Flashcards in 4.0 Bacteriology Deck (36)
What four criteria are needed to identify the causative agent of a particular disease (Koch's postulates)?
1. Bacterium must be present in every case of the disease
2. Bacterium must be isolated from the disease and grown in pure culture
3. Bacterium from pure culture must cause disease when inoculated into a healthy, susceptible host
4. Bacterium must be reisolated from the new host
At low or moderate levels
Sudden appearance of disease (or ↑ above endemic levels)
Define point source outbreaks:
Bacterial infections arising from single origin
Define continuous source:
Point source outbreaks can be continuous outbreaks if source is not eradicated
Define propagated outbreaks:
Host-to-host transmission → even greater numbers of infections
Cell size range for bacteria:
0.5 - 3 um
Comment on the genome of bacteria:
Single + circular
What colour are gram positive bacteria?
What colour are gram negative bacteria?
What bacteria do not gram stain well?
4) Leigonella pneumoniae
What is bacterial cell wall made up of?
Alternating NAG + NAM sugars with oligopeptide cross-links
Functions of bacterial cell membrane:
1) Osmotic barrier
2) Signal transduction
3) Nutrient transport
Differences between Gram +ve and Gram -ve cell envelope:
Thicker cell wall
Thinner cell wall
Outer membrane (with porins and LPS)
What enzymes are found in the gram -ve periplasm?
4) β lactamases
What does the Gram -ve outer membrane?
2) Lipopolysaccarhide (LPS)
- O-antigen (v. variable)
- Lipid A = endotoxin → TNF and IL-1
What is the bacterial capsule made out of?
Role of bacterial capsule?
Prevents drying out and provides protection
How are proteins secreted across the cell membrane (inner membrane)?
Use N-terminal secretion signal + Sec pathway
Complete the blanks:
Bacteria use _____ for mobility. Receptors on the bacterial nose sense chemicals and move towards ______ and away from _________.
__________ rotation of the _______ causes _________ movement. __________ rotation of the _______ causes ___________________
Bacteria use flagella for mobility. Receptors on the bacterial nose sense chemicals and move towards nutrients and away from toxic chemicals.
Counter-clockwise (CCW) rotation of the falgella causes forward movement. Clockwise (CW) rotation of the flagella causes tumbling + changing of direction
What is the signal transduction pathway used by bacteria to sense the environment?
Histidine-aspartate phosphorelay (HAP)
What is Quorom Sensing?
Sensing cell density
Some pathogens switch on their virulence only when cell population is high
Bacteria recognise a 'quorum' by secreting small signal molecules and sensing its concentration (communication)
Segment of DNA containing useful genes that benefit bacteria
Extra-chromosomal genetic elements
(may contain transposons)
Define pathogenicity islands:
Genes required for survival and virulence are usually in pathogenicity islands (higher G+C content)
What are 3 techniques by which bacteria can acquire and transfer DNA?
- From bacteriophage (bacterial virus)
- Uptake from dead (lysed) bacteria
- Direct transfer between 2 bacteria
Direct vs indirect damage:
Direct damage = caused by toxins/bacterial invasion
Indirect damage = caused by host response
What do UPEC use to bind to bladder receptors?
Common (type I) pili
What do UPEC use to bind to kidney receptors?