MRSA CC398 Research Articles

The prevalence of Staphylococcus aureus and the emergence of livestock-associated MRSA CC398 in pig production in eastern China.

Livestock-associated Staphylococcus aureus (LA-MRSA) has been of increasing concern due to its potential risk to humans. This study investigated the prevalence of MRSA in pig production in Eastern China and determined the genomic characteristics of pig-associated MRSA isolates by whole-genome sequencing (WGS). A total of 1,318 samples were collected from pig farms and pig slaughterhouses, and 150 S. aureus were identified, including 63 MRSA isolates and 87 MSSA isolates. MRSA was detected in all pig farms and pig slaughterhouses. The antimicrobial susceptibility test revealed that all MRSA isolates were multidrug-resistant. The WGS and MLST analysis demonstrated that 56 MRSA isolates belonged to clonal complex (CC) 398, and seven MRSA isolates belonged to CC9. All LA-MRSA isolates were absent of phiSa3 phage containing immune evasion cluster (IEC) and possessed an intact hlb gene. In addition, genes associated with Panton-Valentine leukocidin, typically indicative of human adaptation, were not detected. The analysis of antibiotic resistance genes (ARGs) demonstrated that all MRSA isolates contained multiple ARGs. All MRSA isolates had Plthe mecA gene and at least one tetracycline resistance gene. Both tetM and tetK were detected in all MRSA CC398 isolates, while tetL was detected in all MRSA CC9 isolates. The phenicol resistance gene fexA was detected in 51 MRSA isolates, while the linezolid resistance gene cfr was detected in 60 MRSA isolates. The emergence of LA-MRSA CC398 in four pig farms and one slaughterhouse in this study indicates the spread of this clonal complex in the pig production sector in Eastern China. Further investigations are required to understand the potential transmission routes of LA-MRSA CC398 within the pork production chain in China and to assess the potential risks to humans.

Genetic diversity, antibiotic resistance, and virulence characteristics of Staphylococcus aureus from raw milk over 10 years in Shanghai

Staphylococcus aureus (S. aureus) is a major cause of foodborne infections and its persistence in raw milk is a multifaceted phenomenon that poses a considerable public health challenge. Our study investigated the prevalence, virulence genes, antibiotic resistance, and genetic characterization of S. aureus in raw milk in six Shanghai districts from 2013 to 2022. At 18 dairy farms, a total of 704 S. aureus strains were isolated from 1799 samples tested for drug sensitivity. The highest rates of antibiotic resistance were ampicillin (96.7 %), sulfamethoxazole (65 %), and erythromycin (21.6 %). Between 2018 and 2022, there was a significant decrease in the resistance rates of ceftiofur, ofloxacin, tilmicosin, erythromycin, clindamycin, amoxicillin-clavulanic acid, and sulfamethoxazole in comparison to the period from 2013 to 2017. There were 205 S. aureus strains chosen for whole genome sequencing (WGS), with no more than 2 strains of the same resistance phenotype from each farm per year. The prevalence of mecA-positive strains was 14.15 %, while other antibiotic resistance-associated genes were observed as follows: blaI (70.21 %), lnu(B) (5.85 %), lsa(E) (5.75 %), fexA (6.83 %), erm(C) (4.39 %), tet(L) (9.27 %), and dfrG (5.85 %). Isolates harboring the immune evasion cluster (IEC) genes (scn, chp, and sak) were predominantly categorized as sequence types (STs) 7, 188, 15, 59, and 398. The predominant cluster complexes were CC97, CC1, CC398, and CC1651. In 2017–2022, there was a transition in CC1 from the highly antibiotic-resistant ST9 strain that emerged between 2013 and 2018 to the low-resistant but highly virulent ST1 strain. Retrospective phylogenetic analysis elucidated the evolutionary history of the isolates and demonstrated that the human-animal host transition of S. aureus was linked to the genesis of MRSA CC398. The implementation of extended surveillance will aid in the development of innovative strategies to avoid the transmission of S. aureus along the dairy food chain and the occurrence of public health events.

