Clonal complex 398 methicillin susceptible Staphylococcus aureus: a frequent unspecialized human pathogen with specific phenotypic and genotypic characteristics

Prevalence, antimicrobial resistance, and genetic lineages of nasal Staphylococcus aureus among medical students at a Spanish University: detection of the MSSA-CC398-IEC-type-C subclade

Medical students could be a potential source of Staphylococcus aureus transmission to patients. This cross-sectional study involved samples collected from both nasal nostrils. Samples were processed for S. aureus recovery; the antimicrobial resistance (AMR) phenotype was determined by disc diffusion assays and the spa types and AMR genotypes by PCR/sequencing. A structured questionnaire was administered to students to collate data related to potential risk factors of nasal colonization. Ninety-eight students were included, 50 % were colonized by S. aureus and 12.2 % by MRSA. The mecA gene was detected in all MRSA isolates. The MSSA-CC398-IEC-type C lineage was found among 16.3 % of nasal carriers, of which t571 was the predominant spa-type. MRSA isolates were ascribed to spa types t2226 (CC5, 12 isolates) and t3444 (new spa type, 1 isolate). All MRSA were multi-drug resistant and MSSA were predominantly resistant to erythromycin-clindamycin (inducible-type, mediated by ermT gene). High rates of S. aureus and MRSA nasal carriages were observed in this study. The predominance of the CC398 lineage among MSSA (emergent invasive lineage) represent a relevant finding of public health concern. The role of medical students as potential source of MRSA and MSSA-CC398 transmissions in hospital and community needs to be elucidated in detail.

Methicillin Resistant Staphylococcus aureus: Molecular Mechanisms Underlying Drug Resistance Development and Novel Strategies to Combat

Antimicrobial resistance (AMR) represents a major threat to global health. Infection caused by Methicillin-resistant Staphylococcus aureus (MRSA) is one of the well-recognized global public health problem globally. In some regions, as many as 90% of S. aureus infections are reported to be MRSA, which cannot be treated with standard antibiotics. WHO reports indicated that MRSA is circulating in every province worldwide, significantly increasing the risk of death by 64% compared to drug-sensitive forms of the infection which is attributed to its antibiotic resistance. The emergence and spread of antibiotic-resistant MRSA strains have contributed to its increased prevalence in both healthcare and community settings. The resistance of S. aureus to methicillin is due to expression of penicillin-binding protein 2a (PBP2a), which renders it impervious to the action of β-lactam antibiotics including methicillin. The other is through the production of beta-lactamases. Although the treatment options for MRSA are limited, there are promising alternatives to antibiotics to combat the infections. Innovative therapeutic strategies with wide range of activity and modes of action are yet to be explored. The review highlights the global challenges posed by MRSA, elucidates the mechanisms underlying its resistance development, and explores mitigation strategies. Furthermore, it focuses on alternative therapies such as bacteriophages, immunotherapy, nanobiotics, and antimicrobial peptides, emphasizing their synergistic effects and efficacy against MRSA. By examining these alternative approaches, this review provides insights into the potential strategies for tackling MRSA infections and combatting the escalating threat of AMR. Ultimately, a multifaceted approach encompassing both conventional and novel interventions is imperative to mitigate the impact of MRSA and ensure a sustainable future for global healthcare.

Staphylococcus aureus Adaptation to the Skin in Health and Persistent/Recurrent Infections

Staphylococcus aureus is a microorganism with an incredible capability to adapt to different niches within the human body. Approximately between 20 and 30% of the population is permanently but asymptomatically colonized with S. aureus in the nose, and another 30% may carry S. aureus intermittently. It has been established that nasal colonization is a risk factor for infection in other body sites, including mild to severe skin and soft tissue infections. The skin has distinct features that make it a hostile niche for many bacteria, therefore acting as a strong barrier against invading microorganisms. Healthy skin is desiccated; it has a low pH at the surface; the upper layer is constantly shed to remove attached bacteria; and several host antimicrobial peptides are produced. However, S. aureus is able to overcome these defenses and colonize this microenvironment. Moreover, this bacterium can very efficiently adapt to the stressors present in the skin under pathological conditions, as it occurs in patients with atopic dermatitis or suffering chronic wounds associated with diabetes. The focus of this manuscript is to revise the current knowledge concerning how S. aureus adapts to such diverse skin conditions causing persistent and recurrent infections.

Genome Analysis of Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus ST398 Strains Isolated from Patients with Invasive Infection

BACKGROUND

Using genomic data, we determined the origin of MRSA ST398 isolates responsible for invasive infection in patients with no known livestock contact.

