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GI > Microbiology > Flashcards

Microbiology Flashcards

1
Q

H. pylori Virulence Factors

A
  • slender, curved gram - rods
    • motile with polar flagella, microaerophilic
  • VacA - vaculoating cytotoxin
  • PAI encoding Type III secretion system
  • Cag - rearranges cytoskeleton
  • Urease
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2
Q

Diagnosis of H. pylori

A

endoscopy with biopsy & culture

  • urea breath test
  • serology useful to monitor recovery
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3
Q

Treatment of H. pylori

A

-omeprazole, metronidazole, clarithromycin

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4
Q

Campylobacter jejuni

A

-most common GI infection in developed nations
-only few hundred cells needed for infection
Reservoirs: sheep, cattle, chickens, wild birds, dogs
Source: undercooked poultry, unpasteurized milk, contaminated water

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5
Q

Micro: campylobacter jejuni

A

-thin, spiral shaped gram - rod
“gull-winged appearance”
microaerophilic
-1 week incubation

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6
Q

Symptoms of campylobacter jejuni

A

fever, appendicitis-like lower abdominal pain

  • watery diarrhea that progresses to dysentery with blood and pus
  • antecedent to Guillain-Barre
  • self-limited: 3-7 days
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7
Q

Diagnosis of campylobacter jejuni

A

-culturing on media containing abx to prevent growth of resident bowel flora

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8
Q

Treatment of campylobacter jejuni

A

Erythromycin treatment

  • fluoroquinolones (resistance is common)
  • resistant to beta-lactams
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9
Q

Vibrio Micro

A
  • curved, gram - rods
  • motile, polar flagellum, oxidase +
  • found in saltwater, disease in warm months
  • sig: v. cholerae, v. papahaemolyticus, v. vulnificus
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10
Q

Cholera

A

5-10 million cases per year

  • endemic in Asia, Africa, S. America, India subcont
  • poor sanitation
  • seven pandemics since 1817 (increased word travel)
  • 1992 O139 outbreak is 8th
  • spread by contaminated water and food
  • human carriers and environmental reservoirs
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11
Q

Cholera Subtypes

A

> 200 based on O-antigen
O1 and O139 are responsible for epidemic/pandemic
-O1 serogroup subdivided into El Tor, & Classical

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12
Q

Cholera Pathogenesis

A

incubation 2-3 days
high infectious dose >10^8 CFU
-abrupt onset of vomiting & high volume watery diarrhea (20L/day), due to cholera toxin production, death by dehydration
-Rice-water stools: speckled with mucus, loaded with buds (10^9 cfu/mL)

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13
Q

Cholera Virulence Factors

A
  • PAI-encoded pilus (TCP) attach to intestinal cells
  • Phage-encoded toxin: AB toxin comprises 5B and 1A subunit, ADP-ribosylation of GTP-binding protein, activation of adenyl cyclase
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14
Q

Cholera Dx & Treatment

A
  • stool culture on TCBS (thiosulfate or Citrate Bile salts Sucrose) or MacConkey agars
  • treat with oral hydration therapy (+ doxycycline or erythromycin)
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15
Q

V. parahaemolyticus

A
  • free-living sea water
  • seafood-associated food poisoning (most common foodborne illness in Japan)
  • Gulf/Pacific Coasts of US, warm months
  • Watery diarrhea often with abdominal cramps, nausea, vomiting, low-grade fever, 24 hrs after exposure
  • self-limiting, rare treatment needed
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16
Q

V. vulnificus

A
  • free-living in sea water
  • consumption of raw oysters or wound infection (cellulitis)
  • vomiting, diarrhea, abdominal cramps
  • immunocompromised or chronic liver pts (septicemia, bullae)
  • rare, but 20% fatality
  • doxycycline
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17
Q

Bacteroides fragilis

A

-gram - coccobacillus
-antiphagocytic capsule
-major in human GI tract
-opportunistic pathogen: intraabdominal infections, abscesses, PID, pulmonary infections
Treat: erythromycin, clindamycin, metronidazole, cephalosporins (3rd)
NOT: penicillin, aminoglycosides

