The Unfamiliar Alpha
By Barbara L. Fox, MS, MPH, MT (ASCP)
W
ho among us has been reading
urine cultures and come
across a blood plate with a pure or
predominant alpha hemolytic organism
and called it either presumptive alpha
strep or Enterococcus? If the former,
perhaps we thought it was a skin
contaminant and didn’t mention it
descriptively or work it up further. Even
if it was from a catheterized urine
specimen wouldn’t most clinicians fail
to treat what appears to be a common
skin contaminant or innocuous
colonizer?
If we think it might be Enterococcus,
perhaps we performed a Bile Esculin and
6.5%NaCl test. However, this organism
would be Bile Esculin negative, and
NaCl positive. Further testing could
include a PYR, which would be positive
as is Enterococci. But surprisingly, this
organism would have a negative PYR
and a positive LAP! Would a Gram stain
be called for at this point? You would
have seen gram positive cocci but in
pairs, tetrads, and clusters
predominantly. Now it appears to be a
Staph? However, a quick catalase would
be negative! (and you might repeat this
to be sure). So what is it?
Say hello to the relatively uncommon
(or rarely reported) urinary pathogen,
Aerococcus urinae. This organism is
closely related to Aerococcus viridans
(which is usually PYR positive and LAP
negative). In 1992, it was given its own
unique classification.
Aerococci occur naturally in dust, air,
vegetation, and hospital environments.
A. urinae has been known to cause
urinary tract infections,
bacteremia/septicemia, and
endocarditis. Conditions predisposing
patients to infection with this organism
are being over age 65, being male
(although we have isolated the organism
twice in our hospital microbiology lab
from elderly females), and urinary tract
pathology such as stricture, prostate
problems or prior surgery.
The organism is non-motile and strongly
alpha hemolytic on a blood agar plate.
Anaerobic growth is very poor or absent.
After 24 hours of incubation, colonies
appear larger than alpha strep, but
somewhat smaller than Enterococci.
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
providing good patient care in terms of
proper treatment options.
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
Figure 1: Hardy Diagnostics StrepQuick tm
can be a valuable tool in the identification of
all Gram positive, catalase negative
organisms. See ID chart below.
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.