METHODS

We sequenced the genome of seven MSSA and four MRSA ST398 isolates from patients with invasive infections between 2013 and 2017, using the Illumina technique. Prophage-associated virulence genes and resistance genes were identified. To determine the origin of the isolates, their genome sequences were included in phylogenetic analysis also encompassing the ST398 genomes available on NCBI.

RESULTS

All isolates carried the φSa3 prophage, but with variations in the immune evasion cluster: type C in MRSA isolates, and type B in MSSA isolates. All MSSA belonged to the spa type t1451. MRSA strains had the same SCCmec type IVa (2B) cassette and belonged to spa types t899, t4132, t1939 and t2922. All MRSA harbored the tetracycline resistance gene, tet(M). Phylogenetic analysis revealed that MSSA isolates belonged to a cluster of human-associated isolates, while MRSA isolates belonged to a cluster containing livestock-associated MRSA.

CONCLUSION

We showed that the clinical isolates MRSA and MSSA ST398 have different origins. An acquisition of virulence genes by livestock-associated MRSA isolates allows them to induce an invasive infection in human.

A review of new emerging livestock-associated methicillin-resistant Staphylococcus aureus from pig farms

Methicillin-resistant Staphylococcus aureus (MRSA) is a S. aureus strain resistant to β-lactam antibiotics and is often associated with livestock, known as livestock-associated (LA)-MRSA. Using molecular typing with multi-locus sequence typing, MRSA clones have been classified in pigs, including clonal complex 398. Livestock-associated-methicillin-resistant S. aureus was first discovered in pigs in the Netherlands in 2005. Since then, it has been widely detected in pigs in other countries. Livestock-associated-methicillin-resistant S. aureus can be transmitted from pigs to pigs, pigs to humans (zoonosis), and humans to humans. This transmission is enabled by several risk factors involved in the pig trade, including the use of antibiotics and zinc, the size and type of the herd, and the pig pen management system. Although LA-MRSA has little impact on the pigs' health, it can be transmitted from pig to pig or from pig to human. This is a serious concern as people in direct contact with pigs are highly predisposed to acquiring LA-MRSA infection. The measures to control LA-MRSA spread in pig farms include conducting periodic LA-MRSA screening tests on pigs and avoiding certain antibiotics in pigs. This study aimed to review the emerging LA-MRSA strains in pig farms.

Epidemiology and risk factors of nasal carriage of Staphylococcus aureus CC398 in two distinct cohorts in France

Background

We aimed to determine the prevalence and factors associated with nasal carriage of Staphylococcus aureus CC398 in the community and among hospitalized patients.

Methods

We conducted a prospective cohort study in a French university hospital and a cross-sectional study in the surrounding region.

Results

From June 2019 to July 2020, 591 healthy blood donors (HBDs) and 647 hospitalized patients (HPs) were included. S. aureus CC398 was more prevalent in HBDs than in HPs (7.3% [5.3-9.7] vs. 3.8% [2.4-5.5], p = 0.006). Among S. aureus nasal carriers, the prevalence of CC398 isolates was 24.6% in HBDs and 18.3% in HPs (p = 0.19). No MRSA belonged to CC398. In multivariate analysis, prior antibiotic intake in the past year (OR 3.11 [1.37-7.06]) and active smoking (OR 3.01 [1.00-9.05]) were associated with S. aureus CC398 nasal carriage in the HBD cohort. A history of neurological disease was associated with nasal carriage (OR = 5.43 [1.21-24.2]), whereas an age between 82 and 90 years (OR 0.11 [0.02-0.54]) and diabetes (OR 0.18 [0.04-0.85]) were protective factors in the HP cohort. Contact with livestock was not a risk factor in either cohort.

Conclusion

The prevalence of MSSA CC398 was higher in the community than hospitalized patients. Factors associated with nasal carriage of MSSA CC398 were primarily related to general preconditions. No environmental sources of exposure were identified.

mecC MRSA in Israel—genomic analysis, prevalence and global perspective

Background

MRSA is a major global healthcare problem. In 2011, a new mec variant designated mecC was described, presenting partial identity at the DNA level, thus undetectable by routine mecA PCR.

Objectives

Until now, no reliable information regarding mecC MRSA prevalence was available in Israel. In this study, to the best of our knowledge, we describe the first case of mecC MRSA in Israel, with focus on genomic analysis and global context.

Methods

The mecC MRSA isolate was analysed by WGS with focus on phylogeny, global contextualization, virulence and resistance genes. The strain was characterized by antibiotic susceptibility testing, spa typing and presence of mecA/C and pvl genes.

