Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in bulk tank milk, livestock and dairy-farm personnel in north-central and north-eastern Greece: Prevalence, characterization and genetic relatedness

Microbiological and Molecular Investigation of Antimicrobial Resistance in Staphylococcus aureus Isolates from Western Romanian Dairy Farms: An Epidemiological Approach

Antimicrobial therapy is the most frequently used medical intervention for bovine mastitis in the dairy industry. This study aims to monitor the extent of the antimicrobial resistance (AMR) problem in Staphylococcus aureus in the dairy industry in Western Romania. Twenty farms were selected by random sampling in a transverse epidemiological study conducted across four counties in Western Romania and divided into livestock units. This study assessed the association between the resistance genes to phenotypic expression of resistance and susceptibility. Isolates of S. aureus were identified and q-PCR reactions were used to detect antibiotic resistance genes. One hundred and fifty bovine and 20 human samples were positive for S. aureus. Twenty five percent of bovine isolates (30/120) and none(0/30) of the human isolates were methicillin-resistant S. aureus (MRSA). All isolates were susceptible to fosfomycin, ciprofloxacin, netilmicin, and resistant to ampicillin and penicillin. S. aureus isolates regarded as phenotypically resistant (R) were influenced by the origin of the samples (human versus bovine, χ2 = 36.510, p = 0.013), whether they were methicillin-resistant S. aureus (χ2 = 108.891, p < 0.000), the county (χ2 = 103.282, p < 0.000) and farm of isolation (χ2 = 740.841, p < 0.000), but not by the size of the farm (χ2 = 65.036, p = 0.306). The multiple antibiotic resistance index was calculated for each sample as the number regarded as phenotypically resistant (R)/total antibiotics tested (MARI = 0.590 ± 0.023) was significantly higher (p < 0.000) inmethicillin-resistant S. aureus (0.898 ± 0.019) than non-methicillin-resistant S. aureus (0.524 ± 0.024) isolates. For the antibiotics tested, the total penetrance (P%) of the resistance genes was 59%, 83% for blaZ, 56% for cfr, 50% for erm(B), 53% for erm(C), 57% for mecA and 32% for tet(K). Penetrance can be used as a parameter for guidance towards a more accurate targeting of chemotherapy. P% in S. aureus was strongly positively correlated with the multiple antibiotic resistance index (r = +0.878, p < 0.000) with the potential to use the same limit value as an antibiotic management decision criterion. Considering cow mastitis, the penetrance value combined with the multiple antibiotic resistance index suggests that penetrance could serve as a useful parameter for more precise targeting of chemotherapy for S. aureus.

Rapid detection of major enterotoxin genes and antibiotic resistance of Staphylococcus aureus isolated from raw milk in the Yazd province, Iran

INTRODUCTION

Raw milk is a nutrient-rich food, but it may harbour harmful bacteria, such as enterotoxigenic Staphylococcus aureus (S. aureus), which can cause staphylococcal food poisoning. Antibiotic resistance of S. aureus in raw milk can increase the risk of such infections, particularly among susceptible individuals.

OBJECTIVE

This study aimed to investigate the prevalence of enterotoxin genes a, d, g, i and j and the antibiotic resistance of S. aureus isolated from raw milk samples.

METHODS

During a 6-month sampling period, 60 raw milk specimens were obtained from diverse locations in Yazd province, Iran. Antibiogram profiling was conducted via the disc diffusion method. In addition, staphylococcal enterotoxin (SE) genes a, d, g, i, and j were detected through real-time PCR analysis.

RESULTS

Bacteriological assays confirmed the presence of S. aureus in 11 samples (18.3%). All isolates demonstrated 100% resistance to penicillin G but exhibited sensitivity to vancomycin, while resistance to other antibiotics ranged from 36.4% to 45.5%. The prevalence of enterotoxin genes in these strains showed variable distribution, with sea being the predominant SE (45.5%), followed by sed (36.4%), seg (18.2), sej and sei (9.1% each).

CONCLUSIONS

This study discovered the presence of multiple enterotoxins in S. aureus strains obtained from raw milk samples. These strains also demonstrated resistance to a variety of antibiotics. Since enterotoxigenic S. aureus is known to cause human food poisoning, monitoring food hygiene practices, especially during raw milk production, is critical.

Emerging Approaches for Mitigating Biofilm-Formation-Associated Infections in Farm, Wild, and Companion Animals

The importance of addressing the problem of biofilms in farm, wild, and companion animals lies in their pervasive impact on animal health and welfare. Biofilms, as resilient communities of microorganisms, pose a persistent challenge in causing infections and complicating treatment strategies. Recognizing and understanding the importance of mitigating biofilm formation is critical to ensuring the welfare of animals in a variety of settings, from farms to the wild and companion animals. Effectively addressing this issue not only improves the overall health of individual animals, but also contributes to the broader goals of sustainable agriculture, wildlife conservation, and responsible pet ownership. This review examines the current understanding of biofilm formation in animal diseases and elucidates the complex processes involved. Recognizing the limitations of traditional antibiotic treatments, mechanisms of resistance associated with biofilms are explored. The focus is on alternative therapeutic strategies to control biofilm, with illuminating case studies providing valuable context and practical insights. In conclusion, the review highlights the importance of exploring emerging approaches to mitigate biofilm formation in animals. It consolidates existing knowledge, highlights gaps in understanding, and encourages further research to address this critical facet of animal health. The comprehensive perspective provided by this review serves as a foundation for future investigations and interventions to improve the management of biofilm-associated infections in diverse animal populations.

