Microbiology and infection I Flashcards
What can cause an infection?
Infections can be caused by a range of different microorganisms: bacteria, fungi, protozoa, helminths, virus.
Viruses are not living organisms, but they cause infection and so considered in microbiology.
What are some advantageous features of a bacterium?
- Cell wall – protection from osmotic lysis
- Endospore – Resting
- Fimbriae + Pili – attachment to surfaces
- Flagella – Motility
- Glycocalyx (it is a slippery capsule) – Protection from phagocytes
- Plasma membrane – selective permeability
- Ribosomes – Protein synthesis
What are endotoxins?
Endotoxins are agents of pathogenicity of gram-negative bacteria, implicated in the development of gram-negative shock. They are the lipid portion of the lipopolysaccharide that are part of the outer membrane of the cell wall. The endotoxins are liberated when the bacteria die and the cell wall beaks apart.
Endotoxins cause macrophages to release cytokines which attract clotting factors. This leads to clotting of small capillaries leading to cell death. Antibiotics used to treat gram negative cells can lyse the cell, so the condition of the patient immediately worsens.
- Therefore, it’s harder to treat gram negative cells compared to gram positive cells. Gram negative cells also require a greater concentration of penicillin to treat them in comparison to positive.
At what temperature do thermophiles grow?
Thermophiles at room temperate will not grow, at >400C is the optimum temperate for them to grow. They grow via binary division which means exponential growth with the following requirements:
- Water, temperature, pH, Oxygen, other nutrition
What is the most effective form of sterilisation?
Steam is the most effective at 121 degrees for 15 mins.
What are endospores and why do they need to be considered?
When considering treatment endospores need to be considered; they are resistant and can remain dormant during the treatment. They’d regerminate afterwards and lead to an infection.
What are preservatives and why do they need to be considered?
If the formulation does not need to be sterile then the right quantity of preservatives needs to be added. Preservation does not kill all microorganisms, but it does reduce their numbers and maintains a low microbial level. Sterilisation does remove microorganisms.
Inside of the body is sterile so we need to ensure that anything that passes the skin is sterile
How do you initiate antibiotic treatment? and what is this methods disadvantage?
Identify the organism causing the infection then to target it using antimicrobials. If you don’t know the causative microorganism then you’d use a broad spectrum of treatments which targets a range of infections to quickly treat the virus. You would then find something more specific. However, side effects of this are that you end up killing the bodies useful bacteria instead so could lead to resistant pathogens residing in the gut which will spread the resistance.
How could you prevent resistance?
To prevent resistance, we could use a combination of antimicrobial agents or an alternative agent.
Viruses, fungi, protozoa, and helminths are all prokaryotic cells which can cause side effects as we are all eukaryotic organisms. We try to target the specific organism instead.
What are the five criteria used to identify an effective antimicrobial agent?
- It exhibits selective toxicity to reduce side effects
- Broad spectrum (it’s one treatment for multiple infections but does not affect good bacteria.
- Does not produce hypersensitivity in host e.g., allergies.
- Does not harm normal microbiota
- Does not encourage drug resistance
How is genetic material passed from one bacterium to another?
- Conjugation: Transfer of genes between cells that are in physical contact with one another
- Transduction: Transfer of genes from one cell to another by a bacteriophage
- Transformation: Transfer of cell-free or “naked” DNA from one cell to another
