The leukotoxin of Pasteurella (Mannheimia) haemolytica is believed to play a significant role in pathogenesis, causing cell lysis and apoptosis that lead to the lung pathology characteristic of bovine shipping fever. Using a system for Cre-lox recombination, a nonpolar mutation within the lktC transacylase gene of the leukotoxin operon was created. The lktC locus was insertionally inactivated using a loxP-aph3-loxP cassette, and then the aph3 marker was excised from the chromosome by Cre recombinase expressed from a P. haemolytica plasmid. The resulting lktC strain (SH2099) secretes inactive leukotoxin and carries no known antibiotic resistance genes. Strain SH2099 was tested for virulence in a calf challenge model. We inoculated 3 ؋ 10 8 or 3 ؋ 10 9 CFU of wild-type or mutant bacteria into the lungs of healthy, colostrum-deprived calves via transthoracic injection. Animals were observed for clinical signs and for nasal colonization for 4 days, after which they were euthanized and necropsied. The lower inoculum (3 ؋ 10 8 CFU) caused significantly fewer deaths and allowed lung pathology to be scored and compared, while the 3 ؋ 10 9 CFU dose of either the wild-type or mutant was lethal to >50% of the calves. The estimated 50% lethal dose of SH2099 was four times higher than that of the wild-type strain. Lung lesion scores were reduced twofold in animals inoculated with the mutant, while clinical scores were nearly equivalent for both strains. The wild-type and mutant strains were equally capable of colonizing the upper respiratory tracts of the calves. In this study, the P. haemolytica lktC mutant was shown to be less virulent than the parent strain.

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Current lot release testing of conventional vaccines emphasizes quality control of the final product and is characterized by its extensive use of laboratory animals. This report, which is based on the outcome of an ECVAM (European Centre for Validation of Alternative Methods, Institute for Health and Consumer Protection, European Commission Joint Research Centre, Ispra, Italy) workshop, discusses the concept of consistency testing as an alternative approach for lot release testing. The consistency approach for the routine release of vaccines is based upon the principle that the quality of vaccines is a consequence of a quality system and of consistent production of lots with similar characteristics to those lots that have been shown to be safe and effective in humans or the target species.The report indicates why and under which circumstances this approach can be applied, the role of the different stakeholders, and the need for international harmonization. It also gives recommendations for its implementation.

Porphyromonas gingivalis produces a variety of virulence factors that may have a function in the periodontal disease process. Determination of the role of these various factors in pathogenesis and identification of a means for protecting the host from the destructive effects of this organism are areas of vigorous investigation. In this study we demonstrate the potential of avirulent Salmonella typhimurium strains to stimulate a specific systemic and mucosal immune response to a cloned P. gingivalis hemagglutinin (HagB). An avirulent strain of S. typhimurium, X4072, expressing the hagB gene ofP. gingivalis 381 on the plasmid pDMD1 was intragastrically