A urine culture from a young woman grew a catalase-positive gram-positive coccus. The most likely organism is which?

A urine culture from a young woman grew a catalase-positive gram-positive coccus. The most likely organism is which?

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

Answer: (A)

When you see a urine culture that grows a catalase-positive gram-positive coccus, think of Staphylococcus species rather than the streptococci or enterococci (which are catalase-negative). Among staphylococci, the organism classically associated with acute cystitis in young, sexually active women is Staphylococcus saprophyticus. It’s a common cause of UTIs in this group and fits the pattern of isolation from urine without other signs of invasive infection. While Staphylococcus aureus is also catalase-positive, it is typically linked to wound infections, skin/soft tissue infections, or more serious bacteremia rather than uncomplicated UTIs in this demographic. The other organisms listed are catalase-negative and therefore less likely given the initial test result. Thus, the most likely organism is Staphylococcus saprophyticus.

When you see a urine culture that grows a catalase-positive gram-positive coccus, think of Staphylococcus species rather than the streptococci or enterococci (which are catalase-negative). Among staphylococci, the organism classically associated with acute cystitis in young, sexually active women is Staphylococcus saprophyticus. It’s a common cause of UTIs in this group and fits the pattern of isolation from urine without other signs of invasive infection. While Staphylococcus aureus is also catalase-positive, it is typically linked to wound infections, skin/soft tissue infections, or more serious bacteremia rather than uncomplicated UTIs in this demographic. The other organisms listed are catalase-negative and therefore less likely given the initial test result. Thus, the most likely organism is Staphylococcus saprophyticus.