Impact of Staphylococcus aureus on pathogenesis in polymicrobial infections

Variation in Interleukin-4, -6, and -10 in Mastitis Milk: Associations with Infections, Pathogens, Somatic Cell Counts, and Oxidative Stress

Poor mastitis control favors intramammary infection (IMI), which always involves CNS. This study aimed to determine the relationships of IL-4, IL-6, and IL-10 in mastitis milk with concurrent infection, bacterial pathogens, SCC, and MDA, an oxidative stress marker. All mastitis quarters from five smallholder dairy farms were sampled aseptically before morning milking and again before afternoon milking for bacteriological identification using MALDI-TOF mass spectrometry. The samples with the concomitant infection between streptococci and CNS and their pairs of another sample from the quarters were selected. In addition, samples were randomly chosen to have a controlled single infection. IL-4, IL-6, and IL-10 were measured with ELISA kits. MDA was measured using HPLC, while SCC was measured using Fossomatic™ FC. The results from a repeated measure analysis showed that IL-4 positively correlated with SCC, while IL-6 showed a negative trend. IL-4 levels were highest in CNS infections and significantly higher than in non-infected or mixed infections (p < 0.05). The IL-6 level of the mixed bacteria was highest and showed a different trend from non-infection, and the quarter was infected with streptococcal bacteria. In conclusion, from a single infection, the streptococci and CNS quarter showed varied immune responses, including trendily higher IL-6 and IL-4.

Synthetic Peptides Capable of Potent Multigroup Staphylococcal Quorum Sensing Activation and Inhibition in Both Cultures and Biofilm Communities

The pathogen Staphylococcus epidermidis uses a chemical signaling process, i.e., quorum sensing (QS), to form robust biofilms and cause human infection. Many questions remain about QS in S. epidermidis, as it uses this intercellular communication pathway to both negatively and positively regulate virulence traits. Herein, we report synthetic multigroup agonists and antagonists of the S. epidermidis accessory gene regulator (agr) QS system capable of potent superactivation and complete inhibition, respectively. These macrocyclic peptides maintain full efficacy across the three major agr specificity groups, and their activity can be "mode-switched" from agonist to antagonist via subtle residue-specific structural changes. We describe the design and synthesis of these non-native peptides and demonstrate that they can appreciably decrease biofilm formation on abiotic surfaces, underscoring the potential for agr agonism as a route to block S. epidermidis virulence. Additionally, we show that both the S. epidermidis agonists and antagonists are active in S. aureus, another common pathogen with a related agr system, yet only as antagonists. This result not only revealed one of the most potent agr inhibitors known in S. aureus but also highlighted differences in the mechanisms of agr agonism and antagonism between these related bacteria. Finally, our investigations reveal unexpected inhibitory behavior for certain S. epidermidis agr agonists at sub-activating concentrations, an observation that can be leveraged for the design of future probes with enhanced potencies. Together, these peptides provide a powerful tool set to interrogate the role of QS in S. epidermidis infections and in Staphylococcal pathogenicity in general.

Cytotoxic Staphylococcus aureus PSMα3 inhibits the aggregation of human insulin in vitro

Phenol-soluble modulins (PSMs) are extracellular short amphipathic peptides secreted by the bacteria Staphylococcus aureus (S. aureus). They play an essential role in the bacterial lifecycle, biofilm formation, and stabilisation. From the PSM family, PSMα3 has been of special interest recently due to its cytotoxicity and highly stable α-helical conformation, which also remains in its amyloid fibrils. In particular, PSMα3 fibrils were shown to be composed of self-associating "sheets" of α-helices oriented perpendicular to the fibril axis, mimicking the architecture of canonical cross-β fibrils. Therefore, they were called cross-α-fibrils. PSMα3 was synthesised and verified for identity with wild-type sequences (S. aureus). Then, using several experimental techniques, we evaluated its propensity for in vitro aggregation. According to our findings, synthetic PSMα3 (which lacks the N-terminal formyl groups found in bacteria) does not form amyloid fibrils and maintains α-helical conformation in a soluble monomeric form for several days of incubation. We also evaluated the influence of PSMα3 on human insulin fibrillation in vitro, using a variety of experimental approaches in combination with computational molecular studies. First, it was shown that PSMα3 drastically inhibits the fibrillation of human insulin. The anti-fibrillation effect of PSMα3 was concentration-dependent and required a concentration ratio of PSMα3: insulin equal to or above 1 : 100. Molecular modelling revealed that PSMα3 most likely inhibits the production of insulin primary nuclei by competing for residues involved in its dimerization.

Evaluation of the Antioxidant, Cytotoxicity, Antibacterial, Anti-Motility, and Anti-Biofilm Effects of Myrothamnus flabellifolius Welw. Leaves and Stem Defatted Subfractions

The formation of biofilms underscores the challenge of treating bacterial infections. The study aimed to assess the antioxidant, cytotoxicity, antibacterial, anti-motility, and anti-biofilm effects of defatted fractions from Myrothamnus flabellifolius (resurrection plant). Antioxidant activity was assessed using DPPH radical scavenging and hydrogen peroxide assays. Cytotoxicity was screened using a brine shrimp lethality assay. Antibacterial activity was determined using the micro-dilution and growth curve assays. Antibiofilm potential was screened using the crystal violet and tetrazolium reduction assay. Liquid-liquid extraction of crude extracts concentrated polyphenols in the ethyl acetate and n-butanol fractions. Subsequently, these fractions had notable antioxidant activity and demonstrated broad-spectrum antibacterial activity against selected Gram-negative and Gram-positive bacteria and Mycobacterium smegmatis (MIC values < 630 μg/mL). Growth curves showed that the bacteriostatic inhibition by the ethyl acetate fractions was through the extension of the lag phase and/or suppression of the growth rate. The sub-inhibitory concentrations of the ethyl acetate fractions inhibited the swarming motility of Pseudomonas aeruginosa and Klebsiella pneumoniae by 100% and eradicated more than 50% of P. aeruginosa biofilm biomass. The polyphenolic content of M. flabellifolius plays an important role in its antibacterial, anti-motility, and antibiofilm activity, thus offering an additional strategy to treat biofilm-associated infections.

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.

Antimicrobial Potential of Polyphenols: An Update on Alternative for Combating Antimicrobial Resistance

The last decade has encountered an increasing demand for plant-based natural antibiotics. This demand has led to more research-based investigations for natural sources of antimicrobial agents and published reports demonstrating that plant extracts are widely applied in modern medicine, reporting potential activity that may be due to polyphenol compounds. Interestingly, the effects of polyphenols on the sensitivity of bacteria to antibiotics have not been well-studied. Hence, the current review encompasses the prospective application of plant-based phenolic extracts from plants of Indian origin. The emergence of resistance to antimicrobial agents has increased the inefficacy of many antimicrobial drugs. Several strategies have been developed in recent times to overcome this issue. A combination of antimicrobial agents is employed for the failing antibiotics, which restores the desirable effect but may have toxicity-related issues. Phytochemicals such as some polyphenols have demonstrated their potent activity as antimicrobial agents of natural origin to work against resistance issues. These agents alone or in combination with certain antibiotics have been shown to enhance the antimicrobial activity against a spectrum of microbes. However, the information regarding the mechanisms and structure-activity relationships remains elusive. The present review also focuses on the possible mechanisms of natural compounds based on their structure- activity relationships for incorporating polyphenolic compounds in the drug-development processes. Besides this work, polyphenols could reduce drug dosage and may diminish the unhidden or hidden side effects of antibiotics. Pre-clinical findings have provided strong evidence that polyphenolic compounds, individually and in combination with already approved antibiotics, work well against the development of resistance. However, more studies must focus on in vivo results, and clinical research needs to specify the importance of polyphenol-based antibacterials in clinical trials.

