SOP for Operation and Calibration of Colony Counter

To provide a procedure for the operation and calibration of the Colony Counter.

This SOP covers the operation and calibration of the Colony Counter.

Microbiologist: Responsible for operation, calibration, and maintenance of the instrument. Maintain required records.
QA Officer/QAM: Review the records and governing the document.

  • Ensure that the instrument is visibly clean and free from dust.
  • Switch ON the mains, Turn ON the instrument by pressing the reset On/Off Switch, the display will indicate some numbers.
  • Reset the counter by pressing the reset switch. The counter should now read 0000.
  • Place the Petri plate on the graduated Woulffhneugal glass plate provided on the top of the instrument.
  • Position the magnifying lens to focus the Petri plate or clear visibility. Ensure that a sufficient margin is left between the magnifying lens and the Petri plate in order to use the marker conveniently while colony counting.
  • Remove the cap of the Auto-mark and touch the marking point of the probe on the Petri Dish where a Bacteriological Colony is located. Press the probe gently. The counter will register a count, there will be a beep and an ink dot will be marked on the Petri Dish. Continue till all the colonies are thus counted.
  • As a colony is marked with ink while it is being counted, missing a count or double counting is avoided. When the counting is completed note the reading on the counter.
  • The COUNT push button switch (next to the RESET switch) may be used to count sparsely populated plates or for some other counting purpose also.
  • If the Petri plate is not to be contaminated with the marking, then counting can be done in either of the following methods :

  1. If the Petri plate is finely plated (thin layer) then it can be kept upside down, and marking can be done on the bottom side (which is on Top)
  2. The lid can be kept over the plate and marking may be done on the glass cover. But in this case, as there is a gap between the media and the marking, the counting should be done in one sitting without altering the view angle or moving/turning the plate or its cover.

Refilling the ink cartridge in the Auto-mark:
  • Unscrew the body of the Auto-mark and remove the cartridge from the inside.
  • Gently pull, and open the cap at the back of the cartridge.
  • Put about five drops of ink and reverse the procedure for refitting.
  • The body of the Auto-mark should be tightened in such a manner, that the gentle push on the probe would register a count.

  • Operate the instrument as per the above procedure.
  • Electronic digit counts the number accurately, to be tested by using the COUNT switch by manual counting.
  • Record the result in the calibration format as per given in Annexure - 1.

Routine maintenance
  • Clean the instrument with dry cloth.
  • Clean magnifying glass with tissue paper.

Annexure – 1:  Colony Counter Calibration Record Format 
Annexure – 2: Colony counter usage log book

SOP: Standard Operating Procedure
QA: Quality Assurance
QAM: Quality Assurance Manager

Revision History

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