A urinary tract infection in a young woman is most often caused by which catalase-positive gram-positive cocci?

• A. Staphylococcus saprophyticus
• B. Enterococcus faecalis
• C. Streptococcus bovis
• D. Streptococcus viridans

Answer: (A)

Urinary tract infections in young, sexually active women are most often caused by a catalase-positive gram-positive cocci, specifically Staphylococcus saprophyticus. The catalase test differentiates staphylococci (catalase-positive) from streptococci (catalase-negative), so when the organism is a catalase-positive gram-positive cocci in this clinical context, Staphylococcus saprophyticus is the best fit. This species is a common cause of uncomplicated cystitis in this demographic, whereas the other organisms listed are catalase-negative (streptococci) or less typical UTI pathogens for young healthy women. Additionally, Staphylococcus saprophyticus is typically novobiocin-resistant, which helps distinguish it from other coagulase-negative staphylococci in the lab.