Antimicrobial resistance and resistance genes in Staphylococcus aureus strains from rabbits

Retrospective analysis of antimicrobial resistance in bacterial pathogens from pet rabbits in Hong Kong, 2019-2022

Antimicrobial resistance (AMR) is a growing threat to human and animal health. Data are limited on the prevalence of resistant bacteria in pet rabbits. Therefore, we aimed to identify prevalent bacterial infections and AMR profiles among pet rabbits in Hong Kong (HK). Our search of the CityU Veterinary Diagnostic Laboratory (VDL) database found 301 cases of pet rabbits submitted for bacteriologic and antimicrobial susceptibility testing by veterinarians at 20 exotic veterinary clinics across HK between 2019 and 2022. The rabbits were of 8 different breeds and had a median age of 6.5 y, with 54.8% males, 40.2% females, and 5% unspecified. Of the 301 samples received, 168 (55.8%) had positive bacterial growth; 125 (74.4%) had single bacterial isolates, and 43 (25.6%) had mixed cultures. Cultures included Enterococcus faecalis (21.3%) as the most frequently isolated gram-positive bacterium, followed by Streptococcus intermedius (12.5%), and Staphylococcus aureus (11.3%). The most frequently isolated gram-negative bacteria were Pseudomonas aeruginosa (18.1%), followed by Escherichia coli (8.3%), Pasteurella multocida (6.9%), and Klebsiella pneumoniae (4.2%). Approximately 83% of the isolates had acquired resistance to at least one antimicrobial agent, and 49.4% were multidrug-resistant. The isolated bacteria had high levels of resistance to penicillin (69.8%), clindamycin (47.4%), and doxycycline (46.9%). Our findings highlight the high levels of AMR in bacteria isolated from pet rabbit clinical samples in HK; many of these bacteria are zoonotic and pose a public health threat.

Investigation of antimicrobial resistance and antimicrobial resistance genes in Staphylococcus aureus and coagulase-negative staphylococci isolated from rabbit

Background and Aim

Staphylococci, which inhabit skin and mucous membranes in humans and animals, are opportunistic pathogens. Coagulase-positive and coagulase-negative staphylococci (CoNS) are the two main groups. Clinical abscesses in rabbits often harbor Staphylococcus aureus and CoNS. This study estimated S. aureus and CoNS prevalence, resistance profiles, antimicrobial-resistant genes, and the accessory gene regulator (agr) group in rabbit clinical abscesses.

Materials and Methods

Sixty-seven abscesses were gathered from 67 rabbits who visited Prasu-Arthorn Animal Hospital in Nakornpathom, Thailand, from January 2014 to October 2015. Thirty-four subcutaneous, 29 dental, 2 ocular, 1 mammary gland, and 1 uterine abscess were present. Conventional methods, including Gram staining, mannitol fermentation, hemolysis on blood agar, catalase testing, and coagulase production, identified and isolated S. aureus and CoNS from all abscesses. All S. aureus and CoNS isolates underwent antimicrobial susceptibility testing using the disk diffusion method. Polymerase chain reaction was used to detect the presence of blaZ, aacA-aphD, msrA, tetK, gyrA, grlA, dfrG, and cfr antimicrobial-resistant genes. Methicillin resistance was identified through the detection of a cefoxitin-resistant phenotype and the presence of mecA gene. Further investigation was conducted on the agr group of S. aureus isolates.

Results

In 67 abscesses, we found 19 S. aureus isolates in 9 abscesses (13.43%) and 37 CoNS isolates in 18 abscesses (26.87%), both majorly located at subcutaneous sites. About 59.46% of CoNS isolates were methicillin-resistant compared to 5.26% of S. aureus isolates. Methicillin-resistant S. aureus (MRSA) and methicillin-resistant CoNS (MRCoNS) both displayed multidrug resistance (MDR). Both MRSA and MRCoNS expressed multiple antimicrobial resistance genes, including blaZ, aacA-aphD, gyrA, grlA, msrA, tetK, and dfrG. Approximately 73.68% of the agr groups were agr I, 15.79% were agr III, and 10.53% were agr II.

