Classification of Organisms

Major Classifications of Organisms
Microbial Relationships
Independence
two different kinds of organisms live independently without affecting the other
Symbiosis
Close relationship
Mutualism – derives some
benefit from each other
Commensalism – one organism
derives benefit but does not
hurt the other
Parasitism – one organism
derives benefit from the other,
at the other’s expense
Antibiosis
One organism produces substances or causes conditions which are lethal for the other
There are five major classes of organisms
Protozoa
Fungi
Bacteria
Rickettsia
Viruses
Protozoa
Unicellular
Simplest form of animal life
Microscopic
Consume solid food particles
Can reproduce sexually or asexually by fission
Become inactive in adverse conditions
Protozoan Disease
Amebic dysentery
Caused by Entamoeba histolytica
Symptoms: intense diarrhea with bloody, mucous-filled stools
Occurs following fecal contamination of food or drink
Malaria
Caused by a parasite of the Plasodium genus
Transmitted by the female Anopheles mosquito or by contaminated needle or blood transfusion
Characterized by chills and fever
Protozoan Disease
(continued)
Trichomonas infection
Caused by Trichomonas vaginalis
Characterized in women by vaginitis with a profuse, cream-colored, foul smelling discharge. Can be misdiagnosed as a yeast infection.
Transmitted by sexual intercourse, contaminated examination equipment and contaminated towels
Fungi
Are of the plant kingdom
Lack chlorophyll
Over 100,000 species
Include yeasts and molds
Some fungi are common on stale bread, rotten fruit, or damp leather
Have to exist as either
Parasite – existing on another living organism
Saprophyte – living on dead matter
Some like mushrooms are visible to the naked eye
Most medically important fungi are microscopic
Yeast
Are unicellular, microscopic organisms
Reproduce by budding
Some are used commercially in preparing beer, wine, and breads
A common yeast mycosis is Candida infection caused by Candida albicans
Infects mucous membranes of the mouth and is known as thrush
Infects female genitalia and is known as vulvovaginitis or vaginal thrush
Note: Thrush is seen commonly in newborns infected by the mother
Molds
Are multicellular
Are characterized by a fuzzy growth of interlacing filaments called hyphae
Reproduce by spores
Some may be seen on foods such as bread and cheese
Ringworm of the scalp (Tinea capitis) and ringworm of the foot (Tinea pedis – athlete’s foot) are common mycoses caused by molds
Bacteria
Are unicellular
Are simple plant organisms
Ordinarily do not contain chlorophyll
Approx. 2000 know species and are found everywhere
Only about 100 species produce disease in humans
Two classifications
Pathogenic – produce toxins which cause many diseases such as syphilis, gonorrhea, tuberculosis, typhoid and paratyphoid fevers, and whooping cough
Nonpathogenic – essential for life, assist in decomposition of matter, and aid in production of some foods and chemicals such as cheeses, sauerkraut, cultured milk products, and lactic acid
Reproduce asexually by binary fission
Have rigid cell wall which blocks entrance of certain substances
Morphology
Three basic shapes
Coccoid (Cocci)
Round
Bacillus (Bacilli)
Rod
Spiral
Curved or spiral
Mycoplasmas
No cell wall
Growth Rate
Refers to the increase in the number of microbes
Motility
The ability to move
Flagella
Axial filaments
Moisture
Drying may kill some bacteria
Note: There are some bacteria that can withstand drying for a long period of time and become active again.
Food
Autotrophic bacteria use carbon dioxide and other inorganic compounds for food and are nonpathogenic
Heterotrophic bacteria require living or dead organic matter for food and are pathogenic
Parasites utilize living organic matter for food
Saprophytes utilize dead organic matter for food
Examples: tetanus, gas gangrene, and botulism
Two classifications
Aerobic
Need oxygen
Examples: Staphylococcus aureus (responsible for skin and wound infections)
Anaerobic
Cannot live with oxygen
Examples: Clostridium sp.(causes tetanus, gas gangrene, and botulism
Anaerobes
Three types of anaerobes
Obligate
Will not grow in any oxygen
Facultative
Able to survive with or without oxygen
Aerotolerant
Do not need oxygen, grow better without
Can survive in CO2 environment
Moderate temperature
High heat destroys most bacteria
