Microbiology Chapter 14

a disease causing organism

is the scientific study of disease

the cause of disease

the manner in which disease develops

Pathology is first concerned with the cause, or etiology, of disease. Second, it deals with pathogenesis, the man- ner in which a disease develops. Third, pathology is concerned with the structural and functional changes brought about by dis- ease and with their final effects on the body

Infection is the invasion or colonization of the body by pathogenic microor- ganisms;

disease occurs when an infection results in any change from a state of health. Disease is an abnormal state in which part or all of the body is not properly adjusted or incapable of performing its normal functions. An infection may exist in the absence of detectable disease. For example, the body may be infected with the virus that causes AIDS but experience no symptoms of the disease. the presence of a particular type of microorganism in a part of the body where it is not normally found is also called an infection and can lead to disease.

Few microorganisms are pathogenic. In fact, the presence of some microorganisms can even benefit the host. Therefore, before we discuss the role of microorganisms in causing dis- ease, let’s examine the relationship of the microorganisms tohe healthy human body.

the microorganisms that colonize a host without causing disease, also called normal flora.

Many other usually harmless microorganisms establish themselves inside other parts of the normal adult body and on its surface. A typical human body contains 1 * 1013 body cells, yet harbors an estimated 1 * 1014 bacterial cells (10 times more bacterial cells than human cells). This gives you an idea of the abundance of microorganisms that normally reside in the human body.

The Human Microbiome Project began in 2007 to ana- lyze microbial communities called microbiomes that live in and on the human body. Its goal is to determine the relationship be- tween changes in the human microbiome and human health and disease. The human microbiome is more diverse than previously thought. Currently, researchers are comparing the microbiomes of healthy volunteers and volunteers with specific diseases. The microorganisms that establish more or less permanent residence (colonize) but that do not produce disease under normal condi- tions are members of the body’s normal microbiota,

transient microbiota, may be present for several days, weeks, or months and then disappear. Microorganisms are not found throughout the entire human body but are localized in certain regions

Many factors determine the distribution and composition of the normal microbiota. Among these are nutrients, physical and chemical factors, defenses of the host, and mechanical fac- tors. Microbes vary with respect to the types of nutrients that they can use as an energy source. Accordingly, microbes can colonize only those body sites that can supply the appropriate nutrients. These nutrients may be derived from secretory and excretory products of cells, substances in body fluids, dead cells, and foods in the gastrointestinal tract.

defend against pathogens the normal microbiota can benefit the host by preventing the overgrowth of harmful microorganisms. Microbial antagonism involves competition among microbes. One consequence of this competition is that the normal microbiota protect the host against colonization by potentially pathogenic microbes by competing for nutrients, pro- ducing substances harmful to the invading microbes, and affect- ing conditions such as pH and available oxygen. When this balance between normal microbiota and pathogenic microbes is upset, disease can result.

For example, the normal bacterial microbiota of the adult human vagina maintains a local pH of about 4. The presence of normal microbiota inhibits the overgrowth of the yeast Candida albicans, which can grow when the balance be- tween normal microbiota and pathogens is upset and when pH is altered. If the bacterial population is eliminated by antibiotics, excessive douching, or deodorants, the pH of the vagina reverts to nearly neutral, and C. albicans can flourish and become the dom- inant microorganism there. This condition can lead to a form of vaginitis (vaginal infection).
Another example of microbial antagonism occurs in the large intestine. E. coli cells produce bacteriocins, proteins that inhibit the growth of other bacteria of the same or closely re- lated species, such as pathogenic Salmonella and Shigella. A bac- terium that makes a particular bacteriocin is not killed by that bacteriocin but may be killed by other ones. Bacteriocins are used in medical microbiology to help identify different strains of bacteria. Such identification helps determine whether severaloutbreaks of an infectious disease are caused by one or more strains of a bacterium.
A final example involves another bacterium, Clostridium difficile (difʹfi-sē-il), also in the large intestine. The normal microbiota of the large intestine effectively inhibit C. difficile, possibly by making host receptors unavailable, competing for
available nutrients, or producing bacteriocins. However, if the normal microbiota are eliminated (for example, by antibiotics), C. difficile can become a problem. This microbe is responsible for nearly all gastrointestinal infections that follow antibiotic therapy, from mild diarrhea to severe or even fatal colitis (in- flammation of the colon).

