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Microbiology USMLE step 1 > Gram Negative Bacterias > Flashcards

Gram Negative Bacterias Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Diplococci

A

Aerobics

  • Maltose utilization: Neisseria meningitidis
  • No maltose utilization : Neisseria gonorrhoeae and Moraxella
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2
Q

Coccobacilli

A
  • Haemophilus influenzae
  • Bordetella pertussis
  • Francisella Tularensis
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3
Q

Bacilli

A

*Lactose fermentation: Fast: Klebsiella and E. Coli and Enterobacter.
Slow: Citrobacter, Serratia

*No lactose fermentation: oxidase neg: Salmonella, Proteus, Shigella, Yersinia.
Oxidase pos: Pseudomonas

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4
Q

Comma-shaped rods

A

They are oxidase positive

  • Grows in 42C: Campylobacter jejuni
  • Grows in alkaline media: Vibrio cholerae
  • Produces urease: Helicobacter pylori
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5
Q

Neisseria meningitidis

A

KIDNEY BEAN-SHAPED Diplococci gram negative

Large capsule, ferments maltose
Grows on chocolate agar in 5% CO2 atmosphere.
*Reservoir: nasopharynx
* transmission😷: respiratory droplets
* Cause: -meningococcemia: abrupt onset with fever, chills, malaise, prostration, and petechial rash and gangrene of toes. Stiff neck and vomiting. - meningitis on babies.
*Dx: gram stain of the CSF, PCR, Latex agglutination
*Tx: neonats/ infants: ampicillin and cefotaxime.
Adults: ceftriaxone with or without vancomycin

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6
Q

Oxidase test

A

The oxidase test is used to identify bacteria that produce cytochrome c oxidase, an enzyme of the bacterial electron transport chain.

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7
Q

Neisseria gonorrhoeae

A

Diplococci gram negative, metabolized glucose and produce IgA proteases.

  • No capsule
  • No maltose fermentation
  • Transmission: sexually or perinatal
  • Cause: GONORRHEA, neonatal conjunctivitis, pelvic inflammatory disease (PID), urethritis in males, fitz-Hugh-Curtis syndrome
  • Prevention: condoms, erythromycin eye ointments in new borns.
  • Dx: genetic, culture on Thayer-Martin medium
  • Tx: ceftriaxone + (azythromycin, for possible chlamydial coinfection)
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8
Q

Gonorrhea

A

Uptodate

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9
Q

Fitz-Hugh-Curtis syndrome

A

Uptodate

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10
Q

Moraxella catarrhalis

A

Third common agent causal for otitis media/ sinusitis on children.

Tx: augmentin
Bactrim

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11
Q

Haemophilus influenzae

A

Cocobacillary gram negative, unencapsulated.

  • Transmission: aerosol
  • most common agent causal of epligottitis, otitis media, conjunctivitis, bronchitis/pneumonia and meningitis. (EMOP)
  • produces IgA protease.
  • Tx: augmentin for mucosal infections, ceftriaxone for meningitis, rifampin for close contacts like prophylaxis.
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12
Q

Epiglottitis

A

Causal agent: H. Influenzae
Symptoms:
Signs: cherry red on endoscopy, thumbprint signs in the x Ray
Uptodate

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13
Q

Bordetella pertussis

A

Whooping cough

Uptodate

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14
Q

Legionella pneumophila

A
  • weakly gram -
  • pleomorphic rods, requiring cysteine and iron
  • water organisms, transmission by environmental water source habitat.
  • treatment: macrolides or quinolone
  • legionnaire’s disease
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15
Q

Legionnaire’s disease

A

SEVERE ATYPICAL PNEUMONIA often unilateral and lobar

  • transmission aerosols from contaminated air conditioning or water.
  • predisposing factors: smokers, chronic lungs disease, alcoholism.
  • symptoms: pneumonia, mental condition and diarrhea.
  • Dx: direct fluorescent antibody (DFA)
  • tx: quinolone, azythromycin, erythromycine
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16
Q

Tularemia

Francisella tularensis

A

Endemic in USA. Arkansas and Missouri
Zoonosis: reservoir wild animals like rabbits, deer and rodents
*transmission :
-Tick bite: ulceroglandular Disease: fever, ulcer at bite site and regional lymph node enlargement and necrosis.
-aerosols: pneumonia
-Ingestion: undercooked , infected meat or contaminated water.
*Dx: culture
*Tx: streptomycin

17
Q

Whooping cough

A 
Bordetella pertussis 
Coco bacilli gram negative encapsulated
Virulence due to pertussis toxin. Inhibiting negative regulator of Gi ADP-ri 
*Disease: whooping cough
*transmission: respiratory droplets
*Prevention: vaccine DTAP 
Most common in children, but could appears in adults. 12-20% afebril adults with cough>2weeks have pertussis. 
*tx: azythromycin
18
Q

Pseudomona aeruginosa

A

Gram - bacilli, non lactose fermentation, oxidase positive.

