Coliform bacteria are Gram-negative, non-spore-forming, aerobic and facultative anaerobic, rod-shaped bacteria that ferment lactose with the production of acid and gas within 48 hours at 35 degrees Celcius. Genera classified as coliforms are Escherichia, Klebsiella and Enterobacter. Escherichia coli and Klebsiella pneumoniae are the coliform species most commonly isolated from intramammary infections and E. Coli is the predominant coliform species reported as causing intramammary infection in most studies (1). In addition to the coliform bacteria, other Gram-negative bacteria such as species of Serratia, Pseudomonas, Proteus, and Citrobacter also infect the bovine mammary gland and cause clinical cases of mastitis.
Coliform bacteria are significant cause of environmental mastitis in dairy herds and their relative importance in dairy herds has increased with the advent of effective control procedures for the contagious pathogens Staphylococcus aureus and Streptococcus agalactiae (2). While the prevalence of coliform intramammary infection at a point in time in dairy herds seldom exceeds 1-2% of mammary quarters, they are frequently the leading cause of clinical mastitis in well-managed dairies with low bulk tank milk somatic cell counts. Coliform bacteria are typically isolated from 20-40% of clinical cases occurring in herds and they generally account for the majority of peracute cases of clinical mastitis in herds (3).
Control of coliform mastitis has historically been dependent upon reduced teat-end exposure to the pathogen in the environment of the dairy cow. Control efforts concentrate on the use of inorganic bedding materials, limiting exposure to muddy or manure covered areas, and milking clean, dry teats and udders (4). Control of coliform mastitis through increased specific immunity was thought not to be possible until the late 1980's as no common virulence factor associated with the coliform bacteria had been identified.
In 1988 Tyler et al. (5) reported that dairy cows with low naturally occurring titers recognizing the mutant E. Coli strain J5 experienced a five-fold increase in the risk of clinical coliform mastitis. Escherichia coli strain J5 is a genetically stable UDG-4-epimerase-deficient RC mutant that was derived from E. coli 011:B4. Escherichia coli J5 is a rough mutant that is unable to attach the oligosaccharide side chain ("0" or somatic antigens) to the core oligosaccharide-lipid A complex (common core antigens) associated with the outer membrane of all Gram-negative bacteria. This macromolecule referred to as lipopolysaccharide (LPS) or endotoxin is an integral part of the outer membrane of Gram-negative bacteria and is at least partially responsible for the clinical nature of coliform mastitis. While the "O" antigens are extremely heterogeneous, the common core antigens possess striking chemical, structural, and immunologic homology across strains, species and genera of Gram-negative bacteria.
Gonzales et al. (6) first reported that immunization with a whole cell bacterin of E. coli J5 significantly reduced the incidence of clinical cases of coliform mastitis under conditions of natural exposure. Subsequent studies by Cullor (7) and Hogan et al. (8) confirmed the report of Gonzales et al. (6). Interestingly, the study reported by Hogan et al. (8) found no difference in the rate of new coliform infection between vaccinated and unvaccinated cows. However, only 20% of coliform infections became clinical in vaccinates versus 67% in unvaccinated controls.
Two experimental challenge trials (9,10) failed to show protection against the establishment of infection and all challenged cows developed clinical mastitis. However, Hogan et al. (9) found that infections in vaccinated cows were less severe. Vaccinated cows had lower peak numbers of E. coli in infused quarters, and lower rectal temperatures than unvaccinated controls. In addition, milk production and feed intake were more depressed in controls than in vaccinated cows. A second experimental challenge trial reported by Hogan et al. (11) employed a strain of E. coli known to cause a mild form of clinical mastitis. Results from this trial again revealed that vaccination did not prevent the establishment of infection but vaccinated cows had infections of reduced duration and reduced local signs of clinical mastitis.
The mechanism(s) by which immunization reduces the incidence of clinical mastitis in natural exposure trials and the severity of infection in challenge trials is not known. Protection is thought to be afforded by immunoglobulins specific for the core region of the LPS molecule which is structurally conserved among Gram-negative genera. The core region is exposed of RC mutants and is thought to be exposed immediately after division of the bacterial cell prior to the complete synthesis of the outer "O" oligosaccharide side chains. Protective mechanisms suggested include: (1) core LPS antibodies neutralize the toxic effects of LPS; (2) increased complement-mediated bacteriolysis; and (3) core LPS antibodies promote clearance of LPS and/or Gram-negative bacteria through opsonization and enhanced phagocytosis. Infusion of low levels of endotoxin into mammary quarters of vaccinated and unvaccinated cows resulted in elevated somatic cell counts and no differences were observed between the two groups of cows (K.L. Smith & D.A. Todhunter, unpublished observations, 1985). These studies provided no evidence for endotoxin neutralization as the means of protection in vaccinated cows. There is no evidence of increased complement-mediated bacteriolysis.
