Community-acquired methicillin-resistant Staphylococcus aureus infections

Ampelopsin attenuates Staphylococcus aureus Alpha-Toxin-Induced Lung Injury

Staphylococcus aureus is a prevalent cause of lung infections in hospitals and communities, and can cause a wide spectrum of human infections. Due to the bottleneck caused by antibiotic resistance and substantial increases in morbidity and mortality, targeting the virulence factors released by S. aureus as an alternative prevention and treatment method has become a promising approach. Ampelopsin, a component of vine tea, has promising potential for treating S. aureus-induced acute lung injury. In this study, the effects of ampelopsin were investigated on a mouse model of acute lung injury established using S. aureus 8325-4 and the α-hemolysin (hla) silent strain DU1090. The hla silent strain did not cause mortality in mice, whereas lethal and sublethal concentrations of S. aureus 8325-4 caused high mortality. Notably, ampelopsin treatment protected against mortality stemming from S. aureus infection. Ampelopsin yielded enhancements in lung barrier function, decreased total protein leakage in the alveolar lavage fluid, and modulated inflammatory signaling pathway-related proteins, thereby reducing the release of pro-inflammatory factors and improving respiratory dysfunction. Moreover, ampelopsin prevented the upregulation of ADAM10 activity, leading to E-cadherin mucin cleavage. In conclusion, our findings establish the key role of alpha -toxin in infectious lung injury in S. aureus and provide support for ampelopsin as an effective therapeutic approach to improve lung injury.

A Rapid Antimicrobial Resistance Diagnostic Platform for Staphylococcus aureus Using Recombinase Polymerase Amplification

Antimicrobial resistance (AMR) has posed a global threat to public health. The Staphylococcus aureus strains have especially developed AMR to practically all antimicrobial medications. There is an unmet need for rapid and accurate detection of the S. aureus AMR. In this study, we developed two versions of recombinase polymerase amplification (RPA), the fluorescent signal monitoring and lateral flow dipstick, for detecting the clinically relevant AMR genes retained by S. aureus isolates and simultaneously identifying such isolates at the species level. The sensitivity and specificity were validated with clinical samples. Our results showed that this RPA tool was able to detect antibiotic resistance for all the 54 collected S. aureus isolates with high sensitivity, specificity, and accuracy (all higher than 92%). Moreover, results of the RPA tool are 100% consistent with that of PCR. In sum, we successfully developed a rapid and accurate AMR diagnostic platform for S. aureus. The RPA might be used as an effective diagnostic test in clinical microbiology laboratories to improve the design and application of antibiotic therapy. IMPORTANCE Staphylococcus aureus is a species of Staphylococcus and belongs to Gram-positive. Meanwhile, S. aureus remains one of the most common nosocomial and community-acquired infections, causing blood flow, skin, soft tissue, and lower respiratory tract infections. The identification of the particular nuc gene and the other eight genes of drug-resistant S. aureus can reliably and quickly diagnose the illness, allowing doctors to prescribe treatment regimens sooner. The detection target in this work is a particular gene of S. aureus, and a POCT is built to simultaneously recognize S. aureus and analyze genes representing four common antibiotic families. We developed and assessed a rapid and on-site diagnostic platform for the specific and sensitive detection of S. aureus. This method allows the determination of S. aureus infection and 10 different AMR genes representing four different families of antibiotics within 40 min. It was easily adaptable in low-resource circumstances and professional-lacking circumstances. It should be supported in overcoming the continuous difficulty of drug-resistant S. aureus infections, which is a shortage of diagnostic tools that can swiftly detect infectious bacteria and numerous antibiotic resistance indicators.

Luteolin Inhibits the Biofilm Formation and Cytotoxicity of Methicillin-Resistant Staphylococcus aureus via Decreasing Bacterial Toxin Synthesis

Owing to the fact that luteolin has antibacterial activity against Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA), its specific mechanism in MRSA is worthy of investigation, which is the focus of this study. Initially, the collected S. aureus strains were treated with luteolin. Then, the minimum inhibitory concentration (MIC) of luteolin against the S. aureus strains was measured by the broth microdilution. The growth curves, biofilm formation, and cytotoxicity of treated S. aureus were detected using a microplate reader. The live and dead bacteria were evaluated using confocal laser scanning microscopy, the bacterial morphology was observed using scanning electron microscopy, and the S. aureus colony-forming unit (CFU) numbers were assessed. The levels of alpha hemolysin (α-hemolysin), delta hemolysin (δ-hemolysin), and hlaA were detected via western blot and RT-PCR. The mortality of mouse model with S. aureus systemic infection was analyzed, and the levels of IL-6, IL-8, IL-10, and TNF-α were quantitated using ELISA. Concretely, the MIC of luteolin against MRSA N315 was 64 μg/mL. Luteolin at 16 μg/mL did not affect the growth of MRSA N315, but inhibited the biofilm formation and CFU, and promoted the morphological changes and death of MRSA N315. Luteolin decreased the cytotoxicity and the levels of α-hemolysin, δ-hemolysin, and hlaA in MRSA N315, elevated MRSA-reduced mice survival rate, and differentially modulated the inflammatory cytokine levels in MRSA-infected mice. Collectively, luteolin inhibits biofilm formation and cytotoxicity of MRSA via blocking the bacterial toxin synthesis.

