What is Medical Microbiology?
"the study of microorganisms (including bacteria, viruses, fungi, and parasites) which are of medical importance and are capable of causing diseases in human beings"
Why is Medical Microbiology important?
Infection is one of the most important causes of morbidity and mortality in the population.
What is the normal flora?
The population of bacteria, fungi, and parasites that live on the human body.
- Systems include Skin, Nose, Mouth, GI Tract
- Humans are NOT microbiologically sterile!
What functions does the normal flora perform for the host? (3)
Competition with pathogenic microorganisms
- Aids in digestion
produces essential vitamins (e.g. folic acid, Vitamin K)
What could happen if diseases are at the wrong site?
Disease (e.g. E.coli in the bladder → UTI)
What is contamination?
Presence of an organism in a culture that was not there when the sample was taken (e.g. blood culture with an organism from the skin ⇒ contaminated)
What are two definitions for colonization?
- First stage of microbial infection – successful occupation of new habitat not normally found in niche
Presence of bacteria on a body surface (i.e. skin, mouth, intestines) without causing disease in person
What is an infection?
"Colonization and/or invasion and multiplication of pathogenic microorganisms in the host with or without the manifestation of disease"
How are ALL living organisms classified? (4)
- Phylum (family)
What is the Relevance of classifications?
Diseases (bacteria, fungi, and virus most likely cause ACUTE infections)
- Mode of Transmission
Treatments (antibiotics do not cure viral infections)
What are the characteristics of a virus?
- 50-300nm (small)
- Unable to replicate independently (Invade host cells and use replication machinery in cell)
- Often difficult to treat
What are the characteristics of a bacteria?
- Capable of independent replication
- Cause most diseases in hospitals
- Many different species (e.g. Pneumonia, bacterial, meningitis, cellulitis)
- Treat with antibiotics
What are characteristics of a fungus?
- Complex, large eukaryotes (AS ARE HUMANS)
- Separated into Yeast and Molds
- Cause a range of diseases (many are opportunistic)
What are characteristics of a parasite?
- Lives in/on a host
- Retrieves food from or at the expense of the host
- can cause disease in humans (some easily treated)
- Usually exist in the tropics or subtropics (some developing countries)
Why are bacterias classified?
- cause different disease
- susceptible/resistant to different antibiotics
- some related to common flora ()others related to pathogens)
How are bacteria classified?
Bacterium shape and cell arrangement (most basic method)
What are three (3) morphological categories of bacteria?
What are some common cellular arrangements of bacteria?
Some have flagella (enable motile capabilities)
Flow chart for Antibiotic testing
What is a Gram Stain?
Method of differentiating bacteria (gives initial possible identity of organism)
- May be Positive (+) or Negative (-) dependent on bacteria
- Further classified based on shape (e.g. rod, coccus)
- 4 Combinations: G(+) rod, G(+) coccus, G(-) rod, G(-) coccus
First available result on blood cultures (rapid, can be completed without growing organism)
What are bacteria wall differences of Gram Positive and Gram Negative?
Gram Positive: thick peptidoglycan layer ("teichoic acid")
- Retains crystal violet stain (appears deep violet-blue)
- Resist discoloration
Gram Negative: thick lipopolysaccharide layer (little/no teichoic acid)
What is the relevance to Gram reactions?
- Different gram reactions are susceptible to different groups of antibiotics
- Cause different diseases
Differing characteristics (survival, cleaning, infection control, outbreak management)
What is facultative anaerobic respiration?
Microorganism that can perform in either under aerobic or anaerobic respiration depending on environment (prefers aerobic due to higher efficiency, however, no oxygen is a simple switch to anaerobic)
What is the classification (i.e. gram stain) of Streptococcus species?
Gram Positive bacteria
What is the classification (i.e. gram stain) of a Clostridium species?
Anaerobic Gram Positive Rods
What is the classification (i.e. gram stain) of Enterobacteriaceae species?
Gram Negative Rods (e.g. E.coli)
What is the classification (i.e. gram stain) of Neisseria species?
Gram Negative Diplococci
What are some general characteristics of Nonfermenting Gram Negative Rods?
- Predominantly opportunistic
- Pathogenicity related (usually) to altered/already debilitated host
- Nomenclature of these organism changes rapidly (new genera defined with use of molecular techniques)
- do NOT ferment glucose
- may rapidly develop resistance to antimicrobials use in treatment
What is the Catalase test?
- Used to identify organisms that produce the enzyme (catalase)
- Catalase can breakdown compounds such as hydrogen peroxide (release bubbles ⇒ Catalase positive)
What are examples of Catalase Positive bacteria? (Differentiate between Gram stains)
Aerobic Gram Positive Cocci
- Staphylococcus (MRSA)
Aerobic Gram Negative Cocci
- Moraxella catarrhalis
- Neisseria gonorrhoeae
- Neisseria meningiditis
What are examples of Catalase Negative bacteria?
- Enterococcus faecalis
- Enterococcus faecium
Streptococcus agalactiae (Group B)
- Streptococcus pneumoniae
Streptococcus pyogenes (Group A)
- Viridans strept
What is the Coagulase test?
- Coagulase clots blood plasma
- Performed on Gram-positive, catalase-positive Staphylococcus aureus
- Considered a virulence factor
- Formation of a clot around an infection most likely protects bacteria from phagocytosis
What is a Blood Agar Plate? What are different results observed? (give names)
Considered a differential medium, the BAP test observes the ability of an organism to produce hemolysins (enzymes that damage/lyse RBCs – Helpful in differentiating between Streptococcus and Enterococcus species
- ß-hemolysis = complete hemolysis (transparent zone surround the colonies
- alpha-hemolysis = partial hemolysis (colonies surrounded by green/opaque zone)
- gamma hemolysis = no hemolysis (no notable zones)
What is a Taxos P?
Also termed the Optochin Sensitivity Test, used to distinguish between organisms' sensitivity to the antibiotic optochin – used to distinguish between Streptococcus pneumonia (sensitive, right side) and other alpha-hemolytic streptococci (resistant, pictured left side)
What is a Taxos A?
Test used to distinguish organisms that are sensitive to bacitracin (peptide antibiotic, produced by Bacillus subtilis, that inhibits cell wall synthesis and disrupts cell membranes) – commonly used to distinguish between ß-hemolytic streptococci
What is a Macconkey Agar?
Selective and differential medium used to differentiate between the Enterobacteriaceae species
- Selective: Bile salts inhibit growth of Gram-positive bacteria
- Differential: Lactose fermentation is observed as a bright pink-red color from acidic pH
What is the Simmon's Citrate Agar?
Distinguishes organisms that are able to use citrate as sole carbon source – differentiate between different Enterobacteriaceae species (bromthymol blue, alkaline pH, is a citrate positive indicator)