ICAR AICE-JRF/SRF General Microbiology: practice questions

1 · History and scope of microbiology · hard

Pure starter cultures replaced spontaneous souring of cream for butter making in northern Europe around:

1. 1790
2. 1890
3. 1950
4. 1840

2 · History and scope of microbiology · hard

Which concern of dairy microbiology is addressed mainly by the selection, propagation and protection of starter cultures?

1. Safety from pathogens
2. Fermentation
3. Spoilage by psychrotrophs
4. Water activity of powders

3 · Microscopy: light, phase, fluorescence and electron · hard

Which instrument would best show the three-dimensional surface of a biofilm on a stainless-steel coupon at high magnification?

1. Transmission electron microscope
2. Bright-field light microscope
3. Dark-field condenser on a light microscope
4. Scanning electron microscope

4 · Bacterial cell structure: wall, membrane, capsule, flagella, spores · hard

The extreme heat resistance of bacterial endospores is attributed chiefly to:

1. A thick outer membrane of lipopolysaccharide that excludes water at high temperature
2. Very high concentrations of catalase and superoxide dismutase in the spore coat
3. Plasmids that carry heat-shock genes expressed only during sporulation
4. A dehydrated core with calcium dipicolinate and DNA-protecting proteins

5 · Bacterial cell structure: wall, membrane, capsule, flagella, spores · hard

Late blowing of hard cheeses is traced to spores that survive pasteurisation. Their usual source on the farm is:

1. Teat dips containing iodophor at high concentration
2. Water used to wash the bulk tank after milking
3. Concentrate feeds that were dried at high temperature before feeding
4. Silage contaminated with Clostridium tyrobutyricum spores

6 · Bacteriophages · hard

CRISPR–Cas systems protect bacteria against phages by:

1. Modifying the cell-wall receptor so that phages cannot adsorb
2. Killing the infected cell before progeny phages can be assembled
3. Storing phage DNA spacers and cutting matching DNA on reinfection
4. Methylating host DNA so that the phage restriction enzyme ignores it

7 · Bacteriophages · hard

A starter strain carrying an inducible prophage can still cause phage problems in a plant because:

1. Prophages make the strain resistant to all other dairy phages
2. Lysogens cannot ferment lactose until the prophage is lost
3. Induced prophages release phages able to infect other strains
4. Prophage DNA is destroyed by pasteurisation of the milk

8 · Microbial metabolism: respiration and fermentation · hard

A Gram-negative rod from pasteurised milk gives the IMViC pattern + + − −. It is most likely:

1. Enterobacter aerogenes
2. Escherichia coli
3. Pseudomonas fluorescens
4. Klebsiella pneumoniae

9 · Microbial genetics: mutation, plasmids, transformation, conjugation, transduction · hard

Ultraviolet light causes mutations mainly by forming:

1. Double-strand breaks across the whole chromosome
2. Alkylated guanine residues
3. Thymine dimers between adjacent pyrimidines
4. Deaminated adenine residues

10 · Sterilisation and disinfection · hard

A sanitiser reduces a test organism with a D value of 0.5 min. How long must surfaces be exposed to achieve a 5-log reduction?

1. 0.1 min
2. 5.0 min
3. 2.5 min
4. 10.0 min