Community-acquired methicillin-resistant Staphylococcus aureus infections in France: emergence of a single clone that produces Panton-Valentine leukocidin

Antimicrobial Resistance and the Prevalence of the Panton-Valentine Leukocidin Gene among Clinical Isolates of Staphylococcus aureus in Lithuania

This study aimed to determine resistance to antimicrobials of Staphylococcus aureus strains isolated from clinical specimens in Lithuanian hospitals and to identify the genes conferring resistance and virulence. The study was carried out from June 2019 to September 2021. S. aureus strains were isolated from skin, soft tissues, blood, lower respiratory tract, urine and other specimens. Antibiotic susceptibility testing was performed using the disc diffusion method according to EUCAST guidelines. All isolates were analyzed for detection of the ermA, ermC, mecA, mecC, tetK, tetM, and lukF-PV genes by multiplex real-time PCR. The 16S rRNA coding sequence was applied as an internal PCR control. Altogether, 745 S. aureus strains were analyzed. Antimicrobial susceptibility testing revealed that all isolates were susceptible to rifampin and vancomycin. Of the 745 strains, 94.8% were susceptible to tetracycline, 94.5% to clindamycin, and 88.3% to erythromycin. The lowest susceptibility rate was found for penicillin (25.8%). Six percent of the tested strains were methicillin-resistant S. aureus (MRSA). The majority of methicillin-resistant strains were isolated from skin and soft tissues (73.3%), with a smaller portion isolated from blood (17.8%) and respiratory tract (8.9%). The ermC gene was detected in 41.1% of erythromycin-resistant S. aureus strains, whereas ermA was detected in 32.2% of erythromycin-resistant S. aureus strains. 69.2% of tetracycline-resistant S. aureus strains had tetK gene, and 28.2% had tetM gene. 7.3% of S. aureus isolates harbored lukF-PV gene. The frequency of the pvl gene detection was significantly higher in MRSA isolates than in methicillin-susceptible S. aureus isolates (p < 0.0001).

Virulence attributes of successful methicillin-resistant Staphylococcus aureus lineages

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of severe and often fatal infections. MRSA epidemics have occurred in waves, whereby a previously successful lineage has been replaced by a more fit and better adapted lineage. Selection pressures in both hospital and community settings are not uniform across the globe, which has resulted in geographically distinct epidemiology. This review focuses on the mechanisms that trigger the establishment and maintenance of current, dominant MRSA lineages across the globe. While the important role of antibiotic resistance will be mentioned throughout, factors which influence the capacity of S. aureus to colonize and cause disease within a host will be the primary focus of this review. We show that while MRSA possesses a diverse arsenal of toxins including alpha-toxin, the success of a lineage involves more than just producing toxins that damage the host. Success is often attributed to the acquisition or loss of genetic elements involved in colonization and niche adaptation such as the arginine catabolic mobile element, as well as the activity of regulatory systems, and shift metabolism accordingly (e.g., the accessory genome regulator, agr). Understanding exactly how specific MRSA clones cause prolonged epidemics may reveal targets for therapies, whereby both core (e.g., the alpha toxin) and acquired virulence factors (e.g., the Panton-Valentine leukocidin) may be nullified using anti-virulence strategies.

High prevalence of Panton-Valentine leukocidin positive, multidrug resistant, Methicillin-resistant Staphylococcus aureus strains circulating among clinical setups in Adamawa and Far North regions of Cameroon

Staphylococcus aureus (S. aureus) is one of the earliest pathogens involved in human infections, responsible for a large variety of pathologies. Methicillin was the first antibiotic used to treat infections due to S. aureus but infections due to Methicillin resistant Staphylococcus aureus (MRSA) originated from hospital settings. Later, severe infections due to MRSA without any contact with the hospital environment or health care workers arose. Prevalence of MRSA has shown an alarming increase worldover including Cameroon. This Cross-sectional study was designed to evaluate the occurrence of MRSA infections in five different, most frequented Hospitals in northern Cameroon. Socio demographic data was recorded through questionnaire and different clinical specimens were collected for bacterial isolation. Identification of S. aureus was confirmed via 16s rRNA amplification using S. aureus specific primers. Molecular characterisation was performed through mecA gene, Luk PV gene screening and SCCmec typing. A total of 380 S. aureus clinical isolates were obtained of which 202 (53.2%) were nonduplicate multidrug resistant isolates containing, 45.5% MRSA. Higher number of MRSA was isolated from pus (30.4%) followed by blood culture (18.5%), and urine (17.4%). Patients aged 15 to 30 years presented high prevalence of MRSA (30.4%). Majority isolates (97.8%) carried the mecA gene, PVL toxin screening indicated 53.3% isolates carried the lukPV gene. Based on PVL detection and clinical history, CA-MRSA represented 53.3% of isolates. SCCmec typing showed that the Type IV was most prevalent (29.3%), followed by type I (23.9%). Amongst MRSA isolates high resistance to penicillin (91.1%), cotrimoxazole (86.7%), tetracycline (72.2%), and ofloxacin (70.0%) was detected. Meanwhile, rifampicin, fusidic acid, lincomycin and minocycline presented high efficacy in bacterial control. This study revealed a high prevalence of MRSA among infections due to S. aureus in Northern Cameroon. All MRSA recorded were multidrug resistant and the prevalence of CA MRSA are subsequently increasing, among population.

MOLECULAR EPIDEMIOLOGY OF THE TRANSMISSION OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS IN KYIV ACUTE CARE HOSPITALS, UKRAINE

OBJECTIVE

The aim: To evaluate the potential of transmission of methicillin-resistance Staphylococcus aureus (MRSA) in Ukrainian acute care hospitals.

PATIENTS AND METHODS

Materials and methods: We performed a multicenter cross-sectional study. Definitions of HAI were used from the CDC/ NHSN. The susceptibility to antibiotics was determined by disk diffusion method according to the EUCAST. The cefoxitin-resistant isolates S.aureus were analyzed for the presence of the mecA gene and femA endogenous control gene using PCR. The virulence factor encoding genes (lukS-PV and lukF-PV) were detected by PCR.

RESULTS

Results: Of 2,421 patients with HAIs caused S.aureus included in the study, 28.7% patients had MRSA. Prevalence of nasal carriage rate of MRSA among healthcare workers (HCWs) was 33.3%. MRSA contamination of hands and uniforms/gowns of HCW were 32.2% and 29.7%, respectively. MRSA contamination in the inanimate environment surfaces in near- and extended patients areas were 26.9%. The predominant MRSA contamination in hospital environment surfaces were: room inner door knob (32.8%), bed rails (28.9%), room light switch (28.9%), chair (27.9%), bedside table handle (20.6%), bedside table (20.5%), and tray table (13.7%). The PVL gene was present in 38.7% of MRSA strains, isolated from patients with HAIs and in 55.7% of MRSA, isolated from environment surfaces in patient area. In addition, the PVL genes were detected in over 56.3% of MRSA isolated from HCWs carrier.

CONCLUSION

Conclusions: The majority of MRSA is acquired during hospitalization. Environmental surfaces may serve as potential reservoirs for nosocomial MRSA and facilitate transmissions via contact.

Molecular characterization of Staphylococcus aureus isolates derived from severe pneumonia: a retrospective monocentre study

BACKGROUND

Staphylococcus aureus is endowed with a repertoire of virulence factors potentially implicated in its pathogenicity and ability to cause invasive disease. The main objective of this study was to describe the bacterial genotype, including virulence genes and affiliation to clonal complexes (CCs), encountered in severe pneumonia.

METHODS

DNA microarray was used to analyse 18 S. aureus isolates from patients hospitalized with severe pneumonia between 2017 and 2019.

