Microbiology, Sterilization, and Infection Control
I Classification of Microorganisms by Cell Type
II Eukaryotic Cell Structure (Figure 3-1)
1. Cell membrane: Complex lipoprotein structure.
2. Cell wall: Rigid to moderately rigid polysaccharide structure.
1. Endoplasmic reticulum: System of large sacs and smaller tubules responsible for macromolecular transport.
a. Smooth ER (without attached ribosomes): Involved in lipid and steroid synthesis.
b. Rough ER (with attached ribosomes): Involved in protein synthesis.
2. Mitochondria: Responsible for production of adenosine triphosphate and aerobic metabolism (Krebs’ cycle and electron transport chain); seen in animal cells.
3. Chloroplasts: Contain pigments, starches, and enzymes used in photosynthesis; seen in plant cells.
4. Ribosomes: Free or attached to ER; responsible for protein synthesis.
5. Lysosomes: Contain proteolytic enzymes for metabolism of ingested organic material.
III Prokaryotic Cell Structure (Figure 3-2)
1. Cell membrane or plasma membrane
b. The inner layer beneath the cell wall.
c. Acts as osmotic barrier and is the site of some enzyme activity.
2. Cell wall: Moderately rigid to very rigid structure
3. Cell wall in gram-positive bacteria
b. Murein network: Peptide chains attached to larger polysaccharide chains
c. Stains violet on Gram stain because of peptidoglycan in the cell wall
4. Cell wall in gram-negative bacteria: three layers
a. The inner layer is a mucopeptide.
b. The middle layer is lipopolysaccharide.
c. The outer layer is a lipoprotein.
d. Stains pink on Gram stain with counter-safranin stain because of lack of peptidoglycan.
1. No distinct nucleus; no separation from the cytoplasm.
2. The cell may contain one or more regions of nuclear material called nucleoids.
4. Chromosomes exist freely in cytoplasm; may be circular or attached to the cell membrane.
2. Mitochondria are absent. Aerobic metabolic enzymes are present in the form of multienzyme complexes; they are attached to the cell membrane or other internal membranes.
3. Chloroplasts are absent. Photosynthetic enzymes and pigments are present in special arrangements; these are not separated from the cytoplasm by a membrane.
4. Ribosomes: Slightly smaller than eukaryotic ribosomes; exist freely in cytoplasm.
5. Mesosome: They are found in the cell membrane and allow for attachment of DNA in cell division. They are found chiefly in gram-positive forms.
1. They are the intermediate form of the organism that develops in response to adverse environmental conditions.
2. They will regenerate to a vegetative cell when conditions improve.
3. They are notably produced by the aerobic genus Bacillus and the anaerobic genus Clostridium, and Sporosarcina.
4. They resist adverse environmental conditions of dryness, heat, and poor nutrition.
5. A true spore is a highly refractile body formed within the vegetative bacterial cell.
6. They function as a protective coat around nucleic material that may remain inside the cell (endospore) or extend beyond the width of the cell (exospore).
7. They are metabolically active and contain essential enzymes of Krebs’ cycle.
IV Bacterial Growth Requirements
A Growth medium: Needs vary with specific bacteria.
1. Simple nutrients: Water, carbon, hydrogen, nitrogen, oxygen, sulfur, phosphorus, calcium, potassium, and magnesium
2. Complex nutrients: Sugar, amino acids, and blood products
B Atmospheric gas requirements
1. Obligate anaerobes reproduce only in an oxygen-free environment. Oxygen is toxic to these organisms.
2. Aerotolerant anaerobes are organisms unaffected by exposure to oxygen.
3. Facultative anaerobes reproduce under aerobic or anaerobic conditions.
4. Microaerophilic anaerobes reproduce best at low oxygen tensions. High oxygen tensions are inhibitory.
5. Obligate aerobes require oxygen for reproduction.
6. Chemolithotrophic and photolithotrophic bacteria use carbon dioxide as their principal source of carbon.
C Temperature requirements, optimal growth ranges:
1. Psychrophilic: −5° C to 30° C (optimum 10° C to 20° C)
2. Mesophilic (pathogenic): 10° C to 45° C (optimum 20° C to 40° C)
D The osmotic pressure requirement varies with each bacterial species. Most require a 0.9% saline environment.
