Microbe--Human Interactions

How we get sick


Step one: Contact (to touch)
To come in contact with microbes. Contact does not lead to much.
typhoid mary history page
Step two: Colonization (to settle)
Does not mean you will get sick, most microbes cannot even colonize on our bodies

*The majority of the microbes that we come in contact with are considered transients which means that they are removed or destroyed by our bodies defenses long before they are able to colonize.

Step three: Infection (the spread of disease)
Microbes start living where they should not be.

Infection- condition where pathogenic microorganisms penetrate the hosts defenses, enter the tissues and multiply.

Localized Infection- microbes enter the body and remain confined to a specific tissue.


Step four: Disease (any deviation from health where tissues and organs are damaged and disrupted) -Disease-
Leads to disease.

• The human body provides a favorable habitat for microorganisms which includes: *Stable temperature, *Extensive surfaces upon which to colonize, * Constant source of nurishment, and a *Relatively stable pH
• Although, acids in the stomach prevent it from being colonized by most microbes

Remember
Contact usually does NOT result in an infection.
Infection usually does NOT result in a disease.
Sign- objective evidence (Fever, chest sounds, leukopenia, or tachycardia)

Symptom- subjective evidence (chills, nausea, itching, or headache) These are not measurable except by the patient.

Sequelae- long-term permanent damage to tissue or organs

Acute Infection- sudden onset; generally short-lived (flu)

Chronic Infection- persistent, continuous infection.

Q: What term is defined as any deviation from health where tissues and organs are damaged and disrupted?
a. Disease
b. Infection
c. Transient
A: Disease

Axenic = uncontaminated; germfree (FYI)

Resident flora:
• includes bacteria, fungi, protozoa, viruses andarthropods
• most areas of the body in contact with the outside environment harbor resident microbes; large intestine has the highest numbers of bacteria
• internal organs & tissues & fluids are microbe-free • bacterial flora benefit host by preventing overgrowth of harmful microbe

Sites that harbor a normal flora:

• Skin and its contiguous mucous membranes
• Upper respiratory tract
• Gastrointestinal tract (various parts)
• Outer opening of urethra
• External genitalia
• Vagina
• External ear and canal
• External eye (lids, lash follicles)

Q: What greatly influences the presence and numbers of transient flora?
a. Occupational exposure
b. Hygiene
c. Humidity
A: Hygiene

Colonization of newborns
While in the mothers womb a fetus is in a sterile environment.
After the expecting mother's water breaks the baby is exposed to vaginal microbes that enter the womb.
More comprehensive exposure occurs during the birth process as the baby while the baby comes into contact with the birth canal exposing them to streptococci, staphylococci, and lactobacilli.
Breast fed babies gain the intestinal flora of the Bifidobacterium species which metabolizes sugars into acids that protect the infant from infection.


Flora of the Skin:
The normal flora of the skin only resides in or on the dead cell layer (epidermis) or in follicles and glands.
There are two cutaneous populations of flora:

• The transients (exposed flora) cling to the skin surgace but do not ordinarily grow there. These are aquired by contact and greatly influenced by hygeine.
• The resident population lives and multiplies in the deep layers of the epidermis and in glands/follicles. normal skin residents consist of bacteria (staph, corynebacterium, and propionibacterium) and yeasts. Moist areas of the skin are more likely to be colonized with these bacteria.

Flora of the Mouth
The oral cavity has flora that is among the most diverse and abundant of the body. The most common residents are earobic streptococcus species :

• s. sanguis, s.salviarius, and s. mitis colonize the smooth epithelial surfaces
• S. mutans and s. sanguis are major dental carries and establish the basis for biofilm

Saliva has a very high bacterial count of 5x10^9 cells per mL making human bites especially dangerous. This high concentration of bacteria makes mouthwashing quite ineffective.

Flora of the Large Intestine
The Large intestine consists of the cecum and colon. The microbes located in the large intestine and rectum are so abundant that they make up 10-30% of the fecal volume.
The intestinal environment favors strictly anaerobic bacteria( bacteroides, bifidobacterium, fusobacterium, and clostridium.) And coliforms (E.Coli, Enterobacter, citrobacter) are found in smaller numbers.
The bacteria ferment waste generating vitamins and acids of potential value to host.

Flora of the Respiratory tract
Respiratory tract= nasal passages and pharynx

• Oral streptococci colonize the upper respiratory tract.
• Staph Aures resides in the nasal entrance, nasal vestibul, and anterior nasopharynx
• Neisseria species reside in mucous membranes and behind soft palate.
• Haemophilus colonize the tonsils and lower pharynx.

