Bacterial Properties and Disease Flashcards
Bacterial properties: explain the meaning of the following terms when describing bacterial structure and function; coccus, bacillus, rod, Gram-negative, Gram-positive, acid-fast, aerobic, anaerobic, intra-cellular, extra-cellular Bacterial gene transfer: compare the three main ways bacteria use to exchange genetic material Infectivity and virulence: explain the concepts of infectivity and virulence, and define the term infective dose Bacterial sources and routes: list the potential sources an (46 cards)
Features of bacteria?
Small, unicellular. No internal membrane-bound organelles. Haploid. Some have flagella.
Three bacterial forms?
Cocci bacteria – spherical Bacilli – rod shaped Spirilli – spiral
What is Gram stain used for, and how is it done?
Gram stain technique distinguishes between two different cell wall types. Stained with violet dye and iodine, rinsed in alcohol, stained with red dye.
What are the results of Gram stain that enable us to distinguish type of bacteria? Why, briefly, do each retain/not retain stain?
Gram-positive bacteria retain dye in because of peptidoglycan in cell wall. High peptidoglycan = deep violet. Gram-negative bacteria lose dye because of thinner peptidoglycan and presence of outer membrane. Cells absorb counterstain making them pink.
Structure of Gram-positive and Gram-negative bacteria? What does LPS do?
Gram positive = single membrane Cell wall is on extracellular surface which contain peptidoglycan and other proteins. Gram negative = double membrane Periplasm sandwiched between membranes contains peptidoglycan. Extracellular part of cell wall is predominantly lipopolysaccharide (or LPS) – extremely potent for our innate immune system. Immune system receptors are very sensitive to LPS – initiating pro-inflammatory response. So LPS can be dangerous in high quantities.
Name 5 pathogenic Gram negative bacteria?
Escherichia coli (diarrhea, dysentery, kidney failure) Salmonella (‘-typhimurium’ – food poisoning, or ‘-typhi’ – typhoid) Shigella (dysentery – inflammatory disease of intestines) Vibrio cholerae (cholera) Neisseria (‘-meningitidis’ – meningitis, or ‘-gonorrhoeae’ – gonorrhoea)
Name 4 pathogenic Gram positive bacteria?
Staphylococcus aureus (skin diseases, joint diseases, pneumonia)
Streptococcus pneumoniae (pneumonia, meningitis)
Streptococcus pyogenes (tonsilitis, necrotizing fasciitis (flesh-eating bacteria)).
Clostridium (difficile).
What are Myobacteria? Name 2 bacteria?
Evolutionary distinct from Gram +/-. Mycobacterium tuberculosis (TB) Mycobacterium leprae (leprosy)
What do bacterial pathogens need to be adapted for?
CPR in Washington DC Adapted to colonize (surface structures), Persist (avoid host defences), Replicate (acquire nutrients through complex mechanisms e.g. acquire iron which is very low in blood), Disseminate (between cells (being mobile)/between hosts (air-borne, faeces)), Cause disease (produce toxins).
Two ways bacteria colonise host? 3 ways intracellular pathogen survives?
Extracellular replicates outside cell. Intracellular replicates inside cell. [Links with adaptations] Access cell in phagosome (1) Escape phagosome (2) Prevent fusion with lysosomes (3) Survive in phagolysosome
Method of getting into cells – in the case of Salmonella?
Flagella propels bacterium to cell. Injectisome makes translocase complex (hollow pore) in membrane – pump virulence (harmful) proteins across its own membrane and that of host cell. Proteins interfere with actin proteins, causing actin polymerisation membrane ruffling and bacterial internalisation. Allows to invade cells which are not naturally phagocytic.
Recap of previous Q: what are the 2 main functions of injectisomes pathogenically?
Pump pathogenic proteins into cell – contributes to virulence. Manipulates actin for entry into cell.
Method of manipulating actin – in the case of Listeria?
On tip of bacterium, actin polymerisation triggered which provides propulsive force for bacteria to move inside and between cells (they can propel themselves across membrane by pushing membrane of host cell against membrane of another cell so cell membrane of host cell and the bacterium engulfed into invaded cell).
How do bacteria replicate? What is this type of DNA transmission called?
Binary fission. Vertical transmission of DNA. Means daughter cells identical parent.
How does variation occur vertically?
Mutation
3 mechanisms bacteria can exchange DNA?
Transformation Conjugation Transduction Horizontal transmission of DNA.
What is transformation?
DNA uptake Suck up DNA from extracellular space and integrate into its own. Single stranded DNA segment (naked DNA).
What is conjugative transfer?
Transfer from one cell directly to another across a mating bridge. In the form of a plasmid (circular, self-replicating DNA). Plasmid is replicated as it passes across bridge, so plasmid retained in original cell, and injected into other.
What is phage transduction?
Phage (short for bacteriophage – a virus that parasitizes a bacterium) replicates its DNA in bacterium and cuts bacterial DNA into small pieces. The short DNAs are packaged into phage heads – of which some bacterial DNA is picked up. Bacterium lyses and phages released. Phage injects obtained bacterial DNA into new bacterial cell – injected DNA may be incorporated into bacterial chromosome.
What is purpose of horizontal DNA transfer?
Bacteria gain accessory genes which drives evolution – brings variation. Contributes to virulence.
How do accessory proteins contribute to virulence?
Import pathogenicity islands – chunks of DNA that contribute to virulence e.g. producing a toxin, making an injectosome.
What is virulence?
The severity or harmfulness of a disease
What is infectivity?
Ability of an agent to infect. The characteristic of a disease agent that embodies capability of entering, surviving in, and multiplying and causing disease in a susceptible host.
Possible sources of bacterial infection: two types?
Intrinsic – bacteria inside us.
Extrinsic – outside.
