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.

The 34,525 nucleotide sequence of a double-stranded DNA bacteriophage (phiMhaA1-PHL101) from Mannheimia haemolytica serotype A1 has been determined. The phage encodes 50 open reading frames. Twenty-three of the proteins are similar to proteins of the P2 family of phages. Other protein sequences are most similar to possible prophage sequences from the draft genome of Histophilus somni 2336. Fourteen open reading frames encode proteins with no known homolog. The P2 orthologues are collinear in phiMhaA1-PHL101, with the exception of the phage tail protein gene T, which maps in a unique location between the S and V genes. The phage ORFs can be arranged into 17 possible transcriptional units and many of the genes are predicted to be translationally coupled. Southern blot analysis revealed phiMhaA1-PHL101 sequences in other A1 isolates as well as in serotype A5, A6, A9, and A12 strains of M. haemolytica, but not in the related organisms, Mannheimia glucosida or Pasteurella trehalosi.

Un tour d’horizon des premières productions de miroirs en pierre et en métal de la Préhistoire et de la Protohistoire, depuis le Néolithique jusqu’à l’âge du Fer, permet de proposer une nouvelle histoire du reflet dans les régions orientales et méditerranéennes, dont les racines plongent en Égypte et au Proche-Orient ancien. Guidée par une perspective historique, cette démarche a pour but d’enserrer chronologiquement et géographiquement le phénomène dans et autour de l’espace méditerranéen, et de définir son intégration dans les circuits régionaux.