Microbial antagonism involves competition among microbes. One consequence of this competition is that the normal microbiota protect the host against colonization by potentially pathogenic microbes by competing for nutrients, pro- ducing substances harmful to the invading microbes, and affect- ing conditions such as pH and available oxygen. When this balance between normal microbiota and pathogenic microbes is upset, disease can result.

Bacteriocins are used in medical microbiology to help identify different strains of bacteria.

LOOK @ #15 (EXAMPLES)

The relationship between the normal microbiota and the host is called symbiosis, a relationship between two organ- isms in which at least one organism is dependent on the other

In the symbiotic relationship called commensal- ism, one of the organisms benefits, and the other is unaffected.

Mutualism is a type of symbiosis that benefits both organisms. For example, the large intestine contains bacteria, such as E. coli, that synthesize vitamin K and some B vitamins. These vitamins are absorbed into the bloodstream and distributed for use by body cells. In exchange, the large intestine provides nutrients used by the bacteria, resulting in their survival.

bacteria and yeasts that are good for your health. Probiotics (pro 5 for, bios 5 life) are live microbial cultures applied to or ingested that are intended to exert a beneficial effect. Probiotics may be ad- ministered with prebiotics, which are chemicals that selectively promote the growth of beneficial bacteria.
EXAMPLE: Several studies have
SECOND LINE OF DEFENSE
When microbes penetrate the first line of defense, they encounter a second line of defense that includes defensive cells, such as phago- cytic cells; inflammation; fever; and antimicrobial substances.
Before we look at the phagocytic cells, it will be helpful to first have an understanding of the cellular components of blood.
Formed Elements in Blood
LEARNING OBJECTIVES
16-6 Classify leukocytes, and describe the roles of granulocytes and monocytes.
16-7 Describe the six different types of white blood cells, and name a function for each type.
Blood consists of fluid, called plasma, and formed elements— that is, cells and cell fragments suspended in plasma (Table 16.1). Of the formed elements listed in Table 16.1, those that concern us at present are the leukocytes, or white blood cells.
Leukocytes are divided into two main categories based on their appearance under a light microscope: granulocytes and agranulocytes. Granulocytes owe their name to the presence of large granules in their cytoplasm that can be seen under a light microscope after staining. They are differentiated into three types of cells on the basis of how the granules stain: neutrophils, basophils, and eosinophils. The granules of neutrophils stain pale lilac with a mixture of acidic and basic dyes. Neutrophils
shown that ingesting certain lactic acid bacteria (LAB) can al- leviate diarrhea and prevent colonization by Salmonella enterica during antibiotic therapy. If these LAB colonize the large intes- tine, the lactic acid and bacteriocins they produce can inhibit the growth of certain pathogens. Researchers are also testing the use of LAB to prevent surgical wound infections caused by S. aureus and vaginal infections caused by E. coli. In a Stanford University study, HIV infection was reduced in women treated with a LAB that was genetically modified to produce CD4 pro- tein that binds to HIV. Probiotics may not work for all diseases, and studies on probiotics are ongoing. A Dutch medical team, for example, reported increased deaths in pancreatitis patients treated with probiotics.

In still another kind of symbiosis, one organism benefits by deriving nutrients at the expense of the other; this relation- ship is called parasitism. Many disease-causing bacteria are parasites.

Although categorizing symbiotic relationships by type is conve- nient, keep in mind that under certain conditions the relationshipcan change. For example, given the proper circumstances, a mutualistic organism, such as E. coli, can become harmful. E. coli is generally harmless as long as it remains in the large intestine; but if it gains access to other body sites, such as the urinary bladder, lungs, spinal cord, or wounds, it may cause urinary tract infections, pulmonary infections, meningitis, or abscesses, respectively. Microbes such as E. coli are called opportunistic pathogens. They ordinarily do not cause dis- ease in their normal habitat in a healthy person but may do so in a different environment. For example, microbes that gain access through broken skin or mucous membranes can cause opportunistic infections.

f the host is already weakened or compromised by infection, microbes that are usually harmless can cause disease. AIDS is often accompanied by a common opportunistic infection, Pneumocystis pneumonia, caused by the opportunistic organism Pneumocystis jirovecii (see Fig- ure 24.20, page 705). This secondary infection can develop in AIDS patients because their immune systems are suppressed. Before the AIDS epidemic, this type of pneumonia was rare. Opportunistic pathogens possess other features that contribute to their ability to cause disease. For example, they are present in or on the body or in the external environment in relatively large numbers. Some opportunistic pathogens may be found in locations in or on the body that are somewhat protected from the body’s defenses, and some are resistant to antibiotics.

