SCCmec typing in methicillin-resistant Staphylococcus aureus strains of animal origin

Human Infections with Staphylococcus aureus CC398

Staphylococcus aureus isolates belonging to clonal cluster 398 (CC398) have emerged over the previous decade as a risk to livestock workers. Though most of the research to date has focused on colonization with these strains, a number of infections have also been documented, ranging from mild skin infections to more serious invasive infections and even death. Here, we review existing reports of human infections with CC398 and discuss their geographic distribution, general characteristics, and implications for future research. We identified 74 publications describing CC398 infections in humans in 19 different countries, suggesting this is an emerging worldwide issue.

Epidemiology and molecular characterization of methicillin-resistant Staphylococcus aureus nasal carriage isolates from bovines

BACKGROUND

Staphylococcus aureus is a common bacterium usually found on skin and mucous membranes of warm blooded animals. Resistance in S. aureus has been increasingly reported though depending on the clonal lineage. Indeed, while hospital acquired (HA)-methicillin resistant S. aureus (MRSA) are typically multi-resistant, community associated (CA)-MRSA are by large more susceptible to many antibiotics. Although S. aureus isolated from animals are often susceptible to most antibiotics, multi-resistant livestock associated (LA)-MRSA have been recovered from bovine mastitis.In this study, we investigated the prevalence and types of MRSA present in the nose of healthy bovines of different age groups and rearing practices. Since no validated methods for MRSA isolation from nasal swabs were available, we compared two isolation methods. Molecular characterization was performed by means of spa-typing, MLST, SCCmec typing and microarray analysis for the detection of antimicrobial resistance and virulence genes.

RESULTS

MRSA between herd prevalence in bovines was estimated at 19.8%. There was a marked difference between rearing practices with 9.9%, 10.2% and 46.1% of the dairy, beef and veal calve farms respectively being MRSA positive. No significant difference was observed between both isolation methods tested. Most isolates were ST398 spa type t011 or closely related spa types. Few ST239 spa type t037 and t388 and ST8 spa type t121 were also found. SCCmec types carried by these strains were mainly type IV(2B), IV(2B&5) and type V. Type III and non-typeable SCCmec were recovered to a lesser extent. All isolates were multi-resistant to at least two antimicrobials in addition to the expected cefoxitin and penicillin resistance, with an average of resistance to 9.5 different antimicrobials. Isolates selected for microarray analysis carried a broad range of antimicrobial resistance and virulence genes.

CONCLUSION

MRSA were mainly present in veal farms, compared to the lower prevalence in dairy or beef farms. Multi-resistance in these strains was high. Though mainly CC398 spa t011 was found, the genetic diversity was higher than what was found for pigs in Belgium. CC8 strains, a typically human lineage but also recently found also in association with bovines, has been retrieved here also.

Comparison of spa types, SCCmec types and antimicrobial resistance profiles of MRSA isolated from turkeys at farm, slaughter and from retail meat indicates transmission along the production chain

The prevalence of MRSA in the turkey meat production chain in Germany was estimated within the national monitoring for zoonotic agents in 2010. In total 22/112 (19.6%) dust samples from turkey farms, 235/359 (65.5%) swabs from turkey carcasses after slaughter and 147/460 (32.0%) turkey meat samples at retail were tested positive for MRSA. The specific distributions of spa types, SCCmec types and antimicrobial resistance profiles of MRSA isolated from these three different origins were compared using chi square statistics and the proportional similarity index (Czekanowski index). No significant differences between spa types, SCCmec types and antimicrobial resistance profiles of MRSA from different steps of the German turkey meat production chain were observed using Chi-Square test statistics. The Czekanowski index which can obtain values between 0 (no similarity) and 1 (perfect agreement) was consistently high (0.79–0.86) for the distribution of spa types and SCCmec types between the different processing stages indicating high degrees of similarity. The comparison of antimicrobial resistance profiles between the different process steps revealed the lowest Czekanowski index values (0.42–0.56). However, the Czekanowski index values were substantially higher than the index when isolates from the turkey meat production chain were compared to isolates from wild boar meat (0.13–0.19), an example of a separated population of MRSA used as control group. This result indicates that the proposed statistical method is valid to detect existing differences in the distribution of the tested characteristics of MRSA. The degree of similarity in the distribution of spa types, SCCmec types and antimicrobial resistance profiles between MRSA isolates from different process stages of turkey meat production may reflect MRSA transmission along the chain.

