20,21,22 Flashcards
What % of flora in the human body are of human origin
10% the remaining are human commensal microbiota
What microbes supply vitamin K
Microbes in the gut
What are microorganisms that cause disease called
virulent/pathogenic
What is Koch’s postulate
the criteria decide if a microorganisms causes diesease
What are the criteria for Koch’s postulate
Organism must be isolated from every individual suffering the disease
Must be able to artificially culture the organism
Innoculate the pure culture should produce typical symptoms
Must be able to recover the organism from those that you have innoculate
Criteria for Koch’s postulate regarding genes
Gene must be present and expressed in virulent strain
Gene must be silenced or not present in normal
Disruption of the gene in the virulent strain should form a strain that doesn’t cause disease
Introduction of the virulent strain to a non-virulent strain should make it virulent
Gene must be expressed during infection
Antibody against gene or cell-mediated responses should protect experimental subjects against disease
Problems with lochs postulate
Difficult to isolate organism
Some organism can’t be artificially grown
Ethical objections
Animal models not sufficient
Does HIV have an envelope
yes
What causes spongiform encephalopathies
Prions
Are fungi prokaryotes or eukaryotes
Eukaryotes
Describe the fungi cell wall
Made chitin - also seen in arthropods which makes it strong
What are moulds
fungi that grow tiny filaments called hyphae that form mats called mycelia
What is mycelia
mats of hyphae formed in moulds
What are unicellular fungi called
Yeast
What is saccharomyces cervideau
A yeast
Describe structure of simple fungi
No separate compartments
Some divided by septa in more advanced
What disease can moulds cause
ringworm and athletes foot
What does candida albicans cause
Most common yeast infection
Causes white plaques
It is a dimoprhic fungus
Name the 4 types of protista
Apicomplex (formerly Sporoza)
Flagella
Ciliate
Amoeba
Examples of protista
Toxoplasmosis, amoeba meningitis, maaria, trypannosomiasis, leishmania, amoebic dyssntry, diarrhoea
What type of infection is trichomonas vaginalis
Protista infection
Cause foul smelling vaginal disacharge
Effect of trichomonas vaginalis on men
They are asymptomatic carriers
But can cause balantis
What is pneumocystis Jervis
Fungus (although looks like a protista)
Are bacteria prokaryotes or eukaryotes
Prokaryotes as they lack a membrane bound nucleus
What shape is the sypihlis baccteria
cork screw
How to distinguish between gram +ve and gram -ve
1) add crystal violet stain
2) Add iodine
3) wash with ethanol
4) Add counter stain for gram negative bacteria
Describe gram +Ve cell wal
Made of peptidoglycan layers (sugars cross linked by amino acids)
Describe gram -ve cell wall
Few layers of peptidoglycan
Additional outer membrane - outer leaflet of lipid A (causes toxic shock) and sugar molecules sticking into the environment
What do gram -ve bacteria have to adhere to surfaces
Fimbriae
What are plasmids exchanged between bacteria via
Via pili in conjugation
What else can bacteria produce to help make them stick
Slime e.g. streptococcus mutants enables them to stick to teeth form plaques and cause cavities
What bacteria lives on skin
Coagulase negative staphylococci - produce some slime to stick to plastics
What are endospores
Highly resistant structures produced by bacteria
Contain hardly any water
Resist extremely hazardous environments
What are fomites
innominate objects that allow the spread of infection
What are virulence factors
Traits used to complete the infection cycle, i.e. help the pathogen enter our body
What are intoxication illness
Where exposure to the toxin rather than the microorganism causes the illness
Mechanisms by which organisms cause disease
Attach to the surface at which they cause disease
Produce 1 or more toxins
Also produce aggressins - inhibits resistance mechanism of hosts
Cause undesirable consequences of the hosts defences
What is colonisation
Establishment at a site in the body
What is symbiosis
two or more organisms coexisting in a physical environment
What has more flora the skin or the large bowel
Large bowel (10^9 compared to 10^2)
what is mutualism
Both organisms benefit
What is neutralism
Neither organism benefits
What is commensalism
One organism benefits, the other isn’t harmed
What is parasitism
One organism benefits at the others expense
Name some non-sterlie sites
Conjunctiva, nsasopharynx, skin, vagina, GI tract
Exposed to the environment either directly or indirectly
No mechanism in place to maintain sterility
How are sterile sites maintianed
1) Surface cleaning i.e. LRT cilia lining bronchi and trachea
2) Sterility maintained by barriers that allow unidirectional flow i.e. urethra, cervix, middle ear, upper genital tract, eustachian tube
3) Sterility maintained by barriers i.e. closed cavities i.e. pleural cavity, pertioneal cavity, spinal cord and meninges
How does H. Pylori survive in the stomach
Creates an ammonia cloud
What is tissue tropism
The propensity for an organism to grow in a particular place
Is skin a good place for organism to grow?
