Methicillin-resistant Staphylococcus Aureus Lineages Research Articles

Evolution and Population Structures of Prevalent Methicillin-Resistant Staphylococcus aureus in Taiwan.

Global methicillin-resistant Staphylococcus aureus (MRSA) strains were dominated by few genetic lineages, suggesting their inherent advantage of competitive fitness. The information of genome evolution and population structures of prevalent MRSA strains can help gain a better understanding of the success of the pandemic clones. Whole-genome sequencing was performed in 340 MRSA isolates belonging to three prevalent lineages, including ST59 (129 isolates), ST239/241 (140 isolates), and ST5 (71 isolates), collected from 1996 to 2016 in Taiwan. The time-scaled phylogeny and evolutionary pathways were estimated by Bayesian analysis using Markov chain Monte Carlo. The toxome, resistome, and plasmids were characterized by screening the raw reads with a public database. ST59, ST239/241, and ST5 MRSA were estimated to emerge in 1974, 1979, and 1995, respectively, in Taiwan. ST59 evolved through two major pathways, generating two subclones in 1980 and 1984. Both ST59 subclones remained prevalent in the healthcare and community environments in late 2010s. ST239/241 diverged into three subclones, respectively, in 1989, 1993, and 1995. The 1995-emerging ST239 subclone predominated after 2000 by replacing two previous early subclones. ST5 could be subdivided into two clades within 3 years of introduction, but no substantial difference of genomic profiles was identified in the strains of distinct clades. Each of the three pandemic MRSA lineages harbored its own specific toxome, resistome, and plasmids. The frequently identified genetic diversities between the subclones of the same lineage were genes mediating immune evasion, leukocidins, enterotoxins, and resistance to aminoglycosides. In conclusion, MRSA ST59 and ST239/241 emerged in the 1970s and evolved drastically during 1980 and 1995, resulting in three successful subclones prevailing in Taiwan. ST5 was introduced late in 1995 without a significant genetic drift during 20 years of evolution.

Whole-genome analysis uncovers loss of blaZ associated with carriage isolates belonging to methicillin-resistant Staphylococcus aureus (MRSA) clone ST5-VI in Cape Verde

Surveillance studies for Staphylococcus aureus carriage are a primary tool to survey the prevalence of methicillin-resistant S. aureus (MRSA) in the general population, patients and healthcare workers. We have previously reported S. aureus carriage in various African countries, including Cape Verde. Whole-genome sequences of 106 S. aureus isolates from Cape Verde were determined. Staphylococcus aureus carriage isolates in Cape Verde show high genetic variability, with the detection of 27 sequence types (STs) and three primary genetic clusters associated with ST152, ST15 and ST5. One transmission event with less than eight core-genome single nucleotide polymorphisms (cgSNP) differences was detected among the ST5-VI MRSA lineage. Genetic analysis confirmed the phenotypic resistance and allowed the identification of six independent events of plasmid or transposon loss associated with the deletion of blaZ in nine isolates. In the four ST5 MRSA isolates, loss of the blaZ plasmid coincided with the acquisition of SCCmec type VI and an unusual penicillin phenotype with a minimum inhibitory concentration (MIC) at the breakpoint, indicating an adaptation trend in this endemic lineage. Similar events of blaZ plasmid loss, with concomitant acquisition SCCmec elements, were detected among ST5 isolates from different geographical origins. Overall, the genome data allowed to place isolates in a phylogenetic context and to identify different blaZ gene deletions associated with plasmid or transposon loss. Genomic analysis unveiled adaptation and evolution trends, namely among emerging MRSA lineages in the country, which deserve additional consideration in the design of future infection control protocols.

The Surge of Hypervirulent ST398 MRSA Lineage With Higher Biofilm-Forming Ability Is a Critical Threat to Clinics.

