Bilobetin attenuates Staphylococcus aureus virulence by targeting Von Willebrand factor-binding protein and staphylocoagulase

Staphylococcus aureus (S. aureus) induces a variety of infectious diseases in humans and animals and is responsible for hospital- and community-acquired infections. The aim of this study was to investigate how bilobetin, a natural compound, attenuates S. aureus virulence by inhibiting two key virulence factors, von Willebrand factor-binding protein (vWbp) and staphylocoagulase (Coa). The results showed that bilobetin inhibited Coa- or vWbp-induced coagulation without affecting S. aureus proliferation. The Western blotting and fluorescence quenching assays indicated that bilobetin did not affect the expression of vWbp and Coa but directly bound to the proteins with KA values of 1.66 × 104 L/mol and 1.04 × 104 L/mol, respectively. To gain further insight into the mechanism of interaction of bilobetin with these virulence factors, we performed molecular docking and point mutation assays, which indicated that the TYR-6 and TYR-18 residues on vWbp and the ALA-190 and ASP-189 residues on Coa were essential for the binding of bilobetin. In addition, the in vivo studies showed that bilobetin ameliorated lung tissue damage and inflammation caused by S. aureus, thereby improving the survival of mice. Furthermore, the use of bilobetin as an adjuvant in combination with vancomycin was more effective in the treatment of a mouse model of pneumonia. Taken together, bilobetin had a dual inhibitory effect on vWbp and Coa by reducing the virulence of S. aureus, suggesting that it is a viable lead compound against S. aureus infections.

Recovery and virulence factors of sublethally injured Staphylococcus aureus after ohmic heating

Ohmic heating (OH) is an alternative thermal processing technique, which is widely used to pasteurize or sterilize food. However, sublethally injured Staphylococcus aureus induced by OH is a great concern to food safety. The recovery of injured S. aureus by OH and virulence factor changes during recovery were investigated in this study. The liquid media (phosphate-buffered saline, buffered peptone water and nutrient broth (NB)), temperature (4, 25 and 37 °C) and pH (6.0, 7.2 and 8.0) influenced the recovery rate and the injured cells completely repaired in NB at 37 °C, pH 7.2 with the shortest time of 2 h. The biofilm formation ability, mannitol fermentation, hemolysis, and coagulase activities decreased in injured S. aureus and recovered during repair process. Quantitative real-time PCR showed the expression of sek, clfB and lukH involved in virulence factors increased during recovery. The results indicated that the virulence factors of injured S. aureus recovered after repair.

A rare case of a novel coagulase negative Staphylococcus native valve endocarditis in a 28-year-old male

Coagulase negative staphylococci (CoNS) are an emerging cause of native valve endocarditis in community and healthcare settings. We describe a case of a 28-year-old man with no significant risk factors who presented with Staphylococcus pettenkoferi native valve endocarditis. During our patient’s initial hospitalization, he was treated for CoNS bacteraemia and subsequently discharged after a protracted hospital course with a transthoracic echocardiogram (TTE) showing no valvular vegetations. However, during the course of his second hospitalization, speciation identified S. pettenkoferi and transoesophageal echocardiogram (TEE) showed aortic valve perforations with new regurgitation raising concern for left sided endocarditis. We postulate that our patient may have been infected with the same CoNS species causing aortic valve endocarditis during his initial hospitalization. This case highlights the importance of recognizing CoNS as a possible causative bacterium in NVE, as well as the importance of obtaining a TEE when evaluating a patient for suspected endocarditis.

Aortic Root Replacement for Destructive Endocarditis - Clinic and Microbiology

INTRODUCTION

Destructive aortic root endocarditis is associated with high mortality rates. The objective of this article was to characterize the clinical and microbiological profiles of these patients, especially concerning an already implanted aortic valve prosthesis. We also focused on prognostic factors.

METHODS

Eighty patients underwent aortic root replacement due to destructive endocarditis from 1999 to 2018 in our institution. We analyzed their pre, intra, and postoperative data, outcomes, and predictors of mortality.

