Using a microscope, it is possible to observe other cell structures found in microbe cells. The outer cell envelope around microbes may contain a glycocalyx, cell wall, and cell membrane. The glycocalyx is the outer coating of some microbes; and it is called a slime layer or capsule layer. The outer virus capsule is commonly called a capsid. This outer layer protects the microbe and helps the microbe adhere to its environment. Polio and hepatitis viruses have capsids that protect the virus against human digestive juices. Consequently, Sabin introduced an oral polio vaccine; and the hepatitis virus can escape digestion in the human G-I tract and cause food-borne illness. Numerous bacteria have outer capsules; and pathogens that adhere to catheters, IUDs, and pacemakers may be difficult to eliminate. Alcalogenes and Bacillus are involved in causing ropy milk and stringy bread; and other pathogens with capsules include Streptococcus, Haemophilus, and Klebsiella.

Microbes may have an outer cell wall. Plants, fungi, and algae have thick cell walls composed of a carbohydrate called cellulose. This nearly undigestible material provides a rigid shape to the cells. Animals and protozoans do not have a rigid cell wall--in fact these organisms do not have any cell wall. Bacteria possess a thinner cell wall composed of a nitrogen-containing compound called peptidoglycan. This molecule comprises about 90% of the cell wall in gram-positive bacteria and only 10% of cell wall in gram-negative bcteria (remainder of cell wall is comosed of LPS-lipopolysaccharide). The composition of the cell wall of bacteria is the basis for the gram stain and prescribing antibiotic therapy. Some bacteria identified by the Lister Institute are called L-forms and lose their cell wall during life. During this period without a cell wall, microbes appear to be less susceptible to anti-microbic therapy. Streptococcus-A, Proteus, Corynebacterium, Mycobacterium (perhaps related to Crohn's disease--autoimmune disease of the intestine), and the tiny bacillus that causes cat-scratch disease (CSD) have been observed to contain cell-wall deficient forms. The molecules composing the cell walls of gram-negative bacteria like E.coli and Salmonella as well as molecules in gram-positive bacteria like Staphylococcus are toxic to humans and a factor in some diseases.

All living microbe cells must have an intact cell membrane. The cell membrane is the site of numerous metabolic activities, secretions, and transport of materials. The selective-permeability of the membrane permits intake of nutrients, removal of wastes, and the retention of essential cell products. The cell membrane of most microbe cells is approximately 30-40% phospholipid and 60-70% protein.

Only a few of the intracellular or cytoplasmic organelles of cells will be discussed in this course. The Internet and microbiology textbooks have much information on cell structures. We will simply be reminded that ribosomes manufacture proteins, mitochondria mke ATP (energy), and plastids, inclusions, and vacuoles store needed and/or reserve substances. The genome (DNA) of the cell may be enclosed in a membrane (nucleus found in eucaryotic cells) or be concentrated in an area in the cytoplasm called a nucleoid. The DNA is required for the life of the cell in the controlling of cell activities (enzyme manufacturing) and reproduction. Additional loose pieces of DNA called plasmids are found in many bacterial cells. These loose pieces of DNA can be manipulated and transferred to other cells. This genetic engineering is significant in changing the traits of the microbes.

The dormant structures produced by Bacillus and Clostridium are called endospores. These dehydrated structures are very resistant to adverse environmental conditions. The depositing of dipicolinic acid (DPA) has an extreme dehydrating effect on the microbe and makes the microbe less likely to be killed by heat and chemicals because it is completely inactive. Microbial endospores have been viable after 3000 years (archeological find). Bacillus endospores survive in the soil for years as farmers with anthrax are well aware. The anaerobic Clostridium endospores present in the soil or on a piece of farm equipment may germinate in deep puncture wounds (gangrene and tetanus) and sealed cans (botuism). During the heating of pot pies and the covering of meat with oils and spices (marinating), the available oxygen is reduced and Clostridium endospores or the actual living vegetative cells may begin to grow and multiply. So do not reheat and eat previously heated pot pies!