Public health impact and antimicrobial selection of meticillin-resistant staphylococci in animals

Combined antimicrobial effect of two peptide nucleic acids against Staphylococcus aureus and S. pseudintermedius veterinary isolates

BACKGROUND

Staphylococcus aureus and S. pseudintermedius are the major etiological agents of staphylococcal infections in humans, livestock, and companion animals. The misuse of antimicrobial drugs has led to the emergence of antimicrobial-resistant Staphylococcus spp., including methicillin-resistant S. aureus (MRSA) and methicillin-resistant S. pseudintermedius (MRSP). One novel therapeutic approach against MRSA and MRSP is a peptide nucleic acid (PNA) that can bind to the target nucleotide strands and block expression. Previously, two PNAs conjugated with cell-penetrating peptides (P-PNAs), antisense PNA (ASP)-cmk and ASP-deoD, targeting two essential genes in S. aureus, were constructed, and their antibacterial activities were analyzed.

OBJECTIVES

This study analyzed the combined antibacterial effects of P-PNAs on S. aureus and S. pseudintermedius clinical isolates.

METHODS

S. aureus ATCC 29740 cells were treated simultaneously with serially diluted ASP-cmk and ASP-deoD, and the minimal inhibitory concentrations (MICs) were measured. The combined P-PNA mixture was then treated with S. aureus and S. pseudintermedius veterinary isolates at the determined MIC, and the antibacterial effect was examined.

RESULTS

The combined treatment of two P-PNAs showed higher antibacterial activity than the individual treatments. The MICs of two individual P-PNAs were 20 and 25 μM, whereas that of the combined treatment was 10 μM. The application of a combined treatment to clinical Staphylococcus spp. revealed S. aureus isolates to be resistant to P-PNAs and S. pseudintermedius isolates to be susceptible.

CONCLUSIONS

These observations highlight the complexity of designing ASPs with high efficacy for potential applications in treating staphylococcal infections in humans and animals.

Therapeutic potential of natural products and antibiotics against bovine mastitis pathogen of cows and buffaloes

The present study aims to evaluate the prevalence and antimicrobial sensitivity of Staphylococcus aureus associated with bovine mastitis to selected antibiotics and plant extracts. In the current study, 140 milk samples were collected from cows and buffaloes. Among the 140 samples, 93 samples were positive for sub-clinical mastitis based on the California Mastitis Test (CMT). Out of the total positive samples, 45 were confirmed for S. aureus on a Mannitol salt agar media. The antimicrobial susceptibility test revealed that 44.82% of the isolates were resistant to cefoxitin (oxacillin) confirming methicillin-resistant S. aureus (MRSA) with a higher percentage (51.61%) in the buffalo than in the cow samples. Furthermore, the PCR assay confirmed the presence of the mecA gene in all the MRSA isolates. Among the seven tested antibiotics, sulfamethoxazole + trimethoprim showed high efficacy (71.1%) against methicillin-susceptible S. aureus isolates (MSSA). Oxytetracycline and sulfamethoxazole + trimethoprim showed 20% efficacy against MRSA followed by enrofloxacin (10%). On the other hand, the tested samples from Pistacia chinensis revealed that the ethyl acetate extract of bark showed a maximum zone of inhibition of 21.3 mm against MSSA and MRSA isolates at 3 000 μg/disc. Moreover, the methanol extract of Cotoneaster microphyllus formed a 12.3 mm and 9.1 mm zone of inhibition against the MSSA and MRSA isolates, respectively.

The use of aminopenicillins in animals within the EU, emergence of resistance in bacteria of animal and human origin and its possible impact on animal and human health

Aminopenicillins have been widely used for decades for the treatment of various infections in animals and humans in European countries. Following this extensive use, acquired resistance has emerged among human and animal pathogens and commensal bacteria. Aminopenicillins are important first-line treatment options in both humans and animals, but are also among limited therapies for infections with enterococci and Listeria spp. in humans in some settings. Therefore, there is a need to assess the impact of the use of these antimicrobials in animals on public and animal health. The most important mechanisms of resistance to aminopenicillins are the β-lactamase enzymes. Similar resistance genes have been detected in bacteria of human and animal origin, and molecular studies suggest that transmission of resistant bacteria or resistance genes occurs between animals and humans. Due to the complexity of epidemiology and the near ubiquity of many aminopenicillin resistance determinants, the direction of transfer is difficult to ascertain, except for major zoonotic pathogens. It is therefore challenging to estimate to what extent the use of aminopenicillins in animals could create negative health consequences to humans at the population level. Based on the extent of use of aminopenicillins in humans, it seems probable that the major resistance selection pressure in human pathogens in European countries is due to human consumption. It is evident that veterinary use of these antimicrobials increases the selection pressure towards resistance in animals and loss of efficacy will at minimum jeopardize animal health and welfare.

Presence of Staphylococcus spp. carriers of the mecA gene in the nasal cavity of piglets in the nursery phase

The presence of Staphylococcus spp. resistant to methicillin in the nasal cavity of swine has been previously reported. Considering the possible occurrence of bacterial resistance and presence of resistance genes in intensive swine breeding and the known transmissibility and dispersion potential of such genes, this study aimed to investigate the prevalence of resistance to different antibiotics and the presence of the mecA resistance gene in Staphylococcus spp. from piglets recently housed in a nursery. For this, 60 nasal swabs were collected from piglets at the time of their housing in the nursery, and then Staphylococcus spp. were isolated and identified in coagulase-positive (CoPS) and coagulase-negative (CoNS) isolates. These isolates were subjected to the disk-diffusion test to evaluate the bacterial resistance profile and then subjected to molecular identification of Staphylococcus aureus and analyses of the mecA gene through polymerase chain reaction. Of the 60 samples collected, 60 Staphylococcus spp. were isolated, of which 38 (63.33%) were classified as CoNS and 22 (36.67%) as CoPS. Of these, ten (45.45%) were identified as Staphylococcus aureus. The resistance profile of these isolates showed high resistance to different antibiotics, with 100% of the isolates resistant to chloramphenicol, clindamycin, and erythromycin, 98.33% resistant to doxycycline, 95% resistant to oxacillin, and 85% resistant to cefoxitin. Regarding the mecA gene, 27 (45%) samples were positive for the presence of this gene, and three (11.11%) were phenotypically sensitive to oxacillin and cefoxitin. This finding highlights the importance of researching the phenotypic profile of resistance to different antimicrobials and resistance genes in the different phases of pig rearing to identify the real risk of these isolates from a One Health perspective. The present study revealed the presence of samples resistant to different antibiotics in recently weaned production animal that had not been markedly exposed to antimicrobials as growth promoters or even as prophylactics. This information highlights the need for more research on the possible sharing of bacteria between sows and piglets, the environmental pressure within production environments, and the exposure of handlers during their transport, especially considering the community, hospital, and political importance of the presence of circulating resistant strains.

Resistance to Critical Important Antibacterials in Staphylococcus pseudintermedius Strains of Veterinary Origin

Staphylococcal infections represent a challenge in companion animals and hospitalized patients. This study aimed to assess the resistance of Staphylococcus pseudintermedius isolates, against a broad panel of antibacterials, including exclusive to human medicine. A total of 40 S. pseudintermedius were collected from clinical specimens of dogs (n = 31) and cats (n = 5). All strains were tested for 20 antibacterials, namely 14 Critical Important and eight Highly Important Antibacterials (CIA and HIA, respectively), indicative for 18 antimicrobial classes. All strains were susceptible to seven antibiotics (daptomycin, fosfomycin, fusidic acid, linezolid, quinupristin-dalfopristin, teicoplanin/vancomycin, tigecycline). The highest resistance was against penicillin (97.5% Confidence Interval [CI]: 83.8-100.0), whereas the lowest against telavancin (2.5%, CI: 0.0-16.2). Resistance versus Highest Priority CIA was observed, namely against macrolides (70.0, CI: 52.1-84.3), quinolones (62.5, CI: 44.5-78.3), 5th generation cephalosporins (7.5, CI: 1.3-21.6), and glycopeptides (2.5%, CI: 0.0-14.2). Among High Priority CIA, strains were resistant only to aminoglycosides (65.0, CI: 47.0-80.4) and ansamycins (12.5, CI: 3.8-28.1). We observed the highest resistance against veterinary medicine antibacterials, but there was also resistance against antibacterials exclusive to human medicine, namely ceftaroline (7.5, CI: 1.0-23.8) and telavancin. S. pseudintermedius zoonotic potential and its rate of acquisition of new resistance should encourage surveillance on a broad spectrum of antibacterials.