Bioinformatics study of expression from genomes of epidemiologically related MRSA CC398 isolates from human and wild animal samples

One of the most important livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) genetic lineages is the clonal complex (CC) 398, which can cause typical S. aureus-associated infections in people. In this work, whole-genome sequencing, RNA-sequencing, and gel-based comparative proteomics were applied to study the genetic characteristics of three MRSA CC398 isolates recovered from humans (strains C5621 and C9017), and from an animal (strain OR418). Of the three strains, C9017 presented the broadest resistance genotype, including resistance to fluroquinolone, clindamycin, tiamulin, macrolide and aminoglycoside antimicrobial classes. The scn, sak, and chp genes of the immune evasion cluster system were solely detected in OR418. Pangenome analysis showed a total of 288 strain-specific genes, most of which are hypothetical or phage-related proteins. OR418 had the most pronounced genetic differences. RNAIII (δ-hemolysin) gene was clearly the most expressed gene in OR418 and C5621, but it was not detected in C9017. Significant differences in the proteome profiles were found between strains. For example, the immunoglobulin-binding protein Sbi was more abundant in OR418. Considering that Sbi is a multifunctional immune evasion factor in S. aureus, the results point to OR418 strain having high zoonotic potential. Overall, multiomics biomarker signatures can assume an important role to advance precision medicine in the years to come. SignificanceMRSA is one of the most representative drug-resistant pathogens and its dissemination is increasing due to MRSA capability of establishing new reservoirs. LA-MRSA is considered an emerging problem worldwide and CC398 is one of the most important genetic lineages. In this study, three MRSA CC398 isolates recovered from humans and from a wild animal were analyzed through whole-genome sequencing, RNA-sequencing, and gel-based comparative proteomics in order to gather systems-wide omics data and better understand the genetic characteristics of this lineage to identify distinctive markers and genomic features of relevance to public health.

Risk of hospitalization and death within 2years after methicillin-resistant Staphylococcus aureus (MRSA) diagnosis in persons colonized or infected with livestock and non-livestock-associated MRSA-A nationwide register-based cohort study.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) CC398 has emerged in humans throughout Europe and the USA during the last decade and is associated with the spread of LA-MRSA CC398 in production animals. In this study, we investigated the risk of subsequent hospitalization with an S.aureus-related diagnosis and death within the first 2years after MRSA diagnosis. The study included 7,521 carriers of MRSA, an age-matched reference population of 376,041 individuals and 7,607 patients infected with MRSA. Hazard ratios (HR) for hospitalization with an S.aureus-related diagnosis were 4.09 (95% CI: 2.78-6.00) and for death 1.21 (95% CI: 0.80-1.83) in LA-MRSA CC398 carriers compared with the reference population. Comparing carriers of LA-MRSA CC398 and non-CC398 MRSA, HR for hospitalization was 0.61 (95% CI: 0.37-0.99) and death 0.25 (95% CI: 0.16-0.40), respectively. Patients initially diagnosed with LA-MRSA CC398 or non-CC398 MRSA infection differed from MRSA carriers in terms of older age, higher Charlson comorbidity index score and longer hospital stays. HR for subsequent hospitalization and death was similar regardless having infection with LA-MRSA CC398 or non-CC398 MRSA at the time of MRSA diagnosis. We established that MRSA CC398 carriers have a lower risk of hospitalization and death up to 2years after MRSA diagnosis than non-CC398 MRSA carriers do. In contrast, MRSA carriage, regardless the MRSA strain is a burden in terms of hospitalization and death when compared to the background reference population. Further, we established that there are no differences in risk of subsequent hospitalization and death in patients initially diagnosed with MRSA CC398 or non-CC398 MRSA infection. We suggest that public health surveillance of MRSA clearly needs to distinguish between carriage and infection as well as strain type before any inference from number of cases to disease burden is made.

