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Clinical Microbiology (Exam 3) > Anaerobes (Exam #) > Flashcards

Anaerobes (Exam #) Flashcards

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1
Q

Are anaerobes gram + or - ?

A

a mixture of both

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2
Q

What does aerotolerant mean?

A

anaerobic bacteria not killed by small amounts of air (5%)

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3
Q

What two anaerobic species are known to be aerotolerant?

A

Clostridium spp. and Actinomyces spp.

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4
Q

How long does it take for obligate anaerobes to die when exposed to oxygen?

A

As little as 10 minutes

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5
Q

What enzymes do anaerobic bacteria lack?

A

superoxide dismutase and catalase, enzymes required to break down reactive oxygen during aerobic metabolism, which is harmful to bacteria

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6
Q

obligate aerobes

A

grow well in 21% o2 and 0.3% co2 aka ambient air

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7
Q

obligate anaerobes

A

grow only in or near 0% o2 levels, 5-10% hydrogen and co2, and 80%-90% nitrogen

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8
Q

microaerophiles

A

only grow under reduced 02 levels 5-10%, and co2 8-10%

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9
Q

facultative anaerobe

A

can grow under aerobic or anaerobic conditions, potential skin flora. Will respire aerobically until oxygen is depleted then ferment.

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10
Q

Capnophile

A

likes increased co2 5-10%, and 15% o2. Is accomplished in our lab via candle jar

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11
Q

What is the most abundant bacteria in the GI tract?

A

anaerobes, and the number of bacteria increase as you move distally.

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12
Q

what is the most abundant bacteria in the human colon and why is this important?

A

Bacteriodes spp., they break down food products into forms our bodies can use and also break down dietary carcinogens.

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13
Q

Are clostridia normal flora?

A

yes, of the GI and skin

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14
Q

What additional anaerobes are normal flora of the skin and/or upper respiratory tract?

A

propionibacterium, prevotella, and fusobacterium

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15
Q

What bacteria is normal flora of the female genital tract and in rare cases pathogenic?

A

Lactobacillus, microaerophillic, gram positive thin rods with spiral forms. Catalase negative. can be pinpoint on SBAP as well as aplha hemolytic like streptococci.

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16
Q

What are the disease transmission types of anaerobes?

A
  • endogenous infections- opportunistic infections, pathogens gain access to sterile sites (Trauma)
  • exogenous sources- rusty nails, skin puncture
  • ingestion of improperly canned foods (botulism)
  • human to human spread (C. Diff)
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17
Q

Are anaerobe infections common in urine?

A
  • Very rarely urine, only 1% of isolates isolated from urines are anaerobes.
  • Voided or catheterized urine not acceptable (normal flora contaminants).
  • Suprapubic bladder aspirate is acceptable.
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18
Q

What are preferred anaerobe specimens?

A
  • Specimens that limit the amount of normal flora contamination are preferred e.g. aspirates, tissue, blood.
  • Acceptable specimens include aspirated material or tissue biopsy.
  • Needle aspiration preferred over swabs
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19
Q

What are the disadvantages of swabs?

A
  • small amount
  • drying
  • toxic exposure to air
  • normal flora contamination
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20
Q

What should blood collection sites be sanitized with?

A

with iodine or clorhexidine gluconate in combo with 70% isopropyl alcohol

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21
Q

How should anaerobe specimens be transported?

A
  • Anaerobes causing infection often come from warm, moist (humid) areas in the body, thus need to create artificial conditions mimicking this to avoid shocking them.
  • Tissue needs to be placed in anaerobic transport tubes or vials containing Pre-reduced anaerobically sterilized (PRAS) media to keep tissue moist.
  • Specimens should be held at room temperature.
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22
Q

What are the common anaerobe containers?

A

*Anaerobe Jars or Pouches e.g. Gas-Pak by BD
Clear, heavy plastic jar with air tight seal (clamp-lid)
*Pouch systems also available commercially with all necessary agents.
*Holding Jars
*Anaerobe Chambers (Glove boxes)

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23
Q

How do you know you are creating an anaerobic environment using a gas-pak and jar?

A

Heat will be produced and condensation will collect on walls of jar, indicates you are achieving proper conditions, takes ~ 30 minutes.

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24
Q

What media should anaerobes be plated to?