E Hydrogen ion (pH variations)
VI Growth Pattern: A new culture of bacteria will develop similar to the growth curve seen in Figure 3-3.
A Lag phase: Adaptation to new environment; little reproduction.
B Exponential phase: Stage of rapid cell growth.
C Stationary phase: Equal death and growth rates.
D Death phase: Depletion of culture nutrients and buildup of toxic waste; death rate exceeds growth rate.
A Autotroph: An organism capable of using simple inorganic matter as nutrients (nonpathogenic).
B Heterotroph: An organism that requires organic matter for growth and survival (pathogenic).
C Symbiosis: Two dissimilar organisms existing together.
1. Amensalism: One organism is inhibited, and the other is not affected.
2. Commensalism: One organism benefits, and the other is not affected.
3. Mutualism: Each organism benefits and is unable to survive without the other.
4. Parasitism: One organism benefits, and the other is harmed.
5. Synnecrosis: Both organisms are harmed by the relationship.
IX Microbial Shapes (Figure 3-4)
A Purpose: Used to identify and categorize bacteria based on cell components.
1. Bacteria can be separated into two general categories by virtue of their staining properties: gram-positive or gram-negative.
2. Variation in staining is determined by cell wall construction.
a. Basic dye is crystal violet (all organisms take up this dye).
b. The specimen is then covered with Gram’s iodine.
c. A water rinse is then performed.
d. The specimen is then decolorized with acetone.
e. A water wash is then performed.
f. The specimen is counterstained with red dye (usually safranin).
XI Definitions Related to Microorganisms
A Contamination: Presence of a microorganism in an otherwise sterile environment.
B Pathogen: Any disease-producing microorganism.
C Virulence: Heightened ability of an organism to produce infection in its host.
D Aerobic: Growth only in the presence of oxygen.
E Anaerobic: Growth in the absence of oxygen.
F Toxins: Poisonous substances produced by bacteria.
G Vegetative cell: Metabolically active form of a bacterium in which reproduction can occur.
H Vector: An insect, animal, or other carrier that transfers an infecting agent or pathogen from one host to another.
I Host: An organism that harbors or furnishes nutrition to a dissimilar organism.
J Bacteremia: The presence of bacteria in the blood.
K Septicemia: A condition in which pathogens and their associated toxins are present in the blood.
L Toxemia: The presence of bacterial toxins in the blood.
N Pyemia: Condition in which pus-forming bacteria have entered the bloodstream.
XII Definitions Related to Immunologic Response
A Infection: An inflammatory process resulting from the presence and growth of a pathogenic organism.
B Inflammation: A tissue response to injury or stress that can cause local vascular dilation, fluid exudation, and/or leukocyte accumulation at the site caused by a microorganism or some other stress.
C Superinfection: Infection developed primarily in the debilitated or immunosuppressed patient previously treated with antibiotics.
D Nosocomial infection: Hospital-acquired infection.
E Immunity: The ability of the body to resist or overcome infection or disease.
F Plasma cell: Cells that specialize in the production of antibodies.
G Eosinophils: White blood cells with two- or three-lobed nucleus and large cytoplasmic granules.
1. They are able to phagocytize antigen-antibody complexes.
2. Increase in number occurs with hypersensitivity and parasitic infections.
H Lymphocyte: White blood cells formed in the lymphatic system and by the thymus gland.
1. Have a single nucleus with no granules.
2. Can become plasma cells that may form antibodies.
3. Can attract and localize macrophages to an area of infection.
I T lymphocytes: Specialized white blood cells formed by the thymus gland.
J Macrophage: Large mononuclear phagocytic cell.
K Monocyte: White blood cell (leukocyte) with a single nucleus (mononuclear) that is capable of phagocytosis.
L Polymorphonucleated leukocyte (neutrophil): White blood cell with a multilobed nucleus capable of phagocytosis.