Results

An MRSA strain (SA10610), isolated from a urine sample of an 83-year old patient, was found negative for the mecA and pvl genes. The MLST and spa type were ST130 and t1736, respectively. SA10610 presented resistance to oxacillin, penicillin and cefoxitin, and susceptibility to all non-β-lactam agents tested. Phylogenetic comparison with a global dataset of 586 mecC MRSA genomes revealed substantial genomic divergence. The nearest genomic relatives were human and animal isolates from Denmark. A screen of 12 761 S. aureus isolates collected during 2011–18 in Israel indicated this is the only mecC-positive strain.

Conclusions

A high degree of genetic variability was found between the SA10610 strain and previously sequenced mecC MRSA isolated worldwide. The genomic and phylogenetic analysis suggest that mecC MRSA isolates have evolved independently rather than from a common ancestor.

Staphylococcus aureus isolates from Eurasian Beavers (Castor fiber) carry a novel phage-borne bicomponent leukocidin related to the Panton-Valentine leukocidin

Staphylococcus aureus can be a harmless coloniser, but it can also cause severe infections in humans, livestock and wildlife. Regarding the latter, only few studies have been performed and knowledge on virulence factors is insufficient. The aim of the present study was to study S. aureus isolates from deceased wild beavers (Castor fiber). Seventeen isolates from eleven beavers, found in Germany and Austria, were investigated. Antimicrobial and biocide susceptibility tests were performed. Isolates were characterised using S. aureus-specific DNA microarrays, spa typing and whole-genome sequencing. From two isolates, prophages were induced by mitomycin C and studied by transmission electron microscopy. Four isolates belonged to clonal complex (CC) 8, CC12, and CC398. Twelve isolates belonged to CC1956 and one isolate was CC49. The CC49 and CC1956 isolates carried distinct lukF/S genes related to the Panton-Valentine leukocidin (PVL) from human isolates of S. aureus. These genes were located on related, but not identical, Siphovirus prophages. The beavers, from which those isolates originated, suffered from abscesses, purulent organ lesions and necrotising pneumonia, i.e., clinical manifestations resembling symptoms of severe PVL-associated disease in humans. It might thus be assumed that the “Beaver Leukocidin (BVL, lukF/S-BV)”-positive strains are beaver-specific pathogens, and further studies on their clinical role as well as on a possible transmissibility to other species, including humans, are warranted.

Insights into the epidemiology of community-associated methicillin-resistant Staphylococcus aureus in special populations and at the community-healthcare interface

The current epidemic proportions of infections caused by Staphylococcus aureus strains and especially by methicillin-resistant S. aureus (MRSA) are one of today's many threats to global public health, particularly in underdeveloped countries where significant gaps on the subject exist. The rapid spread and diversification of pandemic clones that exhibit remarkably increasing virulence and antimicrobial resistance pose a risk to the effective prevention and treatment of a wide range of infections. Undoubtedly, the remarkable versatility involving the pathogenesis and resistance of these bacteria is perpetuated through geographic and temporal factors inherent to clonal evolution and is reflected in the dramatic epidemiological changes of MRSA which, after decades prevailing in healthcare settings, have emerged in the community. Denominated community-associated [CA]-MRSA, these strains are particularly prevalent in some population groups, facilitating the spread of successful clones that are potentially capable of triggering severe community-acquired infections. Therefore, a broad approach to local epidemiological aspects in less studied regions, but nonetheless at latent risk of endemic spread that may reach global proportions, is necessary. In Brazil, despite limited molecular epidemiology data, CA-MRSA strains predominantly characterized as SCCmec IV, often classified as CC30-ST30, CC5-ST5 and CC8-ST8, seem to be spreading across different population groups in different regions of the country. Another important fact addressed in this review is the identification of the ST398-MRSA-IV/V clone and methicillin-susceptible S. aureus (MSSA) in healthy individuals from the community. Although susceptible to methicillin, the ST398 clone is associated with severe infections in humans and animals, denominated livestock-associated MRSA. It is therefore important to encourage assertive actions by all government sectors and by society, with a reassessment of current public health measures in light of the new perspectives arising from the scientific and epidemiological data on MRSA.

Environmental Surveillance and Characterization of Antibiotic Resistant Staphylococcus aureus at Coastal Beaches and Rivers on the Island of Hawai'i

Staphylococcus aureus are human facultative pathogenic bacteria and can be found as contaminants in the environment. The aim of our study was to determine whether methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolated from coastal beach and river waters, anchialine pools, sand, and wastewater on the island of Hawaiʻi, Hawaiʻi, are a potential health risk. Samples were collected from three regions on Hawaiʻi Island from July to December 2020 during the COVID-19 pandemic and were characterized using whole-genome sequencing (WGS). From WGS data, multilocus sequence typing (MLST), SCCmec type, antimicrobial resistance genes, virulence factors, and plasmids were identified. Of the 361 samples, 98.1% were positive for Staphylococcus spp. and 7.2% were S. aureus positive (n = 26); nine MRSA and 27 MSSA strains were characterized; multiple isolates were chosen from the same sample in two sand and seven coastal beach water samples. The nine MRSA isolates were multi-drug resistant (6–9 genes) sequence type (ST) 8, clonal complex (CC) 8, SCCmec type IVa (USA300 clone), and were clonally related (0–16 SNP differences), and carried 16–19 virulence factors. The 27 MSSA isolates were grouped into eight CCs and 12 STs. Seventy-eight percent of the MSSA isolates carried 1–5 different antibiotic resistance genes and carried 5–19 virulence factors. We found S. aureus in coastal beach and river waters, anchialine pools, and sand at locations with limited human activity on the island of Hawaiʻi. This may be a public health hazard.