Antimicrobial resistance phenotypes and genotypes of methicillin-resistant Staphylococcus aureus CC398 isolates from Spanish hospitals

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) of lineage CC398 is an emerging clone causing human infections but is mostly found in pigs. The aim of this study was to characterize the antimicrobial resistance phenotypes/genotypes of a collection of 137 MRSA CC398 isolates obtained in a previous study from 17 Spanish hospitals, using tetracycline resistance as marker for selection. A multidrug-resistant (MDR) phenotype was present in 79% of analysed isolates, with 17% of them resistant to at least six different antimicrobial families. All tetracycline-resistant isolates (n=137) carried the tetM gene and 75% also carried the tetK gene. Almost 50% of MRSA CC398 isolates showed macrolide and/or lincosamide resistance: a) 39% of isolates were ERYR-CLIR (all with constitutive phenotype), with 87% of them carrying the ermC gene, followed by msrA (25%), ermB (21%), vgaA (17%), ermA (6%), lsaB (4%), linA (2%), linB (2%), and ermT (2%, this isolate with the new spa-type t18071); and b) 9% of MRSA CC398 isolates showed the dissociated ERYS-CLIR phenotype carrying the linA, linB, lsaB and vgaA genes. Other antimicrobial resistance phenotypes in these MRSA CC398 isolates included resistance to ciprofloxacin (67%), aminoglycosides (21%), mupirocin (6%), chloramphenicol (4%) or fusidic acid (2%). The more common resistance genes detected for some of these antimicrobials were: aac(6’)-Ie-aph(2’’)-Ia (16%) and ant(4’)-Ia (12%) for aminoglycosides, and fexA (3%) for chloramphenicol. The high rate of MDR phenotypes with a wide range of antimicrobial resistance genes shown in this study reduce the potential therapeutic options in case of infections.

Core genome multi-locus sequence typing as an essential tool in a high-cost livestock-associated meticillin-resistant Staphylococcus aureus CC398 hospital outbreak

Livestock-associated meticillin-resistant Staphylococcus aureus (LA-MRSA) clonal complex (CC) 398 may be transmitted and cause morbidity and mortality in hospitals. The economic cost of stopping hospital transmission of LA-MRSA CC398 is poorly described. Early detection of transmission may limit the extent of the intervention. To evaluate core genome multi-locus sequence typing (cgMLST) for detecting transmission chains and to estimate the costs for interventions to prevent further spread after discovery of hospital transmission of LA-MRSA CC398. Five patients were involved in two episodes of transmission of LA-MRSA CC398 in a hospital. Standard interventions including MRSA screening of patients and healthcare workers were initiated. Whole genome sequences of the five isolates and 17 epidemiologically unrelated MRSA CC398 isolates from other hospitalized patients were analysed by single nucleotide polymorphism (SNP) comparisons and cgMLST. The economic costs of constraining transmission were calculated from relevant sources. The five isolates suspected to be involved in hospital transmission clustered with ≤2 SNPs in the draft genome sequences with some distance to other isolates. cgMLST allocated the five isolates to the same type, which was different from all but two of the sporadic isolates. Furthermore, cgMLST separated the five transmission isolates from all other isolates. The economic costs of the outbreak interventions exceeded €11,000 per patient. LA-MRSA CC398 is transmittable in hospitals, and intervention against transmission may reach considerable costs. cgMLST is useful in surveillance of hospital transmission of LA-MRSA.

Epidemiology of MRSA CC398 in hospitals located in Spanish regions with different pig-farming densities: a multicentre study.

Tetracycline resistance (TetR) is a marker of livestock-associated MRSA of lineage CC398. To determine the MRSA CC398 prevalence among TetR-MRSA recovered in Spanish hospitals located in regions with different pig-farming densities, and the influence of pig density as a key risk factor for its acquisition. TetR-MRSA isolates (n = 232) recovered from clinical and epidemiological samples during January-June 2016 in 20 hospitals in 13 regions with different pig-farming densities were analysed. MRSA CC398 identification, detection of spa types, methicillin resistance genes and immune evasion cluster (IEC) genes were performed by PCR/sequencing. Statistical analyses were performed to establish the relationships between MRSA CC398 prevalence and pig density. The global MRSA prevalence was 29.7% (6.9% TetR-MRSA/MRSA), with 137 CC398 isolates recovered, representing 4.1% of total MRSA and 59.1% of TetR-MRSA. Among MRSA CC398, 16 different spa types were recorded (t011: 72.3%), and all but two strains were IEC negative. Higher pig-density regions were associated with significant MRSA CC398 increases in hospitals located in adjacent regions (P < 0.001). Linear regression models explained the relationships between MRSA CC398 and pig density (P < 0.001), with an increase of 6.6 MRSA CC398 cases per 100 MRSA per increase of 100 pigs/km2 in a region. High pig density leads to a significant increase in MRSA CC398 in hospitals in Spain, and its combination with a high human population could help its dissemination. In Spain, the prevalence of the zoonotic CC398 lineage is closely related to pig-farming density; therefore, specific tools could be implemented in order to detect its dissemination.