Prevalence, antimicrobial resistance, and molecular characterization of methicillin-resistant Staphylococcus aureus from bulk tank milk of dairy herds

It was the objective of the study to estimate the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in bulk tank milk from German dairy herds and to characterize isolates from bulk tank milk with respect to their Staph. aureus protein A (spa) and staphylococcal cassette chromosome mec (SCCmec) type, their phenotypic antimicrobial resistance and resistance- resp. virulence-associated genes using broth microdilution and a microarray for Staph. aureus. Bulk tank milk samples (25 mL) were tested for MRSA using a 2-step selective enrichment protocol. Presumptive MRSA were confirmed by PCR. Thirty-six isolates collected from bulk tank milk of dairy herds in 2009 and 2010 were included in the characterization. All isolates displayed spa-types assigned to the clonal complex CC398. Based on the epidemiological cut-off values for the interpretation of minimum inhibitory concentrations isolates were resistant to tetracycline (100%), clindamycin (58%), erythromycin (52%), quinupristin/dalfopristin (36%), and kanamycin (27%). Isolates did not carry genes associated with typical virulence factors for Staph. aureus such as the Panton-Valentine leukocidin. However, they did carry hemolysin genes. Livestock-associated MRSA of CC398 does occur in German dairy herds and the strains have similar properties as described for strains from pigs.

Molecular typing of Staphylococcus aureus bloodstream isolates from geriatric patients attending a long-term care Spanish hospital

All Staphylococcus aureus isolates (n=31) that caused bacteraemia in a Spanish geriatric hospital during 1996-2006 were analysed by a simple, rapid and inexpensive PCR technique based on variations in the hsdS1 and hsdS2 genes encoding the sequence recognition subunits of the Sau1 restriction-modification (RM) system. An equal number of isolates collected from surgical wounds over the same time period (control group) were similarly characterized. The RM test allocated 75 % of the isolates to the six major clonal complexes (CC1, CC5, CC8, CC22, CC30 and CC45) for which it was developed. However, recognition of minor CCs and precise identification of the circulating clones required more powerful and comprehensive techniques such as spa typing and multilocus sequence typing (MLST), which are more demanding and expensive. The RM test is not intended to replace spa or MLST typing, but may be of use when time, technical and/or financial resources are limited. Overall, nine and seven CCs were detected in bloodstream and wound isolates, respectively. In both groups, CC5 was the most frequent (35.5 % each), followed by CC45 or CC8 (22.6 and 32.3 % of bloodstream and wound isolates, respectively). The frequency of meticillin resistance was lower in bloodstream (16.1 %) than in wound (51.6 %) isolates (P=0.0025). Among the former, sequence type (ST) 5-staphylococcal cassette chromosome mec (SCCmec) II, ST5-SCCmec IV, ST45-SCCmec IV and ST125-SCCmec IV (now dominant in Spanish hospitals) clones were found. Among the wound isolates, nine meticillin-resistant clones were represented, with three of them (ST125-SCCmec III, ST125-SCCmec V and ST14-SCCmec V) being newly described.

Nasal carriage of methicillin-resistant and methicillin-sensitive strains of Staphylococcus sciuri in the Indonesian population

Staphylococcus sciuri strains were unexpectedly cultured from healthy persons and patients from Indonesia during a population-based survey on nasal Staphylococcus aureus carriage. Fifty-one S. sciuri isolates were further characterized. The S. aureus mecA gene was detected by PCR in 22 isolates (43.1%), whereas S. sciuri mecA was found in 33 isolates (64.7%). The staphylococcal cassette chromosome mec (SCCmec) regions of S. aureus mecA-positive isolates contained elements of classical S. aureus SCCmec types II and/or III.

