Infection and Immunity Flashcards
Staphalococcus aureus
Boils, impetigo of the skin, toxic shock syndrome, food poisoning. If in blood stream possibly endocarditis and osteomyelitis
Gram positive
Streptococcus pyogenes
Strept throat and scarlet fever
Can lead to necrotising fasciitis, flesh eating bacteria
Gram positive
Group B streptococci
Neonatal sepsis, meningitis
Gram positive
Streptococcus pneumoniae
Pneumonia
Also menigitis, sepsis, endocarditis
Gram positive
Neissaria meningitides
Septicaeimia and meningitis
Gram negative
Neissaria Gonorrhoeae
Gonorrhoea
Can lead to pelvic inflammatroy disease and epidiymitis
Gram negative
Clostridium perfringens
Gas Gangrene
Gram positive
Clostridium difficile
Antibiotic associated Diarrhoea
Gram positive
Mycobacterium tuberculosis
TB
Gram stain n/a
Mycobacterium leprae
Leprosy
Gram stain n/a
Echerichia coli
Diarrhoea, acute renal failure, haemolytic uremic syndrome
Gram negative
Salmonella spp
(Gastro)Enteritis with diarrhoea
Typhoid fever
Gram negative
Shigella
Colitis with bloody diarrhoea
Dysentry
Gram negative
Pseudomonas aeruginosa
Pneumonia, potential for septicaemia
Gram negative
Legionella spp
Legionnaires disease, Pontiac fever, acute influenza or pneumonia
Gram negative
Helicobacter pylori
Causal role in peptic ulcers, especially Duodenal ulcers
Gram negative
Bacteroides spp
Abcesses,
Gram negative
Chlamydia spp
Chlamydia
Gram stain n/a
What is infection?
The colonisation/multiplication of a pathogenic microbe on or in a susceptible host with associated disfunction and damage.
The process by which disease is transmitted via microorganisms from one person to another
What causes infection?
Pathogen microbes
Bacteria
Viruses
Fungi
Protazoan
Infestation by worms
Describe Koch Henle Postulates (1882)
The agent must be shown to be present in every case of the disease by isolation in pure culture
The agent must not be found in cases of other disease
Once isolated, the agent must be capable of reproducing the disease in experiemental animals, and must be recovered from the experimental disease produced
Why are some individuals susceptible to particular infections?
Weakened immune systems
Poor nutrition
Poor living circumstances
No access to health care or vaccinations
Genetic predispostion
Lifestyle, for example STDs
What influences the outcome of infection?
The host’s immune system, the affected body systems and the drugs used
How is human DNA affected by microbial interactions?
Describe how viral and bacterial infections may be linked
Human genome hugely shaped by interactions, viral insertions
Viral infections often preced bacterial infections
How can bacteria be stained?
Haemotoxylin and Eosin stain bacteria poorly.
Most bacteria are stained by the gram stain
Acid Fast detects mycobacteria which are not be identified by gram. TB and leprosy.
What are the key properties of eukaryotes?
No cell wall
No envelope
No capsid
Membrane bound organelles
Nucleus
DNA and RNA
No pili or flagella
No reverse transcriptase
What are the key properties of bacteria?
Peptidoglycan or lipopolysaccharide cell wall
No capsid
No membrane bound organelles
No nucleus- circular DNA
plasmids
DNA and RNA
Pili, flagella
No reverse transcriptase
What are the key properties of viruses?
Can be enveloped
No organelles, obligate intracellular parasite
Can have capsids
DNA or RNA
No pili or flagella
Can have reverse transcriptase
How do you carry out a Gram stain?
+ Crystal violet, binds to - cell components
Iodine forms a large molecular complex with crystal violet
Acetone or methanol extract the complexes through gram negative cell wall but not gram positive
A red dys is used to stain the gram negative cells
What is the gram stain used for?
To detect and classify most bacteria
Gram negative or gram positive depending on the cell wall
Reveals medical differences
What is a gram positive bacteria and what colour does it stain?
What is a gram negative bacteria and what colour does it stain?
A gram positive bacteria has a plasma membrane surrounded by a very thick layer of peptidoglycan. Stains purple
A gram negative bacteria has a cytoplasmic plasma membrane, then a thin layer of peptidoglycan, then an outer plasma membrane
Define the term pathogen and non pathogen
A bacterium, virus or other microorganism that can cause disease whereas a non pathogen is a bacterium that does not cause disease.
Non pathogens may have essential ecological roles
Describe variations in bacteria shapes
Cocci: spherical
Bacilli: rods
Coccobacilli
Sprllum: spiral
Vibrio: comma
Staphylococci: grape like clusters
Streptococci: chains
Diplococci: pair
Spirachaete: corkscrew
What is the significance of the genome composition of viruses?
RNA viruses are more likely to mutate as RNA is less stable
Describe the significance of an envelope surrounding a virus
If a virus has an envelope it is more easily sterilised as if holes are punched through the envelope the virus can not survive
What are the different replication strategies used by viruses?
RNA viruses can use reverse transcriptase e.g. HIV
DNA viruses can use cell machinery e.g. HPV
Or a virus can carry its own replicatio enzymes
How can bacteria be grown and measured?
In a broth/liquid, measure turbidity
Agar, count colonies
Both of these are unnatural
Biofilms: this is how bacteria are found in nature, on surfaces as complex communities like on teeth
How do bacteria multiply?
Growth curve
BINARY FISSION replication
Lag, log, stationary, death
What are the requirements for bacteria growth?
Specific energy source
Specific building blocks
Specific atmosphere: aerobes need oxygen, facultative organisms can be with or without oxygen, anaerobes must not have oxygen
Which general types of bacteria are gram positive?