The global increase of community-associated (CA) infections with methicillin-resistant Staphylococcus aureus (MRSA) is a major healthcare problem. Although sequence type (ST) 398 MRSA was first described as a livestock-associated (LA) lineage, human-adapted MRSA (HO-MRSA) ST398 without livestock contact has subsequently been reported from China in our previous study and other later research. The proportion of ST398 HO-MRSA has also remarkably increased in recent years in China. Based on 3878 S. aureus isolates that were collected in a general hospital between 2008 and 2018, we identified 56 ST398 HO-MRSA isolates. The four early appearing isolates of them have been sequenced by whole-genome sequencing (WGS) in our previous study. Here, by usage of WGS on the later-appearing 52 isolates and analyzing the phylogenetic dynamics of the linage, we found that 50 isolates clustered together with the former 4 isolates, making it a main clade out of MSSA clones and other MRSA clones, although ST398 HO-MRSA evolved with multiple origins. Drug resistance and virulence gene analysis based on the WGS data demonstrated that ST398 HO-MRSA main clade exhibited a similar pattern in both parts. Furthermore, they all carried a conserved variant of prophage 3 to guarantee virulence and a short SCCmec type V element of class D to maintain considerable lower methicillin resistance. Further phenotypical research verified that the epidemic HO-MRSA ST398 displayed enhanced biofilm formation ability when keeping high virulence. The dual advantages of virulence and biofilm formation in the HO-MRSA ST398 subtype promote their fitness in the community and even in the healthcare environment, which poses a serious threat in clinical S. aureus infections. Therefore, further surveillance is required to prevent and control the problematic public health impact of HO-MRSA ST398 in the future.

Methicillin-Resistant Staphylococcus aureus Clonal Complex 398 as a Major MRSA Lineage in Dogs and Cats in Thailand.

The aim of this study was to present molecular and antimicrobial resistance characteristics of methicillin-resistant Staphylococcus aureus (MRSA) clonal complex (CC) 398 isolated from diseased dogs and cats in Thailand. A total of 20 MRSA isolates of 134 Staphylococcus aureus isolated from canine and feline clinical samples during 2017–2020 were CC398, consisting of sequence type (ST) 398 (18 isolates), ST5926 (1 isolate), and ST6563 (1 isolate) by multilocus sequence typing. spa t034 and staphylococcal cassette chromosome mec (SCCmec) V were predominantly associated with ST398. Intraclonal differentiation was present by additional spa (t1255, t4653), non-detectable spa, composite SCCmec with a hybrid of ccrA1B1+ccrC and class A mec complex, and DNA fingerprints by pulsed-field gel electrophoresis. The isolates essentially carried antimicrobial resistance genes, mediating multiple resistance to β-lactams (mecA, blaZ), tetracyclines [tet(M)], aminoglycosides [aac(6′)-Ie-aph(2′)-Ia], and trimethoprim (dfr). Livestock-associated MRSA ST398 resistance genes including lnu(B), lsa(E), spw, fexA, and tet(L) were heterogeneously found and lost in subpopulation, with the absence or presence of additional erm(A), erm(B), and ileS2 genes that corresponded to resistance phenotypes. As only a single CC398 was detected with the presence of intraclonal variation, CC398 seems to be the successful MRSA clone colonizing in small animals as a pet-associated MRSA in Thailand.

Comparative genomics of MRSA strains from human and canine origins reveals similar virulence gene repertoire

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen associated with a wide variety of infections in humans. The ability of MRSA to infect companion animals has gained increasing attention in the scientific literature. In this study, 334 dogs were screened for MRSA in two cities located in Rio de Janeiro State. The prevalence of MRSA in dogs was 2.7%. Genotyping revealed isolates from sequence types (ST) 1, 5, 30, and 239 either colonizing or infecting dogs. The genome of the canine ST5 MRSA (strain SA112) was compared with ST5 MRSA from humans—the main lineage found in Rio de Janeiro hospitals—to gain insights in the origin of this dog isolate. Phylogenetic analysis situated the canine genome and human strain CR14-035 in the same clade. Comparative genomics revealed similar virulence profiles for SA112 and CR14-035. Both genomes carry S. aureus genomic islands νSAα, νSAβ, and νSAγ. The virulence potential of the canine and human strains was similar in a Caenorhabditis elegans model. Together, these results suggest a potential of canine MRSA to infect humans and vice versa. The circulation in community settings of a MRSA lineage commonly found in hospitals is an additional challenge for public health surveillance authorities.

