Staphylococcus aureus Colonization: Modulation of Host Immune Response and Impact on Human Vaccine Design

Sex-dependent gastrointestinal colonization resistance to MRSA is microbiota and Th17 dependent

Gastrointestinal (GI) colonization by methicillin-resistant Staphylococcus aureus (MRSA) is associated with a high risk of transmission and invasive disease in vulnerable populations. The immune and microbial factors that permit GI colonization remain unknown. Male sex is correlated with enhanced Staphylococcus aureus nasal carriage, skin and soft tissue infections, and bacterial sepsis. Here, we established a mouse model of sexual dimorphism during GI colonization by MRSA. Our results show that in contrast to male mice that were susceptible to persistent colonization, female mice rapidly cleared MRSA from the GI tract following oral inoculation in a manner dependent on the gut microbiota. This colonization resistance displayed by female mice was mediated by an increase in IL-17A+ CD4+ T cells (Th17) and dependent on neutrophils. Ovariectomy of female mice increased MRSA burden, but gonadal female mice that have the Y chromosome retained enhanced Th17 responses and colonization resistance. Our study reveals a novel intersection between sex and gut microbiota underlying colonization resistance against a major widespread pathogen.

Sex-dependent gastrointestinal colonization resistance to MRSA is microbiota and Th17 dependent

Gastrointestinal (GI) colonization by methicillin-resistant Staphylococcus aureus (MRSA) is associated with a high risk of transmission and invasive disease in vulnerable populations. The immune and microbial factors that permit GI colonization remain unknown. Male sex is correlated with enhanced Staphylococcus aureus nasal carriage, skin and soft tissue infections, and bacterial sepsis. Here, we established a mouse model of sexual dimorphism during GI colonization by MRSA. Our results show that in contrast to male mice that were susceptible to persistent colonization, female mice rapidly cleared MRSA from the GI tract following oral inoculation in a manner dependent on the gut microbiota. This colonization resistance displayed by female mice was mediated by an increase in IL-17A+ CD4+ T cells (Th17) and dependent on neutrophils. Ovariectomy of female mice increased MRSA burden, but gonadal female mice that have the Y chromosome retained enhanced Th17 responses and colonization resistance. Our study reveals a novel intersection between sex and gut microbiota underlying colonization resistance against a major widespread pathogen.

Airborne Staphylococcus aureus Exposure Induces Depression-like Behaviors in Mice via Abnormal Neural Oscillation and Mitochondrial Dysfunction

Airborne Staphylococcus aureus exists widely in the natural environment and is closely related to human health. Growing evidence indicates that environmental air pollution elevates the risk of depressive disorders. However, the potential role of airborne S. aureus in the development of depression remains unclear. This study aims to elucidate the neurotoxic effects and potential mechanisms associated with depression caused by airborne S. aureus. Mice were randomly divided into four groups, and the experimental groups with environmental S. aureus were at 4.89 × 102, 8.89 × 105, and 1.27 × 108 CFU/m3 during four consecutive weeks. Airborne S. aureus exposure contributed to depression-like behaviors in mice, especially in the high-concentration group. The electroencephalography signal analysis identified uncoupling of theta and gamma bands and a shift of the beta rhythm toward delta oscillation in the medial prefrontal cortex of mice. Neuropathological analysis showed uplifted neuroinflammation and elevated levels of oxidative stress in the brain. Neuroinflammation and oxidative stress resulted in mitochondrial dysfunction, which could lead to apoptosis. Together, this study provides a strong basis for understanding the adverse outcomes of airborne S. aureus on mental health disorders.

Zoonotic transmission of asymptomatic carriage Staphylococcus aureus on dairy farms in Canterbury, New Zealand

Zoonotic pathogen transmission is of growing concern globally, with agricultural intensification facilitating interactions between humans, livestock and wild animals. Staphylococcus aureus is a major human pathogen, but it also causes mastitis in dairy cattle, leading to an economic burden on the dairy industry. Here, we investigated transmission within and between cattle and humans, including potential zoonotic transmission of S. aureus isolated from cattle and humans from three dairy farms and an associated primary school in New Zealand. Nasal swabs (N=170) were taken from healthy humans. Inguinal and combined nasal/inguinal swabs were taken from healthy cattle (N=1163). Whole-genome sequencing was performed for 96 S. aureus isolates (44 human and 52 cattle). Multilocus sequence typing and assessments of antimicrobial resistance and virulence were carried out. Potential within- and across-species transmission events were determined based on single nucleotide polymorphisms (SNPs). Thirteen potential transmission clusters were detected, with 12 clusters restricted to within-species and one potential zoonotic transmission cluster (ST5). Potential transmission among cattle was mostly limited to single age groups, likely because different age groups are managed separately on farms. While the prevalence of antimicrobial resistance (AMR) was low among both bovine and human isolates, the discovery of an extended-spectrum beta-lactamase gene (bla TEM-116) in a bovine isolate was concerning. This study provides evidence around frequency and patterns of potential transmission of S. aureus on dairy farms and highlights the AMR and virulence profile of asymptomatic carriage S. aureus isolates.

Occurrence of Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus pseudintermedius colonization among veterinarians in the province of Malaga, Spain

Background and Aim

Staphylococcus pseudintermedius and Staphylococcus aureus are common colonizing pathogens in companion animals. These opportunistic pathogens can cause infections of varying frequency and severity in humans and pets. Studies on Staphylococcus colonization in veterinarians are scarce. This study aimed to investigate the colonization of the nostrils and hands by S. aureus, Staphylococcus epidermidis, and S. pseudintermedius among healthy clinical practice veterinarians in the province of Malaga (Spain), with a particular focus on their potential antibiotic resistance.

Materials and Methods

A request for voluntary participation was extended to professionals from the Official College of Veterinarians of Malaga. Nasal and hand swabs were collected by two trained technicians in January 2024, and all samples were delivered to the laboratory within 24 h. Gram staining, catalase, oxidase, and coagulase tests were performed. The susceptibility of the isolated bacteria to 11 antibiotics was evaluated.

Results

A total of 50 clinical practice veterinarians were enrolled in the study, comprising 36 women and 14 men from 31 veterinary clinics across Málaga province. A total of 32% of the nasal samples yielded S. aureus, whereas 64% were found to contain S. epidermidis. In total, 30% of the hand samples yielded S. aureus and 30% yielded S. epidermidis. The participants did not exhibit any strains of S. pseudintermedius in their nasal samples or hands. Two strains (11.1%) of methicillin-resistant S. aureus were isolated from 18 strains isolated from nostrils. Furthermore, a high prevalence of S. aureus strains resistant to ampicillin (94.4%) and amoxicillin (72.2%) was observed.

Conclusions

The colonization profiles of veterinary professionals were similar to those observed in the general population. Further research is required among veterinary professionals, companion animals, and their owners to better understand the colonization processes and the pet-human interface within a "One Health" approach.

Comparison of the bacterial microbiome in the pharynx and nasal cavity of persistent, intermittent carriers and non-carriers of Staphylococcus aureus

Introduction. Staphylococcus aureus is a bacterium that colonizes various human sites. The pharynx has been considered as a site of little clinical relevance and little studied. Recently, it has been reported that S. aureus can colonize more the pharynx than the nose. In addition, S. aureus can persist in these sites for prolonged periods of time.Hypothesis. The composition of the pharyngeal and nasal microbiome will differ between persistent, intermittent carriers and non-carriers of S. aureus.Aim. Determine whether the pharyngeal and nasal microbiome is different between carriers and non-carriers of S. aureus.Methodology. S. aureus carriers were monitored by means of pharyngeal and nasal exudates of apparently healthy adult university students for 3 months. Samples from individuals of the same carrier type were pooled, and DNA was extracted and the 16S rRNA was sequenced. The sequences were analysed in MOTHUR v.1.48.0 software, by analysing the percentages of relative abundance in the STAMP 2.1.3 program, in addition to the predictive analysis of metabolic pathways in PICRUSt2.Results. A greater colonization of S. aureus was found in the pharynx than in the nose. The microbiomes of S. aureus carriers and non-carriers do not show significant differences. The main microbiome difference found was between pharyngeal and nasal microbiomes. No significant differences were found in the abundance of the genus Staphylococcus in pharyngeal and nasal S. aureus carriers and non-carriers. The nasal microbiome was found to have more variation compared to the pharyngeal microbiome, which appears to be more stable between individuals and pools. Predictive analysis of metabolic pathways showed a greater presence of Staphylococcus-associated pathways in the nose than in the pharynx.Conclusion. S. aureus can colonize and persist in the pharynx in equal or greater proportion than in the nose. No statistically significant differences were found in the microbiome of the pharyngeal and nasal carriers and non-carriers of S. aureus, but the pharyngeal and nasal microbiomes are different independent of the type of S. aureus carrier or non-carrier. Therefore, the microbiome apparently does not influence the persistence of S. aureus.