RESULTS

Among 18 S. aureus isolates, 14 were methicillin-susceptible S. aureus (MSSA), and 4 methicillin-resistant S. aureus (MRSA). There were 14 community-acquired, 3 healthcare-associated, and 1 hospital-acquired infections. Different radiological presentations were observed: necrotizing pneumonia (n = 8, 44%), alveolar consolidation (n = 7, 39%), alveolar-interstitial infiltrates (n = 3, 17%). Sixteen patients (89%) required ICU hospitalization, 13 (72%) an invasive mechanical ventilation, and 12 (67%) a vasopressor support. Mortality affected 6 patients (33%). Panton-Valentine leukocidin (PVL), staphylococcal enterotoxins, toxic shock syndrome toxine-1 (TSST-1) encoding genes were documented in nine (50%), 12 (67%), one (6%) of the isolates, respectively. Accessory regulator gene group I was the most reported (n = 9, 50%) and was found in five deaths. The majority of isolates were affiliated to CC152 (n = 6), followed by CC15 (n = 3), CC45 (n = 2), CC30 (n = 2), CC1 (n = 2), CC8 (n = 1), CC9 (n = 1), and CC25 (n = 1). All the CC152 isolates were PVL-positive.

CONCLUSION

CC152-PVL positive S. aureus strains were the most prevalent in severe pneumonia. Other virulence gene profiles were found coupled to additional clonal lineages. A genotyping strategy contributes to describe the current circulating strains and bacterial genetic backgrounds.

Prognostic factors of severe community-acquired staphylococcal pneumonia in France

PURPOSE

Staphylococcus aureus causes severe forms of community-acquired pneumonia (CAP), namely staphylococcal pleuropneumonia in young children and staphylococcal necrotising pneumonia in older patients. Methicillin resistance and the Panton-Valentine leukocidin (PVL) toxin, as well as less specific factors, have been associated with poor outcome in severe CAP, but their roles are unclear.

METHODS

A prospective multicentre cohort study of severe staphylococcal CAP was conducted in 77 paediatric and adult intensive care units in France between January 2011 and December 2016. After age-clustering, risk factors for mortality, including pre-existing conditions, clinical presentation, laboratory features, strain genetic lineage, PVL, other virulence factors and methicillin resistance were assessed using univariate and multivariable Cox and LASSO (least absolute shrinkage and selection operator) regressions.

RESULTS

Out of 163 included patients, aged 1 month to 87 years, 85 (52.1%) had PVL-positive CAP; there were 20 (12.3%) patients aged <3 years (hereafter "toddlers"), among whom 19 (95%) had PVL-positive CAP. The features of PVL-positive CAP in toddlers matched with the historical description of staphylococcal pleuropneumonia, with a lower mortality (three (15%) out of 19) compared to PVL-positive CAP in older patients (31 (47%) out of 66). Mortality in older patients was predicted by PVL-positivity (hazard ratio (HR) 1.81, 95% CI 1.03-3.17) and methicillin resistance (HR 2.37, 95% CI 1.29-4.34) independently from S. aureus lineages and the presence of other determinants of virulence.

CONCLUSION

PVL was associated with staphylococcal pleuropneumonia in toddlers and was a risk factor for mortality in older patients with severe CAP, independently of methicillin resistance, S. aureus genetic background and other virulence factors.

Interventions for bacterial folliculitis and boils (furuncles and carbuncles)

BACKGROUND

Bacterial folliculitis and boils are globally prevalent bacterial infections involving inflammation of the hair follicle and the perifollicular tissue. Some folliculitis may resolve spontaneously, but others may progress to boils without treatment. Boils, also known as furuncles, involve adjacent tissue and may progress to cellulitis or lymphadenitis. A systematic review of the best evidence on the available treatments was needed.

OBJECTIVES

To assess the effects of interventions (such as topical antibiotics, topical antiseptic agents, systemic antibiotics, phototherapy, and incision and drainage) for people with bacterial folliculitis and boils.

SEARCH METHODS

We searched the following databases up to June 2020: the Cochrane Skin Specialised Register, CENTRAL, MEDLINE, and Embase. We also searched five trials registers up to June 2020. We checked the reference lists of included studies and relevant reviews for further relevant trials.  SELECTION CRITERIA: We included randomised controlled trials (RCTs) that assessed systemic antibiotics; topical antibiotics; topical antiseptics, such as topical benzoyl peroxide; phototherapy; and surgical interventions in participants with bacterial folliculitis or boils. Eligible comparators were active intervention, placebo, or no treatment.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Our primary outcomes were 'clinical cure' and 'severe adverse events leading to withdrawal of treatment'; secondary outcomes were 'quality of life', 'recurrence of folliculitis or boil following completion of treatment', and 'minor adverse events not leading to withdrawal of treatment'. We used GRADE to assess the certainty of the evidence.

MAIN RESULTS

We included 18 RCTs (1300 participants). The studies included more males (332) than females (221), although not all studies reported these data. Seventeen trials were conducted in hospitals, and one was conducted in clinics. The participants included both children and adults (0 to 99 years). The studies did not describe severity in detail; of the 232 participants with folliculitis, 36% were chronic. At least 61% of participants had furuncles or boils, of which at least 47% were incised. Duration of oral and topical treatments ranged from 3 days to 6 weeks, with duration of follow-up ranging from 3 days to 6 months. The study sites included Asia, Europe, and America. Only three trials reported funding, with two funded by industry. Ten studies were at high risk of 'performance bias', five at high risk of 'reporting bias', and three at high risk of 'detection bias'. We did not identify any RCTs comparing topical antibiotics against topical antiseptics, topical antibiotics against systemic antibiotics, or phototherapy against sham light. Eleven trials compared different oral antibiotics. We are uncertain as to whether cefadroxil compared to flucloxacillin (17/21 versus 18/20, risk ratio (RR) 0.90, 95% confidence interval (CI) 0.70 to 1.16; 41 participants; 1 study; 10 days of treatment) or azithromycin compared to cefaclor (8/15 versus 10/16, RR 1.01, 95% CI 0.72 to 1.40; 31 participants; 2 studies; 7 days of treatment) differed in clinical cure (both very low-certainty evidence). There may be little to no difference in clinical cure rate between cefdinir and cefalexin after 17 to 24 days (25/32 versus 32/42, RR 1.00, 95% CI 0.73 to 1.38; 74 participants; 1 study; low-certainty evidence), and there probably is little to no difference in clinical cure rate between cefditoren pivoxil and cefaclor after 7 days (24/46 versus 21/47, RR 1.17, 95% CI 0.77 to 1.78; 93 participants; 1 study; moderate-certainty evidence). For risk of severe adverse events leading to treatment withdrawal, there may be little to no difference between cefdinir versus cefalexin after 17 to 24 days (1/191 versus 1/200, RR 1.05, 95% CI 0.07 to 16.62; 391 participants; 1 study; low-certainty evidence). There may be an increased risk with cefadroxil compared with flucloxacillin after 10 days (6/327 versus 2/324, RR 2.97, 95% CI 0.60 to 14.62; 651 participants; 1 study; low-certainty evidence) and cefditoren pivoxil compared with cefaclor after 7 days (2/77 versus 0/73, RR 4.74, 95% CI 0.23 to 97.17; 150 participants; 1 study; low-certainty evidence). However, for these three comparisons the 95% CI is very wide and includes the possibility of both increased and reduced risk of events. We are uncertain whether azithromycin affects the risk of severe adverse events leading to withdrawal of treatment compared to cefaclor (274 participants; 2 studies; very low-certainty evidence) as no events occurred in either group after seven days. For risk of minor adverse events, there is probably little to no difference between the following comparisons: cefadroxil versus flucloxacillin after 10 days (91/327 versus 116/324, RR 0.78, 95% CI 0.62 to 0.98; 651 participants; 1 study; moderate-certainty evidence) or cefditoren pivoxil versus cefaclor after 7 days (8/77 versus 5/73, RR 1.52, 95% CI 0.52 to 4.42; 150 participants; 1 study; moderate-certainty evidence). We are uncertain of the effect of azithromycin versus cefaclor after seven days due to very low-certainty evidence (7/148 versus 4/126, RR 1.26, 95% CI 0.38 to 4.17; 274 participants; 2 studies). The study comparing cefdinir versus cefalexin did not report data for total minor adverse events, but both groups experienced diarrhoea, nausea, and vaginal mycosis during 17 to 24 days of treatment. Additional adverse events reported in the other included studies were vomiting, rashes, and gastrointestinal symptoms such as stomach ache, with some events leading to study withdrawal. Three included studies assessed recurrence following completion of treatment, none of which evaluated our key comparisons, and no studies assessed quality of life.