Multidrug-Resistant Methicillin-Resistant Staphylococcus aureus Associated with Bacteremia and Monocyte Evasion, Rio de Janeiro, Brazil.

We typed 600 methicillin-resistant Staphylococcus aureus (MRSA) isolates collected in 51 hospitals in the Rio de Janeiro, Brazil, metropolitan area during 2014–2017. We found that multiple new clonal complex (CC) 5 sequence types had replaced previously dominant MRSA lineages in hospitals. Whole-genome analysis of 208 isolates revealed an emerging sublineage of multidrug-resistant MRSA, sequence type 105, staphylococcal cassette chromosome mec II, spa t002, which we designated the Rio de Janeiro (RdJ) clone. Using molecular clock analysis, we hypothesized that this lineage began to expand in the Rio de Janeiro metropolitan area in 2009. Multivariate analysis supported an association between bloodstream infections and the CC5 lineage that includes the RdJ clone. Compared with other closely related isolates, representative isolates of the RdJ clone more effectively evaded immune function related to monocytic cells, as evidenced by decreased phagocytosis rate and increased numbers of viable unphagocytosed (free) bacteria after in vitro exposure to monocytes.

Hospital-Associated Multidrug-Resistant MRSA Lineages Are Trophic to the Ocular Surface and Cause Severe Microbial Keratitis.

Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of severe and difficult to treat ocular infection. In this study, the population structure of 68 ocular MRSA isolates collected at Massachusetts Eye and Ear between January 2014 and June 2016 was assessed. By using a combination of multilocus sequence typing (MLST) analysis, SCCmec typing and detection of the panton-valentine leukocidin (PVL) gene, we found that the population structure of ocular MRSA is composed of lineages with community and hospital origins. As determined by eBURST analysis of MLST data, the ocular MRSA population consisted of 14 different sequence types (STs) that grouped within two predominant clonal complexes: CC8 (47.0%) and CC5 (41.2%). Most CC8 strains were ST8, harbored type IV SCCmec and were positive for the PVL-toxin (93.7%). The CC5 group was divided between strains carrying SCCmec type II (71.4%) and SCCmec type IV (28.6%). Remaining isolates grouped in 6 different clonal complexes with 3 isolates in CC6 and the other clonal complexes being represented by a single isolate. Interestingly, major MRSA CC5 and CC8 lineages were isolated from discrete ocular niches. Orbital and preseptal abscess/cellulitis were predominantly caused by CC8-SCCmec IV PVL-positive strains. In contrast, infections of the cornea, conjunctiva and lacrimal system were associated with the MDR CC5 lineage, particularly as causes of severe infectious keratitis. This niche specialization of MRSA is consistent with a model where CC8-SCCmec IV PVL-positive strains are better adapted to cause infections of the keratinized and soft adnexal eye tissues, whereas MDR CC5 appear to have greater ability in overcoming innate defense mechanisms of the wet epithelium of the ocular surface.

Tracking methicillin-resistant Staphylococcus aureus clones in a hospital in Southern Mexico.

To describe the clinical and molecular characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains that were collected in the Hospital Regional de Alta Especialidad de Veracruz (HRV). A total of 107 MRSA strains from individual patients were examined. The strains were collected between September 2009 and September 2010. The clinical and demographic characteristics of patients were analyzed; molecular typing by pulsed-field gel electrophoresis (PFGE), staphylococcal chromosomal cassette mec (SCCmec) typing and multilocus sequence typing were used to characterize the isolates. Two PFGE patterns (NY/J and IB) were identified with 4 and 3 subtypes respectively. The isolates analyzed showed two SCCmec types (I and II) and two sequence types (ST): ST247 and ST5 related with the Iberian and New York/Japan clones respectively. This study establishes the presence of two very important clonal lineages of MRSA: New York/Japan and Iberian clone in the hospital environment.

