Figure 3.

β-Lactamase present in competitions is found in both pelleted cells and in the collected growth medium. Competitions (50∶50 initial starting proportions of strains or with each strain alone) were conducted at 100 µg ampicillin per millilitre DMM liquid medium or without antibiotic. The values presented here represent samples collected after 48 h growth. (a) β-Lactamase activity expressed as absorbance at 486 nm (A₄₈₆) per minute per microgram of protein. (b) Activity of β-galactosidase. Salmonella enterica serovar Typhimurium ATCC 14028 is unable to produce this enzyme, hence the absence of activity from it and the reduction in specific activity when this organism dominates the cultures. Dark bars—supernatant, filter-sterilized supernatant from competition; light bars—sonic extract, sonic extract of collected cell pellet from competition.