Propionibacterium, Staphylococcus, Corynebacterium, Micrococcus, Acinetobacter, Brevibacterium; Candida (fungus), Malassezia (fungus)

Staphylococcus epidermidis, S. aureus, diphtheroids, Propionibacterium, Corynebacterium, streptococci, Micrococcus

Staphylococcus aureus, S. epidermidis, and aerobic diphtheroids in the nose; S. epidermidis, S. aureus, diphtheroids, Streptococcus pneumoniae, Haemophilus, and Neisseria in the throat

Streptococcus, Lactobacillus, Actinomyces, Bacteroides, Veillonella, Neisseria, Haemophilis, Fusobacterium, Treponema, Staphylococcus, Corynebacterium, and Candida (fungus)

Escherichia coli, Bacteroides, Fusobacterium, Lactobacillus, Enterococcus, Bifidobacterium, Enterobacter, Citrobacter, Proteus, Klebsiella, Candida (fungus)

Staphylococcus, Micrococcus, Enterococcus, Lactobacillus, Bacteroides, aerobic diphtheroids, Pseudomonas, Klebsiella,
and Proteus in urethra; lactobacilli, Streptococcus, Clostridium, Candida albicans (fungus), and Trichomonas vaginalis (protozoan) in vagina

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It is not only competition among microbes that can cause disease; cooperation among microbes can also be a factor in causing dis- ease. For example, pathogens that cause periodontal disease and gingivitis have been found to have receptors, not for the teeth, but for the oral streptococci that colonize the teeth.

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Some diseases—such as polio, Lyme disease, and tuberculosis— have a well-known etiology. Some have an etiology that is not completely understood, for example, the relationship between certain viruses and cancer. For still others, such as Alzheimer disease, the etiology is unknown. Of course, not all diseases are caused by microorganisms. For example, the disease hemophilia is an inherited (genetic) disease; osteoarthritis and cirrhosis are considered degenerative diseases.

The same pathogen must be present in every case of the disease.
2. The pathogen must be isolated from the diseased host and grown in pure culture.
3. The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible laboratory animal.
4. The pathogen must be isolated from the inoculated animal and must be shown to be the original organism.

The bacterium Treponema pallidum is known to cause syphilis, but virulent strains have never been cultured on artificial media. The causative agent of leprosy, Mycobacterium leprae, has also never been grown on artificial media. Moreover, many rickettsial and viral pathogens cannot be cultured on artificial media be- cause they multiply only within cells.
The discovery of microorganisms that cannot grow on artificial media has necessitated some modifications of Koch’s postulates and the use of alternative methods of culturing and detecting certain microbes.

Changes in body function, such as pain and malaise (a vague feeling of body discomfort. These subjective changes are not apparent to an observer.

Sings are objective changes the physician can observe and measure. Frequently evaluated signs include lesions (changes produced in tissue by disease), swelling, fever, and paralysis. A specific group of symptoms or signs may always accompany a particular disease; such a group is called a syndrome.

Diseases are often classified in terms of how they behave within a host and within a given population.

Any disease that spreads from one host to another, either directly or indirectly. (i.e. chickenpox, measles, gentile herpes, typhoid fever, and TB are examples.

Disease that are easily spread from one person to another. (i.e. chickenpox and measles)

Is not spread from one host to another.These diseases are caused by microorganisms that normally inhabit the body and only occasionally produce disease or by microorganisms that reside outside the body and produce disease only when introduced into the body. An example is tetanus: Clostridium tetani produces disease only when it is introduced into the body via abrasions or wounds.

The number of people in a population who develop a disease during a particular time period.

The number of people in a population who develop a disease at a specified time, regardless of when it first appeared. Prevalence takes into account both old and new cases. It’s an indicator of how seriously and how long a disease affects a population.

