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J. Bacteriol., Jun 1996, 3072-3076, Vol 178, No. 11
PA Barrow, MA Lovell and LZ Barber
We have studied the growth suppression seen in early-stationary-phase LB
broth cultures of Salmonella typhimurium. Multiplication of small numbers
of an antibiotic-resistant S. typhimurium mutant was prevented when the
mutant was added to 24-h cultures of the antibiotic-sensitive parent
strain, whereas an antibiotic-resistant mutant of an Escherichia coli
strain added to the same culture grew well. A 24-h E. coli culture produced
a similar specific bacteriostatic inhibition against E. coli. In older
cultures, a specific bactericidal effect similar to that observed by M. M.
Zambrano and R. Kolter (J. Bacteriol. 175:5642-5647, 1993) was also
observed. Whether incubated statically or shaken, sufficient nutrients were
present in the filtered supernatants of 24-h cultures for small inocula of
the same strain to multiply to ca. 10(9) CFU/ml after reincubation.
Introduction of the rpoS mutation had no effect on the specific
bacteriostatic inhibition. Similar specific inhibition was also observed in
strains of Citrobacter freundii, Klebsiella pneumoniae, Enterobacter
agglomerans, and Shigella spp. Experiments in which the 24-h culture was
physically separated from the antibiotic-resistant mutant by using a
dialysis membrane were carried out. These results indicated that the
inhibition might be mediated by a diffusible but labile chemical mediator.
Copyright © 1996, American Society for Microbiology
Growth suppression in early-stationary-phase nutrient broth cultures of Salmonella typhimurium and Escherichia coli is genus specific and not regulated by sigma S
Division of Environmental Microbiology, Institute for Animal Health, Compton Laboratory, Berkshire, United Kingdom. paul.barrow@bbsrc.ac.uk
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