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T A Mcallister - One of the best experts on this subject based on the ideXlab platform.

  • comparative analysis of multiple inducible phages from Mannheimia haemolytica
    BMC Microbiology, 2015
    Co-Authors: Shaun R. Cook, Cassidy L. Klima, Jiaying Wang, Dann Turner, Andrew M Kropinski, T A Mcallister
    Abstract:

    Background Mannheimia haemolytica is a commensal bacterium that resides in the upper respiratory tract of cattle that can play a role in bovine respiratory disease. Prophages are common in the M. haemolytica genome and contribute significantly to host diversity. The objective of this research was to undertake comparative genomic analysis of phages induced from strains of M. haemolytica serotype A1 (535A and 2256A), A2 (587A and 1127A) and A6 (1152A and 3927A).

  • susceptibility to tulathromycin in Mannheimia haemolytica isolated from feedlot cattle over a 3 year period
    Frontiers in Microbiology, 2013
    Co-Authors: Trevor W. Alexander, Cassidy L. Klima, Shaun R. Cook, Edward Topp, T A Mcallister
    Abstract:

    Mannheimia haemolytica isolated from feedlot cattle were tested for tulathromycin resistance. Cattle were sampled over a three-year period, starting 12 months after approval of tulathromycin for prevention and treatment of bovine respiratory disease. Nasopharyngeal samples from approximately 5,814 cattle were collected when cattle entered feedlots (N = 4) and again from the same cattle after ≥ 60 d on feed. The antimicrobial use history for each animal was recorded. Mannheimia haemolytica was isolated from 796 (13.7%) entry samples and 1,038 (20.6%) ≥ 60 d samples. Of the cattle positive for M. haemolytica, 18.5%, 2.9%, and 2.4% were administered therapeutic concentrations of tulathromycin, tilmicosin, or tylosin tartrate, respectively. In addition, 13.2% were administered subtherapeutic concentrations of tylosin phosphate in feed. In years one and two, no tulathromycin-resistant M. haemolytica were detected, whereas 5 isolates (0.4%) were resistant in year three. These resistant isolates were collected from three cattle originating from a single pen, were all serotype 1, and were genetically related (≥ 89% similarity) according to pulsed-field gel electrophoreses patterns. The five tulathromycin-resistant isolates were multi-drug resistant also exhibiting resistance to oxytetracycline, tilmicosin, ampicillin, or penicillin. The macrolide resistance genes erm(42), erm(A), erm(B), erm(F), erm(X) and msr(E)-mph(E), were not detected in the tulathromycin-resistant M. haemolytica. This study showed that tulathromycin resistance in M. haemolytica from a general population of feedlot cattle in western Canada was low and did not change over a three-year period after tulathromycin was approved for use in cattle.

  • comparison of repetitive pcr and pulsed field gel electrophoresis for the genotyping of Mannheimia haemolytica
    Journal of Microbiological Methods, 2010
    Co-Authors: C L Klima, Trevor W. Alexander, Calvin W Booker, Ron Read, L B Selinger, P E Shewan, T A Mcallister
    Abstract:

    Abstract Mannheimia haemolytica is an opportunistic pathogen that can cause fibrinonecrotic pneumonia in cattle and is the main bacterial agent implicated in bovine respiratory disease-complex (BRD). Despite its economic importance to the cattle industry, few studies have characterized the genetic nature of M. haemolytica and none have genotyped isolates from feedlots. Identifying and monitoring genetic variants of M. haemolytica is important to understanding the etiology of BRD in cattle. We investigated the capacity of three genotyping techniques (BOX-PCR, (GTG)5-PCR and PFGE analysis of SalI-restricted DNA) to discriminate among 24 reference strains from the family Pasteurellaceae and 40 M. haemolytica isolates collected from feedlot cattle. From cluster analysis of the M. haemolytica isolates, PFGE was revealed as most discriminating, followed by BOX-PCR and then (GTG)5-PCR (Simpson's diversity index > 0.98, 0.82, and 0.72, respectively). Of these methods, PFGE also had the greatest mean repeatability (0.96). The PFGE and BOX-PCR assays grouped all M. haemolytica in a single cluster but only BOX-PCR and (GTG)5-PCR grouped the Mannheimia glucosida and Mannheimia ruminalis strains together. Refinement of genotyping procedures for M. haemolytica could offer new insight into the etiology of this pathogen in BRD.

