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Flashcards in skin 13: anaerobic infections Deck (35):

Definition of an obligate anaerobe is a bacterium which requires ??

*reduced oxygen tension for growth and fails to grow on the surface of solid media in 10% CO2 in air*


Importance of Anaerobes:

-Anaerobes are the predominant flora of humans and most are harmless commensals.
-Anaerobic infections are the predominant infection at most anatomical sites.
-Some anaerobic NF are capable of causing disease at the anatomical site where they reside (overgrowth) and/or at another site (displacement).


Body sites where anaerobic organisms are the normal flora: ??

Mucosal surfaces and the skin normally harbor large anaerobic NF
mouth/oropharynx: teeth, saliva, gingival crevices (high numbers-10^12)
*most common cause of anaerobic infections*


important anaerobes of mouth/oropharynx:

Treponema denticola, T. vincentii.
Porphyromonas sp:
Prevotella sp:
Fusobacterium nucleatum
Aggregatibacter (formerly Haemophilus, Actinobacillus)
Actinomyces israelii.
Lactobacillus sp
Bifidobacterium sp
Peptostreptococcus sp


NF of gastrointestinal tract conditions

stable after solid food diet begins and only severe in situations such
as malignancy, chemotherapy, broad spec abx tx or long-term
diet changes will alter the gut NF.
Anaerobes outnumber aerobes 200:1


NF of gastrointestinal tract:

*Bacteroides sp., especially Bacteroides fragilis*
*Bifidobacterium sp.*
Lactobacillus sp.
Clostridium perfringens, type A
*Clostridium difficile*
Enterococcus (E. faecalis, E. faecium)
Peptostreptococcus sp


NF of the adult female vagina conditions:

Least stable anaerobic flora at any human site where anaerobes part of the normal flora, anaerobic NF changes with menses. Anaerobes outnumber aerobes 5:1


NF of the adult female vagina:

Gardnerella vaginalis
Mobiluncus sp.
Bacteroides sp.
Lactobacillus sp
Clostridium perfringens, type A
Peptostreptococcus sp


NF of skin and cornea conditions:

Anaerobes are present in fewest numbers.


NF of skin and cornea:

Propionibacterium acnes and other diphtheroids.
Streptococci (*Aerotolerant anaerobic*, G+ cocci in chains)
Enterococcus (*Aerotolerant anaerobic*, G+cocci in chains) Peptostreptococcus sp (*Obligate anaerobic*, G+ cocci in chains)


Aggregatibacter (formerly Haemophilus, Actinobacillus) actinomycetemcomitans:

G- coccobacillus
NF or the mouth;
Associated with periodontitis. (African american w. loose teeth, bone resorption, leukocyte pedesis?-->Localized Juvenile Periodontitis)


Actinomyces israelii:

G+ rods *(facultative anaerobe) but specimens must be cultured anaerobically*
NF of gingival cervices; Associated with:
1. Periodontal infections; Ludwig's angina (OG)
2. Pneumonia by extension from oral lesion. (displacement)
3. Skin and soft tissue infections by extension from oral lesion or dissemination. (displacement)
4. Abscess formation in any visceral organ via hematogenous dissemination. (displacement)


Bacteroides sp:

G- pleomorphic rods.
-Predominant NF of the colonic mucosa, but not in feces, yet still is the dominant genera of the colonic flora.
-NF of the female genital tract.
4 Bacteroides species:
a. 2 of the 4 species predominate in the gut of each individual.
b. One of the 4 species is B. fragilis


Bacteroides fragilis: Virulence factors include:

1. *Oxygen tolerance*, due to expression of *superoxide dismutase and an inducible catalase*.
2. Capsular Polysaccharide Complex (CPC) functions include:
a. Abscessogenic,
b. Antiphagocytic,
c. An adhesin.
3. Hydrolytic enzymes (heparinase producing strains are associated with septic thrombosis).


Bacteroides fragilis: *Major clinical agent of human disease*; is associated with infections/abscesses of the:

Female genital tract.
GI tract (diarrhea).
*Abdomen (the most commonly isolated anaerobe in abdominal infections)*
Skin and soft tissue (i.e., diabetic foot ulcer),
RT (pneumonia, pharyngitis).
brain and teeth


Bacteroides fragilis: Often ??, an exception to the general clues for diagnosis of anaerobic infection.



Bacteroides fragilis: resistance??

