Coagulase-negative staphylococci and mammary gland infections in cows

Polymorphism of Selected Regions of Ovar-MHC and the Health Status of the Ovine Mammary Gland

Udder diseases (mastitis) are a serious cause of economic losses in sheep breeding as they have a negative impact on lamb rearing and the quality of dairy products. Thus far, progress in treatment and prevention of these diseases has been insufficient-giving ground for searching possibilities of using natural immunity to combat mastitis. This study aims to assess the relationship between the microsatellite polymorphism of selected Ovar-MHC genes and the health status of the mammary gland of sheep. The research is carried out on sheep of the Polish Heath and Polish Lowland breeds. In ovine milk, the SCC and the percentage of the lymphocyte subpopulation are assessed. Based on genomic DNA, molecular analysis of the Ovar-MHC gene fragments (OLADRB1, OLADRB2, OMHC1) polymorphism is performed. Significant differences are found in SCC level and the percentage of lymphocytes (CD4, CD8, CD19) in the milk depending on the alleles of the Ovar-MHC genes. Alleles of 488 bp (DRB1) and 284 bp (DRB2) are found more frequently in sheep, which milk contained <200 × 10³/mL SCC, while in carriers of the 508 bp (DRB1) and 272 bp (DRB2) alleles, SCC level in milk is significantly higher (>200 × 10³/mL). The obtained results justify the need for further research to better understand the genetic basis of mastitis, and to search for effective molecular markers that can be used in breeding practice.

Correlation between Milk Bacteriology, Cytology and Mammary Tissue Histology in Cows: Cure from the Pathogen or Recovery from the Inflammation

The aim of the current study was to verify the existence of a significant correlation between bacterial isolation (or not) and mammary gland inflammation, using traditional bacterial culturing and PCR, milk leucocytes distributions, and tissue histology. Twenty-two cows were tested at the level of the individual gland for bacteriological culture and real-time PCR (RT-PCR), milk composition, somatic cells count (SCC), and cell differentiation. Post-slaughter samples of teat-ends and mammary tissues were tested for histology and bacteriology by RT-PCR. The 88 glands were assigned to either outcome: 1. Healthy—no inflammation and no bacterial finding (NBF) (n = 33); 2. Inflammation and NBF (n = 26); 3. Inflammation and intra-mammary infection (n = 22) with different bacteria. Bacteriology of milk samples and that of the RT-PCR showed 91.4% agreement. In the lobule’s tissues of healthy glands, ~50% were milk producers and the other glands had dry areas with increased fat globules with a low number of leukocytes. In contrast, ~75% of the infected glands were identified as inflamed, but with no isolation of bacteria. Infiltration of mononuclear cells and neutrophils into the connective tissue was observed but not in the lobule’s lumen. In summary, the study confirms that not every mastitis/inflammation is also an infection.

Witch Hazel Significantly Improves the Efficacy of Commercially Available Teat Dips

Bovine intramammary infections (IMIs) are the main cause of economic loss in milk production. Antibiotics are often ineffective in treating infections due to antimicrobial resistance and the formation of bacterial biofilms that enhance bacterial survival and persistence. Teat dips containing germicides are recommended to prevent new IMIs and improve udder health and milk quality. IMIs are often caused by staphylococci, which are Gram-positive bacteria that become pathogenic by forming biofilms and producing toxins. As a model for a teat dip (DIP), the BacStop iodine-based teat dip (DIP) was used. Witch hazel extract (whISOBAX (WH)) was tested because it contains a high concentration of the anti-biofilm/anti-toxin phenolic compound hamamelitannin. We found that the minimal inhibitory or bactericidal concentrations of DIP against planktonic S. epidermidis cells increased up to 160fold in the presence of WH, and that DIP was 10-fold less effective against biofilm cells. While both DIP and WH are effective in inhibiting the growth of S. aureus, only WH inhibits toxin production (tested for enterotoxin-A). Importantly, WH also significantly enhances the antibacterial effect of DIP against Gram-negative bacteria that can cause IMIs, like Escherichia coli and Pseudomonas aeruginosa. Put together, these results suggest that the antibacterial activity of DIP combined with WH is significantly higher, and thus have potential in eradicating bacterial infections, both in acute (planktonic-associated) and in chronic (biofilm-associated) conditions.