Strain-dependent interactions of Streptococcus suis and Glaesserella parasuis in co-culture

Streptococcus suis (S. suis) and Glaesserella parasuis (G. parasuis) are ubiquitous colonizers of swine tonsils that can cause systemic disease and death, under undefined conditions. It is not known, however, whether these 2 species interact during initial infection. To investigate whether such interactions occur, the objective of this study was to assess phenotypic differences between mono-and co-cultures of S. suis and G. parasuis when representative strains with different virulence potential were co-cultured in vitro. In cross-streak screening experiments, some G. parasuis (GP) serovar strains (GP3, GP4, GP5) exhibited altered morphology with some S. suis (SS) serovar strains, such as SS2, but not with SS1. Co-culture with GP5 reduced hemolytic activity of SS1, but not of SS2. Although both SS strains outgrew GP isolates in biofilm co-cultures, strain type affected the number of planktonic or sessile cells in co-culture biofilms. Numbers of sessile SS1 increased in co-cultures, but not of GP3. Both planktonic and sessile SS2 increased in co-culture, whereas GP5 decreased. Sessile SS1 increased, but planktonic GP5 decreased in co-culture and planktonic SS2 increased, but sessile GP3 decreased when grown together. The SS2 strain had a competitive advantage over GP3 during mid-exponential co-culture in broth. Streptococcus suis is predicted to use more unique carbon sources, suggesting that S. suis outcompetes G. parasuis in growth and nutrient consumption. This work provides direction for future studies of phenotypic and genotypic interactions between these and other swine tonsil co-colonizers.

Effects of water turbidity on the survival of Staphylococcus aureus in environmental fresh and brackish waters

Staphylococcus aureus is an opportunistic pathogen frequently detected in environmental waters and commonly causes skin infections to water users. S. aureus concentrations in fresh, brackish, and marine waters are positively correlated with water turbidity. To reduce the risk of S. aureus infections from environmental waters, S. aureus survival (stability and multiplication) in turbid waters needs to be investigated. The aim of this study was to measure S. aureus in turbid fresh and brackish water samples and compare the concentrations over time to determine which conditions are associated with enhanced S. aureus survival. Eighteen samples were collected from fresh and brackish water sources from two different sites on the east side of O'ahu, Hawai'i. S. aureus was detected in microcosms for up to 71 days with standard microbial culturing techniques. On average, the greatest environmental concentrations of S. aureus were in high turbidity fresh waters followed by high turbidity brackish waters. Models demonstrate that salinity and turbidity significantly predict environmental S. aureus concentrations. S. aureus persistence over the extent of the experiment was the greatest in high turbidity microcosms with T90 's of 147.8 days in brackish waters and 80.8 days in freshwaters. This study indicates that saline, turbid waters, in the absence of sunlight, provides suitable conditions for enhanced persistence of S. aureus communities that may increase the risk of exposure in environmental waters. PRACTITIONER POINTS: Staphylococcus aureus concentrations, survival, and persistence were assessed in environmental fresh and brackish waters. Experimental design preserved in situ conditions to measure S. aureus survival. Higher initial S. aureus concentrations were observed in fresh waters with elevated turbidity, while sustained persistence was greater in brackish waters. Water turbidity and salinity were both positively associated with S. aureus concentrations and persistence. Climate change leads to more intense rainfall events which increase water turbidity and pathogen loading, heightening the exposure risk to S. aureus.

Quorum-sensing, intra- and inter-species competition in the staphylococci

In Gram-positive bacteria such as Staphylococcus aureus and the coagulase-negative staphylococci (CoNS), the accessory gene regulator (agr) is a highly conserved but polymorphic quorum-sensing system involved in colonization, virulence and biofilm development. Signalling via agr depends on the interaction of an autoinducing peptide (AIP) with AgrC, a transmembrane sensor kinase that, once phosphorylated activates the response regulator AgrA. This in turn autoinduces AIP biosynthesis and drives target gene expression directly via AgrA or via the post-transcriptional regulator, RNAIII. In this review we describe the molecular mechanisms underlying the agr-mediated generation of, and response to, AIPs and the molecular basis of AIP-dependent activation and inhibition of AgrC. How the environment impacts on agr functionality is considered and the consequences of agr dysfunction for infection explored. We also discuss the concept of AIP-driven competitive interference between S. aureus and the CoNS and its anti-infective potential.

Staphylococcus aureus in Polymicrobial Skinand Soft Tissue Infections: Impact of Inter-Species Interactionsin Disease Outcome

Polymicrobial biofilms provide a complex environment where co-infecting microorganisms can behave antagonistically, additively, or synergistically to alter the disease outcome compared to monomicrobial infections. Staphylococcus aureus skin and soft tissue infections (Sa-SSTIs) are frequently reported in healthcare and community settings, and they can also involve other bacterial and fungal microorganisms. This polymicrobial aetiology is usually found in chronic wounds, such as diabetic foot ulcers, pressure ulcers, and burn wounds, where the establishment of multi-species biofilms in chronic wounds has been extensively described. This review article explores the recent updates on the microorganisms commonly found together with S. aureus in SSTIs, such as Pseudomonas aeruginosa, Escherichia coli, Enterococcus spp., Acinetobacter baumannii, and Candida albicans, among others. The molecular mechanisms behind these polymicrobial interactions in the context of infected wounds and their impact on pathogenesis and antimicrobial susceptibility are also revised.

Staphylococcus aureus triggers a protective inflammatory response against secondary Cryptococcus gattii infection in a murine model

Prior infections can provide protection or enhance susceptibility to a subsequent infection through microorganism's interaction or host immunomodulation. Staphylococcus aureus (SA) and Cryptococcus gattii (CG) cause lungs infection, but it is unclear how they interact in vivo. This study aimed to study the effects of the primary SA lung infection on secondary cryptococcosis caused by CG in a murine model. The mice's survival, fungal burden, behavior, immune cells, cytokines, and chemokines were quantified to evaluate murine cryptococcosis under the influence of a previous SA infection. Further, fungal-bacterial in vitro interaction was studied in a culture medium and a phagocytosis assay. The primary infection with SA protects animals from the subsequent CG infection by reducing lethality, improving behavior, and impairing the fungal proliferation within the host. This phenotype was associated with the proinflammatory antifungal host response elicited by the bacteria in the early stage of cryptococcosis. There was no direct inhibition of CG by SA, although the phagocytic activity of macrophages was reduced. Identifying mechanisms involved in this protection may lead to new approaches for preventing and treating cryptococcosis.

