Question

2. List and briefly describe the four phases (stages) of microbial growth. You may also draw a growth curve, but you must still describe each of the four stages (NOT JUST LABEL GROWTH CURVE). 3. Briefly describe the method of assessing the amount of microbial growth you would use in each of the following samples: A. You have to determine how many living bacteria are present in a city pool: B. You have a cloudy broth and you need to determine how many living bacteria are present: 4. Put the following microorganism in order of most susceptible to least susceptible to germicides: protozoan trophozoite, protozoan cyst, Endospores, Mycobacteria, Enveloped viruses, gram negative bacteria, gram positive bacteria. START ANTIMICROBIAL AGENT LECTURE 5. List the six (6) mechanisms of antimicrobial action:

Answer 1

2. There are four phases of bacterial growth curve and they are as follows:

A) Lag phase

B) Log or Exponential phase

C) Stationary phase

D) Decline or Death phase

A) Lag phase: In this initial phase necessary metabolic intermediates and enzymes are synthesized for the growth to proceed in the subsequent phase. The duration of this phase depends upon the type or nature of culture medium used, size of inoculum and various others factors like temperature etc.

B) Log phase: In this phase cells start multiplying and divide exponentially. When log of the viable count of bacteria is plotted against time a straight line is obtained.

C) Stationary phase: Cell division stops in this phase due to depletion of nutrients and accumulation of toxic substances. There exists an equilibrium between the new progeny of cells that are formed and the cells that are dying. Therefore the viable number of bacteria remains Stationary.

D) Decline phase: In this phase number of bacteria declines due to autolytic enzymes which result in cell death.

3. A) For counting the number of living bacteria, Plate Count Method can be used which involves growing bacteria on a nutrtrient agar or medium and number of bacterial colonies on plate are counted.

B) It can be done by spread and pour plate method. In spread plate method inoculum is added to empty petri dish or plate following which melted nutrient agar is added and then swirl gently to mix. Colonies are formed in and on the medium.

4) From most to least susceptible to germicides:

Endospores, Mycobacteria, Protozoan cyst, Protozoan trophozoite, Gram negative bacteria, Gram positive bacteria, Enveloped viruses.