AUTHORS' CONCLUSIONS

We found no RCTs regarding the efficacy and safety of topical antibiotics versus antiseptics, topical versus systemic antibiotics, or phototherapy versus sham light for treating bacterial folliculitis or boils. Comparative trials have not identified important differences in efficacy or safety outcomes between different oral antibiotics for treating bacterial folliculitis or boils. Most of the included studies assessed participants with skin and soft tissue infection which included many disease types, whilst others focused specifically on folliculitis or boils. Antibiotic sensitivity data for causative organisms were often not reported. Future trials should incorporate culture and sensitivity information and consider comparing topical antibiotic with antiseptic, and topical versus systemic antibiotics or phototherapy.

Panton-Valentine Leukocidin Induces Cytokine Release and Cytotoxicity Mediated by the C5a Receptor on Rabbit Alveolar Macrophages

Necrotizing pneumonia caused by Panton-Valentine leukocidin (PVL)-positive community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has high mortality rates and is currently a serious clinical issue. PVL is a two-component toxin (LukS-PV and LukF-PV). It can cause necrosis in target cells by forming pores consisting of an octamer comprised of LukS-PV and LukF-PV. However, considering the specificity of PVL towards several target cells and species, the specific effect of PVL remains controversial. Therefore, we focused on necrotizing pneumonia caused by PVL-positive S. aureus and clarified the effect of PVL on alveolar macrophages, which play a central role in innate immunity in the alveolar space. We constructed recombinant PVL (rPVL) components and stimulated alveolar macrophages isolated from rabbits to evaluate cytotoxicity and pro-inflammatory cytokine release. Recombinant LukS-PV (rLukS-PV), but not recombinant LukF-PV (rLukF-PV), induced pro-inflammatory cytokine release. Specifically, tumor necrosis factor (TNF)-α release was mediated by the C5a receptor (C5aR) expressed on rabbit alveolar macrophages, and the toxicity of rPVL, consisting of rLukS-PV and rLukF-PV, towards rabbit alveolar macrophages was mediated by the same receptor. Overall, our findings shed light on the C5aR-mediated cytotoxic effect of PVL on alveolar macrophages, which may be useful for understanding the mechanism of necrotizing pneumonia caused by PVL.

Distinguishing Pathovars from Nonpathovars: Escherichia coli

Escherichia coli is one of the most well-adapted and pathogenically versatile bacterial organisms. It causes a variety of human infections, including gastrointestinal illnesses and extraintestinal infections. It is also part of the intestinal commensal flora of humans and other mammals. Groups of E. coli that cause diarrhea are often described as intestinal pathogenic E. coli (IPEC), while those that cause infections outside of the gut are called extraintestinal pathogenic E. coli (ExPEC). IPEC can cause a variety of diarrheal illnesses as well as extraintestinal syndromes such as hemolytic-uremic syndrome. ExPEC cause urinary tract infections, bloodstream infection, sepsis, and neonatal meningitis. IPEC and ExPEC have thus come to be referred to as pathogenic variants of E. coli or pathovars. While IPEC can be distinguished from commensal E. coli based on their characteristic virulence factors responsible for their associated clinical manifestations, ExPEC cannot be so easily distinguished. IPEC most likely have reservoirs outside of the human intestine but it is unclear if ExPEC represent nothing more than commensal E. coli that breach a sterile barrier to cause extraintestinal infections. This question has become more complicated by the advent of whole genome sequencing (WGS) that has raised a new question about the taxonomic characterization of E. coli based on traditional clinical microbiologic and phylogenetic methods. This review discusses how molecular epidemiologic approaches have been used to address these questions, and how answers to these questions may contribute to our better understanding of the epidemiology of infections caused by E. coli. *This article is part of a curated collection.

Methicillin-resistant Staphylococcus aureus pneumonia in diabetics: a single-center, retrospective analysis

Background:

Methicillin-resistant Staphylococcus aureus (MRSA) pneumonia is an important issue with significant morbidity and mortality in clinical practice, especially in diabetes mellitus (DM). Studies focusing on S. aureus pneumonia in DM is limited, we sought to make a relatively comprehensive exploration of clinical characteristics, antimicrobial resistance, and risk factors for mortality of S. aureus pneumonia in DM and non-diabetics mellitus (non-DM).

Methods:

A retrospective study was conducted in Ruijin Hospital from 2014 to 2017. The characteristics of DM and non-DM patients were assessed, including demographics, comorbidities, using of invasive mechanical ventilation, Hemoglobin A1c (HbA1C), confusion, urea, respiratory rate, blood pressure, age ≥65 years (CURB-65) score, length of hospital stay, clinical outcomes, antimicrobial susceptibility. Independent risk factors for mortality were identified by univariate and multivariate logistic regression analysis.

Results:

A total of 365 patients with S. aureus pneumonia were included in our study, including 144 with DM and 221 non-DM. DM patients were more susceptible to MRSA infection (65.3% vs. 56.1%, P > 0.05), suffered from much severer pneumonia with a higher CURB-65 score, invasive mechanical ventilation rate (46.5% vs. 28.1%, P < 0.01) and mortality rates (30.6% vs. 23.1%, P > 0.05); almost all DM patients had higher antimicrobial resistance than non-DM patients, the DM group had a higher co-infection rate (47.2% vs. 45.7%, P > 0.05), and Acinetobacter baumannii was the most common bacterium in DM, while Klebsiella pneumoniae ranked first in patients with non-DM. Independent risk factors for pneumonia-related mortality were MRSA and CURB-65. Higher HbA1c levels were linked to a higher MRSA infection and co-infection rate and more severe pneumonia, leading to an increase in mortality.

Conclusions:

DM patients with poor glucose control are more susceptible to MRSA infection. They suffer from higher antimicrobial resistance, a higher co-infection rate, and much severer pneumonia than non-DM. MRSA itself is an independent risk factor for mortality in all patients.

Vaccine display on artificial bacterial spores enhances protective efficacy against Staphylococcus aureus infection

Spores of Bacillus subtilis are encased in a protein coat composed of ∼80 different proteins. Recently, we reconstituted the basement layer of the coat, composed of two structural proteins (SpoVM and SpoIVA) around spore-sized silica beads encased in a lipid bilayer, to create synthetic spore-like particles termed 'SSHELs'. We demonstrated that SSHELs could display thousands of copies of proteins and small molecules of interest covalently linked to SpoIVA. In this study, we investigated the efficacy of SSHELs in delivering vaccines. We show that intramuscular vaccination of mice with undecorated one micron-diameter SSHELs elicited an antibody response against SpoIVA. We further demonstrate that SSHELs covalently modified with a catalytically inactivated staphylococcal alpha toxin variant (HlaH35L), without an adjuvant, resulted in improved protection against Staphylococcus aureus infection in a bacteremia model as compared to vaccination with the antigen alone. Although vaccination with either HlaH35L or HlaH35L conjugated to SSHELs similarly elicited the production of neutralizing antibodies to Hla, we found that a subset of memory T cells was differentially activated when the antigen was delivered on SSHELs. We propose that the particulate nature of SSHELs elicits a more robust immune response to the vaccine that results in superior protection against subsequent S. aureus infection.