In Vitro Bacterial Competition of Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli against Coagulase-Negative Staphylococci from Bovine Mastitis Milk

Intramammary infection (IMI) from the environment and infected quarters can cause co-infection. The objective of this study was to determine the ability of coagulase-negative staphylococci (CNS) to survive in the same environment as Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli as major pathogens. In total, 15 and 242 CNS strains were used in Experiment I and Experiment II, respectively. Both experiments were separated into three conditions: culture with CNS 24 h before (PRIOR), after (AFTER), and at the same time (EQUAL). The lack of a clear zone, regardless of size, was determined to be the key to the survival of both. The CNS species’ percentages of survival against major pathogens were tested using Fisher’s exact test. Differences in the percentages of survival were evident among the CNS species in all conditions. For the PRIOR condition, all CNS mostly survived when living with major strains; however, S. chromogenes could degrade S. agalactiae. Although most CNS strains were degraded in the AFTER and EQUAL conditions, some strains of S. hominis and S. simulans could resist S. aureus and S. agalactiae. In conclusion, some specific strains of CNS are able to survive in an environment with major pathogens. Research into the survival strains may indicate that the concept of novel bacteria with bacteriolytic capabilities might be possible as a novel mastitis treatment.

Biofilm Formation by Staphylococcus aureus in the Specific Context of Cystic Fibrosis

Staphylococcus aureus is a major human pathogen whose characteristics support its success in various clinical settings including Cystic Fibrosis (CF). In CF, S. aureus is indeed the most commonly identified opportunistic pathogen in children and the overall population. S. aureus colonization/infection, either by methicillin-susceptible or methicillin-resistant strains, will become chronic in about one third of CF patients. The persistence of S. aureus in CF patients' lungs, despite various eradication strategies, is favored by several traits in both host and pathogen. Among the latter, living in biofilm is a highly protective way to survive despite deleterious environmental conditions, and is a common characteristic shared by the main pathogens identified in CF. This is why CF has earned the status of a biofilm-associated disease for several years now. Biofilm formation by S. aureus, and the molecular mechanisms governing and regulating it, have been extensively studied but have received less attention in the specific context of CF lungs. Here, we review the current knowledge on S. aureus biofilm in this very context, i.e., the importance, study methods, molecular data published on mono- and multi-species biofilm and anti-biofilm strategies. This focus on studies including clinical isolates from CF patients shows that they are still under-represented in the literature compared with studies based on reference strains, and underlines the need for such studies. Indeed, CF clinical strains display specific characteristics that may not be extrapolated from results obtained on laboratory strains.

Precise spatial structure impacts antimicrobial susceptibility of S. aureus in polymicrobial wound infections

A hallmark of microbial ecology is that interactions between members of a community shape community function. This includes microbial communities in human infections, such as chronic wounds, where interactions can result in more severe diseases. Staphylococcus aureus is the most common organism isolated from human chronic wound infections and has been shown to have both cooperative and competitive interactions with Pseudomonas aeruginosa. Still, despite considerable study, most interactions between these microbes have been characterized using in vitro well-mixed systems, which do not recapitulate the infection environment. Here, we characterized interactions between S. aureus and P. aeruginosa in chronic murine wounds, focusing on the role that both macro- and micro-scale spatial structures play in disease. We discovered that S. aureus and P. aeruginosa coexist at high cell densities in murine wounds. High-resolution imaging revealed that these microbes establish a patchy distribution, only occupying 5 to 25% of the wound volume. Using a quantitative framework, we identified a precise spatial structure at both the macro (mm)- and micro (µm)-scales, which was largely mediated by P. aeruginosa production of the antimicrobial 2-heptyl-4-hydroxyquinoline N-oxide, while the antimicrobial pyocyanin had no impact. Finally, we discovered that this precise spatial structure enhances S. aureus tolerance to aminoglycoside antibiotics but not vancomycin. Our results provide mechanistic insights into the biogeography of S. aureus and P. aeruginosa coinfected wounds and implicate spatial structure as a key determinant of antimicrobial tolerance in wound infections.

Burr hole on polyetheretherketone cranioplasty for the management of chronic subdural hematoma: A case report

Background:

In rare cases, chronic subdural hematoma can be a complication following cranioplasty implantation. Therefore, it can develop spontaneously or after a trauma in the underlying site of a duroplasty and represent, if compression of the brain structures, a life-threatening condition. In case of a patient with cranioplasty in polyetheretherketone (PEEK), performing a burr hole on prosthesis can represent, although unusual, an effective and safe technique for evacuation of the chronic subdural hematoma, avoiding the need to remove the prosthesis itself. Nevertheless, a rare and insidious prosthesis infection can occur, even after years.

Case Description:

A 54-year-old male patient, following severe traumatic brain injury, underwent a right hemispheric decompressive craniectomy associated to acute subdural hematoma evacuation and, subsequently, a PEEK cranioplasty implant with polytetrafluoroethylene (PTFE or Gore-Tex) duroplasty. About 10 years later, he experienced worsening headache with sensory alterations; therefore, he underwent a brain computed tomography scan documenting a right hemispheric chronic subdural hematoma (cSDH), expanding in subsequent radiological examinations. Because of symptoms’ worsening, he underwent cSDH evacuation through a burr hole centered on the parietal region of the PEEK prosthesis, associated with mini-reopening of duroplasty. Two years after the procedure, he went to the emergency department because of the appearance of a serum-purulent material drained from the surgical site. He underwent cranioplasty removal and then started a targeted therapy to treat a triple surgical site infection, often unpredictable and totally accidental.

Conclusion:

Based on the literature evidence, performing a burr hole on a cranial prosthesis in bone-like material such as PEEK represents a surgical procedure never performed before and in our opinion could, in selected cases, guarantee the cSDH evacuation and the treatment of intracranial hypertension, avoiding the cranioplasty removal, although there is a risk of even late surgical site infection.

Hinokiflavone Attenuates the Virulence of Methicillin-Resistant Staphylococcus aureus by Targeting Caseinolytic Protease P

Drug-resistant bacteria was the third leading cause of death worldwide in 2019, which sounds like a cautionary note for global public health. Therefore, developing novel strategies to combat Methicillin-resistant Staphylococcus aureus (MRSA) infections is the need of the hour. Caseinolytic protease P (ClpP) represents pivotal microbial degradation machinery in MRSA involved in bacterial homeostasis and pathogenicity, considered an ideal target for combating S. aureus infections. Herein, we identified a natural compound, hinokiflavone, that inhibited the activity of ClpP of MRSA strain USA300 with an IC₅₀ of 34.36 μg/mL. Further assays showed that hinokiflavone reduced the virulence of S. aureus by inhibiting multiple virulence factors expression. Results obtained from cellular thermal transfer assay (CETSA), thermal shift assay (TSA), local surface plasmon resonance (LSPR) and molecular docking (MD) assay enunciated that hinokiflavone directly bonded to ClpP with confirmed docking sites, including SER-22, LYS-26 and ARG-28. In vivo, the evaluation of anti-infective activity showed that hinokiflavone in combination with vancomycin effectively protected mice from MRSA-induced fatal pneumonia, which was more potent than vancomycin alone. As mentioned above, hinokiflavone, as an inhibitor of ClpP, could be further developed into a promising adjuvant against S. aureus infections.

Heme cross-feeding can augment Staphylococcus aureus and Enterococcus faecalis dual species biofilms

The contribution of biofilms to virulence and as a barrier to treatment is well-established for Staphylococcus aureus and Enterococcus faecalis, both nosocomial pathogens frequently isolated from biofilm-associated infections. Despite frequent co-isolation, their interactions in biofilms have not been well-characterized. We report that in combination, these two species can give rise to augmented biofilms biomass that is dependent on the activation of E. faecalis aerobic respiration. In E. faecalis, respiration requires both exogenous heme to activate the cydAB-encoded heme-dependent cytochrome bd, and the availability of O₂. We determined that the ABC transporter encoded by cydDC contributes to heme import. In dual species biofilms, S. aureus provides the heme to activate E. faecalis respiration. S. aureus mutants deficient in heme biosynthesis were unable to augment biofilms whereas heme alone is sufficient to augment E. faecalis mono-species biofilms. Our results demonstrate that S. aureus-derived heme, likely in the form of released hemoproteins, promotes E. faecalis biofilm formation, and that E. faecalis gelatinase activity facilitates heme extraction from hemoproteins. This interspecies interaction and metabolic cross-feeding may explain the frequent co-occurrence of these microbes in biofilm-associated infections.