Infection with MRSA CC398 Related to Occupational Exposure to Mink: A Case Report

A 59-year old man was hospitalised with dyspnoea, cough and fever, which led to respiratory treatment, later complicated with large central pulmonary embolisms. The only positive finding in samples was MRSA CC398. The patient worked several times as a full-time employee at a mink farm, which was the only exposure to MRSA CC398 in the patient’s occupational history. The Danish Labour Market Insurance recognised the injury as an occupational disease; hence, exposure to LA-MRSA for working on mink farms is a new occupational risk factor in Denmark.

Prevalence and Characterization of Staphylococcus aureus Isolated From Women and Children in Guangzhou, China.

The prevalent Staphylococcus aureus clones and antibiotic susceptibility profiles are known to change dynamically and geographically; however, recent S. aureus strains causing infections in women and children in China have not been characterized. In this study, we analyzed the molecular epidemiology and antimicrobial resistance of S. aureus isolated from patients in four centers for women and children in Guangzhou, China. In total, 131 S. aureus isolates (100 from children and 31 from women) were analyzed by spa typing, multi-locus sequence typing, virulence gene and antimicrobial resistance profiling, staphylococcal chromosomal cassette mec typing, and mutation analyses of rpoB. A total of 58 spa types, 27 sequence types (STs), and 10 clonal complexes (CCs) were identified. While CC59 (ST59-IV, 48.8%; ST338-III, 35.7%) and CC45 (ST45-IV, 100%) were the major clones (84.4%) among MRSA isolates, CC5 (ST188, 24.3%; ST1, 21.6%) and CC398 (ST398, 70%) were the major ones (70.1%) among MSSA isolates. ST338-MRSA-III mostly found in pus but hardly in respiratory tract samples while ST45-MRSA-IV was on the opposite, even though they both found in blood and cerebrospinal fluid sample frequently. Staphylococcal enterotoxin genes seb-seq-sek were strongly associated with ST59 and ST338, while sec was associated with ST45, ST121, ST22, and ST30. All ST338, ST1232, and SCCmec III isolates carried lukF/S-PV genes. A total of 80% of ST338 isolates were resistant to erythromycin, clindamycin, and tetracycline. All ST45 isolates exhibited intermediate or complete resistance to rifampicin. In total, 481 HIS/ASN mutations in rpoB were found in rifampicin-resistant or intermediate-resistant isolates. ST338-III and ST45-IV emerged as two of three major clones in MRSA isolates from women and children in Guangzhou, China, though ST59-MRSA-IV remained the most prevalent MRSA clone. Clonal distribution of S. aureus varied, depending on the specimen source. Virulence genes and antibiograms were closely associated with the clonal lineage. These results clarified the molecular epidemiology of S. aureus from women and children in Guangzhou, China, and provide critical information for the control and treatment of S. aureus infections.

Subdivision of MRSA CC398 isolates using MALDI-TOF MS

Outbreak investigations demand a fast and discriminative typing method. MALDI-TOF MS has been shown to be a rapid, easy and inexpensive method of subtyping MRSA.The aim of the present study is to explore whether it is possible to subdivide isolates of MRSA CC398, commonly livestock associated, using an enhanced version of the MALDI-TOF MS typing method that we previously described (Østergaard et al, 2015). We included MALDI-TOF spectra from 378 isolates of MRSA belonging to CC398, of which 322 were epidemiologically independent. We identified 17 peaks as discriminatorily useful and could therefore reliably subdivide the isolates into 23 subtypes, including a distinct type corresponding to a strain from an unusual and initially undiscovered hospital outbreak. Whole genome sequencing was carried out for 193 of the isolates and compared with both the spa type and an antibiogram of these strains. The proposed MALDI-TOF subdivision method for MRSA CC398 was found to be more discriminative than both spa typing and resistotyping, and had a high negative predictive value for ruling out a close genetic relationship between pairs of strains with different MALDI-TOF types. We conclude that the MALDI-TOF-based typing method can be used for rapid and inexpensive routine subdivision of MRSA belonging to CC398.

