Bacteriology Flashcards
What are biofilms?
Complex multicellular communities that bacteria live in usually in association with eukaryotes
Define Trachoma
Infectious blindness usually caused by a bacterial infection of Chlamydia (STI)
Difference with Gram Negative and Positive bacteria, as illustrated by the Gram Stain
Gram positive bacteria has a thicker peptidoglycan wall (150-500 angstroms thick) and gram negative bacteria has an extra (outer) membrane. Note that both also have a cell membrane (phospholipid bilayer)
Name 2 medically important bacteria that do not gram stain
1) Mycobacteria - causes TB. Called acid fast, as they’re difficult to stain and destain because of their waxy lipid coat
2) Chlamydia and Mycoplasma - Non-gonococcal urethritis, lack a cell wall. Difficult to culture and insensitive to many antibiotics.
O-Antigens
Found on the lipopolysaccharide of the outer membrane. Highly variable, generates different antigens and therefore serotypes. An important defence against host attacks.
Periplasm
Found in the between two membranes of Gram Negative bacteria. Composed of hydrolytic enzymes (proteases/lipases/phosphatases/B-lactamases). Also contains components of transport systems.
What happens to drugs in the stationary phase?
They are not inactive - undergo changes in physiology and gene expression to enable survival and reduce susceptibility to many antibiotics.
Facultative Anaerobes (Salmonella/Staphylococcus)
Pathogenic bacteria that can grow with and without oxygen. When growing aerobically, bacteria use glycolysis, citric acid cycle, and oxidative phosphorylation in order to generate ATP from glucose. Anaerobic respiration = Fermentation
How do bacteria display chemotaxis?
Detect chemical signals and move towards or away from them. Mediated by chemoreceptors at the nose the cell which detect signals, and transmit information via phosphorelay to flagella motor switch. Switch determines the direction in which the helical propeller rotates - counterclockwise to swim / clockwise to randomly tumble and change direction
Histidine-Aspartate-Phosphorelay (HAP) signalling pathway
Signal transduction system which rapidly detects changes in the environment, facilitated by the large surface area to volume ratio of bacterial cells
Cell Density / Quorum Sensing
Special signal whereby some pathogens will switch on virulence genes when its population reaches a specific density. Bacteria recognise a quorum by secreting a small signal molecule and sensing its concentration
Pathogenicity islands
Genes required for infection and survival in the host are grouped together on the chromosome, in the form of pathogenicity islands. Evolved through integration of transposons, plasmids, bacteriophage and incorporation of transformed DNA.
How does bacteria acquire + transfer DNA
- Transformation - uptake of DNA from dead/lysed bacteria
- Transduction - by bacterial virus/bacteriophage
- Conjugation - direct contact between bacteria
