Basic Bacteriology - Dr. Kozel Flashcards
(93 cards)
1
Q
Name 3 characteristics of Viruses.
A
- They are the smallest infectious particles.
- They are about 18-600 nanometers.
- They are true parasites - they require host cells for replication.
2
Q
Name 4 characteristics of Bacteria.
A
- They are prokaryotes (no nucleus or membrane bound organelles).
- They are 1-20 micrometers.
- They are unicellular with no nuclear membrane, mitochondria, Golgi or ER.
- They reproduce via asexual division.
3
Q
Describe Fungi.
A
- Eukaryotic.
- Well defined nucleus, mitochondria, Golgi bodies and an ER.
- There membranes contain a unique sterol - ergosterol.
- Replicate according to if they are unicellular or filamentous.
4
Q
How do unicellular fungi replicate?
A
They replicate asexually - an example is yeast.
5
Q
How do filamentous fungi replicate?
A
They can replicate either sexually or asexually. An example is mold.
6
Q
What is ergosterol?
A
A unique sterol that is located in the membranes of fungi. Humans have cholesterol. Ergosterol is a target of anti-fungal drugs.
7
Q
Describe parasites?
A
- Eukaryotic.
- 1-2 micrometers (protozoa) to 10 meters (tapeworms).
- most complex of the microbes.
- some are unicellular and others are multicellular.
8
Q
Name some ways that bacteria are classified.
A
- Shape
- Arrangements they make
- Cell wall structure
- Presence or absence of specific antigens
- Metabolism
- Ability to lyse erythrocytes
- Fermentation of sugars
9
Q
Name some shapes of bacteria.
A
- Cocci - spherical
- Bacillus - rod-shaped
- Spirillum - Spiral
10
Q
Name some arrangements that bacteria make.
A
They may arrange in chains (single division plane) or in clumps (multiple division plane).
11
Q
Name some properties of the cell wall that help to classify bacteria.
A
- Gram positive
- Gram negative
- Acid fast
12
Q
What is the least effective way of classifying bacteria?
A
Via arrangements.
13
Q
Name the types of bacterial metabolism.
A
- Aerobic - uses oxygen.
- Facultative anaerobe - requires oxygen for metabolism.
- Anaerobic - does not require or use oxygen.
14
Q
What are bacteria called if they can lyse erythrocytes? When they can’t?
A
- Hemolytic
2. Non-hemolytic
15
Q
The concept of whether a bacteria is a fermenter or not is especially important for what type of bacteria?
A
Gram negative rods.
16
Q
Give an example of a fermenter and a non-fermenter.
A
E coli are fermenters and Shigella are non-fermenters.
17
Q
What are some ways to classify pathogenic microbes?
A
- Taxonomic - what type of microbe it is
- Growth habit
- System effected - ie CNS, GI
- Means of acquisition - i.e. food borne, zoonotic
18
Q
What are some growth habits by which we classify pathogenic microbes?
A
- Extracellular - cannot survive in phagocyte, often controlled by antibody
- Intracellular - grows inside phagocytes, often controlled by T cell based immunity
19
Q
Name two general types of intracellular bacteria.
A
- Toxin producer - produce symptoms at distant sites.
2. Pyogenic cocci - pus-forming microbe.
20
Q
Give specific examples of toxin producers.
A
Microbes that cause Tetanus, Botulism, and Diptheria.
21
Q
Give an example of an intracellular bacteria.
A
Mycobacterium tuberculosis.
22
Q
Give an example of an extracellular bacteria.
A
Streptococcus pneumoniae.
23
Q
What provides the basis for constructing anti-bacterial medicines?
A
Differences between mammalian cells and bacterial cells.
24
Q
Name some differences between mammalian cells and bacterial that are common targets of anti-microbials.
A
- bacteria have a cell wall
- cytoplasmic differences
- nucleic acid synthesis differences
- proteins synthesis differences and different proteins
- different metabolic pathways
25
What contributes to the pathogenesis of bacteria?
1. inflammation - triggered when immune system recognizes foreign peptides, helps clear bacteria but also causes collateral damage.
2. Resistance to host factors.
3. Adherence to cells and tissues - for example pilli on bacteria allow bacteria to adhere to cells and tissues.
26
Give an example of a anti-microbial drug target.
