Sequence diversity, cytotoxicity and antigenic similarities of the leukotoxin of isolates of Mannheimia species from mastitis in domestic sheep

Molecular identification and characterisation of Mannheimia haemolytica

Mannheimia haemolytica is known as one of the major bacterial contributors to Bovine Respiratory Disease (BRD) syndrome. This study sought to establish a novel species-specific PCR to aid in identification of this key pathogen. As well, an existing multiplex PCR was used to determine the prevalence of serovars 1, 2 or 6 in Australia. Most of the 65 studied isolates originated from cattle with a total of 11 isolates from small ruminants. All problematic field isolates in the identification or serotyping PCRs were subjected to whole genome sequencing and bioinformatic analysis. The field isolates were also subjected to rep-PCR fingerprinting. A total of 59 out of the 65 tested isolates were conformed as M. haemolytica by the new species-specific PCR which is based on the rpoB gene. The confirmed M. haemolytica field isolates were assigned to serovars 1 (24 isolates), 2 (seven isolates) and 6 (26 isolates) while two of the isolates were negative in the serotyping PCR. The two non-typeable isolates were assigned to serovar 7 and 14 following whole genome sequencing and bioinformatic analysis. The rep-PCR typing resulted in five major clusters with serovars 1 and 6 often within the same cluster. The M. haemolytica-specific PCR developed in this work was species specific and should be a valuable support for frontline diagnostic laboratories. The serotyping results support the relative importance of serovars 1 and 6 in bovine respiratory disease.

Mannheimia bovis sp. nov., Isolated from a Dead Cow with Hemorrhagic Pneumonia

Strain ZY190616^T was isolated from lung of a dead cow with hemorrhagic pneumonia in Yunnan Province, China. The strain was Gram-stain-negative, facultatively anaerobic bacterium. Phylogenetic analysis based on 16S rRNA gene sequence indicated that the strain was closely related to species of the genus Mannheimia and formed an independent clade with M.varigena CCUG 38462 ^T (97.0% similarity). Phylogenetic analysis based on recN gene indicated that the strain formed a clade with M.caviae CCUG 59995 ^T (87.8% similarity). Phylogenetic analysis based on rpoB gene indicated that the strain formed a clade with M.varigena CCUG 38462 ^T (94.7% similarity). The genomic OrthoANI values between strain ZY190616^T and M. ovis, M.haemolytica and M.granulomatis were 84.5%, 82.7% and 81.9%, respectively. The genomic G + C content was 39.8 mol%. The predominant fatty acids (> 5%) of the strain were C_16:0, C_14:0, C_18:1ω7c, summed feature 3 (C_16:1 ω7c and/ or C_16:1ω6c) and summed feature 2 (C14:0 3OH/ C16:1 Iso). The major polar lipids were phosphatidylglycerol (PG), phosphatidylethanolamine (PE), monophosphatidylglycerol (MGDG), triacylglycerol (TAG) and diphosphatidylglycerol (DLCL). The sole respiratory quinone was CoQ-7. Based on evidence from the taxonomic study, strain ZY190616^T represents a novel species of the genus Mannheimia, for which the name Mannheimia bovis sp. nov. is proposed. The type strain is ZY190616^T (= CCTCC AB 2020168 ^T = KCTC 25018 ^T).

Mannheimia ovis sp. nov., Isolated from Dead Sheep with Hemorrhagic Pneumonia

Two Gram-stain-negative, facultatively anaerobic bacteria, designated ZY170218^T and ZY180512, were isolated from lungs of dead sheep with hemorrhagic pneumonia in Yunnan Province, China and their taxonomic positions were studied by a polyphasic approach. The two isolates grew optimally at 37 °C, pH 9.0 and 1.0% NaCl (w/v), and showed identical 16S rRNA, recN and rpoB gene sequences. Phylogenetic analysis based on 16S rRNA gene sequence showed that the two strains fell within the cluster of species in the genus Mannheimia and formed a separated lineage with comparatively low similarity to the closest related species M. granulomatis (96.5%). Phylogenetic analysis based on rpoB gene indicated that the strains formed a monophyletic evolutionary lineage, with low sequence similarity ≤ 89.0% to the species of the genus Mannheimia. The genomic OrthoANI values between strain ZY170218^T and M. granulomatis and M. haemolytica were 80.4% and 83.1%, respectively. The genomic G + C content of strain ZY170218^T was 39.1 mol%. The predominant fatty acids (> 5%) of the two strains were C_16:0, C_14:0, C_18:1ω7c, summed feature 3 (C_16:1 ω7c and/ or C_16:1ω6c) and summed feature 2 (C_14:0 3OH/ C_16:1 Iso). The major polar lipids of strain ZY170218^T were phosphatidylglycerol, phosphatidylcholine, monogalactosyldiacylglycerol, bis(monoacylglycero)phosphate and diacylglycerols. The sole respiratory quinone of the two strains was CoQ-7. On the basis of phylogenetic, phenotypic and chemotaxonomic features, strain ZY170218^T and ZY180512 clearly represents a novel species of the genus Mannheimia, for which the name Mannheimia ovis sp. nov. is proposed. The type strain is ZY170218^T (= CGMCC 1.13620 ^T = KCTC 15731 ^T).

