Biology and classification of Bacteria Flashcards
What is a pathogen?
Organism that causes or is capable of causing disease
What is a commensal?
Organism which colonises the host but causes no disease in normal circumstances
What is an opportunist pathogen?
Microbe that only causes disease if host defences are compromised
What is virulence/pathogenicity?
The degree to which a given organism is pathogenic
What is asymptomatic carriage?
When a pathogen is carried harmlessly at a tissue site where it causes no disease
How does a commensal become an opportunist pathogen?
Commensals can cause disease when they escape areas where they normally reside and become opportunist pathogen
What colour stain do gram positive bacteria have?
Purple
What colour stain do gram negative bacteria have?
Pink
What does bacillus mean?
A rod
What does spirochaete mean?
Spiral rod
How many membranes do gram positive bacteria have?
1
How many membranes do gram negative bacteria have?
2
What is between the outer and inner membrane in gram negative bacteria?
lipoprotein, periplasmic space and peptidoglycan
What is an endotoxin?
component of the outer membrane of bacteria, e.g. lipopolysaccharide in gram negative bacteria only
What is an exotoxin?
secreted proteins of gram positive and gram negative bacteria
- can cause damage to host cell
What pH do bacteria grow between?
4-9
Which type of light can bacteria grow under?
UV
Can survive radiation
How long do viruses take to double?
<1 hr
How long does E.coli, S.aureus etc take to double?
20-30 mins
How long does fungi take to double?
30 mins
Are the actions of exotoxins specific or non-specific?
Specific
Are the actions of endotoxins specific or non-specific?
Non-specific
What is the composition of exotoxins?
Protein
What is the composition of endotoxins?
lipopolysacccharide
What effect does heat have on exotoxins?
Liable to change
What effect does heat have on endotoxins?
Stable
What are exotoxins produced by?
Gram positive and negative bacteria
What are endotoxins produced by?
Gram negative bacteria
Can exotoxins be converted to toxoids?
Yes
Can endotoxins be converted to toxoids?
No
What are some examples of mutation?
- Base substitution
- Deletion
- Insertion
- Transfer
What are 3 types of gene transfer?
- Transformation eg via plasmid
- Transduction eg via phage
- Conjugation eg via sex pilus
What are obligate intracellular bacteria?
grow inside cells, can’t culture normally
What is an example of obligate intracellular bacteria?
Chlamydia
What are the 2 types of bacteria that may be cultured on artificial media?
With and without a cell wall
What are the 2 types of bacteria with a cell wall?
- Growing as single cells
- Growing as filaments
What are the 3 groups of bacteria that grow as single cells?
- Rods
- Cocci
- Spirochaetes
What are the 2 groups of cocci?
- Gram negative
- Gram positive
What can gram negative and gram positive bacteria be further categorised into?
Aerobic and anaerobic
What is N. meningitidis?
Aerobic gram negative cocci
What are examples of aerobic gram negative cocci?
Neisseria
1. N. Meningitidis
2. N. Gonorrhoeae
What are the 2 groups of aerobic gram positive cocci?
Staphylococcus
Streptococcus
What is the main cause of lobar pneumonia?
S. pneumoniae
What is s. pneumoniae?
Alpha-haemolytic streptococcus
What are the 3 groups of rod bacteria?
- Gram positive
- Gram negative
- Ziehl-Neelsen stain positive
What are an example of Ziehl-Neelsen stain positive bacteria?
Mycobacteria
eg. M. tuberculosis
What is the main cause of food poisoning in the UK?
Campylobacter
Describe the gram staining process
- Apply a primary stain such as crystal violet (purple) to heat fixed bacteria
- Add iodide which binds to crystal violet and helps fix it to the cell wall
- Decolourise with ethanol or acetone
- Counterstain with safranin (pink)
What is the coagulase test?
Distinguishes S.aureus from other staphylococci – coagulase positive
What are the 3 types of haemolysis?
Alpha
Beta
Gamma
What is alpha haemolysis?
haemolysis causing by production of hydrogen peroxide oxidising haemoglobin –
the agar appears green
What is beta haemolysis?
haemolysis results because of lysis of red blood cells by haemolysis such as Streptolysin O produced by S.pyogenes
What is gamma haemolysis?
implies no haemolysis
What is the oxidase test?
Tests if micro-organism contains a cytochrome oxidase – implies organism able to use
oxygen as the terminal electron acceptor