Targeting Macrophage Polarization in Infectious Diseases: M1/M2 Functional Profiles, Immune Signaling and Microbial Virulence Factors

INTRODUCTION

An event of increasing interest during host-pathogen interactions is the polarization of patrolling/naive monocytes (MOs) into macrophage subsets (MФs). Therapeutic strategies aimed at modulating this event are under investigation.

METHODS

This review focuses on the mechanisms of induction/development and profile of MФs polarized toward classically proinflammatory (M1) or alternatively anti-inflammatory (M2) phenotypes in response to bacteria, fungi, parasites, and viruses.

RESULTS AND DISCUSSION

It highlights nuclear, cytoplasmic, and cell surface receptors (pattern recognition receptors/PPRs), microenvironmental mediators, and immune signaling. MФs polarize into phenotypes: M1 MФs, activated by IFN-γ, pathogen-associated molecular patterns (PAMPs, e.g. lipopolysaccharide) and membrane-bound PPRs ligands (TLRs/CLRs ligands); or M2 MФs, induced by interleukins (ILs-4, -10 and -13), antigen-antibody complexes, and helminth PAMPs. Polarization toward M1 and M2 profiles evolve in a pathogen-specific manner, with or without canonicity, and can vary widely. Ultimately, this can result in varying degrees of host protection or more severe disease outcome. On the one hand, the host is driving effective MФs polarization (M1 or M2); but on the other hand, microorganisms may skew the polarization through virulence factors to increase pathogenicity. Cellular/genomic reprogramming also ensures plasticity of M1/M2 phenotypes. Because modulation of polarization can occur at multiple points, new insights and emerging perspectives may have clinical implications during the inflammation-to-resolution transition; translated into practical applications as for therapeutic/vaccine design target to boost microbicidal response (M1, e.g. triggering oxidative burst) with specifics PAMPs/IFN-γ or promote tissue repair (M2, increasing arginase activity) via immunotherapy.

General skin and nasal decolonization with octenisan® set before and after elective orthopedic surgery in selected patients at elevated risk for revision surgery and surgical site infections-a single-center, unblinded, superiority, randomized controlled trial (BALGDEC trial)

BACKGROUND

The preoperative body surface and nasal decolonization may reduce the risk of surgical site infections (SSI) but yields conflicting results in the current orthopedic literature.

METHODS

We perform a single-center, randomized-controlled, superiority trial in favor of the preoperative decolonization using a commercial product (octenidine® set). We will randomize a total number of 1000 adult elective orthopedic patients with a high risk for SSI and/or wound complications (age ≥ 80 years, chronic immune-suppression, American Society of Anesthesiologists score 3-4 points) between a decolonization (octenisan® wash lotion 1 × per day and octenisan® md nasal gel 2-3 × per day; during 5 days) and no decolonization. Decolonized patients will additionally fill a questionnaire regarding the practical difficulties, the completeness, and the adverse events of decolonization. The primary outcomes are SSI and revision surgeries for postoperative wound problems until 6 weeks postoperatively (or 1 year for surgeries with implants or bone). Secondary outcomes are unplanned revision surgeries for non-infectious problems and all adverse events. With 95% event-free surgeries in the decolonization arm versus 90% in the control arm, we formally need 2 × 474 elective orthopedic surgeries included during 2 years.

DISCUSSION

In selected adult orthopedic patients with a high risk for SSI, the presurgical decolonization may reduce postoperative wound problems, including SSI.

TRIAL REGISTRATION

ClinicalTrial.gov NCT05647252. Registered on 9 December 2022.

PROTOCOL VERSION

2 (5 December 2022).

A review of chemical signaling mechanisms underlying quorum sensing and its inhibition in Staphylococcus aureus

Staphylococcus aureus is a significant bacterium responsible for multiple infections and is a primary cause of fatalities among patients in hospital environments. The advent of pathogenic bacteria such as methicillin-resistant S. aureus revealed the shortcomings of employing antibiotics to treat bacterial infectious diseases. Quorum sensing enhances S. aureus's survivability through signaling processes. Targeting the key components of quorum sensing has drawn much interest nowadays as a promising strategy for combating infections caused by bacteria. Concentrating on the accessory gene regulator quorum-sensing mechanism is the most commonly suggested anti-virulence approach for S.aureus. Quorum quenching is a common strategy for controlling illnesses triggered by microorganisms since it reduces the pathogenicity of bacteria and improves bacterial biofilm susceptibility to antibiotics, thus providing an intriguing prospect for drug discovery. Quorum sensing inhibition reduces selective stresses and constrains the emergence of antibiotic resistance while limiting bacterial pathogenicity. This review examines the quorum sensing mechanisms involved in S. aureus, quorum sensing targets and gene regulation, environmental factors affecting quorum sensing, quorum sensing inhibition, natural products as quorum sensing inhibitory agents and novel therapeutical strategies to target quorum sensing in S. aureus as drug developing technique to augment conventional antibiotic approaches.

Using contact network dynamics to implement efficient interventions against pathogen spread in hospital settings: A modelling study

BACKGROUND

Long-term care facilities (LTCFs) are hotspots for pathogen transmission. Infection control interventions are essential, but the high density and heterogeneity of interindividual contacts within LTCF may hinder their efficacy. Here, we explore how the patient-staff contact structure may inform effective intervention implementation.

METHODS AND FINDINGS

Using an individual-based model (IBM), we reproduced methicillin-resistant Staphylococcus aureus colonisation transmission dynamics over a detailed contact network recorded within a French LTCF of 327 patients and 263 staff over 3 months. Simulated baseline cumulative colonisation incidence was 21 patients (prediction interval: 11, 31) and 35 staff (prediction interval: 19, 54). We examined the potential impact of 3 types of interventions against transmission (reallocation reducing the number of unique contacts per staff, reinforced contact precautions, and hypothetical vaccination protecting against acquisition), targeted towards specific populations. All 3 interventions were effective when applied to all nurses or healthcare assistants (median reduction in MRSA colonisation incidence up to 35%), but the benefit did not exceed 8% when targeting any other single staff category. We identified "supercontactor" individuals with most contacts ("frequency-based," overrepresented among nurses, porters, and rehabilitation staff) or with the longest cumulative time spent in contact ("duration-based," overrepresented among healthcare assistants and patients in elderly care or persistent vegetative state (PVS)). Targeting supercontactors enhanced interventions against pathogen spread in the LTCF. With contact precautions, targeting frequency-based staff supercontactors led to the highest incidence reduction (20%, 95% CI: 19, 21). Vaccinating a mix of frequency- and duration-based staff supercontactors led to a higher reduction (23%, 95% CI: 22, 24) than all other approaches. Although based on data from a single LTCF, when varying epidemiological parameters to extend to other pathogens, our results suggest that targeting supercontactors is always the most effective strategy, indicating this approach could be applied to prevent transmission of other nosocomial pathogens.

CONCLUSIONS

By characterising the contact structure in hospital settings and identifying the categories of staff and patients more likely to be supercontactors, with either more or longer contacts than others, interventions against nosocomial spread could be more effective. We find that the most efficient implementation strategy depends on the intervention (reallocation, contact precautions, vaccination) and target population (staff, patients, supercontactors). Importantly, both staff and patients may be supercontactors, highlighting the importance of including patients in measures to prevent pathogen transmission in LTCF.

Staphylococcus aureus colonisation and strategies for decolonisation

Staphylococcus aureus is a leading cause of death by infectious diseases worldwide. Treatment of S aureus infections is difficult due to widespread antibiotic resistance, necessitating alternative approaches and measures for prevention of infection. Because S aureus infections commonly arise from asymptomatic colonisation, decolonisation is considered a key approach for their prevention. Current decolonisation procedures include antibiotic-based and antiseptic-based eradication of S aureus from the nose and skin. However, despite the widespread implementation and partial success of such measures, S aureus infection rates remain worrisome, and resistance to decolonisation agents is on the rise. In this Review we outline the epidemiology and mechanisms of S aureus colonisation, describe how colonisation underlies infection, and discuss current and novel approaches for S aureus decolonisation, with a focus on the latest findings on probiotic strategies and the intestinal S aureus colonisation site.

Deciphering Staphylococcus aureus-host dynamics using dual activity-based protein profiling of ATP-interacting proteins

The utilization of ATP within cells plays a fundamental role in cellular processes that are essential for the regulation of host-pathogen dynamics and the subsequent immune response. This study focuses on ATP-binding proteins to dissect the complex interplay between Staphylococcus aureus and human cells, particularly macrophages (THP-1) and keratinocytes (HaCaT), during an intracellular infection. A snapshot of the various protein activity and function is provided using a desthiobiotin-ATP probe, which targets ATP-interacting proteins. In S. aureus, we observe enrichment in pathways required for nutrient acquisition, biosynthesis and metabolism of amino acids, and energy metabolism when located inside human cells. Additionally, the direct profiling of the protein activity revealed specific adaptations of S. aureus to the keratinocytes and macrophages. Mapping the differentially activated proteins to biochemical pathways in the human cells with intracellular bacteria revealed cell-type-specific adaptations to bacterial challenges where THP-1 cells prioritized immune defenses, autophagic cell death, and inflammation. In contrast, HaCaT cells emphasized barrier integrity and immune activation. We also observe bacterial modulation of host processes and metabolic shifts. These findings offer valuable insights into the dynamics of S. aureus-host cell interactions, shedding light on modulating host immune responses to S. aureus, which could involve developing immunomodulatory therapies.

