Streptococcus uberis: a review of its role as a causative organism of bovine mastitis. II. Control of infection

Epidemiology and Classification of Mastitis

Simple Summary

Farmers should focus on milk quality over quantity. However, in some situations, more attention is focused on the amount of milk produced. In the long term, this approach might represent an important economic cost as it leads to increased incidence of mastitis. Mastitis affects herds in all countries and is the most economically burdensome disease encountered by dairy farmers. The current review focuses on the main pathogens that cause this inflammation and their prevalence as well as strategies to prevent their proliferation. We discuss economic loss, with the goal of demonstrating that prevention is always better than disease management.

Abstract

Farmers should focus on milk quality over quantity because milk that contains unsuitable components and/or antibiotic residues, or has a high somatic cell count, cannot be used in food production and thereby results in reduced milk yield. One of the main problems affecting the ultimate milk yield of dairy cows is mastitis. This disease is the most serious economic and health problem associated with dairy cow herds and is a major reason for excessive culling. Therefore, many studies have addressed this problem to further our understanding of the agents causing mastitis and their classification and virulence factors. This review summarizes the current knowledge regarding mastitis prevalence, the characteristics of its main causative agents, and the effects of mastitis on dairy production. The review also intends to provide guidance for future studies by examining external effects influencing dairy production in cows under field conditions.

Incidence of subclinical mastitis and prevalence of major mastitis pathogens in organized farms and unorganized sectors

Subclinical mastitis (SCM) represents a major proportion of the burden of mastitis. Determining somatic cell count (SCC) and electrical conductivity (EC) of milk are useful approaches to detect SCM. In order to correlate grades of SCM with the load of five major mastitis pathogens, 246 milk samples from a handful of organized and unorganized sectors were screened. SCC (>5 × 10(5)/mL) and EC (>6.5 mS/cm) identified 110 (45 %) and 153 (62 %) samples, respectively, to be from SCM cases. Randomly selected SCM-negative samples as well as 186 samples positive by either SCC or EC were then evaluated for isolation of five major mastitis-associated bacteria. Of the 323 isolates obtained, 95 each were S. aureus and coagulase-negative staphylococci (CoNS), 48 were E. coli and 85 were streptococci. There was no association between the distribution of organisms and (a) the different groups of SCC, or (b) organised farms and unorganised sectors. By contrast, there was a significant difference in the distribution of CoNS, and not other species, between organized farms and unorganized sectors. In summary, bacteria were isolated irrespective of the density of somatic cells or the type of farm setting, and the frequency of isolation of CoNS was higher with organized farms. These results suggest the requirement for fine tuning SCC and EC limits and the higher probability for CoNS to be associated with SCM in organized diary sectors, and have implications for the identification, management and control of mastitis in India.

Relationship between teat tissue immune defences and intramammary infections

The teat is the main entrance for pathogens into the mammary gland. It also acts as a sensory, motor and primary defence organ. This latter function is important in preventing intramammary infections while efficiency in preventing new infections is determined by teat tissue integrity. Machine milking may evoke mechanical and circulatory impairment in teat tissues. These local metabolic disorders may decrease the efficiency of the local immune defence mechanisms. Teat tissue changes can be estimated by measuring teat thickness before and after milking. Experimental and field studies showed a high correlation between changes in thickness and infection risk. Teats with > 5% change in thickness have significantly increased teat duct colonisation rates and intramammary infection rates. The link between changes in teat thickness and infections should be found in changes in local immune defences and measurable changes in cytological and biochemical immune factors are expected. Indeed, the application of experimental milking conditions (i.e. no pulsation milking and positive pressure milking) showed to have a significant influence on some non specific immune factors in teat secretion. Positive pressure milking increases PMNs content and decreases macrophages content of teat secretion. Some enzymes such as NAGase and lysozyme were decreased by positive pressure milking, the concentration of the same enzymes were higher after no pulsation milking. A better knowledge on the interaction between the teat apex immune defense mechanisms and the machine milking process is necessary to reduce the new infection rate of the bovine mammary gland.

