study the following four statements :

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p) gram negative bacteria produces potent pyrogenic substances called endotoxins

q) ethylene oxide mixed with the CO2 or fluorinated HC is used in gas sterilization

r) D value is the same ( for the heat or chemical exposure ) or the dose ( for radiation exposure ) required for the microbial population to decline by one logarithmic unit

s) spores of geobacillus stearothermophillus are used for the sterility testing of moist heat sterilization process

choose the correct answer

  1. p, q and r are correct but s is wrong
  2. r, q and s are correct but p is wrong
  3. r, s and p are correct but q is wrong
  4. p, q, r and s all are correct


Saraswathi.B's picture


p, q, r and s all are correct


Sterilization is the process used to kill the micro organisms which consist of bacterial spores. It is an highly resistant method which shows absolute absence of all microorganisms.

The Gram-negative bacteria outer layer consist of Lipopolysaccharides (LPS) which are also known as lipoglycans and produces endotoxins. Endotoxin consist of polysaccharide and a lipid which are large molecules with an O-antigen and outer and inner core is connected by covalent bond.

examples: Escherichia coli, Salmonella, Shigella, Pseudomonas, Neisseria, Haemophilus influenzae, Bordetella pertussis and Vibrio cholerae.

Ethylene oxide is used for the production of ethylene glycol and it is an automotive coolant and antifreeze. It is used in the sterilization of the foodstuffs, medical supplies such as bandages, sutures, and surgical implements, kills bacteria, mould, fungi etc. it is an with sweet odour and colourless flammable gas. Ethylene oxide when mixed with the CO2 or fluorinated HC is used in gas sterilization.

The D value in the sterilization refers to the decimal reduction time is the time required at certain temperature to kill the 90% micro organisms . thus the colony is reduced by 1D , only 10% organisms remains . The population number of micro organisms are reduced by one of the decimal place in the counting scheme. The each number of the lot of the sterilization resistant organism is given by the valve D. When the processing to the D value it is proper to give the temperature as a subscript to the D.

Example: if the organism is exposed to the hypothetical organism is reduced by 90% after exposing its temperatures of 300 degree F for 2 minutes, thus the D value would be written as D300 = 2 MINUTES.

The D value determination is often carried out to measure the disinfectants efficiency to reduce the number of the microbes present in the environment.

Geobacillus stearothermophilus which are formerly Bacillus stearothermophilus spores are used for the sterility testing of moist heat sterilization process ( Positive spore test results)

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