Emergence of Thymidine-Dependent Staphylococcus aureus Small-Colony Variants in Cystic Fibrosis Patients in Southern Brazil

We characterized Staphylococcus aureus small-colony variant (SCV) strains isolated from cystic fibrosis (CF) patients in southern Brazil. Smaller colonies of S. aureus were isolated from respiratory samples collected consecutively from 225 CF patients from July 2013 to November 2016. Two phenotypic methods—the auxotrophic classification and a modified method of antimicrobial susceptibility testing—were employed. PCR was conducted to detect the mecA, ermA, ermB, ermC, msrA, and msrB resistance genes. Furthermore, DNA sequencing was performed to determine the mutations in the thyA gene, and multilocus sequence typing was used to identify the genetic relatedness. S. aureus strains were isolated from 186 patients (82%); suggestive colonies of SCVs were obtained in 16 patients (8.6%). The clones CC1 (ST1, ST188, and ST2383), CC5 (ST5 and ST221), and ST398 were identified. Among SCVs, antimicrobial susceptibility testing showed that 77.7% of the isolates were resistant to multiple drugs, and all of them were susceptible to vancomycin. mecA (2), ermA (1), ermB (1), ermC (3), and msrB (18) were distributed among the isolates. Phenotypically thymidine-dependent isolates had different mutations in the thyA gene, and frameshift mutations were frequently observed. Of note, revertants showed nonconservative or conservative missense mutations. SCVs are rarely identified in routine laboratory tests.

IMPORTANCE Similar findings have not yet been reported in Brazil, emphasizing the importance of monitoring small-colony variants (SCVs). Altogether, our results highlight the need to improve detection methods and review antimicrobial therapy protocols in cystic fibrosis (CF) patients.

Characterization of Staphylococcus aureus ST3320 clone causing fatal respiratory infection in rabbits

<em>Staphylococcus aureus</em> is a well-known pathogen that infects humans and animals. However, information on the fatal respiratory infection in rabbits caused by<em> S. aureus</em> is still limited. In the present study, a <em>S. aureus</em> isolate designated ND01 was recovered from lung samples of rabbits that died of fatal respiratory infection, and the ND01 was characterised by intranasal infection of rabbits, multi-locus sequencing typing, screening virulence genes and testing antimicrobial susceptibility. Clinical signs of matted forepaws and pathological lesions of haemorrhagic tracheitis and necrotising haemorrhagic pneumonia were observed in the ND01 infected rabbits, which were identical to those of naturally infected ones. The sequence type of the ND01 was defined as ST3320 and the ND01 was further grouped into the clonal complex 398. Notably, the ND01 was <em>pvl-positive</em> <em>S. aureus</em> and carried the human-associated scn gene. Moreover, the ND01 was methicillin-susceptible <em>S. aureus</em> and was susceptible to 6 of 10 tested antibiotics. This study described the characteristics of the ND01 causing fatal respiratory infection in rabbits. The results are helpful to further the understanding of the pathogenicity of S. aureus ST3320 clone in rabbits. The results also highlighted that operators must be on the alert for the colonisation of <em>pvl-positive</em> <em>S. aureus</em> in rabbits and potential transmission events between rabbits and humans.

Human Infection of Methicillin-Susceptible Staphylococcus aureus CC398: A Review

Staphylococcus aureus (SA) belonging to the clonal complex 398 (CC398) took a special place within the species due to its spread throughout the world. SA CC398 is broadly separated in two subpopulations: livestock-associated methicillin-resistant SA (MRSA) and human-associated methicillin-susceptible SA (MSSA). Here, we reviewed the global epidemiology of SA CC398 in human clinical infections and focused on MSSA CC398. The last common ancestor of SA CC398 was probably a human-adapted prophage φSa3-positive MSSA CC398 strain, but the multiple transmissions between human and animal made its evolution complex. MSSA and MRSA CC398 had different geographical evolutions. Although MSSA was present in several countries all over the world, it was mainly reported in China and in France with a prevalence about 20%. MSSA CC398 was frequently implicated in severe infections such as bloodstream infections, endocarditis, and bone joint infections whereas MRSA CC398 was mainly reported in skin and soft tissue. The spread of the MSSA CC398 clone is worldwide but with a heterogeneous prevalence. The prophage φSa3 played a crucial role in the adaptation to the human niche and in the virulence of MSSA CC398. However, the biological features that allowed the recent spread of this lineage are still far from being fully understood.