Antibiofilm and Antimicrobial Activities of Chloroindoles Against Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is a nosocomial pathogen associated with urinary tract infections and expresses several virulence factors that cause recurring infections and cystitis of the bladder, which can lead to pyelonephritis. UPEC uses different types of extracellular appendages like fimbriae and pili that aid colonization and adherence to bladder epithelium and can form persistent biofilm-like bacterial communities that aid its survival after the deployment of host immune responses. We investigated the antibiofilm, antimicrobial, and antivirulence properties of three indole derivatives namely, 4-chloroindole, 5-chloroindole, and 5-chloro 2-methyl indole. All the three chloroindoles had MICs of 75 μg/ml and inhibited biofilm formation by an average of 67% at 20 μg/ml. In addition, they inhibited swarming and swimming motilities, which are essential for dissemination from bacterial communities and colonization, reduced cell surface hydrophobicity, and inhibited indole production and curli formation. Gene expression analysis showed all three chloroindoles significantly downregulated the expressions of virulence genes associated with adhesion, stress regulation, and toxin production. A 3D-QSAR analysis revealed substitutions at the fourth and fifth positions of the indole moiety favored antimicrobial activity. Furthermore, these chloroindoles potently inhibited biofilm formation in other nosocomial pathogens and polymicrobial consortia.

Food-web and metabolic interactions of the lung inhabitants Streptococcus pneumoniae and Pseudomonas aeruginosa

Bacteria that successfully adapt to different substrates and environmental niches within the lung and overcome the immune defence can cause serious lung infections. Such infections are generally complex, and recognised as polymicrobial in nature. Both Pseudomonas aeruginosa and Streptococcus pneumoniae can cause chronic lung infections and were both detected in cystic fibrosis (CF) lung at different stages. In this study, single and dual species cultures of Pseudomonas aeruginosa and Streptococcus pneumoniae were studied under well controlled planktonic growth conditions. Under pH-controlled conditions, both species apparently benefited from the presence of the other. In co-culture with P. aeruginosa, S. pneumoniae grew efficiently under aerobic conditions, whereas in pure S. pneumoniae culture, growth inhibition occurred in bioreactors with dissolved oxygen concentrations above the microaerobic range. Lactic acid and acetoin that are produced by S. pneumoniae was efficiently utilised by P. aeruginosa. In pH-uncontrolled co-cultures, the low pH triggered by S. pneumoniae assimilation of glucose and lactic acid production negatively affected the growth of both strains. Nevertheless, ammonia production improved significantly, and P. aeruginosa growth dominated at later growth stages. This study revealed unreported metabolic interactions of two important pathogenic microorganisms and shed new lights into pathophysiology of bacterial lung infection. This article is protected by copyright. All rights reserved.

Relapsed boyhood tibia polymicrobial osteomyelitis linked to dermatophytosis: a case report

Background

Relapsed childhood polymicrobial osteomyelitis associated with dermatophytosis has not been reported in the literature.

Case presentation

Here we report on a case of a 45-year-old man who had left tibial osteomyelitis for 29 years, accompanied by skin fungal infection of the ipsilateral heel for 20 years, and underwent a second operation due to recurrence of polymicrobial infection 6 years ago. The patient had a history of injury from a rusty object, which penetrated the anterior skin of the left tibia middle segment causing subsequent bone infection, but was asymptomatic after receiving treatments in 1983. The patient was physically normal until dermatophytosis occurred on the ipsilateral heel skin in 1998. The patient complained that the dermatophytosis was gradually getting worse, and the tibial wound site became itchy, red, and swollen. The left tibial infection resurged in May 2012, leading to the patient receiving debridement and antibiotic treatment. H&E and Gram-stained histology was performed on biopsy specimens of sequestrum and surrounding inflammatory tissue. Tissue culture and microbiology examination confirmed polymicrobial infection with Staphylococcus aureus (S. aureus) and Corynebacterium and a fungus. Additionally, the patient also received potassium permanganate for dermatophytosis when he was admitted into the hospital.

Conclusions

Together with longitudinal follow-up of medical history, surgical findings, histopathological and microbiology culture evidence, we conclude that boyhood tibia polymicrobial osteomyelitis with S. aureus and Corynebacterium occurred in this patient, and the fungal activation of dermatophytosis may have led to osteomyelitis relapse.

The combination of cloxacillin, thioridazine and tetracycline protects mice against Staphylococcus aureus peritonitis by inhibiting α-Hemolysin-induced MAPK/NF-κB/NLRP3 activation

Staphylococcus aureus (S. aureus) infection is difficult to fight, previous experimental reports have demonstrated thioridazine (TZ) and tetracycline (TC) is an inhibitor of S. aureus efflux pump NorA and autolysin Atl, respectively, here, by means of molecular docking and molecular dynamics simulation, we observed that thioridazine (TZ) and tetracycline (TC) blocked the binding of substrates to NorA and Atl, respectively, and reduced their activities, and our antibacterial susceptibility test and three-dimensional checkerboard method showed that the three-drug combination of antibiotic cloxacillin (CXN), TZ and TC had a synergistic anti-Staphylococcal activity in vitro, and α-Hemolysin tests and scanning electron microscopy showed that the three-drug combination and the subinhibitory concentration of the combination significantly inhibited the secretion of α-hemolysin relative to the number of membrane-derived vesicles produced by S. aureus. Whereas Western blot and pharmacological inhibition assays showed that the three-drug combination significantly inhibited the expression of MAPK/NF-κB/NLRP3 proteins in macrophages induced with S. aureus α-hemolysin. In vivo, the drug combination significantly reduced bacterial colony-forming unit counts in the viscera of a mouse peritonitis model of S. aureus infection, therapy reduced the primary inflammatory pathology and the bacteria-stimulated release of cytokines such as IL-1β and TNF-α, and inhibited the expression of MAPK/NF-κB/NLRP3 proteins in peritoneal macrophages. Thus, the combination of efflux pump inhibitor, autolysis inhibitor and antibiotic, is a novel anti-Staphylococcal and anti-inflammatory strategy who owning good antibacterial activity and significant inhibiting staphylococcal α-hemolysin and inflammation.

Formation of Multispecies Biofilms and Their Resistance to Disinfectants in Food Processing Environments: A Review

ABSTRACT

In food processing environments, various microorganisms can adhere and aggregate on the surface of equipment, resulting in the formation of multispecies biofilms. Complex interactions among microorganisms may affect the formation of multispecies biofilms and resistance to disinfectants, which are food safety and quality concerns. This article reviews the various interactions among microorganisms in multispecies biofilms, including competitive, cooperative, and neutral interactions. Then, the preliminary mechanisms underlying the formation of multispecies biofilms are discussed in relation to factors, such as quorum-sensing signal molecules, extracellular polymeric substances, and biofilm-regulated genes. Finally, the resistance mechanisms of common contaminating microorganisms to disinfectants in food processing environments are also summarized. This review is expected to facilitate a better understanding of interspecies interactions and provide some implications for the control of multispecies biofilms in food processing.

