Isolation and characterization of methicillin-resistant Staphylococcus aureus from swine and workers in China

Development of triplex assay for simultaneous detection of Escherichia coli, methicillin resistant and sensitive Staphylococcus aureus in raw pork samples of retail markets

Escherichia coli and Staphylococcus aureus are the most important food borne pathogen transmitting from animal meat and meat products. Therefore, it is vital to design an accurate and specific diagnostic tool for identifying those food-borne pathogens in animal meat and meat products. In the current study, E. coli, methicillin-resistant and sensitive S. aureus (MRSA and MSSA) were simultaneously detected using a developed triplex PCR-based technique. To obtain an optimal reaction parameter, the multiplex assay was optimised by changing just one parameter while holding the others constant. Specificity of the assay was assessed using several porcine bacterial template DNA. The plasmid DNA was used to test the multiplex PCR assay's sensitivity and interference in spiked pork samples. E. coli, MRSA, and MSSA each have PCR amplified products with sizes of 335, 533, and 209 bp, respectively. The assay detects a minimum microbial load of 102 CFU/μl for all the three pathogens and can identify bacterial DNA as low as 10-2 ng/µl. The assay was validated employing 210 pork samples obtained from retail meat shops and slaughter houses, with MRSA, E. coli, and MSSA with the occurrence rate of 1.9%, 42.38%, and 18.1%, respectively. The rate of mixed bacterial contamination in pork meat samples examined with the developed method was 6.19%, 1.43%, 1.90%, and 1.43% for MSSA & E. coli, MRSA & E. coli, MSSA & MRSA, and E. coli, MSSA & MRSA, respectively. The developed multiplex PCR assay is quick and efficient, and it can distinguish between different bacterial pathogens in a single reaction tube.

Genome-based surveillance reveals cross-transmission of MRSA ST59 between humans and retail livestock products in Hanzhong, China

Methicillin-resistant Staphylococcus aureus (MRSA) has been recognized in hospitals, community and livestock animals and the epidemiology of MRSA is undergoing a major evolution among humans and animals in the last decade. This study investigated the prevalence of MRSA isolates from ground pork, retail whole chicken, and patient samples in Hanzhong, China. The further characterization was performed by antimicrobial susceptibility testing and in-depth genome-based analysis to identify the resistant determinants and their phylogenetic relationship. A total of 93 MRSA isolates were recovered from patients (n = 67) and retail livestock products (n = 26) in Hanzhong, China. 83.9% (78/93) MRSA isolates showed multiple drug resistant phenotype. Three dominant livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) sequence types were identified: ST59-t437 (n = 47), ST9-t899 (n = 10) and ST398 (n = 7). There was a wide variation among sequence types in the distribution of tetracycline-resistance, scn-negative livestock markers and virulence genes. A previous major human MRSA ST59 became the predominant interspecies MRSA sequence type among humans and retail livestock products. A few LA-MRSA isolates from patients and livestock products showed close genetic similarity. The spreading of MRSA ST59 among livestock products deserving special attention and active surveillance should be enacted for the further epidemic spread of MRSA ST59 in China. Data generated from this study will contribute to formulation of new strategies for combating spread of MRSA.

Unraveling the Role of Metals and Organic Acids in Bacterial Antimicrobial Resistance in the Food Chain

Antimicrobial resistance (AMR) has a significant impact on human, animal, and environmental health, being spread in diverse settings. Antibiotic misuse and overuse in the food chain are widely recognized as primary drivers of antibiotic-resistant bacteria. However, other antimicrobials, such as metals and organic acids, commonly present in agri-food environments (e.g., in feed, biocides, or as long-term pollutants), may also contribute to this global public health problem, although this remains a debatable topic owing to limited data. This review aims to provide insights into the current role of metals (i.e., copper, arsenic, and mercury) and organic acids in the emergence and spread of AMR in the food chain. Based on a thorough literature review, this study adopts a unique integrative approach, analyzing in detail the known antimicrobial mechanisms of metals and organic acids, as well as the molecular adaptive tolerance strategies developed by diverse bacteria to overcome their action. Additionally, the interplay between the tolerance to metals or organic acids and AMR is explored, with particular focus on co-selection events. Through a comprehensive analysis, this review highlights potential silent drivers of AMR within the food chain and the need for further research at molecular and epidemiological levels across different food contexts worldwide.

Progress in the Prevalence, Classification and Drug Resistance Mechanisms of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus is a common human pathogen with a variety of virulence factors, which can cause multiple infectious diseases. In recent decades, due to the constant evolution and the abuse of antibiotics, Staphylococcus aureus was becoming more resistant, the infection rate of MRSA remained high, and clinical treatment of MRSA became more difficult. The genetic diversity of MRSA was mainly represented by the continuous emergence of epidemic strains, resulting in the constant changes of epidemic clones. Different classes of MRSA resulted in different epidemics and resistance characteristics, which could affect the clinical symptoms and treatments. MRSA had also spread from traditional hospitals to community and livestock environments, and the new clones established a relationship between animals and humans, promoting further evolution of MRSA. Since the resistance mechanism of MRSA is very complex, it is important to clarify these resistance mechanisms at the molecular level for the treatment of infectious diseases. We firstly described the diversity of SCCmec elements, and discussed the types of SCCmec, its drug resistance mechanisms and expression regulations. Then, we described how the vanA operon makes Staphylococcus aureus resistant to vancomycin and its expression regulation. Finally, a brief introduction was given to the drug resistance mechanisms of biofilms and efflux pump systems. Analyzing the resistance mechanism of MRSA can help study new anti-infective drugs and alleviate the evolution of MRSA. At the end of the review, we summarized the treatment strategies for MRSA infection, including antibiotics, anti-biofilm agents and efflux pump inhibitors. To sum up, here we reviewed the epidemic characteristics of Staphylococcus aureus, summarized its classifications, drug resistance mechanisms of MRSA (SCCmec element, vanA operon, biofilm and active efflux pump system) and novel therapy strategies, so as to provide a theoretical basis for the treatment of MRSA infection.

Comparative review of the nasal carriage and genetic characteristics of Staphylococcus aureus in healthy livestock: Insight into zoonotic and anthroponotic clones

Given the central role of livestock in understanding the genomic epidemiology of S. aureus, the present study systematically reviewed and synthesized data on the nasal S. aureus carriage, resistance patterns to critical antimicrobial agents, virulence factors and genetic lineages among healthy livestock. Bibliographical databases were searched for published studies from May 2003 to May 2022 on nasal S. aureus carriage, their phenotypic and genetic characteristics among healthy pigs (A), sheep and goats (B), cattle (C), poultry (D), camels (E) and buffaloes (F). Special focus was given to the prevalence of nasal MRSA, MRSA-CC398, MRSA-CC9, mecC-MRSA, MSSA-CC398, and resistance to linezolid (LZD^R), chloramphenicol (CLO^R) and tetracycline (TET^R) in S. aureus isolates. Of the 5492 studies identified, 146 comprised groups A(83)/B(18)/C(33)/D(4)/E(5)/F(3), and were found eligible. The overall pooled nasal prevalence of MRSA in healthy livestock was 13.8% (95% CI: 13.5-14.1) among a pooled 48,154 livestock population. Specifically, the pooled prevalence in groups A to F were: 16.0% (95% CI: 15.6-16.4), 3.7% (95% CI: 2.9-4.6), 13.6% (95% CI: 12.8-14.4), 5.8% (95% CI: 5.1-6.5), 7.1% (95% CI: 6.1-10.7), and 2.8% (95% CI: 1.5-4.8), respectively. These values varied considerably by continent. Varied pooled prevalences of CC398 lineage with respect to MRSA isolates were obtained, with the highest from pigs and cattle (>70%). Moreover, other classical animal-adapted MRSA as well as MSSA-CC398-t1928 were reported. TET^R-MSSA was lowest in cattle (18.9%) and highest in pigs (80.7%). LZD^R-S. aureus was reported in 8 studies (mediated by optrA and cfr), mainly in pigs (n = 4), while CLO^R-S. aureus was reported in 32 studies. The virulence genes luk-S/F-PV, tst, etd, sea, see were sparsely reported, and only in non-CC398-MRSA lineages. Certain S. aureus clones and critical AMR appeared to have predominance in some livestock, as in the case of pigs that are high nasal carriers of MRSA-CC398 and -CC9, and MSSA-CC398. These findings highlight the need for adequate prevention against the transmission of zoonotic S. aureus lineages to humans.

Emergence of extensive multidrug resistant Staphylococcus aureus carrying novel Sa-MRRlsa(E) in retail food

OBJECTIVES

The aim of this study was to investigate the prevalence and genetic environment of the multidrug resistance gene lsa(E) in food-related S. aureus in China.

METHODS

1463 S. aureus from retail food products in 39 Chinese cities were investigated to determined the prevalence of lsa(E). Furthermore, antimicrobial susceptibility testing, whole-genome sequencing (WGS) and complete genetic analysis were performed in lsa(E)-positive isolates.

RESULTS

As a result, thirty-five isolates (2.4%) were positive for the lsa(E) gene which had an extensive multidrug-resistance phenotype. ST9-t899 and ST1-t4792 were the common types in positive strains. The lsa(E) genes were located in two different types of novel multiresistance region (MRR_lsa(E)) on the chromosome. The Sa-MRR_lsa(E)-I were inserted into lctP gene. The Sa-MRR_lsa(E)-II were inserted into crtP gene and they were comprised of 7 ARGs interspersed with varieties of ISs, transposons and DNA invertase genes, showing is a novel arrangement harboring lsa(E). Part of transposon Tn1546 was inserted into downstream of lnu(B) in the novel Sa-MRR_lsa(E)-II. Both two types of Sa-MRR_lsa(E) could be excised from chromosome, indicating the Sa-MRR_lsa(E) may be transferable.

