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Background: Necrotizing fasciitis (NF) retains a very high mortality rate despite prompt and adequate antibiotic treatment and surgical debridement. Necrotizing fasciitis has recently been associated with Streptococcus dysgalactiae subspecies equisimilis (SDSE).Methods: We investigated the causes of a very severe clinical manifestation of SDSE-NF by assessing both host and pathogen factors.Results: We found a lack of streptokinase-function blocking antibodies in the patient resulting in increased streptokinase-mediated fibrinolysis and bacterial spread. At the same time, the clinical SDSE isolate produced very high levels of streptokinase. Exogenous immunoglobulin Gs (ex-IgGs) efficiently blocked streptokinase-mediated fibrinolysis in vitro, indicating a protective role against the action of streptokinase. In vivo, SDSE infection severity was also attenuated by ex-IgGs in a NF mouse model.Conclusions: These findings illustrate for the first time that the lack of specific antibodies against streptococcal virulence factors, such as streptokinase, may contribute to NF disease severity. This can be counteracted by ex-IgGs. [ABSTRACT FROM AUTHOR]

Background. Propionibacteria are important members of the human skin microbiota, but are also opportunistic pathogens associated with periprosthetic joint infection (PJI). While the role of Propionibacterium acnes in PJI has been widely described, insight into the capacity of Propionibacterium avidum to cause PJI is limited. Methods. An unusual cluster of 4 hip PJIs caused by P. avidum in one orthopedic center in 2015 prompted us to retrospectively identify and analyze clinical data related to previous P. avidum PJI cases (1997-2015). We also characterized the hemolytic and biofilm-producing capacity of our 4 clinical P. avidum strains isolated in 2015, and investigated their phylogenetic relationships by whole-genome sequencing. Results. We retrospectively identified 13 P. avidum PJIs, with the majority being hip-related infections (n = 11). Preoperative synovial fluid cultures were P. avidum positive in 63.6% of cases. Six of 12 patients (50%) with available case histories were treated with an exchange of the prosthesis. In all but 1 of the 6 patients treated with debridement-retention of the prosthesis, treatment failed, thus requiring a 2-stage revision. The isolated P. avidum strains showed a more pronounced hemolytic activity, but a similar biofilm-forming ability when compared to P. acnes. Whole-genome sequencing identified 2 phylogenetic clusters highly related to P. avidum PJI strains isolated in Sweden. Conclusions. We describe the largest series of P. avidum PJI predominantly located in the hip. Phylogenetic similarity of our P. avidum strains to PJI strains isolated elsewhere suggests that these invasive lineages may be common. [ABSTRACT FROM AUTHOR]

Group A Streptococcus (GAS) has acquired an arsenal of virulence factors, promoting life-threatening invasive infections such as necrotizing fasciitis. Current therapeutic regimens for necrotizing fasciitis include surgical debridement and treatment with cell wall-active antibiotics. Addition of clindamycin (CLI) is recommended, although clinical evidence is lacking. Reflecting the current clinical dilemma, an observational study showed that only 63% of the patients with severe invasive GAS infection received CLI. This work thus aimed to address whether CLI improves necrotizing fasciitis outcome by modulating virulence factors of CLI-susceptible and CLI-resistant GAS in vitro and in vivo. Treatment with CLI reduced extracellular DNase Sda1 and streptolysin O (SLO) activity in vivo, whereas subinhibitory CLI concentrations induced expression and activity of SLO, DNase, and Streptococcus pyogenes cell envelope protease in vitro. Our in vivo results suggest that CLI should be administered as soon as possible to patients with necrotizing fasciitis, while our in vitro studies emphasize that a high dosage of CLI is essential. [ABSTRACT FROM AUTHOR]