Luteolin reduces inflammation in Staphylococcus aureus-induced mastitis by inhibiting NF-kB activation and MMPs expression

Mastitis is a serious and prevalent disease caused by infection by pathogens such as Staphylococcus aureus. We evaluated the anti-inflammatory effects and mechanism of luteolin, a natural flavonoid with a wide range of pharmacological activities, in a mouse model of S. aureus mastitis. We also treated cultured mouse mammary epithelial cells (mMECs) with S. aureus and luteolin. Histopathological changes were examined by H&E staining and the levels of inflammatory cytokine proteins were analyzed using ELISAs. We determined mRNA levels with qPCR and the level of NF-κB and matrix metalloproteinase (MMP) proteins by Western blotting. The observed histopathological changes showed that luteolin protected mammary glands with S. aureus infection from tissue destruction and inflammatory cell infiltration. Luteolin inhibited the expression of TNF-α, IL-1β, and IL-6, all of which were increased with S. aureus infection of mammary tissues and mMECs. S. aureus-induced TLR2 and TLR4 was suppressed by luteolin, as were levels of IκBα and NF-κB p65 phosphorylation and expression of MMP-2 and MMP-9. Levels of tissue inhibitor of metalloproteinases (TIMP)-1 and TIMP-2 were enhanced. These findings suggest luteolin is a potentially effective new treatment to reduce tissue damage and inflammation from S. aureus-induced mastitis.

Phenotypic Antimicrobial Resistance Profile of Isolates Causing Clinical Mastitis in Dairy Animals

Mastitis is the most frequent and costly disease of lactating animals and is associated with a significant reduction in milk yield, increased cost and culling. Early and specific antibiotic based treatment reduces the severity of the disease. Over the years the extensive use of antimicrobials has led to increase antimicrobial resistance. The present study was designed to investigate the prevalence of microorganisms responsible for mastitis and their antimicrobial resistance pattern. A total of 282 milk samples were collected from different animal species (sheep, cows and goats) with clinical mastitis. Antimicrobial resistance was evaluated for Streptococcus spp. and Staphylococcus spp. In cow samples Streptococcus spp. represented the most frequently isolated genus (33.84%), while Staphylococcus spp. was the most prevalent genus in sheep and goat samples (44.4 and 73.86%, respectively). Gentamicin and chloramphenicol were found to be the most effective drugs against the tested isolates, while the highest resistance rates were observed for amoxicillin, ampicillin, tetracycline, trimethoprim-sulfamethoxazole.

Staphylococcus aureus induces TGF-β1 and bFGF expression through the activation of AP-1 and NF-κB transcription factors in bovine mammary gland fibroblasts

Staphylococcus aureus is a common Gram-positive pathogen that causes bovine mastitis, a persistent infection of the bovine mammary gland. To better understand the importance of bovine mammary fibroblasts (BMFBs) and the roles of the TLR-NF-κB and TLR-AP-1 signaling pathways in the regulation of S. aureus-associated mastitis and mammary fibosis, BMFBs cultured in vitro were stimulated with different concentrations of heat-inactivated S. aureus to analyze the gene and protein expression of toll-like receptor 2 (TLR2), toll-like receptor 4 (TLR4), transforming growth factor beta 1 (TGF-β1), basic fibroblast growth factor (bFGF) as well as the protein expression of nuclear factor-kappa B (NF-κB) and activation protein-1 (AP-1) by means of quantitative polymerase chain reaction (qPCR) and western blotting, respectively. Specific NF-κB and AP-1 inhibitors were also used to investigate their effects on the regulation of TGF-β1 and bFGF expression. The results indicated that, in addition to increasing mRNA and protein expression of TLR2 and TLR4, S. aureus could also upregulate TGF-β1 and bFGF mRNA expression and secretion through the activation of NF-κB and AP-1. The increase in TGF-β1 and bFGF expression was shown to be inhibited by AP-1- and NF-κB-specific inhibitors. Taken together, S. aureus induces TGF-β1 and bFGF expression through the activation of AP-1 and NF-κB in BMFBs. This information offers new potential targets for the treatment of bovine mammary fibrosis.

Antimicrobial drug resistance of Staphylococcus aureus in dairy products

OBJECTIVE

To evaluate the prevalence of multidrug resistant Staphylococcus aureus (S. aureus) in dairy products.