Effects of gamma-irradiation on antibiotic resistance and diagnostic molecular markers of methicillin-resistant Staphylococcus aureus in Egyptian cancer patients

Purpose: This in-vitro study aimed to assess in 120 [40 community-acquired (CA-MRSA) & 80 hospital-acquired (HA-MRSA)] isolates from cancer patients whether the transmissible staphylococcal cassette chromosome mec (SCCmec) typing, and the Panton-Valentine leukocidin (PVL) virulence genes detection could be employed as tools for molecular diagnostic purposes to distinguish both methicillin-resistant Staphylococcus aureus (MRSA) categories in radiotherapy treated cancer patients.Materials and methods: SCCmec typing was determined by the combination of the type of the cassette chromosome recombinase genes (ccr) gene complex and the class of the methicillin resistance (mec) gene complex. Besides, a rapid slide latex agglutination test (LAT) and antibiotic resistance spectrum determination before and after irradiation were performed.Results: In the strict sense, with the effect of irradiation; the presence of SCCmec subtypes IVa (22.5% vs. 10.0%), b (47.5% vs. 25.0%), & d (7.5 vs. 2.5%) or type V (15.0% vs. 7.5%) genetic elements and PVL genes (p < .001) were not proved as a signature for CA-MRSA. While, the larger SCCmec types II, and III elements were not detected in 14, and 19 from the 38, and 36 typed HA-MRSA isolates (p < .001), respectively. Remarkable effects on class A & class B mec gene complex and type2, type 3 & type 5 ccr gene complex and an increase in agglutination reaction strength in response to gamma irradiation external stimulus were observed.Conclusions: Different heterogeneous genetic composition with upregulation mecA gene expression was detected after irradiation in the HA- MRSA studied population. CA-MRSA showed remarkable ability to acquire multi-antibiotic resistance after irradiation and propose a novel paradigm for future chemotherapy against the multi-resistant pathogens whose proliferation especially among immunocompromised cancer patients is on the increase.

Role of staphylococci in mastitis in sheep

Staphylococci have been isolated from various sites of the body of healthy sheep, as well as from many infections of those animals, the main one being mastitis. The objective of this review is to appraise the importance and significance of staphylococci in causing mastitis in ewes. The review includes a brief classification and taxonomy of staphylococci and describes the procedures for their isolation and identification, as well as their virulence determinants and the mechanisms of resistance to antibacterial agents. Various staphylococcal species have been implicated in staphylococcal mastitis and the characteristics of isolates are discussed with regards to potential virulence factors. Staphylococcal mastitis is explicitly described, with reference to sources of infection, the course of the disease and the relevant control measures. Finally, the potential significance of staphylococci present in ewes' milk for public health is discussed briefly.

Prevalence and Risk Factors for Positive Nasal Methicillin-Resistant Staphylococcus aureus Carriage Among Orthopedic Patients in Korea

Methicillin-resistant Staphylococcus aureus (MRSA) causes purulent skin and soft tissue infections as well as other life-threatening diseases. Recent guidelines recommend screening for MRSA at the time of admission. However, few studies have been conducted to determine the prevalence and risk factors for MRSA colonization. A prospective data collection and retrospective analysis was performed. MRSA screening tests were performed using nasal swabs in patients enrolled between January 2017 and July 2018. Demographic data, socio-economic data, medical comorbidities, and other risk factors for MRSA carriage were evaluated among 1577 patients enrolled in the study. The prevalence of MRSA nasal carriage was 7.2%. Univariate regression analysis showed that colonization with MRSA at the time of hospital admission was significantly related to patient age, body mass index, smoking, alcohol, trauma, recent antibiotic use, and route of hospital admission. Multiple logistic regression analysis for the risk factors for positive MRSA nasal carriage showed that being under- or overweight, trauma diagnosis, antibiotic use one month prior to admission, and admission through an emergency department were related to MRSA colonization. This study highlights the importance of a preoperative screening test for patients scheduled to undergo surgery involving implant insertion, particularly those at risk for MRSA.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Deciphering pathogenicity and antibiotic resistance islands in methicillin-resistant Staphylococcus aureus genomes

Staphylococcus aureus is a versatile pathogen that is capable of causing infections in both humans and animals. It can cause furuncles, septicaemia, pneumonia and endocarditis. Adaptation of S. aureus to the modern hospital environment has been facilitated, in part, by the horizontal acquisition of drug resistance genes, such as mecA gene that imparts resistance to methicillin. Horizontal acquisitions of islands of genes harbouring virulence and antibiotic resistance genes have made S. aureus resistant to commonly used antibiotics. To decipher genomic islands (GIs) in 22 hospital- and 9 community-associated methicillin-resistant S. aureus strains and classify a subset of GIs carrying virulence and resistance genes as pathogenicity and resistance islands respectively, we applied a host of methods for localizing genomic islands in prokaryotic genomes. Surprisingly, none of the frequently used GI prediction methods could perform well in delineating the resistance islands in the S. aureus genomes. Rather, a gene clustering procedure exploiting biases in codon usage for identifying horizontally transferred genes outperformed the current methods for GI detection, in particular in identifying the known islands in S. aureus including the SCCmec island that harbours the mecA resistance gene. The gene clustering approach also identified novel, as yet unreported islands, with many of these found to harbour virulence and/or resistance genes. These as yet unexplored islands may provide valuable information on the evolution of drug resistance in S. aureus.

Global Scale Dissemination of ST93: A Divergent Staphylococcus aureus Epidemic Lineage That Has Recently Emerged From Remote Northern Australia

Background: In Australia, community-associated methicillin-resistant Staphylococcus aureus (MRSA) lineage sequence type (ST) 93 has rapidly risen to dominance since being described in the early 1990s. We examined 459 ST93 genome sequences from Australia, New Zealand, Samoa, and Europe to investigate the evolutionary history of ST93, its emergence in Australia and subsequent spread overseas. Results: Comparisons with other S. aureus genomes indicate that ST93 is an early diverging and recombinant lineage, comprising of segments from the ST59/ST121 lineage and from a divergent but currently unsampled Staphylococcal population. However, within extant ST93 strains limited genetic diversity was apparent with the most recent common ancestor dated to 1977 (95% highest posterior density 1973-1981). An epidemic ST93 population arose from a methicillin-susceptible progenitor in remote Northern Australia, which has a proportionally large Indigenous population, with documented overcrowded housing and a high burden of skin infection. Methicillin-resistance was acquired three times in these regions, with a clade harboring a staphylococcal cassette chromosome mec (SCCmec) IVa expanding and spreading to Australia's east coast by 2000. We observed sporadic and non-sustained introductions of ST93-MRSA-IVa to the United Kingdom. In contrast, in New Zealand, ST93-MRSA-IVa was sustainably transmitted with clonal expansion within the Pacific Islander population, who experience similar disadvantages as Australian Indigenous populations. Conclusion: ST93 has a highly recombinant genome including portions derived from an early diverging S. aureus population. Our findings highlight the need to understand host population factors in the emergence and spread of antimicrobial resistant community pathogens.

Genetics of bi-component leukocidin and drug resistance in nasal and clinical Staphylococcus aureus in Lagos, Nigeria

BACKGROUND

Resistant and virulent Staphylococcus aureus is a global public health challenge. Staphylococcal Bi-component leukotoxins are cytolytic to immune cells and evolve to disarm the innate immunity during infections, hence the severity of the disease.

OBJECTIVE

We studied drug resistance profile and the occurrence of bi-component leukocidin in clinical and nasal S. aureus in Lagos, Nigeria.

METHOD

Ninety-two S. aureus (70 clinical and 22 nasal) strains were characterized by conventional and molecular methods.

RESULT

Of the resistance profiles generated, no isolate was resistant to fosfomycin, fusidic acid, teicoplanin, vancomycin, linezolid, mupirocin, nitrofurantoin and tigecycline. Twelve MRSA carrying staphylococcal cassette chromosome mecA gene types I, III, and IV elements were identified only in the clinical samples and type I dominated. High rates of lukE/D (100% among MRSA) and lukPV (dominated MSSA) were recorded among the nasal and clinical isolates. Staphylococcus aureus harboring only lukE/D (from clinical & colonizing MSSA) and combined lukE/D and lukPV (mostly from clinical MSSA, colonizing MSSA and clinical MRSA) toxins were found.

