Prediction of Mannheimia haemolytica serotypes based on whole genomic sequences

Macrolide resistance in Mannheimia haemolytica isolates associated with bovine respiratory disease from the German national resistance monitoring program GERM-Vet 2009 to 2020

Data collected from the German national resistance monitoring program GERM-Vet showed slowly increasing prevalence of macrolide resistance among bovine respiratory disease (BRD)-associated Pasteurellacae from cattle over the last decade. The focus of this study was to analyze the genetic basis of antimicrobial resistance (AMR) and the prevalence of multidrug-resistance (MDR)-mediating integrative and conjugative elements (ICEs) in 13 German BRD-associated Mannheimia haemolytica isolates collected between 2009 and 2020 via whole-genome sequencing. Antimicrobial susceptibility testing (AST) was performed via broth microdilution according to the recommendations of the Clinical and Laboratory Standards Institute for the macrolides erythromycin, tilmicosin, tulathromycin, gamithromycin, tildipirosin, and tylosin as well as 25 other antimicrobial agents. All isolates either had elevated MICs or were resistant to at least one of the macrolides tested. Analysis of whole-genome sequences obtained by hybrid assembly of Illumina MiSeq and Oxford Nanopore MinION reads revealed the presence of seven novel Tn7406-like ICEs, designated Tn7694, and Tn7724- Tn7729. These ICEs harbored the antimicrobial resistance genes erm(T), mef (C), mph(G), floR, catA3, aad(3")(9), aph(3')-Ia, aac(3)-IIa, strA, strB, tet(Y), and sul2 in different combinations. In addition, mutational changes conferring resistance to macrolides, nalidixic acid or streptomycin, respectively, were detected among the M. haemolytica isolates. In addition, four isolates carried a 4,613-bp plasmid with the β-lactamase gene blaROB - 1. The detection of the macrolide resistance genes erm(T), mef (C), and mph(G) together with other resistance genes on MDR-mediating ICEs in bovine M. haemolytica may explain the occurrence of therapeutic failure when treating BRD with regularly used antimicrobial agents, such as phenicols, penicillins, tetracyclines, or macrolides. Finally, pathogen identification and subsequent AST is essential to ensure the efficacy of the antimicrobial agents applied to control BRD in cattle.

Immune Cells in the Spleen of Mice Mediate the Inflammatory Response Induced by Mannheimia haemolytica A2 Serotype

(1) Background: Mannheimia haemolytica (M. haemolytica) is an opportunistic pathogen and is mainly associated with respiratory diseases in cattle, sheep, and goats. (2) Methods: In this study, a mouse infection model was established using a M. haemolytica strain isolated from goats. Histopathological observations were conducted on various organs of the mice, and bacterial load determination and RNA-seq analysis were specifically performed on the spleens of the mice. (3) Results: The findings of this study suggest that chemokines, potentially present in the spleen of mice following a M. haemolytica challenge, may induce the migration of leukocytes to the spleen and suppress the release of pro-inflammatory factors through a negative feedback regulation mechanism. Additionally, an interesting observation was made regarding the potential of hematopoietic stem/progenitor cells congregating in the spleen to differentiate into immune cells, which could potentially collaborate with leukocytes in their efforts to counteract M. haemolytica invasion. (4) Conclusions: This study revealed the immune regulation mechanism induced by M. haemolytica in the mouse spleen, providing valuable insights into host-pathogen interactions and offering a theoretical basis for the prevention, control, and treatment of mannheimiosis.

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.

Prediction of Pasteurella multocida serotypes based on whole genomic sequences

The serotypes of Pasteurella multocida were predicted based on whole genomic sequences (WGS) with specific genes of the capsular and liposaccharide (LPS) outer core polysaccharide regions as targets. A total of 56 strains were whole genomic sequenced and in addition all assembled genomes from NCBI were included for comparison. BIGSdb (Bacterial Isolate Genome Sequence Database) was installed on a Linux server and targets for capsular types A, B, D, E and F were defined as gene sequences of hyaD, bcbD, dcbF, ecbJ and fcbD, respectively and targets for LPS groups 1, 2, 3, 4, 5, 6, 7 and 8 were defined as gene sequences of pcgB, nctA, gatF, latB, rmlA, nctB, ppgB and natG, respectively. The serotypes of P. multocida were predicted from WGS by designating the capsular type and LPS group as well as subtype alleles to isolates. Comparisons between WGS predictions of capsular types and classical phenotypic typing showed correspondence in 87 % of cases whereas comparisons of WGS predictions of LPS groups to phenotypic typing corresponded for 82 % of the strains. In total 93 % and 94 % of the strains available with WGS could be capsular and LPS group typed, respectively. The server is free to access from https://ivsmlst.sund.ku.dk.