Bacteria Flashcards
1
Q
What causes infectious disease?
A
Pathogens
2
Q
How can disease be controlled?
However…
A
Combinations of vaccination, antibiotics, personal hygiene and drastic control measures
However too many antibiotics can cause antibiotic resistance! And newly emerging diseases may cause more problems due to research and treatment availabilities!
3
Q
What about an agar plate encourages bacteria culture growth?
A
Low levels of carbon
4
Q
What are the three domains of life?
A
Eukaryotes, Bacteria (prokaryotes), Archaea
5
Q
List 4 characteristics of Archaea
A
- Presence of characteristic tRNAs and ribosomal RNAs
- Absence of peptidoglycan cell walls, as they’re replaced by a large proteinaceous coat
-Occurrence of either linked lipids built from phytanyl chains - In cases known, they occur in unusual habitats as they are found in places with no oxygen
6
Q
Typical microbial cell size: virus
A
0.01-0.2 um
7
Q
Typical microbial cell size: Bacteria
A
0.2 - 5 um
8
Q
Typical microbial cell size: Eukaryotes
A
5 - 10 um
9
Q
Typical microbial cell size: Yeast (Eukaryotic)
A
5 - 10 um
10
Q
Typical microbial cell size: Algae
A
10 - 100 um
(Micrometers)
11
Q
Typical microbial cell size: Protists
A
50 - 1000 um
12
Q
How many S (Svedberg) unit is a eukaryotic ribosome compared to a prokaryote?
A
Eukaryote: 80S
Prokaryote: 70S
13
Q
Why S-layer?
(Bacteria)
A
Layer of protein function - not fully understood - crystalline
14
Q
Why inclusions?
(Bacteria)
A
- Chemical storage systems
- these chemicals can be used during times of famine
15
Q
List the different cell wall shapes?
A
- Coccus
- Rod
- Spirillum
- Vibrio
- Spirochete
- hypha (budding and appendage bacteria)
- stalk (budding and appendage bacteria)
- filamentous
16
Q
Give 3 types of Bacterial cell clusters?
A
- Diplococci
- streptococci
- clump of cocci
17
Q
Gram-positive cell wall are made up of 90% of…?
A
Peptidoglycan
(Also known as murein) is composed of polysaccharide and peptide chains, that forms a mesh-like layer surrounding the bacterial cytoplasmic membrane!
18
Q
Feature of gram-positive cell wall?
(Bacteria)
A
- Almost 90% peptidoglycan (thick layer)
- Many have trichroic acids embedded within them
- Negatively charged so lead to cell surface being negatively charged
- Can also bind divalanet cations like magnesium and calcium
- some covalently bound to lipids (lipoteichoic acids)
19
Q
Features of gram-negative cell wall?
(Bacteria)
A
- more complex than gram-positive
- only 10% peptidoglycan (thin layer)
- mostly outer membrane
- lipid bilayer containing polysaccharide, therefore referred to as the LPS layer
- contains porins
- has periplasm
20
Q
What is periplasm?
(Bacteria)
A
- within gram-negative cell wall
- contains several important enzymes involved in processing nutrients / substrates and chemoreceptors
21
Q
What are porins?
(Bacteria)
A
- within gram-negative cell wall
- proteins that allow hydrophilic, small molecules to cross the outer membrane
22
Q
Features of Archaeal / Mycobacterial cell wall?
A
- not well defined as gram-positive, but can be
- S-layer consists of proteins or glycoproteins
- No Peptidoglycan
- has psudomurein and a cytoplasmic membrane
23
Q
Peptidoglycan structure?
A
- only found in bacteria
- rigid layer
- glycan strands linked by glycosidic bobds
- strand cross linked by peptides
- more than 100 different types known with differences in bridging peptides
- backbone always the same
24
Q
Fimbriae vs Pili?
A
Fimbriae (singular = fimbria)
- short, thin, hair-like, proteinaceous appendages (up to 1000/cell)
- recognition and attachment to surfaces
- short term
Pili (pilus; sometimes sex Pili)
- similar to fimbriae except longer, thicker and less numerous (1-10/cell), required for mating
- long term
25
Polar flagellum?
Flagellum at end of cell
26
Monotrichous?
One flagellum
27
Amphitrichous?
One flagellum at each end of cell
28
Lophotrichous?
Cluster of flagella at one or both ends
29
Peritichous?
Spread over entire surface of cell
30
What is cellular inclusions (Bacteria)
Granules of organic or inorganic material that are reserved for future use (storage)
- glycogen (polymer of glucose units)
- poly-B-hydroxybutyrate
- polyphosphate granules
- sulphur granules
31
Cellular inclusions
Specialist bacteria with magnetosomes
- contain iron in the form of magnetite
- use is to orient cells in magnetic fields
32
True or false
Cellular inclusions can also be used as gas vesicles?
