Microbiology: Unit II

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Microbiology Unit II

• By Julie E. Davis BSN, RN
• 08-09

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Classification of Microorganisms Bacteria

• Simple, single-celled or unicellular
• Found virtually everywhere
• Most are not harmful
• Are decomposers recyclers
• Some are pathogens such as
• Streptococcus/strep throat
• Klebsiella/pneumonia
• Pneumococcal/meningitis

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Bacteria (cont)

• Made of single chromosome of DNA surrounded by
  cell membrane, enclosed by cell wall
• Cell wall gives bacteria its shape makes it
  rigid
• Some bacteria are killed by the HCL acid in the
  stomach (however, some have mutated to become
  resistant can survive)

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Bacteria (cont)

• Grouped by shape
• Coccus (plural is cocci)-means sphere or round
• Prefixes describe arrangement
• Staphylo clusters
• Streptochains
• Diplopairs
• Bacillus (plural is bacilli)- means rod shaped
• Some have whip-like tails called flagella
• Spirillum (plural spirilla)-long cell with one or
  more curves or coils. AKA spirochaetes
• Many have flagella or tail that helps w/ movement

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Bacteria (cont)

• Reproduce by binary fusion-chromosome duplicates
  itself divides into two identical cells
• Aerobic-can reproduce only in the presence of
  oxygen
• Anaerobic-can reproduce only in the absence of
  oxygen
• Facultatively anaerobic-not inhibited either with
  or without oxygen

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Bacteria (cont)

• Gram Stain
• Way of grouping bacteria based on chemicals in
  their cell wall
• Gram negative or positive
• Gram positive appear blue or purple
• Gram negative appear pink or red
• Gram positive or negative never changes
• Useful to help identify the organism
• Eliminates one group or the other
• arrangement, stain, shape are all used to
  classify microbes

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Bacteria Special Characteristics

• Capsules
• Some bacilli cocci have these gelatinous
  sheaths that enclose the entire cell inhibits
  phagycytosis or engulfing by hosts white blood
  cells
• Makes these bacteria harder to treat giving them
  more time to reproduce establish themselves
  inside the host
• However, they are antigenic meaning they
  stimulate antibody production within the host
• Used in some vaccines

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Bacteria Special Characteristics (cont)

• Spores
• Some bacilli molds form spores in order to
  survive unfavorable conditions
• Dormant inactive stage that consists of the
  chromosome a small amount of cytoplasm
  surrounded by thick wall
• Some can survive heat, dehydration freezing
  that would normally kill the bacteria
• Spores are NOT susceptible to heat drying
• Few form spores but gas gangrene, botulism
  tetanus do
• Can survive for several years in this state
• Only way to kill is with autoclave (steam
  pressure)

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Bacteria Special Characteristics (cont)

• Toxins
• Chemicals produced by some bacteria that are
  harmful to host
• Digestion of host tissue allows the bacteria to
  absorb the digested nutrients
• Some toxins act on specific cells of host
• Neurotoxins disrupt the functioning of nerve
  cells, leading to the characteristic symptoms of
  each disease (botulism tetanus)

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Bacteria Special Characteristics (cont)

• Endotoxin
• Found in the cell walls of all gram negative
  cells
• All have the same effect on the host, causing
  possible fever circulatory shock
• Endotoxin shock is a life-threatening condition
  that may accompany any serious infection by Gram
  negative bacteria

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Antibiotics

• Chemicals used to treat bacterial infections
• Broad spectrum-used to treat many different kinds
  of bacteria (Ex Tetracycline)
• Narrow spectrum-affects just a few kinds of
  bacteria (Ex PCN)
• These chemicals disrupt or inhibit the chemical
  reactions that bacteria must carry out to survive.

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Antibiotics (cont)

• Work by
• Block the formation of cell walls
• Inhibit DNA synthesis
• Inhibit protein synthesis
• Our own cells carry out many of the same
  functionswhich is why our own cells may be
  damaged by antibiotics
• Most serious side effects are liver kidney
  damage depression of red bone marrow

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Antibiotics (cont)

• Another complication of ATB therapy is resistance
• Bacteria can develop an enzyme that destroys the
  antibiotic, rendering it useless.
• This is why C S is important before
  administering antibiotics
• Antibiotics are NOT a long term cure because
  bacteria will always evolve as their environment
  changes.
• Therefore, we have to try keep up, making new
  antibiotics.