Distance to pig farms as risk factor for community-onset livestock-associated MRSA CC398 infection in persons without known contact to pig farms-A nationwide study.

MRSA CC398 is an emerging MRSA strain found in livestock, mainly in pigs. Direct occupational livestock contact is the principal risk factor for human MRSA CC398 infection. Nonetheless, in recent years, an increasing number of MRSA CC398 cases has been observed in persons without known pig contact. Such cases, referred to as MRSA CC398 of unknown origin (MUO CC398), have, like livestock-onset (LO) MRSA CC398 cases, been found concentrated in rural, livestock-producing areas. The presence of MUO CC398 cases indicates alternative and unknown MRSA CC398 transmission pathways into the community. We performed a nationwide study in Denmark of the geographic distributions of MRSA cases in general and persons with MUO CC398 or LO MRSA CC398 infections (1 January 2006-11 February 2015), with the Danish population as background population. Place of living of study persons was mapped using the ArcGIS software, and information on pig farms was retrieved from the Central Husbandry Register. The incidence of MUO CC398 infections was clearly higher in rural than in urban areas, and such cases lived on average closer to pig farms than the general population. However, within three pig-farming-dense municipalities, patients with MUO CC398 infections did not live closer to pig farms than population controls. This shows that direct environmental spread from neighbouring pig farms of MRSA CC398 is unlikely. Instead, community spread through other means of transmission than direct spread from farms may more likely explain the clustering of MUO CC398 in livestock-dense areas.

Increase of zinc resistance in German human derived livestock-associated MRSA between 2000 and 2014

Problem addressedLivestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA), particularly of the clonal complex (CC) 398, emerged as zoonotic pathogens predominantly among humans with direct or indirect livestock contact, but also in healthcare settings. The factors contributing to the success of LA-MRSA are only poorly understood. ObjectiveDuring the past years, the use of heavy metal compounds as feed-supplements was found to influence the co-selection of LA-MRSA in pig herds. This study aimed to determine the prevalence of zinc resistance among MRSA CC398 isolated from patients of a German university hospital located in a pig farming-dense area. Methods and approachIn comparison to concurrent healthcare-associated MRSA (HA-MRSA), LA-MRSA CC398 comprising isolates from their first appearance in 2000 to recent isolates from 2014 were included. ResultsAmong MRSA CC398, the overall resistance rate towards zinc chloride was 57% compared to only 3% among concurrently isolated HA-MRSA. Zinc resistance correlated with the presence of the czrC gene in 100% of the MRSA CC398 and in 67% of the HA-MRSA. ConclusionsThe zinc resistance rate in MRSA CC398 significantly increased from 2009 to 2014 with a maximum in 2014. Alarmingly, zinc resistance has become a frequent phenotype of human LA-MRSA in Germany potentially facilitating co-selection of antibiotic resistance genes.

Assessment of the Risk to Public Health due to Use of Antimicrobials in Pigs-An Example of Pleuromutilins in Denmark.