Efficacy of two antibiotic treatments in curing clinical and subclinical mastitis in lactating dairy cows

AIM

To compare the bacteriological and clinical cure rates for clinical and subclinical mastitis in New Zealand dairy cows following treatment with either an intramammary penicillin-dihydrosptreptomycin preparation or a subcutaneous injection of penethamate hydriodide.

METHODS

Milk samples were collected from clinical and subclinical cases of mastitis before and 14 and 21 days after initiation of treatment for bacteriological culture, somatic cell count determination and conductivity testing.

RESULTS

No significant differences in the bacteriological cure rate of major Gram-positive pathogens, clinical cure rate, somatic cell count or conductivity were found between treatments. However, the bacteriological cure rate of coagulase-negative staphylococcus infections and the overall bacteriological cure rate was lower for quarters treated with penethamate than with penicillin-dihydrosptreptomycin.

CONCLUSIONS

The bacteriological cure rate of mastitis caused by major Gram-positive pathogens, the clinical cure rate, somatic cell count and conductivity did not differ between the two antibiotic treatments. .

Virulence factors of Streptococcus uberis isolated from cows with mastitis

For intramammary infections (IMI) to occur, mechanisms associated with avoidance of phagocytic defenses, rapid growth of bacteria, adherence of bacteria to epithelial cells, and/or bacterial colonization of mammary tissue are probably present. During the last decade, several potential virulence factors of Streptococcus uberis have been identified. Some of these factors are cell-associated while other factors are extracellular. Proposed antiphagocytic factors of S. uberis include capsule, neutrophil toxin, M-like protein and R-like protein. Activation of plasminogen by S. uberis has been proposed as an important mechanism for this organism to obtain nutrients for optimal bacterial growth. Potential virulence factors produced by S. uberis and released extracellularly include hyaluronic acid capsule, hyaluronidase and uberis factor. Streptococcus uberis isolated from bovine IMI adhere to and invade mammary epithelial cells. Involvement of intact microfilaments and de novo eukaryotic protein synthesis are required for bacterial invasion of mammary epithelial cells; a process that appeared to occur by a receptor-mediated endocytosis mechanism. De novo bacterial protein synthesis was also required for invasion of S. uberis into mammary epithelial cells. Furthermore, S. uberis survived within mammary epithelial cells for extended periods of time without losing viability or damaging the eukaryotic cell. Further research directed towards characterization of host-pathogen interactions that take place during the early stages of S. uberis intramammary infection are needed to enhance our understanding of pathogenesis and thus contribute to development of methods to minimize production losses associated with S. uberis mastitis in dairy cows.

In vitro expression of adhesion receptors and diapedesis by polymorphonuclear neutrophils during experimentally induced Streptococcus uberis mastitis

The expression of adhesion receptors and diapedesis by polymorphonuclear neutrophils (PMN) were studied before and during experimentally induced Streptococcus uberis mastitis. Both quarters of the left half of the udders of five midlactation cows were inoculated with a suspension containing approximately 500 CFU of S. uberis 0140J. Clinical signs of an inflammatory reaction and leukocyte influx were observed 24 h after challenge. The expression of CD11b/CD18 adhesion receptors, determined by flow cytometry, was upregulated 24 h after challenge. A confluent monolayer of bovine secretory mammary epithelial cells on collagen-coated inserts was used to study PMN diapedesis. Bovine C5a was used as the chemoattractant. An 80% decrease in PMN diapedesis was observed 24 h after challenge. The decrease in diapedesis continued for 3 weeks after challenge.

Subtyping of Streptococcus uberis by DNA amplification fingerprinting

Total DNA of Streptococcus uberis from cows with mastitis was analyzed by DNA amplification fingerprinting (DAF) and compared with restriction endonuclease fingerprinting (REF). DAF grouped 22 strains into 15 distinct patterns, while REF grouped them into 12 patterns. These results suggest that DAF is a useful technique for subtyping strains of S. uberis.

