A fully defined, clear and protein-free liquid medium permitting dense growth of Neisseria gonorrhoeae from very low inocula

Neisseria gonorrhoeae is difficult to cultivate in liquid medium. Currently there are no liquid media, defined or undefined, that reliably permit growth of this bacterium from low inocula. Standard clinical laboratory broths may allow multiplication of some strains of gonococci from large inocula, but such media incorporate infusates, extracts or digests and are therefore undefined. In this study, 20 gonococci of ten auxotypes were tested in various experimental media in the development of an easily prepared chemically defined, clear and protein-free liquid medium. The final medium - GW medium - allowed the growth of three clinical isolates of gonococci from inocula of < 10(3) CFU mL(-1) to > 10(8) CFU mL(-1) by 24 h. None of four commercially-available broths (nutrient broth, brain heart infusion, tryptone soya broth, and Mueller-Hinton broth) tested in parallel reliably supported growth of these isolates to the same extent. GW medium should be useful for studies of the growth of gonococci under different conditions and, as the medium is clear and colorless, this can be monitored turbidometrically. GW medium may be suitable as a basal medium for biochemical identification tests, antimicrobial susceptibility determinations and antimicrobial synergy studies.