Frequency of occurrence is another citron that is used in the classification of diseases. If a particular disease occurs only occasionally it is called a sporadic disease. i.e. typhoid fever

A disease constantly present is a population. I.e. the common cold.

If many people in a given area acquire a certain disease in relatively short period. i.e. influenza

An epidemic disease that occurs worldwide.

Influenza is an epidemic disease. An example of a pandemic disease is AIDS.

Is one that develops rapidly but only lasts a short time, and example is influenza.

A chronic disease develops more slowly, and the body’s reaction may be less serve, but the disease is likely to continue or reoccur for long periods. Infectious mononucleosis, TB, and hepatitis B fall into this category.

A disease that is intermediate between acute and chronic. i.e.subacute sclerosing pan encephalitis, rare brain disease characterized by diminished intellectual function and loss of nervous function.

Is one in which the causative agent remains inactive for a time but then becomes active to produce symptoms of the disease; an example is shingles, one of the disease caused by varicella virus.

Determined in part by the immunity of the population.

When many immune people are present in a community.

Is one in which the invading microorganisms are limited to a relatively small are of the body. Some examples of local infections are boils and abscesses.

Microorganisms or their products are spread throughout the body by the blood or lymph. Measles is an example of a systemic infection.

Very often, agents of a local infection enter a blood or lymphatic vessel and spread to other specific parts of the body, where they are confined to specific area of the body. Focal infections can arise from infections in areas such as the teeth, tonsils, or sinuses.

Sepsis is a toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection.

-Septicemia: also called blood poisoning, is a systemic infection arising from the multiplication of pathogens in the blood. Septicicemia is common example of sepsis.
-The presence of bacteria in the blood is known as bacteremia.
-Toxemia refers to the presence of toxins in the blood and viremia refers to the presence of viruses in blood.

A primary infection is an acute infection that cause the initial illness. A secondary infection is one caused by an opportunistic pathogen after the primary infection has weakened the body’s defenses. Secondary infections of the skin are respiratory tract are common and are sometimes more dangerous that the primary infections.

Is one that does not cause any noticeable illness. Poliovirus and hepatitis A virus, for example, can be carried by people who never develop the illness.

As you will learn shortly, for an infectious disease to occur, there must be a reservoir of infection as a source of patho- gens. Next, the pathogen must be transmitted to a susceptible host by direct contact, by indirect contact, or by vectors. Transmission is followed by invasion, in which the microorganism enters the host and multiplies. Following invasion, the microorganism in- jures the host through a process called pathogenesis (discussed further in the next chapter). The extent of injury depends on the degree to which host cells are damaged, either directly or by toxins. Despite the effects of all these factors, the occurrence of disease ultimately depends on the resistance of the host to the activities of the pathogen.

A predisposing factor makes the body more susceptible to a disease and may alter the course of the disease.ender is some- times a predisposing factor; for example, females have a higher incidence of urinary tract infections than males, whereas males have higher rates of pneumonia and meningitis. Other aspects of genetic background may play a role as well. For example, sickle cell disease is a severe, life-threatening form of anemia that occurs when the genes for the disease are inherited from both parents. Individuals who carry only one sickle cell gene have a condi- tion called sickle cell trait and are normal unless specially tested. However, they are relatively resistant to the most serious form of malaria. The potential that individuals in a population might in- herit a life-threatening disease is more than counterbalanced by protection from malaria among carriers of the gene for sickle cell trait. Of course, in countries where malaria is not present, sickle cell trait is an entirely negative condition.
Climate and weather seem to have some effect on the incidence of infectious diseases. In temperate regions, the incidence of respiratory diseases increases during the winter. This increase may be related to the fact that when people stay indoors, the closer contact with one other facilitates the spread of respiratory pathogens.
Other predisposing factors include inadequate nutrition, fatigue, age, environment, habits, lifestyle, occupation, preexist- ing illness, chemotherapy, and emotional disturbances. It is often difficult to know the exact relative importance of the various predisposing factors.

