Disinfectants Effectiveness

Which disinfectant is the most effective

The disinfectant that is most effective is A. The purpose of the culture medium used in the test is supposed to neutralize the test substance active in the carrier or stainless steel cylinders. The culture should recover any surviving test organism. What is basically evaluate in the use dilution test is the absence or presence of growth. The disinfectant should display effectiveness by killing bacteria or any other foreign microorganism on a pre-determined number of carriers that are inoculated. Effectiveness is demonstrated by lack of growth in the varying concentrations of the disinfectants. Using table 7.5. growth for disinfectant A was witnessed in the third concentration level used for the Gram-positive bacteria and for the second concentration level used for the Gram-negative bacteria. 

The gram-positive bacteria stain the cells purple as they have a thick cell wall made of peptidoglycan (a protein). The gram-positive bacteria are supposed to maintain the purple or the violet color. On the other hand, the gram-negative do not retain the violet stain, it is gets a pink stain, as they contain a thin peptidoglycan layer which is sandwiched between the periplasmic space and also the outer membrane and the plasma membrane. The gram-positive bacteria are ‘good’ in nature as they help in some of the body processes such as digestion. Disinfectant A displaying no growth in gram-positive means the body is well protected. Disinfectant B on the other hand shows early growth for gram-positive bacteria which is a sign of ineffectiveness. The growth of gram-negative for both disinfectants is similar. Most of the gram-negative bacteria are harmful to the body and are a source of illnesses such as food-borne diseases and cholera. Both of the disinfectants are quite ineffective with respect to gram-negative bacteria as there are early signs of growth in the early concentration or dilution levels. 


Against which group of bacteria is disinfectant A most effective?

Disinfectant A is most effective in Gram-positive bacteria. The gram-positive bacteria contain a thick layer (20 – 80 nm) of protein (peptidoglycan) that enables it to retain the purple stain thus having a high resistance to physical disruption and inhibition by basic dyes. The peptidoglycan for the Gram-negative bacteria is quite thin as it measures about 2 – 3 nm. The gram-positive bacteria have high susceptibility to anionic detergents and antibiotics. This explains why disinfectant A is more effective in gram-positive than gram-negative which has opposite features to the former such as high resistance to antibiotics but low resistance to physical disruption. 

In the Gram stain test, a decolorizing solution is used to wash the bacteria after it is dyed with crystal purple. After washing, a counterstain such as fuchsine or safranin is added, the Gram-positive bacteria retains the violet color while the Gram-negative bacteria is stained pink or red. The two types of bacteria have different types of cell wall, which were mentioned above, that make them behave differently. Gram-negative bacteria do have an outer cell membrane but Gram-positive does not have. The thick protein wall for Gram-positive bacteria is responsible for retaining the violet color of the cell wall. 

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