The Journal of Medical Microbiology, Vol 48, Issue 12 1111-1114, Copyright © 1999 by Society for General Microbiology
A comparison of blood agar supplemented with NAD with plain blood agar and chocolated blood agar in the isolation of Streptococcus pneumoniae and Haemophilus influenzae from sputum. Bacterial Methods Evaluation Group
K. J. Nye, D. Fallon, B. Gee, S. Messer, R. E. Warren and N. Andrews
Public Health Laboratory Service (Midlands), Royal Shrewbury Hospital, London.
Streptococcus pneumoniae grows well and generally exhibits typical
morphology on Columbia blood agar, whereas Haemophilus influenzae requires
a more complex medium to meet its growth requirements - usually chocolated
blood agar - on which S. pneumoniae is less easily recognisable. Therefore,
a single medium that produces typical morphology of S. pneumoniae and
facilitates the growth of H. influenzae would have considerable potential
advantages. It has been claimed that blood agar supplemented with
nicotinamide adenine dinucleotide (NAD) is such a medium. However, despite
its routine use in several large diagnostic laboratories its performance
has never been properly evaluated. In the present study, 1724 sputum
samples were examined in four laboratories. The isolation rates of H.
influenzae and S. pneumoniae on NAD-supplemented blood agar (SBA) were
compared with those on a two-plate combination of plain blood (BA) and
chocolated blood agar (CBA). The two-plate combination performed
significantly better for both organisms; isolation rates for H. influenzae
were increased from 8.16% on SBA to 11.07% on BA plus CBA and for S.
pneumoniae from 4.18% to 4.68%. Isolation rates were also compared after
incubation for 24 and 48 h. With the two-plate combination, isolation rates
for H. influenzae and S. pneumoniae were increased by 0.98% and 0.16%,
respectively, and for SBA by 0.57% and 0.32% after 48 h. However, despite
this increase, SBA still performed less well than the two-plate
combination.