Sulfa drugs target the metabolic pathways of bacteria but not humans.
27
Describe the bacterial chromosome.
Bacteria have a single chromosome that forms a double stranded circle.
28
Do bacteria have a nucleus or nuclear membrane?
No.
29
What is a plasmid?
A plasmid is extra-chromosomal DNA that is present in bacteria. This DNA forms a small circle.
30
What do plasmids encode for?
They may encode for extra, non-essential functions like toxins or antibiotic resistance.
31
How are bacterial ribosomes different from human?
Humans have an 80s ribosome while bacteria have a 70s ribosome (from 30s and 50s subunits) and the proteins themselves are very different than eukaryotic proteins.
32
How are cytoplasmic membranes of bacteria different from human membranes?
Human membranes have cholesterol as one of the constituents while bacterial membranes do not contain any sterols. There is one exception - mycoplasma.
33
Describe the structure of a basic bacterial cell wall.
1. A backbone is formed by repeating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). These are saccharides - also called the glycan unit.
2. Attached to the NAM is a tetrapeptide - also called the stem peptides.
3. Attached to the tetrapeptide stem is a peptide made of glycine - this form cross links between rows and 'sheets' of the disaccharide/stem peptide units. This structure forms a matrix like a net around the inner cell membrane of the bacteria.
4. The cell wall is referred to as peptidoglycan.
34
Name the 4 basic steps of cell wall formation.
1. The first step occurs in the cytoplasm with the synthesis of a water soluble precursor.
2. The precursors are attached to a cell membrane lipid.
3. Trans glycosylation Formation of linear polymers outside the membrane.
4. Transpeptidization - cross linking of polymers into a three dimensional matrix.
35
Describe the steps of cell wall formation.
1. The prescursor starts with UDP-NAM.
2. The tetra-peptide chain and its link is added next, starting with L-Alanine, then D-Glutamate, then L-Lysine followed by a dipeptide of D-Alanine forming a pentapeptide.
3. This precursor is attached to a membrane lipid and the entire structure is flipped to the outside of the cell membrane.
4. A UDP-NAG is added to the NAM.
5. A pentapeptide formed of glycine is added to the stem pentapeptide.
6. The disaccharide with its attached side chain and cross bridge chain is added to an existing backbone of disaccharide units.
7. The cross bridges are formed that link the rows and sheets of peptidoglycan together creating a three dimensional structure. This is called transpeptidization and the terminal Alanine of the stem peptide is released upon linkage.
36
What does vancomycin inhibit?
It inhibits the last two steps of bacterial cell wall formation - adding of disaccharide unit to existing backbone and transpeptidization.
37
What do B-lactam antibiotics inhibit?
They inhibit the transpeptidization step of bacterial cell wall formation.
38
Name two B-lactam antibiotics.
Penicillin and cephalosporin.
39
Describe a gram positive cell wall.
1. thick, multilayered
2. primary constituent is peptidoglycan
3. surrounds cytoplasmic membrane
4. degraded by lysozyme since the cell wall is on the outside
5. contains teichoic acid and lipoteichoic acid
40
Describe Teichoic acid.
1. polymer of polyol phosphates
2. covalently linked to peptidoglycan
3. several functions in virulence
41
Describe Lipoteichoic acid.
1. consists of Teichoic acid with fatty acid
2. anchored in cytoplasmic membrane
3. stimulates innate host responses in manner similar to endotoxin of gram negative bacteria
42
Describe a gram negative cell wall.
1. 2 layers of membrane with peptidoglycan cell wall in-between. The cytoplasmic membrane surrounds cytoplasm, peptidoglycan wall in the middle and an outer membrane.
2. peptidoglycan cell wall is thin and is a small part of cell wall by weight, has no teichoic or lipoteichoic acids.
3. Has an outer membrane - unique to gram negative bacteria.
43
Describe the outer membrane of the gram negative bacteria.
The outer membrane provides a barrier to large molecules like lysozyme and hydrophobic molecules including some antibiotics. The membrane is an asymmetrical bilayer, with an inner layer of phospholipids and an outer layer composed primarily of lipopolysaccharide. The membrane has porins that allows the passage of small hydrophilic molecules.
44
Do gram negative cell walls contain teichoic and lipteichoic acids?
No
45
Do lysosymes break down gram negative cell walls?
