No abstract

Mycoplasma gallisepticum strains, including a series of field strains from North Carolina, were examined by homologous and heterologous hemagglutination-inhibition (HI) tests and by restriction endonuclease DNA analysis to determine whether they were closely related. HI results indicated wide antigenic diversity. Generally, homologous HI titers were higher than heterologous titers; exceptions were probably due to relative insensitivity of individual antigen batches. Strain A5969, commonly used as an HI antigen strain in many laboratories, was insensitive for detecting antibodies against all of the strains studied. None of the antigens was efficient in detecting HI antibodies against all other strains studied. Restriction endonuclease analysis indicated that North Carolina strains K501, K1453, and K1503 were closely related or identical, as were strains K1545, K1659, and K1486. Strain K1528, isolated from a peacock originally felt to be the source of many of the outbreaks, was not closely related to any of the other strains. Most strains identical or closely related by restriction endonuclease analysis were also closely related by HI. Strains 383T and 236C were identical by restriction enzyme analysis but unrelated by HI tests.

A special chamber was constructed with the goal of controlling the process of aerosol infection of chickens with Mycoplasma gallisepticum (MG). The virulent Australian MG field strain Ap3AS was used in each of three experiments. The response to infection of layer-strain pullets was measured serologically, by the incidence and severity of gross lesions in tracheas and air sacs, and by the relative numbers of MG isolated from tracheas and air sacs 2 wk after challenge. In two of the experiments tracheal sections were assessed microscopically. Exposure to a nebulized, undiluted broth culture of MG for 10, 20, or 30 min produced uniformly severe lesions and serological responses. By contrast, results were less severe and less consistent when doses of up to 10(8) color-changing units (CCU) were injected directly into the abdominal air sacs. Gross air sac lesions were consistently produced in almost all pullets by exposure to an infectious aerosol containing 10(2)-10(3) CCU/liter of air for 10 min and an air flow rate of 40 liters/min. This can be achieved by nebulizing a 10(-3) dilution of a fresh, early stationary phase culture of MG strain Ap3AS. However, under the conditions of these experiments, this dose did not produce significant gross or histologic lesions in the trachea.

A major innovation in the delivery of the veterinary curriculum is being implemented at The University of Melbourne using the subject of systematic bacteriology and mycology as a pilot project. Students receive course information as interactive, multimedia databases. These consist of text and an associated library of catalogued digital images, movies and sounds. The databases employ a hypermedia information system to achieve efficient integration within and between subjects. The new delivery method encourages greater autonomy and more active learning roles for students than occurs in traditionally taught courses. Students will use their databases as the principal resource of information for undergraduate studies. A unique feature of this system for delivering the curriculum is that students will modify and expand their databases during the course. The ultimate aim is for students at graduation to receive, on disc, a copy of their own databases, adapted by themselves to their particular future professional needs. As graduate veterinarians they will continue to use their databases as a major resource for information and learning, thus providing continuity from undergraduate to continuing postgraduate education.