Diagnostic Aids

There are many methodologies in determining a current infection with Salmonella enterica serotype Dublin. These include conventional culture with serotyping or polymerase chain reaction (PCR). In addition, diagnostic laboratories in the United States and several countries in Europe also utilize an enzyme linked immunosorbent assay (ELISA) to measure the level of antibodies directed against O-antigens from Salmonella enterica serotype Dublin in both blood and milk samples. These ELISAs measure the humoral immune response as an indicator of current or previous infections. ELISA results are reported as a semi-quantitative percentage value, giving an optical density reading referable to a standard set of controls. Individual or bulk tank milk samples can also be conducted on ELISAs and have been used for screening / active surveillance programs for this serovar. Sensitivity for the serum ELISA is considerably higher than fecal culture for the identification of Salmonella enterica serotype Dublin infected cattle. As a diagnostic test, the serum ELISA is reported to perform best when used in animals between 3 and 10 months of age

Contagious Pathogens-Infection with contagious pathogens occurs from the milk of other infected animals. These infections can be prevented with proper milking hygiene including post-milking teat disinfection, milking infected animals last and effective management of clinical cases.
Gram-positive
Streptococcus agalactiae
Streptococcus uberis
Gram-positive, Coagulase-positive
Staphylococus aureus
Mycoplasma sp.
Prototheca sp.
Environmental Pathogens-Infection with environmental pathogens occurs from bacteria entering the teat end from dirt, manure, bedding, milking machines that have been contaminated with these pathogens. These infections can be prevented with proper hygiene, milk machine maintenance and pre-milking teat disinfection.

E. coli and other coliform species, such as Klebsiella, Enterobacter, and Serratia, are gram negative bacteria found in the environment. These gram negative bacteria release endotoxin when they are engulfed by a white blood cell which can cause fever, decreased appetite, weight loss, a decrease in milk production and exacerbate the inflammatory response. Coliform mastitis will lead to inflammation of the mammary glands and damage of the mammary epithelial cells. An increase in vascular permeability in the mammary gland can also result in watery or serous milk.

Salmonella diagnostic testing can be challenging to interpret and apply to clinical or pathology samples. The WVDL has a workflow for the identification of Salmonella enterica subspecies enterica utilizing molecular detection, culture, serogroup and serotyping. This workflow was created based on existing data from published literature and data collected at the WVDL. We have analyzed the data collected from 2014-2020 to provide clients with a better understanding of why the WVDL has implemented the current Salmonella testing scheme.

Streptococcus agalactiae is a gram-positive, chained coccus bacterium and the reservoir in which it is found is infected udders. Strep. ag. is an obligate pathogen of the udder of dairy cattle. The presence of Strep. ag. infections has been reduced by modern milking technologies. This bacterium still is a threat for all dairies that do not have a closed herd. Strep. ag. cannot persist very long outside of the mammary gland. Cattle infected by Strep. ag. often have more than one quarter infected.

Coagulase-negative Staphylococci (CNS) are normally found at the level of the teat, nasal mucosa, as well as on the hands of milking personnel. The CNS group is made up of over 50 bacteria and are most frequently isolated from infected glands. This group includes S. chromogenes, S. hyicus, S. simulans, and S. epidermidis. S. xylosus, S. saprophyticus, S. sciuri, and S. cohni are Novobiocin-resistant Staphylococci and found as free-living in the environment. These bacteria are considered environmental causes of mastitis. Due to their high prevalence, CNS infections are usually subclinical, but can result in a 2-3 times increase in SCC within the infected quarter. The amount of increase in SCC is reflective of the Staphylococcus species causing the infection.

Staphylococcus aureus is a coagulase-positive bacteria, which is a general name for a class of bacteria that are small, round, and gram-positive. Staph. aureus is a contagious pathogen, which is transmitted from infected glands or teats during the milking process. It is a major cause of chronic or recurring clinical mastitis infections in dairy cattle and is believed to be the most significant contagious mastitis pathogen

Prototheca sp are colorless algae that are found in a variety of environmental sources and can cause chronic mastitis in cows. Currently, there is no effective treatment for protothecal mastitis, resulting in significant economic losses for producers.

Due to the treatment and prevention programs set in place for Streptococcus agalactiae and Staphylococcus aureus, there has been an increase in Mycoplasma-induced mastitis occurrence. Mycoplasmas are very small microorganisms that lack a bacterial cell wall and can be cultured from various locations on both the bodies of sick and healthy cattle. Several species can cause mastitis, including M. bovis (the most common species cultured from the udder; commensal organism of the respiratory tract), M. alkalescens (commonly cultured from the respiratory tract as well), M. bovigenitalium (commonly cultured from the reproductive tract), and M. canadense (commonly cultured from the joints). M. bovis is an important cause of respiratory disease in calves and feedlot cattle. M. bovis has also been involved in joint infections, as well as in abortions and ear infections in calves.

Microorganisms are ubiquitous in the environment. Microorganism can be found in soil, water, plants, decaying organic matter, exudates of animals or within contaminated treatment preparations on any dairy farm. These microorganisms can be isolated from an infected udder, respiratory, reproductive, and digestive tracts. The potential always exists for these microorganisms to gain access to the mammary gland during favorable conditions. When these isolates are present, it is possible that the samples were not collected in an aseptic technique. Care should be taken when deciding if these isolates were the true cause of an infection or if they are indicative of contamination. Therefore, it is important to evaluate the bulk tank milk (BTM) culture results using all available information.