Microbiology Chapter 11

What is the human microbiome?

The sum total of all microbes found on and in a normal human, critically important to the health and functioning of its host.

What is the difference between infection and disease?

Infection occurs when microbes get past host defenses and multiply; disease is a pathologic state resulting from the cumulative effects of infection that damage tissues and organs.

What is the Human Microbiome Project (HMP)?

A worldwide research effort since 2007 to characterize microbes living on or in human bodies when healthy and determine how the microbiome differs in various diseases.

How many protein-encoding genes do humans have compared to microbiota?

Humans have 22,000 protein-encoding genes, while microbiota have about 8 million.

What is microbial antagonism?

A concept where normal biota are unlikely to be displaced by incoming microbes due to limited attachment sites and a hostile environment created by resident biota.

What factors can weaken host defenses and increase susceptibility to infection?

Old age, extreme youth, genetic defects in immunity, underlying diseases, chemotherapy, and physical or mental stress.

What is a pathogen?

A microbe whose relationship with its host is parasitic and results in infection and disease.

What are true pathogens?

Microbes capable of causing disease in healthy persons with normal immune defenses.

What are opportunistic pathogens?

Microbes that cause disease when the host's defenses are compromised or when they establish in an unnatural part of the body.

What is virulence?

The relative severity of a disease caused by a particular microbe, determined by its ability to establish itself in a host and cause damage.

What is an infectious dose (ID)?

The minimum number of microbes necessary to cause an infection to proceed; organisms with smaller IDs have greater virulence.

How do newborns acquire their microbiota?

Primarily from their trip through the vagina during birth and through human milk, which contains beneficial bacteria.

What is the role of Lactobacillus in newborns?

It provides the necessary enzymes for the baby to digest milk and protects against skin disorders.

What is the significance of the intestinal biota?

The makeup of one's intestinal biota can influence overall health and is essential for proper growth and development.

What are polymicrobial infections?

Infections that involve contributions from more than one microbe, such as influenza leading to pneumonia.

What is a portal of entry?

The route that a microbe takes to enter the tissues of the body to initiate an infection.

What is the difference between exogenous and endogenous portals of entry?

Exogenous portals originate from outside the body, while endogenous portals come from normal biota or previously silent infections within the body.

What are some common organisms that enter through the gastrointestinal tract?

Salmonella, Shigella, Vibrio, Escherichia coli, and various enteric protozoans.

What is the role of the immune system in microbial colonization?

The immune system destroys most microbes that come into contact with the human body, allowing only a few to survive and establish a relationship with the host.

What is the significance of the uterus in microbial colonization?

Recent studies suggest that the uterus may not be sterile during embryonic and fetal development, as newborns show a diversity of bacteria in their stools.

What are the potential consequences of separating humans from their resident microbes?

Humans do not do well if separated from their resident microbes, which are essential for health during growth and development.

What is the relationship between microbial colonization and health?

Healthy individuals have a peaceful coexistence with microbes, while an imbalance can lead to disease.

What is the importance of understanding the human microbiome?

Understanding the human microbiome can help determine how it differs in various diseases and its role in health.

What is the relationship between infectious dose and virulence?

Organisms with smaller infectious doses have greater virulence.

What is the infectious dose (ID) for rickettsia?

A single cell.

What is the ID for tuberculosis?

About 10 cells.

What is the ID for gonorrhea?

1,000 cells.

What is the ID for typhoid fever?

10,000 cells.

What is the ID for cholera?

1,000,000,000 cells.

What is adhesion in the context of pathogens?

The process by which microbes gain a stable foothold on host tissues.

What are some mechanisms of adhesion used by pathogens?

Fimbriae (pili), surface proteins, adhesive slimes or capsules.

What are phagocytes?

Cells that engulf and destroy pathogens using enzymes and antimicrobial chemicals.

What are leukocidins?

Virulence factors that kill phagocytes outright.

What are exoenzymes?

Enzymes secreted by microbes that break down and inflict damage on tissues.

What is a toxin?

A specific chemical product of microbes that is poisonous to other organisms.

What are neurotoxins?

Toxins that act on the nervous system.

What are enterotoxins?

Toxins that act on the intestines.

What are nephrotoxins?

Toxins that damage the kidneys.

What are hemolysins?

A class of bacterial exotoxin that disrupts the cell membrane of red blood cells.

What is an endotoxin?

Lipopolysaccharide (LPS) that is part of the outer membrane of gram-negative cell walls.

What are the systemic effects of endotoxins?

Causes fever, inflammation, hemorrhage, and diarrhea.

What is a localized infection?

Infection where microbes remain confined to a specific tissue.

What is a systemic infection?

Infection that spreads to several sites and tissue fluids, usually via the bloodstream.

What is a focal infection?

Infection where the infectious agent spreads from a local site to other tissues.

What is a mixed infection?

An infection where several agents establish themselves simultaneously at the infection site.

What is a primary infection?

The initial infection caused by any microbe.

What is a secondary infection?

A second infection caused by a different microbe, often complicating a primary infection.

What is an acute infection?

An infection that comes on rapidly with severe but short-lived effects.

What is a chronic infection?

An infection that progresses and persists over a long period of time.

What is latency in infectious diseases?

A dormant state of microbes in certain chronic infectious diseases.

What are sequelae?

Long-term or permanent damage to tissues or organs caused by infectious disease.

What is the incubation period?

The time from initial contact with the infectious agent to the appearance of symptoms.

What is the prodromal stage of an infection?

A 1-2 day period when the earliest notable symptoms of infection appear, including vague discomfort, head and muscle aches, fatigue, upset stomach, and general malaise.

