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.
