Carlos Shared "Microbiology" - 32 Picmonics

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Microbiology

Staphylococcus aureus
Gram ⊕, β-hemolytic, catalase ⊕, coagulase ⊕ cocci in clusters
Protein A (virulence factor) binds Fc-IgG, inhibiting complement activation and phagocytosis.
Commonly colonizes the nares, axilla, and groin.
Causes
Inflammatory disease—skin infections, organ abscesses, pneumonia (often after influenza virus infection), endocarditis, septic arthritis, osteomyelitis and cellulitis.
Toxin-mediated disease—toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), rapid-onset food poisoning (enterotoxins).
MRSA (methicillin-resistant S aureus) infection—important cause of serious nosocomial and community-acquired infections; resistant to methicillin and nafcillin because of altered penicillinbinding protein.
Staphylococcal toxic shock syndrome
Staphylococcal toxic shock syndrome (TSS) presents as fever, vomiting, rash, desquamation, shock, end-organ failure.
TSST-1 is a superantigen that binds to MHC II and T-cell receptor, resulting in polyclonal T-cell activation. Cause overwhelming release of IL-1, IL-2, IFN-γ, and TNF-α leading to shock.
TSS results in increased AST, increased ALT, increased bilirubin.
Associated with prolonged use of vaginal tampons or nasal packing.
Compare with Streptococcus pyogenes TSS (a toxic shock–like syndrome associated with painful skin infection).
other
S aureus food poisoning due to ingestion of preformed toxin leads to short incubation period (2–6 hr) followed by nonbloody diarrhea and emesis.
Enterotoxin is heat stable, meaning that it is not destroyed by cooking.
Forms fibrin clot around self causing abscess.
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Staphylococcus epidermidis and Staphylococcus saprophyticus
Staphylococcus epidermidis
Gram ⊕, catalase ⊕, coagulase ⊝, urease ⊕ cocci in clusters.
Novobiocin sensitive.
Does not ferment mannitol (vs S aureus).
Normal flora of skin; contaminates blood cultures
Infects prosthetic devices (> 3 months) (eg, hip implant, heart valve) and IV catheters by producing adherent biofilms.
Can cause peritonitis from infection, causing erythema surrounding the site
Staphylococcus saprophyticus
Gram ⊕, catalase ⊕, coagulase ⊝, urease ⊕ cocci in clusters.
Novobiocin resistant.
Normal flora of female genital tract and perineum.
Second most common cause of uncomplicated UTI in young women (most common is E coli).
Can cause staghorn calculi/struvite stones since it is urease positive
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Streptococcus pneumoniae and Viridans group streptococci
Streptococcus pneumoniae
Gram ⊕, lancet-shaped diplococci. Catalase negative.
Alpha hemolytic
Encapsulated (Polysaccharide capsule). Positive Quellung Reaction.
IgA protease
Optochin sensitive.
Most common cause of: Meningitis, Otitis media (in children), Bacterial pneumonia, and Sinusitis
Pneumococcus is associated with “rusty” sputum, sepsis in patients with sickle cell disease, and asplenic patients.
No virulence without capsule
Viridans group streptococci
Gram ⊕, α-hemolytic cocci.
They are normal flora of the oropharynx that cause dental caries (Streptococcus mutans and S mitis) and subacute bacterial endocarditis at damaged heart valves (S sanguinis).
Resistant to optochin, differentiating them from S pneumoniae, which is α-hemolytic but is optochin sensitive.
S sanguinis makes dextrans, which bind to fibrin-platelet aggregates on damaged heart valves.
Treatment
Macrolides
Ceftriaxone
23 valent vaccine only causes an IgM response in Adults, while the seven valent vaccine causes an IgG in children
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Streptococcus pyogenes (group A streptococci)
Gram ⊕ cocci in chains
can cause
Pyogenic—pharyngitis, cellulitis, impetigo (“honey-crusted” lesions), erysipelas
Toxigenic—scarlet fever, toxic shock–like syndrome, necrotizing fasciitis
Immunologic—rheumatic fever, glomerulonephritis (can present with facial edema)
caracteristics
Bacitracin sensitive, β-hemolytic, pyrrolidonyl arylamidase (PYR) ⊕.