Genotypic Characterization of Clinical Isolates of Staphylococcus aureus from Pakistan

In this study, we compared pulsed-field gel electrophoretic (PFGE), multilocus sequence typing (MLST), Staphylococcal cassette chromosome mec (SCCmec), spa typing, and virulence gene profiles of 19 Panton–Valentine leucocidin (PVL)-positive, multidrug-, and methicillin-resistant clinical Staphylococcus aureus (MRSA) isolates obtained from a hospital intensive care unit in Pakistan. The isolates exhibited 10 pulsotypes, contained eight adhesin genes (bbp, clfA, clfB, cna, fnbA, fnbB, map-eap, and spa), 10 toxin genes (hla, hlb, hld, hlg, pvl, sed, see, seg, seh, and tst), and two other virulence genes (cfb, v8) that were commonly present in all isolates. The spa-typing indicated seven known spa types (t030, t064, t138, t314, t987, t1509, and t5414) and three novel spa types. MLST analysis indicated eight ST types (ST8, ST15, ST30, ST239, ST291, ST503, ST772, and ST1413). All isolates belonged to the agr group 1. Most of the isolates possessed SCCmec type III, but some isolates had it in combination with types SCCmec IV and V. The presence of multidrug-resistant MRSA isolates in Pakistan indicates poor hygienic conditions, overuse of antibiotics, and a lack of rational antibiotic therapy that have led to the evolution and development of hypervirulent MRSA clones. The study warrants development of a robust epidemiological screening program and adoption of effective measures to stop their spread in hospitals and the community.

Proto-Oncogenes and Cell Cycle Gene Expression in Normal and Neoplastic Oral Epithelial Cells Stimulated With Soluble Factors From Single and Dual Biofilms of Candida albicans and Staphylococcus aureus

This study was aimed at analyzing proto-oncogenic signaling pathway activation in normal oral keratinocytes (NOK-si) and neoplastic cell lines (SCC 25 and Detroit 562) stimulated with metabolites (soluble factors) from single and dual biofilms of Candida albicans and Staphylococcus aureus. Soluble factors (SF) from early (16-h) and mature (36-h) biofilms of C. albicans and S. aureus were collected and incubated with cell cultures, which were subsequently evaluated using gene expression via RT-qPCR, cell viability via AlamarBlue^TM, and flow cytometry cell cycle analysis. In general, exposure to the SF of early and mature biofilms from C. albicans and dual species caused a major reduction in NOK-si cell viability and enhanced the sub G0 phase. This led to a decrease in gene expression. However, in this cell line, SF of S. aureus biofilms upregulated the CDKN1A gene followed by the maintenance of cell viability and a significant increase in the G2/M population. For tumor cells, SCC 25 and Detroit 562, the stimuli of SF biofilms upregulated oncogenes such as hRAS and mTOR, as well as Bcl-2 and CDKN1A. SCC 25 and Detroit 562 cells could survive even after 24 h of stimuli from both SF (early and mature). This occurred without significant changes taking place in the cell cycle progression for SCC 25, and with a significant tendency to increase the G2/M phase for Detroit 562. These results point to the fact that metabolites from prevalent clinical fungal and bacterial biofilms, C. albicans and S. aureus, can disrupt the homeostasis of normal and neoplastic oral epithelial cells. This changes proto-oncogenes’ expression, specifically PI3KCA, hRAS, mTOR, BRAF, and cell cycle genes CDKN1A and Bcl-2, thus causing a disturbance in cell viability, survival, and the cell cycle profile.

Clinical, Epidemiologic, and Laboratory Aspects of Methicillin-Resistant Staphylococcus aureus Infections

Oxacillin-resistant Staphylococcus aureus (abbreviated MRSA for historical reasons) is a major pathogen responsible for both hospital- and community-onset disease. Resistance to oxacillin in most clinical isolates of S. aureus is mediated by PBP2a, a penicillin-binding protein with low affinity to beta-lactams, encoded primarily by the mecA gene. Rapid and accurate methods of susceptibility testing of S. aureus isolates to identify MRSA infections are important tools to limit the spread of this organism. This review focuses on the clinical significance of MRSA infections and new approaches for the laboratory diagnosis and epidemiologic typing of MRSA strains.

Allicin causes fragmentation of the peptidoglycan coat in Staphylococcus aureus by effecting synthesis and aiding hydrolysis: a determination by MALDI-TOF mass spectrometry on whole cells

PURPOSE

To determine the effect of allicin on Staphylococcus aureus cell wall peptidoglycans by the application of MALDI-TOF mass spectrometry on whole cells and to relate this to current knowledge of wall-processing enzymes.

METHODOLOGY

Two different S. aureus strains were grown for 48 h after which period each culture was split into two, one part was then treated with sub-inhibitory levels of allicin while the other part left untreated as a control. After a further 24 h whole cells were recovered and analysed by MALDI-TOF mass spectrometry.

RESULTS

Changes in the mass spectra between the treated and untreated cells revealed fragmented peptidoglycans identified by mass calculation only in the treated cells. These peptidoglycan fragments where identified as the products of specific peptidoglycan hydrolases.

CONCLUSIONS

Allicin is known to target cysteine thiol groups. These are absent in peptidoglycan hydrolases and we might have expected identical results in both of the treated and untreated cells. Peptidoglycan synthesis enzymes such as the Fem family of enzymes do contain cysteines. Fem enzymes A, B and X all have a conserved conformation of 99 % for over 100 S. aureus strains and are therefore potential targets for allicin. Examination of FemA structure showed that cysteine102 is accessible from the surface. We propose that allicin has an inhibitory mechanism alongside others of targeting FemA and possibly other Fem enzymes by curtailing glycine bridging and leading to fragmentation. This study provided an insight into yet another antimicrobial mechanism of allicin.

Nanomaterial-based optical and electrochemical techniques for detection of methicillin-resistant Staphylococcus aureus: a review

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for a number of life-threatening complications in humans. Mutations in the genetic sequence of S. aureus due to the presence of certain genes results in resistance against β-lactamases. Thus, there is an urgent need for developing highly sensitive techniques for the early detection of MRSA to counter the rise in resistant strains. This review (142 refs.) extensively covers literature reports on nanomaterial-based optical and electrochemical sensors from the year 1983 to date, with particularly emphasis on recent advances in electrochemical sensing (such as voltammetry and impedimetric) and optical sensing (such as colorimetry and fluorometry) techniques. Among the electrochemical methods, various nanomaterials were employed for the modification of electrodes. Whereas, in optical assays, formats such as enzyme linked immunosorbent assay, lateral flow assays or in optical fiber systems are common. In addition, novel sensing platforms are reported by applying advanced nanomaterials which include gold nanoparticles, nanotitania, graphene, graphene-oxide, cadmium telluride and related quantum dots, nanocomposites, upconversion nanoparticles and bacteriophages. Finally, closing remarks and an outlook conclude the review. Graphical abstract Schematic of the diversity of nanomaterial-based methods for detection of methicillin-resistant Staphylococcus aureus (MRSA). AuNPs: gold nanoparticles; QDs: quantum dots; PVL: Panton-Valentine leukocidin; mecA gene: mec-gene complex encoding methicillin resistance.