Staphylococcus
Streptococcus
Clostridium (bacilli)
Which general types of bacteria are gram negative?
Neisseria (cocci)
BACILLI:
Escheria, Salmonella, Shigella, Pseudomonas, Legionella, Helicobacter, Bacteriodes, Chlamydia
Name examples of b Lactam antibiotics and what they target
Penicillin, amoxicillin, flucloxacillin, cephalexin
They target the bacteria cell wall
What glycopeptide antibiotic targets bacterial cell walls?
Vancomycin
Which antibiotics target protein synthesis?
Try and give which group they are in
Gentamicin (Aminoglycoside)
Erythromycin (macrolide)
Tertracycline (polyketide)
What is antibiotic that targets DNA?
Ciprofloxacin, a chemotherapeutic
What is an antibiotic that targets RNA polymerase?
Rifampicin
Describe some properties of viruses
Acellualr
Can not multiply without the support of cells, need biosynthetic machinery
All that infect humans are pathogens, but many can not parasitise us
Different types infect eukaryotes and prokaryotes (bacteriophages)
How can a virus be surrounded?
A protein coat called a capsid
Which may or may not be surrounded
By a host cell derived lipid envelope, gained by budding off
What are indications of a viral infection?
Intracellualr
Viral inclusion bodies - NEGRI BODIES
Abundant ribonuceloprotein in the inclusion
Owls eye inclusion for cytomegalovirus infections such as herpes
Damage to cells: CYTOPATHIC EFFECT
What do viruses have no genes for?
Encoding proteins for metabolic energy generation
Encoding proteins for metabolic protein synthesis
Some have no genes encoding enzymes for nucleic acid synthesis, it depends on the group
What types of nucleic acids can viruses contain?
Single or double stranded DNA or RNA
Can be linear, circular, nicked
Unsegmented or segmented - allows for chromosomal reassortment such as in flu
SS RNA can be + or - sense
+RNA: genomic RNA can serves as mRNA and be directly translated into protein
-RNA: can’t serve as mRNA, needs to be processed before translation, such as retroviruses
Describe a capsid
Protein outer coat
Composed of individual sub units, CAPSOMERS
Protects from harsh conditions
Involved in attachment to host cells
2 structure types: icosahedral, helical
What are the requirements for a virus to infect a host cell?
Cell must contain a receptor for the virus to bind to
The part of the virus that binds to a receptor is a LIGAND
Some infections are tissue specific, for example HIV in T lymphocytes (CD4 receptor/CXCR4) or macrophages(CCR5 receptor)
Needs cellular machinery for viral replication
What is a ligand?
The part of a virus that bind to a host cell
It is on the capsid of a naked virus, and the envelope of an enveloped virus
What is a host range?
Spectrum of host cells that a virus can successfully infect or replicate in
What are examples of DNA enveloped viruses?
What are their effects?
Hepatitis B: inflamed liver
Herpes: oral/genital sores
Small pox
What are examples of DNA non enveloped viruses?
HPV warts: cervical cancer
Causes cells to proliferate uncontrollably
What are some examples of RNA enveloped viruses and what are their effects?
HIV: AIDS
Rubella: rash, congenital rubella syndrome
Rotavirus: diarrhoea
Coronavirus: colds/SARS
What are some examples of RNA non enveloped viruses?
Picornaviruses
Polio: inflammation of the spinal cord
Hepatitis A: liver disease
What are the modes of transmission?
Direct contact
Sex
Vertical transmission
Environment
Respiratoty
GI: fecal oral
Transcutaneous: innoculation
How can infection be spread around the body?
How can they be curtailed?
Nerves, blood , lymph
Cell mediated immunity
What are sources of infection?
Ruminant faeces
Animal to person (zoonosis)
Meat
Waterborne
Cross contamination in food preparation
Person to person
Other foods of animal origin
Describe key figures in the recognition of infection and microbiology
Hippocrates 3BC, Leuwenhoek 17C
Describe key figures in the study of infection transmission
Snow: broad street pump
Hunter: study of inflammation and venereal disease
Semmelweiss: hand washing
Nightingale: cleanliness stopping infection
Key figures in proving microbes cause disease and fighting them
Pasteur
Lister
Koch
Ehrlich
Fleming
What are the limitations of Koch Hele postulates?
Fine for acute diseeases
But not for
chronic or minor conditions
Multiple causes
If pathogen can’t be grown
What are the different habitats that may be occupied by microbes?
Air
Soil
Bodily fluids
Animals
Plants
Humans
What is a reservoir?
Any person, animal, plant, soil or substance in which an infectious agent lives/multiplies
What is a source?
Readily available form of infection agent
What are modes of transmission?
Ingestion
Inhalation
Physical contact
Inoculation
Sexual
How does infection spread?
Decribe method
Reservoir
to
Immediate source
to
Mode of transmission
to
Susceptible host
Define Carriage
Passage taken by a microorganism
EG nasal, throat
What is normal flora?
Non pathogenic bacteria normally found in our bodies: eg the gut
What is commensal?
Symbiotic relationship where one species derives benefit (microne) and the other is unaffected (host)
This is the time when the microbe may be replicating or waiting for the immune system to become compromised
Describe how microbes infect a host
Encounter
Entry/establishment
Colonisation
Either then commensal or
Spread, multiply, damage, outcome
Increasing damage
How can spread of infection be prevented in hospitals?
Eliminate microbe from reservoir/immediate source
Isolate susceptible host from immediate source or protect
Protect transmission
What is R0?
The number of secondary cases derived from one infected individual
How is the R0 value interpreted?
If R0 >1: infection propagates
If R0<1: infection dies out
How can infection be prevented (give specific examples)
Put in decreasing order of effectiveness
Handwashing (most effective)
Cohorting of staff
Antibiotic use