What characterizes the acute phase of an infection?

The infectious agent multiplies at high levels, exhibits great toxicity, and becomes well established in host tissue, marked by fever and prominent signs and symptoms.

What happens during the convalescent period of an infection?

The patient begins to respond to the infection, symptoms decline, and strength and health gradually return due to the immune response.

What is a significant risk during the convalescent period?

Many patients stop taking antibiotics, leading to potential antibiotic resistance even though pathogens may still be present.

What is the continuation phase of an infection?

A phase where some infections linger for months or years after recovery, or symptoms continue even after the pathogen is gone, as seen in 'long haulers' of COVID-19.

What is a reservoir in the context of infectious diseases?

The primary habitat in the natural world from which a pathogen originates, often a human or animal carrier, but can also include soil, water, and plants.

What is the role of a transmitter in the spread of infection?

An individual or object from which an infection is acquired, such as a sick person contaminating a surface.

Give an example of a reservoir and transmitter being the same.

In the case of syphilis, the reservoir and transmitter are the same.

How can pathogens from animals be transmitted to humans?

Directly, through vectors, or via vehicles such as water.

What are asymptomatic carriers?

Individuals who are infected but show no symptoms of disease, such as those with gonorrhea or genital herpes.

What are incubating carriers?

Individuals who spread the infectious agent during the incubation period before symptoms appear.

What are convalescent carriers?

Recuperating patients who continue to shed viable microbes and convey the infection to others despite not showing symptoms.

What are chronic carriers?

Individuals who harbor the infectious agent for a long period after recovery due to its latency, such as in tuberculosis or typhoid fever.

What are passive carriers?

Medical and dental personnel who may accidentally transfer pathogens from contaminated materials to other patients.

What is zoonosis?

An infection indigenous to animals but naturally transmissible to humans, making humans dead-end hosts that do not contribute to the microbe's persistence.

What percentage of new emerging diseases worldwide are zoonotic infections?

Zoonotic infections make up 70% of all new emerging diseases.

What is the significance of zoonotic spread of disease?

It is promoted by close associations between humans and animals, and eradication of zoonotic diseases often requires eradicating the animal reservoir.

What is the difference between a biological vector and a mechanical vector?

A biological vector actively participates in a pathogen's life cycle, while a mechanical vector carries the microbe accidentally on its body parts.

What are some common zoonotic infections?

Rabies (mammals), yellow fever (wild birds, mammals, mosquitoes), hantavirus (rodents), and psittacosis (birds).

What are nonliving reservoirs?

Sources such as soil, water, and air where some pathogens can survive and be transmitted to humans upon contact.

What is a communicable disease?

A disease in which an infected host can transmit the infectious agent to another host and establish infection.

What is a contagious disease?

A disease that is highly communicable, especially through direct contact, such as influenza and measles.

What is the role of environmental sources in disease acquisition?

Humans are in regular contact with environmental sources, making the acquisition of pathogens from natural habitats important for diagnosis and epidemiological studies.

What is a noncommunicable infectious disease?

An infectious disease that does not arise through transmission from host to host.

How can a compromised person become infected?

They can be invaded by their own microbiota or have accidental contact with a microbe from a nonliving reservoir.

What is vertical transmission?

Transmission from parent to offspring via the ovum, sperm, placenta, or milk.

What is horizontal transmission?

Spread of disease through a population from one infected individual to another.

What is a fomite?

An inanimate object that can transfer infectious agents.

What is a vehicle in the context of disease transmission?

Natural, nonliving material like air, water, soil, and food that can carry pathogens.

What are healthcare-associated infections (HAIs)?

Infectious diseases acquired or developed during a hospital or healthcare facility stay.

What percentage of admitted patients may acquire HAIs?

From 0.1% to 20%, with an average of 4%.

What factors contribute to healthcare-associated infections?

Compromised patients, collection points for pathogens, and lowered defenses allowing normal biota to enter the body.

What are common types of HAIs?

Pneumonia, gastrointestinal illness, urinary tract infections, bloodstream infections, and surgical site infections.

What is Koch's postulates?

A series of proofs that became the standard for determining causation of infectious disease.

What are some exceptions to Koch's postulates?

Some infectious agents cannot be isolated or grown in the lab, and some infections cannot be elicited in animals.

What is the difference between incidence and prevalence?

Incidence is the number of new cases over a certain time period; prevalence is the total number of existing cases in a population.

What is a point-source epidemic?

An epidemic where the infectious agent came from a single source, and all victims were exposed to it from that source.

What is a common-source epidemic?

An epidemic resulting from common exposure to a single source of infection over a period of time.

What is a propagated epidemic?

An epidemic that results from an infectious agent that is communicable from person to person and sustained over time.

What is an endemic disease?

An infectious disease that exhibits a relatively steady frequency over a long time period in a particular geographic locale.

What defines a pandemic?

The spread of an epidemic across continents.

Who is Florence Nightingale?

The founder of modern nursing who laid the foundations of modern epidemiology.

What role does epidemiology play in public health?

It helps track disease frequency and distribution, identify causative agents, and develop prevention and treatment programs.

What is the mortality rate?

The total number of deaths in a population due to a certain disease.

What is an index case?

The first patient found in an epidemiological investigation.

What is the significance of reportable diseases?

Certain diseases must be reported to authorities to monitor and control outbreaks.

What is the average number of HAIs in the U.S. per year?

750,000 cases resulting in 75,000 deaths.

What is the role of healthcare processes in HAIs?

Treatments using reusable instruments and indwelling devices create portals of entry for pathogens.