No, the cell wall is in between the two cell membranes and is not available to lysozymes.
46
Describe the process of gram staining.
1. The cells are fixed to a slide via alcohol.
2. The cells are stained with crystal violet dye - both cells will be blue at this point.
3. The slides are washed with Gram's iodine. This precipitates crystal violet and the complex is trapped in thick cell wall of gram positive cells. The cells will both be blue at this point.
4. The slides are washed with alcohol or acetone. This removes crystal violet/iodine complex from thin gram negative cell walls. The gram positive cell will be blue and the gram negative cells will be colorless at this point.
5. The slides are washed with Safranin. This counterstains the decolorized gram negative cells. The gram positive cells will be blue and the gram negatives will be red at this point.
47
What can influence the success of gram staining?
The gram staining process relies on the integrity of the cell wall. A breach in the cell wall can affect the process. In the case of a breach, gram positive cells can stain as if they were gram negative but gram negatives will never stain as if they are gram positive.
48
What can cause a breach of cell wall integrity?
1. Cell age - old cells continue to have functional autolytic enzymes even after cell growth ceases.
2. Too much heat fixation in step one of the process.
3. If antibiotics are started they can attack cell wall synthesis and gram staining will not be successful.
49
Can gram negative cells stain as if they are gram positive?
No, but if there is a loss of cell wall integrity then gram positive cells may stain as gram negative.
50
What is Lipopolysaccharide (LPS)?
This is a structure that is present on the outer layer of the outer membrane of gram negative bacteria.
51
What is another name for LPS?
Endotoxin.
52
What are the characteristics of LPS?
LPS is highly toxic when shed into the body during infection and it has many biological activities. It has 3 components.
1. Lipid A - bound by polymyxin B, responsible for endotoxin activity.
2. Core polysaccharide - 9-12 sugars including an unusual sugar called 2-keto-3-deoxy-octanoate or KDO.
3. With few exceptions, LPS contains O antigen which is formed of 50-100 repeating units of 4-7 sugars. This component is highly antigenic and is used to classify bacteria.
53
What bacteria is an example of a bacteria whose LPS lacks O antigen?
Neisseria.
54
Give an example of antigenic activity of an O-antigen.
The O antigen of O157:H7 E. coli cause hemolytic-uremic syndrome.
55
Do gram positive bacteria have an outer membrane?
No
56
Is the cell wall of gram negative bacteria thick?
No, it is thin.
57
Do gram positive bacteria have LPS?
No
58
Which type- gram positive or gram negative - cells produce spores?
Gram negative cells do not form spores and some genera of gram positive cells do produce spores.
59
Do gram negative and gram positive cells have capsules?
Sometimes
60
Which type - gram positive or gram negative cells produce exotoxins?
Gram positive cells commonly produce exotoxins while gram negative cells sometimes produce it.
61
Which type - gram positive or gram negative cells are more sensitive to penicillin?
Gram positive cells are more sensitive while gram negative cells are more resistant.
62
What are some external structures of Bacteria?
1. capsules
2. Flagella
3. Fimbriae
63
Describe some characteristics of bacterial capsules.
They are usually formed of polysaccharides except in Bacillus anthraces (made from poly-glutamic acid). They are antiphogocytic, contain T-cell independent antigens and are a common target of vaccines.
64
Describe Flagella.
Flagella are rope-like propellers composed of coiled protein subunits that provide motility to bacteria.
65
Describe Fimbriae.
Fimbriae are hair-like structures composed of protein subunits of the protein pilin. They function as adherence factors except for F pili. F pili or sex pili are tubes for transfer of bacterial chromosomes between different bacteria.
66
What types of bacteria have capsules?
Extracellular bacteria have capsules to evade phagocytosis.
67
Name 2 types of bacteria that are unique in structure.
Mycobacteria and mycoplasma.
68
Describe Mycoplasma.
Mycoplasma are small parasitic bacteria that are unique because they do not have cells walls and they incorporate host sterols into their membranes. They are unaffected by antibiotics that target cell wall formation.
69
Describe Mycobacteria.
Mycobacteria such as Mycobacterium tuberculosis are unique because their peptidoglycan is intertwined with a polmer of arabinogalactan. The cell wall also contains a wax like lipid coat (made from mycolic acid) as wells as cord factor and Wax D. The cell walls of mycobacterium are resistant to disinfectants and many stains. Their resistance to staining is called Acid fast because the cell wall can be stained with high concentrations but the dye will be resistant to removal with acid.
