Microbial Growth and Antibiotics, Microbial Disease Flashcards
Cocci
Spherical shaped bacteria
Staphylococci
Multiple spherical cocci
Causes boils and food poisoning
Skin infections
MRSA
Diplococci
Pairs of cocci
Meningitis
Gonorrhoea
Strepococci
Chains of cocci
Causes sore throats
Used in yogurt making
Desiccation
State of extreme dryness
Light sensitive pigment found in bacteria
Bacteriochlorophyll
How do bacteria obtain their energy?
Sunlight
Oxidation of chemical compounds
Photoautotrophs
Phototrophs which carry out photosynthesis using an inorganic source of carbon (e.g. carbon dioxide)
Photoheterotrophs
Phototrophs which carry out photosynthesis using an organic source of carbon
Chemoautotrophs
Chemotrophs which obtain their energy by oxidising inorganic compounds
Chemoheterotrophs
Chemotrophs which obtain their energy by oxidising organic compounds
Mesosome
Infoldings of the cell surface membrane and possess enzymes used in respiration
Plays a part in cell division aiding the separation of DNA into new cells
Bacterial cell wall
Rigid structure that maintains shape of cell
Made of my rein and is a mucopeptude
Gram stain
Allows distinction of bacteria by gram positive/negative
Gram positive bacteria retain the stain due to the cell wall containing at least 40% murein. Gram negative don’t retain the stain as they have as little as >
>5%
Halophile
Extremophile that can grow in areas of high salt concentrations or in salt crystals.
Habitats include salt marshes and salt lakes
Adaptations of halophiles
1) High salt conc. in cytoplasm to prevent water loss
2) Optimal protein folding to tolerate conditions
3) Cell wall made of glycoproteins and stabilised by Na+ to maintain cell structure
4) Na+ pumped out for K+ to exploit energy transfer differences
5) Bacteriorhodopsin and other pigments give red/orange colour of salt flats
Psychophile
Extremophile that’s optimal growth temperature is below 15 degrees in places like the artic
Why are low temperatures bad for cells
Freezes water which prevents metabolic processes
And forms ice crystals which pierce the cell membrane
Adaptations of psychrophiles
- Cold adapted enzymes
- Very fluid cell membranes due to increased unsaturated fatty acids
- Antifreeze proteins bind to ice crystals preventing them from piercing cell membranes
Thermophile
Extremophile with optimum growth temperatures of above 45 degrees
(Hyperthermophiles live in 80+)
Problems for cells with high temperatures
Denature protein and increase membrane fluidity
Adaptations of thermophiles
- more Saturated fatty acids in membrane lipids to reduce fluidity
- more chemical bonds (e.g. Disulfide) to maintain protein shape.
- Fewer branching polypeptides on the surface of proteins.
- Chaperones to help refold denatured enzymes/proteins
- DNA is stabilised using DNA binding proteins and reverse DNA gyrase
Reverse DNA gyrase
Introduces positive supercoils into DNA
Alkalinophiles
Grow at pH values over 9
Soda lakes
High carbonate soils
Acidophiles
Grow in pH values below 5
Sulphuric pools
Geysers
Mine drainage polluted areas
Adaptations of alkalinophiles
- membrane lipids and cell walls that resist dissolution by alkali
- maintain intracellular pH around 9 so their proteins are adapted to this
- have low H+ concentrations which is important for ATP synthase to provide energy, so H+ is actively pumped in
Adaptations of acidophiles
- Acid resistant cell walls and membranes
- Excess H+ is actively pumped out
What are aseptic techniques?
