Two quick methods for Voges-Proskauer test.

Two previously described methods for rapidly performing a Voges-Proskauer (VP) test were modified so that results could be obtained even more quickly. On MacConkey agar, colonies of lactose-fermenting, VP-positive organisms usually contain enough acetoin to give a positive reaction when a dense suspension is prepared in creatine and tested directly with Barritt reagents. With this direct-screening test, no "false" positive results were seen, but 29 of 429 lactose-fermenting strains of Enterobacteriaceae initially gave "false" negative results. Thus, another technique was needed for quickly confirming negative results. A 0.2-ml amount of MR-VP Broth culture, inoculated with one colony or less, can be tested after 4 to 6 hr at 37 C by adding two drops of a 0.5% creatine solution followed by Barritt reagents. No "false" positive results were seen with 508 cultures, but one atypical coliform bacillus was negative with this method and VP positive after 48 hr of incubation in MR-VP Broth. With these two quick methods, the common VP positive organisms can be recognized within a few minutes or at most after a few hours.