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These are Gram-positive, sporing non-acid fast straight rods. If motile they have peritrichous flagellae. They include aerobes, facultative anaerobes, and strict anaerobes and are generally nonhalophylic with a wide growth range depending on the group. Many will grow on most simple bacteriological media. A variety of biochemical activities are noted in this family, including fermentative, proteolytic activities and the ability to grow on minimal media. Some species can fix nitrogen. A number of species are also characterised by producing specific toxins. Bacillus is the type genus. The two main genera Bacillus and Clostridium are distiguished by the former being aerobic, while the latter is anaerobic. Most of these include a wide variety of species.

Aerobic Genera

This is characteristic of the Bacillus and related groups. They are able to survive in air.

Bacillus: These are peritrichoulsly flagellated, form ellipsoidal or spherical, endospores, which may or may not swell the sporangium. They are aerobic to facultatively anaerobic and generally catalase positive. There are currently very many species in this genus, including, B. anthracis, B. azotoformans, B. cereus, B. coagulans, B. israelensis, B. larvae, B. mycoides, B. polymyxa, B. pumilis, B. stearothormophillus, B. subtilis, B. thuringiensis and B. validus. Many of these species form distinct groups of closely related species. One of these is the B. cereus group, which comprises apart from B. cereus, B. anthracis, B. mycoides and B. thuringiensis as well as newly described species, B. weihenstephanensis and B. pseudomycoides.

Sporolactobacillus:

Sporocarcina

Filibacter

Caryophanum

Group Profile

B. cereus Group.

This is a group of gram-positive, spore-forming, generally motile, aerobic rod-shaped bacteria, which also grow well anaerobically. Based on recent 16S rRNA analysis the species including B. cereus, B. anthracis, B. mycoides and B. thuringiensis and the more recently identified B. pseudomycoides and B. weihendtephanensis, make up the group. The cells of these six species are all large, being >0.9µm wide. They produce ellipsoidal or cylindrical spores either centrally or subterminally. The spores do not distend the cells. They all form spores readily on most media. Based on detailed 16S and 23S rRNA analyses the members of the group have diverged only recently from a common evolutionary line. Due to its highly virulent pathogenicity B. anthracis has been maintained as a separate species, as has B. thuringiensis, whose strains form the crystalline inclusion (Cry protein) or d-endotoxin, which is highly toxic for certain types of insect. B. anthracis and B. cereus are the only members of the Bacillus genus, which are human pathogens.

Species Profiles

B. anthracis

B. cereus

B. thuringiensis

B. mycoides

Anaerobic Genera

This is the characteristic of the Clostridium group related groups and characterised generally by an inability to grow in air, although some may tolerate it.

Clostridium: These include many species, which can be psychrophilic, mesophilic or thermophilic. They are generally Gram-positive with peritrichous flagellation, they degrade organic materials to acids, alcohols, CO2, H2 and minerals. Acids, particularly butyric acid, are a frequent product of clostridial fermentation. They form ellipsoidal or spherical, endospores, which may or may not swell the sporangium. They tend to be grouped into saccharolytic, proteolytic species but some are both and there are also some species, which are specialised in being limited in their biochemical activities.

The saccharolytic species include: Cl. aerotolerans, Cl. aurantibutyricum, Cl. beijerinckii, Cl. botulinum B,E,F*, Cl. butyricum, Cl. chauvoei, Cl.difficile, Cl. intestinale, Cl. novyi A, Cl. pateurianum, Cl. saccharolyticum, Cl. septicum, Cl. thermoaceticum, and Cl. thermosaccharolyticum.

The proteolytic species include: Cl. argeninense, Cl. ghoni, Cl. limosum, Cl.putrefaciens, Cl. subterminale and Cl. tetani.

The proteolytic and saccharolytic species include: Cl. acetobutylicum, Cl. bifermenans, Cl. botulinum A, B, F (prot.)*, Cl. botulinum C,D*, Cl. cadaveris, Cl. haemolyticum, Cl. novyi B,C,* Cl. perfringens, Cl. putrefaciens, Cl. sordelli and Cl.sporogenes.

The specialist species include: Cl. acidiurici, Cl. irregularis, Cl. kluyveri, Cl. oxalicum, Cl. propionicum, Cl. sticklandii and Cl. villosum.

*Cl. botulinum is subdivided into a number of types according to the serological specificities of the toxins produced. These specificities are based on neutralisation studies. Other Clostridium species can also produce botulinum toxins.

Desulfotomaculum

Species Profiles

CI botulinum

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