Introduction to Medical Microbiology

Question 1

What is Medical Microbiology?

Answer 1

“the study of microorganisms (including bacteria, viruses, fungi, and parasites) which are of medical importance and are capable of causing diseases in human beings”

Question 2

Why is Medical Microbiology important?

Answer 2

Infection is one of the most important causes of morbidity and mortality in the population.

Question 3

What is the normal flora?

Answer 3

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!

Question 4

What functions does the normal flora perform for the host? (3)

Answer 4

• Competition with pathogenic microorganisms
• Aids in digestion
• produces essential vitamins (e.g. folic acid, Vitamin K)

Question 5

What could happen if diseases are at the wrong site?

Answer 5

Disease (e.g. E.coli in the bladder → UTI)

Question 6

What is contamination?

Answer 6

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)

Question 7

What are two definitions for colonization?

Answer 7

1. First stage of microbial infection – successful occupation of new habitat not normally found in niche
2. Presence of bacteria on a body surface (i.e. skin, mouth, intestines) without causing disease in person

Question 8

What is an infection?

Answer 8

“Colonization and/or invasion and multiplication of pathogenic microorganisms in the host with or without the manifestation of disease”

Question 9

How are ALL living organisms classified? (4)

Answer 9

1. Kingdom
2. Phylum (family)
3. Genus
4. Species

Question 10

What is the Relevance of classifications?

Answer 10

• Diseases (bacteria, fungi, and virus most likely cause ACUTE infections)
• Mode of Transmission
• Treatments (antibiotics do not cure viral infections)

Question 11

What are the characteristics of a virus?

Answer 11

• 50-300nm (small)
• Unable to replicate independently (Invade host cells and use replication machinery in cell)
• Often difficult to treat
  *

Question 12

What are the characteristics of a bacteria?

Answer 12

• 500-800nm
• Capable of independent replication
• Cause most diseases in hospitals
• Many different species (e.g. Pneumonia, bacterial, meningitis, cellulitis)
• Treat with antibiotics

Question 13

What are characteristics of a fungus?

Answer 13

• Complex, large eukaryotes (AS ARE HUMANS)
• Separated into Yeast and Molds
• Cause a range of diseases (many are opportunistic)

Question 14

What are characteristics of a parasite?

Answer 14

• 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)

Question 15

Why are bacterias classified?

Answer 15

Different bacteria:

• cause different disease
• susceptible/resistant to different antibiotics
• some related to common flora ()others related to pathogens)

Question 16

How are bacteria classified?

Answer 16

Bacterium shape and cell arrangement (most basic method)

Question 17

What are three (3) morphological categories of bacteria?

Answer 17

• Bacilli (rod)
• Cocci (round)
• Spirilla (spiral)

Question 18

What are some common cellular arrangements of bacteria?

Answer 18

• Singly
• Chains
• Clusters

Some have flagella (enable motile capabilities)

Question 19

Flow chart for Antibiotic testing

Answer 19

Question 20

What is a Gram Stain?

Answer 20

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)

Question 21

What are bacteria wall differences of Gram Positive and Gram Negative?

Answer 21

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)

Question 22

What is the relevance to Gram reactions?

Answer 22

• Different gram reactions are susceptible to different groups of antibiotics
• Cause different diseases
• Differing characteristics (survival, cleaning, infection control, outbreak management)

Question 23

What is facultative anaerobic respiration?

Answer 23

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)

Question 24

What is the classification (i.e. gram stain) of Streptococcus species?

Answer 24

Gram Positive bacteria

Question 25

What is the **classification (i.e. gram stain)** of a **Clostridium** species?

Answer 25

Anaerobic Gram **Positive** Rods

Question 26

What is the **classification (i.e. gram stain)** of ***Enterobacteriaceae*** species?

Answer 26

Gram **Negative** Rods (e.g. *E.coli)*

Question 27

What is the **classification (i.e. gram stain)** of **Neisseria** species?

Answer 27

Gram **Negative** Diplococci

Question 28

What are some **general characteristics** of **Nonfermenting Gram Negative Rods**?

Answer 28

* 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

Question 29

What is the **Catalase test**?

Answer 29

* Used to **identify organisms that produce the enzyme (catalase)** * Catalase can breakdown compounds such as hydrogen peroxide (release bubbles ⇒ Catalase positive)

Question 30

What are examples of **Catalase Positive** bacteria? (Differentiate between Gram stains)

Answer 30

Aerobic Gram **_Positive_** **Cocci** * Micrococcus * Staphylococcus (MRSA) Aerobic Gram **_Negative_** **Cocci** * *Moraxella catarrhalis* * *Neisseria gonorrhoeae* * *Neisseria meningiditis*

Question 31

What are examples of **Catalase Negative** bacteria?

Answer 31

* *Enterococcus faecalis* * *Enterococcus faecium* * *Streptococcus agalactiae* (Group B) * *Streptococcus pneumoniae* * *Streptococcus pyogenes* (Group A) * *Viridans strept*

Question 32

What is the **Coagulase test**?

Answer 32

* 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**

Question 33

What is a **Blood Agar Plate**? What are different results observed? (give names)

Answer 33

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)

Question 34

What is a **Taxos P**?

Answer 34

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)

Question 35

What is a **Taxos A**?

Answer 35

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**

Question 36

What is a **Macconkey Agar**?

Answer 36

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_

Question 37

What is the Simmon's Citrate Agar?

Answer 37

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)