Saran's Learn Microbiology

INDIRECT MEASUREMENT OF MICROBIAL GROWTH  1) Turbidity Estimating turbidity is a practical way of monitoring bacterial growth.  As bacteria multiply in a Liquid medium, the medium becomes Turbid, or Cloudy with cells.  The instrument used to measure Turbidity is a Spectrophotometer or Colorimeter. In the Spectrophotometer, a beam of light is transmitted through a bacterial suspension to a light sensitive Detector. As bacterial numbers increase, less light will reach the Detector. This change of light will register on the instrument’s scale as the Percentage transmission. Also printed on the instrument’s scale is a logarithmic expression called the Absorbance (sometimes called Optical density, or OD, which is calculated as Abs = 2 − log of % transmittance).  The Spectrophotometer meter has two scales. The bottom scale displays Absorbance and the top scale, Percent transmission. Absorbance increases as percent transmission decreases. The Absorbance is used to plot...

DIRECT MEASUREMENT OF MICROBIAL GROWTH   1) Direct Microscopic Count  A specially designed slide called a Petroff-Hausser Cell Counter is also used in Direct Microscopic Count. Petroff-Hausser Cell Counter. In the Direct Microscopic Count method, a measured volume of a bacterial suspension is placed within a defined area on a Microscope slide. Because of time considerations, this method is often used to count the number of bacteria in milk.  A 0.01 ml sample is spread over a marked square centimeter of slide, stain is added so that the bacteria can be seen, and the sample is viewed under the oil immersion objective lens. The area of the viewing field of this objective can be determined. Once the number of bacteria has been counted in several different fields, the average number of bacteria per viewing field can be calculated. From these data, the number of bacteria in the square centimeter over which the sample was spread can also be calculated. Petroff-Hausser C...

  SYNCHRONOUS GROWTH Synchronous or Synchronized culture is a microbiological culture or a cell culture that contains cells that are all in the same growth stage. Synchronous growth helps studying particular stages or the cell division cycle and their interrelations. A Synchronous culture can be obtained either by manipulating environmental conditions such as by repeatedly changing the temperature or by adding fresh nutrients to cultures as soon as they enter the Stationary phase, or by physical separation of cells by Centrifugation or Filtration. An excellent and most widely used method to obtain synchronous cultures is the Helmstetter-Cummings Technique in which an unsynchronized bacterial culture is filtered through Cellulose nitrate membrane filter. The loosely bound bacterial cells are washed from the filter, leaving some cells tightly associated with th...

  DIAUXIC GROWTH Diauxic growth or Diauxie or Diphasic growth is the cell growth characterized by cellular growth in two phases, and can be illustrated with a Diauxic growth curve. This Diauxic growth was discovered and named Diauxie in the early 1940s by the French Biochemist Jacques Monod. Diauxic growth, meaning Double growth, is caused by the presence of two sugars on a culture growth media, one of which is easier for the target bacterium to metabolize. The preferred sugar is consumed first, which leads to rapid growth, followed by a lag phase. During the lag phase the cellular machinery used to metabolize the second sugar is activated and subsequently the second sugar is metabolized.  A simple example involves the bacterium  Escherichia coli . The Escherichia coli is grown on a growth media containing two types of sugars, one of...

CONTINIOUS CULTURE OF MICROORGANISMS A Continuous culture is an Open system. The concept of the Continuous cultures dates from the 19 th Century when a continuous process for the conversion of waste Beers and Wines to Vinegar was developed. Continuous culture systems can be operated as (i) Chemostat or (ii) Turbidostat. The Turbidostat operates best at high dilution rates; the Chemostat is most stable and effective at low dilution rates. The most common Continuous culture is Chemostat. (i) Chemostat A Chemostat (from  chem ical environment is  stat ic) is a Bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms are continuously removed at the same rate to keep the culture volume constant. In Chemostat, both Growth rate and Cell density can be controlled independently. ü   Growth rate - How fast the cells divide. ü   Cell density - How many ...

FACTORS INFLUENCING BACTERIAL GROWTH A) SOLUTE AND WATER ACTIVITY (i) Osmotolerant ·        Able to grow over wide ranges of water activity or osmotic concentration. ·        Example - Staphylococcus aureus. (ii) Halophile ·        Requires high levels of sodium chloride, usually above about 0.2 M to grow. ·        Examples - Halobacterium, Dunaliella and Ectothiorhodospira. B) pH (i) Acidophiles ·        Grow optimum between pH 0 to 5.5. ·        Examples - Sulfolobus, Picrophilus, Ferroplasma, Acontium and Cyanidium caldarium (ii) Neutrophiles ·        Grow optimum between pH 5.6 to 8.0. ·        Example – Escherichia coli. (iii) Alkalophiles ·        Grow optimum between pH 8.1 to 11.5. ·     ...

BACTERIAL GROWTH In microbiology, growth refers the “Increase number of cells”. More than 2000 chemical processes were occurred during growth. Step wise reactions occur during the growth: ü   Synthesis of the macromolecules viz ., DNA, RNA, protein, polysaccharides, lipids polymerization.  ü   Assembly of macromolecules. ü   Cell organelles formation ·       Growth rate : Increase of bacterial cell number per unit time is referred as growth rate. ·       Generation : The interval of formation of daughter cells from parental cell is called as generation. ·    Generation time : Time required to form two daughter cells from a single cell is called as Generation time.  This is also called as Doubling time. GROWTH CURVE OF BACTERIA ·       Assuming a single bacterium has been inoculated to a liquid medium and the bacterium starts multiplying by Binary fission gives increase of populat...