SdrI, a serine-aspartate repeat protein identified in Staphylococcus saprophyticus strain 7108, is a collagen-binding protein

Detection of virulence genes among Staphylococcus saprophyticus isolated from women with urinary tract infections: first report from Iran

OBJECTIVE

The purpose of the present study was to investigate the biofilm production, and the presence of virulence genes and biochemical characteristics among the S. saprophyticus clinical isolates. A total of 35 clinical isolates of S. saprophyticus were collected from patients referred to several hospitals. By the crystal violet staining method, the capability of biofilm formation was performed. The genes associated with surface of S. saprophyticus were investigated by the PCR-sequencing techniques. Hemagglutination and lipase activity assays were also performed.

RESULTS

The results of crystal violet staining assay showed that 32 isolates (91%) form biofilm. Moreover, seven (20%), 13 (37%), and 12(34%) isolates were categorized as weak, moderate, and strong biofilm producers, respectively. virulence genes including UafA, Aas and Ssp had an overall prevalence of 88%, 91% and 80%, respectively. None of the isolates exhibited lipolytic activities. Regarding hemagglutination properties, only 11 (31%) isolates demonstrated hemagglutination of sheep erythrocytes. The results of this study indicate a high prevalence of UafA and Aas genes that can enhance the pathogenicity of S. saprophyticus, and Identification and better understanding of the functions of these genes can be used for therapeutic purposes. Maybe in the future we will be switch to anti-adhesion therapy because of drug resistance.

Virulence factors of uropathogens and their role in host pathogen interactions

Gram-positive and Gram-negative bacterial pathogens are commonly found in Urinary Tract Infection (UTI), particularly infected in females like pregnant women, elder people, sexually active, or individuals prone to other risk factors for UTI. In this article, we review the expression of virulence surface proteins and their interaction with host cells for the most frequently isolated uropathogens: Escherichia coli, Enterococcus faecalis, Proteus mirabilis, Klebsiella pneumoniae, and Staphylococcus saprophyticus. In addition to the host cell interaction, surface protein regulation was also discussed in this article. The surface protein regulation serves as a key tool in differentiating the pathogen isotypes. Furthermore, it might provide insights on novel diagnostic methods to detect uropathogen that are otherwise easily overlooked due to limited culture-based assays. In essence, this review shall provide an in-depth understanding on secretion of virulence factors of various uropathogens and their role in host-pathogen interaction, this knowledge might be useful in the development of therapeutics against uropathogens.

Baicalin inhibits biofilm formation by influencing primary adhesion and aggregation phases in Staphylococcus saprophyticus

The ability to form biofilms on surfaces makes Staphylococcus saprophyticus (S. saprophyticus) becomes the main pathogenic factor in nosocomial infections. Previously, we demonstrated that baicalin (Bac) inhibited azithromycin-resistant S. saprophyticus (ARSS) biofilm formation. This investigation aims to explore the influence of baicalin on primary adhesion and aggregation phases of biofilm formation, and the treatment effect of baicalin and azithromycin on ARSS biofilm-associated infection. Crystal violet (CV) staining and scanning electron microscope (SEM) observations clearly showed that sub-inhibitory concentration baicalin inhibited ARSS biofilm formation when baicalin was added before the adhesion and aggregation phases. Baicalin significantly increased the relative adhesion inhibition rate and decreased the rate of bacteria aggregation in a dose-dependent manner. Moreover, CLSM and cell lysis assays revealed that baicalin inhibited the production of surface proteins and cell autolysis in bacteria adhesion and aggregation phases of biofilm formation. Meanwhile, the relative expressions of adhesion-related and autolysis-related genes were down-regulated by baicalin. In vivo, the combination of baicalin and azithromycin succeeded in eradicating ARSS from the mouse cutaneous infection model and decreasing the pathological injuries, the expressions of cytokines in infected tissue, and the number of inflammatory cells in the blood. Simultaneously, baicalin decreased the bacterial burdens in tubes, the level of TNF-α, and the number of monocytes and neutrophils compared with that of the SS and azithromycin groups. Based on these results, baicalin inhibited the adhesion and aggregation phases of biofilm formation by influenced the production of surface proteins and cell autolysis. Baicalin and azithromycin synergetically treated ARSS biofilm-associated infection.

Identification of Three Clf-Sdr Subfamily Proteins in Staphylococcus warneri, and Comparative Genomics Analysis of a Locus Encoding CWA Proteins in Staphylococcus Species