Antimicrobial Resistance and Molecular Characterization of Methicillin-Resistant Staphylococcus aureus from Two Pig Farms: Longitudinal Study of LA-MRSA

Pigs were identified as the most important reservoir of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA), mostly belonging to the emergent zoonotic clonal complex (CC) 398. Here, we investigated the presence of MRSA in sows and piglets over a period of several months in two pig farms (intensive farm A and family-run farm B). Isolates underwent antimicrobial susceptibility testing, PCR characterization and spa typing. We collected 280 samples, namely 206 nasal swabs from pigs and 74 environmental samples from pig housings at 12 consecutive time points. A total of 120/161 (74.5%) and 75/119 (63.0%) samples were MRSA-positive in farms A and B, respectively. All isolates harbored mecA but lacked mecC and PVL-encoding genes. The identified spa types (t571, t034, t1250 and t898 in farm A, t1451 and t011 in farm B) were indicative of CC398. Antimicrobial resistance patterns (all multidrug resistant in farm A, 57.2% in farm B) depended on the farm, suggesting the impact of farm size and management practices on the prevalence and characteristics of MRSA. Due to the intermittent colonization of pigs and the high contamination of their immediate environment, MRSA status should be determined at the farm level when considering preventive measures or animal trade between farms.

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

Background

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

Objectives

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

Methods

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

Results

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

Conclusions

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

Occurrence and characterization of methicillin-resistant Staphylococcus spp. in diseased dogs in Brazil

Staphylococcus pseudintermedius is a major commensal bacterium of the skin and mucosae of dogs and an opportunistic agent responsible for several clinical infections, such as pyoderma, otitis, and surgical wound infections. The emergence of methicillin-resistant S. pseudintermedius (MRSP) has become a problem of great concern in veterinary and human medicine because it is multidrug resistant (MDR) and can also infect humans. This study aimed to identify the occurrence of Staphylococcus spp. in infected patients and investigate the antimicrobial resistance profiles and molecular structure of MRSP isolates. Samples were obtained from two different veterinary clinics; suggestive colonies were submitted to matrix-assisted laser desorption ionization-time of flight (MALDI-ToF) mass spectrometry and confirmed at the species level by polymerase chain reaction (PCR). Sequencing of the 16S rRNA and rpoB genes were used in selected samples that were not identified by MALDI-ToF and by the species-specific PCR. Antimicrobial susceptibility and PCR detection of mecA were performed. MRSP isolates were subjected to multilocus sequence typing. Of all the clinical staphylococci (n = 131), 98 (74.8%) were identified as S. pseudintermedius. Multidrug resistance (resistance to ≥3 classes of antimicrobials) was observed in 63.2% of S. pseudintermedius isolates, and 24.5% of S. pseudintermedius isolates were methicillin-resistant. Half of the MRSP isolates were isolated from surgical site infections. Among the ten sequence types (ST) identified, nine were novel. ST71 was the most prevalent and associated with resistance to fluoroquinolones. Prior antimicrobial therapy, hospitalization, and surgical site infections seemed to be risk factors for MRSP acquisition. The present study showed a high rate of MDR staphylococci in infected dogs. MRSP was isolated from different clinical conditions, mainly surgical site infections. Additionally, this is the first study to extensively investigate the population structure of MRSP in Brazil, which revealed the dispersion of CC71 and nine novel ST. These findings raise concerns for both animal and human health due to the zoonotic potential of this species and limited therapeutic options available for MRSP infections.

Antibiotic Resistance and Molecular Profiling of the Clinical Isolates of Staphylococcus aureus Causing Bovine Mastitis from India

Staphylococcus aureus is an opportunistic bacterium known to cause severe infections in humans and animals. It is one of the major bacteria causing subclinical and clinical mastitis, leading to significant economic losses in livestock industry. In this study, we have isolated and characterized 80 S. aureus clinical isolates from mastitis-infected animals. The analysis of antimicrobial susceptibility, molecular typing, biofilm production and genetic determinants was performed to understand molecular and phenotypic features of the prevalent pathogen. Our antibiotic susceptibility assays showed the majority (57.5%) of isolates to be multidrug-resistant (MDR), 38.75% resistant and 3.75% sensitive. We found 25% isolates to be methicillin-resistant S. aureus (MRSA) based on oxacillin susceptibility assays. In the MRSA group, maximum isolates (95%) were MDR compared to 45% in MSSA. Multilocus sequence typing (MLST) revealed 15 different STs; ST-97 was the most common ST, followed by ST-2459, ST-1, ST-9 and ST-72. The agr typing showed agr-I as the most common type, followed by type II and III. Most isolates developed biofilms, which ranged in intensity from strong to weak. The presence or absence of lukS, a virulence-related gene, was found to have a substantial relationship with the biofilm phenotype. However, no significant association was found between biofilm formation and antimicrobial resistance or other virulence genes. We also found four MRSA isolates that were mecA negative based on molecular assays. Our findings reveal the prevalence of multidrug-resistant S. aureus clinical isolates in India that are biofilm positive and have critical genetic factors for disease pathogenesis causing bovine mastitis. This study emphasizes the need for the comprehensive surveillance of S. aureus and other mastitis-causing pathogens to control the disease effectively.

Diversity and pathogenesis of Staphylococcus aureus from bovine mastitis: current understanding and future perspectives

Staphylococcus aureus is a leading cause of bovine mastitis worldwide. Despite some improved understanding of disease pathogenesis, progress towards new methods for the control of intramammary infections (IMI) has been limited, particularly in the field of vaccination. Although herd management programs have helped to reduce the number of clinical cases, S. aureus mastitis remains a major disease burden. This review summarizes the past 16 years of research on bovine S. aureus population genetics, and molecular pathogenesis that have been conducted worldwide. We describe the diversity of S. aureus associated with bovine mastitis and the geographical distribution of S. aureus clones in different continents. We also describe studies investigating the evolution of bovine S. aureus and the importance of host-adaptation in its emergence as a mastitis pathogen. The available information on the prevalence of virulence determinants and their functional relevance during the pathogenesis of bovine mastitis are also discussed. Although traits such as biofilm formation and innate immune evasion are critical for the persistence of bacteria, the current understanding of the key host-pathogen interactions that determine the outcome of S. aureus IMI is very limited. We suggest that greater investment in research into the genetic and molecular basis of bovine S. aureus pathogenesis is essential for the identification of novel therapeutic and vaccine targets.

Prevalence of coagulase-positive methicillin-resistant Staphylococcus aureus and Staphylococcus pseudintermedius in dogs in Bangladesh

Background

The emergence of methicillin‐resistant Staphylococcus aureus (MRSA) and methicillin‐resistant Staphylococcus pseudintermedius (MRSP) have a significant health impact on people with direct or supportive occupations in veterinary medicine including veterinarians, animal handlers, laboratory personnel and pet owners.

Objectives

This cross‐sectional survey was conducted to determine the prevalence of and risk factors for S. aureus, S. pseudintermedius, MRSA and MRSP in dogs in Bangladesh.

Methods

A total of 358 swab samples were collected from different body sites of 150 dogs attending a university teaching veterinary hospital between January and June 2018. Standard bacteriological procedures were followed to isolate Staphylococcus, and identification was confirmed to the species level by PCR to detect the nuc gene. MRSA and MRSP were confirmed by the presence of the mecA gene.

