Puzzling Pathogen in a Urine Culture

July 1, 2006

What is the next step when a patient’s urine culture shows -hemolytic streptococci?

What is the next step when a patient's urine culture shows ß-hemolytic streptococci?
-Joseph Schube, MD
  Yorba Linda, Calif

I share your puzzlement. The group A ß-hemolytic streptococcus(Streptococcus pyogenes) is not ordinarily consideredto be a urinary pathogen, and I am aware of nounique syndromes or implications associated withgroup A streptococci in urine cultures. However, the answersto the following 3 questions may prove helpful:

  • Was the patient systemically ill? Bacteriuria can be a"spillover" from bloodstream infection. For example, patientswith Staphylococcus aureus in urine cultures frequentlyhave positive blood cultures, and the urine isolateis often of incidental significance (although a renal abscessor carbuncle, which can be life-threatening, does developin some patients).
  • Did the microbiology laboratory do special studies onthe isolate or send it to a reference laboratory? Thestreptococci are a diverse group of microorganisms, andbacteriologic tests sometimes misclassify them. For example,not all ß-hemolytic streptococci are group A. Conversely,occasional group A streptococci do not exhibitß-hemolysis on blood agar plates (these have beenlikened to a "rattlesnake without a rattle"). Conceivably,the isolate in question could have been a group B streptococcusor an enterococcus.
  • What was the clinical scenario? Enterococci, the "streptococci"that most frequently cause urinary tract infection,are often associated with obstructive uropathy of variousorigins.

If the patient had asymptomatic bacteriuria, I wouldrepeat the culture and, if the culture were confirmed,possibly prescribe a short course of a ß-lactam antibiotic.Assuming the patient had normal renal function, oral penicillinV would be a good choice; like most ß-lactam antibiotics,it is eliminated mainly by renal excretion.-

Charles S. Bryan, MD
  Professor of Medicine
  Director, Division of Infectious Diseases
  University of South Carolina School of Medicine