A combination of (nonselective) 5% sheep blood and (selective) MacConkey agars is sufficient for the recovery of the pathogenic microorganisms that are most commonly encountered in urinary tract infections (UTIs). MacConkey is the selective culture medium that is most commonly used to inhibit growth of gram-positive organisms (most UTIs are caused by gram-negative organisms).
Eosin methylene blue (EMB) is a selective agar that also inhibits the growth of gram-positive organisms.
Therefore, using only a combination of MacConkey and EMB would prevent the detection of a gram-positive organism, if this were the cause of the infection.
Chocolate agar or other enriched media may be needed in addition to blood and MacConkey if a more fastidious organism is suspected.
Thayer-Martin would be used specifically for recovery of Neisseria gonorrhoeae. Thayer-Martin (or Modified Thayer-Martin) inhibits other microorganisms and allows the selective recovery of both N. gonorrhoeae and N. meningitidis.
Microbiology
Which culture agar combinations below will usually be sufficient for MOST routine urine culture investigations?