Epinephrine and norepinephrine regulate the expression of virulence factors in Gallibacterium anatis.

Gallibacterium anatis is a member of the Pasteurellaceae family and is an opportunistic pathogen that causes gallibacteriosis in chickens. Stress plays a relevant role in promoting the development of pathogenicity in G. anatis. Epinephrine (E) and norepinephrine (NE) are relevant to stress; however, their effects on G. anatis have not been elucidated. In this work, we evaluated the effects of E and NE on the growth, biofilm formation, expression of adhesins, and proteases of two G. anatis strains, namely, the hemolytic 12656-12 and the nonhemolytic F149T biovars. E (10 µM/mL) and NE (30 and 50 µM/mL) increased the growth of G. anatis 12656-12 by 20 % and 25 %, respectively. E did not affect the growth of F149T, whereas 40 µM/mL NE decreased bacterial growth by 25 %. E and NE at a dose of 30-50 µM/mL upregulated five fibrinogen adhesins in the 12565-12 strain, whereas no effect was observed in the F149T strain. NE increased proteolytic activity in both strains, whereas E diminished proteolytic activity in the 12656-12 strain. E and NE reduced biofilm formation (30 %) and increased Congo red binding (15 %) in both strains. QseBC is the E and NE two-component detection system most common in bacteria. The qseC gene, which is the E and NE receptor in bacteria, was identified in the genomic DNA of the 12565-12 and F149TG. anatis strains via PCR amplification. Our results suggest that QseC can detect host changes in E and NE concentrations and that catecholamines can modulate the expression of several virulence factors in G. anatis.

Isolation and characterization of a Mannheimiahaemolytica secreted serine protease that degrades sheep and bovine fibrinogen.

Mannheimiahaemolytica is an opportunistic agent of the respiratory tract of bovines, a member of the Pasteurellaceae family, and the causal agent of fibrinous pleuropneumonia. This bacterium possesses different virulence factors, allowing it to colonize and infect its host. The present work describes the isolation and characterization of a serine protease secreted by M. haemolytica serotype 1. This protease was isolated from M. haemolytica cultured media by precipitation with 50 % methanol and ion exchange chromatography on DEAE-cellulose. It is a 70-kDa protease able to degrade sheep and bovine fibrinogen or porcine gelatin but not bovine IgG, hemoglobin, or casein. Mass spectrometric analysis indicates its identity with protease IV of M. haemolytica. The proteolytic activity was active between pH 5 and 9, with an optimal pH of 8. It was stable at 50 °C for 10 min but inactivated at 60 °C. The sera of bovines with chronic or acute pneumonia recognized this protease. Still, it showed no cross-reactivity with rabbit hyperimmune serum against the secreted metalloprotease from Actinobacilluspleuropneumoniae, another member of the Pasteurellaceae family. M. haemolytica secreted proteases could contribute to the pathogenesis of this bacterium through fibrinogen degradation, a characteristic of this fibrinous pleuropneumonia.

A putative siderophore receptor of Gallibacterium anatis 12656-12 under Fur control also binds hemoglobin.

Pasteurellaceae family members obtain iron directly from host proteins or through siderophore-dependent mechanisms. Although Gallibacterum anatis expresses different virulence factors, its response to growth under iron restriction is unknown. G. anatis cultured in the presence of 2,2'-dipyridyl, up-expressed an approximately 65 kDa protein and repressed the expression of a 70 kDa protein. MALDI-TOF analysis of those proteins indicated homology with CirA (65 kDa), a protein involved in iron-siderophore acquisition in Mannheimia succinoproducens and a TonB-dependent receptor (70 kDa protein), a protein that binds chicken hemoglobin; however, G. anatis siderophore production was not detected by chromo azurol S (CAS)-BHI agar determination. This putative G. anatis siderophore receptor is under Fur control, but not the hemoglobin binding protein, as observed in G. anatis 12656-12 fur mutant (Ω fur 126.13) grown in the presence or not of 2,2'-dipyridyl. The addition of FeCl3 to the culture medium diminished the growth and biofilm production in approximately 30% and 35%, respectively, in the wild-type strain, but the growth of Ω fur 126.13 strain was not affected and biofilm production increased in 35%. G. anatis Ω fur 126.13 presented lower virulence when it was inoculated to 35-day-old chickens in comparison to the wild-type strain. The induction of more than one iron uptake mechanism could benefit pathogenic microorganisms such as Gallibacterium.

Genome Sequence of Actinobacillus seminis Strain ATCC 15768, a Reference Strain of Ovine Pathogens That Causes Infections in Reproductive Organs.

The draft genome sequence of Actinobacillus seminis strain ATCC 15768 is reported here. The genome comprises 22 contigs corresponding to 2.36 Mb with 40.7% G+C content and contains several genes related to virulence, including a putative RTX protein.