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MICROBIOLOGYfor the Health Sciences

. العمرين : ابو فريد أ اعداد

Chapter 10

Microbial Ecology and Microbial Biotechnology

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Chapter 10 Outline

• Introduction

•Symbiotic Relationships Involving Microorganisms

• Indigenous Microflora of Humans

•Beneficial and Harmful Roles of Indigenous Microflora

•Microbial Communities (Biofilms)

•Agricultural Microbiology

•Microbial Biotechnology

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Introduction

• Ecology is the systematic study of the interrelationships that

exist between organisms and their environment.

•Microbial ecology is the study of the numerous

interrelationships between microbes and the world around

them.

•Most relationships between humans and microbes are

beneficial, rather than harmful.

•Microorganisms are present both on and in our bodies;

collectively, they are referred to as our indigenous microflora

(older term = normal flora).

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Symbiotic Relationships Involving Microorganisms

•Symbiosis

– Defined as two dissimilar organisms living together in a

close association.

– The organisms in the relationship are referred to as

symbionts.

– Many microorganisms participate in symbiotic relationships.

•Neutralism

– Refers to a symbiotic relationship in which neither symbiont

is affected by the relationship.

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Symbiotic Relationships Involving Microorganisms, cont.

•Commensalism

– A symbiotic relationship that is beneficial to one symbiont

and of no consequence to the other.

– Many organisms in the indigenous microflora of humans are

considered to be commensals.

•Mutualism

– A symbiotic relationship that is beneficial to both symbionts;

examples humans and intestinal bacterium, Escherichia

coli, which obtains nutrients from food materials ingested and

produces vitamins (such as vitamin K): blood-clotting factor.

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Symbiotic Relationships Involving Microorganisms, cont.

•Parasitism

– A symbiotic relationship that is beneficial to one symbiont

(the parasite) and detrimental to the other symbiont (the

host).

• A host is a living organism that harbors another living

organism.

• The parasite may or may not cause disease in the host.

•A change in conditions can cause one type of

symbiotic relationship to shift to another type.

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Various Symbiotic Relationships

Lichen (a mutualistic relationship)

Demodex mites in human hair follicles (a commensalistic relationship)

Cause of African sleeping sickness (a parasitic relation-ship)

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Indigenous Microflora of Humans “normal flora”

• Includes all the microbes (bacteria, fungi, protozoa and viruses) that

reside on and within a person; sometimes referred to as our “normal

flora”

• Our indigenous microflora is composed of between 500 and 1,000

different species!

• Blood, lymph, spinal fluid, and most internal tissues and organs are

normally free of microorganisms (i.e., they are sterile).

• Transient microflora take up temporary residence on and within humans.

• Destruction of resident microflora disturbs the balance between host

and microorganisms.

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Areas of the body where most of the indigenous microflora reside.

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Microflora of the Skin

– Primarily bacteria and fungi – about 30 different types; most

common = Staphylococcus spp.

– Number and variety of microorganisms depend on:

1. Anatomical location

2. Amount of moisture present

3. pH

4. Temperature

5. Salinity

6. Presence of chemical wastes

7. Presence of other microbes, which may be producing toxic

substances

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Frequent washing with soap and water removes

most of the potentially harmful transient

microorganisms.

Healthcare professionals must be particularly

careful to keep their skin and clothing as free of

transient microbes as possible to help prevent

personal infections and to avoid transferring

pathogens to patients.

Microflora of the Skin

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Microflora of the Respiratory Tract

URT

LRT

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Microflora of the Respiratory Tract

– Divided into upper respiratory tract (nasal passages and throat)

and lower respiratory tract (larynx, trachea, bronchi and lungs)

– Upper respiratory tract (nasal passages and throat) has an

abundance of microorganisms; many are harmless, some are

opportunistic pathogens

– Carriers harbor virulent pathogens in their nasal passages or

throats, but do not have the diseases usually caused by these

pathogens

• Examples: people harboring the bacteria that cause diphtheria,

pneumonia, meningitis, and whooping cough

– Lower respiratory tract is usually free of microbes

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Microflora of the Ears and Eyes

– Middle ear and inner ear are usually sterile; outer ear and

auditory canal contain the same microorganisms as on the

skin.

