7. "Cereus" Hot Chocolate or "Is your hot chocolate 'cereus-ly' clean? (adapted from: Hall, et al. 2011, Development of

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7 Cereus Hot Chocolate Or Is Your Hot Chocolate Cereus Ly Clean Adapted From Hall Et Al 2011 Development Of 1 (191.89 KiB) Viewed 87 times

7. "Cereus" Hot Chocolate or "Is your hot chocolate 'cereus-ly' clean? (adapted from: Hall, et al. 2011, Development of a Microbial Population within a Hot-Drinks Vending Machine and the Microbial Load of Vended Hot Chocolate Drinks) Vending machines dispensing food products must be thoroughly cleaned on a regular basis. If one isn't, and you use it, you might get sick. In 1997, employees at a manufacturing plant in Minnesota experienced nausea and vomiting after drinking hot chocolate from a vending machine at the plant. Hot chocolate dispensed from the machine contained high levels of Bacillus cereus. B. cereus spores can be found in low concentrations in many food products. The investigation concluded that the warm, wet environment in certain areas of the machine facilitated bacterial growth over an extended period of time. In order to study the growth of B. cereus in this type of machine, researchers purchased a new hot chocolate vending machine. They set the machine to vend for free and at least 50 drinks were dispensed per day. The machine was cleaned twice a day for 14 weeks using the machine's automatic flush feature. For the remaining 5 weeks of the study this feature was turned off, but yet drinks were still dispensed! Samples (10 ml) of hot chocolate were taken each week, diluted by serial dilution, and plated on plate count agar (PCA) plates. These were incubated at 30°C for 48 hours and subsequently counted. a. The data from the study are shown in Table 1. Calculate the standard plate count for each week of these serial dilutions (given that 100 ul was plated for each dilution) and record the data in the table below. Remember to sow your working out. Dilution 100 10-1 102 Table 1: Microbial load of vended hot chocolate Week 4 Week 8 Week 12 Week 16 >300 >>>300 TMTC TMTC 44 74 128 191 4 6 13 20 O 1 2 3 0 O 0 0 Week 19 TMTC 224 22 3 0 10-3 10-4 Week 4 Week 8 Week 12 Week 16 Week 19 Standard Plate Count (cfu/ml) b. What does the data say about the number of microbes in the hot chocolate after 19 weeks? By what factor did the number change?