Coagulase-negative Staphylococcus warneri is an opportunistic pathogen that is capable of causing several infections, especially in patients with indwelling medical devices. Here, we determined the complete genome sequence of a clinical S. warneri strain isolated from the blood culture of a 1-year-old nursling patient with acute upper respiratory infection. Genome-wide phylogenetic analysis confirmed the phylogenetic relationships between S. warneri and other Staphylococcus species. Using comparative genomics, we identified three cell wall-anchored (CWA) proteins at the same locus (sdr), named SdrJ, SdrK, and SdrL, on the chromosome sequences of different S. warneri strains. Structural predictions showed that SdrJ/K/L have structural features characteristic of Sdr proteins but exceptionally contained an unusual N-terminal repeat region. However, the C-terminal repetitive (R) region of SdrJ contains a significantly larger proportion of alanine (142/338, 42.01%) than the previously reported SdrI (37.00%). Investigation of the genetic organization revealed that the sdrJ/K/L genes were always followed by one or two glycosyltransferase genes, gtfA and gtfB and were present in an ∼56 kb region bordered by a pair of 8 bp identical direct repeats, named Sw-Sdr. This region was further found to be located on a 160-kb region subtended by a pair of 160-bp direct repeats along with other virulence genes and resistance genes. Sw-Sdr contained a putative integrase that was probably a remnant of a functional integrase. Evidence suggests that Sw-Sdr is improbably an efficient pathogenicity island. A large-scale investigation of Staphylococcus genomes showed that sdr loci were a potential hotspot of insertion sequences (ISs), which could lead to intraspecific diversity at these loci. Our work expanded the repository of Staphylococcus Sdr proteins, and for the first time, we established the connection between sdr loci and phylogenetic relationships and compared the sdr loci in different Staphylococcus species, which provided large insights into the genetic environment of CWA genes in Staphylococcus.

Virulence Factors in Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) have emerged as major pathogens in healthcare-associated facilities, being S. epidermidis, S. haemolyticus and, more recently, S. lugdunensis, the most clinically relevant species. Despite being less virulent than the well-studied pathogen S. aureus, the number of CoNS strains sequenced is constantly increasing and, with that, the number of virulence factors identified in those strains. In this regard, biofilm formation is considered the most important. Besides virulence factors, the presence of several antibiotic-resistance genes identified in CoNS is worrisome and makes treatment very challenging. In this review, we analyzed the different aspects involved in CoNS virulence and their impact on health and food.

Surface Proteins of Staphylococcus epidermidis

Staphylococcus epidermidis is a ubiquitous commensal of human skin. The widespread use of indwelling medical devices in modern medicine provides an opportunity for it to cause infections. Disease causing isolates can come from many different genetic backgrounds. Multiply antibiotic resistant strains have spread globally. S. epidermidis has a smaller repertoire of cell wall anchored (CWA) surface proteins than Staphylococcus aureus. Nevertheless, these CWA proteins promote adhesion to components of the extracellular matrix including collagen, fibrinogen, and fibronectin and contribute to the formation of biofilm. The A domain of the accumulation associated protein Aap can promote adhesion to unconditioned biomaterial but must be removed proteolytically to allow accumulation to proceed by homophilic Zn²⁺-dependent interactions. Mature biofilm contains amyloid structures formed by Aap and the small basic protein (Sbp). The latter contributes to the integrity of both protein and polysaccharide biofilm matrices. Several other CWA proteins can also promote S. epidermidis biofilm formation.

Staphylococci: Evolving Genomes

Staphylococci, and in particular Staphylococcus aureus, cause an extensive variety of infections in a range of hosts. The comprehensive analysis of staphylococcal genomes reveals mechanisms controlling the organism's biology, pathobiology, and dissemination. Whole-genome sequencing technologies led to a quantum leap in our understanding of bacterial genomes. The recent cost reduction of sequencing has resulted in unprecedented volumes of genomic information about S. aureus, one of the most sequenced bacterial species. Collecting, comparing, and interpreting big data is challenging, but fascinating insights have emerged. For example, it is becoming clearer which selective pressures staphylococci face in their habitats and which mechanisms allow this pathogen to adapt, survive, and spread. A key theme is the constant evolution of staphylococci as they alter their genome, exchange DNA, and adapt to new environments, leading to the emergence of increasingly successful, antibiotic-resistant, immune-evading, and host-adapted colonizers and pathogens. This article introduces the structure of staphylococcal genomes, details how genomes vary between strains, outlines the mechanisms of genetic variation, and describes the features of successful clones.

The MSCRAMM Family of Cell-Wall-Anchored Surface Proteins of Gram-Positive Cocci

The microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) are a family of proteins that are defined by the presence of two adjacent IgG-like folded subdomains. These promote binding to ligands by mechanisms that involve major conformational changes exemplified by the binding to fibrinogen by the 'dock-lock-latch' mechanism or to collagen by the 'collagen hug'. Clumping factors A and B are two such MSCRAMMs that have several important roles in the pathogenesis of Staphylococcus aureus infections. MSCRAMM architecture, ligand binding, and roles in infection and colonization are examined with a focus on recent developments with clumping factors.

Occurrence of virulence-associated genes among Staphylococcus saprophyticus isolated from different sources

Staphylococcus saprophyticus is an important pathogen responsible for community urinary tract infections (UTI). Besides composing the human microbiota, this species is widely distributed in the environment and the origins of this organism for human infection is not fully characterized. Although some virulence determinants are known, such as d-serine deaminase (DsdA), urease and cell-wall associated proteins, few studies investigated the distribution of virulence-associated genes and analyzed the pathogenic potential of S. saprophyticus strains from different sources. The aim of the present study was to detect the presence of S. saprophyticus genes encoding surface proteins UafA, Aas, Ssp, SdrI, SssF as well as the DsdA and urease enzymes. A total of 142 S. saprophyticus strains were obtained from four sources: UTI, colonization, water and food. It was found, in every tested strain, the presence of genes encoding the surface proteins UafA, Aas, Ssp and SssF and the DsdA and urease enzymes. In contrast, the gene encoding SdrI surface protein was not detected in any of the strains of S. saprophyticus. These results provide a better understanding of the characteristics of S. saprophyticus strains and suggest that isolates from non-human sources have a potential to colonize the urinary tract.

