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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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Biology 101 flashcards USMLE® Step 1 flashcards
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
Q

Opportunistic pathogens

A
  • Organisms that are typically members of the patient’s normal microbial flora
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26
Q

Opportunistic pathogens and disease

A
  • Do not produce disease in their normal place

- Establish disease when introduced into unprotected body sites

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27
Q

Strict pathogen examples

A
  • Mycobacterium tuberculosis
  • Neisseria gonorrhoeae
  • Francisella tularensis
  • Plasmodium spp.
  • Rhabdovirus
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28
Q

Mycobacterium tuberculosis

A
  • Tuberculosis

- Acid-fast bacilli

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29
Q

Neisseria gonorrhoeae

A
  • Gonorrhea)

- Gram negative diplococci

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30
Q

Francisella tularensis

A
  • Tularemia

- Small Gram negative cocci

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31
Q

Plasmodium spp.

A
  • Malaria

- Protozoan

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32
Q

Rhabdovirus

A
  • Rabies virus
33
Q

Opportunistic pathogen examples

A
  • Staphylococcus aureus
  • Escherichia coli
  • Candida albicans
34
Q

Opportunistic pathogens and infections

A
  • Easily cause infections in unprotected body sites (blood, tissues)
  • Defective immune system: more susceptible to disease caused by opportunistic pathogens
35
Q

Colonization and disease

A
  • “Infection” is often used to describe any time that microorganisms are present
  • Important to distinguish between colonization (natural and important, versus disease)
36
Q

Killing of normal flora through antibiotics

A
  • Gives opportunistic pathogens an advantage
37
Q

Infant colonization process

A
  • Skin, then oropharynx, gastrointestinal tract, and other mucosal surfaces
  • Throughout life, this population continues to change
38
Q

Human fetus

A
  • Microbiologically sterile until birth

- Exposed to microbes from the mother and the environment

39
Q

Factors affecting the continual flux of microbial flora

A
  • 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
Q

Factors affecting microbial flora

A
  • Relationships with other microorganisms

- Rule of microbial flora ecology

41
Q

Microbial flora relationships with other microorganisms

A
  • Competition for nutrients and niche (space)
  • Production of antibiotic products
  • Symbiotic relationships with other microorganisms
42
Q

Rule of microbial flora ecology

A
  • Best adapted organisms persist and become residential on areas exposed to the environment
43
Q

Microbial flora exception

A
  • 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
Q

Sterile body fluids

A
  • Blood
  • CSF
  • Urine
  • Pleural fluid
  • Essentially, all body fluids except superficial tissues (including cornea)
45
Q

Common upper respiratory tract bacteria

A
  • Peptostreptococcus and related anaerobic cocci
  • Veillonella
  • Actinomyces
  • Fusobacterium species
  • Staphylococus and Streptococcus species
  • Haemophilus species
  • Neisseria species
  • Fungi
  • Candida
46
Q

Upper respiratory bacteria and disease

A
  • Rarely associated with disease unless they are introduced into normally sterile sites such as sinuses, middle ear, and brain
47
Q

Potentially pathogenic organisms of the upper respiratory tract

A
  • Streptococcus pyogenes
  • Streptococcus pneumoniae
  • Staphylococcus aureus
  • Neisseria meningitidis
  • Haemophilus influenzae
  • Moraxella catarrhalis
48
Q

Coagulase-negative Staphylococcus (CNS)

A
  • Common organism colonizing outer ear
49
Q

Organisms also colonizing the skin that have been isolated from the ear

A
  • S. pneumoniae
  • Pseudomonas aeruginosa
  • Some enterobacteriaceae family
50
Q

The surface of the eye is colonized with

A
  • Coagulase-negative staphylococci
51
Q

Rare numbers of organisms found in the nasopharynx

A
  • Haemophilus spp.
  • Neisseria spp.
  • Viridans streptococci
52
Q

Nasopharynx disease typical with

A
  • S. pneumoniae
  • S. aureus
  • H. influenzae
  • N. gonorrhoeae
  • Pseudomonas aeruginosa
53
Q

Transient colonization with secretions of the upper respiratory tract may occur via