  • a multiplex polymerase chain reaction assay for the identification of Mannheimia haemolytica Mannheimia glucosida and Mannheimia ruminalis
    Veterinary Microbiology, 2008
    Co-Authors: Trevor W. Alexander, Shaun R. Cook, Jay L Yanke, Calvin W Booker, Paul S Morley, Ron Read, T A Mcallister
    Abstract:

    The objective of this study was to design a multiplex PCR assay to identify Mannheimia haemolytica, Mannheimia glucosida and Mannheimia ruminalis. The multiplex PCR included primer sets HP, amplifying a DNA region from an unknown hypothetical protein, Lkt and Lkt2, amplifying different regions of the leukotoxinD gene, and 16S to amplify universal bacterial sequences of the 16S rRNA gene. Based on positive amplification, isolates were delineated as M. haemolytica (HP, Lkt, 16S), M. glucosida (HP, Lkt, Lkt2, 16S), or M. ruminalis (HP, 16S). The validity of the assay was examined against 22 reference strains within the family Pasteurellaceae and 17 field isolates (nasal) that had been collected previously from feedlot cattle and tentatively identified as M. haemolytica based on morphology and substrate utilization. Additionally, 200 feedlot cattle were screened for M. haemolytica using multiplex PCR. Forty-four isolates from 25 animals were identified as M. haemolytica. The PCR assay positively identified all M. haemolytica, as confirmed by phenotypic tests and clustering based upon cellular fatty acid methyl ester (FAME) profiles. Selected nasal isolates that exhibited evidence of haemolysis, but were M. haemolytica-negative based on PCR, were also confirmed negative by phenotypic and FAME analyses. The multiplex PCR assay required no additional phenotypic tests for confirmation of M. haemolytica, within the group of bacteria tested.

Magne Bisgaard - One of the best experts on this subject based on the ideXlab platform.

  • Evidence for Vertical Inheritance and Loss of the Leukotoxin Operon in Genus Mannheimia
    Journal of Molecular Evolution, 2007
    Co-Authors: Jesper Larsen, Henrik Christensen, Magne Bisgaard, Oystein Angen, Anders G. Pedersen, Peter Ahrens, John E. Olsen
    Abstract:

    The Mannheimia subclades belong to the same bacterial genus but have taken divergent paths toward their distinct lifestyles. M. haemolytica + M. glucosida are potential pathogens of the respiratory tract in the mammalian suborder Ruminantia, whereas M. ruminalis , the supposed sister group, lives as a commensal in the ovine rumen. We have tested the hypothesis that horizontal gene transfer of the leukotoxin operon has catalyzed pathogenic adaptation and speciation of M. haemolytica + M. glucosida , or other major subclades, by using a strategy that combines compositional and phylogenetic methods. We show that it has been vertically inherited from the last common ancestor of the diverging Mannheimia subclades, although several strains belonging to M. ruminalis have lost the operon. Our analyses support that divergence within M. ruminalis following colonization of the ovine rumen was very rapid and that functional decay of most of the leukotoxin operons occurred early when the adaptation to the rumen was fastest, suggesting that antagonistic pleiotropy was the main contributor to losses in the radiating lineages of M. ruminalis . To sum up, the scenario derived from these analyses reflects two aspects. On one hand, it opposes the hypothesis of horizontal gene transfer as a catalyst of pathogenic adaptation and speciation. On the other hand, it indicates that losses of the leukotoxin operons in the radiating lineages of M. ruminalis have catalyzed their adaptation to a commensal environment and reproductive isolation (speciation).