Antibiotic consumption in pigs can be optimized by developing treatment guidelines, which encourage veterinarians to use effective drugs with low probability of developing resistance of importance for human health. In Denmark, treatment guidelines for use in swine production are currently under review at the Danish Veterinary and Food Administration. Use of pleuromutilins in swine has previously been associated with a very low risk for human health. However, recent international data and sporadic findings of novel resistance genes suggest a change of risk. Consequently, a reassessment was undertaken inspired by a risk assessment framework developed by the European Medicines Agency. Livestock-associated methicillin-resistant Staphylococcus aureus of clonal complex 398 (MRSA CC398) and enterococci were identified as relevant hazards. The release assessment showed that the probability of development of pleuromutilin resistance was high in MRSA CC398 (medium uncertainty) and low in enterococci (high uncertainty). A relatively small proportion of Danes has an occupational exposure to pigs, and foodborne transmission was only considered of relevance for enterococci, resulting in an altogether low exposure risk. The human consequences of infection with pleuromutilin-resistant MRSA CC398 or enterococci were assessed as low for the public in general but high for vulnerable groups such as hospitalized and immunocompromised persons. For MRSA CC398, the total risk was estimated as low (low uncertainty), among other due to the current guidelines on prevention of MRSA in place at Danish hospitals, which include screening of patients with daily contact to pigs on admittance. Moreover, MRSA CC398 has a medium human–human transmission potential. For enterococci, the total risk was estimated as low due to low prevalence of resistance, low probability of spread to humans, low virulence, but no screening of hospitalized patients, high ability of acquiring resistance genes, and a limited number of alternative antimicrobials (high uncertainty). This assessment reflects the current situation and should be repeated if pleuromutilin consumption increases substantially, resulting in increased prevalence of mobile, easily transmissible resistance mechanisms. Continuous monitoring of pleuromutilin resistance in selected human pathogens should therefore be considered. This also includes monitoring of linezolid resistance, since resistance mechanisms for pleuromutilins and oxazolidones are often coupled.

First report on MRSA CC398 recovered from wild boars in the north of Portugal. Are we facing a problem?

The aim of the present study was to evaluate the resistance of Staphylococcus aureus recovered from wild boars, to analyze their genetic lineages, and to investigate the susceptibility to oxacillin. Samples from mouth and nose of 45 wild boars (Sus scrofa) were collected during hunt activity from November 2012 to January 2013 in the North of Portugal. S. aureus isolates were recovered from 30 of these samples (33%); one isolate/sample was further studied. The susceptibility of the isolates was tested by disk-diffusion test against 14 antimicrobial agents and minimal inhibitory concentration was used to test oxacillin according to EUCAST guidelines. The genetic lineages of S. aureus were characterized by agr-typing, spa-typing and MLST. From the 30 isolates, 18 S. aureus were susceptible to all antibiotics tested and 7 presented resistance to one or more of the following antibiotics: penicillin (n=3), oxacillin (n=4), cefoxitin (n=1), clindamycin (n=2), gentamicin (n=1), fusidic acid (n=1), ciprofloxacin (n=2), tetracycline (n=1) and linezolid (n=1). One MRSA CC398 (spa-type t899) isolate was detected (oxacillin MIC=32mg/L and mecA-positive), which presented resistance to penicillin, tetracycline, and ciprofloxacin and contained the genes of immune evasion cluster (IEC) system (type B). The 29 methicillin-susceptible isolates were typed as ST1 (t1533), ST133 (t3583), ST1643 (t10712), ST2328 (t3750) and the new STs (3220, 3222, 3223, 3224) associated to new spa-types t14311 and t14312. The agr-types I, II, III and IV were identified. It is a matter of concern when MRSA and some specific lineages of S. aureus are taken as commensal habitants of the skin and nose of wild animals and are characterized with resistance to various antimicrobial agents in clinical use.

In the centre of an epidemic: Fifteen years of LA-MRSA CC398 at the University Hospital Münster

Ten years after initial publications on livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in 2005, we report on the course of the LA-MRSA CC398 epidemic among patients of the University Hospital Münster. This tertiary care facility is located in the Dutch-German border region (EUREGIO), which is characterized by a high density of livestock production and is hence a hotspot for the occurrence of LA-MRSA CC398. Taking advantage of the unique opportunity to track the emergence and spread of MRSA CC398 among humans from the very beginning of the epidemic until today, a total of 6555 non-duplicate MRSA isolates from all screenings and clinical specimens cultivated within the period from 2000 to 2014 were included in the analysis. Retrospectively, the first MRSA CC398 isolate (spa type t034) was obtained from a screening specimen of a patient in 2000, which represents one of the first human-associated LA-MRSA CC398 isolates reported in Europe. After sporadic detections between 2000 and 2004, this clonal lineage accounted for 9.6% of all local MRSA in 2005; a proportion which increased to 35% in 2013 and became stable since then. Considering the period from 2000 to 2014, the group of MRSA CC398 isolates comprised a total of 45 different spa types among which t011 (48.3%), t034 (39.3%) and t108 (3.5%) were predominant and so far unreported types were found. Overall, LA-MRSA CC398 emerged rapidly during the past decade, developed enormous sublineage diversity and contributed substantially to the total burden of MRSA colonization and infection at the hospital.