M Antibody: Developed in response to antigen.
1. Produced by lymphoid tissue in response to an antigen.
2. Antibodies can cause invading antigens or microbes to clump, rendering them easier for ingestion by macrophages and granulocytes.
N Antigen: A substance, often a protein, that gains access to the bloodstream or a body tissue.
A Infection occurs when a pathogen is able to overcome the barriers of a host.
B Three elements must be present for an infection to develop:
C Factors that increase host susceptibility to infection include:
D The high incidence of nosocomial gram-negative bacterial pneumonias is associated with factors that promote colonization of the pharynx (Box 3-1).
E Patients with artificial airways are at highest risk of nosocomial pneumonia.
F Pathogens can be transmitted to a host by five major routes (Table 3-1).
TABLE 3-1
Routes of Infectious Disease Transmission
| Mode | Type | Examples |
| Contact | Direct | Hepatitis A |
| Venereal disease | ||
| HIV | ||
| Staphylococcus | ||
| Enteric bacteria | ||
| Indirect | Pseudomonas aeruginosa | |
| Enteric bacteria | ||
| Hepatitis B and C | ||
| HIV | ||
| Droplet | Haemophilus influenzae (type B) pneumonia and epiglottitis | |
| Neisseria meningitidis pneumonia | ||
| Diphtheria | ||
| Pertussis | ||
| Streptococcal pneumonia | ||
| Influenza | ||
| Mumps | ||
| Rubella | ||
| Adenovirus | ||
| Vehicle | Waterborne | Shigellosis |
| Cholera | ||
| Foodborne | Salmonellosis | |
| Hepatitis A | ||
| Airborne | Aerosols | Legionellosis |
| Droplet nuclei | Tuberculosis | |
| Varicella | ||
| Measles | ||
| Dust | Histoplasmosis | |
| Vectorborne | Ticks and mites | Rickettsia, Lyme disease |
| Mosquitoes | Malaria | |
| Fleas | Bubonic plague |
From Wilkins RL, et al: Egan’s Fundamentals of Respiratory Care, ed 8. St. Louis, Mosby, 2003,
2. Droplet: Contact with large droplets produced by an infected or contaminated individual.
4. Common vehicle: Pathogen transmitted to host in contaminated food or water.
5. Vectorborne: Transmission by an animal from infected individual to host, usually by insects.
XIV Notable Gram-Positive Pathogenic Bacteria
A Bacillus anthracis: Causes skin infections, septicemia, enteritis, meningitis, anthrax, and pneumonia (woolsorter’s disease).
XV Notable Gram-Negative Bacteria (see Box 3-1)
1. Gram-negative aerobe and facultative anaerobe.
2. Rod shaped and found as a single organism.
3. Causes up to 10% of all hospital-acquired infections.
4. Causes pneumonia with characteristic green odoriferous sputum.
5. Causes wound infection, urinary tract infection, empyema, meningitis, and septicemia.
1. Gram-negative aerobe and facultative anaerobe.
2. Rod shaped and found as a single organism.
3. Responsible for approximately 45% of all nosocomial infections.
4. Causes necrotizing pneumonia, septicemia, endocarditis, meningitis, wound infections, and urinary tract infections.
1. Gram-negative aerobe and facultative anaerobe.
2. Short rod and found as a single organism.
4. Causes necrotizing pneumonia with characteristic “red currant jelly” sputum.
1. Gram-negative aerobe and facultative anaerobe.
2. Minute rod found as a single organism.
3. Most common cause of epiglottitis in children.
4. Causes meningitis, laryngitis, croup, and subacute bacterial endocarditis.
1. Gram-negative aerobe and facultative anaerobe.
2. Rod shaped and found as single organism.
5. Transmitted through contaminated water and, less frequently, contaminated food.
1. Found in animals, particularly shellfish, swine, and fowl.
2. Causes enteritis that may progress to meningitis, encephalitis, or nephritis.
3. Transmitted orally via contaminated milk, turtles, eggs, undercooked chicken, fish, clams, and pork.