METHODS

Isolation and identification of S. aureus were performed in 3 dairy-based food products. The isolates were tested for their susceptibility to 5 different common antimicrobial drugs.

RESULTS

Of 50 samples examined, 5 (10%) were contaminated with S. aureus. Subsequently, the 5 isolates were subjected to antimicrobial resistance pattern using five antibiotic discs (methicillin, vancomycin, kanamycin, chloramphenicol and tetracycline). Sample 29 showed resistance to methicillin and vancomycin. Sample 18 showed intermediate response to tetracycline. The other samples were susceptible to all the antibiotics tested.

CONCLUSIONS

The results provide preliminary data on sources of food contamination which may act as vehicles for the transmission of antimicrobial-resistant Staphylococcus. Therefore, it enables us to develop preventive strategies to avoid the emergence of new strains of resistant S. aureus.

The Immunology of Mammary Gland of Dairy Ruminants between Healthy and Inflammatory Conditions

The health of dairy animals, particularly the milk-producing mammary glands, is essential to the dairy industry because of the crucial hygienic and economic aspects of ensuring production of high quality milk. Due to its high prevalence, mastitis is considered the most important threat to dairy industry, due to its impacts on animal health and milk production and thus on economic benefits. The MG is protected by several defence mechanisms that prevent microbial penetration and surveillance. However, several factors can attenuate the host immune response (IR), and the possession of various virulence and resistance factors by different mastitis-causing microorganisms greatly limits immune defences and promotes establishment of intramammary infections (IMIs). A comprehensive understanding of MG immunity in both healthy and inflammatory conditions will be an important key to understand the nature of IMIs caused by specific pathogens and greatly contributes to the development of effective control methods and appropriate detection techniques. Consequently, this review aims to provide a detailed overview of antimicrobial defences in the MG under healthy and inflammatory conditions. In this sense, we will focus on pathogen-dependent variations in IRs mounted by the host during IMI and discuss the potential ramifications of these variations.

Some coagulase-negative Staphylococcus species affect udder health more than others

A longitudinal study in 3 dairy herds was conducted to profile the distribution of coagulase-negative Staphylococcus (CNS) species causing bovine intramammary infection (IMI) using molecular identification and to gain more insight in the pathogenic potential of CNS as a group and of the most prevalent species causing IMI. Monthly milk samples from 25 cows in each herd as well as samples from clinical mastitis were collected over a 13-mo period. Coagulase-negative staphylococci were identified to the species level using transfer-RNA intergenic spacer PCR. The distribution of CNS causing IMI was highly herd-dependent, but overall, Staphylococcus chromogenes, Staphylococcus xylosus, Staphylococcus cohnii, and Staphylococcus simulans were the most prevalent. No CNS species were found to cause clinical mastitis. The effect of the most prevalent species on the quarter milk somatic cell count (SCC) was analyzed using a linear mixed model, showing that Staph. chromogenes, Staph. simulans, and Staph. xylosus induced an increase in the SCC that is comparable with that of Staphylococcus aureus. Almost all CNS species were able to cause persistent IMI, with Staph. chromogenes causing the most persistent infections. In conclusion, accurate species identification cannot be ignored when studying the effect of CNS on udder health, as the effect on SCC differs between species and species distribution is herd-specific. Staphylococcus chromogenes, Staph. simulans, and Staph. xylosus seem to be the more important species and deserve special attention in further studies. Reasons for herd dependency and possible cow- and quarter-level risk factors should be examined in detail for the different species, eventually leading to cost-benefit analyses for management changes and, if needed, treatment recommendations.

