Isolation of virulent Rhodococcus equi from transtracheal aspirates of foals serodiagnosed by enzyme-linked immunosorbent assay.

This research investigates the virulence (disease-causing potential) of the bacteria Rhodococcus equi obtained from lung samples (transtracheal aspirates) of foals displaying respiratory symptoms. The study also evaluates the effectiveness of a specific blood test (ELISA) for early detection of this infection. The results reveal the bacteria isolated to be highly virulent and the test to be sensitive in diagnosing the infection.

Research Approach and Methods

• The study collected transtracheal aspirates (samples from the lungs) from 31 foals aged 1 to 6 months who showed signs of respiratory infection.
• Rhodococcus equi, which is a bacteria associated with pneumonia, was isolated from these aspirates, and these isolates were then analyzed for certain features – virulence plasmids and virulence-associated antigens – that make them more likely to cause disease.
• In addition to this isolation and analysis method, the research also conducted a serodiagnosis using an enzyme-linked immunosorbent assay (ELISA). This is a test that measures the blood serum levels of antibodies, which are immune system proteins that fight off infection.

Key Findings

• Out of the 31 foals, positive cultures for R. equi were obtained in 21 of them. Of these 21, 20 (95%) had an ELISA test result that indicated a significant level of antibodies (which is a sign of an ongoing infection).
• All of the bacterial samples obtained from the lung aspirates were virulent, or highly capable of causing disease.
• Of the remaining 10 foals that did not yield a positive culture for R. equi, 3 still managed to test positive in the ELISA assay, indicating that they were infected with the bacteria despite not displaying all symptoms or microbial growth in the lung samples.
• Out of the 6 foals that died while the study was underway, a post-mortem examination revealed that 5 had R. equi infection with large abscesses in their lungs, and 3 of these also had lesions in their intestine.
• All the bacterial cultures obtained from these lesions were confirmed to be virulent R. equi.

Implications of Research

• This study shows clear evidence that Rhodococcus equi, isolated from the transtracheal aspirates of infected foals, are indeed virulent and a significant cause of disease.
• The research also demonstrates the effectiveness of the ELISA assay in diagnosing R. equi infection, as indicated by the high detection rate among the symptomatic foals.
• Thus, these findings provide valuable insights into the diagnosis and prognosis of Rhodococcus equi infection in foals, potentially informing improved strategies for disease detection and treatment.