Targeting Hidden Pathogens: Cell-Penetrating Enzybiotics Eradicate Intracellular Drug-Resistant Staphylococcus aureus

Staphylococcus aureus is a major concern in human health care, mostly due to the increasing prevalence of antibiotic resistance. Intracellular localization of S. aureus plays a key role in recurrent infections by protecting the pathogens from antibiotics and immune responses. Peptidoglycan hydrolases (PGHs) are highly specific bactericidal enzymes active against both drug-sensitive and -resistant bacteria. However, PGHs able to effectively target intracellular S. aureus are not yet available. To overcome this limitation, we first screened 322 recombineered PGHs for staphylolytic activity under conditions found inside eukaryotic intracellular compartments. The most active constructs were modified by fusion to different cell-penetrating peptides (CPPs), resulting in increased uptake and enhanced intracellular killing (reduction by up to 4.5 log units) of various S. aureus strains (including methicillin-resistant S. aureus [MRSA]) in different tissue culture infection models. The combined application of synergistic PGH-CPP constructs further enhanced their intracellular efficacy. Finally, synergistically active PGH-CPP cocktails reduced the total S. aureus by more than 2.2 log units in a murine abscess model after peripheral injection. Significantly more intracellular bacteria were killed by the PGH-CPPs than by the PGHs alone. Collectively, our findings show that CPP-fused PGHs are effective novel protein therapeutics against both intracellular and drug-resistant S. aureusIMPORTANCE The increasing prevalence of antibiotic-resistant bacteria is one of the most urgent problems of our time. Staphylococcus aureus is an important human pathogen that has acquired several mechanisms to evade antibiotic treatment. In addition, S. aureus is able to invade and persist within human cells, hiding from the immune response and antibiotic therapies. For these reasons, novel antibacterial strategies against these pathogens are needed. Here, we developed lytic enzymes which are able to effectively target drug-resistant and intracellular S. aureus Fusion of these so-called enzybiotics to cell-penetrating peptides enhanced their uptake and intracellular bactericidal activity in cell culture and in an abscess mouse model. Our results suggest that cell-penetrating enzybiotics are a promising new class of therapeutics against staphylococcal infections.

Propionibacterium avidum: A Virulent Pathogen Causing Hip Periprosthetic Joint Infection

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.

Immunoglobulin Attenuates Streptokinase-Mediated Virulence in Streptococcus dysgalactiae Subspecies equisimilis Necrotizing Fasciitis

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 withStreptococcus dysgalactiae subspeciesequisimilis (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.

Synovial C-reactive protein features high negative predictive value but is not useful as a single diagnostic parameter in suspected periprosthetic joint infection (PJI)

OBJECTIVES

Synovial fluid C-reactive protein (syCRP) has been recently described as a new biomarker in preoperative diagnostics to identify periprosthetic joint infections (PJI). The aim of this study was to evaluate syCRP in a large cohort of patients with suspected PJI and to calculate the optimal cut-off to diagnose PJI.

METHODS

Between September 2015 and June 2017, we prospectively included patients with suspected PJI, in which syCRP was additionally measured along with routine preoperative diagnostic serum and synovial biomarkers. We analysed the sensitivity and specificity of syCRP using receiver operating characteristic curves.

RESULTS

We included 192 cases (hip n = 80, knee n = 91, shoulder n = 21) with a final diagnosis of PJI in 26 cases (14.0%). Combined for all joints, the syCRP values were significantly higher in the PJI group than in the no PJI group (median: 13.8 vs. 0 mg/l; p < 0.001). The optimal cut-off (Youden Index: 0.71) for the PJI diagnosis combined for all joints was at a syCRP value of 2.9 mg/l with a sensitivity of 88%, a specificity of 82%, and a negative predictive value of 98%.

CONCLUSIONS

SyCRP features high negative predictive value but is not useful as a single diagnostic parameter in suspected periprosthetic joint infection (PJI).

