Diagnostic Laboratory Section

STREAK PLATE METHOD

Materials

• Nutrient agar medium
• Inoculating loop
• Incubator
• Clinical sample
• Gas burner

Methods

• This method is routinely employed for the isolation of bacteria  from clinical specimen
• The clinical specimens are obtained aseptically from body fluid (blood, CSF), discharges (sputum, urine, feces) etc.
• The loops made from nichrome, with internal diameter 2-4 mm are used .
• A loop of specimen is spread over the surface of the nutrient agar plate with an inoculating loop to give a  inoculum.
• The loop is resterilized and drawn from the inoculom in 2 or 3 parallel lines on the fresh surface of the medium. This process is repeated as shown in the picture in different directions. Care must be taken to sterilize the loop, and cool it on unseeded medium, between each sequence.
• Incubate the inoculated palte at 37° C for overnight.
• On incubation, growth may be confluent at the site well , but becomes progressively thinner and well seperated colonies are obtained over the final series of streaks.