FACTORS AFFECTING BACTERIA GROWTH - TEMPERATURE Isabel O’Brien (Year 10) Science Faculty, The Illawarra Grammar School, Western Avenue, Mangerton, 2500 Abstract Food consumed by humans is stored and refrigerated or more commonly cooked before being consumed. In this experiment, bacteria sample Staphylococcus epidermidis was placed on 4 petri dishes. A control was incubated at 30 degrees, and the other three stored in the refrigerator at 5oC. Staphylococcus epidermidis was also boiled at 95 degrees Celsius for 10 minutes and then placed on a further three petri dishes, and then grown in an incubator at 30 degrees to test the hypothesis that bacteria do not grow outside the temperature range of 5 – 60 degrees Celsius, hence the reason food consumed by humans is stored outside of this temperature range. The study found that the boiled and refrigerated bacteria did not grow at all after 24 hours, yet the control petri dish was covered in bacteria.
Introduction The aim of this study was to investigate the way in which temperature affects the growth of bacteria. When bacteria is grown below or above its growth range, it will not grow. But if it is grown within the growth range it will thrive. Bacterial growth is defined as the increase in the bacterial population rather than the growth in size of individual cells. Bacteria multiply using mitosis, with the division of cells. Mitosis occurs in the parent cell, where DNA is copied and the cell splits into two daughter cells. Many factors influence the rate and growth of bacteria which include temperature, nutrients, pH, water, salt, and gaseous concentration. Temperature affects the growth of bacteria in various ways. There is a minimum and maximum temperature at which bacteria can grow, and an optimal temperature within this range where the bacteria can thrive. This range changes between different types of bacteria. Bacteria that grow in food have a growth range between around 6 to 60
degrees Celsius. The bacteria will not grow below the minimum as the membrane solidifies and nutrients cannot be transferred or above the maximum temperatures where proteins and enzymes denature. If temperature increases consistently from the minimum, bacterial growth increases until a maximum growth rate is reached, known as the optimal temperature. If the temperature continues increasing, the growth rate of bacteria declines until the maximum temperature is reached bacterial growth ceases. Availability of nutrients affects the growth of bacteria. Furthermore, pH affects bactericidal growth as well as Water availability and Gaseous concentration which are important factors in bacterial growth. The temperature at which bacteria grow is of particular importance as bacteria can grow in food that we eat and therefore can cause us diseases and food poisoning. When food is stored in the refrigerator or heated up before eating, this is to prevent or kill bacterial growth. When we leave food out on the bench, or when food is lukewarm for long periods of 38