Results

The prevalence of coagulase‐positive S. aureus and S. pseudintermedius in dogs were 16% and 45.3%, respectively. S. aureus and S. pseudintermedius isolates displayed the highest resistance against nalidixic acid (95.2% and 91%, respectively) and erythromycin (89.3% and 84.7%, respectively). Notably, all the staphylococcal isolates showed resistance to ≥3 antimicrobial classes. The prevalence of MRSA and MRSP in dogs was 8.7% and 6%, respectively. Multivariable logistic regression analysis identified the following variables as risk factors for MRSA colonisation in dogs: dogs with dermatitis (odds ratio [OR], 12.24, 95% CI: 3.12–57.33; p < 0.001) and history of antibiotic use (OR 8.73, 95% CI: 2.23–43.10; p < 0.001). Presence of otitis (OR 14.22; 95% CI: 1.64–103.58; p = 0.008) and oral lesions (OR 9.48, 95% CI: 1.14–64.82; p = 0.002) were identified as the significant risk factors for the carriage of MRSP.

Conclusions

The circulation of multidrug‐resistant S. aureus and S. pseudintermedius is a serious concern to dogs and humans. To our knowledge, this is the first report of S. pseudintermedius and MRSP affecting dogs in Bangladesh.

Phenotypic and genotypic study on antibiotic resistance and pathogenic factors of Staphylococcus aureus isolates from small ruminant mastitis milk in South of Italy (Sicily)

Staphyloccoccus aureus is the major cause of mastitis in small ruminants in the Mediterranean farms causing severe losses to dairy industry. Antibiotic treatment has been the most common approach to control these infections. Aim of this study was to investigate antimicrobial resistance (AMR), virulence factors and biofilm-related genes of 84 Sicilian strains of S. aureus isolated from sheep and goats milk during two different periods δT1 (2006-2009) and δT2 (2013-2015). Kirby Bauer method and Polymerase Chain Reaction (PCR) were utilized to monitor AMR and related genes (mecA, tetK, tetM, ermA, ermC). Moreover, toxin genes (tsst-1, sea-see, seg-sej, and sep) and biofilm genes (bap, ica, sasC) were studied. Twenty-six isolates (30.9%) showed multidrug resistance. The two groups showed similar results with exception for higher values of resistance for tilmicosin and lower for sulfamethoxazole and vancomycin of the second group. MecA gene was detected in one isolate. Tetracycline resistance was higher than 20%, with an increase in δT2 group. Toxin genes were found in 5 isolates (5.9%), belonging of δT2 group, while 57 of isolates (67.8%) showed biofilm related genes. The high presence of multi-resistant isolates suggests the need of more responsible use of antibiotic therapy for the control of these infections.

Antibiotic resistance of Staphylococcus aureus isolated from raw cow and goat milk produced in the Tiaret and Souk Ahras areas of Algeria

Background and Aim:

Staphylococcus aureus is a leading cause of infection in both humans and animals. Most livestock strains have shown antibiotic resistance to the many molecules used in veterinary therapeutics. This study aimed to assess the resistance patterns of these bacteria, we carried out our study in the Tiaret and Souk Ahras areas of Algeria.

Materials and Methods:

We collected 116 samples of bovine and goat milk to detect S. aureus. We used a selective media to isolate the strains, followed by biochemically identifying the isolates. We determined the susceptibility of the strains to antibiotic molecules using the disk diffusion method and confirmed the methicillin-resistant S. aureus (MRSA) with oxacillin minimum inhibitory concentration (MIC).

Results:

Our results showed that 26.72% of the samples were contaminated with S. aureus, and we recovered 31 isolates from the positive samples. We ascribed a high resistance profile to penicillin G (96.77%), fusidic acid (67.74%), and tobramycin (45.16%) and isolated 4MRSA strains.

Conclusion:

The presence of S. aureus, including MRSA strains in raw milk, can present a public health hazard, because these strains can cause widespread food poisoning. This finding will be useful to the veterinarians to choose an adequate treatment and to sensitize livestock breeders and milk producers to ensure the health of consumers.

A Three-Year Biocrime Sanitary Surveillance on Illegally Imported Companion Animals

The illegal trade of companion animals in the European Union poses several legal, ethical and health issues to the entire community. In the framework of the Biocrime Interreg project between Italy and Austria, we surveyed puppies and kittens confiscated at the borders to identify the most frequent pathogens associated with (i) the risk of spread within the shelter, (ii) the development of fatal disease and (iii) the zoonotic potential. From January 2018 to December 2020, we examined a total of 613 puppies and 62 kittens coming from 44 requisitions. Feces, skin specimens and blood sera from confiscated animals were tested to verify the presence of major infections and to assess the rabies post-vaccination immunity. Out of the total of individuals under investigation, necropsies and laboratory investigations were also performed on 79 puppies and three kittens that had died during the observation period. Results indicated a high prevalence of Canine Parvovirus (CPV) and Giardia spp. infections, CPV as the most likely cause of fatal gastroenteritis in puppies and Salmonella and Microsporum canis as major zoonotic pathogens. Conversely, both extended spectrum beta lactamases Escherichia coli and methicillin resistant Staphylococcus pseudintermedius strains as rare findings. Results highlighted that illegal animal trade could expose the human population to potential zoonotic risk and naïve animal population to potentially disrupting epidemic waves, both of these issues being largely underestimated when buying companion animals.

Occurrence of Methicillin-Resistant Coagulase-Negative Staphylococci (MRCoNS) and Methicillin-Resistant Staphylococcus aureus (MRSA) from Pigs and Farm Environment in Northwestern Italy

Swine farming as a source of methicillin-resistant Staphylococcus aureus (MRSA) has been well documented. Methicillin-resistant coagulase-negative staphylococci (MRCoNS) have been less studied, but their importance as pathogens is increasing. MRCoNS are indeed considered relevant nosocomial pathogens; identifying putative sources of MRCoNS is thus gaining importance to prevent human health hazards. In the present study, we investigated MRSA and MRCoNS in animals and environment in five pigsties in a high farm-density area of northwestern Italy. Farms were three intensive, one intensive with antibiotic-free finishing, and one organic. We tested nasal swabs from 195 animals and 26 environmental samples from three production phases: post-weaning, finishing and female breeders. Phenotypic tests, including MALDI-TOF MS, were used for the identification of Staphylococcus species; PCR and nucleotide sequencing confirmed resistance and bacterial species. MRCoNS were recovered in 64.5% of nasal swabs, in all farms and animal categories, while MRSA was detected only in one post-weaning sample in one farm. The lowest prevalence of MRCoNS was detected in pigs from the organic farm and in the finishing of the antibiotic-free farm. MRCoNS were mainly Staphylococcus sciuri, but we also recovered S. pasteuri, S. haemolyticus, S. cohnii, S. equorum and S. xylosus. Fifteen environmental samples were positive for MRCoNS, which were mainly S. sciuri; no MRSA was found in the farms’ environment. The analyses of the mecA gene and the PBP2-a protein highlighted the same mecA fragment in strains of S. aureus, S. sciuri and S. haemolyticus. Our results show the emergence of MRCoNS carrying the mecA gene in swine farms. Moreover, they suggest that this gene might be horizontally transferred from MRCoNS to bacterial species more relevant for human health, such as S. aureus.

S. aureus Biofilm Protein Expression Linked to Antimicrobial Resistance: A Proteomic Study

Simple Summary

Biofilm formation represents one of the most effective forms of bacterial persistence in surfaces where nutrients are available or in the tissues of living hosts as humans or animals. Such persistence is due to the high rate of antimicrobial resistance of this shell conformation. It often represents a burden when the pathogen colonizes niches from where it is not removable such as food facilities, farm facilities or parts of living organisms. In this study, we investigated biofilm formation mechanisms and enhanced antimicrobial resistance of 6 different S. aureus strains. The detected mechanisms were primarily related to the control of catabolites, the production of proteins with moonlighting activities and the detoxification of compounds with antimicrobial activities (i.e., alcohol). Glycolysis and aerobic metabolisms were found to be less active in the biofilm conformation. Consequently, less H₂O₂ production from aerobic metabolism was translated into a measurable under-representation of catalase protein.

