A comparison of solid and liquid media for measuring the sensitivity of heat-injured Salmonella typhimurium to selenite and tetrathionate media, and the time needed to recover resistance

Sensitivity of heat-injured Salmonella typhimurium to selenite and tetrathionate media was measured by viable counts in liquid and on agar-solidified versions of these media and on nutrient media. All solid media, including the supposedly non-inhibitory nutrient agar, were more inhibitory to injured cells than the corresponding liquid media. Catalase or pyruvate increased counts on nutrient agar to the level obtained in nutrient broth. Therefore nutrient agar plus pyruvate was the most suitable reference medium against which to compare recoveries on other media. Although recoveries of injured cells varied widely depending on the composition and physical state of the medium, this had a minor effect on estimates of repair time because resistance to all selective media was regained by the end of the lag phase.