plate count

Examples of plate count in the following topics:

• Viable Cell Counting

  • Plate counting is used to estimate the number of viable cells that are present in a sample.
  • The plate count method or spread plate relies on bacteria growing a colony on a nutrient medium.
  • The colony becomes visible to the naked eye and the number of colonies on a plate can be counted.
  • Typical media include Plate count agar for a general count or MacConkey agar to count gram-negative bacteria such as E. coli.
  • Examples of a viable cell count are spread plates from a serial dilution of a liquid culture and pour plates.

• Direct Counting

  • Direct counting methods include microscopic counts using a hemocytometer or a counting chamber.
  • One can also quantify the number of cells in a culture by plating a known volume of the cell culture on a petri dish with a growth medium, which is also known as a streak plate.
  • The colonies can then be counted and, based on the known volume of the culture that was spread on the plate, the cell concentration can be calculated.
  • Bacterial colony counts made from plating dilutions of bacteria are useful to estimate the strength of bacterial infections; for example, a urinary tract bacterial infection.
  • As with hemocytometers or counting chambers, cultures need to be heavily diluted prior to plating.

• Measurements of Microbial Mass

  • An additional method for the measurement of microbial mass is the quantification of cells in a culture by plating the cells on a petri dish.
  • If the cells are efficiently distributed on the plate, it can be generally assumed that each cell will give rise to a single colony.
  • The colonies can then be counted, and based on the known volume of culture that was spread on the plate the cell concentration can be calculated.
  • As is with counting chambers, cultures usually need to be heavily diluted prior to plating; otherwise, instead of obtaining single colonies that can be counted, a so-called "lawn" will form, resulting in thousands of colonies lying over each other.
  • Additionally, plating is the slowest method of all: most microorganisms need at least 12 hours to form visible colonies.

• Aseptic Technique, Dilution, Streaking, and Spread Plates

  • Microbiologists rely on aseptic technique, dilution, colony streaking and spread plates for day-to-day experiments.
  • The dilution of microbes is very important to get to microbes diluted enough to count on a spread plate (described later).
  • Spread plates are simply microbes spread on a media plate.
  • The glass rod is sterilized and used to spread the microbe-containing liquid uniformly on the plate.
  • Four streak plates.

• Permutations and Combinations

  • The topics covered are: (1) counting the number of possible orders, (2) counting using the multiplication rule, (3) counting the number of permutations, and (4) counting the number of combinations.
  • Suppose you had a plate with three pieces of candy on it: one green, one yellow, and one red.
  • It is important to note that order counts in permutations.
  • That is, choosing red and then yellow is counted separately from choosing yellow and then red.
  • Unlike permutations, order does not count.

• Parallel-Plate Capacitor

  • The parallel-plate capacitor is one that includes two conductor plates, each connected to wires, separated from one another by a thin space.
  • The purpose of a capacitor is to store charge, and in a parallel-plate capacitor one plate will take on an excess of positive charge while the other becomes more negative.
  • where z is the axis perpendicular to both plates.
  • Accordingly, capacitance is greatest in devices with high permittivity, large plate area, and minimal separation between the plates.
  • In a capacitor, the opposite plates take on opposite charges.

• Parallel-Plate Capacitor

  • For the purpose of this atom, we will focus on parallel-plate capacitors .
  • For a parallel-plate capacitor, capacitance (C) is related to dielectric permittivity (ε), surface area (A), and separation between the plates (d):
  • Voltage (V) of a capacitor is related to distance between the plates, dielectric permittivity, conductor surface area, and charge (Q) on the plates:
  • Charges in the dielectric material line up to oppose the charges of each plate of the capacitor.
  • An electric field is created between the plates of the capacitor as charge builds on each plate.

• Capacitance

  • The most common capacitor is known as a parallel-plate capacitor which involves two separate conductor plates separated from one another by a dielectric .
  • The product of length and height of the plates can be substituted in place of A.
  • For a capacitor with plates holding charges of +q and -q, this can be calculated:
  • In a parallel-plate capacitor, this can be simplified to:
  • The dielectric prevents charge flow from one plate to the other.

• Counting

• Lead Storage Battery

  • Planté plates are still used in some stationary applications, where the plates are mechanically grooved to increase surface area.
  • Each plate consists of a rectangular lead grid.
  • An odd number of plates is usually used, with one more negative plate than positive.
  • Each alternate plate is connected.
  • The discharge process is driven by the conduction of electrons from the negative plate back into the cell at the positive plate in the external circuit.