Microbiology Chapter 11

Course of an Infection: Prodromal Stage

- 1 to 2 day period when the earliest notable symptoms of infection appear - Vague feeling of discomfort: head and muscle aches, fatigue, upset stomach, general malaise - The initial, brief period of early, general symptoms such as fatigue and muscle aches

The Human Microbiome Project (HMP)

- A worldwide research effort under way since 2008. - Characterize microbes living on human bodies when healthy. - Determine how the microbiome differs in various diseases - Provide comprehensive characterization of microbiota relating to human health and disease. - Utilizes powerful techniques of genome sequencing and "big data" tools

Patterns of Transmission in Communicable Diseases

- Direct or indirect contact with animate or inanimate objects - Horizontal transmission: disease is spread through a population from one infected individual to another *Three major modes of transmission: ^Direct contact - close contact between people ^Indirect transmission - an object or substance carries the agent from one person to another ^Vector transmission - arthropods that harbor an infectious agent and transfer it to a human - Vertical transmission: disease transmitted from parent to offspring via ovum, sperm, placenta, milk

Colonization, Infection, Disease

- For the most part, our resident microbiota colonize us for the long term and do not cause disease - Resident biota can be called: normal biota. *Normal microbiota, indigenous biota or commensals. - Infection: microbes get past host defenses, enter tissues, and multiply (pathogens enter and multiply in body tissues). *Not every infection will cause a disease. - Disease: deviation from health; pathologic state that results when cumulative effects of infection damage or disrupt tissues and organs. - Infectious disease: a pathogenic state caused directly by microorganisms or their products. *Not all diseases are infectious.

Summary

- Human microbiome is the sum of all microbes found on and in a normal human. - Human milk provides baby with microbiota. - Pathogenicity is an organism's potential to cause disease. - Virulence is a relative severity of a disease caused by a microbe. - Steps involved when a microbe causes disease: *Entry *Attaching to host cells *Surviving host defenses *Causing disease *Exit. - Course of an infection: *Incubation *Prodromal *Acute phase *Convalescent period *Continuation. - Vertical transmission is from parent to offspring.

The Human Microbiome

- Human microbiome: The sum total of all microbes found on and in a normal human. - Humans and other mammals have the form and physiology that they have due to having been formed in intimate contact with their microbes. - Critically important to the health and functioning of its host organism.

Where Do Babies Get a Microbiome?

- In Utero: Previously thought to be sterile, but the womb has its own microbiota. - Birth: Vaginal and C-Section births contribute different initial microbiomes to the baby. - Milk: Breast milk and formula have differing microbes in them. - Caregivers: Family, siblings, and others share microbes with the baby. - Environment: Baby can pick up microbes from anything she comes in contact with.

Course of an Infection: All of the Stages/Phases

- Incubation Period - Prodromal Stage - Acute Phase - Convalescent Period - Continuation Phase

Course of an Infection: Acute Phase

- Infectious agent multiplies at high levels, exhibits its greatest virulence, becomes well established in its target tissue - Marked by fever and other prominent and specific signs and symptoms - Extremely variable in length of this period

Infections that go Unnoticed

- No noticeable symptoms are produced - Microbe is active in host tissues - Host does not seek medical attention - These infections are known as asymptomatic, or subclinical (inapparent)

Course of an Infection: Continuation Phase

- Only some infections have this phase - Either the organism lingers for months, years, or indefinitely after the patient is well or the organism is gone but symptoms continue

When Colonization Leads to Disease

- Pathogen: a microbe whose relationship with its host is parasitic and results in infection and disease. - Pathogenicity: an organism's potential to cause disease. - True pathogens: capable of causing disease in healthy persons with normal immune defenses. - Opportunistic pathogens: cause disease when the host's defenses are compromised or when the pathogens become established in a part of the body that is not natural to them. *In immuno-compromised people.