RESULTS

Thirty-one patients had native valve endocarditis (NVE), eight patients had early-onset prosthetic valve endocarditis (PVE), and 41 patients had late-onset PVE. Streptococcus was found in 19.4% of NVE cases and no PVE case. Coagulase-negative Staphylococcus was responsible for 62.5% of the cases of earlyonset PVE. Thirty-four (42.5%) patients had received inappropriate antibiotics before admission. No microorganism was associated with higher risk of mortality. Aortoventricular dehiscence was identified as an independent risk factor of mortality along with PVE, concomitant bypass surgery, and delayed diagnosis. The incidence of postoperative complications was similar in all three groups. Rates of long-term survival (P=0.044) and freedom from the composite endpoint (P=0.024) defined as death, stroke, aortic valve reinfection, and aortic valve reoperation were the lowest within the NVE group and the highest among the PVE patients.

CONCLUSION

In endocarditis, prolonged diagnostics, inadequate antimicrobial treatment, and late surgery led to destructive local complications and worsened the prognosis. PVE is associated with higher mortality than NVE.

Unique fibrinogen-binding motifs in the nucleocapsid phosphoprotein of SARS CoV-2: Potential implications in host-pathogen interactions

Novel Coronavirus (SARS CoV-2), the etiological agent for the highly contagious Corona virus disease-2019 (COVID-19) pandemic has threatened global health and economy infecting around 5.8 million people and causing over 359,200 deaths (as of 28th May 2020, https://www.worldometers.info/coronavirus/). The clinical manifestations of infected patients generally range from asymptomatic or mild to severe illness, or even death. The ability of the virus to evade the host immune response have been major reasons for high morbidity and mortality. One of the important clinical observations under conditions of critical illness show increased risk of developing disseminated intravascular coagulation. Molecular mechanisms of how SARS CoV-2 induces such conditions still remain unclear. This report describes the presence of two unique motifs in the SARS CoV-2 nucleocapsid phosphoprotein (N-protein) that can potentially interact with fibrinogen and possibly prothrombin. This is based on an established function of secretory proteins in Staphylococcus aureus (S. aureus)-coagulase, Efb (Extracellular fibrinogen binding) and vWBP (von Willebrand factor Binding Protein), which are known to regulate the blood clotting cascade and the functions of host immune response. It is hypothesized that having protein interaction motifs that are homologous to these S. aureus proteins, the N-protein of this virus can mimic their functions, which may in turn play a crucial role in formation of blood clots in the host and help the virus evade host immune response. However, this hypothesis needs to be tested in vitro. Considering the overwhelming increase in the incidence of SARS CoV-2 infection globally, this information may be useful for further investigation and could help in deducing new therapeutic strategies to combat advanced stages of this disease.

Targeting the R domain of coagulase by active vaccination protects mice against lethal Staphylococcus aureus infection

Coagulase (Coa) secreted by Staphylococcus aureus is associated with the establishment of staphylococcal disease, which activates host prothrombin and generates fibrin shields. The R domain of Coa, consisting of several conserved repeats, is important in immune evasion during S. aureus infection. However, previous research showed that the Coa R domain induced very weak specific antibody responses. In this study, we constructed a new R domain, CoaR6, consisting of 6 repeats that occur most frequently in clinical isolates. By fusing CoaR6 with Hc, the C-terminal fragment of the heavy chain of tetanus neurotoxin, we successfully increased anti-CoaR6 IgG levels in immunized mice which were hardly detected in mice immunized with CoaR6 plus alum. To further improve anti-CoaR6 responses, the combination adjuvants alum plus CpG were formulated with the antigen and exhibited a significantly higher specific antibody response. Moreover, active Th1/Th17 immune responses were observed in Hc-CoaR6 immunized group rather than CoaR6. Active immunization of Hc-CoaR6 with alum plus CpG showed protective effects in a peritonitis model induced by two S. aureus strains with different coagulase types. Our results provided strategies to improve the immunogenicity of R domain and supporting evidences for R domain to be an S. aureus vaccine candidate.

aureus from Ahvaz, Iran

BACKGROUND

Staphylococcus aureus is one of the important causes of clinical infections that can be more destructive by its antibiotic resistant strains.