Abstract

Antimicrobial resistance (AMR) represents one of the most critical challenges that humanity will face in the following years. In this context, a “One Health” approach with an integrated multidisciplinary effort involving humans, animals and their surrounding environment is needed to tackle the spread of AMR. One of the most common ways for bacteria to live is to adhere to surfaces and form biofilms. Staphylococcus aureus (S. aureus) can form biofilm on most surfaces and in a wide heterogeneity of environmental conditions. The biofilm guarantees the survival of the S. aureus in harsh environmental conditions and represents an issue for the food industry and animal production. The identification and characterization of biofilm-related proteins may provide interesting insights into biofilm formation mechanisms in S. aureus. In this regard, the aims of this study were: (i) to use proteomics to compare proteomes of S. aureus growing in planktonic and biofilm forms in order to investigate the common features of biofilm formation properties of different strains; (ii) to identify specific biofilm mechanisms that may be involved in AMR. The proteomic analysis showed 14 differentially expressed proteins among biofilm and planktonic forms of S. aureus. Moreover, three proteins, such as alcohol dehydrogenase, ATP-dependent 6-phosphofructokinase, and fructose-bisphosphate aldolase, were only differentially expressed in strains classified as high biofilm producers. Differentially regulated catabolites metabolisms and the switch to lower oxygen-related metabolisms were related to the sessile conformation analyzed.

The porcine respiratory microbiome: recent insights and future challenges

Understanding the structure of the respiratory microbiome and its complex interactions with opportunistic pathogenic bacteria has become a topic of great scientific and economic interest in livestock production, given the severe consequences of respiratory disease on animal health and welfare. The present review focuses on the microbial structures of the porcine upper and lower airways, and the factors that influence microbiome development and onset of respiratory disease. Following a literature search on PubMed and Scopus, 21 articles were selected based on defined exclusion criteria (20 studies performed by 16S rRNA gene sequencing and one by shotgun metagenomics). Analysis of the selected literature indicated that the microbial structure of the upper respiratory tract undergoes a remarkable evolution after birth and tends to stabilise around weaning. Antimicrobial treatment, gaseous ammonia concentration, diet and floor type are amongst the recognized environmental factors influencing microbiome structure. The predominant phyla of the upper respiratory tract are Proteobacteria and Firmicutes with significant differences at the genus level between the nasal and the oropharyngeal cavity. Only five studies investigated the lower respiratory tract and their results diverged in relation to the relative abundance of these two phyla and even more in the composition of the lung microbiome at the genus level, likely because of methodological differences. Reduced diversity and imbalanced microbial composition are associated with an increased risk of respiratory disease. However, most studies presented methodological pitfalls concerning specimen collection, sequencing target and depth, and lack of quality control. Standardization of sampling and sequencing procedures would contribute to a better understanding of the structure of the microbiota inhabiting the lower respiratory tract and its relationship with pig health and disease.

Assessment of the Antibiotic Resistance Profile, Genetic Heterogeneity and Biofilm Production of Methicillin-Resistant Staphylococcus aureus (MRSA) Isolated from The Italian Swine Production Chain

The main aim of the present study was to evaluate the level of antibiotic resistance, prevalence and virulence features of methicillin-resistant Staphylococcus aureus (MRSA) isolated from heavy swine at abattoir level and farming environments in Lombardy (Northern Italy). With this scope, 88 different heavy swine farms were surveyed, obtaining a total of n = 440 animal swabs and n = 150 environmental swabs. A total of n = 87 MRSA isolates were obtained, with an overall MRSA incidence of 17.50% (n = 77) among animal samples and a 6.67% (n = 10) among environmental. Molecular characterisation using multilocus sequence typing (MLST) plus spa-typing showed that sequence type ST398/t899 and ST398/t011 were the most commonly isolated genotypes, although other relevant sequence types such as ST1 or ST97 were also found. A lack of susceptibility to penicillins, tetracycline and ceftiofur was detected in >91.95, 85.05 and 48.28% of the isolates, respectively. Resistance to doxycycline (32.18%), enrofloxacin (27.59%) and gentamicin (25.29%) was also observed. Additionally, a remarkable level of antibiotic multiresistance (AMR) was observed representing a 77.01% (n = 67) of the obtained isolates. Genetic analysis revealed that 97.70% and 77.01% of the isolates harboured at least one antibiotic resistance or enterotoxin gene, respectively, pointing out a high isolate virulence potential. Lastly, 55.17% (n = 48) were able to produce measurable amounts of biofilm after 24 h. In spite of the current programmes for antibiotic reduction in intensively farming, a still on-going high level of AMR and virulence potential in MRSA was demonstrated, making this pathogen a serious risk in swine production chain, highlighting once more the need to develop efficient, pathogen-specific control strategies.

Antimicrobial prescriptions in cats in Switzerland before and after the introduction of an online antimicrobial stewardship tool

BACKGROUND

Antimicrobial stewardship activities are essential to improve prudent antimicrobial use. The aim of the present study was to evaluate changes in antimicrobial prescriptions in cats after the introduction of prudent use guidelines promoted by an online antimicrobial stewardship tool (AntibioticScout.ch) in Switzerland. Data from 792 cats presented to two university hospitals and 14 private practices in 2018 were included and compared to 776 cases from 2016. Cats were diagnosed with acute upper respiratory tract disease (aURTD), feline lower urinary tract disease (FLUTD) and abscesses. Clinical history, diagnostic work-up and antimicrobial prescriptions (class, dosage, duration) were assessed. Type and proportions [95% confidence intervals] of antimicrobial prescriptions were compared between the two evaluation periods and a mixed effects logistic regression model was applied to evaluate compliance with Swiss prudent use guidelines.

RESULTS

From 2016 to 2018, the proportion of antimicrobial prescription in all included cases decreased from 75.0% [71.8-78.0] to 66.7% [63.3-69.9]; this decrease was most pronounced for treatments at university hospitals (67.1% [59.5-74.0] to 49.3% [40.9-57.8]) and for cats with FLUTD (60.1% [54.6-65.4] to 48.8% [43.2-54.4]). Use of 3rd generation cephalosporins in private practices declined from 30.7% [26.5-35.1] to 22.1% [18.4-26.2], while overall use of non-potentiated aminopenicillins increased from 19.6% [16.4-23.0] to 27.8% [24.1-31.9]. In cases where antimicrobial therapy was indicated, compliance with guidelines did not increase (33.3% [26.6-40.6] to 33.5% [27.2-40.2]), neither at universities nor in private practices. On the other hand, antimicrobial treatment was more often withheld in cases with no indication for antimicrobial therapy (35.6% [30.1-41.4] to 54.0% [47.6-60.4]); this was found for private practices (26.7% [20.8-33.4] to 46.0% [38.4-53.7]) and for aURTD cases (35.0% [26.5-44.2] to 55.4% [44.7-65.8]).

CONCLUSIONS

Overall proportions of antimicrobial prescription, unjustified antimicrobial therapy and, in private practices, use of 3rd generation cephalosporins decreased from 2016 to 2018 for the investigated feline diseases. However, overall compliance with Swiss prudent use guidelines was still low, implying that further efforts are required to foster prudent antimicrobial use in cats.

Coagulase-positive methicillin-resistant Staphylococcus aureus circulating in clinical mastitic goats in Bangladesh

BACKGROUND AND AIM

Staphylococcus aureus is argued as one of the principal organisms responsible for mammary gland infection in lactating goats, causing both clinical and subclinical mastitis. Being highly zoonotic potential, pathogen emergence of methicillin-resistant S. aureus (MRSA) has a significant clinical impact on treatment and management of clinical mastitis. We conducted a cross-sectional study to investigate the prevalence of coagulase-positive S. aureus (CoPS), antimicrobial resistance profile of Staphylococcus spp., prevalence of MRSA, and association between different clinical parameters with CoPS.

MATERIALS AND METHODS

A total of 67 clinical mastitic goats were sampled based on clinical examination and California mastitis test. Standard bacteriological methods were performed to isolate and identify Staphylococcus spp. CoPS were confirmed by nuc gene using polymerase chain reaction (PCR). All staphylococcal isolates were further examined for antimicrobial susceptibility testing by disk diffusion method. MRSA was confirmed based on mecA gene-based PCR.

