N S Uyeda wrote:
>> This gram pos cocci has been isolated twice from midstream and cath urine
> of same individual. The very beta, non-sticky, colony resembles Staph; on
> gram stain too. It's coagulase and thermonuclease positive, beta lactam
> neg. Vitek ID is S. aureus if catalase pos.; if catalase neg the Vitek
> calls it strep group B, or unidentified.
>> It's PYR pos but fails all other tests for Strep group A or enterococci
> (latex, SxT disk). Only problem is that it's repeatedly catalase neg on
> all media.
> Any ideas?
> Sue Uyeda
> Dominican Hosp. Microbiology
> Santa Cruz, CA
Hello: If you refer to Chapter 22 of the 6th edition of the ASM Manual
of Clinical Microbiology, you will see that Staphylococcus aureus subsp.
anaerobius is listed as catalase negative but is is otherwise
biochermically identical to the commonly encountered variety in all
respects except, among a few other distinctions, the following easily
performed tests: B-glucosidase, nitrate reduction, acetoin production
(VP)and aerobic acid production from D-mannose & D-trehalose which are
all negative for the anaerobius strain but positive for the routine
strain. The urinary tract of the afflicted patient may have provided a
comfortable niche for the anaerobius strain which amy prefer ecological
conditions with little or no oxygen. Another possibility is that this is
a routine strain of Staph aureus but heme supplementation may be
necessary to exhibit its true enzymatic character. Another possibility
is described in a recent paper that reports a catalase negative Listeria
strain. The article mentions the hypothesis that catalases are enzymes
which have cofactors with iron cores. Restricted iron access by the
organism under particular ecological conditions where iron resources are
depleted or unavailable may prevent the catalase enzyme from performing
its function...weak or negative reactions would ensue. This theory would
be consistent with the observation that heme supplementaion may reverse
this catalase negative condition. Hope this helps. It;s good to remember
that anything that might serve to "stress" the physiochemical tolerance
and thereby effect the primary,secondary or tertiary structure of the
enzyme can hamper or negate any enzymes proper function. Under certain
conditions, eg. antiobitic assault, an organism may be unale to
manufacture an enzyme and may require a recovery period and perhaps may
even need nuritional or physiochemical support to "rehabilitate" its
common characteristics. I see these "damaged" organisms quite often in
our clinical facility.
Ken