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18
Q

Prevotella Melaninogenica

A
  • gram - coccobacillus
  • antiphagocytic capsule
  • GI tract, nasopharyngeal & vaginal flora
  • opportunistic pathogen, abscesses: pulmonary periodontal
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19
Q

Clostridium micro

A
  • gram + spore-forming rods
  • only anaerobic endospore-forming bacteria (resistant to heat/harsh environment)
  • exotoxin & secreted hydrolytic enzymes responsible for pathogenesis
  • colon and soil (spores)
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20
Q

C. perfrigens

A

-large “boxcar” gram + rods
-soil, human/animal intestine
-from spores in soil or food
-gas gangrene & cellulitis
-food poisoning
Treat: surgical debridement, large amounts of penicillin & protein-inhibiting antibiotic, hyperbaric oxygen chamber

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21
Q

C. perfrigens food poisoning

A

3ed most common in US
enterotoxin-producing strains
-rich meat dishes at low temperatures allow spores to germinate
8-24hrs post consumption: nausea, pain, diarrhea, no fever, vomiting rare
-full recovery in 24 hrs

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22
Q

C. tetani

A

-spore contamination of wounds
-tetanospasmia (toxin) is AB neurotoxin
-enters at neuromuscular junction and is transported by motor neurons to ganglia (incubation time depends on distance of wound from CNS)
-Cuts a V-snare (vesicle with neurotransmitter cannot fuse with neuron membrane)
prevents release of inhibitory neurotransmitters (glycine and GABA), blocking postsynaptic inhibition of spinal motor reflexes)

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23
Q

Tetanus

A
  • trismus (lock jaw)
  • risus sardonicus
  • generalized intermittent spasms
  • patient is aware and sensitive to stimuli
  • death occur from exhaustino and respiratory failure
  • Treat with HTIG to soak up excess toxin
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24
Q

C. botulinum

A

-contaminated food baby(from spores in carpet)
-infection of wounds with spres
-AB toxins: seven (A-G) antigenic types
may be most toxic bacterial exotoxin, 1g could kill 1 million people, cleave V- and/or T-snares, prevent release of ACh

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25
Q

E. coli and opportunistic Enterobacteriaceae

A 
Gram- facultative anaerobic rods
Ferment glucose with acid production
Oxidase negative
Reduce nitrates to nitrite (basis for the dipstick)
Motile except Shigella and Klebsiella
Antigenic structures used in serotyping
K (capsular) antigens: capsular polysaccharide (Klebsiella) H (flagellar) antigens O antigens: O-side chain of LPS
Many are part of normal GI flora
26
Q

E. coli

A 
Diarrhea and dysentery
Variety of opportunistic infections
UTIs (#1 cause)
Septicemia and meningitis in neonates
Important pathogen in U.S.
Big pathogen in the developing world

Resident E. coli flora do not cause diarrhea
Lack PAIs

27
Q

EHEC: Hemorrhagic Colitis

A 
Caused mostly by 0157:H7
Undercooked beef (bovine reservoir)
Fruits, unpasteurized juices, lettuce, spinach, sprouts
Human to human
Little fever, acute onset cramps, watery diarrhea
Diarrhea becomes bloody within 24 hrs
Non-inflammatory, no fecal leukocytes
Diarrhea lasts up to 8 days
Hospitalization often necessary
28
Q

EHEC Pathogenesis

A 
Low infectious dose (100 bacteria)
Shiga toxin (Stx)
AB toxin
Cleaves 28S RNA of ribosome
Lysogenic phage encoded
Locus of Enterocyte Effacement (LEE) 
PAI
Type III secretion system
Delivers E. coli receptor to host cell
Pedestal formation for attachment
Responsible for the diarrhea
29
Q

Hemolytic Uremic Syndrome (HUS)

A

2-7% patients (children/elderly)
anemia
acute renal failure

30
Q

EHEC Diagnosis and Treatment

A 
O157:H7 cannot use sorbitol
White on Sorbitol MacConkey agar
Other STEC and E. coli are red/pink
RADT for Stx in stool
Antibiotics are contraindicated
Believed to “stress” bacteria leading to increased phage expression of Stx
Fluid replacement
Blood transfusion
Temporary dialysis
31
Q