Course of an Infection: Convalescent Period

- Patient begins to respond to the infection and symptoms decline - Patient's strength and health gradually return due to the healing nature of the immune response - Many patients stop taking antibiotics during this period, even though pathogens are still in their system, leading to antibiotic resistance

Acute Infection

Infection comes on rapidly, with severe but short-lived effects. Examples: - Influenze

Systemic Infection

Infection spreads to several sites and tissue fluids—usually via the bloodstream—but may travel by other means such as nerves (rabies) and cerebrospinal fluid (meningitis). Examples: - Mumps - Rubella - Chickenpox - AIDS - Anthrax - Typhoid - Syphilis

Chronic Infection

Infection that progresses and persists over a long period of time. Examples: - HIV

Focal Infection

Infectious agent spreads from a local site and is carried to other tissues. Examples: - Tuberculosis - Streptococcal Pharyngitis

Quantity of Microbes in the Inoculating Dose

Infectious dose (ID): The minimum number of microbes necessary to cause an infection to proceed - Microorganisms with smaller infectious doses have greater virulence. *If one cell causes a disease within a host, that disease is considered extremely dangerous. Examples: - ID for Q fever is a single cell - ID for tuberculosis, giardiasis, and coccidioidomycosis is about 10 cells - ID for gonorrhea is 1,000 cells - ID for typhoid fever is 10,000 cells - ID for cholera is 1,000,000,000 cells

Mixed Infection (Polymicrobial Infection)

Several agents establish themselves simultaneously at the infection site. Examples: - Human bite infections - Wound infections - gas gangrene

Patterns of Transmission in Communicable Diseases: Horizontal

Disease is spread through a population from one infected individual to another - Direct (contact) transmission (such as droplet infection) - Indirect transmission *Fomite - inanimate object that harbors and transmits a pathogen *Vehicle - natural, nonlivingmaterial like air, water, soil,and food - Vector transmission

Signs of Infection in the Blood

Signs: - Leukocytosis: increase in white blood cell levels - Leukopenia: decrease in white blood cell levels - Septicemia: a general state in which microorganisms are multiplying in the blood and are present in large numbers - Bacteremia: bacteria are present in the blood in small numbers but not multiplying Notes: - Cytosis = High - Penia = Low

Patterns of Transmission in Communicable Diseases: Vertical

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

Endotoxins are indicative of ________________ organisms

Gram-Negative

Microbes Causing Disease: Step 3 (Surviving Host Defenses)

- Phagocytes: cells that engulf and destroy host pathogens by means of enzymes and antimicrobial chemicals *Phagocytes are also known as white blood cells. - Antiphagocytic factors: *Virulence factors used by some pathogens to avoid phagocytes *Leukocidins: kill phagocytes outright *Extracellular surface layer (slime or capsule) makes it difficult for the phagocyte to engulf the pathogen *Some bacteria survive inside the phagocyte. - Phago = Eats

Microbes Causing Disease: Step 1 (Becoming Established - Portals of Entry)

- Portal of entry: the route that a microbe takes to enter the tissues of the body to initiate an infection - The greatest number of pathogens enter the body through the respiratory system - Exogenous: microbe originating from a source outside the body from the environment or another person or animal. *Outside of the body. - Endogenous: microbe already existing on or in the body—normal biota or a previously silent infection. *Inside of the body.

Warning Signals of Disease

- Sign: objective evidence of disease as noted by an observer. *Ex: Fever, Rapid Breathing Rate, X-Ray - Symptom: subjective evidence of disease as sensed by the patient. *Ex: Cough, Chest Pain, Fatigue - Syndrome: a disease identified by a certain complex of signs and symptoms.

Course of an Infection: Incubation Period

- The time from initial contact with the infectious agent to the appearance of symptoms - Agent is multiplying at the portal of entry but has not caused enough damage to elicit symptoms - Varies according to host resistance, degree of virulence, and distance between the target organ and the portal of entry - Ranges from several hours to several years - Majority of infections range from 2 to 30 days

Microbes Causing Disease: Step 4 (Causing Disease)

- Virulence factors are simply adaptations a microbe uses to establish itself in a host - Three ways that microorganisms cause damage to their host: *Directly through the action of enzymes or toxins (both endotoxins and exotoxins) *Indirectly by inducing the host's defenses to respond excessively or inappropriately *Epigenetic changes made to host cells by microbes

Virulence

- Virulence: *Relative severity of a disease caused by a particular microbe *Degree of pathogenicity *Example: what makes a pathogen, a pathogen. - Virulence of a microbe is determined by its ability to: *Establish itself in a host *Cause damage - Virulence factor: any characteristic or structure of the microbe that contributes to its ability to establish itself in the host and cause damage