Conclusion

This study found a high prevalence of MRCoNS with antimicrobial resistance and multiple antimicrobial-resistant genes in rabbits with clinical abscesses. The effectiveness of antibiotics against infections caused by such strains is a matter of concern. Owners should be educated about the importance of good hygiene practices and judicious antibiotic use to prevent widespread antimicrobial resistance.

Occurrence of antimicrobial resistance and antimicrobial resistance genes in methicillin-resistant Staphylococcus aureus isolated from healthy rabbits

Background and Aim

Methicillin-resistant globally, Staphylococcus aureus (MRSA) is a major cause of disease in both humans and animals. Several studies have documented the presence of MRSA in healthy and infected animals. However, there is less information on MRSA occurrence in exotic pets, especially healthy rabbits. This study aimed to look into the antimicrobial resistance profile, hidden antimicrobial-resistant genes in isolated bacteria, and to estimate prevalence of MRSA in healthy rabbits.

Materials and Methods

Two-hundreds and eighteen samples, including 42 eyes, 44 ears, 44 oral, 44 ventral thoracic, and 44 perineal swabs, were taken from 44 healthy rabbits that visited the Prasu-Arthorn Animal Hospital, in Nakornpathom, Thailand, from January 2015 to March 2016. The traditional methods of Gram stain, mannitol fermentation, hemolysis on blood agar, catalase test, and coagulase production were used to confirm the presence of Staphylococcus aureus in all specimens. All bacterial isolates were determined by antimicrobial susceptibility test by the disk diffusion method. The polymerase chain reaction was used to identify the antimicrobial-resistant genes (blaZ, mecA, aacA-aphD, msrA, tetK, gyrA, grlA, and dfrG) in isolates of MRSA with a cefoxitin-resistant phenotype.

Results

From 218 specimens, 185 S. aureus were isolated, with the majority of these being found in the oral cavity (29.73%) and ventral thoracic area (22.7%), respectively. Forty-seven (25.41%) MRSAs were found in S. aureus isolates, with the majority of these being found in the perineum (16, 34.04%) and ventral thoracic area (13, 27.66%) specimens. Among MRSAs, 29 (61.7%) isolates were multidrug-resistant (MDR) strains. Most of MRSA isolates were resistant to penicillin (100%), followed by ceftriaxone (44.68%) and azithromycin (44.68%). In addition, these bacteria contained the most drug-resistance genes, blaZ (47.83%), followed by gyrA (36.17%) and tetK (23.4%).

Conclusion

This study revealed that MRSA could be found even in healthy rabbits. Some MRSAs strains were MDR-MRSA, which means that when an infection occurs, the available antibiotics were not effective in treating it. To prevent the spread of MDR-MRSA from pets to owners, it may be helpful to educate owners about effective prevention and hygiene measures.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): antimicrobial-resistant Staphylococcus aureus in cattle and horses

Staphylococcus aureus (S. aureus) was identified among the most relevant antimicrobial-resistant (AMR) bacteria in the EU for cattle and horses in previous scientific opinions. Thus, it has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as in Article 9, and Article 8 for listing animal species related to the bacterium. The assessment has been performed following a methodology previously published. The outcome is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with uncertain outcome. According to the assessment here performed, it is uncertain whether AMR S. aureus can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (60-90% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that the bacterium does not meet the criteria in Sections 1, 2 and 4 (Categories A, B and D; 1-5%, 5-10% and 10-33% probability of meeting the criteria, respectively) and the AHAW Panel was uncertain whether it meets the criteria in Sections 3 and 5 (Categories C and E, 33-90% and 60-90% probability of meeting the criteria, respectively). The animal species to be listed for AMR S. aureus according to Article 8 criteria include mainly mammals, birds, reptiles and fish.

Treatment efficacy of Thunbergia laurifolia, Curcuma longa, Garcinia mangostana, and Andrographis paniculata extracts in Staphylococcus aureus-induced rabbit dermatitis model

Background and Aim:

Dermatitis is a soft-tissue infection caused by Staphylococcus aureus. The recurrence of inflammatory skin is linked to clinical manifestations. Anti-inflammatory cytokines, which are essential for tissue damage, are released by bacteria through skin tissues. Oxidative stress causes inflammatory cells to necrotize and reduces their antioxidant profile, resulting in toxic damage to surrounding tissues. Although studies on the antibacterial effects of Thunbergia laurifolia Lindl., Curcuma longa L., Garcinia mangostana L., and Andrographis paniculata (Burm.). Bacterial infection of S. aureus have been conducted, most of these studies have been in vitro and were not related to the rabbit model. In addition, anti-inflammatory and antioxidant studies need to be evaluated. Thus, this study aims to compare the antibacterial, anti-inflammatory, and antioxidant properties of four local herbs with a standard antibiotic in S. aureus-induced rabbit dermatitis model.