Hyaluronic acid capsule inhibits phagocytosis.
Antibodies to M protein enhance host defenses against S pyogenes but can give rise to rheumatic fever.
ASO (Antistreptolysin O) titer or anti-DNase B antibodies indicate recent S pyogenes infection. Streptokinase is another virulence factor.
J♥NES (major criteria for acute rheumatic fever):
Joints—polyarthritis
♥—carditis
Nodules (subcutaneous)
Erythema marginatum
Sydenham chorea
other
Pharyngitis can result in rheumatic “phever” and glomerulonephritis.
Impetigo usually precedes glomerulonephritis.
Scarlet fever—blanching, sandpaper-like body rash, strawberry tongue, and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin ⊕, also known as SPE).
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Streptococcus agalactiae (group B streptococci)
Gram ⊕ cocci, bacitracin resistant, β-hemolytic. Catalase Negative.
Polysaccharide Capsule
Colonizes Vagina
Causes pneumonia, meningitis, and sepsis, mainly in babies.
Produces CAMP factor, which enlarges the area of hemolysis formed by S aureus.
Hippurate test ⊕
PYR ⊝
Screen pregnant women at 35–37 weeks of gestation with rectal + vaginal swabs
Patients with ⊕ culture receive intrapartum penicillin prophylaxis.
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Streptococcus bovis (Group D streptococci NonEnterococcus)
Gram ⊕ cocci, colonizes the gut.
Bile Resistant
S gallolyticus (S bovis biotype 1) causes
Bacteremia (bacteria in blood)
Subacute Endocarditis in Colon Cancer Patients
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Enterococci
Gram ⊕ cocci. Catalase negative.
Enterococci (E faecalis and E faecium) are normal colonic flora that are penicillin G resistant and cause UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures)
Catalase ⊝, PYR ⊕, variable hemolysis.
VRE (vancomycin-resistant enterococci) are an important cause of nosocomial infection.
Enterococci, hardier than nonenterococcal group D, can grow in 6.5% NaCl and bile (lab test).
Treatment
Linezolid
Tigecycline
Ampicillin
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Bacillus anthracis
Gram ⊕, spore-forming rod that produces anthrax toxin.
The only bacterium with a polypeptide capsule (contains d-glutamate).
Colonies show a halo of projections, sometimes referred to as “medusa head” appearance.
three AB Toxins (EXOTOXINS)
Edema Factor extoxin Mimics the adenylate cyclase enzyme (increases cAMP)
Lethal toxin
Has a protective antigen
Cutaneous anthrax
Painless papule surrounded by vesicles causing an ulcer with black eschar (IMAGE) (painless, necrotic) which uncommonly progresses to bacteremia and death.
Pulmonary anthrax
Inhalation of spores
Flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock.
Also known as woolsorter’s disease
gastrointestinal anthrax
Consuming Anthrax-infected Meat
Treatment
Fluoroquinolones
Doxycycline
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Bacillus Cereus Characteristics
Gram-Positive
Bacilli
Endospore Forming
B Hemolytic
Toxins and Enterotoxins
Reheated Rice
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1 min
Bacillus Cereus Disease
Signs and Symptoms
Emetic Form
Short Incubation (1-6 Hours)
Nausea and Vomiting
Diarrheal Form
Long Incubation (8-16 Hours)
Diarrhea and GI Pain
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Clostridium tetani
Gram ⊕, spore-forming, obligate anaerobic rod
Spores found in rusty nails and soil
Produces tetanospasmin, an AB exotoxin causing tetanus.
The Tetanus toxin (and botulinum toxin), are proteases that cleave SNARE proteins for neurotransmitters
Blocks release of inhibitory neurotransmitters, GABA and glycine, from Renshaw cells in spinal cord.
Causes spastic paralysis, trismus (lockjaw), risus sardonicus (raised eyebrows and open grin), opisthotonos (spasms of spinal extensors).
Prevent with tetanus vaccine (toxoid)
Treat with antitoxin +/− vaccine booster, diazepam (for muscle spasms), and wound debridement.
