The GD Animal Health laboratory uses various methods to trace veterinary pathogenic bacteria. This covers a wide field of knowledge comprising veterinary bacteriology, water microbiology and food bacteriology. A wide range of tests is available, part of which was developed by GD Animal Health. Every year the bacteriological laboratory carries out 350,000 bacteriological tests (this refers to classical culture methods).
Insight into animal health
GD Animal Health has a keen insight into the health of farmed animals in the Netherlands. It collects information on the pathogens that endanger the livestock and knows their susceptibility for antibiotics. That makes GD Animal Health the ideal partner for projects like clinical effectiveness studies, monitoring antibiotic resistance development, and collecting field isolates for antibiotic resistance tests.
In addition to the classic culture methods and microscopic studies, GD Animal Health uses serological (e.g. ELISA), histological and molecular-biological (PCR) tests to detect pathogens and, if applicable, their toxins. Quicker, more efficient and cheaper methods are used, provided that they comply with the quality requirements. For carrying out ELISA tests, GD Animal Health has a completely robotised laboratory with a capacity of 15,000 tests per day. Various materials can be tested, including organs, tissues, milk, blood and feces. Much bacteriological testing takes place in the framework of health and monitoring programmes, including salmonella in poultry, mastitis and Johne’s disease in cattle, atrophic rhinitis and PIA in swine and CEM in horses.
If applicable, bacteriological identification is followed by a susceptibility test of the isolated pathogens to antibiotics. This is the basis for a therapy with the lowest risk of development of resistance.
If no registered vaccine is available for a certain pathogenic bacterium, GD Animal Health can produce an autogenous vaccine. That is a made-to-measure, farm-specific vaccine. Producing autogenous vaccines is a unique cooperative product of the pathology and bacteriology departments. After the pathologist has diagnosed that the agent that was cultured after necropsy was the cause of the disease, this bacterium is used for producing a farm-specific vaccine.
Core of the bacteriology department
Bacteriological testing is carried out at the departments of immunology, molecular biology, histology and bacteriology. They work with classical culture methods, microscopic testing methods, molecular biological techniques (PCR) and various immunological tests. A number of these tests have been developed within GD Animal Health itself (in cooperation with GD Animal Health R&D laboratory).
The pathogenic micro-organisms are first cultured. For that purpose a representative sample of material, possibly harboring the agent, is inoculated onto a suitable culture medium. The inoculated medium is incubated a certain time at a certain temperature. Selective and non-selective media are used which can be solid culture media, such as blood agar, or fluid media. The incubation period depends on the bacteria in question and varies from mostly one to two days to sometimes seven days for rapidly growing bacteria and up to eight to ten weeks for slowly propagating mycobacteria (EEv1) . The bacterium is finally identified on the basis of morphological and physiological properties of pure cultures, through biochemical testing, MALDI-TOF MS testing or serological testing.
The antibiotic susceptibility testing of the isolated pathogens is the basis for the therapy that the practitioner uses at the farm, with the lowest risk of resistance development. Susceptibility tests are carried out with a microbroth dilution assay.
This type of testing is used to quickly acquire a general impression about the presence or absence of morphologically different bacteria. Various staining techniques are available to visualisethe bacteria, including Gram staining, immunofluorescence tests, acid-fast staining (Ziehl-Neelsen) and capsule staining.
PCR testing (polymerase chain reaction)
This test method is increasingly being used within the GD Animal Health aboratory. The principle is based on amplification of a specific DNA or RNA fragment of a bacterium. The size and composition of the amplified DNA or RNA is characteristic of the bacterium to be identified. What is known as ‘real-time PCR’ makes it possible to detect a specific bacterium as well as to measure the number of bacteria present in the material within one day. GD Animal Health uses the PCR method among other things for detecting Salmonella spp, Mycobacterium (EEv2) paratuberculosis, mycoplasmas and toxin genes of Pasteurella multocida. For some pathogens, GD Animal Health is capable of typing the bacteria (SA3). Typing is useful for epidemiology to distinguish different strains of a particular bacterial species from each other.
The most popular method is ELISA (Enzyme-linked Immunosorbent (EEv4) Assay) that is used to detect antibodies against micro-organisms in milk or serum from animals. With this technique, antigen-antibody bounding is visualised, resulting in a rapid, easy, robust and reliable method. GD Animal Health carries out millions of ELISA tests every year. For that purpose it has a completely robotised laboratory with a capacity of 15,000 tests per day. In addition to ELISA, the GD Animal Health laboratory carries out other serological tests, such as various agglutination tests, agar gel diffusion tests and serum neutralisation tests.