HIGHLIGHTS

Investigation of hub gene associated with the infection of Staphylococcus aureus via weighted gene co-expression network analysis

Introduction

Staphylococcus aureus is a gram-positive bacterium that causes serious infection. With the increasing resistance of bacteria to current antibiotics, it is necessary to learn more about the molecular mechanism and cellular pathways involved in the Staphylococcus aureus infection.

Methods

We downloaded the GSE33341 dataset from the GEO database and applied the weighted gene co-expression network analysis (WGCNA), from which we obtained some critical modules. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) were applied to illustrate the biological functions of genes in these modules. We constructed the protein-protein interaction (PPI) network by Cytoscape and selected five candidate hub genes. Five potential hub genes were validated in GSE30119 by GraphPad Prism 8.0. The diagnostic values of these genes were calculated and present in the ROC curve based on the GSE13670 dataset. Their gene functions were analyzed by Gene Set Enrichment Analysis (GSEA).

Results

A co-expression network was built with 5000 genes divided into 11 modules. The genes in green and turquoise modules demonstrated a high correlation. According to the KEGG and GO analyses, genes in the green module were closely related to ubiquitination and autophagy. Subsequently, we picked out the top five hub genes in the green module. And UBB was determined as the hub gene in the GSE30119 dataset. The expression level of UBB, ASB, and MKRN1 could significantly differentiate between Staphylococcus aureus infection and healthy controls based on the ROC curve. The GSEA analysis indicated that lower expression levels of UBB were associated with the P53 signal pathway.

Conclusions

We identified some hub genes and significant signal enrichment pathways in Staphylococcus aureus infection via bioinformatics analysis, which may facilitate the development of potential clinical therapeutic strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02392-y.

Impact of Healthcare-Associated Infections Connected to Medical Devices-An Update

Healthcare-associated infections (HAIs) are caused by nosocomial pathogens. HAIs have an immense impact not only on developing countries but also on highly developed parts of world. They are predominantly device-associated infections that are caused by the planktonic form of microorganisms as well as those organized in biofilms. This review elucidates the impact of HAIs, focusing on device-associated infections such as central line-associated bloodstream infection including catheter infection, catheter-associated urinary tract infection, ventilator-associated pneumonia, and surgical site infections. The most relevant microorganisms are mentioned in terms of their frequency of infection on medical devices. Standard care bundles, conventional therapy, and novel approaches against device-associated infections are briefly mentioned as well. This review concisely summarizes relevant and up-to-date information on HAIs and HAI-associated microorganisms and also provides a description of several useful approaches for tackling HAIs.

Prospective assessment of catheter-associated bacteriuria clinical presentation, epidemiology, and colonization dynamics in nursing home residents

BACKGROUND

Catheterization facilitates continuous bacteriuria, for which the clinical significance remains unclear. This study aimed to determine the clinical presentation, epidemiology, and dynamics of bacteriuria in a cohort of long-term catheterized nursing home residents.

METHODS

Prospective urine culture, urinalysis, chart review, and assessment of signs and symptoms of infection were performed weekly for 19 study participants over 7 months. All bacteria ≥ 1 × 10³ cfu/mL were cultured, isolated, identified, and tested for susceptibility to select antimicrobials.

RESULTS

In total, 226 of the 234 urine samples were polymicrobial (97%), with an average of 4.7 isolates per weekly specimen. A total of 228 urine samples (97%) exhibited ≥ 1 × 10⁶ CFU/mL, 220 (94%) exhibited abnormal urinalysis, 126 (54%) were associated with at least 1 possible sign or symptom of infection, and 82 (35%) would potentially meet a standardized definition of catheter-associated urinary tract infection (CAUTI), but only 3 had a caregiver diagnosis of CAUTI. Bacterial isolates (286; 30%) were resistant to a tested antimicrobial agent, and bacteriuria composition was remarkably stable despite a combined total of 54 catheter changes and 23 weeks of antimicrobial use.

CONCLUSION

Bacteriuria composition was largely polymicrobial, including persistent colonization by organisms previously considered to be urine culture contaminants. Neither antimicrobial use nor catheter changes sterilized the urine, at most resulting in transient reductions in bacterial burden followed by new acquisition of resistant isolates. Thus, this patient population exhibits a high prevalence of bacteriuria coupled with potential indicators of infection, necessitating further exploration to identify sensitive markers of true infection.

FUNDING

This work was supported by the NIH (R00 DK105205, R01 DK123158, UL1 TR001412).

Foodborne ESKAPE Biofilms and Antimicrobial Resistance: lessons Learned from Clinical Isolates

The ESKAPE pathogens (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) are identified to be multidrug-resistant (MDR), extensively drug-resistant (XDR), and pan drug-resistant (PDR); thereby, imposing severe challenges in the treatment of associated infections. ESKAPE pathogens colonize on various biotic and abiotic surfaces; biofilms formed by these pathogens are a potential source for food contamination. Moreover, biofilms play a pivotal role in the development of antimicrobial-resistant (AMR) strains. Hence, the frequent isolation of antimicrobial-resistant ESKAPE pathogens from food products across the globe imposes a threat to public health. A comprehensive understanding of the adhesion signaling involved in the polymicrobial and single-species biofilm will assist in developing alternative preservation techniques and novel therapeutic strategies to combat ESKAPE pathogens. The review provides a comprehensive overview of the signaling mechanisms that prevail in the ESKAPE pathogens for adhesion to abiotic and biotic surfaces and molecular mechanisms associated with poly-microbial biofilm-assisted AMR in ESKAPE.

Staphylococcus aureus Synergized with Candida albicans to Increase the Pathogenesis and Drug Resistance in Cutaneous Abscess and Peritonitis Murine Models

The mixed species of Staphylococcus aureus and Candida albicans can cause infections on skin, mucosa or bloodstream; however, mechanisms of their cross-kingdom interactions related to pathogenesis and drug resistance are still not clear. Here an increase of S. aureus proliferation and biofilm formation was observed in S. aureus and C. albicans dual-species culture, and the synergistic pathogenic effect was then confirmed in both local (cutaneous abscess) and systemic infection (peritonitis) murine models. According to the transcriptome analysis of the dual-species culture, virulence factors of S. aureus were significantly upregulated. Surprisingly, the beta-lactams and vancomycin-resistant genes in S. aureus as well as azole-resistant genes in C. albicans were also significantly increased. The synergistic effects on drug resistance to both antibacterial and antifungal agents were further proved both in vitro and in cutaneous abscess and peritonitis murine models treated by methicillin, vancomycin and fluconazole. The synergistic interactions between S. aureus and C. albicans on pathogenesis and drug resistance highlight the importance of targeting the microbial interactions in polyspecies-associated infections.

Long-term coexistence of Pseudomonas aeruginosa and Staphylococcus aureus using an in vitro cystic fibrosis model

Aim: To investigate the role of pre-established Staphylococcus aureus on Pseudomonas aeruginosa adaptation and antibiotic tolerance. Materials & methods: Bacteria were cultured mimicking the sequential pattern of lung colonization and exposure to ciprofloxacin. Results: In the absence of ciprofloxacin exposure, S. aureus and P. aeruginosa coexisted supported by the physicochemical characteristics of the artificial sputum medium. S. aureus had no role in P. aeruginosa tolerance against ciprofloxacin and did not select P. aeruginosa small-colony variants during antibiotic treatment. rhlR and psqE were downregulated after the contact with S. aureus indicating that P. aeruginosa attenuated its virulence potential. Conclusion: P. aeruginosa and S. aureus can cohabit in cystic fibrosis airway environment for long-term without significant impact on P. aeruginosa adaptation and antibiotic tolerance.

