Obligate anaerobes are killed by exposure to oxygen mainly because they lack:

Superoxide dismutase and catalase

Tubes of thioglycollate broth with resazurin have been stored for 3 weeks. The upper half of each tube is now pink, and a Clostridium control grew poorly in one of them. What should be done with the remaining tubes?

Heat once in a boiling water bath, then cool undisturbed

Shake each tube to mix the reduced layer upwards

Add more agar so that oxygen cannot diffuse in

Incubate the tubes in a CO2 incubator before use

A lawn (carpet) culture, in which the inoculum is spread evenly over the whole plate, is used mainly for:

Disk diffusion tests and phage typing

Counting viable bacteria in a sample

Isolating colonies from mixed growth

Showing motility in a semisolid medium

Bacterial nutrition, growth and culture

33 Kerala MSc MLT Entrance practice questions on Bacterial nutrition, growth and culture, part of Microbiology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Obligate anaerobes are killed by exposure to oxygen mainly because they lack:
1. ACytochrome oxidase
2. BBeta-galactosidase
3. CSuperoxide dismutase and catalase
4. DNitrate reductase
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Answer: C · Superoxide dismutase and catalase
When oxygen is present, cells form toxic superoxide radicals and hydrogen peroxide. Aerobes destroy these with superoxide dismutase and catalase or peroxidase. Strict anaerobes lack these enzymes, so the toxic products build up and kill them. Specimens for anaerobic culture must therefore be protected from air.
- A: Lacking cytochrome oxidase does not by itself make oxygen toxic.
- B: Beta-galactosidase concerns lactose use.
- D: Nitrate reductase is a respiration enzyme unrelated to oxygen toxicity.
Question 2 · Easy
A basal medium to which blood or serum is added so that fastidious bacteria can grow is called an:
1. AAnaerobic medium
2. BEnriched medium
3. CEnrichment medium
4. DIndicator medium
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Answer: B · Enriched medium
Enriched media are basal media with extra nutrients such as blood, serum or egg, which let fastidious organisms grow. Blood agar, chocolate agar and Loeffler's serum slope are examples. An enrichment medium is a liquid medium that favours one organism over the competing flora, such as selenite F broth. The similar names are a common source of confusion.
- A: Anaerobic media contain reducing agents to remove oxygen.
- C: Enrichment media are liquid media that suppress competing flora.
- D: Indicator media contain a substance that changes colour with growth.
Question 3 · Easy
In a batch culture, the phase in which bacteria enlarge and make enzymes but do not yet divide is the:
1. AStationary phase
2. BLag phase
3. CDecline phase
4. DLog phase
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Answer: B · Lag phase
After inoculation, bacteria adapt to the new medium by making the enzymes and building blocks they need. Cells grow in size but the count does not rise. The cells reach their largest size towards the end of the lag phase. The length of the lag depends on the inoculum's age and on how different the new medium is.
- A: In the stationary phase division and death are balanced.
- C: In the decline phase the viable count falls.
- D: In the log phase cells divide at a constant, maximal rate.
Question 4 · Hard
Tubes of thioglycollate broth with resazurin have been stored for 3 weeks. The upper half of each tube is now pink, and a Clostridium control grew poorly in one of them. What should be done with the remaining tubes?
1. AShake each tube to mix the reduced layer upwards
2. BAdd more agar so that oxygen cannot diffuse in
3. CIncubate the tubes in a CO2 incubator before use
4. DHeat once in a boiling water bath, then cool undisturbed
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Answer: D · Heat once in a boiling water bath, then cool undisturbed
Resazurin is pink when oxidized, so the pink layer shows dissolved oxygen. When more than about the upper third is pink, the medium can be restored once by heating in a boiling water bath to drive off oxygen. The tubes are then cooled without shaking. If they oxidize again, they should be discarded.
- A: Shaking mixes more oxygen into the broth.
- B: Adding agar to finished medium is not done and would not remove oxygen.
- C: CO2 incubation does not remove the dissolved oxygen.
Question 5 · Medium
A lawn (carpet) culture, in which the inoculum is spread evenly over the whole plate, is used mainly for:
1. ACounting viable bacteria in a sample
2. BDisk diffusion tests and phage typing
3. CIsolating colonies from mixed growth
4. DShowing motility in a semisolid medium
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Answer: B · Disk diffusion tests and phage typing
A lawn gives uniform, confluent growth over the plate. Zones of inhibition around antibiotic disks, or clear plaques where phages lyse the bacteria, can then be read. It is also used to grow large amounts of one organism for antigens. Isolation needs a streak plate, and counting needs a pour or spread plate of a dilution.
- A: Viable counts need a pour or spread plate of a known dilution.
- C: Isolated colonies need a streak plate.
- D: Motility is shown by a stab into semisolid agar.
Question 6 · Medium
In Robertson's cooked meat broth, what mainly keeps the conditions anaerobic?
1. AA palladium catalyst placed in the tube
2. BHaemin released from the cooked muscle
3. CSulphydryl compounds and unsaturated fats in the meat
4. DSodium thioglycollate added to the broth
Answer and explanation in LearnFree account
Question 7 · Hard
A laboratory keeps its QC strains on agar slopes at 4 °C. The Neisseria gonorrhoeae and Haemophilus influenzae stocks are repeatedly found dead within a week. The best way to keep them is to:
1. AKeep them on chocolate slopes at 4 °C under paraffin oil
2. BSubculture them every month onto blood agar slopes
3. CStore sealed plates at 4 °C for each new batch
4. DFreeze them in broth with 15% glycerol at -70 °C
