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

Epidemiology of Antimicrobial Resistance Genes in Staphylococcus aureus Isolates from a Public Database from a One Health Perspective-Sample Origin and Geographical Distribution of Isolates

Staphylococcus aureus are commensal bacteria that are found in food, water, and a variety of settings in addition to being present on the skin and mucosae of both humans and animals. They are regarded as a significant pathogen as well, with a high morbidity that can cause a variety of illnesses. The Centers for Disease Control and Prevention (CDC) has listed them among the most virulent and resistant to antibiotics bacterial pathogens, along with Escherichia coli, Staphylococcus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterococcus faecalis, and Enterococcus faecium. Additionally, S. aureus is a part of the global threat posed by the existence of antimicrobial resistance (AMR). Using 26,430 S. aureus isolates from a global public database (NPDIB; NCBI Pathogen Detection Isolate Browser), epidemiological research was conducted. The results corroborate the evidence of notable variations in isolate distribution and ARG (Antimicrobial Resistance Gene) clusters between isolate sources and geographic origins. Furthermore, a link between the isolates from human and animal populations is suggested by the ARG cluster patterns. This result and the widespread dissemination of the pathogens among animal and human populations highlight how crucial it is to learn more about the epidemiology of these antibiotic-resistance-related infections using a One Health approach.

Mammary gland inflammation in rabbits does (Oryctolagus cuniculus): A systematic review

Mastitis is a common condition in rabbit (Oryctolagus cuniculus) does, especially in rabbitries where mammae inflammations are the leading pathological expression of Staphylococcus aureus infections in reproductive females. It affects both the litter and the lactating female, including subsequent lactations. Non-septic (i.e. galactostasis and cystic mastitis) and septic (i.e. Mastitis acuta; including Mastitis gangrenosa; and Mastitis chronica) mammary inflammations are acknowledged; however, the literature is scarce regarding non-septic inflammations or subclinical mastitis. Thus, the present systematic review highlights and summarizes the existing data concerning mastitis in rabbit does, including diagnosis and treatment plans.

Comprehensive RNA-seq profiling to evaluate the rabbit mammary gland transcriptome after mastitis

Mastitis is a relatively common disease in rabbit does. The aim of this study was to investigate a relationship between the severity of clinical signs and pathological observations and to analyze differentially expressed genes (DEGs) in the mammary gland with mastitis versus healthy mammary gland. The result showed that rectal temperatures of the rabbits with both mild mastitis and severe mastitis were higher than that of control. Cell counting results showed that the somatic cell count (SCC) only in milk of the rabbit with severe mastitis was significantly higher than that in the control group. However, the number of heterophils in the histological sections of mammary glands with mild mastitis was significantly higher than that of control. A total of 1,096 DEGs between the control and mastitis mammary glands was identified by RNA-sequencing (RNA-seq). Gene ontology (GO) showed that most of up-regulated genes were enriched in terms such as response to stimulus, signal transduction, and cell communication. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that these genes were mostly enriched in the pathways such as Rap1 signaling pathway, proteoglycans in cancer, and PI3K-Akt signaling pathway. However, the downregulated genes were mainly enriched in metabolic processes and significantly involved in metabolic pathways. The data provides useful information to further dissect the molecular genetic mechanisms underlying rabbit mastitis, which is a prerequisite for designing effective intervention strategies.

Virulence Potential of Biofilm-Producing Staphylococcus pseudintermedius, Staphylococcus aureus and Staphylococcus coagulans Causing Skin Infections in Companion Animals

Coagulase-positive staphylococci (CoPS) account for most bacteria-related pyoderma in companion animals. Emergence of methicillin-resistant strains of Staphylococcus pseudintermedius (MRSP), Staphylococcus aureus (MRSA) or Staphylococcus coagulans (MRSC), often with multidrug-resistant (MDR) phenotypes, is a public health concern. The study collection comprised 237 staphylococci (S. pseudintermedius (n = 155), S. aureus (n = 55) and S. coagulans (n = 27)) collected from companion animals, previously characterized regarding resistance patterns and clonal lineages. Biofilm production was detected for 51.0% (79/155), 94.6% (52/55) and 88.9% (24/27) of the S. pseudintermedius, S. aureus and S. coagulans, respectively, and was a frequent trait of the predominant S. pseudintermedius and S. aureus clonal lineages. The production of biofilm varied with NaCl supplementation of the growth media. All S. pseudintermedius and S. aureus strains carried icaADB. Kaplan–Meier survival analysis of Galleria mellonella infected with different CoPS revealed a higher virulence potential of S. aureus when compared with other CoPS. Our study highlights a high frequency of biofilm production by prevalent antimicrobial-resistant clonal lineages of CoPS associated with animal pyoderma, potentially related with a higher virulence potential and persistent or recurrent infections.