CONCLUSION

Although, mecA resistant genes were found only among clinical MRSA, the occurrence of other bi-component leukocidin genes in a large proportion among the isolates from both community and clinical settings is a major concern. The need for effective resistance and virulence factor surveillance, re-enforcement of antibiotic stewardship and good infection control policy, to prevent dissemination of epidemic strains is highlighted.

Staphylococcus Aureus Carriage in French Athletes at Risk of CA-MRSA Infection: a Prospective, Cross-sectional Study

Background

Staphylococcus aureus (SA) is a leading cause of infectious diseases in sports teams. In recent decades, community-associated SA (CA-SA) strains have emerged worldwide and have been responsible for outbreaks in sports teams. There are very few data on the prevalence of these strains in France, and none on the carriage among athletes.

Methods

We conducted a cross-sectional study to determine the SA carriage proportion among athletes practicing sports at risk for CA-SA infection in a French county, and determined the methicillin-resistant and/or CA-SA proportion. We also analyzed SA carriage according to risks factors and studied the SA clonality in a sample of our population.

Results

We included 300 athletes; SA carriage proportion was 61% (n = 183) and one was MRSA carrier (0.33%). The MRSA strain belonged to the clonal complex ST5. None of the strain produced Panton Valentine Leucocidin, and we did not find clonal distribution within the teams. Interestingly, we found a high throat-only carriage (n = 57), 31.1% of the SA carriers.

Conclusion

We found a high SA carriage with a local epidemiology quite different than that reported in a similar population in the USA. Further studies on SA carriage should include throat sampling.

Trial registration

The approved protocol was registered on ClinicalTrial.gov, NCT01148485.

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.

High Nasal Carriage Rate of Staphylococcus aureus Containing Panton-Valentine leukocidin- and EDIN-Encoding Genes in Community and Hospital Settings in Burkina Faso

The objectives of the present study were to investigate the rate of S.aureus nasal carriage and molecular characteristics in hospital and community settings in Bobo Dioulasso, Burkina Faso. Nasal samples (n = 219) were collected from 116 healthy volunteers and 103 hospitalized patients in July and August 2014. Samples were first screened using CHROMagar Staph aureus chromogenic agar plates, and S. aureus strains were identified by mass spectrometry. Antibiotic susceptibility was tested using the disk diffusion method on Müller-Hinton agar. All S. aureus isolates were genotyped using DNA microarray. Overall, the rate of S. aureus nasal carriage was 32.9% (72/219) with 29% in healthy volunteers and 37% in hospital patients. Among the S. aureus isolates, only four methicillin-resistant S. aureus (MRSA) strains were identified and all in hospital patients (3.9%). The 72 S. aureus isolates from nasal samples belonged to 16 different clonal complexes, particularly to CC 152-MSSA (22 clones) and CC1-MSSA (nine clones). Two clones were significantly associated with community settings: CC1-MSSA and CC45-MSSA. The MRSA strains belonged to the ST88-MRSA-IV or the CC8-MRSA-V complex. A very high prevalence of toxinogenic strains 52.2% (36/69), containing Panton-Valentine leucocidin- and EDIN-encoding genes, was identified among the S. aureus isolates in community and hospital settings. This study provides the first characterization of S. aureus clones and their genetic characteristics in Burkina Faso. Altogether, it highlights the low prevalence of antimicrobial resistance, high diversity of methicillin-sensitive S. aureus clones and high frequency of toxinogenic S. aureus strains.

Prevalence and Characterization of Oxacillin Susceptible mecA-Positive Clinical Isolates of Staphylococcus aureus Causing Bovine Mastitis in India

Bovine mastitis caused by multidrug resistant Staphylococcus aureus is a huge problem reported worldwide, resulting in prolonged antibiotic treatment and death of livestock. The current study is focused on surveillance of antibiotic susceptibility along with genotypic and phenotypic characterization of the pathogenic S. aureus strains causing mastitis in India. One hundred and sixty seven milk samples were collected from mastitis-affected cows from different farms in India resulting in thirty nine isolated S. aureus strains. Antibiotic sensitivity profiling revealed the majority of the strains (n = 24) to be multidrug resistant and eleven strains showed reduced susceptibility to vancomycin (MICs = 2μg/ml). All strains were oxacillin sensitive, but 19 strains were positive for the mecA gene, which revealed the occurrence of oxacillin susceptible mecA positive strains (OS-MRSA) for the first time from India. Additionally, 32 strains were positive for the pvl gene, a virulence determinant; of these 17 were also OS-MRSA strains. Molecular characterization based on multilocus sequence typing (MLST), spa typing, agr typing and SCCmec classification revealed strains belonging to different groups. Moreover, strains showed spa types (t2526, t9602) and MLST sequence types, ST-72, ST-88 and ST-239 which have been earlier reported in human infections. The prevalence of OS-MRSA strains indicates the importance of including both the genetic and phenotypic tests in characterizing S. aureus strains. Increased genotypic variability with strain related to human infections and pvl positive isolates indicates a worrisome situation with the possibility of bilateral transfer.

Emergence of Community-Associated Methicillin-ResistantStaphylococcus aureusInfection Among Patients With End-Stage Renal Disease

Objective.

To evaluate the frequency of infections due to community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) strains among our patients with end-stage renal disease.

Design.

Prospective observational clinical and laboratory study of patients in 2005. Molecular features of isolates recovered from these patients were compared with those of isolates recovered in 2000 from patients with end-stage renal disease.

Setting.

A 600-bed urban academic medical center.

Patients.

Thirty-two patients with end-stage renal disease and MRSA infection at the time of hospitalization from 2005 were evaluated. For comparison, laboratory analysis was performed for 17 MRSA isolates recovered from patients with end-stage renal disease in 2000.

Results.

The patients from 2005 were more likely than the patients from 2000 to have infection with strains that carried the staphylococcal cassette chromosome (SCC)mectype IV complex (50% vs 11.8%; relative risk, 4.25 [95% confidence interval, 1.17-25.98];P= .012) and the Panton-Valentine leukocidin toxin genes (25% vs 0%;P= .038). Eight patients from 2005 were infected with a strain that is identical to MRSA clone USA300 in terms of molecular type and presence of SCCmectype IV and Panton-Valentine leukocidin genes. Among the patients from 2005, those infected with SCCmectype IV strains (ie, CA-MRSA strains) and those infected with SCCmectype II strains (ie, healthcare-associated MRSA [HA-MRSA] strains) were similar with respect to demographic characteristics, risk factors, and outcomes.

Conclusions.

We documented an increased proportion of infections with CA-MRSA strains, including clone USA300, among our population of patients undergoing dialysis. Patients infected with CA-MRSA strains and HA-MRSA strains were similar with respect to presenting illness and outcomes.

Clinical and Laboratory Features of Community-Associated Methicillin-ResistantStaphylococcus aureus:Is It Really New?

Objective.

To review the epidemiologic and molecular characteristics of community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) in Detroit, Michigan, to assess the risk factors for infection and the response to therapy.

Design.

Prospective clinical and laboratory study of 2003-2004 CA-MRSA isolates. Molecular features were compared with CA-MRSA isolates from 1980.

Setting.

A 600-bed urban academic medical center.

Patients.

Twenty-three patients with CA-MRSA infections from 2003-2004 were evaluated. In addition, laboratory analysis was performed on 13 CA-MRSA isolates from 1980.

Main Outcome Measures.

Laboratory analysis of isolates included antimicrobial susceptibility testing, pulsed-field genotyping, testing for Panton-Valentine leukocidin (PVL) genes, and staphylococcal cassette chromosomemectyping.

Results.