RESULTS

Here, 49 (73.13%; 95% confidence interval [CI], 61.41-82.35) samples were positive for Staphylococcus spp., of which 17 (34.69%; 95% CI, 22.88-48.73) isolates were CoPS and rest of the isolates (32; 65.30%; 95% CI, 51.27-77.12) were identified as coagulase-negative Staphylococcus spp. (coagulase-negative staphylococci [CNS]). Both, CoPS and CNS isolates displayed the highest resistance against tetracycline (76.47% and 75%, respectively) and oxacillin (70.58% and 68.75%, respectively). Notably, all staphylococcal isolates were multidrug-resistant (showed resistance to ≥3 classes of antimicrobials). mecA gene was found in 6 (8.96%; 95% CI, 3.84-18.52) CoPS isolates indicating MRSA strains. Among different clinical parameters, presence of high body temperature (p<0.05), firm udder consistency (p<0.01), bloodstained milk (p<0.00), and pus in milk (p<0.00) were significantly associated with the presence of CoPS in mastitic caprine milk.

CONCLUSION

To the best of our knowledge, this is the first report of MRSA isolated from clinical caprine mastitis cases in Bangladesh. The findings of this study would help in cautious selection as well as administration of antimicrobials for therapeutic management of mastitic goats.

In Vitro Efficacy of Essential Oils from Melaleuca Alternifolia and Rosmarinus Officinalis, Manuka Honey-based Gel, and Propolis as Antibacterial Agents Against Canine Staphylococcus Pseudintermedius Strains

Essential oils (EOs) and honeybee products (e.g., honey and propolis) are natural mixtures of different volatile compounds that are frequently used in traditional medicine and for pathogen eradication. The aim of this study was to evaluate the antibacterial properties of tea tree (Melaleuca alternifolia) EO (TTEO), Rosmarinus officinalis EO (ROEO), manuka-based gel, and propolis against 23 strains of Staphylococcus pseudintermedius (SP) isolated from canine pyoderma. Antimicrobial resistance screening was assessed using a panel of nine antimicrobial agents coupled with a PCR approach. An aromatogram was done for both EOs, using the disk diffusion method. The minimum inhibitory concentration (MIC) was determined for all the compounds. Among the 23 SP strains, 14 (60.9%) were multidrug-resistant (MDR), 11 strains (47.8%) were methicillin-resistant (MRSP), and 9 (39.1%) were non-MDR. The mean diameter of the inhibition zone for Melaleuca and Rosmarinus were 24.5 ± 8.8 mm and 15.2 ± 8.9 mm, respectively, resulting as statistically different (p = 0.0006). MIC values of TTEO and ROEO were similar (7.6 ± 3.2% and 8.9 ± 2.1%, respectively) and no statistical significances were found. Honeybee products showed lower MIC compared to those of EOs, 0.22 ± 0.1% for Manuka and 0.8 ± 0.5% for propolis. These findings reveal a significant antibacterial effect for all the tested products.

Prevalence of Livestock-Associated Methicillin-Resistant Staphylococcus Aureus (LA-MRSA) Among Farm and Slaughterhouse Workers in Italy

OBJECTIVE

We measured the prevalence of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in swine livestock workers, examined LA-MRSA resistance profile, and associated carriage with the working activities.

METHODS

Information was collected on demographics and occupational history. Swabs were collected and tested for the isolation of S. aureus, examined for antimicrobial susceptibility, and all MRSA underwent ST398qPCR assay.

RESULTS

LA-MRSA was isolated in 7.3% of the 396 enrolled workers. LA-MRSA colonization was more likely in farmers than in slaughterhouse workers (Fisher exact P = 0.001). Carriage was associated with herd size, being less frequent in small/medium farms (odds ratio = 0.20; 95% confidence interval = 0.07 to 0.53), and with the number of working days per week (OR = 2.11; 95% confidence interval = 1.07 to 4.19).

CONCLUSIONS

LA-MRSA carriage is strongly animal-exposure related, and educational intervention informing about the risks related to the activity with livestock is needed.

Dogs as reservoir of methicillin resistant coagulase negative staphylococci strains - A possible neglected risk

The antibiotic resistance among coagulase - negative Staphylococcus (CoNS) species towards methicillin is rarely reported in veterinary medicine. Under the aspect/concept of One Health, those strains pose a risk to human health due to the presence in canine pets where the transfer of resistant genetic markers might occur to other staphylococci species. The aim of this study was to investigate the antimicrobial resistance pattern among Coagulase Negative Staphylococci (CoNS) isolated from asymptomatic dogs and those affected by topic infections. Swabs from 254 dogs were first seeded in Mannitol Salt Agar. Species identification was conducted by Matrix Assisted Laser Desorption ionization - time of flight (MALDI-TOF ms) as previously described. The susceptibility test was performed by disk diffusion according to CLSI standards. Detection of mecA gene was performed. CoNS could be recovered from both groups of dogs and an alarming presence of methicillin-resistant coagulase negative staphylococci (MRCoNS) was confirmed, in 10.2% (17/166) of the samples. Eight of those methicillin resistant strains were isolated from asymptomatic dogs whereas nine were present in dogs affected by pyoderma and otitis externa.

Prevalence and characterization of methicillin-resistant Staphylococcus pseudintermedius from symptomatic companion animals in Northern Italy: Clonal diversity and novel sequence types

The aim of this study was to assess the prevalence, the genotypic diversity, the antimicrobial resistance traits of canine and feline clinical methicillin-resistant Staphylococcus pseudintermedius (MRSP) isolates in a diagnostic laboratory in Italy during 2015-2016. All isolates were characterized by multilocus sequence typing (MLST), staphylococcal cassette chromosome (SCC)-mec typing and staphylococcal protein A (spa)-typing. The resistance profiles were assessed by antimicrobial susceptibility testing and confirmed genotypically by the detection of mecA gene and by microarray analyses. The prevalence of MRSP isolates was high (31.6%). All the strains were multidrug resistant and the most frequent clone was ST71-SCCmec type II-III. These results confirm a high prevalence of MRSP amongst clinical samples from pets in Italy. These isolates show multidrug resistance features that are of concern both in veterinary and human medicine for clinical and epidemiological reasons.

Outbreaks of a Methicillin-Resistant Staphylococcus aureus Clone ST398-t011 in a Hungarian Equine Clinic: Emergence of Rifampicin and Chloramphenicol Resistance After Treatment with These Antibiotics

Between July 2011 and May 2016, a total of 40 Staphylococcus aureus strains originating from 36 horses were confirmed as methicillin resistant (methicillin-resistant Staphylococcus aureus [MRSA]) in a university equine clinic. An additional 10 MRSA strains from 36 samples of clinic workers were obtained in October 2017. The first equine isolate represented the sequence type ST398, spa-type t011, and SCCmec IV. This isolate was resistant to a wide spectrum of antimicrobial agents. MRSA strains with the same genotype and with very similar resistance profiles were isolated on 21 more occasions from September 2013 to September 2014. A second outbreak occurred from May 2015 until May 2016. The first isolate in this second outbreak shared the same genotype, but was additionally resistant to chloramphenicol. The second isolate from August 2015 also showed resistance to rifampicin. The clone was isolated 18 times. Most of the human isolates shared the same genotype as the isolates from horses and their resistance patterns showed only slight differences. We can conclude that the MRSA-related cases at the Department and Clinic of Equine Medicine were all nosocomial infections caused by the same clonal lineage belonging to the clonal complex 398. The clonal complex 398 of equine origin is reported for the first time in Hungary. In addition, our observation of the emergence of new resistance to antimicrobial agents within the clonal lineage after treatment with antibiotics is of concern. Strict hygiene regulations have been introduced to lower the incidence of MRSA isolation and the related clinical disease.