Antimicrobial use and resistance in food animal production: food safety and associated concerns in Sub-Saharan Africa

The use of antimicrobials in food animal (FA) production is a common practice all over the world, with even greater usage and dependence in the developing world, including Sub-Saharan Africa (SSA). However, this practice which serves obvious economic benefits to producers has raised public health concerns over the last decades, thus driving the selection and dissemination of antimicrobial resistance and adversely impacting food safety and environmental health. This review presents the current and comprehensive antimicrobial usage practices in food animal production across SSA. We further highlighted the overall regional drivers as well as the public health, environmental, and economic impact of antimicrobial use in the production of food animals. Antimicrobial use is likely to increase with even exacerbated outcomes unless cost-effective, safe, and sustainable alternatives to antibiotics, especially probiotics, prebiotics, bacteriocins, antimicrobial peptides, bacteriophages, vaccines, etc. are urgently advocated for and used in food animal production in SSA. These, in addition to the implementation of strong legislation on antimicrobial use, and improved hygiene will help mitigate the public health concerns associated with antimicrobial use in food animals and improve the well-being and safety of food animals and their products.

Molecular Surveillance of MRSA in Raw Milk Provides Insight into MRSA Cross Species Evolution

Methicillin-resistant Staphylococcus aureus (MRSA) in foods has been associated with severe infections in humans and animals worldwide. In the present study, the molecular characteristics of livestock-associated MRSA (LA-MRSA) and human-associated MRSA (hMRSA) isolates obtained in China, as well as MRSA isolates obtained from raw milk in 2018, were investigated. In total, 343 (20.38%; 343/1,683) S. aureus isolates were obtained from 1,683 raw milk samples from 100 dairy farms in 11 provinces across China. Among these, 49 (2.91%; 49/1,683) were mecA-positive MRSA. All LA-MRSA isolates were resistant to penicillin and highly resistant to erythromycin, sulfisoxazole, and clindamycin. Bioinformatic analysis the 49 genomes of LA-MRSA and 71 previously published hMRSA genomes isolated from Chinese individuals in 2018 indicated that blaZ, erm, ant(6)-Ia, aph(3')-III, tet(K), cat, and aph(2″)-Ia were more prevalent in MRSA from raw milk (P < 0.05) compared to hMRSA. Additionally, hMRSA isolates were more significantly associated with ST5 (P < 0.01) compared to LA-MRSA; in contrast, ST338 was more prevalent among LA-MRSA isolates (P < 0.01). Likewise, the SCCmec type II was only detected in hMRSA isolates, whereas SCCmec type V and IV were more prevalent among LA-MRSA (P < 0.01). Furthermore, core-genome phylogenetic analysis showed the endemic characteristics of LA-MRSA in local provinces, as well as the close evolutionary relationships between MRSA from cattle and humans. Finally, homology analysis of mecA and blaZ genetic contexts revealed a high possibility of horizontal transmission of MRSA resistance genes among raw milk-associated and hMRSA strains, which increases the risk for public health. IMPORTANCE Methicillin-resistant Staphylococcus aureus (MRSA) is considered a public health concern as it is resistant to multiple antibiotics, thus being in zoonotic transmission of antibiotic resistance genes. MRSA causes serious public health issues and leads to hard-to-treat infections in humans and animals; therefore, it was meaningful to determine the prevalence of MRSA in raw milk samples and investigate phenotype and genotype of antimicrobial resistance and molecular characteristics in livestock-associated MRSA (LA-MRSA) and human-associated MRSA (hMRSA) in China, which could provide a theoretical basis for preventing and controlling the spread of MRSA between livestock and humans.

Pulsed-Field Gel Electrophoresis Analysis of Bovine Associated Staphylococcus aureus: A Review

For decades now, DNA fingerprinting by means of pulsed-field gel electrophoresis (PFGE) continues to be the most widely used to separate large DNA molecules and distinguish between different strains in alternating pulses. This is done by isolating intact chromosomal DNA and using restriction enzymes with specific restriction sites to generate less than 30 restriction fragments from 50 Kb to 10 Mbp. These results make clone-specific band profiles easy to compare. Specialized equipment is required for the optimization of DNA separation and resolution, among which a contour-clamped homogeneous electric field (CHEF) apparatus is the most commonly used. As a result, the PFGE analysis of a bacterial genome provides useful information in terms of epidemiological investigations of different bacterial pathogens. For Staphylococcus aureus subtyping, despite its limitations and the emergence of alternative methods, PFGE analysis has proven to be an adequate choice and the gold standard for determining genetic relatedness, especially in outbreak detection and short-term surveillance in the veterinary field.

Evolution and implementation of One Health to control the dissemination of antibiotic-resistant bacteria and resistance genes: A review

Antibiotic resistance is a serious threat to humanity and its environment. Aberrant usage of antibiotics in the human, animal, and environmental sectors, as well as the dissemination of resistant bacteria and resistance genes among these sectors and globally, are all contributing factors. In humans, antibiotics are generally used to treat infections and prevent illnesses. Antibiotic usage in food-producing animals has lately emerged as a major public health concern. These medicines are currently being utilized to prevent and treat infectious diseases and also for its growth-promoting qualities. These methods have resulted in the induction and spread of antibiotic resistant infections from animals to humans. Antibiotics can be introduced into the environment from a variety of sources, including human wastes, veterinary wastes, and livestock husbandry waste. The soil has been recognized as a reservoir of ABR genes, not only because of the presence of a wide and varied range of bacteria capable of producing natural antibiotics but also for the usage of natural manure on crop fields, which may contain ABR genes or antibiotics. Fears about the human health hazards of ABR related to environmental antibiotic residues include the possible threat of modifying the human microbiota and promoting the rise and selection of resistant bacteria, and the possible danger of generating a selection pressure on the environmental microflora resulting in environmental antibiotic resistance. Because of the connectivity of these sectors, antibiotic use, antibiotic residue persistence, and the existence of antibiotic-resistant bacteria in human-animal-environment habitats are all linked to the One Health triangle. The pillars of support including rigorous ABR surveillance among different sectors individually and in combination, and at national and international level, overcoming laboratory resource challenges, and core plan and action execution should be strictly implemented to combat and contain ABR under one health approach. Implementing One Health could help to avoid the emergence and dissemination of antibiotic resistance while also promoting a healthier One World. This review aims to emphasize antibiotic resistance and its regulatory approaches from the perspective of One Health by highlighting the interconnectedness and multi-sectoral nature of the human, animal, and environmental health or ill-health facets.