Staphylococcus aureus Causing Skin and Soft Tissue Infections in Companion Animals: Antimicrobial Resistance Profiles and Clonal Lineages

Staphylococcus aureus is a relevant agent of skin and soft tissue infections (SSTIs) in animals. Fifty-five S. aureus comprising all SSTI-related isolates in companion animals, collected between 1999 and 2018 (Lab 1) or 2017 and 2018 (Lab 2), were characterized regarding susceptibility to antibiotics and heavy metals and carriage of antimicrobial resistance determinants. Clonal lineages were established by PFGE, MLST and agr typing. Over half of the isolates (56.4%, 31/55) were methicillin-resistant S. aureus (MRSA), and 14.5% showed a multidrug resistance (MDR) phenotype. Resistance was most frequently observed for beta-lactams (81.8%, related to blaZ and/or mecA), fluoroquinolones (56.4%) and macrolides/lincosamides (14.5%, related to erm(A) or erm(C)). The distributions of heavy-metal MICs allowed the detection of non-wild-type populations associated with several resistance genes. The collection showed genetic diversity, with prevalence of clonal lineage ST22-agrI (45.5%, 25/55), comprising only MRSA isolates, and several less frequently detected clones, including ST5-agrII (14.6%, 8/55), ST398-agrI (9.1%, 5/55) and ST72-agrI (7.3%, 4/55). This work highlights the high frequency of SSTI-related MRSA strains that reflect the clonal lineages circulating both in companion animals and humans in Portugal, reinforcing the need for a One Health approach when studying staphylococci causing infections in companion animals.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Rabbit

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the laboratory rabbit used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Health, performance and soiling of breeding does and their kits kept in two different housing systems on a German rabbit farm

<p>The aim of the present study was to compare a new housing (NC) for rabbit does and their kits that complies with German welfare regulations with established wire mesh cages (CC) on a commercial rabbit farm. Rabbit does were single-housed from five days antepartum until weaning at 31 d postpartum either in large pens (80×80 cm with an open top) with slatted plastic flooring (11 mm slats and 11 mm gaps), nestbox, elevated platform (15% perforated) and different manipulable materials (NC) or in cages (70×50×30 cm) with wire mesh flooring (12×70 mm holes and 3 mm wire diameter), nestbox and one gnawing stick (CC). Skin lesions, weight development, fertility, morbidity, cleanliness and kit performance of 272 rabbit does in a total of six batches were investigated. While there was no difference in performance of their kits, rabbit does showed an impaired performance with less weight gain and less body weight at weaning, lower fertility, more injuries and a higher incidence of mastitis and diarrhoea at the end of the rearing period in NC housing compared to CC housing. Additionally, soiling of hind feet was higher in NC than in CC housing. Overall, the poor hygienic conditions may have affected the animals’ health and make an improvement in the new housing system necessary, especially with regard to the floor design.</p>

Mammary Diseases in a Captive Reared Agouti (Dasyprocta leporina) in Trinidad

The agouti (Dasyprocta leporina) is a neotropical rodent that is utilized for its meat by hunters as well as wildlife farmers. There is a dearth of information on infectious diseases that affect these animals. At present, there has been no recording in the literature on diseases of mammary tissue in these animals. This case reported on the abnormal mammary enlargement of a four year old female agouti post-partum. Blood, milk and tissue samples were taken for diagnostics to determine the cause of disease. Histological samples confirmed the swelling of the mammary gland as a diffuse mammary hyperplasia. Hematological values obtained were within the reference range of agoutis reared in captivity. The milk samples that were taken cultured Staphylococcus spp. in one mammary gland (left inguinal). The cultured bacteria in the milk samples confirmed this animal had mastitis. The bacterial cultured (Staphylococcus aureus) was sensitive to tetracyclines, ampicillin, trivetrin and ceftiofur. To the authors' knowledge, this is the first record in the literature on mastitis in the agouti. Thus, this information will add to the knowledge of diseases in captive reared agoutis.

