GROWTH CURVE OF BACTERIA (PHARMACEUTICAL MICROBIOLOGY NOTES)(S.Y B.PHARM SEM III)PCI SYLLABUS

GROWTH CURVE OF BACTERIA

BACTERIAL GROWTH CURVE

Bacteria are unicellular, prokaryotic, free living microorganism most commonly replicate by the asexual process of binary fission. When grown in culture, a predictable pattern of growth in a bacterial population occurs.

This pattern can be graphically represented as the number of living cells in a population over time and is known as a bacterial growth curve.

Normal growth curve of bacteria can be determined by inoculating a small number of bacterial cells into a suitable culture medium and counting the bacteria in aliquot samples at regular intervals.

When the logarithms of the viable cells are plotted against time on a graph paper, it gives a typical curve called as bacterial growth curve or growth cycle of bacteria.

The resulting bacterial growth curve has the following four distinct phases:

1. Lag phase
2. Log or logarithmic or exponential phase
3. Stationary phase
4. Death or decline phase. 

LAG PHASE:-        

This is the initial phase characterized by cellular activity but not growth. When bacteria are inoculated into a fresh medium, the multiplication of bacteria does not start immediately. the microbial population, remains constant for an initial period. The period between inoculation and the beginning of multiplication is known as the lag phase.

In this phase bacterial cells adjust itself to adopt the new environment. The enzymes coenzymes and other essential molecules are synthesized by the bacterial cell during this phase.

During this phase, there is an increase in size of bacteria but no appreciable increase in number of bacterial cells. The cells are metabolically and physiologically very active but do not divide.

The length of the lag phase depends upon the nature of medium, species of microorganisms and other various physical and chemical growth factors; it may vary from 1 hour to several days.

LOG PHASE (EXPONENTIAL PHASE):

After the initial phase or lag phase, bacterial cells enter in to the log phase. During these phase the cells are dividing steadily at a constant rate by binary fission and doubling in numbers. The time required for one bacterial division during this phase is known as generation time. the log of the number of cells plotted against time results in a straight line. The bacteria multiply at their maximum rate and their number increases exponentially or by geometric progression with time. In these phase the metabolic activity is high as DNA, RNA, cell wall components, and other substances necessary for growth are generated for division. The number of bacteria present in each generation period is almost twice that in the previous period

All bacteria do not have the same generation time. E.g. Escherichia coli may have 15 10 20 minutes, staphylococcus aureus, 25 to 30 minutes, mycobacterium tuberculosis may have 780 to 940 minutes. Generation time is mainly dependent on type of species, nutrients in the medium and physical conditions.

STATIONARY PHASE: -

After log phase the stationary phase started in this phase a constant high population of cells is maintained by a balance between cell division and cell death. In these phase the rate of multiplication is reduced due to lack of essential nutrients, lack of water oxygen, change in pH of the medium, etc. and accumulation of their own toxic metabolic wastes.

 At the cellular level during stationary phase reserved food materials get consumed, a proportion of ribosome’s may be degraded and enzymes may still be synthesized. A viable population count at this stage shows no change.

In this phase spore forming bacteria produce endospores and pathogenic bacteria begin to generate substances (virulence factors) that help them survive harsh conditions and consequently cause disease.

DEATH OR DECLINE PHASE: -

Death phase are also known as the logarithmic death phase. During death phase, the number of viable cells decreases exponentially, and population growth experiences a sharp decline.

Bacteria die at different rates, just as they grow at different rates, between each of these phases, there is a small curved portion called the transitional period.

The death phase starts due to the variety of conditions but the most important are.

  Ø  Depletion of nutrients

  Ø  Accumulation of toxic waste products and autolytic enzymes.

Involution and irregular forms are common in this phase. Some cells assume various shapes, becoming long, filamentous rods or branching or globular forms that are difficult to identify.

Some develop without a cell wall and are referred to as protoplasts, spheroplasts, or L-phase variants (L-forms). When these involuted forms are inoculated into a fresh nutrient medium, they usually revert to the original shape of the healthy bacteria.

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1.      INTRODUCTION OF MICROBIOLOGY

2.      BRANCHES OF MICROBIOLOGY

3.      SCOPE OF MICROBIOLOGY

4.      HISTORY OF MICROBIOLOGY {PART 1}

5.       HISTORY OF MICROBIOLOGY {PART 2}

6.      HISTORY OF MICROBIOLOGY {PART 3}

7.        PROKARYOTES VS EUKARYOTES DIFFERENCES

8.      MORPHOLOGY OF BACTERIA

9.      ULTRASTRUCTURE OF BACTERIA

1.   NUTRITIONAL REQUIREMENTS OF BACTERIA

1.   RAW MATERIAL USED FOR CULTURE MEDIA

1.   TYPES OF CULTURE MEDIA IN MICROBIOLOGY

1.   PHYSICAL PARAMETERS FOR GROWTH

1.   GROWTH CURVE OF BACTERIA

1.   MEASUREMENT OF BACTERIAL GROWTH.

1.    ISOLATION OF PURE CULTURE