Background: Neutrophils and monocytes are crucial for controlling bacterial infections. More-frequent bacterial infections are accordingly encountered in neutropenic patients undergoing chemotherapy. This is not the case for pegylated interferon α (IFN-α)-induced neutropenia. We hypothesized that IFN-α induces a compensatory innate antibacterial state that prevents bacterial infections despite the neutropenia.Methods: To investigate whether patients with hepatitis C virus infection treated with IFN-α killed group A Streptococcus (GAS) better than before initiating therapy, whole blood was used to perform ex vivo GAS killing assays before, during, and after IFN-α therapy.Results: We found that IFN-α therapy enhanced GAS killing in whole blood ex vivo despite the decreased neutrophil and monocyte numbers during IFN-α therapy. IFN-α also boosted neutrophil- and monocyte-mediated GAS killing in vitro. Underlying mechanisms included increased production of the antibacterial properdin, a regulator of the complement activation, as well as reactive oxygen species.Conclusions: These findings help to explain the rather discrepant facts of neutropenia but preserved antibacterial immune defenses in patients treated with IFN-α. [ABSTRACT FROM AUTHOR]

Background: Staphylococcus aureus-infected patients treated with antibiotics that are effective in vitro often experience relapse of infection because the bacteria hide in privileged locations. These locations include abscesses and host cells, which contain low-pH compartments and are sites from which nonstable S. aureus small-colony variants (SCVs) are frequently recovered.Methods: We assessed the effect of low pH on S. aureus colony phenotype and bacterial growth, using in vitro and in vivo models of long-term infection.Results: We showed that low pH induced nonstable SCVs and nonreplicating persisters that are capable of regrowth. Within host cells, S. aureus was located in phagolysosomes, a low-pH compartment. Therapeutic neutralization of phagolysosomal pH with ammonium chloride, bafilomycin A1, or the antimalaria drug chloroquine reduced SCVs in infected host cells. In a systemic mouse infection model, treatment with chloroquine also reduced SCVs.Conclusions: Our results show that the acidic environment favors formation of nonstable SCVs, which reflect the SCVs found in clinics. They also provide evidence that treatment with alkalinizing agents, together with antibiotics, may provide a novel translational strategy for eradicating persisting intracellular reservoirs of staphylococci. This approach may also be extended to other intracellular bacteria. [ABSTRACT FROM AUTHOR]

Neutrophil extracellular trap (NET) formation is described as a tool of the innate host defence to fight against invading pathogens. Fibre-like DNA structures associated with proteins such as histones, cell-specific enzymes and antimicrobial peptides are released, thereby entrapping invading pathogens. It has been reported that several bacteria are able to degrade NETs by nucleases and thus evade the NET-mediated entrapment. Here we studied the ability of three different Yersinia serotypes to induce and degrade NETs.We found that the common Yersinia enterocolitica serotypes O:3, O:8 and O:9 were able to induce NETs in human blood-derived neutrophils during the first hour of co-incubation. At later time points, the NET amount was reduced, suggesting that degradation of NETs has occurred. This was confirmed by NET degradation assays with phorbol-myristate-acetate-pre-stimulated neutrophils. In addition, we found that the Yersinia supernatants were able to degrade purified plasmid DNA. The absence of Ca2+ and Mg2+ ions, but not that of a protease inhibitor cocktail, completely abolished NET degradation. We therefore postulate that Y. enterocolitica produces Ca2+/Mg2+-dependent NET-degrading nucleases as shown for some Gram-positive pathogens. [ABSTRACT FROM AUTHOR]

The Gram-positive human pathogen Staphylococcus aureus causes a variety of human diseases such as skin infections, pneumonia, and endocarditis. The micrococcal nuclease Nuc1 is one of the major S. aureus virulence factors and allows the bacterium to avoid neutrophil extracellular trap (NET)-mediated killing. We found that addition of the protein synthesis inhibitor clindamycin to S. aureus LAC cultures decreased nuc1 transcription and subsequently blunted nuclease activity in a molecular beacon-based fluorescence assay. We also observed reduced NET degradation through Nuc1 inhibition translating into increased NET-mediated clearance. Similarly, pooled human immunoglobulin specifically inhibited nuclease activity in a concentration-dependent manner. Inhibition of nuclease activity by clindamycin and immunoglobulin enhanced S. aureus clearance and should be considered in the treatment of S. aureus infections. [ABSTRACT FROM AUTHOR]