Epidemiology and risk factors of Staphylococcus aureus CC398 bone and joint infections

Background

A particular ability of the Staphylococcus aureus clonal complex 398 (CC398) to cause bone and joint infections (BJI) remains questionable, since some studies have described high prevalence of MSSA CC398 in prosthetic joint infection (PJI) and diabetic foot ostemolyelitis (DFO). Here, we described the long-term epidemiology of CC398 among S. aureus isolated from BJI and identified risk factors associated with CC398.

Methods

We included all bone and joint samples with S. aureus-positive culture in our university hospital between January 2010 and December 2017. Logistic regression was used for univariate and multivariate analysis.

Results

We identified 124 CC398 isolates among the 958 BJI-associated S. aureus. The proportion of CC398 among S. aureus increased steadily from 4% in 2010 to 26% in 2017. Only 4 isolates of CC398 were resistant to methicillin. The distribution of BJI types due to CC398 and non CC398 isolates was similar. In multivariate analysis, age (p = 0.034, OR = 3.9), McCabe score (p = 0.005, OR = 5) and inoculation mechanism (p = 0.020, OR = 3.7) were associated with PJI-related CC398. The year of infection (p < 0.001, OR = 1.6), Charlson’s score (p = 0.001, OR = 1.5) and grade 4 (severe) of the International Working Group of the Diabetic Foot classification (p < 0.001, OR = 8.5) were associated with DFO-related CC398.

Conclusion

We highlighted here the emergence and spread of CC398-MSSA in BJI. Patients with comorbidities are at high risk of CC398 MSSA PJI and DFO. The spread of CC398 in the community and hospital settings remains unclear and further epidemiological studies are needed to identify the determinants of its success.

Severe Disseminated Infection with Emerging Lineage of Methicillin-Sensitive Staphylococcus aureus

We report a case of severe disseminated infection in an immunocompetent man caused by an emerging lineage of methicillin-sensitive Staphylococcus aureus clonal complex 398. Genes encoding classic virulence factors were absent. The patient made a slow recovery after multiple surgical interventions and a protracted course of intravenous flucloxacillin.

High prevalence of spa type t571 among methicillin-susceptible Staphylococcus aureus from bacteremic patients in a French University Hospital

Staphylococcus aureus bacteremia is one of the most frequent severe bacterial infections worldwide, with an associated mortality of about 20–40% in developed countries. In 2013, we noted an increase in this infection in the teaching hospital in Grenoble, France, compared to 2012. The mean incidence of S. aureus bacteremia was 0.28 per 1,000 patient-days in 2012 and 0.35 per 1,000 patient-days in 2013. This trend was confirmed in 2014 (0.35 per 1,000 patient-days). In the present work we aimed to study the population of patients presenting with S. aureus bacteremia in 2013 and to genotype the corresponding S. aureus strains in order to identify a successful and/or virulent genotype to design a specific infection control program. One hundred ninety-one S. aureus isolates (including 9 methicillin-resistant) out of 199 corresponding cases of bacteremia were characterized with the spa typing method. Among 108 spa types, t571, t002, t008 and t084 were the most prevalent. Although not widely prevalent, t571 was the most frequently identified clone (8.4% of all isolates). Spa type t571 has been described in previous studies as belonging to the clonal complex CC398, which is consistent with the recent emergence of methicillin-susceptible S. aureus CC398 reported in blood cultures in Europe.

CC398 Staphylococcus aureus subpopulations in Belgian patients

Studies based on genome-wide single nucleotide polymorphisms (SNPs) supported the existence of two subpopulations in clonal complex (CC) 398 Staphylococcus aureus: an ancestral human-adapted clade (HC) and an animal-associated clade (AC). In this study, we have investigated the occurrence of genetic markers that allow discrimination of these subpopulations among CC398 isolates collected during 2014 to 2016 from human patients in Belgium. A collection of isolates was investigated by means of spa-typing and 16S-mecA-nuc PCR. CC398 isolates were classified as belonging to the human or the animal clade by using a canonical SNPs PCR and further studied by antimicrobial susceptibility and the presence of toxins, immune evasion cluster (IEC), and resistance genes. A total of 124 (7.8%) human isolates belonged to CC398. They were grouped into HC (n = 58) or AC (n = 66). The genes erm(T), pvl, chp, and scn were predominantly found in HC-CC398, while AC-CC398 isolates carried more frequently than the mecA, erm(C), tet(K), tet(M), and tet(L) genes. Different combinations of gene profiles were observed according to the clade. CC398 isolates from Belgian patients belonged to different subpopulations including typical HC and AC-isolates. Few HC-strains with mecA and AC-isolates harboring IEC were found. CC398 isolates from Belgian patients belonged to different subpopulations including typical HC and AC-isolates, as well as new emerging subpopulations that underline the ability of this lineage to acquire resistance and virulence genes. Further research is needed to evaluate the emergence of these subpopulations in the clinical setting.

