Three new serotypes of Rhodococcus equi in Prescott’s serotyping system – Short communication.

The research article discusses the discovery of three new serotypes of Rhodococcus equi, a bacterium, that were previously unclassifiable under Prescott’s serotyping system. The identification of these new serotypes further expands the classification of this bacterium, providing insights into potential correlations between the bacterium’s host species, geographic origin and serotype.

Introduction to Rhodococcus equi and Serotyping

• Rhodococcus equi is a bacterium that can cause severe infections in humans and animals.
• Previously, the identification and classification of R. equi strains were based on Prescott’s serotyping system which recognises seven serotypes.
• Serotyping refers to the classification of bacteria based on their antigenic properties which allows scientists to distinguish between different strains of the same species.

Discovery of New Serotypes

• Three new serotypes (8,9 and 10) were identified from 43 out of 44 previously unclassified R. equi strains using the agar gel immunodiffusion (AGID) test. The AGID test is used to detect antigens or antibodies in a sample.
• The new serotypes were proposed with certain reference strains: serotype 8 (reference strain: HNCMB-138003), serotype 9 (reference strain: HNCMB-138004) and serotype 10 (reference strain: HNCMB-138005).

Reactivity of New Serotypes

• The process of identifying new serotypes involved producing hyperimmune sera in rabbits against each new serotype and reference strains.
• The resultant hyperimmune sera gave precipitation only with their homologous antigens, meaning they reacted only with the specific strains of the bacteria for which they were developed, indicating the uniqueness of each serotype.

Hosts and Origins of New Serotypes

• The strains from clinical samples of horses (lung abscesses, intestinal lymph nodes, mediastinal lymph nodes) were found to be of serotype 8.
• Serotypes 8, 9, and 10 could also be isolated from nasal and rectal swabs of horses and from soil samples.
• Serotype 9 was found to be the most common among the previously uncategorized strains of swine origin.
• One of the previously undefined human strains was identified as serotype 10. This serotype was also isolated from pigs, horses, and soil samples, suggesting cross-species transmission possibility.

Significance of New Serotypes

• The three new serotypes enhance the serotyping system of R. equi and can help scientists draw new correlations between the host species, geographical origin, and serotype of R. equi strains.
• This has potential use in future epidemiological studies, outbreak investigations and control and prevention strategies.