Metronidazole resistance has been reported n Europe and Asia, now in the USA. Resistance is due to 1 of 5 nim nitroreductase genes. Cases was due to importation of an infection acquired in Europe.


Metronidazole is a ??

prodrug which is activated by nitrate reductase which is only expressed under anaerobic conditions.


Bifidobacterium sp.:

G+ rod,
NF of gingival cervices and colon.


Bilophila wadsworthia:

nonmotile, G- rod.
Isolated from GI tract, but not present in high numbers.
A frequently isolated anaerobe in clinical specimens, recovered from abscesses from:
1. Abdomen
2. Joints
3. Appendicitis patients
4. Patients with colon cancer?


Clostridium sp.:

Short, G+ *spore-forming rods* (Bacillis is the G- spore forming rod)
-C. botulinum (soil, water, NF of animals) and C. tetani (soil).
-C. perfringens, type A (soil, NF of GIT in humans).
(vomiting, assoc. w. gravy)
-C. difficile (NF of GIT in humans).


Clostridium sp.: Major diseases include:

Toxemia (botulism [C. botulinum]and tetanus [C. tetani]).
Food poisoning (C. perfringens, type A).
Female urogenital infections - (C. perfringens, type A, etc.).
Traumatic wounds/colon surgery infections (C. perfringens, type A, etc.).
Antibiotic therapy/antibiotic-associated pseudomembranous colitis; C. difficile).


Enterococcus (formerly Streptococcus) sp.:

Major species are:
a. E. faecalis.
b. E. faecium.
Aerotolerant anaerobic, G+ cocci, catalase negative

Vancomycin-resistant enterococci (VRE).
-Vancomycin is a marker for MDR strains
-due to an alteration in the pentapeptide side
chain (lactic acid replaces last 2 amino acids, D-alanine, D-alanine,).


Enterococcus (formerly Streptococcus) sp.: 2

NF or GIT and skin
Present on fomites in hospitals, railings of hospital beds, stethoscopes, etc.
-Significant agents of nosocomial infection, especially bacteremia in immunocompromised patients or those with chronic, debilitating disease.


Fusobacterium nucleatum and other species:

G- rods with pointed ends,
NF of the oral cavity and colon,
Associated with periodontal and other infections.


Gardnerella vaginalis:

G+, pleomorphic rod-->cells stain Gram variable or G-
NF of vaginal tract,
Agent of vaginosis.


Lactobacillus sp.:

Aerotolerant anaerobic, long, G+ rods.
NF of:
1. Vaginal tract,
2. Oral cavity (gingival crevices),
3. GI tract (colon).
-Some species cause peridontal disease.


Mobiluncus sp.:

G+ curved rod-->cells stain Gram variable or G-.
N.F. of vaginal tract
Agent of vaginosis.


Peptostreptococcus sp:

*Obligate anaerobic*, G+ cocci in chains.
NF of human mucocutaneous surfaces, including the mouth, intestinal tract, vagina, urethra, and skin.
Associated with vaginosis; skin and soft tissue infections.


Peptostreptococcus sp: name changes?

The taxonomy of this genus is in question and several prominent species have already
been re-named:
1. Finegoldia magna (AKA Peptostreptococcus magnus).
2. Micromonas micros (AKA Peptostreptococcus. Micros) – an illigimate genus name.


Porphyromonas sp:

G- rods
NF of oral cavity (isolated from gingival cervices);
Associated with gingivitis, periodontitis, periodontosis and polymicrobic infections at many
other body sites.


Prevotella sp:

G- rods
NF of oral cavity (isolated from gingival cervices);
Associated with gingivitis, periodontitis, periodontosis and polymicrobic infections at many other body sites.


Propionibacterium acnes:

G+ diphtheroid/club-shaped rods
NF of skin surfaces:
Associated with inflammatory acnes.
Common contaminant of human specimens (i.e. blood, urine).


Streptococci sp.:

Aerotolerant anaerobic G+ cocci.
Some species are NF of: Mouth/oropharynx, GIT, Skin.
Others species are frank pathogens: S. pneumoniae, S. pyogenes, S. agalactiae.
Oral streptococci: S. mutans, sanguis, salivarius, mitis. (a- hemolytic, G+ strep, agents of endocarditis)
GIT strep: S. bovis (a-hemolytic, G+ strep, agent of endocarditis)


Treponema denticola, T. vincentii

NF of mouth
Agents of periodontal disease. (trench mouth)
-can also get 2o syphilis of mouth-ddx

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