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Medical Microbiology I > Commensal & Pathogenic Microbial Flora in Humans > Flashcards

Commensal & Pathogenic Microbial Flora in Humans Flashcards

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1
Q

4 general groups of microbes

A
  • Viruses
  • Bacteria
  • Fungi
  • Parasites
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2
Q

Viruses

A
  • Smallest infectious particle
  • 18 to 600 nanometers (nm)
  • Cannot be seen with light microscope
  • Cellular parasites
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3
Q

Bacteria

A
  • 0.2 to 2.0 micrometers (µm) in size
  • Prokaryotic organisms
  • Unicellular organisms, no nuclear membrane
  • Reproduce by asexual division
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4
Q

Medical microbiology definition

A
  • The study of the interactions between animals & microorganisms
  • Primary interest is diseases caused by these interactions
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5
Q

Role of microorganisms in human survival

A
  • Participate in the metabolism of food products
  • Protects against infections with highly virulent microorganisms
  • Stimulates the immune response
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6
Q

Fungi

A
  • Cellular structure more complex than bacteria
  • Eukaryotic organisms
    Yeast- single cells, asexual reproduction
  • Mold (filamentous forms, sexual & asexual)
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7
Q

Parasites

A
  • Eukaryotic, unicellular & multicellular

- Protozoa, tapeworms, arthropods

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8
Q

Comparative sizes of organisms (units of measurement)

A
  • Humans: meters (m)
  • Helminths: micrometers (µm) to meters
  • Arthropods: µm to centimeters (cm)
  • Protozoa: micrometers
  • Fungi: micrometers
  • Bacteria: nanometers (nm) to µm
  • Viruses: nanometers
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9
Q

Microbial flora

A
  • Microorganisms occurring and adapted for living in a specific environment
  • Normal commensal population
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10
Q

Microbiota

A
  • Equivalent term used to refer to microscopic organisms of a given area
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11
Q

Normal flora

A
  • Organisms found in their expected places

- Example: normal respiratory flora present

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12
Q

Commensalism

A
  • Relationship of organisms of different species
  • Neither is harmful to the other
  • One gains some benefit (such as protection or nourishment)
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13
Q

Pathogen

A
  • Microorganisms which cause disease in a host
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14
Q

Pathogenicity

A
  • Ability of a pathogen to cause pathology or disease
  • May be a function of host immunity as well as the virulence of the microorganism
  • A pathogen may be derived from the microbiota / normal microbial flora
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15
Q

Colonization

A
  • When one of more species populate an area
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16
Q

Resident microbiota (or microbial flora)

A
  • Establish long-lasting relationship with particular host occupying a defined niche with host immunity
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17
Q

Transient microbiota

A
  • Colonize for a short, finite period of time
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18
Q

Normal commensal population consists mainly of

A
  • Bacteria
  • Fungi
  • Some parasites
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19
Q

Normal commensal population lives on

A
  • Surface of the skin
  • All mucosal membranes
  • Bacteria live on these surfaces and protect us from colonization with pathogenic microbes
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20
Q

Carrier state

A
  • Pathogens that transiently colonize apparently healthy individuals
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21
Q

Disease

A
  • Occurs when the interaction between microbe and human leads to a pathologic process characterized by damage to the human host
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22
Q

Exposure to an organism can lead to one of three outcomes

A
  • Transiently colonize the person
  • Permanently colonize the person
  • Produce disease
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23
Q