Intra-species diversity and epidemiology varies among coagulase-negative Staphylococcus species causing bovine intramammary infections

Although many studies report coagulase-negative staphylococci (CNS) as the predominant cause of subclinical bovine mastitis, their epidemiology is poorly understood. In the current study, the genetic diversity within four CNS species frequently associated with bovine intramammary infections, Staphylococcus haemolyticus, S. simulans, S. chromogenes, and S. epidermidis, was determined. For epidemiological purposes, CNS genotypes recovered from bovine milk collected on six Flemish dairy farms were compared with those from the farm environment, and their distribution within the farms was investigated. Genetic diversity was assessed by two molecular typing techniques, amplification fragment length polymorphism (AFLP) and random amplification of polymorphic DNA (RAPD) analysis. Subtyping revealed the highest genetic heterogeneity among S. haemolyticus isolates. A large variety of genotypes was found among environmental isolates, of which several could be linked with intramammary infection, indicating that the environment could act as a potential source for infection. For S. simulans, various genotypes were found in the environment, but a link with IMI was less obvious. For S. epidermidis and S. chromogenes, genetic heterogeneity was limited and the sporadic isolates from environment displayed largely the same genotypes as those from milk. The higher clonality of the S. epidermidis and S. chromogenes isolates from milk suggests that specific genotypes probably disseminate within herds and are more udder-adapted. Environmental sources and cow-to-cow transmission both seem to be involved in the epidemiology of CNS, although their relative importance might substantially vary between species.

An evaluation of casein hydrolyzate in combination with antibiotic for bacterial cure and subsequent increase in milk yield in dairy cows

Background

A 3-yr study examined whether prepartum treatment with casein hydrolyzate in combination with antibiotic, as routinely used in Israel for dry cow therapy, improved bacterial cure and increased milk yield in subsequent lactations in comparison with treatment with antibiotic alone. The vast majority of bacterial isolates in samples collected prior to drying-off comprised coagulase-negative staphylococci, mostly as Staph. chromogenes.

Results

Bacterial cure associated with the combined treatment was 73.8% in cows, significantly higher than the 51.7% cure recorded when cows were treated only with antibiotic. During the study, the annual milk yield of non-casein hydrolyzate treated and treated control cows increased at ~2% per year, which is consistent with the national annual increase attributed to genetic selection. In cows treated with casein hydrolyzate the increase was 9% (above the 2% expected) in the first lactation after the treatment, and 6.3% (above the 4% expected for 2 years) in the second lactation after treatment. These increases were significantly higher than those in the controls and those expected through genetic improvement.

Conclusions

Treatment with casein hydrolyzate at dry-off was shown to be a viable mean to eliminate existing environmental bacterial infection, and to improve milk yield in the next lactation.

Protective effects of recombinant staphylococcal enterotoxin type C mutant vaccine against experimental bovine infection by a strain of Staphylococcus aureus isolated from subclinical mastitis in dairy cattle

Staphylococcus aureus is one of the main etiological agents of bovine mastitis; however, antibiotics that are effective against bovine strains of S. aureus are not currently available. Staphylococcal enterotoxin type C (SEC), a superantigen, is the enterotoxin most frequently expressed by bovine strains of S. aureus and one of immunogenic determinants. The purpose of this study was to evaluate the protective effectiveness of recombinant SEC mutant vaccine (MastaVactrade mark) against experimentally induced bovine infection. Three representative SEC secreting strains were selected from 9 candidate isolates that showed various intensities of pathogenicity on mice and inoculated into 5 lactating dairy cattle at a concentration of 50-5.0x10(8) CFU per quarter. The optimal experimental bovine subclinical mastitis model was produced by inoculation with 50 CFU of S. aureus 409 per quarter, a level which was not lethal to mice. After the experimental model was determined, other 3 cattle were intramuscularly administered three doses of vaccine at day 0, at 2 wks and at 6 wks. Nine quarters of 3 vaccinated cattle and 8 quarters of 3 control cattle were then challenged with S. aureus 409. An SEC-specific ELISA test conducted at 4 wks post-immunization confirmed the presence of a high antibody titer against SEC in all vaccinated cattle. The somatic cell counts from the vaccinated group remained relatively low, whereas those of control group increased significantly after challenge with S. aureus. After challenge, S. aureus was not isolated from any cattle in the vaccinated group, whereas it was isolated from 75% of the cattle in the control group. These results indicate that recombinant SEC mutant vaccine had a protective effect against S. aureus intramammary infection in lactating cattle.