– Eye is lubricated and cleansed by tears, mucus and sebum

– few microorganisms present

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Microflora of the Oral Cavity (Mouth)

– A shelter for numerous anaerobic and aerobic bacteria;

remaining food particles provide a rich nutrient medium for

bacteria

– Careless dental hygiene may cause:

• Dental caries (tooth decay)

• Gingivitis (gum disease)

– The most common organisms within the indigenous

microflora of the mouth are various species of alpha-

hemolytic streptococci

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Microflora of the Gastrointestinal (GI) Tract

The GI tract is designed for digestion of food, absorption of nutrients, and elimination of undigested materials

The colon (large intestine) contains the largest number and variety of microorganisms of any colonized area of the body; an estimated 500-600 different species - primarily bacteria.

Colon is anaerobic; bacteria in colon are mostly obligate-, aerotolerant-, and facultative anaerobes.

Many of the microflora of the colon are opportunists.

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Microflora of the Gastrointestinal (GI) Tract

All humans have E. coli bacteria in their colon.

They are opportunists, usually causing us no

problems at all, but they can cause urinary tract

infections (UTIs) when they gain access to the

urinary bladder.

In fact, E. coli is the most common cause of UTIs.

Gastric enzymes and the extremely acidic pH

(approximately pH 1.5) of the stomach usually

prevent growth of indigenous microflora, and

most transient microbes are killed as they pass

through the stomach.

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Microflora of the Genitourinary (GU) Tract

The GU tract consists of the kidneys, ureters, urinary

bladder, urethra, and parts of the female/male

reproductive systems

Kidney, ureters and urinary bladder are usually sterile.

The distal urethra and its external opening harbor

many microbes including bacteria, yeasts and viruses

Most frequent causes of urethral infections include

Chlamydia trachomatis, Neisseria gonorrhoeae, and

mycoplasmas

The male and female reproductive systems are

usually sterile, with the exception of the vagina

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Beneficial and Harmful Roles of Indigenous Microflora

•Humans derive many benefits from their indigenous

microflora; examples - vitamins K and B12.

•Microbial Antagonism

– Means “microbes versus microbes”

– Many members of our indigenous microflora are beneficial in

that they prevent other microbes from becoming established

– Other examples of microbial antagonism involve:

• Production of antibiotics and bacteriocins (antibacterial proteins);

an example is colicin, produced by E. coli

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Opportunistic Pathogens and Biotherapeutic Agents

•Opportunistic pathogens are those microorganisms that

“hang around,” waiting for the opportunity to cause infection

• Examples: E. coli, other members of the family

Enterobacteriaceae, S. aureus, and Enterococcus spp.

– The delicate balance of the indigenous microflora can be

upset by antibiotics, other types of chemotherapy, and

changes in pH

– Bacteria and yeasts used to stabilize the microbial balance are

called biotherapeutic agents or probiotics

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Microbial Communities

•Microorganisms are often organized into biofilms – complex communities of assorted organisms.

•Biofilms are everywhere; example – dental plaque.

•Biofilms consist of a variety of different species of bacteria plus a gooey polysaccharide that the bacteria secrete; the bacteria grow in tiny clusters called microcolonies, separated by water channels

•Biofilms have medical significance; they form on urinary catheters and medical equipment and can cause diseases like endocarditis

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Microbial Communities, cont.

• Microbes commonly associated with biofilms on medical

devices include the yeast, Candida albicans, and bacteria like

Staphylococcus aureus, Enterococcus spp., Klebsiella

pneumoniae, and Pseudomonas aeruginosa.

• Biofilms are very resistant to antibiotics and disinfectants

– Antibiotics that are effective against pure cultures of

organisms have been found to be ineffective against

those same organisms within an actual biofilm

Bacteria within biofilms are protected from antibiotics

and certain types of host defense mechanisms.

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Synergistic Infections

•When 2 or more organisms “team up” to produce a

disease that neither could cause by itself.

•The diseases are called synergistic infections,

polymicrobial infections, or mixed infections

– Examples:

• Certain oral bacteria can work together to cause a serious oral

disease called acute necrotizing ulcerative gingivitis (ANUG;

also known as Vincent disease and “trench mouth”).

• Similarly, the disease known as Bacterial Vaginosis is the

result of the combined efforts of several different species of

bacteria.

Chapter 11