Streptococci. Streptococci are spherical bacteria that divide in parallel planes to produce chains. The bacteria are Gram‐positive, and certain species are aerobic, while others are anaerobic. On blood agar, certain species partly destroy the red blood cells and are said to be alpha‐hemolytic. Other species completely destroy the blood cells and are beta‐hemolytic. Those streptococci producing no blood cell destruction are gamma‐hemolytic.
One species of streptococcus (Streptococcus pneumoniae) is the cause of secondary bacterial pneumonias, while another species (Streptococcus pyogenes) causes strep throat and rheumatic fever. Other species are associated with dental caries. Harmless strains of streptococci are used in the production of yogurt, buttermilk, and cheese.
Staphylococci. Staphylococci are Gram-positive bacteria that divide in planes to produce clusters or packets. Normally associated with the skin and mucous membranes, certain species of staphylococci are involved in skin boils, abscesses, and carbuncles, especially if they produce the enzyme coagulase, which causes blood clotting. Staphylococcus aureus is involved in cases of food poisoning, toxic shock syndrome, pneumonia, and staphylococcal meningitis.
Lactobacilli. Lactobacilli are Gram-positive, rod-shaped bacteria occurring as single cells or chains. They produce lactic acid in their metabolism and are associated with the flora of the mouth and the vagina. Certain species are associated with the production of dairy products such as yogurt, sour cream, and buttermilk.
Bacillus and Clostridium species. Species of Bacillus and Clostridium are Gram-positive, rod-shaped bacteria able to produce highly resistant endospores (spores). The spores are found in the soil, air, and all environments of the body. Species ofBacillus grow aerobically, and Bacillus anthracis is the cause of anthrax. Clostridiumspecies grow anaerobically, and different species cause tetanus, botulism, and gas gangrene.
Bacillus and Clostridium species are also used for industrial purposes. Bacillus thuringiensis forms an insecticide useful against various forms of caterpillars, andClostridium species are used to produce various types of chemicals, such as butanol.
Corynebacteria. Corynebacteria are pleomorphic members of the genusCorynebacterium, which are Gram-positive rods found in various environments, including the soil. The bacteria contain cytoplasmic phosphate granules that stain as characteristic metachromatic granules. One species, Corynebacterium diphtheriae, causes human diphtheria.
Actinomyces and Arthrobacter. Actinomyces species are Gram-positive rods that assume many shapes and usually form branching filaments. Most species are anaerobic, and one species is responsible for a human and cattle infection called lumpy jaw.
Arthrobacter species live primarily in the soil. These Gram-positive rods assume many shapes during their life cycles, including branching rods and spherical forms. Arthrobacterspecies are widely found in the soil, and many degrade herbicides and pesticides.