Persistent methicillin-resistant Staphylococcus aureus bacteremia owing to placental abscess

Staphylococcus aureus as a pathogen in human gestational membranes, a rather rare phenomenon, has recently been the focus of several researches. S. aureus forms biofilms on these membranes and potentially causes chorioamnionitis in pregnant women. We report a case of persistent methicillin-resistant S. aureus (MRSA) bacteremia owing to placental infection, causing chorioamnionitis and preterm birth. A 29-year-old Japanese woman at the 27th gestational week was diagnosed with acute promyelocytic leukemia and underwent all-trans retinoic acid therapy. Soon after hospitalization, the patient presented with persistent MRSA bacteremia of unknown origin. Despite various antimicrobial therapies, she experienced 12 MRSA bacteremia episodes over 6 weeks. However, after child birth, MRSA bacteremia disappeared without any complications. A pathologic examination of her placenta revealed placenta abscess, resulting in a diagnosis of MRSA-associated chorioamnionitis. Molecular analysis proved that a single MRSA strain (SCCmec Type IVa), which tested negative for Panton-Valentine leukocidin and toxic shock syndrome toxin-1, caused the obstinate infection. We should be aware that persistent MRSA bacteremia in pregnant women can originate from placental abscess.

The Unexpected Impact of Vaccines on Secondary Bacterial Infections Following Influenza

Influenza virus infections remain a significant health burden worldwide, despite available vaccines. Factors that contribute to this include a lack of broad coverage by current vaccines and continual emergence of novel virus strains. Further complicating matters, when influenza viruses infect a host, severe infections can develop when bacterial pathogens invade. Secondary bacterial infections (SBIs) contribute to a significant proportion of influenza-related mortality, with Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, and Haemophilus influenzae as major coinfecting pathogens. Vaccines against bacterial pathogens can reduce coinfection incidence and severity, but few vaccines are available and those that are, may have decreased efficacy in influenza virus-infected hosts. While some studies indicate a benefit of vaccine-induced immunity in providing protection against SBIs, a comprehensive understanding is lacking. In this review, we discuss the current knowledge of viral and bacterial vaccine availability, the generation of protective immunity from these vaccines, and the effectiveness in limiting influenza-associated bacterial infections.

Soluble factors from biofilm of Candida albicans and Staphylococcus aureus promote cell death and inflammatory response

Background

The objective of this study was to better understand the effects of soluble factors from biofilm of single- and mixed-species Candida albicans (C. albicans) and methicillin-sensitive Staphylococcus aureus (MSSA) cultures after 36 h in culture on keratinocytes (NOK-si and HaCaT) and macrophages (J774A.1). Soluble factors from biofilms of C. albicans and MSSA were collected and incubated with keratinocytes and macrophages, which were subsequently evaluated by cell viability assays (MTT). Lactate dehydrogenase (LDH) enzyme release was measured to assess cell membrane damage to keratinocytes. Cells were analysed by brightfield microscopy after 2 and 24 h of exposure to the soluble factors from biofilm. Cell death was detected by labelling apoptotic cells with annexin V and necrotic cells with propidium iodide (PI) and was visualized via fluorescence microscopy. Soluble factors from biofilm were incubated with J774A.1 cells for 24 h; the subsequent production of NO and the cytokines IL-6 and TNF-α was measured by ELISA.

Results

The cell viability assays showed that the soluble factors of single-species C. albicans cultures were as toxic as the soluble factors from biofilm of mixed cultures, whereas the soluble factors of MSSA cultures were less toxic than those of C. albicans or mixed cultures. The soluble factors from biofilm of mixed cultures were the most toxic to the NOK-si and HaCaT cells, as confirmed by analyses of PI labelling and cell morphology. Soluble factors from biofilm of single-species MSSA and mixed-species cultures induced the production of IL-6, NO and TNF-α by J744A.1 macrophages. The production of IL-6 and NO induced by the soluble factors from biofilm of mixed cultures was lower than that induced by the soluble factors from biofilm of single-species MSSA cultures, whereas the soluble factors from biofilm of C. albicans cultures induced only low levels of NO.

Conclusions

Soluble factors from 36-h-old biofilm of C. albicans and MSSA cultures promoted cell death and inflammatory responses.

Community-Associated Methicillin-Resistant Staphylococcus aureus: New Bug, Old Drugs

Objective:

To discuss community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections and evaluate older antibiotics as suitable therapeutic treatment options.

Data Sources:

Searches of MEDLINE, EMBASE, and the Cochrane Library (1966–May 2006) were performed using the key terms methicillin resistance, community-acquired, community associated, treatment, Staphylococcus aureus, mec, and Panton-Valentine leukocidin.

Study Selection and Data Extraction:

All articles were critically evaluated and all relevant information was included in this review.

Data Synthesis:

There has been a documented shift of methicillin resistance occurring in staphylococcal infections manifested within the community. Infections caused by CA-MRSA possess unique characteristics including lack of hospital-associated risk factors, improved susceptibility patterns, distinct genotypes, faster doubling times, and additional toxins. Potential therapeutic options to treat these infections include trimethoprim/sulfamethoxazole (TMP/SMX), clindamycin, tetracyclines, fluoroquinolones, and new antimicrobials.

Conclusions:

CA-MRSA infections can be successfully treated with older, oral antibiotic agents including TMP/SMX, clindamycin, and tetracyclines. Fluoroquinolones and linezolid should be avoided as first-line agents.