Procedures used to prevent the introduction of extraneous organisms into a culture or sterile apparatus
Sources of contamination
Non-sterile apparatus
An individual (skin/breath)
Work surfaces
The air
Aseptic techniques used to avoid contamination
Use of sterile apparatus (syringe/pipette)
Avoid contact of sterile apparatus with work surfaces/skin
Flame top of test tubes/bottles/inoculating loop
Minimal exposure to air
Binary fission
Asexual reproduction of bacteria
1) cell elongation, DNA replicates and attaches to mesosome
2) septum begins synthesis, dividing the cell
3) septum divides genetic material and forms 2 daughter cells
4) daughter cells separate and cycle repeats
Staphylococci
Clusters of cocci
Causes boils and food poisoning
Diplococci
Pairs of cocci
Causes pneumonia, meningitis, gonorrhoea
Streptococci
Chains of cocci
Causes sore throat, used in yogurt making
Bacilli
Rod shaped
Singular - causes typhoid fever
Chains of rods - free living, nitrogen fixing bacteria
Spirillia
Rigid spiral structure
Found in stagnant water
Causes syphillis
Vibrio
Curved, rod shape
Causes cholera
Capsule
Consists of polysaccharide and polypeptide
Protects against phagocytosis and antibodies
Prevents dehydration
Prokaryote cell wall
Rigid structure that maintains the shape of bacteria cell
Made of murein and is a mucopeptide
Prokaryote cell membrane
Similar fluid mosaic structure to eukaryotes
Is selectively permeable and controls what enters and leaves the cell
Prokaryote mesosome
Infoldings of the cell surface membrane and possess enzymes involved in respiration
Plays a part in cell division aiding the separation of DNA into new cells
Circular DNA
No defined nucleus
Unassociated with histones
Prokaryote flagellum
Allows mobility
Simpler than eukaryotes
Made of contractile protein flagellin
Lag phase
- Little/no cell division occurs, but cells may increase in size
- Cells are synthesising rna, proteins and enzymes
- Some enzymes may be produced to utilise particular nutrients in the culture
Log/exponential phase
- Cells divide at maximum rate
- nutrient levels, temperature and pH are all optimal for growth
- no limiting factor
- primary metabolites required for growth secreted here
Stationary phase
- population stays consistent due to equal numbers of produced cells and dying cells
- level of nutrients decreases
- pH/temp becomes unfavourable
- toxin/waste increase
- secondary metabolites are secreted
Death phase
Unfavourable conditions cause death rate to be greater than growth rate
Autolysis may occur
Obligate aerobes
Can only grow with oxygen present
Obligate anaerobes
Can only divide in anaerobic conditions
Facultative aerobes
respire aerobically when oxygen level is higher and anaerobically when low
Aerotolerant anaerobes
Grow well in anaerobic conditions but can tolerate aerobic conditions
Filamentous fungi
Consist of fine, branched threads known as hyphae that form a mass known as mycelium
Fungal cell wall
Made of chitin
Strong and rigid allowing enzyme secretion and absorbing of soluble products
Coenocytic hyphae
Filamentous fungi consisting of a multinucleotide cytoplasm with no cross walls (aseptate)
Mechanisms of antibiotic action
1) inhibiting cell wall synthesis
2) cell membrane disruption
3) inhibiting mRNA translation
4) inhibiting nucleic acid synthesis
Exotoxins
Proteins secreted by bacteria which cause many symptoms of disease
Endotoxins
Lipopolysaccharides present in bacterial walls which can be released during break down of the bacterium after death
How do pathogens cause disease
Damaging host tissues
Production of toxins
Factors affecting pathogenicity of bacteria
- cell wall/capsule features affecting attachment + entry
- types of toxins
- infectivity
- invasiveness
What on bacterial cell walls allows attachment?
Ligands and glycocalyx
Ligand
Attachment protein made of polysaccharide
Glycocalyx
Attachment protein made of glycoproteins
Infectivity
Number of bacteria needed to cause infection
Very Infectious bacteria example
Typhoid fever
Not very infectious bacterium
Salmonella food poisoning
Many are required
Invasiveness
Ability of the bacteria to spread
How does a bacteria typically invade the host
Blood and nymph systems
Very invasive bacteria
Bubonic plague and anthrax
Characteristics of an invasive bacteria
Able to avoid phagocytosis and other body defences.
Able to get through tough fibres, connective tissues and intercellular cement.
