The Journal of Medical Microbiology, Vol 33, Issue 2 101-106, Copyright © 1990 by Society for General Microbiology
Plasmid profiles of Shigella dysenteriae type 1 isolates from Ethiopia with special reference to R-plasmids
A. Gebre-Yohannes and B. S. Drasar
Department of Microbiology, National Research Institute of Health, Addis Ababa, Ethiopia.
Plasmid profiles of 80 Shigella dysenteriae type 1 (Shiga's bacillus)
strains, collected between 1974 and 1985 in Ethiopia, were examined.
Strains with the dominant antibiotic-resistance (R-) type--resistance to
ampicillin (A), chloramphenicol (C), streptomycin (S), sulphadiazine (Su)
and tetracycline (T)--showed two distinct plasmid profiles (PP). Six
plasmid bands were demonstrated in "Ethiopian strains" with PP-1A isolated
between 1974 and 1982. In mating experiments with these strains,
Escherichia coli K12 recipients showed plasmids pYH10a (72 Mda, atypical
Inc FIme, coding for ACSSuT resistance). Eight plasmid bands were
demonstrated in strains with PP-2A. These strains were first isolated in
1980 and carried plasmid pYH11a (40 Mda, Inc X, coding for ACT resistance).
Strains with PP-2A were identical with a "Zairian strain" described
elsewhere. Strains with R-type ACT were "Zairian strains" lacking the 5.1-
and 4.2-Mda plasmids. Those with R-type CSSuT were temporally clustered in
1978-1980 and carried plasmid pYH12 (58 Mda, Inc B, coding for the same
R-type). A trimethoprim-resistant strain (Gimira strain) had a pattern of
small plasmids similar to those of the "Zairian strain" and is probably a
subclone of the latter. The fact that a limited number of plasmid profiles
have remained constant over many years shows the limitation of plasmid
profile analysis as an epidemiological tool. However, when the usual
profile is known for a given area, identification of a distinctly different
pattern becomes easy and epidemiologically useful.