CONCLUSION

Our study is the first systematical investigation of lsa(E)-positive S. aureus in retail foods in China. It indicated that the origin of most food-related lsa(E)-positive S. aureus in China might be associated with livestock or poultry breeding farm and has been transmitted between animal and food. Moreover, the emergence of S. aureus carrying novel Sa-MRR_lsa(E), especially serve as a reservoir of antibiotic resistance traits, should warrants further attention.

A Survey of Chinese Pig Farms and Human Healthcare Isolates Reveals Separate Human and Animal Methicillin-Resistant Staphylococcus aureus Populations

There has been increasing concern that the overuse of antibiotics in livestock farming is contributing to the burden of antimicrobial resistance in people. Farmed animals in Europe and North America, particularly pigs, provide a reservoir for livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA ST398 lineage) found in people. This study is designed to investigate the contribution of MRSA from Chinese pig farms to human infection. A collection of 483 MRSA are isolated from 55 farms and 4 hospitals in central China, a high pig farming density area. CC9 MRSA accounts for 97.2% of all farm isolates, but is not present in hospital isolates. ST398 isolates are found on farms and hospitals, but none of them formed part of the "LA-MRSA ST398 lineage" present in Europe and North America. The hospital ST398 MRSA isolate form a clade that is clearly separate from the farm ST398 isolates. Despite the presence of high levels of MRSA found on Chinese pig farms, the authors find no evidence of them spilling over to the human population. Nevertheless, the ST398 MRSA obtained from hospitals appear to be part of a widely distributed lineage in China. The new animal-adapted ST398 lineage that has emerged in China is of concern.

The emergence and molecular study of methicillin-resistant Staphylococcus aureus ST239, ST59, ST9, and ST630 in food animals, Chongqing, China

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) in animals is an increasing concern for the agriculture and public health. A four-years (2016) successional study was conducted to investigate the antimicrobial resistant profiles and molecular characterizations of the livestock-associated MRSA (LA-MRSA) from animal farms or slaughterhouses in Chongqing, China. A total of 1667 samples were collected from 2013 to 2016 in different animal farms and hog markets. LA-MRSA were isolated and subjected to antimicrobial susceptibility testing and whole genome sequencing (WGS). S. aureus was detected at a ratio of 3.7% (n = 62), in which 18 isolates were identified as MRSA. All the S. aureus isolates were multidrug-resistant (MDR) with the resistance to at least four drugs; however, none of those isolates was resistant to linezolid, vancomycin, or nitrofurantoin. The resistance was more obvious in the pig-associated S. aureus isolates than the strains associated with chickens or cows. The majority of multilocus sequence typing (MLST) types of the MRSA isolates were ST239, subsequently ST59, ST9, and ST630. Among these isolates, 18 MRSA possessed SCCmec type Ⅲ (n = 10), Ⅳa (n = 4), Ⅻ (n = 3) and Ⅴ(n = 1). Multiple spa types were also detected in the isolates, such as 899, 437, 30, 421, 969, 37, and 4549. This study indicates that MRSA could be transferred between humans and animals, and highlights the necessity of continuous surveillance of MRSA.

Ecology and Genetic Lineages of Nasal Staphylococcus aureus and MRSA Carriage in Healthy Persons with or without Animal-Related Occupational Risks of Colonization: A Review of Global Reports

In this conceptual review, we thoroughly searched for appropriate English articles on nasal staphylococci carriage among healthy people with no reported risk of colonization (Group A), food handlers (Group B), veterinarians (Group C), and livestock farmers (Group D) published between 2000 and 2021. Random-effects analyses of proportions were performed to determine the pooled prevalence of S. aureus, MRSA, MRSA-CC398, and MSSA-CC398, as well as the prevalence of PVL-positive S. aureus from all eligible studies. A total of 166 eligible papers were evaluated for Groups A/B/C/D (n = 58/31/26/51). The pooled prevalence of S. aureus and MRSA in healthy humans of Groups A to D were 15.9, 7.8, 34.9, and 27.1%, and 0.8, 0.9, 8.6, and 13.5%, respectively. The pooled prevalence of MRSA-CC398 nasal carriage among healthy humans was as follows: Group A/B (<0.05%), Group C (1.4%), Group D (5.4%); and the following among Group D: pig farmers (8.4%) and dairy farmers (4.7%). The pooled prevalence of CC398 lineage among the MSSA and MRSA isolates from studies of the four groups were Group A (2.9 and 6.9%), B (1.5 and 0.0%), C (47.6% in MRSA), and D (11.5 and 58.8%). Moreover, MSSA-CC398 isolates of Groups A and B were mostly of spa-t571 (animal-independent clade), while those of Groups C and D were spa-t011 and t034. The MRSA-CC398 was predominately of t011 and t034 in all the groups (with few other spa-types, livestock-associated clades). The pooled prevalence of MSSA and MRSA isolates carrying the PVL encoding genes were 11.5 and 9.6% (ranges: 0.0-76.9 and 0.0-28.6%), respectively. Moreover, one PVL-positive MSSA-t011-CC398 isolate was detected in Group A. Contact with livestock and veterinary practice seems to increase the risk of carrying MRSA-CC398, but not in food handlers. Thus, this emphasizes the need for integrated molecular epidemiology of zoonotic staphylococci.

Reducing the Risk of Transmission of Critical Antimicrobial Resistance Determinants From Contaminated Pork Products to Humans in South-East Asia

Antimicrobial resistance (AMR) is a critical challenge worldwide as it impacts public health, especially via contamination in the food chain and in healthcare-associated infections. In relation to farming, the systems used, waste management on farms, and the production line process are all determinants reflecting the risk of AMR emergence and rate of contamination of foodstuffs. This review focuses on South East Asia (SEA), which contains diverse regions covering 11 countries, each having different levels of development, customs, laws, and regulations. Routinely, here as elsewhere antimicrobials are still used for three indications: therapy, prevention, and growth promotion, and these are the fundamental drivers of AMR development and persistence. The accuracy of detection of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) depends on the laboratory standards applicable in the various institutes and countries, and this affects the consistency of regional data. Enterobacteriaceae such as Escherichia coli and Klebsiella pneumoniae are the standard proxy species used for indicating AMR-associated nosocomial infections and healthcare-associated infections. Pig feces and wastewater have been suspected as one of the hotspots for spread and circulation of ARB and ARG. As part of AMR surveillance in a One Health approach, clonal typing is used to identify bacterial clonal transmission from the production process to consumers and patients - although to date there have been few published definitive studies about this in SEA. Various alternatives to antibiotics are available to reduce antibiotic use on farms. Certain of these alternatives together with improved disease prevention methods are essential tools to reduce antimicrobial usage in swine farms and to support global policy. This review highlights evidence for potential transfer of resistant bacteria from food animals to humans, and awareness and understanding of AMR through a description of the occurrence of AMR in pig farm food chains under SEA management systems. The latter includes a description of standard pig farming practices, detection of AMR and clonal analysis of bacteria, and AMR in the food chain and associated environments. Finally, the possibility of using alternatives to antibiotics and improving policies for future strategies in combating AMR in a SEA context are outlined.

Evolution and genomic insight into methicillin-resistant Staphylococcus aureus ST9 in China

OBJECTIVES

To reconstruct the evolutionary history and genomic epidemiology of Staphylococcus aureus ST9 in China.

METHODS

Using WGS analysis, we described the phylogeny of 131 S. aureus ST9 isolates collected between 2002 and 2016 from 11 provinces in China, including six clinical samples from Taiwan. We also investigated the complex structure and distribution of the lsa(E)-carrying multiresistance gene cluster, and genotyped prophages in the genomes of the ST9 isolates.

RESULTS

ST9 was subdivided into one major (n = 122) and one minor (n = 9) clade. Bayesian phylogeny predicted the divergence of ST9 isolates in pig farming in China as early as 1987, which then evolved rapidly in the following three decades. ST9 isolates shared similar multiresistance properties, which were likely acquired before the ST9 emergence in China. The accessory genome is highly conserved, and ST9 harboured similar sets of phages, but lacked certain virulence genes.

CONCLUSIONS

Host exchange and regional transmission of ST9 have occurred between pigs and humans. Pig rearing and trading might have favoured gene exchanges between ST9 isolates. Resistance genes, obtained from the environment and other isolates, were stably integrated into the chromosomal DNA. The abundance of resistance genes among ST9 is likely attributed to the extensive use of antimicrobial agents in livestock. Phages are present in the genomes of ST9 and may play a role in the rapid evolution of this ST. Although human ST9 infections are rare, ST9 isolates may constitute a potential risk to public health as a repository of antimicrobial resistance genes.

Molecular Evolution and Adaptation of Livestock-Associated Methicillin-Resistant Staphylococcus aureus (LA-MRSA) Sequence Type 9

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) sequence type 9 (ST9) has emerged and disseminated in Asia. It is associated with colonization or infection in both humans and animal hosts; however, the genetic factors underpinning its adaptation to animal and human population remain to be determined. Here, we conducted a genomic analysis of 191 ST9 S. aureus genomes collected from 12 different countries, including 174 genomes retrieved from public databases and 17 sequenced in this study. In silico spa typing, staphylococcal cassette chromosome mec (SCCmec) typing, and antimicrobial resistance and virulence gene mining were conducted, and the temporal phylogenetic signal was assessed by Bayesian inference. Our results point toward a human methicillin-susceptible S. aureus (MSSA) origin of ST9 that evolved approximately 2 centuries ago. Three major genetic events occurred during ST9 host shift from human to animals: the loss of the immune evasion cluster genes (scn, chp, and sak), which were reported to contribute to virulence in human infections, the acquisition of the SaPIbov4-like element-encoding vwb gene, which is an animal-specific virulence factor responsible for the clotting of animal plasma, and the acquisition of antibiotic resistance genes, including SCCmec, quinolone resistance-determining region (QRDR) mutations, and a multidrug resistance genetic element (MDR_ST9). Evidence of direct transmission of animal-adapted strains to human hosts also suggest that transmission could potentially reshape the resistance and virulence genetic pool in these isolates. The rapid clonal expansion of MDR ST9 strains in mainland China and Taiwan highlights the increasing need for effective surveillance of antibiotic consumption in animal husbandry to control antimicrobial resistance spread.

