From the Guidelines
In patients with suspected Staphylococcus saprophyticus infections, urinalysis and culture are crucial for diagnosis, with urinalysis typically showing pyuria, hematuria, and positive nitrites, and culture growing gram-positive cocci in clusters on blood agar. The urine culture will likely show bacterial counts exceeding 10^5 CFU/mL, indicating a true infection rather than contamination 1. When collecting samples, proper midstream clean-catch technique is essential to minimize contamination, and culture results typically take 24-48 hours, during which empiric antibiotic therapy may be initiated 1. Some key points to consider when interpreting urinalysis and culture results include:
- Pyuria (white blood cells in urine) and hematuria (red blood cells) are common findings in patients with S. saprophyticus infections
- Positive nitrites may also be present, although this is not exclusive to S. saprophyticus
- Quantitative cultures usually show bacterial counts exceeding 10^5 CFU/mL, indicating a true infection rather than contamination
- S. saprophyticus is distinguished by its novobiocin resistance, which helps differentiate it from other staphylococci
- The organism primarily affects sexually active young women and is the second most common cause of uncomplicated UTIs in this population after E. coli
- S. saprophyticus is generally susceptible to many antibiotics including trimethoprim-sulfamethoxazole, nitrofurantoin, and fluoroquinolones, though susceptibility testing should guide definitive treatment 1.
From the Research
Urinalysis and Culture Expectations
In patients with Staphylococcus saprophyticus infections, the following can be expected in urinalysis and culture:
- The urine sediment may have a characteristic appearance microscopically 2
- Chemical screening methods for bacteriuria may not always succeed in diagnosing UTI caused by S. saprophyticus 2
- Low numbers of colony-forming units (less than 10(5) cfu/ml) of S. saprophyticus may be found in the bladder and voided urine, even when the infection occurs above the neck of the bladder 2
- Coagulase-negative, nonhemolytic staphylococcal colonies with yellow pigmentation can be identified presumptively as S. saprophyticus with a sensitivity of 97.8% and a specificity of 98.3% 3
- Novobiocin susceptibility testing can also be used to identify S. saprophyticus with a sensitivity of 100% and a specificity of 96.9% 3
Culture Characteristics
- S. saprophyticus is usually susceptible to antibiotics commonly prescribed for patients with UTI, with the exception of nalidixic acid 2
- The bacterium has a capacity for selective adherence to human urothelium and causes direct hemagglutination 2
- The adhesin for S. saprophyticus is a lactosamine structure 2
- S. saprophyticus produces an extracellular enzyme complex that can inhibit growth of both gram-positive and gram-negative bacteria 2