Materials and Methods:

The skin of New Zealand white rabbits were artificially wounded using a sterile blade and then infected with S. aureus. The rabbits were divided into seven groups, each with three rabbits (Total 21 rabbits): The first group was the no infection group (no infection and no treatment with scarification), the second group was the no treatment group (S. aureus infection of the wound but no treatment), and the other five treated groups were T. laurifolia, C. longa, G. mangostana, A. paniculata, and bacitracin cream, all of which involved wound infection and treatments. The treatment lasted for 7 days. The antibacterial, anti-inflammatory, and antioxidant properties after treatment were measured.

Results:

The efficacy of T. laurifolia, C. longa, G. mangostana, and A. paniculata was similar to that of an antioxidant and free radical scavenging property. The bacterial infection process gradually reduced the activities of antioxidant systems (i.e., enzymatic levels and gene expressions) and total glutathione. However, the activities of the antioxidant system were steadily increased when treated with herbal extracts. During bacterial invasion of the skin, the concentration of thiobarbituric acid reactive molecules, the level of lipid peroxidation, and the expression of anti-inflammatory cytokine genes were increased. All these were decreased when herbal extracts were used to treat the lesion.

Conclusion:

It can be concluded that T. laurifolia, C. longa, G. mangostana, and A. paniculate extract have antibacterial, anti-inflammatory, and antioxidant properties and are effective antibacterial agents. G. mangostana is the most effective herbal extract for antidermatitis and has the potential to be used as an alternative topical treatment.

The Effect of Age and Sampling Site on the Outcome of Staphylococcus aureus Infection in a Rabbit (Oryctolagus cuniculus) Farm in Italy

Simple Summary

Staphylococcus aureus contamination has been described in food-producing animals and farm workers involved in the primary industrial production of rabbits, pigs, cattle and poultry. This study describes the effects of age and colonization of body on S. aureus detection from rabbits raised intensively for meat production, and evaluates these parameters as possible risk factors for lesions by S. aureus. In addition, a genotypic characterization was performed for 96 S. aureus strains out of 595 that were isolated, including three from farm workers. It was observed that the risk of skin lesions increased with the number of colonized body sites and with age. All isolates were low-virulence methicillin-sensitive-Staphylococcus aureus (LV-MSSA). We found five different clonal lineages: spa-t2802, the most frequently detected (53.1%), also in all human samples; spa-t491, the second most detected (38.5%); spa-t094; t605; and spa-t2036. The same spa-type was observed in both animal and worker samples, showing that S. aureus strains could easily circulate in a community. The two most frequent strains were associated with noses, but not with age categories nor with the number of colonized sites. The circulation of LV-MSSA should not be underestimated, as they could determine damage or even acquire and spread resistance genes.

Abstract

A study in an intensive Italian rabbit farm was carried out to assess the effect of age category and anatomical site on detection of S. aureus and to describe the diversity of spa-types within farm, including workers. On 400 rabbits of different age, 2066 samples from the ear, nose, axilla, groin, perineum and lesions were analyzed and 595 S. aureus were isolated. In total, 284 (71.0%) were colonized by S. aureus in at least one anatomical site and 35 animals (8.8%) had lesions. S. aureus prevalence was higher in adults than other age categories. Ear (29.4%) and nose (27.2%) were the most frequently colonized sites. The presence of lesions due to S. aureus was strongly associated with the colonization of at least one body site and the risk of lesions was proportionate to the number of sites colonized by S. aureus. In addition, a genotypic characterization was performed for 96 S. aureus strains randomly selected. All isolates resulted as low-virulence methicillin-sensitive-Staphylococcus aureus (LV-MSSA). Five different clonal lineages were found: spa-t2802, the most frequently detected (53.1%), also in human samples; spa-t491 (38.5%); spa-t094; t605; and spa-t2036. Strains t094, t491 and t2036 have not been isolated in Italy before.

