WEEK 3 - Host-Microbe Interactions 1

A person who harbors the etiologic agent but shows no apparent signs or symptoms of infection or disease

Carrier

A single source of reservoir from which an etiologic agent responsible for an epidemic or outbreak originates

Common source

The number of new diseases or infected persons in a population

Disease incidence

The percentage of diseased persons in a given population at a particular time

Disease prevalence

A disease constantly present at some rate of occurrence in a particular location

Endemic

A larger-than-normal number of diseased or infected individuals in a particular location

Epidemic

A microorganism responsible for causing infection or infectious disease

Etiologic agent

Infections acquired as a result of a medical procedure, such as insertion of a central line, catheter, or ventilator, or as a result of participation or admission into a health care facility

Health care-associated infection

An individual's microbiologic environment, present in or on the human host

Microbiome

The means by which etiologic agents are brought in contact with the human host (e.g., infected blood, contaminated water, insect bite)

Mode of transmission

The state of disease and its associated effects on the host

Morbidity

The incidence of a particular disease state

Morbidity rate

Death resulting from disease

Mortality

The incidence in which a disease results in death

Mortality rate

Infection for which the etiologic agent was acquired in a hospital or long-term health care center or facility

Nosocomial infection

A larger than normal number of diseased or infected individuals that occurs over a relatively short period

Outbreak

What is the term for an epidemic that spans the world?

Pandemic

What is the origin of the etiologic agent or location from which it disseminates (e.g., water, food, insects, animals, other humans)?

Reservoir

What refers to laboratory-based characterization of etiologic agents designed to establish their relatedness during an outbreak or epidemic?

Strain typing

What is any type of epidemiologic investigation involving data collection to characterize disease incidence or prevalence?

Surveillance

What is a living entity (animal, insect, or plant) that transmits the etiologic agent?

Vector

What is a nonliving entity contaminated with the etiologic agent and acts as its mode of transmission?

Vehicle

What is the first stage of host-microbe interaction?

Physical encounter between host and microorganism

What is the second stage of host-microbe interaction, where microbes persist on host surfaces?

Colonization and survival of the microorganism

What is the third stage involving microbe entry, invasion, and spread to deeper tissues?

Microbial entry, invasion and dissemination

What is the final stage of interaction between host and microbe?

Resolution or outcome

Why are human encounters with microorganisms considered inevitable?

Microorganisms are found everywhere and exposure is unavoidable

How are human encounters with microorganisms influenced?

By a person’s activity or behavior

What infection can be caused by eating inadequately cooked chicken?

Salmonellosis

What infection is associated with living in overcrowded communities?

Tuberculosis

What do we call the means by which human hosts acquire microbial agents?

Modes of transmission

What are living agents of microbial transmission called?

Vectors

What are non-living agents of microbial transmission called?

Vehicle/fomite

Why is knowledge about an infectious agent’s mode of transmission important?

To determine the optimal specimen for isolation and apply precautions to reduce infection risks

What is the mode of transmission where microorganisms are acquired directly from another human?

Direct transmission

What is the term for transmission where a microorganism contaminates a vehicle like water and infects another person?

Indirect transmission

What are two examples of infections associated with indirect transmission in healthcare settings?

Nosocomial infections; Health care-associated infections

What kind of infection occurs when a microorganism primarily infects animals but transfers to humans?

Zoonotic infection

What is an example of direct animal-to-human transmission?

Rabies via animal bite

What is an example of indirect animal-to-human transmission?

Bite of insect vector (e.g., mosquito)

How can animals contaminate food and water supplies with infectious agents?

By depositing microorganisms in water and food supplies

What foodborne microorganism can be transmitted by animals used as food?

Salmonella (Typhoid fever)

What is the most common role of insects in infectious disease?

Transmission of viral, parasitic, and bacterial disease

How is malaria maintained in human populations?

Through feeding and survival of mosquitoes

What are arthropods like lice and scabies considered as?

Ectoparasites – agents of disease that survive on skin without internal invasion

Where in the environment are fungal spores commonly acquired from?

Inhalation of dust particles containing microorganisms

Where can tetanus endospores be acquired from?

Penetrating wounds

What is the environment that serves as a microbial reservoir for countless organisms?

Soil and natural debris

What is colonization in the context of microorganisms?

Persistent survival of microorganisms on a surface of the human body

What determines the ability of microorganisms to colonize the human body?

Defenses protecting internal organs against microbial invasion

What are the first lines of defense against microbial invasion?

External surfaces like skin and mucous membranes

Which surfaces are part of the body's first defense mechanisms?

Skin, conjunctiva, mouth, respiratory tract, GI tract, genitourinary tract

What are skin colonizers?

