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36 Cards in this Set

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normal (resident) flora

Microbes that engage in mutual or commensual associations on you


A condition in which pathogenic microbes penetrate host defense, enter tissues, and multiply.


Any deviation from health, disruption of a tissue or organ.

Resident Flora

-Includes bacteria, fungi, protozoa, viruses and arthropods

- Most areas of the body

- Large intestine (colon) has largest number

- Internal organs, fluids, and tissues microbe-free

Will be on the exam!

microbial antagonism

Bacterial flora benefit host by preventing overgrowth of harmful microbes.

Portals of entry

Characteristic route a microbe follows to enter the tissues of the body.

-skin, gastrointestinal tract, respiratory tract, urogenital tract, transplacental

Requirements for an Infectious Dose (ID)

• Minimum number of microbes required for infection to proceed.

• Microbes with small IDs have greater virulence.


microbes gain a stable foothold at the portal of entry; dependent on binding between specific molecules on host and pathogen

• examples: fimbrae, flagella, adhesive slimes or capsules, cilia, Suckers, hooks, barbs

Surviving Host Defenses

• The initial response of host defenses comes from phagocytes (WBC).

Antiphagocytic factor: used to avoid phagocytosis

• Species of Staphylococcus and streptococcus produce leukodins, toxic to WBCs.

Slime layer or capsule: makes phagocytosis difficult

Virulence factors

severity of disease


• Capacity to produce toxins at the site of multiplication.

• toxins = poisons

-endotoxins: lipid A of Gram- bacteria.

-exotoxins: proteins secreted by Gram + and Gram- bacteria.

4 Different stages of clinical infections

1. Incubation period

2. Prodromal stage

3. Period of invasion

4. Convalescent period

Patterns of Infections

Primary infection

Secondary Infection

Acute infection

Chronic infection

Signs vs. symptoms

Sign: objective evidence of disease as noted by an observer

Examples: fever, septicemia, chest sounds, rash, leukocytosis

Symptoms: Subjective evidence of disease as sensed by patient.

Examples: chills, pains, nausea, ache, headache, fatigue

Signs and symptoms of inflammation

• Earliest symptoms of disease as a result of the activation of the body defenses.

• Signs of inflammation:

- edema: accumulation of fluid

- granulomas and abscesses: walled-off collections of inflammatory cells and microbes

- lymphadenitis: swollen lymph nodes

Signs of infection in the blood

• Changes in the number of circulating white blood cells.

- Leukocytosis: increase in white blood cells

- leukopenia: decrease in white blood cells

- septicemia: microorganisms are multiplying in the blood and present in large numbers.

Asymptomatic (subclinical) infections

Although infected, host shows no signs of disease.

Portals of Exit

• Pathogens depart by a specific avenue; greatly influences the dissemination of infection.

- respiratory: mucus, sputum, nasal drainage, saliva

- skin scales

- fecal exit

- urogenital tract

- removal of blood


A live animal (other than human) that transmits an infectious agent from one host to another.

• Majority are arthropods - fleas, mosquitoes, flies, and ticks.

• Some larger animals can also spread infection - mammals, birds, lower vertebrates.

Acquisition and transmission of infectious agents

Communicable disease: spreads

• Highly communicable disease: contagious, spreads very easily

Non-Communicable: does not arise through transmission from host to host

Nosocomial Infections

• Any disease developed during hospital stay.

• Obtained from surgical procedures, equipment, personnel, and exposure to drug-resistant microorganisms.

Number of Nosocomial Infections

• 2 to 4 million cases per year with approx. 90,000 deaths.

• 1/3rd of infections can be prevented.

Most Common Infection sites of Nosocomial Infections

1. Urinary tract (39%)

2. Respiratory tract (18%)

3. Surgical incisions (17 %)


The study of the frequency and distribution of disease and health-related factors in human populations.


Steady frequency of disease in a particular area.


When prevalence of disease is increasing beyond what is expected.


Epidemic across the world.

Koch's Postulates

Determining the causative or etiologic agent of infectious disease:

- Find evidence of a particular microbe in every case of a disease.

- Isolate that microbe from an infected subject and cultivate it artificially in the lab.

- Inoculate a susceptible healthy subject with the laboratory isolate and observe the disease.

- Reisolate the agent from this subject.

Incubation period

time from contact to first symptoms

Prodromal Stage

Vague feelings of discomfort

Period of Invasion

High levels of microbes causing severe signs and symptoms.

Convalescent period

Symptoms decline, start to feel better.

Primary Infection

initial infection

Secondary Infection

Another infection by a different microbe.

Acute Infection

Comes on rapidly, with severe but short-lived effects.

Chronic Infection

Progress and persist over a long period of time.