Distribution of the Most Prevalent Spa Types among Clinical Isolates of Methicillin-Resistant and -Susceptible Staphylococcus aureus around the World: A Review

Background:Staphylococcus aureus, a leading cause of community-acquired and nosocomial infections, remains a major health problem worldwide. Molecular typing methods, such as spa typing, are vital for the control and, when typing can be made more timely, prevention of S. aureus spread around healthcare settings. The current study aims to review the literature to report the most common clinical spa types around the world, which is important for epidemiological surveys and nosocomial infection control policies.

Methods: A search via PubMed, Google Scholar, Web of Science, Embase, the Cochrane library, and Scopus was conducted for original articles reporting the most prevalent spa types among S. aureus isolates. The search terms were “Staphylococcus aureus, spa typing.”

Results: The most prevalent spa types were t032, t008 and t002 in Europe; t037 and t002 in Asia; t008, t002, and t242 in America; t037, t084, and t064 in Africa; and t020 in Australia. In Europe, all the isolates related to spa type t032 were MRSA. In addition, spa type t037 in Africa and t037and t437 in Australia also consisted exclusively of MRSA isolates. Given the fact that more than 95% of the papers we studied originated in the past decade there was no option to study the dynamics of regional clone emergence.

Conclusion: This review documents the presence of the most prevalent spa types in countries, continents and worldwide and shows big local differences in clonal distribution.

The pathogenicity and host adaptation of livestock-associated MRSA CC398

The presence of methicillin-resistant Staphylococcus aureus (MRSA) CC398 in livestock and their transmission to humans followed by their introduction into hospitals led to a significant burden for the human healthcare system, especially in regions with a high density of livestock breeding. The CC398 lineage made two host changes in its evolutionary history: From humans to pigs and other livestock-associated animals and back to the human host. These adaptation processes are mirrored by changes of the equipment with virulence factors necessary for successful host change. Here, we consider these factors and their special role during human colonization and infection. Host adaptation of S. aureus CC398 is accompanied by genetic changes that are mainly driven by exchanges of mobile genetic elements. So far, it is not clear, which virulence or adhesion factors are important for S. aureus CC398 in host interaction. Among human and animal-derived MRSA CC398 virulence factors, e.g. (entero-) toxins, were rarely found. Overall, this review provides a comprehensive overview on the emerging S. aureus lineage CC398 by summarizing current knowledge from microbiological, molecular and cellular interaction studies in relation to clinical and epidemiological perspectives.

The Emergence and Spread of Multiple Livestock-Associated Clonal Complex 398 Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus Strains among Animals and Humans in the Republic of Ireland, 2010-2014

Clonal complex (CC) 398 methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) are associated with carriage and infection among animals and humans but only a single case of CC398 MRSA has been reported in the Republic of Ireland (ROI). The present study investigated the molecular epidemiology of CC398 MRSA (n = 22) and MSSA (n = 10) from animals and humans in the ROI from 2010-2014. Isolates underwent antimicrobial susceptibility testing, spa typing, DNA microarray profiling and PCR for CC398-associated resistance genes. All MRSA underwent SCCmec IV or V subtyping. Four distinct CC398-MRSA incidents were identified from (i) a man in a nursing home (spa type t011-SCCmec IVa, immune evasion complex (IEC) negative), (ii) a horse and veterinarian who had recently travelled to Belgium (t011-IVa, IEC positive), (iii) pigs (n = 9) and farm workers (n = 9) on two farms, one which had been restocked with German gilts and the other which was a finisher farm (t034-VT, IEC negative, 3/9 pigs; t011-VT, IEC negative, 6/9 pigs & 9/9 farm workers), and (iv) a child who had worked on a pig farm in the UK (t034-VT, IEC negative). Isolates also carried different combinations of multiple resistance genes including erm(A), erm(B), tet(K), tet(M) & tet(L), fexA, spc, dfrG, dfrK aacA-aphD and aadD further highlighting the presence of multiple CC398-MRSA strains. CC398 MSSA were recovered from pigs (n = 8) and humans (n = 2). CC398 MSSA transmission was identified among pigs but zoonotic transmission was not detected with animal and human isolates exhibiting clade-specific traits. This study highlights the importation and zoonotic spread of CC398 MRSA in the ROI and the spread of CC398 MSSA among pigs. Increased surveillance is warranted to prevent further CC398 MRSA importation and spread in a country that was considered CC398 MRSA free.