Staphylococcus argenteus from rabbits in Thailand

Staphylococcus argenteus, a novel species of the genus Staphylococcus or a member of the S. aureus complex, is closely related to S. aureus and is usually misidentified. In this study, the presence of S. argenteus in isolated S. aureus was investigated in 67 rabbits with abscess lesions during 2014-2016. Among 19 S. aureus complex isolates, three were confirmed to be S. argenteus by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, nonribosomal peptide synthetase gene amplification, and multilocus sequence type. All S. aureus complex isolates, including the S. aureus isolates, were examined for their antimicrobial resistance phenotype by disk diffusion and for their resistance genotype by PCR assays. Among the S. argenteus isolates, one was susceptible to all antimicrobial drugs and the other two were resistant to penicillin and doxycycline. In contrast, most S. aureus isolates were resistant to penicillin (37.5%), and gentamicin (12.5%). Moreover, S. aureus isolates harbored the blaZ, mecA, aacA-aphD, and mrs(A) as well as mutations of gyrA and grlA, but S. argenteus isolates carried solely the blaZ. S. argenteus isolates were investigated for enterotoxin (sea-sed) and virulence genes by PCR. One isolate carried sea, sec, and sed, whereas the other two isolates carried only sea or sed. No isolate carried seb and see. All three S. argenteus isolates carried hla, hlb, and clfA, followed by pvl, whereas coa, spa (IgG-binding region), and spa (x region) were not detected in the three isolates. This paper presents the first identification of S. argenteus from rabbits in Thailand. S. argenteus might be pathogenic because the isolates carried virulence genes. Moreover, antimicrobial resistance was observed. Investigations of this new bacterial species should be conducted in other animal species as well as in humans.

Antimicrobial Resistance among Staphylococci of Animal Origin

Antimicrobial resistance among staphylococci of animal origin is based on a wide variety of resistance genes. These genes mediate resistance to many classes of antimicrobial agents approved for use in animals, such as penicillins, cephalosporins, tetracyclines, macrolides, lincosamides, phenicols, aminoglycosides, aminocyclitols, pleuromutilins, and diaminopyrimidines. In addition, numerous mutations have been identified that confer resistance to specific antimicrobial agents, such as ansamycins and fluoroquinolones. The gene products of some of these resistance genes confer resistance to only specific members of a class of antimicrobial agents, whereas others confer resistance to the entire class or even to members of different classes of antimicrobial agents, including agents approved solely for human use. The resistance genes code for all three major resistance mechanisms: enzymatic inactivation, active efflux, and protection/modification/replacement of the cellular target sites of the antimicrobial agents. Mobile genetic elements, in particular plasmids and transposons, play a major role as carriers of antimicrobial resistance genes in animal staphylococci. They facilitate not only the exchange of resistance genes among members of the same and/or different staphylococcal species, but also between staphylococci and other Gram-positive bacteria. The observation that plasmids of staphylococci often harbor more than one resistance gene points toward coselection and persistence of resistance genes even without direct selective pressure by a specific antimicrobial agent. This chapter provides an overview of the resistance genes and resistance-mediating mutations known to occur in staphylococci of animal origin.

Antimicrobial Formulations of Absorbable Bone Substitute Materials as Drug Carriers Based on Calcium Sulfate

Substitution of bones is a well-established, necessary procedure to treat bone defects in trauma and orthopedic surgeries. For prevention or treatment of perioperative infection, the implantation of resorbable bone substitute materials carrying antibiotics is a necessary treatment. In this study, we investigated the newly formulated calcium-based resorbable bone substitute materials containing either gentamicin (CaSO4-G [Herafill-G]), vancomycin (CaSO4-V), or tobramycin (Osteoset). We characterized the released antibiotic concentration per unit. Bone substitute materials were implanted in bones of rabbits via a standardized surgical procedure. Clinical parameters and levels of the antibiotic-releasing materials in serum were determined. Local concentrations of antibiotics were measured using antimicrobial tests of bone tissue. Aminoglycoside release kinetics in vitro per square millimeter of bead surface showed the most prolonged release for gentamicin, followed by vancomycin and, with the fastest release, tobramycin. In vivo level in serum detected over 28 days was highest for gentamicin at 0.42 μg/ml, followed by vancomycin at 0.11 μg/ml and tobramycin at 0.04 μg/ml. The clinical parameters indicated high biocompatibility for materials used. None of the rabbits subjected to the procedure showed any adverse reaction. The highest availability of antibiotics at 14.8 μg/g on day 1 in the cortical tibia ex vivo was demonstrated for gentamicin, decreasing within 14 days. In the medulla, vancomycin showed a high level at 444 μg/g on day 1, decreasing continuously over 14 days, whereas gentamicin decreased faster within the initial 3 days. The compared antibiotic formulations varied significantly in release kinetics in serum as well as locally in medulla and cortex.