IMPORTANCE

This study uses a chemoproteomic approach to target active ATP-interacting proteins and examines the dynamic proteomic interactions between Staphylococcus aureus and human cell lines THP-1 and HaCaT. It uncovers the distinct responses of macrophages and keratinocytes during bacterial infection. S. aureus demonstrated a tailored response to the intracellular environment of each cell type and adaptation during exposure to professional and non-professional phagocytes. It also highlights strategies employed by S. aureus to persist within host cells. This study offers significant insights into the human cell response to S. aureus infection, illuminating the complex proteomic shifts that underlie the defense mechanisms of macrophages and keratinocytes. Notably, the study underscores the nuanced interplay between the host's metabolic reprogramming and immune strategy, suggesting potential therapeutic targets for enhancing host defense and inhibiting bacterial survival. The findings enhance our understanding of host-pathogen interactions and can inform the development of targeted therapies against S. aureus infections.

Staphylococcus aureus skin colonization is mediated by SasG lectin variation

Staphylococcus aureus causes the majority of skin and soft tissue infections, but this pathogen only transiently colonizes healthy skin. However, this transient skin exposure enables S. aureus to transition to infection. The initial adhesion of S. aureus to skin corneocytes is mediated by surface protein G (SasG). Here, phylogenetic analyses reveal the presence of two major divergent SasG alleles in S. aureus: SasG-I and SasG-II. Structural analyses of SasG-II identify a nonaromatic arginine in the binding pocket of the lectin subdomain that mediates adhesion to corneocytes. Atomic force microscopy and corneocyte adhesion assays indicate that SasG-II can bind to a broader variety of ligands than SasG-I. Glycosidase treatment results in different binding profiles between SasG-I and SasG-II on skin cells. In addition, SasG-mediated adhesion is recapitulated using differentiated N/TERT keratinocytes. Our findings indicate that SasG-II has evolved to adhere to multiple ligands, conferring a distinct advantage to S. aureus during skin colonization.

Antibiotic susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated at tertiary care hospital in Riyadh, Saudi Arabia

Staphylococcus aureus is an important human pathogen that has a major impact on public health. The objective of the present work was to determine the prevalence and the pattern of antibiotic susceptibility in S aureus (MRSA) isolates from the King Khalid University Hospital (KKUH) in Riyadh, Saudi Arabia. The isolates were collected from different body sites of infection and the antibiotic susceptibility was confirmed on the Vitek 2 system. A total of 371 MRSA isolates from clinical samples were received over a 12-month period from January 2021 to December 2021. The results showed that infection was predominant among males (55.8%) and most of the isolates occurred in the older age groups, with a mean age of 43.7 years and an age span from <1 to 89 years old. The majority (34.5%) recovered from wound infection followed by (14.6%) from blood. We have observed peaks of MRSA infections during the autumn, especially in September and November. All MRSA isolates were resistant to Amoxicillin + clavulanic acid, Ampicillin, Imipenem, Oxacillin, Cloxacillin, and Penicillin while all isolates were sensitive to Daptomycin and Nitrofurantoin. Furthermore, Vancomycin was resistant in (0.3%) of MRSA isolates, and (2.9%) was resistant to Linezolid. The current study concluded that MRSA strains had developed resistance toward 24 tested antibiotics, including the previous effective drugs vancomycin and linezolid. Therefore, there is an urgent need for continuous review of infection control practices to prevent any further spread of resistant strains.

Nitroreductase-Responsive Photosensitizers for Selective Imaging and Photo-Inactivation of Intracellular Bacteria

Intracellular Staphylococcus aureus (S. aureus), especially the methicillin resistant staphylococcus aureus (MRSA), are difficult to detect and eradicate due to the protection by the host cells. Antibacterial photodynamic therapy (aPDT) offers promise in treating intracellular bacteria, provided that selective damage to the bacteria ranther than host cells can be realized. According to the different nitroreductase (NTR) levels in mammalian cells and S. aureus, herein NTR-responsive photosensitizers (PSs) (T)CyI-NO2 were designed and synthesized. The emission and 1O2 generation of (T)CyI-NO2 are quenched by the 4-nitrobenzyl group, but can be specifically switched on by bacterial NTR. Therefore, selective imaging and photo-inactivation of intracellular S. aureus and MRSA were achieved. Our findings may pave the way for the development of more efficient and selective aPDT agents to combat intractable intracellular infections.

Strategies for the eradication of intracellular bacterial pathogens

Intracellular pathogens affect a significant portion of world population and cause millions of deaths each year. They can invade host cells and survive inside them and are extremely resistant to immune systems and antibiotics. Current treatments have limitations, and therefore, new effective therapies are needed to combat this ongoing health challenge. Active research efforts have been made to develop many new strategies to eradicate these intracellular pathogens. In this review, we focus on the intracellular bacterial pathogens and first introduce several representative intracellular bacteria and the diseases they cause. We then discuss the challenges in eradicating these bacteria and summarize the current therapeutics for intracellular bacteria. Finally, recent advances in intracellular bacteria eradication are highlighted.

Reduced Glycolysis and Cytotoxicity in Staphylococcus aureus Isolates from Chronic Rhinosinusitis as Strategies for Host Adaptation

Chronic rhinosinusitis (CRS) is a multifactorial infection of the nasal cavity and sinuses. In this study, nasal swabs from control donors (N = 128) and patients with CRS (N = 246) were analysed. Culture methods and metagenomics revealed no obvious differences in the composition of the bacterial communities between the two groups. However, at the functional level, several metabolic pathways were significantly enriched in the CRS group compared to the control group. Pathways such as carbohydrate transport metabolism, ATP synthesis, cofactors and vitamins, photosynthesis and transcription were highly enriched in CRS. In contrast, pathways related to lipid metabolism were more representative in the control microbiome. As S. aureus is one of the main species found in the nasal cavity, staphylococcal isolates from control and CRS samples were analysed by microarray and functional assays. Although no significant genetic differences were detected by microarray, S. aureus from CRS induced less cytotoxicity to lung cells and lower rates of glycolysis in host cells than control isolates. These results suggest the differential modulation of staphylococcal virulence by the environment created by other microorganisms and their interactions with host cells in control and CRS samples. These changes were reflected in the differential expression of cytokines and in the expression of Agr, the most important quorum-sensing regulator of virulence in S. aureus. In addition, the CRS isolates remained stable in their cytotoxicity, whereas the cytotoxic activity of S. aureus isolated from control subjects decreased over time during in vitro passage. These results suggest that host factors influence the virulence of S. aureus and promote its adaptation to the nasal environment during CRS.

Genetic diversity of macrolides resistant Staphylococcus aureus clinical isolates and the potential synergistic effect of vitamins, C and K3

BACKGROUND

Macrolide antibiotics have been extensively used for the treatment of Staphylococcus aureus infections. However, the emergence of macrolide-resistant strains of S. aureus has become a major concern for public health. The molecular mechanisms underlying macrolide resistance in S. aureus are complex and diverse, involving both target site modification and efflux pump systems. In this study, we aim to overcome the molecular diversity of macrolide resistance mechanisms in S. aureus by identifying common molecular targets that could be exploited for the development of novel therapeutics.

METHODS

About 300 Staphylococcus aureus different isolates were recovered and purified from 921 clinical specimen including urine (88), blood (156), sputum (264), nasal swabs (168), pus (181) and bone (39) collected from different departments in Tanta University Hospital. Macrolide resistant isolates were detected and tested for Multi Drug Resistant (MDR). Gel electrophoresis was performed after the D test and PCR reaction for erm(A), (B), (C), msr(A), and mph(C) genes. Finally, we tried different combinations of Erythromycin or Azithromycin antibiotics with either vitamin K3 or vitamin C.

RESULTS

Macrolide resistance S. aureus isolates exhibited 7 major resistance patterns according to number of resistance markers and each pattern included sub patterns or subgroups. The PCR amplified products of different erm genes; analysis recorded different phenotypes of the Staphylococcus aureus isolates according to their different genotypes. In addition, our new tested combinations of Erythromycin and vitamin C, Erythromycin, and vitamin K3, Azithromycin and vitamin C and Azithromycin and vitamin K3 showed significant antibacterial effect when using every antibiotic alone. Our findings provide new insights into the molecular mechanisms of macrolide resistance in S. aureus and offer potential strategies for the development of novel protocols to overcome this emerging public health threat.

