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Microbiology 2 > M3 GI Tract Infections > Flashcards

M3 GI Tract Infections Flashcards

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1
Q

How many host defenses against GI tract infections can you list?

A
  • Acidity of stomach*
  • Normal peristalsis
  • Mucous layer coating the epithelium
  • Normal flora, preventing colonization by potential pathogens (antimicrobials-affected?)
  • Follicles and Peyer patches in intestine: contain M cells, macrophages, B&T cells
  • Age of patient
  • Immunological (antibodies & leukocytes)
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2
Q

What action can we take to prevent a GI tract infection?

A

Hygiene (fecal-oral route of entry)

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3
Q

What organisms are more resistant to stomach acidity?

A

Shigella, E coli O157, C.diff, TB are more resistant,

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4
Q

What is the normal flora of the small intestine?

A
  1. upper small intestine contains sparse flora
  2. distal ileum counts are significantly higher
    - Enterics
    - Bacteroides spp.
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5
Q

What kind of bacteria are the GI tracts of infants colonized by?

A

Infants are colonized by normal skin flora.

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6
Q

What organisms are the normal flora of the adult GI tract?

A

In the adult large bowel, anaerobes outnumber aerobes 1000 to 1.
ANO2:
- Bacteroides
- Clostridioides (Clostridium)
- Peptostreptococcus spp.
- Bifidobacterium spp.
- Eubacterium spp.
Enterics (e.g., Escherichia coli)
Enterococci
Streptococci

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7
Q

What are risk factors for a GI tract infection?

A
  1. Infectious dose or other organism related factors
  2. Compromised host defenses
  3. Antimicrobial exposure
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8
Q

What is the method of introduction of the pathogen into the GI tract?

A

First, ingestion happens (fecal-oral route)
Through food and water

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9
Q

What are the primary pathogenic mechanisms?

A
  1. Changing balance H2O/electrolyte–> massive fluid excretion (non-inflammatory process). Mostly done by enterotoxins.
  2. Invasion of host cells (possibly with cytotoxins)–> Causing cell destruction & marked inflammatory response (mainly in colon).
  3. Penetration of intestinal mucosa–>spread outside of bowel (systemic infections)
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10
Q

What are the various types of toxins that bacterial organisms can produce?

A
  1. Enterotoxins: act by increasing fluid & electrolyte excretion to lumen (small intestine). Watery Diarrhea.
  2. Cytotoxins: destruct cells/tissue which brings inflammation (PMN’s, blood) called dysentery, mainly in colon.
  3. Neurotoxins: pre-ingestion produced. Not really an infection (intoxication). Bacteria not always present: S. aureus, B.cereus, Clostridium botulinum & perfringens.
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11
Q

What type of organisms produce enterotoxins?

A

Vibrio cholera, other Vibrios, E.coli ETEC, Shig, Salm (some), C.diff, Aeromonas, Campy

Note: Enterotoxins alter metabolic activity of intestinal epithelial cell and increase fluid & electrolyte excretion to lumen (small intestine).

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12
Q

What type of organisms produce cytotoxins?

A

Shigella, C.diff, E. coli EHEC.

Note: Cytotoxins destruct cells/tissue which brings inflammation (PMN’s, blood) called dysentery, mainly in colon.

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13
Q

What organisms produce neurotoxins?

A

S. aureus, B.cereus, Clostridium botulinum & perfringens.

Note: Neurotoxins are often pre-ingestion produced. Not really an infection (intoxication). Bacteria not always present.

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14
Q

How does Vibrio cholerae cause diarrhea?

A

Cholerae’s toxins consist of two subunits that catalyze the transformation of adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP) which then stimulates the cell to secrete more ions in the intestinal lumen which results in fluid secretion into the lumen to maintain osmotic balance. Hence watery diarrhea.

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15
Q

Where can Vibrio cholerae often be found in the environment?

A

Sea and stagnant water.

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16
Q

How does Shigella (and some other bacteria) pass through the mucous membrane?

A

Shigella or other bacteria cross the mucous membrane into tissues. Macrophages engulf bacteria and then they get released from macrophages and enter host cells by endocytosis. Bacteria also move from cell to cell propelled by actin filaments.

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17
Q

Give an example of how one neurotoxin presents muscle contraction?