Methods of disease transmission
- airborne
- food-borne
- water-borne
- contact
- sexual intercourse
- vector-borne
How is malaria transmitted
Vector-borne
Diseases transmitted by sexual intercourse
HIV
Gonorrhoea
How is athletes foot transmitted
Contact
Water-borne disease examples
E. coli
Typhoid
Cholera
Food-borne disease examples
Salmonella food poisoning
Typhoid
Airborne disease examples
Influenza
Measles
Whooping cough
Cholera
Water-borne disease caused by vibrio cholerae
Contamination examples leading to transmission of vibrio cholerae
Transmitted by ingestion of improperly purified water, sewage contaminated water and contaminated food
Vibrio-cholerae structure
Comma shaped
Flagellum
Plasmid
Capsule
Oral rehydration solution
Treatment of diarrhoea which restores the water and ions lost.
Contains H2O, Cl-, Na+ and C6H12O6
Cholera symptoms
Diarrhoea
Dehydration
Stomach cramps, vomiting, fever
Bacteria that causes boils and food poisoning
Staphylococci
Bacteria causes pneumonia
Diplococci
Bacteria which causes sore throats and used in yogurt making
Streptococci
Bacteria causes typhoid fever
Bacilli
Free living nitrogen fixing bacterium
Chains of bacilli
Bacteria causes anthrax
Bacilli
Bacteria that is a common symbiont of gut
E. Coli bacilli
Saprotroph of fresh water and causes syphillis
Spirilla
Bacteria causes cholera
Vibrio
How is diarrhoea treated?
Using oral rehydration solution
What does ORS contain?
H2O
Cl-
Na+
C2H12O6
What does the influenza virus contain
RNA
RNA polymerase
What is the significance of the influenza virus and its strains
There are 3 strains A, B and C due to the virus having such a high rate of mutation.
A causes serious epidemics
Which epithelial cells does the influenza virus typically infect
Nose, throat and sometimes bronchi
Transmission of influenza virus
Airborne so enters via respiratory passages in air droplets when coughing/sneezing
Poor ventilation and overcrowding increase infectivity
Incubation period
Time between infection and development of symptoms
Influenza incubation period
2 days
Symptoms of influenza
Sore throat, head ache, back ache, joint pain, fever up to 40 degrees, sweating, shivering, dry cough.
Symptoms can last up to 7 days
What are typical complication of influenza and why?
Development of bronchitis and pneumonia due to damage to epithelial lining of trachea and bronchi making secondary invasion by bacterial pathogens more likely.
Reverse transcriptase in viruses
Produces DNA in the host cell using RNA as a template
HIV
Human immunodeficiency virus
A retrovirus containing RNA and reverse transcriptase.
Enzyme and nucleic acid are surrounded by a nucleocapsid and then a lipid envelope.
This contains glycoproteins on the surface.
HIV attacks helper T cells
Nucleocapisd
Structure on a virus made from an inner protein coat and then an outer protein capsid
What is the first phase of symptoms of HIV?
Body produces HIV antibodies
Short flu like illness
Skin rash
Swollen glands
Antibody/HIV positive phase
Period between infection and onset of clinical signs
May last a a few weeks or years
AIDS related complex (ARC)
- Opportunistic bacterial, viral and fungal infections
- Loss of weight and a reduction in the number of T lymphocytes
Phase 4 of symptoms of HIV
Opportunistic infections of body organs
Development of secondary cancers
Development of HIV wasting syndrome and dramatic weight loss
Typically death from pneumonia
Antiretroviral therapy (ART)
Used method of treatment for HIV infection
Reduces levels of HIV in the blood
Allows immune system to repair itself
Prevents any resulting illnesses
Antiretroviral (ARV) HIV drugs
- Prevent multiplication of the virus
- Classified based on how they interfere with the HIV life cycle
Classes of HIV life cycle ARV interferes with
- Reverse transcriptase inhibitors
- Protease inhibitors
- Fusion and entry inhibitors
- Integrase inhibitors
Combination therapy
Taking two or more ARV drugs at a time
Highly active antiretroviral therapy
Taking 3 or more anti-HIV drugs
Dependant factors on drug choices for HIV infection
Availability Price of drugs Number of pills Side effects of the drugs Pre-existing medical conditions
How does HIV bind to T lymphocytes
Via CD4 receptors
And CCR5 receptors
Preventing HIV infection
Reduced promiscuity Safe sex Blood screening Provision of clean needles for drug users Possible elective Caesarean section Bottle feeding over breast feeding
Post exposure prophylaxis (PEP)
Taken by an individual if they believe they’ve been infected.