Bacteria or microbiome organisms that inhibit growth of more harmful bacteria

What mucosal structure removes bacteria through rapid sloughing and prevents penetration through tight intercellular junctions?

Mucosal cells

Which mucosal cell produces mucus for lubrication, traps bacteria, and provides antibacterial substances like lysozyme, lactoferrin, and lactoperoxidase?

Goblet cells

Which enzyme found in mucus degrades bacterial cell walls?

Lysozyme

Which substance in mucus competes with bacteria for iron, limiting their growth?

Lactoferrin

Which enzyme in mucus produces toxic substances to kill bacteria?

Lactoperoxidase

Which lymphoid tissue mediates specific immune responses against bacteria that penetrate mucosal layers?

Mucosa-associated lymphoid tissue (MALT)

Which internal body surface uses sloughing cells, saliva flow, lysozyme, and resident microflora for protection?

Mouth

Which area of the body is protected by resident microflora, lysozyme, phagocytes, and ciliated cells?

Nasopharynx

Which internal organ relies on macrophages as its main defense?

Lungs

What organ uses low pH and proteolytic enzymes to kill pathogens?

Stomach

Which part of the digestive tract uses fast flow, mucus, bile salts, and peristalsis as defense mechanisms?

Small intestine

Which part of the digestive tract has slow flow but high resident microflora and bile salts for protection?

Colon

Which female reproductive organ is protected by low pH and resident microflora?

Vagina

Which organ uses flushing action of urine, low pH, and a physical urethral barrier for protection?

Bladder

Which urinary structure prevents microbial entry through continuous urine flow?

Urethra

What term refers to microorganisms that normally inhabit body surfaces and are part of the human microbiome?

Colonizers

What type of colonizers can survive temporarily on body surfaces but do not multiply and are easily shed?

Transient colonizers

What type of microbiota persistently survive, thrive, and multiply on body surfaces?

Resident microbiota

What determines which microorganisms inhabit specific anatomical locations in the body?

Their ability to survive under local physiologic conditions

What microbial colonization factor includes localization in moist areas, protection in debris, and salt tolerance?

Survival Against Environmental Conditions

What type of microbial structures or proteins aid in attachment and adherence to host cells?

Pili, Adherence proteins, Biofilms, Protein adhesins

Which microbial factor enhances colonization by enabling movement and competing for nutrients like iron?

Motility and production of siderophores

What molecule do microbes produce to capture iron from the host?

Siderophores

Why is understanding the human microbiota crucial in diagnostic microbiology?

To determine the clinical significance of organisms found in patient specimens

Why are normal microbiota often found in clinical specimens?

Due to contamination during collection or involvement in infection

What determines whether colonization leads to harmless infection or disease?

The host condition and microorganism characteristics

What is the first requirement for a microorganism to successfully colonize a host?

Ability to survive initial environmental conditions on host surfaces

What general process involves penetration of host barriers by microbes?

Microorganisms Entry, Invasion, and Dissemination

What allows microorganisms to penetrate the host's physical barriers?

Disruption of surface barriers

Which physical event allows microbes to enter via broken skin?

Trauma (e.g., penetrating wounds)

Which minor skin injury can allow microbial entry?

Abrasions

Which types of burns can disrupt skin barrier defenses?

Chemical and fire burns

What type of medical procedure-related wound can permit microbial invasion?

Surgical wounds

What type of injury common in healthcare can introduce microbes directly into tissue or blood?

Needle sticks

What inhaled substances can damage mucosal surfaces and promote microbial invasion?

Noxious or toxic gases

What airborne particles can contribute to mucosal barrier disruption?

Particulate matter

What common habit weakens mucosal defenses and promotes microbial colonization?

Smoking

What man-made medical insertion can compromise natural barriers and introduce microbes?

Implantation of Medical Devices

What type of diseases may compromise host defense and allow easier microbial invasion?

Malignancies, Diabetes, Infections, Alcoholism

What natural physiological process can lead to microbial exposure and colonization?

Childbirth

What common medical treatment can disrupt normal microbiota and promote pathogen colonization?

Overuse of Antibiotics

Which immune cells are involved in the nonspecific response to microbial invasion and include PMNs, macrophages, and dendritic cells?

Phagocytes

What process do phagocytes use to ingest bacteria?

Endocytosis

What is the name of the membrane-lined compartment that forms after phagocytosis?

Phagosome

Which organelle fuses with the phagosome to digest bacteria?

Lysosome

What are the two major types of phagocytic cells?

Polymorphonuclears (PMNs) and macrophages

Which phagocyte type develops in the bone marrow and circulates briefly in blood and tissues?

Polymorphonuclears (PMNs)