EFFECT OF SORBED WATER ON THE DEATH RATE OF WASHED SERRATIA MARCESCENS

Persistence of Salmonella typhimurium on Fabrics

“…Viable organisms persisted throughout the 24-week test period on swatches of the following fabrics which had been exposed by direct contact VOL. 18 and held in 35% relative humidity: wool gabardine, cotton sheeting, cotton knit jersey, and cotton terry cloth (Fig. 2-5).…”

“…The persistence of S. typhimurium on cotton VOL. 18,1969 wash-and-wear swatches (contaminated by direct contact) held in 35 or 78% humidities was relatively brief when compared to the persistence time of the organism on the other cotton materials which had been contaminated by direct contact (Fig. 3-6).…”

“…The dishes were then stored at the desired humidity. The bacterial population density on five swatches was determined at time zero (immediately after exposure to the bacteria) and at the following time intervals: 2 hr, 1,2,4,6,8,10,12,14,16,18,20,22, and 24 weeks after exposure of the swatches to the organism, or at least two time intervals after bacteria could no longer be recovered from the fabric. The bacterial population density on each fabric swatch was determined by macerating the swatch with 25 ml of physiological saline in a Sorvall omnimix homogenizer (Ivan Sorvall, Inc., Norwalk, Conn.) and determining the number of viable bacteria by quantitative plating of each eluate on tryptic soy-agar plates (28).…”

Relative Humidity and the Killing of Bacteria

“…Some observations on the ability of washed Escherichia coli and Mficrococcus lysodeikticus to form colonies when plated after having been freeze-dried and exposed to water vapor in vacuo will be presented in this paper. Serratia marcescens treated in this manner is rapidly killed within a rather narrowly limited range of relative humidities around 90 per cent (Monk and McCaffrey, 1957). It was of interest to determine whether other organisms would behave similarly.…”

“…The suspensions were freeze-dried in 0.5-ml portions for 1 hr in the glass inverted U manifold described by Monk and McCaffrey (1957) and equilibrated in vacuo at relative humidities of 0, 11, 75, or 93 per cent. At intervals from } to 5 hr tubes were detached from the apparatus and the contents diluted with 0.5 ml of water and plated after serial dilution.…”