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response

The staphylococci comprise a diverse genus of Gram-positive, nonmotile commensal organisms that inhabit the skin and mucous membranes of humans and other mammals. In general, staphylococci are benign members of the natural flora, but many species have the capacity to be opportunistic pathogens, mainly infecting individuals who have medical device implants or are otherwise immunocompromised. Staphylococcus aureus and Staphylococcus epidermidis are major sources of hospital-acquired infections and are the most common causes of surgical site infections and medical device-associated bloodstream infections. The ability of staphylococci to form biofilms in vivo makes them highly resistant to chemotherapeutics and leads to chronic diseases. These biofilm infections include osteomyelitis, endocarditis, medical device infections, and persistence in the cystic fibrosis lung. Here, we provide a comprehensive analysis of our current understanding of staphylococcal biofilm formation, with an emphasis on adhesins and regulation, while also addressing how staphylococcal biofilms interact with the immune system. On the whole, this review will provide a thorough picture of biofilm formation of the staphylococcus genus and how this mode of growth impacts the host.

Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract

Gram-positive bacteria are a common cause of urinary-tract infection (UTI), particularly among individuals who are elderly, pregnant, or who have other risk factors for UTI. Here we review the epidemiology, virulence mechanisms, and host response to the most frequently isolated Gram-positive uropathogens: Staphylococcus saprophyticus, Enterococcus faecalis, and Streptococcus agalactiae. We also review several emerging, rare, misclassified, and otherwise underreported Gram-positive pathogens of the urinary tract including Aerococcus, Corynebacterium, Actinobaculum, and Gardnerella. The literature strongly suggests that urologic diseases involving Gram-positive bacteria may be easily overlooked due to limited culture-based assays typically utilized for urine in hospital microbiology laboratories. Some UTIs are polymicrobial in nature, often involving one or more Gram-positive bacteria. We herein review the risk factors and recent evidence for mechanisms of bacterial synergy in experimental models of polymicrobial UTI. Recent experimental data has demonstrated that, despite being cleared quickly from the bladder, some Gram-positive bacteria can impact pathogenic outcomes of co-infecting organisms. When taken together, the available evidence argues that Gram-positive bacteria are important uropathogens in their own right, but that some can be easily overlooked because they are missed by routine diagnostic methods. Finally, a growing body of evidence demonstrates that a surprising variety of fastidious Gram-positive bacteria may either reside in or be regularly exposed to the urinary tract and further suggests that their presence is widespread among women, as well as men. Experimental studies in this area are needed; however, there is a growing appreciation that the composition of bacteria found in the bladder could be a potentially important determinant in urologic disease, including susceptibility to UTI.

Biofilm Matrix Composition Affects the Susceptibility of Food Associated Staphylococci to Cleaning and Disinfection Agents

Staphylococci are frequently isolated from food processing environments, and it has been speculated whether survival after cleaning and disinfection with benzalkonium chloride (BC)-containing disinfectants is due to biofilm formation, matrix composition, or BC efflux mechanisms. Out of 35 food associated staphylococci, eight produced biofilm in a microtiter plate assay and were identified as Staphylococcus capitis (2), S. cohnii, S. epidermidis, S. lentus (2), and S. saprophyticus (2). The eight biofilm producing strains were characterized using whole genome sequencing. Three of these strains contained the ica operon responsible for production of a polysaccharide matrix, and formed a biofilm which was detached upon exposure to the polysaccharide degrading enzyme Dispersin B, but not Proteinase K or trypsin. These strains were more tolerant to the lethal effect of BC both in suspension and biofilm than the remaining five biofilm producing strains. The five BC susceptible strains were characterized by lack of the ica operon, and their biofilms were detached by Proteinase K or trypsin, but not Dispersin B, indicating that proteins were major structural components of their biofilm matrix. Several novel cell wall anchored repeat domain proteins with domain structures similar to that of MSCRAMM adhesins were identified in the genomes of these strains, potentially representing novel mechanisms of ica-independent biofilm accumulation. Biofilms from all strains showed similar levels of detachment after exposure to alkaline chlorine, which is used for cleaning in the food industry. Strains with qac genes encoding BC efflux pumps could grow at higher concentrations of BC than strains without these genes, but no differences were observed at biocidal concentrations. In conclusion, the biofilm matrix of food associated staphylococci varies with respect to protein or polysaccharide nature, and this may affect the sensitivity toward a commonly used disinfectant.