Novel Methicillin-Resistant Staphylococcus aureus CC8 Clone Identified in a Hospital Setting in Armenia.

Whole-genome sequencing (WGS) of methicillin-resistant Staphylococcus aureus (MRSA) has been sparse in low- and middle-income countries, therefore, its population structure is unknown for many regions. We conducted a pilot surveillance of MRSA in the maternity ward of a teaching hospital in Armenia, to characterize the genotypes of circulating MRSA clones. In total, 10 MRSA isolates from a hospital environment (n = 4) and patients (n = 6) were recovered between March and May 2015 and April and May 2016, respectively. WGS analysis showed that the isolates belonged to two clonal complexes (CCs): CC8 (n = 8) and CC30 (n = 2). MRSA CC30 isolates carried staphylococcal cassette chromosome mec (SCCmec) type IVa, whereas MRSA CC8 revealed a type-VT-related SCCmec, which contained a CRISPR/Cas array and showed a high similarity to SCCmec found in coagulase-negative staphylococci. All but one MRSA CC8 isolates carried a plasmid identical to the pSK67 and four also carried a pathogenicity island similar to SaPI5. Phylogenetic analysis showed that the MRSA CC8 isolates formed a monophyletic cluster, which emerged around 1995 and was distinct from representatives of globally-distributed MRSA CC8 lineages. WGS characterization of MRSA in countries with no previous S. aureus genomic surveillance can therefore reveal an unrecognized diversity of MRSA lineages.

Local Diversification of Methicillin- Resistant Staphylococcus aureus ST239 in South America After Its Rapid Worldwide Dissemination.

The global spread of specific clones of methicillin-resistant Staphylococcus aureus (MRSA) has become a major public health problem, and understanding the dynamics of geographical spread requires worldwide surveillance. Over the past 20 years, the ST239 lineage of MRSA has been recognized as an emerging clone across the globe, with detailed studies focusing on isolates from Europe and Asia. Less is known about this lineage in South America, and, particularly, Brazil where it was the predominant lineage of MRSA in the early 1990s to 2000s. To gain a better understanding about the introduction and spread of ST239 MRSA in Brazil we undertook a comparative phylogenomic analysis of ST239 genomes, adding seven completed, closed Brazilian genomes. Brazilian ST239 isolates grouped in a subtree with those from South American, and Western, romance-language-speaking, European countries, here designated the South American clade. After an initial worldwide radiation in the 1960s and 1970s, we estimate that ST239 began to spread in South America and Brazil in approximately 1988. This clone demonstrates specific genomic changes that are suggestive of local divergence and adaptational change including agrC single-nucleotide polymorphisms variants, and a distinct pattern of virulence-associated genes (mainly the presence of the chp and the absence of sea and sasX). A survey of a geographically and chronologically diverse set of 100 Brazilian ST239 isolates identified this virulence genotype as the predominant pattern in Brazil, and uncovered an unexpectedly high prevalence of agr-dysfunction (30%). ST239 isolates from Brazil also appear to have undergone transposon (IS256) insertions in or near global regulatory genes (agr and mgr) that likely led to rapid reprogramming of bacterial traits. In general, the overall pattern observed in phylogenomic analyses of ST239 is of a rapid initial global radiation, with subsequent local spread and adaptation in multiple different geographic locations. Most ST239 isolates harbor the ardA gene, which we show here to have in vivo anti-restriction activity. We hypothesize that this gene may have improved the ability of this lineage to acquire multiple resistance genes and distinct virulence-associated genes in each local context. The allopatric divergence pattern of ST239 also may suggest strong selective pressures for specific traits in different geographical locations.

A Distinct Geographic Variant of sasX in Methicillin-Resistant Staphylococcus aureus ST239 and ST368 Lineage from South India.

