Chapter 10: Bacteria and Diseases

Disease

result of an undesirable relationship between the host and the pathogen, marked by interruption in the normal functioning of a body part/s

Infection

• invasion of the body by pathogenic microorganisms

• not synonymous with disease

Symbiosis

prolonged and close interaction between organisms of different species

Mutualism

a form of symbiosis in which both organisms benefit from the relationship

Commensalism

a form of symbiosis in which one organism benefits from another organism without causing harm to it

Parasitism

a form of symbiosis where one organism benefits from another organism and at the same time causes harm to the other

Pathogenicity

ability of an organism to produce disease

pathogenic

An organism that can produce disease in humans is said to be ___

Virulence

describes the degree of pathogenicity of an organism or the degree to which an organism can produce disease

Contamination

• presence of unwanted materials (chemical, biological, or radiological) where they should not be or at concentrations above the normal

• presence of these substances may not necessarily lead to harm

Pollution

presence of contaminants that can cause adverse biological effects to humans and communities

TRUE

[TRUE OR FALSE] All pollutants are contaminants, but not all contaminants are pollutants.

Bacteremia

presence of bacteria in the blood

Septicemia

presence of actively multiplying bacteria in the blood, usually from a source of infection

sepsis

What do you call the source of infection where presence of actively multiplying bacteria in the blood comes from?

Pyemia

presence of pus-producing bacteria in the bloodstream

Viremia

presence of viruses in the blood

Toxemia

presence of toxins in the blood

Robert Koch

• was a German physician who made significant contributions to the field of microbiology

• One of his greatest and well-known contributions was proving certain microorganisms caused certain diseases.

• This experimental procedure was published in 1884 and came to be known as Koch’s Postulates.

1. Suspected organisms are absent in healthy individuals but present in those with the disease.

2. Suspected organisms must be isolated from the infected host and grown in pure culture.

3. The organisms grown from pure culture must produce the same disease as that of the infected source when inoculated to a susceptible animal.

4. The same organism must be isolated from pure culture from the experimentally-infected host.

What are the Koch’s Postulates?

ability of the pathogen to grow in the laboratory

The validity of Koch’s postulates lies in the ___ using artificial culture media. However, some organisms cannot be grown in artificial culture media.

Viruses

obligate intracellular parasites that need to be grown in living cells

Mycobacterium leprae

causative agent of leprosy needs to be grown on foot pads of mice and armadillo

Not all people who acquire an infection develop overt disease. Most of the time, infections are subclinical.

What is the limitation of Koch’s Postulates?

1. Requirement that the cultured organism must be inoculated into a susceptible animal. There are certain organisms that are species-specific (human-human; animal-animal).

2. Ethical issues in testing procedures.

3. Some pathogens are altered when grown in artificial media.

4. Some become less pathogenic or lose their pathogenicity.

What are the issues with Koch’s Postulates?

1. etiologic agent

2. host

3. environment

What are the three components that interacts to cause development of an infectious disease?

chain of infection

Transmission starts when the pathogenic organism leaves its host/reservoir through a portal of exit. A susceptible organism acquires the infection through a given mode of transmission through a portal of entry. Once inside the body, the organism multiplies and produces disease.

reservoir

• serves as the continual source of disease-producing microorganisms

• site where an infectious agent normally resides and multiplies

• provides the organisms with conditions that enable them to survive and multiply

1. animal reservoirs

2. human reservoirs

3. environmental reservoirs

What are the different types of reservoirs?

Zoonotic Infections

infectious diseases that can be transmitted from an animal to humans

Animal Reservoirs

Humans serve only as an incidental host and dead-end host and thus the disease will not be transmitted to another human.

Human Reservoirs

• These organisms may be transmitted directly from an individual to another.

• It may not necessarily manifest with the disease.

• They may be subclinical; or develop the disease, recover, and yet still harbor the organism and transmit it to others.

Carriers

transmits the causative agent to others; they are individuals who are not aware that they are transmitting the infectious agent which makes them public health hazards

1. asymptomatic/healthy carriers

2. incubatory carriers

3. chronic carriers

4. convalescent carriers

What are the different types of carriers?

Asymptomatic/Healthy Carriers

those who are infected but do not manifest symptoms

Incubatory Carriers

those who transmit the causative agent during the incubation period of the illness

Chronic Carriers

those who harbor the organism for months or longer after the patient developed the initial infection

Convalescent Carriers

individuals who developed the disease, recovered but remain capable of transmitting the causative agent

Environmental Reservoirs

water, soil and plants can harbor infectious organisms

Histoplasma capsulatum

fungus associated with soil

Entamoeba histolytica

its reservoir is water; a protozoan parasite that causes amoebiasis

Fasciola hepatica

aquatic vegetation such as watercress and ‘kangkong’ harbor this organism’s larvae, which causes liver damage

portal of exit

• route by which an infectious agent exits its host

• usually the site where the infectious agent is commonly located or localized

Schistosoma haematobium

blood fluke that preferentially infects the urinary bladder exits the host via urine; enters through skin penetration by the infective larvae

droplets or aerosols

Infectious agents causing respiratory tract infections will leave the host via ____ from the respiratory tract.

Sexually transmitted infectious agents

exit via vaginal or urethral secretions

Plasmodium spp.

• causative agent of malaria

• exit the host through blood-sucking arthropods (among other organisms)

1. direct contact

2. indirect contact

3. vector transmission

What are the ways in which infectious agents may be transmitted from the source to a susceptible host?

direct contact

• most agents are transmitted through this way

• contact with environmental sources harboring infectious agents

Schistosoma spp.