Fibrinogen and ceruloplasmin in plasma and milk from dairy cows with subclinical and clinical mastitis

The potential using of Acute Phase Proteins (APPs) in the assessment of mammary gland health was studied by examining the levels of Fibrinogen (Fb) and Ceruloplasmin (Cp) in plasma and milk from dairy cows with different grades of mastitis. Plasma samples were taken from jugular vein and milk samples were collected from quarters of cows with subclinical and clinical mastitis, as well as healthy controls. California Mastitis Test (CMT) were performed on each udder quarter of cows for detection of CMT2+ and CMT3+ quarters. CMT (0) and culture negative cases were considered healthy cows. Clinical mastitis, was graded as mild (clots in milk) or moderate (clots in milk and visible signs of inflammation in the mammary gland/s). The concentrations of Fb in the plasma of the cows with subclinical and clinical mastitis were higher than in the plasma of the healthy cows (p<0.01). There was no significant difference in plasma concentration of Cp between healthy and subclinical groups (p>0.05), but differences between clinical and healthy groups were significant (p<0.05). The concentrations of Fb and Cp in the milk of the cows with subclinical and clinical mastitis were higher than in the milk of the healthy cows (p<0.01). The results indicated that measurement of Fb in plasma and milk and Cp only in milk might be suitable for early diagnosis of mastitis in dairy cows.

Internalization of Staphylococcus aureus by bovine endothelial cells is associated with the activity state of NF-kappaB and modulated by the pro-inflammatory cytokines TNF-alpha and IL-1beta

Bacterial internalization is an important process in the pathogenesis of infectious diseases in which nuclear factor kappaB (NF-kappaB) plays a prominent role. We present pharmacological evidence indicating that in bovine endothelial cells (BEC) the internalization of Staphylococcus aureus, a pathogenic bacterium that causes mastitis in bovine cattle, was associated with the activation of NF-kappaB. The internalization of S. aureus increased when BEC were stimulated with alpha-tumour necrosis factor (TNF-alpha) or beta-interleukin 1 (IL-1beta) which are known activators of NF-kappaB. SN50 (an inhibitor peptide of NF-kappaB nuclear translocation) and BAY 11-7083 (a chemical that inhibits the IkappaBalpha phosphorylation) caused significant reduction in S. aureus intracellular number, indicating that its internalization was associated with the NF-kappaB activity. Furthermore, specific inhibition of c-Jun N-terminal kinase with SP600125 (SP) or p-38 with SB203580 (SB) did not cause any change in the S. aureus intracellular number compared with the untreated control. Finally, TNF-alpha treatment of BEC after the addition of both SP and SB, induced a significant increase in S. aureus internalization above the control value. These data indicate that NF-kappaB activity is associated with S. aureus internalization and suggest that this transcription factor may play a role in the pathophysiology of bovine mastitis caused by this bacterium.

Bovine Intramammary Infections Caused by Coagulase-Negative Staphylococci May Persist Throughout Lactation According to Amplified Fragment Length Polymorphism-Based Analysis

Persistence of coagulase-negative staphylococci (CNS) in intramammary infections during lactation was studied in a research dairy herd of University of Helsinki. Milk samples from 328 udder quarters of 82 dairy cows (30 primiparous, 52 multiparous) were collected 2 wk before calving, at calving, and every 4 wk thereafter until the end of lactation or until the cow left the herd. The CNS isolated from the milk samples were analyzed with the API Staph ID 32 (bioMérieux, Marcy l'Etoile, France) test (API) and genotyped using amplified fragment length polymorphism (AFLP) analysis. The AFLP patterns were used for similarity analysis between CNS isolates and for species identification. For the latter, AFLP patterns of CNS isolates and staphylococcal type strains were used as operational taxonomic units in numerical analysis. In addition, the somatic cell count (SCC) of the milk samples was measured during lactation. A CNS infection was considered persistent when isolates originating from the same quarter had identical AFLP patterns on at least 3 consecutive samplings. In total, 63 CNS infections were detected during lactation in 30 and 33 quarters in the first and later lactations, respectively. Twenty-nine of these infections persisted and 34 were transient. Most of the persistent infections lasted until the end of lactation. In 57 quarters, CNS infection was detected before calving, at calving, or both, but only half of these quarters were infected by CNS during subsequent lactation. The geometric mean of SCC in quarters during persistent CNS infection was 657,600 cells/mL, and the mean of SCC in quarters with transient CNS infection was 619,100 cells/mL. The median of SCC in quarters during persistent CNS infection was 355,400 cells/mL, and the median of SCC in quarters with transient CNS infection was 133,500 cells/mL. According to both the API test and AFLP results, Staphylococcus chromogenes and Staphylococcus simulans were the CNS species isolated most often. Identification results for API and AFLP corresponded in 71.9% of the isolates.

