[Show abstract][Hide abstract] ABSTRACT: Coagulase-negative staphylococci (CoNS) form a thick, multilayered biofilm on foreign bodies and are a major cause of nosocomial implant-associated infections. Although foreign body infection models are well-established, limited in vivo data are available for CoNS with small-colony-variant (SCV) phenotype described as causative agents in implant-associated infections. Therefore, we investigated the impact of the Staphylococcus epidermidis phenotype on colonization of implanted PVC catheters and abscess formation in three different mouse strains. Following introduction of a catheter subcutaneously in each flank of 8- to 12-week-old inbred C57BL/6JCrl (B6J), outbred Crl:CD1(ICR) (CD-1), and inbred BALB/cAnNCrl (BALB/c) male mice, doses of S. epidermidis O-47 wild type, its hemB mutant with stable SCV phenotype, or its complemented mutant at concentrations of 10(6) to 10(9) colony forming units (CFUs) were gently spread onto each catheter. On day 7, mice were sacrificed and the size of the abscesses as well as bacterial colonization was determined. A total of 11,500 CFUs of the complemented mutant adhered to the catheter in BALB/c followed by 9,960 CFUs and 9,900 CFUs from S. epidermidis wild type in BALB/c and CD-1, respectively. SCV colonization was highest in CD-1 with 9,500 CFUs, whereas SCVs were not detected in B6J. The minimum dose that led to colonization or abscess formation in all mouse strains was 10(7) or 10(8) CFUs of the normal phenotype, respectively. A minimum dose of 10(8) or 10(9) CFU of the hemB mutant with stable SCV phenotype led to colonization only or abscess formation, respectively. The largest abscesses were detected in BALB/c inoculated with wild type bacteria or SCV (64 mm(2) vs. 28 mm(2)). Our results indicate that colonization and abscess formation by different phenotypes of S. epidermidis in a foreign body infection model is most effective in inbred BALB/c followed by outbred CD-1 and inbred B6J mice.
PLoS ONE 05/2012; 7(5):e36602. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Small-colony variants (SCVs) of Staphylococcus aureus represent a slow-growing subpopulation causing chronic and relapsing infections due to their physiological adaptation on an intracellular lifestyle. In this first proteomic study on physiological changes associated with a natural, clinically derived SCV, its proteomic profile was investigated in comparison to corresponding isogenic strains displaying normal (clinical wild-type strain, complemented hemB mutant and spontaneous revertant of the clinical SCV) and SCV phenotypes (hemB mutant and gentamicin-induced SCV). Applying an ultra-high resolution chromatography and high mass accuracy MS(E) -based label-free relative and absolute protein quantification approach, the whole cytoplasmic proteome of this strain sextet was investigated in a growth phase-controlled manner covering early-exponential, late-exponential and stationary phases. Of 1019 cytoplasmic proteins identified, 154 were found to be differently regulated between strains. All SCV phenotypes showed down-regulation of the tricarboxylic acid (TCA) cycle-related proteins and of a protein cluster involved in purine/pyrimidine and folate metabolism. In contrast to hemB mutant and gentamicin-induced SCVs, the clinically derived SCVs showed no prominent up-regulation of glycolytic proteins. The spontaneous switch into the normal phenotype resulted in up-regulation of TCA cycle-related parts, while oxidative stress-related proteins were down-regulated. However, the natural revertant from the clinical SCV retained also dominant protein features of the clinical SCV phenotype. In conclusion, physiological changes between normal and SCV S. aureus phenotypes are more complex than reflected by defined electron transport chain-interrupting mutants and their complemented counterparts.
[Show abstract][Hide abstract] ABSTRACT: An alignment of upstream regions of anaerobically induced genes in Staphylococcus aureus revealed the presence of an inverted repeat, corresponding to Rex binding sites in Streptomyces coelicolor. Gel shift experiments of selected upstream regions demonstrated that the redox-sensing regulator Rex of S. aureus binds to this inverted repeat. The binding sequence--TTGTGAAW(4)TTCACAA--is highly conserved in S. aureus. Rex binding to this sequence leads to the repression of genes located downstream. The binding activity of Rex is enhanced by NAD+ while NADH, which competes with NAD+ for Rex binding, decreases the activity of Rex. The impact of Rex on global protein synthesis and on the activity of fermentation pathways under aerobic and anaerobic conditions was analysed by using a rex-deficient strain. A direct regulatory effect of Rex on the expression of pathways that lead to anaerobic NAD+ regeneration, such as lactate, formate and ethanol formation, nitrate respiration, and ATP synthesis, is verified. Rex can be considered a central regulator of anaerobic metabolism in S. aureus. Since the activity of lactate dehydrogenase enables S. aureus to resist NO stress and thus the innate immune response, our data suggest that deactivation of Rex is a prerequisite for this phenomenon.
