Growth factors are
Answer: D
Correct answer: Essential substances that bacteria cannot synthesise for themselves
A growth factor is an organic compound - a vitamin, amino acid, purine or pyrimidine - that an organism must have but cannot make, so it has to be supplied in the medium. Mineral salts and the bulk elements are nutrients, but they are not growth factors.
Please log in or register to report this question.
Which of the following is a simple staining method
Answer: D
Correct answer: Burri
A simple stain uses a single dye and shows shape and arrangement without distinguishing types of cell. Burri’s India-ink method is of that kind - strictly a negative stain, colouring the background rather than the cell. Gram, Neisser and Ziehl-Neelsen are all differential stains, using more than one reagent to separate one group of organisms from another.
Please log in or register to report this question.
The covalent bond which links the cell walls of gram-positive bacteria containing two modified sugars - N - acetylmuramic acid (NAM) and N-acetyl glucosamine (NAG) is
Answer: B
Correct answer: 1,4-glycosidic bond
The glycan backbone is an alternating chain of NAM and NAG joined by β-1,4-glycosidic bonds - the same linkage as in cellulose and chitin. It is precisely this bond that lysozyme hydrolyses, which is why tears and saliva can lyse many bacteria.
Please log in or register to report this question.
The function of an adjuvant in a vaccine is
Answer: C
Correct answer: antigenicity
An adjuvant makes the antigen more immunogenic: it holds the antigen at the injection site so that it is released slowly, and it provokes a local inflammatory response that draws in and activates antigen-presenting cells. The result is a stronger and longer-lasting response to the same amount of antigen.
Please log in or register to report this question.
Gram-positive microorganisms appear
Answer: A
Correct answer: violet color
Gram-positive cells keep the primary stain, so they appear violet or purple. The safranin counterstain is applied afterwards but is masked by the darker dye already held.
Please log in or register to report this question.
Active immunity is not acquired by
Answer: C
Correct answer: immunoglobulin transfer
Receiving ready-made immunoglobulin gives passive immunity: the recipient’s own immune system never responds, so no memory is left and the protection fades within weeks. Active immunity is what the body builds for itself - after an infection, a subclinical infection, or a vaccination.
Please log in or register to report this question.
Differential media contain all of the following EXCEPT
Answer: B
Correct answer: Substances that inhibit microorganisms
A differential medium contains a basal medium, the substrate in question (often a sugar) and an indicator to reveal what has been done to it - it lets everything grow and tells the colonies apart. Inhibitory substances belong to a selective medium, whose purpose is the opposite: to stop unwanted organisms growing at all.
Please log in or register to report this question.
The spore has
Answer: D
Correct answer: all of the above
The spore is built in layers: an inner membrane round the core, a cortex of modified peptidoglycan between two membranes, and an outer keratin-like coat of protein - with an exosporium outside that in some species. Each layer contributes to its extraordinary resistance.
Please log in or register to report this question.
Lysis reaction is a
Answer: D
Correct answer: all of the above
A lysis reaction is antibody plus complement dissolving a cell, and it is named after whatever is dissolved: haemolysis of red cells, spirochaetolysis of spirochaetes, vibriolysis of vibrios. The mechanism is the same in each - the membrane attack complex of complement.
Please log in or register to report this question.
H antigen is a
Answer: C
Correct answer: flagellar antigen
H is the flagellar antigen, from the German Hauch, the spreading film that motile organisms make on a plate. It is protein - flagellin - and heat labile, unlike the O antigen, which is polysaccharide and heat stable.
Please log in or register to report this question.