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Clostridium Botulinum
Gram ⊕, spore-forming, obligate anaerobic rod
Transmited by improper canning of food
Produces a heat-labile toxin that inhibits ACh release at the neuromuscular junction, causing botulism
In adults, disease is caused by ingestion of preformed toxin
In babies, ingestion of spores (eg, in honey) leads to disease (floppy baby syndrome)
Botulinum is from bad bottles of food, juice, and honey (causes a descending flaccid paralysis)
Treat with antitoxin.
Symptoms
Diplopia
Dysarthria
Dysphagia
Ptosis
Dyspnea
uses
Local botox injections used to treat focal dystonia, achalasia, and muscle spasms.
Also used for cosmetic reduction of facial wrinkles
AB EXOTOSIN
Botulinum exotoxin is protease that cleaves SNARE (soluble NSF attachment protein receptor), a set of proteins required for neurotransmitter release via vesicular fusion
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Clostridium perfringens
Gram ⊕, spore-forming, obligate anaerobic rod
Spores can be found in soil
Produces α toxin (an exotoxin) (lecithinase, a phospholipase) that can cause myonecrosis (gas gangrene IMAGE) and hemolysis.
“Double zone” of hemolysis on blood agar
Gas Gangrene - organism produces gas under tissue
Spores can survive in undercooked food; when ingested, bacteria release heat-labile enterotoxin causing food poisoning.
Associated with military combat wounds
Infection associated with motorcycle accidents
Slow onset watery diarrhea caused by spore ingestion
Treatment
IV Penicillin G
Hyperbaric O2 Chamber
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Clostridium difficile
Gram ⊕, spore-forming, obligate anaerobic rod
Produces 2 toxins
Toxin A, an enterotoxin, binds to brush border of gut and alters fluid secretion.
Toxin B, a cytotoxin, disrupts cytoskeleton via actin depolymerization.
Both toxins lead to diarrhea leading to pseudomembranous colitis (IMAGE)
Toxins cause cell apoptosis
Often 2° to antibiotic use, especially clindamycin or ampicillin; associated with PPI use.
Diagnosed by detecting one or both toxins in stool by antigen detection or PCR.
Commonly seen in hospitals. Doctors contaminate patients.
Watery Diarrhea
Toxic Megacolon can be developed
Treatment
Metronidazole or oral vancomycin.
For recurrent cases, consider repeating prior regimen, fidaxomicin, or fecal microbiota transplant.
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Corynebacterium diphtheriae
Gram ⊕ rod
Plated on Loeffler's medium
Transmitted via respiratory droplets.
Lysogeny
Causes diphtheria via exotoxin encoded by β-prophage.
Black colonies on cystine-tellurite agar.
AB EXOTOXIN
Potent diphteria exotoxin inhibits protein synthesis via ADP-ribosylation of Elongation Factor 2 (EF-2), inhibiting translocation
Symptoms
Pseudomembranous pharyngitis (grayish-white membrane IMAGE) with lymphadenopathy ("bull's neck")
Myocarditis
Arrhythmias
Heart block
Polyneuritis (nerve deficit starts in the posterior oropharynx)
diagnosis
Organism tends to lie parallel to one another or at acute angles resembling Chinese letters and can help with bacteria identification
Lab diagnosis based on gram ⊕ rods with metachromatic (blue and red) granules and ⊕ Elek test for toxin. V or Y formation.
Aniline Stains Deeply Methylene Blue
Toxoid vaccine prevents diphtheria.
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Listeria monocytogenes
Only Gram-Positive With Endotoxin-Like Structure
Gram ⊕, facultative intracellular rod
Acquired by ingestion of unpasteurized dairy products and cold deli meats, via transplacental transmission, or by vaginal transmission during birth.
Catalase Positive
Grows well at refrigeration temperatures (4°–10°C; “cold enrichment”).
Forms “rocket tails” (red in IMAGE) via actin polymerization that allow intracellular movement and cell -to- cell spread across cell membranes, thereby avoiding antibody.
Monocytes In CSF
Characteristic tumbling motility in broth.
