The Journal of Medical Microbiology, Vol 24, Issue 4 351-357, Copyright © 1987 by Society for General Microbiology
Plasmid stability and antibiotic resistance of Neisseria gonorrhoea during glucose-limited continuous culture
C. W. Keevil, B. J. Spillane and N. C. Major
Pathogenic Microbes Research Laboratory, PHLS Centre for Applied Microbiology and Research, Salisbury, Wilts.
Clinical isolates of Neisseria gonorrhoeae harbouring resistance (R)
plasmids of mol. wts 4.4 x 10(6) (Asian) or 3.2 x 10(6) (African) were
grown in prolonged glucose-limited continuous culture to determine the
segregation efficiency of each type of plasmid and their expression of
penicillinase activity in the absence of antibiotic selective pressure. One
strain contained the African plasmid and cryptic and conjugative plasmids,
which were all retained after 96 generations in the chemostat. By contrast,
the other strain lost all plasmids after 100 generations. Both strains
showed increased sensitivity to a range of antibiotics, particularly to the
penicillins. Loss of penicillinase activity as minimal inhibitory
concentration decreased was confirmed for both strains by assaying the
enzyme spectrophotometrically. Activity decreased with the number of
generations and none was detectable at the time of complete plasmid loss.
This decrease was apparently due to individual bacteria ceasing to produce
enzyme rather than a gradual decline in production by the whole population.
The sensitivities to a broad range of antibiotics also generally increased
during glucose-limited growth, but one strain became more resistant to
clindamycin and the other to tetracycline.