In-host evolution of Staphylococcus epidermidis in a pacemaker-associated endocarditis resulting in increased antibiotic tolerance

Treatment failure in biofilm-associated bacterial infections is an important healthcare issue. In vitro studies and mouse models suggest that bacteria enter a slow-growing/non-growing state that results in transient tolerance to antibiotics in the absence of a specific resistance mechanism. However, little clinical confirmation of antibiotic tolerant bacteria in patients exists. In this study we investigate a Staphylococcus epidermidis pacemaker-associated endocarditis, in a patient who developed a break-through bacteremia despite taking antibiotics to which the S. epidermidis isolate is fully susceptible in vitro. Characterization of the clinical S. epidermidis isolates reveals in-host evolution over the 16-week infection period, resulting in increased antibiotic tolerance of the entire population due to a prolonged lag time until growth resumption and a reduced growth rate. Furthermore, we observe adaptation towards an increased biofilm formation capacity and genetic diversification of the S. epidermidis isolates within the patient.

Antibiotics Stimulate Formation of Vesicles in Staphylococcus aureus in both Phage-Dependent and -Independent Fashions and via Different Routes

Bacterial membrane vesicle research has so far focused mainly on Gram-negative bacteria. Only recently have Gram-positive bacteria been demonstrated to produce and release extracellular membrane vesicles (MVs) that contribute to bacterial virulence. Although treatment of bacteria with antibiotics is a well-established trigger of bacterial MV formation, the underlying mechanisms are poorly understood. In this study, we show that antibiotics can induce MVs through different routes in the important human pathogen Staphylococcus aureus DNA-damaging agents and antibiotics inducing the SOS response triggered vesicle formation in lysogenic strains of S. aureus but not in their phage-devoid counterparts. The β-lactam antibiotics flucloxacillin and ceftaroline increased vesicle formation in a prophage-independent manner by weakening the peptidoglycan layer. We present evidence that the amount of DNA associated with MVs formed by phage lysis is greater than that for MVs formed by β-lactam antibiotic-induced blebbing. The purified MVs derived from S. aureus protected the bacteria from challenge with daptomycin, a membrane-targeting antibiotic, both in vitro and ex vivo in whole blood. In addition, the MVs protected S. aureus from killing in whole blood, indicating that antibiotic-induced MVs function as a decoy and thereby contribute to the survival of the bacterium.

Improved Biodistribution and Extended Serum Half-Life of a Bacteriophage Endolysin by Albumin Binding Domain Fusion

The increasing number of multidrug-resistant bacteria intensifies the need to develop new antimicrobial agents. Endolysins are bacteriophage-derived enzymes that degrade the bacterial cell wall and hold promise as a new class of highly specific and versatile antimicrobials. One major limitation to the therapeutic use of endolysins is their often short serum circulation half-life, mostly due to kidney excretion and lysosomal degradation. One strategy to increase the half-life of protein drugs is fusion to the albumin-binding domain (ABD). By high-affinity binding to serum albumin, ABD creates a complex with large hydrodynamic volume, reducing kidney excretion and lysosomal degradation. The aim of this study was to investigate the in vitro antibacterial activity and in vivo biodistribution and half-life of an engineered variant of the Staphylococcus aureus phage endolysin LysK. The ABD sequence was introduced at different positions within the enzyme, and lytic activity of each variant was determined in vitro and ex vivo in human serum. Half-life and biodistribution were assessed in vivo by intravenous injection of europium-labeled proteins into C57BL/6 wild-type mice. Our data demonstrates that fusion of the endolysin to ABD improves its serum circulation half-life and reduces its deposition in the kidneys in vivo. The most active construct reduced S. aureus counts in human serum ex vivo by 3 logs within 60 min. We conclude that ABD fusions provide an effective strategy to extend the half-life of antibacterial enzymes, supporting their therapeutic potential for treatment of systemic bacterial infections.

