catalase-negative

**Catalase test:** Catalase converts 2 H2O2 → 2 H2O + O2. In the lab, a drop of 3% H2O2 is placed on a colony. Bubbling (O2 release) means catalase-positive. No bubbling means catalase-negative. Do not pick colonies from blood agar, because RBCs contain catalase and can give a false positive.

**Primary use:** It is the first step in separating Gram-positive cocci. Staphylococci are catalase-positive, and streptococci/enterococci are catalase-negative. After that, coagulase separates S. aureus (coagulase-positive) from coagulase-negative staphylococci. Hemolysis pattern, bacitracin or optochin sensitivity, and bile esculin growth separate the streptococci and enterococci.

**Catalase-negative organisms (high-yield):** - *Streptococcus pyogenes* (group A): beta-hemolytic, bacitracin-sensitive, PYR-positive. - *Streptococcus agalactiae* (group B): beta-hemolytic, bacitracin-resistant, hippurate-positive, CAMP-positive. - *Streptococcus pneumoniae*: alpha-hemolytic, optochin-sensitive, bile-soluble, encapsulated. - Viridans streptococci: alpha-hemolytic, optochin-resistant. These include *S. mutans* (dental caries) and *S. sanguinis* (subacute bacterial endocarditis). - *Enterococcus faecalis/faecium*: grow in bile and 6.5% NaCl, and are PYR-positive. - *S. bovis/gallolyticus*: group D, nonenterococcus. Bacteremia or endocarditis is associated with colon cancer. - Anaerobes such as *Clostridium* spp. and *Bacteroides* lack catalase in the sense that they are aerotolerant at most. Many anaerobes lack catalase and superoxide dismutase, which is why oxygen is toxic to them.

**Catalase-positive organisms (contrast):** - *Staphylococcus* spp. - *Listeria monocytogenes* - *Nocardia* - *Aspergillus* - *Candida* - *Pseudomonas* - *E. coli* - *Serratia* - *Burkholderia cepacia* - *H. pylori* - *Bartonella* - *Legionella*

**Clinical significance, chronic granulomatous disease (CGD):** CGD is an NADPH oxidase deficiency, so neutrophils have no respiratory burst. Patients are prone to infection with catalase-positive organisms (**S**taphylococcus aureus, **B**urkholderia cepacia, **S**erratia, **N**ocardia, **A**spergillus, **K**lebsiella, **P**seudomonas, **E**. coli, **L**isteria, mnemonic variants exist). These organisms break down their own H2O2, so the host cannot use it as a substitute. Catalase-negative organisms produce H2O2 themselves, and the host phagocyte can use that H2O2 to generate bleach-like (HOCl) products, so these infections are not a problem in CGD. The diagnostic test is a negative dihydrorhodamine (DHR) flow cytometry test (formerly the nitroblue tetrazolium test). Treatment includes TMP-SMX and itraconazole prophylaxis and interferon-gamma.

**Pearls:** - Catalase-negative, Gram-positive cocci in chains or pairs suggest *Streptococcus* or *Enterococcus*. - Catalase-positive, Gram-positive cocci in clusters suggest *Staphylococcus*. - Catalase-positive and facultatively intracellular suggests *Listeria*, which shows tumbling motility.