Staphylococcus aureus and MRSA in Livestock: Antimicrobial Resistance and Genetic Lineages

Animal production is associated with the frequent use of antimicrobial agents for growth promotion and for the prevention, treatment, and control of animal diseases, thus maintaining animal health and productivity. Staphylococcus aureus, in particular methicillin-resistant S. aureus (MRSA), can cause a variety of infections from superficial skin and soft tissue infections to life-threatening septicaemia. S. aureus represents a serious public health problem in hospital and community settings, as well as an economic and animal welfare problem. Livestock-associated MRSA (LA-MRSA) was first described associated with the sequence (ST) 398 that was grouped within the clonal complex (CC) 398. Initially, LA-MRSA strains were restricted to CC398, but over the years it has become clear that its diversity is much greater and that it is constantly changing, a trend increasingly associated with multidrug resistance. Therefore, in this review, we aimed to describe the main clonal lineages associated with different production animals, such as swine, cattle, rabbits, and poultry, as well as verify the multidrug resistance associated with each animal species and clonal lineage. Overall, S. aureus ST398 still remains the most common clone among livestock and was reported in rabbits, goats, cattle, pigs, and birds, often together with spa-type t011. Nevertheless, a wide diversity of clonal lineages was reported worldwide in livestock.

Prevalence of methicillin-resistant Staphylococcus aureus in dairy farms: A systematic review and meta-analysis

Methicillin-resistant Staphylococcus aureus (MRSA) is an opportunistic bacterium that causes many human and animal infections worldwide. MRSA infections are classified as priority infections owing to their high morbidity and mortality, with a significant risk of zoonotic transmission. This study aimed to determine the pooled prevalence of MRSA in dairy cattle farms and its heterogeneity. Relevant studies were retrieved from three databases: PubMed, Web of Science, and Scopus. The pooled prevalence of MRSA in dairy farms was estimated using a random-effects model. Subgroup and meta-regression analyses were used to assess the probable sources of heterogeneity. Sensitivity and publication bias analyses were also performed. A total of 94 articles were eligible for inclusion in this meta-analysis. The pooled prevalence of MRSA was estimated to be 3.81% [95% confidence interval (95% CI) = 2.61-5.20] with significantly high heterogeneity (I ² = 96.6%, p = 0.00). For the subgroup analysis among continents, the prevalence was highest in Asia (4.89%; 95% CI = 2.88-7.35) and lowest in South America (1.33%, 95% CI = 0.00-5.49). As for the year of publication, MRSA prevalence was highest in reports published from 2015 to 2018 (4.36%, 95% CI = 2.41-6.80) and lowest in reports published before 2015 (2.65%, 95% CI = 0.75-5.52). As for sample type, the prevalence of MRSA in cattle milk (3.91%, 95% CI = 2.64-5.39) was higher than that in other sample types (1.19%, 95% CI = 0.05-3.24). These three factors were not significantly associated with the pooled prevalence of MRSA (p > 0.05). Therefore, the findings of this study indicate that the prevalence of MRSA has been minimal and consistent in dairy cattle farms over time.

Detection of Methicillin-Resistant Staphylococcus aureus in Clinical and Subclinical Mastitis in Ruminants and Studying the Effect of Novel Green Synthetized Nanoparticles as One of the Alternative Treatments

Mastitis is an important disease in dairy animals worldwide. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common causes of clinical and subclinical intramammary infections. In the current study, we isolated bacteria from 150 mastitic milk samples. Multiplex PCR was used to detect the methicillin resistance genes in S. aureus to detect the occurrence of MRSA isolates. Green synthesized titanium dioxide nanoparticles (TiO2 NPs) using aqueous leaf extracts of Artemisia herb Alba (A. herb Alba TiO2 NPs). The antibacterial efficacy of these nanoparticles was evaluated (in vitro and in vivo) against collected MRSA isolates using the disc diffusion method and SPF rats. Out of 150 mastitic milk samples, the frequency of S. aureus was 38 (25.3%), that of E. coli was 45 (30%), that of Klebsiella spp. Was 7 (4.7%), and that of Streptococcus spp. Was 11 (7.3%). Among 38 positive isolates of S. aureus, MRSA was 16 (42.1%) by antimicrobial sensitivity testing (AST) and 14 (38.8%) by multiplex PCR. The MRSA isolates were shown to have 100% resistance to penicillin and methicillin, 87.5% resistance to gentamicin, 50% resistance to cefoxitin and amoxicillin, and 75% resistance to ampicillin and ampicillin/sublactam with low resistance against erythromycin, ciprofloxacin, tetracycline, and levofloxacin by AST, respectively. A. herb Alba TiO2 NP formation was observed by changing the colour from white to dark green. The UV spectrum revealed absorbance peaks at 240-250 nm, and their sizes ranged from 42-66 nm and 11 to 45 nm by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). ‏A. herb Alba TiO2 NP suspensions were evaluated against MRSA, with the highest zone of inhibition (43 ± 0.45 mm) at a concentration of 40 μg/ml. Hematological parameters and histological examination after oral administration of 20 mg/kg of A. herb Alba TiO2 NPs indicated that A. herb Alba TiO2 NPs can be used as a new antimicrobial against resistant bacteria (MRSA) with consideration of the dose and methods of synthesis of plant-based compounds.

