Lecture 6 Flashcards
Define colonization.
When there is a sufficiently high concentration of organisms at a site that they can be detected.
Define contamination.
Organism not present initially, but was introduced (modes of transmission-pervious lectures, arthropods, sexual, etc.)
Define carrier.
Person colonized with an organism and is able to transmit the organism to other people.
Define infectious disease.
Disorders caused by organisms such as bacteria, viruses, fungi or parasites.
How long can colonization persist?
For days to years
What is colonization influenced by?
Factors such as immune response to the organism, competition at the site from other organisms, use of antimicrobials, etc.
What is the typical size of bacteria? What size does 10^12 of bacteria occupy and weigh?
- typical size is 1 to 2 um
- 10^12 bacteria occupies 1 cubic meter
- weighs 1 gram
How many bacteria on on a human?
10 to 100 trillion bacteria
How quickly does metabolic efficiency replicate?
*every 20 minutes (average)
Note: mycobacteria is slower
The amazing speed of nutrient conversion and biosynthesis is necessary for what?
- to anticipate bacterial weaknesses
* suggest how to intervene therapeutically against pathogenic bacteria
What is growth in bacterial culture also known as?
population dynamics
Describe population dynamics in a chart.
- lag: at 2 and slowly rises
- exponential rises quickly
- stationary starts to die off
Total count is the highest point of the chart and viable count is the amount in the stationary section.
How long is exponential growth?
5 to 10 hours of growth
What are some examples of mechanisms of action of drugs that treat bacteria?
- inhibition of protein synthesis
- inhibition of metabolic pathways
- decrease cell wall integrity
- inactivation of cell wall synthesis
Bacteria grow in a large variety of habitats. What are the most abundantly populated by microbes?
- humans
* anatomic sites: colon, large bowel, urethra, vagina, and nasopharynx are highly colonized
Other than humans, where can bacteria grow?
Basically anywhere including deep sea vents, in ponds, oceans, air conditioners, in food, etc.
What are the 3 requirements for bacterial growth?
- energy
- nutrients (environment must contain all nutrients needed)
- environment
What kind of energy is required for bacterial growth?
Chemical energy is required for the synthesis of new cellular components.
What type of environment is needed for bacterial growth?
- aeration
- pH
- temperature
What are auxotrophs?
Bacteria that derive energy from inorganic substrates plus minimal carbon source. They need water, inorganic salts, glucose, and carbon dioxide. (Pseudomonas)
What are heterotrophs?
Includes all bacteria of medical importance. Need organic carbon source (various), inorganic salts, and carbon dioxide. (Staphylococcus, Streptococcus)
What are some examples of nutrients needed for bacterial growth?
- Nitrogen: must be fixed from environment by certain bacteria and converted to a useable form such as NH3.
- Phosphorus: found in nature as free inorganic phosphorus
- Sulfur: can’t be used in its elemental form. Some auxotrophs oxidize it to SO4 -2 which can be used by most bacteria.
- Others: pathogenic bacteria can’t make or get one or more essential metabolites (amino acids, vitamins, iron, growth factors)
Where is free iron scarce? Why?
In the blood and tissues because it is bound by proteins like transferrin, lactoferrin, or ceruloplasmin.
Is free iron essential for bacterial growth?
Yes
What do pathogenic bacteria excrete?
Chelating compounds, siderophores, which bind iron with great avidity.
What kind of bacteria are more dependent on free iron? Why?
- pathogenic bacteria
* most have multiple siderophores, thus trying to gain an edge on the other organisms in the same environment
Bacteria have a wide range of responses to oxygen. What are they?
- Strict or obligate aerobes: must have oxygen to grown.
- Obligate anaerobes: can’t grow in the presence of oxygen.
- Facultative anaerobes: can grow whether or not oxygen is present.
The largest of pathogenic bacteria belong to what type of oxygen requirement group?
Facultative anaerobes
Describe the reaction of superoxide dismutase (SOD).
2 oxygen + 2 hydrogen –> H2O2 (peroxide) + oxygen
SOD breaks down into peroxides and oxygen which is further down into water and oxygen.
What does 2 H2O2 break down to?
2 H2O2 –> 2 water + oxygen
What is the relationship between aerobes and oxygen?
They require oxygen. (mycobacterium, pseudomonas)
SOD +
Catalase +
What is the relationship between anaerobes and oxygen?
Oxygen is toxic. (ABC organisms)
SOD -
Catalase +
What is the relationship between facultative anaerobes and oxygen?
Can survive with or without oxygen. (E. coli, Staphylococcus)
SOD +
Catalase +
Why can’t strict anaerobes (ABC organisms) live in an oxygen atmosphere? (examples: actinomyces, bactericides, and clostridium)
Because they lack SOD and catalase that protect from oxygen free radicals. They have a primitive mechanism that transfers electrons (reducing equivalents) to ‘oxidants’ like nitrates instead of to molecular oxygen.
Note: selected antibiotics are used to exploit this metabolic characteristic of anaerobes.
What is SOD?
Superoxide Dismutase
What does liquid media contain?
All essential nutrients and factors, usually in the form of complex extracts (yeast, beef heart).
What happens when liquid media is inoculated?
When it is inoculated with a small number of bacteria results in growth of a clonal population over time.
How is solid media made?
It is produced by adding agar to liquid media. An inoculum is placed on to the plate medium and then spread by streaking out.
The technique to make solid media is used for what?
- to isolate colonies of bacteria of medical importance
* determine the number of living or viable counts
What is a colony?
A clonal population of bacteria derived from a single bacterium.
When is a bacterium called viable?
When it is able to produce a colony on plates
What type of technique needs to be used to prevent contamination on plates?
aseptic technique
In response to the competition for iron, most pathogenic bacteria use which of the following?
a. Hemoglobins
b. Lactoferrins
c. Myoglobins
d. Siderophores
e. Transferrins
Siderophores
Bacteria have a wide range of responses to oxygen. Most pathogenic bacteria belong to which of the groups for efficient parasitism?
Facultative anaerobes
What do you need to make a plate streak of bacteria?
- source of bacteria
- liquid culture/bacteria on previous plate
- new plate
- inoculating loop
- lighters
- bunsen burner
- safety glasses
When removing bacteria from a plate, how much should you take? How should you handle the cover?
- take only one colony
- never completely remove the cover to prevent contamination and store with the cover on the bottom to prevent condensation from contaminating the sample