  • IDENTIFICATION OF A NOVEL Mannheimia GRANULOMATIS LINEAGE FROM LESIONS IN ROE DEER (CAPREOLUS CAPREOLUS)
    Journal of wildlife diseases, 2007
    Co-Authors: Anders Miki Bojesen, Jesper Larsen, Anders Gorm Pedersen, Torsten Mörner, Roland Mattson, Magne Bisgaard
    Abstract:

    Eight atypical Mannheimia isolates were isolated from lesions in roe deer (Capreolus capreolus). Traditional classification based on morphologic and physiologic traits showed that they belong to a distinct biogroup (taxon) within genus Mannheimia. Extensive phenotypic characterization suggested that the isolates should be classified as M. granulomatis, although the presence of distinct traits justified their classification into a separate biogroup within this species. Phylogenetic analyses based on 16S rRNA sequences from two roe deer isolates and 41 other Mannheimia strains supported that the roe deer isolates form a monophyletic group within M. granulomatis. The lktA genotype was present in all roe deer isolates based on Southern blot analysis, whereas the corresponding β-hemolytic phenotype was absent in one of these isolates.

  • phenotypic and genotypic characterization of Mannheimia pasteurella haemolytica like strains isolated from diseased animals in denmark
    Veterinary Microbiology, 2002
    Co-Authors: Oystein Angen, Peter Ahrens, Magne Bisgaard
    Abstract:

    Abstract Trehalose-negative strains of the Pasteurella haemolytica complex have recently been transferred to a new genus, Mannheimia. This genus presently consists of five named species: M. haemolytica, M. glucosida, M. granulomatis, M. ruminalis and M. varigena. The purpose of this study was to investigate the occurrence of these species and lesions associated with these isolates in Denmark. In all 106 M. haemolytica-like strains isolated from pathological material from cattle, sheep, pigs and hares submitted to the Danish Veterinary Laboratory between 1994 and 1998 were investigated. Phenotypic characterization and ribotyping were used for identification in addition to sequencing of the 16S rRNA genes for selected strains. The species allocation was determined by comparison to results from a previous polyphasic taxonomic study. Seventy-one percent of the strains belonged to M. haemolytica, 18% to M. varigena and 8% to unnamed groups within the genus Mannheimia. Single isolates identified as M. glucosida and P. trehalosi, respectively, were detected. Two isolates belonged to M. granulomatis. Forty-three percent of the strains belonged to serotype 1, 41% were untypeable, while the rest belonged to serotypes 2, 7, 9, and 16. The present investigation also showed that a simplified phenotypic characterization using Diatabs® Diagnostic Tablets (Rosco, Denmark) represents a useful method for obtaining a quick and reliable species identification. Finally, the investigation confirmed that serotyping does not represent a reliable method for species identification. The heterogeneity of species associated with bovine “pasteurellosis” should be considered in future studies to improve our understanding of the pathogenesis of pneumonic disease.

  • phenotypic characterisation of australian sheep and cattle isolates of Mannheimia haemolytica Mannheimia granulomatis and Mannheimia varigena
    Australian Veterinary Journal, 2002
    Co-Authors: P J Blackall, Magne Bisgaard, C P Stephens
    Abstract:

    Objective: To perform a comprehensive phenotypic characterisation of 35 isolates of bacteria previously identified as haemolytic Pasteurella-Actinobacillus and obtained from cattle and sheep. Design: The 35 isolates that had been obtained from Australian animals, 30 from cattle and five from sheep, were compared with reference strains of the five recognised species of the genus Mannheimia – M haemolytica, M glucosida, M granulomatis, M ruminalisand M varigena. Results: Thirty-four of the isolates could be confidently assigned to three species of the genus Mannheimia. Twenty-nine were M haemolytica, with 25 being isolated from cattle and four from sheep. All but three of the bovine M haemolytica were isolated from pneumonic lungs. Of the three remaining bovine M haemolytica isolates, one was obtained in pure culture from a bovine milk sample and the other two as part of a mixed flora associated with a middle ear infection of a calf suffering mucosal disease. Of the four ovine M haemolytica isolates, two were isolated in pure culture from milk and two, also in pure culture, from pneumonic lungs. Three bovine isolates were identified as M granulomatis – one from a tongue abscess, one from a jaw abscess and one from a lung showing suppurative bronchopneumonia. Two bovine isolates were identified as M varigena – one coming from an udder and the other from a spleen. The available diagnostic records provided no information on whether these isolates were associated with a disease process. The remaining isolate was obtained from an ovine tongue abscess and could not be assigned to a recognised species within the genus Mannheimia. Conclusion: The study represents the first time that M haemolytica, M granulomatis and M varigena have been recognised as being present in cattle and sheep in Australia. Veterinary laboratories that encounter Pasteurella-Actinobacillus-like organisms from cattle and sheep should attempt as complete a characterisation as possible to help improve our knowledge of the disease potential of these organsims.