Differentiation of Streptococcus uberis from Streptococcus parauberis by polymerase chain reaction and restriction fragment length polymorphism analysis of 16S ribosomal DNA

Streptococcus uberis type II has been proposed recently as a separate species designated Streptococcus parauberis (A. M. Williams and M. D. Collins, J. Appl. Bacteriol. 68:485-490, 1990). Differentiation of S. parauberis from S. uberis has been possible only by DNA-DNA hybridization or 16S rRNA sequencing, since the biochemical and serological characteristics of the two species are indistinguishable. A simple and reliable technique was developed for differentiating S. parauberis (S. uberis type II [ATCC 13386]) from S. uberis (S. uberis type I [ATCC 9927, ATCC 13387, and ATCC 27958]) by restriction fragment length polymorphism (RFLP) analysis of 1.4-kb 16S ribosomal DNA (rDNA). Oligonucleotide primers complementary to 16S rRNA genes were used to amplify 16S ribosomal gene fragments from genomic DNA by polymerase chain reaction. The 1.4-kb 16S rDNA fragment was digested with ScaI, NspI, DdeI, and AvaII restriction endonucleases. Restriction fragments produced by all four restriction endonucleases were characteristic for each species. RFLP analysis of 16S rDNA from 24 "S. uberis" isolates obtained from mammary secretions of dairy cows indicated that all 24 isolates were indeed S. uberis.

Antigenic and genetic homogeneity of Streptococcus uberis strains from the bovine udder

DNA- fingerprints (Hind III) of Streptococcus uberis field isolates from New York State and Europe showed substantial homogeneity, but were different to those of the type strain of the newly proposed psychrophilic species S. parauberis. S. uberis strains had major SDS-heat extracted antigens of molecular masses (Mr) less than 14, 40-41, 42-43, 59-61, 80-86 and 118-122 kDa following immunoblotting with rabbit hyperimmune sera. Bovine sera and milk reacted with the 40-41 and 118-122 kDa antigens. Variations in the Mr of particular bands were too unevenly distributed to permit formation of subgroups. Although cross reactive, the sizes of the antigens of S. parauberis strain NCDO 2020 were substantially different to those of S. uberis, the most prominent antigen having a Mr of 50 kDa. The antigenic and genetic data therefore strongly support the introduction of S. parauberis as a distinct species. S. uberis strains reacted with antiserum to Lancefield groups B, E, G and P, their grouping reactions showing no correlation with DNA and immunoblot fingerprints. Lancefield grouping of S. uberis therefore appears to have little value in identification.

In vitro growth of mastitis-associated streptococci in bovine mammary secretions

Cell-free, fat-free mammary secretions were tested in vitro for ability to support growth of streptococci associated with mastitis. Secretions were obtained prior to drying off, during the dry period, at calving, and during lactation from four cow treatment groups. Treatment groups were dry cow therapy, dry cow therapy and mammary glands subjected to induced inflammation 7 d post-drying-off, no dry cow therapy and no induced inflammation, no dry cow therapy but mammary glands subjected to induced inflammation. Growth of Streptococcus uberis, Streptococcus faecalis, and Streptococcus agalactiae in secretions from nonlactating glands was unaffected by induced inflammation. Growth of Streptococcus bovis was significantly inhibited in secretion obtained 14 d after induced inflammation. Dry cow therapy had no effect on streptococcal growth in secretion obtained 7 d after therapy. Streptococcal growth was greatest in secretions from involuted glands, and there was little or no evidence for growth inhibitory factors in cell-free, fat-free secretions obtained during the dry period. Milk from lactating glands inhibited streptococcal growth, and the inhibitory factor was presumptively identified as lactoperoxidase. Apolactoferrin, immunoglobulin, or both had little effect on streptococcal growth.

