A HEURISTIC APPROACH TO CHARACTERIZING STAPHYLOCOCCUS
SPECIES USING FATTY ACID ANALYSIS AND BIOCHEMICAL TESTS

Gabriella V. Brescacin
School of Science aud Natural Resources

	Members of the genus Staphylococcus, though considered to be endogenous
microflora of humans and animals, are frequently found as etiological agents of a variety
of infections. During the past decade there has been increased concern for those
Staphylococcus species that constitute a major component of our normal flora. Their
prevalence in the cause of nosocomial infections in humans is a major concern for
medical centers today making it necessary for clinical laboratories to identify all those
species known to be indigenous. Identification, of most members of this genus, presently
incorporates the use of biochemical data compiled from varying methodologies and
sources. The use of inconsistent or outdated data challenges clinical laboratories in the
identification of staphylococci. The objective ofthis research project was to overcome
identification problems by characterizing all of the aerobic taxa of the genus
Staphylococcus by using an objective, self-learning system combining both whole-cell
fatty acid (FA) analysis and the results of 35 standardized biochemical tests. The type
strain for each taxon, 33 species and 8 subspecies, was initially used to generate an FA
profile library and a biochemical table of test responses. The testing of additional isolates
from reference, clinical, veterinary and environmental sources followed and were
compared to the type strain profiles of each system. Isolates were accepted into the
system if they had a similarity index of >_0.6 for a taxon within the FA profile library and
if they were identified as the same taxon, with a relative probability of over 98%, by a
computer program called Reference Identification (RefiD) using a probability matrix
constructed from the biochemical data. These stringent criteria led to acceptance of 1,117
strains assigned to legitimate taxa. Additional FA groups were assembled from selected
strains that did not meet the inclusion criteria based on the type strains and were added to
the system as separate entries. Currently, from a total of 1,644 organisms that have been
exposed to this system ofidentification, 1,512 isolates have been accepted into the
system. This approach has resulted in a comprehensive table of biochemical test results
and an FA library, which together has overcome most identification errors providing
reference and clinical laboratories a practical system for valid identification.

Selected References
Kloos, W.E., and T.L. Bannerman. 1994. Update on clinical significance of coagulase-
	negative staphylococci. Clin. Microbiol. Rev. 7: 117-140.

Renneberg, J., K. Reineck, and E. Gutecheck. 1995. Evaluation of Staph ID 32
	system and Staph-Zym system for the identification of coagulase-negative
	staphylococci. J. Clin. Microbiol. 33:1150-1153.

Welch, D.F. 1 991 . Applications of cellular fatty analysis. Clin. Microbiol. Rev.
	4:422-438.