Flora of the Genitourinary Tract
Women: vagina and outter opening of urethra have microflora

• The shortness of the urethra in women frequently causes UTI's

Men: Anterior urethra contains microflora

Internal reproductive organs are kept sterile through physical barriers.
The composition of normal flora changes with changes in physiology such as puberty.

Pathogen
Pathogen a microbe whose relationship with its host is parasitic and results in infection and diseases. True pathogens (primary pathogens) are able to cause disease in anyone whether or not they are healthy. They can be as mild as a cold or as serious as rabies. Opportunistic pathogens cause disease when the host's defense's are compromised or when they become established in a part of the body that is not natural to them. One is not known to cause disease in humans, and four is highly contagious and highly virulent. Host deficiencies are the most important cause of disease, and also the most important factors contributing to the outcome of someone who is sick.

Portal of Entry (becoming established---step 1)
The portals of entry are usually located where normal flora is. The most common sites are the skin, GI tract, respiratory tract, and the GU tract. Most pathogens have a specific portal of entry but some can enter multiple portals. Effects of the same pathogen can differ depending on which portal the pathogen enters through. The respiratory system is the portal for the largest amount of pathogens. The source of exogenous, originating from a source outside the body (the environment or another person or animal), or endogenous, already, already existing on or in the body (normal flora or latent infection)

Bacterial pathogens attach most often by the following mechanisms:
1. Fimbriae (pili)
2. Flagella
3. Capsules
4. Adhesive slimes

Portals of exit
• Respiratory, saliva
• Skin scales
• Fecal exit
• Urogenital tract
• Removal of blood

Infectious agents that enter the skin
Any break in the skin is big enough to let bacteria through to cause boils, impetigo, tetanus, and a number of other infections. Entry into the skin could be caused by mosquito bites or ticks, which are vectors. Some microbes are able to enter through sweat glands and also hair follicles. When microbes enter through a route other than the digestive tract it is called the parenteral route. These include injections, bites, wounds, cuts, and surgical sites.

Gastrointestinal Portal
The GI tract is a portal for pathogens that are contained in food, drink and other ingested subtances.
These pathogens are adapted to survive digestive enzymes and extreme pH.
Although the Anus is not normally a portal of entry in becomes one during anal sex.

Respiratory Portal
The oral and nasal cavities are gateways to the respiratory tract. (portal of entry for the greatest number of pathogens)
Pathogens that are inhaled into the lower regions of the respiratory tract can cause pneumonia. The size of the microorganism affects the extent to which an organism is carried into the bronchial tree following inhalation.

Urogenital Portal
Portal of entry for sexually transmitted pathogens also known as Venereal diseases or STD. These diseases account for 4% of infections worldwide.
The microbes of STD's enter the skin or mucosa of the penis, external genitilia, vagina, cervix, and urethra.
Not all urogenital infections are STD's. Some of these infetions are cause by displaced organisms or buy opportunistic overgrowth of normal flora (yeast infections).
*The flow of urine helps to keep the kidney, ureter, bladder and upper urethra sterile.

Pregnancy that infect during pregnancy or Birth:
The placenta is usually an effective barrier against microorganisms in the maternal circulation but a few microbes such as the syphilis spiochete can cross the placenta and spread into fetal tissues.
Other infections such as genital herpes occur perinatally when the child is contaminated by the birth canal.
STORCH infections can cause spontaneous abortions, congenital abnormalities, brain damage, prematurity, and still birth.

Step 2---Attaching to the host: Adhesion Properties of Microbes

Microbe	Disease	Adhesion Mechanism
Neisseria gonorrhoeae	Gonorrhea	Fimbriae attach to genital epithelium
Escherichia coli	Diarrhea	Well-developed fimbrial adhesion
Shigella	Dysentery	Fimbriae can attach to intestinal epithelium
Vibrio	Cholera	Glycocalyx anchors microbe to intestinal epithelium
Treponema	Syphillis	Tapered hook embeds in host cell
Mycoplasma	Pneumonia	Specialized tip at ends of bacteria fuse tightly to lung epithelium
Pseudomonas aeruginosa	Burn, lung infections	Fimbriae and slime layer
Streptococcus pyogenes	Pharyngitis, impetigo	Lipotechoic acid and capsule anchor cocci to epithelium
Streptococcus mutans, S. sobrinus	Dental caries	Dextran slime layer glues cocci to tooth surface
Influenza virus	Influenza	Viral spikes react with receptor on cell surface
Poliovirus	Polio	Capsid proteins attach to receptors on susceptible cells
HIV	AIDS	Viral spikes adhere to white blood cell receptors
Giardia lamblia (protozoan)	Giardiasis	Small suction disc on underside attaches to intestinal surface

Step 3----Surviving Host Defenses:
Microbes are likely to encounter resistance from host defences when first entering the portal of entry. Phagocytes can engulf pathogens and destroy them.
Some microbes have antiphagocytic factors which make them resitant to phagocytes.