IMPORTANCEStaphylococcus aureus sequence type 9 (ST9) is the main LA-MRSA clone spreading in the Asian continent. It can colonize and cause mild to severe infections both in animal and humans. Previous work described its genotypic characteristics; however, the molecular history of global spread of ST9 strains remains largely unclear. We conducted a detailed analysis of genomic evolution of global ST9 strains and identified key genetic changes associated with its adaptation to specific hosts. Our results suggest that the ST9 clone originated from human-adapted strains, which lost genes related to the evasion of the immune system. The introduction of ST9 strains in animal populations was aligned with the acquisition of animal-specific virulent factors and mobile elements harboring multiple antimicrobial resistance genes, especially in isolates from mainland China and Taiwan.

Characterisation of Staphylococcus aureus isolates from bovine mastitis in Ningxia, Western China

OBJECTIVES

The aim of this study was to explore the antimicrobial resistance, virulence genes and molecular characteristics of Staphylococcus aureus from bovine mastitis cases.

METHODS

A total of 125 non-duplicate S. aureus isolates from bovine mastitis cases in Ningxia, China, were characterised by antimicrobial susceptibility and molecular testing to determine the antimicrobial resistance, virulence genes and molecular characteristics.

RESULTS

All methicillin-resistant S. aureus (MRSA) isolates were resistant to ampicillin, oxacillin, ceftiofur, erythromycin, gentamicin and clindamycin, with resistance to nine different categories of antibiotics observed amongst the MRSA isolates. Of the methicillin-susceptible S. aureus (MSSA) isolates, 62.1% were resistant to ampicillin and sulfisoxazole. Nine clonal complexes (CCs) and 16 spa types were identified by multilocus sequence typing (MLST) and spa typing. The dominant CCs were CC97 (51.2%) and CC50 (30.4%), while t224 (30.4%), t518 (20.0%) and t359 (16.8%) were the most common spa types. A relatively high proportion (27.2%) of the S. aureus isolates belonged to ST4053, a novel sequence type identified in this study. In addition, two CC30 MSSA isolates and two CC59 MRSA isolates were positive for Panton-Valentine leukocidin, while one CC239 MRSA isolate and three CC5 MSSA isolates were positive for TSST-1. All MRSA isolates carried the immune evasion cluster (IEC) genes, including scn (100%; 9/9) and sak (100%; 9/9), which were classified into type E.

CONCLUSION

Our study indicates severe antibiotic resistance and complicated molecular characterisation of S. aureus causing bovine mastitis. Additional studies should be conducted to monitor infection and transmission of S. aureus.

Genomic Insights into Methicillin-Resistant Staphylococcus aureus spa Type t899 Isolates Belonging to Different Sequence Types

This study showed the genetic diversity and population structure of S. aureus presenting the same spa type, t899, but belonging to different STs. Our findings revealed that these isolates vary deeply in their core and accessory genomes, contrary to what is regularly inferred from studies using spa typing only.

Methicillin-resistant Staphylococcus aureus (MRSA) presenting spa type t899 is commonly associated with sequence type 9 (ST9) but is also increasingly linked to ST398. This study provides genomic insight into the diversity of t899 isolates using core genome multilocus sequence typing (cgMLST), single nucleotide polymorphism (SNP)-based phylogeny, and the description of selected antimicrobial resistance and virulence markers. The SNP-based phylogenic tree showed that isolates sharing the same spa type (t899) but different STs highly diverged in their core and accessory genomes, revealing discriminant antimicrobial resistance (AMR) and virulence markers. Our results highlighted the idea that in a surveillance context where only spa typing is used, an additional multiplex PCR for the detection of the tet(M), sak, and seg genes would be valuable in helping distinguish ST9 from ST398 isolates on a routine basis.

IMPORTANCE This study showed the genetic diversity and population structure of S. aureus presenting the same spa type, t899, but belonging to different STs. Our findings revealed that these isolates vary deeply in their core and accessory genomes, contrary to what is regularly inferred from studies using spa typing only. Given that identical spa types can be associated with different STs and that spa typing only is not appropriate for S. aureus isolates that have undergone major recombination events which include the passage of the spa gene (such as in t899-positive MRSA), the combination of both MLST and spa typing methods is recommended. However, spa typing alone is still largely used in surveillance studies and basic characterization. Our data suggest that additional markers, such as tet(M), sak, and seg genes, could be implemented in an easy and inexpensive manner in order to identify S. aureus lineages with a higher accuracy.

Antimicrobial Resistance and Molecular Characterization of Methicillin-Resistant Staphylococcus aureus Isolated from Slaughtered Pigs and Pork in the Central Region of Thailand

Methicillin-resistant Staphylococcus aureus (MRSA) have been a major public health concern in humans. Among MRSA, livestock-associated (LA)-MRSA strains have always been associated with exposure to livestock or their products and have emerged in different countries globally. Although studies have identified LA-MRSA from healthy pigs and pork in Thailand, prevalence in slaughtered pigs is still unknown. In addition, there are few reports on the epidemiology and molecular characteristics of LA-MRSA in Thailand. Hence, this is the first report investigating the epidemiology and molecular characteristics of MRSA in individual slaughtered pigs and pork in Thailand. A total of 204 nasal swab and 116 retailed pork samples were collected from three slaughterhouses and four fresh markets, respectively. Individual samples were used for screening for MRSA and obtained isolates were examined for drug- resistance profiling for 12 antimicrobial agents of 10 drug classes. In addition, SCCmec typing and multi-locus sequence typing were conducted to obtain genotype profiles. MRSA were isolated from 11 and 52 nasal swab and pork samples, respectively. The prevalence was significantly higher in the pork than in the nasal swab samples (p-value < 0.05). A high prevalence of ST9-SCCmecIX and ST398-SCCmecV with high-level antimicrobial resistance from markets and slaughterhouses indicated the spreading of MRSA with these genotypes in the Thai swine processing chains and suggested the need for further investigation to determine a control.

Genotypic Characteristics and Correlation of Epidemiology of Staphylococcus aureus in Healthy Pigs, Diseased Pigs, and Environment

China is one of the largest producers of pigs and pork in the world. However, large-scale studies on pig-associated Staphylococcus aureus in relation to healthy pigs, diseased pigs and environment are scarce. The objective of the present study was to characterize and compare S. aureus isolates from healthy pigs, diseased pigs and environment through antimicrobial susceptibility testing, multiple locus sequence typing, spa typing, and antimicrobial resistance gene screening. Results showed all isolates were susceptible to linezolid and vancomycin. However, 66.7% (104/156) isolates were multidrug-resistant by displaying resistance to three or more antibiotics and high rates of resistance to penicillin, tetracycline, clindamycin, and clarithromycin were observed. Of the 20 multilocus sequence types (STs) identified among the isolates, ST9, ST188, and ST7 were most commonly isolated from healthy pigs and environment, while ST1 was most commonly isolated from diseased pigs. In total, 17 spa types were represented among the isolates, while t4792 was most commonly isolated from diseased pigs and t899, t189 were most commonly isolated from healthy pigs and environment. In conclusion, the genotypic and epidemiology characteristics observed among the isolates suggest pigs and pork could be important players in S. aureus dissemination.

Prevalence and Characterisation of Class 1 and 2 Integrons in Multi-drug Resistant Staphylococcus Aureus Isolates from Pig Farms in Chongqing, China

Introduction

Integrons are mobile DNA elements that allow for acquisition and dissemination of antibiotic-resistance genes among pig farm-derived bacteria. Limited information is available on integrons of Staphylococcus aureus from pig farms. The aim of this study was to characterise and investigate the prevalence of class 1 and 2 integrons in multi-drug resistant (MDR) S. aureus isolates from pig farms.

Material and Methods

A total of 724 swabs were collected from 12 pig farms in Chongqing, China, and examined by conventional microbial and molecular methods.

Results

In total, 68 isolates were S. aureus, 57 of which were methicillin resistant (MRSA). All 68 isolates were MDR strains and carried integrons, of which 88.2% (60/68) harboured both class 1 and 2. In addition, 85.3% (58/68) of the class 2 integron-positive isolates carried the β-lactam resistance gene (bla_TEM-1 ), and 66.7% (40/60) of the class 1 integron-positive isolates carried the aadA1c, aadA1 or dfrA1 gene for respective streptomycin and spectinomycin or trimethoprim resistance.

Conclusions

Class 1 and 2 integrons are common among the pig farm-derived S. aureus isolates. On account of their significance for public health, the prevalence of the integrons and their associated resistance genes in pig farm-derived S. aureus isolates should be paid special attention.

Multidrug-resistance in methicillin-resistant Staphylococcus aureus (MRSA) isolated from a subtropical river contaminated by nearby livestock industries

Methicillin-resistant Staphylococcus aureus (MRSA) is a major threat to public health that causes infections in hospitals, communities, and animal husbandry. Livestock-associated MRSA (LA-MRSA) is defined as MRSA possessing staphylococcal cassette chromosome mec (SCCmec) IV or V, both of which lacks the Panton-Valentine leukocidin (PVL) gene but has variable combinations of antimicrobial susceptibility. This study focused on Taiwan's subtropical river basin and the Puzih River, which converges from tributaries flowing through downtown and animal husbandry areas. MRSA was detected at a rate of 7.8% in the tributaries, which was higher than downstream (2.1%). The ratio of multidrug-resistant (MDR) MRSA (n = 30) to total MRSA isolates (n = 39) was 0.769, and most of the MDR MRSA isolates (66.7%, 20/30) exhibited resistance to chloramphenicol, ciprofloxacin, clindamycin, erythromycin, sulfamethoxazole-trimethoprim, and tetracycline. The number of MDR MRSA isolates in the tributaries was also higher than the downstream regions of the Puzih River. The majority of MRSA isolates (64.1%) observed in this study possessed SCCmec type IV without PVL, which is typical for LA-MRSA. Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) typing aided the discrimination of resistance patterns among SCCmec types. This study highlights the threat to human health posed by the waterborne transmission of MDR LA-MRSA.

