BRAINCAKEBacteria and Disease
Revision notes for Bacteria and Disease in Edexcel Biology (9BI0). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- Culturing MicroorganismsMicroorganisms such as bacteria and fungi can be grown in the laboratory in a culture medium, a mixture that supplies everything they need to grow…
- Aseptic Culture TechniquesAseptic technique is a set of procedures that prevents unwanted microorganisms contaminating a culture, and stops the cultured microorganisms…
- Selective MediaMany samples contain a mixture of microorganisms.
- Growing a Pure CultureA pure culture contains only one species (or strain) of microorganism.
- Counting the Number of CellsMicrobiologists often need to know how many cells are in a culture, for example to follow its growth over time.
- TurbidityAs bacteria multiply in a liquid broth, the broth becomes cloudy, or turbid.
- Dilution PlatingDilution plating gives a viable count: it counts only cells that are alive and able to divide.
- Area and Mass of FungiMoulds such as Penicillium grow as long, branching threads called hyphae, which form a tangled network called a mycelium.
- Growth of Bacterial ColoniesWhen bacteria are put into fresh nutrient broth in a closed culture (no nutrients added and no waste removed), the population follows a typical…
- Logarithmic ScaleBacterial populations can grow from a few hundred cells to billions in a day.
- Exponential GrowthBacteria reproduce by binary fission: one cell divides into two.
- Bacterial ToxinsPathogenic bacteria cause disease in two main ways: by invading and damaging host tissues, and by producing toxins.
- EndotoxinsEndotoxins are lipopolysaccharides (LPS): molecules made of a lipid part joined to a chain of carbohydrate.
- Salmonella spp.Salmonella species are rod-shaped, Gram-negative bacteria.
- ExotoxinsExotoxins are soluble proteins made by living bacteria and secreted into their surroundings.
- Staphylococcus spp.Staphylococcus species are Gram-positive, spherical bacteria (cocci) that grow in grape-like clusters.
- Host Tissue InvasionTo cause disease, many bacteria must first enter the body and invade host tissues.
- Mycobacterium tuberculosisMycobacterium tuberculosis is the rod-shaped bacterium that causes tuberculosis (TB).
- AntibioticsAn antibiotic is a chemical that kills bacteria or inhibits their growth, without harming the cells of the host.
- Broad-spectrum, Narrow spectrum, Bacteriostatic and BactericidalAntibiotics can be described in two separate ways: by the range of bacteria they act on, and by what they do to the bacteria.
- AntimetabolitesAn antimetabolite is a substance that interferes with a normal metabolic pathway, usually because it has a similar shape to one of the pathway's…
- Protein synthesis InhibitorsBacteria have 70S ribosomes, made of a small 30S subunit and a large 50S subunit.
- Cell Wall AgentsBacterial cells are surrounded by a cell wall made of peptidoglycan (murein): long polysaccharide chains held together by short peptide cross-links.
- Cell Membrane AgentsThe cell membrane (plasma membrane) of a bacterium controls what enters and leaves the cell.
- DNA Gyrase InhibitorsBacterial DNA is a long, circular molecule packed into a small cell.
- Antibiotic ResistanceAntibiotic resistance means that an antibiotic no longer kills or inhibits the growth of a bacterium at the doses normally used.
- Creating Drug-Resistant BacteriaAntibiotics do not cause resistance mutations, but they select for bacteria that already carry them.
- MRSAMRSA stands for methicillin-resistant Staphylococcus aureus.
- Clostridium difficileClostridium difficile (often called C. difficile or C. diff) is a Gram-positive, rod-shaped, anaerobic bacterium that forms spores.
- Prevention and Control of InfectionHospitals have strict codes of practice to prevent and control healthcare-associated infections (HCAIs), such as MRSA and C. difficile.