Week 1 Flashcards
What are commensals/microbiota
Normal bacteria that don’t cause any harm
What is an infection?
Invasion and multiplication of microorganisms which are not normally present within the body
When can commensals be harmful?
If they get into wrong places in the body
What are the modes of transmission of an infection?
Horizontal transmission
Inhalation
Ingestion
Vertical transmission
How do microorganisms cause disease?
Exposure Adherence Invasion Multiplication Dissemination
What is virulence?
The degree of pathogenicity within a group of parasites as indicated by fatality rates and/or ability of the organism to invade host’s tissues
Ability to cause serious disease
What is pathogenicity
Ability to cause disease. Determined by virulence factors
Give some virulence factors
Exotoxins
Endotoxins
What do endotoxins do?
Stimulate macrophages to produce interleukin-1 (IL-1) and tumour necrosis factor (TNF)
What do exotoxins do?
Cause local or distant damage.
- cause non-specific activation of T cells causing inflammatory cytokine production
- interfere with host cell protein synthesis
- interfere with neurological or neuromuscular signalling
How does cholera cause diarrhoea (briefly)
Secretes exotoxin
B subunit binds to the epithelial cell
A activates adenylyl cyclase causing Na and Cl efflux from the cell.
What are the disease determinants?
Pathogen
Patients
Practice
Place
What factors affect the pathogen as a disease determinant?
Virulence factors
Inoculum size
Antimicrobial resistance
Examples of some supportive investigations
FBC CRP Liver and renal function Imaging - X-ray, MRI, ultrasound Histopathology
What factors affect the patient as a disease determinant?
Site of infection
Co-morbidities
Structure of a Gram positive cell wall?
Thick peptidoglycan layer and a cell membrane
Structure of a Gram negative cell wall?
Three layers
- inner and outer membrane
- thin peptidoglycan layer
Function of bacterial cell wall?
Maintains shape and protects cell from differences in osmotic tension between the cell and the environment
Structure and function of the capsule?
Loose polysaccharide structure
Protects the cell from phagocytosis and desiccation
What does the lipopolysaccharide do?
Protects Gram negative bacteria from complement mediated lysis. A potent stimulator of cytokine release.
What allows E. coli to bind to ureteric epithelial cells?
Specialised fimbriae (P fimbriae) that bind to mannose receptors on the cells
What does slime allow?
Polysaccharide material secreted by some bacteria growing in biofilms.
Protect the organism from immune attack and antibiotics
What are spores?
Metabolically inert form triggered by adverse environmental conditions. Adapted for long-term survival. Allow re growth under suitable conditions
How is DNA stored in prokaryotes?
Packed into a chromosome.
DNA is coiled and then supercoiled - DNA gyrase
Accessory DNA in plasmids
What can plasmids code for?
Antimicrobials resistance
Pathogenicity factors
What characteristics are used to help to classify bacteria?
Gram reaction Cell shape Endospore (presence, shape, position) Atmospheric preference Fastidiousness Key enzymes Serological reactions DNA sequences
What are the major groups of Gram positive bacteria?
Staphylococci (catalase positive)
Streptococci (catalase negative)
Gram positive bacilli - further divided into sporing and non-sporing
What are the major groups of gram negative bacteria?
Gram negative cocci, coccobacilli, bacilli
What are obligate pathogens?
Always associated with disease
Eg HIV
What are conditional pathogens?
Cause disease if certain conditions are met
Give some examples of double stranded DNA viruses
Poxvirus Herpesvirus Adenoviruses Popovaviruses Polyomaviruses
With regard to its DNA, what type of virus is hepatitis B?
Double stranded with single stranded portions
Give some single stranded DNA viruses
Parvoviruses
How do DNA viruses usually replicate?
In the nucleus of host cells
Produce a polymerase which reproduces viral DNA.
Not normally incorporated into host’s chromosomal DNA
How is RNA sense (+ss) viruses reproduced?
May serve directly as mRNA
It is translated into structural protein and an RNA-dependent RNA polymerase
How do RNA antisense (-ss) replicate?
Contains an RNA-dependent RNA polymerase that transcribes the viral genome into mRNA.
Or, the transcribed RNA can act as a template for further viral (antisense) RNA.
Which virus has ss+ RNA that cannot act as mRNA? What happens instead?
Retroviruses
Transcribed into DNA by reverse transcriptase and incorporated into host DNA.
Subsequent transcription to make mRNA and viral genomic RNA is under control of host transcriptase enzymes.
What are capsids?
Protein coat made up of repeating units
Have icosahedral or helical symmetry
Describe icosahedral symmetry and helical symmetry
Icosahedral - capsids form an almost spherical structure
Helical - found in RNA viruses that have capsids bound around the helical nucleic acid
List some enveloped DNA viruses
Hepatitis B
Herpes
(Smallpox)
List some DNA non-enveloped viruses
Human papilloma virus
Name some RNA enveloped viruses
HIV Rubella Rotavirus Coronavirus Influenza
List some RNA non-enveloped viruses
Polio
Hep A
What is enveloped in enveloped viruses?
Nucleic acid and capsid proteins
Where does the envelope come from in enveloped viruses?
A lipid envelope derived from the membrane
What antibiotic would you give to treat streptococcus pneumoniae?
Amoxicillin
What antibiotic would you use to rear pseudomonas aeruginosa in pneumonia?
Ciprofloxacin
What is different about Staph aureus that distinguishes it from other species of staphylococcus?
What is significant about it?
It is coagulase positive
Catalyses conversion of fibrinogen to fibrin and may help the organism to form a protective barricade
What is the most common/important of coagulase negative staphylococci?
Staphylococcus epidermis
What are the two categories that Streptococci can be divided into?
Type of haemolysis
α haemolytic - incomplete
β-haemolytic - complete