Can cause
Amnionitis
Septicemia
Spontaneous abortion in pregnant women
Granulomatosis Infantiseptica
Neonatal meningitis
Meningitis in immunocompromised patients and elderly
Mild, selflimited gastroenteritis in healthy individuals
Treatment
Ampicillin
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Nocardia
Gram ⊕ and forms long, branching filaments resembling fungi
Catalase Positive
Beaded filament
Urease Positive
Aerobe
Acid fast (weak) IMAGE, stains with carbol fuchsin
Found in soil
Has a mycolic acid cell wall
Causes pulmonary infections in immunocompromised/AIDS patients (can mimic TB but with ⊝ PPD)
Pulmonary infection can cause lung cavitations, presenting as a chronic cough or hemoptysis (pneumonia-like symptoms)
Cutaneous infections after trauma in immunocompetent. Indurated lesions and inflammatory reaction
Can spread to CNS, causing brain abscess
Can also present as kidney abscess
Treat with sulfonamides (TMP-SMX)
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Actinomyces
Gram ⊕ and forms long, branching filaments resembling fungi
Obligate Anaerobe
Not acid fast IMAGE
Normal oral, reproductive, and GI flora
Causes oral/facial abscesses that drain through sinus tracts
Often associated with dental caries/ extraction
Forms yellow “sulfur granules”
Can also cause PID with IUDs
Treat with penicillin
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Mycobacterium tuberculosis
Stains Acid Fast (IMAGE)
Mycolic acid cell wall (high concentration)
Carbolfuchsin stain red
Grows on Lowenstein-Jensen Medium
Obligate Aerobe
Transmited by respiratory droplets
TB proliferates inside macrophages
Serpentine cord factor, Essential for virulance. Protected the bacteria from being destroyed by eliciting granuloma formation, increasing TNF-∝ and other inflammatory cytokines, activating other macrophages
Sulfatides - Allow TB to survive inside cells like macrophages by inhibiting phagolysosomal fusion.
Primary TB symptoms
Positive tuberculin skin test (PPD ⊕ if current infection, past exposure or had BCG vaccine)
Interferon-γ release assay (IGRA) has fewer false positives from BCG vaccination.
PPD ⊝ if no infection and in sarcoidosis or HIV infection (especially with low CD4+ cell count).
Most cases of primary TB resolve, heal by fibrosis, calcification and become lantent
Prolonged fever, most commonly on children in endemic areas.
paths of progression after primary infection
healed latent infection
Affects lower or middle lung
After it heals, lesion becomes fibrotic and eventually calcifies as do nearby draining lymph nodes. Together this forms the Ghon complex.
Ghon complex are visible calcifications of the lung parenchyma and hilar lymph nodes that can be seen on chest xray.
systemic infection (miliary TB) (bacteremia)
In some rare cases, TB can spread and affect other organs in the body
Can be lethal
Reactivation TB (Secondary TB)
Caseating granulomas (IMAGE) with central necrosis (upper left) and Langhans giant cells (arrow) are characteristic of 2° tuberculosis.
Reactivation only seen in 5 - 10% of people
Seen in Immunosupressed patients (HIV, old age, cancer) due to downregulation of TNF-∝ release, leading to an uncontained infection
If you want to start a patient with a TNF-∝ inhibitor, such as infliximab, you need to do screen them with a PPD test to make sure you are not putting them at risk for a reactivation of TB
Affected the upper lobes (apex)
Symptoms: Cough, Night Sweats and Hemoptysis
Many patients present cachexia due to the TNF-∝ produced in response to chord factor, which promotes wasting.
Can cause osteomyelitis
Pott's disease, when affecting the spinal column affecting multiple vertebrae, causing demineralization of the bone with soft tissue swelling, causing pain
CNS involvement in 10 - 15% of patients, manifesting as meningitis or tuberculoma (cavitary lesion in the brain)
Addison's when affects adrenal glands
Treatment
Rifampin
Isoniazid
Pyrazinamide
Ethambutol
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Other Mycobacteria (avium–intracellulare, scrofulaceum, marinum and kansasii)
All mycobacteria are acid-fast organisms (pink rods; arrows in IMAGE)
M avium–intracellulare
Causes disseminated, non-TB disease in AIDS
Often resistant to multiple drugs
Prophylaxis with azithromycin when CD4+ count < 50 cells/mm3
M scrofulaceum
Cervical lymphadenitis in children
M marinum
Hand infection in aquarium handlers
M kansasii
Resembles TB
Average age of onset 60 years
Treat with rifampin + ethambutol
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