Within 72 hours following high exposure.
Month long treatment with serious side effects and non guaranteed effectivity.
Involves same drugs given to HIV+ patients
Pre-exposure prophylaxis (PEP)
Course of HIV drugs intended for HIV negative individuals at risk of infection.
Drugs taken prior to sex to reduce risk of contracting HIV.
No major side effects.
Transmission of HIV
Blood, semen or vaginal secretions.
- Sexual transmission
- Blood products/transmission of infected blood
- Sharing needles
- Mother to baby
How does HIV attach to CD4 helper T cells
Glycoproteins (gp120) on their surface binding specifically to receptor sites on the membrane of the helper T cells.
How does HIV DNA enter the host nucleus
Viral RNA and reverse transcriptase are released and enter the T lymphocyte.
In the helper T cell, viral DNA is formed by the enzyme reverse transcriptase using the viral RNA as a template.
Viral DNA enters the nucleus and attached to host DNA and then replicates with it.
Can remain latent for up to 10 years in the nucleus depending on activation of infected T lymphocyte.
Following entry to the nucleus, how does HIV lead to infection of other cells in the host?
Viral DNA controls synthesis of viral proteins and RNA within the cell.
HIV particles are assembled and the cell is destroyed as viruses are released. The infect other T lymphocytes causing their concentration in the blood to decrease.
Common opportunistic diseases resulting from AIDS
Kaposis sarcoma and pneumonia
How does HIV lead to opportunistic infections and ultimately death.
Virus attacks T lymphocytes which stimulate antibody production by B lymphocytes in the immune response to combat infection. As the immune response breaks down, the individual suffers opportunistic disease and then death.
Bioassay
Enables the effectiveness of a compound (antibiotic or disinfectant) to be determined by its effect on the growth of a microorganism.
What can bioassays be used to screen?
Microorganisms to determine if they produce an effective antibiotic.
By measuring their ability to inhibit bacterial growth on a bacterial lawn
Antibiotic
Compound usually produced by a microorganisms which inhibits it kills bacteria
Mechanisms of antibiotic action
1) inhibiting cell wall synthesis
2) cell membrane disruption
3) inhibiting mRNA translation
4) inhibiting Nucleic acid synthesis
5) antimetabolite activity
Inhibiting cell wall synthesis
Mechanism of antibiotic action
E.g. Penicillins and ampicillin
Inhibit enzymes involved in synthesis of peptide cross links in the cell wall, causing it to weaken. Results in osmotic lysis.