Dynamics of biofilm formation and the interaction between Candida albicans and methicillin-susceptible (MSSA) and -resistant Staphylococcus aureus (MRSA)

Polymicrobial biofilms are an understudied and a clinically relevant problem. This study evaluates the interaction between C. albicans, and methicillin- susceptible (MSSA) and resistant (MRSA) S. aureus growing in single- and dual-species biofilms. Single and dual species adhesion (90 min) and biofilms (12, 24, and 48 h) were evaluated by complementary methods: counting colony-forming units (CFU mL-1), XTT-reduction, and crystal violet staining (CV). The secretion of hydrolytic enzymes by the 48 h biofilms was also evaluated using fluorimetric kits. Scanning electron microscopy (SEM) was used to assess biofilm structure. The results from quantification assays were compared using two-way ANOVAs with Tukey post-hoc tests, while data from enzymatic activities were analyzed by one-way Welch-ANOVA followed by Games-Howell post hoc test (α = 0.05). C. albicans, MSSA and MRSA were able to adhere and to form biofilm in both single or mixed cultures. In general, all microorganisms in both growth conditions showed a gradual increase in the number of cells and metabolic activity over time, reaching peak values between 12 h and 48 h (ρ<0.05). C. albicans single- and dual-biofilms had significantly higher total biomass values (ρ<0.05) than single biofilms of bacteria. Except for single MRSA biofilms, all microorganisms in both growth conditions secreted proteinase and phospholipase-C. SEM images revealed extensive adherence of bacteria to hyphal elements of C. albicans. C. albicans, MSSA, and MRSA can co-exist in biofilms without antagonism and in an apparent synergistic effect, with bacteria cells preferentially associated to C. albicans hyphal forms.

Clinical, epidemiologic, and laboratory aspects of methicillin-resistant Staphylococcus aureus infections

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen responsible for both hospital and community onset disease. Resistance to methicillin in S. aureus is mediated by PBP2a, a penicillin-binding protein with low affinity to beta-lactams, encoded by the mecA gene. Accurate susceptibility testing of S. aureus isolates and screening of patients for colonization with MRSA are important tools to limit the spread of this organism. This review focuses on the clinical significance of MRSA infections and new approaches for the laboratory diagnosis and epidemiologic typing of MRSA strains.

Prevalence and risk factors for Staphylococcus aureus colonization in individuals entering maximum-security prisons

To assess the prevalence and risk factors for colonization with Staphylococcus aureus in inmates entering two maximum-security prisons in New York State, USA, inmates (N=830) were interviewed and anterior nares and oropharyngeal samples collected. Isolates were characterized using spa typing. Overall, 50·5% of women and 58·3% of men were colonized with S. aureus and 10·6% of women and 5·9% of men were colonized with MRSA at either or both body sites. Of MSSA isolates, the major subtypes were spa type 008 and 002. Overall, risk factors for S. aureus colonization varied by gender and were only found in women and included younger age, fair/poor self-reported general health, and longer length of prior incarceration. Prevalence of MRSA colonization was 8·2%, nearly 10 times greater than in the general population. Control of epidemic S. aureus in prisons should consider the constant introduction of strains by new inmates.

Effects of linezolid on suppressing in vivo production of staphylococcal toxins and improving survival outcomes in a rabbit model of methicillin-resistant Staphylococcus aureus necrotizing pneumonia

BACKGROUND

 Linezolid is recommended for treatment of pneumonia and other invasive infections caused by methicillin-resistant Staphylococcus aureus (MRSA). The premise underlying this recommendation is that linezolid inhibits in vivo production of potent staphylococcal exotoxins, including Panton-Valentine leukocidin (PVL) and α-hemolysin (Hla), although supporting evidence is lacking.

METHODS

 A rabbit model of necrotizing pneumonia using MRSA clone USA300 was used to compare therapeutic effects of linezolid (50 mg/kg 3 times/day) and vancomycin (30 mg/kg 2 times/day) administered 1.5, 4, and 9 hours after infection on host survival outcomes and in vivo bacterial toxin production.

RESULTS

 Mortality rates were 100% for untreated rabbits and 83%-100% for vancomycin-treated rabbits. In contrast, mortality rates were 25%, 50%, and 100% for rabbits treated with linezolid 1.5, 4, and 9 hours after infection, respectively. Compared with untreated and vancomycin-treated rabbits, improved survival of rabbits treated 1.5 hours after infection with linezolid was associated with a significant decrease in bacterial counts, suppressed bacterial production of PVL and Hla, and reduced production of the neutrophil-chemoattractant interleukin 8 in the lungs.

CONCLUSIONS

 Across the study interval, only early treatment with linezolid resulted in significant suppression of exotoxin synthesis and improved survival outcomes in a rabbit model of MRSA necrotizing pneumonia.

Ceftaroline fosamil: a novel broad-spectrum cephalosporin with activity against methicillin-resistant Staphylococcus aureus

OBJECTIVE

To review the pharmacology, microbiology, chemistry, in vitro activity, pharmacokinetics, clinical efficacy, safety, dosage, and administration of ceftaroline fosamil (Teflaro, Forest Laboratories, Inc.), a novel parenteral broad-spectrum cephalosporin approved by the Food and Drug Administration (FDA) on October 29, 2010, for the treatment of adults with acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP).

DATA SOURCES

A search of MEDLINE (1966-July 2011) using the search terms ceftaroline fosamil, ceftaroline, TAK-599, PPI-0903, PPI-0903M, and T-91825 was performed. Supplementary sources included program abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy, American Society of Microbiology, European Congress on Clinical Microbiology and Infectious Diseases, and the Infectious Diseases Society of America from 2005 to 2010, as well as information available from the manufacturer's Web site.

STUDY SELECTION AND DATA EXTRACTION

All English-language articles identified from the data sources were evaluated. In vitro, preclinical, and Phase 1, 2, and 3 clinical trials were included.