Relationship between leukocyte population and nutritive conditions in dairy herds with frequently appearing mastitis

To clarify the relationship between cellular immune status and nutritive condition, feeding program, blood profiles, and leukocyte populations were analyzed in two dairy herds experiencing frequent mastitis. Fourteen of the 35 lactating cows in herd A, and 18 of the 50 lactating cows in herd B scored positive on the California Mastitis Test (CMT), and 3 of the 73 lactating cows were CMT positive in herd C, which was the control. All herds were evaluated during five different milking stages, and blood was collected from five cows at each stage. With regard to feed content, the percentages of total digestible nutrients (TDN) and crude protein (CP) were found to be lower in herds A and B than in herd C. Levels of serum total cholesterol and blood urea nitrogen were lower in herds A and B than those in herd C. Neutrophil counts in herds A and B were increased compared to the neutrophil counts in herd C. On the other hand, the numbers of CD3(+) T cells and CD14-MHC class(+) cells were lower in herd A and B than in herd C. A decrease in peripheral lymphocytes and undernourishment were observed in the herds with frequent occurring mastitis.

Contagem de Staphylococcus sp. e detecção de enterotoxinas estafilocócicas e toxina da síndrome do choque tóxico em amostras de leite cru refrigerado

Analisaram-se 80 amostras de leite cru refrigerado a 4°C e estocado por 48 horas em tanques refrigeradores de propriedades rurais do estado de Minas Gerais quanto à contagem e identificação de Staphylococcus sp. e detecção de enterotoxinas estafilocócicas (SE) e da toxina da síndrome do choque tóxico (TSST-1). Staphylococcus sp. foi detectado em 100% das amostras de leite de tanque refrigerador em contagens que variaram de 1,0 × 10(5) a 2,5 × 10(7) UFC/ml (média = 5,60 log UFC/ml; s = 0,53 e CV = 9,5%). Isolaram-se e identificaram-se 436 estirpes como: S. aureus, S hyicus, S. epidermidis, S. intermedius, S. cohnii, S. sciuri, S. schleirferi e S. delphini. As estirpes de mesmo perfil bioquímico, oriundas da mesma amostra, foram agrupadas (pools) e induzidas a produzir SE e TSST-1. A detecção dessas enterotoxinas foi feita pelo método optimum sensitivity plate, usando-se técnica de celofane sobre ágar. Identificou-se a produção de SEA, SEB, SEC, SED e de TSST-1 em percentuais variados. Dos 138 pools preparados, 91 produziram, pelo menos, uma toxina isoladamente ou em associação a outras toxinas. Dos pools enterotoxigênicos, 24,6% eram coagulase positiva e 41,3%, coagulase negativa. A confirmação de estirpes enterotoxigênicas de Staphylococcus coagulase negativa isoladas de amostras de leite é importante em relação à saúde pública.

Correlations among the somatic cell count of individual bulk milk, result of the California Mastitis Test and bacteriological status of the udder in dairy cows

In a survey of about 3000 dairy cows producing low somatic cell count (SCC) milk and kept on a large-scale dairy farm, California Mastitis Test (CMT) positivity was found in 2714 udder quarters of 1491 cows. Pathogenic microorganisms were isolated from 57.6% of these 2714 udder quarters during bacteriological examination. The commonest pathogens were coagulase-negative staphylococci (CNS, 41%) and Staphylococcus aureus (32.5%); however, udder infections caused by environmental streptococci (12.8%) and coliform bacteria (6.8%) were also common. All pathogens resulted in a significant increase of the SCC in individual bulk milk (IBM) samples. In the case of CNS, this SCC elevation in IBM was significantly lower than in the case of infection by the other pathogens. In spite of this, because of the high number of udder infections caused by CNS, the adverse effect exerted by CNS on dairy herds is considered to be substantial. It was found that 54.6% of all CMT-positive cows produced IBM of an SCC below 400 thousand per ml. The milk produced by 41% of the 315 cows excreting S. aureus also had an SCC below 400 thousand per ml. This poses a serious risk of infection to the healthy herdmates. At the same time, 11% of the infected cows produced IBM with an SCC below 100 thousand per ml. On the basis of these findings, only the regular analysis of SCC of IBM can be a reliable indicator of chronic intramammary infection. As the SCC of milk produced by CMT-positive cows (and especially of those excreting pathogens) tended to increase with advancing lactation, the authors suggest that an efficient drying-off therapy should be used to restore udder health and, whenever justified, culling of cows cannot be avoided either.