OBJECTIVE

This study aimed to determine the antibiotic susceptibility pattern and distribution of mecA and coa genes in clinical isolates of S. aureus.

METHODS

Two hundred seventy-three specimens suspected to S. aureus were taken from hospitals of Ahvaz, southwest of Iran. Isolates were identified by standard microbiologic tests and confirmed by the molecular method. Antimicrobial susceptibility testing was carried out by disk diffusion method. The presence of mecA and coa genes was determined by PCR method.

RESULTS

Of a total of 200 isolates which were tested for coagulase tube test, 143 (71.5%) showed coagulase positive, and 57 (28.5%) showed a coagulase-negative reaction. Antibacterial susceptibility pattern of 200 S. aureus isolates showed the highest and lowest susceptibility rate to linezolid (98%) and ciprofloxacin (42%), respectively. The prevalence of methicillin-resistant S. aureus (MRSA) by detection of mecA gene was estimated as 47.5 % (95/200), of which the rate of MRSA in coagulase positive and negative isolates was 35% (50/143), and 65% (45/57), respectively. Meanwhile, coa gene was detected in 100% of coagulase positive and 28.1% of coagulasenegative isolates.

CONCLUSION

The results of this study showed that the number of atypical CNSA in our area is high. Since the coagulase test is an essential test for diagnosis of S. aureus, our findings regarding the emergence of CNSA are a warning about the misdiagnosis and selection of appropriate treatment approach for S. aureus isolates.

Exoenzyme activity and possibility identification of Candida dubliniensis among Candida albicans species isolated from vaginal candidiasis

OBJECTIVES

Vulvovaginal candidiasis (VVC) or vaginal candidiasis is a common fungal infection of the genitals causing inflammation, irritation, itching, and vaginal discharge. Common yeast infections are caused by the yeast species C. albicans. However, there are other species of Candida such as C. dubliniensis which are considered as the causative agents of this infection. Hydrolytic enzymes such as proteinase and coagulase are known as virulence factors. The aim of this study was the molecular confirmation and differentiation of C. dubliniensis among C. albicans strains isolated from women with vulvovaginal candidiasis by PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) and the evaluation of proteinase and coagulase activities.

METHODS

A total of 100 C. albicans strains isolated from women with vulvovaginal candidiasis referred to Shiraz medical clinics were enrolled in the study. All the isolates were primarily identified by conventional methods. PCR-RFLP method was used for the confirmation and identification of C. albicans and C. dubliniensis. Moreover, in vitro proteinase and coagulase activities of these isolates were evaluated using bovine serum albumin media and classical rabbit plasma tube test.

RESULTS

As a result, PCR-RFLP identified 100% of the isolates as C. albicans, and no C. dubliniensis could be identified in this study. 84% of the isolates showed proteinase activity, whereas coagulase activity was only detected in 5% of the isolates.

CONCLUSIONS

This study reveals that C. dubliniensis plays no role in vaginal candidiasis in Iranian patients. Proteinase production could be an essential virulence factor in C. albicans pathogenicity, but coagulase activity has less potential in this matter.

Phenotypic Characteristics of Vancomycin-Non-Susceptible Staphylococcus aureus

Background:

Staphylococcus aureus, with reduced vancomycin susceptibility, is probably under the regulation of several genes and various express phenotypes.

Objectives:

This study aimed to investigate the phenotypic differences between vancomycin-susceptible S. aureus (VSSA), vancomycin-intermediate S. aureus (VISA), and heterogeneous VISA (hVISA) isolates.

Materials and Methods:

A total of 130 methicillin-resistant S. aureus (MRSA) isolates were studied, including 49 VSSA, 28 hVISA, and 5 VISA isolates from blood cultures and 48 isolates (two VSSA, six hVISA, and 40 VISA) derived in vitro (laboratory-induced/sub-passaged). Their phenotypes were examined using a coagulase tube test, colony spreading on soft agar, and urease activity. The SCCmec and agr typing were performed using multiplex PCR.