Molecular epidemiology and mechanisms of antibiotic resistance in Enterococcus spp., Staphylococcus spp., and Streptococcus spp. in Africa: a systematic review from a One Health perspective

A systematic review of antibiotic-resistant Gram-positive bacteria in Africa from a One Health perspective is lacking. Here, we report result from a search for English-language articles on the resistance mechanisms and clonality of Gram-positive bacteria in Africa between 2007 and 2019 reported in PubMed, Web of Science, ScienceDirect, and African Journals OnLine; 172 studies from 22 different African countries were identified. Resistance genes, such as mecA, erm(B), erm(C), tet(M), tet(K), tet(L), vanB, vanA, vanC, and tet(O), were found to be common. Staphylococcus spp., Enterococcus spp., and Streptococcus spp. were the main species reported by the studies, with clones such as Staphylococcus aureus ST5 (n = 218 isolates), ST8 (n = 127 isolates), ST80 (n = 133 isolates), and ST88 (n = 117 isolates), and mobile genetic elements such as IS16 (n = 28 isolates), IS256 (n = 96), Tn916 (n = 107 isolates), and SCCmec (n = 4437 isolates) identified. SCCmec IV (n = 747 isolates) was predominant, followed by SCCmec III (n = 305 isolates), SCCmec II (n = 163 isolates), SCCmec V (n = 135 isolates), and SCCmec I (n = 79 isolates). Resistance to penicillin (n = 5926 isolates), tetracycline (n = 5300 isolates), erythromycin (n = 5151 isolates), rifampicin (n = 3823 isolates), gentamycin (n = 3494 isolates), sulfamethoxazole/trimethoprim (n = 3089 isolates), and ciprofloxacin (n = 2746 isolates) was common in most reports from 22 countries. Clonal dissemination of resistance across countries and between humans, animals, and the environment was observed. Resistance rates ranged from 1.4% to 100% for 15 of the studies; 10 were One Health-related studies. Strict infection control measures, antimicrobial stewardship, and periodic One Health epidemiological surveillance studies are needed to monitor and contain the threat of increasing antibiotic resistance in Africa.

The Genomic Context for the Evolution and Transmission of Community-Associated Staphylococcus aureus ST59 Through the Food Chain

Sequence type 59 (ST59) is a predominant clonal lineage of community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) in Asia. Despite its increasing clinical relevance in China, the evolution and geographic expansion of ST59 has been relatively uncared for. Previous study has shown that ST59 was the predominant clone in food-related MRSA in China. This study compared the genomes of 87 clonal complex (CC) 59 S. aureus isolates sourced from food chain and infection cases to reconstruct the molecular evolution and geographical spread of ST59. Accordingly, three major sub-clades of ST59 were identified and these did not correlate with isolation source or location. Phylogenetic analysis estimated that ST59 in mainland China diverged from a most common recent ancestor around 1974, and most of the cases of cross-country transmission occurred between 1987 and 2000. Notably, two recent events of cross-country transmission through the food chain were observed, the isolates from these events diverged within relatively short time intervals. These isolates also showed high similarity in terms of their core genome, accessory genes, and antibiotic resistance patterns. These findings provide a valuable insight into the potential route of ST59 expansion in China and indicate a need for robust food chain surveillance to prevent the spread of this pathogen.

Livestock-Associated Methicillin-Resistant Staphylococcus aureus in Patients Admitted to Kuwait Hospitals in 2016-2017

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has been reported to colonize and cause infections in animals as well as in humans. LA-MRSA isolates have only recently been identified in patients admitted to Kuwait hospitals. This study was conducted to characterize LA-MRSA isolates obtained from patients admitted to Kuwait hospitals. A total of 202 (7.1%) of 2,823 MRSA isolates obtained from clinical samples in 2016 and 2017 in 11 public Kuwait hospitals were assigned to lineages previously known to be associated with livestock. They were characterized using antibiogram, spa typing, and DNA microarray for the assignment of clonal complexes (CCs) and detection of antibiotic resistance and virulence determinants. Identification as putative LA-MRSA clones was based on the molecular definition inferred from DNA microarray. The LA-MRSA isolates consisted of CC96 (N = 31), CC97 (N = 169), and CC398 (N = 2). Isolates belonging to CC96 and CC398 were resistant to erythromycin and clindamycin mediated by erm(A) and erm(C). CC97 isolates were multiresistant to gentamicin, kanamycin, erythromycin, clindamycin, tetracycline, chloramphenicol, fusidic acid, trimethoprim, and ciprofloxacin and harbored aacA-aphD, erm(A), erm(C), msr(A), tet(K), cat, fusC, and dfrS1. In total, 35 spa types were identified among the isolates. CC398 isolates consisted of t899 and t034. Ten spa types were identified among CC96 with t11822 (N = 13) as the most prevalent. CC97 consisted of 26 spa types with most belonging to t267 (N = 73) followed by t359 (N = 39). CC398 was composed of CC398-MRSA-IV and CC398-MRSA-V (PVL+). CC96 belonged to CC96-MRSA-IV and CC96-MRSA-IV (PVL+) Central Asian caMRSA/WA MRSA-119. CC97 consisted of six strains including CC97-MRSA-V (fusC +), CC97-MRSA-IV WA MRSA-54/63, CC97-MRSA-V, CC97-MRSA-(V+fus), CC97-MRSA-(mec VI+fus), and CC97-MRSA (mecV/VT+fus+ccrAB2). Whereas CC96 and CC97 isolates were identified in 2016 and 2017, CC398 isolates were detected only in 2016. This study identified four LA-MRSA clones among MRSA isolated from patients in Kuwait hospitals in 2016-2017 with CC97-MRSA-V (fusC +) as the dominant clone. The presence of LA-MRSA with different genetic backgrounds suggests its independent acquisition from different sources.

Antibiotic Resistance Patterns of Staphylococcus aureus Isolates from Retail Foods in Mainland China: A Meta-Analysis

Foodborne Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), is increasingly threatening human health. Pooled prevalence rates of S. aureus contamination have been extensively studied in retail food products in mainland China, but data regarding antibiotic resistance rates of S. aureus remain scattered. This study was designed to collect researches published between 2007 and 2017 in mainland China and to evaluate the antibiotic resistance of S. aureus from retail foods using a meta-analytic approach. We systematically searched the China National Knowledge Infrastructure (CNKI) and Web of Science databases to identify peer-reviewed literature. A number of multilevel random-effects models were fitted to estimate mean occurrence rates of antibiotic-resistant S. aureus, and subgroup analyses were performed to compare antibiotic resistance rates of S. aureus throughout the years and among the methods to determine the antimicrobial susceptibility. Among the considered antibiotics, S. aureus showed the highest resistance rate to penicillin G (87%, 95% confidence interval [CI] 83-90%), followed by ampicillin (72%, 95% CI 62-81%) and erythromycin (41%, 95% CI 36-46%). MRSA showed the highest resistance rate to ampicillin (98%, 95% CI 89-100%), followed by oxacillin (97%, 95% CI 80-100%) and penicillin G (96%, 95% CI 89-99%). Multidrug resistance (MDR) of S. aureus was most frequently observed to three antibiotics (17%, 95% CI 12-22%), and MRSA showed the highest resistance rate to four antibiotics (24%, 95% CI 5-67%). Subgroup analyses results proved that sources of heterogeneity among studies were neither publication year nor detection method. In conclusion, the meta-analysis showed that β-lactam antibiotics resistance of S. aureus and MRSA strains isolated from retail foods remained the most serious, and MDR of S. aureus and MRSA were also observed. Therefore, it is important to monitor the antibiotic resistance of S. aureus and MRSA in food chain, and food safety measures should be taken to reduce the transmission of this bacterium from foods to human beings.

Characterization of an Oxacillin-Susceptible mecA-Positive Staphylococcus aureus Isolate from an Imported Meat Product

Methicillin-resistant Staphylococcus aureus (MRSA) isolates that carry mecA but are oxacillin susceptible (OS-MRSA; oxacillin minimum inhibitory concentration [MIC] ≤2 μg/mL) are increasingly reported worldwide in the past decade. In this study, an OS-MRSA isolate FC1102921 from an imported meat sample was characterized and the oxacillin resistance mutation frequency and mutant prevention concentration (MPC) to oxacillin was determined. Isolate FC1102921 was pvl negative and contained SCCmec V (5C2&5), the sequence type and spa type were identified as ST398-t034. The MPCs of isolate FC1102921 to oxacillin was 16 μg/mL. The resistance mutation frequency of isolate FC1102921 to oxacillin was 0.036%. The expression of mecA in isolate FC1102921 was detectable, but the mecA expression in the mutant isolate FC1102921m increased 13.8-folds. Our data indicated that S. aureus FC1102921 was not a hypermutator, and the high-resistance mutation frequency of S. aureus FC1102921 was specific to oxacillin and penicillin. SCCmec V region of isolate FC1102921 and FC1102921m was identical, functional blaI and blaR1 were identified in SCCmec region of both isolates, and no plasmid loss was identified in mutant isolate FC1102921m. To the best of our knowledge, this is the first report of the resistance mutation frequency and MPC study of an OS-MRSA ST398-t034 isolate. The high oxacillin MPC value and high oxacillin resistance mutation frequency was not related to a curable plasmid as previously reported, which further highlighted that an in-depth study should be carried out to clarify the mechanism and role of the OS-MRSA isolates in the emergence and transmission of MRSA ST398-t034.