Medicated multi-targeted alginate-based dressings for potential treatment of mixed bacterial-fungal infections in diabetic foot ulcers

Recently developed medicated dressings target either bacterial or fungal infection only, which is not effective for the treatment of mixed infections common in diabetic foot ulcers (DFUs). This study aimed to develop advanced bioactive alginate-based dressings (films and wafers) to deliver therapeutically relevant doses of ciprofloxacin (CIP) and fluconazole (FLU) to target mixed bacterial and fungal infections in DFUs. The alginate compatibility with the drugs was confirmed by SEM, XRD, FTIR and texture analysis, while the medicated wafers showed better fluid handling properties than the films in the presence of simulated wound fluid. The dressings showed initial fast release of FLU followed by sustained release of CIP which completely eradicated E. coli, S. aureus, P. aeruginosa and reduced fungal load (C. albicans) by 10-fold within 24 h. Moreover, the medicated dressings were biocompatible (>70% cell viability over 72 h) with human primary adult keratinocytes and in-vitro scratch assay showed 65-68% wound closure within 7 days.

The Intestinal Biofilm of Pseudomonas aeruginosa and Staphylococcus aureus Is Inhibited by Antimicrobial Peptides HBD-2 and HBD-3

Background: The intestinal microbiota is a very active microbial community interacting with the host in maintaining homeostasis; it acts in cooperation with intestinal epithelial cells, which protect the host from the external environment by producing a diverse arsenal of antimicrobial peptides (AMPs), including β-defensins-2 and 3 (HBD-2 and HBD-3), considered among the most studied in this category. However, there are some circumstances in which an alteration of this eubiotic state occurs, with the triggering of dysbiosis. In this condition, the microbiota loses its protective power, leading to the onset of opportunistic infections. In this scenario, the emergence of multi-drug resistant biofilms from Pseudomonas aeruginosa and Staphylococcus aureus is very frequent. Methods: We created a Caco-2 intestinal epithelial cell line stably transfected with the genes, encoding HBD-2 and HBD-3, in order to evaluate their ability to inhibit the intestinal biofilm formation of P. aeruginosa and S. aureus. Results: Both HBD-2 and HBD-3 showed anti-biofilm activity against P. aeruginosa and S. aureus. Conclusions: The exploitation of endogenous antimicrobial peptides as a new anti-biofilm therapy, in isolation or in combination with conventional antibiotics, can be an interesting prospect in the treatment of chronic and multi-drug resistant infections.

Surfaceome and Exoproteome Dynamics in Dual-Species Pseudomonas aeruginosa and Staphylococcus aureus Biofilms

Bacterial biofilms are an important underlying cause for chronic infections. By switching into the biofilm state, bacteria can evade host defenses and withstand antibiotic chemotherapy. Despite the fact that biofilms at clinical and environmental settings are mostly composed of multiple microbial species, biofilm research has largely been focused on single-species biofilms. In this study, we investigated the interaction between two clinically relevant bacterial pathogens (Staphylococcus aureus and Pseudomonas aeruginosa) by label-free quantitative proteomics focusing on proteins associated with the bacterial cell surfaces (surfaceome) and proteins exported/released to the extracellular space (exoproteome). The changes observed in the surfaceome and exoproteome of P. aeruginosa pointed toward higher motility and lower pigment production when co-cultured with S. aureus. In S. aureus, lower abundances of proteins related to cell wall biosynthesis and cell division, suggesting increased persistence, were observed in the dual-species biofilm. Complementary phenotypic analyses confirmed the higher motility and the lower pigment production in P. aeruginosa when co-cultured with S. aureus. Higher antimicrobial tolerance associated with the co-culture setting was additionally observed in both species. To the best of our knowledge, this study is among the first systematic explorations providing insights into the dynamics of both the surfaceome and exoproteome of S. aureus and P. aeruginosa dual-species biofilms.

Friend or Foe: Interbacterial Competition in the Nasal Cavity

Like other microbes that live on or in the human body, the bacteria that inhabit the upper respiratory tract, in particular the nasal cavity, have evolved to survive in an environment that presents a number of physical and chemical challenges; these microbes are constantly bombarded with nutritional fluctuations, changes in humidity, the presence of inhaled particulate matter (odorants and allergens), and competition with other microbes. Indeed, only a specialized set of species is able to colonize this niche and successfully contend with the host's immune system and the constant threat from competitors. To this end, bacteria that live in the nasal cavity have evolved a variety of approaches to outcompete contenders for the limited nutrients and space; broadly speaking, these strategies may be considered a type of "bacterial warfare." A greater molecular understanding of bacterial warfare has the potential to reveal new approaches or molecules that can be developed as novel therapeutics. As such, there are many studies within the last decade that have sought to understand the complex polymicrobial interactions that occur in various environments. Here, we review what is currently known about the age-dependent structure and interbacterial relationships within the nasal microbiota and summarize the molecular mechanisms that are predicted to dictate bacterial warfare in this niche. Although the currently described interactions are complex, in reality, we have likely only scratched the surface in terms of a true understanding of the types of interbacterial competition and cooperation that are thought to take place in and on the human body.

Clinical Implications of Polymicrobial Synergism Effects on Antimicrobial Susceptibility

With the development of next generation sequencing technologies in recent years, it has been demonstrated that many human infectious processes, including chronic wounds, cystic fibrosis, and otitis media, are associated with a polymicrobial burden. Research has also demonstrated that polymicrobial infections tend to be associated with treatment failure and worse patient prognoses. Despite the importance of the polymicrobial nature of many infection states, the current clinical standard for determining antimicrobial susceptibility in the clinical laboratory is exclusively performed on unimicrobial suspensions. There is a growing body of research demonstrating that microorganisms in a polymicrobial environment can synergize their activities associated with a variety of outcomes, including changes to their antimicrobial susceptibility through both resistance and tolerance mechanisms. This review highlights the current body of work describing polymicrobial synergism, both inter- and intra-kingdom, impacting antimicrobial susceptibility. Given the importance of polymicrobial synergism in the clinical environment, a new system of determining antimicrobial susceptibility from polymicrobial infections may significantly impact patient treatment and outcomes.

Profiling structural diversity and activity of 2-alkyl-4(1H)-quinolone N-oxides of Pseudomonas and Burkholderia

We synthesized all major saturated and unsaturated 2-alkyl-4(1H)-quinolone N-oxides of Pseudomonas and Burkholderia, quantified their native production levels and characterized their antibiotic activities against competing Staphylococcus aureus. We demonstrate that quinolone core methylation and position of unsaturation in the alkyl-chain dictate antibiotic potency which supports the proposed mechanism of action.

Polymicrobial interactions in the urinary tract: is the enemy of my enemy my friend?

The vast majority of research pertaining to urinary tract infection has focused on a single pathogen in isolation, and predominantly Escherichia coli. However, polymicrobial urine colonization and infection are prevalent in several patient populations, including individuals with urinary catheters. The progression from asymptomatic colonization to symptomatic infection and severe disease is likely shaped by interactions between traditional pathogens as well as constituents of the normal urinary microbiota. Recent studies have begun to experimentally dissect the contribution of polymicrobial interactions to disease outcomes in the urinary tract, including their role in development of antimicrobial-resistant biofilm communities, modulating the innate immune response, tissue damage, and sepsis. This review aims to summarize the epidemiology of polymicrobial urine colonization, provide an overview of common urinary tract pathogens, and present key microbe-microbe and host-microbe interactions that influence infection progression, persistence, and severity.

