The Unfamiliar Alpha By Barbara L. Fox, MS, MPH, MT (ASCP) ho among us has been reading W urine cultures and come across a blood plate with a pure or Say hello to the relatively uncommon predominant alpha hemolytic organism (or rarely reported) urinary pathogen, and called it either presumptive alpha Aerococcus urinae. This organism is strep or Enterococcus? If the former, closely related to Aerococcus viridans perhaps we thought it was a skin (which is usually PYR positive and LAP contaminant and didn’t mention it negative). In 1992, it was given its own descriptively or work it up further. Even unique classification. if it was from a catheterized urine specimen wouldn’t most clinicians fail Aerococci occur naturally in dust, air, to treat what appears to be a common vegetation, and hospital environments. skin contaminant or innocuous A. urinae has been known to cause colonizer? urinary tract infections, bacteremia/septicemia, and If we think it might be Enterococcus, endocarditis. Conditions predisposing perhaps we performed a Bile Esculin and patients to infection with this organism 6.5%NaCl test. However, this organism are being over age 65, being male would be Bile Esculin negative, and (although we have isolated the organism NaCl positive. Further testing could twice in our hospital microbiology lab include a PYR, which would be positive from elderly females), and urinary tract as is Enterococci. But surprisingly, this pathology such as stricture, prostate organism would have a negative PYR problems or prior surgery. and a positive LAP! Would a Gram stain be called for at this point? You would The organism is non-motile and strongly have seen gram positive cocci but in alpha hemolytic on a blood agar plate. pairs, tetrads, and clusters Anaerobic growth is very poor or absent. predominantly. Now it appears to be a After 24 hours of incubation, colonies Staph? However, a quick catalase would appear larger than alpha strep, but be negative! (and you might repeat this somewhat smaller than Enterococci. to be sure). So what is it? They can also look like Lactobacilli, but are quickly differentiated by the Gram stain. They are catalase and PYR negative and LAP positive. Treatment options include penicillin for less severe cases, and penicillin or vancomycin with gentamicin for more severe cases. All Aerococci are sensitive to vancomycin, which differentiates them from the Pediococci. They are resistant to sulfonamides and trimethoprim, which are commonly used to treat urinary tract infections. Currently, automated ID/AST systems contain this organism in their data base without a standardized sensitivity. I urge all labs to be on the lookout for this uropathogen when an alpha colony presents on culture, especially from elderly male or female patients. The puzzle of identifying organisms keeps microbiology interesting and relevant. Accurate identification of etiologic agents of infection, when possible, has public health and infection control implications, as well as Figure 1: Hardy Diagnostics StrepQuick tm providing good patient care in terms of can be a valuable tool in the identification of proper treatment options. all Gram positive, catalase negative organisms. See ID chart below. It is this art of clinical microbiology as much as the science, which keeps one passionate about the field. Barbara L. Fox, MS, MPH, MT (ASCP) Microbiologist, Lodi Memorial Hospital Consultant and Educator This chart was taken from the technical insert of the Hardy Diagnostics StrepQuicktm (cat. no. Z122). The StrepQuick tm is a rapid 10 minute test for PYR, LAP, and ESC within a card format. More information can be found at www.HardyDiagnostics.com. .