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Section 4: Anaerobic Bacteriology
4.9 Rapid Disk, Spot Tests, and Other Rapid or Primary Methods for the Identification of Anaerobes
Authors:Last Updated:2023
4.9.1 Introduction
Rapid disk tests, biochemical spot tests, and other methods described in this section provide a cost‐effective and efficient mechanism for the characterization and identification of anaerobes isolated from clinical specimens…
4.9.2 Indole Test
The indole test is helpful in obtaining an identification for certain anaerobic bacteria. Indole is hydrolyzed from tryptophan through reductive deamination by certain organisms possessing the enzyme tryptophanase…
4.9.3 Nitrate Disk Reduction Test
The glutamic acid decarboxylase test is used to determine the enzymatic ability of an organism to decarboxylate glutamic acid to form an amine, with resulting alkalinity. Glutamic acid decarboxylase is…
4.9.4 Catalase Test
Some anaerobic bacteria produce catalase, an enzyme that breaks down hydrogen peroxide (H2O2) into oxygen and water. When a catalase‐positive organism is emulsified with H2O2, it releases oxygen gas…
4.9.5 Identification by Using Special‐Potency Disks
Special‐potency disks can aid in confirming phenotypic characteristics and providing presumptive identification of anaerobic bacteria. Incubation of the organism in the presence of vancomycin (VA, 5 μg)…
4.9.6 Sodium Polyanethol Sulfonate (SPS) Disk for Differentiation of Gram‐Positive Anaerobic Cocci
Sodium polyanethol sulfonate (SPS), a commonly used anticoagulant, inhibits growth of certain bacteria, including Peptostreptococcus anaerobius, Peptostreptococcus stomatis, and, variably…
4.9.7 Bile Disk Test/Bile Broth Test/Bacteroides Bile Esculin Agar for Differentiation of Anaerobic Gram‐Negative Rods
Most Bacteroides and Parabacteroides spp. (with the notable exception of Phocaeicola [formerly Bacteroides] vulgatus), Bilophila wadsworthia…
4.9.8 Fluorescence
Fluorescence describes the absorption and subsequent emission of light. Some anaerobic species produce compounds which absorb and emit colored fluorescence when excited by a long‐wavelength UV light source…
4.9.9 Lipase Test
Anaerobic bacteria that produce enzymatic lipases can hydrolyze fats contained in egg yolk agar (EYA) to produce glycerol and free fatty acids. The production of insoluble fatty acids causes an iridescent sheen…
4.9.10 Lecithinase Test
Fluorescence describes the absorption and subsequent emission of light. Some anaerobic species produce compounds which absorb and emit colored fluorescence when excited by a long‐wavelength UV light source…
4.9.11 Pigment Production
Some species of Prevotella and Porphyromonas produce a dark pigment that causes their colonies to become brown to black when grown on standard media. Prevotella spp.…
4.9.12 Urease Test
Some organisms can hydrolyze urea into two molecules of ammonia through the enzymatic action of the enzyme urease. The resulting release of ammonia shifts the pH toward alkalinity, causing the pH indicator phenol…
4.9.13 Gelatinase Production
Gelatin is a proteinaceous material used as a solidifying agent and as a substrate for the detection and differentiation of proteolytic bacteria. Gelatinase enzymes are produced by relatively few anaerobes, so the ability…
4.9.14 Alkaline Phosphatase
Alkaline phosphatase (ALP) production is helpful for differentiation among anaerobic Gram‐positive cocci. Hydrolysis of 4‐nitro‐phenyl phosphate by ALP releases free 4‐nitrophenol…
4.9.15 Glutamic Acid Decarboxylase
The glutamic acid decarboxylase (GDC) test is used to determine the enzymatic ability of an organism to decarboxylate glutamic acid to form an amine, with resulting alkalinity. The assay is rapid, yielding a presumptive…
4.9.16 L‐Alanyl‐Alanylaminopeptidase
Hydrolysis of L‐alanyl‐alanylaminopeptide by alanylaminopeptidase releases β‐naphthylamine. This compound complexes with p‐dimethylaminocinnamaldehyde…
4.9.17 L‐Proline Aminopeptidase
Hydrolysis of L‐proline‐β‐naphthylamide by proline aminopeptidase releases β‐naphthylamine. This compound complexes with p‐dimethylaminocinnamaldehyde in the presence of acetic acid to produce a red to…
4.9.18 4‐Methylumbelliferone Derivative Substrates
Linkage of an enzymatic substrate to the compound 4‐methylumbelliferone (4MU) results in the release of a fluorescent end product in the presence of hydrolytic enzymes. 4MU fluorescence can be detected…
4.9.19 Combination Enzymatic Tablets for Nitrophenol, Aminopeptidase, and Glycosidases
Some anaerobic bacteria may produce, as part of their metabolism, unique digestive enzymes that are useful for identification. Combination tablets allow the detection of the activity of two or more such enzymes to be performed…
Section Editor: Audrey N. Schuetz
Editors in Chief: Amy L. Leber and Carey-Ann D. Burnham
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