• blood fluke

• can be transmitted when one wades in fresh water containing snails that harbor the larvae of the parasite

1. person-to-person contact

2. droplet spread

What are the types of direct contact?

Person-to-person contact

involves transmission through skin-to-skin contact, kissing, or sexual transmission.

Warts

can be transmitted through direct contact with the lesion

“Kissing Disease” Infectious Mononucleosis

caused by Epstein Barr Virus; transmitted through saliva

Syphilis, Gonorrhea, and other STIs

are spread through vaginal and urethral secretions of infected persons

Droplet Spread

patients with respiratory tract infections can transmit the causative agents during coughing and sneezing

Droplets

• are differentiated from aerosols by their larger size (> 5 microns in size)

• spray over a few feet before they fall to the ground

• Close proximity with the source is necessary for transmission.

1. airborne transmission

2. vehicle transmission

What are the types of indirect contact?

Airborne Transmission

infectious agents may be transferred through dust and aerosols

Aerosols

• droplets with nuclei less than 5 microns in size

• Due to their small size, they remain suspended in air for a longer time and may cover farther distances than droplets.

Cryptococcus neoformans

can be transmitted through inhalation of aerosolized pigeon or fowl droppings.

Measles

a common childhood illness; transmitted through aerosols

Vehicle Transmission

refers to the transmission of organisms through media (i.e. water, milk, or biologic substances such as blood and body secretions)

Fomites

(inanimate objects capable of transmission) may also serve as vehicles

Vehicles

may carry organisms or provide an environment that promotes growth and multiplication.

Food and Water

most common vehicle

Cholera and Typhoid

gastrointestinal infections transmitted through contaminated water

food-borne transmission

In ____, the causative agent is transmitted through ingestion of raw/improperly cooked/poorly refrigerated food that is contaminated.

Vector Transmission

usually insects that can transmit an infectious agent

Mechanical Transmission

refers to the passive transport of the organism on the insect’s feet/body parts

Biological Transmission

• active transport of the organism; organism enters the insect vector after the insect vector bites an infected person

• organism multiples within the insect and is transmitted through humans through insect bites.

Malaria

transmitted through the bite of the female Anopheles mosquito

Dengue Virus, Chikungunya Virus, and Zika Virus

are also transmitted through bites of mosquito vectors

Yersinia pestis

causative agent of the plague; transmitted through rat flea bites

portal of entry

• how the infectious agent enters a host

• provides access to tissues where the infectious agent can multiply

TRUE

[TRUE OR FALSE] The portal of exit of an infectious agent is the portal of entry into another host. For example, organisms leaving through the respiratory tract will enter the host through respiratory tract (inhalation).

feces

Organisms transmitted through food and water enter the host through the mouth but exit the host through ___

Hepatitis B and HIV

are transmitted through blood and blood products

Host

final link in the chain of infection

1. constitutional/genetic factors

2. immune status

The host’s susceptibility is affected by factors such as ___ and ___.

Susceptibility to infection

may be increased/decreased in certain individuals with specific genetic make-up

Immune Status

• probably the most important factor that can affect development of a disease

• Humans have natural barriers that prevent entry of potential pathogenic organisms.

• They are equipped with a highly functional immune system that can mount defenses to fight and destroy invading pathogens.

• If defenses break down, pathogens may gain entrance into the body and produce disease.

1. mechanical: invasiveness

2. chemical: toxin production

3. immunologic

What are the ways on how organisms produce disease?

mechanical: invasiveness

Organisms can produce disease by directly damaging tissues/body surfaces. This involves invasion of the epithelial surface and penetration into deeper tissues.

1. colonization

2. ability to evade host immune defenses

3. production of extracellular substances that promote invasion

What are the three important steps in invasiveness?

Colonization

ability of the invading organism to enter the host and establish itself in the portal of entry

Adhesins

substances produced by the organism that facilitate adhesion to target cells.

Gram-negative bacteria

possess pili or fimbriae that promote adherence of organisms to susceptible cells

TRUE

[TRUE OR FALSE] Promotion of adhesion makes invasion of surfaces and entering the host body easier.

Ability to evade host immune defenses

certain factors allow organisms to evade the immune defenses designed to kill invading pathogens.

Bacteria

possess a capsule which enables evasion of phagocytosis

Staphylococcus aureus

secretes the enzyme coagulase that promotes coagulum formation within which the organism hides to escape detection by immune surveillance cells

Mycobacterium tuberculosis

can survive and multiply in macrophages by inhibiting phagosome-lysosome fusion

Production of extracellular substances that promote invasion

microorganisms produce substances or develop mechanisms that promote invasion

Neisseria gonorrhea

enters and multiples within cells and after multiplication is extruded from the host cell allowing it to infect other host cells

extrusion process

causes direct destruction of host cells

Collagenase

enzyme produced by Clostridium perfringens that causes breakdown of collagen, a major component of connective tissue thereby contributing to the development of the disease called gas gangrene

chemical: toxin production

Toxins - poisonous substances; often the primary factors that contribute to disease production.

1. Exotoxin

2. Endotoxin

What are the two types of toxins?

Exotoxin

• intracellular products of some bacteria as part of their growth and metabolism; released into the surrounding medium

• mainly proteins and many of them are enzymes; are disease specific

• Usually produced by gram-positive bacteria (some gram-negative bacteria too).

• Soluble in body fluids and easily diffused in blood and rapidly transported throughout the body.

• Diseases produced by exotoxin-producing bacteria are often due to the effects of this and not the bacteria themselves.