Patients were predominantly young African American males and presented with skin and soft-tissue infections. All isolates were resistant to erythromycin and highly susceptible to other agents. Patients were generally treated successfully with combination incision and drainage and systemic antibiotics. Among the 23 isolates, 20 (87%) were the same strain. This strain carried the staphylococcal cassette chromosomemectype IV and PVL genes and is genetically identical to USA 300. Thirteen isolates of patients from our community who presented with CA-MRSA infections in 1980 represented a single clone that is unique compared with the 2003-2004 isolates. This strain carried staphylococcal cassette chromosomemectype IVA but did not carry the PVL genes.

Conclusions.

In our community, CA-MRSA is largely due to a single clone with a type IVmecgene and PVL gene. The type IV staphylococcal cassette chromosomemectype can be demonstrated in CA-MRSA isolates from a remote period, suggesting that earlier outbreaks were not related to healthcare exposure.

Epidemiology of Staphylococcus aureus Nasal Carriage Patterns in the Community

Staphylococcus aureus (S. aureus) is a Gram-positive opportunistic pathogen that colonizes frequently and asymptomatically the anterior nares of humans and animals. It can cause different kinds of infections and is considered to be an important nosocomial pathogen. Nasal carriage of S. aureus can be permanent or intermittent and may build the reservoir for autogenous infections and cross-transmission to other individuals. Most of the studies on the epidemiology of S. aureus performed in the past were focused on the emergence and dissemination of methicillin-resistant Staphylococcus aureus (MRSA) in healthcare settings. There are, however, a number of more recent epidemiological studies have aimed at analysing carriage patterns over time in the community settings providing new insights on risk factors for colonization and important data for the development of strategies to prevent infections. This chapter aims to give a review of current epidemiological studies on S. aureus carriage patterns in the general community and put them into perspective with recent, yet unpublished, investigations on the S. aureus epidemiology in the general population in northern Germany.

Antimicrobial susceptibility and molecular characteristics of methicillin-resistant Staphylococcus aureus in a Japanese secondary care facility

Methicillin-resistant Staphylococcus aureus (MRSA) is prevalent in Japan, and the Staphylococcus cassette chromosome mec (SCCmec) type II is common among hospital-acquired MRSA isolates. Information pertaining to MRSA characteristics is limited, including SCCmec types, in primary or secondary care facilities. A total of 128 MRSA isolates (90 skin and soft tissue isolates and 38 blood isolates) were collected at a secondary care facility, Kawatana Medical Center, from 2005 to 2011. Antimicrobial susceptibility testing for anti-MRSA antibiotics and molecular testing for SCCmec and virulence genes (tst, sec, etb, lukS/F-PV) were performed. Strains positive for lukS/F-PV were analyzed by multilocus sequence typing and phage open-reading frame typing. SCCmec typing in skin and soft tissue isolates revealed that 65.6% had type IV, 22.2% had type II, 8.9% had type I, and 3.3% had type III. In blood isolates, 50.0% had type IV, 47.4% had type II, and 2.6% had type III. Minimum inhibitory concentrations, MIC(50)/MIC(90), against vancomycin, teicoplanin, linezolid, and arbekacin increased slightly in SCCmec II isolates from skin and soft tissue. MICs against daptomycin were similar between sites of isolation. SCCmec type II isolates possess tst and sec genes at a greater frequently than SCCmec type IV isolates. Four lukS/F-PV-positive isolates were divided into two clonal patterns and USA300 was not included. In conclusion, SCCmec type IV was dominant in blood, skin, and soft tissue isolates in a secondary care facility in Japan. Because antimicrobial susceptibility varies with the SCCmec type, SCCmec typing of clinical isolates should be monitored in primary or secondary care facilities.

Characterization of Staphylococcus aureus from Humans and a Comparison with İsolates of Animal Origin, in North Dakota, United States

Different clones of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus have been found in humans as well as in animals and retail meat. However, more information about the genetic characteristics and similarities between strains is needed. The aim of this study was to identify and characterize Staphylococcus aureus from humans, and to compare their characteristics with isolates of animal origin. A total of 550 nasal swabs were taken from healthy humans, and S. aureus was isolated and identified. Positive S. aureus isolates were subjected to molecular typing and susceptibility testing. In addition, 108 MRSA isolates recovered from clinical patients in the state of North Dakota and 133 S. aureus isolates from animals and meat previously analyzed were included. The nasal carriage of S. aureus in healthy people was 7.6% and, in general, clones were genetically diverse. None of the S. aureus strains obtained from healthy people were mecA- or PVL-positive. A total of 105 (97.2%) MRSA isolates from clinical cases harbored the mecA gene and 11 (10.2%) isolated from blood stream infections harbored the PVL gene. The most common resistance profile among S. aureus from healthy people was penicillin, and from clinical cases were erythromycin-penicillin-ciprofloxacin. The rate of multidrug resistance (MDR) was 70% in humans. Most of the S. aureus harboring mecA and PVL genes were identified as ST5 and ST8, and exhibited MDR. However, S. aureus isolates of animal origin used for comparison exhibited a lower rate of MDR. The most common resistance profiles in isolates of animal origin were penicillin-tetracycline and penicillin-tetracycline-erythromycin, in animals and raw meat, respectively. The ST5 was also found in animals and meat, with ST9 and ST398 being the major clones. The genetic similarity between clones from humans and meat suggests the risk of spread of S. aureus in the food chain.

Variability in gene cassette patterns of class 1 and 2 integrons associated with multi drug resistance patterns in Staphylococcus aureus clinical isolates in Tehran-Iran

Background

To investigate antibiotic resistance, the occurrence and distribution of class 1 and 2 integrons in multidrug- resistant Staphylococcus aureus isolates from hospitals in Tehran, Iran.

The isolates were examined for susceptibility to antimicrobial agents. The mecA gene, class 1 and 2 integrons were detected by PCR. Integrase positive strains were further analysed for the presence of resistance gene cassettes using specific primers and were sequenced.

Results

Among 139 S.aureus isolates, 109 (78.4 %) and 112 (80.5 %) strains were considered as multidrug resistant and mecA positive, respectively. Class 1 integrons and internal variable regions were found in 72.6 % (101/139) and 97 % (98/101) and class 2 integrons and variable regions also in 35.2 % (49/139) and 65.3 % (32/49) of S.aureus clinical isolates, respectively. Twelve distinct cassette arrays were found, containing genes encoding resistance to β-lactams, aminoglycosides, streptothricin, trimethoprim, chloramphenicol,a putative glucose dehydrogenase precursor and a protein with unknown function. Gene cassette arrays aadB, aadA2 and dhfrA1-sat2-aadA1 were common in S.aureus isolates. We detected a completely new gene cassettes which contained aadB, oxa2, aacA4, orfD-aacA4-catB8, aadB-catB3, orfD-aacA4 and aadB-aadA1-cmlA6 of class 1 and dhfrA1-sat2-aadA1, dhfrA11, dhfrA1-sat2 of class 2 integrons.

Conclusions

This is the first study to report carriage of class 1 and 2 integrons and associated gene cassettes among in S.aureus isolates from Iran.

Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management

Staphylococcus aureus is a major human pathogen that causes a wide range of clinical infections. It is a leading cause of bacteremia and infective endocarditis as well as osteoarticular, skin and soft tissue, pleuropulmonary, and device-related infections. This review comprehensively covers the epidemiology, pathophysiology, clinical manifestations, and management of each of these clinical entities. The past 2 decades have witnessed two clear shifts in the epidemiology of S. aureus infections: first, a growing number of health care-associated infections, particularly seen in infective endocarditis and prosthetic device infections, and second, an epidemic of community-associated skin and soft tissue infections driven by strains with certain virulence factors and resistance to β-lactam antibiotics. In reviewing the literature to support management strategies for these clinical manifestations, we also highlight the paucity of high-quality evidence for many key clinical questions.