A

Clostridium botulinum bacteria produces BTXA which inhibits the neurotransmitter acetylcholine release from acetylcholine vesicles in the nerve endings, without acetylcholine being released muscles do not contract. This causes flaccid (rag doll) paralysis.

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18
Q

What kind of pathogenesis does an E. coli EPEC use?

A

Attachment, adherence
and Effacement (EPEC) through
Pili.

EPEC, EHEC, Criptosporidium,
misc. viruses.

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19
Q

What does the term “invasion” mean in regards to pathogenesis abilities of certain bacteria?

A

After initial and essential adherence to GI mucosal cells, some enteric pathogens can gain access to the intracellular environment. Invasion allows the organism to reach deeper tissues, access nutrients for growth, and possibly avoid the host immune system.

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20
Q

What bacteria have invasion pathogenesis capabilities?

A

Shigella, E. coli EIEC,
Campy, Yersinia, some
Parasites.

Cause bloody diarrhea.

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21
Q

What symptom/clinical features are caused by bacteria that can upset the fluid and electrolyte balance (noninflammatory)?

A

Watery diarrhea.
No fecal leukocytes.
No fever.

See slide 14 or p1053 (T74.3) of textbook.

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22
Q

What type of pathogenic mechanism causes dysenteric-like diarrhea (mucus, blood, white cells)? What are symptoms/clinical features are there?

A

Invasion and possible cytotoxin production / cell destruction and inflammation occur which results in dysentery.

Other signs include fever and fecal leukocytes.

See slide 14 or p1053 (T74.3) of textbook.

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23
Q

What symptoms occur if an enteric bacteria enters the bloodstream and the term for it?

A

Enteric fever; signs of systemic infection (headache, malaise, sore throat) and fever.

Also called “disseminated infections” (spread to other sites).

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24
Q

What typical bugs cause enteric fever?

A

Salmonella typhi and Yersinia enterocolitica.

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25
Q

What are the main 5 that are routinely cultured for the GI tract?

A

Salmonella spp.
Shigella spp.
Yersinia spp.
Campylobacter spp.
E.coli 0157:H7

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26
Q

What other bugs may be cultured on request for the GI tract?

A

Aeromonas and Vibrio.

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27
Q

Which bugs are never cultured for the GI tract?

A

S. aureus
B. cereus
ANO2

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28
Q

Who may rectal swabs be used on (likely)?

A

Rectal swabs may be used on infants (visibly soiled).

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29
Q

Are specimens submitted over 3 consecutive days or greater than 1/day acceptable?

A

No increases chances but … not good use of resources (later is my explanation.

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30
Q

What are the various terms used in the macroscopic evaluation of stools?

A

Macroscopic evaluation:
1. Formed
2. Semi-formed / mushy
3. Viscous soupy
4. Watery

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31
Q

How long can unpreserved specimens be refrigerated for if processing is delayed?

A

Refrigerate up to 24 hours from the time of collection.

32
Q

Who’s stool is rejected if the macroscopic evaluation shows it is formed?

A

Stool samples sent for C. difficile culture are rejected if they are formed.

33
Q

Can a preserved stool specimen for O & P be used for bacterial culture?

A

No because the formalin used to preserve the ova and parasites will kill the bacteria and it won’t be able to be cultured.

This is my explanation.

34
Q

Do we usually do Gram stain on stools?

A

No, the types that are pathogenic are going to look like the non-pathogenic (normal flora bacteria), so in general it is useless, unless they want to see PMN cells but gauge an inflammatory reaction.

35
Q

What does neutral red do in an an agar and what media used for stools uses neutral red?

A

Neutral red is a pH indicator and turns the media pink/red when the pH lowers (acidic).

Media with neutral red are:
MAC, SMAC, SS, and CIN.

36
Q

What are the differential and selective media that can be used for Salmonella and Shigella?

A

MAC, XLD, HE, and SS.

MAC - Salmonella, Shigella, and Yersinia are NLF and look colorless while LF are pink/red.

XLD - Salmonella is red w/black ctr, Shigella is red and normal enteric flora typically appears yellow.

HE - Salmonella appears colorless with black ctr and Shigella appears
colorless/color of media. Other GN’s appear orange when
pH gets acid.

SS - Salmonella appears colorless with black
centers and Shigella appears colorless.

37
Q

What are the dyes and their purpose in EMB agar?