A

Typically always plate an anaerobic blood agar and one or all of the following PRAS media:

  • Anaerobic Phenylethyl alcohol agar (PEA)
  • Kanamycin-vancomycin laked blood (KVLB)
  • Kanamycin-vancomycin blood agar
  • Bacteroides bile-esculin agar (BBE)
  • Thioglycollate broth
25
Q

Should suspected anaerobe infections be plated to aerobic media?

A

t ypically also plate AEROBIC SBAP, chocolate and MacConkey as most anaerobic infections are POLYMICROBIC and can include aerobic or facultative anaerobic bacteria

26
Q

What should anaerobic media be supplemented with?

A
  • hemin
  • blood
  • vitamin K
  • sodium bicarbonate
27
Q

What is the name of the common media type used for anaerobes?

A

Pre-Reduced, Anaerobically Sterilized (PRAS) media

28
Q

What’s in an anaerobic BAP?

A
  • yeast
  • hemin
  • cysteine
  • vitamin K
29
Q

What’s in Kanamycin-vancomycin laked blood/blood agar?

A

*Selective for gram negative obligate anaerobes (preferred media for these specific bacteria).
Specifically Prevotella and Bacteroides spp.

  • Vancomycin inhibits growth of all gram positive organisms (both aerobic and anaerobic)
  • Kanamycin inhibits growth of gram negative, facultative anaerobic bacilli
  • laked blood helps pigment production by prevotella melaninogenica
30
Q

What is the antibiotic in bacteriodes bile esculin agar?

A

gentamicin- inhibits facultative anaerobes and most gram negative anaerobes

31
Q

Should you gram stain suspected anaerobic bacteria?

A

all species should be gram stained, may be polymicrobial or show things such as epithelial cells etc that can help with media selection or narrowing of possible organuisms.

32
Q

What are the clues that anaerobic bacteria are present?

A
  • Foul odor upon opening a anaerobic jar or bag e.g. metabolic end-products from C. difficile, Fusobacterium are fetid.
  • Colonies present on anaerobic media, but not on non-anaerobically incubated/prepared media.
33
Q

How is bacteriodes fragilis group id’ed?

A
  • gram negative rods
  • bile esculin positive
  • Resistant to vancomycin, penicillin, kanamycin, and typically colistin.
  • Growth on BBE agar (blackening)
34
Q

porphyromonas

A
  • gram negative rod
  • pigmented- bright red fluorescence under UV
  • asacchrolytic
  • normal flora of oral cavity
  • more commonly cause infections of head region
35
Q

prevotella melaninogenica

A
  • gram negative rods
  • normal flora of oral cavity, respiratory, GI, and genitourinary tracts
  • opportunistic pathogen
  • Pigmented and non pigmented strains- black pigment on laked blood agar after several days, brick-red fluorescence under UV
  • ferments carbs, distinguishes it from porphyromonas
36
Q

fusobacterium spp.

A
  • Gram negative rods
  • slightly curved appearance on gram stain
  • normal flora of oral cavity
  • infections above the thorax typically
37
Q

Clostridium spp.

A
  • gram positive bacilli
  • endospore forming
  • catalase negative
  • obligately anaerobic, some aerotolerant
  • many species normal flora of the gut, female GI tract, and oral mucosa.
38
Q

why is clostridium good at causing disease?

A
  • Ubiquitous in nature.
  • Spores allow them to survive harsh environmental conditions.
  • Can rapidly proliferate in nutrient rich, oxygen deprived environments.
  • Produce various toxins (enterotoxins, neurotoxins).
39
Q

What do clostridium botulinum look like?

A

Spores are subterminal, bacteria resemble a tennis racket as seen in an endospore stain.

40
Q

What are the botulism groups and which cause disease in humans?

A

Groups I and II cause human botulism, Group III animal botulism, Group IV not typically associated with disease.

41
Q

What virulence factors do C.Botulinum have?

A
  • Neurotoxin causing flaccid paralysis.

* 7 types of toxin exist A-G; A, B E and F types cause human disease

42
Q

What are the 4 forms of botulism?

A
  • foodborne -canned foods
  • infant- associated with honey consumption
  • wound– this is the only form that antibiotics are typically used as treatment. Antibiotics may hasten release of toxin thus contraindicated in non-wound botulism.
  • inhalation- seen in bioterrorism
43
Q

What is the pathogenesis of botulism?