Osmotic lysis
When water constantly enters a cell due the wall becoming weaker resulting in a pressure increase which causes the cell to burst
Cell membrane disruption
Mechanism of antibiotic action
E.g. polymyxin B
Alteration of the cell membrane structure making it more permeable and leading to cell death by osmotic lysis
Examples of antibiotics mechanisms that are bacteriocidal
Inhibition of cell wall synthesis
Cell membrane disruption
Antimetabolite activity
Examples of antibiotic mechanisms that are bacteriostatic
Inhibition of mRNA translation
Inhibition of nucleic acid synthesis
Why are antibiotics ineffective against viruses
They possess none of the structures or processes that antibiotics typically act against
Inhibiting mRNA translation
Mechanism of antibiotic action
E.g. streptomycin and tetracyclines
Inhibit protein synthesis by binding across bacterial ribosomes but don’t affect eukaryotic cells
Inhibiting nucleic acid synthesis
Mechanism of antibiotic action
E.g.ciprofloxacin
Inhibits dna replication
Antimetabolite activity
Mechanism of antibiotic action
E.g. Sulfonamides
Inhibition of enzyme reaction
Interference with metabolic pathways
Broad spectrum antibiotics
Effective against a wide range of bacteria
May be used to treat undetermined bacterial infections
Tetracyclines
Bacteriostatic Antibiotic
Mechanism works by inhibiting mRNA translation
Broad spectrum antibiotic
Narrow spectrum antibiotic
Effective against a small specific group of bacteria
Streptomycin
Bacteriostatic antibiotic
Mechanism works via inhibition of mRNA translation
Narrow spectrum antibiotic used to test streptococcus bacteria
Antibiotic resistance to penicillin
Bacteria possessing a genetic mutation enabling production of penicillinase which breaks down the antibiotic.
How can a bacteria obtain the genes for drug resistance
Spontaneous mutation
Transfer of genes for resistance from other bacteria
Vertical gene transmission
Resistance arisen due to random mutation which are passed on to future generations of bacteria.
Repeated exposure to antibiotics can lead to more bacteria surviving, causing their number in the population to increase.
Increase in allele frequency
Horizontal gene transmission
Occurs by conjugation
Does not involve gene transmission to the next generation, instead increases the number of antibiotic-resistant bacteria in a population.
Can occur between different bacterial species
Conjugation
Process of gene transmission
Occurs when one bacterium transfers a copy of its plasmid (or multiple) to another bacterial cell.
- Donor cell produces pilus connecting cells.
- Donor cell replicates plasmid and passes copy.
- Recipient cell receives plasmid which may contain gene for antibiotic resistance.
Transmission of dna via transduction
Bacteriophage (vector) infects a bacterium and it’s DNA and the host DNA split.
New bacteriophages are assembled w/ bacteriophage DNA or bacterial DNA.
When a bacteriophage containing bacterial DNA infects a new cell, the DNA can be integrated into the new cells DNA.
Transmission of dna via transformation
- DNA from a lysed bacterial cell (or environment) is bound to DNA binding protein in host cell wall.
- One foreign strand enters the host cell as the other strand breaks down.
- Single DNA strand is bound to the DNA of the host cell.
- Host cell is transformed.
Virus
Obligate intracellular parasite which reproduces inside a living host cell.
They cause disease by the combined effects of damage to host cells via replication and toxins produced during replication.
MRSA
- Methicillin-resistant staphylococcus aureus
- Name given to any of this strain resistant to one or more antibiotics
- difficult to treat
- prevalent in hospitals
Why is MRSA prevalent in hospitals?
- Many antibiotics are being used which enables development of multiple-resistance
- Close proximity of patients ideal for infection transmission
- Weak and sick individuals more vulnerable to infection by MRSA
C. Difficile
- Most important cause of hospital acquired diarrhoea
- Anaerobic bacteria present in gut in 3% healthy adults and 66% infants
- Causes problems in patients given incorrect antibiotic as it disturbs balance of bacteria
Capsomere
Protein subunits which make up the outer protein coat/capsid of a virus.
Ebola virus
Aggressive pathogen that causes a highly lethal haemorrhagic fever syndrome.
Why is the Ebola virus difficult to control?
It’s natural host is unknown.
Has rapid progression.
Can survive for several days outside of body.
General structure of Ebola virus
Member of the Filovirus family.
Contains RNA, RNA polymerase, glycoproteins.
Which strain of the Ebola virus has the highest death rate?
Zaire strain
Transmission of Ebola virus
In blood, body fluids or organs of infected.