Methicillin-resistant Staphylococcus aureus among urban rodents, house shrews, and patients in Guangzhou, Southern China

BACKGROUND

The transmission of methicillin-resistant Staphylococcus aureus (MRSA) between humans and animals has been identified in a number of countries. In this study, MRSA in urban rodents and shrews in a community was investigated. Further, comparisons of MRSA isolates from rodents, shrews, and humans were conducted to evaluate the relationships of these isolates from different origins.

RESULTS

Between 2015 and 2016, 397 oropharynx samples from 212 rodents and 185 shrews, and 8 MRSA isolates from hospital patients were collected. Twelve MRSA were isolated from the small mammals (3.0, 95%CI: 1.3-4.7%), including 11 isolates from rodents and one from a shrew. Three MRSA isolates from Rattus norvegicus were PVL-positive, and seven isolates were IEC-negative (one from Suncus murinus, five from Rattus norvegicus, and one from a patient). The spa type, MLST, and antimicrobial resistance patterns showed that the MRSA retrieved from rodents and shrews are likely related to human strains.

CONCLUSION

MRSA derived from rodent shares similar antimicrobial resistance and molecular characteristics to those from humans, suggesting that urban rodents may play as maintenance host or vectors for MRSA which is important to human health.

Genotypes, Enterotoxin Gene Profiles, and Antimicrobial Resistance of Staphylococcus aureus Associated with Foodborne Outbreaks in Hangzhou, China

Staphylococcal food poisoning is an illness caused by the consumption of food that contains sufficient amounts of one or more enterotoxins. In the present study, a total of 37 S. aureus isolates were recovered from leftover food, swabs from a kitchen environment, and patient feces associated with four foodborne outbreaks that occurred in Hangzhou, southeast China, and were characterized by multilocus sequence typing (MLST), spa typing, pulse-field gel electrophoresis (PFGE), and antimicrobial susceptibility. Classical enterotoxin and enterotoxin-like genes were profiled by PCR analysis. ST6-t304 was the most common clone (40.54%), followed by ST2315-t11687 (32.43%). Six clusters (A to F) were divided based on PFGE patterns, and Clusters A and C were the most common types, constituting 86.49% of all isolates. Moreover, sea was the most frequently identified enterotoxin gene (81.08%), followed by the combination of seg-sei-selm-seln-sleo-selu and sec-sell (each 48.65%). Five isolates also harbored the exotoxin cluster sed-selj-ser. In addition, resistance to penicillin (97.30%), erythromycin (37.85), tetracycline (32.43%), clindamycin, gentamicin, and sulfamethoxazole (each 10.81%) was observed. Our research demonstrated the link between leftover foods and patients by molecular typing and detecting the profiles of enterotoxin or enterotoxin-like genes in human and food isolates. S. aureus maintains an extensive repertoire of enterotoxins and drug resistance genes that could cause potential health threats to consumers.

Staphylococcus aureus in Animals

Staphylococcus aureus is a mammalian commensal and opportunistic pathogen that colonizes niches such as skin, nares and diverse mucosal membranes of about 20-30% of the human population. S. aureus can cause a wide spectrum of diseases in humans and both methicillin-sensitive and methicillin-resistant strains are common causes of nosocomial- and community-acquired infections. Despite the prevalence of literature characterising staphylococcal pathogenesis in humans, S. aureus is a major cause of infection and disease in a plethora of animal hosts leading to a significant impact on public health and agriculture. Infections in animals are deleterious to animal health, and animals can act as a reservoir for staphylococcal transmission to humans.Host-switching events between humans and animals and amongst animals are frequent and have been accentuated with the domestication and/or commercialisation of specific animal species. Host-switching is typically followed by subsequent adaptation through acquisition and/or loss of mobile genetic elements such as phages, pathogenicity islands and plasmids as well as further host-specific mutations allowing it to expand into new host populations.In this chapter, we will be giving an overview of S. aureus in animals, how this bacterial species was, and is, being transferred to new host species and the key elements thought to be involved in its adaptation to new ecological host niches. We will also highlight animal hosts as a reservoir for the development and transfer of antimicrobial resistance determinants.

Genomic analysis of Staphylococcus aureus along a pork production chain and in the community, Shandong Province, China

Livestock-associated meticillin-resistant Staphylococcus aureus (LA-MRSA) is an increasingly important public health concern worldwide; however, data on LA-MRSA from Asian countries is scarce. As such, a comprehensive molecular epidemiological survey of S. aureus along a pork production chain and in the community was undertaken in Shandong Province, China. spa typing and whole-genome sequencing were used to survey the occurrence and potential transmission of S. aureus in various sectors, including 899 porcine samples (snout or skin swabs, carcass swabs and pork portions), 845 human nasal samples and 239 environmental samples from commercial farms, a slaughterhouse, a pork wholesale market and the surrounding community. MRSA was detected in higher frequencies in samples from two commercial pig farms (pigs, 49%; farm workers, 64%; environmental samples, 16%) than in samples from the slaughterhouse (fatteners, 8.2%; carcasses, 1.1%; operation workers, 0%; environmental samples, 3.8%), the pork wholesale market (pork, 14%; sellers, 0%) and individuals in the community (6.8%). There were significant differences in population structures, antimicrobial susceptibility profiles, and the presence of resistance and virulence genes between human- and pig-associated isolates. The phylogenetic analysis confirmed the dissemination of LA-MRSA between various segments along the pork production chain. However, MRSA of the same sequence type was not found to be disseminated between the commercial farms and the surrounding communities. Furthermore, one MRSA ST398 was observed, and a novel CC9 variant ST3597 was detected within the chain. The high MRSA carriage rates and the emergence of a new MRSA CC9 variant identified in this study highlight the need for MRSA surveillance.

Prevalence and Characterization of Staphylococcus aureus Isolated From Pasteurized Milk in China

Staphylococcus aureus is one of the most important food-borne pathogens globally. It produces various toxins and invasive enzymes and can be found in numerous food products. Milk is an important source of staphylococcal food poisoning. After pasteurization, this microorganism or its enterotoxins might still remain in pasteurized milk. Therefore, this study was to investigate the contamination of S. aureus in 258 pasteurized milk from 39 cities of China. The prevalence and levels of S. aureus in these samples as well as antibiotic susceptibility profiles, virulence genes, biofilm formation, and biofilm related genes, spa typing and MLST were used to determine the characterization among the isolates. It was found 3.9% of samples were detected S. aureus in 8 of 39 cities in China. The contaminated level were not very excessive which showed the MPN values of the most positive samples (9/10) were less than 1 MPN/g. All pasteurized milk-related S. aureus isolates have ability to produce biofilm and harbored icaA, icaD, eno, clfA, clfB, fnbA, fnbB, fib genes, other biofilm related genes icaC were showed in 91.7% of isolates and cna gene were showed in 50%, except bap gene which were free in all isolates. The antibiotic susceptibility test showed that all isolates were resistant or intermediate-resistant to different concentrations of the antibiotics. Furthermore, 75.0% of the isolates were resistant to three or more antibiotic classes, which indicated multidrug resistance. The isolates had virulence potential, which showed 66.7% (8/12) of the isolates carried one or more virulence-associated genes. Molecular typing by MLST and spa typing enabled classification of these isolates into a total of 11 sequence types (STs) and spa types, which indicated high genetic diversity. Most of these types were related to various clinical S. aureus infections. Thus, the findings of this study reflect the potential risk of S. aureus infection in China. Our study also provides comprehensive analysis of the prevalence of S. aureus in pasteurized milk and helps ensure more accurate treatment of human infection with effective antibiotics.

MRSA in swine, farmers and abattoir workers in Southern Italy

Methicillin-resistant Staphylococcus aureus (MRSA) is an important medical issue, since it causes serious and sometimes fatal infections in humans. Intensively reared swine may serve as reservoirs for MRSA that can infect swine workers, and also consumers (via contaminated meat). In this study, MRSA strains were isolated from 55 of the 85 (64.7%) intensive pig farms surveyed, and prevalence was greater on pig fattening farms than on breeding farms. In addition, we included in the study 63 foreign pigs imported for slaughter. Overall, the prevalence of MRSA in the 418 sampled swine was 59.1%; 12 genotypes were identified among the isolates; ST398 (96.4%) was most prevalent, followed by ST97 (2%), ST9 (0.8%) and ST1 (0.8%). MRSA isolates were also detected in 26 (17.3%) of the 150 operators included in the study; the genotypes detected were ST398 (85%), ST9 (7.6%), ST5 (3.8%) and ST1 (3.8%). All the strains were pvl negative and pia positive. Both swine and human strains displayed a multi-resistance pattern, and almost all were resistant to tetracycline. The results obtained in this study confirm the high prevalence of MRSA in swine reared and slaughtered in Italy, and underline the public health risk linked to the spread of antimicrobial-resistant Staphylococcus aureus among intensively reared pigs.