Marked Presence of Methicillin-Resistant Staphylococcus aureus in Wild Lagomorphs in Valencia, Spain

Simple Summary

The presence of bacteria resistant to antibiotics, such as Staphylococcus aureus resistant to methicillin (MRSA), is becoming an increasing everyday concern for their implications for human and animal health. This is even more alarming when such bacteria are isolated in wild animals which, in principle, should not come into contact with antibiotics. This work studied 353 rabbits and 10 hares hunted in rabbit high-density areas. Of these, 41.3% carried S. aureus in some sampled locations, of which 63.3% were MRSA. These are surprising results given the unexpected high presence of MRSA in the studied animals. This finding is very worrying because these animals tend to enter the food chain with no veterinary control, which implies a risk for human health. Thus it is necessary to extend this study to other, less-populated areas with other animal species (ruminants, rabbit predators, hunting dogs, etc.) or even water sources to obtain further knowledge about the origin of bacterial resistances in nature.

Abstract

The appearance of methicillin-resistant strains of Staphylococcus aureus (MRSA) in several animal species (including rabbits) has set off alarms for their capacity to act as reservoirs for this bacterium. This is especially important in wild animals given its epidemiological implications. The objectives of this study were to identify and characterize S. aureus, specifically MRSA, strains in wild lagomorph high-density areas. Ten hares and 353 wild rabbits from 14 towns with a high rabbit density in the Valencian region (eastern Spanish coast) were sampled. Swabs from the nasal cavity, ears, perineum and lesions (when present) were taken for microbiological studies. The detection of different genes and antibiotic susceptibility studies were also carried out. Of all the animals, 41.3% were positive for S. aureus, of which 63.3% were MRSA. Ears were the anatomical location with more S. aureus and MRSA strains. The more frequently identified MLST type was ST1945 (97.1%, 136/140). The mecA gene was found only in one sample. The rest (n = 139) carried the mecC gene and were included in CC130, except one. Penicillin resistance was detected in 28 mec-negative isolates and, in one case, bacitracin resistance. mecA isolate presented resistance to enrofloxacin and tetracycline, and 10 mecC isolates also showed bacitracin resistance. No MRSA isolate was positive for genes chp, sea, tst and PVL. Two ST1945 isolates contained IEC type E (comprising genes scn and sak). mecA-isolate was positive for blaZ. Of the 28 MSSA strains showing resistance to penicillin, 22 carried the blaZ gene. These surprising results highlight the marked presence of MRSA strains in wild rabbits in high-density areas.

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.

Pathogenesis of Intradermal Staphylococcal Infections: Rabbit Experimental Approach to Natural Staphylococcus aureus Skin Infections

Despite the enormous efforts made to achieve effective tools that fight against Staphylococcus aureus, the results have not been successful. This failure may be due to the absence of truly representative experimental models. To overcome this deficiency, the present work describes and immunologically characterizes the infection for 28 days, in an experimental low-dose (300 colony-forming units) intradermal model of infection in rabbits, which reproduces the characteristic staphylococcal abscess. Surprisingly, when mutant strains in the genes involved in virulence (JΔagr, JΔcoaΔvwb, JΔhla, and JΔpsmα) were inoculated, no strong effect on the severity of lesions was observed, unlike other models that use high doses of bacteria. The inoculation of a human rabbitized (FdltB^r) strain demonstrated its capacity to generate a similar inflammatory response to a wild-type rabbit strain and, therefore, validated this model for conducting these experimental studies with human strains. To conclude, this model proved reproducible and may be an option of choice to check both wild-type and mutant strains of different origins.

Differences in virulence between the two more prevalent Staphylococcus aureus clonal complexes in rabbitries (CC121 and CC96) using an experimental model of mammary gland infection

Staphylococcal mastitis is a major health problem in humans and livestock that leads to economic loss running in millions. This process is currently one of the main reasons for culling adult rabbit does. Surprisingly, the two most prevalent S. aureus lineages isolated from non-differentiable natural clinical mastitis in rabbits (ST121 and ST96) generate different immune responses. This study aimed to genetically compare both types of strains to search for possible dissimilarities to explain differences in immune response, and to check whether they showed similar virulence in in vitro tests as in experimental intramammary in vivo infection. The main differences were observed in the enterotoxin gene cluster (egc) and the immune-evasion-cluster (IEC) genes. While isolate ST121 harboured all six egc cluster members (seg, sei, selm, seln, selo, selu), isolate ST96 lacked the egc cluster. Strain ST96 carried a phage integrase Sa3 (Sa3int), compatible with a phage integrated into the hlb gene (β-haemolysin-converting bacteriophages) with IEC type F, while isolate ST121 lacked IEC genes and the hlb gene was intact. Moreover, the in vitro tests confirmed a different virulence capacity between strains as ST121 showed greater cytotoxicity for erythrocytes, polymorphonuclear leukocytes and macrophages than strain ST96. Differences were also found 7 days after experimental intramammary infection with 100 colony-forming units. The animals inoculated with strain ST121 developed more severe gross and histological mastitis, higher counts of macrophages in tissue and of all the cell populations in peripheral blood, and a significantly larger total number of bacteria than those infected by strain ST96.

