Microbial Growth Flashcards
1
Q
Bacterial Division
A
- bacterial growth refers to an increase in bacterial numbers, not an increase in the size of individual cells
- bacteria reproduces by binary fission
2
Q
Generation Time
A
- the time required for a cell to divide
- varies between organisms and environmental mental conditions i.e temperature
3
Q
Microbial Growth
A
- refers to the number of cells, not the size of the cells
- microbes that are growing in number accumulate into colonies
- group of cells large enough to be seen without a microscope
- hundreds of thousands of cells or populations of billion of cells
- many bacteria survive and grow slowly in nutrient poor environments by forming biofilms
- biofilms are frequently sources of health care associated infections
4
Q
Temperature
A
- most microorganisms grow well at the termpertatures that humans favor, but some bacteria are capable of growing at extreme temperature that would prob kill all eukaryotic organisms
- Are classified into three primary groups on their range of preffered temperature
- Psychrophiles: cold loving microbes
- Mesophiles: moderate temperature loving microbes
- thermophiles: heat loving microbes
- most bacteria grow only within a limit range of temperatures and their maximum and minimum growth temperatures are about 30 degrees Celsius apart
5
Q
Bacterial Growth
A
- Each bacteria grow at a particular minimum, optimum, and maximum temperatures
- The minimum growth temperature: the lowest temperature at which the species will grow
- The optimum growth temperature is the temperature at which the species grow the best
- Maximum growth temperature is the highest temperature at which growth is possible
6
Q
Growth for Psychrophiles, Mesophiles, and Thermophiles
A
- most of these organisms are so sensitive to higher temperatures that they will not grow in a warm room 25C
- Psychrotrophs and Psychrophiles could both grow at 0C but psychrophiles has a lower optimum growth temperature.
- Psychrotrophs are more common than psychrophiles and are most likely to be encountered in low temperature food spoilage because they grow fairly well at refridgerator temperatures
7
Q
Refrigerators and Microorganisms
A
- microbial reproductive rates decrease at low temperatures
- altough microbes usually survive in subfreezing temperatures or even become completely dormant they slowly decline in number
- Psychotrops do not grow well at low temeratures but with time they can slowly degrade food
- the temperature inside a properly set fridge will greatly slow the growth of most spoilage organisms and will prevent the growth of all but few pathogenic bacteria
- remember that a large quantity of warm food cools at a slow rate
- in that chart the large quantity of food takes more time to cool off so it gives time for bacillus cereus to multiply in the rice 43C to 15C
8
Q
Mesophiles
A
- have an optimum growth temperature of 25-40C are the most common type of microbe
- organisms that have adapted to live in the bodies of animals usually have an optimum temperature close to that of their host
- include most of the common spoilage and disease organisms
- the optimum temperature for many pathogenic bacteria is about 37C that’s why incubators are set at this temperature
9
Q
Thermophiles
A
- are microorganisms capable of growth at high temperatures
- have an optimum growth temperature of 50-60C about the temperature of water from a hot water tap, sunlit soil, and thermal waters in hot springs
- cant grow at temperatures below at 45C
- Endospores by thermophilic bacteria are heat resistant and survive usual heat treatment in canned goods…when the endospores germinate and grows it spoils the food, but thermophiles are not considered a public health problem
- hyperthermophiles or sometimes extreme theromphiles have an optimum growth of 80C or higher
- live in hot springs or volcanic activity and sulfur is important in their metabolic activity
10
Q
ph
A
-most bacteria grow best ina narrow ph range near neutrality
between pH 6.5 and 7.5
-very few bacteria grow at an acidic PH below about ph 4
-that’s why foods like sauerkraut, pickles, and many cheese are preserved from spoilage by acids produced by bacterial fermentation
-Acidophiles though are tolerant of acidity
-when bacteria are cultured in the laboratory they often produce acids that eventually interfere with their own growth
-to neutralize the acids and maintain the proper pH, chemical buffers are included in the growth medium
11
Q
osmotic pressure
A
- MOs obtain almost all their nutrients in solution from the surrounding water so they need water for growth and 80-90% of their composition is water
- high osmotic pressures have the effect of removing necessary water from a cell
- when the cell is in a solution when the out the outside solutes is higher than in the cell…the cellular water passes out through the plasma membrane to the higher concentration
- osmotic loss of water causes Plasmolysis or shrinkage of the cells cytoplasm. Most organisms live in hypertonic enviormenents and if youre in a hypertonic enviorment you are at risk for Plasmolysis.
- the growth of the cell is inhibited as the plasma membrane pulls away from the cell wall
- so salts to a solution causes increase in osmotic pressure could be used to preserve foods ex. Salted fish, honey, sweetened milk
- the high salt or sugar concentration draw water out of any microbial cells that are present and this prevents their growth
12
Q
halophiles
A
- extreme halophiles that have adapted so well to high salt concentrations that they require them to grow and are called Obligate halophiles
- Facultative halophiles are more common which do not require high salt concentrations but are able to grow at salt concentrations to 2%, a concentration that inhibits the growth of many other organisms.
13
Q
Carbon
A
- besides water the most important requirements for microbial growth is carbon
- carbon is the structural backbone of living matter and it is needed for all the organic compounds that make up a living cell
14
Q
Nitrogen, Sulfur, and Phosphorus
A
- in addition to carbon, MOs need other elements to synthesize cellular material
- protein synthesis requires good amounts of nitrogen as well as some sulfur
- The synthesis of DNA, RNA, and ATP(important for storage and transfer of chemical energy within the cell) require nitrogen and some phosphorus
- Nitrogen makes up about 14% of the dry weight of a bacterial cell. Sulfure and Phosphorus 4% combined
15
Q
Nitrogen
A
- use nitrogen primarily to form the amino group of the amino acids of protein
- some bacteria including cyanobacteria uses nitrogen directly from the atmosphere (Nitrogen Fixation)