Pre-vacuum steam autoclaves enables the heat to penetrate resistant strains
Freezing does not always destroy bacteria, but does reduce growth
Darkness
Most bacteria are killed by direct sunlight
Spore formation is stimulated by sunlight (because the bacterium is stressed)
Neutral pH
Most bacteria grow best close to the neutral point on the pH scale or slightly on the alkaline side
Both acids and alkalis are harmful to bacteria
Pathogenicity and Metabolism
Their ability to cause disease
Endotoxins
Contained in the cell wall
Released when cell dies
When released it produces symptoms
Examples: typhoid fever and bacillary dysentery
Exotoxins
Most potent toxins known
Secreted out of the intact cell into the surrounding tissue
Will produce the symptoms and lesions of the disease
Example: Tetanus, gas gangrene, diphtheria, and scarlet fever
Eukaryotic and Prokaryotic Cells
Eukaryotes
Prokaryotes
Simple cell structure such as bacteria
Bacteria and the diseases
they cause
Cocci
Certain strains of Staphylococci
Food poisoning
Staphylococcus aureus
Most post-operative wound infections
Neisseria gonorrhoeae
Gonorrhea
Neisseria meningitis
Bacterial (meningococcal) meningitis
Bacilli
Salmonella typhi - typhoid fever
Shigella dysenteriae – bacterial dysentery
Escherichia coli – gastroenteritis, UTI, epidemic diarrhea in newborn nurseries
Clostridium tetani – tenanus (lock jaw)
Clostridium perfringens – gas gangrene
Clostridium botulinum – botulism
Pseuomonas aeruginosa – severe wound infections, , osteomyelitis, meningitis, and septicemia when resistance of host is especially low, such as in burn patients.
Spiral Shaped bacteria
Spirochete – Treponema pallidum – causes syphilis
Vibrio – Vibrio cholerae – causes cholera
Rickettsia
Are much smaller than bacteria, but larger than viruses
Are obligate intracellular parasites
Meaning that they can only reproduce and thrive within the cell of the host
Transmitted to humans through the bites of mite and ticks, or the feces of lice and fleas
Typhus Group
Rickettsia prowazekii – epidemic typhus (old world)
Transmitted by the bite or feces of human body lice
Cause high fever, rash, chills, delirium vomiting and shock
Mortality rate can reach up to 30% if left untreated
Can remain dormant in lymph nodes for years
Scrub Typhus Group
Caused by Rickettsia tsutsgamushi – scrub typhus
Transmitted by a mite that normally live on rodents
Similar syptoms as epidemic typhus with an addition of a red nodule that turns into a black scab
Mortality can reach 40% if untreated
Found in Japan, Southeast Asia, and the Southwest Pacific
No vaccine
Spotted Fever Group
Rickettsia akarii - rickettsialpox
Rickettsia rickettsii – Rocky mountain spotted fever
Transmitted by American dog tick and other tick species
Found mostly in southeastern and south central US
Symptoms include sudden high fever, severe headache, fatigue, muscle pain, chills, and rash
Q fever group
Coxiella burnetii – Q fever
Transmitted to humans through animals that have been bitten by an infected tick.
Can be transmitted through milk, products of conception, or animal excrement
Especially in sheep, cattle or goats
If left untreated can lead to bacterial endocarditis or atypical pneumonia
Viruses
Smallest organism known: can only be seen with the aid of an electron microscope
Approx 2500 viruses could fit on the tip of a pin
Intracellular parasites
Shapes vary
Viruses of humans and animals are spherical
Viruses of plants are rod-shaped or many-sided
Viruses that attack bacteria are known as bacteriophages and are rod shaped
Viruses have no metabolic function: they borrow the ribosomes of the host cell to make new viruses
Inclusion bodies are found in host cells that have been affected by a virus
Their presence helps the pathologist diagnose a viral disease
They are transmitted by both direct and indirect contact
Relationship between viruses and interferon
Interferon is a protein produced by a normal body cell that is being attacked by a virus
It blocks the effect of the virus and is part of the body’s defense against a viral infection
Research is being done into “interferon inducers”, substances that stimulate the cell to produce interferon, which would help to expand our control over viral diseases
Viral Diseases
There are five types of viruses
Dermotrophic
Pneumotrophic
Neurotrophic
Viscerotrophic
Immunotrophic