Prolonged bacterial lag time results in small colony variants that represent a sub-population of persisters

Persisters are a subpopulation of bacteria that are not killed by antibiotics even though they lack genetic resistance. Here we provide evidence that persisters can manifest as small colony variants (SCVs) in clinical infections. We analyze growth kinetics of Staphylococcus aureus sampled from in vivo conditions and in vitro stress conditions that mimic growth in host compartments. We report that SCVs arise as a result of a long lag time, and that this phenotype emerges de novo during the growth phase in various stress conditions including abscesses and acidic media. We further observe that long lag time correlates with antibiotic usage. These observations suggest that treatment strategies should be carefully tailored to address bacterial persisters in clinics.

Persisters are bacterial subpopulations that are not killed by antibiotics even though they lack genetic resistance. Here, the authors show that persisters can manifest as small colony variants in clinical infections, and arise as a result of a long lag time in stress conditions including antibiotic exposure.

Increased Pathogen Identification in Vascular Graft Infections by the Combined Use of Tissue Cultures and 16S rRNA Gene Polymerase Chain Reaction

Background: Vascular graft infections (VGI) are difficult to diagnose and treat, and despite redo surgery combined with antimicrobial treatment, outcomes are often poor. VGI diagnosis is based on a combination of clinical, radiological, laboratory and microbiological criteria. However, as many of the VGI patients are already under antimicrobial treatment at the time of redo surgery, microbiological identification is often difficult and bacterial cultures often remain negative rendering targeted treatment impossible. We aimed to assess the benefit of 16S rRNA gene polymerase chain reaction (broad-range PCR) for better microbiological identification in patients with VGI.

Methods: We prospectively analyzed the clinical, microbiological, and treatment data of patients enrolled in the observational Vascular Graft Cohort Study (VASGRA), University Hospital Zurich, Switzerland. The routine diagnostic work-up involved microbiological cultures of minced tissue samples, and the use of molecular techniques in parallel. Patient-related and microbiological data were assessed in descriptive analyses, and we calculated sensitivity, specificity, negative and positive predictive value for broad-range 16S rRNA gene PCR versus culture (considered as gold standard).

Results: We investigated 60 patients (median age 66 years (Interquartile range [IQR] 59–75)) with confirmed VGI between May 2013 and July 2017. The prevalence of antimicrobial pretreatment at the time of sampling was high [91%; median days of antibiotics 7 days (IQR 1–18)]. We investigated 226 microbiological specimens. Thereof, 176 (78%) were culture-negative and 50 (22%) were culture-positive. There was a concordance of 70% (158/226) between conventional culture and broad-range PCR (sensitivity 58% (95% CI 43–72); specificity 74% (67–80%)). Among the group of 176 culture-negative specimens, 46 specimens were broad-range PCR-positive resulting in identification of overall 69 species. Among the culture and/or broad-range PCR-positive specimens (n = 96), 74 (77%) were monomicrobial and 22 (23%) polymicrobial, whereas the rate of polymicrobial samples was higher in broad-range PCR-positive specimens (93%).

Conclusions: Combined cultures and broad-range 16S rRNA gene PCR from periprosthetic tissue and/or explanted vascular grafts increased the diagnostic accuracy in VGI, particularly in patients already under antimicrobial treatment at the time of redo surgery. Ideally, antimicrobial treatment should be withheld until surgical sampling in order to optimize microbiological diagnostics.Clinical trials.gov identifier: NCT01821664

Human Streptococcal Necrotizing Fasciitis Histopathology Mirrored in a Murine Model

Streptococcal necrotizing fasciitis (NF) causes high morbidity and mortality despite state-of-the-art therapy. Low incidence and rapid disease progression, necessitating immediate initiation of therapy, have proven challenging aspects for setting up prospective randomized trials. This has resulted in little therapeutic progress over the past decade. The validation of reliable murine NF models to study both pathogenesis and optimized therapeutic regimens of streptococcal NF are thus essential. In this study, we characterized a murine NF model and compared the pathology with an in-depth tissue analysis of streptococcal NF in patients. We found that the streptococcal murine NF model closely reflected all histologic characteristics encountered in human streptococcal NF. This murine NF model helps understanding of human NF pathology better in a time-dependent manner and will allow studying novel therapeutic options in the future.

