Staphylococcus saprophyticus

Staphylococcus saprophyticus is a Gram-positive, coagulase-negative bacterium belonging to the Staphylococcus genus.^[1] S. saprophyticus is a common cause of community-acquired urinary tract infections.^[2][3]

History

Staphylococcus saprophyticus was not recognized as a cause of urinary tract infections until the early 1970s, more than ten years after its original demonstration in urine specimens. Prior to this, the presence of coagulase-negative staphylococci (CoNS) in urine specimens was dismissed as contamination.^{[citation needed]}

Epidemiology and pathogenesis

In humans, S. saprophyticus is found in the normal flora of the female genital tract^[3] and perineum.^[4] It has been isolated from other sources too including meat and cheese products, vegetables, the environment, and human and animal gastrointestinal tracts.^[4] S. saprophyticus causes 10-20% of urinary tract infections (UTIs). In females 17–27 years old, it is the second most common cause of community-acquired UTI, after Escherichia coli.^[5] Sexual activity increases the risk of S. saprophyticus UTI because bacteria are displaced from the normal flora of the vagina and perineum into the urethra.^[3] Most cases occur within 24 hours of sex,^[3] earning this infection the nickname "honeymoon cystitis".^[6] S. saprophyticus has the capacity to selectively adhere to human urothelium. The adhesin for S. saprophyticus is a lactosamine structure. S. saprophyticus produces no exotoxins.^[3]

Clinical features

Patients with urinary tract infections caused by S. saprophyticus usually present with symptomatic cystitis. Symptoms include a burning sensation when passing urine, the urge to urinate more often than usual, a 'dripping effect' after urination, weak bladder, a bloated feeling with sharp razor pains in the lower abdomen around the bladder and ovary areas, and razor-like pains during sexual intercourse. Signs and symptoms of renal involvement are also often registered.^[7]

Laboratory diagnosis

The urine sediment of a patient with a S. saprophyticus urinary tract infection has a characteristic appearance under the microscope. Chemical screening methods for bacteriuria do not always detect S. saprophyticus infection because, even when such an infection occurs above the neck of the bladder, low numbers of colony-forming units (less than 10⁵ cfu/ml) are often present.^{[citation needed]}

S. saprophyticus is identified as belonging to the Staphylococcus genus using the Gram stain and catalase test. It is identitified as a species of coagulase negative staphylococci (CoNS) using the coagulase test. Lastly, S. saprophyticus is differentiated from S. epidermidis, another species of pathogenic CoNS, by testing for susceptibility to the antibiotic novobiocin. S. saprophyticus is novobiocin-resistant, whereas S. epidermidis is novobiocin-sensitive.^[3]

Treatment

S. saprophyticus urinary tract infections are usually treated with trimethoprim-sulfamethoxazole or with a quinolone such as norfloxacin.^[3]

Different sub-species

Two subspecies of S. saprophyticus exist: S. saprophyticus subsp. bovis and S. saprophyticus subsp. saprophyticus, the latter more commonly found in human UTIs. S. saprophyticus subsp. saprophyticus is nitrate reductase negative and pyrrolidonyl arylamidase negative while S. Saprophyticus subsp. bovis is nitrate reductase positive and pyrolidonyl arymamidase negative.^[8]

References