Toxic Shock Syndrome: A Literature Review

Toxic shock syndrome (TSS) is a rare, life-threatening, toxin-mediated infectious process linked, in the vast majority of cases, to toxin-producing strains of Staphylococcus aureus or Streptococcus pyogenes. The pathophysiology, epidemiology, clinical presentation, microbiological features, management and outcome of TSS are described in this review. Bacterial superantigenic exotoxins induces unconventional polyclonal lymphocyte activation, which leads to rapid shock, multiple organ failure syndrome, and death. The main described superantigenic exotoxins are toxic shock syndrome toxin-1 (TSST-1) and enterotoxins for Staphylococcus aureus and Streptococcal pyrogenic exotoxins (SpE) A, B, and C and streptococcal superantigen A (SsA) for Streptococcus pyogenes. Staphylococcal TSS can be menstrual or nonmenstrual. Streptococcal TSS is linked to a severe group A streptococcal infection and, most frequently, to a necrotizing soft tissue infection. Management of TSS is a medical emergency and relies on early detection, immediate resuscitation, source control and eradication of toxin production, bactericidal antibiotic treatment, and protein synthesis inhibiting antibiotic administration. The interest of polyclonal intravenous immunoglobulin G administration as an adjunctive treatment for TSS requires further evaluation. Scientific literature on TSS mainly consists of observational studies, clinical cases, and in vitro data; although more data on TSS are required, additional studies will be difficult to conduct due to the low incidence of the disease.

Detection of Staphylococcus aureus from nares of elderly living in a Brazilian nursing home

Asymptomatically nasal colonization by Staphylococcus aureus is a well-established risk factor for S. aureus infections. The aimed of the study was to identify the prevalence and factors associated with nasal carriage of S. aureus and Methicillin-resistant S. aureus (MRSA) from individuals residing in one Brazilian nursing home (NH). Three time-separate nasal swab collections were obtained from the elderly enrolled. The S. aureus isolates identified were submitted to Antimicrobial Susceptibility test (AST). The study showed a high prevalence of S. aureus (n = 9; 60%) and MRSA (n = 4; 26.7%) among elderly. Resistance to erythromycin was the most detected. S. aureus or MRSA colonization could not be associated to the data collected on demographics, personal habits, and medical history of the participants. Despite the small number of individuals enrolled, our study can contribute to improve the control of S. aureus and MRSA dissemination within the community, especially among the most vulnerable like the elderly.

Exploring alternative strategies for Staphylococcus aureus nasal decolonization: insights from preclinical studies

Nasal decolonization of Staphylococcus aureus with the antibiotic mupirocin is a common clinical practice before complex surgical procedures, to prevent hospital acquired infections. However, widespread use of mupirocin has led to the development of resistant S. aureus strains and there is a limited scope for developing new antibiotics for S. aureus nasal decolonization. It is therefore necessary to develop alternative and nonantibiotic nasal decolonization methods. In this review, we broadly discussed the effectiveness of different nonantibiotic antimicrobial agents that are currently not in clinical practice, but are experimentally proved to be efficacious in promoting S. aureus nasal decolonization. These include lytic bacteriophages, bacteriolytic enzymes, tea tree oil, apple vinegar, and antimicrobial peptides. We have also discussed the possibility of using photodynamic therapy for S. aureus nasal decolonization. This article highlights the importance of further large scale clinical studies for selecting the most suitable and alternative nasal decolonizing agent.

Regulatory T cells control Staphylococcus aureus and disease severity of cutaneous leishmaniasis

Cutaneous leishmaniasis causes alterations in the skin microbiota, leading to pathologic immune responses and delayed healing. However, it is not known how these microbiota-driven immune responses are regulated. Here, we report that depletion of Foxp3+ regulatory T cells (Tregs) in Staphylococcus aureus-colonized mice resulted in less IL-17 and an IFN-γ-dependent skin inflammation with impaired S. aureus immunity. Similarly, reducing Tregs in S. aureus-colonized and Leishmania braziliensis-infected mice increased IFN-γ, S. aureus, and disease severity. Importantly, analysis of lesions from L. braziliensis patients revealed that low FOXP3 gene expression is associated with high IFNG expression, S. aureus burden, and delayed lesion resolution compared to patients with high FOXP3 expression. Thus, we found a critical role for Tregs in regulating the balance between IL-17 and IFN-γ in the skin, which influences both bacterial burden and disease. These results have clinical ramifications for cutaneous leishmaniasis and other skin diseases associated with a dysregulated microbiome when Tregs are limited or dysfunctional.

Assessing Galleria mellonella as a preliminary model for systemic Staphylococcus aureus infection: Evaluating the efficacy and impact of vancomycin and Nigella sativa oil on gut microbiota

Background

Staphylococcus aureus is a Gram-positive bacterium that can cause various infections. The Galleria mellonella has been used as a preliminary test for infection model. The study aimed to evaluate the effectiveness of G. mellonella as a microbiome model and compare the efficacy of vancomycin and antimicrobial activity of Nigella sativa (NS) on the gut flora.

Methods

G. mellonella larvae were subjected to metagenomic analysis. The larvae's guts were collected, homogenized in phosphate-buffered saline (PBS), and the gut contents isolated for bacterial DNA extraction. Larvae were assigned into the following groups: negative control (PBS only); positive control (MRSA only); vancomycin treated group; NS oil treated group and combination (vancomycin and NS oil) treated group. Larvae were cultured, inoculated with S. aureus, and treated with vancomycin and NS oil. Larval activity, cocoon formation, growth, melanization, and survival were monitored. The toxicity of vancomycin and NS oil was tested, and S. aureus burden and natural microbiota were determined. Hemocyte density was measured. Statistical analysis was conducted using R.

Results

Enterococcus related species dominated approximately 90 % of the gastrointestinal tract of the larvae. The survival rate following treatment was 85 % with vancomycin, 64 % with NS oil, and 73 % with a combination of both. The count of Enterococcus Colony Forming Units (CFUs) was significantly lower in the vancomycin treatment group (8.14E+04) compared to those treated with NS oil (1.97E+06) and the combination treatment (8.95E+05). Furthermore, the S. aureus burden was found to be lower in the NS oil (1.04E+06) and combination treatment groups (9.02E+05) compared to the vancomycin treatment group (3.38E+06). Hemocyte densities were significantly higher in the NS oil (8.29E+06) and combination treatment groups (8.18E+06) compared to the vancomycin treatment group (4.89E+06).

Conclusions

The study supported the use of G. mellonella model as a preliminary test to assess the effect of different antimicrobials against S. aureus and gut microbiota. NS oil showed more selectivity against S. aureus and protectiveness for the natural Enterococcus gut flora.

Metabolism Shapes Immune Responses to Staphylococcus aureus

BACKGROUND

Staphylococcus aureus (S. aureus) is a common cause of hospital- and community-acquired infections that can result in various clinical manifestations ranging from mild to severe disease. The bacterium utilizes different combinations of virulence factors and biofilm formation to establish a successful infection, and the emergence of methicillin- and vancomycin-resistant strains introduces additional challenges for infection management and treatment.

SUMMARY

Metabolic programming of immune cells regulates the balance of energy requirements for activation and dictates pro- versus anti-inflammatory function. Recent investigations into metabolic adaptations of leukocytes and S. aureus during infection indicate that metabolic crosstalk plays a crucial role in pathogenesis. Furthermore, S. aureus can modify its metabolic profile to fit an array of niches for commensal or invasive growth.

KEY MESSAGES

Here we focus on the current understanding of immunometabolism during S. aureus infection and explore how metabolic crosstalk between the host and S. aureus influences disease outcome. We also discuss how key metabolic pathways influence leukocyte responses to other bacterial pathogens when information for S. aureus is not available. A better understanding of how S. aureus and leukocytes adapt their metabolic profiles in distinct tissue niches may reveal novel therapeutic targets to prevent or control invasive infections.

Staphylococcus warneri strain XSB102 exacerbates psoriasis and promotes keratinocyte proliferation in imiquimod-induced psoriasis-like dermatitis mice

Psoriasis is one of the common chronic inflammatory skin diseases worldwide. The skin microbiota plays a role in psoriasis through regulating skin homeostasis. However, the studies on the interactions between symbiotic microbial strains and psoriasis are limited. In this study, Staphylococcus strain XSB102 was isolated from the skin of human, which was identified as Staphylococcus warneri using VITEK2 Compact. To reveal the roles of Staphylococcus warneri on psoriasis, XSB102 were applied on the back of imiquimod-induced psoriasis-like dermatitis mice. The results indicated that it exacerbated the psoriasis and significantly increased the thickening of the epidermis. Furthermore, in vitro experiments confirmed that inactivated strain XSB102 could promote the proliferation of human epidermal keratinocytes (HaCaT) cell. However, real-time quantitative PCR and immunofluorescence results suggested that the expression of inflammatory factors such as IL-17a, IL-6, and so on were not significantly increased, while extracellular matrix related factors such as Col6a3 and TGIF2 were significantly increased after XSB102 administration. This study indicates that Staphylococcus warneri XSB102 can exacerbate psoriasis and promote keratinocyte proliferation independently of inflammatory factors, which paves the way for further exploration of the relationship between skin microbiota and psoriasis.