Staphylococcal surface protein sasX is a colonization mediating virulence factor in ST239 methicillin-resistant Staphylococcus aureus (MRSA) strains, which potentially contribute to its successful establishment. We aimed to study the presence and dissemination of sasX in clinical MRSA isolates and among MRSA carriers. A total of 450 nonduplicate clinical MRSA isolates recovered from blood cultures between 2013 and 2017 were included in this study. In addition, 93 nasal swabs were collected from patients receiving hemodialysis, after obtaining consent and screening for MRSA colonization. sasX polymerase chain reaction and sequencing were carried out for all isolates. Multilocus sequence typing was performed for all sasX-positive isolates. Of the tested clinical MRSA isolates, 11% (n = 48) were positive for sasX gene. Among hemodialysis patients, 26% (n = 24) were characterized as MRSA carriers. However, all MRSA strains isolated from nasal swab were negative for sasX gene. Overall, we observed 10% (11% in clinical MRSA isolates and 0% in MRSA carriers) of sasX-positive MRSA in this study. ST239 and ST368 were the predominant sasX carrying MRSA lineages. The majority of sasX carrying MRSA strains were characterized as Staphylococcus epidermidis surface protein I (sesI; 71%), a sasX homolog native to S. epidermidis. This study highlights the dissemination of sasX/sesI to ST368 (CC8), ST3324 (CC8), ST772 (CC1), and ST22 (CC22). The presence of S. epidermidis-specific invasive factor sesI in clinical MRSA strains provides evidence for horizontal transfer between these closely related species.

Distribution of virulence genes in bacteremic methicillin-resistant Staphylococcus aureus isolates from various sources.

Methicillin-resistant Staphylococcus aureus (MRSA) can encode proteins which directly bind bacteria to many tissues and medical devices or catheters to trigger pathogenesis. However, the relationship between genetic backgrounds and virulent factors in MRSA isolates remained incompletely understood yet. MRSA isolates were collected from blood cultures of patients with infective endocarditis, bone/joint infection, skin/soft tissue infection, or catheter-related bacteremia in hemodialysis at a tertiary medical center between 2005 and 2011. MRSA isolates were characterized by the methods of spa, multilocus sequence, and staphylococcal cassette chromosome mec (SCCmec) typing. Identification of virulence gene expression was measured by Power SYBR Green PCR Master Mix. Overall collected were 136 MRSA bacteremic isolates, including those from the cases of infective endocarditis (n=23), bone/joint infection (n=49), skin/soft tissue infection (n=20), or catheter-related bacteremia in patients with acute kidney injury or end-stage renal stage receiving hemodialysis (n=54). CC8-ST239-MRSA-SCCmec type III-spa type t037 was the most prevalent type observed in all of 136 MRSA bacteremic isolates. The prevalent genes in the group of infective endocarditis were clfA, clfB, fnbA, ebpS, eap, emp, sae, and eno; bone/joint infections clfA, emp, sae, and eno; skin/soft tissue infection eno; hemodialysis catheter-related bacteremia clfA and sae. The distribution of each gene was not statically different among four groups. A major MRSA lineage, CC8-ST239-MRSA-SCCmec type III-spa type t037, is noted among bacteremic MRSA isolates. No disease-specific virulent genes can be identified.

First report on USA300 outbreak in a neonatal intensive care unit detected by polymerase chain reaction-based open reading frame typing in Japan

Outbreaks of methicillin-resistant Staphylococcus aureus (MRSA) in the neonatal intensive care unit (NICU) have been reported worldwide. Some outbreaks were caused by USA300, which is a community-associated MRSA clone. In 2011, polymerase chain reaction-based open reading frame typing (POT) for the initial MRSA isolates from all inpatients was started at the Tokyo Metropolitan Children's Medical Center. From March 2014 to April 2015, a total of 131 MRSA strains were isolated, 104 of which were analyzed as healthcare-associated MRSA. Thirteen stains (12.5%) had a POT number of 106-9-93, which strongly suggested USA300; these included 6 from nasal swabs, 6 from blood cultures and 1 from subcutaneous pus. All the MRSA strains were isolated from patients in the NICU; were typed as sequence type 8, spa type t008, and staphylococcal cassette chromosome type mec IVa; and possessed the lukS-lukF and arginine catabolic mobile element-arcA gene. Pulsed-field gel electrophoresis of all the strains, with USA300-0114 as a reference, showed indistinguishable banding pattern. Based on these results, POT was useful in recognizing this first MRSA outbreak of USA300 in a Japanese NICU and was advantageous in terms of swiftness, less cost and monitoring change of the epidemic MRSA lineage.

