The Journal of Medical Microbiology, Vol 35, Issue 1 49-52, Copyright © 1991 by Society for General Microbiology
Provisional identification of Haemophilus influenzae from sputum cultures within 1 h by rapid enzyme tests
S. F. Dealler, J. Foweraker, P. Lawson and S. Fortune
Microbiology Department, University of Leeds.
Possible Haemophilus influenzae colonies in cultures of sputum samples are
currently identified by tests for dependence on X and V factors. This
method requires further overnight culture and may give a relatively high
number of false negative results. Identification of suspected H. influenzae
colonies by a 5-min test for production of indole and beta-galactosidase
followed by a 1-h porphyrin test was compared with tests for dependence on
X and V factors. A commercially produced form of the rapid tests
(Haemstrip, Lab M, Bury, Lancs) was used to test 252 potential haemophilus
colonies from cultures of sputum samples on heated blood agar. Colonies
that were beta-galactosidase-positive after 5 min were considered to be
non-H. influenzae and those that were beta-galactosidase-negative but
indole-positive were considered to be H. influenzae. At this stage the test
had a sensitivity of 99.4% and a specificity of 90.9%. After 1 h, only
colonies that were beta-galactosidase- and porphyrin-negative were
considered to be H. influenzae, the sensitivity was then 99.5% and the
specificity 100%. Similar results were found with colonies from sputum
cultures on selective heated blood agar containing bacitracin. The X and V
dependence and Haemstrip results were in 97.6% agreement in a double blind
test. Of 100 non-haemophilus colonies tested by Haemstrip, two pseudomonads
could have been identified as H. influenzae by this method. The high
positive predictive value of Haemstrip results depends partly on the
initial recognition of potential haemophilus colonies.