Staphylococcus aureus skin colonization is mediated by SasG lectin variation

Staphylococcus aureus causes the majority of skin and soft tissue infections, but this pathogen only transiently colonizes healthy skin. However, this transient skin exposure enables S. aureus to transition to infection. Initial adhesion of S. aureus to skin corneocytes is mediated by surface protein G (SasG). Here, phylogenetic analyses reveal the presence of two major divergent SasG alleles in S. aureus, SasG-I and SasG-II. Structural analyses of SasG-II identified a unique non-aromatic arginine in the binding pocket of the lectin subdomain that mediates adhesion to corneocytes. Atomic force microscopy and corneocyte adhesion assays indicated SasG-II can bind to a broader variety of ligands than SasG-I. Glycosidase treatment resulted in different binding profiles between SasG-I and SasG-II on skin cells. Additionally, SasG-mediated adhesion was recapitulated using differentiated N/TERT keratinocytes. Our findings indicate that SasG-II has evolved to adhere to multiple ligands, conferring a distinct advantage to S. aureus during skin colonization.

Clinical Staphylococcus aureus inhibits human T-cell activity through interaction with the PD-1 receptor

IMPORTANCE

Therapies that target and aid the host immune defense to repel cancer cells or invading pathogens are rapidly emerging. Antibiotic resistance is among the largest threats to human health globally. Staphylococcus aureus (S. aureus) is the most common bacterial infection, and it poses a challenge to the healthcare system due to its significant ability to develop resistance toward current available therapies. In long-term infections, S. aureus further adapt to avoid clearance by the host immune defense. In this study, we discover a new interaction that allows S. aureus to avoid elimination by the immune system, which likely supports its persistence in the host. Moreover, we find that blocking the specific receptor (PD-1) using antibodies significantly relieves the S. aureus-imposed inhibition. Our findings suggest that therapeutically targeting PD-1 is a possible future strategy for treating certain antibiotic-resistant staphylococcal infections.

The Sympathetic Nervous System Is Necessary for Development of CD4+ T-Cell Memory Following Staphylococcus aureus Infection

Lymph nodes and spleens are innervated by sympathetic nerve fibers that enter alongside arteries. Despite discovery of these nerve fibers nearly 40 years ago, the role of these nerves during response to infection remains poorly defined. We have found that chemical depletion of sympathetic nerve fibers compromises the ability of mice to develop protective immune memory to a Staphylococcus aureus infection. Innate control of the primary infection was not impacted by sympathectomy. Germinal center formation is also compromised in nerve-depleted animals; however, protective antibody responses are still generated. Interestingly, protective CD4+ T-cell memory fails to form in the absence of sympathetic nerves after S aureus infection.

Hydrophobic modification improves the delivery of cell-penetrating peptides to eliminate intracellular pathogens in animals

Infections induced by intracellular pathogens are difficult to eradicate due to poor penetration of antimicrobials into cell membranes. It is of great importance to develop a new generation of antibacterial agents with dual functions of efficient cell penetration and bacterial inhibition. In this study, the association between hydrophobicity and cell-penetrating peptide delivery efficiency was investigated by fragment interception and hydrophobicity modification of natural porcine antimicrobial peptide PR-39 and the combination of cationic cell-penetrating peptide (R6) with antimicrobial peptide fragments modified with hydrophobic residues. The chimeric peptides P3I7 and P3L7, obtained through biofunctional screening, exhibited potent broad-spectrum antibacterial activity and low cytotoxicity. Moreover, P3I7 and P3L7 can effectively penetrate cells to eliminate intracellular pathogens mainly through endocytosis. The membrane destruction mechanism makes the peptides fast sterilizers and less prone to developing drug resistance. Finally, their good biocompatibility and antibacterial infection effects were verified in mice and piglets. To conclude, the chimeric peptides P3I7 and P3L7 show great potential as affordable and effective antimicrobial agents and may serve as ideal candidates for the treatment of intracellular bacterial infections. STATEMENT OF SIGNIFICANCE: The low permeability of antibacterial drugs makes infections induced by intracellular bacteria extremely difficult to treat. To address this issue, we designed chimeric peptides with dual cell-penetrating and antibacterial functions. The active peptides P3I7 and P3L7, acquired through functional screening have strong broad-spectrum antibacterial activity and powerful bactericidal effects against intracellular Staphylococcus aureus. The membrane permeation mechanism of P3I7 and P3L7 against bacteria endows fast bactericidal activity with low drug resistance. The biosafety and antibacterial activity of P3I7 and P3L7 were also validated by in vivo trials. This study provides an ideal drug candidate against intracellular bacterial infections.

Carriage of Antibiotic Resistant Bacteria and Associated Factors Among Food Handlers in Tamale Metropolis, Ghana: Implications for Food Safety

Background

Bacteria pathogens constitute a significant proportion of diarrhoea-causing food contaminants. Transmission of antibiotic resistant foodborne pathogens to humans is a major threat to food safety, especially in developing countries where quality hygiene and sanitation facilities are lacking. Factors related to antibiotic use, sanitation and hand hygiene have been associated with the spread of infectious diseases as well as antibiotic resistant bacteria. Proper food handling ensures that food is not contaminated with potential pathogenic bacteria. This study assessed the carriage of antibiotic resistant bacteria and associated factors.

Methods

A cross-sectional study was conducted among food handlers who sell ready to eat food in the Tamale metropolis of the Northern Region of Ghana. Food vending stations with huge customer base were randomly selected and the food handlers recruited using written informed consent. Structured questionnaires were used to collect participants sociodemographic details and information on sanitation, hand hygiene practice and antibiotic use. Sterile cotton swabs soaked in phosphate buffered saline was used to swab the palms of participating food handlers for bacteria isolation. All identified bacteria were tested for susceptibility to 12 antibiotics.

Results

In all, 406 food handlers participated in this study, the mean (SD) age was 26.5 (2.64) years. Bacteria isolated were predominantly Staphylococci 60 (14.8%) and Escherichia coli 54 (13.3%). All the isolates were resistant to at least one antibiotic tested. The isolates showed high resistance to broad-spectrum antibiotics such as ampicillin (40.0%-75.0%), tetracycline (40.0%-80.0%), amoxiclav (20.0%-80.0%) and chloramphenicol (7.7%-50.0%). Logistic regression model revealed that the carriage of antibiotic resistant bacteria by food handlers was significantly associated with age, educational level, years on the job, training in food preparation, hygiene practice, water source, type of toilet facility used and antibiotic use.

Conclusion

Street food handlers could be potential sources of food-borne transmission of antibiotic resistant bacteria.

Staphylococcus aureus populations from the gut and the blood are not distinguished by virulence traits-a critical role of host barrier integrity

BACKGROUND

The opportunistic pathogen Staphylococcus aureus is an asymptomatically carried member of the microbiome of about one third of the human population at any given point in time. Body sites known to harbor S. aureus are the skin, nasopharynx, and gut. In particular, the mechanisms allowing S. aureus to pass the gut epithelial barrier and to invade the bloodstream were so far poorly understood. Therefore, the objective of our present study was to investigate the extent to which genetic differences between enteric S. aureus isolates and isolates that caused serious bloodstream infections contribute to the likelihood of invasive disease.

RESULTS

Here, we present genome-wide association studies (GWAS) that compare the genome sequences of 69 S. aureus isolates from enteric carriage by healthy volunteers and 95 isolates from bloodstream infections. We complement our GWAS results with a detailed characterization of the cellular and extracellular proteomes of the representative gut and bloodstream isolates, and by assaying the virulence of these isolates with infection models based on human gut epithelial cells, human blood cells, and a small animal infection model. Intriguingly, our results show that enteric and bloodstream isolates with the same sequence type (ST1 or ST5) are very similar to each other at the genomic and proteomic levels. Nonetheless, bloodstream isolates are not necessarily associated with an invasive profile. Furthermore, we show that the main decisive factor preventing infection of gut epithelial cells in vitro is the presence of a tight barrier.

CONCLUSIONS

Our data show that virulence is a highly variable trait, even within a single clone. Importantly, however, there is no evidence that blood stream isolates possess a higher virulence potential than those from the enteric carriage. In fact, some gut isolates from healthy carriers were more virulent than bloodstream isolates. Based on our present observations, we propose that the integrity of the gut epithelial layer, rather than the pathogenic potential of the investigated enteric S. aureus isolates, determines whether staphylococci from the gut microbiome will become invasive pathogens. Video Abstract.