Epstein-Barr virus (EBV) infects >90% of the human population within the first 2 decades of life and establishes reversible latent infection in B cells. The stimuli that lead to switching from latent to lytic EBV infection in vivo are still elusive. Group A streptococci (GAS) are a common cause of bacterial pharyngotonsillitis in children and adolescents and colonize the tonsils and pharynx of up to 20% of healthy children. Thus, concomitant presence of EBV and GAS in the same individual is frequent. Here, we show that EBV carriers who are colonized with GAS shed EBV particles in higher numbers in their saliva, compared with EBV carriers not colonized with GAS. Messenger RNA levels of the master lytic regulatory EBV gene BZLF1 were more frequently detected in tonsils from EBV carriers colonized with GAS than from EBV carriers not colonized. Heat-killed GAS, potentially mimicking GAS colonization, elicited lytic EBV in latently infected lymphoblastoid cell lines (LCLs) partially via Toll-like receptor 2 triggering, as did purified GAS peptidoglycan. Thus, colonization by GAS might benefit EBV by increasing the EBV load in saliva and thereby enhancing the likelihood of EBV spread to other hosts. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factor (HIF)-1α is activated on exposure to bacterial pathogens and regulates the innate immune functions of phagocytes. We show here that the HIF-1α agonist mimosine can boost the capacity of human phagocytes and whole blood to kill the leading pathogen Staphylococcus aureus in a dose-dependent fashion and reduce the lesion size in a murine model of S. aureus skin infection. This provides the first proof of principle for a novel approach to the treatment of bacterial infection by pharmacologically augmenting the host phagocytic cell function. [ABSTRACT FROM AUTHOR]

Background. Data on the incidence of hepatitis C virus (HCV) infection among human immunodeficiency virus (HIV)-infected persons are sparse. It is controversial whether and how frequently HCV is transmitted by unprotected sexual intercourse. Methods. We assessed the HCV seroprevalence and incidence of HCV infection in the Swiss HIV Cohort Study between 1988 and 2004. We investigated the association of HCV seroconversion with mode of HIV acquisition, sex, injection drug use (IDU), and constancy of condom use. Data on condom use or unsafe sexual behavior were prospectively collected between 2000 and 2004. Results. The overall seroprevalence of HCV infection was 33% among a total of 7899 eligible participants and 90% among persons reporting IDU. We observed 104 HCV seroconversions among 3327 participants during a total follow-up time of 16,305 person-years, corresponding to an incidence of 0.64 cases per 100 person-years. The incidence among participants with a history of IDU was 7.4 cases per 100 person-years, compared with 0.23 cases per 100 person-years in patients without such a history (P< .001). In men who had sex with men (MSM) without a history of IDU who reported unsafe sex, the incidence was 0.7 cases per 100 person-years, compared with 0.2 cases per 100 person-years in those not reporting unsafe sex (P = .02), corresponding to an incidence rate ratio of 3.5 (95% confidence interval, 1.2-10.0). The hazard of acquiring HCV infection was elevated among younger participants who were MSM. Conclusions. HCV infection incidence in the Swiss HIV Cohort Study was mainly associated with IDU. In HIV-infected MSM, HCV infection was associated with unsafe sex. [ABSTRACT FROM AUTHOR]

We developed quantitative fimA genotype assays and applied them in a pilot study investigating the fimbrial genotype distribution of Porphyromonas gingivalis in European subjects with or without chronic periodontitis. P. gingivalis was found in 71% and 9% of the samples from patients and healthy subjects, respectively. Enumeration of total P. gingivalis cell numbers by polymerase chain reaction and immunofluorescence showed excellent correspondence (r=0.964). 73% of positive samples contained multiple fimA genotypes, but generally one genotype predominated by one to three orders of magnitude. Genotype II predominated in 60% of the samples. Genotype IV occurred with similar prevalence (73%) as genotype II but predominated in only 20% of the samples. Genotypes I, III and V were of much lower prevalence and cell densities of the latter two remained sparse. Our results suggest marked differences among the fimA genotypes’ ability to colonize host sites with high cell numbers. [Copyright &y& Elsevier]