Antimicrobial Resistance, Multilocus Sequence, and spa Typing of Staphylococcus aureus Isolated from Retail Raw Meat Products

With a high capacity to acquire antimicrobial resistance, Staphylococcus aureus is an important pathogen causing severe infections in animals and humans. A total of 50 Staphylococcus aureus isolates from retail ground beef, chicken meat, and fish were characterized by antimicrobial resistance profiling, staphylococcal protein A gene (spa) typing, and multilocus sequence typing (MLST). The broth microdilution test results showed that all isolates were resistant to penicillin and sulphamethoxazole but had varying resistance rates to tetracycline (24%), erythromycin (4%), gentamicin (2%), ciprofloxacin (2%), trimethoprim (2%), and chloramphenicol (0%). The blaZ and sulI genes were detected in 100% of the isolates followed by grlA (94%), norA (92%), tetK (80%), chlA (60%), tetM (26%), aacA-aphD (2%), ermA (2%), fexA (0%), and dfrA (0%). Moreover, 26% of the isolates were multidrug-resistant, with five or more resistance genes. The spa typing analysis revealed 22 spa types, with t091 (16%), t1677 (8%), and t14538 (8%) being the most common, and one new spa type, t19851, was uncovered. MLST identified seven sequence types (STs), with ST7 (40%), ST15 (20%), and ST199 (13%) being the most common, and two STs (ST7435 and ST7436) were newly identified. In this study, S. aureus isolated from raw meat showed multidrug resistance and different clones associated with human infections. As a result, foods of animal origin may act as potential vehicles for transmission of multidrug-resistant S. aureus isolates, and the dissemination of potentially pathogenic clonal types, posing a health risk to humans.

Role of milk and milk products in the spread of methicillin-resistant Staphylococcus aureus in the dairy production chain

Milk and milk products can harbor a multiple varieties of microorganisms. Therefore, they can be an important source of foodborne pathogens, including multidrug-resistant bacteria. Methicillin-resistant Staphylococcus aureus (MRSA) causes a wide spectrum of infections both in animals and humans. Over the last two decades, the presence of MRSA in foods and food-producing animals, including milk and milk products, has been frequently reported worldwide, raising public health concerns. In order to monitor and prevent foodborne MRSA contamination, it is necessary to understand their sources, the pheno/genotypic characteristics of the strains, and their transmission dynamics. In this review, studies conducted worldwide were summarized in order to assess the prevalence and diversity of MRSA circulating in milk and milk products. The risk factors for the occurrence of MRSA in milk and milk products were also discussed with preventive and control measures to avoid MRSA contamination in the dairy food chain.

Relevant safety aspects of raw milk for dairy foods processing

The concern with food safety in the milk chain begins with the quality of the raw milk. Due to the health hazard that this food can carry when contaminated, the focus of studies has turned to microbiological and chemical contaminants that may be present in raw milk. There is an essential concern about conventional pathogens (Shiga toxin-producing Escherichia coli, Salmonella spp., Listeria monocytogenes, Campylobacter spp., Salmonella spp., and coagulase-positive Staphylococcus spp.) and emerging pathogens (Arcobacter butzleri, Yersinia enterocolitica, Mycobacterium avium ssp. paratuberculosis, Helicobacter pylori, and Cronobacter sakazakii) found in raw milk and dairy products. In addition, a growing public health issue has been raised regarding antimicrobial-resistant pathogens and commensal strains found in milk and dairy products. The antibiotic residues in milk can also damage health, such as allergies, and cause technological problems in dairy products processing. This health issue extends to other chemical contaminants such as heavy metals, pesticides, polycyclic aromatic hydrocarbons, melamine, dioxins, polychlorinated biphenyls, plasticizers, and additives in milk and dairy products. Other chemical substances formed by microorganisms are also of high importance, such as biogenic amines and mycotoxins. Therefore, this chapter aimed to revise and discuss relevant biological and chemical risks to ensure the safety and quality of raw milk and dairy products.

Selective laser welding in liquid: A strategy for preparation of high-antibacterial activity nanozyme against Staphylococcus aureus

Nanozyme was considered as one of the most promising substitutes for antibiotics, due to the selective catalysis for pathogens. In this work, a high-antibacterial activity SOD-like nanozyme based on hybrid Ag/CeO₂ nanocomposite was facilely prepared by using an innovative approach of selective laser welding in liquid. This prepared nanozyme displayed a high antimicrobial effect against Staphylococcus aureus under visible light illumination, the sterilization rate as high as 82.4%, which was 2.93 and 2.99 times higher than those of pure Ag and pure CeO₂, respectively. The enhanced antibacterial activity was attributed to the anchoring of Ag nanospheres on the surface of CeO₂ nanosheets, which induced the reduction of CeO₂ bandgap and boosted the visible light harvesting. Therefore, the charge carriers can be effectively stimulated to produce abundant reactive oxygen species on the Ag/CeO₂ nanocomposite via a SOD-like route. This work demonstrated a facile strategy for the preparation of high-antibacterial activity nanozyme, giving it great potential for scalable application in the biomedical and pharmaceutical industry.

Hazard of Staphylococcal Enterotoxins in Food and Promising Strategies for Natural Products against Virulence

Staphylococcal enterotoxins (SEs) secreted by Staphylococcus aureus frequently contaminate food and cause serious foodborne diseases but are ignored during food processing and even cold-chain storage. Notably, SEs are stable and resistant to harsh sterilization environments, which can induce more serious hazards to public health than the bacterium itself. Therefore, it is necessary to develop promising strategies to control SE contamination in food and improve food safety. Natural products not only have various pharmaceutical properties, such as antimicrobial and antitoxin activities, but they are also eco-friendly, safe, nutritive, and barely drug-resistant. Here, the hazards of SEs and the promising natural compounds with different inhibitory mechanisms are summarized and classified. The key points of future research and applications for natural products against bacterial toxin contamination in food are also prospected. Overall, this review may provide enlightening insights for screening effective natural compounds to prevent foodborne diseases caused by bacterial toxins.

Intraspecific and interspecific extracellular metabolites remodel biofilms formed by thermophilic spoilage bacteria

AIMS

Thermophilic spoilage bacteria and their biofilms formed during milk powder processing posed threats to safety and quality of dairy products. This research aims to understand more about the bacterial behaviours and their social models in biofilms.