Alhoot M, Abdul Karim S. Multidrug-Resistant Staphylococcus aureus as Coloniser in Healthy Individuals

Staphylococcus aureus is a common human pathogen that can cause mild superficial infections to deep-seated abscesses and sepsis. One of the characteristics of S. aureus is the ability to colonise healthy individuals while leaving them asymptomatic. These carriers’ risk harbouring an antibiotic-resistant strain that may be harmful to the individual and the community. S. aureus carriage in healthcare personnel is being studied extensively in many parts of the world. However, the relationship between colonisation and disease among those with no previous exposure to healthcare remains untouched. Colonisation of the nasal cavity and its surrounding by pathogenic organisms such as S. aureus leads to the increased risk of infection. Hospital-acquired infections associated with S. aureus infections are common and studies related to these types of infections among various study groups are largely documented. However, over the last decade, an increase in community-associated methicillin-resistant S. aureus has been noted, increasing the need to identify the prevalence of the organism among healthy individuals and assessing the antibiotic resistance patterns. Systemic surveillance of the community for colonisation of S. aureus and identifying the antibiotic-resistant pattern is critical to determine the appropriate empiric antibiotic treatment.

MRSA and Skin Infections in Psoriatic Patients: Therapeutic Options and New Perspectives

Psoriatic patients present various infectious risk factors, but there are few studies in the literature evaluating the actual impact of psoriasis in severe staphylococcal skin infections. Our narrative review of the literature suggests that psoriatic patients are at increased risk of both colonization and severe infection, during hospitalization, by S. aureus. The latter also appears to play a role in the pathogenesis of psoriasis through the production of exotoxins. Hospitalized psoriatic patients are also at increased risk of MRSA skin infections. For this reason, new molecules are needed that could both overcome bacterial resistance and inhibit exotoxin production. In our opinion, in the near future, topical quorum sensing inhibitors in combination with current anti-MRSA therapies will be able to overcome the increasing resistance and block exotoxin production. Supplementation with Vitamin E (VE) or derivatives could also enhance the effect of anti-MRSA antibiotics, considering that psoriatic patients with metabolic comorbidities show a low intake of VE and low serum levels, making VE supplementation an interesting new perspective.

Nasopharyngeal Bacterial Microbiota Composition and SARS-CoV-2 IgG Antibody Maintenance in Asymptomatic/Paucisymptomatic Subjects

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the coronavirus disease 2019 (COVID-19), ranging from asymptomatic conditions to severe/fatal lung injury and multi-organ failure. Growing evidence shows that the nasopharyngeal microbiota composition may predict the severity of respiratory infections and may play a role in the protection from viral entry and the regulation of the immune response to the infection. In the present study, we have characterized the nasopharyngeal bacterial microbiota (BNM) composition and have performed factor analysis in a group of 54 asymptomatic/paucisymptomatic subjects who tested positive for nasopharyngeal swab SARS-CoV-2 RNA and/or showed anti-RBD-IgG positive serology at the enrolment. We investigated whether BNM was associated with SARS-CoV-2 RNA positivity and serum anti-RBD-IgG antibody development/maintenance 20–28 weeks after the enrolment. Shannon’s entropy α-diversity index [odds ratio (OR) = 5.75, p = 0.0107] and the BNM Factor1 (OR = 2.64, p = 0.0370) were positively associated with serum anti-RBD-IgG antibody maintenance. The present results suggest that BNM composition may influence the immunological memory against SARS-CoV-2 infections. To the best of our knowledge, this is the first study investigating the link between BNM and specific IgG antibody maintenance. Further studies are needed to unveil the mechanisms through which the BNM influences the adaptive immune response against viral infections.

Staphylococcus aureus-induced immunosuppression mediated by IL-10 and IL-27 facilitates nasal colonisation

Staphylococcus aureus persistently colonises the anterior nares of a significant proportion of the healthy population, however the local immune response elicited during S. aureus nasal colonisation remains ill-defined. Local activation of IL-17/IL-22 producing T cells are critical for controlling bacterial clearance from the nasal cavity. However, recurrent and long-term colonisation is commonplace indicating efficient clearance does not invariably occur. Here we identify a central role for the regulatory cytokine IL-10 in facilitating bacterial persistence during S. aureus nasal colonisation in a murine model. IL-10 is produced rapidly within the nasal cavity following S. aureus colonisation, primarily by myeloid cells. Colonised IL-10^-/- mice demonstrate enhanced IL-17+ and IL-22+ T cell responses and more rapidly clear bacteria from the nasal tissues as compared with wild-type mice. S. aureus also induces the regulatory cytokine IL-27 within the nasal tissue, which acts upstream of IL-10 promoting its production. IL-27 blockade reduces IL-10 production within the nasal cavity and improves bacterial clearance. TLR2 signalling was confirmed to be central to controlling the IL-10 response. Our findings conclude that during nasal colonisation S. aureus creates an immunosuppressive microenvironment through the local induction of IL-27 and IL-10, to dampen protective T cell responses and facilitate its persistence.

Nasal colonisation by the bacterium Staphylococcus aureus is a very common occurrence in the human population. However there is a lack of knowledge on the immune response that controls nasal colonisation. It is known that a local pro-inflammatory immune response is important for bacterial clearance, however sustained colonisation is commonplace suggesting efficient clearance may not be occurring. Here we demonstrate for the first time that S. aureus is manipulating the host immune response by promoting immunosuppression in the nasal cavity which enables bacterial survival. We found that the regulatory proteins IL-10 and IL-27 are central to this suppressive response and result in reduced protective T cell responses. We also demonstrate that S. aureus is inducing IL-27 production to enhance IL-10 production in order to prolong bacterial colonisation. Our findings show that the host-pathogen interaction during nasal colonisation is more complex than previously described and that S. aureus is capable of manipulating the regulatory immune response of the host for its’ own benefit.

Distribution of Leukocidins, Exfoliative Toxins, and Selected Resistance Genes Among Methicillin-resistant and Methicillin-sensitive Staphylococcus aureus Clinical Strains in Egypt

Background:

Infection with Staphylococcus aureus (S.aureus) is an increasing health problem worldwide. This pathogen has multiple virulence factors that contribute to its pathogenesis in a wide range of diseases. The present study aimed to investigate the prevalence of leukocidins, exfoliative toxins, and common antimicrobial resistance genes among Methicillin-Resistant Staphylococcus aureus (MRSA) and Methicillin-Sensitive Staphylococcus aureus (MSSA) strains collected from various clinical sources in Egypt.

Methods:

Isolates were identified as S.aureus by the standard microbiological methods. Methicillin resistance was detected phenotypically by cefoxitin disc diffusion method and genotypically by PCR for detection of mecA gene. PCR was also used to detect the presence of leukocidin genes (LukD, LukE, LukF-PV, and LukS-PV), exfoliative toxin genes (eta and etb), and antibiotic resistance genes (tetK, tetM, ermA, ermC, msrA, and aacA-aphD).

Results:

About 50.5% of tested isolates were methicillin resistant by cefoxitin disc assay, while mecA gene was amplified in 64.6% of isolates. The highest prevalent toxin gene was lukE (93%) and the least prevalent one was eta (1%). The resistance genes tetK and tetM were detected in nearly 50% of the tested strains but lower prevalence rates were recorded for aacA-aphD, msrA, ermA, and ermC genes.

Conclusion:

Methicillin resistance was highly prevalent among tested S.aureus strains. Regarding the studied virulence and resistance genes, no significant difference was detected between MRSA and MSSA strains, except for ermA gene p<0.05 which was highly prevalent in MRSA strains. So, the variation between MRSA and MSSA strains in the response to treatment may be attributed to the resistance of MRSA strains to all β-lactams in addition to other possible acquired resistance mechanisms. Accordingly, fewer options of antimicrobial medications are available to treat MRSA infections.

Prevalence and Clindamycin Resistance Profile of Staphylococcus aureus and Associated Factors among Patients Attending the University of Gondar Comprehensive Specialized Hospital, Gondar, Northwest Ethiopia

Clindamycin can serve as an alternative treatment for staphylococcal infections. Routine susceptibility tests may fail to determine inducible type clindamycin resistance and can be a source of failure in clinical therapeutics. Therefore, this study aimed to determine Staphylococcus aureus (S. aureus) prevalence, inducible clindamycin resistance pattern, and associated factors among patients attending the University of Gondar Comprehensive Specialized Hospital, Gondar, northwest Ethiopia. Methods. A cross-sectional study was conducted from January to April 2018. Clinical samples were inoculated on appropriate culture media. Standard bacteriological tests, including Gram stain, catalase, and coagulase tests, identified the presence of S. aureus. The antimicrobial susceptibility tests and the D-test were performed by using the Kirby-Bauer disk diffusion technique on the Mueller-Hinton agar. The D-test was performed using clindamycin (CLI) 2 ug and erythromycin (ERY) 15 ug disks located approximately 15 mm apart, and the cefoxitin susceptibility test was used to characterize methicillin-resistant S. aureus (MRSA). The association between S. aureus infection and different variables was assessed using bivariate and multivariate analysis. A P value <0.05 was considered statistically significant. Result. Of 388 study participants, the overall prevalence of S. aureus was 17% (66/388). Of these, the inducible type of clindamycin resistance was 25.8% (17/66) and 21.2% (14/66) were MRSA. All isolates were susceptible to chloramphenicol and resistant to tetracycline. A family size of 4-6 (AOR = 2.627, 95% CI (1.030-6.702)) and >7 (AOR = 3.892, 95% CI (1.169-12.959)), inpatient study participants (AOR = 3.198, 95% CI (1.197-8.070)), illness in the previous 4 weeks (AOR = 2.116, 95% CI (1.080-4.145)), and a history of chronic disease (AOR = 0.265, 95% CI (0.094-0.750)) were likely to have S. aureus infection. Conclusion. This study shows a considerable high magnitude of MRSA and inducible clindamycin resistance S. aureus isolates. To rule out clindamycin susceptibility testing, the D-test should be routinely performed.