Causes: 
Pneumonia
Sepsis
Ecthyma gangrenosum
UTIs
Diabetes, drug use
Osteomyelitis
Mucous polysaccharide capsule
Otitis externa (swimmer's ear)
Nosocomial infections
A exotoxin 
Skin infection (hot tub folliculitis)
19
Q

Campylobacter jejuni

A

Comma or S shaped gram negative rod with polar flagella ,
Oxidase +
Grows at 42C
Most common agent causal of bloody diarrhea .
Fecal oral transmission or undercooked contaminated poultry or meat
*symptoms: ten or more stools/day, abdominal pain, malaise, nausea, vomiting and fever
*complications : Guillain-Barré syndrome or reactive arthritis
Dx: culture in skirrow agar at 42C
*tx: erythromycine, fluoroquinolonas, penicillin resistant

20
Q

Bacteroides fragilis

A

Patient with abdominal trauma, emergency abdominal surgery which is complicate with septicemia, peritonitis, abscess

Gram negative bacilli anaerobic

21
Q

Vibrio cholerae

A

Gram negative curved rod with polar flagella
Oxidase positive
Growth on alkaline media
Human colon reservoir
Transmission: fecal oral
Pathogenesis: cholera enterotoxin, activate ADP-ribosylates Gs, increased cAMP, efflux of Cl and H2O.
CHOLERA: Rice water stools, fluid loss 20lts/day
Complication: hypovolemia shock
Dx: clinical, culture on TCBS, oxidase test positive
Tx: fluid and electrolyte replacement , doxycycline or Ciprofloxacin

22
Q

Klebsiella

A

Bacilli gram negative , oxidase negative, major capsule (some Killers have pretty nice capsule)
Klebsiella pneumoniae: PNEUMONIA, UTI, SEPTICEMIA.
Cause lobar pneumonia in alcoholics and diabetics when aspirated (transmission endogenous)
Dx: Mckonkey culture of sputum (jelly, thick and bloody) , lactose ferment
Tx: Fluoroquinolona

23
Q

Proteus mirabilis

A

Gram negative rod, flagellar (high motility), non lactose fermenting, urease positive.
Patient with UTI and Lowe back pain or septicemia.
Swarming motility
Reservoir: human colon and environment
Transmission: endogenous
Pathogenesis: urease raise urine pH to cause kidney stones.
Tx: Fluoroquinolona, TMX-SMX or cefepime

24
Q

Yersinia enterocolitica

A

Gram negative rod, motile at 25C, no motile at 37C, cold growth
Reservoir zoonotic
Transmission : unpasteurized milk, pork.
Disease: ENTEROCOLITIS: -very young febrile bloody diarrhea and pus. -older kids/young adults: PSEUDOAPENDICITIS , - Adults: enterocolitis with post incite sequelae like reactive arthritis
Dx: stool culture, cold enrichment at 25C.
Tx: supportive care and in inmunocompromised Fluoroquinolona or third generation cephalosporins.

25
Q

Family enterobacteriaceae

A 
Gram negative rods
Facultative anaerobics
Ferment glucose
Oxidase negative
Catalase positive

Family Pathogenesis : endotoxins LPS and antigens ( O,H, K, Vi)
Dx: blood agar B-hemolytic
MacConkey agar: lactose fermentation: + colored colonies
Escherichia, Klebsiella, Citrobacter
- colorless colonies
shigella, Yersinia, salmonella, proteus

26
Q

Escherichia Coli

A

Gram negative rod, ferments lactose, enterobacteriaceae
Oxidase negative
*Reservoir: Human colon
*Transmission: fecal oral or endogenous
*Diseases: UTI (most common cause)(fimbriae)
Neonatal septicemia/ meningitis (second cause) (K-cap)
Pneumonia (k-capsule)
Septicemia (LPS endotoxin)
Gastroenteritis : ETEC, EPEC, EIEC, EHEC, EAEC, DAEC