METHODS AND RESULTS

Interactional effects from both extracellular metabolites and co-culture on biofilms formation of the contaminating thermophilic bacteria were determined. The results showed that strong biofilm formers always had high AI-2 activities, including Geobacillus stearothermophilus gs1, Bacillus licheniformis bl1 and Thermoactinomyces vulgaris tv1. Metabolites from themself or other species altered their biofilm biomass detected by crystal violet staining. Dual-species cultures observed by confocal laser scanning microscope indicated either synergistic or inhibitory effects between B. circulans bc1 and G. stearothermophilus gs1, as well as B. licheniformis bl1 and G. stearothermophilus gs1. Fourier transform infrared spectrometry results revealed the significant diversities in polysaccharides of the biofilm matrix.

CONCLUSIONS

Cell communication played an important role on biofilm formation in the complex microbial community. Intraspecific and interspecific extracellular metabolites influenced collective bacterial behaviours under mixed circumstances.

SIGNIFICANCE AND IMPACT OF STUDY

This research provided evidences on cell communication and biofilm formation of thermophilic bacteria in dairy industry.

Prevalence and Characteristics of Staphylococcus aureus Isolated From Retail Raw Milk in Northern Xinjiang, China

Staphylococcus aureus is one of the main pathogens causing mastitis in dairy animals worldwide. It is an important opportunistic pathogen of raw milk, and the enterotoxin causes significant food poisoning. Monitoring the antibiotic resistance of S. aureus in raw milk is helpful for a risk assessment of S. aureus. In this study, 62 strains (43.1%) of S. aureus were isolated from 144 retail raw milk samples of different varieties from four regions in northern Xinjiang, China. Among them, the isolation rates at Shihezi, Hami, Altay, and Tacheng were 58.1% (54/93), 12.9% (4/31), 18.2% (2/11), and 22.2% (2/9), respectively. The isolation rate of positive strains in cow milk samples was the highest (61.7%, 37/60), followed by camel milk (35.9%, 23/64), and horse milk (10.0%, 2/20). The results of the classical virulence genes test showed that 12.9% (8/62) of the isolates carried at least one virulence gene. The main genotype was see (6.5%, 4/62), followed by sea+sec (3.2%, 2/62), sea (1.6%, 1/62), and sec (1.6%, 1/62). The analysis of 13 resistance genes and the susceptibility to 12 different antibiotics of 62 isolates showed that 80.6% (50/62) of the strains were resistant to at least one antibiotic, and 46.8% (29/62) were resistant to three or more antibiotics. The isolated strains had the highest resistance rate to penicillin (72.6%, 45/62), and 25.8% (16/62) of the isolates carried the blaZ resistance gene. In addition, 32 strains (51.6%, 32/62) of methicillin-resistant S. aureus were detected. All isolates had the ability to form biofilms. The pulsed-field gel electrophoresis results showed that the 47 isolates revealed 13 major pulsotypes (P1–P13) and 26 subtypes with 80% similarity, indicating the overall genetic diversity in the distribution area and sources of the samples. These findings indicate that S. aureus causes serious pollution of raw milk in northern Xinjiang, which has a negative effect on public health. Therefore, control measures and continuous monitoring should be undertaken to ensure the quality and safety of raw milk.

Genetic characterization of livestock-associated methicillin-resistant Staphylococcus aureus isolated in Greece

The interest in livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) strains is increasing due to their wide distribution and transmission even in persons without previous contact with livestock, and these strains pose a public health threat. The aim of the study was the genetic characterization of the whole genome of two epidemiologically unrelated t034 LA-MRSA strains previously isolated from the nasal cavities of a goat and a farmer in Greece. Both strains were assigned to the ST398-Vc-t034 type and they were carrying a single transposon identical to Tn6133. They harbored genes conferring resistance to several antibiotics (aminoglycosides, β-lactams, macrolides, streptogramin B, tetracycline, and trimethoprim), and genes associated with virulence (enterotoxins, γ-hemolysins, and aureolysin). The present study can serve as baseline for further LA-MRSA epidemiological and evolutionary studies in Greece, while awareness and increased surveillance are needed to avoid their spread.

Genetic characterization of two methicillin-resistant Staphylococcus aureus spa type t127 strains isolated from workers in the dairy production chain in Greece

Methicillin-resistant Staphylococcus aureus (MRSA) constitutes a constant threat for the public health. Aim of the present study was to analyse the whole genome sequences of two MRSA strains belonging to Staphylococcus protein A (spa) type t127 isolated from humans working in two distantly located dairy production farms in Greece.MRSA strains were isolated from the nasal cavity of a food handler in a milk industry in Epirus, northwestern Greece (E-MRSA), and a person working in a cattle farm in Thrace, northeastern Greece (T-MRSA). Whole genome sequences taken using next generation sequencing were analysed for resistance and virulence genes applying various bioinformatic tools.Both isolates were assigned to ST1-IVa-t127 type, and they were transferring genes conferring resistance to tetracycline, β-lactams, and aminoglycosides; T-MRSA was carrying additional genes leading to macrolide, lincosamide and streptogramin B (MLSB) resistance. Both isolates were carrying three plasmid replicon types, rep5, rep7 and rep16, while T-MRSA harboured also rep10 and rep15. E-MRSA carried scn and sak genes which were absent from T-MRSA.In conclusion, the genetic characterization of two unrelated ST1-IVa-t127 MRSA strains isolated from humans in close contact with livestock in Greece can be used as basis for further epidemiological and evolutionary studies.

Prevalence, antibiotic resistance, virulence and genetic diversity of Staphylococcus aureus isolated from bulk tank milk samples of U.S. dairy herds

Background

Colonization of dairy cows by Staphylococcus aureus (S. aureus), especially those which are multi-drug resistant and toxin producing, is a concern for animal health and well-being as well as public health. The objective of this study was to investigate the prevalence, antibiotic resistance, gene content and virulence determinants of S. aureus in bulk tank milk samples (BTM) from U.S. dairy herds.

