why do microbes fit neither into traditional plant nor animal kingdom classifications?

plants: non-motile, photosynthetic

animals: motile, non-photosynthetic

microbes: may be non-motile, non-photosynthetic (fungi); or motile, photosynthetic (some bacteria)

as a result, a third kingdom, PROKARYOTE was established

• bacteria
• cyanobacteria
• methanogens (formerly known as archaebacteria)

differentiated from plants and animals based on relative simplicity of their cellular organization

• smaller than eukaryotes
• little subcellular structure
• DNA lies loose in cytoplasm
• archaebacteria and eubacteria are prokaryotes

what is the size of most bacteria of medical interest, and for comparison's sake, how big is an erythrocyte?

• most bacteria of medical interest: .5-2μm
• erythrocyte: 6-7μm

microbes can get SMALL though. "large viruses" can be as small as .2-.35μm, which is around the size of the smallest bacteria.

why can viruses be SO much smaller than the smallest bacteria?

the lower size for prokaryotic cells is set by molecular limitations; any cell requires a certain number of types and quantities of enzymes/proteins needed to sustain life (precise number unknown). the fact remains that a bacteria can only be as small as the essential components of cellular functions can be packed into a cell.

since viruses are not cellular organisms, they can be much smaller.

sphere-shaped

some organisms have characteristic shapes/variations from the sphere, like:

• pneumococcus (streptococcus pneumoniae)- slightly elongated coccus, one end is lancet-shaped.
• gonococcus or meningococcus-coffee-bean shape

rod (cylindrical)-shaped

the shape of individual rods is characteristically different for different species and may be useful for identification.  for instance, the rod may be long and slender, or short and thick.  the ends of the rod may appear square or rounded.

NOTE: with some bacteria, the line of demarcation between a "coccus" and a "bacillus" is difficult to draw, with the resultant category of "coccobacilli".

helix-shaped

treponema(the causative agent of syphilis) and Borrelia (the causative agent of Lyme disease)

chain arrangement with SEVERAL component units

ie: STREPTOCOCCUS (chain of cocci, or spheres), or STREPTOBACCILUS (chain of baccili, or rods)

a random arrangement

ie: staphylococcus (randomly arranged unit of cocci subunits)

conformations following cell division; most bacteria divide by transverse fission. this binary fission occurs by the formation and subsequent splitting of the transverse wall, and many cell aggregates may result. very common among the cocci, where the specific form of the aggregate is a stable characteristic of an organism, and is therefore useful for identification. form of aggregate is determined by the planes of successive division.

• successive divisions in same plane=streptococcus
• 3 successive divisions at right angles=sarcina (or cuboidal arrangement). uncommon.
• successive divisions in ANY direction results in irregular clusters, as in STAPHYLOCOCCUS.

1. add crystal violet for 1 minute
   • all cells turn purple
2. add iodine solution for 1-3 minutes
   • all cells still purple; crystal violet-iodine complex formed
3. decolorize with alcohol
   • alcohol removes crystal violet complex from gram negative cells, making them colorless. alchohol has NO EFFECT on stained gram positive cells (retain the purple color)
4. counterstain with safranin.
   • no effect on the gram positive (purple) cells; gram negative cells take up the counterstain and turn red!
5. differentiate between purple (gram positive) and red (gram negative) cells.
   

what are some major components of the cell wall of the gram positive bacteria?

• protein
• lipoteichoic acids (extend thru cell wall)
• thick layer of peptidoglycans: N-acetylglycosamine & muramic acids (extend thru cell wall)

what are some main components of the outer membrane of the gram negative cell wall?

• lipopolysaccharides (LPS):
  
• lipoproteins:
• porin proteins: able to keep out large molecules; attachment site for bacteriophages (viruses), and bacteriocins (protein materials elaborated by some related bacteria which have killing affect on other organisms; PP are receptor sites for these bacteriocins and bacteriophages)
  
• periplasmic space:
  
• small, thin layer of peptidoglycans

1. lipid portion (innermost layer)- lipid A; may be responsible for endotoxin activity ass'd with gram negative infections
2. core polysaccharide- group carbohydrate
3. specific polysaccharide region- project from surface of outer membrane and may help to protect the surface of the cell from the action of antibody and complement.

