Carlos Shared "Microbiology" - 32 Picmonics
With Picmonic, facts become pictures. We've taken what the science shows - image mnemonics work - but we've boosted the effectiveness by building and associating memorable characters, interesting audio stories, and built-in quizzing. Whether you're studying for your classes or getting ready for a big exam, we're here to help.
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.
- Most common cause of purulent pericarditis in dialysis patients
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
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
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).
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.
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
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
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
Bacillus Cereus Characteristics
- Gram-Positive
- Bacilli
- Endospore Forming
- B Hemolytic
- Toxins and Enterotoxins
- Reheated Rice
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
2 mins
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.
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
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
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.
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.
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
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)
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
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
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