Genetic Profiling and Comparison of Human and Animal Methicillin-Resistant Staphylococcus aureus (MRSA) Isolates from Serbia

The aim of this study was to characterize a collection of methicillin-resistant Staphylococcus aureus (MRSA) isolates of human and animal origin from Serbia. In total, 36 MRSA isolates-30 obtained from humans and six from companion animals-were investigated by PCR for the presence of antibiotic and biocide resistance determinants and virulence genes (PVL-Panton⁻Valentine leukocidin, ETs-exfoliative toxins, TSST-toxic shock syndrome toxin, SEs-staphylococcal enterotoxins, and MSCRAMMs-microbial surface components recognizing adhesive matrix molecules and biofilm). Isolates were analyzed by staphylococcal cassette chromosome mec (SCCmec), spa, and dru typing, as well as by multiple locus variable number of tandem repeat analyses (MLVA), multilocus sequence typing (MLST), and subsequently, eBURST. The majority of human MRSA isolates were resistant to gentamicin, erythromycin, clindamycin, and ciprofloxacin. Different antibiotic resistance genes were detected: aac-aphD, ant(6')-Ia, erm(A), erm(B), erm(C), tet(K), tet(M), fexA, and catpC221. All isolates were susceptible to teicoplanin and linezolid. SCCmec type III was prevalent in human isolates, while SCCmec elements in animals were mostly nontypeable. t037 was the predominant spa type in human and t242 in animal MRSA isolates. The prevalent dru type was dt11c in human and dt10a in animal MRSA isolates. MRSA isolates exhibited 27 different MLVA types. ST239 was predominant in human, while ST5 was prevalent in canine MRSA isolates. PVL was found in two, while tsst-1 was detected in three human isolates. Human-associated clones belonging to ST5, ST45, and ST239 MRSA clones were discovered in companion animals, which suggests anthropozoonotic transmission.

Genetic characterisation of methicillin-resistant Staphylococcus aureus and Staphylococcus pseudintermedius in pets and veterinary personnel in Iran: new insights into emerging methicillin-resistant S. pseudintermedius (MRSP)

OBJECTIVES

Methicillin-resistant staphylococci, including methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP), pose a threat to animal and human health worldwide. Veterinary staff and pets may play a role in the spread of resistant clones.

METHODS

A total of 125 samples from veterinary staff (n=50), dogs (n=49) and cats (n=26) were investigated. Obtained isolates were tested for the methicillin resistance gene mecA and were subjected to multiplex PCR to differentiate coagulase-positive species. Following SCCmec and spa typing, isolates were tested for the presence of various toxin and virulence genes and phenotypic resistance to common antimicrobials.

RESULTS

Overall, 4 MRSA were isolated from two veterinarians and two dogs and 19 MRSP were found in eleven dogs (12 isolates) and five cats (7 isolates). The MRSA isolates possessed sea (2) and eta (3) virulence genes and the MRSP isolates possessed sea (6), expA (15), expB (1) and siet (19) genes. SCCmec type II and three spa types (t186, t1816 and t10897) were identified in the MRSA isolates. Most of the MRSP isolates belonged to SCCmec types II (2 isolates) and V (10 isolates); however, the remaining 7 isolates were untypeable and contained class C1 mec. The majority of isolates were multidrug-resistant (MDR).

CONCLUSION

These findings show that pets and veterinarians could be potential sources of MDR-MRSA and MDR-MRSP in Iran. Taken together, these findings warrant future investigations on the epidemiology and public-health significance of MDR-MRSA and MDR-MRSP both in veterinarians and companion animals in Iran.

Mechanistic modelling of interventions against spread of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) within a Danish farrow-to-finish pig herd

Knowledge on successful interventions against livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) within pig herds is sparse. In situations like this, a mechanistic simulation model can be a valuable tool for assessing the effect of potential intervention strategies, and prioritising which should be tested in the field. We have simulated on-farm interventions in a farrow-to-finish pig herd, with a previously published LA-MRSA spread model, within four different areas: 1) Reduced antimicrobial consumption, 2) Reduced number of pigs within each section, 3) Reduced mixing of pigs, and 4) Improved internal biosecurity. To model a decrease in the selective pressure, the transmission rates were reduced after LA-MRSA had become fully established within a herd, which resulted in a marked decrease in the prevalence within all stable units. However, LA-MRSA rarely disappeared completely from the herd; this was only observed in scenarios where the transmission rates were reduced to ≤ 30% of the original level. While changes in antimicrobial consumption patterns might be a very important step towards reducing the spread of LA-MRSA, the simulation results indicate that it may need to be paired with other preventive or intervention measures. Reducing the number of pigs within each section, reducing mixing of pigs, or improving internal biosecurity after LA-MRSA had become established within the herd only resulted in marginal changes in the median prevalence within the herd. However, these factors might be important in relation to being able to achieve or maintain a low level of antimicrobial consumption, and thus still indirectly influence the LA-MRSA prevalence within the herd. The results of a sensitivity analysis indicated the assumptions regarding the existence of pigs persistently shedding MRSA have a noticeable influence on the model results. The assumptions regarding transmission from sow to offspring at the day of birth also had a considerable influence on the MRSA prevalence within the farrowing unit but did not cause any marked changes in the simulated effect of interventions. Effects might differ between different farm types contaminated in different levels and this simulation study highlights a strong need for more knowledge from on-farm trials.

Quantitative PCR coupled with sodium dodecyl sulfate and propidium monoazide for detection of viable Staphylococcus aureus in milk

Conventional quantitative PCR (qPCR) are unable to differentiate DNA of viable Staphylococcus aureus cells from dead ones. The aim of this study was to use sodium dodecyl sulfate (SDS) and propidium monoazide (PMA) coupled with lysostaphin to detect viable Staph. aureus. The cell suspensions were treated with SDS and PMA before DNA extraction. The SDS is an anionic surfactant, which can increase the permeability of dead cells to PMA without compromising the viability of live cells. The lysostaphin was applied to improve the effectiveness of DNA extraction. The reliability and specificity of this method were further determined by the detection of Staph. aureus in spiked milk. The results showed that there were significant differences between the SDS-PMA-qPCR and qPCR when a final concentration of 200 μg/mL of lysostaphin was added in DNA extraction. The viable Staph. aureus could be effectively detected when SDS and PMA concentrations were 100 µg/mL and 40 μM, respectively. Compared with conventional qPCR, the SDS-PMA-qPCR assay coupled with lysostaphin was more specific and sensitive. Therefore, this method could accurately detect the number of viable Staph. aureus cells.

A mechanistic model for spread of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) within a pig herd

Before an efficient control strategy for livestock-associated methicillin resistant Staphylococcus aureus (LA-MRSA) in pigs can be decided upon, it is necessary to obtain a better understanding of how LA-MRSA spreads and persists within a pig herd, once it is introduced. We here present a mechanistic stochastic discrete-event simulation model for spread of LA-MRSA within a farrow-to-finish sow herd to aid in this. The model was individual-based and included three different disease compartments: susceptible, intermittent or persistent shedder of MRSA. The model was used for studying transmission dynamics and within-farm prevalence after different introductions of LA-MRSA into a farm. The spread of LA-MRSA throughout the farm mainly followed the movement of pigs. After spread of LA-MRSA had reached equilibrium, the prevalence of LA-MRSA shedders was predicted to be highest in the farrowing unit, independent of how LA-MRSA was introduced. LA-MRSA took longer to spread to the whole herd if introduced in the finisher stable, rather than by gilts in the mating stable. The more LA-MRSA positive animals introduced, the shorter time before the prevalence in the herd stabilised. Introduction of a low number of intermittently shedding pigs was predicted to frequently result in LA-MRSA fading out. The model is a potential decision support tool for assessments of short and long term consequences of proposed intervention strategies or surveillance options for LA-MRSA within pig herds.

Antimicrobial policies in animals and human health

This invited commentary aims to highlight 3 recommendations to rationalize antimicrobial consumption in livestock, in order to minimize the spread of resistant bacteria and simultaneously safeguarding animal and public health.

Genetic characterization and antimicrobial resistance of Staphylococcus aureus isolated from bovine milk in Tunisia

Staphylococcus aureus is a major agent of bovine mastitis in dairy herds, causing economic losses in dairy industry worldwide. In addition, milk and milk-products contaminated by Staph. aureus can cause harmful human diseases. The aim of this study was to characterize Staph. aureus strains isolated from dairy farms in Tunisia. Bulk tank milk (n = 32) and individual cow milk (n = 130) samples were collected during the period of 2013-2014. Forty-three Staph. aureus isolates were recovered and typed by spa typing, 16S-23S rRNA intergenic spacer (RS-PCR) and multiplex PCRs for 22 virulence genes. Antimicrobial resistance was also investigated with a disc diffusion test. A selected subsample of 22 strains was additionally genotyped by multilocus sequence typing. Seventeen spa types were recovered, and t2421 (n = 10), t521 (n = 6) and t2112 (n = 5) were the most common. Fourteen different RS-PCR genotypes grouped into 11 clusters were detected in our study, with predominance of the R^VI genotype (n = 24). Eight sequence types were identified and Clonal Complex 97, corresponding to RS-PCR cluster R, was the most common (n = 10), followed by CC1 (n = 4), CC15 (n = 3) and other four accounting for one or two strains. Different combinations of virulence genes were reported, and enterotoxin genes were present in few strains (seh, n = 4; sea, n = 2; sea and seh, n = 2; sec and sel, n = 2). The majority of strains were resistant only to penicillin; only one strain was found to be multiresistant and no methicillin-resistant Staph. aureus was demonstrated. Our study reported the isolation of CC97 from bovine milk in Tunisia for the first time and confirmed the relevance of this lineage in intramammary infection in cows.