In Vivo and In Vitro Assessments of the Antibacterial Potential of Chitosan-Silver Nanocomposite Against Methicillin-Resistant Staphylococcus aureus-Induced Infection in Rats

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most threatening multidrug-resistant bacteria worldwide. Owing to their efficient antimicrobial properties, nanoparticles have been widely used as an alternative approach for combating the antibiotic-resistant bacteria. Consequently, this study was designed to compare in between the bactericidal effect of low doses (5 mg/kg bwt) of nanoparticles of chitosan (Ch-NPs), silver (Ag-NPs), and chitosan-silver nanocomposites (Ch-Ag NCs) both in vitro and in vivo against experimentally chronic infection induced by methicillin-resistant Staphylococcus aureus (MRSA). The three forms of nanoparticles were tested for their in vitro antimicrobial potential against MRSA by detection of MICs and MBCs using microdilution method. In vivo, thirty-five male albino Wistar rats were used and divided into five groups (n = 7). Group l (negative control), group 2 (MRSA infected and untreated), groups 3, 4, and 5 (MRSA infected then treated with Ch-NPs, Ag-NPs, and Ch-Ag NCs respectively for 7 days). After 6 weeks, blood samples were collected then rats were euthanized to collect different organs (liver, spleen, lungs, and kidneys). Some of them were kept in 10% formalin for histopathological investigations while others used for bacterial re-isolation. Ch-Ag NCs showed the lowest MIC and MBC among the tested nanoparticles. Moreover, the highest histopathological scoring was observed in the infected and untreated group while the lowest scoring was detected in groups treated with Ch-Ag NCs in comparison with the negative control group. The highest bacterial count was noticed in the infected and untreated group followed by those treated with Ch-NPs while the lowest count was observed in group treated with Ch-Ag NCs. Depending on these results, it can be concluded that Ch-Ag NCs have a strong bactericidal effect against MRSA and may be used as alternative option to antibiotics.

Significant increase in the secretion of extracellular vesicles and antibiotics resistance from methicillin-resistant Staphylococcus aureus induced by ampicillin stress

Extracellular vesicles (EVs) containing specific cargo molecules from the cell of origin are naturally secreted from bacteria. EVs play significant roles in protecting the bacterium, which can contribute to their survival in the presence of antibiotics. Herein, we isolated EVs from methicillin-resistant Staphylococcus aureus (MRSA) in an environment with or without stressor by adding ampicillin at a lower concentration than the minimum inhibitory concentration (MIC). We investigated whether EVs from MRSA under stress condition or normal condition could defend susceptible bacteria in the presence of several β-lactam antibiotics, and directly degrade the antibiotics. A comparative proteomic approach was carried out in both types of EVs to investigate β-lactam resistant determinants. The secretion of EVs from MRSA under antibiotic stressed conditions was increased by 22.4-fold compared with that of EVs without stress. Proteins related to the degradation of β-lactam antibiotics were abundant in EVs released from the stressed condition. Taken together, the present data reveal that EVs from MRSA play a crucial role in the survival of β-lactam susceptible bacteria by acting as the first line of defense against β-lactam antibiotics, and antibiotic stress leads to release EVs with high defense activity.

Biofilms in Diabetic Foot Ulcers: Significance and Clinical Relevance

Foot infections are the main disabling complication in patients with diabetes mellitus. These infections can lead to lower-limb amputation, increasing mortality and decreasing the quality of life. Biofilm formation is an important pathophysiology step in diabetic foot ulcers (DFU)-it plays a main role in the disease progression and chronicity of the lesion, the development of antibiotic resistance, and makes wound healing difficult to treat. The main problem is the difficulty in distinguishing between infection and colonization in DFU. The bacteria present in DFU are organized into functionally equivalent pathogroups that allow for close interactions between the bacteria within the biofilm. Consequently, some bacterial species that alone would be considered non-pathogenic, or incapable of maintaining a chronic infection, could co-aggregate symbiotically in a pathogenic biofilm and act synergistically to cause a chronic infection. In this review, we discuss current knowledge on biofilm formation, its presence in DFU, how the diabetic environment affects biofilm formation and its regulation, and the clinical implications.

Quorum Sensing and Toxin Production in Staphylococcus aureus Osteomyelitis: Pathogenesis and Paradox

Staphylococcus aureus is a Gram-positive pathogen capable of infecting nearly every vertebrate organ. Among these tissues, invasive infection of bone (osteomyelitis) is particularly common and induces high morbidity. Treatment of osteomyelitis is notoriously difficult and often requires debridement of diseased bone in conjunction with prolonged antibiotic treatment to resolve infection. During osteomyelitis, S. aureus forms characteristic multicellular microcolonies in distinct niches within bone. Virulence and metabolic responses within these multicellular microcolonies are coordinated, in part, by quorum sensing via the accessory gene regulator (agr) locus, which allows staphylococcal populations to produce toxins and adapt in response to bacterial density. During osteomyelitis, the Agr system significantly contributes to dysregulation of skeletal homeostasis and disease severity but may also paradoxically inhibit persistence in the host. Moreover, the Agr system is subject to complex crosstalk with other S. aureus regulatory systems, including SaeRS and SrrAB, which can significantly impact the progression of osteomyelitis. The objective of this review is to highlight Agr regulation, its implications on toxin production, factors that affect Agr activation, and the potential paradoxical influences of Agr regulation on disease progression during osteomyelitis.

Contamination of wounds with fecal bacteria in immuno-suppressed mice

Immunocompromised patients are predisposed to chronically infected wounds. Especially ulcers in the dorsal region often experience secondary polymicrobial infections. However, current wound infection models mostly use single-strain bacteria. To mimic clinically occurring infections caused by fecal contamination in immunocompromised/immobile patients, which differ significantly from single-strain infections, the present study aimed at the establishment of a new mouse model using infection by fecal bacteria. Dorsal circular excision wounds in immunosuppressed mice were infected with fecal slurry solution in several dilutions up to 1:8,000. Impact of immunosuppressor, bacterial load and timing on development of wound infections was investigated. Wounds were analyzed by scoring, 3D imaging and swab analyses. Autofluorescence imaging was not successful. Dose-finding of cyclophosphamide-induced immunosuppression was necessary for establishment of bacterial wound infections. Infection with fecal slurry diluted 1:166 to 1:400 induced significantly delayed wound healing (p < 0.05) without systemic reactions. Swab analyses post-infection matched the initial polymicrobial suspension. The customized wound score confirmed significant differences between the groups (p < 0.05). Here we report the establishment of a simple, new mouse model for clinically occurring wound infections by fecal bacteria and the evaluation of appropriate wound analysis methods. In the future, this model will provide a suitable tool for the investigation of complex microbiological interactions and evaluation of new therapeutic approaches.

Complete Genome Sequence of Staphylococcus aureus Phage SA75, Isolated from Goat Feces

Antibiotic-resistant Staphylococcus aureus is an opportunistic pathogen causing serious human infections worldwide. Here, we report the complete annotated genome of bacteriophage SA75, a member of the Siphoviridae family which could be an alternative to traditional antibiotics for treating Staphylococcus infections. We used a hybrid approach combining MinION and Illumina MiSeq sequencing, which yielded a 43,134-bp genome and 65 open reading frames.

