Three new serotypes of Rhodococcus equi in Prescott's serotyping system - Short communication.

Three new serotypes were found among Rhodococcus equi strains, which could not be assigned into any of the seven serotypes of Prescott's system. Fortythree R. equi strains out of 44 previously nontypable ones isolated in Hungary could be allocated into one of the three new serotypes using the agar gel immunodiffusion (AGID) test. The three new suggested serotypes are serotype 8 (proposed reference strain: HNCMB-138003), serotype 9 (proposed reference strain: HNCMB-138004) and serotype 10 (proposed reference strain: HNCMB-138005). Hyperimmune sera produced in rabbits against the new serotypes and reference strains gave precipitation only with their homologous antigens, and no crossreactions were observed. All of the previously nontypable isolates from clinical samples of horses (lung abscesses, intestinal lymph nodes, mediastinal lymph nodes) proved to be serotype 8, while strains of serotypes 8, 9 and 10 could be isolated from nasal and rectal swabs of horses and from the soil. Serotype 9 dominated among the previously nontypable strains of swine origin. One of the previously nontypable human strains was serotype 10. This serotype was also isolated from pigs, horses and the soil. The description of the three new serotypes can help us reveal new correlations between the host species, geographical origin and serotype of R. equi isolates.