Validation of amplified fragment length polymorphism genotyping for species identification of bovine associated coagulase-negative staphylococci

Differentiation of non-aureus staphylococci species isolated from bovine mastitis by PCR-RFLP of groEL and gap genes in comparison to MALDI-TOF mass spectrometry

Intramammary infections (IMI) cause serious economic losses for farmers and the dairy industry. Cases of subclinical mastitis are commonly the result of infection by minor pathogens such as non-aureus staphylococci (NAS), so their correct identification is important for appropriate therapeutic intervention and management. The aim of this study was to assess the reliability of PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) of the groEL and gap genes to discriminate between bovine-associated NAS species, using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) as the reference method. MALDI-TOF MS was able to correctly identify 112 NAS isolates from bovine IMI at species level out of a total of 115 (97.4%). These results were considered definitive and thus compared with those from the PCR-RFLP analyses. Only 50% (56/112) of the samples classified through groEL PCR-RFLP matched the molecular identity determined by MALDI-TOF MS, whereas coincidence rose to 96.4% (108/112) when comparing results from gap PCR-RFLP and the spectral analysis. This study demonstrates that gap PCR-RFLP is a useful and reliable tool for the identification of NAS species isolated from bovine mastitis.

Short communication: Subtyping of Staphylococcus haemolyticus isolates from milk and corresponding teat apices to verify the potential teat-skin origin of intramammary infections in dairy cows

Coagulase-negative staphylococci (CNS) are a major cause of intramammary infections (IMI) in dairy cows and they colonize the teat skin. Staphylococcus haemolyticus, one of the more common CNS, has been identified as a highly versatile opportunistic species. The aim of the present study was to gain better insight into the adaptation of S. haemolyticus subtypes to the udder ecosystem with respect to IMI development. During a longitudinal observational study conducted over 13 mo on 6 Flemish dairy herds, S. haemolyticus isolates were recovered from milk and teat apices. A total of 44 S. haemolyticus isolates originating from milk (24 isolates) and teat apices (20 isolates) of 6 selected udder quarters were singled out and analyzed using a combined methodology of (GTG)5-PCR and amplified fragment length polymorphism (AFLP) fingerprinting to determine intraspecies differences. Combining both fingerprinting methods, 4 S. haemolyticus subtypes were obtained (I to IV). Subtypes I, II, and IV were recovered from both milk and teat apex samples and were found to be associated with persisting IMI. Subtype III, not apparently related to IMI, was isolated solely from teat apices and not from milk. In general, S. haemolyticus subtypes found in milk from infected quarters could be recovered from the corresponding teat apices, although the latter could be colonized with up to 3 different subtypes. Comparing subtypes from milk and teat apices indicates that the IMI-causing agent likely originates from the teat skin.

Identification, typing, ecology and epidemiology of coagulase negative staphylococci associated with ruminants

Since phenotypic methods to identify coagulase negative staphylococci (CNS) from the milk of ruminants often yield unreliable results, methods for molecular identification based on gene sequencing or fingerprinting techniques have been developed. In addition to culture-based detection of isolates, culture-independent methods may be of interest. On the basis of molecular studies, the five CNS species commonly causing intramammary infections (IMI) are Staphylococcus chromogenes, Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus simulans and Staphylococcus xylosus. Current knowledge suggests that S. chromogenes is a bovine-adapted species, with most cases of IMI due to this bacterium being opportunistic. S. haemolyticus also appears to be an opportunistic pathogen, but this bacterium occupies a variety of habitats, the importance of which as a source of IMI remains to be elucidated. S. xylosus appears to be a versatile species, but little is known of its epidemiology. S. epidermidis is considered to be a human-adapted species and most cases of IMI appear to arise from human sources, but the organism is capable of residing in other habitats. S. simulans typically causes contagious IMI, but opportunistic cases also occur and the ecology of this bacterium requires further study. Further studies of the ecology and epidemiology of CNS as a cause of IMI in cattle are required, along with careful attention to classification of these bacteria and the diseases they cause.