Planning a One Health Case Study to Evaluate Methicillin Resistant Staphylococcus aureus and Its Economic Burden in Portugal.

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important multidrug-resistant nosocomial pathogens worldwide with infections leading to high rates of morbidity and mortality, a significant burden to human and veterinary clinical practices. The ability of S. aureus colonies to form biofilms on biotic and abiotic surfaces contributes further to its high antimicrobial resistance (AMR) rates and persistence in both host and non-host environments, adding a major ecological dimension to the problem. While there is a lot of information on MRSA prevalence in humans, data about MRSA in animal populations is scarce, incomplete and dispersed. This project is an attempt to evaluate the current epidemiological status of MRSA in Portugal by making a single case study from a One Health perspective. We aim to determine the prevalence of MRSA in anthropogenic sources liable to contaminate different animal habitats. The results obtained will be compiled with existing data on antibiotic resistant staphylococci from Portugal in a user-friendly database, to generate a geographically detailed epidemiological output for surveillance of AMR in MRSA. To achieve this, we will first characterize AMR and genetic lineages of MRSA circulating in northern Portugal in hospital wastewaters, farms near hospitals, farm animals that contact with humans, and wild animals. This will indicate the extent of the AMR problem in the context of local and regional human-animal-environment interactions. MRSA strains will then be tested for their ability to form biofilms. The proteomes of the strains will be compared to better elucidate their AMR mechanisms. Proteomics data will be integrated with the genomic and transcriptomic data obtained. The vast amount of information expected from this omics approach will improve our understanding of AMR in MRSA biofilms, and help us identify new vaccine candidates and biomarkers for early diagnosis and innovative therapeutic strategies to tackle MRSA biofilm-associated infections and potentially other AMR superbugs.

Characterization of Biofilms Formed by Foodborne Methicillin-Resistant Staphylococcus aureus.

The objective of this study was to evaluate the capacity of 49 methicillin resistant Staphylococcus aureus (MRSA) from foods of animal origin (42 from dairy products and 7 from meat and meat products) to form biofilms. Overall, a higher biofilm biomass was observed for those MRSA strains harboring SCCmec type IV, while 8 MRSA strains (5 from dairy products and 3 from meat and meat products) were classified as strong biofilm formers in standard Tryptic Soy Broth medium. When a prolonged incubation period (48 h) was applied for those 8 MRSA strains, an increased biofilm biomass accumulation was observed during the time course, whereas the number of viable cells within the biofilms decreased as the biomass increased. The capacity of biofilm production correlated pretty well between the experiments using polystyrene microtiter plates and stainless steel micro-well plates, and significant higher values were observed in stainless steel when glucose was added to TSB during the enrichment. Biofilms were further characterized by confocal laser scanning microscope (CLSM), confirming that proteins and α-polysaccharides were the predominant components inside the extracellular polymeric matrix of biofilms formed by MRSA strains. In conclusion, our results confirm that MRSA isolates from foods of animal origin have significant capacity for forming biofilms with a high protein content, which can play a key role for the successful dissemination of MRSA lineages via food. Knowledge of the capacity of MRSA strains to produce biofilms, as well as characterization of the main MRSA biofilms matrix components, can help both to counteract the mechanisms involved in biofilm formation and resistance and to define more rational control strategies by using tailor-made cleaning agents.