The clinical impact of livestock-associated methicillin-resistant Staphylococcus aureus of the clonal complex 398 for humans

In the past decade, livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) strains in particular of the clonal complex (CC) 398 have emerged in many parts of the world especially in areas with a high density of pig farming. In those regions, farmworkers and other individuals with professional contact to livestock are very frequently colonized with LA-MRSA. These persons are the presumably source for LA-MRSA transmission to household members and other parts of the human population. Altogether, colonization and/or infection of these individuals lead to the introduction of LA-MRSA into hospitals and other healthcare facilities. Since LA-MRSA CC398 have been found to be specifically adapted to their animal hosts in terms of the equipment with virulence factors, their pathogenicity to human patients is a matter of debate with first reports about clinical cases. Meanwhile, case reports, case series and few studies have demonstrated the capability of LA-MRSA to cause all types of infections attributed to S. aureus in general including fatal courses. Human infections observed comprise e.g. bacteremia, pneumonia, osteomyelitis, endocarditis and many manifestations of skin and soft tissue infections. However, inpatients affected by MRSA CC398 generally show different demographic (e.g. younger, shorter length of hospital stay) and clinical characteristics (e.g. less severe complications) which may explain or at least contribute to a lower disease burden of LA-MRSA compared to other MRSA clonal lineages.

MRSA colonization and infection among persons with occupational livestock exposure in Europe: Prevalence, preventive options and evidence

Colonization with livestock-associated Methicillin-resistant Staphylococcusaureus (LA-MRSA) among persons occupationally exposed to pigs, cattle or poultry is very frequent. In Europe, LA-MRSA mostly belong to the clonal lineage CC398. Since colonized persons have an increased risk of developing MRSA infections, defining the burden of work-related infection caused by LA-MRSA CC398 is of interest to exposed personnel, insurance companies and infection control staff. This review summarizes data on the types of occupation-related infections caused by LA-MRSA CC398, the incidence of such infections as well as potential preventive strategies.We identified twelve case reports on infections among livestock-exposed persons. Overall, there is a lack of data describing the incidence of occupation-related infections due to MRSA CC398. Currently, no specific guidance towards the prevention of LA-MRSA CC398 colonization of persons with routine exposure exists. In vitro, MRSA CC398 strains are susceptible (>95%) to mupirocin. Single reports have described effective decolonization of persons carrying LA-MRSA CC398, but long-term success rates are low in case of continuous livestock contact.Overall, the occupational health risk due to LA-MRSA CC398 is not well understood. Currently, prevention of human LA-MRSA CC398 infection is mostly based on the recommendation to perform screening and decolonization therapies prior to elective medical interventions in order to avoid nosocomial infections, but there is no conclusive evidence to perform specific measures aiming to forestall community-acquired infections.

Clonal diversity, virulence patterns and antimicrobial and biocide susceptibility among human, animal and environmental MRSA in Portugal.

The objective of this study was to identify the Staphylococcus aureus clonal types currently circulating in animals, humans in contact with animals and the environment in Portugal based on genetic relatedness, virulence potential and antimicrobial/biocide susceptibility. Seventy-four S. aureus isolates from pets, livestock, the environment and humans in contact with animals were characterized by SCCmec typing, spa typing, PFGE and CC398-specific PCR, by antimicrobial and biocide susceptibility testing and by detection of resistance genes and genes for efflux pumps. Representative strains were analysed by DNA microarray and MLST. The S. aureus isolates represented 13 spa types and 3 SCCmec types and belonged to three clonal complexes (CC5, CC22 and CC398). Most of the isolates were multiresistant and harboured the resistance genes that explained the resistance phenotype. The qacG and qacJ genes for biocide resistance were detected in 14 isolates (all MRSA CC398), while 4 isolates (3 CC5 and 1 CC22) had insertions in the -10 motif of the norA promoter. Isolates of the clonal lineages associated with pets (CC5 and CC22) harboured specific sets of virulence genes and often a lower number of resistance genes than isolates of the clonal lineage associated with livestock animals (CC398). We found, for the first time in animals in Portugal, four strains belonging to CC5, including ST105-II, a lineage that has been previously reported as vancomycin-resistant S. aureus in Portugal. Moreover, for the first time the qacG and qacJ genes were detected in MRSA CC398 strains. Active surveillance programmes detecting MRSA not only in livestock animals but also in companion animals are urgently needed.

