Chapter 5/MicrobiologyJoe Pistack MS/ED

Disease

Disease-failure of the body to function normally.

A leading cause of disease in humans is invasion of the body by pathogens.

Pathogen-disease-producing microorganism.

Infection

Infection-invasion of the body by a pathogen and the symptoms that develop in response to this invasion.

Localized infection-restricted to a small area of the body.

Systemic infection-widespread infection throughout the body, usually spread by the blood.

Microorganisms (Microbes)

Bacteria-single-cell organisms found everywhere.

Normal flora-organisms that normally and harmoniously live in or on the human body without causing disease.

Prevents the overgrowth of other organisms, keeps them under control.

Bacteria

Bacteria make up the largest group of pathogens.

Successful invasion of pathogens can cause damage in two ways:

(1)-entering and growing in the human cell.

(2)-secreting toxins that damage the cells.

Classification of Bacteria

Bacteria are classified into three groups based on shape:

(1)coccus (round) (2)bacillus (rod-shaped) (3)curved rod

Rickettsiae and chlamydiae are also classified as bacteria, although they differ in several ways from cocci, bacilli, and curved rods.

Cocci

Cocci-round cells arranged in patterns.

Diplococci-cocci arranged in pairs.

Staphylococci-look like bunches of grapes and are arranged in clusters.

Cocci- responsible for many diseases such as

gonorrhea, meningitis and pneumonia.

Bacilli

Bacilli-long and slender and shaped like a cigar.

Diseases caused by bacilli include tetanus, diphtheria, and tuberculosis.

Curved Rods

Curved rods-include: vibrio

spirillum spirochete Cholera is caused by

the vibrio.Tightly coiled spirilla

are called spirochetes and are the cause of syphilis.

Bacteria

Many bacteria form spores, they allow the bacteria to survive in a dormant state during extreme conditions or when exposed to disinfectants.

When the conditions improve, the spores will wake from their dormant state and resume activity.

Ex. Clostridium botulinum, causes a deadly form of food poisoning. The spores that cause this disease can withstand several hours of boiling water.

Bacteria

Rickettsia and chlamydia are classified as bacteria, they are smaller than most bacteria and must reproduce within the living cells of a host.

Called parasites, because they require a living host.

Rickettsia are often carried by fleas, ticks and body lice.

Bacteria

Chlamydiae are smaller than rickettsiae and cause several diseases.

Chlamydia trachomatis is responsible for one of the most prevalent sexually transmitted diseases in the US today.

Chlemydial infection is also responsible for trachoma, a serious eye infection that is the leading cause of blindness in the world.

Viruses

Virus-smallest infectious agent.

Viruses are parasites, they can only reproduce within the living cells of a host.

Ex. of viral diseases, measles, mumps, influenza, poliomyelitis and AIDS.

Most upper respiratory infections are viral and are not responsive to antibiotics.

Virus

Fungus

Fungus-plantlike organism, grows best in dark, damp, places.

Mycotic infections-pathogenic fungal infections. Usually localized.

Ex. of fungal infections include athlete’s foot, ringworm, thrush, and vaginitis.

Athlete’s Foot

Fungal infection that causes redness, itching, burning.

Mildly contageous.Passed by direct

contact such as walking in locker rooms or around pools.

Rx. Topical antifungal lotion.

Ringworm

Skin infection caused by a fungus.

The fungus grows outwards from the center.

Skin becomes itchy, red, raised scales that may blister and ooze.

Rx. Antifungal lotions or pills.

Protozoa

Protozoa-single-cell, animal-like microbes.

Found in soil and most bodies of water.

The parasites are ingested in contaminated water and food and cause diarrhea.

Parasitic Worms

Helminths-multicellular animals that are parasitic and pathogenic to humans.

Microscopic examination of body samples is required to identify the worm.

The worms are classified as round-worms and flat-worms.

Parasitic Worms

Pinworm is a type of roundworm that is common in children.

The pinworm lives in the intestinal tract but deposits their eggs on the outer perianal area.

The deposition of the eggs causes itching, (pruritis).

Parasitic Worms

The child may scratch the anal area and transfer the eggs to the mouth.

The eggs are swallowed and newly hatched pinworms grow into adulthood in the intestine.