Answer and explanation in LearnFree account
Question 8 · Medium
Proteus spreading over a blood agar plate hides the other colonies in a mixed culture. Which change to the blood agar prevents this swarming?
1. ARaising the agar concentration to about 6%
2. BIncubating the plate in 5-10% CO2
3. CAdding more blood to make it 10%
4. DUsing horse blood instead of sheep blood
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Question 9 · Hard
Broth is inoculated with 2 x 10^3 bacteria/mL. After a lag of 1 hour the organism grows exponentially, with a generation time of 30 minutes. What count is expected 4 hours after inoculation?
1. A1.2 x 10^4/mL
2. B5.12 x 10^5/mL
3. C1.6 x 10^4/mL
4. D1.28 x 10^5/mL
Answer and explanation in LearnFree account
Question 10 · Easy
Which method preserves bacterial stock cultures for the longest time, often for decades?
1. ASealing slopes under paraffin oil
2. BLyophilisation (freeze-drying)
3. CStorage of slopes at 4 °C
4. DMonthly subculture on fresh slopes
Answer and explanation in LearnFree account
Question 11 · Medium
A candle jar is used for culturing Neisseria gonorrhoeae because the burning candle provides:
1. AComplete removal of oxygen from the jar
2. BExtra moisture alone to prevent drying
3. CAbout 3% carbon dioxide with some oxygen left
4. DA hydrogen-rich atmosphere for anaerobes
Answer and explanation in LearnFree account
Question 12 · Easy
Deoxycholate citrate agar (DCA) is used in stool culture mainly to isolate:
1. AShigella and Salmonella
2. BCampylobacter jejuni
3. CVibrio cholerae
4. DClostridioides difficile
Answer and explanation in LearnFree account
Question 13 · Medium
Cary-Blair medium is used to:
1. AGrow mycobacteria from decontaminated sputum
2. BTransport urethral swabs for gonococci
3. CEnrich Salmonella from stool before plating
4. DTransport stool specimens for enteric pathogens
Answer and explanation in LearnFree account
Question 14 · Hard
A 12-year-old girl has diarrhoea and right lower abdominal pain suggesting appendicitis. Routine stool culture at 37 °C is negative. Her stool is kept in phosphate-buffered saline at 4 °C and subcultured weekly. Which organism is this method meant to recover?
1. AYersinia enterocolitica
2. BShigella sonnei
3. CCampylobacter jejuni
4. DSalmonella Typhimurium
Answer and explanation in LearnFree account
Question 15 · Easy
The usual concentration of agar used to make a solid culture medium such as nutrient agar is:
1. A10-12%
2. B1-2%
3. C0.1-0.2%
4. D5-6%
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Question 16 · Medium
Peptone water with 8% sodium chloride supports growth of the organism isolated from a patient with diarrhoea after eating raw shellfish, while 0% NaCl does not. This organism is:
1. AShigella flexneri
2. BVibrio parahaemolyticus
3. CVibrio cholerae O1
4. DEscherichia coli
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Question 17 · Medium
In peptone water sugar containing Andrade's indicator and an inverted Durham's tube, fermentation with acid and gas is shown by:
1. AA colourless medium with a pellicle on the surface
2. BA blue medium with the Durham's tube completely filled
3. CA pink medium with a gas bubble in the Durham's tube
4. DA yellow medium with a black precipitate at the bottom
Answer and explanation in LearnFree account
Question 18 · Hard
Three isolates are inoculated into tubes of thioglycollate broth. After 48 hours, isolate 1 grows only as a film at the surface, isolate 2 only in a narrow band a few millimetres below the surface, and isolate 3 only at the bottom of the tube. Which isolate is most likely Campylobacter jejuni?
1. AIsolate 1, an obligate aerobe
2. BIsolate 3, an obligate anaerobe
3. CNone, as it grows evenly throughout
4. DIsolate 2, a microaerophile
Answer and explanation in LearnFree account
Question 19 · Easy
In Lowenstein-Jensen medium, the ingredient that inhibits contaminating bacteria is:
1. AMalachite green
2. BGlycerol
3. CWhole egg
4. DAsparagine
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Question 20 · Medium
Campylobacter jejuni is isolated from stool by incubating selective media under:
1. AOrdinary air at 37 °C for 18 hours
2. BAir with 5% CO2 at 25 °C
3. CStrict anaerobic conditions at 37 °C
4. DAbout 5% oxygen and 10% CO2 at 42 °C
Answer and explanation in LearnFree account
Question 21 · Medium
Thayer-Martin medium for endocervical swabs is made selective for pathogenic Neisseria by adding:
1. AMalachite green and glycerol
2. BPotassium tellurite and cystine
3. CBile salts and crystal violet
4. DVancomycin, colistin and nystatin
Answer and explanation in LearnFree account
Question 22 · Hard
A new batch of chocolate agar is tested. Streptococcus pneumoniae grows well, but Haemophilus influenzae ATCC 49247 does not grow. The worksheet shows that the blood was added to the base at 50 °C and the plates were poured at once. What is the most likely error?
1. AThe base was autoclaved for too long and burnt
2. BThe H. influenzae control needs X factor only
3. CThe plates were incubated without added CO2
4. DThe blood was not heated enough to release V factor
Answer and explanation in LearnFree account
Question 23 · Medium
Penicillin and other cell wall-active antibiotics kill bacteria most effectively when the cells are in which growth phase?
1. ADecline (death) phase
2. BLog (exponential) phase
3. CStationary phase
4. DLag phase
Answer and explanation in LearnFree account
Question 24 · Medium
Selenite F broth, used for stool specimens from suspected enteric fever, is best classed as:
1. AA differential medium
2. BA transport medium
3. CAn enriched medium
4. DAn enrichment medium
Answer and explanation in LearnFree account
Question 25 · Hard
A 5-year-old unvaccinated child has fever and a greyish membrane over the tonsils. The clinician wants a culture result the same day so that granules can be stained from the growth. Which medium should be inoculated first?
1. APotassium tellurite blood agar
2. BMacConkey agar
3. CLowenstein-Jensen medium
4. DLoeffler's serum slope
Answer and explanation in LearnFree account

