Interpretive categorical accuracy of fluoroquinolone reference broth microdilution MIC results when testing Streptococcus pneumoniae: selection of a surrogate testing agent.

The categorical agreement among MIC results for the fluoroquinolones tested (levofloxacin, moxifloxacin, gatifloxacin and gemifloxacin) was high (99.16-99.85%), and error rates were nil or very low when 1 compound was used as a surrogate for predicting susceptibility (not resistance) to another agent in the class. No error was observed when levofloxacin was selected as the group surrogate for pneumococcal testing.

Temporal and spatial distribution of clonal complexes of Streptococcus pneumoniae isolates resistant to multiple classes of antibiotics in Belgium, 1997 to 2004.

We performed multilocus sequence typing on 203 invasive disease isolates of Streptococcus pneumoniae to 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. pneumoniae population 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.

Risk factors for development of multiple-class resistance to Streptococcus pneumoniae Strains in Belgium over a 10-year period: antimicrobial consumption, population density, and geographic location.

We investigated the impact of the usage of antibiotics in ambulatory patients in Belgium in 147 defined geographical circumscriptions and at the individual isolate level. The study included 14,448 Streptococcus pneumoniae strains collected by the Belgium national reference lab from 1994 to 2004. Additional risk factors for resistance, such as population density/structure and day care attendance, were investigated for the same time-space window. A statistical model that included resistance to two or more antimicrobial classes offered the best fit for measuring the changes in nonsusceptibility to penicillin, macrolides, and tetracycline over time and place in Belgium. Analysis at the geographic level identified antimicrobial consumption with a 1-year lag (0.5% increase per additional defined daily dose) and population density as independent predictors of multiple resistance. Independent risk factors at the isolate level were age (odds ratio [OR], 1.55 for children aged <5 years), population density (7% increase in multiple resistance per 100 inhabitants/km(2)), conjugate 7-valent vaccine serotype (OR, 14.3), location (OR, 1.55 for regions bordering high-resistance France), and isolate source (OR, 1.54 for ear isolates). The expansion of multiple-resistant strains explains most of the overall twofold increase and subsequent decrease in single antimicrobial resistance between 1994 and 2004. We conclude that factors in addition to antibiotic use, such as high population density and proximity to high-resistance regions, favor multiple resistance. Regional resistance rates are not linearly related to actual antibiotic use but are linked to past antibiotic use plus a combination of demographic and geographic factors.

Molecular evolution perspectives on intraspecific lateral DNA transfer of topoisomerase and gyrase loci in Streptococcus pneumoniae, with implications for fluoroquinolone resistance development and spread.

Fluoroquinolones are an important class of antibiotics for the treatment of infections arising from the gram-positive respiratory pathogen Streptococcus pneumoniae. Although there is evidence supporting interspecific lateral DNA transfer of fluoroquinolone target loci, no studies have specifically been designed to assess the role of intraspecific lateral transfer of these genes in the spread of fluoroquinolone resistance. This study involves a comparative evolutionary perspective, in which the evolutionary history of a diverse set of S. pneumoniae clinical isolates is reconstructed from an expanded multilocus sequence typing data set, with putative recombinants excluded. This control history is then assessed against networks of each of the four fluoroquinolone target loci from the same isolates. The results indicate that although the majority of fluoroquinolone target loci from this set of 60 isolates are consistent with a clonal dissemination hypothesis, 3 to 10% of the sequences are consistent with an intraspecific lateral transfer hypothesis. Also evident were examples of interspecific transfer, with two isolates possessing a parE-parC gene region arising from viridans group streptococci. The Spain 23F-1 clone is the most dominant fluoroquinolone-nonsusceptible clone in this set of isolates, and the analysis suggests that its members act as frequent donors of fluoroquinolone-nonsusceptible loci. Although the majority of fluoroquinolone target gene sequences in this set of isolates can be explained on the basis of clonal dissemination, a significant number are more parsimoniously explained by intraspecific lateral DNA transfer, and in situations of high S. pneumoniae population density, such events could be an important means of resistance spread.

A review of the antimicrobial activity of clavulanate.

Clavulanate is a broad-spectrum beta-lactamase inhibitor, with activity against many of the chromosomally and plasmid-mediated beta-lactamases of both Gram-positive and Gram-negative bacteria. Although clavulanate has minimal antibacterial activity in vitro, accumulating evidence suggests that it may have an effect on pathogenic bacteria regardless of beta-lactamase production. Like other beta-lactams, clavulanate has been shown to bind to penicillin-binding proteins (PBPs) in Gram-positive and Gram-negative bacteria. It was found to bind selectively to PBP3 in Streptococcus pneumoniae. It has been suggested that complementary binding to different PBPs and subsequent effects on autolysis contribute to the enhancement of the activity of other beta-lactams by clavulanate. In addition, co-amoxiclav has been shown to enhance the intracellular killing functions of human polymorphonuclear cells (PMNs) in studies undertaken with beta-lactamase-producing and non-beta-lactamase-producing strains of bacteria. These data from in vitro and cell culture systems have been reflected in vivo, where clavulanate enhanced the activity of amoxicillin against non-beta-lactamase-producing organisms. Further studies are required to determine whether the effects seen within in vitro and in vivo animal studies have clinical significance.