Invited review: effect, persistence, and virulence of coagulase-negative Staphylococcus species associated with ruminant udder health

The aim of this review is to assess the effect of coagulase-negative staphylococci (CNS) species on udder health and milk yield in ruminants, and to evaluate the capacity of CNS to cause persistent intramammary infections (IMI). Furthermore, the literature on factors suspected of playing a role in the pathogenicity of IMI-associated CNS, such as biofilm formation and the presence of various putative virulence genes, is discussed. The focus is on the 5 CNS species that have been most frequently identified as causing bovine IMI using reliable molecular identification methods (Staphylococcus chromogenes, Staphylococcus simulans, Staphylococcus haemolyticus, Staphylococcus xylosus, and Staphylococcus epidermidis). Although the effect on somatic cell count and milk production is accepted to be generally limited or nonexistent for CNS as a group, indications are that the typical effects differ between CNS species and perhaps even strains. It has also become clear that many CNS species can cause persistent IMI, contrary to what has long been believed. However, this trait appears to be quite complicated, being partly strain dependent and partly dependent on the host's immunity. Consistent definitions of persistence and more uniform methods for testing this phenomenon will benefit future research. The factors explaining the anticipated differences in pathogenic behavior appear to be more difficult to evaluate. Biofilm formation and the presence of various staphylococcal virulence factors do not seem to (directly) influence the effect of CNS on IMI but the available information is indirect or insufficient to draw consistent conclusions. Future studies on the effect, persistence, and virulence of the different CNS species associated with IMI would benefit from using larger and perhaps even shared strain collections and from adjusting study designs to a common framework, as the large variation currently existing therein is a major problem. Also within-species variation should be investigated.

Effective application of multiple locus variable number of tandem repeats analysis to tracing Staphylococcus aureus in food-processing environment

A total of 256 isolates of Staphylococcus aureus were isolated from 98 samples (34 swabs and 64 food samples) obtained from small or medium meat- and cheese-processing plants in Slovakia. The strains were genotypically characterized by multiple locus variable number of tandem repeats analysis (MLVA), involving multiplex polymerase chain reaction (PCR) with subsequent separation of the amplified DNA fragments by an automated flow-through gel electrophoresis. With the panel of isolates, MLVA produced 31 profile types, which was a sufficient discrimination to facilitate the description of spatial and temporal aspects of contamination. Further data on MLVA discrimination were obtained by typing a subpanel of strains by multiple locus sequence typing (MLST). MLVA coupled to automated electrophoresis proved to be an effective, comparatively fast and inexpensive method for tracing S. aureus contamination of food-processing factories.

SIGNIFICANCE AND IMPACT OF THE STUDY

Subspecies genotyping of microbial contaminants in food-processing factories may facilitate identification of spatial and temporal aspects of the contamination. This may help to properly manage the process hygiene. With S. aureus, multiple locus variable number of tandem repeats analysis (MLVA) proved to be an effective method for the purpose, being sufficiently discriminative, yet comparatively fast and inexpensive. The application of automated flow-through gel electrophoresis to separation of DNA fragments produced by multiplex PCR helped to improve the accuracy and speed of the method.

Invited review: Mastitis in dairy heifers: nature of the disease, potential impact, prevention, and control