CAUSING DISEASE:
Virulence factors:
• exoenzymes – digest epithelial tissues & permit invasion of pathogens
• Toxigenicity – capacity to produce toxins at the site of multiplication – endotoxins – lipid A of LPS of gram-negative bacteria – exotoxins – proteins secreted by a living gram-positive and gram-negative bacteria • antiphagocytic factors – help them to kill or avoid phagocytes, include leukocidins and capsules
** A very virulent microorganism has an ID of one.

Differential Characteristics of Bacterial Exotoxins and Endotoxins

Characteristic	Exotoxins	Endotoxins
Toxicity	Toxic in tiny amounts	Toxic in higher doses
Effects on the body	Specific to a cell type	Systemic: fever, inflammation
Chemical Composition	small proteins	lipopolysaccharide of cell wall
Heat Denaturation @ 60 Deg. C	unstable	stable
Toxoid Formation	Can be converted to toxoid	cannot be converted to toxoid
Immune response	stimulate antitoxins	does not stimulate antitoxins
Fever stimulation	usually not	yes
manner of release	secreted from live cell	released from cell wall during lysis
Typical sources	A few gram positive and gram negative	All gram-negative bacteria

Stages of Infection-

1. Incubation period: Time between contact and first appearance of the signs or symptoms of infection. (2-30 days)
2. Prodromal period: A short period (1-2 days) of discomfort, when vague, notable symptoms of infection appear.
   
3. Invasion period: (Period of illness) When disease is most acute. Worst period.
4. Covalescence period: Signs and symptoms subside, one regains strength.
   
   ***Can be contagious in all stages.***

Sign- objective evidence (Fever, chest sounds, leukopenia, or tachycardia)

Symptom- subjective evidence (chills, nausea, itching, or headache) These are not measurable except by the patient.

Common signs and symptoms of infectious diseases

Signs	Symptoms
Fever	Chills
Septicemia	Pain, ache, soreness, irritation
Microbes in tissue fluids	Nausea
Chest sounds	Malaise, fatigue
Skin eruptions	Chest tightness
Leukocytosis	Itching
Leukopenia	Headache
Swollen lymph nodes	Nausea
Abscesses	Abdominal cramps
Tachycardia	Anorexia
Antibodies in serum	Sore throat

Sequelae- long-term permanent damage to tissue or organs

Acute Infection- sudden onset; generally short-lived (flu)

Chronic Infection- persistent, continuous infection.

PATTERNS OF INFECTION
A localized infection enters the body and stays in a specific tissue. A systemic infection is when the infection spreads to different sites and in the fluids (usually the blood). A focal infection is when the infection breaks free from the local infection and is then carried into other tissues. A mixed infection is when two or more infectious agents infect the same site.

Endemic- Disease that exhibits a relatively steady frequency over a long period of time in a particular geographic locale.
Sporadic- When occasional cases are reported at irregular intervals.
Epidemic- When prevalence of a disease is increasing beyond what is expected.
Pandemic- Epidemic across continents.
Prevalance- The total number of existing cases with respect to the entire population.
Incidence- The number of new cases over a certain time period.

TOXEMIA
A pattern of infection where the infection itself remains localized at the portal of entry, but the toxins produced by the pathogen are carried by the blood to the actual target tissue.

SEPTICEMIA
Clinical term for bacteria multiplying in the blood.

Factors that weaken host defenses and increase susceptibility to infection:

• Old age and extreme youth (infancy, prematurity)
• Genetic defects in immunity and acquired defects in immunity (AIDS)
• Surgery and organ transplants
• Organic disease: cancer, liver malfunction, diabetes
• Chemotherapy/immunosuppressive drugs
• Physical and mental stress
• Other infections

Portal of Exit :Vacating the Host

Respiratory and Salivary Portals of Exit:
Mucus, Sputum, nasal drainage, and other moist secretions are the media of escape for the pathogens of the respiratory tract. Coughing and sneezing is very effective to release pathogens.
Droplets of saliva are the exit route for several viruses.

Epithelial Cells:

Fecal Exit:

Urogenital tract:

Removal of Blood or Bleeding:

Persistance of Microbes
In chronic infections the infectious agent retreats into a state call persistence or latency. Can periodically become active and produce a recurrent disease
Some diseases leave sequela in the form of long term or permanant damage to tissues or organs.

Sources and Spread of Microbes
Living Reservoirs
A carrier by definition is an individual who inconspicuously shelters a pathogen and spreads it to others without any notice.

Asymptomatic Carriers- are infected carriers but they show no symptoms.