The social life of microbes in chronic infection

Chronic infections place a significant burden on healthcare systems, requiring over $25 billion in treatment annually in the United States alone [1,2]. Notably, the majority of chronic infections, which include cystic fibrosis (CF), chronic wounds, otitis media, periodontitis, urinary tract infections, and osteomyelitis, are considered polymicrobial and are often recalcitrant to antibiotic treatment [1-9]. Although we know that diverse communities of microbes comprise these infections, how microbes interact and the impacts of these interactions on human disease are less understood. Here, we discuss recent advances in our understanding of how bacteria communicate in chronic infection, with a focus on Staphylococcus aureus and Pseudomonas aeruginosa, and we highlight outstanding questions and controversies in the field.

Medically important interactions of staphylococci with pathogenic fungi

Staphylococci are common inhabitants at several human body sites and are also implicated in infections either as primary or opportunistic pathogens. These bacteria can thus both contribute to the host defense being a part of the commensalistic microbiota or synergize with the other microbes during the infection process. Among fungi, staphylococci interact synergistically with Candida spp. and Aspergillus fumigatus, and antagonistically with Cryptococcus neoformans and Trichosporon asahii. These interactions are highly dynamic and are orchestrated by a multitude of microbial and host factors. During such cross-talks, staphylococci can modulate the virulence, immune response or drug resistance of the coexisting microbe(s), thereby influencing the infection course, disease severity, treatment strategy and the clinical outcome.

Sanguinarine Inhibits Mono- and Dual-Species Biofilm Formation by Candida albicans and Staphylococcus aureus and Induces Mature Hypha Transition of C. albicans

Previous studies have reported that sanguinarine possesses inhibitory activities against several microorganisms, but its effects on mono- and dual-species biofilms of C. albicans and S. aureus have not been fully elucidated. In this study, we aimed to evaluate the efficacy of sanguinarine for mono- and dual-species biofilms and explore its ability to induce the hypha-to-yeast transition of C. albicans. The results showed that the minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC90) of sanguinarine against C. albicans and S. aureus mono-species biofilms was 4, and 2 μg/mL, respectively, while the MIC and MBIC90 of sanguinarine against dual-species biofilms was 8, and 4 μg/mL, respectively. The decrease in the levels of matrix component and tolerance to antibiotics of sanguinarine-treated mono- and dual-species biofilms was revealed by confocal laser scanning microscopy combined with fluorescent dyes, and the gatifloxacin diffusion assay, respectively. Meanwhile, sanguinarine at 128 and 256 μg/mL could efficiently eradicate the preformed 24-h biofilms by mono- and dual-species, respectively. Moreover, sanguinarine at 8 μg/mL could result in the transition of C. albicans from the mature hypha form to the unicellular yeast form. Hence, this study provides useful information for the development of new agents to combat mono- and dual-species biofilm-associated infections, caused by C. albicans and S. aureus.

A Rare Opportunist, Morganella morganii, Decreases Severity of Polymicrobial Catheter-Associated Urinary Tract Infection

Catheter-associated urinary tract infections (CAUTIs) are common hospital-acquired infections and frequently polymicrobial, which complicates effective treatment. However, few studies experimentally address the consequences of polymicrobial interactions within the urinary tract, and the clinical significance of polymicrobial bacteriuria is not fully understood. Proteus mirabilis is one of the most common causes of monomicrobial and polymicrobial CAUTI and frequently cocolonizes with Enterococcus faecalis, Escherichia coli, Providencia stuartii, and Morganella morganiiP. mirabilis infections are particularly challenging due to its potent urease enzyme, which facilitates formation of struvite crystals, catheter encrustation, blockage, and formation of urinary stones. We previously determined that interactions between P. mirabilis and other uropathogens can enhance P. mirabilis urease activity, resulting in greater disease severity during experimental polymicrobial infection. Our present work reveals that M. morganii acts on P. mirabilis in a contact-independent manner to decrease urease activity. Furthermore, M. morganii actively prevents urease enhancement by E. faecalis, P. stuartii, and E. coli Importantly, these interactions translate to modulation of disease severity during experimental CAUTI, predominantly through a urease-dependent mechanism. Thus, products secreted by multiple bacterial species in the milieu of the catheterized urinary tract can directly impact prognosis.

Airway exposure to Staphylococcal enterotoxin type B (SEB) enhances the number and activity of bone marrow neutrophils via the release of multiple cytokines

BACKGROUND

The lung infections by Staphylococcus aureus are strongly associated with its ability to produce enterotoxins. However, little is known about the mechanisms underlying trafficking of bone marrow (BM) neutrophils during airway inflammation induced by Staphylococcal enterotoxin B (SEB). We therefore aimed to investigate the effects of mouse airways SEB exposure on BM neutrophil counts and its adhesive properties as well as on the release of cytokines/chemokines that orchestrate BM neutrophils trafficking to lung tissue.

METHODS

Male BALB/c mice were intranasally exposed to SEB (1 µg), and at 4, 16 and 24 h thereafter, BM, circulating blood, bronchoalveolar lavage (BAL) fluid and lung tissue were collected. BM neutrophils adhesion, MAC-1 and LFA1-α expressions (by flow cytometry) as well as measurement of cytokine and/or chemokines levels were assayed after SEB-airway exposure.

RESULTS

Prior exposure to SEB promoted a marked influx of neutrophils to BAL and lung tissue, which was accompanied by increased counts of BM immature neutrophils and blood neutrophilia. BM neutrophil expressions of LFA1-α and MAC-1 were unchanged by SEB exposure whereas a significant enhancement of adhesion properties to VCAM-1 was observed. The early phase of airway SEB exposure was accompanied by high levels of GM-CSF, G-CSF, IFN-γ, TNF-α and KC/CXCL1, while the latter phase by the equilibrated actions of SDF1-α and MIP-2.

CONCLUSION

Mouse airways exposure to SEB induces BM cytokines/chemokines release and their integrated actions enhance the adhesion of BM neutrophils leading to acute lung injury.

Development of a Staphylococcus aureus reporter strain with click beetle red luciferase for enhanced in vivo imaging of experimental bacteremia and mixed infections

In vivo bioluminescence imaging has been used to monitor Staphylococcus aureus infections in preclinical models by employing bacterial reporter strains possessing a modified lux operon from Photorhabdus luminescens. However, the relatively short emission wavelength of lux (peak 490 nm) has limited tissue penetration. To overcome this limitation, the gene for the click beetle (Pyrophorus plagiophtalamus) red luciferase (luc) (with a longer >600 emission wavelength), was introduced singly and in combination with the lux operon into a methicillin-resistant S. aureus strain. After administration of the substrate D-luciferin, the luc bioluminescent signal was substantially greater than the lux signal in vitro. The luc signal had enhanced tissue penetration and improved anatomical co-registration with infected internal organs compared with the lux signal in a mouse model of S. aureus bacteremia with a sensitivity of approximately 3 × 10⁴ CFU from the kidneys. Finally, in an in vivo mixed bacterial wound infection mouse model, S. aureus luc signals could be spectrally unmixed from Pseudomonas aeruginosa lux signals to noninvasively monitor the bacterial burden of both strains. Therefore, the S. aureus luc reporter may provide a technological advance for monitoring invasive organ dissemination during S. aureus bacteremia and for studying bacterial dynamics during mixed infections.