Results

BTM samples were collected, once in winter and once in summer, from 189 U.S. dairy herds. Of 365 BTM samples cultured, the sample and herd prevalence of S. aureus in BTM was 46.6% (170 of 365 samples) and 62.4% (118 of 189 herds), respectively. Among a subset of 138 S. aureus isolates that were stored for further analysis, 124 were genome sequenced after being confirmed as S. aureus using phenotypic tests. The most commonly identified antimicrobial resistance-associated gene was norA (99.2%) and mecA gene responsible for methicillin resistance (MRSA) was identified in one isolate (0.8%). The most frequently detected putative virulence genes were aur (100%), hlgB (100%), hlgA, hlgC, hlb (99.2%), lukE (95.9%) and lukD (94.3%). In the 53 staphylococcal enterotoxin positive isolates, sen (37.9%), sem (35.5%), sei (35.5%) and seg (33.1%) were the most frequently detected enterotoxin genes. Among the 14 sequence types (ST) and 18 spa types identified, the most common was ST2187 (20.9%) and t529 (28.2%), respectively. The most predominant clone was CC97 (47.6%) followed by CC unknown (36.3%). The single MRSA isolate belonged to ST72-CC8, spa type t126 and was negative for the tst gene but harbored all the other virulence genes investigated.

Conclusion

Our findings indicated a high prevalence of S. aureus in BTM of U.S. dairy herds, with isolates showing little evidence of resistance to antibiotics commonly used to treat mastitis. However, isolates often carried genes for the various enterotoxins. This study identified predominant genetic clones. Despite lower prevalence, the presence of MRSA and multi-drug resistant strains in BTM poses a significant risk to animal and public health if their number were to increase in dairy environment. Therefore, it is necessary to continuously monitor the use of antibiotics in dairy cows.

Occurrence and Quantification of Antimicrobial Resistance Genes in the Gastrointestinal Microbiome of Two Wild Seabird Species With Contrasting Behaviors

Antimicrobial resistance genes (ARGs) are environmental pollutants and anthropization indicators. We evaluated human interference in the marine ecosystem through the ocurrence and quantification (real-time PCRs) of 21 plasmid-mediated ARGs in enema samples of 25 wild seabirds, upon admission into rehabilitation: kelp gull (Larus dominicanus, n = 14) and Magellanic penguin (Spheniscus magellanicus, n = 11). Overall, higher resistance values were observed in kelp gulls (non-migratory coastal synanthropic) in comparison with Magellanic penguins (migratory pelagic non-synanthropic). There were significant differences between species (respectively, kelp gull and Magellanic penguin): ARGs occurrence (bla _TEM [p = 0.032]; tetM [p = 0.015]; tetA [p = 0.003]; and sulII [p = 0.007]), mean number of ARGs per sample (p = 0.031), ARGs mean load percentage (aadA [p = 0.045], tetA [p = 0.031], tetM [p = 0.016], bla _TEM [p = 0.032], sulII [p = 0.008]), percentage of genes conferring resistance to an antimicrobial class (betalactams [p = 0.036] and sulfonamides [p = 0.033]), mean number of genes conferring resistance to one or more antimicrobial classes (p = 0.024]), percentage of multiresistant microbiomes (p = 0.032), and clustering (p = 0.006). These differences are likely due to these species' contrasting biology and ecology - key factors in the epidemiology of ARGs in seabirds. Additionally, this is the first report of mecA in seabirds in the Americas. Further studies are necessary to clarify the occurrence and diversity of ARGs in seabirds, and their role as potential sources of infection and dispersal within the One Health chain of ARGs.

Staphylococcus aureus Isolated from Ruminants with Mastitis in Northern Greece Dairy Herds: Genetic Relatedness and Phenotypic and Genotypic Characterization

Staphylococcus aureus is the most common mastitis-related pathogen in dairy cattle, goats, and sheep worldwide. However, the population structure and genomic characteristics of mastitis-associated S. aureus in small ruminants are limited. Furthermore, the genotypic and phenotypic characteristics involved in the pathogenicity of S. aureus have been thoroughly defined, yet their association with the severity of mastitis is not fully established. Here, we performed genotyping by pulsed-field gel electrophoresis (PFGE) and spa analyses to assess the genetic diversity and relatedness of 162 S. aureus strains recovered from clinical mastitis (CM) and subclinical mastitis (SCM) cases from goats, sheep, and bovines. PFGE analysis revealed 108 distinguishable pulsotypes and 3 main clusters that comprised isolates from the three host species, while according to spa typing, 32 different spa types were identified. Genotypic analysis revealed a spreading of genetically related or indistinguishable S. aureus strains among ovine, caprine, and bovine farms of distant geographical regions. In total, 28 different staphylococcal enterotoxin (SE) gene profiles were observed, revealing a diverse range of SE genes among isolates. By evaluating the antimicrobial resistance, we found low phenotypic antimicrobial resistance among all ruminant isolates. We also performed multiple correspondence analysis, which indicated that the presence of the sec gene, biofilm production, and high autoaggregation ability are associated with CM cases.

