The population structure of Staphylococcus aureus in China and Europe assessed by multiple-locus variable number tandem repeat analysis; clues to geographical origins of emergence and dissemination.

To compare the genetic population structure of Staphylococcus aureus from China and Europe, 1294 human isolates were characterized by multiple-locus variable number tandem repeat analysis (MLVA). In total, MLVA identified 17 MLVA complexes (MCs), comprising 260 MLVA types (MTs) among the Chinese isolates and 372 MTs among the European isolates. The five most frequent MCs among the Chinese isolates belonged to MC398, MC5 subclade a, MC8, MC437 and MC7 and made up 55% of the sample. For the European isolates, the five most frequent MCs consisted of MC5 subclade a, MC45, MC8, MC30 and MC22, which accounted for 64% of the sample. Phylogeographic analysis of the major MCs shared between China and Europe points to a European origin of MC8 but cannot provide a consistent signal for MC5 subclade a, probably indicating a different origin. Diversity and frequency distributions of other lineages were also compared. Altogether, this study provides the first snapshot of two extant populations of S. aureus from Europe and China, and important clues on the emergence and dissemination of different lineages of S. aureus.

Staphylococcus aureus spa type t437: identification of the most dominant community-associated clone from Asia across Europe.

Methicillin-resistant Staphylococcus aureus (MRSA) belonging to the multilocus sequence type clonal complex 59 (MLST CC59) is the predominant community-associated MRSA clone in Asia. This clone, which is primarily linked with the spa type t437, has so far only been reported in low numbers among large epidemiological studies in Europe. Nevertheless, the overall numbers identified in some Northern European reference laboratories have increased during the past decade. To determine whether the S. aureus t437 clone is present in other European countries, and to assess its genetic diversity across Europe, we analysed 147 S. aureus t437 isolates from 11 European countries collected over a period of 11 years using multiple locus variable number tandem repeat fingerprinting/analysis (MLVF/MLVA) and MLST. Additionally 16 S. aureus t437 isolates from healthy carriers and patients from China were included. Most isolates were shown to be monophyletic with 98% of the isolates belonging to the single MLVA complex 621, to which nearly all included isolates from China also belonged. More importantly, all MLST-typed isolates belonged to CC59. Our study implies that the European S. aureus t437 population represents a genetically tight cluster, irrespective of the year, country and site of isolation. This underpins the view that S. aureus CC59 has been introduced into several European countries, not being restricted to particular geographical regions or specific host environments. The European S. aureus t437 isolates thus bear the general hallmarks of a high-risk clone.

The dynamic changes of dominant clones of Staphylococcus aureus causing bloodstream infections in the European region: results of a second structured survey.

Staphylococcus aureus is one of the most important human pathogens and meticillin-resistant S. aureus (MRSA) presents a major cause of healthcare- and community-acquired infections. This study investigated the spatial and temporal changes of S. aureus causing bacteraemia in Europe over a five-year interval and explored the possibility of integrating pathogen-based typing data with epidemiological and clinical information at a European level. Between January 2011 and July 2011, 350 laboratories serving 453 hospitals in 25 countries collected 3,753 isolates (meticillin-sensitive S. aureus (MSSA) and MRSA) from patients with S. aureus bloodstream infections. All isolates were sent to the national staphylococcal reference laboratories and characterised by quality-controlled spa typing. Data were uploaded to an interactive web-based mapping tool. A wide geographical distribution of spa types was found, with some prevalent in all European countries. MSSA was more diverse than MRSA. MRSA differed considerably between countries with major international clones expanding or receding when compared to a 2006 survey. We provide evidence that a network approach of decentralised typing and visualisation of aggregated data using an interactive mapping tool can provide important information on the dynamics of S. aureus populations such as early signalling of emerging strains, cross-border spread and importation by travel.

Prevalence of methicillin-resistant Staphylococcus aureus carrying mecA or mecC in dairy cattle.

In the Netherlands, livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has been found in pigs, veal calves, horses and poultry. However, little is known about its prevalence in healthy dairy cattle. Recently, a new mec gene, called mecC, has been found in methicillin-resistant S. aureus (MRSA) isolates from humans and animals in several countries. The objective of our pilot study was to investigate the prevalence of MRSA (mecA and mecC) in dairy cows at a large slaughterhouse. Samples from the skin between the udder and hind leg were taken from 411 cows. The samples were incubated in Mueller-Hinton enrichment broth with 6.5% NaCl, followed by selective enrichment and plated onto Columbia agar with 5% sheep blood, Brilliance MRSA 2 agar and Baird-Parker agar. Suspected colonies were tested by PCR for a S. aureus specific DNA fragment, the mecA and mecC genes and the Panton-Valentine leucotoxin (PVL) genes. All MRSA isolates and methicillin-susceptible S. aureus (MSSA) isolates were typed by spa typing and MLVA typing. Sixteen of 411 (3.9%) cows, all originating from different farms, were found to be MRSA positive and this prevalence is lower than in Dutch pigs, veal calves and broilers. All MRSA isolates belonging to livestock-associated MLVA complex 398, were PVL-negative and spa type t011 predominated. MSSA isolates (n=39) were of many different MLVA types and spa type t543 was found most often. Four MSSA isolates belonging to MLVA clonal complex 398 and spa types t011 (n=2), t108 and t034 were isolated from different MRSA-negative animals. In conclusion, the prevalence of MRSA in dairy cows was low and isolates carrying the mecC gene were not found, indicating that it is absent or has a low prevalence (<0.73%) in Dutch dairy cows.