Environmental mastitis: cause, prevalence, prevention

Rate of intramammary infection by coliform bacteria and species of streptococci other than Streptococcus agalactiae (environmental pathogens) was studied in a dairy herd in total confinement. Rate was higher during the dry period than during lactation and increased progressively as parity increased. Rate was maximal during summer and coincided with maximum exposure to coliforms in bedding. Streptococcal infections were longer than coliform. Approximately 59% of streptococcal infections and 69% of coliform infections were present for 30 lactation days or less. Percent quarters infected by day of year varied between .7 and 3.0% for coliform bacteria and between 1.6 and 4.7% for streptococci. Approximately 81% of coliform infections and 53% of streptococcal infections during lactation were clinical. Clinical cases were highest during the first 76 days of lactation and during summer. Only 6.7% of coliform infections resulted in acute coliform mastitis, and all acute cases were during summer or early lactation. Dry cow therapy reduced rate of streptococcal infection during the early dry period but was without effect during the prepartum period. There was no effect of dry cow therapy on coliform infection rate during the dry period. Problems associated with prevalence and control of environmental mastitis were discussed.

Environmental pathogens and intramammary infection during the dry period

Rate of coliform and streptococcal intramammary infection during the dry period was studied in 168 dry periods. Coliform infection rate was influenced by stage of dry period, parity, and season during which dry periods occurred. Effects of dry cow therapy, immunization, or induced inflammation on coliform infection rate were minimal. Coliform infections originating in the first 50% of the dry period and persisting to lactation were predominantly other than Escherichia coli, whereas the majority originating in the last 50% of the dry period and persisting to lactation were Escherichia coli. Duration of streptococcal infections was greater than coliform infections. Dry cow therapy reduced streptococcal infection rate, and the effect was exerted primarily during the first 25% of the dry period. Effects of parity and season were not significant and likely masked by the positive effects of dry cow therapy. Results support the contention that all quarters of all cows should be dry treated for maximum reduction of new streptococcal infection during the dry period. Results suggest that methods other than conventional dry cow therapy are required for control of coliform infection during the dry period and streptococcal infection during the latter half of the dry period.

Efficacy of an iodine backflush for preventing new intramammary infections

Efficacy of an iodine backflush system for reducing new intramammary infection was tested in two 11-wk trials. Forty cows in each trial were paired by breed, age, stage of lactation, and intramammary infection status. Each pair was assigned randomly either to a group milked with clusters that were reverse flushed with water, 25 ppm iodine, water and air or to a group milked with clusters receiving no backflush treatment between cows. Backflushing clusters reduced infections caused by Corynebacterium bovis and coagulase-positive staphylococci in both trials. However, backflushing clusters produced no clear advantage for reducing new infections with coagulase-negative staphylococci, Gram-negative bacilli, or streptococci (species other than Streptococcus agalactiae). No differences in somatic cell counts between experimental groups were observed. Teat cup liners and teat ends were swabbed after 120 and 1200 milkings/liner. Total microbial counts were significantly greater for liners that were not backflushed than from backflushed liners at each swabbing. However, no differences were significant between groups for mean teat end microbial counts in either trial.

Germicidal teat dip in a herd with low prevalence of Streptococcus agalactiae and Staphylococcus aureus mastitis

Effectiveness of an iodophor teat dip in reducing new intramammary infection and clinical mastitis was tested in a herd free of Streptococcus agalactiae and with a low prevalence of Staphylococcus aureus infections. In this 6-mo study with an average of 152 lactating cows on trial on sampling dates, right rear and left front teats were dipped after each milking while right front and left rear teats were undipped controls. Teat dipping significantly reduced new infections by Staphylococcus aureus, streptococci (other than Streptococcus agalactiae), coagulase-negative staphylococci, and Corynebacterium bovis and reduced clinical cases caused by infections established during the trial. However, the dip did not reduce new infections or clinical mastitis caused by coliform bacteria. Therefore, use of a germicidal dip is recommended for herds with a low prevalence of Streptococcus agalactiae and Staphylococcus aureus, but the practice should not be expected to control coliform mastitis.