Abstract
BackgroundHaemophilus parasuis, the causative agent of Glässer’s disease, is prevalent in swine herds and clinical signs associated with this disease are meningitis, polyserositis, polyarthritis, and bacterial pneumonia. Six to eight week old pigs in segregated early weaning herds are particularly susceptible to the disease. Insufficient colostral antibody at weaning or the mixing of pigs with heterologous virulent H. parasuis strains from other farm sources in the nursery or grower-finisher stage are considered to be factors for the outbreak of Glässer’s disease. Previously, a Mu-like bacteriophage portal gene was detected in a virulent swine isolate of H. parasuis by nested polymerase chain reaction. Mu-like bacteriophages are related phyologenetically to enterobacteriophage Mu and are thought to carry virulence genes or to induce host expression of virulence genes. This study characterizes the Mu-like bacteriophage, named SuMu, isolated from a virulent H. parasuis isolate.ResultsCharacterization was done by genomic comparison to enterobacteriophage Mu and proteomic identification of various homologs by mass spectrometry. This is the first report of isolation and characterization of this bacteriophage from the Myoviridae family, a double-stranded DNA bacteriophage with a contractile tail, from a virulent field isolate of H. parasuis. The genome size of bacteriophage SuMu was 37,151 bp. DNA sequencing revealed fifty five open reading frames, including twenty five homologs to Mu-like bacteriophage proteins: Nlp, phage transposase-C-terminal, COG2842, Gam-like protein, gp16, Mor, peptidoglycan recognition protein, gp29, gp30, gpG, gp32, gp34, gp36, gp37, gpL, phage tail tube protein, DNA circulation protein, gpP, gp45, gp46, gp47, COG3778, tail fiber protein gp37-C terminal, tail fiber assembly protein, and Com. The last open reading frame was homologous to IS1414. The G + C content of bacteriophage SuMu was 41.87% while its H. parasuis host genome’s G + C content was 39.93%. Twenty protein homologs to bacteriophage proteins, including 15 structural proteins, one lysogeny-related and one lysis-related protein, and three DNA replication proteins were identified by mass spectrometry. One of the tail proteins, gp36, may be a virulence-related protein.ConclusionsBacteriophage SuMu was characterized by genomic and proteomic methods and compared to enterobacteriophage Mu.
Highlights
Haemophilus parasuis, the causative agent of Glässer’s disease, is prevalent in swine herds and clinical signs associated with this disease are meningitis, polyserositis, polyarthritis, and bacterial pneumonia
Since the bacteriophage SuMu genes and proteins identified are related to bacteriophage Mu, they could potentially confer the necessary factors for this bacteriophage to be able to transduce virulence factors, which could affect the epidemiology of H. parasuis field isolates [9,10]
A potential diagnostic test such as a bacteriophage-specific Polymerase chain reaction (PCR) test was developed to assay for the presence of bacteriophage genes in bacterial isolates from H. parasuisinfected animals [11]. In summary, this is the first report on the characterization of a bacteriophage of a virulent field strain of H. parasuis named SuMu (Accession No JF832915) by DNA sequencing and by 1-D and 1- and 2- dimensional (2-D) SDS-PAGE electrophoresis of bacteriophage proteins, followed by mass spectrometry
Summary
Haemophilus parasuis, the causative agent of Glässer’s disease, is prevalent in swine herds and clinical signs associated with this disease are meningitis, polyserositis, polyarthritis, and bacterial pneumonia. Insufficient colostral antibody at weaning or the mixing of pigs with heterologous virulent H. parasuis strains from other farm sources in the nursery or grower-finisher stage are considered to be factors for the outbreak of Glässer’s disease. A Mu-like bacteriophage portal gene was detected in a virulent swine isolate of H. parasuis by nested polymerase chain reaction. Haemophilus parasuis causes Glässer’s disease in pigs, with symptoms of pneumonia, fibrinous polyserositis, pericarditis, polyarthritis, and meningitis [1]. Due to lack of protective immunity to H. parasuis, introduction of conventionally raised pigs into segregated early weaning (SEW) herds may result in infection and high economic losses [2,3]. Many field isolates of H. parasuis are nontypeable (NT) [6]
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