No
Varying temps, abrasion, dry, nutrient-poor
Is the gingival crevice a good place for organisms
Yes
Warm, moist, anaerobic, few physical challeneged, bathed in nutrients, mucosal surface
Name some skin bacteria
Staphyloccous aurues - especially in nasal area
Coagulase negative staphylococci e.g. staph epidermis
Proprionibacterius s species - can cause acne
What bacteria can cause acne
Proprionibacterius species
Name some mouth flora
Streptococci viridans
Anaerobes
Types of flora in nostrils
Skin flora
S. aureus (nose is main carrier site)
Type of flora in pharynx
Respiratory and other pathogens e.g. streptococcus progenies, ugly, pneumonia, neisseries meningitidis
Type of flora in vagina
Pre puberty - E.coli, skin, GI flora
Post puberty - glycogen produced due to circulating oestrogen, lactobacillus ferment this glycogen to make low pH. Mainly get skin flora and Candida Albicans
Type of bacteria in stomach and small intestine
Predominantly aerobic
Low pH keep bacteria down
BUT acid tolerant lactobacillus and H. Pylori
Number of bacteria increases as you go distally
Type of bacteria in the large intesetine
95-99% are anaerobic e.g. bacteriodes, clostridium, bifidobacteria
Some aerobic gram -ve bacilli e.g. E. coli, enterbacetr, proteus, citrobcater
Benefits of normal gut flroa
Synthesis and release vitamins
Colonisation resistance
Induction of cross reactive antibodies - may have a protective effect
How does normal gut flora prevent colinisation
Manipulates the environment e.g. low pH due to bacteria antibacterial agents, collisions, bacteriocins, fatty acids and metabolic waste
Main risk factor for C. Diff
Antibiotic treatment
Pathology of normal flora
Overgrowth
Translocation
Cross infection
What happens in vaginal thrush
Overgrowth of normal vaginal flora due to inhibition of colinsation resistance
Treat with broad spectrum antibiotics!
Vaginal itch with creamy discharge
How does conjunctivitis occur
Occurs following URI infection - cause by haemophilia influenza TRANSLOCATION
Get red eyes and purulent discharge
Describe infection with an intravascular catheter
TRANSLOCATION
2 weeks post bowel resection, spiking fevers associated with administration of IV drugs
Blood cultures grow coagulase negative staphylococci
What cause endocarditis
Staph aureus - occurs more on damaged/prosthetic heart valves
What is pathogenicity
The capacity of a micro-organism to cause an infection
Chain of infection
Pathogenic organism - reservoir - exit - entry - susceptible host
What is virulence
Used interchangeably with pathogenicity
The capacity of a micro-organism to cause an infection
What is the LD/ID50
The dose required of an organism to cause an infection
What is infectivity
The ability of an organism to become established in a host
How do microbes becomes established in a host
Through ligand/receptor interactions
How does E.coli become established
Fimbriae attach to glycopeptides on the cell surface
How does S.pyogenes become established
Through Protein-F-fibronectin - a large multifunctional gylcoprotein expressed in connective tissues, on cell surfaces and in bodily fluids
How does influenza haemagluttinin become established
Binds to silica acid on respiratory epithelium
What are virulence factors t
The components of microorganisms that cause disease
What are virulence factors sometimes referred to
Adhesins, aggresins, interferins, modulins
What are endotoxins
Endotoxins are heat stable lipopolysaccharide-protein
Form structural components of cell wall of Gram Negative Bacteria
Liberated only on cell lysis or death of bacteria
Produced in E. Coli
What is the active compound in endotoxins
Lipopolysaccharide - made of Lipid A and oligosaccharides
How are endotoxins released
Released only on cell lysis or death of bacteria
What is the host response to endotoxins
T cell activation - releases inflammatory cytokines, fevers rigors, hypotension, bradycardia, cardiac/renal failure
Activation of the clotting cascade
Activation of the complement system
How does peritonitis occur
By endotoxins
E. coli and bacteriodes fragilis (anaerobe) due to a perforated appendix
How does neisseria meningitides occur
Endotoxin mediated
Causes an increase in vascular permeability - proteins, fluid and plasma goes into tissue, get vascoconstrictoin
What are exotoxins
Proteins produced by living bacteria
How does botulism cause infection
Due to clostridium botulinism (an anaerobe)
Produces an exotoxin that binds to presynaptic ACh vesicles preventing their release
Cause diplopia, dysphagia, dysarthria, dry mouth, death due to respiratory failure, flaccid paralysis
Difference between botulism and tetanus symptoms
botulism is flaccid paraylsis
Tetanus is rigid paralysis
What organism causes botulism
Clostridium botulism an obligate anaerobe
Its spores are highly resistant so organism can survive for a long time outside the body
How do we catch botulism
Through infected food or through dirty wounds
What causes tetansu
Clostridium tetani (obligate anaerobe)
How do we get tetanus
Dirty wounds
How does tetanus cause disease
Exotoxin that binds to nerve synapses in the CNS inhibiting the release of neurotransmitters (Gamma amino buticylic acid GABA)
Causes uncontrolled spasms and rigid paralyis
Death due to respiratory failure
What is opisthotonos
The specific shapes the body is thrown into due to the rigid paralysis in tetanus
Some exotoxin mediated infections
Cholera, botulism, tetanus, C Diff, E. Coli, Streptococcal scaled skin syndrome, whooping cough (pertussis), scarlet fever
What causes whooping cough
Pertussis toxin
What causes scarlett fever
Streptococcus pyogenes
Symptoms of streptococcus pyogenes
Scarlett Fever
erysipelas - large raised red patches on the skin
Streptococcal sore throat
Necrotizing fasciitis
How do we treat necrotising fasciitis
Antibiotics not sufficient - need to remove the infected tissue
What are the virulence factors of streptococcal pyogenes
Hyaluronidase and streptokinase - break down connective tissue
C5a peptidase - inactivates complement C5a
Streptolysis O- H - breaks down RBCs and WBCs
Erythrogenic toxin - causes scarlet fever not a virulence factor
Toxic shock syndrome - streptococaal toxic shock syndrome is superficially sumilar to a syndrome of endotoxin release
How does streptococcus pyogenes inhibit phagocytosis
M-protein binds fibrinogen to hide the bacteria
Prevents opsonisation and complement binding
How does s. pneumonia inhibit phagocytosis
Polysaccharide capsule to inhibt opsonisation and phagocytosis
Methods of immune evasion
1) inhibit phagocytosis
2) Intracellular pathogens
Examples of intracellular pathogens
Listeria, Salmonella, TB
Virus life cycle
Adsoprtion Penetration Uncoating Replication Assembly Release