SIGNIFICANCE AND IMPACT OF THE STUDY

This paper describes the characteristics of Staphylococcus aureus isolated from bulk tank and individual cow milk in Tunisia. All strains were genotyped by spa typing and RS-PCR, a method based on the amplification of the 16S-23S rRNA intergenic spacer region, and multiplex PCRs for 22 virulence genes. A selected subsample of strains was also genotyped by multilocus sequence typing. All strains were tested for antimicrobial resistance. Our study evidences a predominance of strains belonging to Clonal Complex 97. Methicillin-resistant strains were not detected, and overall low level of antimicrobial resistance was reported.

Prevalence of Staphylococcus aureus and of methicillin-resistant S. aureus clonal complexes in bulk tank milk from dairy cattle herds in Lombardy Region (Northern Italy)

Staphylococcus aureus is the most important causative agent of subclinical mastitis in cattle resulting in reduced milk production and quality. Methicillin-resistant S. aureus (MRSA) strains has a clear zoonotic relevance, especially in the case of occupational exposure. The aim of the study was to evaluate the prevalence of S. aureus and MRSA in bulk tank milk (BTM) from dairy cattle herds in the Lombardy Region (Northern Italy) and to identify the main MRSA circulating genotypes. MRSA strains were characterized by susceptibility testing, multi-locus sequence typing (MLST), spa typing and SCCmec typing. A total 844 BTM samples were analysed and S. aureus and MRSA were detected in 47·2% and 3·8% of dairy herds, respectively. MLST showed that the majority (28/32) of isolates belonged to the typical livestock-associated lineages: ST398, ST97 and ST1. Interestingly, in this study we report for the first time the new ST3211, a single locus variant of ST(CC)22, with the newly described 462 aroE allele. Our study indicates high diffusion of S. aureus mastitis and low, but not negligible, prevalence of MRSA in the considered area, suggesting the need for planning specific control programmes for bovine mastitis caused by S. aureus, especially when MRSA is implicated.

Differential Analysis of the Nasal Microbiome of Pig Carriers or Non-Carriers of Staphylococcus aureus

Staphylococcus aureus is presently regarded as an emerging zoonotic agent due to the spread of specific methicillin-resistant S. aureus (MRSA) clones in pig farms. Studying the microbiota can be useful for the identification of bacteria that antagonize such opportunistic veterinary and zoonotic pathogen in animal carriers. The aim of this study was to determine whether the nasal microbiome of pig S. aureus carriers differs from that of non-carriers. The V3-V5 region of the 16S rRNA gene was sequenced from nasal swabs of 44 S. aureus carriers and 56 non-carriers using the 454 GS FLX titanium system. Carriers and non-carriers were selected on the basis of quantitative longitudinal data on S. aureus carriage in 600 pigs sampled at 20 Danish herds included in two previous studies in Denmark. Raw sequences were analysed with the BION meta package and the resulting abundance matrix was analysed using the DESeq2 package in R to identify operational taxonomic units (OTUs) with differential abundance between S. aureus carriers and non-carriers. Twenty OTUs were significantly associated to non-carriers, including species with known probiotic potential and antimicrobial effect such as lactic acid-producing isolates described among Leuconostoc spp. and some members of the Lachnospiraceae family, which is known for butyrate production. Further 5 OTUs were significantly associated to carriage, including known pathogenic bacteria such as Pasteurella multocida and Klebsiella spp. Our results show that the nasal microbiome of pigs that are not colonized with S. aureus harbours several species/taxa that are significantly less abundant in pig carriers, suggesting that the nasal microbiota may play a role in the individual predisposition to S. aureus nasal carriage in pigs. Further research is warranted to isolate these bacteria and assess their possible antagonistic effect on S. aureus for the pursuit of new strategies to control MRSA in pig farming.

Antimicrobial synergy between carprofen and doxycycline against methicillin-resistant Staphylococcus pseudintermedius ST71

Background

New therapeutic strategies are needed to face the rapid spread of multidrug-resistant staphylococci in veterinary medicine. The objective of this study was to identify synergies between antimicrobial and non-antimicrobial drugs commonly used in companion animals as a possible strategy to restore antimicrobial susceptibility in methicillin-resistant Staphylococcus pseudintermedius (MRSP).

Results

A total of 216 antimicrobial/non-antimicrobial drug combinations were screened by disk diffusion using a clinical MRSP sequence type (ST) 71 strain resistant to all six antimicrobials tested (ampicillin, ciprofloxacin, clindamycin, doxycycline, oxacillin and trimethoprim/sulfamethoxazole). The most promising drug combination (doxycycline-carprofen) was further assessed by checkerboard testing extended to four additional MRSP strains belonging to ST71 or ST68, and by growth inhibition experiments.

Seven non-antimicrobial drugs (bromhexine, acepromazine, amitriptyline, clomipramine, carprofen, fluoxetine and ketoconazole) displayed minimum inhibitory concentrations (MICs) ranging between 32 and >4096 mg/L, and enhanced antimicrobial activity of one or more antimicrobials. Secondary screening by checkerboard assay revealed a synergistic antimicrobial effect between carprofen and doxycycline, with the sum of the fractional inhibitory concentration indexes (ΣFICI) ranging between 0.3 and 0.5 depending on drug concentration. Checkerboard testing of multiple MRSP strains revealed a clear association between synergy and carriage of tetK, which is a typical feature of MRSP ST71. An increased growth inhibition was observed when MRSP ST71 cells in exponential phase were exposed to 0.5/32 mg/L of doxycycline/carprofen compared to individual drug exposure.

Conclusions

Carprofen restores in vitro susceptibility to doxycycline in S. pseudintermedius strains carrying tetK such as MRSP ST71. Further research is warranted to elucidate the molecular mechanism behind the identified synergy and its linkage to tetK.

Methicillin-resistant and methicillin-susceptible Staphylococcus aureus in dairy sheep and in-contact humans: An intra-farm study

Staphylococcus aureus is involved in a wide variety of diseases in humans and animals, and it is considered one of the most significant etiological agents of intramammary infection in dairy ruminants, causing both clinical and subclinical infections. In this study, the intra-farm prevalence and circulation of methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) were investigated on an Italian dairy sheep farm previously identified as MRSA-positive by testing bulk tank milk (first isolation in 2012). Human samples (nasal swabs, hand skin samples, and oropharyngeal swabs) from 3 persons working in close contact with the animals were also collected, and the genetic characteristics and relatedness of the MRSA isolates from human and animal sources within the farm were investigated. After 2yr from the first isolation, we confirmed the presence of the same multidrug-resistant strain of MRSA sequence type (ST)1, clonal complex (CC)1, spa type t127, staphylococcal cassette chromosome mec (SCCmec) type IVa, showing identical pulsed field gel electrophoresis (PFGE) and resistance profiles at the farm level in bulk tank milk. Methicillin-resistant S. aureus isolates were detected in 2 out of 556 (0.34%) individual milk samples, whereas MSSA isolates were detected in 10 samples (1.8%). The MRSA were further isolated from udder skin samples from the 2 animals that were MRSA-positive in milk and in 2 of the 3 examined farm personnel. All MRSA isolates from both ovine and human samples belonged to ST(CC)1, spa type t127, SCCmec type IVa, with some isolates from animals harboring genes considered markers of human adaptation. In contrast, all MSSA isolates belonged to ruminant-associated CC130, ST700, spa type t528. Analysis by PFGE performed on selected MRSA isolates of human and animal origin identified 2 closely related (96.3% similarity) pulsotypes, displaying only minimal differences in gene profiles (e.g., presence of the immune evasion cluster genes). Although we observed low MRSA intra-farm prevalence, our findings highlight the importance of considering the possible zoonotic potential of CC1 livestock-associated MRSA, in view of the ability to persist over years at the farm level. Biosecurity measures and good hygiene practices could be useful to prevent MRSA spread at the farm level and to minimize exposure in the community and in categories related to farm animal industry (e.g., veterinarians, farmers, and farm workers).