Dermotrophic

Affect skin and mucous membranes
Smallpox – Variola virus
Chickenpox – Varicella virus
Measles - Rubeola virus
German measles – Rubella virus
Fever blisters (cold sores) – Herpes simplex virus
Shingles (Herpes zoster) – Varicella-zoster virus
Pneumotrophic
Affects the respiratory tract
Common cold (coryza)
Influenza
Infectious mononucleosis
Viral pneumonia
Neurotrophic
Affects the central nervous system
Poliomyelitis
Rabies
Encephalitis
Viscerotrophic
Affects a specific organ
Hepatitis
Immunotrophic
Affects the immune system
AIDS
Hepatitis
Chemically induced
Caused by chemical toxins including alcohol
Not infectious
Viral
Caused by primary or secondary viruses
Very contagious
Two herpes viruses can result in secondary hepatitis
Presently there are five hepatrophic viruses that can cause hepatitis

HAV (HepA)
Primarily transmitted by the fecal-oral route
Also found in semen and blood
More prevalent in developing and third world countries than in US due to required vaccination of school children.
HBV (HepB)
Acquired Parenterally through blood transfusions and contaminated needles.
Causes jaundice, weakness, fever, and nausea
1 in 20 infections result in Chronic hepatitis
Persistent hepatitis six months after the onset of the illness
Chronic HBV can be benign with normal liver tests or may be an aggressive inflammatory process that can lead to cirrhosis (hardening of the liver).
The vaccine consists of three injections and is highly recommended for OR personnel.
HCV (HepC)
Acquired parenterally and sexually
Mode of transmission is unknown in 20% of cases
Produces flu like symptoms without jaundice. Because the liver enzymes are not tested for these symptoms, the infection may not be detected for many years.
Chronic HCV occurs in 50-60% of cases, and most carriers remain contagious for life.
Many develop aggressive hepatitis and eventually cirrhosis and liver failure, requiring liver transplant.
HDV (Delta Virus)
Infects only those liver cells that are already infected with HBV.
Uses the HBV enzyms for replication and the acquisistion of a protein coat that allows it to survive outside of the liver
Those infected develop super infections that can be fatal, neither interferon or transplant is effective.

Human Immunodeficiency Virus
Although AIDS (acquired immunodeficiency syndrome) was discovered by the CDC in 1981, the virus that causes it, HIV, was not discovered until 1983
The chief routes of transmission are blood, sexual contact, and mother to child.
The main target cell for the virus is CD4 T lymphocytes (T-cells)
Of the 28 million that had HIV in 1997, it is estimated that 8 million will acquire AIDS. By 2000, 36 million were infected and to date approx 20 million have died.
Patients infected may be asymptomatic for many years before they are diagnosed with AIDS.
It weakens the immune system and allows opportunistic infections, malignancies and neurological diseases to occur.
Example: Kaposi’s sarcoma, lymphoma of the brain, Pheumocystis carinii pneumonia, etc.
There is a new class of antiretroviral drugs that have been developed called protease inhibitors (PI) that inhibit the maturation and replication of the virus, but
AIDS is a fatal disease, there is no cure
Implications for the STSR
STSRs are frequently exposed to blood-borne pathogens
Vaccination for HBV is strongly recommened
Universal precautions should be used on all surgical procedures
All surgical patients should be treated as if they are infected

Protective eyewear should be worn in all cases and double gloving is recommended to help prevent needle sticks
Always wear gloves when handling contaminated items
Needles should not be recapped to prevent needle sticks
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