70
What types of bacteria are resistant to penicillin?
Gram negative bacteria and mycoplasma.
71
What unique type of bacteria can have cholesterol in their cell membranes?
Mycoplasma
72
Which type of bacteria form spores?
Some gram-positive genera.
73
What is the purpose of sporulation in bacteria?
It allows bacterium to survive harsh environments.
74
What are the contents of spores?
1. complete copy of chromosome.
2. minimal proteins and ribosomes.
3. High concentration of dilpicolinic acid bound to Calcium.
75
What constituent is unique to spores?
Dilpicolinic acid.
76
What triggers sporulation?
Depletion of nutrients.
77
How are spores germinated?
Germination is triggered by some form of host stressor and water and nutrient availability.
78
Name two types of bacteria that form spores.
Clostridium (causes tetanus) and Bacillus (causes anthrax).
79
Are spores made by gram-negative bacteria?
No
80
What are some nutritional requirements for bacterial growth?
1. carbon
2. nitrogen
3. growth factors such as B vitamins
4. inorganic ions
5. oxygen
81
What are some physical requirements for bacteria?
1. oxidation-reduction potential
2. optimal temperature
3. hydrogen ion concentration
4. optimal osmotic conditions
82
Describe the special temperature requirements of bacteria.
1. Psychrophilic bacteria require temps of -5 to 30 degrees celsius
2. Mesophilic bacteria require temps of 10-45 degrees celsius
3. Thermophilic bacteria require temps of 25-80 degrees celsius
83
Describe energy production methods in bacteria.
1. Aerobic respiration - very efficient and uses oxygen as terminal electron acceptor
2. Fermentation - least efficient method of energy production and uses an organic molecule as its terminal electron acceptor
3. Anaerobic respiration - uses an inorganic compound as the terminal electron acceptor - for example nitrate, sulfate or carbonate
84
Which type of energy production is most efficient?
Aerobic respiration is more efficient than anaerobic respiration and fermentation.
Fermentation is the least efficient.
85
Describe some characteristics of an obligate aerobe.
This type of energy production requires oxygen and may result in the production of reactive oxygen species. Because of this these bacteria may produce dismutase and catalase to detoxify the ROS's or they may excrete the ROS's.
86
Describe some characteristics of facultative anaerobic bacteria.
These type of bacteria can grow in the presence or absence of oxygen. Will use oxygen as terminal electron acceptor if available but can use others under anaerobic conditions.
87
Describe some characteristics of obligate anaerobic bacteria.
Oxygen is toxic to these type of bacteria and they must use an inorganic compound as their terminal electron acceptors.
88
What are some measurements of bacterial growth?
1. Determination of bacterial mass - using dry weight or optical density (bacteria express turbidity in solution).
2. Determination of cell number - can count directly using microscopy or can prepare cultures with colonies and then count the colonies using - # of colonies on plate X reciprocal of dilution of sample = # of bacteria per mL.
89
Describe the bacterial growth curve.
The growth of bacteria have four phases that can be visualized when plotting.
1. Lag phase - little or no cell division but do have increase in cell size - initial flat area on graph.
2. Exponential growth phase - a balanced growth where both cell number and cell mass increase. Growth rate expressed by natural exponential function. Growth rate depends on species and environment. Vertical, increasing area following lag phase on graph.
3. Stationary phase - marked by accumulation of waste, exhaustion of nutrients and other factors that decrease growth rate. Flat area following exponential growth on graph.
4. Death or decline - cells have depleted nutrients and cells are dying. Looks like downward sloping region following stationary phase on graph.
90
At what stage of growth are bacteria most sensitive?
During the exponential growth phase - for instance this is the time of maximal sensitivity to penicillin.
91
What is the function of transpeptidases in cell wall synthesis?
These enzymes are responsible for generating cross linking between the peptides of peptidoglycan to produce a complex matrix.
92
Where are porins located?
On the outer membrane of gram negative bacteria.
93
What is the terminal electron acceptor in the pathway that would maximize total ATP production?
Oxygen. The most efficient pathway is the aerobic process of ATP production.
