Staphylococcus lugdunensis endocarditis following vasectomy – report of a case history and review of the literature

Staphylococcus lugdunensis is a coagulase‐negative Staphylococcus (CoNS), and part of the normal skin flora. The bacterium is an emerging pathogen that, unlike other CoNS, resembles coagulase‐positive Staphylococcus aureus infections in virulence, tissue destruction, and clinical course. We report a fatal case following minor surgery. The frequency of S. lugdunensis infections has probably been underestimated and under‐reported in the past as few clinical laboratories routinely identify coagulase‐negative Staphylococci.     

Molecular characteristics of Staphylococcus aureus associated with chronic rhinosinusitis

The anterior nares have been regarded as the major carriage site of Staphylococcus aureus. From here, the organism can spread to other parts of the body where it might act as harmless commensal or cause mild to severe infections. Nasal sinuses are normally sterile, but in patients with chronic rhinosinusitis (CRS), the finding of S. aureus in maxillary sinus cultures is common. Isolates were obtained from the nares and maxillary sinus of patients with CRS and the nares of healthy controls. A significantly higher frequency of S. aureus was found in nares samples from patients (24/42) compared to controls (16/57) (p = 0.004). There is no consensus regarding whether S. aureus is a relevant pathogen in CRS. A DNA microarray was used to investigate the prevalence of S. aureus virulence genes with focus on staphylococcal enterotoxins, toxic shock syndrome toxin‐1, agr types, and cell wall‐associated proteins. The genotyping of S. aureus isolates revealed only small and non‐significant differences in gene prevalence between isolates collected from patients with CRS and those collected from healthy nasal carriers. This study provides an increased knowledge of the genetic pattern of virulence genes among S. aureus collected in CRS.     

Mast cells are activated by Staphylococcus aureus in vitro but do not influence the outcome of intraperitoneal S. aureus infection in vivo

Staphylococcus aureus is a major pathogen that can cause a broad spectrum of serious infections including skin infections, pneumonia and sepsis. Peritoneal mast cells have been implicated in the host response towards various bacterial insults and to provide mechanistic insight into the role of mast cells in intraperitoneal bacterial infection we here studied the global effects of S. aureus on mast cell gene expression. After co‐culture of peritoneal mast cells with live S. aureus we found by gene array analysis that they up‐regulate a number of genes. Many of these corresponded to pro‐inflammatory cytokines, including interleukin‐3, interleukin‐13 and tumour necrosis factor‐α. The cytokine induction in response to S. aureus was confirmed by ELISA. To study the role of peritoneal mast cells during in vivo infection with S. aureus we used newly developed Mcpt5‐Cre⁺ × R‐DTA mice in which mast cell deficiency is independent of c‐Kit. This is in contrast to previous studies in which an impact of mast cells on bacterial infection has been proposed based on the use of mice whose mast cell deficiency is a consequence of defective c‐Kit signalling. Staphylococcus aureus was injected intraperitoneally into mast‐cell‐deficient Mcpt5‐Cre⁺ × R‐DTA mice using littermate mast‐cell‐sufficient mice as controls. We did not observe any difference between mast‐cell‐deficient and control mice with regard to weight loss, bacterial clearance, inflammation or cytokine production. We conclude that, despite peritoneal mast cells being activated by S. aureus in vitro, they do not influence the in vivo manifestations of intraperitoneal S. aureus infection.     

The YvqE two‐component system controls biofilm formation and acid production in Streptococcus pyogenes

In Streptococcus pyogenes, proteins involved in determining virulence are controlled by stand‐alone response regulators and by two‐component regulatory systems. Previous studies reported that, compared to the parental strain, the yvqE sensor knockout strain showed significantly reduced growth and lower virulence. To determine the function of YvqE, we performed biofilm analysis and pH assays on yvqE mutants, and site‐directed mutagenesis of YvqE. The yvqE deletion mutant showed a slower acid production rate, indicating that YvqE regulates acid production from sugar fermentation. The mutant strain, in which the Asp²⁶ residue in YvqE was replaced with Asn, affected biofilm formation, suggesting that this amino acid senses hydrogen ions produced by fermentative sugar metabolism. Signals received by YvqE were directly or indirectly responsible for inducing pilus expression. This study shows that at low environmental pH, biofilm formation in S. pyogenes is mediated by YvqE and suggests that regulation of pilus expression by environmental acidification could be directly under the control of YvqE.     

