Gram staining of the sample may demonstrate bacteria in bacterial meningitis, but absence of bacteria does not exclude bacterial meningitis as they are only seen in 60% of cases; this figure is reduced by a further 20% if antibiotics were administered before the sample was taken.
Gramfärgning av provet kan påvisa bakterier vid bakteriell meningit, men frånvaro av bakterier exkluderar inte bakteriell meningit, eftersom de bara ses i 60 % av fallen; denna siffra minskar med ytterligare 20 % om antibiotika administrerats före provtagningen.