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.

Worldwide Epidemiology and Antibiotic Resistance of Staphylococcus aureus

Staphylococcus aureus is an important human pathogen, responsible for infections in the community and the healthcare setting. Although much of the attention is focused on the methicillin-resistant "variant" MRSA, the methicillin-susceptible counterpart (MSSA) remains a prime species in infections. The epidemiology of S. aureus, especially of MRSA, showed a rapid evolution in the last years. After representing a typical nosocomial multidrug-resistant pathogen, MRSA has recently emerged in the community and among farmed animals thanks to its ability to evolve and adapt to different settings. Global surveillance has shown that MRSA represents a problem in all continents and countries where studies have been carried out, determining an increase in mortality and the need to use last-resource expensive antibiotics. S. aureus can easily acquire resistance to antibiotics and MRSA is characteristically multidrug resistant. Resistance to vancomycin, the principal anti-MRSA antibiotic is rare, although isolates with decreased susceptibility are recovered in many areas. Resistance to the more recently introduced antibiotics, linezolid and daptomycin, has emerged; however, they remain substantially active against the large majority of MSSA and MRSA. Newer antistaphylococcal drugs have been developed, but since their clinical use has been very limited so far, little is known about the emergence of resistance. Molecular typing techniques have allowed to identify the major successful clones and lineages of MSSA and MRSA, including high-risk clones, and to trace their diffusion. In the face of a continuously evolving scenario, this review depicts the most common clones circulating in different geographical areas and in different settings at present. Since the evolution of S. aureus will continue, it is important to maintain the attention on the epidemiology of S. aureus in the future with a global view.

Prevalence and Characterization of Staphylococcus aureus in Growing Pigs in the USA

A decade of research of methicillin-resistant S. aureus (MRSA) in pigs shows that the prevalence and predominant genotypes (i.e., ST398, ST9, ST5) of MRSA vary widely geographically, yet knowledge of the epidemiology of S. aureus generally in swine remains rudimentary. To characterize S. aureus, including MRSA, in the US swine industry, we sampled 38 swine herds in 11 states in major swine producing regions. The herds sampled included pigs sourced from 9 different breeding stock companies, and the sample was likely biased towards larger herds that use regular veterinary services. Twenty nasal swabs were collected from 36 groups of growing pigs by 36 swine veterinarians, 2 more herds were sampled opportunistically, and a historically MRSA-positive herd was included as a positive control. S. aureus was detected on 37 of the 38 herds, and in 77% of pigs sampled. Other than the positive control herd, no MRSA were detected in the study sample, yielding a 95% upper confidence limit of 9.3% for MRSA herd prevalence. All but two (ST1-t127; ST2007-t8314) of 1200 isolates belonged to three MLST lineages (ST9, ST398, and ST5) that have been prominent in studies of MRSA in pigs globally. A total of 35 spa types were detected, with the most prevalent being t337 (ST9), t034 (ST398), and t002 (ST5). A purposively diverse subset of 128 isolates was uniformly negative on PCR testing for major enterotoxin genes. The findings support previous studies suggesting a relatively low herd prevalence of MRSA in the US swine industry, but confirm that methicillin susceptible variants of the most common MRSA genotypes found in swine globally are endemic in the US. The absence of enterotoxin genes suggests that the source of toxigenic S. aureus capable of causing foodborne enterotoxicosis from pork products is most likely post-harvest contamination.