Rapid identification of Staphylococcus aureus directly from positive blood culture media using quantum dots as fluorescence probes

The subcultivation of positive blood cultures for organism identification is a time‐consuming process. We explored the use of fluorescent quantum dots (QDs) as probes for the improved detection and identification of Staphylococcus aureus directly from positive blood culture media. Immunofluorescence probes were synthesized by linking biotin‐conjugated QDs to streptavidin‐conjugated IgG molecules. This QDs‐IgG complex is capable of binding anti‐SPA antibodies which specifically bind to a cell surface protein of S. aureus. The specificity of the method was confirmed using reference strains. Among 372 positive blood cultures, 73 containing gram‐positive cocci in clusters were investigated. Relative to the standard culture method, the immunofluorescence assay showed 90.5% (19/21) sensitivity and 100% (52/52) specificity for S. aureus. These results suggest that this immunofluorescence assay allows the rapid identification of S. aureus directly from specimens.     

Modulation of ENaC,CFTR, and iNOS expression in bronchial epithelial cells after stimulation with Staphylococcus epidermidis (94B080) and Staphylococcus aureus (90B083)

Bacteria affect the respiratory epithelium, which is covered by airway surface liquid (ASL) and mucus. Ion concentrations in the ASL are determined by the cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial Na⁺ channel (ENaC). Neonatal sepsis is a major risk factor for subsequent pulmonary disease in preterm newborns. Predominating are coagulase‐negative staphylococci (e.g., Staphylococccus epidermidis and Staphylococccus aureus). The aim of this study was to investigate modulation of CFTR, ENaC, mucins, proinflammatory cytokines, and inducible nitric oxide synthase (iNOS) in respiratory epithelial cells after S. epidermidis 94B080 and S. aureus 90B083 exposure. Bronchial epithelial cells were incubated with S. epidermidis 94B080 and S. aureus 90B083 (neonatal blood isolates) for 1–36 h. Expression of CFTR, ENaC, iNOS, and mucins was analyzed by real‐time PCR and Western blotting. Release of cytokines was analyzed by ELISA, and production of NO by the Griess assay. Expression of CFTR significantly decreased after 36 h incubation with S. epidermidis and more prominently with S. aureus, whereas S. epidermidis caused a significant increase in the expression of β‐ and γ‐ENaC. Expression of iNOS increased, but NO was not detected. Both staphylococci caused a decrease in the intracellular Ca²⁺ concentration. S. aureus induced increased secretion of IL‐6, IL‐8, and transforming nuclear factor (TNF)‐α in a time‐dependent manner as compared with S. epidermidis. In conclusion, expression of ENaC, CFTR, and iNOS is modulated by exposure to S. aureus 90B083 and S. epidermidis 94B080. S. aureus is more potent in causing release of IL‐6, IL‐8, and TNF‐α by bronchial epithelial cells as compared with S. epidermidis. The mRNA expression for the mucus proteins MUC2, MUC5AC, and MUC5B could not be measured, neither in the presence nor in the absence of bacteria.     

Evaluation of phytochemicals from medicinal plants of Myrtaceae family on virulence factor production by Pseudomonas aeruginosa

Virulence factors regulated by quorum sensing (QS) play a critical role in the pathogenesis of an opportunistic human pathogen, Pseudomonas aeruginosa in causing infections to the host. Hence, in the present work, the anti‐virulence potential of the medicinal plant extracts and their derived phytochemicals from Myrtaceae family was evaluated against P. aeruginosa. In the preliminary screening of the tested medicinal plant extracts, Syzygium jambos and Syzygium antisepticum demonstrated a maximum inhibition in QS‐dependent violacein pigment production by Chromobacterium violaceum DMST 21761. These extracts demonstrated an inhibitory activity over a virulence factor, pyoverdin, production by P. aeruginosa ATCC 27853. Gas chromatography–mass spectrometric (GC‐MS) analysis revealed the presence of 23 and 12 phytochemicals from the extracts of S. jambos and S. antisepticum respectively. Three top‐ranking phytochemicals, including phytol, ethyl linoleate and methyl linolenate, selected on the basis of docking score in molecular docking studies lowered virulence factors such as pyoverdin production, protease and haemolytic activities of P. aeruginosa to a significant level. In addition, the phytochemicals reduced rhamnolipid production by the organism. The work demonstrated an importance of plant‐derived compounds as anti‐virulence drugs to conquer P. aeruginosa virulence towards the host.     