DATA SYNTHESIS

Clinical trials have been conducted evaluating use of ceftaroline for treatment of ABSSSI and CABP. Safety data from Phase 1, 2, and 3 clinical trials suggest that it is well tolerated and has a safety and tolerability profile common to the cephalosporin class. Ceftaroline has excellent in vitro activity against gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), which makes it an attractive monotherapy for the treatment of ABSSSI. However, it lacks activity against problem gram-negative bacteria (eg, Pseudomonas spp.), which will likely limit its use for serious health care-associated infections. While its role in treating CABP is supported by excellent in vitro activity against Streptococcus pneumoniae and clinical efficacy data, currently available comparators may offer some advantages over ceftaroline. Finally, data are lacking to assess its role in the treatment of serious infections due to MRSA (eg, pneumonia, bacteremia).

CONCLUSIONS

These considerations should be part of the formulary review process; however, when considering the significant role MRSA plays in ABSSSI in both the community and hospital settings, we believe that ceftaroline will provide clinicians with a welcome option in addition to currently available anti-MRSA therapies for the treatment of ABSSSI.

Methicillin-resistant Staphylococcus aureus laryngitis

Infections due to methicillin-resistant Staphylococcus aureus (MRSA) have become more prevalent, in part because of the emergence and spread of community-acquired MRSA. This trend is particularly concerning because of the significant rates of morbidity and mortality associated with MRSA infections, and because MRSA strains are often resistant to many classes of antibiotics. Reports of infections of the head and neck, including wound infections, cellulitis, sinusitis, otitis media, and otitis externa, are well documented. However, to our knowledge, there have been no reports of bacterial laryngitis due to MRSA. We report the first published case of bacterial laryngitis caused by MRSA.

Public health surveillance for methicillin-resistant Staphylococcus aureus: comparison of methods for classifying health care- and community-associated infections

OBJECTIVES

We compared 3 methods for classifying methicillin-resistant Staphylococcus aureus (MRSA) infections as health care associated or community associated for use in public health surveillance.

METHODS

We analyzed data on MRSA infections reported to the Michigan Department of Community Health from October 1, 2004, to December 31, 2005. Patient demographics, risk factors, infection information, and susceptibility were collected for 2151 cases. We classified each case by the health care risk factor, infection-type, and susceptibility pattern methods and compared the results of the 3 methods.

RESULTS

Demographic, clinical, and microbiological variables yielded similar health care-associated and community-associated distributions when classified by risk factor and infection type. When 2 methods yielded the same classifications, the overall distribution was similar to classification by 3 methods. No specific combination of 2 methods was superior.

CONCLUSIONS

MRSA categorization by 2 methods is more accurate than it is by a single method. The health care risk factor and infection-type methods yield comparable classification results. Accuracy is increased by using more variables; however, further research is needed to identify the optimal combination.

Poor functional status is an independent predictor of surgical site infections due to methicillin-resistant Staphylococcus aureus in older adults

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has become a common surgical site infection (SSI) pathogen, particularly in older adults. Risk factors for MRSA SSI in elderly patients have not been described.

METHODS

A nested case-control study was conducted. Patients were enrolled from seven study hospitals (one medical center and six community hospitals) between January 1, 1998, and April 1, 2003. Risk factors for MRSA SSI were identified by comparing cases with two reference groups: uninfected surgical patients and patients with SSI due to methicillin-susceptible S. aureus (MSSA). Two separate multivariate models were created using logistic regression and then compared and contrasted.

RESULTS

Eighty-six patients with MRSA and 64 with MSSA SSI were identified. One hundred sixty-seven uninfected surgical patients were selected. In multivariate analysis using uninfected surgical patients as controls, requiring assistance in three or more activities of daily living (ADLs) was an independent risk factor for MRSA SSI (odds ratio (OR)=2.73, 95% confidence interval (CI)=1.16-6.46). Using patients with MSSA SSIs as a reference group, requiring assistance in three or more ADLs was also a significant predictor for MRSA SSI (OR=3.78, 95% CI=1.43-9.98) in multivariate analysis. Other independent predictors included Charlson score, wound class, and surgical duration. Lack of independence in ADLs was an independent risk factor for MRSA SSI in elderly patients in both models.

CONCLUSION

Poor functional status (requiring assistance in >or=3 ADLs) was specifically associated with MRSA SSI. Functional status is an objective, readily available variable that can be used to stratify patients at risk for MRSA SSI.

The emergence of severe, community-acquired methicillin-resistant Staphylococcus aureus infections

The number of community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections is rapidly increasing. Most CA-MRSA infections are localized soft tissue infections; however, severe life-threatening infections have been occasionally described. This report serves to increase the awareness of severe CA-MRSA infections by presenting a fulminant CA-MRSA infection with sepsis, endocarditis, septic pulmonary emboli, and extensive soft tissue and bone destruction. A review of the literature revealed 14 cases of severe CA-MRSA infections with a median age of 13 y; 93% had no underlying medical condition. Only 1 case was initially treated with antibiotics effective for MRSA. The fatality rate was 64%, and 40% of patients who survived had significant disabilities.

Encapsulated Staphylococcus aureus strains vary in adhesiveness assessed by atomic force microscopy

Staphylococcus aureus capsular polysaccharides are believed to play a role in adhesion to surfaces and may contribute to their antimicrobial resistance, thereby increasing the rates and severity of associated infections. The purpose of this study was to compare the adhesiveness of distinct S. aureus capsular polysaccharides to determine whether adhesiveness was a general or specific feature across different S. aureus strains. Atomic force microscopy was used to confirm the presence or absence of capsular polysaccharides and to measure adhesive forces on a noncapsulated, serotype 8, and serotype 2 strain of S. aureus. Serotype 8 displayed a larger range of adhesive forces (1-19 nN) than the noncapsulated (0-4 nN) and serotype 2 (0-4 nN) strain. The majority of adhesive forces for serotype 8 were in the 10-15 nN range. Removal of capsular polysaccharides gave a marked decrease in adhesive forces measured for serotype 8 and, to a lesser extent, a decrease for serotype 2. Noncapsulated, serotype 8, and serotype 2 S. aureus had water contact angles of 23.8 (+/-8.9), 34.4 (+/-2.5), and 56.7 (+/-11.2) degrees (mean +/- standard deviation), respectively. For the first time, capsular polysaccharides from serotype 8 (clinically common) and serotype 2 (clinically rare) were demonstrated to have different physical properties, which may account for variations in studies in which clinical isolates are utilized, and the conflict in proposed roles for capsular polysaccharides on S. aureus is explained.

