Can gram-positive bacteria be rod shaped?

In the classical sense, six gram-positive genera are typically pathogenic in humans. Two of these, Streptococcus and Staphylococcus, are cocci (sphere-shaped). The remaining organisms are bacilli (rod-shaped) and can be subdivided based on their ability to form spores.

What is gram-positive rods?

A gram-positive bacillus doesn’t have an outer cell wall beyond the peptidoglycan membrane. This makes it more absorbent. Its peptidoglycan layer is much thicker than the peptidoglycan layer on gram-negative bacilli. Gram-positive bacilli are shaped like rods.

What organisms are gram-positive rods?

Gram positive rods; Actinomyces, Atopobium, Bacillus, Bifidobacterium, Clostridium, Corynebacterium, Erysipelothrix, Gardnerella, Listeria, Lactobacillus, Mycobacterium sp. (other than M. tuberculosis), Nocardia and Cutibacterium (Proprionibacterium).

What color are gram-positive rods?

The staining method uses crystal violet dye, which is retained by the thick peptidoglycan cell wall found in gram-positive organisms. This reaction gives gram-positive organisms a blue color when viewed under a microscope.

What can go wrong in Gram staining?

Several factors may affect the results of Gram staining: If the smear is too thick, proper decolorizing will not be possible. If the smear is overheated during heat fixing, the cell walls will rupture. Concentration and freshness of reagents may affect the quality of the stain.

Are gram-positive rods aerobic or anaerobic?

The non–spore-forming gram-positive bacilli are a diverse group of aerobic and anaerobic bacteria. This chapter focuses on the aerobic members of this group.

What is difference between Gram-positive and negative?

Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane.

Why is counterstain necessary in Gram staining?

The important aspect is to ensure that all the color has come out that will do so easily. This step washes away unbound crystal violet, leaving Gram-positive organisms stained purple with Gram-negative organisms colorless. The counterstain stains both gram-negative and gram-positive cells.

What are 3 factors that affect a good Gram stain?

The many variables that can affect this stain are age of the culture, amount of decolorizer used, the time of decolorization, the type of organism (acid-fast bacteria and spores do not stain well), thickness of the smear, and the general care of the stainer.