Chapter 6 Microbiology Flashcards
How is microbial growth usually assessed? What are 2 outcomes of bacterial growth?
Microbes are classified based on –
1. their source of nutrient carbon
Autotrophs (CO2), Heterotrophs (organic compounds)
2. their source of energy
Phototrophs (light), Chemotrophs (electron transfer reactions from
chemicals)
What are heterotrophs, autotrophs, chemotrophs and phototrophs? How are most animals and bacteria classified?
Heterotrophs feed off of (organic compounds) (humans, animals & bacteria)
Autotrophs feed off of (CO2),
Phototrophs; feed off of (light),
Chemotrophs feed off of (electron transfer reactions from chemicals)
Why is oxygen deadly for an obligate anaerobe?
Obligate anaerobes do not have protective mechanisms against Reactive Oxygen Species (ROS)
• Reactive oxygen species (ROS): different toxic forms of oxygen that are highly reactive and can cause irreparable damage to cells
Obligate anaerobes do not have protective mechanisms against Reactive Oxygen Species (ROS)
• Reactive oxygen species (ROS): different toxic forms of oxygen that are highly reactive and can cause irreparable damage to cells
All aerobes have protective mechanisms against ROS
• Detoxifying enzymes (catalase, superoxide dismutase, peroxidase)
• Antioxidants (such as vitamin E, vitamin C; mannitol)
What is one enzyme that detoxifies hydrogen peroxide, a reactive oxygen species?
Catalase
What are aerotolerant anaerobes? Give one example of such an organism.
Aerotolerant anaerobes – do not use aerobic respiration, but they can tolerate O2 by having some of the detoxifying enzymes (Lactobacillus)
Which major nutrient do all cells recycle?
Nitrogen
In addition to C, H, O, and N, what other nutrients are required for growth of most microbes?
– Phosphorus, Sulfur (important in many biomolecules)
– Trace elements (iron and other inorganic ions)
– Growth factors (required vitamins, amino acids, and other organic compounds; see Table 6.1)
Which term describes an organism that grows best either at neutral pH, at acidic pH, or at alkaline pH?
– Neutrophiles (best around neutral pH)
– Acidophiles (best in acidic habitats)
– Alkalinophiles (high pH soils and water)
Which term describes an organism that grows best at low temperatures? ..at moderate temperatures? ..or at elevated temperatures? Which term describes the growth of an organism at body temperature?
Psychrophiles – grow best below 15oC (low temp)
Mesophiles – grow best at 20-42o C (growth @ body temp)(body temp is 37C)
Thermophiles – grow best at 45-75o C (moderate temp)
Hyperthermophiles – grow best above 75oC (elevated temp)
. What type of molecules are secreted by bacteria to assess their cell densities when forming a biofilm?
Quorum-sensing molecules
What is an inoculum? What are 2 common types of culture media?
• Inoculum – any sample introduced into a growth medium
- Liquid media (broths) or solid media (e.g. agar)
- Form colonies (visible cultures on the surface of a medium)
What are several clinical specimen that can be used as sources of an inoculum?
Skin, open wounds, blood, CSF, stomach, urine, lungs, diseased tissue
. What is an axenic culture? What is a colony forming unit?
Axenic culture refers to a pure culture
– Requires aseptic technique (sterile handling procedures)
A colony forming unit = the number of cells that produce one colony
. What are 2 common techniques to isolate pure cultures of bacteria? Describe how each is performed.
– Two common isolation techniques
– Streak-plates - The back loop of an inoculum is spread across the surface of a petri dish in a streak pattern. The loop is sterilized by flame between streaks. The set of (4) streak patterns gradually dilute the sample to a point that CFUs are isolated from one another
– Pour-plates – CFUs are separated from one another using a series of dilutions. An initial 1mL sample is mixed into 9.0 mL of medium in a test tube. After mixing, a new sample from this medium is then used to inoculate 2nd tube of liquid medium. The process is repeated to establish a series of dilutions.
What are the 4 general types of culture media, and their characteristics, that we discussed?
. Defined media – known chemical composition and pH
Simple ones – inorganic salts, C source
More diverse media – large number of vitamins, and growth factors (for fastidious
organisms)
2. Complex media – undefined, broader array of nutrients from digests of beef, yeast, soy, or milk proteins (nutrient broth, TSA agar)
3. Selective media – contain substances that either favor or inhibit the growth of specific microbes (methylene blue or crystal violet to inhibit Gram positive bacteria; pH control)
4. Differential media - either the presence of visible changes in the medium or an induced growth difference in the appearance of the colonies can differentiate bacteria
Which type of culture medium is often best to use with an unknown clinical specimen?
Complex Media
. What is the most common means of reproduction in prokaryotes? Is this sexual or asexual reproduction?
Binary fission; asexual reproduction
. What is meant by exponential growth? What is a typical generation time for a bacterial cell grown in a lab culture?
Exponential growth/ logarithmic growth: 2 cells form 4; 4 cells form 8, and so on… produces very different results from simple addition, known as arithmetic growth.
Growth time 20 minutes
What are the 4 phases of a microbial growth curve? In which phase is growth most rapid?
- Lag phase
- Log (exponential) phase most active/rapid
- Stationary phase
- Death (decline phase)
What are 5 different direct methods of counting microbes? Which ones do not require incubation for new growth?
- Serial dilution and viable plate counts
- Membrane filtration
- Most probable number
- Microscopic counts (no incubation)
- Electronic counters (no incubation)
What is the most common indirect method for assessing microbial growth?
Turbidity and the use of spectrophotometry
. Under what condition are serial dilutions and viable plate counts used to count microbes?
When the number of cells in a VERY small sample is TOO GREAT to count.
Under what conditions is membrane filtration used to count microbes?
To estimate the number of microbial population
What is the name of a statistical method used to count microbes?
Most Probable Number (MPN) method
What is a simple device that consists of a microscope slide with an etched grid of defined area and volume, which is often used to directly count microbes and blood cells?
Cell counter