Results:

Most of the MRSA isolates were SCCmec III-agr I (84.5%), followed by SCCmec II-agr II (11.8%). The average plasma coagulation time of vancomycin-non-susceptible isolates was longer than that of the susceptible isolates (12 vs. 2.6 hours). Four hVISA (P = 0.023) and nine VISA (P < 0.001) isolates yielded a negative coagulase test after 24-hour incubation. The percentage of VSSA isolates showing non-spreading colonies (accessory gene regulator (agr) dysfunction) was significantly lower than in the VISA group (P = 0.013), but no significant difference was found between VSSA and hVISA. The VISA group showed higher urease activity than that of the VSSA and hVISA groups (P = 0.002).

Conclusions:

There were diverse phenotypic changes among vancomycin-non-susceptible S. aureus isolates. This may be due to the variety of related regulatory systems. The diversity of phenotypic expression may result in its misidentification in routine laboratory checks.

Prophylactic Effect of Vancomycin on Infection after Cranioplasty in Methicillin-Resistant Staphylococcus Aureus Carriers with Traumatic Brain Injury

Objective

Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase negative staphylococci (MRCNS) are major causes of neurosurgical infection. Nasal colonization of MRSA is the most important risk factor and MRSA screening can be a screening method to identify MRSA and MRCNS colonization. We retrospectively evaluated prophylactic effect of vancomycin on MRSA or MRCNS surgical site infection (SSI) after cranioplasty following decompressive craniectomy (DC) after traumatic brain injury (TBI) in MRSA carriers.

Methods

The study included 21 patients who were positive in MRSA screening before cranioplasty. These patients underwent DC after TBI and subsequent cranioplasty with autologous bone. The patients were separated into SSI group and no SSI group according to the development of SSI due to MRSA or MRCNS after cranioplasty. Mean follow-up period after cranioplasty was 23.5±22.8 months (range, 3 to 73 months). The rate of MRSA or MRCNS SSI and factors including the prophylactic preoperative antibiotics were compared between groups.

Results

The rate of MRSA or MRCNS SSI was 23.8% (5/21 patients). Mean time from cranioplasty to confirm the SSI was 19.6±10.9 days (6 to 63 days). The rate of MRSA or MRCNS SSI was significantly different from the use of preoperative prophylactic antibiotics (p=0.047). MRSA or MRCNS SSI developed in 1 of 13 patients (7.6%) who received vancomycin and in 4 of 8 patients (50%) who received 3rd generation cephalosporin.

Conclusion

Preoperative MRSA screening and administration of vancomycin as a preoperative prophylactic antibiotic should be considered in MRSA carriers who are scheduled to cranioplasty to reduce MRSA or MRCNS SSI.

Detection of Methicillin-Resistant Coagulase-Negative Staphylococci and Surveillance of Antibacterial Resistance in a Multi-Center Study from Iran

BACKGROUND

Coagulase-negative staphylococci (CNS) are a common cause of nosocomial infections. In recent years, an increase in the incidence of methicillin-resistant coagulase-negative staphylococci (MRCNS) has led to the severity of the disease.

OBJECTIVES

The aim of this study was to isolate and identify MRCNS strains by oxacillin disk agar diffusion, oxacillin agar screening, and polymerase chain reaction (PCR) and to evaluate their antibacterial resistance patterns.

PATIENTS AND METHODS

Totally, 122 CNS isolates were collected from the clinical specimens of four hospitals in Iran. Susceptibility testing was performed by disk agar diffusion against 15 antimicrobial agents. Then, disk agar diffusion, agar screening, and PCR were applied to determine susceptibility to oxacillin.

RESULTS

Out of the 122 isolates, 92 isolates were found to be MRCNS by PCR. The sensitivities and specificities of disk agar diffusion and agar screening were 89.2% and 69% and 93.8% and 96.3%, respectively. Also, 93 CNS isolates were resistant to Methicillin according to disk agar diffusion.

DISCUSSION

Our results indicated that agar screening was superior to oxacillin disk agar diffusion. A comparison between the antibiotic sensitivity patterns of the MRCNS and the Methicillin-Susceptible Coagulase-Negative Staphylococci (MSCNS) showed that the MRCNS were predominantly multiple-drug resistant isolates as the simultaneous resistance rate to 4 or more antibiotics in the MRCNS and MSCNS was 93% and 56%, respectively.