Presence of arginine catabolic mobile element among community‐acquired meticillin‐resistant staphylococcus aureus is linked to a specific genetic background

The prevalence of arginine catabolic mobile element (ACME) among diverse and heterogeneous community‐associated methicillin‐resistant Staphylococcus aureus community‐associated Methicillin‐resistant S. aureus (CA‐MRSA) (n = 114) in a low‐endemic area, i.e. Sweden, was investigated. Among the CA‐MRSA, represented by 47 different spa types, ACME was only found in 10 isolates with a common genetic background [t008, SCCmec type IV, Panton‐Valentine leukocidin (PVL) positive, and indistinguishable or closely related pulsed‐field gel electrophoresis (PFGE)‐patterns] corresponding to USA300. This strain does not seem to be established in our area as most of the patients contracted the CA‐MRSA abroad. Presence of ACME does not seem to be associated with colonization, long‐term carriership, or intra‐familiar transmission in a higher extent than CA‐MRSA in general.     

Innate and adaptive immune responses against <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> skin infections

Staphylococcus aureus is an important human pathogen that is responsible for the vast majority of bacterial skin and soft tissue infections in humans. S. aureus can also become more invasive and cause life-threatening infections such as bacteremia, pneumonia, abscesses of various organs, meningitis, osteomyelitis, endocarditis, and sepsis. These infections represent a major public health threat due to the enormous numbers of these infections and the widespread emergence of methicillin-resistant S. aureus (MRSA) strains. MSRA is endemic in hospitals worldwide and is rapidly spreading throughout the normal human population in the community. The increasing frequency of MRSA infections has complicated treatment as these strains are more virulent and are increasingly becoming resistant to multiple different classes of antibiotics. The important role of the immune response against S. aureus infections cannot be overemphasized as humans with certain genetic and acquired immunodeficiency disorders are at an increased risk for infection. Understanding the cutaneous immune responses against S. aureus is essential as most of these infections occur or originate from a site of infection or colonization of the skin and mucosa. This review will summarize the innate immune responses against S. aureus skin infections, including antimicrobial peptides that have direct antimicrobial activity against S. aureus as well as pattern recognition receptors and proinflammatory cytokines that promote neutrophil abscess formation in the skin, which is required for bacterial clearance. Finally, we will discuss the recent discoveries involving IL-17-mediated responses, which provide a key link between cutaneous innate and adaptive immune responses against S. aureus skin infections.     

Molecular characterization of Staphylococcus aureus isolates from skin and soft tissue infections samples and healthy carriers in the Central Slovenia region

Staphylococcus aureus is among the most important human pathogens. It is associated with different infections and is a major cause of skin and soft tissue infections (SSTIs). The aim of our study was to compare S. aureus isolates associated with SSTIs with isolates obtained from healthy carriers in the Central Slovenia region in terms of antimicrobial susceptibility, genetic diversity by clonal complex (CC)/sequence type, spa type, and by toxin gene profiling. In total, 274 S. aureus isolates were collected prospectively by culturing wound samples from 461 SSTI patients and nasal samples from 451 healthy carriers. We have demonstrated high heterogeneity in terms of CCs and spa type in both groups of isolates. The main clone among SSTI strains was Panton–Valentine leukocidin gene (pvl) positive CC121, whereas the main clone among carrier strains was CC45 carrying a large range of toxin genes. The main spa type in both groups was t091. Pvl was more frequently present in SSTI strains (31.2% SSTI vs 3.6% carrier strains) and staphylococcal enterotoxin C was more frequently present in carrier strains (1.6% SSTI vs 17.0% carrier strains). We have also demonstrated that methicillin‐resistant S. aureus was a rare cause (2.8%) of SSTIs in our region.     

Molecular characterization and antibiotic resistance of clinical isolates of methicillin‐resistant Staphylococcus aureus obtained from Southeast of Iran (Kerman)

Staphylococcus aureus infections, particularly infections caused by methicillin‐resistant S. aureus (MRSA) strains, are emerging as a major public health problem. The aim of this study was to determine the prevalence of MRSA, antibiotic resistance profile and staphylococcal cassette chromosome mec (SCCmec) type of MRSA isolates obtained from clinical samples. Totally, 162 S. aureus isolates were obtained from clinical samples at three university hospitals in Kerman, Iran from March 2011 to February 2012. All isolates were identified as S. aureus by phenotypic methods and confirmed by PCR amplification of the nuc gene . MRSA isolates were screened by phenotypic tests and confirmed by presence of mecA gene. The minimum inhibitory concentrations (MICs) of the MRSA isolates against antibacterial agents were determined by E‐test. All isolates were analyzed by PCR for the presence of mecA and pvl genes. SCCmec typing of MRSA isolates was performed by multiplex PCR assay. Strain typing was carried out with REP‐PCR. Using mecA gene PCR and phenotypic methods, 56.8% of the isolates were identified as MRSA. All MRSA isolates were susceptible to vancomycin and linezolid. The sensitivity of MRSA isolates to trimethoprim‐sulfamethoxazole, clindamycin, ciprofloxacin, gentamicin, and erythromycin was 70.66, 66.53, 42.4, 38.05, and 29.35%, respectively. The most frequent SCCmec types were type III (48.31%) followed by type V (19.1%), type I (16.85%), and type IV (3.37%). The pvl gene was detected in 3.08% of isolates (two MRSA and three MSSA isolates). REP‐PCR typing divided the 92 MRSA isolates into 10 distinct clusters. Our results indicate that vancomycin and linezolid are the most effective antibacterial agents against MRSA isolates and SCCmec type III is predominant in MRSA strains in this area.     