Hogan et al. (12) have reported enhanced opsonization by serum from vaccinated cows and the enhanced opsonization coincided with high serum IgM titers to E. coli J5. A trend for enhanced opsonic activity of colostrum from vaccinates was noted in these studies, and colostrum and milk collected 21 days after calving from vaccinated cows had higher IgM titers to E. coli J5 than did mammary secretions from control cows. A working hypothesis is that improved opsonization leads to reduced bacterial numbers, less severe infections, and subsequently a reduction in clinical cases of mastitis. Cost-benefit modeling indicated vaccination is an economically sound strategy on well-managed dairies with clinical coliform mastitis problems (13).
Currently, there are three core antigen vaccines commercially available in the US. Two of these vaccines are based on E. coli J5 and the third is based on an RC mutant of Salmonella typhimurium (14). A recent survey by the National Animal Health Monitoring Survey indicated that approximately 54% of the cows in the US were being immunized with one of the three available vaccines.
1. Todhunter, D.A., Smith, K.L., Hogan, J.S. & Schoenberger, P.S. Gram-negative bacterial infections of the mammary gland in cows. Am. J. Vet. Res. 52: 184-188 (1991)
2. Smith, K.L., Todhunter, D.A. & Schoenberger, P.S. Environmental mastitis: cause, prevalence, prevention. J. Dairy Sci. 68: 1531-1553 (1985)
3. Hogan, J.S., Smith, K.L., Hoblet, K.H., Schoenberger, P.S., Todhunter, D.A., Hueston, W.D., Pritchard, D.E., Bowman, G.L., Heider, L.E., Brockett, B.L. & Conrad, H.R. Field survey of clinical mastitis in low somatic cell count herds. J. Dairy Sci. 72: 1547-1556 (1989)
4. Smith K.L. & Hogan, J.S. Environmental mastitis. In: K.L. Andersen (Editor), The Veterinary Clinics of North America: Food Animal Practice. Vol 9, No. 3 pp. 489-498 (1993)
5. Tyler, J.W., Cullor, J.S., Osburn, B.I., Bushnell, R.B. & Fenwick, B.W. Relationship between serologic recognition of Escherichia coli 0111:B4 (J5) and clinical coliform mastitis in cattle. Am. J. Vet. Res. 49: 1950-1954 (1988)
6. Gonzales, R.N., Cullor, J.S., Jasper, D.E., Farver, T.B., Bushnell, R.B. Oliver, M.N. Prevention of clinical coliform mastitis in dairy cows by a mutant Escherichia coli vaccine. Can. J. Vet. Res. 53: 301-305 (1989)
7. Cullor, J.S. The Escherichia coli J5 vaccine: Investigating a new tool to combat coliform mastitis. Vet. Med. 86: 836-844 (1991)
8. Hogan, J.S., Smith, K.L., Todhunter, D.A. & Schoenberger, P.S. Field trial to determine efficacy of an Escherichia coli J5 mastitis vaccine. J. Dairy Sci. 75: 78-84 (1992)
9. Hogan, J.S., Weiss, W.P., Todhunter, D.A., Smith, K.L. & Schoenberger, P.S. Efficacy of an Escherichia coli J5 mastitis vaccine in an experimental challenge trial. J. Dairy Sci. 75: 415-422 (1992)
10. Hill, A.W. Vaccination of cows with rough Escherichia coli mutants fails to protect against experimental intramammary bacterial challenge. Vet. Res. Commun. 15: 7-16 (1991)
11. Hogan, J.S., Weiss, W.P., Smith, K.L., Todhunter, D.A. Schoenberger, P.S. Effects of an Escherichia coli J5 vaccine on mild clinical coliform mastitis. J. Dairy Sci. 78:285-290 (1995)
12. Hogan, J.S., Todhunter, D.A., Tomita, G.M., Smith K.L. Schoenberger, P.S. Opsonic activity of bovine serum and mammary secretion after Escherichia coli J5 vaccination. J. Dairy Sci. 75: 72-77 (1992)
13. Degraves, F.J., & Fetrow, J. Partial budget analysis of vaccinating dairy cattle against coliform mastitis with an Escherichia coli J5 vaccine. J. Am. Vet. Met. Assoc. 199: 451-455 (1991)
14 . McClure, A.M., Christopher, E.E., Wolff, W.A., Fales, W.H., Krause, G.F. & Miramonti, J. Effect of Re-17 mutant Salmonella typhimurium bacteria toxoid on clinical coliform mastitis. J. Dairy Sci. 77: 2272-2280 (1994)