A (encoded by spa), fibronectin-binding proteins (encoded by fnbA and fnbB), and coagulase (encoded by coa) are expressed during the exponential growth phase, whereas most secreted proteins (e.g., hemolysins, enterotoxins, and proteases) and the capsule (enzymes encoded by the capA-capP operon) are expressed mainly during the postexponential phase (22, 37). In many bacteria, the transition to postexponential growth is accompanied by a profound reprogramming of gene expression. Several underlying mechanisms are thought to be involved in such a transition. Quorum sensing allows the bacteria to detect their own density. Basically, bacteria secrete small diffusible molecules (autoinducers) which are also effectors of their own synthesis. Upon passing a critical concentration threshold, the autoinducers activate specific transcriptional regulators, leading to the differential expression of target genes. The agr locus of S. aureus is a prototypic quorum-sensing system m...

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Since 1995, a methicillin-resistant Staphylococcus aureus (MRSA) clone has spread in southern Germany. The strain was assigned to the Rhine-Hesse pulsed-field gel electrophoresis (PFGE) type by the staphylococcal reference center and was highly similar to epidemic clones known to belong to clonal complex 5 (CC5; USA100) based on multilocus sequence typing (MLST). Here we analyzed a defined collection of strains assigned to the Rhine-Hesse/USA100 PFGE type. Using sequence-based typing methods (MLST, spa), the isolates were divided into two distinct clusters, ST5 and its single-locus variant ST225. These two lineages are not distinguishable by PFGE or phage typing. Most of the ST5 isolates were derived from patients and volunteers from the Tübingen area in southwest Germany, whereas the ST225 isolates were mostly from other locations in Germany. The locally restricted ST5 isolates were shown to contain different SSCmec islands and exhibited different antibiotic resistance profiles. In contrast, the ST225 isolates form a highly homogenous group and are emerging all over Germany. The two lineages are clearly distinguishable by their phage content and spa type: ST5 strains from Tübingen are characterized by a Sa7int phage that carries the virulence gene sak, which codes for staphylokinase, and ST225 isolates are characterized by a Sa1int phage. In conclusion, based on sequence typing and phage content, CC5 strains can be subdivided into two distinct lineages with different epidemicities.