Comparison of tigecycline and vancomycin for treatment of experimental foreign-body infection due to methicillin-resistant Staphylococcus aureus.

Twice-daily 7-day regimens of tigecycline (7 mg/kg) and vancomycin (50 mg/kg) were compared in a rat tissue cage model of chronic foreign-body infection due to methicillin (meticillin)-resistant Staphylococcus aureus strain MRGR3. Subcutaneously administered tigecycline reached levels in tissue cage fluid that were nearly equivalent or slightly superior to the antibiotic MIC (0.5 microg/ml) for strain MRGR3. After 7 days, equivalent, significant reductions in bacterial counts were recorded for tigecycline-treated and vancomycin-treated rats, compared with those for untreated animals.

Transcriptomic and metabolic responses of Staphylococcus aureus exposed to supra-physiological temperatures.

BACKGROUND: Previous evaluation by different molecular and physiological assays of Staphylococcus aureus (S. aureus) responses to heat shock exposure yielded a still fragmentary view of the mechanisms determining bacterial survival or death at supra-physiological temperatures. This study analyzed diverse facets of S. aureus heat-shock adjustment by recording global transcriptomic and metabolic responses of bacterial cultures shifted for 10 min from 37 degrees C to a sub-lethal (43 degrees C) or eventually lethal (48 degrees C) temperature. A relevant metabolic model of the combined action of specific stress response mechanisms with more general, energy-regulating metabolic pathways in heat-shocked S. aureus is presented. RESULTS: While S. aureus cultures shifted to 43 degrees C or left at 37 degrees C showed marginal differences in growth and survival rates, bacterial cultures exposed to 48 degrees C showed a rapid growth arrest followed by a subsequent decline in viable counts. The most substantial heat shock-induced changes at both 43 degrees C and 48 degrees C occurred in transcript levels of HrcA- and CtsR-regulated genes, encoding classical chaperones DnaK and GroESL, and some Hsp100/Clp ATPases components, respectively. Other metabolic pathways up-regulated by S. aureus exposure at 48 degrees C included genes encoding several enzymes coping with oxidative stress, and DNA damage, or/and impaired osmotic balance. Some major components of the pentose phosphate cycle and gluconeogenesis were also up-regulated, which reflected depletion of free glucose by bacterial cultures grown in Mueller-Hinton broth prior to heat shock. In contrast, most purine- and pyrimidine-synthesis pathway components and amino acyl-tRNA synthetases were down-regulated at 48 degrees C, as well as arginine deiminase and major fermentative pathway components, such as alcohol, lactate and formate dehydrogenases. Despite the heat-induced, increased requirements for ATP-dependent macromolecular repair mechanisms combined with declining energy sources, intracellular ATP levels remained remarkably constant during heat shock. CONCLUSION: The sequential loss of replication and viability at 48 degrees C cannot be explained by significant reductions in intracellular ATP levels, but may reflect ATP rerouting for macromolecular repair mechanisms and cell survival. Our metabolic model also suggests that heat-stressed S. aureus should down-regulate the production of potential, DNA-damaging reactive oxygen species that might result from electron transport-generated ATP, involving excessive levels of free heavy metals, in particular iron.

Prevalence and distribution of the insertion element ISMag1 in Mycoplasma agalactiae.

In characterising Mycoplasma agalactiae strains from various European countries and from Africa, a new insertion sequence (IS), ISMag1, which is related to IS of the family of IS30 insertion elements, has been identified by DNA sequence analysis and Southern blot hybridisation. ISMag1 has a size of 1515bp, and contains inverted repeats of 3bp and a gene encoding the putative transposase on a single open reading frame. ISMag1 is present only in the rarely isolated serotypes E, F, G and H of M. agalactiae, where it is found in 1 to approximately 30 copies. The different patterns obtained by hybridisation of a labelled probe of ISMag1 to genomic DNA cut with various restriction enzymes correlate to some extent to the different serotypes and to variations of the nucleotide sequences of the uvrC genes of the different strains. Based on uvrC sequences, the strains of M. agalactiae carrying ISMag1 form a cluster, separate from the other strains. IS patterns obtained with ISMag1 allow a fine subtyping of the serotypes E, F, G and H of M. agalactiae for epidemiological studies. The potential role of ISMag1 and of its copy numbers on virulence and persistence of the respective strains requests further studies.

The p40* adhesin pseudogene of Mycoplasma bovis.

An analogue of the adhesin gene p40 of Mycoplasma agalactiae was found in Mycoplasma bovis. Nucleotide sequence analysis of the p40* gene in M. bovis revealed the presence of a large deletion involving a frameshift that causes premature truncation of the translated protein, indicating that p40* exists as a pseudogene in M. bovis.

Use of an automated multiple-locus, variable-number tandem repeat-based method for rapid and high-throughput genotyping of Staphylococcus aureus isolates.

Fast and reliable genotyping methods that allow real-time epidemiological surveillance would be instrumental to monitoring of the spread of methicillin-resistant Staphylococcus aureus. We describe an automated variable-number tandem repeat-based method for the rapid genotyping of Staphylococcus aureus. Multiplex PCR amplifications with eight primer pairs that target gene regions with variable numbers of tandem repeats were resolved by microcapillary electrophoresis and automatically assessed by cluster analysis. This genotyping technique was evaluated for its discriminatory power and reproducibility with clinical isolates of various origins, including a panel of control strains previously characterized by several typing methods and collections from either long-term carriers or defined nosocomial outbreaks. All steps of this new procedure were developed to ensure a rapid turnaround time and moderate cost. The results obtained suggest that this rapid approach is a valuable tool for the genotyping of S. aureus isolates in real time.

Characterization of P40, a cytadhesin of Mycoplasma agalactiae.

An immunodominant protein, P40, of Mycoplasma agalactiae was analyzed genetically and functionally. The gene encoding P40 was cloned from type strain PG2, sequenced, submitted to point mutagenesis in order to convert mycoplasma-specific TGA(Trp) codon to the universal TGG(Trp) codon, and subsequently expressed in Escherichia coli. Nucleotide sequence-derived amino acid sequence comparisons revealed a similarity of P40 to the adhesin P50 of Mycoplasma hominis and to protein P89 of Spiroplasma citri, which is expected to be involved in adhesion. The amino acid sequence of P40 revealed a recognition site for a signal peptidase and strong antigenic and hydrophilic motifs in the C-terminal domain. Triton X-114 phase partitioning confirmed that P40 is a membrane protein. Fab fragments of antibodies directed against recombinant purified P40 significantly inhibited adherence of M. agalactiae strains PG2 to lamb joint synovial cells LSM 192. Sera taken sequentially from sheep infected with PG2 revealed that P40 induced a strong and persistent immune response that gave strong signals on immunoblots containing recombinant P40 even 3 months after infection. The gene encoding P40 was present in a single copy in all of the 26 field strains of M. agalactiae analyzed and was not detected in closely related mycoplasma species. P40 was expressed as a protein with an apparent molecular mass of 37 kDa on sodium dodecyl sulfate-acrylamide gels by all M. agalactiae strains except for serotype C strains, which showed nonsense mutations in their p40 genes.