Prediction and characterization of helper T‐cell epitopes from pneumococcal surface adhesin A

Pneumococcal surface adhesin A (PsaA) is a multifunctional lipoprotein known to bind nasopharyngeal epithelial cells, and is significantly involved in bacterial adherence and virulence. Identification of PsaA peptides that optimally bind human leucocyte antigen (HLA) and elicit a potent immune response would be of great importance to vaccine development. However, this is hindered by the multitude of HLA polymorphisms in humans. To identify the conserved immunodominant epitopes, we used an experimental dataset of 28 PsaA synthetic peptides and in silico methods to predict specific peptide‐binding to HLA and murine MHC class II molecules. We also characterized spleen and cervical lymph node (CLN) ‐derived T helper (Th) lymphocyte cytokine responses to these peptides after Streptococcus pneumoniae strain EF3030 challenge in mice. Individual, yet overlapping, peptides 15 amino acids in length revealed residues of PsaA that consistently caused the highest interferon‐γ, interleukin‐2 (IL‐2), IL‐5 and IL‐17 responses and proliferation as well as moderate IL‐10 and IL‐4 responses by ex vivo re‐stimulated splenic and CLN CD4⁺ T cells isolated from S. pneumoniae strain EF3030‐challenged F₁ (B6 ×  BALB/c) mice. In silico analysis revealed that peptides from PsaA may interact with a broad range of HLA‐DP, ‐DQ and ‐DR alleles, due in part to regions lacking β‐turns and asparagine endopeptidase sites. These data suggest that Th cell peptides (7, 19, 20, 22, 23 and 24) screened for secondary structures and MHC class II peptide‐binding affinities can elicit T helper cytokine and proliferative responses to PsaA peptides.     

Phagocytosis and cytokine response to rough and smooth colony variants of Mycobacterium abscessus by human peripheral blood mononuclear cells

Mycobacterium abscessus is a non‐tuberculous mycobacteria able to cause opportunistic infections in selected patient groups. During the last decades it has emerged as a cause of chronic pulmonary infection in patients with cystic fibrosis (CF). M. abscessus strains exhibit either smooth or rough colony morphology. Strains exhibiting the rough phenotype more often cause pulmonary infections in CF patients than did the smooth ones. Here, we examined phagocytosis and production of cytokines by human peripheral blood mononuclear cells, in response to M. abscessus strains with smooth and rough colony phenotype. The rough isolates all formed multicellular cords, similar to what is observed in Mycobacterium tuberculosis. Monocytes were generally unable to internalize these rough cord isolates, in contrast with the smooth ones. Furthermore, the rough M. abscessus strains induced a distinct cytokine profile differing from that induced by the smooth ones. Rough isolates induced significantly less IL‐10 and tumour necrosis factor compared to smooth strains, but more IL‐1β. Both varieties induced equal amounts of IFN‐γ, IL‐17, IL‐23, IL‐6, IL‐8 and equally little IL‐12. The ability to withstand phagocytosis might be a virulence factor contributing to the capacity of rough M. abscessus strains to give persistent pulmonary infections.     