A Novel MSCRAMM Subfamily in Coagulase Negative Staphylococcal Species

Coagulase negative staphylococci (CoNS) are important opportunistic pathogens. Staphylococcus epidermidis, a coagulase negative staphylococcus, is the third leading cause of nosocomial infections in the US. Surface proteins like Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) are major virulence factors of pathogenic gram positive bacteria. Here, we identified a new chimeric protein in S. epidermidis, that we call SesJ. SesJ represents a prototype of a new subfamily of MSCRAMMs. Structural predictions show that SesJ has structural features characteristic of a MSCRAMM along with a N-terminal repeat region and an aspartic acid containing C-terminal repeat region, features that have not been previously observed in staphylococcal MSCRAMMs but have been found in other surface proteins from gram positive bacteria. We identified and analyzed structural homologs of SesJ in three other CoNS. These homologs of SesJ have an identical structural organization but varying sequence identities within the domains. Using flow cytometry, we also show that SesJ is expressed constitutively on the surface of a representative S. epidermidis strain, from early exponential to stationary growth phase. Thus, SesJ is positioned to interact with protein targets in the environment and plays a role in S. epidermidis virulence.

Characterization of Staphylococcus caprae Clinical Isolates Involved in Human Bone and Joint Infections, Compared with Goat Mastitis Isolates

Staphylococcus caprae is an emerging microorganism in human bone and joint infections (BJI). The aim of this study is to describe the features of S. caprae isolates involved in BJI (H for human) compared with those of isolates recovered in goat mastitis (A for animal). Fourteen isolates of each origin were included. Identifications were performed using a Vitek 2 GP ID card, tuf gene sequencing, and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) Vitek MS. Molecular typing was carried out using pulsed-field gel electrophoresis (PFGE) and DiversiLab technology. The crystal violet method was used to determine biofilm-forming ability. Virulence factors were searched by PCR. Vitek MS technology provides an accurate identification for the two types of isolates compared to that of gold-standard sequencing (sensitivity, 96.4%), whereas the Vitek 2 GP ID card was more effective for H isolates. Molecular typing methods revealed two distinct lineages corresponding to the origin despite few overlaps: H and A. In our experimental conditions, no significant difference was observed in biofilm production ability between H and A isolates. Nine isolates (5 H isolates and 4 A isolates) behaved as weak producers while one A isolate was a strong producer. Concerning virulence factors, the autolysin atlC and the serine aspartate adhesin (sdrZ) genes were detected in 24 isolates (86%), whereas the lipase gene was always detected, except in one H isolate (96%). The ica operon was present in 23 isolates (82%). Fibrinogen-binding (fbe) or collagen-binding (cna) genes were not detected by using primers designed for Staphylococcus aureus or Staphylococcus epidermidis, even in low stringency conditions. Although S. caprae probably remains underestimated in human infections, further studies are needed to better understand the evolution and the adaptation of this species to its host.

Structure, Function, and Assembly of Adhesive Organelles by Uropathogenic Bacteria

Bacteria assemble a wide range of adhesive proteins, termed adhesins, to mediate binding to receptors and colonization of surfaces. For pathogenic bacteria, adhesins are critical for early stages of infection, allowing the bacteria to initiate contact with host cells, colonize different tissues, and establish a foothold within the host. The adhesins expressed by a pathogen are also critical for bacterial-bacterial interactions and the formation of bacterial communities, including biofilms. The ability to adhere to host tissues is particularly important for bacteria that colonize sites such as the urinary tract, where the flow of urine functions to maintain sterility by washing away non-adherent pathogens. Adhesins vary from monomeric proteins that are directly anchored to the bacterial surface to polymeric, hair-like fibers that extend out from the cell surface. These latter fibers are termed pili or fimbriae, and were among the first identified virulence factors of uropathogenic Escherichia coli. Studies since then have identified a range of both pilus and non-pilus adhesins that contribute to bacterial colonization of the urinary tract, and have revealed molecular details of the structures, assembly pathways, and functions of these adhesive organelles. In this review, we describe the different types of adhesins expressed by both Gram-negative and Gram-positive uropathogens, what is known about their structures, how they are assembled on the bacterial surface, and the functions of specific adhesins in the pathogenesis of urinary tract infections.

The N-terminal repeat and the ligand binding domain A of SdrI protein is involved in hydrophobicity of S. saprophyticus

Staphylococcus saprophyticus is an important cause of urinary tract infection, and its cell surface hydrophobicity may contribute to virulence by facilitating adherence of the organism to uroepithelia. S. saprophyticus expresses the surface protein SdrI, a member of the serine-aspartate repeat (SD) protein family, which has multifunctional properties. The SdrI knock out mutant has a reduced hydrophobicity index (HPI) of 25%, and expressed in the non-hydrophobic Staphylococcus carnosus strain TM300 causes hydrophobicity. Using hydrophobic interaction chromatography (HIC), we confined the hydrophobic site of SdrI to the N-terminal repeat region. S. saprophyticus strains carrying different plasmid constructs lacking either the N-terminal repeats, both B or SD-repeats were less hydrophobic than wild type and fully complemented SdrI mutant (HPI: 51%). The surface hydrophobicity and HPI of both wild type and the complemented strain were also influenced by calcium (Ca(2+)) and were reduced from 81.3% and 82.4% to 10.9% and 12.3%, respectively. This study confirms that the SdrI protein of S. saprophyticus is a crucial factor for surface hydrophobicity and also gives a first significant functional description of the N-terminal repeats, which in conjunction with the B-repeats form an optimal hydrophobic conformation.

