Microbiology unit 5

Infection

• colonization of part of the body by a

  pathogen

• colonization of the “wrong” part of

  the body by an opportunistic pathogen

Infectious Disease

altered state of health caused by infection

Aymptomatic carriers

People with infection, but not related disease

When a person is ill, the first step in deciding what to do is to

Identify the causal agent

diagnosis

Identifying the microbe

Three ways to ID bacteria

1. Nucleic acid tests

2. Serological tests

3. Traditional microscopy, culturing, and testing

Nucleic acid tests (bacterial)

• Based on microbe’s DNA or RNA

• very sensitive and very accurate; highly technical

Example of Nucleic acid tests (bacterial)

Detect DNA of M. tuberculosis in sputum

Serological tests (bacterial)

• based microbe’s specific antigens

• Accurate, fast

Example of Serological tests (bacterial)

• Rapid strep tests

• Show binding between a surface protein of strep bacteria + antibodies in the test materials

2 examples of Traditional microscopy, culturing, and testing (bacterial)

1. Gram stain

2. Blood agar showing hemolysis are + for Streptococcus pyogenes

Three ways to ID viruses

1. Nucleic acid tests

2. Serological tests

3. Cell culture and infectivity assays

Nucleic acid tests (viral)

• based on viral DNA or RNA

• very sensitive and very accurate; highly technical

2 examples of Nucleic acid tests (viral)

1. Donated blood is screened for HIV

2. The SARS CoV-2 test

Serological tests (viral)

based on virus-specific antigens

Example of Serological tests (viral)

diagnose Hepatitis A and B

Cell culture and infectivity assays (viral)

1. A suspected virus sample can be added to a cell culture

2. If the virus is active, the cells will show abnormalities

communicable diseases

pathogen or parasite is transmitted host-to-host

The vast majority of diseases are

communicable

non-communicable diseases

germ is not transmitted from host-to-host (indirect)

Non-communicable diseases are

uncommon

2 examples of non-communicable diseases

1. Botulism

2. tetanus

   germ comes indirectly from soil → host

zoonosis

disease transmitted from animals → humans

Example of zoonosis disease

Rabies

Non-infectious disease

Diseases not caused by microorganisms

3 examples of non-infectious disease

1. Genetic disease

2. Diabetes

3. Most cancers

Sickle cell anemia is what type of disease

Non-infectious/genetic disease

Most peptic + duodenal ulcers are caused by

Helicobacter pylori

Treatment for peptic + duodenal ulcers

Antiobiotic therapy

Pneumonia caused by bacteria

1. Streptococcus

2. Haemophilus

Pneumonia caused by virus

respiratory syncytial virus

Pneumonia caused by fungi

Pneumocystis (affects AIDS patients)

Meningitis caused by bacteria

1. Neisseria

2. Streptococcus

3. Haemophilus

Meningitis caused by virus

Picornaviridae

Meningitis caused by fungi

Cryptococcus (yeast-like fungus)

Staphylococcus aureus can cause

1. Urinary tract infections

2. pneumonia

3. septicemia

4. heart infections

5. toxic shock syndrome

Escherichia coli can cause

1. Pneumonia

2. urinary tract infections

3. peritonitis

4. wound infections

5. septicemia

Streptococcus pyogenes (GAS) can cause

1. Puerperal sepsis

2. strep throat

3. scarlet fever

4. necrotizing fasciitis

5. heart infections

Haemophilus influenzae can cause

1. Ear infections

2. meningitis

3. pneumonia

4. bronchitis

Local infection

limited to one area of body

Systemic infection

• spread throughout body

• microbe usually moves in blood or lymph after local infection

Endemic

• normally present

• number of cases remains stable (no big changes)

Epidemic

large increase in number of cases in short period of time

Pandemic

world-wide epidemic

Reservoir

source of pathogens

Transmission

movement of pathogens

Septicemia

bacteria multiplying in blood

Toxemia

toxins in blood (usually bacterial)

Viremia

virus particles in blood

Pathogenicity

ability to cause disease

Virulence

measure of pathogenicity

Opportunist

need predisposing factor

True pathogen

need no predisposing factor

leukocidins

kills white blood cells

what two bacterial genus form leukocidins

1. staphylococci

2. streptococci

hemolysins

kill red blood cells

what two bacterial genus form hemolysins

1. Clostridium

2. Streptococcus pyogenes (GAS)

Coagulase

exoenzyme formed by Staphylococcus aureus that clots blood

exotoxins

• proteins

• circulate in blood and lymph

• good antigens

• cause strong immune response (antibody production)

Endotoxins

• lipid molecules (lipid A)

• gram - cell wall

• Not toxic until freed by disintegration of cell

• poor antigens = poor immunity

septic shock

• Gram - sepsis

• life-threatening condition