Q.79. Which one of the following statements about control of microbial growth is NOT correct?
(A) Nonionizing radiation leads to thymine dimers formation in DNA
(B) Spirochetes and mycoplasma can pass through membrane filters ( 0.22 −0.45𝜇 m )
(C) Use of high concentration of salts and sugars to preserve food is a chemical method of microbial control
(D) Thermoduric bacteria can survive pasteurization
The correct answer is (C), as high concentrations of salts and sugars preserve food through physical osmotic dehydration, not a chemical method of microbial control.
Option Analysis
(A) Nonionizing Radiation and Thymine Dimers
Nonionizing radiation, like UV light, causes thymine dimers in DNA by linking adjacent thymine bases, blocking replication and leading to cell death. This statement is correct, as it’s a standard physical method for microbial control.
(B) Spirochetes and Mycoplasma Filtration
Spirochetes (spiral-shaped) and mycoplasma (wall-less, smallest bacteria) have sizes around 0.1-0.3 μm, allowing passage through 0.22-0.45 μm membrane filters used for sterilization. This statement is correct, explaining filtration limits.
(C) Salts/Sugars as Chemical Method (Incorrect)
High salt/sugar concentrations reduce water activity via osmosis, dehydrating microbes physically rather than through chemical reactions like disinfectants. This is a physical preservation method, making the statement wrong.
(D) Thermoduric Bacteria and Pasteurization
Thermoduric bacteria, such as certain Bacillus or Clostridium spores, endure pasteurization temperatures (e.g., 63°C for 30 min) without sporulating but remain viable. This statement is correct, highlighting pasteurization’s limits.
