Novobiocin Susceptibility Test- Principle, Procedure, Results


The main objective of the novobiocin susceptibility test is to differentiate Staphylococcus saprophyticus from other Coagulase Negative Staphylococci (CONS). This is important because S. saprophyticus is a common cause of urinary tract infections (UTIs), especially in young women, and it has a distinctive resistance to novobiocin, an antibiotic that inhibits bacterial DNA synthesis. By using a novobiocin disk on a culture medium, we can observe whether the test bacteria form a zone of inhibition (indicating susceptibility) or not (indicating resistance) around the disk.

Another objective of the test is to classify CONS into two groups based on their novobiocin sensitivity. CONS are a diverse group of bacteria that are usually harmless commensals on human skin and mucous membranes but can also cause opportunistic infections in immunocompromised patients or when they contaminate medical devices. Some of the most common CONS species are S. epidermidis, S. haemolyticus, S. hominis, and S. capitis. Most of these species are susceptible to novobiocin, except for some rare ones like S. kloosii and S. cohnii. By performing the novobiocin susceptibility test, we can narrow down the possible identification of CONS isolates and guide the appropriate antibiotic therapy.