LPS: THE MAIN SURFACE ANTIGENIC COMPONENT OF GRAM NEGATIVE BACTERIA!!!

• pyrogenicity (via IL 1)
• tissue necrosis (via TNF & free radicals)
• C' activation
• B-cell mitogen (in mice)
• immunoadjuvant

alcohol solubilizes the lipid rich cell wall of gram negative bacteria; gram positive cells have no such lipid content in their cell walls, rendering them untouched by the alcohol decolorization step in gram staining

1. outer membrane: LPS, porin protein, phospholipids, lipoproteins
2. periplasmic space: contains the thin layer of peptidoglycans; also the site of enzymatic and synthetic activity
3. inner membrane: proteins, proton channels, and phospholipids

aka: mureins, mucopeptide

alternating units of N-acetyl glucosamine and N-acetyl muramic acid

responsible for rigidity of bacterial cell

50-80% Gm+ cell wall

1-10% Gm- cell wall

how are N-acetyl glucosamine and N-acetyl muramic acid linked?

beta 1,4 linkage

lysozymes (enzyme found in tears, saliva, and other bodily fluids) cleave this linkage, leading to loss of integrity of cell wall

besides the beta 1,4 linkage of peptidoglycans, how else does their structure maximize integrity of the cell wall?

alternating D and L isomers of amino acids gives improved rigidity to cell wall. this is the only place in structure where the D-form of these amino acids is found

what enzymes are involved in linking the monomeric subunits of peptidoglycans and what is their special relationship to penicillin?

transpeptidases and carboxypeptidases

they are penicillin binding proteins! penicillin irreversibly binds to and inhibits the activity of the transpeptidase enzyme by forming a highly stable penicilloyl-enzyme intermediate. Because of the interaction between penicillin and transpeptidase, this enzyme is also known as "penicillin-binding protein."

will change shapes to a sphere (spheroplast)

stable L forms may result (cell wall lacking bacteria)

occurs in orgs like strep ; important because they are refractory to the antibiotic which normally would be used to treat them; as such, need to choose a different treatment.

why are the capsules/slime layer/glycoclyces important?

many bacteria owe their virulence to the presence of these components on their cell wall

• pneumococcus: polysaccharide (glucosamine)
• beta-hemolytic streptococci: (hyaluronic acid)
• anthrax bacillus: (D-glutamic acid)

these particular components of the bacteria aid in their ability to evade phagocytosis and to be extra virulent

which is virulent, the encapsulated or rough form of a bacteria?

ENCAPSULATED! when mice are injected solely with the capsules of some bacteria, they die!  rough forms cause no death.

slime layers and other surface structures of bacteria that aid in preventing their ingestion and subsequent destruction

• small, hair-like filamentous appendages outside cell wall
• comprised of the protein, pilin
• several antigenic types
• F (fimbriae)-pilus: involved in the transfer of genetic information between conjugating bacteria; also a receptor site for bacteriophages
• colonization factor antigens (adhesins): aid in the adherence of bacteria to mucosal cells; must occur before elaboration of toxin into target cell.

• single protein, flagellin (similar to muscle myosin)
• organelles of locomotion
• respond to chemotactic stimuli
• distribution on cell surface is species-dependent (ie: about 50% rods have them)

gram negative motile bacteria that have flexible, undulating, spiral-shaped rods on their end. Not parasitic, free-living in slime– commonly found in sewage or foul waters.

they have axial filaments (specialized organelles of locomotion in the spirochetes) located between the cytoplasmic membrane and the outer membrane; they are INTERNAL and produce a wave-like motion.

what are unique components of bacterial cytoplasmic membranes?

mesosomes: convoluted invaginations of the cytoplasmic membrane which function to:

1. aid in the formation of the division septum during binary fission
2. serve as an attachment point for the replicating chromosome

• sediment at 70S
• 30S subunit (16S rRNA + 21 proteins)
• 50S subunit (5S rRNA + 34 proteins)
• polyribosomes function similarly to those in cells of higher organisms
• discrete differences which allow use of antibiotics that selectively target protein sythesis
  • chloramphenicol
  • tetracycline

• single molecule of super coiled dsDNA
• associated with smaller amounts of RNA, RNApol, and maybe other proteins
• chromosome appears to be looped around an RNA core which holds the DNA in its compact form