8 more Bacterial nutrition, growth and culture questions

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Study Microbiology

Bacterial nutrition, growth and culture

Obligate anaerobes are killed by exposure to oxygen mainly because they lack:

A basal medium to which blood or serum is added so that fastidious bacteria can grow is called an:

In a batch culture, the phase in which bacteria enlarge and make enzymes but do not yet divide is the:

Tubes of thioglycollate broth with resazurin have been stored for 3 weeks. The upper half of each tube is now pink, and a Clostridium control grew poorly in one of them. What should be done with the remaining tubes?

A lawn (carpet) culture, in which the inoculum is spread evenly over the whole plate, is used mainly for:

In Robertson's cooked meat broth, what mainly keeps the conditions anaerobic?

A laboratory keeps its QC strains on agar slopes at 4 °C. The Neisseria gonorrhoeae and Haemophilus influenzae stocks are repeatedly found dead within a week. The best way to keep them is to:

Proteus spreading over a blood agar plate hides the other colonies in a mixed culture. Which change to the blood agar prevents this swarming?

Broth is inoculated with 2 x 10^3 bacteria/mL. After a lag of 1 hour the organism grows exponentially, with a generation time of 30 minutes. What count is expected 4 hours after inoculation?

Which method preserves bacterial stock cultures for the longest time, often for decades?

A candle jar is used for culturing Neisseria gonorrhoeae because the burning candle provides:

Deoxycholate citrate agar (DCA) is used in stool culture mainly to isolate:

Cary-Blair medium is used to:

A 12-year-old girl has diarrhoea and right lower abdominal pain suggesting appendicitis. Routine stool culture at 37 °C is negative. Her stool is kept in phosphate-buffered saline at 4 °C and subcultured weekly. Which organism is this method meant to recover?

The usual concentration of agar used to make a solid culture medium such as nutrient agar is:

Peptone water with 8% sodium chloride supports growth of the organism isolated from a patient with diarrhoea after eating raw shellfish, while 0% NaCl does not. This organism is:

In peptone water sugar containing Andrade's indicator and an inverted Durham's tube, fermentation with acid and gas is shown by:

Three isolates are inoculated into tubes of thioglycollate broth. After 48 hours, isolate 1 grows only as a film at the surface, isolate 2 only in a narrow band a few millimetres below the surface, and isolate 3 only at the bottom of the tube. Which isolate is most likely Campylobacter jejuni?

In Lowenstein-Jensen medium, the ingredient that inhibits contaminating bacteria is:

Campylobacter jejuni is isolated from stool by incubating selective media under:

Thayer-Martin medium for endocervical swabs is made selective for pathogenic Neisseria by adding:

A new batch of chocolate agar is tested. Streptococcus pneumoniae grows well, but Haemophilus influenzae ATCC 49247 does not grow. The worksheet shows that the blood was added to the base at 50 °C and the plates were poured at once. What is the most likely error?

Penicillin and other cell wall-active antibiotics kill bacteria most effectively when the cells are in which growth phase?

Selenite F broth, used for stool specimens from suspected enteric fever, is best classed as:

A 5-year-old unvaccinated child has fever and a greyish membrane over the tonsils. The clinician wants a culture result the same day so that granules can be stained from the growth. Which medium should be inoculated first?