  • investigations on the species specificity of Mannheimia pasteurella haemolytica serotyping
    Veterinary Microbiology, 1999
    Co-Authors: Oystein Angen, Malcolm Quirie, Willie Donachie, Magne Bisgaard
    Abstract:

    Abstract Eleven serotypes (1, 2, 5–9, 12–14 and 16) have been demonstrated within Mannheimia haemolytica . Subsequent serotyping of 166 Mannheimia haemolytica -like strains, genetically and phenotyphically distinct from Mannheimia haemolytica , and isolated from ruminants, pigs, hares and rabbits showed that 13.2% were typeable, 19 of which were serotype 11 representing strains now being classified as M. glucosida . In addition, three strains belonged to serotypes 6, 9 and 16, respectively. Additionally, the serotyping results of 98 (P.) haemolytica -like isolates from non-ruminant sources collected by the UK Veterinary Investigation Centres during the period 1982–1996 were investigated. None of these isolates have been kept, making further genetic characterization impossible. Among these isolates, 25.5% were typeable representing serotypes 1, 2, 3, 5, 6, 9, 10, 13 and 15. Substantial evidence has been reported indicating that M. haemolytica -like isolates from non-ruminant sources represent species different from M. haemolytica . The present investigation underlines that serotyping does not represent a reliable method for the identification of M. haemolytica or M. glucosida . These observations emphasize that extended phenotypic and genetic characterization is necessary for the proper identification of these organisms.

Subramaniam Srikumaran - One of the best experts on this subject based on the ideXlab platform.

  • Leukotoxin of Bibersteinia trehalosi Contains a Unique Neutralizing Epitope, and a Non-Neutralizing Epitope Shared with Mannheimia haemolytica Leukotoxin
    Toxins, 2018
    Co-Authors: Arumugam Murugananthan, Sai Arun Batra, Sudarvili Shanthalingam, Sitara Alahan, Subramaniam Srikumaran
    Abstract:

    Bibersteinia trehalosi and Mannheimia haemolytica, originally classified as Pasteurella haemolytica biotype T and biotype A, respectively, under Genus Pasteurella has now been placed under two different Genera, Bibersteinia and Mannheimia, based on DNA-DNA hybridization and 16S RNA studies. While M. haemolytica has been the predominant pathogen of pneumonia in ruminants, B. trehalosi is emerging as an important pathogen of ruminant pneumonia. Leukotoxin is the critical virulence factor of these two pathogens. While the leukotoxin of M. haemolytica has been well studied, the characterization of B. trehalosi leukotoxin has lagged behind. As the first step towards addressing this problem, we developed monoclonal antibodies (mAbs) against B. trehalosi leukotoxin and used them to characterize the leukotoxin epitopes. Two mAbs that recognized sequential epitopes on the leukotoxin were developed. One of them, AM113, neutralized B. trehalosi leukotoxin while the other, AM321, did not. The mAb AM113 revealed the existence of a neutralizing epitope on B. trehalosi leukotoxin that is not present on M. haemolytica leukotoxin. A previously developed mAb, MM601, revealed the presence of a neutralizing epitope on M. haemolytica leukotoxin that is not present on B. trehalosi leukotoxin. The mAb AM321 recognized a non-neutralizing epitope shared by the leukotoxins of B. trehalosi and M. haemolytica. The mAb AM113 should pave the way for mapping the leukotoxin-neutralizing epitope on B. trehalosi leukotoxin and the development of subunit vaccines and/or virus-vectored vaccines against this economically important respiratory pathogen of ruminants.