Incubation Period
The incubation period is the interval between the initial infection and the first appearance of any signs or symptoms. In some dis- eases, the incubation period is always the same; in others, it is quite variable. The time of incubation depends on the specific microorganism involved, its virulence (degree of pathogenicity), the number of infecting microorganisms, and the resistance of the host. (See Table 15.1, page 431, for the incubation periods of a number of microbial diseases.)
Prodromal Period
The prodromal period is a relatively short period that follows the period of incubation in some diseases. The prodromal period is characterized by early, mild symptoms of disease, such as general aches and malaise.
Period of Illness
During the period of illness, the disease is most severe. The per- son exhibits overt signs and symptoms of disease, such as fever, chills, muscle pain (myalgia), sensitivity to light (photophobia), sore throat (pharyngitis), lymph node enlargement (lymphade- nopathy), and gastrointestinal disturbances. During the period of illness, the number of white blood cells may increase or decrease. Generally, the patient’s immune response and other defense mechanisms overcome the pathogen, and the period of illness ends. If the disease is not successfully overcome (or successfully treated), the patient dies during this period.
Period of Decline
During the period of decline, the signs and symptoms subside. The fever decreases, and the feeling of malaise diminishes. Dur- ing this phase, which may take from less than 24 hours to several days, the patient is vulnerable to secondary infections.
Period of Convalescence
During the period of convalescence, the person regains strength and the body returns to its prediseased state. Recovery has occurred. We all know that during the period of illness, people can serve as reservoirs of disease and can easily spread infections to other people. However, you should also know that people can spread infection during incubation and convalescence as well. This is especially true of diseases such as typhoid fever and chol- era, in which the convalescing person carries the pathogenic
microorganism for months or even years.

Reservoirs of Infection & Transmission of Disease

Human reservoirs:The principal living reservoir of human disease is the human body itself. Many people harbor pathogens and transmit them di- rectly or indirectly to others. People with signs and symptoms of a disease may transmit the disease; in addition, some people can harbor pathogens and transmit them to others without exhibiting any signs of illness. These people, called carriers, are important living reservoirs of infection. Some carriers have inapparent in- fections for which no signs or symptoms are ever exhibited. Other people, such as those with latent diseases, carry a disease during its symptom-free stages—during the incubation period (before symptoms appear) or during the convalescent period (recovery). Typhoid Mary is an example of a carrier (see page 721). Human carriers play an important role in the spread of such diseases as AIDS, diphtheria, typhoid fever, hepatitis, gonorrhea, amebic dysentery, and streptococcal infections.
Animal Reservoirs:Both wild and domestic animals are living reservoirs of micro- organisms that can cause human diseases. Diseases that occur primarily in wild and domestic animals and can be transmitted to humans are called zoonoses (zō-ō-noʹ sēz) (singular: zoonosis). Rabies (found in bats, skunks, foxes, dogs, and coyotes), and Lyme disease (found in field mice) are examples of zoonoses. Other rep- resentative zoonoses are presented in Table 14.2.
About 150 zoonoses are known. The transmission of zoo- noses to humans can occur via one of many routes: by direct contact with infected animals; by direct contact with domestic pet waste (such as cleaning a litter box or bird cage); by con- tamination of food and water; by air from contaminated hides, fur, or feathers; by consuming infected animal products; or by insect vectors (insects that transmit pathogens).
Nonliving Reservoirs:The two major nonliving reservoirs of infectious disease are soil and water. Soil harbors such pathogens as fungi, which cause mycoses such as ringworm and systemic infections; Clostridium botulinum, the bacterium that causes botulism; and C. tetani, the bacterium that causes tetanus. Because both species of clostridia are part of the normal intestinal microbiota of horses and cattle, the bacteria are found especially in soil where animal feces are used as fertilizer.
Water that has been contaminated by the feces of humans and other animals is a reservoir for several pathogens, notably those responsible for gastrointestinal diseases. These include Vibrio cholerae, which causes cholera, and Salmonella typhi, which causes typhoid fever. Other nonliving reservoirs include foods that are improperly prepared or stored. They may be sources of diseases such as trichinellosis and salmonellosis.