Prevalence and Characterization of Food-Related Methicillin-Resistant Staphylococcus aureus (MRSA) in China

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging pathogen that is difficult to treat due to the multiresistance of the bacteria upon infection. From 2011 to 2016, 1581 S. aureus strains were isolated from 4300 samples from retail foods covering most provincial capitals in China. To determine the prevalence of food-related MRSA and its genetic background in China, antibiotic resistance, staphylococcal toxin genes, staphylococcal cassette chromosome mec (SCCmec) typing, spa-typing and MLST were carried out in this study. In total, 108 (7.4%) isolates were confirmed for MRSA by phenotyping (cefoxitin) and genotyping (mecA/mecC gene). A total of 52.8% (57/108) of the MRSA isolates belonged to clonal complex 59 (CC59) (ST59, ST338, and ST3355), which was the predominant clone in this study. These CC59 isolates carried SCCmec elements of type IV, V, or III and exhibited spa type t437, t441, t543, t163, t1785, or t3485, and half of them carried major virulence genes, such as the Panton-Valentine leucocidin (PVL) gene. The secondary clones belonged to ST9 (15.7%, 17/108) with a type of t899-SCCmec III and showed a broader range of antimicrobial resistance. The remaining MRSA isolates (31.5%, 34/108) were distributed in 12 different STs and 18 different spa types. All isolates harbored at least one of the enterotoxin genes, whereas only 4 isolates (3.70%) were positive for the toxic shock syndrome toxin tsst alleles. For antibiotic susceptibility testing, all isolates were resistant to more than three antibiotics, and 79.6% of the isolates were resistant to more than 10 antibiotics. Amoxycillin/clavulanic acid, ampicillin, cefoxitin, penicillin, ceftazidime, kanamycin, streptomycin, clindamycin, and telithromycin was the most common antibiotic resistance profile (55.6%, 60/108) in the study. In summary, the results of this study implied that the major food-related MRSA isolate in China was closer to community-associated MRSA, and some of the remaining isolates (ST9-t899-SCCmec III) were supposed to livestock-associated MRSA. In addition, most MRSA isolates showed resistance to multiple drugs and harbored staphylococcal toxin genes. Thus, the pathogenic potential of these isolates cannot be ignored. In addition, further studies are needed to elucidate the transmission routes of MRSA in relation to retail foods and to determine how to prevent the spread of MRSA.

Regional outbreak of community-associated methicillin-resistant Staphylococcus aureus ST834 in Japanese children

Background

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has recently become a challenging problem worldwide and in Japan. We experienced 10 pediatric patients infected with CA-MRSA and hospitalized from 2011 to 2014 in a tertiary care hospital in Saitama, Japan, and assessed the characteristic of the strains using a whole genome sequencing (WGS)-based approach.

Methods

CA-MRSA strains isolated from infected patients who required hospitalization for treatment were evaluated in this study. Antimicrobial susceptibility tests, molecular typing by PCR and pulse-field gel electrophoresis (PFGE) were performed to characterize MRSA strains. WGS was performed for detailed genetic analysis.

Results

A total of 582 MRSA strains (35.2%) were identified among 1625 S. aureus strains collected during the study period. Ten MRSA strains (1.7%) were defined as CA-MRSA clinically, and all were isolated from pediatric patients. All strains mainly caused purulent lymphadenitis, were susceptible to fluoroquinolone and tetracycline, exhibited sequence type (ST) 834 or its single-locus variants and contained staphylococcal cassette chromosome mec (SCCmec) type IVc. Phylogenic analysis by PFGE and WGS revealed close relatedness of all strains, with the number of single nucleotide polymorphisms ranging from 35 to 119 by WGS. Out of the ten strains, nine possessed the genomic island SaPISaitama2 containing tst, sec and sel genes. SaPISaitama2 comprises a mosaic of genomic islands SaPIm4 and SaPIm1 harbored by a hospital-associated MRSA strain Mu50.

Conclusions

This study describes a regional outbreak of ST834-related CA-MRSA in children with a unique pathogenicity island in Japan. Pediatric patient tropism of this clone could be enhanced by susceptibility to fluoroquinolones and tetracyclines, which cannot be prescribed to children.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3646-z) contains supplementary material, which is available to authorized users.

Characterization of the Multi-Drug Resistance Gene cfr in Methicillin-Resistant Staphylococcus aureus (MRSA) Strains Isolated From Animals and Humans in China

We investigated cfr-positive and -negative MRSA strains isolated from animals and humans in different geographical areas of China, from 2011 to 2016. Twenty cfr-positive strains (15.6%) were identified from 128 MRSA strains including 17 from food animals and three from humans. The resistance rates and prevalence of the tested antibiotic resistance genes (ARGs) in the cfr-positive MRSA isolates were higher than that in the cfr-negative MRSA isolates. All cfr-positive MRSA isolates were co-carrying fexA and ermC, and had significantly higher optrA incidence rate vs. the cfr-negative isolates (P < 0.05). In addition, multilocus sequence typing (MLST) assays showed that ST9 and spa-type t899 were the most prevalent ST and spa types in the study strains. However, all of the 20 cfr-positive and 10 randomly selected cfr-negative MRSA isolates were clonally unrelated as determined by pulsed-field gel electrophoresis (PFGE) analyses. Importantly, the cfr gene was successfully transferred to a recipient Staphylococcus aureus strain RN4220 from 13 of the 20 cfr-positive MRSA isolates by electroporation. Among these 13 cfr-positive MRSA isolates, two different genetic contexts surrounding cfr were determined and each was associated with one type of cfr-carrying plasmids. Of note, the predominant genetic context of cfr was found to be a Tn558 variant and locate on large plasmids (∼50 kb) co-harboring fexA in 11 of the 13 MRSA isolates. Furthermore, the cfr gene was also identified on small plasmids (∼ 7.1 kb) that co-carried ermC in two of the 13 MRSA isolates. Our results demonstrated a high occurrence of multi-drug resistance in cfr-positive MRSA isolates, and the spread of cfr might be attributed to horizontal dissemination of similar cfr-carrying transposons and plasmids.

Novel SCCmec type XII methicillin-resistant Staphylococcus aureus isolates identified from a swine production and processing chain

Methicillin-resistant Staphylococcus aureus (MRSA) has been a major public health concern. In this study, a total of 1485 samples from three swine farms, one slaughterhouse and one indoor market in Xiamen, China were collected in 2015, and the prevalence and profiles of MRSA were assessed. All the MRSA isolates were characterized by molecular typing, antibiotic susceptibility, coagulation activity, as well as PCR screening for 38 antibiotic resistance genes, two mobile genetic elements (lsa(E)-containing multiresistance gene cluster and Tn558), and 36 virulence genes. During the study, 54 of 1485 (3.6%) samples from the swine production, processing and retail chain were found positive for MRSA. A relatively rare SCCmecXII genotype was prevalent in swine farm (84.6%, 11/13) and slaughterhouse isolates (80.6%, 25/31), but absent in the market isolates (0%, 0/10). Notably, all staphylococcal cassette chromosome mec (SCCmec) type XII MRSA isolates were resistant to at least 6 classes of antibiotics, carried two mobile genetic elements (lsa(E)-containing multiresistance gene cluster and Tn558) and harbored multiple virulence genes. These multidrug resistant MRSA isolates could also coagulate both bovine and caprine plasma. Our results on the SCCmecXII MRSA isolates, particularly their profiles of related genotypes, antibiotic resistance and virulence determinants, illustrated the evolvement of livestock-associated (LA)-MRSA in the swine production environment and spread along the processing chain. The dominance of the SCCmecXII in MRSA isolates found in this study, differed from previous reports from China, indicated potential contribution associated with the production process.

Phenotypic and molecular characteristics of methicillin-resistant and methicillin-susceptible Staphylococcus aureus isolated from pigs: implication for livestock-association markers and vaccine strategies

Background

Routine non-therapeutic antimicrobial use and overcrowding in animal farming may facilitate the propagation of methicillin-resistant Staphylococcus aureus (MRSA). This study aimed to examine the carriage prevalence and phenotype–genotype characteristics of MRSA and methicillin-susceptible S. aureus isolated from pigs.

Methods

Nasal swabs were collected from 1,458 pigs in 9 pig farms and 3 slaughterhouses. All strains were tested for antimicrobial susceptibility, resistance genes, and virulence genes, and characterized by multilocus sequence typing. The correspondence analysis was conducted to explore the relationships between multiple phenotypic and molecular characteristics of S. aureus isolates.

Results

In the 1,458 pigs, the carriage prevalence was 9.5% for S. aureus, 3.3% for MRSA, and 9.3% for multidrug-resistant S. aureus. Notably, 97.1% S. aureus isolates were multidrug resistant, and the predominant resistance pattern was non-susceptible to clindamycin, tetracycline, and erythromycin. The predominant genotype was CC9 (ST9) for S. aureus and MRSA isolates. Importantly, all S. aureus isolates were negative for the scn gene and resistant to tetracycline. Notably, all 9 linezolid-resistant isolates were classified as multidrug resistance, including 1 expressing the cfr gene and 6 expressing the optrA gene. The correspondence analysis showed a significant relationship between clonal complexes and resistance pattern or virulence genes. For example, CC9 was associated with extensive drug-resistance and co-carrying chp, sak, and hlb, and CC1 was associated with multidrug resistance and co-carrying sak and hlb.

Conclusion

The significant correspondence relationship between multiple characteristics provides some implication for vaccine strategies and new ideas for monitoring new epidemiologic clones.

Prevalence, Molecular Characterization, and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus from Different Origins in Sichuan Province, China, 2007-2015

Methicillin-resistant Staphylococcus aureus (MRSA) is a major multidrug-resistant (MDR) opportunistic pathogen that is responsible for nosocomial infections worldwide. The emergence of MRSA in food-producing animals has heightened concerns regarding the presence of MRSA in foods having an animal origin. The objectives of this study were to determine the prevalence of MRSA in different sources, including retail food, food-producing animals, and food handlers in Sichuan province. During 2007-2015, S. aureus was isolated from samples having different origins. Susceptibilities of MRSA to a panel of 12 antimicrobial agents were determined according to Clinical and Laboratory Standards Institute (CSLI) procedures. Pulsed-field gel electrophoresis, spa typing, staphylococcal chromosomal cassette (SCC) mec typing, and multilocus sequence typing (MLST) were used to characterize the relationship between these isolates. A total of 756 S. aureus were isolated from 11,067 samples. Of these, 52 isolates were classified as MRSA based on the presence of mecA genes. An antimicrobial susceptibility assay indicated that CHL-CLI-ERY-FOX-OXA-PEN-TET (n = 10) and CHL-CIP-CLI-ERY-FOX-OXA-PEN-TET (n = 8) were the two predominant MDR profiles in the isolates. Using 60% genetic similarity as a cutoff, the 52 MRSA isolates were grouped into 6 clusters having 34 pulsotypes. MLST typing showed seven multilocus sequence types (STs) with ST59 and ST9 being the most common. Six SCCmec types were identified in all MRSA isolates. The MRSA isolates had relatively low prevalence in Sichuan province. Clonal expansion is not involved in the dissemination of MRSA from food origins. Considering the threat of MRSA to public health, further surveillance is required to monitor the prevalence of food-related MRSA.

