Chapter 4: Infection

Ms. HarrisPathophysiology

Fall 2009

• What is an infection?– Colonization of a host organism by a foreign

species.– The infecting organism is called a pathogen.

• Can be infected by a number of microscopic organisms including bacteria, protozoa, fungi, and viruses (although viruses are NOT considered living).

Germ Theory

• Provided a link between microorganisms and disease– Was not verified until Robert Koch (Koch’s

Postulates) proved this by experimenting with mice and anthrax cultures in the 1880s.

Types of microbes

• BACTERIA– Prokaryotes- ???

• No nucleus• Unicellular

– Can be good or bad• Normal flora

Normal Flora

Resident flora present Sterile areas

Skin Blood and cerebrospinal fluid

Nose, pharynx, mouth Lungs, stomach

Colon, rectum, vagina, distal urethra

Uterus, fallopian tubes, ovary; bladder and kidney

Bacteria continued…

• Classified by their shape– Cocci = round (MRSA)– Bacilli = tic-tac or rod shaped (Clostridium

tetani)– Spirilla = spiral (Treponema pallidum)

Bacterial Structure

• Cell walls are either – Gram positive: has peptidoglycan in the cell

wall stains purple– Gram negative: no peptidoglycan in the cell

wall stains pinkishy red

• Antibiotics work on the cell walls of bacteria, that’s why they cannot hurt our cells!

• Bacteria usually cause disease by producing toxins and/or enzymes– Exotoxins- usually produced by G+. Can

interfere with nerve conduction (neurotoxin), cause vomiting (enterotoxin). Stimulate antibody production

– Endotoxins- usually produced by G-. Released once the bacteria dies. Causes fever, weakness, serious effects on circulatory system.

– Enzymes- you already know

Last bit of bacteria stuff

• Bacteria can form spores– Allow bacteria to survive long periods; highly

resistant (tetanus and botulism).

• Bacteria repro. By binary fission

VIRUSES

• Non-living- do NOT listen to your book! – Requires a living host to reproduce

• Capsid (protein coat) surrounding some DNA(usually) or RNA.– If RNA, its called a retrovirus…can you name

a retrovirus?

How viruses cause disease

• Attach to host cell and injects its genetic material

• Uses the host cell’s machinery to reproduce

• Lyses the cell (too many virus babies makes the cell explode)

• Some can enter latent phases

• Viruses are famous for mutating– Flu, colds

• Difficult to control

• Some are capable of causing cancer because they alter the host’s DNA…think HPV and link to cervical cancer.

Infection Part 2

Chapter 4

K. Harris

Major Grade Poster

• Create a disease awareness poster for your assigned disease

• Must include: – Prevelance/incidence/death rate– Is it epidemic or pandemic– Signs and symptoms– Potential complications– Geographic location of disease– Pictures – Pathophysiology of the disease

Fungal Infections

• Fungi are found everywhere.– Usually on places where its warm and moist.

• Fungal Infections are also called mycotic infections.

• Eukaryotic– Uni or multicellular

Good vs. Bad

• Just like bacteria and people, some fungi are good and some fungi are bad.– Good: a source of antibiotic drugs like

penicillin– Bad: the ones that cause disease.

Examples of Fungal Diseases

• Athletes foot

• Candida species– Cause of vaginal yeast infections and thrush

in infants

• Histoplasmas cause lung infections

Protozoan Infections

• Also called protists– Eukaryotic, can be uni or multicellular

• Examples include malaria, trichomonas,

amebic dysentery, etc.

Other parasites

• Helminths (actually worms…ewww…)– Eggs and larvae are found in contaminated

water and can be ingested.

Transmission of infection

• Direct contact

• Indirect contact (contaminated food or surfaces)

• Droplet transmission (oral or respiratory)

• Vector borne (carried by insect or other animal)

• Nosocomal infections- occurs in a healthcare facility

Host Resistance

• Interferons are produced by host cells in response to a virus to help nearby cells become resistant to viral attachment.

• Age, genetics, immunodeficiency, malnutrition, chronic disease

Other terms

• Pathogenicity- capability to become disease

• Virulence- degree of pathogenicity– Mutation of microbe

• “Superbugs” like MRSA---huge issue, especially in hospitals.

Infection Control

• Isolation; quarantine

• Universal precautions like handwashing

• Sterilization of materials (autoclaving)

• Disinfectants- chemicals to clean inanimate objects

• Antiseptics- chemicals to clean animate objects

Onset and Course

• Incubation period, then prodromal period, then acute period, then (usually) recovery.

• If not recovery:– Chronic infection– Septicemia- life threatening, systemic,

infection is active in the bloodstream (BAD)

Signs and symptoms

• Local: inflammation- pain, swelling, redness and warmth; purulent exudate if infection is bacterial in nature; serous exudate if viral; necrosis

• Systemic: fatigue, nausea, headache, pyrexia, subnormal temp., disorientation, seizures

Diagnosis

• Culture/staining to figure out what specifically is causing the infection

Drugs

• Usually, body can fight off infection on its own. Sometimes, drugs are required.

• Prophylactic treatment- given as a precaution.

Types of drugs

• Antibiotic- derived from living organisms (usually molds like penicillin and amoxycillin)– Broad spectrum: both G+ and G-– Narrow spectrum: either G+ or G-, not both

• Better because it is less likely to kill normal flora

• Antibacterials, antivirals, antifungals• Bactericidal- kill bacteria• Bacteriostatic- reduce reproduction rate

DRUUUUUUUUUUUGS

• How do they work?– Read and take notes on mode of action for

infection fighting drugs on pgs 98-99. – In your notes, after your summary, answer

the Think About questions on page 99.

Current Event

1. Write three cause/effect statements from the article.

2. What are the potential problems of antibiotics becoming obsolete.

3. Write a letter to your senator explaining the problem and what you think should be done about it.

Current event article

http://www.cnn.com/2009/HEALTH/10/01/antibiotic.penicillin.resistance/index.html?iref=newssearch