The ArlRS two-component system is a regulator of Staphylococcus aureus-induced endothelial cell damage

Staphylococcus aureus endovascular infections retain a high morbidity and mortality despite antibiotics and supportive care. The destruction of endothelial cells (ECs) is a critical step in the pathogenesis of S. aureus endovascular infections. In order to better understand S. aureus-induced EC damage, we systematically screened a collection of two-component regulatory system mutants of methicillin-resistant S. aureus (MRSA) USA300 strain JE2 for damage induction in human umbilical vein ECs (HUVECs). This screen revealed that the two-component regulatory system ArlRS is required for maximum damage: arlRS inactivation leads to a > 70% reduction in damage. In a different genetic S. aureus background (RN6390, MSSA strain) arlRS inactivation had a smaller but also significant effect on EC damage. In both strains, the reduction in EC damage was accompanied by a significant reduction in internalization. In conclusion, we determined a novel role of ArlRS in S. aureus-induced EC damage, which will help to better understand the pathogenesis of S. aureus endovascular infection.

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Zusammenfassung. Wir präsentieren den Fall eines 49-jährigen Patienten mit linksseitiger Carotidynie. Als Ursache fand sich eine Lymphknotentuberkulose. Unter tuberkulostatischer Therapie zeigte sich eine rasche Besserung der Symptome.

Impact of oral gut decontamination on Staphylococcus aureus colonisation in patients undergoing allogeneic haematopoietic stem cell transplantation

Recipients of allogeneic haematopoietic stem cell transplantation (allo-HSCT) are severely immunocompromised and are at increased risk of infection. In this prospective, observational, single-centre study including 110 allo-HSCT recipients, the rate of Staphylococcus aureus colonisation was reduced from 11.8% to 0% (P <0.001) following peritransplant oral gut decontamination. No invasive S. aureus infections were observed.

Clindamycin Affects Group A Streptococcus Virulence Factors and Improves Clinical Outcome

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.

Cutaneous Corynebacterium Infection Presenting with Disseminated Skin Nodules and Ulceration

In the context of the European migrant crisis, more and more cases of cutaneous diphtheria are seen. A typical presentation includes painful cutaneous ulcerations with grayish-whitish pseudomembranes. Here we present 2 male Eritrean patients suffering from cutaneous nontoxigenic Corynebacterium diphtheriae (patient 1) and Corynebacterium striatum (patient 2) infection.

Chloroquine enhances the antimycobacterial activity of isoniazid and pyrazinamide by reversing inflammation-induced macrophage efflux

Mycobacterium tuberculosis (MTB) is notorious for persisting within host macrophages. Efflux pumps decrease intracellular drug levels, thus fostering persistence of MTB during therapy. Isoniazid (INH) and pyrazinamide (PZA) are substrates of the efflux pump breast cancer resistance protein-1 (BCRP-1), which is inhibited by chloroquine (CQ). In this study, BCRP-1 was found to be expressed on macrophages of human origin and on foamy giant cells at the site of MTB infection. In the current in vitro study, interferon-gamma (IFNγ) increased the expression of BCRP-1 in macrophages derived from the human monocytic leukaemia cell line THP-1. Using a BCRP-1-specific fluorescent dye and radioactively labelled INH, it was demonstrated that efflux from macrophages increased upon activation with IFNγ. CQ was able to inhibit active efflux and augmented the intracellular concentrations both of INH and the dye. In agreement, CQ and specific inhibition of BCRP-1 increased the antimycobacterial activity of INH against intracellular MTB. Although PZA behaved differently, CQ had comparable advantageous effects on the intracellular pharmacokinetics and activity of PZA. The adjunctive effects of CQ on intracellular killing of MTB were measurable at concentrations achievable in humans at approved therapeutic doses. Therefore, CQ, a widely used and worldwide available drug, may potentiate the efficacy of standard MTB therapy against bacteria in the intracellular compartment.