Molecular characterisation of PFGE non-typable methicillin-resistant Staphylococcus aureus in The Netherlands, 2007.

In 2007 in The Netherlands, 30% of all human isolates of methicillin-resistant Staphylococcus aureus (MRSA) sent to the National Institute for Public Health and the Environment could not be typed by pulsed-field gel electrophoresis (non-typable (NT)-MRSA). Molecular characterisation of the NT-MRSA isolates revealed 27 different spa types and two distinct SCCmec types, type IV and V. All NT-MRSA isolates were closely related based on spa and multi-locus sequence typing and belonged to the ST398 lineage. The rapid increase of NT-MRSA (ST398) isolates over the last years shows the importance of this relatively new clonal lineage.

Multiple cases of familial transmission of community-acquired methicillin-resistant Staphylococcus aureus.

The worldwide emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) can have severe public health implications. Familial transmissions of CA-MRSA in The Netherlands were investigated. Among the families studied, two clusters of CA-MRSA could be identified. This report demonstrates that family members can serve as reservoirs of CA-MRSA which may become a serious problem in containing the spread of MRSA.

Emergence of virulent methicillin-resistant Staphylococcus aureus strains carrying Panton-Valentine leucocidin genes in The Netherlands.

Methicillin-resistant Staphylococcus aureus (MRSA) strains carrying the Panton-Valentine leucocidin (PVL) genes have been reported worldwide and are a serious threat to public health. The PVL genes encode a highly potent toxin which is involved in severe skin infections and necrotizing pneumonia, even in previously healthy individuals. We assessed the prevalence of PVL-positive MRSA in The Netherlands for two periods of time: (i) 1987 through 1995 and (ii) 2000 and 2002, and determined their characteristics by using multilocus sequence typing and staphylococcal chromosome cassette (SCCmec) typing. It was found that up to 15% of all MRSA isolates detected in The Netherlands harbored the PVL genes. Most PVL-positive MRSA isolates were obtained from severe soft tissue infections in relatively young individuals. The first PVL-positive MRSA described in The Netherlands, isolated in 1988, was a single-locus variant of the "Berlin" epidemic MRSA clone. The 20 PVL-positive MRSA isolates studied in 2000 and 2002 consisted of five different sequence types (STs) that belonged to four clonal complexes. One of the STs, ST80, is considered to be a widespread European clone and was the most predominant ST (60%) in this study, while ST37 had never been found to be associated with PVL-positive MRSA. Most isolates harbored SCCmec type IV, a supposed marker for community-acquired MRSA. The number and type of virulence-associated genes varied among the different STs.

Panton-Valentine leukocidin positive MRSA in 2003: the Dutch situation.

Analysis of methicillin-resistant Staphylococcus aureus (MRSA) isolates in the Netherlands in 2003 revealed that 8% of the hospital isolates carried the loci for Panton-Valentine leukocidin (PVL). Molecular subtyping showed that most Dutch PVL-MRSA genotypes corresponded to well-documented global epidemic types. The most common PVL-MRSA genotypes were sequence type ST8, ST22, ST30, ST59 and ST80. MRSA with ST8 increased in the Netherlands from 1% in 2002 to 17% in 2003. It is emphasised that PVL-MRSA might not only emerge in the community, but also in the hospital environment.

Widespread dissemination in The Netherlands of the epidemic berlin methicillin-resistant Staphylococcus aureus clone with low-level resistance to oxacillin.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen and represents a growing public health burden due to the emergence and spread of epidemic strains, particularly within the hospital environment. An epidemic MRSA clone, with characteristic low-level resistance to oxacillin, emerged in the year 2000 and became endemic in the Netherlands. Multilocus sequence typing characterized the strain as sequence type 45, which was previously designated the Berlin epidemic MRSA clone. In 2 years, this strain has become the predominant MRSA clone in the Netherlands.

Panton-Valentine leukocidin positive MRSA in 2003: the Dutch situation.

Analysis of methicillin-resistant Staphylococcus aureus (MRSA) isolates in the Netherlands in 2003 revealed that 8% of the hospital isolates carried the loci for Panton-Valentine leukocidin (PVL). Molecular subtyping showed that most Dutch PVL-MRSA genotypes corresponded to well-documented global epidemic types. The most common PVL-MRSA genotypes were sequence type ST8, ST22, ST30, ST59 and ST80. MRSA with ST8 increased in the Netherlands from 1% in 2002 to 17% in 2003. It is emphasised that PVL-MRSA might not only emerge in the community, but also in the hospital environment.