Staphylococci: colonizers and pathogens of human skin

 Staphylococci are abundant bacteria of the human skin microbiome. Several species, particularly Staphylococcus aureus and Staphylococcus epidermidis, are opportunistic pathogens and cause significant disease. The human skin serves many functions and here we review its role as an antimicrobial barrier and the staphylococcal mechanisms to colonize and counteract the various stresses present in this niche. Successful colonization is achieved using a diversity of adhesins, surface proteins and secreted enzymes to counteract the antimicrobial peptides, enzymes and lipid matrix components present in the acid mantle. Further mechanisms enable these bacteria to overcome osmotic and acid stresses and desiccation in order to survive the exacting demands of an ever-changing landscape.

N-acetylglucosaminylation of serine-aspartate repeat proteins promotes Staphylococcus aureus bloodstream infection

Staphylococcus aureus secretes products that convert host fibrinogen to fibrin and promote its agglutination with fibrin fibrils, thereby shielding bacteria from immune defenses. The agglutination reaction involves ClfA (clumping factor A), a surface protein with serine-aspartate (SD) repeats that captures fibrin fibrils and fibrinogen. Pathogenic staphylococci express several different SD proteins that are modified by two glycosyltransferases, SdgA and SdgB. Here, we characterized three genes of S. aureus, aggA, aggB (sdgA), and aggC (sdgB), and show that aggA and aggC contribute to staphylococcal agglutination with fibrin fibrils in human plasma. We demonstrate that aggB (sdgA) and aggC (sdgB) are involved in GlcNAc modification of the ClfA SD repeats. However, only sdgB is essential for GlcNAc modification, and an sdgB mutant is defective in the pathogenesis of sepsis in mice. Thus, GlcNAc modification of proteins promotes S. aureus replication in the bloodstream of mammalian hosts.

Significance of the D-serine-deaminase and D-serine metabolism of Staphylococcus saprophyticus for virulence

Staphylococcus saprophyticus is the only species of Staphylococcus that is typically uropathogenic and possesses a gene coding for a D-serine-deaminase (DsdA). As D-serine is prevalent in urine and toxic or bacteriostatic to many bacteria, it is not surprising that the D-serine-deaminase gene is found in the genome of uropathogens. It has been suggested that D-serine-deaminase or the ability to respond to or to metabolize D-serine is important for virulence. For uropathogenic Escherichia coli (UPEC), a high intracellular D-serine concentration affects expression of virulence factors. S. saprophyticus is able to grow in the presence of high D-serine concentrations; however, its D-serine metabolism has not been described. The activity of the D-serine-deaminase was verified by analyzing the formation of pyruvate from D-serine in different strains with and without D-serine-deaminase. Cocultivation experiments were performed to show that D-serine-deaminase confers a growth advantage to S. saprophyticus in the presence of D-serine. Furthermore, in vivo coinfection experiments showed a disadvantage for the ΔdsdA mutant during urinary tract infection. Expression analysis of known virulence factors by reverse transcription-quantitative PCR (RT-qPCR) showed that the surface-associated lipase Ssp is upregulated in the presence of D-serine. In addition, we show that S. saprophyticus is able to use D-serine as the sole carbon source, but interestingly, D-serine had a negative effect on growth when glucose was also present. Taken together, D-serine metabolism is associated with virulence in S. saprophyticus, as at least one known virulence factor is upregulated in the presence of D-serine and a ΔdsdA mutant was attenuated in virulence murine model of urinary tract infection.

Inhibition of urease activity in the urinary tract pathogen Staphylococcus saprophyticus

Urease is a virulence factor for the Gram-positive urinary tract pathogen Staphylococcus saprophyticus. The susceptibility of this enzyme to chemical inhibition was determined using soluble extracts of Staph. saprophyticus strain ATCC 15305. Acetohydroxamic acid (Ki = 8.2 μg ml(-1) = 0.106 mmol l(-1) ) and DL-phenylalanine hydroxamic acid (Ki = 21 μg ml(-1) = 0.116 mmol l(-1) ) inhibited urease activity competitively. The phosphorodiamidate fluorofamide also caused competitive inhibition (Ki = 0.12 μg ml(-1) = 0.553 μmol l(-1) = 0.000553 mmol l(-1) ), but the imidazole omeprazole had no effect. Two flavonoids found in green tea extract [(+)-catechin hydrate (Ki = 357 μg ml(-1) = 1.23 mmol l(-1) ) and (-)-epigallocatechin gallate (Ki = 210 μg ml(-1) = 0.460 mmol l(-1) )] gave mixed inhibition. Acetohydroxamic acid, DL-phenylalanine hydroxamic acid, fluorofamide, (+)-catechin hydrate and (-)-epigallocatechin gallate also inhibited urease activity in whole cells of strains ATCC 15305, ATCC 35552 and ATCC 49907 grown in a rich medium or an artificial urine medium. Addition of acetohydroxamic acid or fluorofamide to cultures of Staph. saprophyticus in an artificial urine medium delayed the increase in pH that normally occurs during growth. These results suggest that urease inhibitors may be useful for treating urinary tract infections caused by Staph. saprophyticus.