True!
They’re used for buoyancy in some aquatic bacteria!
The gas vessels are arranged in bundles and are made of protein! They’re usually about 100nm in diameter and show in transverse and longditudional section.
33
What is an endospore?
Made by some gram-positive bacteria when stressed!
34
Advantages of endospores?
- can survive for hundreds/thousands of years (produced under unfavourable conditions)
- highly resistant to heat, radiation, drying and chemicals very low water content
- contain calcium dipicolinate (binds free water and helps dehydrate the cell and stabilise DNA)
- special proteins protect DNA
35
What is halophilic bacteria?
Salt loving bacteria!
36
What is a pathogen?
An organism causing disease to its host, with severity of disease symptoms being referred to as virulence
37
Two main categories of pathogens?
Facultative and Obligate
- reflecting how intimately their life cycle is tied to their host
38
What do bacteria cultures need for growth?
(Nutrients must provide all elements that take part in the synthesis of cell material)
Macroelements (macronutrients)
- required in large amounts
- present in all cells
Microelements (micronutrients, trace elements)
- required in small amounts
- not required by all organisms
39
Describe aseptic technique when working with bacteria?
Flaming the loop to sterilise
Tube cap is removed
Flaming tube too sterilise surface
Only sterilised portion of loop enters tube
Tube is reclaimed
Tube is recapped; loop is resterilised
40
Most bacteria divide by what process,
Binary fission
41
Define growth within microbiology
Increase in cell numbers
42
Typical growth curve for bacterial population phases?
Lag phase
Log (exponential) phase
Stationary phase
Death (decline) phase
43
Bacterial growth curve: lag phase
- starting phase
- time interval between inoculation and maximal division rate.
- cells adjust to the new environment
44
Bacterial growth curve: log (exponential) phase
- 2nd phase
- bacteria grow exponentially:
- constant doubling time
- growth rate is maximal
45
Bacterial growth curve: stationary phase
- 3rd phase
- bacteria can no longer reproduce but are still alive
(Eg no nutrients left or growth inhibited by bacterial products)
46
Bacterial growth curve: death phase
- last phase
- bacteria die.
- typically slower than growth phase
- they cannot grow indefinitely, a single bacterium with a 20min doubling time would yield a population 400times the weight of the earth in 48hours.
47
What are the 3 different ways to count bacteria by microscopy
Total count
Viable count
Culturable count
48
Monitoring vibrio cholerae
Usually found in rivers where low sanitation is, so water is usually monitored.
If culture positive the water isn’t safe!
While negative culture would be safe if not present, HOWEVER if could be present, (viable but not culturable) it’s still pathogenic so not safe!
49
List 3 anti microbial agents
Bacteriostatic
Bacteriocidal
Bacteriolytic
50
Bacteriostatic - antimicrobal agent on growth
Don’t kill bacteria just stop it growing, which allows the immune system to catch up
Eg tetracycline
51
Bacteriocidal - antimicrobal agent on growth
Bacteria culture die as antibiotic kills it
52
Bacteriolytic - antimicrobal agent on growth
Both cell count and viable cell count reduce
53
Metabolic classifications of bacteria
Carbon source
- heterotrophs: require organic molecules made by other organisms
- autotrophs: CO2 is principal carbon source
Energy source
- photographs: use light as energy source
- chemotrophs: oxidise organic or inorganic compounds
54
Temperature and bacteria growth: Psychrophiles
Grow best below -15°
Don’t grow above 20
Can grow below 0
(Lipids have polyunsaturated fatty acids - double bonds mean it’s more fluid than saturated hydrocarbons)
55
Temperature and bacteria growth: mesophiles
Grow best between 20 - 40
Many bacteria in our body are mesophiles
(Body temp is 37°)
56
Temperature and bacteria growth: thermophiles
Grow best between 45-80
Live in hot springs, compost heaps, etc
57
Temperature and bacteria growth: hyperthermophiles
Grow best above 80
Live in hot springs
58
Temperature and bacteria growth: geogemma barossii
Grows between 80-121
Survives at least 2 hours at 130°
(Current record holder)
59
What bacteria survive / grow best in acidic habitats?
Acidiophiles
(pH6 to 0)
60
What bacteria survive / grow best in alkaline habitats?
Alkaliphiles
(pH8 to 14)
Many of these are also haliphilic!
61
Osmolarity and bacterial growth:
Where do halophiles grow?
Grow in habitats with high salt concentration
Mild halophiles: grow with 1-6% NaCl
Moderate: 7-15% NaCl
Extreme: 15-30% NaCl
High salt concentrations found in salt lakes.
62
How does a hyperthermophile differ from a psychrophile?
Grows in More than 80° while 15° or less
63
What useful enzyme produced by thermophiles bacteria?
