Microbiology week 1

Question 1

Describe viruses

Answer 1

Viruses:
– Smallest infectious particle with nucleic acid (18-300 nm)
– DNA or RNA; not both plus proteins for replication (categorized by DNA/RNA; RNA makes more mistakes)
– Enclosed in a protein coat
Lipid membrane
– True parasites: require host cells for replication

Question 2

Describe Fungi

Answer 2

Fungi:
- Eukaryotic organisms with nucleus, mitochondria, Golgi bodies, and endoplasmic reticulum
– Can exist as yeast or filamentous mold
– Some fungi can exist as both forms, called dimorphic

Question 3

Outline the steps required for establishment of infectious diseases

Answer 3

• Encounter: Exogenously acquired diseases (from contact with microbes in the environment)[ie food, water, air, objects, insect bites, animals]
• Entry: sites of the body in direct contact with exterior (eyes, nose, moth, respiratory tract, alimentary tract, genital tract, urinary tract
• Microbe remains on mucosa. Examples:After inhalation: agent of whooping cough, After ingestion: agent of cholera
• Microbe penetrates mucosal or skin barrier into tissue. Examples: After insect bite: agent of malaria, After cuts and wounds: agents of subacute endocarditis, After blood transfusion: HIV
• Spread/ Multiplication: For microbe to cause disease, initial inoculum size matters, and it is organism and site of entry dependent. The number of organism must reach a certain threshold (multiply) to cause disease in the face of host defenses.
• Damage: colonization through adherence or invation: tissue destruction, toxins, immunopathology and immune evasion
• Outcome

Question 4

Differentiate between exogenous versus endogenous causes of infectious diseases.

Answer 4

Exogenous vs. Endogenous Bacteria
A small fragment of bacteria causes disease in humans,and many species colonize in the human body to create an ecosystem know as bacterial flora. Bacterial flora is endogenous bacteria, which is defined as bacteria that naturally reside in a closed system.[8] Disease can occur when microbes included in normal bacteria flora enter a sterile area of the body such as the brain or muscle.[9]This is considered an endogenous infection. A prime example of this is when the residential bacterium E. coli of the GI tract enters the urinary tract.[10] This causes a urinary tract infection. Infections caused by exogenous bacteria occurs when microbes that are noncommensal enter a host.[11] These microbes can enter a host via inhalation of aerosolized bacteria, ingestion of contaminated or ill-prepared foods, sexual activity, or the direct contact of a wound with the bacteria

Question 5

Relate the sites in the human body that are colonized by normal microbial flora:

Answer 5

• Skin
• Respiratory tract: nose and throat
• Digestive tract: mouth and large intestine
• Genital tract: vagina

Question 6

Explain the critical role of normal human flora in health and disease states

Answer 6

Health:
•Immune stimulation
• Possible role in human nutrition and metabolism
• Keeping out invaders

Harm:
• Can produce carcinogens
• Can be source of infection,e.g aspiration pneumonia
• Can be imbalanced

c-diff can form in the gut after treatment with antibiotics, especially for patients who are hospitalized. stool transplants are helpful with treatment of this issue

Question 7

Describe bacteria

Answer 7

Bacteria

• Unicellular prokaryotes, i.e., no nuclear membrane, mitochondria, Golgi bodies, or endoplasmic reticulum
• 1 to 20 microns; different shapes: rod or cocci, spirals
• Divided by binary fisson
• Either gram positive (blue) with a thick cell wall or gram negative (pink) with a thin cell wall = peptidoglycan is what antibiotics target = selective toxicity

Question 8

Describe parasites

Answer 8

Parasites:
– Complex eukaryotes
– Some are unicellular and others are multicellular
– Can range in size from tiny protozoa to 10 meter tapeworms (malaria, hook worms)

Question 9

Describe prions

Answer 9

Prions.
– Small proteinacious infectious particles
– Mutant form of a host protein
– Classified as slow viruses BUT unlike viruses, they have no virion structure or
genome.
– Resistant to chemicals, heat, and ionizing radiation

Question 10

Describe host factors that inhibit establishment of infection:

Answer 10

• Saliva-washes away bacteria and has anti-microbial factors
• Cough reflex
• Acidic ph of stomach
• Peristalsis in gut
• Presence of normal flora
• Skin as a barrier to sterile sites
• Shedding of infected epithelial cells