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A small number of clonal lineages dominates the global population structure of methicillin-resistant Staphylococcus aureus (MRSA). resulting in the concept that MRSA has emerged on a few occasions after penicillinase-stable β-lactam antibiotics were introduced to clinical practice, followed by intercontinental spread of individual clones. We investigated the evolutionary history of an MRSA clone (ST5) by mutation discovery at 108 loci (46 kb) within a global collection of 135 isolates. The SNPs that were ascertained define a radial phylogenetic structure within ST5 consisting of at least 5 chains of mutational steps that define geographically associated clades. These clades are not concordant with previously described groupings based on staphylococcal protein A gene (spa) typing. By mapping the number of independent imports of the staphylococcal cassette chromosome methicillin-resistance island, we also show that import has occurred on at least 23 occasions within this single sequence type and that the progeny of such recombinant strains usually are distributed locally rather than globally. These results provide strong evidence that geographical spread of MRSA over long distances and across cultural borders is a rare event compared with the frequency with which the staphylococcal cassette chromosome island has been imported. [ABSTRACT FROM AUTHOR]

We performed a prospective, international, observational study of 844 hospitalized patients with blood cultures positive for Streptococcus pneumoniae. Fifteen percent of isolates had in vitro intermediate susceptibility to penicillin (minimum inhibitory concentration [MIC], 0.12-1 mg/mL), and 9.6% of isolates were resistant (MIC, 32 mg/mL). Age, severity of illness, and underlying disease with immunosuppression were significantly associated with mortality; penicillin resistance was not a risk factor for mortality. The impact of concordant antibiotic therapy (i.e., receipt of a single antibiotic with in vitro activity against S. pneumoniae) versus discordant therapy (inactive in vitro) on mortality was assessed at 14 days. Discordant therapy with penicillins, cefotaxime, and ceftriaxone (but not cefuroxime) did not result in a higher mortality rate. Similarly, time required fordefervescence and frequency of suppurative complications were not associated with concordance of b-lactam antibiotic therapy. b-Lactam antibiotics should still be useful for treatment of pneumococcal infections that do not involve cere-brospinal fluid, regardless of in vitro susceptibility, as determined by current NCCLS breakpoints. [ABSTRACT FROM AUTHOR]