ETEC: Enterotoxigenic E. coli

A 
Traveler’s diarrhea
CFA I or II
Attachment
Hi volume watery diarrhea
Heat labile toxin (LT)
Mode as cholera toxin
Heat stabile toxin (ST)
Hormone-like (Not AB)
32
Q

EIEC: Enteroinvasive E. coli

A 
EIEC is very similar to Shigella
Lac-
Non-motile
Dysentery similar to shigellosis
Infectious dose much higher
Low incidence in US
Children under 5 yo in developing countries
33
Q

EPEC: Enteropathogenic E. coli

A

Profuse, watery infant diarrhea in developing countries
Clustered microcolonies in small intestine that degenerate with loss of brush border and microvilli
Pedestal formation via LEE, but no Stx, ST or LT
Attachment and effacing (A/E) lesion

34
Q

Other E. coli Infections

A

Hospital-acquired infections
In many hospital labs, E. coli is the most commonly isolated organism
Sepsis
Neonatal meningitis
Encapsulated strains (K1-antigen)
Uropathogenic E. coli (UPEC)
UPEC cause 90% of urinary tract infections (UTI)
More common in females than males
Symptoms include frequency, dysuria, pyuria, suprapubic pain, cloudy urine, cramping, afebrile or low-grade fever
Diagnosis: bacteria in urine
>10 per ml in females
>10 per ml in males
Virulence factors include a P fimbriae (also called PAP pili), and a capsule (K antigen)

35
Q

Salmonella

A

Frank pathogens that are a significant source of gastroenteritis from food poisoning
S. Typhi does not cause gastroenteritis
Disseminated disease known as typhoid fever
Gram-, Lac-, Glu+,
produce gas (not Typhi)
and H S

36
Q

Salmonella Nomenclature

A

Only one significant species, S. enterica
Over 1500 serotypes (O, H antigens)
Past genus and species names now converted to serotype names
S. typhimurium = S. enterica serotype Typhimurium = S. Typhimurium

37
Q

Salmonellosis

A 
S. Enteriditis, Typhimurium, and other non-Typhi 
Gastroenteritis that is grossly under reported
Sources
Meat
Dairy products
Poultry and EGGS
Pet turtles, reptiles
Humans (postinfection carriage)

Symptoms begin 20-72 hrs post consumption of improperly cooked food
Nausea, vomiting, followed by or concomitant with abdominal cramps and diarrhea lasting 3-4 days
Fever in half of patients
Diarrhea ranges from loose stools to dysentery
Antibiotics usually not necessary

38
Q

S. Enteritidis Pathogenesis

A

After consumption, bacteria swim thru intestinal mucosa layer to reach the small bowel
PAI encoded type III secretion system
Injects effectors in M cells that form membrane “ruffles” that endocytose bacteria
Bacteria cross to basal membrane, enter lamina propria
Inflammatory response ensues
S. Enteritidis kills macrophages
Enterotoxin role in diarrhea??

39
Q

Disseminated Salmonellosis

A 
Rare, but possible concern
Bacteremia, sepsis
Osteomyelitis
Endocarditis
Renal problems
At risk groups
AIDS, Hodgkin’s pts (bactermia)
Sickle cell children (osteomyelitis)
Elderly, very young
40
Q

Typhoid (Enteric) Fever

A

S. Typhi, exclusively human reservoir
Fecal-oral route, infected food handler
Developing nations
Invade M cells, survive in macrophages
Vi capsule antigen inhibits neutrophil uptake
Spread to mesenteric lymph nodes and RES in macrophages
Subsequent spread to blood
Sepsis can occur
Perforations of GI tract at necrotic Peyer’s patches can lead to severe hemorrhage

41
Q

Typhoid Fever

A

Insidious, rising fever with headache, abdominal pain
Slow pulse, mental confusion
Diarrhea late if at all
Death possible by ruptured spleen or intestine
Chronic infection of gall bladder possible
Culture from blood (or feces)
DOC: ceftriaxone
Oral vaccine for travelers to endemic areas

42
Q

Shigella

A 
S. dysenteriae
Epidemics in Central and South America
1000X Stx compared to other species
HUS
High fatality rate (20%)
S. sonnei
70% of US cases, mostly children
S. flexneri
2nd most common in US, most common worldwide
Gay men (STD)
43
Q