Extracellular enzymes and susceptibility to fluconazole in Candida strains isolated from patients with vaginitis and healthy individuals

BACKGROUND

Extracellular phospholipase, proteinase, and coagulase are accounted as the major virulence factors in Candida albicans. Several reports showed that the incidence of resistance to fluconazole has risen during last two decades.

OBJECTIVES

The present study has investigated the extracellular enzymes of C. albicans and non-albicans species isolated from both patients with vaginitis and healthy women. In addition, susceptibility of the isolates was evaluated against fluconazole.

PATIENTS AND METHODS

Vaginal samples were collected using sterile cotton swabs and inoculated on CHROMagar Candida. Routine morphological tests and ID 32C and API 20C AUX Kits were used to identify species. Phospholipase, proteinase, and coagulase activity were determined by standard methods. Susceptibility to fluconazole was also evaluated using ATB Fungus 3 Kits.

RESULTS

The phospholipase activity was detected in 66.7% of the tested isolates recovered from patients with vaginitis. In the present study, phospholipase activity with higher Pz values (< 0.70) was more common in patients with vaginitis (28 of 66 isolates) whereas this rate in the normal individual was 13 of 42. Proteinase activity was detected in 74.2% and 61.9% of tested isolates recovered from patients and normal individuals, respectively. All tested isolates were negative for coagulase activity. In the present study, resistance to fluconazole was found in 34.8% of isolates. C. dubliniensis was the most common isolate (6 out of 11 isolates) that showed resistance to fluconazole.

CONCLUSIONS

Our results showed that C. albicans was the most frequently isolated from both patients with vaginitis and normal individual. In the present study, we could not find any correlation between extracellular activities and sources of isolates (patients and normal flora) and sensitivity or resistance to fluconazole.

Association between the enterotoxin production and presence of Coa, Nuc genes among Staphylococcus aureus isolated from various sources, in Shiraz

The present study was aimed to identify the frequency of coagulase (Coa) and thermonuclease (Nuc) genes and Staphylococcal enterotoxin A (Sea) production among Staphylococcus aureus isolated from various sources in Shiraz. Moreover, the correlation between the Sea gene and coagulase and thermonuclease enzymes is also considered. A total of 100 S. aureus were isolated from various sources including 40 humans, 30 animals and 30 food samples by the routine biochemical tests. The frequency of Coa, Nuc and Sea genes was evaluated by PCR assay. Correlation among those genes was finally evaluated by statistical analysis. The PCR results showed that the prevalence of Coa, Nuc and Sea genes was 91%, 100% and 14%, respectively. The evaluation of the enterotoxin production indicated that 78.6% of the Sea gene was expressed. The presence of enterotoxin A was not necessarily correlated to the production of toxin. As a final conclusion to detect the enterotoxigenic strains, both genotypic and phenotypic methods are highly recommended.

Antibiotic Susceptibility and mecA Frequency in Staphylococcus epidermidis, Isolated From Intensive Care Unit Patients

Background:

Coagulase-negative staphylococci (CoNS), especially Staphylococcus epidermidis, are considered as normal flora of human epithelia and also important opportunistic pathogens for nosocomial infections. S. epidermidis can also act as a reservoir for mecA, responsible for high-level resistance to methicillin and transferring it to S. aureus.

Objectives:

The aim of this study was to determine the prevalence of S. epidermidis as well as antibiotic susceptibility pattern and mecA prevalence in S. epidermidis isolated from intensive care unit (ICU) patients.

Materials and Methods:

A cross-sectional study was conducted from September 2010 to September 2011 and 184 coagulase-negative staphylococci were collected from different clinical samples in three hospitals. S. epidermidis was identified by conventional bacteriological tests. Antibiotic susceptibility testing was performed using disk diffusion method. Frequency of mecA was detected by specific PCR.