Heifer mastitis is a disease that potentially threatens production and udder health in the first and subsequent lactations. In general, coagulase-negative staphylococci (CNS) are the predominant cause of intramammary infection and subclinical mastitis in heifers around parturition, whereas Staphylococcus aureus and environmental pathogens cause a minority of the cases. Clinical heifer mastitis is typically caused by the major pathogens. The variation in proportions of causative pathogens between studies, herds, and countries is considerable. The magnitude of the effect of heifer mastitis on an individual animal is influenced by the form of mastitis (clinical versus subclinical), the virulence of the causative pathogen(s) (major versus minor pathogens), the time of onset of infection relative to calving, cure or persistence of the infection when milk production has started, and the host's immunity. Intramammary infection in early lactation caused by CNS does not generally have a negative effect on subsequent productivity. At the herd level, the impact will depend on the prevalence and incidence of the disease, the nature of the problem (clinical, subclinical, nonfunctional quarters), the causative pathogens involved (major versus minor pathogens), the ability of the animals to cope with the disease, and the response of the dairy manager to control the disease through management changes. Specific recommendations to prevent and control mastitis in late gestation in periparturient heifers are not part of the current National Mastitis Council mastitis and prevention program. Control and prevention is currently based on avoidance of inter-sucking among young stock, fly control, optimal nutrition, and implementation of hygiene control and comfort measures, especially around calving. More risk factors for subclinical and clinical heifer mastitis have been identified (e.g., season, location of herd, stage of pregnancy) although they do not lend themselves to the development of specific intervention strategies designed to prevent the disease. Pathogen-specific risk factors and associated control measures need to be identified due to the pathogen-related variation in epidemiology and effect on future performance. Prepartum intramammary treatment with antibiotics has been proposed as a simple and effective way of controlling heifer mastitis but positive long-lasting effects on somatic cell count and milk yield do not always occur, ruling out universal recommendation of this practice. Moreover, use of antibiotics in this manner is off-label and results in an increased risk of antibiotic residues in milk. Prepartum treatment can be implemented only as a short-term measure to assist in the control of a significant heifer mastitis problem under supervision of the herd veterinarian. When CNS are the major cause of intramammary infection in heifers, productivity is not affected, making prepartum treatment redundant and even unwanted. In conclusion, heifer mastitis can affect the profitability of dairy farming because of a potential long-term negative effect on udder health and milk production and an associated culling risk, specifically when major pathogens are involved. Prevention and control is not easy but is possible through changes in young stock and heifer management. However, the pathogenesis and epidemiology of the disease remain largely unknown and more pathogen-specific risk factors should be identified to optimize current prevention programs.

Staphylococcus agnetis sp. nov., a coagulase-variable species from bovine subclinical and mild clinical mastitis

Thirteen Gram-positive-staining coagulase-variable staphylococci were isolated from subclinical and mild clinical mastitic bovine milk (n = 12) and a teat apex (n = 1). The results of sequence analysis of the 16S rRNA gene and two housekeeping genes, rpoB and tuf, and DNA fingerprinting with amplified fragment length polymorphism (AFLP) analysis showed that the isolates formed a separate branch within the genus Staphylococcus. The phylogenetically most closely related species were Staphylococcus hyicus and Staphylococcus chromogenes. DNA–DNA hybridization with S. hyicus DSM 20459T and S. chromogenes DSM 20674T confirmed that the isolates belonged to a separate species. The predominant fatty acids were i-C15 : 0, ai-C15 : 0, i-C17 : 0 and C20 : 0 and the peptidoglycan type was A3α l-Lys–Gly5. Based on the results of genotypic and phenotypic analyses, it is proposed that the thirteen isolates represent a novel species, for which the name Staphylococcus agnetis sp. nov. is proposed. Strain 6-4T ( = DSM 23656T = CCUG 59809T) is the type strain.

Culture-independent exploration of the teat apex microbiota of dairy cows reveals a wide bacterial species diversity

Due to their close proximity to the mammary gland tissue, the bacterial communities lining the teat apex of the udders from lactating cows influence udder health. Denaturing gradient gel electrophoresis of the amplified V3 variable region of the 16S rRNA gene was used as a culture-independent method to reveal the bacterial composition of 48 samples originating from the teat apices of twelve Friesian-Holstein dairy cows suffering from clinical mastitis in one quarter. The microbiota belonged to four bacterial phyla: the Actinobacteria (32% of all genera), the Bacteroidetes (1%), the Firmicutes (42%), and the Proteobacteria (25%), encompassing 17 bacterial genera. Some differences in occurrence of these genera were seen when comparing quarters that were non-infected (n=22), subclinically infected (n=14), or clinically infected (n=12). Besides commensal skin-associated bacteria, opportunistic pathogenic bacteria, and mastitis-causing pathogens were found as well. The species diversity varied considerably among the most prevalent bacterial genera. While Corynebacterium and Staphylococcus displayed a large diversity among the recovered sequences, indicating the possible presence of a variety of different species, only a single bacterial species (represented by one sequence) was obtained for the genera Aerococcus, Acinetobacter, and Psychrobacter. In conclusion, introducing culture-independent analysis of teat apical skin swabs in mastitis research revealed an unexpected wide bacterial diversity, with variations between quarters with a different clinical status. In addition to potential mastitis-causing pathogens, it exposed the yet poorly mapped presence of skin-associated and other bacteria residing in close proximity to the mammary gland tissue. PCR-DGGE may thus be considered as a useful tool for the entanglement of animal skin microbiota, in casu the teat apices of dairy cows.