Causes of Mortality and Disease in Rabbits and Hares: A Retrospective Study

In this study we determined the causes of mortality and disease in a total of 325 lagomorphs (rabbits and hares) in northern Spain between 2000 and 2018. Risk factors such as the species, age, sex, time of year and origin were also considered. Clinical signs, gross and histopathological findings and ancillary test results were the basis for the final diagnoses that were reviewed to classify and identify the different disorders. A total of 26 different conditions were identified. A single cause of death or illness was detected in 267 animals. They were grouped into parasitic conditions (n= 65; 24.34%) represented by encephalitozoonosis, hepatic coccidiosis, hepatoperitoneal cysticercosis, intestinal coccidiosis, parasitic gastritis and cutaneous ectoparasitosis; bacterial diseases (n = 56; 20.97%) including pseudotuberculosis, blue breast, skin abscesses, tularemia, pneumonic pasteurellosis and staphylococcal infections; nutritional and metabolic diseases (n = 48; 17.97%) with epizootic rabbit enteropathy, hepatic steatosis and pregnancy toxemia as prominent diseases; viral infections (n= 31; 11.61%) comprising rabbit hemorrhagic disease and myxomatosis and miscellaneous causes (n = 31; 11.61%) where rabbit enteritis complex, renal conditions (nephrosis), heat stroke, and arterial bone metaplasia were included; neoplasms (n = 12; 4.49%) represented by uterine adenocarcinoma, mammary adenocarcinoma, cutaneous fibroma, intestinal lymphoma and hepatic cholangiocarcinoma; toxicoses (n = 11; 4.11%); trauma-related injuries (n = 9; 3.37%) and finally congenital diseases (n = 4; 1.49%). In 58 animals of the study, some of these conditions were presented jointly. We discuss the detection frequency, possible causes or associated factors of the different pathologies as well as the importance of the different variables considered.

Health and welfare of rabbits farmed in different production systems

The AGRI committee of the European Parliament requested EFSA to assess the welfare of rabbits farmed in different production systems, including organic production, and to update its 2005 scientific opinion about the health and welfare of rabbits kept for meat production. Considering reproducing does, kits and growing rabbits, this scientific opinion focusses on six different housing systems, namely conventional cages, structurally enriched cages, elevated pens, floor pens, outdoor/partially outdoor systems and organic systems. To compare the level of welfare in the different housing systems and rabbit categories, welfare impact scores for 20 welfare consequences identified from the literature were calculated, taking their occurrence, duration and severity into account. Based on the overall welfare impact score (sum of scores for the single welfare consequences), obtained via a 2‐step expert knowledge elicitation process, the welfare of reproducing does is likely (certainty 66–90%) to be lower in conventional cages compared to the five other housing systems. In addition, it is likely to extremely likely (certainty 66–99%) that the welfare of kits is lower in outdoor systems compared to the other systems and that the welfare is higher in elevated pens than in the other systems. Finally, it is likely to extremely likely (certainty 66–99%) that the welfare of growing rabbits is lower in conventional cages compared to the other systems and that the welfare is higher in elevated pens than in the other systems. Ranking of the welfare consequences allowed an analysis of the main welfare consequences within each system and rabbit category. It was concluded that for reproducing does, as well as growing rabbits, welfare consequences related to behavioural restrictions were more prominent in conventional cages, elevated pens and enriched cages, whereas those related to health problems were more important in floor pens, outdoor and organic systems. Housing in organic rabbit farming is diverse, which can result in different welfare consequences, but the overall welfare impact scores suggest that welfare in organic systems is generally good.