Clinical and molecular features of MDR livestock-associated MRSA ST9 with staphylococcal cassette chromosome mecXII in humans

Objectives

Clonal complex (CC) 9 is a prevalent livestock-associated (LA) MRSA clone in Asia whose pathogenicity in humans remains unknown.

Methods

In 2012, we identified a patient with CC9-MRSA infection linked to livestock. After screening 3328 clinical MRSA isolates from a national database, eight isolates (0.24%) collected between 1998 and 2012 were further confirmed to be of CC9. The detailed molecular features of the nine human CC9 strains and phylogenetic relatedness to animal CC9 strains were characterized with WGS. The antibiotic susceptibilities were determined and the clinical information was abstracted from medical records.

Results

WGS grouped the CC9 strains into two clades, which were respectively associated with distinct toxome profiles, resistance gene profiles and staphylococcal cassette chromosomes (SCCmecXII for 7 isolates and SCCmecVT for 2 isolates). The SCCmecXII strains were phylogenetically related to animal CC9-MRSA strains, negative for Panton-Valentine leucocidin and 100% resistant to ciprofloxacin, erythromycin, clindamycin, gentamicin and tigecycline. Four of the seven SCCmecXII isolates were associated with invasive diseases including bacteraemia leading to death (2) and osteomyelitis (2). Two SCCmecXII isolates were from patients with exposure to pigs before development of the MRSA diseases.

Conclusions

The CC9-SCCmecXII MRSA prevailing in pigs in Asia is multidrug resistant and potentially pathogenic to humans. It is critical to continuously monitor the local epidemiology of MRSA and implement effective control measures to limit the spread of LA-MRSA between animals, to humans and in healthcare facilities.

Prevalence, resistance pattern, and molecular characterization of Staphylococcus aureus isolates from healthy animals and sick populations in Henan Province, China

Background

Staphylococcus aureus is one of the most prevalent pathogens and a causative agent of a variety of infections in humans and animals. A total of 640 samples were collected from healthy animals and patients from 2013 to 2014 in Henan Province, China, to investigate the prevalence and perform molecular characterization of S. aureus. Antimicrobial resistance and virulence genes were determined and pulsed-field gel electrophoresis (PFGE) and staphylococcal cassette chromosome mec (SCCmec) typing were performed.

Results

Overall, 22.3% (n = 143) of the samples were positive for S. aureus. The prevalence of methicillin-resistant S. aureus (MRSA) was 5.59%. Capsular polysaccharide locus type 5 (Cap5; 56.64%) was the dominant serotype. S. aureus strains showed high resistance to penicillin (96.50%), ciprofloxacin (52.45%), amikacin (67.83%), erythromycin (96.50%), lincomycin (97.20%), and tetracycline (68.53%) and 109 (76.2%) isolates harbored six or more tested resistance genes. The most predominant resistance genes were aphA (52.45%), ermC (53.15%), and tetM (52.45%). Eighty-seven (60.8%) isolates harbored six or more tested virulence genes. The most predominant enterotoxin genes were sed (20.28%), sej (20.98%), sep (14.69%), and set (37.76%). The prevalence of lukED gene was (57.34%), and a small number of isolates carried pvl (5.59%) and TSST-1 (2.80%). A total of 130 (82.52%) isolates could be typed by PFGE with SmaI digestion. PFGE demonstrated that 45 different patterns (P) that were grouped into 17 pulsotypes and 28 separate pulsotypes using a 90% cut-off value. A total of 118 (82.52%) isolates were successfully typed by spa, and 26 spa types were identified, t15075 (14.00%) and t189 (12.59%) were the most common types. SCCmec types were detected from eight MRSA isolates, with the most prevalent type being SCCmec IVa. MRSA-SCCmec Iva-t437 was observed in human isolates.

Conclusion

This study revealed a high prevalence of S. aureus in healthy animals and patients from Henan Province, China. Resistant S. aureus exhibited varying degrees of multidrug resistance. The presence of antibiotic resistance and virulence genes may facilitate the spread of S. aureus strains and pose a potential threat to public health, highlighting the need for vigilant monitoring of these isolates at the human–animal interface.

Electronic supplementary material

The online version of this article (10.1186/s13099-018-0254-9) contains supplementary material, which is available to authorized users.

Geographic distribution of livestock-associated Staphylococcus aureus in the United States

Sampling for livestock-associated Staphylococcus aureus (LA-SA) in the United States is haphazard. The diversity of LA-S. aureus in the U.S. appears to be greater than in other countries. We review the epidemiology of LA-S. aureus in U.S. pigs, occupationally-exposed individuals, and environmental samples to assess the diversity and abundance of U.S. LA-S. aureus.

Occurrence of Staphylococcus aureus in swine and swine workplace environments on industrial and antibiotic-free hog operations in North Carolina, USA: A One Health pilot study

Occupational exposure to swine has been associated with increased Staphylococcus aureus carriage, including antimicrobial-resistant strains, and increased risk of infections. To characterize animal and environmental routes of worker exposure, we optimized methods to identify S. aureus on operations that raise swine in confinement with antibiotics (industrial hog operation: IHO) versus on pasture without antibiotics (antibiotic-free hog operation: AFHO). We associated findings from tested swine and environmental samples with those from personal inhalable air samplers on worker surrogates at one IHO and three AFHOs in North Carolina using a new One Health approach. We determined swine S. aureus carriage status by collecting swab samples from multiple anatomical sites, and we determined environmental positivity for airborne bioaerosols with inhalable and impinger samplers and a single-stage impactor (ambient air) cross-sectionally. All samples were analyzed for S. aureus, and isolates were tested for antimicrobial susceptibility, absence of scn (livestock marker), and spa type. Seventeen of twenty (85%) swine sampled at the one IHO carried S. aureus at >1 anatomical sites compared to none of 30 (0%) swine sampled at the three AFHOs. All S. aureus isolates recovered from IHO swine and air samples were scn negative and spa type t337; almost all isolates (62/63) were multidrug resistant. S. aureus was recovered from eight of 14 (67%) ambient air and two (100%) worker surrogate personal air samples at the one IHO, whereas no S. aureus isolates were recovered from 19 ambient and six personal air samples at the three AFHOs. Personal worker surrogate inhalable sample findings were consistent with both swine and ambient air data, indicating the potential for workplace exposure. IHO swine and the one IHO environment could be a source of potential pathogen exposure to workers, as supported by the detection of multidrug-resistant S. aureus (MDRSA) with livestock-associated spa type t337 among swine, worker surrogate personal air samplers and environmental air samples at the one IHO but none of the three AFHOs sampled in this study. Concurrent sampling of swine, personal swine worker surrogate air, and ambient airborne dust demonstrated that IHO workers may be exposed through both direct (animal contact) and indirect (airborne) routes of transmission. Investigation of the effectiveness of contact and respiratory protections is warranted to prevent IHO worker exposure to multidrug-resistant livestock-associated S. aureus and other pathogens.

Variability of SCCmec elements in livestock-associated CC398 MRSA

The most common livestock-associated lineage of methicillin-resistant Staphylococcus aureus (MRSA) in Western Europe is currently clonal complex (CC) 398. CC398-MRSA spread extensively across livestock populations in several Western European countries, and livestock-derived CC398-MRSA strains can also be detected in humans. Based on their SCCmec elements, different CC398 strains can be distinguished. SCCmec elements of 100 veterinary and human CC398-MRSA isolates from Germany and Austria were examined using DNA microarray-based assays. In addition, 589 published SCC and/or genome sequences of CC398-MRSA (including both, fully finished and partially assembled sequences) were analysed by mapping them to the probe sequences of the microarrays. Several isolates and sequences showed an insertion of a large fragment of CC9 genomic DNA into the CC398 chromosome. Fifteen subtypes of SCCmec elements were detected among the 100 CC398 isolates and 41 subtypes could be discerned among the published CC398 sequences. Eleven of these were also experimentally detected within our strain collection, while four subtypes identified in the isolates where not found among the sequences. A high prevalence of heavy metal resistance genes, especially of czrC, was observed among CC398-MRSA. A possible co-selection of resistances to antibiotics and zinc/copper supplements in animal feed as well as a spill-over of SCCmec elements that have evolved in CC398-MRSA to other, possibly more virulent and/or medically relevant S. aureus lineages might pose public health problems in future.

