[Pasteurella] caballi infection not limited to horses – a closer look at taxon 42 of Bisgaard.

This research investigates taxon 42 of Bisgaard, isolated from pigs, as potential carriers of [Pasteurella] caballi, a bacteria previously thought to only infect horses. The team’s findings suggest that the bacterium is not limited to equine hosts, but can also be found in pigs, hinting at a broader distribution of the bacterium.

Study Overview

• The study looked into 15 samples from horses and pigs extracted from five different countries across three continents.
• The researchers conducted an extended phenotypical characterization of the samples, which means they studied the physical and biological traits of the bacteria.
• Despite some minor differences, the researchers could not categorically separate taxon 42 and [P.] caballi based solely on their phenotypical characteristics.

Ribotyping and 16S rRNA gene sequencing

• The team used two ribotyping methods, based on HindIII and HpaII digestion, to get a full genetic profile of the samples.
• The profiles revealed a high level of diversity, with one strain of [P.] caballi and two of taxon 42 sharing identical profiles with HindIII, while none sharing with HpaII. However, a pattern analysis revealed 91% similarity between two taxon 42 isolates and a [P.] caballi isolate.
• Further examination of the 16S rRNA gene sequence of one strain each from taxon 42 and [P.] caballi, showed nearly identical sequences, with at least 99.8% similarity with the published sequence for the type strain of [P.] caballi.

DNA Re-Associations

• Through the use of the micro-well method for measuring DNA re-associations, the study found 79% and 77% similarities respectively between the type strain of [P.] caballi and two strains of taxon 42.
• This high level of similarity led the researchers to confirm that taxon 42 actually belongs to [P.] caballi.

Findings and Implications

• The study found that [P.] caballi can also be isolated from the respiratory specimens of pigs, in addition to horses. It also confirmed that strains classified as taxon 42 are effectively [P.] caballi isolated from pigs.
• For both horses and pigs, the most common symptoms observed are respiratory tract infections. The bacterium’s association was also recognized with horse bite infections in humans.
• This research suggests that understanding of the bacterium’s virulence and epidemiology can be improved by recognizing that [P.] caballi is not limited to horses.