Taq polymerase, from thermos aquaticus, used for PCR
64
What three mechanisms bring together prokaryotic DNA from different cells
Transformation
Transduction
Conjugation
65
What is horizontal gene transfer
When individuals are members of different species and move genes from one organism to another
66
Transformation (prokaryotes)
- genome and possibly phenotype are altered by uptake of foreign DNA from its surroundings
- occurs when nonpathogenic cell takes up piece of DNA carrying allele for pathogenicity and replaces its own allele with the foreign one (exchange of homologous DNA segments)
- Cell is not recombinant: it’s chromosome contains DBA derived from two different cells.
67
Transduction (prokaryotes)
Phases (bacteriophage) may carry prices of bacterial chromosome from one cell (donor) to another (recipient).
If crossing over occurs after the transfer, genes from donor may be incorporated into recipients genome
68
Conjugation (prokaryotes)
DNA transferred between two prokaryotic cells that are temporarily joined.
It’s always one-way: one cell donates the DNA, and the other receives it.
69
Where does metabolic cooperation between different prokaryotic species occur?
In surface-coating colonies called biofilms.
70
Why does metabolic cooperation happen between prokaryotic cells
It allows them to use environmental resources they couldn’t use as individual cells
71
Some prokaryotes engage in parasitism, what is parasitism?
An ecological relationship in which a parasite eats the cell contents, tissues, or body fluids if it’s host
72
Two types of bacterial toxins are?
Endotoxin (LPS): bound to cell
- action is indirect: activates many host systems that cause damage
Exotoxin
- act on specific targets eg protein synthesis
73
Fimbriae structure (prokaryotes)
Hairlike appendages that help cells adhere to other cells or to a substrate
74
Pilus structure (prokaryote)
Appendage that facilitates conjugation
75
Capsule structure (prokaryote)
Sticky layer of polysaccharide or protein that can help cell adherence and/or evasion of a host’s immune system
76
Internal organisation structure (prokaryote)
No nucleus or other membrane-enclosed organelles; usually no complex compartmentalisation
77
Flagella structure (prokaryote)
Structures used by most motile bacteria for propulsion; many species can move towards or away from certain stimuli
78
In brief, what is nitrogen fixation ?
Prokaryotes, unlike eukaryotes, can metabolise nitrogen in many different forms. Some can convert atmospheric nitrogen into ammonia, which is known as nitrogen fixation
79
Who was Robert Koch, what did his lab establish?
(1843-1910)
He thought that microbes were “suspects” of infectious disease, but proof was lacking, especially as some travel through the air!
His lab established germ theory of disease. His formulated criteria for providing that a specific microorganism causes disease: Koch’s Postulates
He developed simple methods for obtaining bacteria in pure culture
80
Koch’s Postulates lead to?
The discovery of the causes for: Anthrax, Tuberculosis, Cholera
He was awarded a Noble prize for Physiology and Medicine 1905
81
Koch’s Postulates: Step 1
Microorganisms are isolated from a diseased or dead animal,
The microorganisms are grown in a pure culture and identified
82
Koch’s Postulates: Step 2
Microorganisms are inoculated into a healthy laboratory animal,
Disease is reproduced in a laboratory animal
83
Koch’s Postulates: step 3
Microorganisms are isolated from the animal and grown in pure culture
Microorganisms are identified
(Microorganisms from the diseased host caused the same disease in a laboratory host)
84
Successful bacteria pathogens are divided into two broad groups. What are these?
- Opportunistic pathogens
Only cause serous disease when host defences are impaired (eg Pseudomonas aerginosa)
They often exist in the environment
- Primary pathogens (obligate)
Capable of causing disease in absence of immune defects (eg Treponema pallidum-syphilis)
They need to cause disease to survive,
Human-human transmission
Animal-human transmission (zoonotic)
85
Steps in infectious disease cycle: 1
Reservoirs
(If the cycle breaks, disease is removed)
Bacteria pathogens must have at least one reservoir:
- other humans
- animals
- environment
86
Steps in infectious disease cycle: 1
Transfer to host - Direct
Airborne: aerosols (coughing and sneezing)
Body contact: touching, kissing, sexual intercourse
87
Steps in infectious disease cycle: 1
Transfer to host - Indirect
Vector-borne transmission = living organism
- arthropods (insects, ticks, mites)
- vertebrates (rats, dogs, cats, bats, birds)… zoonosis
Vehicles: non-living materials or objects m
- food, water, soil
- eating, utensils, bedding, surgical instruments
88
Steps in infectious disease cycle: 2
Colonisation
Colonisation is establishment of a stable population of bacteria in the host
Human body contains a large number of bacteria (microflora = microbiota)
The pathogen must be able to compete successfully for nutrients & surface attachment sites
89
Steps in infectious disease cycle: 2
Adherence
Stage 1: association
Involved non-specific forces (eg charge and hydrophobicity)
2nd stage: adhesion
Involves specific bacterial adhesions and host receptors
- subsequent stages may result in aggregation to produce a biofilm
- biofilms may disperse and seed nee sites of infection
90
What is a biofilm?
