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.
Chlamydias are
Answer: D
Correct answer: All the above
Chlamydiae are non-motile, obligate intracellular parasites that cannot be grown on cell-free media - they must be cultured in living cells, because they cannot make their own ATP and depend on the host’s. That energy dependence is what defines them.
Please log in or register to report this question.
Dark ground microscopy is used for detection of
Answer: A
Correct answer: spirochetes
Dark-ground (dark-field) microscopy lights the specimen obliquely so that only scattered light enters the objective, making a very thin unstained object shine against a black background. It is the standard way of seeing Treponema pallidum, which is too slender for ordinary bright-field work and stains poorly.
Please log in or register to report this question.
Which of the following is true about the viral envelope?
Answer: D
Correct answer: All the above
All three are true of the viral envelope: it is derived from a host cell membrane as the virus buds out; it is therefore lipoprotein in nature; and it carries projecting spikes (peplomers) of virus-coded glycoprotein, which are what bind the receptor on the next cell. Being lipid, it is destroyed by soap and by ether - which is why enveloped viruses are the easier ones to disinfect.
Please log in or register to report this question.
Killed corpuscular vaccines contain
Answer: C
Correct answer: inactivated bacteria
A killed corpuscular vaccine contains whole bacteria inactivated by heat or chemicals. Nothing multiplies, so it is safe and stable but generally needs a larger dose and booster injections. The old typhoid, cholera and whooping cough vaccines were of this kind.
Please log in or register to report this question.