Prevalence, Antimicrobial Resistance, and Molecular Characterization of Staphylococcus aureus Isolated from Animals, Meats, and Market Environments in Xinjiang, China

Staphylococcus aureus has been recognized as an important foodborne pathogen. However, knowledge about the epidemiology and genetic characteristics of S. aureus in the meat production chain from farm to market is limited. The aim of this study was to investigate the genetic characteristics of S. aureus in animal samples isolated from Xinjiang province farms and farmer' markets, by determining staphylococcal protein A (spa) repeat region and virulence factor typing, and by assessment of antimicrobial resistance. Out of 1324 samples, 128 (9.7%) were positive for S. aureus, 26 (2.0%) of them were identified as methicillin-resistant S. aureus (MRSA) and 88 (6.6%) of them were identified as vancomycin-resistant S. aureus (VRSA). Antimicrobial resistance was determined using the disk diffusion method. S. aureus isolates showed resistance to penicillin G (98.4%), clarithromycin (69.5%), erythromycin (69.5%), vancomycin (68.8%), and tetracycline (67.2%). A total of 80.4% of isolates showed resistance to three or more antimicrobial classes. PCR was used to detect ten virulence genes such as the enterotoxin (sea, seb, and sec), hemolysin (hla and hlb), clumping factor (clfA), and fibronectin-binding proteins A and B (fnbA and fnbB). Our study showed that isolates harbored two or seven virulence genes. All strains encode hla and clfA, and half of them encode hlb and enterotoxin genes. The spa typing results showed that the 128 isolates were grouped into 32 spa types. The main spa types were t127 (22.7%), t2592 (12.5%), t437 (10.9%), and t2616 (10.9%). Notably, isolates of t437 type accounted for 46.2% of the MRSA. Our data indicate that meats in the slaughterhouse and farmers' markets were contaminated with S. aureus. S. aureus virulence genes and spa types were diverse, and its antibiotic resistance was serious. The presence of MRSA and VRSA represents potential public health risks and warrants further investigation regarding the driving factors of such resistance and their transmission to humans.

Whole genome sequencing of coagulase positive staphylococci from a dog-and-owner screening survey

BACKGROUND

Staphylococcus aureus and S. pseudintermedius are the two most common coagulase positive staphylococci (CPS). S. aureus is more prevalent among humans, whereas S. pseudintermedius is more commonly isolated from dogs, however, both can cause various community and hospital acquired diseases in humans.

METHODS

In the current study we screened 102 dogs and 84 owners in Hungary. We tested the antibiotic susceptibility of the strains and in order to get a better picture of the clonal relationship of the strains, we used pulsed-field gel electrophoresis. In addition, three pairs of isolates with identical PFGE patterns were whole genome sequenced, MLST and spa types were established.

RESULTS

Carriage rate of S. aureus was 23.8% in humans and 4.9% in dogs and two cases of co-carriage were found among dogs and owners. S. pseudintermedius carriage rate was 2.4% and 34.3%, respectively, with only one co-carriage. The isolates were generally rather susceptible to the tested antibiotics, but high tetracycline resistance of S. pseudintermedius strains was noted. The co-carried isolates shared almost the same resistance genes (including tet(K), bla(Z), norA, mepR, lmrS, fosB) and virulence gene pattern. Apart from the common staphylococcal enzymes and cytotoxins, we found enterotoxins and exfoliative toxins as well. The two S. aureus pairs belonged to ST45-t630, ST45-t671 and ST15-t084, ST15-t084, respectively. The co-carried S. pseudintermedius isolates shared the same housekeeping gene alleles determining a novel sequence type ST1685.

CONCLUSIONS

Based on the genomic data, dog-owner co-carried strains displayed only insignificant differences therefore provided evidence for potential human-to-dog and dog-to-human transmission.

Genomic Distinctions of LA-MRSA ST398 on Dairy Farms From Different German Federal States With a Low Risk of Severe Human Infections

Methicillin-resistant Staphylococcus aureus (MRSA) have been found on German dairy farms and may be the cause of difficult-to-treat bovine mastitis. Considering the one health approach, MRSA might be transmitted from animals to humans raising the risk for severe infections. On 17 German dairy farms with a history of MRSA detection, MRSA strains were isolated from quarter milk, bulk tank milk, and swab samples of calves, heifers, pigs, and the environment. A selection of 33 isolates was analyzed using whole-genome sequencing and antimicrobial resistance testing. All detected MRSA strains were attributed to the livestock-associated sequence type 398. Methicillin-resistance was associated with the mecA gene in the staphylococcal cassette chromosome (SCC)mec types IVa (7/33) or V (26/33). The MRSA strains across the German federal states showed large allelic differences indicating independent development and distribution. On one farm, a clonal MRSA isolate was widely spread among different animals and the milking equipment. Moreover, MRSA transmission between two dairy farms in one federal state seems to be likely. In depth studies indicated that the resistance gene prediction and phenotypic resistance are in good agreement. Twenty eight strains were determined to exhibit a non-wildtype phenotype (resistant) against up to seven antimicrobial substances with an overall resistance to β-lactams and tetracycline. Ten different phenotypic antimicrobial resistance patterns were found among the MRSA strains. The strains harbored a wide virulence gene repertoire, of which some of them are related to bovine mastitis. However, the isolates lacked typical human infection associated factors such as the immune evasion cluster genes, staphylococcal enterotoxin genes, or Panton-Valentine leukocidin genes leading to the assumption for a low risk for severe human infections and foodborne diseases.

Short communication: First detection of Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus ST30 in raw milk taken from dairy cows with mastitis in South Korea

We identified 199 Staphylococcus aureus isolates from quarter milk samples of 1,289 dairy cattle between 2014 and 2018. About 66% of the isolates were resistant to at least 1 antimicrobial agent; the highest rate of resistance was to penicillin, followed by resistance to ampicillin, erythromycin, and sulfadimethoxine. We obtained 30 methicillin-resistant S. aureus (MRSA) strains from 6 farms in 3 provinces. The MRSA strains exhibited a significantly higher resistance rate to most of the tested antimicrobials than the oxacillin-susceptible strains. The MRSA strains represented 5 genotypes: ST72-t324-SCCmec IV (n = 14), ST30-t1752-SCCmec IV (n = 8), ST188-t189-SCCmec NT (n = 6), ST188-t2284-SCCmec NT (n = 1), and NT-NT-SCCmec IV (n = 1). One of the ST188 MRSA strains represented a novel staphylococcal protein A (spa) type (t2284). In addition, 7 of the 8 ST30 MRSA strains were Panton-Valentine leukocidin (PVL)-positive and carried various staphylococcal enterotoxin encoding genes. This is the first report of PVL-positive ST30 MRSA-t1752-SCCmec IV from bovine mastitis in Korea. All of ST72-t324-SCCmec IV MRSA strains carried staphylococcal enterotoxin and leukotoxin encoding genes. They were also sensitive to most of the tested non-β-lactam antimicrobials. In contrast, ST188-t189 MRSA strains were resistant to multiple antimicrobials and predominantly carried the leukotoxin encoding gene. Taken together, these findings may indicate that dairy cows could be a major source for spreading MRSA strains, and contaminated milk could be a vehicle for transmission. Suitable hygienic measures should be established in dairy farms and processing plants to limit the likelihood of introducing MRSA into the food chain.