A
  • Aspiration
54
Q

Commonly more virulent bacteria present in the mouth and upper airway

A
  • S. pneumoniae
  • S. aureus
  • Klebsiella
  • Cause acute disease of the lower airway
  • Fungi rarely cause disease in the lower airway
55
Q

Gastrointestinal tract is heavily colonized with

A
  • Microbes at birth

- Diverse population of organisms throughout life

56
Q

GI tract population remains relatively constant unless

A
  • Exogenous factors such as antibiotic treatment disrupt the balanced flora
57
Q

Bacteria and esophagus (GI) infections

A
  • Rarely cause disease

- Most infections caused by herpes simplex virus (HSV), cytomegalovirus (CMV) and Candida

58
Q

Bacteria of the esophagus (GI)

A
  • Oropharyngeal bacteria and yeast
  • Bacteria from stomach
  • Transient colonizers
59
Q

Stomach population

A
  • Contains hydrochloric acid and pepsinogen

- Small numbers of acid-tolerant bacteria present

60
Q

Potential stomach organisms present

A
  • Lactobacillus
  • Helicobacter pylori
  • Streptococcus spp.
  • H. pylori can cause gastritis and ulcerative disease
61
Q

Small intestine population

A
  • Many different bacteria, fungi and parasites present

- Mainly anaerobic organisms (Peptostreptococcus, Porphyromonas, Prevotella)

62
Q

Large intestine population

A
  • More microbes present than anywhere else in the human body
  • More than 1011 bacteria per gram of feces
  • Anaerobic bacteria predominate
63
Q

Large intestine organisms

A
  • Bifidobacterium
  • Eubacterium
  • Bacteroides
  • Enterococcus
  • Enterobacteriaceae
  • E. coli present in virtually all humans
64
Q

E. coli

A
  • Less than 1% of the intestinal population

- Most common aerobic organism responsible for intrabdominal disease

65
Q

Bacteroides fragilis

A
  • Most common anaerobe responsible for disease in large intestine
66
Q

Commensal population of the urethra consists of a variety of organisms

A
  • Lactobacilli, streptococci, and coagulase-negative staphylococci the most numerous
  • Relatively avirulent and are rarely associated with human disease
67
Q

Urethra can be colonized transiently with fecal organisms

A
  • Enterococcus, Enterobacteriaceae, and Candida

- All can invade the urinary tract, multiply in urine, and lead to significant disease

68
Q

Common causes of urethritis

A
  • Pathogens such as Neisseria gonorrhoeae and Chlamydia trachomatis
  • Can persist as asymptomatic colonizers of the urethra
69
Q

Microbial population of the vagina

A
  • More diverse

- Influenced by hormonal factors

70
Q

Newborn vaginal colonization

A
  • Colonized with lactobacilli at birth

- These bacteria predominate for approximately 6 weeks

71
Q

Vaginal floral changes after birth

A
  • Levels of maternal estrogen decline

- Changes to include staphylococci, streptococci, and Enterobacteriaceae

72
Q

As estrogen production is initiated at puberty, the microbial flora again changes

A
  • Lactobacilli reemerge as the predominant organisms
73
Q

Other organisms isolated from vaginal flora

A
  • Staphylococci (S. aureus , coagulase-negative species)
  • Streptococci (including group B Streptococcus)
  • Enterococcus
  • Gardnerella
  • Mycoplasma
  • Ureaplasma
  • Enterobacteriaceae
  • Various anaerobic bacteria
74
Q

Skin surfac

A
  • Relatively hostile

- Many organisms, but environment does not support their survival

75
Q

Most common organisms found on the skin surface

A
  • Gram-positive bacteria
76
Q

Other organisms on the skin surface

A
  • More commonly coagulase-negative Staphylococcus

- Less commonly S. aureus, corynebacteria, and propionibacteria

77
Q

Clostridium perfringens

A
  • Isolated on the skin of approximately 20% of healthy individuals
78
Q

Gram-negative rods

A
  • Do not permanently colonize the skin surface (except Acinetobacter and a few other less common genera)
  • Skin is too dry
79
Q

Streptococci can colonize the skin transiently, but

A
  • Fatty acids produced by the anaerobe propionibacteria are toxic for these organisms

Medical Microbiology I (8 decks)

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