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      Pathogenesis of infections due to coagulasenegative staphylococci

      , ,
      The Lancet Infectious Diseases
      Elsevier BV

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          Abstract

          As a group, the coagulase-negative staphylococci (CoNS) are among the most frequently isolated bacteria in the clinical microbiology laboratory and are becoming increasingly important, especially as causes of hospital-acquired infections. These bacteria are normal inhabitants of human skin and mucous membranes and, therefore, one of the major challenges of daily diagnostic work is to distinguish clinically significant CoNS from contaminant strains. This overview addresses current knowledge of the pathogenesis of infections due to CoNS and particularly focuses on virulence factors of the species Staphylococcus epidermidis. S epidermidis has been identified as a major cause of nosocomial infections, especially in patients with predisposing factors such as indwelling or implanted foreign polymer bodies. Most important in the pathogenesis of foreign-body-associated infections is the ability of these bacteria to colonise the polymer surface by the formation of a thick, multilayered biofilm. Biofilm formation takes place in two phases. The first phase involves the attachment of the bacteria to polymer surfaces that may be either unmodified or coated with host extracellular matrix proteins. In the second phase, the bacteria proliferate and accumulate into multilayered cell clusters that are embedded in an extracellular material. The bacterial factors involved in both phases of biofilm formation are discussed in this review. In addition, the most important aspects of the pathogenic potential of S saprophyticus, S lugdunensis, and S schleiferi are described, although, compared with S epidermidis, much less is known in these species concerning their virulence factors.

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          Most cited references51

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          Survey of infections due to Staphylococcus species: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, Latin America, Europe, and the Western Pacific region for the SENTRY Antimicrobial Surveillance Program, 1997-1999.

          Between January 1997 and December 1999, bloodstream isolates from 15,439 patients infected with Staphylococcus aureus and 6350 patients infected with coagulase-negative Staphylococcus species (CoNS) were referred by SENTRY-participating hospitals in the United States, Canada, Latin America, Europe, and the Western Pacific region. S. aureus was found to be the most prevalent cause of bloodstream infection, skin and soft-tissue infection, and pneumonia in almost all geographic areas. A notable increase in methicillin (oxacillin) resistance among community-onset and hospital-acquired S. aureus strains was observed in the US centers. The prevalence of methicillin (oxacillin)-resistant S. aureus varied greatly by region, site of infection, and whether the infection was nosocomial or community onset. Rates of methicillin resistance were extremely high among S. aureus isolates from centers in Hong Kong and Japan. Uniformly high levels of methicillin resistance were observed among CoNS isolates. Given the increasing multidrug resistance among staphylococci and the possible emergence of vancomycin-resistant strains, global strategies are needed to control emergence and spread of multiply resistant staphylococci.
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            Evidence for autolysin-mediated primary attachment of Staphylococcus epidermidis to a polystyrene surface.

            Biofilm formation on a polymer surface which involves initial attachment and accumulation in multilayered cell clusters (intercellular adhesion) is proposed to be the major pathogenicity factor in Staphylococcus epidermidis foreign-body-associated infections. We have characterized two distinct classes of biofilm-negative Tn917 mutants in S. epidermidis affected in initial attachment (class A) or intercellular adhesion (class B). mut1 (class A mutant) lacks five surface-associated proteins with molecular masses of 120, 60, 52, 45 and 38 kDa and could be complemented by transformation with a 16.4 kb wild-type DNA fragment. The complemented mutant was able to attach to a polystyrene surface, to form a biofilm, and produced all of the proteins missing from mut1. Subcloning experiments revealed that the 60 kDa protein is sufficient for initial attachment. Immunofluorescence microscopy using an antiserum raised against the 60 kDa protein showed that this protein is located at the cell surface. DNA-sequence analysis of the complementing region revealed a single open reading frame which consists of 4005 nucleotides and encodes a deduced protein of 1335 amino acids with a predicted molecular mass of 148kDa. The amino acid sequence exhibits a high similarity (61% identical amino acids) to the atl gene product of Staphylococcus aureus, which represents the major autolysin; therefore the open reading frame was designated atlE. By analogy with the S. aureus autolysin, AtlE is composed of two bacteriolytically active domains, a 60 kDa amidase and a 52 kDa glucosaminidase domain, generated by proteolytic processing. The 120 kDa protein missing from mut1 presumably represents the unprocessed amidase and glucosaminidase domain after proteolytic cleavage of the signal- and propeptide. The 45 and 38kDa proteins are probably the degradation products of the 60 and 52 kDa proteins, respectively. Additionally, AtlE was found to exhibit vitronectin-binding activity, indicating that AtlE plays a role in binding of the cells not only to a naked polystyrene surface during early stages of adherence, but also to plasma protein-coated polymer surfaces during later stages of adherence. Our findings provide evidence for a new function of an autolysin (AtlE) in mediating the attachment of bacterial cells to a polymer surface, representing the prerequisite for biofilm formation.
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              Characterization of the N-acetylglucosaminyltransferase activity involved in the biosynthesis of the Staphylococcus epidermidis polysaccharide intercellular adhesin.

              The polysaccharide intercellular adhesin (PIA) is an important factor in the colonization of medical devices by Staphylococcus epidermidis. The genes encoding PIA production are organized in the icaADBC (intercellular adhesion) operon. To study the function of the individual genes, we have established an in vitro assay with UDP-N-acetylglucosamine, the substrate for PIA biosynthesis, and analyzed the products by thin-layer chromatography and mass spectrometry. IcaA alone exhibited a low N-acetylglucosaminyltransferase activity and represents the catalytic enzyme. Coexpression of icaA with icaD led to a significant increase in activity. The newly identified icaD gene is located between icaA and icaB and overlaps both genes. N-Acetylglucosamine oligomers produced by IcaAD reached a maximal length of 20 residues. Only when icaA and icaD were expressed together with icaC were oligomer chains that react with PIA-specific antiserum synthesized. IcaA and IcaD are located in the cytoplasmic membrane, and IcaC also has all the structural features of an integral membrane protein. These results indicate a close interaction between IcaA, IcaD, and IcaC. Tunicamycin and bacitracin did not affect the in vitro synthesis of PIA intermediates or the complete PIA biosynthesis in vivo, suggesting that a undecaprenyl phosphate carrier is not involved. IcaAD represents a novel protein combination among beta-glycosyltransferases.
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                Author and article information

                Journal
                The Lancet Infectious Diseases
                The Lancet Infectious Diseases
                Elsevier BV
                14733099
                November 2002
                November 2002
                : 2
                : 11
                : 677-685
                Article
                10.1016/S1473-3099(02)00438-3
                12409048
                4dd4efdb-9a64-4283-8b37-cece6b219fa2
                © 2002

                https://www.elsevier.com/tdm/userlicense/1.0/

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