SIGNIFICANCE AND IMPACT OF THE STUDY

The enzyme urease is a virulence factor for the Gram-positive urinary tract pathogen Staphylococcus saprophyticus. We have shown that urease activity in cell-free extracts and whole bacterial cells is susceptible to inhibition by hydroxamates, phosphorodiamidates and flavonoids, but not by imidazoles. Acetohydroxamic acid and fluorofamide in particular can temporarily delay the increase in pH that occurs when Staph. saprophyticus is grown in an artificial urine medium. These results suggest that urease inhibitors may be useful as chemotherapeutic agents for the treatment of urinary tract infections caused by this micro-organism.

Characterisation of a cell wall-anchored protein of Staphylococcus saprophyticus associated with linoleic acid resistance

Background

The Gram-positive bacterium Staphylococcus saprophyticus is the second most frequent causative agent of community-acquired urinary tract infections (UTI), accounting for up to 20% of cases. A common feature of staphylococci is colonisation of the human skin. This involves survival against innate immune defenses including antibacterial unsaturated free fatty acids such as linoleic acid which act by disrupting bacterial cell membranes. Indeed, S. saprophyticus UTI is usually preceded by perineal skin colonisation.

Results

In this study we identified a previously undescribed 73.5 kDa cell wall-anchored protein of S. saprophyticus, encoded on plasmid pSSAP2 of strain MS1146, which we termed S. saprophyticus surface protein F (SssF). The sssF gene is highly prevalent in S. saprophyticus clinical isolates and we demonstrate that the SssF protein is expressed at the cell surface. However, unlike all other characterised cell wall-anchored proteins of S. saprophyticus, we were unable to demonstrate a role for SssF in adhesion. SssF shares moderate sequence identity to a surface protein of Staphylococcus aureus (SasF) recently shown to be an important mediator of linoleic acid resistance. Using a heterologous complementation approach in a S. aureus sasF null genetic background, we demonstrate that SssF is associated with resistance to linoleic acid. We also show that S. saprophyticus strains lacking sssF are more sensitive to linoleic acid than those that possess it. Every staphylococcal genome sequenced to date encodes SssF and SasF homologues. Proteins in this family share similar predicted secondary structures consisting almost exclusively of α-helices in a probable coiled-coil formation.

Conclusions

Our data indicate that SssF is a newly described and highly prevalent surface-localised protein of S. saprophyticus that contributes to resistance against the antibacterial effects of linoleic acid. SssF is a member of a protein family widely disseminated throughout the staphylococci.

L-Proline nutrition and catabolism in Staphylococcus saprophyticus

Staphylococcus saprophyticus strains ATCC 15305, ATCC 35552, and ATCC 49907 were found to require L-proline but not L-arginine for growth in a defined culture medium. All three strains could utilize L-ornithine as a proline source and contained L-ornithine aminotransferase and Δ(1)-pyrroline-5-carboxylate reductase activities; strains ATCC 35552 and ATCC 49907 could use L-arginine as a proline source and had L-arginase activity. The proline requirement also could be met by L-prolinamide, L-proline methyl ester, and the dipeptides L-alanyl-L-proline and L-leucyl-L-proline. The bacteria exhibited L-proline degradative activity as measured by the formation of Δ(1)-pyrroline-5-carboxylate. The specific activity of proline degradation was not affected by addition of L-proline or NaCl but was highest in strain ATCC 49907 after growth in Mueller-Hinton broth. A membrane fraction from this strain had L-proline dehydrogenase activity as detected both by reaction of Δ(1)-pyrroline-5-carboxylate with 2-aminobenzaldehyde (0.79 nmol min(-1) mg(-1)) and by the proline-dependent reduction of p-iodonitrotetrazolium (20.1 nmol min(-1) mg(-1)). A soluble fraction from this strain had Δ(1)-pyrroline-5-carboxylate dehydrogenase activity (88.8 nmol min(-1) mg(-1)) as determined by the NAD(+)-dependent oxidation of DL-Δ(1)-pyrroline-5-carboxylate. Addition of L-proline to several culture media did not increase the growth rate or final yield of bacteria but did stimulate growth during osmotic stress. When grown with L: -ornithine as the proline source, S. saprophyticus was most susceptible to the proline analogues L-azetidine-2-carboylate, 3,4-dehydro-DL-proline, DL-thiazolidine-2-carboxylate, and L-thiazolidine-4-carboxylate. These results indicate that proline uptake and metabolism may be a potential target of antimicrobial therapy for this organism.

UafB is a serine-rich repeat adhesin of Staphylococcus saprophyticus that mediates binding to fibronectin, fibrinogen and human uroepithelial cells

Staphylococcus saprophyticus is an important cause of urinary tract infection (UTI), particularly among young women, and is second only to uropathogenic Escherichia coli as the most frequent cause of UTI. The molecular mechanisms of urinary tract colonization by S. saprophyticus remain poorly understood. We have identified a novel 6.84 kb plasmid-located adhesin-encoding gene in S. saprophyticus strain MS1146 which we have termed uro-adherence factor B (uafB). UafB is a glycosylated serine-rich repeat protein that is expressed on the surface of S. saprophyticus MS1146. UafB also functions as a major cell surface hydrophobicity factor. To characterize the role of UafB we generated an isogenic uafB mutant in S. saprophyticus MS1146 by interruption with a group II intron. The uafB mutant had a significantly reduced ability to bind to fibronectin and fibrinogen. Furthermore, we show that a recombinant protein containing the putative binding domain of UafB binds specifically to fibronectin and fibrinogen. UafB was not involved in adhesion in a mouse model of UTI; however, we observed a striking UafB-mediated adhesion phenotype to human uroepithelial cells. We have also identified genes homologous to uafB in other staphylococci which, like uafB, appear to be located on transposable elements. Thus, our data indicate that UafB is a novel adhesin of S. saprophyticus that contributes to cell surface hydrophobicity, mediates adhesion to fibronectin and fibrinogen, and exhibits tropism for human uroepithelial cells.

