Oral associated bacterial infection in horses: studies on the normal anaerobic flora from the pharyngeal tonsillar surface and its association with lower respiratory tract and paraoral infections.

The research focuses on examining the normal anaerobic bacteria found on the pharyngeal tonsillar surface in horses and their relationship to lower respiratory tract and paraoral infections.

Study Design and Process

• The researchers took bacteria samples from the pharyngeal tonsillar surfaces of 12 normal horses, yielding a total of 270 isolates. These bacteria were primarily anaerobic, and 98 of them were characterized in detail.
• Among these 98 anaerobic bacteria, 57 isolates belonging to 7 different genera, including Peptostreptococcus, Eubacterium, Clostridium, Veillonella, Megasphera, Bacteroides, and Fusobacterium were identified. Out of 57, 16 were identified at the species level.
• Further, the researchers obtained 320 isolates from 23 samples taken from horses with lower respiratory tract (LRT) or paraoral (PO) bacterial infections. These 143 bacteria selected for detailed characterisation were split into obligate anaerobes (100 isolates), facultative anaerobes (42 isolates), and obligate aerobes (one isolate).

Findings and Comparisons

• After the characterization of these isolates, a variety of bacteria were found. Among the obligately anaerobic strains, the most common were Gram-positive cocci such as P. anaerobius, accounting for 25% of all isolates, followed by E. fossor, and other Gram-positive rods, which totalled 18% of isolates. Gram-negative rods such as B. fragilis and B. heparinolyticus together comprised 10% of isolates.
• Among the facultatively anaerobic strains, S. equi subsp zooepidemicus was the most common, accounting for 31% of isolates, followed by Pasteurella spp., Escherichia coli, Actinomyces spp., and Streptococcus spp.
• Comparative analysis based on DNA hybridization data and/or phenotypic characteristics showed some similarities in bacterial species between the samples taken from the normal pharyngeal tonsillar surfaces and those from LRT and PO diseases of horses. These include E. fossor and B. heparinolyticus.

Conclusions of the study

• Conclusions drawn from the study suggest that the bacteria involved in lower respiratory tract and paraoral diseases are likely to originate from the oral cavity.
• This study lays the foundation for further investigations into the role and control of oral cavity bacteria in preventing and treating respiratory and paraoral infections in horses.