A

Dyes in EMB agar are:
1. Eosin Y
2. Methylene Blue
Purpose is to inhibit gram positives.

The sugar in EMB is lactose.

38
Q

What are the two dyes in Hektoen (HE) agar and their purpose?

A

Acid fuschin - inhibits negative rods, and
Bromothymol Blue - indicator and dye to inhibit negative rods.

39
Q

What bile salts does Hektoen (HE) agar have in it and their purpose?

A

Biles salts in HE agar are:
- Sodium thiosulphate
- Ferric ammonium citrate

Purpose is to inhibit all other gram negatives and gram positive organisms and react with H2S to show black.

40
Q

What is the purpose of the salicin in HE agar?

A

Salicin helps differentiate Salmonella from Proteus better than XLD.

Note: Not clear how but see slide 29.

41
Q

What are the sugars in XLD?

A

Xylose, Lactose, and sucrose

42
Q

What is the indicator in XLD agar? What bio test also has that indicator?

A

Phenol Red
It turns from red to yellow when the pH is low (acidic).

TSI also uses phenol red!

43
Q

What do HE-XLD-SS have in common?

A

HE-XLD-SS all have:
- Lactose and bile salts (Sodium thiosulphate and Ferric ammonium citrate for H2S detection)
BUT:
- Indicators all vary but they all have some type of indicator
XLD - phenol red
HE - Bromothymol blue
SS - neutral red
- also some have other sugars

44
Q

What is the key ingredient of SMAC and its purpose?

A

Sorbitol

Non-pathogenic strains of
Escherichia coli are able to ferment sorbitol, but E.
coli O157:H7 cannot. The pH indicator in the SMAC
agar will make E coli O157:H7 appear colorless
(similar to a non-lactose fermenter) and other E coli
pink.

45
Q

What is the purpose of Selenite Broth, GN Broth, and Tetrathionate Broth?

A

They are enrichment media but needs to be subbed to a selective/diff agar be useful.

Selenite broth enriches the detection of Salmonella when subbed to a selective/differential media.

46
Q

Why does Salmonella keep the pH alkaline in XLD?

A

Salmonella ferments Xylose but also lysine + so pH keeps alk.

47
Q

What temperature and environment do you incubate the Campy agar?

A

Incubate at 42C in a microaerophilic jar
because Campylobactor grows ideally at 42C and that also inhibits grow of other bacteria.

Note: Campylobactor will also grow at 35C but so will the other bugs.

48
Q

What is the purpose of TCBS agar

A

To selectively isolate Vibrio cholerae and Vibrio parahemolyticus

49
Q

What ingredient in TCBS agar differentiates between the Vibrios species? What makes TCBS selective?

A

Sucrose (yellow if pos).

Note: Bromothymol blue is a dye.

High pH inhibits other negative rods (NR).

50
Q

What other test is done to confirm Aeromonas after finding a beta-hem on BA?

A

Oxidase, if positive then perform API 20NE to fully ID Aeromonas (last part is me).

51
Q

What bugs is an enteric screen performed on and what are the tests in an enteric screen?

A

Any suspicious NLF colonies.

Tests are:
- TSI
- SIM (optional)
- Urea
- BA checkplate (don’t forget!)

Incubate at 35C for 18 to 24 hours.

52
Q

What is the morphology of Aeromonas spp. on BA and typical TSI reaction?

A

Beta-hem, lg-gy (E.coli like)
NLF (some LF strains)
Oxidase +
TSI is K/AG/- or A/AG/-

53
Q

What is the morphology of Campylobacter spp on a campy plate?

A

Small-tiny grey-silvery, shiny mucoid, irregular, colonies.
Might grow very pinpoint at 24 hours.

54
Q

What tests do you perform to confirm Campylobactor and their results?

A

Gram stain (1st) - G-b, that resemble gull wings, curved , s-shaped (very distinctive morphology)
Oxidase +
Catalase +

55
Q

What test can be done to differentiate species of Campylobacter spp.?

A

Hippurate hydrolysis.
C. jejuni is positive
C. coli is negative

56
Q

What does EHEC stand for? How do you find EHEC?

A

Enterohemorrhagic E. coli (E. coli O157:H7)

Causes effacing lesion but in the colon GNB shiga toxin leading to systemic absorption & potential life-threatening conditions.