Necrotizing pneumonia and septic shock: suspecting CA-MRSA in patients presenting to Canadian emergency departments

We report a case of fatal necrotizing pneumonia and sepsis caused by community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) in an otherwise well, 48-year-old Canadian man with type 2 diabetes mellitus who had travelled to Texas. Despite therapy that included intravenous antibiotics, intravenous immune globulin and other supportive measures, the patient succumbed to his illness. Recently, CA-MRSA pneumonia has been reported in several countries. The virulence of this organism may in part be related to its ability to produce toxins, such as Panton-Valentine leukocidin. As rates of CA-MRSA increase worldwide, physicians should be aware of the potential for MRSA to cause life-threatening infections in patients presenting to Canadian emergency departments (EDs). Necrotizing pneumonia caused by MRSA must be considered in the differential diagnosis of acute, severe respiratory illness. Early recognition of this syndrome in the ED may help physicians initiate appropriate antibiotic therapy in a timely manner.

The bacterial pneumonias: a new treatment paradigm

Pneumonia is a common disease that carries a high mortality. Traditionally, pneumonia has been classified and treated according to the setting where the pneumonia develops, namely community-acquired pneumonia, health-care-associated pneumonia, and hospital-acquired pneumonia. This classification was based on the risk of a patient being infected with a hospital-acquired drug-resistant pathogen. A new treatment paradigm has been proposed based on the risk of the patient being infected with a community-acquired drug-resistant pathogen. The risk factors for infection with a community-acquired drug-resistant pathogen include (1) hospitalization for > 2 days during the previous 90 days, (2) antibiotic use during the previous 90 days, (3) nonambulatory status, (4) tube feeds, (5) immunocompromised status, (6) use of acid-suppressive therapy, (7) chronic hemodialysis during the preceding 30 days, (8) positive methicillin-resistant Staphylococcus aureus history within the previous 90 days, and (9) present hospitalization > 2 days. This article reviews this new treatment paradigm and other issues relevant to the diagnosis and management of pneumonia based on information from MEDLINE, EMBASE, and the Cochrane Register of Controlled Trials.

Effect of Nosocomial Infections Due to Antibiotic-Resistant Organisms on Length of Stay and Mortality in the Pediatric Intensive Care Unit

Objective.

To determine the prevalence, risk factors, and outcomes of nosocomial infection due to antimicrobial resistant bacteria in patients treated in the pediatric intensive care unit (PICU).

Design.

Nested case-cohort study. Patient data were collected prospectively, and antimicrobial susceptibility data were abstracted retrospectively.

Setting.

A large pediatric teaching hospital.

Patients.

All PICU patients admitted from September 1, 1999, to September 1, 2001, unless they died within 24 hours after PICU admission, were 18 years old or older, or were neonatal intensive care unit patients receiving extracorporeal membrane oxygenation.

Results.

A total of 135 patients with more than 1 nosocomial bacterial infection were analyzed; 52% were male, 75% were white, the mean Pediatric Risk of Mortality score was 10.5, and the mean age was 3.5 years. Of these patients, 37 (27%) had nosocomial infections due to antibiotic-resistant organisms. In univariate analysis, transplantation (odds ratio [OR], 2.83 [95% confidence interval (CI), 1.05-7.66]) and preexisting lung disease (OR, 2.63 [95% CI, 1.18-5.88]) were associated with nosocomial infections due to antibiotic-resistant organisms. Age, Pediatric Risk of Mortality score at admission, length of hospital stay before infection, and other underlying conditions were not associated with infections due to antibiotic-resistant organisms. Patients infected with antibiotic-resistant organisms had greater mean PICU lengths of stay after infection, compared with patients infected with antibiotic-susceptible organisms (22.9 vs 12.8 days;P= .004), and higher crude mortality rates (OR, 2.40 [95% CI, 1.03-5.61]).

Conclusions.

Identifiable risk factors exist for nosocomial infections due to antibiotic-resistant organisms. In univariate analysis, infections due to antibiotic-resistant bacteria are associated with increased length of stay in the PICU after onset of infection and increased mortality.

Evidence for increasing severity of community-onset boils and abscesses in UK General Practice

In England, hospital admissions for severe staphylococcal boils and abscesses trebled between 1989 and 2004. We investigated this trend using routine data from primary and secondary care. We used The Health Improvement Network (THIN), a large primary-care database and national data on hospital admissions from Hospital Episode Statistics (HES). Time trends in the incidence of primary-care consultations for boils and abscesses were estimated for 1995-2010. HES data were used to calculate age-standardized hospital admission rates for boils, abscesses and cellulitis. The incidence of boil or abscess was 450 [95% confidence interval (CI) 447-452] per 100 000 person-years and increased slightly over the study period (incidence rate ratio 1·005, 95% CI 1·004-1·007). The rate of repeat consultation for a boil or abscess increased from 66 (95% CI 59-73) per 100 000 person-years in 1995 to peak at 97 (95% CI 94-101) per 100 000 person-years in 2006, remaining stable thereafter. Hospital admissions for abscesses, carbuncles, furuncles and cellulitis almost doubled, from 123 admissions per 100 000 in 1998/1999 to 236 admissions per 100 000 in 2010/2011. Rising hospitalization and recurrence rates set against a background of stable community incidence suggests increased disease severity. Patients may be experiencing more severe and recurrent staphylococcal skin disease with limited treatment options.

Antimicrobial distribution from local delivery depends on dose : a pilot study with MRI

BACKGROUND

Tissue distribution after local delivery has been quantified over a period of 5 hours on 7-T MRI in a rabbit model using gadolinium-labeled diethylenetriamine pentaacetic acid (Gd-DTPA) as an antimicrobial surrogate; however, it is unknown how the Gd-DTPA load in a local depot will affect the duration of high-concentration Gd-DTPA in local tissues after surgical débridement.

QUESTIONS/PURPOSES

We determined whether the Gd-DTPA load in bone cement affected its local tissue distribution over a period of 1 month after local delivery.

METHODS

A 1-cm3 soft tissue dead space was created in the quadriceps of seven rabbits and filled with gadolinium-loaded bone cement. At 7, 14, and 33 days, the volume of tissue with a Gd-DTPA concentration of more than 14 μg/mL was calculated from T1-weighted images using 7-T MRI. Differences in volumes of distribution were analyzed with ANOVA.

RESULTS

The volume of tissue with more than 14 μg/mL Gd-DTPA was much larger from higher gadolinium loads on Day 7 (p=0.02) (2121 mm3 for 10 g and 665 mm3 for 1 g) and smaller with time for the 10-g formulation (2121 mm3 on Day 7 and 1241 mm3 on Day 14).

CONCLUSIONS

Volume of distribution and duration of Gd-DTPA after local delivery increased with increasing load in the cement and decreased with time.

CLINICAL RELEVANCE

For local delivery, high antimicrobial concentrations would be expected in greater volumes of tissue, for longer durations, when higher antimicrobial loads are used.

Origin and evolution of European community-acquired methicillin-resistant Staphylococcus aureus

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) was recognized in Europe and worldwide in the late 1990s. Within a decade, several genetically and geographically distinct CA-MRSA lineages carrying the small SCCmec type IV and V genetic elements and the Panton-Valentine leukocidin (PVL) emerged around the world. In Europe, the predominant CA-MRSA strain belongs to clonal complex 80 (CC80) and is resistant to kanamycin/amikacin and fusidic acid. CC80 was first reported in 1993 but was relatively rare until the late 1990s. It has since been identified throughout North Africa, the Middle East, and Europe, with recent sporadic reports in sub-Saharan Africa. While strongly associated with skin and soft tissue infections, it is rarely found among asymptomatic carriers. Methicillin-sensitive S. aureus (MSSA) CC80 strains are extremely rare except in sub-Saharan Africa. In the current study, we applied whole-genome sequencing to a global collection of both MSSA and MRSA CC80 isolates. Phylogenetic analyses strongly suggest that the European epidemic CA-MRSA lineage is derived from a PVL-positive MSSA ancestor from sub-Saharan Africa. Moreover, the tree topology suggests a single acquisition of both the SCCmec element and a plasmid encoding the fusidic acid resistance determinant. Four canonical SNPs distinguish the derived CA-MRSA lineage and include a nonsynonymous mutation in accessory gene regulator C (agrC). These changes were associated with a star-like expansion into Europe, the Middle East, and North Africa in the early 1990s, including multiple cases of cross-continent imports likely driven by human migrations.

