The Journal of Medical Microbiology, Vol 37, Issue 2 109-117, Copyright © 1992 by Society for General Microbiology
Evaluation of methods for typing coagulase-negative staphylococci
M. S. Dryden, H. G. Talsania, S. Martin, M. Cunningham, J. F. Richardson, B. Cookson, R. R. Marples and I. Phillips
Department of Microbiology, St Thomas' Hospital, London.
One hundred and forty-two coagulase-negative staphylococci (CNS) isolated
from dialysate effluent or skin of patients receiving continuous ambulatory
peritoneal dialysis (CAPD) were typed by extended antibiogram (16
antibiotics) and biotype (26 reactions). These isolates were then typed by
supplementary methods to determine the most suitable typing method for an
epidemiological study of antibiotic resistance. These included phage
typing, reverse phage typing, plasmid typing, whole-cell protein typing by
SDS-PAGE with analysis by densitometry, and immunoblotting. The percentage
of isolates typed successfully by the supplementary methods were: phage
typing 20%, reverse phage typing 0%, plasmid typing 66%, SDS-PAGE 100%,
immunoblotting 100%. The discrimination of each method was: phage typing
20%, plasmid typing 37%, SDS-PAGE 69%, immunoblotting 57%. Reproducibility
was 88% for phage typing and 97% for plasmid typing. The reproducibility of
the whole-cell protein typing was 83% if the same extracts were used but
only 43% when separate protein extracts were analysed on separate
occasions. However, strain relatedness was highly reproducible. The
determination of an antibiogram-biotype profile was not a sufficiently
accurate typing method for an epidemiological study of antibiotic
resistance. Whole-cell protein typing by SDS-PAGE or immunoblotting was
technically demanding but was the most effective of the supplementary
methods for detecting erroneous discrimination and false matching produced
by antibiogram-biotype combinations.
