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Microbiology USMLE step 1 > Gram Positives Bacterias > Flashcards

Gram Positives Bacterias Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Bacilli

A

Aerobic: listeria, bacillus, corynebacterium

Anaerobic: clostridium

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2
Q

Cocci

A

Catalase +: staphylococcus

Catalase -: streptococcus

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3
Q

Staphylococcus

A

Coagulase

  • positive: S. Aureus : B hemolytic
  • negative : Novobiocin sensitivity :
    - positive: s. Epidermidis
    - negative: S. Saprophyticus
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4
Q

Streptococcus

A

HEMOLYSIS TYPE:
Alfa (partial hemolysis) : optochin sensitive: S. Pneumoniae
Resistance: S. mutans
Beta (complete) : bacitracin: sensitive: S. pyogenes (group A)
Resistance: S. agalactiae ( group B)
Gamma (no hemolysis): growth in 6.5% NaCl : group D ( enterococcus) : E.faecium, E. Faecalis

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5
Q

Branching filaments

A

Nocardia: aerobic, acid fast

Actinomycetes: anaerobic, not acid fast

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6
Q

Listeria monocytogenes

A

Bacilli gram +, intracellular rod
Acquired: deli foods , transplacenta, vaginal during delivery.
Disease: neonatal meningitis, meningitis in inmunocompromised patients, mild self limited gastroenteritis in healthy individuals.
Treatment: ampicillin + gentamicin
Dx: cold growth, blood or CSF culture.

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7
Q

Bacillus anthracis

A 
Spore forming rod, gram +, anthrax toxin 
Types: 
-Cutaneous anthrax 
-Pulmonary anthrax 
Transmission: contact
Diagnosis: serology+ PCR
Tx: Ciprofloxacine
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8
Q

Cutaneous anthrax

A

Papule-ulcer with black eschar
Painless
Surrounded by vesicles

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9
Q

Pulmonary anthrax

A

Transmission: inhalation of spores
Flu-like symptoms that rapidly progress to fever, hemorrhage, shock
“Woolsorter’ disease”

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10
Q

Bacillus cereus

A

Fried rice , Chinese

Emetic within 1-5 hrs
Diarrheawithin 8 hrs: watery, no blood, GI pain

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11
Q

Corynebacterium diphtheriae

A

Diphtheria:
- pseudomembranous pharyngitis, lymphadenopathy , bull neck,myocarditis, arrhytmias, recurrent laryngeal nerve palsy, polyneuritis.
-Dx: Elek test +
- exotoxin: B- prophage : inhibits protein synthesis by adding ADP- ribose to eEF-2
Tx: erythromicine + antitoxin
Complications: obstruction of the airway

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12
Q

Clostridium tetani

A

TETANUS

Blocks release of GABA.

Cause: spastic paralysis, trismus, risks sardonicus.
Tx: antitoxin, diazepam and wound debridement.
Prevent: vaccination

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13
Q

Clostridium botulinum

A

Botulismo
Inhibits ACh release at the neuromuscular junction.
Causing descending flaccid paralysis.
Tx: antitoxin
Note: local Botox is used to treat dystonias, Achalasia and muscles spams. Facial wrinkles.

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14
Q

Clostridium perfringens

A

Produce Alfa toxin (lecithinase)
Myonecrosis and hemolysis due to NAGLER REACTION
Transmitted by food poisoning.

High mortality

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15
Q

Clostridium difficile

A

Pseudomembranous colitis

Often due to antibiotic use (clindamycin, ampicillin)
Cause diarrhea
Tx: metronidazole

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16
Q

Most common cause of neonatal sepsis

A

Streptococcus agalactiae (group B)

Hyppurate test +
PYR -
Bacitracin resistant

Colonize the vagina, transmitter by vaginal delivery

Tx: ampicillin with aminoglycoside

17
Q

Complications of strep throat

A

Acute rheumatic fever

Acute glomerulonephritis

Streptococcus group A: S. Pyogenes: gram +, catalase -, bacitracin sensitive, B-hemolytic, PYR (+)

18
Q

Can grow in 6.5% NaCl and bile

A

Enterococci

Gram positive
Case UTI, Biliary tract infections, subacute endocarditis
PYR +
Variable hemolysis

19
Q

Mycobacterium tuberculosis

A

Primary and secondary tuberculosis

High risk patients: poverty, HIV, IV drug user
Symptoms: fever, night sweats, weight loss, chronic cough, hemoptysis.
Obligate aerobe, ACID FAST ROD, facultative intracellular, produce niacin and are catalase negative on 68C.
AURAMINE RHODAMINE STAINING
GHON COMPLEX
Transmission: respiratory droplets
Complications: miliary TB
DX: microscopy of sputum: AURAMINE RHODAMINE stain
PPD skin test
Quantiferon-TB gold standard
Slow growing (2-3 weeks) on lowestein-Jensen medium