Comparison of Transcriptional Signatures of Three Staphylococcal Superantigenic Toxins in Human Melanocytes

Staphylococcus aureus, a gram-positive bacterium, causes toxic shock through the production of superantigenic toxins (sAgs) known as Staphylococcal enterotoxins (SE), serotypes A-J (SEA, SEB, etc.), and toxic shock syndrome toxin-1 (TSST-1). The chronology of host transcriptomic events that characterizes the response to the pathogenesis of superantigenic toxicity remains uncertain. The focus of this study was to elucidate time-resolved host responses to three toxins of the superantigenic family, namely SEA, SEB, and TSST-1. Due to the evolving critical role of melanocytes in the host’s immune response against environmental harmful elements, we investigated herein the transcriptomic responses of melanocytes after treatment with 200 ng/mL of SEA, SEB, or TSST-1 for 0.5, 2, 6, 12, 24, or 48 h. Functional analysis indicated that each of these three toxins induced a specific transcriptional pattern. In particular, the time-resolved transcriptional modulations due to SEB exposure were very distinct from those induced by SEA and TSST-1. The three superantigens share some similarities in the mechanisms underlying apoptosis, innate immunity, and other biological processes. Superantigen-specific signatures were determined for the functional dynamics related to necrosis, cytokine production, and acute-phase response. These differentially regulated networks can be targeted for therapeutic intervention and marked as the distinguishing factors for the three sAgs.

High prevalence of MRSA and VRSA among inpatients of Mettu Karl referral hospital, southwest Ethiopia

OBJECTIVE

To assess the prevalence of methicillin and vancomycin-resistant Staphylococcus aureus among patients admitted to Mettu Karl referral hospital.

METHODS

A cross-sectional study was conducted to study the point prevalence of MRSA and VRSA. A total of 384 patients (male=201 and female=183) admitted to medical (109), pediatric (109), and surgical (166) wards of Mettu Karl referral hospital from November 2019 to April 2020 were included in the study. We studied 384 samples (166 wound swabs and 218 nasal swabs) collected from inpatients. Staphylococcus aureus was isolated, characterized, and identified based on morphological and biochemical features and confirmed by PCR amplification of the nuc gene. The isolates were checked against 12 antibiotics, and MRSA isolates were primarily identified using cefoxitin (30 μg) and confirmed by amplification of mecA gene. Staphylococcus aureus resistance to Vancomycin was tested by the broth microdilution method.

RESULTS

The rate of isolation of Staphylococcus aureus was 32.8% (126/384). The point prevalence of MRSA and VRSA from clinical specimens was 18.8% (72/384) and 2.6% (10/384) respectively. Of 126 Staphylococcus aureus isolated, 57.1% (72) were MRSA and 7.9% (10) were VRSA. Of the 166 samples collected from patients in the surgical ward, the rates of isolation of MRSA and VRSA were 21.1% (35/166) and 4.8% (8/166), respectively. A high rate of isolation of MRSA and VRSA was recorded among patients admitted to surgical wards compared to medical and pediatric wards.

CONCLUSIONS

This study showed a high prevalence of MRSA and VRSA in the hospital. Proper implementation of infection control practices and investigation of underlying risk factors are urgently needed to mitigate the further spread of the pathogen.

The Influence of Antibiotic Resistance on Innate Immune Responses to Staphylococcus aureus Infection

Staphylococcus aureus (S. aureus) causes a broad range of infections and is associated with significant morbidity and mortality. S. aureus produces a diverse range of cellular and extracellular factors responsible for its invasiveness and ability to resist immune attack. In recent years, increasing resistance to last-line anti-staphylococcal antibiotics daptomycin and vancomycin has been observed. Resistant strains of S. aureus are highly efficient in invading a variety of professional and nonprofessional phagocytes and are able to survive inside host cells. Eliciting immune protection against antibiotic-resistant S. aureus infection is a global challenge, requiring both innate and adaptive immune effector mechanisms. Dendritic cells (DC), which sit at the interface between innate and adaptive immune responses, are central to the induction of immune protection against S. aureus. However, it has been observed that S. aureus has the capacity to develop further antibiotic resistance and acquire increased resistance to immunological recognition by the innate immune system. In this article, we review the strategies utilised by S. aureus to circumvent antibiotic and innate immune responses, especially the interaction between S. aureus and DC, focusing on how this relationship is perturbed with the development of antibiotic resistance.

Multiple Domains of Staphylococcal Superantigen-like Protein 11 (SSL11) Contribute to Neutrophil Inhibition

Staphylococcus aureus is an opportunistic pathogen producing many immune evasion molecules targeting various components of the host immune defense, including the Staphylococcal superantigen-like protein (SSL 1-14) family. Despite sharing similar structures with the powerful superantigens (SAgs), which cause massive T cell activation, SSLs interfere with a wide range of innate immune defenses. SSLs are divided into two subgroups, SSLs that contain a conserved carbohydrate Sialyl Lewis X [Neu5Acα2-3Galβ1-4(Fucα1-3) GlcNAcβ, SLeX] binding site and SSLs that lack the SLeX binding site. SSL2-6 and SSL11 possess the SLeX binding site. Our previous studies showed that SSL11 arrests cell motility by inducing cell adhesion in differentiated HL60 (dHL60) cells, while SSL7 did not bind dHL60 cells. SSL7-based chimeras were engineered by exchanging the SSL7 sequence with the corresponding SSL11 sequence and assaying for a gain of SSL11 function, namely, the induction of cell spreading and motility arrest. In addition to the SLeX-binding site, we observed that three beta-strands β6, β7, and β9 and the N-terminal residues, Y16 and Y17, transitioned SSL7 to gain SSL11 activities. These studies define the structure-function properties of SSL11 that may allow SSL11 to inhibit S. aureus clearance by the host innate immune system, allowing S. aureus to maintain a carrier state in humans, an understudied aspect of S. aureus pathogenesis.

Clonal Diversity, Antimicrobial Susceptibility and Presence of Genes Encoding Virulence Factors in Staphylococcus aureus Strains Isolated from Cut Wound Infections

The aim of the study was to evaluate the clonal relatedness and antimicrobial susceptibility in 52 Staphylococcus aureus strains isolated from cut wound infections in non-related community patients and to determine the presence of selected virulence genes. To analyse the clonal relatedness of investigated strains, pulsed-field gel electrophoresis (PFGE) of macrorestricted DNA fragments was conducted. Antimicrobial susceptibility testing was performed using the AST-P644 card in the VITEK 2 Compact system. All strains were tested for the presence of selected virulence genes using Single and Multiplex PCR. All isolates were classified into 15 PFGE genotypes and seven unique patterns. The vast majority of investigated S. aureus strains were susceptible to all tested antimicrobial agents. Among examined S. aureus strains, 24 combinations of virulence factors were identified. 62.5% of S. aureus strains contained various egc types, alone or together with other staphylococcal enterotoxin genes. A high percentage (86.5%) of isolates harboured superantigen genes. The most frequent enterotoxin gene identified was encoding for sep. All S. aureus strains were classified as agr-positive, and the most frequent agr gene was agr-1. Our results indicate that all examined strains isolated from cut wound infections demonstrated high clonal diversity, diversified gene distribution and good susceptibility to antimicrobial agents.

Natural Human Immunity Against Staphylococcal Protein A Relies on Effector Functions Triggered by IgG3

Staphylococcal protein A (SpA) is a multifunctional, highly conserved virulence factor of Staphylococcus aureus. By binding the Fc portion of all human IgG subclasses apart from IgG3, SpA interferes with antibody and complement deposition on the bacterial surface, impairing staphylococcal clearance by phagocytosis. Because of its anti-opsonic properties, SpA is not investigated as a surface antigen to mediate bacterial phagocytosis. Herein we investigate human sera for the presence of SpA-opsonizing antibodies. The screening revealed that sera containing IgG3 against SpA were able to correctly opsonize the target and drive Fcγ receptor-mediated interactions and phagocytosis. We demonstrated that IgG3 Fc is significantly more efficient in inducing phagocytosis of SpA-expressing S. aureus as compared to IgG1 Fc in an assay resembling physiological conditions. Furthermore, we show that the capacity of SpA antibodies to induce phagocytosis depends on the specific epitope recognized by the IgGs on SpA molecules. Overall, our results suggest that anti-SpA IgG3 antibodies could favor the anti-staphylococcal response in humans, paving the way towards the identification of a correlate of protection against staphylococcal infections.