Molecular epidemiology of mastitis pathogens of dairy cattle and comparative relevance to humans

Mastitis, inflammation of the mammary gland, can be caused by a wide range of organisms, including gram-negative and gram-positive bacteria, mycoplasmas and algae. Many microbial species that are common causes of bovine mastitis, such as Escherichia coli, Klebsiella pneumoniae, Streptococcus agalactiae and Staphylococcus aureus also occur as commensals or pathogens of humans whereas other causative species, such as Streptococcus uberis, Streptococcus dysgalactiae subsp. dysgalactiae or Staphylococcus chromogenes, are almost exclusively found in animals. A wide range of molecular typing methods have been used in the past two decades to investigate the epidemiology of bovine mastitis at the subspecies level. These include comparative typing methods that are based on electrophoretic banding patterns, library typing methods that are based on the sequence of selected genes, virulence gene arrays and whole genome sequencing projects. The strain distribution of mastitis pathogens has been investigated within individual animals and across animals, herds, countries and host species, with consideration of the mammary gland, other animal or human body sites, and environmental sources. Molecular epidemiological studies have contributed considerably to our understanding of sources, transmission routes, and prognosis for many bovine mastitis pathogens and to our understanding of mechanisms of host-adaptation and disease causation. In this review, we summarize knowledge gleaned from two decades of molecular epidemiological studies of mastitis pathogens in dairy cattle and discuss aspects of comparative relevance to human medicine.

Distribution of coagulase-negative Staphylococcus species from milk and environment of dairy cows differs between herds

In many parts of the world, coagulase-negative staphylococci (CNS) are the predominant pathogens causing intramammary infections (IMI) in dairy cows. The cows' environment is thought to be a possible source for CNS mastitis and this was investigated in the present paper. A longitudinal field study was carried out in 6 well-managed dairy herds to determine the distribution and epidemiology of various CNS species isolated from milk, causing IMI and living freely in the cows' environment, respectively. In each herd, quarter milk samples from a cohort of 10 lactating cows and environmental samples from stall air, slatted floor, sawdust from cubicles, and sawdust stock were collected monthly (n=13). Isolates from quarter milk samples (n=134) and the environment (n=637) were identified to species level using amplified fragment length polymorphism (AFLP) genotyping. Staphylococcus chromogenes, S. haemolyticus, S. epidermidis, and S. simulans accounted for 81.3% of all CNS milk isolates. Quarters were considered infected with CNS (positive IMI status) only when 2 out of 3 consecutive milk samples yielded the same CNS AFLP type. The species causing IMI were S. chromogenes (n=35 samples with positive IMI status), S. haemolyticus (n=29), S. simulans (n=14), and S. epidermidis (n=6). The observed persistent IMI cases (n=17) had a mean duration of 149.4 d (range 63.0 to 329.8 d). The CNS species predominating in the environment were S. equorum, S. sciuri, S. haemolyticus, and S. fleurettii. Herd-to-herd differences in distribution of CNS species were observed in both milk and the environment, suggesting that herd-level factors are involved in the establishment of particular species in a dairy herd. Primary reservoirs of the species causing IMI varied. Staphylococcus chromogenes and S. epidermidis were rarely found in the environment, indicating that other reservoirs were more important in their epidemiology. For S. haemolyticus and S. simulans, the environment was found as a reservoir, suggesting that IMI with these species were possibly environmental in origin.