Shigella Transmission

A

Human reservoir, frank pathogen
Fecal-oral route, foodborne rare
Most common in children, institutions, gay men

44
Q

Shigella Micro Reactions

A

Gram-, non-motile rod
Lac-, Glu+, no gas, no H S
Leukocytes prominent in stool samples

45
Q

Shigellosis

A 
Acute inflammatory colitis and bloody diarrhea– dysentery like EIEC
S. sonnei often less bloody, more watery
Very low infectious dose: 10-100 cfu
Entry into M cells in gut
Escape from phagocytic vesicle
Extension to neighboring enterocytes
Rarely leaves GI tract
Cultured on standard enteric media
Antibiotics used, but resistant to several beta-lactams
46
Q

Yersinia enterocolitica

A

Gram- coccobacilli with bipolar staining
Primarily animal pathogens
Human outbreaks linked to consumption of milk, pork in US
Gastroenteritis
Relatively rare
Abdominal pains can mimic appendicitis – “pseudoappendicitis”
Usually self-limiting

47
Q

Opportunistic Enterobacteriaceae

A 
Klebsiella pneumoniae
Encapsulated – “currant jelly” pneumonia
Alcoholics (aspiration pneumonia)
Proteus and Morganella
UTIs
48
Q

Rotavirus Microbiology

A
  • single most important agent of severe diarrheal illness of infants and young children worldwide
  • Reo: respiratory, enteric, orphan
  • non-enveloped particles consisting of 2-3 concentric icosahedral capsids
  • segmented, double-stranded RNA genome (high antigenic diversity, 11G(VP7) & 12P(VP4) serotypes)
49
Q

What is the basis for the development of Rotavirus vaccine?

A

only 4 G-P combinations cause ~90% of disease in humans

50
Q

Replication of Rotavirus

A
  • taken in by endocytosis, delivered to late endosomes or lysosomes
  • proteolytic processing results in sequential loss of outer capsid proteins
  • after penetration, enzymes within core begin synthesizing mRNAs (extruded through vertices of capsid structure) asymmetric transcription
  • some capped mRNAs are assembled into “assortment complexes” capped + strand RNA serve as templates to make - strand
  • assembly in cytoplasm
  • released by lysis
51
Q

Noroviruses Microbiology

A
  • nonenveloped, non-segmented, + strand RNA
  • major cause of foodborne epidemic acute gastroenteritis in older children and adults (~50% of community based outbreaks, “winter vomiting disease”)
52
Q

Norovirus Replication

A
  • not known

- similar to picornavirus

53
Q

Transmission of Rotavirus and Norovirus

A

by fecal-oral route

-extremely stable in environment

54
Q

Symptoms of Rotavirus and Norovirus

A

nausea, vomiting, diarrhea, fever, dehydration

-more vomiting with norovirus

55
Q

Rotavirus Vaccine

A
  1. RotaTeq: pentavalent bovine-human reassortant viruses (G1-G4 and P8), live attenuated given at 2,4,6 months
  2. Rotarix: human derived monovalent (G1,P8), live, attenuated, 2 doses starting at 6 weeks of age
56
Q

Norovirus Vaccine

A

none

57
Q

Preventive measures for norovirus

A
  • careful hand-washing
  • effective disinfection of contaminated surfaces
  • proper food preparation
58
Q

Enteroviruses Microbiology

A
  • small, nonenveloped, + stranded RNA

- picorna = “pico” + RNA (small RNA virus) (polio, insensitivity to ether, coxsackie, orphan, rhinovirus)

59
Q

Enteroviruses

A
  1. Poliovirus: causes flaccid paralysis
  2. Coxsackieviruses: various illness (meningoencephalitis, diarrhea, muscle pain, inflammation of myocardium & pericardium)
  3. Echoviruses: mild gastroenteritis (enteric cytopathic human orphan)
60
Q

Transmission of enteroviruses?

A

oral-fecal route

61
Q

Reservoir for enteroviruses?

A

humans

62
Q

Hand, Foot, Mouth Disease

A
  • coxsackievirus A16
  • universal initial symptom is enanthema (ulcerative lesions on mucosa of mouth)
  • exanthema soon follows on hands and feet with vesicular lesions
  • fever, sore throat, headache, abdominal pain

GI (19 decks)

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