Victory for the ACT Student Text 15e

S CIENCE T EST M ECHANICS • 289

Ǥ Œ‡Œ—‹ is unable to grow and multiply at the temperatures normally used to store food. The temperature range for growth is 30°C–45°C, with an optimum of 42°C. Survival at room temperature is poor, but Ǥ Œ‡Œ—‹ can survive for a short time at refrigeration temperatures—up to 15 times longer at 2°C than at 22°C. The bacteria die out slowly at freezing temperatures. Figure 1 shows the growth rate of Ǥ Œ‡Œ—‹ at 42°C over time.

Figure 1

Garlic ( ŽŽ‹— •ƒ–‹˜— ) has been recognized as a food that has broad-spectrum antimicrobial potential against many genera of bacteria. Researchers treated cocktails of four strains of Ǥ Œ‡Œ—‹ in Mueller Hinton broth at different temperatures with varying concentrations of garlic extract. Counts of the number of viable cells were made at intervals and recorded in Table 2. Table 2

Number of viable bacterial cells/ml

Concentration of garlic extract ƫO PO

Temp (°C)

0 hours

24 hours

36 hours

2

0 25 50 75 100 0 25 50 75 100 0 25 50 75 100

10 4 3.01 u 10 5 1.00 u 10 4 1.50 u 10 5 4.37 u 10 5 5.13 u 10 4 8.71 u 10 5 4.78 u 10 4 3.90 u

10 4 3.69 u 10 3 3.46 u 10 2 1.20 u 10 2 8.51 u 10 2 3.63 u 10 3 8.91 u 10 7 1.41 u 10 2

10 3 10 2 10 2 10 10 10 2 10 7

9.95 u 1.12 u 9.33 u 1.04 u 1.25 u 8.32 u 1.31 u 9.55 u 8.31 u 1.23 u 7.94 u 7.76 u 9.77 u 1.02 u 1.31 u

22 42

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0

10 4 10 4 10 5 10 4 10 4 10 5 10 5

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