With increasing levels of CA-MRSA reported from most parts of the Western world, there is a great interest in understanding the origin and factors associated with the emergence of these epidemic lineages. To trace the origin, evolution, and dissemination pattern of the European CA-MRSA clone (CC80), we sequenced a global collection of strains of the S. aureus CC80 lineage. Our study determined that a single descendant of a PVL-positive methicillin-sensitive ancestor circulating in sub-Saharan Africa rose to become the dominant CA-MRSA clone in Europe, the Middle East, and North Africa. In the transition from a methicillin-susceptible lineage to a successful CA-MRSA clone, it simultaneously became resistant to fusidic acid, a widely used antibiotic for skin and soft tissue infections, thus demonstrating the importance of antibiotic selection in the success of this clone. This finding furthermore highlights the significance of horizontal gene acquisitions and underscores the combined importance of these factors for the success of CA-MRSA.

Community-associated methicillin-resistant Staphylococcus aureus clonal complex 80 type IV (CC80-MRSA-IV) isolated from the Middle East: a heterogeneous expanding clonal lineage

Background

The emergence of community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) has caused a change in MRSA epidemiology worldwide. In the Middle East, the persistent spread of CA-MRSA isolates that were associated with multilocus sequence type (MLST) clonal complex 80 and with staphylococcal cassette chromosome mec (SCCmec) type IV (CC80-MRSA-IV), calls for novel approaches for infection control that would limit its spread.

Methodology/Principal Findings

In this study, the epidemiology of CC80-MRSA-IV was investigated in Jordan and Lebanon retrospectively covering the period from 2000 to 2011. Ninety-four S. aureus isolates, 63 (67%) collected from Lebanon and 31 (33%) collected from Jordan were included in this study. More than half of the isolates (56%) were associated with skin and soft tissue infections (SSTIs), and 73 (78%) were Panton-Valentine Leukocidin (PVL) positive. Majority of the isolates (84%) carried the gene for exofoliative toxin d (etd), 19% had the Toxic Shock Syndrome Toxin-1 gene (tst), and seven isolates from Jordan had a rare combination being positive for both tst and PVL genes. spa typing showed the prevalence of type t044 (85%) and pulsed-field gel electrophoresis (PFGE) recognized 21 different patterns. Antimicrobial susceptibility testing showed the prevalence (36%) of a unique resistant profile, which included resistance to streptomycin, kanamycin, and fusidic acid (SKF profile).

Conclusions

The genetic diversity among the CC80 isolates observed in this study poses an additional challenge to infection control of CA-MRSA epidemics. CA-MRSA related to ST80 in the Middle East was distinguished in this study from the ones described in other countries. Genetic diversity observed, which may be due to mutations and differences in the antibiotic regimens between countries may have led to the development of heterogeneous strains. Hence, it is difficult to maintain “the European CA-MRSA clone” as a uniform clone and it is better to designate as CC80-MRSA-IV isolates.

Methicillin-resistant Staphylococcus aureus: an evolving pathogen

The horizontal transmission of methicillin resistance to Staphylococcus aureus (MRSA) in hospital and community settings, and growing prevalence of these strains, presents a significant clinical challenge to the management of serious infections worldwide. While infection control initiatives have stemmed the rising prevalence, MRSA remains a significant pathogen. More recently, evidence that MRSA is becoming resistant to glycopeptides and newer therapies raises concern about the use of these therapies in clinical practice. Vancomycin resistance has become evident in select clinical settings through rising MICs, growing awareness of heteroresistance, and emergence of intermediate-resistant and fully resistant strains. While resistance to linezolid and daptomycin remains low overall, point mutations leading to resistance have been described for linezolid, and horizontal transmission of cfr-mediated resistance to linezolid has been reported in clinical isolates. These resistance trends for newer therapies highlight the ongoing need for new and more potent antimicrobial therapies.

Patterns of initial antibiotic therapy for community-acquired pneumonia in U.S. hospitals, 2000 to 2009

BACKGROUND

Although clinical guidelines for management of community-acquired pneumonia (CAP) in non-intensive care unit ("non-ICU") hospitalized patients have changed substantially over the last decade, it is unknown how treatment of this disease has evolved over this period.

METHODS

Using data from >100 U.S. hospitals, we identified all adults (aged ≥18 years) hospitalized for CAP between January 1, 2000, and June 30, 2009 ("study period"). We excluded patients admitted to ICU <24 hours of admission, those not starting antibiotics <24 hours of admission, those not receiving antibiotics for ≥48 hours (if alive), and those with probable healthcare-associated pneumonia. We defined "initial therapy" as all parenteral antibiotics received ≤24 hours of admission, and we examined changes in such therapy over the study period. The statistical significance of changes in initial therapy was ascertained using 2-tailed χ tests.

RESULTS

We identified 40,392 patients who met all selection criteria. In 2000, the most frequently used initial regimens were levofloxacin (24.0% of all such admissions), ceftriaxone (9.0%), cefotaxime (7.3%), ceftriaxone plus levofloxacin (3.2%) and azithromycin plus cefotaxime (3.0%); in 2009, they were ceftriaxone plus azithromycin (18.5%), levofloxacin (12.7%), ceftriaxone (6.6%), moxifloxacin (4.7%) and ceftriaxone + levofloxacin (3.2%). Use of single-agent regimens declined between 2000 and 2009 (from 48.2%-30.0%); use of vancomycin almost doubled (13.1%-23.3%). All findings were statistically significant (P < 0.01).

CONCLUSIONS

Initial antibiotic therapy for non-ICU CAP has changed substantially in the United States over the past decade, in line with evidence of widespread antibiotic resistance, evolving treatment guidelines and, most recently, quality improvement initiatives that tie hospital payments to guideline-based care.

Multiplex real-time PCR for detection of Staphylococcus aureus, mecA and Panton-Valentine Leukocidin (PVL) genes from selective enrichments from animals and retail meat

The aim of this study was to compare a real-time PCR assay, with a conventional culture/PCR method, to detect S. aureus, mecA and Panton-Valentine Leukocidin (PVL) genes in animals and retail meat, using a two-step selective enrichment protocol. A total of 234 samples were examined (77 animal nasal swabs, 112 retail raw meat, and 45 deli meat). The multiplex real-time PCR targeted the genes: nuc (identification of S. aureus), mecA (associated with methicillin resistance) and PVL (virulence factor), and the primary and secondary enrichment samples were assessed. The conventional culture/PCR method included the two-step selective enrichment, selective plating, biochemical testing, and multiplex PCR for confirmation. The conventional culture/PCR method recovered 95/234 positive S. aureus samples. Application of real-time PCR on samples following primary and secondary enrichment detected S. aureus in 111/234 and 120/234 samples respectively. For detection of S. aureus, the kappa statistic was 0.68–0.88 (from substantial to almost perfect agreement) and 0.29–0.77 (from fair to substantial agreement) for primary and secondary enrichments, using real-time PCR. For detection of mecA gene, the kappa statistic was 0–0.49 (from no agreement beyond that expected by chance to moderate agreement) for primary and secondary enrichment samples. Two pork samples were mecA gene positive by all methods. The real-time PCR assay detected the mecA gene in samples that were negative for S. aureus, but positive for Staphylococcus spp. The PVL gene was not detected in any sample by the conventional culture/PCR method or the real-time PCR assay. Among S. aureus isolated by conventional culture/PCR method, the sequence type ST398, and multi-drug resistant strains were found in animals and raw meat samples. The real-time PCR assay may be recommended as a rapid method for detection of S. aureus and the mecA gene, with further confirmation of methicillin-resistant S. aureus (MRSA) using the standard culture method.