Gram Stain

This is the most important stain in bacteriology and is so central to identification that it should be practised until the operator is fully competent. A number of different variations are found, and the laboratory should standardise on one method.

A General Model for Biofilm Development

Biofilm formation is a developmental process in which bacteria undergo a regulated lifestyle switch from a nomadic unicellular state to a sedentary multicellular state where subsequent growth results in structured communities and cellular differentiation. Results of prior work by many groups allow the construction of a hypothetical developmental model for biofilm formation that can be generalized for many different bacterial species. This model can be adjusted to fit either of two general modes of unicellular lifestyle: nonmotile and motile.

Unusual Types of Bacteria (Part 3)

. Actinomycetes

Actinomycetes are gram-positive filamentous bacteria characterized by mycelial growth (i.e., branching filaments), which is analogous to fungal growth. However, the diameter of the filaments is similar in size to bacteria (approximately 1 mm). Most actinomycetes are strict aerobes, but a few of them require anaerobic conditions. Most of these microorganisms produce spores, and their taxonomy is based on these reproductive structures (e.g., single spores in Micromonospora or chains of spores in Streptomyces). They are commonly found in water, wastewater treatment plants, and soils (with preference for neutral and alkaline soils). Some of them (e.g., Streptomyces) produce a

Unusual Types of Bacteria (Part 2)

. Gliding Bacteria

These filamentous gram-negative bacteria move by gliding, a slow motion on a solid surface. They resemble certain cyanobacteria except that they are colorless. Beggiatoa and Thiothrix are gliding bacteria that oxidize H2S to S0, which accumulates as sulfur granules inside the cells. Thiothrix filaments are characterized by their ability to form rosettes. Myxobacteria are another group of gliding microorganisms. They feed by lysing bacterial, fungal, or algal cells. Vegetative cells aggregate to make “fruiting bodies,” which lead to the formation of resting structures called myxospores. Under favorable conditions, myxospores germinate into vegetative cells.

. Bdellovibrio (B. bacteriovorus)

These small (0.2–0.3 mm), flagellated (polar flagellum) bacteria are predatory on gram-negative bacteria. After attaching to the bacterial prey, Bdellovibrio penetrates the cells and multiplies in the periplasmic space (space between the cell wall and the plasma membrane). Because they lyse their prey, they are able to form plaques on a lawn of the host bacterium. Some Bdellovibrio can grow independently on complex organic media.

Unusual Types of Bacteria (Part 1)

. Sheathed Bacteria

These bacteria are filamentous microorganisms surrounded by a tubelike structure called a sheath. The bacterial cells inside the sheath are gram-negative rods that become flagellated (swarmer cells) when they leave the sheath. The swarmer cells produce a new sheath at a relatively rapid rate. They are often found in polluted streams and in wastewater treatment plants. This group includes three genera: Sphaerotilus, Leptothrix, and Crenothrix. These bacteria have the ability to oxidize reduced