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ABSTRACTPanton-Valentine leukocidin (PVL), encoded by the lukSF-PVgenes, is a putative virulence factor and marker for community-associated methicillin-resistant Staphylococcus aureus. Here we report the prevalence of PVL among a representative sample of 1,055 S. aureusinfection isolates from the United States and describe the sequence variation of the lukSF-PVgenes. We performed multilocus sequence typing (MLST) on all isolates and sequenced fragments of the lukSF-PVgenes from a sample of 86 isolates. We assigned isolates to a PVL R or H sequence type based on a polymorphism that results in an amino acid change from arginine (R) to histidine (H). Overall, we found that 36% of S. aureusisolates were positive for lukSF-PV. Among the 86 we typed, we identified 72 R variants and 14 H variants. Among the 47 methicillin-resistance S. aureus(MRSA) isolates, 43 harbored the R variant, and among the 39 methicillin-susceptible S. aureus(MSSA) isolates, 29 harbored the R variant. Almost all (97%) of the R variants were found in MLST clonal complex 8 (CC8), while the H variant was broadly distributed among 6 CCs. Within CC8, all 38 MRSA (USA300) and all 28 MSSA isolates harbored the R variant. Of the 20 isolates from blood and the lower respiratory tract, 19 (95%) harbored the R variant. While the R variant had been linked primarily to USA300 MRSA, we found that all CC8 MSSA isolates also contained the R variant, suggesting that some strains of USA300 may have lost methicillin resistance as an adaptation in the community.

ABSTRACTDetermining the genetic characteristics of Staphylococcus aureusis important for better understanding of the global and dynamic epidemiology of this organism as we witness the emergence and spread of virulent and antibiotic-resistant clones. We genotyped 292 S. aureusisolates (105 methicillin resistant and 187 methicillin susceptible) using a combination of pulsed-field gel electrophoresis, multilocus sequence typing, and SCCmectyping. In addition, S. aureusisolates were tested for the presence of the Panton-Valentine leukocidin (PVL) genes. Isolates were recovered from patients with uncomplicated skin infections in 10 different countries during five phase III global clinical trials of retapamulin, a new topical antibiotic agent. The most common methicillin-resistant clone had multilocus sequence type 8, pulsed-field type USA300, and SCCmectype IV and possessed the PVL genes. This clone was isolated exclusively in the United States. The most common PVL-positive, methicillin-susceptible clone had multilocus sequence type 121 and pulsed-field type USA1200. This clone was found primarily in South Africa and the Russian Federation. Other clones were found at lower frequencies and were limited in their geographic distribution. Overall, considerable genetic diversity was observed within multilocus sequence type clonal complexes and pulsed-field types.

ABSTRACTWe performed multilocus sequence typing on 203 invasive disease isolates of Streptococcus pneumoniaeto assess the clonal compositions of isolates from two provinces in Belgium and to determine the relationship between clones and antibiotic nonsusceptibility, particularly nonsusceptibility to two or more classes of antibiotics. The frequency of multiclass nonsusceptibility (MCNS) was higher in the province of West Flanders (38%) than in Limburg (21%). This difference was largely attributable to five clonal complexes (CC156, CC81, CC143, CC193, and CC1848), which contained high proportions of isolates with MCNS (>47%) and which were circulating at higher frequencies in West Flanders. The S. pneumoniaepopulation changed over time, as CC156 and CC81 declined in frequency from 1997 to 1999 to 2001 to 2004. Over the same time period, the frequency of pneumococcal conjugate vaccine 7 (PCV7) serotypes dropped from 69% to 41%. In contrast, the nonvaccine serotype 19A increased in frequency from 2.1% to 6.6%. None of these changes can be attributed to PCV7 vaccine, as it was not in use in Belgium during the time period studied. There was evidence that MCNS clones flowed from West Flanders to Limburg.

Readers familiar with the nine-point circle property of a triangle (Figure 1) may have wondered whether there is a similar result for a tetrahedron.In general the answer is “No”: there is no equivalent of the orthocentre for a tetrahedron, since the altitudes from the vertices onto the opposite faces do not intersect. There is, however, a special kind of tetrahedron for which these four lines do have a point Hin common.