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Viruses

• Are NOT cellscannot carry out life functions on
  their own
• They REQUIRE a host cell.
• Consist of DNA or RNA surrounded by protein
  shell.
• Can reproduce only when inside a cell
• Uses the host cells chromosomes to reproduce
• Cause disease by reproducing in the cell.
• Can remain dormant in the body for extended
  periods of

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Viruses (cont)

• Smaller simpler than bacteria
• All are parasites because they can only carry out
  life functions within a cell.
• All viruses are pathogenic, or cause disease.
  They cause disease by reproducing inside of cells
  causing cell death.
• Some can remain dormant for extended period of
  time (Chickenpox virus, which most of us acquire
  as children is in the family of the herpes virus.
  It can lie dormant in nerves for years, then be
  reactivated cause shingles as adult.)

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Antivirals

• Not very many of them
• In order to effectively kill a virus, the med
  must be able to enter the host cell or infected
  cell. Many kill host cell trying to kill virus.
• Antivirals are NOT considered cures, they are
  treatments only.
• Examples are acyclovir (Zovirax) or famvir,
  Valtrex for Herpes ribavirin for RSV virus many
  new HIV/AIDS treatment drugs fall into this
  category

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Fungi

• Also known as decomposers
• May be unicellular (yeasts) or multicellular
  (molds mushrooms)
• Most are saprophytes meaning they live on dead
  organic matter decompose it to recycle the
  chemicals as nutrients.
• Some are pathogenic causing infections that are
  called mycoses.
• Mycosis is an infection caused by a fungus.

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Fungi (cont)

• May be a part of normal flora, but in larger
  number may cause disease such as Candida albicans
  (vaginal yeast infection). The normal flora of
  the vagina create an acidic pH environment that
  prevents growth of pathogens
• Antibiotics may disrupt growth of normal flora
  allowing overgrowth of yeast.
• Candida is an important cause of nosocomial
  infection.
• Ringworm is another superficial mycosis.
• Systemic are more serious occur when spores
  gain access to the interior of the body
  (bloodstream).
• Spores are produces by many fungi ( some
  bacteria) are extremely difficult to destroy.
• Spores can often be inhaled.
• Other examples of mycosis is ringworm, althletes
  foot a certain type of meningitis

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Antifungal Meds

• Amphotericin B is one of the most effective use
  to treat serious systemic mycoses (but has
  serious side effects)
• These patients need periodic liver kidney
  function tests.
• There are also many superficial meds things
  life fluconazole.

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Protozoa

• Unicellular animals (ex amoebas)
• Most live in fresh water, soil salt water are
  NOT pathogenic. Only a few are pathogenic cause
  disease
• Frequently cause intestinal problems when
  ingested from contaminated food or water
  (fecal-oral route)
• Ex malaria, amoebic dysentery, pneumocystis
  pneumonia (common in AIDS patients)

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Anti-Protozoa Drugs

• Antimalarial antifungal drugs are used to treat
  these conditions
• Ex Quinine Flagyl

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Worms (Helminthes)

• Simple multicellular animals
• Live within hosts
• Most are free-living nonpathogenic
• Infestations include trichinosis (larvae in
  uncooked pork), hookworms, roundworms, tapeworms
  (live in small intestine).
• Harboring of worm parasites is called
  infestation
• There are meds available to treat

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Arthropods jointed legs

• Multicellular animals
• Ex lobsters, shrimp, lice, ticks mites
• Most important thing about arthropods is that
  many serve as vectors (spread pathogens from
  host to host)
• Ticks, for example, are vectors of Lymes disease

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Supplemental Reading

• Thibodeau, G. Patton, K. (2005). The human body
  in health and disease. (4th Ed.). St. Louis
  Elsevier Mosby.
• Chapter 5, pp. 116-124