Channel Formation by LktA of Mannheimia (Pasteurella) haemolytica in Lipid Bilayer Membranes and Comparison of Channel Properties with Other RTX-Cytolysins

Cytolysin LktA is one of the major pathogenicity factors of Mannheimia haemolytica (formerly Pasteurella haemolytica) that is the cause of pasteurellosis, also known as shipping fever pneumonia, causing substantial loss of sheep and cattle during transport. LktA belongs to the family of RTX-toxins (Repeats in ToXins) that are produced as pathogenicity factors by a variety of Gram-negative bacteria. Sublytic concentrations of LktA cause inflammatory responses of ovine leukocytes. Higher concentrations result in formation of transmembrane channels in target cells that may cause cell lysis and apoptosis. In this study we investigated channel formation by LktA in artificial lipid bilayer membranes made of different lipids. LktA purified from culture supernatants by polyethylene glycol 4000 precipitation and lyophilization had to be activated to frequently form channels by solution in 6 M urea. The LktA channels had a single-channel conductance of about 60 pS in 0.1 M KCl, which is about one tenth of the conductance of most RTX-toxins with the exception of adenylate cyclase toxin of Bordetella pertussis. The LktA channels are highly cation-selective caused by negative net charges. The theoretical treatment of the conductance of LktA as a function of the bulk aqueous concentration allowed a rough estimate of the channel diameter, which is around 1.5 nm. The size of the LktA channel is discussed with respect to channels formed by other RTX-toxins. We present here the first investigation of LktA in a reconstituted system.

Molecular study on Pasteurella multocida and Mannheimia granulomatis from Kenyan Camels (Camelus dromedarius)

BACKGROUND

Outbreaks of a Haemorrhagic Septicaemia (HS) like disease causing large mortalities in camels (Camelus dromedarius) in Asia and in Africa have been reported since 1890. Yet the aetiology of this condition remains elusive. This study is the first to apply state of the art molecular methods to shed light on the nasopharyngeal carrier state of Pasteurellaceae in camels. The study focused on HS causing Pasteurella multocida capsular types B and E. Other Pasteurellaceae, implicated in common respiratory infections of animals, were also investigated.

METHODS

In 2007 and 2008, 388 nasopharyngeal swabs were collected at 12 locations in North Kenya from 246 clinically healthy camels in 81 herds that had been affected by HS-like disease. Swabs were used to cultivate bacteria on blood agar and to extract DNA for subsequent PCR analysis targeting P. multocida and Mannheimia-specific gene sequences.

RESULTS

Forty-five samples were positive for P. multocida genes kmt and psl and for the P. multocida Haemorrhagic Septicaemia (HS) specific sequences KTSP61/KTT72 but lacked HS-associated capsular type B and E genes capB and capE. This indicates circulation of HS strains in camels that lack established capsular types. Sequence analysis of the partial 16S rRNA gene identified 17 nasal swab isolates as 99% identical with Mannheimia granulomatis, demonstrating a hitherto unrecognised active carrier state for M. granulomatis or a closely related Mannheimia sp. in camels.

CONCLUSIONS

The findings of this study provide evidence for the presence of acapsular P. multocida or of hitherto unknown capsular types of P. multocida in camels, closely related to P. multocida strains causing HS in bovines. Further isolations and molecular studies of camelid P. multocida from healthy carriers and from HS-like disease in camels are necessary to provide conclusive answers. This paper is the first report on the isolation of M. granulomatis or a closely related new Mannheimia species from camelids.

The upper respiratory tract is a natural reservoir of haemolytic Mannheimia species associated with ovine mastitis

Lamb suckling has been suggested to be an important way of infecting a ewe's udder with different bacteria, including Mannheimia haemolytica. To test the potential role of lambs in transferring Mannheimia species to the ewe's udder, the restriction endonuclease cleavage patterns of isolates obtained from nasopharyngeal swabs were compared with those obtained from cases of mastitis. Sterile cotton swabs were used to collect nasopharyngeal samples from 50 ewes and 36 lambs from three flocks. M. haemolytica and Mannheimia glucosida as well as haemolytic Mannheimia ruminalis-like organisms were detected in the upper respiratory tract of lambs and ewes. Comparison of the restriction endonuclease cleavage patterns of the isolates suggested that the M. haemolytica isolates obtained from different milk samples from ewes with mastitis were more clonal than those obtained from the nasal swabs. However, some nasal isolates within both Mannheimia species had restriction endonuclease cleavage patterns identical to those obtained from milk samples from ewes with mastitis, indicating that lambs may have a role in transferring these organisms to the udder. More clonality was observed between the M. glucosida isolates than between M. haemolytica isolates.

Human Wound Infection with Mannheimia glucosida following Lamb Bite

Mannheimia spp. are veterinary pathogens that can cause mastitis and pneumonia in domestic cattle and sheep. While Mannheimia glucosida can be found as normal flora in oral and respiratory mucosa in sheep, there have been no reported cases of human infection with this organism.