Virulence factors and genetic variability of Staphylococcus aureus strains isolated from raw sheep's milk cheese

Contamination of dairy products with Staphylococcus aureus can be of animal or human origin. The host pathogen relationship is an important factor determining genetic polymorphism of the strains and their potential virulence. The aim of the present study was to carry out an extensive characterization of virulence factors and to study the genetic variability of S. aureus strains isolated from raw ewe's milk cheese. A total of 100 S. aureus strains isolated from cheese samples produced in 10 artisan cheese factories were analyzed for the presence of enterotoxins (sea-see) and enterotoxins-like genes (seh, sek, sel, sem, seo, sep), leukocidins, exfoliatins, haemolysins, toxic shock syndrome toxin 1 (TSST-1) and the accessory gene regulator alleles (agr). Strains were also typed using pulsed-field gel electrophoresis (PFGE). AMOVA analysis carried out on PFGE and PCR data showed that the major component explaining genetic distance between strains was the dairy of origin. Of the total isolates 81% had a pathogenicity profile ascribable to "animal" biovar while 16% could be related to "human" biovar. The biovar allowed to estimate the most likely origin of the contamination. Minimum inhibitory concentrations (MICs) of nine antimicrobial agents and the presence of the corresponding genes coding for antibiotic resistance was also investigated. 18 strains carrying blaZ gene showed resistance to ampicillin and penicillin and 6 strains carrying tetM gene were resistant to tetracycline. The presence of mecA gene and methicillin resistance, typical of strains of human origin, was never detected. The results obtained in the present study confirm that S. aureus contamination in artisan cheese production is mainly of animal origin.

Strains of Staphylococcus aureus and pathology associated with chronic suppurative mastitis in rabbits

Staphylococcal mastitis is one of the main reasons for culling adult does from commercial rabbitries. The aim of this study was describe the spectrum of gross and microscopic lesions in 178 cases of chronic staphylococcal mastitis in adult does and to determine whether there is a correlation between Staphylococcus aureus genotypes and pathology. On the basis of histopathology, chronic mastitis was differentiated into abscesses (66.3%), suppurative mastitis with a lobular pattern (7.9%), cellulitis (19.6%) and mixed lesions (6.2%). Pathological presentations were not related to S. aureus genotype.

Characteristics ofStaphylococcus aureus isolated from rabbits

The occurrence of Staphylococcus aureus in rabbit feces, cecum and meat and its enterotoxin production, susceptibility to antibiotics and its sensitivity or resistance to bacteriocins produced by enterococci with probiotic properties were determined. Isolates were resistant to ampicillin, penicillin, phosphomycin and methicillin; a high percentage of susceptibility was also recorded to vancomycin, chloramphenicol, tetracycline and tobramycin. S. aureus isolates did not produce enterotoxins and were sensitive to partially purified enterocins (PPB) EK13, AL41 and EF2019 in the range of 100 to 12800 AU/mL; all S. aureus isolates, except the strain SA 2A/3, exhibited the highest sensitivity to PPB EK13. On the other hand, all strains were resistant to PPB CCM4231.

