Requirement for Egg Yolk and Pyruvate

The benefits of including egg or egg yolk in culture media for isolation of MAP have been noted since 1912 but the reasons it is needed are still not clear (Twort and Ingram, 1912).

Certainly some strains of the organism can be grown in some media without egg, while it is vital in other circumstances (Cousins et al., 1995; Whittington et al., 1999; Grant et al., 2003). When benzalkonium chloride (BAC) or hexadecylpyridinium chloride (HPC) is used to decontaminate faecal samples, egg yolk is required in 7H10 or 7H9 media to enable growth of MAP; simply washing the MAP pellet once in water enabled growth in these media without addition of egg yolk (Whipple and Merkal, 1983). Thus egg may play a role in neutralizing disinfectants carried over into the culture medium with the inoculum (Merkal and Curran, 19 74). This may explain why egg yolk was a necessary ingredient for primary isolation but not for subculture (Cousins et al., 1995). There is more information about egg yolk in section 18.6.

Sodium pyruvate was reported to stimulate the growth of MAP and is included in both the Lowenstein Jensen medium (LJ) and the Herrold's egg yolk medium (HEYM) used by some laboratories (Merkal and Curran, 19 74; Jorgensen, 1982; Kim et al., 1989; Juste et al., 1991; Eamens et al., 2000). Pyruvate enables MAP colonies to grow to a larger size on LJ medium, compensating for the inhibitory effects of the antibiotics that are included in this medium (Jorgensen, 1982).

18.6

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Source: Behr Marcel A., Stevenson K., Kapur V. (eds.). Paratuberculosis: Organism, Disease, Control. 2nd edition. — CAB International,2020. — 439 p.. 2020

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Requirement for Egg Yolk and Pyruvate

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