Organisms that colonize humans

A
  • Transient/non-permanent colonization

- Do not interfere with normal body functions

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24
Q

Strict pathogens

A
  • Organisms always associated with human disease
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25
Opportunistic pathogens
- Organisms that are typically members of the patient's normal microbial flora
26
Opportunistic pathogens and disease
- Do not produce disease in their normal place | - Establish disease when introduced into unprotected body sites
27
Strict pathogen examples
- Mycobacterium tuberculosis - Neisseria gonorrhoeae - Francisella tularensis - Plasmodium spp. - Rhabdovirus
28
Mycobacterium tuberculosis
- Tuberculosis | - Acid-fast bacilli
29
Neisseria gonorrhoeae
- Gonorrhea) | - Gram negative diplococci
30
Francisella tularensis
- Tularemia | - Small Gram negative cocci
31
Plasmodium spp.
- Malaria | - Protozoan
32
Rhabdovirus
- Rabies virus
33
Opportunistic pathogen examples
- Staphylococcus aureus - Escherichia coli - Candida albicans
34
Opportunistic pathogens and infections
- Easily cause infections in unprotected body sites (blood, tissues) - Defective immune system: more susceptible to disease caused by opportunistic pathogens
35
Colonization and disease
- "Infection" is often used to describe any time that microorganisms are present - Important to distinguish between colonization (natural and important, versus disease)
36
Killing of normal flora through antibiotics
- Gives opportunistic pathogens an advantage
37
Infant colonization process
- Skin, then oropharynx, gastrointestinal tract, and other mucosal surfaces - Throughout life, this population continues to change
38
Human fetus
- Microbiologically sterile until birth | - Exposed to microbes from the mother and the environment
39
Factors affecting the continual flux of microbial flora
- Age - Diet - Hormonal state - Overall health - Personal hygiene - Available nutrients - Sites for attachment - pH and oxidation potential of specific niches - Physiology of host - Resistance or susceptibility of organisms to antimicrobial agents used by the host
40
Factors affecting microbial flora
- Relationships with other microorganisms | - Rule of microbial flora ecology
41
Microbial flora relationships with other microorganisms
- Competition for nutrients and niche (space) - Production of antibiotic products - Symbiotic relationships with other microorganisms
42
Rule of microbial flora ecology
- Best adapted organisms persist and become residential on areas exposed to the environment
43
Microbial flora exception
- Despite large numbers of organisms in the microbiota, humans are mostly free of microbial colonization - Exception: Surfaces of the body in contact with the environment
44
Sterile body fluids
- Blood - CSF - Urine - Pleural fluid - Essentially, all body fluids except superficial tissues (including cornea)
45
Common upper respiratory tract bacteria
- Peptostreptococcus and related anaerobic cocci - Veillonella - Actinomyces - Fusobacterium species - Staphylococus and Streptococcus species - Haemophilus species - Neisseria species - Fungi - Candida
46
Upper respiratory bacteria and disease
- Rarely associated with disease unless they are introduced into normally sterile sites such as sinuses, middle ear, and brain
47
Potentially pathogenic organisms of the upper respiratory tract
- Streptococcus pyogenes - Streptococcus pneumoniae - Staphylococcus aureus - Neisseria meningitidis - Haemophilus influenzae - Moraxella catarrhalis
48
Coagulase-negative Staphylococcus (CNS)
- Common organism colonizing outer ear
49
Organisms also colonizing the skin that have been isolated from the ear
- S. pneumoniae - Pseudomonas aeruginosa - Some enterobacteriaceae family
50
The surface of the eye is colonized with
- Coagulase-negative staphylococci
51
Rare numbers of organisms found in the nasopharynx
- Haemophilus spp. - Neisseria spp. - Viridans streptococci
52
Nasopharynx disease typical with
- S. pneumoniae - S. aureus - H. influenzae - N. gonorrhoeae - Pseudomonas aeruginosa
53
Transient colonization with secretions of the upper respiratory tract may occur via
- Aspiration
54
Commonly more virulent bacteria present in the mouth and upper airway
- S. pneumoniae - S. aureus - Klebsiella - Cause acute disease of the lower airway - Fungi rarely cause disease in the lower airway
55
Gastrointestinal tract is heavily colonized with
- Microbes at birth | - Diverse population of organisms throughout life
56
GI tract population remains relatively constant unless
- Exogenous factors such as antibiotic treatment disrupt the balanced flora
57
Bacteria and esophagus (GI) infections
- Rarely cause disease | - Most infections caused by herpes simplex virus (HSV), cytomegalovirus (CMV) and Candida
58
Bacteria of the esophagus (GI)
- Oropharyngeal bacteria and yeast - Bacteria from stomach - Transient colonizers
59
Stomach population
- Contains hydrochloric acid and pepsinogen | - Small numbers of acid-tolerant bacteria present
60
Potential stomach organisms present
- Lactobacillus - Helicobacter pylori - Streptococcus spp. - H. pylori can cause gastritis and ulcerative disease
61
Small intestine population
- Many different bacteria, fungi and parasites present | - Mainly anaerobic organisms (Peptostreptococcus, Porphyromonas, Prevotella)
62
Large intestine population
- More microbes present than anywhere else in the human body - More than 1011 bacteria per gram of feces - Anaerobic bacteria predominate
63
Large intestine organisms
- Bifidobacterium - Eubacterium - Bacteroides - Enterococcus - Enterobacteriaceae - E. coli present in virtually all humans
64
E. coli
- Less than 1% of the intestinal population | - Most common aerobic organism responsible for intrabdominal disease
65
Bacteroides fragilis
- Most common anaerobe responsible for disease in large intestine
66
Commensal population of the urethra consists of a variety of organisms
- Lactobacilli, streptococci, and coagulase-negative staphylococci the most numerous - Relatively avirulent and are rarely associated with human disease
67
Urethra can be colonized transiently with fecal organisms
- Enterococcus, Enterobacteriaceae, and Candida | - All can invade the urinary tract, multiply in urine, and lead to significant disease
68
Common causes of urethritis
- Pathogens such as Neisseria gonorrhoeae and Chlamydia trachomatis - Can persist as asymptomatic colonizers of the urethra
69
Microbial population of the vagina
- More diverse | - Influenced by hormonal factors
70
Newborn vaginal colonization
- Colonized with lactobacilli at birth | - These bacteria predominate for approximately 6 weeks
71
Vaginal floral changes after birth
- Levels of maternal estrogen decline | - Changes to include staphylococci, streptococci, and Enterobacteriaceae
72
As estrogen production is initiated at puberty, the microbial flora again changes
- Lactobacilli reemerge as the predominant organisms
73
Other organisms isolated from vaginal flora
- Staphylococci (S. aureus , coagulase-negative species) - Streptococci (including group B Streptococcus) - Enterococcus - Gardnerella - Mycoplasma - Ureaplasma - Enterobacteriaceae - Various anaerobic bacteria
74
Skin surfac
- Relatively hostile | - Many organisms, but environment does not support their survival
75
Most common organisms found on the skin surface
- Gram-positive bacteria
76
Other organisms on the skin surface
- More commonly coagulase-negative Staphylococcus | - Less commonly S. aureus, corynebacteria, and propionibacteria
77
Clostridium perfringens
- Isolated on the skin of approximately 20% of healthy individuals
78
Gram-negative rods
- Do not permanently colonize the skin surface (except Acinetobacter and a few other less common genera) - Skin is too dry
79
Streptococci can colonize the skin transiently, but
- Fatty acids produced by the anaerobe propionibacteria are toxic for these organisms

Medical Microbiology I (8 decks)

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