[Show abstract][Hide abstract] ABSTRACT: The Cpx two-component signal transduction system regulates the expression of genes in response to stimuli associated with the maintenance of the bacterial cell envelope. Additionally, the Cpx system is important for virulence in several bacterial pathogens. In this study, we analyzed the Cpx system of the human enteropathogen Yersinia enterocolitica. We provide evidence that transcription of cpxR is autoregulated and that the response regulator CpxR negatively affects transcription of rpoE, coding for the extracytoplasmic function sigma factor sigma(E), thereby linking at the transcriptional level two systems involved in envelope maintenance. A mutated form of CpxR that cannot be phosphorylated, CpxRD51A, affects transcription of cpxR and rpoE similar to the wild-type CpxR. In contrast, CpxR and CpxRD51A differentially regulate transcription of htrA, indicating phosphorylation-dependent and -independent mechanisms of transcriptional regulation. Moreover, overproduction of CpxR, CpxRD51A and CpxA result in a growth defect. Interestingly, a cpxA mutant strain could not be obtained. We conclude that the phosphorylation status of CpxR needs to be tightly controlled by CpxA, and that the Cpx system has a central role in regulating basic cellular functions. In addition, we show that cpxR and cpxP mutant strains have no defect in Y. enterocolitica invasion of host cells.
[Show abstract][Hide abstract] ABSTRACT: Small-colony variants (SCVs) of Staphylococcus aureus are associated with persistent infections and may be selectively enriched during antibiotic therapy. Three pairs of clonally related S. aureus isolates were recovered from patients receiving systemic antibiotic therapy. Each pair consisted of an isolate with a normal phenotype and an isolate with an SCV phenotype. These SCVs were characterized by reduced susceptibility to gentamicin, reduced hemolytic activity, slow growth, and menadione auxotrophy. Sequencing of the genes involved in menadione biosynthesis revealed mutations in menB, the gene encoding naphthoate synthase, in all three strains with the SCV phenotype. The menB mutations were (i) a 9-bp deletion from nucleotides 55 to 63, (ii) a frameshift mutation that resulted in a premature stop codon at position 230, and (iii) a point mutation that caused the amino acid substitution Gly to Val at codon 233. Fluctuation tests showed that growth-compensated mutants arose in the SCV population of one strain, strain OM1b, at a rate of 1.8 x 10(-8) per cell per generation. Sequence analyses of 23 independently isolated growth-compensated mutants of this strain revealed alterations in the menB sequence in every case. These alterations included reversions to the wild-type sequence and intragenic second-site mutations. Each of the growth-compensated mutants showed a restoration of normal growth and a loss of menadione auxotrophy, increased susceptibility to gentamicin, and restored hemolytic activity. These data show that mutations in menB cause the SCV phenotype in these clinical isolates. This is the first report on the genetic basis of menadione-auxotrophic SCVs determined in clinical S. aureus isolates.
Antimicrobial Agents and Chemotherapy 10/2008; 52(11):4017-22. · 4.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recently, a rapid screening tool for methicillin-resistant Staphylococcus aureus (MRSA) has been introduced that applies a novel detection technology allowing the rapid presence or absence of MRSA to be determined from an enrichment broth after only a few hours of incubation. To evaluate the reliability of this new assay to successfully detect MRSA strains of different origin and clonality, well-characterized S. aureus strains were tested in this study.
More than 700 methicillin-susceptible and methicillin-resistant strains covering >90% of all registered European MRSA spa types within the SeqNet network were studied.
All 513 MRSA strains tested were recognized as methicillin-resistant: among these, 96 MRSA strains were from an institutional collection, each presenting a unique spa type. None of the 211 methicillin-susceptible strains were detected as positive.
The new growth-based rapid MRSA assay was shown to detect without exception all MRSA strains of large collections of strains comprising highly diverse genetic backgrounds, indicating that such a phenotypic test might be potentially more likely to cope with new strains.
Journal of Antimicrobial Chemotherapy 07/2008; 61(6):1277-80. · 5.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: While coagulase-negative staphylococci (CoNS), with their ability to form a thick, multilayered biofilm on foreign bodies, have been identified as the major cause of implant-associated infections, no data are available about biofilm formation by staphylococcal small-colony variants (SCVs). In the past years, a number of device-associated infections due to staphylococcal SCVs were described, among them, several pacemaker infections due to SCVs of CoNS auxotrophic to hemin. To test the characteristics of SCVs of CoNS, in particular, to study the ability of SCVs to form a biofilm on foreign bodies, we generated a stable mutant in electron transport by interrupting one of the hemin biosynthetic genes, hemB, in Staphylococcus epidermidis. In fact, this mutant displayed a stable SCV phenotype with tiny colonies showing strong adhesion to the agar surface. When the incubation time was extended to 48 h or a higher inoculum concentration was used, the mutant produced biofilm amounts on polystyrene similar to those produced by the parent strain. When grown under planktonic conditions, the mutant formed markedly larger cell clusters than the parental strain which were completely disintegrated by the specific beta-1,6-hexosaminidase dispersin B but were resistant to trypsin treatment. In a dot blot assay, the mutant expressed larger amounts of polysaccharide intercellular adhesin (PIA) than the parent strain. In conclusion, interrupting a hemin biosynthetic gene in S. epidermidis resulted in an SCV phenotype. Markedly larger cell clusters and the ability of the hemB mutant to form a biofilm are related to the augmented expression of PIA.
Journal of Bacteriology 07/2007; 189(12):4494-501. · 2.69 Impact Factor