An atypical CD8 T‐cell response to Chlamydia muridarum genital tract infections includes T cells that produce interleukin‐13

Chlamydia trachomatis urogenital serovars D–K are intracellular bacterial pathogens that replicate almost exclusively in human reproductive tract epithelium. In the C. muridarum mouse model for human Chlamydia genital tract infections CD4 T helper type 1 cell responses mediate protective immunity while CD8 T‐cell responses have been associated with scarring and infertility. Scarring mediated by CD8 T cells requires production of tumour necrosis factor‐α (TNF‐α); however, TNF‐α is associated with protective immunity mediated by CD4 T cells. The latter result suggests that TNF‐α in‐and‐of itself may not be the sole determining factor in immunopathology. CD8 T cells mediating immunopathology presumably do something in addition to producing TNF‐α that is detrimental during resolution of genital tract infections. To investigate the mechanism underlying CD8 immunopathology we attempted to isolate Chlamydia‐specific CD8 T‐cell clones from mice that self‐cleared genital tract infections. They could not be derived with antigen‐pulsed irradiated naive splenocytes; instead derivation required use of irradiated immune splenocyte antigen‐presenting cells. The Chlamydia‐specific CD8 T‐cell clones had relatively low cell surface CD8 levels and the majority were not restricted by MHC class Ia molecules. They did not express Plac8, and had varying abilities to terminate Chlamydia replication in epithelial cells. Two of the five CD8 clones produced interleukin‐13 (IL‐13) in addition to IL‐2, TNF‐α, IL‐10 and interferon‐γ. IL‐13‐producing Chlamydia‐specific CD8 T cells may contribute to immunopathology during C. muridarum genital tract infections based on known roles of TNF‐α and IL‐13 in scar formation.     

High frequency of multidrug‐resistant Staphylococcus aureus with SCCmec type III and Spa types t037 and t631 isolated from burn patients in southwest of Iran

Methicilin resistance Staphylococcus aureus (MRSA) infections are the major challenges in hospitals, especially in the burn units. The use of molecular typing methods is essential for tracking the spread of S. aureus infection and epidemiological investigations. The aim of this study was to find the profile of the spa types and also the prevalence of each SCCmec type of S. aureus strains in a central burn hospital in southwest of Iran. A total of 81 non‐duplicate S. aureus were isolated from burn patients between April 2011 and February 2012. The susceptibility of the isolates against 13 different antibiotics was tested by disk agar diffusion (DAD) method. MRSA strains were identified by amplification of mecA gene. Multiplex‐polymerase chain reaction (PCR) technique was used to determine the SCCmec types of MRSA strains and all the S. aureus isolates were typed by spa typing method. Detection of mecA gene showed that 70 (86.4%) of the isolates were MRSA. The highest rate of resistance was observed for penicillin (97.5%) and erythromycin (77.8%). None of the isolates were resistant to vancomycin. Sixty‐seven of the 70 MRSA isolates harbored only SCCmec type III and three untypeable isolates. Five different spa types were detected. The most common spa types were t037 (42.5%) and t631 (34.5%) and were only found in MRSA isolates. Only SCCmec type III was found in burn patients which emphasizes the HA‐MRSA origin of these strains. Only five different spa types identified in this study are in accordance with one SCCmec type which indicates that a limited number of bacterial colons are circulated in the burn unit in this hospital.     

Peptidoglycan recognition protein–peptidoglycan complexes increase monocyte/macrophage activation and enhance the inflammatory response

Peptidoglycan recognition proteins (PGRP) are pattern recognition receptors that can bind or hydrolyse peptidoglycan (PGN). Four human PGRP have been described: PGRP‐S, PGRP‐L, PGRP‐Iα and PGRP‐Iβ. Mammalian PGRP‐S has been implicated in intracellular destruction of bacteria by polymorphonuclear cells, PGRP‐Iα and PGRP‐Iβ have been found in keratinocytes and epithelial cells, and PGRP‐L is a serum protein that hydrolyses PGN. We have expressed recombinant human PGRP and observed that PGRP‐S and PGRP‐Iα exist as monomer and disulphide dimer proteins. The PGRP dimers maintain their biological functions. We detected the PGRP‐S dimer in human serum and polymorphonuclear cells, from where it is secreted after degranulation; these cells being a possible source of serum PGRP‐S. Recombinant PGRP do not act as bactericidal or bacteriostatic agents in the assayed conditions; however, PGRP‐S and PGRP‐Iα cause slight damage in the bacterial membrane. Monocytes/macrophages increase Staphylococcus aureus phagocytosis in the presence of PGRP‐S, PGRP‐Iα and PGRP‐Iβ. All PGRP bind to monocyte/macrophage membranes and are endocytosed by them. In addition, all PGRP protect cells from PGN‐induced apoptosis. PGRP increase THP‐1 cell proliferation and enhance activation by PGN. PGRP‐S–PGN complexes increase the membrane expression of CD14, CD80 and CD86, and enhance secretion of interleukin‐8, interleukin‐12 and tumour necrosis factor‐α, but reduce interleukin‐10, clearly inducing an inflammatory profile.