A colony of prokaryotic organisms that attach to a surface with a slime layer
91
Steps in infectious disease cycle: 2
Adherence: adhesions and receptors include
Adhesins include:
- Fimbriae & Pili
- capsules & slime layers
- flagella (in some species)
- (lipo)teichoic acids (gram-positives)
Host receptors include:
- blood group antigens
- extracellular matrix proteins eg fibronectin, collagen
92
Steps in infectious disease cycle: 3
Invasion of tissues - using lytic compounds
Often accomplished by lytic compounds that attack the host tissue
Examples: collagenase, phospholipases, haemolysins (attack mechanisms to defend themselves against the immune system)
Invasiveness also determined by evasion of host defended
93
Steps in infectious disease cycle: 3
Invasion of tissues
Invasins =
Virulence factors
94
Steps in infectious disease cycle: 4
Evasion of host defence
Macrophages and other phagocytes: engulf and kill bacteria
Cytotoxic cells: kill cells infected with bacteria (protecting us)
95
Steps in infectious disease cycle: 4
What are the 2 types of bacterial avoidance phagocytosis
Resisting phagocytosis;
Bacteria produce structures preventing effective contact: capsules, special surface proteins
Survival inside phagocytic cells;
Often by very pathogenic bacteria - they can escape one of the most effective defences
96
Steps in infectious disease cycle: 4
Evasion of host defence: antibody avoidance
- capsules (sometimes not immunogenicity because they resemble host structures)
- Antigenic variation: bacteria can switch between different types of a surface structure
- sometimes degradation of antibodies
97
Steps in infectious disease cycle: 4
Evasion of host defence: avoidance of complement
- capsules can prevent complement activation
- lipopolysaccharides (gram-negative) sometimes hinder pore formation
98
Steps in infectious disease cycle: 5
Tissue damage: may occur in what ways?
- Iron acquisition
- Direct effects of bacterial toxins
- Indirect effects of bacterial toxins
- induction of autoimmune responses
Toxins = Virulence Factors
99
What is a facilitative aerobe?
Not required but grows better with oxygen
100
Steps in infectious disease cycle: 5
How do bacteria acquire iron?
- Siderophores: bind iron with high affinity
- Direct binding: of iron transport proteins eg transferrin
101
Features of exotoxins
Made by gram + and -
Protein
Secreted by loving bacteria
Usually heat labile
Highly immunogenic
Potentially lethal
102
Features of endotoxins
Made by gram -
Lipopolysaccharide (LPS)
Part of cell membrane, released on cell lysis
Usually heat stable
Weakly immunogenic
Lethal at higher concentrations
103
Human exposure to exotoxin can occur in different ways?
- ingestion of performed exotoxin (eg food poisoning by staphylococcus aureus)
- colonisation of mucosal surface or tissue followed by toxin production (eg vibrio cholerae, cause of cholera)
- colonisation of wound followed by toxin production (eg clostridium perfingens)
104
About the endotoxin?
- bound to cells, released when bacterium lyses or during cell growth
- lipid A part can have many endotoxin activity
- activates many host systems that cause damage, leading to fever, shock, blood coagulation, inflammation
- important for gram negative pathogens
105
Steps in infectious disease: 6
Excretion from body
Exit routes for continued life of pathogens include:
Ear, eyes, skin, urethra, anus, etc
106
Define host
Organism which supports growth of viruses, bacteria and parasites
107
Define pathogen
Organism that causes disease, by impairing or interfering with the normal physiological activities of the host
108
2 types of pathogen functions?
- Pathogenicity: the ability to cause disease
- Virulence: the degree or intensity of pathogenicity (determined by toxicity and invasiveness)
109
Infection vs disease definitions?
Infection: bacteria persist in host without necessarily causing tissue damage
Disease: overt damage to the host, parts of body cannot fulfil their normal functions
110
What is the Miasma theory (1800s)?
‘Bad air’ origin of epidemics from rotting organic matter; get rid of the smells you get rid of the illness such as cholera or ‘plague’
111
How do antibiotics such as penicillin affect cause bacteria to die?
Target peptidoglycan in cell wall. Lysozymes break G-M bonds, in the polymer chains linked via peptide bridges. Cell loses water so cannot function
112
How do antibiotics such as penicillin affect cause bacteria to die?
Target peptidoglycan in cell wall. Lysozymes break G-M bonds, in the polymer chains linked via peptide bridges. Cell loses water so cannot function