Transmission of methicillin-resistant Staphylococcus aureus CC398 from livestock veterinarians to their household members.

There are indications that livestock-associated MRSA CC398 has a reduced human-to-human transmissibility, limiting its impact on public health and justifying modified control measures. This study determined the transmissibility of MRSA CC398 from livestock veterinarians to their household members in the community as compared to MRSA non-CC398 strains. A one-year prospective cohort study was performed to determine the presence of MRSA CC398 in four-monthly nasal and oropharyngeal samples of livestock veterinarians (n = 137) and their household members (n = 389). In addition, a cross-sectional survey was performed to detect the presence of MRSA non-CC398 in hospital derived control patients (n = 20) and their household members (n = 41). Staphylococcus aureus isolates were genotyped by staphylococcal protein A (spa) typing and multiple-locus variable-number tandem repeat analysis (MLVA). Mean MRSA CC398 prevalence over the study period was 44% (range 41.6–46.0%) in veterinarians and 4.0% (range 2.8–4.7%) in their household members. The MRSA CC398 prevalence in household members of veterinarians was significantly lower than the MRSA non-CC398 prevalence in household members of control patients (PRR 6.0; 95% CI 2.4–15.5), indicating the reduced transmissibility of MRSA CC398. The impact of MRSA CC398 appears to be low at the moment. However, careful monitoring of the human-to-human transmissibility of MRSA CC398 remains important.

High genetic diversity of methicillin-susceptible Staphylococcus aureus (MSSA) from humans and animals on livestock farms and presence of SCCmec remnant DNA in MSSA CC398

To investigate the genetic diversity of methicillin-susceptible Staphylococcus aureus (MSSA) carriage isolates from animals and humans on pig, veal, dairy, beef and broiler farms. S. aureus isolates were genotyped using spa typing and multilocus sequence typing (MLST). Antimicrobial susceptibility phenotypes and genotypes were determined. The presence of staphylococcal cassette chromosome mec (SCCmec)-associated DNA was characterized by PCR and sequencing among isolates of clonal complex (CC) 398. Overall, 41 MSSA isolates in humans and 141 in animals were found, originating from all farm types. These MSSA were mainly assigned to CC398, CC1, CC5, CC9, CC30, CC97, CC133 and CC705/151. MSSA CC398 showed resistance to tetracycline, trimethoprim, macrolides and/or lincosamides, aminoglycosides, ciprofloxacin, spectinomycin and quinupristin/dalfopristin, whereas non-CC398 MSSA showed considerably less resistance. Three porcine MSSA CC398-t011 isolates harboured remnant DNA of a composite SCCmec V(5C2&5)c element that lacked the mec gene complex. This resulted from an MRSA-to-MSSA conversion due to recombination between the ccrC genes flanking the mec gene complex. The SCC remnant still contained an intact J1 region harbouring czrC and tet(K), encoding zinc and tetracycline resistance, respectively, thereby illustrating the capacity of S. aureus CC398 to adapt to different antibiotic selection pressures in the farming environment. Processes such as mec gene complex deletion probably contribute to the enormous diversity of SCC(mec) elements observed in staphylococci. MSSA CC398 precursors from which MRSA CC398 might (re)emerge were present on pig, veal and broiler farms, all of which are livestock sectors commonly known to be affected by MRSA CC398. The multiresistance phenotype of S. aureus CC398 appears to be independent of methicillin resistance.