Culturing and controlling microorganisms
Culturing a bacterium in the laboratory is, at heart, a matter of feeding it and keeping an eye on it. Controlling its growth — in a hospital, in a yoghurt factory or in your own fridge — means stopping it from growing where it is not wanted. And understanding why some bacteria no longer respond to antibiotics is one of the public health emergencies of this century.
Culture media and aseptic technique
If you rub a sterile swab over a clean table and then wipe it over an empty glass dish, you see no change the next day; but if you rub it over a plate of gelatine at 25 °C, dozens of shiny spots appear that are visible to the naked eye: what exactly does a bacterium need to multiply outside its natural environment?
What is a culture medium and which conditions (nutrients, temperature, pH, oxygen) are controlled when culturing bacteria in the laboratory? State the difference between…
What is a culture medium and which conditions (nutrients, temperature, pH, oxygen) are controlled when culturing bacteria in the laboratory? State the difference between a solid and a liquid medium.
Explain what aseptic technique is in the microbiology laboratory and discuss the purpose of two specific practices: flaming the inoculating loop until it is red hot and…
Explain what aseptic technique is in the microbiology laboratory and discuss the purpose of two specific practices: flaming the inoculating loop until it is red hot and working close to the burner.
Viruses do not grow on agar plates. Discuss why (what do they lack in order to multiply on their own?) and indicate which systems laboratories use to culture them (cell…
Viruses do not grow on agar plates. Discuss why (what do they lack in order to multiply on their own?) and indicate which systems laboratories use to culture them (cell cultures, embryonated eggs).
The bacterial growth curve
The graph represents the growth curve of a closed bacterial culture, with its four phases labelled with numbers (1 to 4). Name each phase and explain what happens to…
The graph represents the growth curve of a closed bacterial culture, with its four phases labelled with numbers (1 to 4). Name each phase and explain what happens to nutrients and waste in each.
A bacterium divides every $20$ minutes. Starting from $1\,000$ cells in the exponential phase, calculate how many there will be after two hours (how many generations fit…
A bacterium divides every $20$ minutes. Starting from $1\,000$ cells in the exponential phase, calculate how many there will be after two hours (how many generations fit in?). Then discuss why exponential growth cannot be sustained in a closed culture (which factors slow it down?).
Sterilisation, disinfection and food preservation
A sealed tin can last for years at room temperature without going off, opened milk in the fridge lasts only a few days, and bleach cleans worktops but would damage the skin of a wound: why can't we use the same procedure to preserve food, clean objects or treat a patient?
Differentiate between sterilisation, disinfection, and antisepsis, and give an example of a situation (operating theatre, kitchen worktop, superficial wound) in which…
Differentiate between sterilisation, disinfection, and antisepsis, and give an example of a situation (operating theatre, kitchen worktop, superficial wound) in which each is applied.
Name four methods of microbial control in the food industry (pasteurisation, UHT sterilisation, refrigeration and freezing, salting or curing) and explain the principle…
Name four methods of microbial control in the food industry (pasteurisation, UHT sterilisation, refrigeration and freezing, salting or curing) and explain the principle each one is based on (does it kill, inhibit or hinder growth?).
Explain what pasteurisation consists of (temperature and time, for example $72\ \text{°C}$ for $15$ seconds), why it does not sterilise the food (what survives?) and…
Explain what pasteurisation consists of (temperature and time, for example $72\ \text{°C}$ for $15$ seconds), why it does not sterilise the food (what survives?) and which historical diseases it helped control in milk (tuberculosis, brucellosis).
Antibiotics, resistance and the antibiogram
Distinguish between a bactericidal and a bacteriostatic antibiotic, give an example of each type (penicillin versus tetracyclines) and explain what happens to the…
Distinguish between a bactericidal and a bacteriostatic antibiotic, give an example of each type (penicillin versus tetracyclines) and explain what happens to the bacterial population when each one is discontinued.
What is an antibiogram and how is it performed (antibiotic discs on the inoculated plate)? Explain what it tells the doctor (sensitive, intermediate, resistant) and why…
What is an antibiogram and how is it performed (antibiotic discs on the inoculated plate)? Explain what it tells the doctor (sensitive, intermediate, resistant) and why an antibiotic should not be prescribed without this information when it is possible to obtain it.
Explain, using natural selection, how a bacterial population resistant to an antibiotic arises when treatment is stopped early, and why the antibiotic does not 'create'…
Explain, using natural selection, how a bacterial population resistant to an antibiotic arises when treatment is stopped early, and why the antibiotic does not 'create' resistance.