Staphylococcus aureus in Animals

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

Characterization of Livestock-Associated Methicillin-Resistant Staphylococcus aureus Isolates Obtained From Commercial Rabbitries Located in the Iberian Peninsula

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have been a growing problem in human medicine since the 1960s, and more recently in veterinary medicine with the appearance of livestock-associated MRSA (LA-MRSA). Nevertheless, information about the presence of MRSA in rabbits is quite scarce since only one LA-MRSA identification has been previously reported. The present study aimed to determine genotypic characterization by verifying the presence of resistance determinants, virulence, and toxin genes of different S. aureus strains that cause lesions in rabbits, and their phenotypic traits based on the antimicrobial susceptibility profile. The analysis of 240 S. aureus isolates obtained from different lesion types collected from 89 Spanish and Portuguese rabbit commercial farms in the last 4 years (2014-2017) was performed. The methicillin-resistant gene mecA was found in 11.25% of the studied isolates (27 of 240) from 19 farms (13 Spanish and 6 Portuguese). Staphylococcal cassette chromosome mec (SCCmec) typing predominantly revealed type III (n = 15). Additionally, three MRSA isolates carrying the mecC gen were detected in samples from three different farms (two Spanish and one Portuguese). None of the 30 MRSA isolates was PVL-positive or tst-positive. After the multilocus sequence typing (MLST) procedure, 16 belonged to ST2855, 6 to ST146, 6 to ST398, and 2 ST4774. No ST121 isolate was mec-positive. ST398 and ST4774 isolates lacked the immune-evasion-cluster (IEC) genes. ST2855 strains were associated with the presence only of the sak gene, and ST146 isolates were ascribed to IEC type E. Therefore, this is the first description of LA-MRSA from rabbits belonging to ST2855. Interestingly, one ST2855 and two ST4774 isolates were mecC-positive, which could act as a mecC-MRSA reservoir. More studies are needed to further characterize these isolates and their relationship with humans and other animal species.

Mastitis on Rabbit Farms: Prevalence and Risk Factors

In this cross-sectional study, prevalence of clinical mastitis (PCM) and farm-specific risk factors were determined on 531 doe rabbit farms in Spain and Portugal, from January 2001 through March 2017. The information was obtained by carrying out 2367 visits and doing physical examinations of 144,455 lactating does, sorted in 2635 cohorts. Overall mean PCM was 4.05% (CI95% [3.87⁻4.22]), (minimum to maximum: 0⁻36.00% PCM). This study suggests that PCM was influenced by the variable number of batches (a batch was a group of does served the same day), per maternity barn (p < 0.0001). The duo system (does being moved to clean disinfected barns for parturition), was also an enabling risk factor for CM. The day of service or lactation stage also affected PCM. Lastly, there was an effect of the breeds or lines (p < 0.0001); mean PCM ranged between 1.29% and 7.09%. A subset of data obtained from 200 farms visited during January 2012⁻March 2017, was recorded to describe the use of antimicrobials against mastitis. Changes in host, husbandry, environment, and biosecurity practices, are highlighted to provide health and welfare benefits for breeding rabbits.

The Mammary Microenvironment in Mastitis in Humans, Dairy Ruminants, Rabbits and Rodents: A One Health Focus

The One Health concept promotes integrated evaluation of human, animal, and environmental health questions to expedite advances benefiting all species. A recognition of the multi-species impact of mastitis as a painful condition with welfare implications leads us to suggest that mastitis is an ideal target for a One Health approach. In this review, we will evaluate the role of the mammary microenvironment in mastitis in humans, ruminants and rabbits, where appropriate also drawing on studies utilising laboratory animal models. We will examine subclinical mastitis, clinical lactational mastitis, and involution-associated, or dry period, mastitis, highlighting important anatomical and immunological species differences. We will synthesise knowledge gained across different species, comparing and contrasting disease presentation. Subclinical mastitis (SCM) is characterised by elevated Na/K ratio, and increased milk IL-8 concentrations. SCM affecting the breastfeeding mother may result in modulation of infant mucosal immune system development, whilst in ruminants notable milk production losses may ensue. In the case of clinical lactational mastitis, we will focus on mastitis caused by Staphylococcus aureus and Escherichia coli. Understanding of the pathogenesis of involution-associated mastitis requires characterization of the structural and molecular changes occurring during involution and we will review these changes across species. We speculate that milk accumulation may act as a nidus for infection, and that the involution 'wound healing phenotype' may render the tissue susceptible to bacterial infection. We will discuss the impact of concurrent pregnancy and a 'parallel pregnancy and involution signature' during bovine mammary involution.

