Experiment 245 Techniques to Distinguish Nonfermentative Gram Negative Bacilli from Enterobacteriaceae

A variety of gram-negative bacilli that normally inhabit soil and water or live as commensals on human mucous membranes may contaminate specimens sent to the microbiology laboratory for culture or, more importantly, may produce opportunistic human infections. Although the Gram-stain appearance and cultural characteristics of the organisms may resemble those of Enterobacteriaceae, they are relatively inactive in the common biochemical tests. In particular, they either fail to metabolize glucose or they degrade it by oxidative rather than fermentative pathways. For this reason these organisms are often referred to as "glucose nonfermenters" (as opposed to the glucose-fermenting enteric bacilli). A number of bacterial genera and species are included in this group of nonfermenters. The most important from a medical aspect is Pseudomonas aeruginosa, which is most often involved in human infection. Because of the different clinical implications and the varying antimicrobial susceptibility patterns (nonfermenters are more highly resistant to common antimicrobial agents) it is important to distinguish nonfermenters from enteric bacilli. The characteristics of a few nonfermenting bacteria are listed in table 24.5-1 and compared with those of the Enterobacteriaceae.

Table 24.5-1 Characteristics of Nonfermenting Gram-Negative Bacilli

Butt of TSI

O-F glucose*

Oxidase

Complete Hemolysis

Diffusible Green Pigment

Open

Closed

Pseudomonas

No change

+

-

+

+

+

aeruginosa

Acinetobacter

No change

+

-

-

-

-

baumannii

Acinetobacter Iwoffi

No change

-

-

-

-

-

Alcaligenes faecalis

No change

-

-

+

-

-

Enterobacteriaceae

Yellow

+

+

-

- or +

-

*A positive test is a yellow color. Yellow in the open tube only indicates glucose degradation or oxidation. A yellow color in the closed tube (with mineral oil) indicates the organism is fermentative rather than oxidative. Glucose fermenters produce acid (yellow color) in the open as well as the closed tube.

*A positive test is a yellow color. Yellow in the open tube only indicates glucose degradation or oxidation. A yellow color in the closed tube (with mineral oil) indicates the organism is fermentative rather than oxidative. Glucose fermenters produce acid (yellow color) in the open as well as the closed tube.

Morello-Mizer-Granato: I III. Diagnostic I 9. Microbiology of the I I © The McGraw-Hill

Laboratory Manual and Microbiology in Action Intestinal Tract Companies, 2003 Workbook in Microbiology, 7/e

Purpose

To study some biochemical reactions of glucose nonfermenting bacteria

Materials

Blood agar plates

Nutrient agar plates

TSI slant

O-F glucose deeps

Oxidase reagent (di- or tetramethyl-p-phenylenediamine)

Dropper bottle with sterile mineral oil

Slant cultures of Pseudomonas aeruginosa, Acinetobacter baumannii, and Escherichia coli

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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