27
Q

E. Coli UTI

A
  • transmission: endogenous and ascend, most common agent causal in women due to anatomy
  • pathogenesis: Motility , adherence to uroepithelium with the pili and fimbrias
  • Dx: uroanalisis and urine culture > 10(5) CFU/ml
  • Tx: Ciprofloxacin (Fluoroquinolona) or sulfonamides. Augmentin some times.
28
Q

E. Coli gastroenteritis

PITCH

A

-ETEC ( enterotoxigenic e. Coli) traveler’s diarrhea
Watery diarrhea due to heat-Labile and heat-stable enteroToxins. No inflammation or invasion. Tx: tmp/smx
-EIEC ( enteroinvasive e. Coli) microbe invades intestinal mucosa and causes necrosis and inflammation. Dysentery diarrhea (shigella-like )
- EPEC (enteropathogenic) watery diarrhea usually in pediatrics.(second common cause in pediatrics diarrhea) Tx: beta lactams
- EHEC (enterohemorragic) O157:H7 most common serotype in US. Bloody diarrhea (dysentery) . Does not ferment sorbitol.
Transmitted via undercooked meat, raw leafy vegetables. Tx: NO ATB.
Complications: Hemorrhagic colitis and HUS ( hemolytic uremic syndrome) most common in children<5y

29
Q

Shigella

A

*Patient with acute bloody diarrhea and fever.
*Gram (-) bacilli, non-motile, non-lactose fermenters, do not produce H2S
*Two types: Shigella sonnei (most common in US)
Shigella dysenteriae (most severe disease)
* Reservoir: human colon only
* Transmission : fecal oral (day care)
* Pathogenesis: - Endotoxin (fever) - Shigella invade M cells - Shiga toxin( produce by S. Dysenteriae type 1, neurotoxic, cytotoxic, enterotoxic)
* Disease: Enterocolitis/shigellosis
Fever, lower abdominal cramps, tenesmu.s, diarrhea first watery then bloody; invasive but rarely causes septicemia;shallow ulcers
* Dx: culture win McConkey agar (colorless colonies)
* Tx: fluids replacement, severe cases antibiotics

30
Q

Yersinia pestis

A 
Gram negative rods with bipolar staining
Facultative intracellular parasite 
Coagulase positive 
Zoonosis: rodents
Potential biofarware agent 
Human to human transmissions respiratory droplets.
-Bubonic plague disease, BLACK DEATH : rapidly increasing fever, regional buboes, conjuctivitis.
- Tx: aminoglycosides
31
Q

Yersinia enterocolitica

A

Zoonotic. Gram negative bacilli, non lactose fermenters, non H2S producers.
Patient with inflammatory diarrhea or PSEUDOAPENDICITIS
Cold climates
Unpasteurized milk, pork
Disease: ENTEROCOLITIS
Transmission: from pet feces (puppies), contaminated milk or pork.
DX: stool culture in 25C, cold enrichment
TX: usually supportive care

32
Q

Helicobacter pylori

Gram negative, helical bacilli, oxidase positive, urease positive, catalase positive

A

UREASE POSITIVE
Reservoir: humans
Transmission: fecal-oral, Oral-oral
Pathogenesis: motile, urease positive, mucinase, invasive, inflammation.
Disease: chronic gastritis and duodenal ulcers: associated with stomach cancer.
Dx: biopsy with culture , breath test, serology
Tx: 1) omeprazole+amoxicillin+clarithromycin (triple therapy)
2) treat for 10-14 days
3) quadruple therapy: bismuth, proton pump inhibitor (ppi), tetracycline, metronidazole.

33
Q

Peptic ulcer disease

A

Up to date

34
Q

Salmonella

A
  • Gram negative rods, non lactose fermenters, oxidase negative and can invade the GI tract via M cells of Peyer patches.
  • Two types: Salmonella typhi, Salmonella spp.
35
Q

Salmonella typhi

A

Reservoirs: humans only
H2S production
Flagellar
GI manifestations: constipation followed by diarrhea
Cause: typhoid fever: rose spots on abdomen, constipation, abdominal pain and fever.
Tx: ceftriaxone or Fluoroquinolone

36
Q

Spirochetes

A

Spiral shaped bacteria with axial filaments.

  • Borrelia: wright or giemsa stain
  • Leptospira
  • Treponema is visualized by dark field microscopy or direct fluorescent antibody microscopy.

Microbiology USMLE step 1 (8 decks)

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