Screen with SMAC. Confirm with serology.

57
Q

What are the possible TSI reactions for Salmonella spp.? Urea test result?

A

K/AG/-
K/AG/+
K/A/weak+

Urea NEG

Note: Serology & full ID is MANDATORY after the enteric SCREEN (this is NOT
enough for reporting it as Salmonella (or anything else…)

58
Q

Finish this sentence: Shigella spp. is biochemically _______.

A

inert

59
Q

What is the TSI and Urea test reaction for Shigella? Motility?

A

TSI: K/A/-
Urea NEG
Non-motile

Use serology to differentiate species (A-B-C-D)

60
Q

What test can differentiate Shigella sonnei from the other Shigellas?

A

S. sonnei is ONPG+, whereas the others are not. S. sonnei is serology group D.

61
Q

What might cause you to suspect Yersinia on plates?

A

Yersinia has smaller colonial growth compared to other enteric pathogens although it grows well at room temperatures.

62
Q

What is useful to isolate Yersinia?

A

Media specific for isolation beneficial, like CIN agar.

63
Q

What is Yersinia’s Urea and TSI reactions?

A

Yersinia is
Urea: weakly +
TSI: A/A/- with orange-peachy butt.

Note: Micro 1 had Yersinia in the Urea neg algorithm. Statistically it can be neg some of the time but mostly weakly + (25% neg/ 75% as I recall M. said)

64
Q

What does the gram stain of vibrio spp. look like?

A

Vibro microscopically: small “curved” or “comma” shaped
gull-wings

65
Q

What is vibrio TSI and oxidase result?

A

TSI: K/A/-
Oxidase +

Fully ID with API 20E or APINE

66
Q

What is done after the enteric screen or “quick tests”

A

Suspect colony is worked up for full identification.

Report what is NOT isolated in culture and send a preliminary report as you rule out pathogens.

67
Q

What does EPEC stand for and what does the bug do?

A

EPEC –
Enteropathogenic E. coli.

EPEC adheres to enterocytes in small bowel producing effacing lesions (BFP is bundle-forming pili)- no toxin.

Certain serotypes cause diarrheal outbreaks and chronic diarrhea in infants (<= 2 years).

68
Q

What does EIEC stand for and what does the bug do?

A

Entero-invasive E. coli.
Invades the epithelial cells of the colon lyzing the phagosomes and moves thru cell via actin filaments. Bacteria move laterally cell to cell or exit and renter cells.

Causes dysentery, usually in young children living in unsanitary conditions.

69
Q

What does ETEC stand for and what does the bug do?

A

Enterotoxigenic E. coli

Attachment (pili) and secretion of stable and labile toxins (similar to cholera effecting electrolyte pump).

Causes traveler’s and childhood diarrhea characterized by profuse watery stools. Transmitted by contaminated food and water.

70
Q

What type of E.coli causes biofilm formation in small and large bowel epithelium?

A

EAEC - Enteraggregative E.coli

Mainly isolated from children with chronic diarrhea.

Also secretes cytotoxin and enterotoxin.

70
Q

How do you check for helicobacter in the stomach?

A

Perform gastric biopsies and do a urea test. If it is positive within 2 hrs then it is Helicobacter.

Helicobacter is a rapid urease producer.

71
Q

How long of time does helicobacter need to incubate on media?

A

5-7 days at 35-37C.

72
Q

How long does Campylobacter typically take to incubate?

A

2 days (can grow in 1 day but not normally).

Grows optimally at 42C (it can still grow at 36C but it likes 42C).

73
Q

Is C. diff apart of the normal GI flora?

A

Yes, it is a minor component of normal GI flora but some strains are toxigenic. Toxins can stimulate an inflammatory response. Produces Pseudo-membranous colitis.

74
Q

What toxins does C. diff produce?

A

Some strains produce both toxin A (enterotoxin) and B (cytotoxin); some only produce B.

Toxin has a cytopathic effect in tissue culture.

75
Q

How do labs typically look for pathogenic C. diff?

A

Typically, labs screen for presence of bacteria. If present then they test for toxin for diagnosis.

76
Q

What are the different testing methods for C. difficile?

A
  1. Immunological techniques for toxins A & B and/or antigens of C. diff.
  2. Molecular techniques, i.e. Illumigene (PCR).

Microbiology 2 (22 decks)

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