Individual predisposition to Staphylococcus aureus colonization in pigs on the basis of quantification, carriage dynamics, and serological profiles

Previous research on Staphylococcus aureus in pigs focused on livestock-associated methicillin-resistant S. aureus (MRSA) and had a qualitative cross-sectional design. This study aimed to elucidate the frequency, load, and stability of S. aureus nasal carriage in pigs over time and investigated possible associations between carriage and immune response. Nasal swabs were collected three times weekly from 480 tagged adult pigs in 20 Danish production farms. S. aureus and MRSA were quantified on selective media by the most-probable-number method. The levels of IgG against 10 S. aureus antigens in serum were quantified in selected pigs by a Luminex assay. All the farms were positive for S. aureus and 15 for MRSA, leading to overall prevalences of persistent and intermittent carriers and noncarriers of 24, 52, and 23%, respectively. Carriage frequency and nasal loads were significantly higher on MRSA-positive farms. Logistic-regression modeling revealed the presence of individual pigs characterized by high nasal loads (>10,000 CFU per swab) and stable carriage regardless of farm- and pen-associated factors. On the other hand, the humoral response was strongly influenced by these environmental factors. The existence of a minority of shedders contributing to maintenance of S. aureus within farms opens up new perspectives on the control of MRSA in pig farming.

Human health risks associated with antimicrobial-resistant enterococci and Staphylococcus aureus on poultry meat

Enterococci and staphylococci are frequent contaminants on poultry meat. Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus are also well-known aetiological agents of a wide variety of infections resulting in major healthcare costs. This review provides an overview of the human health risks associated with the occurrence of these opportunistic human pathogens on poultry meat with particular focus on the risk of food-borne transmission of antimicrobial resistance. In the absence of conclusive evidence of transmission, this risk was inferred using data from scientific articles and national reports on prevalence, bacterial load, antimicrobial resistance and clonal distribution of these three species on poultry meat. The risks associated with ingestion of antimicrobial-resistant enterococci of poultry origin comprise horizontal transfer of resistance genes and transmission of multidrug-resistant E. faecalis lineages such as sequence type ST16. Enterococcus faecium lineages occurring in poultry meat products are distantly related to those causing hospital-acquired infections but may act as donors of quinupristin/dalfopristin resistance and other resistance determinants of clinical interest to the human gut microbiota. Ingestion of poultry meat contaminated with S. aureus may lead to food poisoning. However, antimicrobial resistance in the toxin-producing strains does not have clinical implications because food poisoning is not managed by antimicrobial therapy. Recently methicillin-resistant S. aureus of livestock origin has been reported on poultry meat. In theory handling or ingestion of contaminated meat is a potential risk factor for colonization by methicillin-resistant S. aureus. However, this risk is presently regarded as negligible by public health authorities.

A Livestock-Associated, Multidrug-Resistant, Methicillin-Resistant Staphylococcus aureus Clonal Complex 97 Lineage Spreading in Dairy Cattle and Pigs in Italy

Pandemic methicillin-resistant Staphylococcus aureus (MRSA) clonal complex 97 (CC97) lineages originated from livestock-to-human host jumps. In recent years, CC97 has become one of the major MRSA lineages detected in Italian farmed animals. The aim of this study was to characterize and analyze differences in MRSA and methicillin-susceptible S. aureus (MSSA) mainly of swine and bovine origins. Forty-seven CC97 isolates, 35 MRSA isolates, and 6 MSSA isolates from different Italian pig and cattle holdings; 5 pig MRSA isolates from Germany; and 1 human MSSA isolate from Spain were characterized by macrorestriction pulsed-field gel electrophoresis (PFGE) analysis, multilocus sequence typing (MLST), spa typing, staphylococcal cassette chromosome mec (SCCmec) typing, and antimicrobial resistance pattern analysis. Virulence and resistance genes were investigated by PCR and microarray analysis. Most of the isolates were of SCCmec type V (SCCmec V), except for two German MRSA isolates (SCCmec III). Five main clusters were identified by PFGE, with the German isolates (clusters I and II) showing 60.5% similarity with the Italian isolates, most of which (68.1%) grouped into cluster V. All CC97 isolates were Panton-Valentine leukocidin (PVL) negative, and a few (n = 7) tested positive for sak or scn. All MRSA isolates were multidrug resistant (MDR), and the main features were erm(B)- or erm(C)-mediated (n = 18) macrolide-lincosamide-streptogramin B resistance, vga(A)-mediated (n = 37) pleuromutilin resistance, fluoroquinolone resistance (n = 33), tet(K) in 32/37 tet(M)-positive isolates, and blaZ in almost all MRSA isolates. Few host-associated differences were detected among CC97 MRSA isolates: their extensive MDR nature in both pigs and dairy cattle may be a consequence of a spillback from pigs of a MRSA lineage that originated in cattle as MSSA and needs further investigation. Measures should be implemented at the farm level to prevent spillover to humans in intensive farming areas.

Antimicrobial stewardship in small animal veterinary practice: from theory to practice

Despite the increasing recognition of the critical role for antimicrobial stewardship in preventing the spread of multidrug-resistant bacteria, examples of effective antimicrobial stewardship programs are rare in small animal veterinary practice. This article highlights the basic requirements for establishing stewardship programs at the clinic level. The authors provide suggestions and approaches to overcome constraints and to move from theoretic concepts toward implementation of effective antimicrobial stewardship programs in small animal clinics.

Short communication: Prevalence of Staphylococcus aureus and methicillin-resistant S. aureus in bulk tank milk from dairy goat farms in Northern Italy

Staphylococcus aureus is regarded as a leading cause of mastitis in goats. However, few data are available on the presence of methicillin-resistant S. aureus (MRSA) in this species. The aim of this study was to assess the prevalence of S. aureus and MRSA in bulk tank milk samples from dairy goat farms in Northern Italy. Eighty-five out of 197 samples (43.1%) tested positive for S. aureus with counts ranging from 10 to more than 1.5 × 10(4) cfu/mL. The MRSA was screened by both direct plating followed by a disk diffusion test to evaluate methicillin resistance and a selective enrichment method. Methicillin-resistance was confirmed by mecA-specific PCR. Methicillin-resistant S. aureus was identified in 4 samples (2.0%) and multilocus sequence typing (MLST) showed the presence of livestock-associated MRSA belonging to lineages ST398 (n = 3) and ST1 (n = 1). In one case we demonstrated that the same MRSA strain was able to persist over time on the farm, being isolated from both bulk tank milk and the udder of 3 goats 1 yr after the first isolation. The high prevalence of S. aureus-positive herds detected in this study and the presence of MRSA strains belonging to livestock-associated genotypes is of concern, and represents a novel finding in the Italian dairy goat production system. The application of stringent measures for the control of S. aureus mastitis at the farm level seems appropriate to reduce the economic losses, and to minimize the risk of foodborne illness and the transmission of MRSA to humans by occupational exposure.

Sixty years of antimicrobial use in animals: what is next?

This, the last in our series of feature articles celebrating 125 years of Veterinary Record, aims to provide an overview of antimicrobial use in animals. Starting with a journey through the history of antimicrobial use in animals, Luca Guardabassi gives his opinion on the current zoonotic risks associated with antimicrobial resistance and on how these risks might be tackled in the years to come.

Changes in Chinese policies to promote the rational use of antibiotics

Xonghong Xiao and colleagues analyze the challenge of antimicrobial resistance in China. A government strategy to promote rational use of antimicrobials in health care reduced antibiotic sales and percentage of prescriptions for antimicrobials for both hospitalized patients and outpatients, and offers insights to shape future initiatives. Please see later in the article for the Editors' Summary.