Diagnosis, Therapy, and Prevention of Bacterial Diseases

Chapter 8


Diagnosis, Therapy, and Prevention of Bacterial Diseases




Laboratory Identification of Bacteria




Gram staining



1. Protocol



2. Results



• Purple (positive reaction): organisms with thick peptidoglycan cell wall


• Red (negative reaction): organisms with thin peptidoglycan layer and an outer membrane


• Gram-variable or gram-resistant: modified cell wall old cultures or cells treated with β-lactam antibiotics in which the peptidoglycan is weakened—therefore, poor or no color retention; modified cell wall (Box 8-1)




Growth and isolation of bacteria



1. Culture media



• Most bacteria will grow on blood agar or other nonselective media.



a. Table 8-1 lists common media used to isolate or identify particular bacteria.



• Selective medium inhibits growth of some bacteria (e.g., EMB agar inhibits gram-positive bacteria).


• Differential medium incorporates an identifying test.



• Special medium incorporates particular metabolites or provides specific culture conditions required by certain bacteria.


2. Colony characteristics (Table 8-2)



Biochemical tests



1. Metabolic tests for fermentation of various sugars and production of byproducts (e.g., acid or gases)



2. Tests for enzymes


Jun 18, 2016 | Posted by in IMMUNOLOGY | Comments Off on Diagnosis, Therapy, and Prevention of Bacterial Diseases
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