Evaluation of the Vitek 2 system with a variety of Staphylococcus species

The Vitek 2 gram-positive (GP) card was compared with an oligonucleotide array approach for the identification of 190 Staphylococcus strains, including 35 species, isolated from clinical and environmental specimens. The GP card provided a rapid and reliable identification of most species, whatever their origin.

In vitro evaluation of antibiotics' combinations for empirical therapy of suspected methicillin resistant Staphylococcus aureus severe respiratory infections

Background

Methicillin resistant Staphylococcus aureus (MRSA) is an increasingly common cause of nosocomial infections, causing severe morbidity and mortality worldwide, and accounting in some hospitals for more than 50% of all S. aureus diseases. Treatment of infections caused by resistant bacterial pathogens mainly relies on two therapeutic modalities: development of new antimicrobials and use of combinations of available antibiotics.

Combinations of antibiotics used in the empiric treatment of infections with suspected methicillin resistant Staphylococcus aureus etiology were investigated.

Methods

Double (vancomycin or teicoplanin with either levofloxacin or cefotaxime) and triple (vancomycin or teicoplanin + levofloxacin + one among amikacin, ceftazidime, cefepime, imipenem, piperacillin/tazobactam) combinations were evaluated by means of checkerboard assay and time kill curves. Mutational rates of single and combined drugs at antimicrobial concentrations equal to the resistance breakpoints were also calculated.

Results

Vancomycin or teicoplanin + levofloxacin showed synergy in 16/50 and in 9/50 strains respectively, while vancomycin or teicoplanin + cefotaxime resulted synergic for 43/50 and 23/50 strains, respectively. Triple combinations, involving teicoplanin, levofloxacin and ceftazidime or piperacillin/tazobactam gave synergy in 20/25 strains. Teicoplanin + levofloxacin gave synergy in triple combinations more frequently than vancomycin + levofloxacin.

For single antibiotics, mutational frequencies ranged between 10^-5 and <10^-9 for levofloxacin, cefotaxime, amikacin and imipenem, and <10^-9 for vancomycin and teicoplanin. When tested in combinations, mutational frequencies fell below 10^-9 for all the combinations.

Conclusion

In vitro evidence of synergy between glycopeptides, fluoroquinolones (levofloxacin) and β-lactams and of reduction of mutational frequencies by combinations are suggestive for a potential role in empirical therapy of severe pneumonia with suspected MRSA etiology.

Epidemiology and genetic diversity of methicillin-resistant Staphylococcus aureus strains in residential care homes for elderly persons in Hong Kong

OBJECTIVE

To determine the prevalence and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) strains among residents in residential care homes for the elderly in Hong Kong.

DESIGN

Cross-sectional and descriptive study.

PARTICIPANTS

A total of 949 residents in 13 residential care homes for elderly persons in Hong Kong in January 2005.

METHODS

MRSA colonization was assessed by culture of swab specimens from anterior nares and active skin lesions. Characteristics of residents were obtained by a standard questionnaire. All MRSA isolates were analyzed by polymerase chain reaction for their staphylococcal cassette chromosome (SCC) mec content and were typed by pulsed-field gel electrophoresis (PFGE) and multilocus sequencing.

RESULTS

MRSA colonization was detected in 27 residents (2.8%). No MRSA was found in 2 facilities. The rate of MRSA carriage in the other 11 facilities ranged from 1.9% to 4.2%. In univariate analysis, functional immobility (odds ratio [OR], 1.4), history of hospital admission (OR, 2.3), and the use of nebulized medication (OR, 5.4) were significantly associated with MRSA colonization. The isolates had 11 unique antibiograms, with 14 isolates susceptible to all but 1 or 2 of the non- beta -lactam antimicrobial agents tested. The isolates exhibited SCCmec types I (1 isolate), II (2 isolates), III (1 isolate), IV/IVA (10 isolates), and V (13 isolates). No isolates had the Panton-Valentine leukocidin genes. PFGE analysis clustered all except 1 isolate into 7 PFGE types, designated HKU10 to HKU70. Between 1 and 4 unique PFGE types were found in the individual residential care facilities.

CONCLUSION

This study documented the emergence of SCCmec types IV and V among genetically diverse MRSA strains in residential care homes for elderly persons in Hong Kong.

Clinical, epidemiological, and laboratory aspects of methicillin-resistant Staphylococcus aureus (MRSA) infections

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen responsible for both hospital- and community-onset disease. Resistance to methicillin in S. aureus is mediated by PBP2a, a penicillin-binding protein with low affinity to beta-lactams, encoded by the mecA gene. Accurate susceptibility testing of S. aureus isolates and screening of patients for colonization with MRSA are important tools to limit the spread of this organism. This review focuses on the clinical significance of MRSA infections and new approaches for the laboratory diagnosis and epidemiological typing of MRSA strains.

[Current epidemiology of microbial low respiratory tract infections]

La littérature récente n'apporte guère de grandes nouveautés, exposant les résultats d'enquêtes parcellaires utiles, mais qui s'insèrent dans les fourchettes de prévalence déjà connues pour les différentes bactéries. La fréquence des germes retrouvés varie dans le temps et l'espace, mais les trois germes les plus fréquemment en cause dans toutes les séries se recrutent, quel que soit le lieu, parmi les cinq agents que sont Streptococcus pneumoniae, Influenza A, Mycoplasma pneumoniae, Haemophilus influenzae et Legionella pneumophila. Ainsi, parmi les pneumopathies documentées, plus de 90 % sont dues à : S. pneumoniae, le plus fréquent chez les malades hospitalisés ; Mycoplasma, Chlamydia et les virus respiratoires, prédominant en ville, avec des variations selon le lieu et l'époque ; Staphylococcus aureus et entérobactéries qui peuvent également être en cause chez le vieillard et les patients atteints de tares majeures ; des associations de germes, avec le pneumocoque notamment, qui sont de plus en plus fréquemment identifiées. Enfin, l'agent causal reste méconnu dans 25 à 50 % des cas. On voit récemment notifier des pneumonies aiguës communautaires à staphylocoques résistants à la méticilline. Le diagnostic virologique (et celui des bactéries liées aux cellules) progresse, grâce à la PCR. Il reste de nombreuses incertitudes sur l'intérêt de ce diagnostic en dehors d'études épidémiologiques, mais aussi sur sa pertinence en pratique clinique. Rien de nouveau pour l'épidémiologie des bronchites aiguës ; pour les exacerbations de bronchopneumopathie chronique obstructive (BPCO), le rôle de H. influenzae, colonisant ou infectant, dans la genèse de l'inflammation bronchique fait toujours l'objet de débats.

Personal hygiene and methicillin-resistant Staphylococcus aureus infection

Methicillin-resistant Staphylococcus aureus (MRSA) infections outside the healthcare setting are an increasing concern. We conducted a case-control study to investigate an MRSA outbreak during 2002-2003 in a Missouri prison and focused on hygiene factors. Information on sociodemographic characteristics, medical history, and hygiene practices of study participants was collected by interview and medical record review. Logistic regression was used to evaluate MRSA infection in relation to hygiene factors individually and as a composite hygiene score; potential confounding factors were controlled. Selected MRSA isolates were analyzed by pulsed-field gel electrophoresis (PFGE). MRSA infection was significantly associated with a low composite hygiene score. Transmission among prison inmates appeared to be responsible for this outbreak. PFGE analysis showed that isolates were indistinguishable and associated with community-onset MRSA infections in other US prisons. Improving hygiene practices and environmental conditions may help prevent and interrupt future MRSA outbreaks in prison settings.

Personal hygiene and methicillin-resistant Staphylococcus aureus infection

Improving personal hygienic practices may prevent and control MRSA outbreaks.

Methicillin-resistant Staphylococcus aureus (MRSA) infections outside the healthcare setting are an increasing concern. We conducted a case-control study to investigate an MRSA outbreak during 2002–2003 in a Missouri prison and focused on hygiene factors. Information on sociodemographic characteristics, medical history, and hygiene practices of study participants was collected by interview and medical record review. Logistic regression was used to evaluate MRSA infection in relation to hygiene factors individually and as a composite hygiene score; potential confounding factors were controlled. Selected MRSA isolates were analyzed by pulsed-field gel electrophoresis (PFGE). MRSA infection was significantly associated with a low composite hygiene score. Transmission among prison inmates appeared to be responsible for this outbreak. PFGE analysis showed that isolates were indistinguishable and associated with community-onset MRSA infections in other US prisons. Improving hygiene practices and environmental conditions may help prevent and interrupt future MRSA outbreaks in prison settings.

Increased Prevalence of Community-Acquired Methicillin-Resistant Staphylococcus aureus in Hand Infections at an Urban Medical Center

BACKGROUND

The purpose of this article is to report the increased incidence of community-acquired methicillin-resistant S. aureus in hand infections at an urban medical center.

METHODS

The authors performed a retrospective review of all patients with hand infections over a 21-month period, and all patients with culture-positive methicillin-resistant S. aureus were identified. Cases determined to be nosocomial were excluded. The study period was divided into three 7-month periods.

RESULTS

A total of 343 hand infections were treated over a 21-month period. Eighty-nine patients (26 percent) with culture positive methicillin-resistant S. aureus were identified; of these, 75 were determined to be community-acquired methicillin-resistant S. aureus patients. Statistical analysis was performed using the Fisher's exact test (p < 0.0001), the chi-square test for equal proportions, the Cochran-Armitage trend test, and two-way analysis of variance. The demographics of the patients were compared using two-way analysis of variance, and patients were found to be similar in all three time periods with respect to mean age and sex. The incidence of community-acquired methicillin-resistant S. aureus increased to 40 percent during the last 7-month period compared with 14 percent during the first two periods. Overall, the incidence of methicillin-resistant S. aureus increased to 47 percent during the last 7 months compared with 16 percent and 17 percent in the first two 7-month periods, respectively. Based on their treatment approach and literature review, the authors have developed an algorithm to treat community-acquired methicillin-resistant S. aureus hand infections.

CONCLUSIONS

The authors' findings at Temple University Hospital may help to alert health care providers to take necessary steps to control the spread of methicillin-resistant S. aureus in the community and in the inpatient setting. Cultures should be carefully followed and infections should be treated with appropriate antibiotics.

An outbreak of new, nonmultidrug-resistant, methicillin-resistant Staphylococcus aureus strain (sccmec type iiia variant-1) in the neonatal intensive care unit transmitted by a staff member

A methicillin-resistant Staphylococcus aureus (MRSA) strain was recovered in a neonatal intensive care unit from 3 blood and 3 sputum specimens with antibiotic susceptibility profile characteristic of community-acquired MRSA. Epidemiologic survey resulted in isolation of an identical strain from the nares of one nurse. All isolates carried a new SCCmec type IIIA variant. Treatment of the nurse with topical mupirocin resulted in cessation of the outbreak.