Prevalence and Characteristics of Methicillin-Resistant Staphylococcus aureus Isolates in Pigs and Pig Farmers in Korea.

In this study, we investigated the prevalence and characteristics of methicillin-resistant Staphylococcus aureus (MRSA) isolates from pigs and pig farmers in Korea. A total of 1245 nasal swabs were collected from pigs and farmers at 53 pig farms in nine provinces from 2012 to 2016. The prevalence of MRSA was 7.9% (88/1119) in pigs and 16.7% (21/126) in farmers. Among 119 farmers working on conventional farms, 21 (17.6%) tested positive for MRSA. However, no MRSA was detected in either pigs or farmers at four organic farms. The individual pig-level prevalence of MRSA differed between age groups, with the percentage of positive samples being highest in weaners (17.3%), followed by growers (9.0%), piglets (6.5%), finishers (4.4%), and sows (0%). Two different lineages of MRSA were detected among the 109 isolates from pigs and farmers: (1) livestock-associated types of MRSA belonging to 27 isolates of ST541-t034-V, 24 isolates of ST398-t571-V, 17 isolates of ST398-t034 variant (G420A)-V, and one isolate of ST541-t8588-V; and (2) community-associated types of MRSA belonging to 21 isolates of ST188-t189-IV, 14 isolates of ST72-t324-IV, three isolates of ST72-t664-IV, one isolate of ST72-t148-IV, and one isolate of ST72-t5440-IV. Identical genotypes were detected in both pigs and farmers at six farms. New MRSA clones were isolated from pigs (ST398-t034 (G420A)-V, ST188-t189-IV, and ST398-t571-V) and pig farmers (ST541-t8588-V and ST72-t5440-IV). The prevalence of MRSA was also correlated with antibiotic usage, and the clones showed diversification between pigs and farmers. Ultimately, the increased frequency and diversification of livestock-associated MRSA could be a potential threat to public health in Korea. To our knowledge, this is the first study to report the prevalence and characteristics of MRSA in pigs and pig farmers in Korea.

Metabolic niche adaptation of community- and hospital-associated methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) originally emerged in nosocomial settings and has subsequently spread into the community. In turn, community-associated (CA) MRSA lineages are nowadays introduced from the community into hospitals where they can cause hospital-associated (HA) infections. This raises the question of how the CA-MRSA lineages adapt to the hospital environment. Previous studies implicated particular virulence factors in the CA-behaviour of MRSA. However, we hypothesized that physiological changes may also impact staphylococcal epidemiology. With the aim to identify potential metabolic adaptations, we comparatively profiled the cytosolic proteomes of CA- and HA-isolates from the USA300 lineage that was originally identified as CA-MRSA. Interestingly, enzymes for gluconeogenesis, the tricarboxylic acid cycle and biosynthesis of amino acids are up-regulated in the investigated CA-MRSA isolates, while enzymes for glycolysis and the pentose phosphate pathway are up-regulated in the HA-MRSA isolates. Of note, these data apparently match with the clinical presentation of each group. These observations spark interest in central carbon metabolism as a key driver for adaptations that streamline MRSA for propagation in the community or the hospital.

Prevalence, multidrug resistance and molecular typing of methicillin-resistant Staphylococcus aureus (MRSA) in retail meat from Punjab, India