Human mecC-Carrying MRSA: Clinical Implications and Risk Factors

A new methicillin resistance gene, named mecC, was first described in 2011 in both humans and animals. Since then, this gene has been detected in different production and free-living animals and as an agent causing infections in some humans. The possible impact that these isolates can have in clinical settings remains unknown. The current available information about mecC-carrying methicillin resistant S. aureus (MRSA) isolates obtained from human samples was analyzed in order to establish its possible clinical implications as well as to determine the infection types associated with this resistance mechanism, the characteristics of these mecC-carrying isolates, their possible relation with animals and the presence of other risk factors. Until now, most human mecC-MRSA infections have been reported in Europe and mecC-MRSA isolates have been identified belonging to a small number of clonal complexes. Although the prevalence of mecC-MRSA human infections is very low and isolates usually contain few resistance (except for beta-lactams) and virulence genes, first isolates harboring important virulence genes or that are resistant to non-beta lactams have already been described. Moreover, severe and even fatal human infection cases have been detected. mecC-carrying MRSA should be taken into consideration in hospital, veterinary and food safety laboratories and in prevention strategies in order to avoid possible emerging health problems.

Isolation and characterization of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) from milk of dairy goats under low-input farm management in Greece

The presence of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in raw milk is a challenge for veterinarians and public health professionals. In this study, we investigated the presence and clonality of S. aureus and MRSA in milk of individual dairy goats with subclinical mastitis reared under the low-input farming system in Greece and determined the isolates' enterotoxin gene carriage and their ability to form biofilms. S. aureus was isolated from 162 out of the 559 milk samples examined (29 %) and one isolate per S. aureus-positive sample was further characterized. S. aureus isolates were very closely related even among farms of distant geographical regions. Nine S. aureus isolates carried a functional mecA gene and were classified as MRSA. The S. aureus protein A (spa) typing in the MRSA isolates showed that four belonged to spa type t127 (44.4 %), three to t2049 (33.3 %) and two to t7947 (22.2 %). The spa type t7947 is reported for the first time in Greece. The MRSA isolates originated from two very distantly located farms, one located in the island of Skopelos and the other in Central Macedonia. Four of the MRSA isolates carried the staphylococcal enterotoxin genes sea or sec. Most of the isolates (92 % of S. aureus and 77.8 % of the MRSA) possessed moderate or weak biofilm-formation ability. Raw milk from low-input goat herds may serve as a potential vector of antimicrobial-resistant S. aureus to raw-milk consumers.

Antimicrobial resistance genes in bacteria from animal-based foods

Antimicrobial resistance is a worldwide public health threat. Farm animals are important sources of bacteria containing antimicrobial resistance genes (ARGs). Although the use of antimicrobials in aquaculture and livestock has been reduced in several countries, these compounds are still routinely applied in animal production, and contribute to ARGs emergence and spread among bacteria. ARGs are transmitted to humans mainly through the consumption of products of animal origin (PAO). Bacteria can present intrinsic resistance, and once antimicrobials are administered, this resistance may be selected and multiply. The exchange of genetic material is another mechanism used by bacteria to acquire resistance. Some of the main ARGs found in bacteria present in PAO are the bla, mcr-1, cfr and tet genes, which are directly associated to antibiotic resistance in the human clinic.

Genotyping and antimicrobial resistance of Staphylococcus aureus isolates from dairy ruminants: differences in the distribution of clonal types between cattle and small ruminants

Staphylococcus aureus is part of the normal flora of animals, and represents one of the leading causes of contagious mastitis in dairy herds worldwide. Sixty-seven epidemiologically unrelated S. aureus isolates from nasal and mastitis milk samples of dairy-producing animals (32 cows, 25 sheep, and 10 goats) were characterized by antimicrobial susceptibility testing and spa typing followed by multilocus sequence typing (MLST) on representative isolates and SCCmec-typing on methicillin-resistant S. aureus (MRSA) isolates. The highest resistance was observed to penicillin (64.2%, 43/67), followed by tetracycline (23.9%, 16/67), erythromycin (22.4%, 15/67), and streptomycin (17.9%, 12/67). In general, 18 spa types (including newly identified t16958) and 13 sequence types (STs) belonging to 8 clonal complexes (CCs) were detected. The cow-associated isolates were mainly assigned to CC5 (n = 18, related to t267-ST97, t521-ST352, t527-ST97, t304-ST6, and t084-ST15), followed by CC398 (n = 6, t937-ST291), CC45 (n = 3, t230-ST45), CC88 (n = 2, t2526-ST88), CC22 (n = 2, t3680-ST22), and CC522 (n = 1, t3576-ST522). Small ruminant isolates were mostly clustered into CC522 (n = 29, related to t3576, t1534, t16958, t7308, t7311, t7305 [ST522], t1534-ST2057, and t5428-ST2079). Two isolates from cows with mastitis were found to be MRSA, exhibited a composite profile of t937-ST291-SCCmecIV. No isolates carried the PVL and mecC genes. A significant difference in clonal types of S. aureus isolates from cows in comparison with those from small ruminants was found. This study demonstrated the circulation of diverse clones of S. aureus among dairy animals in Iran, with a different clonal composition between cows and small ruminants. The current study also reports MRSA-related mastitis in dairy cows, emphasizing the need for comprehensive surveillance.