A

enters the body through GI tract or mucous membranes, makes its way to bloodstream and/or lymphatics until it reaches neuromuscular junctions blocking neurotransmitter release. Can lead to paralysis and death via respiratory failure.

44
Q

foodborne botulism

A
  • symptoms can begin in 6 hours but typically 18-36 hours after ingestion of pre-formed toxin.
  • treat with ventilation and antitoxin
  • recovery can take months to years, nerve endings have to regrow
  • 3-5% mortality rate
  • Toxin can be inactivated by boiling
45
Q

how is foodborne botulism identified?

A
  • Not included on the Vitek 2 ANC card.
  • Specimens can include: serum, gastric contents, feces, food
  • ELISA
  • Molecular Techniques
  • Mouse Bioassay for ID of botulinum toxin
46
Q

infant botulism

A
  • neurotoxin production in vivo
  • bacteria colonize GI mucosa
  • treatment is high support care- nutrition and respiratory functions
47
Q

C. Tetani

A
  • spore are oval with terminal or subterminal locations
  • looks like a drumstick or tennis racket on gram stain
  • narrow zone of beta hemolysis on anaerobic blood agar plates and may swarm
  • DTaP vaccine
  • difficult to identify without good H and P
48
Q

C. perfringens

A
  • found in soil and water, some are normal flora, can also be found on kitchen counters
  • produce 12 different toxins
  • double zone of hemolysis on anaerobic blood agar
  • Strains producing C. perfringens enterotoxin (CPE), third most common cause of bacterial food poisoning in U.S.
  • alpha hemolysis due to alpha toxin and lecithinase activity
49
Q

What types of infections do C. Perfringens cause?

A

Soft tissue infections

  • Cellulitis
  • Myonecrosis (Gas gangrene), high mortality rate)
  • Food poisoning (meat products)
  • Enteritis necroticans
50
Q

How is C. Perfringens identified?

A
  • feces needs to be sent to public health lab for confirmation of ID at 4 degrees C
  • round, subterminal spores
  • reverse CAMP positive
  • VITEK 2 ANC card
  • molecular studies
51
Q

What are the two toxins C.Diff produces?

A
  • Enterotoxin, causes inflammation of intestinal mucosa

* Cytotoxin- causes cellular death

52
Q

How should C.Diff cultures be?

A
  • Stool cultures should be watery, not formed, to distinguish infection from colonization.
  • Emit a horse stable odor on blood agar
  • cycloserine-cefoxitin-fructose agar (CCFA)- Egg yolk based selective for C. diff creates yellow ground glass colonies. Others may grow but do not produce a yellow color change.
53
Q

How is C.Diff identified?

A
  • Culture then automation (Vitek 2 ANC card)
  • Agglutination tests for Ag detection
  • Enzyme immunoassays for toxin A, B or both
  • Molecular
54
Q

Actinomyces israelii

A

*normal flora of the mouth, gums, teeth, entry via injured oral mucosa
*gram positive rods, non-spore forming
*fungus-like bacteria
*produce hyphal strands
*molar tooth appearance on agar
*

55
Q

what disease does actinomyces cause?

A
  • Chronic infection with local abscesses with formation of oozing sinus tracts containing sulfur granules
  • Gain entry to deeper tissues via injury, more common in males
56
Q

peptostreptococcus anaerobius

A

*gram positive coccobaccilus, often in chains
*normal flora
*Can cause endocarditis, infection of GU and GI tracts.
Also implicated in periodontal disease, gingivitis.

57
Q

peptococcus niger

A
  • gram positive cocci in pairs, tetrads
  • normal flora, not usually disease causing
  • Produce tiny black, convex, smooth colonies on anaerobic BAP which turn light gray if exposed to air.
58
Q

Veilonella Paruvula

A
  • Gram negative, diplococci in pairs, clusters and/or short chains.
  • Normal flora of human mouth, GI tracts.
  • Can cause infection in sinuses, lung, heart, bone and CNS.
  • Produce a red fluorescence under UV light.
  • Has been found to create a biofilm along with Streptococcus mutans (normal flora of the mouth) that in combination imparts greater resistance to S. mutans to various antimicrobials.

Clinical Microbiology (Exam 3) (4 decks)

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