Results:

Frequency of S. epidermidis was 34.8%, the most susceptibility was seen to linezolid and vancomycin, and the least susceptibility was seen to tetracycline.Majority of the S. epidermidis isolates carried mecA (92.2%). The most common resistant pattern was trimethoprim-sulfamethoxazole, tetracycline, erythromycin, and methicillin resistance, found in 23.4% of the isolates, followed by resistance to methicillin as the second-most common resistant pattern, observed in 20.3% of the isolates.

Conclusions:

Frequency of S. epidermidis was significantly lower, compared to other studies. Presence rate of mecA and susceptibility to linezolid and vancomycin did not show significant differences with other investigations, while resistant to trimethoprim-sulfamethoxazole was significantly lower compared to other investigations, and resistance to tetracycline was significantly higher in comparison to other investigations. Presence of methicillin-resistant S. epidermidis in ICU patients, especially in individuals with compromised immune systems, may cause infection and would be more complicated in the case of antibiotic resistance.

Multiple ligands of von Willebrand factor-binding protein (vWbp) promote Staphylococcus aureus clot formation in human plasma

Staphylococcus aureus secretes coagulase (Coa) and von Willebrand factor-binding protein (vWbp) to activate host prothrombin and form fibrin cables, thereby promoting the establishment of infectious lesions. The D1-D2 domains of Coa and vWbp associate with, and non-proteolytically activate prothrombin. Moreover, Coa encompasses C-terminal tandem repeats for binding to fibrinogen, whereas vWbp has been reported to associate with von Willebrand factor and fibrinogen. Here we used affinity chromatography with non-catalytic Coa and vWbp to identify the ligands for these virulence factors in human plasma. vWbp bound to prothrombin, fibrinogen, fibronectin, and factor XIII, whereas Coa co-purified with prothrombin and fibrinogen. vWbp association with fibrinogen and factor XIII, but not fibronectin, required prothrombin and triggered the non-proteolytic activation of FXIII in vitro. Staphylococcus aureus coagulation of human plasma was associated with the recruitment of prothrombin, FXIII, and fibronectin as well as the formation of cross-linked fibrin. FXIII activity in staphylococcal clots could be attributed to thrombin-dependent proteolytic activation as well as vWbp-mediated non-proteolytic activation of FXIII zymogen.

Bacterial meningitis: a new risk factor

BACKGROUND

The purpose of this study is to discuss a possible new risk factor for the bacterial meningitis.

METHODS

Cerebrospinal fluid collected from 270 patients was assayed. An enzyme immunosorbent assay for the detection of Staphylococcal enterotoxins A to E was used.

RESULTS

The results indicated that the frequency of Coagulase Negative Staphylococci (CoNS) was 35 (20.46%). An important finding of this research was that the CoNS isolates produced enterotoxin C and D or enterotoxin C and E.

CONCLUSIONS

This is the first report of enterotoxin-producing Coagulase Negative Staphylococci isolated from CSF patients. Therefore, these enterotoxins probably act as risk factors in the bacterial invasion into central nervous system.

Evaluation of Coagulase Activity and Protein A Production for the Identification of Staphylococcus aureus

The activities of coagulase and thermostable nuclease (TNase) and the production of protein A were studied in 338 bacterial strains. These included 213 isolates of Staphylococcus aureus to determine which characteristic was most specific for the identification of S. aureus . The evaluation of different protocols for interpretation of coagulase results was also undertaken. Protein A was analyzed by a sandwich enzyme-linked immunosorbent assay using microtiter plates coated with antiprotein A antibodies. Coagulase activities were determined according to the criteria recommended by Association of Official Analytical Chemists (AOAC; any degree of clot formation is a positive reaction), American Public Health Association (APHA; coagulase activities ≥ 3+ are positive reactions), and the Bacteriological Analytical Manual (BAM; only 4+ reaction is positive). It was found that the AOAC protocol, which had a test sensitivity of 97.7% and a specificity of 95.1% and could be completed within six hours, was more practical than the methods used by APHA and BAM. Compared with coagu1ase and TNase, protein A was a better marker of S. aureus ; a high sensitivity (100%) and specificity (96.8%) were obtained by using protein A for the identification of S. aureus .