Mycolic Acid‐Containing Glycolipid as a Possible Virulence Factor of Rhodococcus equi for Mice

Abstract

By the use of various Rhodococcus equi strains differing in the length of carbon chains of glycolipid, we examined whether the glycolipid, glucose monomvcolate, was contributing to the virulence of R. equi for mice.R. equi strains with longer carbon chain mycolic acid showed a higher virulence as determined by lethality and granuloma formation in mice than those with shorter ones. When purified glycolipid was injected into mice, granuloma formation and liver damage were most prominent with the glycolipid having longer carbon chain mycolic acid. Only a representative strain with longer carbon chain mycolic acid persisted in the spleen of mice after intravenous injection, while a strain with shorter carbon chain mycolic acid was readily eliminated.These results suggested that glycolipid was at least one of the virulence factors of R. equi and that the carbon chain length of mycolic acid might be critical in the expression of virulence.

The medically important aerobic actinomycetes: epidemiology and microbiology

“…In a recent study, McNeil et al identified three distinct mycolic acid patterns among a collection of R. equi reference strains and clinical isolates; these patterns were also associated with differences in the antimicrobial susceptibility and colony morphology of these strains and isolates (380). In another study, Gotoh et al associated three different mycolic acid patterns of R equi isolates with their virulence in vivo in a mouse model (223). In this study, R equi isolates having longer carbon chains for mycolic acid-glycolipid showed a higher degree of virulence, as determined by lethality and granuloma formation in mice, than did those having shorter carbon chains (223).…”

“…It is difficult to compare these three studies (89,223,380), since there were no common internal control strains in the study of Gotoh et al (223). It is apparent that mycolic acid patterns constitute useful phenotypic markers for the rhodococci; however, representative strains from all of the 13 validly described Rhodococcus spp.…”

“…In another study, Gotoh et al associated three different mycolic acid patterns of R equi isolates with their virulence in vivo in a mouse model (223). In this study, R equi isolates having longer carbon chains for mycolic acid-glycolipid showed a higher degree of virulence, as determined by lethality and granuloma formation in mice, than did those having shorter carbon chains (223). In addition, when purified glycolipid was injected into mice, granuloma formation and liver damage were most prominent with the glycolipid having longer-carbonchain mycolic acids.…”

“…The Gotoh et al studied R. equi isolates from swine and also found marked differences in their mycolic acid chromatographic patterns (223). On the basis of the average length of the carbon chain in each isolate, R. equi isolates were classified into three patterns (223). Furthermore, these investigators found that the mycolic acids with relatively longer carbon chains were derived from R. equi isolates that caused abscesses in the lymph nodes of swine, while the mycolic acids with shorter carbon chains were derived from R. equi isolates from normal tonsils.…”

“…by using high-performance liquid chromatography and found a single chromatographic pattern for both R. erythropolis and R. rhodochrous but two different chromatographic patterns for R. equi. The Gotoh et al studied R. equi isolates from swine and also found marked differences in their mycolic acid chromatographic patterns (223). On the basis of the average length of the carbon chain in each isolate, R. equi isolates were classified into three patterns (223).…”