Phenotypic and genotypic traits of Staphylococcus aureus strains isolated from pig carcasses

A total of 142 S. aureus strains isolated from pig carcasses from abattoirs A (n=98) and B (n=44) were characterized by phenotypic and genotypic traits. Phenotypically, 96% showed yellow-pigmented colonies, 63% beta/delta hemolysis, 85% were egg yolk-positive and 99% were positive for clumping factor/protein A. Only 25% of the strains were resistant to the antimicrobials tested (abattoir A: 19%; abattoir B: 39%), especially to penicillin and ampicillin. None of the strains harbored the mecA gene, which is conserved in methicillin-resistant S. aureus. The biofilm associated genes icaA, icaD and bap were present in 100%, 100% and 0% of the strains. Genes for staphylococcal enterotoxin (SE) were detected in 51% (abattoir A) and 14% of the strains (abattoir B). Among strains harboring SE genes (n=56), 63%, 31%, 4% and 2% tested positive for seg/sei, seg, sei and sec, respectively. The amplification of the 3' end of the coagulase gene (coa) yielded amplicons of 400, 436, 602, 682 or 776bp. Coa restriction profile (CRP) analysis using HaeIII resulted in seven patterns (a-d, e1-e3). CRP (c) was detected most frequently at both abattoirs, whereas CRP (a) was restricted to abattoir A and CRP (e3) to abattoir B. In the slaughter process (abattoir B), (i) two CRPs (b and d) were only found before dehairing/singeing, and (ii) four CRPs (c, e1-e3) were identified throughout the process. The genotyping revealed a remarkable homogeneity in S. aureus strains from the two different abattoirs and the slaughter process stages. These results may be explained by the distribution of a limited number of S. aureus genotypes in the pig population. Moreover, as the predominant CRPs (c, e1-e3) persisted throughout the slaughter process in abattoir B, it may be hypothesized that these types are characterized by colonization advantages.

Prevalence of genes encoding exfoliative toxins, leucotoxins and superantigens among high and low virulence rabbit Staphylococcus aureus strains

Staphylococcus aureus is an important cause of pododermatitis, subcutaneous abscesses and mastitis in rabbits. On rabbitry level, two types of S. aureus infections can be distinguished. In the first type, caused by low virulence strains, the infection affects only a small number of animals. The second type of infection is caused by high virulence strains and spreads throughout the rabbit flock. The pathogenic capacity of a particular S. aureus strain is attributed to a combination of invasive properties and extracellular factors such as toxin production. Therefore, 22 high virulence and 37 low virulence S. aureus isolates were compared regarding the prevalence of genes encoding exfoliative toxins, leucotoxins and superantigens. This study revealed a clearly significant difference between HV and LV rabbit S. aureus strains. All typical HV isolates were positive for the egc cluster, containing the enterotoxin(like) genes seg, sei, selm, seln, selo and selu, whereas these genes were not detected in any of the LV isolates. Further research is necessary to clarify the importance of the egc cluster in the pathogenesis of infections with high virulence S. aureus strains in rabbits.

Molecular and phenotypic typing of Staphylococcus aureus isolates from rabbit meat

Twenty-six Staphylococcus aureus isolates were recovered from rabbit carcasses and cuts during a period of seven months. Samples from 51 different animals, flocks and farms were obtained from five establishments in four Spanish provinces. To determine their diversity and possible origin, isolates were typed by three molecular and three phenotypic methods. PFGE, with the highest discrimination index (D=0.966), identified 19 patterns (more than one band difference) and 10 types (more than three band differences). Based on > or = 90% similarity, RAPD (D=0.877) produced nine patterns while ribotyping (D=0.786) produced seven types. On the basis of biotyping (D=0.644), 11 isolates belonged to human ecovars and 15 to the non-host-specific crystal violet type C (NHS CV:C) biotypes. By direct phage typing (D=0.761), 17 isolates were lysed by human phages into groups II (8 isolates), III (5 isolates), I/III (2 isolates) and V (2 isolates). The overall resistance to antimicrobials (D=0.783) was 76.9%, with most isolates being resistant to tetracycline (61.5%) and penicillin G (26.9%). PFGE showed that samples from each processing plant carried different S. aureus types, some of them persisting over time. There also was evidence of interestablishment dissemination of genetically related clones, most of them belonging to the PFGE type A and phenotype "NHS CV:C biotypes-3A/3C/55/71 phage type", which is highly virulent for European commercial rabbitries. The ubiquity of the virulent phenotype, as well as the high incidence of resistance to antibiotics with application in human medicine, is a matter of concern in public and animal health.