Inflammatory Response Against Staphylococcus aureus via Intracellular Sensing of Nucleic Acids in Keratinocytes

Staphylococcus aureus is one of the clinically most relevant pathogens causing infections. Humans are often exposed to S. aureus. In approximately one-third of the healthy population it can be found on the skin either for long or short periods as colonizing "commensals", without inducing infections or an inflammatory immune response. While tolerating S. aureus seems to be limited to certain individuals and time periods in most cases, Staphylococcus epidermidis is tolerated permanently on the skin of almost all individuals without activating overwhelming skin inflammation. To investigate this, we co-cultured a keratinocyte cell line (HaCaT) with viable S. aureus or S. epidermidis to study the differences in the immune activation. S. aureus activated keratinocytes depicted by a profound IL-6 and IL-8 response, whereas S. epidermidis did not. Our data indicate that internalization of S. aureus and the subsequent intracellular sensing of bacterial nucleic acid may be essential for initiating inflammatory response in keratinocytes. Internalized dsRNA activates IL-6 and IL-8 release, but not TNF-α or IFNs by human keratinocytes. This is a non-specific effect of dsRNA, which can be induced using Poly(I:C), as well as RNA from S. aureus and S. epidermidis. However, only viable S. aureus were able to induce this response as these bacteria and not S. epidermidis were actively internalized by HaCaT. The stimulatory effect of S. aureus seems to be independent of the TLR3, -7 and -8 pathways.

Staphylococcus aureus β-Toxin Exerts Anti-angiogenic Effects by Inhibiting Re-endothelialization and Neovessel Formation

Staphylococcus aureus causes severe, life-threatening infections that often are complicated by severe local and systemic pathologies with non-healing lesions. A classic example is S. aureus infective endocarditis (IE), where the secreted hemolysin β-toxin potentiates the disease via its sphingomyelinase and biofilm ligase activities. Although these activities dysregulate human aortic endothelial cell activation, β-toxin effect on endothelial cell function in wound healing has not been addressed. With the use of the ex vivo rabbit aortic ring model, we provide evidence that β-toxin prevents branching microvessel formation, highlighting its ability to interfere with tissue re-vascularization and vascular repair. We show that β-toxin specifically targets both human aortic endothelial cell proliferation and cell migration and inhibits human umbilical vein endothelial cell rearrangement into capillary-like networks in vitro. Proteome arrays specific for angiogenesis-related molecules provided evidence that β-toxin promotes an inhibitory profile in endothelial cell monolayers, specifically targeting production of TIMP-1, TIMP-4, and IGFBP-3 to counter the effect of a pro-angiogenic environment. Dysregulation in the production of these molecules is known to result in sprouting defects (including deficient cell proliferation, migration, and survival), vessel instability and/or vascular regression. When endothelial cells are grown under re-endothelialization/wound healing conditions, β-toxin decreases the pro-angiogenic molecule MMP-8 and increases the anti-angiogenic molecule endostatin. Altogether, the data indicate that β-toxin is an anti-angiogenic virulence factor and highlight a mechanism where β-toxin exacerbates S. aureus invasive infections by interfering with tissue re-vascularization and vascular repair.

Fibrin(ogen) engagement of S. aureus promotes the host antimicrobial response and suppression of microbe dissemination following peritoneal infection

The blood-clotting protein fibrin(ogen) plays a critical role in host defense against invading pathogens, particularly against peritoneal infection by the Gram-positive microbe Staphylococcus aureus. Here, we tested the hypothesis that direct binding between fibrin(ogen) and S. aureus is a component of the primary host antimicrobial response mechanism and prevention of secondary microbe dissemination from the peritoneal cavity. To establish a model system, we showed that fibrinogen isolated from Fibγ^Δ5 mice, which express a mutant form lacking the final 5 amino acids of the fibrinogen γ chain (termed fibrinogenγ^Δ5), did not support S. aureus adherence when immobilized and clumping when in suspension. In contrast, purified wildtype fibrinogen supported robust adhesion and clumping that was largely dependent on S. aureus expression of the receptor clumping factor A (ClfA). Following peritoneal infection with S. aureus USA300, Fibγ^Δ5 mice displayed worse survival compared to WT mice coupled to reduced bacterial killing within the peritoneal cavity and increased dissemination of the microbes into circulation and distant organs. The failure of acute bacterial killing, but not enhanced dissemination, was partially recapitulated by mice infected with S. aureus USA300 lacking ClfA. Fibrin polymer formation and coagulation transglutaminase Factor XIII each contributed to killing of the microbes within the peritoneal cavity, but only elimination of polymer formation enhanced systemic dissemination. Host macrophage depletion or selective elimination of the fibrin(ogen) β2-integrin binding motif both compromised local bacterial killing and enhanced S. aureus systemic dissemination, suggesting fibrin polymer formation in and of itself was not sufficient to retain S. aureus within the peritoneal cavity. Collectively, these findings suggest that following peritoneal infection, the binding of S. aureus to stabilized fibrin matrices promotes a local, macrophage-mediated antimicrobial response essential for prevention of microbe dissemination and downstream host mortality.

The Gram-positive bacterium Staphylococcus aureus (S. aureus) produces a number of soluble and surface-associated proteins that bind the host coagulation protein fibrinogen. The contribution of fibrinogen-S. aureus binding through the fibrinogen receptor clumping factor A (ClfA) in peritoneal infection has not been defined. Elimination of the binding motif on fibrinogen for ClfA or deletion of ClfA from S. aureus significantly reduced S. aureus-fibrinogen binding and bacterial clumping in solution. In a mouse model of peritonitis, loss of these activities resulted in diminished bacterial killing, increased bacterial dissemination, and worsened host survival. Although fibrin polymer formation and fibrin(ogen)-macrophage binding are mechanistically linked to the local antimicrobial response, fibrin formation in and of itself is not sufficient to suppress microbe dissemination. These discoveries have identified important components of the fibrin(ogen)-dependent host antimicrobial response against S. aureus, providing further understanding of this physiological response to infection which could uncover potential therapeutic strategies for peritonitis patients.

A Lateral Flow Test for Staphylococcus aureus in Nasal Mucus Using a New DNAzyme as the Recognition Element

Detection of pathogenic bacteria in complex biological matrices remains a major challenge. Herein, we report the selection and optimization of a new DNAzyme for Staphylococcus aureus (SA) and the use of the DNAzyme to develop a simple lateral flow device (LFD) for detection of SA in nasal mucus. The DNAzyme was generated by in vitro selection using a crude extra/intracellular mixture derived from SA, which could be used directly for simple solution or paper-based fluorescence assays for SA. The DNAzyme was further modified to produce a DNA cleavage fragment that acted as a bridging element to bind DNA-modified gold nanoparticles to the test line of a LFD, producing a simple colorimetric dipstick test. The LFD was evaluated with nasal mucus samples spiked with SA, and demonstrated that SA detection was possible in minutes with minimal sample processing.

Molecular studies of immunological enzyme clumping factor B for the inhibition of Staphylococcus aureus with essential oils of Nigella sativa

Essential oils from black cumin seeds (Nigella sativa) have largely been used in the manufacturing of nutraceuticals and functional food products due to the presence of a wide variety of bioactive compounds. However, their applications in the pharmaceutical sector have recently attracted interest and started blooming. The present research elucidates the in silico and in vitro efficacies of active leads from essential oil of N sativa against the human pathogenic bacterium Staphylococcus aureus. Biofilm development has become an inevitable situation in the health care sector. Lowering the efficacies of antimicrobial drugs is one of the vital ramifications that resulted in the emergence of multidrug resistance. Clumping factor B (clfB) of S aureus plays a key role in the human immune functions during pathogenesis. Through STRING analysis, the interacting protein partners of clfB were found to regulate biofilm pathway. Therefore, eight ligands from essential oil are docked with the critical clfB protein, which revealed p-cymene, thymoquinone and carvacrol as the robust ligands with highest binding affinity. Therefore, antibiofilm potential of N sativa essential oil at in vitro states was evaluated against S aureus. Further, real time PCR analysis showed that the expression of clfB and intercellular adhesion gene (icaA and icaD) was significantly altered upon treatment with essential oil. Altogether, the findings confirmed the antibiofilm efficacy of N sativa essential oil against S aureus. Hence, the essential oil from N. sativa was envisaged to be promising candidate to treat S aureus biofilm mediated infection.