Development of a Staphylococcus aureus vaccine against mastitis in dairy cows. II. Field trial

A recently described new Staphylococcus aureus vaccine "MASTIVAC I" (Patent no. PTC/IL98/00627) against S. aureus udder infection elicited protection against experimentally induced infection in cows. In the present paper we describe a large-scale vaccination field trial. A total of 452 Israeli Holstein heifers were included in the study over two consecutive years. Approximately half of the heifers (228) were vaccinated while the others (224) served as a control group. Antibody response was detected in all vaccinated animals 4-5 weeks post-primary immunization and it was sustained throughout the experimental period (300-330 days). S. aureus infection could be detected in only 3 out of 228 animals (1.3%) in the vaccinated group and in 6 out of 224 (2.7%) in the control group. These numbers were too low to be statistically evaluated. However, when somatic cell counts (SCC) and milk yields were considered, a significant difference was found between the two groups, namely, the vaccinated cows in first and second lactation had 42 and 54%, respectively, lower SCCs and milk yields 0.5 kg per day higher than the non-vaccinated control cows. These results suggest that the new vaccine elicits a non-specific health improvement of the udder in addition to specific protection against S. aureus.

Staphylococcus aureus isolates from dairy cows and humans on a farm differ in coagulase genotype

Staphylococcus aureus is a frequent cause of animal and human infections. The aim of the present study was to test diversity of the populations of S. aureus colonising cattle and humans sharing an infected environment. Eighty-six S. aureus isolates obtained from dairy cows, from people coming into contact with dairy cows on the farm and the other farm personnel were characterized by restriction fragment length polymorphism of the coagulase gene. Molecular analyses identified ten polymorphism types with prevalent presentation of type II in isolates from cow's milk and type IV in isolates from people coming into contact with dairy cows on the farm (the cattlemen) and the other farm personnel. Seven further genotypes were identified among the isolates from the cattlemen. The results indicate that the strains dominating in human population did not equate to the causative agents of bovine mastitis.

Staphylococcus aureus strains isolated from bovine mastitis: virulence, antibody production and protection from challenge in a mouse model

Septic arthritis in mice was used as a model to evaluate the virulence of Staphylococcus aureus and coagulase-negative staphylococci (CNS) isolated from cases of bovine mastitis. In addition, the model was used to evaluate the cross protection elicited by heterologous antibodies. Mice were intramuscularly inoculated with serial bacterial doses of different strains of S. aureus or CNS, for virulence determination; they were monitored for arthritis, gangrene or death up to 20 days. Antibody response, cross reactivity and resistance to challenge were tested by subcutaneous inoculation with a low dose of one of the S. aureus or CNS strains followed by challenge with two S. aureus strains. S. aureus alpha-hemolysin isolate was the most virulent, followed by alpha+beta-hemolysin and beta-hemolysin isolates. The least virulent isolates were the non-hemolytic S. aureus strains but even they were more virulent than the CNS strains tested. Antibodies against three different S. aureus antigens were detected by the ELISA in all mice that were inoculated with the S. aureus strains but not in any of those with the CNS strains. Immunoblot test against various S. aureus strains as antigens showed high cross-reactivity among the S. aureus strains but only a slight similarity, restricted to the bands above 36 kDa, with the CNS sera. Low-dose inoculation of alpha or alpha+beta strains before challenge with homologous and heterologous strains protected the mice, whereas the two beta strains provided only partial protection. The inoculations of non-hemolytic S. aureus or the CNS strains did not elicit any protection. Our findings demonstrate that pre-exposure of mice to a low dose of certain S. aureus strains could provide protection and that the antibodies produced could have an important protective role.

