Dictionary > Gram-positive bacilli

Gram-positive bacilli

Definition
noun, singular: gram-positive bacillus
A group of rod-shaped bacterial cells that appears violet through Gram’s method
Supplement
Gram’s method has become an essential laboratory diagnostic tool for the rapid identification of a bacterial species. Through this method, the observer can classify if the bacterial species is a gram-positive or not. Bacterial cells that stain violet or bluish in color under the microscope are described as gram-positive. This indicates that they resist the red dye counterstain. Those that appear pinkish under the microscope are described as gram-negative, indicating that they have taken the counterstain.
Gram-positive bacteria are not able to take the color of the counterstain because of their thick peptidoglycan layer. This layer of peptidoglycan chains forms a thick and rigid cell wall. This cell wall becomes dehydrated when treated with a decolorizing agent in Gram’s method. As a result, the primary dye cannot readily diffuse and is retained in the cell. Thus, they appear violet or bluish under the microscope. Despite the thick cell walls of gram-positive bacteria, they are generally more susceptible to antibiotic treatments than gram-negative bacteria.1
Based on gram staining results and cell morphology as observed under the microscope, gram-positive bacteria may be gram-positive cocci or gram-positive bacilli (rods). Gram-positive bacilli appear rods in contrast to cocci that are spherical in shape. Gram-positive bacilli include the Bacillus spp., Clostridium spp., Listeria spp. and Corynebacterium spp.
See also:

Reference(s):

1 Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall.


You will also like...

primitive arthropods
Arthropods

The arthropods were assumed to be the first taxon of species to possess jointed limbs and exoskeleton, exhibit more adva..

Biosecurity and Biocontrol
Biosecurity and Biocontrol

This lesson explores the impact of biosecurity threats, and why they need to be identified and managed. Examples to incl..

Neurology of Illusions
Neurology of Illusions

Illusions are the perceptions and sensory data obtained from situations in which human error prevents us from seeing the..

Neural Control Mechanisms
Neural Control Mechanisms

Neurons generate electric signals that they pass along to the other neurons or target tissues. In this tutorial, you wil..

temperature - abiotic factor
Abiotic and Biotic Factors

This tutorial deals with the abiotic factors of the freshwater environment that determine what sort of life would be sui..

Schematic diagram of bacterial lactose operon
Gene Action – Operon Hypothesis

Learn how the way genes control and determine every aspect of the body. This lesson uses lac operon as an example. ..

..