Methicillin-resistant Staphylococcus aureus (MRSA) in food production animals

Until recently, reports on methicillin-resistant Staphylococcus aureus (MRSA) in food production animals were mainly limited to occasional detections in dairy cattle mastitis. However, since 2005 a MRSA clone, CC398, has been reported colonizing pigs, veal calves and broiler chickens and infecting dairy cows. Many aspects of its prevalence in pigs remain unclear. In other livestock, colonizing capacity and reservoir status still require elucidation. MRSA CC398 has also been detected in meat, but, as for other MRSA, the risk this poses is somewhat unclear. Currently, the most worrying aspect of MRSA CC398 appears to be its capacity to spread to humans. This might complicate MRSA control measures in human healthcare, urging research into risk factors and transmission routes. Although infections with MRSA CC398 are much less reported than carriage, more investigation into its pathogenic potential is required. Moreover, the origin and evolution of this clone remain unknown.

High heterogeneity within methicillin-resistant Staphylococcus aureus ST398 isolates, defined by Cfr9I macrorestriction-pulsed-field gel electrophoresis profiles and spa and SCCmec types

During recent years, the animal-associated methicillin-resistant Staphylococcus aureus clone ST398 has extensively been studied. The DNA of these isolates turned out to be refractory to SmaI restriction, and consequently, SmaI is unsuitable for subtyping this clone by standard pulsed-field gel electrophoresis (PFGE). Very recently, ST398 DNA was shown to be digested by Cfr9I, a neoschizomer of SmaI. In the present study, we employed Cfr9I PFGE on 100 German and 5 Dutch ST398 isolates and compared their PFGE profiles, protein A gene variable repeat regions (spa types), and types of the staphylococcal cassette chromosome mec (SCCmec). The isolates (from healthy carrier pigs, clinical samples from pigs, dust from farms, milk, and meat) were assigned to 35 profiles, which were correlated to the SCCmec type. A dendrogram with the Cfr9I patterns assigned all profiles to two clusters. Cluster A grouped nearly all isolates with SCCmec type V, and cluster B comprised all SCCmec type IVa and V* (a type V variant first identified as III) carriers plus one isolate with SCCmec type V. Both clusters also grouped methicillin-susceptible S. aureus isolates. The association of the majority of isolates with SCCmec type V in one large cluster indicated the presence of a successful subclone within the clonal complex CC398 from pigs, which has diversified. In general, the combination of Cfr9I PFGE with spa and SCCmec typing demonstrated the heterogeneity of the series analyzed and can be further used for outbreak investigations and traceability studies of the MRSA ST398 emerging clone.

Multiplex real-time PCR for rapid Staphylococcal cassette chromosome mec typing

Rapid identification and typing of methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) is important for understanding the molecular epidemiology and evolution of MRSA and offers many advantages for controlling transmission in both health care and community settings. We developed a rapid molecular beacon real-time PCR (MB-PCR) assay for staphylococcal cassette chromosome mec (SCCmec) typing. The design of this system is based on the established definition of SCCmec types, namely, the combination of the mec class complex with the ccr allotype. The assay consists of two multiplex panels, the combination of which results in two targets (mec class, ccr) for each SCCmec type. MB-PCR panel I targets mecA, ccrB2, mecI, and the DeltamecR1-IS1272 junction (mec class B); it can definitively identify SCCmec types II and IV. MB-PCR panel II detects ccrC, ccrB1, ccrB3, ccrB4, and the DeltamecR1-IS431 junction (mec class C2) and is therefore capable of identifying SCCmec types I, III, V, and VI in combination with panel I. The method can also detect the recently described novel SCCmec type VIII (ccrAB4 with mec class A). Our assay demonstrated 100% concordance when applied to 162 MRSA strains previously characterized by traditional SCCmec typing schemes. Four geographically and temporally diverse S. aureus collections were also successfully classified by our assay, along with 1,683 clinical isolates comprising both hospital- and community-associated MRSA and methicillin-susceptible S. aureus strains. As many as 96 isolates can be classified easily within 3 to 4 h, including DNA isolation, PCR cycling, and analysis. The assay is rapid, robust, sensitive, and cost-effective, allowing for high-throughput SCCmec typing of MRSA isolates.