3 Ways Microbes Damage the Host

1. Directly through the action of enzymes 2. Directly through the action of toxins (both endotoxins and exotoxins) 3. Indirectly by inducing the host's defenses to respond excessively or inappropriately

Secondary Infection

A second infection caused by a different microbe, which complicates a primary infection; often a result of lowered host immune defenses. Examples: - Influenza complicated by pneumonia - Common cold complicated by bacterial otitis media

Microbes Causing Disease: Step 2 (Attaching to Host Cells)

Adhesion: - Process by which microbes gain a more stable foothold on host tissues. *Adhesion can be a virulence factor. - Dependent on binding between specific molecules on both the host and pathogen. - Pathogen is limited to only those cells (and organisms) to which it can bind. *Ex: some microbes only effect the digestive tract because it can only attach there. - Firm attachment is almost always a prerequisite for causing disease, since the body has so many mechanisms for flushing microbes from tissues. - Microbes need a strong attachment to the host in order to attack.

Adhesion Mechanisms

Bacterial, fungal, and protozoal pathogens attach by: - Fimbriae - Surface proteins - Adhesive slimes or capsules - Viruses attach by specialized receptors - Parasitic worms fastened by suckers, hooks, and barbs

Origins and Effects of Circulating Exotoxins and Endotoxins

Exotoxins: - Toxic in minute amounts. - Specific to a cell type; induces TNF production resulting in a fever. - Chemical composition is small proteins. - Is unstable (heat denaturation at 60*C) - Can be converted to toxoid - Stimulates antitoxins (immune response) - Usually not fever stimulating. - Secretes from live cell (manner of release). - A few are gram-positive and gram-negative. Endotoxin: - Toxic in high doses. - Systemic: causes fever and inflammation. - Chemical composition is the lipopolysaccharide of cell wall. Is stable (heat denaturation at 60*C). - Cannot be converted to toxoid. - It does not stimulate antitoxins. - Is fever stimulating. - Released by cell via shedding or during lysis. - All are gram-negative bacteria.

Steps Involved When a Microbe Causes Disease in a Host

Finding a Portal of Entry - Skin - GI tract - Respiratory tract - Urogenital tract - Endogenous biota Attaching Firmly and Negotiating the Microbiome - Fimbriae - Capsules - Surface proteins - Viral spikes Surviving Host Defenses - Avoiding phagocytosis - Avoiding death inside phagocyte - Absence of specific immunity Causing Disease (Disease) - Direct damage via enzymes or toxins - Inducing excessive host response - Causing epigenetic changes in host chromosome Exiting Host - Portals of Exit: *respiratory tract *salivary glands *skin cells *fecal matter *urogenital tract *blood

Localized Infection

Microbes enter the body and remain confined to a specific tissue. Examples: - Boils - Warts - Fungal Skin Infections

Microbes Causing Disease: Step 5 (Vacating the Host - Portals of Exit)

Portal of exit: - Specific avenue by which pathogens exit - Shed through secretion, excretion, discharge, or sloughed tissue - High number of microbes in these materials increases the likelihood that the pathogen will reach other hosts - Portal of exit is usually the same as the portal of entry, but some pathogens use a different route Major Portals of Exit of Infectious Diseases: - Coughing/Sneezing - Insect Bites - Skin Cells and Open Lesions - Urine - Feces - Removal of Blood

How Does a Microbe Cause a Disease?

Step One: Becoming Established—Portals of Entry (Entry) Step Two: Becoming Established—Attaching to Host Cells (Attachment) Step Three: Becoming Established—Surviving Host Defenses (Survival) Step Four: Causing Disease (Causation) Step Five: Vacating the Host—Portals of Exit (Exit)

Signs and Symptoms of Inflammation

Symptoms: - Fever - Pain - Soreness - Swelling Signs: - Edema: the accumulation of fluid in afflicted tissue - Granulomas and abscesses: walled-off collections of inflammatory cells and microbes in the tissues - Lymphadenitis: swollen lymph nodes

Primary Infection

The initial infection. Examples: - Can be any infection