Antimicrobial resistance in gram-positive bacteria

Gram-positive bacteria are common causes of bloodstream and other infections in hospitalized patients in the United States, and the percentage of nosocomial bloodstream infections caused by antibiotic-resistant gram-positive bacteria is increasing. Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are of particular concern. In the United States, approximately 60% of staphylococcal infections in the intensive care unit are now caused by MRSA, and percentages continue to rise. Outbreaks of hospital-acquired MRSA (HA-MRSA) are typically the result of clonal spread by MRSA being transferred from patient to patient, frequently using healthcare personnel as intermediaries. HA-MRSA strains are generally multidrug resistant. Vancomycin is the standard treatment for serious MRSA infections, but a few cases of vancomycin-resistant S aureus (VRSA) have recently emerged in the United States. Community-acquired MRSA (CA-MRSA) is also increasing. Soft tissue infections are the most frequent presentations of CA-MRSA, but life-threatening invasive infections occur as well, including necrotizing pneumonia. The mechanisms of methicillin resistance are the same for CA-MRSA and HA-MRSA, but susceptibilities to non-â-lactam antibiotics often differ. CA-MRSA exhibits broader antibiotic susceptibility than does HA-MRSA. The proportion of enterococci resistant to vancomycin continues to rise in the hospital setting, with the overwhelming majority of infections due to Enterococcus faecium. Clonal spread of VRE has been documented, but polyclonal outbreaks associated with antimicrobial use are also common. The relations between antibiotic use and VRE colonization are complex and related to the antienterococcal activity, biliary excretion, and antianaerobic activity of the antibiotic. Recent results show a decline in invasive pneumococcal disease (IPD) since the introduction of 7-valent pneumococcal conjugate vaccine, and suggest that, where available, vaccines may be useful in the battle to slow the spread of resistant gram-positive cocci.

Antimicrobial resistance in gram-positive bacteria

Gram-positive bacteria are common causes of bloodstream and other infections in hospitalized patients in the United States, and the percentage of nosocomial bloodstream infections caused by antibiotic-resistant gram-positive bacteria is increasing. Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are of particular concern. In the United States, approximately 60% of staphylococcal infections in the intensive care unit are now caused by MRSA, and percentages continue to rise. Outbreaks of hospital-acquired MRSA (HA-MRSA) are typically the result of clonal spread by MRSA being transferred from patient to patient, frequently using healthcare personnel as intermediaries. HA-MRSA strains are generally multidrug resistant. Vancomycin is the standard treatment for serious MRSA infections, but a few cases of vancomycin-resistant S aureus (VRSA) have recently emerged in the United States. Community-acquired MRSA (CA-MRSA) is also increasing. Soft tissue infections are the most frequent presentations of CA-MRSA, but life-threatening invasive infections occur as well, including necrotizing pneumonia. The mechanisms of methicillin resistance are the same for CA-MRSA and HA-MRSA, but susceptibilities to non-beta-lactam antibiotics often differ. CA-MRSA exhibits broader antibiotic susceptibility than does HA-MRSA. The proportion of enterococci resistant to vancomycin continues to rise in the hospital setting, with the overwhelming majority of infections due to Enterococcus faecium. Clonal spread of VRE has been documented, but polyclonal outbreaks associated with antimicrobial use are also common. The relations between antibiotic use and VRE colonization are complex and related to the antienterococcal activity, biliary excretion, and antianaerobic activity of the antibiotic. Recent results show a decline in invasive pneumococcal disease (IPD) since the introduction of 7-valent pneumococcal conjugate vaccine, and suggest that, where available, vaccines may be useful in the battle to slow the spread of resistant gram-positive cocci.

MRSA in Urology: A UK Hospital Experience

OBJECTIVE

Methicillin-resistant Staphylococcus aureus (MRSA) infection appears to be increasing, the UK has one of the worst MRSA rates in Europe. As urological patients are at high risk, the aim of this study was to determine the number of newly diagnosed cases of MRSA detected in a urology ward.

PATIENTS AND METHODS

The urology department serves an annual local population of greater than 500,000 with 30 inpatient beds and a tertiary population of 1 million. Over a five year period, we retrospectively recorded all patients with a new diagnosis of MRSA. We also determined colonization site and if the diagnosis of MRSA was made in an elective surgical patient or a patient admitted as an emergency.

RESULTS

The mean number of newly diagnosed cases of MRSA was 20.6 per year. The percentage of patients with a new diagnosis of MRSA was less than or equal to 1% per year with no significant difference of new cases of MRSA over five years. Emergency patients had a trend towards a mean higher rate of MRSA. The commonest site of MRSA colonization was from catheters (32%) and open wounds (18%).

DISCUSSION

MRSA is of concern, as compared to methicillin-sensitive staphylococcus aureus, because it is associated with high rates of clinically relevant infection, increased hospital stay and cost, greater mortality and high vancomycin usage. Mandatory reporting has shown a steady increase in the number of cases of MRSA infection over the past four years. We found that the number of newly diagnosed cases of MRSA was low, at less than or equal to 1% of patients per year. Furthermore, the number of new cases of MRSA remained constant over five years suggesting low acquisition rates in a busy UK urology ward.

Kinetic characterization of the monofunctional glycosyltransferase from Staphylococcus aureus

The glycosyltransferase (GT) module of class A penicillin-binding proteins (PBPs) and monofunctional GTs (MGTs) belong to the GT51 family in the sequence-based classification of GTs. They both possess five conserved motifs and use lipid II precursor (undecaprenyl-pyrophosphate-N-acetylglucosaminyl-N-acetylmuramoyl- pentapeptide) to synthesize the glycan chain of the bacterial wall peptidoglycan. MGTs appear to be dispensable for growth of some bacteria in vitro. However, new evidence shows that they may be essential for the infection process and development of pathogenic bacteria in their hosts. Only a small number of class A PBPs have been characterized so far, and no kinetic data are available on MGTs. In this study, we present the principal enzymatic properties of the Staphylococcus aureus MGT. The enzyme catalyzes glycan chain polymerization with an efficiency of approximately 5,800 M(-1) s(-1) and has a pH optimum of 7.5, and its activity requires metal ions with a maximum observed in the presence of Mn2+. The properties of S. aureus MGT are distinct from those of S. aureus PBP2 and Escherichia coli MGT, but they are similar to those of E. coli PBP1b. We examined the role of the conserved Glu100 of S. aureus MGT (equivalent to the proposed catalytic Glu233 of E. coli PBP1b) by site-directed mutagenesis. The Glu100Gln mutation results in a drastic loss of GT activity. This shows that Glu100 is also critical for catalysis in S. aureus MGT and confirms that the conserved glutamate of the first motif EDXXFXX(H/N)X(G/A) is likely the key catalytic residue in the GT51 active site.