Microbiology Chapter 12 part 1: Infection and Disease.

What is symbiosis?

Close association between different species.

What is commensalism?

One cell benefits while the other is unchanged.

What is mutualism?

Both cells benefit.

What is parasitism?

One cell benefits while harming the host.

What is amensalism?

One cell is inhibited while the other cell is unaffected.

What is an example of mutualism?

Gut bacteria receive nutrients and provide useful products.

What is an example of commensalism?

Skin microbes obtain nutrients without harming the host.

What is an example of parasitism?

Giardia, Plasmodium, tapeworms, or lice exploit humans.

What is an example of amensalism?

Penicillium produces penicillin that inhibits susceptible bacteria.

What is normal microbiota?

They normally inhabit the body without causing disease.

What are the other names for normal microbiota?

Normal flora or indigenous microbiota.

How do resident and transient types of normal microbiota differ?

Resident organisms persist at specific site such as skin, mucosa, mouth, upper respiratory tract, intestine and vagina. Transient organisms remain temporary.

How are normal microbiota acquired after birth and how do they protect the host?

Through the birth environment, feeding, caregivers, and other environmental contact. They compete with pathogens for nutrients and attachment sites and produce inhibitory substances. This is called microbial antagonism.

Which normal microbiota are listed for skin?

Skin: Staphylococcus, Propionibacterium (Cutibacterium), and Corynebacterium.

Upper respiratory tract: Staphylococcus, Streptococcus, Moraxella, Haemophilus.

Mouth: Streptococcus, and Lactobacillus.

Which normal microbiota are listed for the lower digestive tract and female urinary tract?

Lower digestive tract: Escherichia coli, Bacteroides, Lactobacillus, Enterococcus, Enterobacter.

Female urogenital tract: Lactobacillus and Candida.

What is the purpose of vaginal Lactobacillus?

To help maintain an acidic environment that inhibits manty pathogens.

When can normal flora cause disease?

When defenses weaken or the microbiota reach an unusual site. Ie. intestinal E. coli entering the urinary tract can cause a UTI.

What is an endemic?

Usual ongoing presence in population.

What is an epidemic?

Cases exceed the expected level.

What is a pandemic?

An epidemic that spreads across multiple countries or continents.

What is a sporadic disease?

Infrequent, irregular and scattered cases.

What is a reservoir and what are the main types?

The usual habitat in which an infectious agent lives, grows, or persists. The main types are animals, humans, and nonliving environments such as soil and water.

What are zoonoses and by which routes are they acquired?

Infections that are naturally transmitted between animals and humans. Routes include bites, scratches, direct contact, contaminated food or water, inhalation, and arthropod vectors.

What are examples of zoonoses?

Rabies, anthrax, leptospirosis, salmonellosis, plague, swine influenza, avian influenza, and brucellosis.

What causes rabies and anthrax and how are they acquired?

Rabies virus: usually through infected mammal saliva introduced by a bite.

Anthrax: Bacillus anthracis spores from infected animals, animal products, or contaminated environments. Entry may be through skin, inhalation, or ingestion.

What causes zoonotic salmonellosis and plague and how are they acquired?

Salmonellosis: nontyphoidal Salmonella is acquired through contaminated food or fecal contact with animals such as poultry and reptiles.

Plague: Yersinia pestis is acquired through infected rodent-associated fleas. Pneumonic plague can spread by respiratory droplets.

How are avian influenza, swine influenza, and brucellosis acquired?

Swine and avian influenza: Influenza A viruses associated with pigs or birds are acquired usually after exposure to infected animals or contaminated secretions.

Brucellosis: Brucella species is acquired through unpasteurized dairy, infected animal tissues, or fluids and inhalation.

What are human carriers?

They harbor and shed a pathogen sometimes without symptoms.

How do human carriers transmit infection? Name an example of bacterium.

Secretions, excretions, blood, and contaminated hands. Salmonella typhi can persist in the gallbladder and be shed in feces.

What environmental reservoirs or sources are associated with tetanus, cholera, Listeria, and Salmonella?

C. tetani: soil and animal or human intestines.

V. cholerae: aquatic environments, water contaminated with feces transmits infection.

L. monocytogenes: soil, water, vegetation, and animal intestines. Contaminated food transmits infection.

Salmonella: animal and human intestines. S. typhi primarily has a human reservoir.

What is contamination?

Unwanted microbes are present. Ie. can be found in water, food, soil etc.

What is colonization?

Happens when microbes establish and grow at a site without necessarily causing disease.

What is an infection?

When an agent enters and multiplies in a host with or without symptoms.

What is invasion?

Penetration into tissues or cells and spread beyond initial attachment.

What is a pathogen?

An agent capable of causing disease.

What is pathogenicity?

The ability to cause disease.

What is virulence?

The degree of disease-causing ability.

What are virulence factors?

Traits that promote attachment, invasion, immune evasion, survival, or damage such as adhesions, capsules, enzymes, biofilms, and toxins.

What are the major portals of entry and exit for microbes?

Entry: respiratory, gastrointestinal, genitourinary, conjunctival mucosa, damaged skin, punctures, bites, or injections.

Exit: respiratory secretions, feces, urine, genital secretions, blood, skin lesions, or breast milk. Some agents can also cross the placenta during pregnancy.

What does germ theory state?

Specific microbes can cause particular diseases.

What are Koch’s four postulates?

1. An organism that is associated with disease and absent from healthy hosts.

2. To isolate and grow a pure culture

3. To reproduce the disease in a healthy susceptible host.

4. To reisolate the same organism.

Why do some microorganisms not satisfy classical Koch’s postulates?

Some cannot grow in artificial pure culture because they require living cells, have healthy carriers, or cannot ethically be tested in humans. Mycobacterium leprae is an example because it cannot grow in artificial culture. Viruses require living cells.

What are adhesions?

An attachment to host tissues.

What are ligands?

A ligand binds a specific receptor or target. 

What are adhesins?

A microbial attachment molecule on fimbriae or pili, surface proteins, glycocalyces, or viral attachment proteins. Some E. coli strains use fimbrial adhesins.

What is the purpose of hyaluronidase do?

It breaks down hyaluronic acid.

What does collagenase do?

It breaks down collagen and aids in spreading it.

What does kinase do?

Kinases such as streptokinase promote fibrin-clot breakdown.

What does coagulase do?

It promotes fibrin clot formation which can shield organisms such as S. aureus.

What are exotoxins?

Proteins produced and released by certain gram-positive or gram-negative bacteria.

What are endotoxins?

Lipid A of LPS or LOS in gram-negative outer membranes released with lysis and shedding during growth.

What are probiotics?

They are live microorganisms that confer a benefit when given in adequate amounts.