In microbiology, bacteria are classified as either "Gram-positive" or "Gram-negative" depending on their appearance at the microscopic level following a particular staining procedure called the Gram stain. Originally developed by Hans Christian Gram, the Gram stain is always written with an upper case "G" as it refers to the name of a person.

Gram-positive bacteria appear dark blue or violet due to the crystal violet stain following the Gram stain procedure; Gram-negative bacteria, which cannot retain the crystal violet stain, appear red or pink due to the counterstain (usually safranin).

The reason bacteria are either Gram-positive or Gram-negative is due to the structure of their cell envelope. (The cell envelope is defined as the cell membrane and cell wall plus an outer membrane, if one is present.) Gram-positive bacteria, for example, retain the crystal violet due to the amount of peptidoglycan in the cell wall. It can be said therefore that the Gram-stain procedure separates bacteria into two broad categories based on structural differences in the cell envelope.

Further reading: Microbiology

Labels: Gram stain, Gram-negative bacteria, Gram-positive bacteria

Legionellosis, also known as Legionnaires' disease, is caused by a type of bacterium called Legionella. In 1976 many people who attended a convention of the American Legion in Philadelphia, USA suffered from an outbreak of this disease, a type of pneumonia. Legionellosis is a disease of significant medical and public interest.

The bacterium Legionella is found in aquatic habitats where it can survive and multiply in various protozoa. The bacterium is transmissible to humans and pathogenic to humans.

Legionella is used in the laboratory as a model system for the analysis of bacterial survival, acquisition of nutrients and replication inside cells. The genome sequences of four L. pneumophila strains have been published.

Further reading: Legionellosis

Labels: Legionella, Legionellosis, Legionnaires disease

Pasteurella bacteria are Gram-negative bacteria. Some members of the Pasteurellaceae family are important pathogens such as Haemophilus influenzae and others are harmless commensals and live in the gut of humans and other mammals. Information on the biology of these organisms has grown in recent years, due mainly to genetic and molecular studies. The family consists of thirteen genera. Many members of the Pasteurellaceae are used as models of bacterial pathogenesis and host-pathogen-interactions.

Further reading at Pasteurella

Labels: commensal, Haemophilus, pasteurella, Pasteurellaceae, pathogen

Biodegradation refers to the breakdown of substances by living organisms or, more usually, by the enzymes produced by the organisms. Microorganisms in nature breakdown many substances in the course of their normal lives. Different microorganisms are able to breakdown different substances. Variour microorganisms possess the ability to degrade, transform or accumulate a huge range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radionuclides and metals. Many of these substances are considered (by humans) to be pollutants and therefore there has been much interest in harnessing the naturally occurring ability of microorganisms to remove of pollutants from contaminated areas.

In addition, there has been considerable interest in genetically modifying microorganisms to increase their usefulness for this purpose.

Further reading: Microbial Biodegradation: Genomics and Molecular Biology

Labels: biodegradation, bioremediation, contamination, pollutants

The peptidoglycan sacculus is the stress-bearing structure of bacterial cells. It consists of glycan strands cross-linked by peptide bridges. Peptidoglycan, or murein as it is also known, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid residues. Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the three-dimensional mesh-like layer.

The peptidoglycan layer is much thicker in Gram-positive bacteria than in Gram-negative bacteria.

Peptidoglycan biosynthesis is the target for many antibiotics such as β-lactams, D-cycloserine and glycopeptide-antibiotics such as vancomycin. Bacteria have developed a number of different antibiotic resistance mechanisms for coping with these antibiotics.


Further reading:
Bacterial Polysaccharides
Biopolymers and Polymer Precursors

Labels: biopolymers, Gram-positive bacteria, peptidoglycan, polysaccharides

Acanthamoeba is a type of amoeba that lives in the environment, in the soil, in fresh water and in other habitats. Acanthamoeba rarely causes infections but when it does cause infection, however, it can be extremely serious. Diseases caused by Acanthamoeba include amoebic keratitis and encephalitis. Encephalitis is caused by Acanthamoeba entering cuts and spreading to the central nervous system. Amoebic keratitis is a rare disease where the amoebae (Acanthamoeba) invade the cornea of the eye. Recently, there have been multiple reports of increasing incidence of Acanthamoeba keratitis especially among contact lens wearers.

Further reading: Acanthamoeba: Biology and Pathogenesis
See also: Acanthamoeba pictures, illustrations and figures

An informative series of articles on all aspects of microbiology written by scientists and medical professionals describing various topics of microbiology. Invaluable for students, teachers, scientists, clinicians, and everyone with an interest in microbiology.

Microbiology is the study of tiny living organisms. These can be single cell microscopic organisms or microscopic organisms consisting of many cells. Microbiology includes the study of eukaryotes such as fungi and protists but is mainly concerned with the study of prokaryotes such as bacteria and certain algae. Viruses are also included. Microbiology is subdivided into branches including bacteriology, virology, mycology, parasitology and others.

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