Identification bacteria, Lecture notes of Microbiology

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Bacterial

identification

Bacterial

identification

General approach for bacterial

identification

General approach for

General approach for

bacterial identification

bacterial identification

Different

identification

techniques

Physical methods

Based on the

characterization of

proteome of the bacteria

Genetical methods

Based on the

characterization of

specifics genes of the

bacteria

Biochemical methods

Based on the

characterization of

metabolic pathways of

the bacteria

To identify unknown bacteria , results are

compared to databases

Bacterial

identification

Metabolism of the bacteria and

biochemical bacterial

identification

Metabolism of the

Metabolism of the

bacteria

bacteria

The main metabolic pathways :

Carbohydrates

Acidic

molecules

Bacteria

Proteins, aminoacids

Ammonia,

CO

2

, amino…

Enzymes

These waste are frequently acidic

or alkaline

 Possibility of detection with a

colorimetric pH indicator

For some particular produced

molecules, detection requires some

special reagents

Application to the

Application to the

identification

identification

Example : research the ability to use glucose

Bacteria

inoculation

Medium + glucose + pH indicator :

-green color for pH = 7

-yellow color for acid pH (pH <7)

incubation

Yellow color :

 Acid pH

 Production of acidic waste

by bacteria

 Proves the presence of

enzymes which allow the

use of glucose as nutrient

by bacteria

 Bacteria « glucose + »

Application to the

Application to the

identification

identification

How to identify an unknown bacteria with a

biochemical method ??

4 steps :

1 -Incubate bacteria to test in media with different nutrient (usually

5 to 20)

 one medium for one nutrient

2 -After incubation, for each medium, determine the results

positive or negative for each nutrient

3 -Write the complete biochemical profile (+ - + + + - - + …)

4 -Compare the profile with a database to identify your bacteria

Bacterial

identification

Identification media

Bacterial

identification

Multi-test miniaturized system :

The API system

The API system

The API system

The most used API system…

API Strep

 Identification of

Streptococcu s species

API Staph

 Identification of

Staphylococcu s species

API 20NE

 Identification of Non

Enterobacteria

( Pseudomonas for example)

API 20E

 Identification of

Enterobacteria

The API system

The API system

With an unknown bacteria to identify, which API system use?

Catalase

Catalase

Results

for the

Gram

stain

Cocci Cocci

Gram Gram

++

API Staph

for Staphylococcus

API Strep

for Streptococcus

Cocci Cocci

Gram Gram

API NH

for Neisseria

Rods Gram

API Listeria

for Listeria

Rods Gram

Oxidase

Oxidase

API 20E

for Enterobacteria

API 20NE

for no

Enterobacteria

API 50CH

for Bacillus

The API system

The API system

Introducing the API 20E system for Enterobacteria

identification…

1 bacterial 1 bacterial

colony colony

5 mL of sterile water

Fill microtubes gallery

with the bacterial

suspension

The API system

The API system

API 20 E after incubation…Positive results for all tests :

API 20 E after incubation…Negative results for all tests :

The API system

The API system

Example of results for bacteria to test :

1-Reading results :

2-Entering results in the database software: