Why is MacConkey agar inoculated with Urine specimen?

Answer 1

MacConkey agar medium differentiates between the lactose fermenting and nonlactose fermenting bacteria. Most of the bacterial commensals from our large intestine are lactose fermenting, Escherichia coli being one of them. When bacterial growths and colonies on MacConkey agar is pink coloured, then the organism is fermenting lactose from the medium, on the other hand, if transparent/transluscent, colourless growths and colonies appear on the medium, the bacterium does not ferment lactose. The flushing action of urine, make it sterile in an uninfected healthy person. In an event where the patient is suspected to have urinary tract infection (UTI), urine of patient is inoculated on MacConkey agar medium and incubated at 37 degree centigrade overnight. In most of the cases, UTI is caused by Escherichia coli that is lactose fermenting and produces pink coloured colonies on MacConkey agar medium. Although the urine is sterile, it may get contaminated by the organisms of skin microflora or by surrounding microbes due to improper collection of urine. In such cases, UTI is diagnosed by counting bacteria in urine sample. For significant bacteriuria (bacteria in urine), the count must be equal to or more than 1 lack bacteria per mL of urine. Answered by: M. F. Khan, Dept. of Microbiology, GMC, jagdalpur (CG)