  • sequence diversity cytotoxicity and antigenic similarities of the leukotoxin of isolates of Mannheimia species from mastitis in domestic sheep
    Veterinary Microbiology, 2014
    Co-Authors: Lida Omaleki, Subramaniam Srikumaran, Glenn F Browning, Stuart R Barber, Joanne L Allen, Philip F Markham
    Abstract:

    Species within the genus Mannheimia are among the most important causes of ovine mastitis. Isolates of these species can express leukotoxin A (LktA), a primary virulence factor of these bacteria. To examine the significance of variation in the LktA, the sequences of the lktA genes in a panel of isolates from cases of ovine mastitis were compared. The cross-neutralising capacities of rat antisera raised against LktA of one Mannheimia glucosida, one haemolytic Mannheimia ruminalis, and two Mannheimia haemolytica isolates were also examined to assess the effect that variation in the lktA gene can have on protective immunity against leukotoxins with differing sequences. The lktA nucleotide distance between the M. haemolytica isolates was greater than between the M. glucosida isolates, with the M. haemolytica isolates divisible into two groups based on their lktA sequences. Comparison of the topology of phylogenetic trees of 16S rDNA and lktA sequences revealed differences in the relationships between some isolates, suggesting horizontal gene transfer. Cross neutralisation data obtained with monospecific anti-LktA rat sera were used to derive antigenic similarity coefficients for LktA from the four Mannheimia species isolates. Similarity coefficients indicated that LktA of the two M. haemolytica isolates were least similar, while LktA from M. glucosida was most similar to those for one of the M. haemolytica isolates and the haemolytic M. ruminalis isolate. The results suggested that vaccination with the M. glucosida leukotoxin would generate the greatest cross-protection against ovine mastitis caused by Mannheimia species with these alleles.

  • genome sequences of Mannheimia haemolytica serotype a2 ovine and bovine isolates
    Journal of Bacteriology, 2010
    Co-Authors: Paulraj K Lawrence, Weerayuth Kittichotirat, Jason E Mcdermott, Roger E. Bumgarner, David R. Herndon, Donald P Knowles, Subramaniam Srikumaran
    Abstract:

    This report describes the genome sequences of Mannheimia haemolytica serotype A2 isolated from pneumonic lungs of two different ruminant species, one from Ovis aries, designated ovine (O), and the other from Bos taurus, designated bovine (B).

Robert L. Davies - One of the best experts on this subject based on the ideXlab platform.

  • pathogenic Mannheimia haemolytica invades differentiated bovine airway epithelial cells
    Infection and Immunity, 2019
    Co-Authors: Daniel Cozens, Erin Sutherland, Miquel Lauder, Geraldine Taylor, Catherine C Berry, Robert L. Davies
    Abstract:

    ABSTRACT The Gram-negative bacterium Mannheimia haemolytica is the primary bacterial species associated with bovine respiratory disease (BRD) and is responsible for significant economic losses to livestock industries worldwide. Healthy cattle are frequently colonized by commensal serotype A2 strains, but disease is usually caused by pathogenic strains of serotype A1. For reasons that are poorly understood, a transition occurs within the respiratory tract and a sudden explosive proliferation of serotype A1 bacteria leads to the onset of pneumonic disease. Very little is known about the interactions of M. haemolytica with airway epithelial cells of the respiratory mucosa which might explain the different abilities of serotype A1 and A2 strains to cause disease. In the present study, host-pathogen interactions in the bovine respiratory tract were mimicked using a novel differentiated bovine bronchial epithelial cell (BBEC) infection model. In this model, differentiated BBECs were inoculated with serotype A1 or A2 strains of M. haemolytica and the course of infection followed over a 5-day period by microscopic assessment and measurement of key proinflammatory mediators. We have demonstrated that serotype A1, but not A2, M. haemolytica invades differentiated BBECs by transcytosis and subsequently undergoes rapid intracellular replication before spreading to adjacent cells and causing extensive cellular damage. Our findings suggest that the explosive proliferation of serotype A1 M. haemolytica that occurs within the bovine respiratory tract prior to the onset of pneumonic disease is potentially due to bacterial invasion of, and rapid proliferation within, the mucosal epithelium. The discovery of this previously unrecognized mechanism of pathogenesis is important because it will allow the serotype A1-specific virulence determinants responsible for invasion to be identified and thereby provide opportunities for the development of new strategies for combatting BRD aimed at preventing early colonization and infection of the bovine respiratory tract.