20
Q

Hansen disease

A

Leprosy by Mycobacterium leprosae

Acid fast rod, obligate aerobe, facultative intracellular
Immigrant patient with sensory loss in extremities
Reservoir: armadillos in Texas and lousiana
Transmission: nasal discharge
Affect skin, mucous membranes, peripheral nerves
Forms of leprosy: lepromatous and tuberculoid and borderline
Dx: punch biopsy or nasal scrapings.
Lepromine test
No cultures
Treatment: dapsone and rifampin. Dapsone profilactic for the members of family

21
Q

Acid fast organisms

A

Mycobacteria

That means pink rods

22
Q

Streptococcus of group A.

Streptococcus pyogenes

A

PYOGENIC: pharyngitis, cellulitis, impetigo, erysipelas.
TOXIGENIC: scarlet fever, toxic shock like syndrome, necrotizing fasciitis
INMUNO: rheumatic fever, glomerulonephritis.

GRAM +, BACITRACIN SENSITIVE, B-HEMOLYTIC, PYR (+)

Diagnosis: ASO levels /ELISA
TX: b-Lactamicos, macrolides

23
Q

Most common causal agent for neonatal sepsis

A

Streptococcus agalactiae
GRAM (+), Bacitracin resistant, PYR (-), HIPPURATE TEST

Cause : PNEUMONIA, MENINGITIS AND SEPSIS IN BABIES DUE TO IS A NORMAL FLORA OF THE VAGINA.

TX: ampicillin + aminoglycoside

24
Q

Staphylococcal toxic shock syndrome

A

Fever
Vomiting
Desquamation due to a scalded skin syndrome
End organ failure: hepatic failure high ast, alt, Bil,

Associated with prolonged use of vaginal tampons or nasal packing.

25
Q

Rheumatic fever

A

Nonsuppurative sequela that occurs two to four weeks following group A pharyngitis.

Consist: migrate polyarthritis, carditis (pancarditis), chorea, erythema marginatum, subcutaneous nodules.

Jones criteria
Joint pain during 4 weeks

26
Q

NAGLER reaction Or lecithinase test

A

Used it for diagnosis of microorganism which produce lecithinase, like clostridium perfringens.

27
Q

Clostridium perfringens

A

High mortality

  • MYONECROSIS (gas grangrene) due to Alfa toxin (lecithinase) . Dx: NAGLER reaction.
  • Food poisoning due to spores which survive in undercooked food: watery diarrhea self-limiting
28
Q

Clostridium difficile

A 
Pseudomembranous colitis
Toxin A and B 
Secondary to antibiotic use (ampicillin and clindamycin) 
Dx: PCR, Toxin in stools 
Tx: vancomycin or metronidazole
29
Q

Listeria monocytogenes

A
  • Gram + rod, aerobic, intracellular , COLD GROWTH, rocket tails
  • Acquire: principal: deli foods, unpasteurized dairy products and cold deli meats . Secondary: transplacental or during birth
  • cause: neonatal meningitis
  • Dx: cold growth in culture agar of blood or CSF
  • tx: ampicillin + gentamicin
30
Q

Corynebacterium diphtheriae

A
  • Gram+ rod, aerobic.
  • Pathogenesis of Diphtheria via exotoxin encoded by beta-prophage, this exotoxin inhibits protein synthesis via ADP- ribosylation of EF-2
  • Symptoms: pseudomembranous pharyngitis , lymphadenopathy, myocarditis and arrhythmias, causing bull neck and respiratory obstruction.
  • Dx: + Elek test for toxin, culture in cystine- tellurite agar ( black colonies)
  • Tx: Erythromicine plus antitoxin
  • prevention: toxoid vaccine
31
Q

Nocardia

A

Gram +, branching filaments , resembling fungi.
Aerobic
Acid fast
Found in soil
Cause NOCARDOSIS pulmonary infections in inmunocompromised . Cutaneous infections after trauma in inmunocompetent (cellulitis with mycetomas)
Tx: TMX-SMX
Complication: may spread to brain: multi focal abscesses.

32
Q

Actinomyces

A

Gram +, branching filaments, anaerobic
Not acid fast
Found in normal oral, reproductive and GI flora.
Causes oral/ facial abscesses , forms yellow sulfur granules and drainage through the sinus tract.
Tx: penicillin

Microbiology USMLE step 1 (8 decks)

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