Characterization of the structure and biological functions of a capsular polysaccharide produced by Staphylococcus saprophyticus

Staphylococcus saprophyticus is a common cause of uncomplicated urinary tract infections in women. S. saprophyticus strain ATCC 15305 carries two staphylococcal cassette chromosome genetic elements, SCC(15305RM) and SCC(15305cap). The SCC(15305cap) element carries 13 open reading frames (ORFs) involved in capsular polysaccharide (CP) biosynthesis, and its G+C content (26.7%) is lower than the average G+C content (33.2%) for the whole genome. S. saprophyticus strain ATCC 15305 capD, capL, and capK (capD(Ssp), capL(Ssp), and capK(Ssp)) are homologous to genes encoding UDP-FucNAc biosynthesis, and gtaB and capI(Ssp) show homology to genes involved in UDP-glucuronic acid synthesis. S. saprophyticus ATCC 15305 CP, visualized by immunoelectron microscopy, was extracted and purified using anionic-exchange and size exclusion chromatography. Analysis of the purified CP by (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy and gas-liquid chromatography revealed two types of branched tetrasaccharide repeating units composed of the following: -4)-beta-Glc-(1-3)-Sug-(1-4)-beta-GlcA-(1- | beta-GlcNAc-(1-2) Sug represents two stereoisomers of 2-acetamido-2,6-dideoxy-hexos-4-ulose residues, one of which has an arabino configuration. The encapsulated ATCC 15305 strain was resistant to complement-mediated opsonophagocytic killing by human neutrophils, whereas the acapsular mutant C1 was susceptible. None of 14 clinical isolates reacted with antibodies to the ATCC 15305 CP. However, 11 of the 14 S. saprophyticus isolates were phenotypically encapsulated based on their resistance to complement-mediated opsonophagocytic killing and their failure to hemagglutinate when cultivated aerobically. Ten of the 14 clinical strains carried homologues of the conserved staphylococcal capD gene or the S. saprophyticus gtaB gene, or both. Our results suggest that some strains of S. saprophyticus are encapsulated and that more than one capsular serotype exists.

Genotypic and phenotypic variation among Staphylococcus saprophyticus from human and animal isolates

Background

The main aim of this study was to examine the genotypic and phenotypic diversity of Staphylococcus saprophyticus isolates from human and animal origin.

Findings

In total, 236 clinical isolates and 15 animal isolates of S. saprophyticus were characterized in respect of the occurrence of 9 potential virulence genes and four surface properties. All strains were PCR positive for the regulatory genes agr, sar >it>A and rot as well as for the surface proteins UafA and Aas. Nearly 90% of the clinical isolates were found to possess the gene for the surface-associated lipase Ssp and 10% for the collagen binding MSCRAMM SdrI. All animal isolates were negative forsdrI. Lipolytic activity could be detected in 66% of the clinical and 46% of the animal isolates. Adherence to collagen type I was shown of 20% of the clinical strains and 6% of the strains of animal origin. Most S. saprophyticus strains showed hydrophobic properties and only few could agglutinate sheep erythrocytes.

Conclusions

We described a broad analysis of animal and human S. saprophyticus isolates regarding virulence genes and phenotypic properties such as lipase activity, hydrophobicity, and adherence. While S. saprophyticus strains from animal sources have prerequisites for colonization of the urinary tract like the D-serine-deaminase, out findings suggested that they need to acquire new genes e.g. MSCRAMMS for adherence like sdrI and to modulate their existing properties e.g. increasing the lipase activity or reducing hydrophobicity. These apparently important new genes or properties for virulence have to be further analyzed.

Screening for genes involved in Klebsiella pneumoniae biofilm formation using a fosmid library

Klebsiella pneumoniae is a well-known opportunistic pathogen, often causing catheter-associated urinary tract infections. Biofilm formation on the catheter surfaces is an important step in the development of these infections. To identify the genes involved in the ability of K. pneumoniae to form a biofilm on abiotic surfaces, a novel strategy was used. A clone library was constructed by cloning the entire K. pneumoniae genome of the clinical isolate C3091 into a fosmid vector and the clone library was expressed in Escherichia coli. A total of 1152 clones were screened for enhanced biofilm formation compared with the E. coli parent strain using a biofilm microtiter plate assay. Nine clones with significantly enhanced biofilm formation were identified, subjected to random Tn5 transposon mutagenesis, screened for biofilm deficiency and the biofilm-promoting genes identified. Five of the clones contained the type 3 fimbriae gene cluster, a well-known K. pneumoniae virulence factor and biofilm promoter. Thus, the effectiveness of our approach was confirmed. Furthermore, genes encoding cell surface proteins and proteins involved in metabolism, none of them previously associated with biofilm formation in K. pneumoniae, were identified by our screening method. In conclusion, the use of fosmid libraries is an effective high throughput screening method to identify the genes involved in biofilm formation.