Characterization of Staphylococcus aureus Isolated from Food Products in Western Algeria

The current study aimed to characterize Staphylococcus aureus isolates from foodstuffs collected from western Algeria. A total of 153 S. aureus isolates from various raw and processed foods were obtained and identified using matrix-assisted laser desorption and ionization time-of-flight mass spectrometry. Isolates were characterized by antimicrobial susceptibility testing and toxin gene detection. Methicillin-resistant Staphylococcus aureus (MRSA) isolates were identified by detection of the mecA gene and characterized by staphylococcal cassette chromosome mec (SCCmec) typing. We found that 30.9% (153/495) of food samples were contaminated with S. aureus. Thirty-three (21.5%) S. aureus isolates were identified as MRSA, and 16.9% (26/153) carried the mecA gene. Three SCCmec types were identified of which type IV was the most common (69.2%) followed by type V (15.3%) and type II (7.6%). Two MRSA isolates were not typable with SCCmec typing. None of the examined isolates harbored mecC. Furthermore, 14.3% (22/153) of the isolates were toxigenic S. aureus. The cytotoxin gene pvl was detected in 11.1% of the S. aureus isolates. This gene was more commonly detected (76.4%) in MRSA isolates than in methicillin-suceptible Staphylococcus aureus (MSSA) isolates. The tsst-1 gene coding for toxic shock syndrome toxin was isolated rarely (3.2%) and only in MSSA isolates. According to disk diffusion test results, 70 isolates were resistant to only one antimicrobial drug, and 51 (33.3%) isolates were multidrug resistant. Other 32 isolates were susceptible to all antibiotics. Our study highlights, for the first time, a high prevalence of multidrug-resistant S. aureus isolates carrying pvl or tsst-1 found in food products in Algeria. The risk of MRSA transmission through the food chain cannot be disregarded, particularly in uncooked foods.

Multilocus Sequence Typing and Virulence-Associated Gene Profile Analysis of Staphylococcus aureus Isolates From Retail Ready-to-Eat Food in China

The aim of this study was to characterize the subtypes and virulence profiles of 69 Staphylococcus aureus isolates obtained from retail ready-to-eat food in China. The isolates were analyzed using multilocus sequence typing (MLST) and polymerase chain reaction (PCR) analysis of important virulence factor genes, including the staphylococcal enterotoxin (SE) genes (sea, seb, sec, sed, see, seg, seh, sei, sej), the exfoliative toxin genes (eta and etb), the toxic shock syndrome toxin-1 gene (tst), and the Panton-Valentine leucocidin-encoding gene (pvl). The isolates encompassed 26 different sequence types (STs), including four new STs (ST3482, ST3484, ST3485, ST3504), clustered in three clonal complexes and 17 singletons. The most prevalent STs were ST1, ST6, and ST15, constituting 34.8% of all isolates. Most STs (15/26, 57.7%) detected have previously been associated with human infections. All 13 toxin genes examined were detected in the S. aureus isolates, with 84.1% of isolates containing toxin genes. The three most prevalent toxin genes were seb (36.2%), sea (33.3%), and seg (33.3%). The classical SE genes (sea–see), which contribute significantly to staphylococcal food poisoning (SFP), were detected in 72.5% of the S. aureus isolates. In addition, pvl, eta, etb, and tst were found in 11.6, 10.1, 10.1, and 7.2% of the S. aureus isolates, respectively. Strains ST6 carrying sea and ST1 harboring sec-seh enterotoxin profile, which are the two most common clones associated with SFP, were also frequently detected in the food samples in this study. This study indicates that these S. aureus isolates present in Chinese ready-to-eat food represents a potential public health risk. These data are valuable for epidemiological studies, risk management, and public health strategies.

Breast Milk Is a Potential Reservoir for Livestock-Associated Staphylococcus aureus and Community-Associated Staphylococcus aureus in Shanghai, China

Breast milk is the first choice in feeding newborn infants and provides multiple benefits for their growth and development. Staphylococcus aureus usually exists in breast milk and is considered one of the most important causative infective agents. To be effective in preventing and controlling S. aureus infections among infants, the aim of this study was to determine the occurrence and molecular characteristics of S. aureus isolated from 1102 samples of breast milk between 2015 and 2016 in Shanghai, China. Out of 71 S. aureus strains isolated, 15 (21.1%, 15/71) were MRSA and all the strains were characterized by spa typing, Multi-Locus Sequence Typing, SCCmec typing, antibiotic resistance testing and virulence-associated genes. A total of 18 distinct sequence types (STs) and 36 spa types were identified within the 71 isolates, among which the most frequently represented was ST398 (19.7%, 14/71), followed by ST7 (18.3%, 13/71), ST59 (16.9%, 12/71). The three predominant STs accounted for more than one half of all S. aureus isolates. The most prevalent spa types were t091 (12.7%, 9/71), followed by t571 (8.5%, 6/71), t189 (7.0%, 5/71), t034 (5.6%, 4/71), t437 (5.6%, 4/71), and t701 (4.2%, 3/71). All MRSA isolates belonged to SCCmec IV and V, accounting for 66.7 and 33.3% respectively. Notably, 23 (32.4%) S. aureus strains were multidrug resistance (MDR), including 4 (5.6%) MRSA and 19 (26.8%) MSSA strains, and MDR isolates were mostly resistant to penicillin, erythromycin and clindamycin. All isolates exhibited simultaneous carriage of at least 5 of 33 possible virulence genes and the most prevalent genes detected were icaA (100%), clfA (100%), hla (100%), sdrC (94.4%), hlg2 (88.7%), lukE (57.8%). 39 (54.9%, 39/71) isolates, including 9 (12.7%) of MRSA isolates, harbored ≥10 tested virulence genes evaluated in this study. The pvl gene was detected in 8 strains, which represented 5 different STs, with ST59 being the most one. Overall, our findings showed that S. aureus strains isolated from breast milk were mainly MSSA (78.9%, 56/71) and exhibited high genetic diversity in Shanghai area of China. Breast milk was a reservoir for LA-SA (ST398) and CA-SA (ST59), which was likely a vehicle for transmission of multidrug-resistant S. aureus and MRSA lineages. This is a potential public health risk and highlights the need for good hygiene practices to reduce the risk of infant infections.

Enterotoxigenicity and Antimicrobial Resistance of Staphylococcus aureus Isolated from Retail Food in China

Staphylococcus aureus is one of the most common causes of zoonotic agent in the world, which are attributable to the contamination of food with enterotoxins. In this study, a total of 1,150 S. aureus isolates were cultured from 27,000 retail foods items from 203 cities of 24 provinces in China in 2015 and were test for antimicrobial susceptibility. Additionally, the role of the genes responsible for the staphylococcal enterotoxins (SEA to SEE), methicillin resistance (mecA) and the toxigenic capabilities were also assessed. The results showed that 4.3% retail foods were contaminated with S. aureus, and 7.9% retail foods isolates were mecA positive. Some 97.6% of S. aureus isolates were resistant to at least one antimicrobial compound, and 57.5% of these were multi drug resistant (MDR). Resistance to penicillin (83.7%, 963/1,150), was common, followed by linezolid (67.7%, 778/1,150) and erythromycin (52.1%, 599/1,150). The isolates cultured from raw meats showed high levels of resistant to tetracycline (42.8%), ciprofloxacin (17.4%), and chloramphenicol (12.0%) and expressed a MDR phenotype (62.4%). A total of 29.7% S. aureus isolates harbored the classical SEs genes (sea, seb, sec, and sed). The sea and seb genes were the most frequent SEs genes detected. Of note, 22% of the SEs genes positive S. aureus harbored two or three SEs genes, and 16 isolates were confirmed with the capacity to simultaneously produce two or three enterotoxin types. Moreover, nearly 50% of the MRSA isolates were positive for at least one SE gene in this study. Therefore, it is important to monitor the antimicrobial susceptibility and enterotoxigenicity of MDR S. aureus and MRSA in the food chain and to use these data to develop food safety measures, designed to reduce the contamination and transmission of this bacterium.

MRSA in Pig Population

Methicillin resistant Staphylococcus aureus (MRSA) is widespread worldwide in different types of animal species and as a zoonosis takes a great risk for human health not only as a food toxicoinfection, but also as a highly resistant pathogen causing serious soft tissue infectious, septicaemia and even death. One of the most affected food-producing animal species is swine in the production of which new antibiotics in big amounts are used more and more continuously, increasing antimicrobial resistance. In this study several commercial pig farms and pigs with different age groups as well as farm workers and samples from environment were examined with the purpose of detecting MRSA prevalence and evaluating antimicrobial resistance. A total of 85 isolated MRSA strains were characterised by conventional microbial and molecular methods. MRSA was found in all farms. MRSA prevalence in different pig age groups and farms varied from none to 79.2% reaching higher values among 3-3.5 (26.6%) and 4-4.5 (31.9%) old pigs. The 98.7% of 74 further investigated MRSA isolates were resistant to penicillin, 94.9% to tetracycline, 45.6% to cephalexin and 10 different spa types were found among which spa type t011 was the most widespread. To the best of our knowledge, this is the first time MRSA was researched in sow milk and the first description of the presence of MRSA in several age groups of pigs in Latvia.

Presence of Methicillin-resistant Staphylococcus Aureus in Slaughterhouse Environment, Pigs, Carcasses, and Workers

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) is a highly resistant and difficult to cure zoonotic microorganism, which makes up a large part of food toxic infections and has shown high prevalence among pig population all over the world. The aim of the study was to establish the occurrence of MRSA in slaughterhouses, evaluate its antimicrobial resistance, and verify whether there are any differences or similarities with reference to other European countries.

Material and Methods

A total of 100 pigs, 105 carcasses, 19 workers, and 24 samples from the environment of several slaughterhouses were examined by conventional microbial and molecular methods.

Results

In total, 78 MRSA isolates were found. MRSA prevalence in slaughtered pigs varied from 8.0% to 88.6% depending on the slaughterhouse, reaching higher prevalence in slaughterhouses with higher slaughter capacity. In total, 21.1% of all workers were carriers of MRSA and 6.7% of carcasses were contaminated with MRSA. The 98.2% of MRSA isolates were resistant to penicillin, 89.1% to tetracycline, 60.1% to erythromycin, 65.5% to gentamycin, and 15 different spa types were found, among which spa type t01333 was most widespread.

Conclusion

The study indicated that MRSA prevalence and spa types differed according to slaughterhouse slaughter capacity and good hygiene practices. Quite high MRSA occurrence among slaughterhouse workers is one of the main factors which increase pork contamination risk.