Bovine Staphylococcus aureus: Subtyping, evolution, and zoonotic transfer

Staphylococcus aureus is globally one of the most important pathogens causing contagious mastitis in cattle. Previous studies using ribosomal spacer (RS)-PCR, however, demonstrated in Swiss cows that Staph. aureus isolated from bovine intramammary infections are genetically heterogeneous, with Staph. aureus genotype B (GTB) and GTC being the most prominent genotypes. Furthermore, Staph. aureus GTB was found to be contagious, whereas Staph. aureus GTC and all the remaining genotypes were involved in individual cow disease. In addition to RS-PCR, other methods for subtyping Staph. aureus are known, including spa typing and multilocus sequence typing (MLST). They are based on sequencing the spa and various housekeeping genes, respectively. The aim of the present study was to compare the 3 analytic methods using 456 strains of Staph. aureus isolated from milk of bovine intramammary infections and bulk tanks obtained from 12 European countries. Furthermore, the phylogeny of animal Staph. aureus was inferred and the zoonotic transfer of Staph. aureus between cattle and humans was studied. The analyzed strains could be grouped into 6 genotypic clusters, with CLB, CLC, and CLR being the most prominent ones. Comparing the 3 subtyping methods, RS-PCR showed the highest resolution, followed by spa typing and MLST. We found associations among the methods but in many cases they were unsatisfactory except for CLB and CLC. Cluster CLB was positive for clonal complex (CC)8 in 99% of the cases and typically positive for t2953; it is the cattle-adapted form of CC8. Cluster CLC was always positive for tbl 2645 and typically positive for CC705. For CLR and the remaining subtypes, links among the 3 methods were generally poor. Bovine Staph. aureus is highly clonal and a few clones predominate. Animal Staph. aureus always evolve from human strains, such that every human strain may be the ancestor of a novel animal-adapted strain. The zoonotic transfer of IMI- and milk-associated strains of Staph. aureus between cattle and humans seems to be very limited and different hosts are not considered as a source for mutual, spontaneous infections. Spillover events, however, may happen.

Molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization and infection isolates in a Veterans Affairs hospital

Background

Nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) is associated with increased infection risk, yet colonization and infection isolates are rarely compared within the same study. The objectives of this study were to compare colonization and infection isolates from a Veterans Administration hospital in Iowa, and to determine the prevalence of livestock-associated MRSA (LA-MRSA) colonization and infection in a state with high livestock density.

Methods

All patients with available MRSA isolates collected through routine nasal screening (73%; n = 397) and from infections (27%; n = 148) between December 2010 and August 2012 were included and tested for spa type and presence of PVL and mecA genes. Clinical isolates were tested for antibiotic resistance patterns. Paired colonization and infection isolates were compared for genetic and phenotypic congruity.

Results

The most common spa types were t002 (and other CC5-associated strains; 65%) and t008 (and other CC8-associated strains; 20%). No classic LA-MRSA spa types were identified. CC5-associated strains were less likely to be associated with infections (22%; 77/353) compared with CC8-associated strains (49%; 53/109). MRSA colonization was more common among patients with infections (71%) compared with the general screening population (7%). In most cases (82%; 28/34), paired colonization and infection isolates were genetically and phenotypically indistinguishable.

Conclusions

Our data demonstrate a direct link between antecedent nasal colonization and subsequent MRSA infection. Further, our data indicate variability in colonization and infection efficiency among MRSA genotypes, which points to the need to define the molecular determinants underlying emergence of S. aureus strains in the community and nosocomial setting.

Dissemination of Methicillin-Susceptible CC398 Staphylococcus aureus strains in a rural Greek area

A large collection of Staphylococcus aureus including a. 745 clinically significant isolates that were consecutively recovered from human infections during 2012–2013, b. 19 methicillin-susceptible (MSSA), randomly selected between 2006–2011 from our Staphylococcal Collection, c. 16 human colonizing isolates, and d. 10 strains from colonized animals was investigated for the presence and the molecular characteristics of CC398. The study was conducted in Thessaly, a rural region in Greece. The differentiation of livestock-associated clade from the human clade was based on canSNPs combined with the presence of the φ3 bacteriophage and the tetM, scn, sak, and chp genes. Among the 745 isolates, two MRSA (0.8% of total MRSA) and thirteen MSSA (2.65% of total MSSA) were found to belong to CC398, while, between MSSA of our Staphylococcal Collection, one CC398, isolated in 2010, was detected. One human individual, without prior contact with animals, was found to be colonized by a MSSA CC398. No CC398 was identified among the 10 S. aureus isolated from animals. Based on the molecular markers, the 17 CC398 strains were equally placed in the livestock-associated and in the human clades. This is the first report for the dissemination of S. aureus CC398 among humans in Greece.

Methicillin-susceptible Staphylococcus aureus CC398: first description in prosthetic joint infection and genetic background comparison with nasal carriage isolates

Few reports described infections with CC398 methicillin-susceptible Staphylococcus aureus (MSSA). We compared the genetic background of CC398 MSSA strains from nasal carriage and knee arthroplasty infection. DNA microarray analysis shows acquisition of particular adhesin, iron capture system and immune defense evasion mechanisms. These characteristics could explain pathogenesis in this type of infection.

Methicillin-susceptible Staphylococcus aureus clonal complex 398: high prevalence and geographical heterogeneity in bone and joint infection and nasal carriage

The prevalence of clonal complex (CC) 398 methicillin-susceptible Staphylococcus aureus (MSSA) was unexpectedly high among bone and joint infections (BJIs) and nasal-colonizing isolates in France, with surprising geographical heterogeneity. With none of the major, most-known staphylococcal virulence genes, MSSA CC398 BJI was associated with lower biological inflammatory syndrome and lower treatment failure rates.