Prevalence of and resistance to anti-microbial drugs in selected microbial species isolated from bulk milk samples

The prevalence of strains of Staphylococcus aureus, coagulase-negative (CN) staphylococci, Listeria monocytogenes, Escherichia coli, Enterococcus faecalis, E. faecium and Bacillus cereus, was investigated in 111 bulk milk samples. Staphylococcus aureus was isolated from 38 samples, CN staphylococci from 63 samples, E. coli from 49 samples, E. faecalis or E. faecium from 107 samples, and L. monocytogenes from two samples. Bacillus cereus was not found in any of the samples and three samples were free of any of the selected species. Sensitivity to the anti-microbial drugs amikacin, ampicillin, ampicillin + sulbactam, cephalothin (CLT), cephotaxime, clindamycin, chloramphenicol (CMP), co-trimoxazole, erythromycin (ERY), gentamicin, neomycin, norfloxacin, oxacillin, penicillin, streptomycin (STR), tetracycline (TTC) and vancomycin was tested using the standard dilution technique. Minimum inhibitory concentration (MIC) characteristics (MIC50, MIC90, MIC range) were determined for each microbial species. Resistance against one or more anti-microbial drugs was found in 93% of S. aureus, 40% of CN staphylococci, 73% of E. coli, 88% of E.faecalis, 55% of E.faecium, and one L. monocytogenes strain. Most of the strains, particularly enterococci, were resistant to STR, TTC, and ERY (MIC50 4 microg/ml). A high percentage of staphylococci were resistant to beta-lactam antibiotics. High resistance to CLT was found in 11 strains of E. coli (MIC 256 microg/ml) and strains resistant to CMP (MIC90 16 microg/ml) were detected. The highest numbers of resistance phenotypes were found in E. coil (16) and CN staphylococci (12). Eighteen identical resistance phenotypes were demonstrated in indicator bacteria (E. coli, E. faecalis, E. faecium) and pathogens (S. aureus, CN staphylococci) isolated from the same bulk milk sample. The obtained resistance data were matched against the herd owners' information on therapeutic use of the drugs. This confrontation could not explain the findings of strains resistant to ERY or CMP. Our findings are evidence of selection of resistant strains among not only pathogenic agents, but also among indicator bacteria which can become significant carriers of transmissible resistance genes.

Udder disease etiology, milk somatic cell counts and NAGase activity in Israeli Assaf sheep throughout lactation

Bacterial pathogens causing udder infections in Israeli Assaf dairy sheep were identified and changes occurring throughout lactation were monitored to study the correlation between the contaminant and the severity of the infection, as measured by somatic cell count (SCC) and NAGase tests. A total of 159 Israeli Assaf dairy sheep on one farm, in their first (69), second (13) or third and more (77) lactations were included in this study. Udder halves were tested for bacterial condition, SCC and NAGase activity 2-3 weeks post lambing and every 4 weeks after until drying-off. At first sampling, in 60.7% (193/318 quarters) of the halves no bacterial growth (NBG) was detected. Different species of coagulase negative staphylococci (CNS) were the main pathogen group in infected udders. Streptococci were isolated from 14 halves, most of them in the two udder halves. The percent of udder infection in sheep in their third or further lactations was 2.8 greater (P<0.05) than in that of sheep in their first lactation. During the lactation, 90.6% of the halves did not change their classification status, suggesting that most infections occur before lambing and/or during the following first few days. The arithmetic mean of SCC and NAGase of total half udder milk and samplings (during the lactation) were 1144+/-48x10(3)cells/ml and 49.4+/-2.5, respectively. The average SCC in the milk of halves classified as NBG was 321+/-35x10(3)cells/ml and was not significantly changed during the lactation period. In halves infected with CNS, average SCC was 1371+/-150x10(3)cells/ml at the first testing and increased to 2129+/-347x10(3)cells/ml at drying-off. No significant differences were found in SCC and NAGase activity between the different species of the CNS. The mean SCC over the types of bacteria isolated, lactation number and days in lactation was significantly different (P<0.0001). In 4% of the halves, from all samples, SCC was above 5000x10(3)cells/ml although no bacteria were detected in their milk. The higher SCC in the CNS infected halves contrasted with the more moderate SCC found in dairy cows similarly infected, suggesting that the sheep udder has a lower resistance and an augmented immunological response against this group of bacteria. Thus, this should be considered accordingly in schemes for sheep's milk quality payment.