•giving care to infected
•handling unsterilised needles or medical equipment
• unprotected sex with an infected person
Viral replication of Ebola
- Glycoproteins bind to receptors on cell membrane
- Virus enters by endocytosis
- Protein coat removed on entry, RNA + RNA polymerase are released
- RNA is replicated, transcribed and translated to produce viral RNA and proteins
- New viruses are assembled which bud out the cell
Cells targeted by Ebola virus
- Liver cells
- Immune system cells
- Endothelial cells (line inside of blood vessels)
Initial symptoms of ebola
Fever, headache, joint and muscle pain, sore throat, intense muscle weakness, 2 to 21 days after infection.
Later symptoms of ebola
Diarrhoea, vomiting, rash, stomach pair, impaired kidney and liver function.
Patient bleeds internally, may bleed from ears, eyes, nose or mouth.
Diagnosis of ebola
Blood or body fluid samples can be tested, a diagnosis can be made.
Those suspected of infection are isolated.
If +ve, transferred to a hospital high-level isolation unit.
If negative, other diseases are tested for.
Treatment of Ebola
No vaccine or licensed drug available.
Treatment of symptoms:
- Provision of intravenous fluids (IV) and balancing electrolytes (body salts)
- Maintenance of oxygenstatus and blood pressure
- Treatment of other infections if they occur
Possible treatments of ebola
- Vaccines
- siRNA to prevent translation by binding to viral RNA
- Antibodies which bind to glycoproteins
Bacteriophage
Viruses that infect prokaryotic cells
Lytic cycle of bacteriophage
Pathway following infection of host cell which results in lysis of cell.
Lysogeny
Viral DNA is incorporated into the DNA of the prokaryote host and remains dormant as most virus genes are not expressed. However, the viral genome is replicated every time the host cell divides. Virus referred to as provirus. Host cell considered lysogenic.
Malaria
Caused by infection with the protozoan Plasmodium. Transmitted by a female Anopheles mosquito.
Life cycle of Plasmodium in mosquito
- Mosquito picks up Plasmodium from infected humans when feeding (provide eggs w/ protein).
- It reproduces in gut of mosquito, making thousands, which move to salivary glands.
- Mosquito feeds again on uninfected person, Plasmodium passes into blood, w/ anticoagulant in saliva.
Symptoms of Malaria
- Fever, headache, nausea, sweating, vomiting, diarrhoea, general aches and pains.
- Complications such as severe anaemia
- With some species, parasite can accumulate in blood vessels of the kidney causing kidney failure, or accumulate in the brain causing seizures, brain damage and coma.
Prevention methods of malaria
- Avoid being bitten, insect repellent + mosquito nets
- Insecticides (spraying breeding sites and bed nets).
- Antimalarial drugs prior to and after travel
Examples of antimalarial drugs
Atovaquone + proguanil mefloquine (Larium)
Doxycycline.
Treatment of malaria
- Chloroquine + proguanil, although rarely used due
to ineffectiveness against the main malaria parasite. - Injection of high doses of drugs used to prevent parasite.
Why is eradication of malaria difficult?
- Increase in drug resistant Plasmodium, increase in insecticide resistant mosquitoes.
- Difficult to produce vaccine due to plasmodium occupying liver + red blood cells.
- Larvae of mosquitos live in stagnant water, so draining removes breeding sites.
Possibility of vaccine against malaria?
Recent trials with vaccines against malaria at various points in its life cycle where it is vulnerable to attack are successful.
Virus
Intracellular parasite which reproduce inside living host cells, using their metabolic processes.
Cause damage by toxins and damage to tissues.
Protozoan plasmodium
Type of parasite which causes malaria in humans. Travels in female Anopheles mosquitos, being picked up when mosquito feeds to provide eggs w/ protein.
Life cycle of plasmodium upon entry into human host
- Once in blood stream, they travel to the liver, enter cells and multiply.
- They leave the liver, enter red blood cells and multiply again.
- Plasmodium causes cell to burst, releasing more for further infection. Coincides with associated symptoms of malaria.
Anticoagulant
Substance that helps prevent blood clots. Used by mosquitos so they can more easily take up blood.
Individuals most at risk of malaria
- Pregnant women with depressed immune systems
- Children with weaker immune systems
Dominant allele
Always expressed in the phenotype