Some can harbor pathogens and transmit them to others without exhibiting any signs of illness, they are important living reservoirs of infection

Diseases that occur primarily in wild and domestic animals and can be transmitted to humans
Ex: rabies( found in bats, skunks,foxes) Lyme disease( found in field mice) the transmission can occur via one of many routes by direct contact with infected animals, by contamination of food or water, by air from contaminated hides,fur,or feathers, by consuming infected animal products

Soil and water are the 2 major nonliving reservoirs, both harbors pathogenic fungi and bacteria

Direct contact transmission- also known as person- to- person transmission, direct transmission of an agent by physical contact between its source and a susceptible host, no intermediate object involved
Indirect contact transmission- occurs when the agent of disease is transmitted from its reservoir to a susceptible host by means of a nonliving object
Direct transmission- 3rd type of contact transmission in which microbes are spread in droplet nuclei (mucus droplets) that travel only short distances

Is the transmission of disease agents by a medium, such as water,food, or air other media include blood and other body fluids, drugs, and intravenous fluids

Is the passive transport of the pathogens on the insects feet or other body part
Ex: houseflies can transfer pathogens of typhoid fever and bacillary dysentery from the feces of infected people to food

Is an active process and is more complex,
Ex: arthropod bites an infected person or animal and ingests some of the infected blood, the pathogens then reproduce in the vector and the increase in the number of pathogens increases the possibility that they will be transmitted to another host

Does not show any evidence of being present or incubating at the time of admission to a hospital, it is acquired as a result of a hospital stay

They estimate that 5-15% of all hospital patients acquire some type of nosocomial infection and cause 20,000 people every year to die as a result

Microorganisms in the hospital environment, the compromised status of the host, and the chain of transmission in the hospital

Gram positive bacteria, staphylococcus aureus
Gram negative, E. coli, and pseudomonas aeruginosa

Is one whose resistance to infection is impaired by disease, therapy, or burns, broken skin or mucous membranes compromise the host and a suppressed immune system

urinary tract infections are the most common, occurrence depends on the surgical procedure, and other infection sites

Direct contact transmission from hospital staff to patient and from patient to patient, indirect contact transmission through fomites and the hospitals ventilation system

Fomite- the general term for any nonliving object involved in the spread of an infection
Ex- tissues, handkerchiefs, towels, bedding, diapers, drinking cups, eating utensils, toys, money

Handling contaminated materials carefully, insisting on frequent and thorough hand washing, educating staff members about basis infection control measures and using isolation rooms and wards the single most important means of preventing spread of infection is hand washing

Are ones that are new or changing, showing an increase in incidence in the recent past or a potential to increase in the near future

Present symptoms that are clearly distinctive from all other diseases, some recognized because improved diagnostic techniques allow the identification of a new pathogen

Bacteria- anthrax, whooping cough, Lyme disease
Fungi- coccidiodomycosis, pneumonia
Protozoa-Chanas’, cryptosporidiosis
Helminths- raccoon roundworm encephalitis
Viruses- Ebola, west Nile, hepatitis

new strains may result from genetic recombination between organisms, a new serovar may result from changes in or the evolution of existing microorganisms, the wide spread and sometimes unwarranted, use of antibiotics and pesticides, global warming, and failures in public health measures may be contributing factor to the emergence of previously controlled infections

the science that studies when and where diseases occur and how they are transmitted in populations

field work to determine what causes disease or injury, what the risks are, who is at risk and how to prevent further incidences

entails collecting all data that describe the occurrence of the disease under study. relevant information usually includes information about the affected individuals and the place and period in which the disease occurred

looking backward after the episode has ended, in other words the epidemiologist backtracks to the cause and source of the disease

looking forward, studies in which an epidemiologist chooses a group of people who are free of a particular disease to study

analyzes a particular disease to determine its probable cause.

the cause method- the epidemiologist looks for factors that might have preceded the disease a group of people who have the disease is compared with another group of people who are free of the disease
the cohort method- the epidemiologist studies 2 populations one that has had contact with the agent causing disease and another that has not

begins with the hypothesis about a particular disease, experiments to test the hypothesis are then conducted with a group of people

an effective way of establishing the chain of transmission, case reporting is a procedure that requires health care workers to report specified diseases to local, state, and national health officials

centers for disease control and prevention,

the incidence of species notifiable diseases,
morbidity rate- is the number of people affected by a disease in a given period of time in relation to the total population

the number of deaths from these diseases
mortality rate- is the number of deaths resulting from a disease in a population in a given period of time in relation to the total population

are diseases for which physicians are required by law to report cases to the U.S. public health service some examples are Anthrax, Babesiosis, cholera, dengue