Ed Metzger from Southwest Ontario Veterinary Service, Not All P. multocida Are Created Equal

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Pasteurella  multocida  type  A  (PmA)  has usually been considered to be a secondary agent  of  pneumonia  in  pigs.  The  general assumption  was  that  unless  some  other primary  pathogen  such  as  PRRS,  Influenza  or Mycoplasma hyopneumoniae started the respiratory disease the PmA would not be a disease issue on it’s own.  These  Brazilian  researchers  challenged  that traditional thinking and used some newer diagnostic technology to dig a bit deeper on the potential role of  PmA  as  a  primary  pathogen.

 

Test  pigs  were challenged  with  eight  “field  strains”  isolated  from pneumonia  and  serositis  in  six  Brazilian  states. Eight  groups  of  eight  pigs  each  were  intranasally inoculated  with  different  strains  of  PmA  (1.5  mL/nostril  of  10e7  CFU/mL).  The  control  group  (n  = 12) received sterile PBS. The pigs were euthanized by  electrocution  and  necropsied  by  5  days  post infection. Visual lesions were recorded, and swabs and  fragments  of  thoracic  and  abdominal  organs were  analyzed  by  bacteriological  and  pathological assays.  The  PmA  strains  were  analyzed  for  four virulence  genes  by  PCR  and  sequencing  and submitted to multilocus sequence typing (MLST).

 

The eight PmA strains were classified as follows;

  • five highly pathogenic (HP) for causing necrotic bronchopneumonia   and   diffuse   fibrinous pleuritis and pericarditis;
  • one  low  pathogenic  for  causing  only  focal bronchopneumonia;
  • two non-pathogenic because they did not cause injury to any pig.

PCR  for  the  gene pfhA  that  causes  adhesions  was positive for all five HP isolates.

The low and non-pathogenic strains did not contain the genes tpsB2 and pfhA2. MLST clustered the HP isolates in one

group  and  the  low  and  non-pathogenic  isolates  in another. Only the non-pathogenic as a primary isolates  matched  sequence  type  10;  the  other isolates  did  not  match  any  type  available  in  the MLST database.

 

Take Home Message

Not  all  strains  of  Pasteurella  multocida  type  A are  created  equal  in  terms  of  their  disease

causing abilities and this can help explain some of the variation in clinical outcomes when what

appears on the surface to be the same organism.

 

Submitted by Ed Metzger, DVM

Ref: Oliveira  Filho  JX,  Morés  MAZ,  Rebellato  R,  Kich  JD,  Cantão  ME, Klein  CS,  Guedes  RMC,  Coldebella  A,  Barcellos  DESN,

Morés  N. Pathogenic  variability  among  Pasteurella  multocida type  A  isolates  from Brazilian  pig  farms.  BMC  Vet  Res.  2018  Aug  22;14(1):244.  doi:  10.1186/s12917-018-1565-2.

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