Sinus-like dilatations of the mammary milk ducts, Ki67 expression, and CD3-positive T lymphocyte infiltration, in the mammary gland of wild European rabbits during pregnancy and lactation

Sinus-like dilatations of the mammary duct are recognisable in the mammary gland of pregnant and lactating wild European rabbits. These dilatations exhibit a bilaminar epithelial lining, with luminal epithelial cells expressing basal and lateral E-cadherin. Occasional binucleated mammary epithelial cells are present in the luminal layer. Underlying the luminal epithelial cells is a basal layer of cytokeratin 14-positive cells, supported by a thin layer of fibrous tissue. Multi-segmental epithelial proliferation, as indicated by Ki67 expression, is apparent in the luminal epithelial cells, suggesting a capacity for division during pregnancy and lactation. CD3-positive T lymphocytes are present both intraepithelially, suggesting exocytosis, and in foci subjacent to the ductular epithelium. We consider that sinus-like dilatations of the mammary duct may have the potential to give rise to a subset of the mammary gland neoplasms classified as ductal in origin. Milk accumulation in these sinus-like dilatations is likely to provide a niche for bacterial replication in cases of mastitis in rabbits. These structures are an important component of the innate immune system of the mammary gland, both as a physical barrier and as an interface between the milk and mammary immune cells.

Host responses associated with chronic staphylococcal mastitis in rabbits

Staphylococcal infection causes substantial economic losses in commercial rabbit production systems, and is associated with a wide variety of lesions, including chronic suppurative mastitis, which mainly affects breeding females. Most chronic staphylococcal infections in rabbits are caused by the ST121 lineage of Staphylococcus aureus, although other less common lineages, such as ST96 can also be involved. The aims of the present study were to characterise the host immune response in natural cases of mastitis in rabbits caused by S. aureus, to evaluate any relationship between peripheral and local immunity and to investigate the effect of different S. aureus genotypes on these immune responses. Adult multiparous female rabbits that were affected with chronic staphylococcal mastitis (n = 204) were enrolled into the study. Histological and immunohistochemical evaluations of mammary glands were undertaken, as well as flow cytometric analyses of blood. S. aureus isolates from the mammary glands were identified by multilocus sequence typing. Differences in the number of infiltrating cells were detected, depending on the type of pathology, with more immature lesions demonstrating greater cellularity, characterised by greater numbers of T lymphocytes, macrophages and plasma cells. A relationship was seen between the cells in blood and mammary tissues, the most notable being the positive correlation between monocytes and tissue macrophages. When glands were infected with ST96 strains, fewer granulocytes (P < 0.01) and greater numbers of B cells (P < 0.01), T cells (P < 0.001), CD4(+) T cells (P < 0.001) and CD8(+) T cells (P < 0.01) were detected, compared with mammary glands that were infected by ST121 strains of S. aureus.

Fine-tuned characterization of Staphylococcus aureus Newbould 305, a strain associated with mild and chronic mastitis in bovines

S. aureus is a major aetiological agent of ruminant mastitis worldwide. The chronic nature of S. aureus mastitis makes it difficult to cure and prone to resurgence. In order to identify the bacterial factors involved in this chronicity, Newbould 305 (N305), a strain that can reproducibly induce mild and chronic mastitis in an experimental setting, was characterized in depth. We employed genomic and proteomic techniques combined with phenotype characterization, in order to comprehensively analyse N305. The results were compared with data obtained on S. aureus RF122, a strain representative of the major clone involved in severe bovine mastitis worldwide. Five mobile genetic elements were identified in the N305 genome as carrying virulence factors which correlated with phenotypic features such as cytotoxicity, mammary epithelial cell invasion or host-adaptation. In particular, the presence and characteristics of surface exposed proteins correlated well with the greater adhesion and internalization capacities of N305 in bovine mammary epithelial cells. N305 also displayed less diversity of toxin genes but secreted larger quantities of these toxins, associated with a higher cytotoxicity potential. Our data are consistent with the invasiveness and host-adaptation features which contribute to the chronicity of S. aureus mastitis. Mobile genetic elements, exoproteins and surface exposed proteins constitute good targets for further research to explore the underlying mechanisms related to mastitis chronicity.

Staphylococcus aureus in veterinary medicine

Staphylococcus aureus is a major opportunistic pathogen in humans and one of the most important pathogenic Staphylococcus species in veterinary medicine. S. aureus is dangerous because of its deleterious effects on animal health and its potential for transmission from animals to humans and vice-versa. It thus has a huge impact on animal health and welfare and causes major economic losses in livestock production. Increasing attention is therefore being paid to both livestock and companion animals in terms of this pathogen. In this review, we summarise the current knowledge on the animal host adaptation of S. aureus. Different types of S. aureus infections in animals are also presented, with particular emphasis on mastitis in dairy herds, which is probably the costliest and therefore the best documented S. aureus infection seen in animals.