Microbiology Flashcards
Define pathogen
Organism that causes disease
Define commensal
Organisms that are part of the hosts flora but in normal circumstances are non-pathogenic
Define opportunist pathogen
Microbe that only causes disease if host defences are compromised eg if in antibacterial treatments
Define virulence/pathogenicity
The degree to which a given organism is pathogenic
What are the 4 stages of pathogenesis?
- Exposure (contact)
- Adhesion (colonisation)
- Invasion
- Infection
Give 2 examples of an opportunistic pathogen
Staphylococcus epidermidis - part of the normal microbiota of skin (avirulent)
Yeast candida - normally found in skin, mouth, intestine and vagina
How are bacteria pathogenic?
- Direct (desert phagocytes/cells)
- Toxin (endotoxins & exotoxins)
- Indirect (inflammation, immune pathology)
- Diarrhoea
What is a gram +ve cocci in clusters?
Staphylococcus
What is a gram +ve cocci in chains?
Streptococcus
What is a staphylococcus that’s coagulase positive?
Staphylococcus aureus
What is a staphylococcus that’s coagulase negative?
Staphylococcus epidermis
What’s alpha haemolysis?
Partial haemolysis
What’s beta haemolysis?
Complete haemolysis
What’s gamma haemolysis?
No haemolysis
What’s an optochin sensitive (positive) alpha haemolytic streptococcus?
Strep. pneumoniae
What’s an optochin negative alpha haemolytic streptococcus?
Strep. viridans
What’s a beta haemolytic Lancefield A streptococcus?
Strep. pyogenes
What’s a gamma haemolytic Lancefield D streptococcus?
Enterococcus, S.bovis
Give an example of an enterococcus
E. faecalis
What does a pink/red MacConkey test suggest?
Lactose fermenters
What does a colourless/ orange MacConkey test indicate?
Non-lactose fermenters
When would you use MacConkey?
Gram -ve bacillus
Give examples of lactose fermenting gram -ve bacilli
E. coli
Klebsiella (pneumoniae)
Enterobacter spp
Give examples of non-lactose fermenting gram -ve bacilli
Shigella
Salmonella
Pseudomonas aeruginosa
Proteus mirabilis
What do you do if the MacConkey is yellow/colourless?
Oxidase test
What gram -ve bacilli give a positive oxidase test? (4)
Pseudomonas
V. cholerae
Campylobacter jejuni
Helicobacter
What gram -ve bacilli give a negative oxidase test?
Shigella
Salmonella
Proteus
How do you differentiate between salmonella and shigella?
Salmonella: black spots on XLD agar amongst red/pink colonies
Shigella: red/pink colonies
What is a gram +ve diplococci?
Strep. pneumoniae
What is a gram -ve diplococci?
Neisseria