• incubation carrier-spread infection during incubation period
• convalescent carrier-spread infection during the time they are recuperating and have no symptoms
• chronic carrier-carries a latent form of the infection ("Typhoid Mary")

Passive Carrier- Process in which pathogens are picked up mechanically and transferred to other people. Most common in medical and dental personnel.

Nosocomial Infections - occur in the presence of compromised patients and pathogen in hospitals. These infections occur when indwelling medical devices are used or when treatments utilizing reusable instruments are implemented. The use of effective infection control measures helps to contribute to the management of nosocomial infections.


VECTOR is a live animal that transmits an infectious from one host to another (such as a mosquito)

Koch's Postulates- the principal criteria for determining the etiologic or causitive agents of an infection.
STEPS...
1- Find evidence of a specific type of microbe in every case of disease.
2- Isolate the microbe from an infected subject and cultivate it artificially in the lab.
3- Inoculate a healthy subject and observe results.
4- Reisolate the agent from this subject.

CHECK THIS OUT!!! Mosquitos don't necessarily carry bot fly larva. This time is an exception. A mosquito carrying Bot fly eggs. This is Awesome!!!

A disease is communicable when an infected host can transmit the infectious agent to another host and etablish infection in that host.

Notecards for this chapter are available on www.flashcardexchange.com under kevin young's micro chapter 13.

Questions
1- Virulence factor can contribute to tissue damage, which one of these is not a contributor?
a) Collagenase
b) Hyaluronidase
c) Kinases
d) coagulase
e) all of the above
f) none of the above

2- What is the most common route of entry when you are infected with a pathogen?
a) Skin
b) Urogenital
c) Respiratory
d) Gastrointestinal tract


3- Why does normal flora, that can keep us from getting infections, can also cause infection? Is this known as opportunistic pathogens, or true pathogens?

4. A _______ infection is acquired in a hospital.
a. sub-clinical
b. focal
c. nosocomial
d. zoonosis

5. A ________ is a passive animal transporter of pathogens.
a. zoonosis
b. biological vector
c. mechanical vector
d. asymptomatic carrier

6. Which of the following would not be a portal of entry?
a. the meninges
b. the placenta
c. skin
d. small intestines

7. ________ ________ cause infectious disease in healthy hosts.
a. True pathogens
b. Opportunistic pathogens
c. both a and b
d. neither

8. The best descriptive term for the resident flora is
a. commensals
b. parpasites
c. pathogens
d. mutualists

9. Resident flora is commonly found in the
a. stomach
b. kidney
c. salivary glands

10. Resident flora is absent from the
a. pharynx
b. lungs
c. intestine
d. hair follicles

11. Virulence factors include
a. toxins
b. enzymes
c. capsules
d. all of these

12.The emergence of new infectious diseases is probably due to all of the following except
a. the need of bacteria to cause disease
b. the ability of humans to travel by air
c. changing environments (e.g. floods, drought, pollution)
d. a pathogen crossing the species barrier
e. the increasing human population

13. Which of the following is not a portal of entry for pathogens
a. mucous membranes of the respiratory tract
b. mucous membranes of the gatrointestinal tract.
c. skin.
d. blood
e. parenteral route.

14. A _______ is an animal that transmits a microbe.
a. portal
b. vector
c. pathogen
d. bacillus

15.What greatly influences the presence and numbers of transient flora?

	A) Occupational exposure
	B) Hygiene
	C) Humidity
	D) Oils
	E) Clothing

16.What factor prevents the stomach from being colonized by most microbes?

	A) Peristalsis
	B) Digestive enzymes
	C) Secretory IgA
	D) Bile
	E) Acids

17.Why are human bites especially dangerous?

	A) Because the oral cavity and saliva contain high numbers of bacteria
	B) Because saliva contains lysozyme
	C) Because human teeth are exceedingly sharp
	D) Because the protozoa that reside in the mouth are harmful when transferred to others
	E) Because normal flora of the mouth are pathogenic

18.What are the first organism(s) to colonize the upper respiratory tract?

	A) Oral streptococci
	B) Lactobacilli
	C) Staphylococcus aureus
	D) Neisseria sp
	E) Haemophilus sp

19. What keeps the kidney, ureter, bladder, and upper urethra sterile?

	A) pH
	B) Peristalsis
	C) Salts
	D) Flow of urine
	E) IgA in mucous

20.Axenic animals display all but which of the following?

	A) Degenerative diseases of the intestinal tract
	B) Shortened life span
	C) Absence of dental caries
	D) Vitamin deficiencies
	E) Increased sensitivity to enteric pathogens

Link for Flashcard study/chapter 13
http://highered.mcgraw-hill.com/classware/ala.do?alaid=ala_1722698
From the books website.