This study reports the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in retail meat from Punjab, India. Classical microbiological methods were applied to isolate and identify S. aureus isolates. Isolates also underwent Etest. PCR and sequencing were used to identify and characterise antimicrobial resistance genes. MLST, SCCmec and spa typing were performed. A total of 408 meat and 101 swab samples were processed for S. aureus isolation. Phenotypic resistance was highest to penicillin (90.97%), followed by ciprofloxacin (61.80%), tetracycline (45.14%) and erythromycin (11.11%). Isolates from chicken samples showed significantly higher MICs for tetracycline than chevon and pork samples and significantly higher MICs for trimethoprim/sulfamethoxazole and gentamicin than chevon and swab samples (P<0.05). No isolates were phenotypically resistant to vancomycin (MICs of 0.5-2μg/mL). Most isolates (52.78%, 95% CI 44.63-60.93%) were multidrug-resistant and carried resistance genes to penicillin (blaZ), oxacillin (mecA), gentamicin (aacA-aphD), erythromycin (ermB, ermC) and tetracycline (tetK, tetL, tetM). MRSA was only found in chicken samples (2.72%; 4/147). Seven S. aureus (5.07%) were borderline oxacillin-resistant (MIC range 4-8μg/mL). All MRSA were SCCmecV-pvl+-t442, among which three isolates were ST5. Their genotype was mecA+, blaZ+, aacA-aphD+, tetK+, ermC+/-. Among the erythromycin-resistant isolates, 25% were MRSA, of which 12.5% isolates expressed an inducible macrolide-lincosamide-streptogramin B (iMLSB) phenotype. These data confirm the presence of ST5-t442-MRSA-SCCmecV-pvl+ and iMLSB MRSA in meat samples, indicating a potential role of meat in the dissemination of multidrug-resistant S. aureus strains and successful MRSA lineages in Punjab.

Characteristics of methicillin-resistant Staphylococcus aureus in patients on admission to a teaching hospital in Rio de Janeiro, Brazil

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are associated with greater mortality and morbidity; however, risk factors for community-acquired infections caused by MRSA have not been established. Therefore, community patients who are admitted to hospitals without the necessary contact precautions and are infected with community-acquired lineages eventually cause these lineages to spread to these settings. The aim of this study was to detect community-acquired lineages of MRSA in patients on admission to a Brazilian teaching hospital. The antimicrobial susceptibility of the MRSA isolates from nasal swabs was evaluated as was the molecular characteristics of the staphylococcal cassette chromosome mec (SCCmec). The clonality was determined using pulsed-field gel electrophoresis and multilocus sequence type analysis. A total of 702 patients were evaluated between March 2012 and March 2013; 180 (25%) of them were colonized by S aureus, and 21 (3%) were MRSA. The SCCmec IV/USA1100/sequence type (ST) 30 was the predominant MRSA lineage (42.8%), followed by SCCmec IV/USA800/ST5 (23.8%). The occurrence of MRSA colonization was very low, and only 1 patient from cardiac surgery developed an infection, which was caused by an SCCmec II/USA100/ST5 isolate. Screening for MRSA colonization on admission does not seem to be productive; however, for populations submitted to specific surgeries, active surveillance should be implemented.

Methicillin-resistant Staphylococcus aureus emerged long before the introduction of methicillin into clinical practice

BackgroundThe spread of drug-resistant bacterial pathogens poses a major threat to global health. It is widely recognised that the widespread use of antibiotics has generated selective pressures that have driven the emergence of resistant strains. Methicillin-resistant Staphylococcus aureus (MRSA) was first observed in 1960, less than one year after the introduction of this second generation beta-lactam antibiotic into clinical practice. Epidemiological evidence has always suggested that resistance arose around this period, when the mecA gene encoding methicillin resistance carried on an SCCmec element, was horizontally transferred to an intrinsically sensitive strain of S. aureus.ResultsWhole genome sequencing a collection of the first MRSA isolates allows us to reconstruct the evolutionary history of the archetypal MRSA. We apply Bayesian phylogenetic reconstruction to infer the time point at which this early MRSA lineage arose and when SCCmec was acquired. MRSA emerged in the mid-1940s, following the acquisition of an ancestral type I SCCmec element, some 14 years before the first therapeutic use of methicillin.ConclusionsMethicillin use was not the original driving factor in the evolution of MRSA as previously thought. Rather it was the widespread use of first generation beta-lactams such as penicillin in the years prior to the introduction of methicillin, which selected for S. aureus strains carrying the mecA determinant. Crucially this highlights how new drugs, introduced to circumvent known resistance mechanisms, can be rendered ineffective by unrecognised adaptations in the bacterial population due to the historic selective landscape created by the widespread use of other antibiotics.