  • evidence for a common gene pool and frequent recombinational exchange of the tbpba operon in Mannheimia haemolytica Mannheimia glucosida and bibersteinia trehalosi
    Microbiology, 2011
    Co-Authors: Robert L. Davies
    Abstract:

    The tbpBA operon was sequenced in 42 representative isolates of Mannheimia haemolytica (32), Mannheimia glucosida (6) and Bibersteinia trehalosi (4). A total of 27 tbpB and 20 tbpA alleles were identified whilst the tbpBA operon was represented by 28 unique alleles that could be assigned to seven classes. There were 1566 (34.8 % variation) polymorphic nucleotide sites and 482 (32.1 % variation) variable inferred amino acid positions among the 42 tbpBA sequences. The tbpBA operons of serotype A2 M. haemolytica isolates are, with one exception, substantially more diverse than those of the other M. haemolytica serotypes and most likely have a different ancestral origin. The tbpBA phylogeny has been severely disrupted by numerous small- and large-scale intragenic recombination events. In addition, assortative (entire gene) recombination events, involving either the entire tbpBA operon or the individual tbpB and tbpA genes, have played a major role in shaping tbpBA structure and it's distribution in the three species. Our findings indicate that a common gene pool exists for tbpBA in M. haemolytica, M. glucosida and B. trehalosi. In particular, B. trehalosi, M. glucosida and ovine M. haemolytica isolates share a large portion of the tbpA gene, and this probably reflects selection for a conserved TbpA protein that provides effective iron uptake in sheep. Bovine and ovine serotype A2 lineages have very different tbpBA alleles. Bovine-like tbpBA alleles have been partially, or completely, replaced by ovine-like tbpBA alleles in ovine serotype A2 isolates, suggesting that different transferrin receptors are required by serotype A2 isolates for optimum iron uptake in cattle and sheep. Conversely, the tbpBA alleles of bovine-pathogenic serotype A1 and A6 isolates are very similar to those of closely related ovine isolates, suggesting a recent and common evolutionary origin.

  • Diversity of temperate bacteriophages induced in bovine and ovine Mannheimia haemolytica isolates and identification of a new P2-like phage
    FEMS microbiology letters, 2006
    Co-Authors: Robert L. Davies, Inkyoung Lee
    Abstract:

    The diversity of temperate bacteriophages was examined in 32 Mannheimia haemolytica, six Mannheimia glucosida and four Pasteurella trehalosi isolates. Phage particles were induced and identified by electron microscopy in 24 (75%) M. haemolytica isolates, but in only one (17%) M. glucosida and one (25%) P. trehalosi isolate. The M. haemolytica phages were relatively diverse as seven Siphoviridae, 15 Myoviridae and two Podoviridae-like phages were identified; the Myoviridae-type phages also exhibited structural variation of their tails. The bacteriophages induced in M. glucosida and P. trehalosi were of the Myoviridae type. Restriction endonuclease (RE) analysis identified nine distinct RE types among the M. haemolytica bacteriophages, providing further evidence of their relative diversity. A limited number of phages caused plaques on indicator strains and the phages exhibited a narrow host range. A subgroup of 11 bovine serotype A1 and A6 isolates contained Myoviridae-type phages of the same RE type (type A), but these differed in their abilities to infect and form plaques on the same panel of indicator strains. A P2-like phage (φPHL213.1), representative of the RE type A phages, was identified from the incomplete M. haemolytica genome sequence. The φPHL213.1 genome contains previously unidentified genes and represents a new member of the P2 phage family.

  • mosaic structure and molecular evolution of the leukotoxin operon lktcabd in Mannheimia pasteurella haemolytica Mannheimia glucosida and pasteurella trehalosi
    Journal of Bacteriology, 2002
    Co-Authors: Robert L. Davies, Susan Campbell, Thomas S Whittam
    Abstract:

