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Growth and Physiology Of Bacteria


Bacteria divide by binary fission

Nuclear division precedes cell division

Generation time

  1. Time required for a bacterium to give rise to two daughter cells
  2. E.coli 20 mintues, M.tuberculosis 20 hours, M. leprae 20 days
  3. Total count :(TC) Total number of bacteria present in a specimen irrespective of whether they are living or dead                         
  4. Viable count : (VC) This measures only living cells which are capable of growing and producing a colony on a suitable medium 

B. Bacterial growth curve

  1. Lag phase: Multiplication does not begin immediately, adapt themselves, and increase in size and metabolic activity, duration varies for every bacterium and medium, VC and Tc constt
  2. Log phase: Bacteria multiply at their maximal rate, number increases exponentially, limited duration, VC and TC increase
  3. Stationary phase: Number of viable cells remains constant, VC constt, TC increases, stage where toxin production occurs
  4. Phase of decline: Death rate exceeds the rate of reproduction, VC decreases, TC constt/decreases in case of autolytic bacteria.
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Measurements of microbial death

  1. Thermal death time- minutes required to kill all cells in a suspension at a given temperature
  2. Zfactor / Z value – no. of degrees centigrade required to produce 10 fold change in thermal death   time. It is a measure of thermal resistance of spore to a particular process. eg B. sterothermophilus with Z factor of 10-14 is control for autoclave.
  3. D-value – no. of minutes exposure to produce a log reduction in the number of viable spores at the temperature of the test.

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