The aims of the present study were (i) to develop and test a sensitive and reproducible method for the study of gene expression in staphylococci and (ii) to study the expression of five housekeeping genes which are involved in nucleic acid metabolism (gmk, guanylate kinase; the dihydrofolate reductase [DHFR] gene), glucose metabolism (tpi, triosephosphate isomerase), and protein metabolism (the 16S rRNA gene; hsp-60, heat-shock protein 60) during in vitro exponential and stationary growth. A modified method for instant mRNA isolation was combined with gene quantification via Taqman real-time quantitative PCR. The detection limit of our method was 10 copies of RNA. The average intersample variability was 16%. A 10-fold increase in the expression of the hsp-60 gene was induced by exposure to a 10°C heat shock (37 to 47°C) for 10 min. During in vitro growth, the expression of all five housekeeping genes showed rapid up-regulation after inoculation of the bacteria in brain heart infusion medum and started to decline during the mid-exponential-growth phase. Maximal gene expression was 110-to 300-fold higher than gene expression during stationary phase. This indicates that housekeeping metabolism is a very dynamic process that is extremely capable of adapting to different growth conditions. Expression of the 16S rRNA gene decreases significantly earlier than that of other housekeeping genes. This confirms earlier findings for Escherichia coli that a decline in bacterial ribosomal content (measured by 16S rRNA gene expression) precedes the decline in protein synthesis (measured by mRNA expression).In recent years, coagulase-negative staphylococci (CNS) have emerged as major pathogens that are mainly associated with indwelling or implanted foreign body infections (22,29,30,33). Their impact on public health is enormous (24, 31). It remains enigmatic why these normally innocent skin saprophytes become virulent in association with indwelling foreign bodies (17). CNS infections seem to be the result of a complex interaction between bacterium-related factors, host-related factors, and foreign body-related-factors. Genes involved in cell accumulation (13,33,34) and in initial adhesion (12) are presumed virulence factors in initial foreign body colonization and biofilm formation. A state of bacterial dormancy and a suppressed housekeeping metabolism are hypothesized to contribute to the persistent nature of foreign body-related CNS infections (5,25,26).For study of the pathogenesis of infectious diseases, researchers have access to a rapidly growing amount of genetic information. However, the exact links between the information encoded in the genome and the final virulence and housekeeping behavior of bacteria remain unclear. Methods to unravel these links are mutagenesis and the study of gene expression. Mutagenesis is a valuable phenotypical assay (1). However, mutations in important genes may lead to only minor phenotypical changes or to lethal mutants. In these cases it is not possible to draw firm conclusions on the role...
Several well-studied proteins with defined roles in Staphylococcus epidermidis biofilm formation are LPXTG motif-containing proteins. Here, we investigate the possible use of the LPXTG motif-containing protein SesC (S. epidermidis surface protein C; accession no. NP_765787) as a target for antibodies to prevent biofilm formation. In vitro and in a in vivo rat model of catheter infection, gene and protein expression analysis showed that SesC is expressed more strongly in biofilm-associated cells than in planktonic cells and is expressed particularly during the late phase of in vivo biofilm formation. Polyclonal rabbit antibodies raised against SesC reduced the fibrinogen-binding ability of S. epidermidis RP62A and Staphylococcus aureus RN4220 transformants expressing SesC, inhibited in vitro biofilm formation by S. epidermidis strains 10b and 1457, and significantly reduced the numbers of bacteria in a 1-day-old in vivo biofilm (P < 0.001, one-way analysis of variance). Our findings revealed that SesC is a promising target for prevention and treatment of S. epidermidis biofilms because it affects both the primary attachment and biofilm accumulation phases. The precise role of SesC in biofilm formation remains to be identified.
The high prevalence of aap and icaA in skin isolates and their higher prevalence in colonizing than in invasive isolates led to a low specificity when these genes were used to differentiate between contamination, colonization and invasive infection. We conclude that, although the prevalence of these genes differs in the three groups, their presence cannot be used for clinical decision-making.
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