Characterization of a novel murine model of Staphylococcus saprophyticus urinary tract infection reveals roles for Ssp and SdrI in virulence

Staphylococcus saprophyticus, an obligate human pathogen, is the most common Gram-positive causative agent of urinary tract infection (UTI) in young, healthy women. Despite the clinical importance of S. saprophyticus, little is known about how it causes disease in the urinary tract or how the host responds to the infection. Here we established an in vivo model to study both host and bacterial factors contributing to S. saprophyticus UTI. Using this model, we show that S. saprophyticus preferentially infects C3H/HeN murine kidneys instead of the bladder, a trait observed for multiple clinical isolates. Bacterial persistence in the kidneys was observed in C3H/HeN mice but not in C57BL/6 mice, indicating that host factors strongly contribute to the ability of S. saprophyticus to cause UTI. Using C3H/HeN mice as a model, histologic and immunofluorescence analyses of infected tissues revealed that S. saprophyticus induced epithelial cell shedding in the bladder and an inflammatory response characterized by macrophage and neutrophil infiltration in the bladder and kidneys. The inflammatory response correlated with increased production of proinflammatory cytokines and chemokines in both the bladder and the kidneys. Finally, we observed that the putative S. saprophyticus virulence factors Ssp and SdrI were important for persistence, but not for initial colonization, in the murine urinary tract. Thus, we characterized both host and bacterial factors involved in progression of S. saprophyticus UTI, and we describe a useful model system for studying factors involved in the pathogenesis of this Gram-positive uropathogen.

SdrI of Staphylococcus saprophyticus is a multifunctional protein: localization of the fibronectin-binding site

Staphylococcus saprophyticus, an important cause of urinary tract infections in young women, expresses the surface protein SdrI, a member of the serine-aspartate repeat (SD) protein family. Here we analyse the fibronectin-binding ability of SdrI, as S. saprophyticus is known to bind fibronectin and there is no known SD protein with this function. This protein does not contain the binding motif typical for fibronectin-binding proteins. Using recombinant fragments of SdrI, we localized the binding domain in the A region and show that SdrI bound to the N-terminal 30-kDa fragment of fibronectin. The fibronectin-binding function was shown in the natural host using an SdrI knockout mutant that showed decreased binding to fibronectin compared with wild-type strain 7108.

The uropathogenic species Staphylococcus saprophyticus tolerates a high concentration of D-serine

Human urine contains a relatively high concentration of d-serine, which is toxic to several nonuropathogenic bacteria, but can be utilized or detoxified by uropathogenic Escherichia coli (UPEC). The sequenced genome of uropathogenic Staphylococcus saprophyticus contains a gene with homology to the d-serine deaminase gene (dsdA) of UPEC. We found the gene in several clinical isolates of S. saprophyticus; however, the gene was absent in Staphylococcus xylosus and Staphylococcus cohnii, phylogenetically close relatives of S. saprophyticus, and could also not be detected in isolates of Staphylococcus aureus, Staphylococcus epidermidis and 13 other staphylococcal species. In addition, the genomes of other sequenced staphylococci do not harbor homologues of this operon. Interestingly, S. saprophyticus could grow in media supplemented with relatively high concentrations of d-serine, whereas S. aureus, S. epidermidis and other staphylococcal species could not. The association of the dsdA gene with growth in media including d-serine was proved by introducing the gene into S. aureus Newman. Given the fact that UPEC and S. saprophyticus tolerate this compound, d-serine utilization and detoxification may be a general property of uropathogenic bacteria.

The surface protein Srr-1 of Streptococcus agalactiae binds human keratin 4 and promotes adherence to epithelial HEp-2 cells

Streptococcus agalactiae is frequently the cause of bacterial sepsis and meningitis in neonates. In addition, it is a commensal bacterium that colonizes the mammalian gastrointestinal tract. During its commensal and pathogenic lifestyles, S. agalactiae colonizes and invades a number of host compartments, thereby interacting with different host proteins. In the present study, the serine-rich repeat protein Srr-1 from S. agalactiae was functionally investigated. Immunofluorescence microscopy showed that Srr-1 was localized on the surface of streptococcal cells. The Srr-1 protein was shown to interact with a 62-kDa protein in human saliva, which was identified by matrix-assisted laser desorption ionization-time-of-flight analysis as human keratin 4 (K4). Immunoblot and enzyme-linked immunosorbent assay experiments allowed us to narrow down the K4 binding domain in Srr-1 to a region of 157 amino acids (aa). Furthermore, the Srr-1 binding domain of K4 was identified in the C-terminal 255 aa of human K4. Deletion of the srr-1 gene in the genome of S. agalactiae revealed that this gene plays a role in bacterial binding to human K4 and that it is involved in adherence to epithelial HEp-2 cells. Binding to immobilized K4 and adherence to HEp-2 cells were restored by introducing the srr-1 gene on a shuttle plasmid into the srr-1 mutant. Furthermore, incubation of HEp-2 cells with the K4 binding domain of Srr-1 blocked S. agalactiae adherence to epithelial cells in a dose-dependent fashion. This is the first report describing the interaction of a bacterial protein with human K4.