This transfer of eggs is called the fecal-oral route.

Pinworms

Flatworms

Tapeworm-form of flatworm.

Acquired by eating poorly cooked contaminated food such as beef, fish, or pork.

Tapeworms that live in the intestines may grow from 5ft. To 50ft. In length.

Tapeworms

Tapeworms attach to the intestines of the host.

Once anchored to the intestinal wall the tapeworm absorbs nutrients through it’s skin.

Symptoms include increased appetite, insomnia irritability.

Rx. Medications.

Ectoparasites

Ectoparasites-arthropods with jointed legs and include insects and ticks.

They live on the skin and mucous membrane.

Cause itching and discomfort.

Ex. lice, insects and ticks.

Ectoparasites

Mosquitoes, biting flies, fleas, and ticks act as vectors of disease.

Vector-object, living or non-living, that transfers a pathogen from one organism to another.

The bite of the vector introduces pathogens into the host causing infection.

Ectoparasites

Mosquito can carry the pathogens for malaria and encephalitis.

The tick can carry the pathogen that causes Lyme disease and Rocky

Mountain Spotted Fever.

Laboratory Identification

Methods of identifying pathogens: (1) Gram stain (2) Culture

Gram stain-bacteria are classified according to staining characteristics.

A dye is used to gram-stain the bacteria, gram-positive bacteria will stain purple or blue. Ex. streptococcus

Laboratory Identification

Gram-negative-bacteria will not absorb the dye, it will pick up a pink or red stain.

Ex. Escherichia coli

Bacteria is either gram-positive or gram-negative, gram staining may be an important step in identification of organisms.

Laboratory Identification

Acid-fast stain-the bacteria is first stained with a red dye and then washed with an acid.

Many bacteria lose the red stain when washed with acid, but several others retain the red stain and are therefore called acid-fast.

Ex. Mycobacterium tuberculosis (TB).

Gram stain

Laboratory Identification

Culture-growth of pathogens in a culture medium. Ex. Wound drainage

Culture and sensitivity-when the pathogen is cultured for susceptibility to

various antibiotics.

Antibiotic is placed in the same culture and stops the growth of the pathogen, it is assumed to be sensitive to the antibiotic.

Culture and Sensitivity

Modes of Transmission

Portal of Entry

Portal of Entry-how pathogens enter the body.

Portals of entry include:

Respiratory tract GI tract GU tract Eyes Skin

Portals of Entry

Parenteral route- includes injuries

that penetrate the skin or mucous membranes such as bites, cuts, or surgery.

Break in the skin is an excellent way for pathogens to enter the body.

Portals of Exit

Portals of Exit-the way that pathogens leave an infected body.

Portals of exit include:

Respiratory tract GI tract GU tract Eyes(tears) Breasts (milk)

Portals of Exit

Most common exits are the respiratory and gastrointestinal tracts.

Ex. Cold virus is sneezed or coughed into room air from the passages of the infected person.

Salmonella is excreted in stool.

Preventing Infection

By knowing the portal of exit we can set up procedures or take precautions to prevent the spread of disease.

Preventing Infection

Pathogens are spread :

Person to personEnvironment to

personInsects to person

Most important procedure in the prevention the spread of disease is

Handwashing!

Person-to-Person Contact

An infected person can spread germs by coughing or sneezing.

When a person sneezes, the cold virus is sprayed into the room in droplets.

The droplets are inhaled by co-workers.

The virus is spread by droplet contact.

Person-to Person Contact

A person with contaminated hands touches other objects in the office, ex. doorknobs, desktops, handshaking.

Vector-an object, living or non-living, that transfers a pathogen from one organism to another.

Fomite-nonliving vector.

Person-to-Person Contact

Environment-to-Person Contact

This mode includes contact with contaminated water, air, food, or soil.

Ex. You can develop food poisoning if you eat food contaminated with E-coli.

Animal-to-Person Contact

Insects act as vectors to transmit disease.

Ex. A mosquito bites a person with malaria, the malaria germ matures in the stomach of the insect. The insect then bites another person.

Nosocomial Infections

A hospital acquired infection- formerly known as nosocomial infection

Most often transmitted from person to person by direct contact.

Most frequently spread by professionals who Do Not Wash Their Hands!

Prevent the Spread of Infection