High level methicillin resistance correlates with reduced Staphylococcus aureus endothelial cell damage

There has been controversy about the intrinsic virulence of methicillin-resistant Staphylococcus aureus (MRSA) as compared to methicillin-susceptible S. aureus (MSSA). To address this discrepancy, the intrinsic virulence of 42 MRSA and 40 MSSA clinical isolates was assessed by testing endothelial cell (EC) damage, a surrogate marker for virulence in blood stream infections. Since these clinical isolates represent a heterogeneous group, well characterized S. aureus laboratory strains with SCCmec loss- and gain-of-function mutations were used in addition. The clinical MRSA isolates carrying typical hospital acquired SCCmec types (I, II or III) induced significantly less damage (47.8%) as compared to isolates with other SCCmec types (62.3%, p=0.03) and MSSA isolates (64.2%, p<0.01). There was a strong inverse correlation between high-level oxacillin resistance and low EC damage induction (R²=0.4464, p<0.001). High-level oxacillin resistant strains (MIC >32μ/ml) grew significantly slower as compared to isolates with low-level resistance (p=0.047). The level of EC damage positively correlated with α- and δ-toxin production (p<0.0001 and p<0.05, respectively) but not with β-toxin production. Invasive MRSA isolates (n=21, 56.3%) were significantly less cytotoxic as compared to invasive MSSA isolates (n=20, 68.0%, p<0.05). There was no difference between EC damage induced by superficial versus invasive isolates in either MRSA or MSSA strains. Our data suggest that the intrinsic virulence of MRSA is similar or even reduced as compared to MSSA strains but is linked to the level of methicillin resistance.

Interferon α-Enhanced Clearance of Group A Streptococcus Despite Neutropenia

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.

Yersinia enterocolitica-mediated degradation of neutrophil extracellular traps (NETs)

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 Ca(2+) and Mg(2+) ions, but not that of a protease inhibitor cocktail, completely abolished NET degradation. We therefore postulate that Y. enterocolitica produces Ca(2+)/Mg(2+)-dependent NET-degrading nucleases as shown for some Gram-positive pathogens.

Protein adsorption steers blood contact activation on engineered cobalt chromium alloy oxide layers

Biomaterials upon implantation are immediately covered by blood proteins which direct the subsequent blood activation. These early events determine the following cascade of biological reactions and consequently the long-term success of implants. The ability to modulate surface properties of biomaterials is therefore of considerable clinical significance. Goal of this study was an in-depth understanding of the biological response to cobalt chromium stent alloys with engineered surface oxide layers, which showed altered body reactions in vivo. We analyzed in vitro the biological events following initial blood contact on engineered cobalt chromium surfaces featuring said oxide layers. Surface-specific blood reactions were confirmed by scanning electron microscopy and the adsorbed protein layers were characterized by mass spectrometry. This powerful proteomics tool allowed the identification and quantification of over hundred surface-adhering proteins. Proteins associated with the coagulation cascade, platelet adhesion and neutrophil function correlated with the various blood surface activations observed. Furthermore, results of pre-coated surfaces with defined fibrinogen-albumin mixtures suggest that neutrophil adhesion was controlled by fibrinogen orientation and conformation rather than quantity. This study highlights the importance of controlling the biological response in the complex protein-implant surface interactions and the potential of the surface modifications to improve the clinical performance of medical implants.

STATEMENT OF SIGNIFICANCE

The blood contact activation of CoCr alloys is determined by their surface oxide layer properties. Modifications of the oxide layer affected the total amount of adsorbed proteins and the composition of the adsorbed protein layer. Additionally fibrinogen coatings mediated the surface-dependent neutrophil adhesion in a concentration-independent manner, indicating the influence of conformation and/or orientation of the adsorbed protein. Despite the complexity of protein-implant interactions, this study highlights the importance of understanding and controlling mechanisms of protein adhesion in order to improve and steer the performance of medical implants. It shows that modification of the surface oxide layer is a very attractive strategy to directly functionalize metallic implant surfaces and optimize their blood interaction for the desired orthopedic or cardiovascular applications.