    The mosaic structure and molecular evolution of the leukotoxin operon (lktCABD) was investigated by nucleotide sequence comparison of the lktC, lktB, and lktD genes in 23 Mannheimia (Pasteurella) haemolytica, 6 Mannheimia glucosida, and 4 Pasteurella trehalosi strains. Sequence variation in the lktA gene has been described previously (R. L. Davies et al., J. Bacteriol. 183:1394–1404, 2001). The leukotoxin operon of M. haemolytica has a complex mosaic structure and has been derived by extensive inter- and intraspecies horizontal DNA transfer and intragenic recombination events. However, the pattern of recombination varies throughout the operon and among the different evolutionary lineages of M. haemolytica. The lktA and lktB genes have the most complex mosaic structures with segments derived from up to four different sources, including M. glucosida and P. trehalosi. In contrast, the lktD gene is highly conserved in M. haemolytica. The lktC, lktA, and lktB genes of strains representing the major ovine lineages contain recombinant segments derived from bovine or bovine-like serotype A2 strains. These findings support the previous conclusion that host switching of bovine A2 strains from cattle to sheep has played a major role in the evolution of the leukotoxin operon in ovine strains of M. haemolytica. Homologous segments of donor and recipient alleles are identical, or nearly identical, indicating that the recombinational exchanges occurred relatively recent in evolutionary terms. The 5′ and 3′ ends of the operon are highly conserved in M. haemolytica, which suggests that multiple horizontal exchanges of the complete operon have occurred by a common mechanism such as transduction. Although the lktA and lktB genes both have complex mosaic structures and high nucleotide substitution rates, the amino acid diversity of LktB is significantly lower than that of LktA due to a higher degree of evolutionary constraint against amino acid replacement. The recombinational exchanges within the leukotoxin operon have had greatest effect on LktA and probably provide an adaptive advantage against the host antibody response by generating novel antigenic variation at surface-exposed sites.

Charles J Czuprynski - One of the best experts on this subject based on the ideXlab platform.

  • Mannheimia haemolytica biofilm formation on bovine respiratory epithelial cells
    Veterinary Microbiology, 2016
    Co-Authors: Ismail Boukahil, Charles J Czuprynski
    Abstract:

    Abstract Mannheimia haemolytica is the most important bacterial agent associated with the bovine respiratory disease complex (BRDC), which causes worldwide economic losses to the cattle industry. M. haemolytica cells initially colonize the tonsillar crypts in the upper respiratory tract of cattle, from where they can subsequently descend into the lungs to cause disease. Many bacteria exist as biofilms inside their hosts. We hypothesize that M. haemolytica colonization of cattle during its commensal state may include biofilm formation. To begin to assess this possibility, we developed an in vitro system to study biofilm formation directly on bovine respiratory epithelial cells. Using fixed primary bovine bronchial epithelial cells, we observed M. haemolytica biofilm formation after a 48 h incubation period at 37 °C. Addition of mucin, the main component of mucus present in the upper respiratory tract, decreased M. haemolytica biofilm formation on bovine epithelial cells. We investigated the effects of prior viral infection of the epithelial cells on subsequent biofilm formation by M. haemolytica and found negligible effects. Utilization of this model system will provide new insights into the potential role of biofilm formation by M. haemolytica in the pathogenesis of BRDC.

  • characterization of Mannheimia haemolytica biofilm formation in vitro
    Veterinary Microbiology, 2015
    Co-Authors: Ismail Boukahil, Charles J Czuprynski
    Abstract:

    : Mannheimia haemolytica is the primary bacterial agent in the bovine respiratory disease complex. It is thought that M. haemolytica colonizes the tonsillar crypts of cattle as a commensal and subsequently descends into the lungs to cause disease. Many bacterial species persist in the host as biofilms. There is limited information about the ability of M. haemolytica to form biofilms. The aim of this study was to develop an in vitro model for M. haemolytica biofilm formation. We found that M. haemolytica required at least 36 h to form robust biofilms on plastic in vitro when incubated in RPMI-1640 tissue culture medium at 37 °C, with maximal biofilm formation being evident at 48 h. Biofilm formation was inhibited by adding the monosaccharides d(+) galactose and d(+) mannose to the growth medium. Addition of antibodies to the M. haemolytica surface protein OmpA also reduced biofilm formation. Upon evaluating the macromolecules within the biofilm extracellular polymeric substance we found it contained 9.7 μg/cm(2) of protein, 0.81 μg/cm(2) of total carbohydrate, and 0.47 μg/cm(2) of extracellular DNA. Furthermore, proteinase K treatment significantly decreased biofilms (P<0.05) while α-amylase and micrococcal nuclease decreased biofilms to a lesser extent. M. haemolytica biofilm cells were more resistant than planktonic cells to the antibiotics florfenicol, gentamicin, and tulathromycin. These results provide evidence that M. haemolytica can form biofilms, which could contribute to its ability to persist as a commensal in the bovine upper respiratory tract.