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Microbiology I Step I Review. Devin Gillaspie. First the Basics…. Gram Positive Organisms Stain purple/blue Cell wall + cell membrane Contains techoic acid – induces TNF and IL-1 Gram Negative Organisms Stain red Outer membrane + Periplasmic space + cytoplasmic membrane
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Microbiology IStep I Review Devin Gillaspie
First the Basics… • Gram Positive Organisms • Stain purple/blue • Cell wall + cell membrane • Contains techoic acid – induces TNF and IL-1 • Gram Negative Organisms • Stain red • Outer membrane + Periplasmic space + cytoplasmic membrane • LPS in outer membrane
Who doesn’t Gram stain? • Treponema – too thin; use dark field microscopy or fluorescent Ab staining • Rickettsia, Legionellaand Chlamydia – intracellular. (Silver stain for Legionella) • Mycobacteria – high lipid content, use acid fast stain • Mycoplasma – no cell wall
Stains • Giemsa Stain – Borrelia, Plasmodium, trypanosomes, Chlamydia • PAS – Stains glycogen, mucopolysaccharides; to diagnose Whipple’s disease • Ziehl-Neelsen – Acid Fast organisms • India Ink – Cryptococcus neoformans (thick polysaccharide capsule) • Silver stain – Fungi and Legionella
Special Culture Media • H. influenza – Chocolate agar with factor V and X • N. gonorrhoea – Thayer-Martin media • B. pertussis – Bordet-Gengou • C. diphtheriae – Telluritepalte, Loffler’s media • M. pneumoniae – Eaton’s agar • Lactose fermenters – MacConkey’s agar (pink colonies); E. coli turns black-blue on EMB agar • Legionella– Charcoal yeast extract agar with cystein • Fungi – Sabouraud’s agar
Obligate Aerobes • Use oxygen dependent system to make ATP • Examples: • Nocardia • Pseudamonasaeruginosa • Mycobacterium tuberculosis (reactivation TB usually in apices of lungs which have highest PO2) • Bacillus
Obligate anaerobes • Lack catalase susceptible to superoxide dismutase • Foul smelling, difficult to culture, produce gas in tissue • Examples: • Clostridium • Bacteroides (GI tract normal flora) • Actinomyces
Intracellular Organisms • Obligate intracellular • Chalmydia, Rickettsia • Facultative intracellular • Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Fracncisella, Legionella
Encapsulated Bacteria • Capsules serve as anti-phagocytic virulence factor • Positive Quellung reaction – capsule swells when specific anticapsularantisera is added • Examples: • Klebsiellapneumoniae • Salmonella • Strep. pneumoniae • H. influenza type B • Neisseriameningitidis
Others • Urease positive bugs • Proteus, Klebsiella, H.pylori, Ureaplasma • Pigment producing bacteria • Actinomycesisralii– yellow “sulfur” granules • S. aureus– yellow pigment • Pseudamonasaeruginosa– blue-green pigment • Serratiamarcescens– red pigment
Bacterial Virulence Factors • Protein A – Binds Fc region of Ig, preventing opsonization and phagocytosis (S. aureus) • IgA protease – cleaves IgA, to colonize respiratory mucosa (S. penumoniae, H. flu type B, and Neisseria) • M protein – Prevents phagocytosis
Spores • Certain gram positive rods • Form at end of stationary phase – no metabolic activity in spore form • Highly resistant to destruction by heat and chemicals – autoclave required to kill spores
Exotoxins and you • Super antigens • S. aureus– TSST-1 causes toxic shock syndrome • S. pyogenes – Scarlet fever-erythrogenic toxin • A-B toxins • C. diphtheriae – inactivates EF2; causespseudomembrane in throat • Vibriocholerae – inactivates Gs protein, stimulating adenylylcyclase and increase pumping Cl into gut and decreased Na absorption causing rice water diarrhea • E. coli (ETEC) – Heat-labile toxin (stimulates adenylatecyclase); Heat-stable toxin (stimulates Guanylatecyclase) watery diarrhea • B. pertussis – increases cAMP by inhibiting Gαi whooping cough; inhibits chemokine receptor lymphocytosis
Other exotoxins • Clostridium perfringens – α toxin gas gangrene • C. tetani – blocks release of inhibitory neurotransmitters GABA and glycine lockjaw • C. botulinum – Blocks release of Ach, causes anticholninergic symptoms, CNS paralysis • Bacillus anthracis – Edema factor, and adenylatecyclase • Shigella – Shiga toxin cleaves host cell rRNA (inactivates 60S ribosome), and enhances cytokine release HUS • S. pyogenes – Streptolysin O, a hemolysin.
Bacterial Genetics • Transformation • Take up DNA from environment • Especially encapsulated bacteria • Conjugation • F+ plasmid contains genes required for conjugation (bacteria w/o plasmid are F-) • Plasmid is replicated and transferred through pilus to F- bacteria (no chromosomal DNA) • If F+ plasmid is incorporated into chromosomal DNA = Hfr • Replication of plasmid DNA may include some flanking genes
Bacterial Genetics • Transduction • Generalized – LyticBacteriophage infects bacteria cleavage of host DNA production of viral proteins some bacterial DNA may be packaged in viral capsid • Specialized – Lysogenic phage infects bacteria viral DNA incorporated into bacterial chromosome phage DNA excised with flanking genes • Transposition • Segment of DNA that “jumps” from one location to another • Plasmid to chromosome and vice versa
GRAM POSITIVES Clostridium Bacillus Corynebacterium Listeria Enterococcus Peptostrep S. viridans S. pneumo S. pyogenes(GAS) S. agalactiae(GBS) S. aureus S. epidermidis S. saprophyticus
Staphylococcus sp. – Staph aureus • Causes: • Inflammatory disease – skin infections, organ abscesses, pneumonia, etc. • Toxin-mediated disease – toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), rapid-onset food poisoning (enterotoxins) • MRSA – nosocomial and community acquired infections. Resistant to β-lactams due to altered penicillin binding protein • Vireulence factors
Staphylococcus sp. – Staph epidermidis • Infects prosthetic devices and IV catheters • Biofilm • Normal skin flora – contaminates blood cultures • Endocarditis in IVDA
Streptococcus sp. • Streptococcus pneumoniae– encapsulated, IgA protease • Most common causes of: • Meningitis • Otitis media (in kids) • Pneumonia • Sinusitis • Viridans group strep - α-hemolytic • Normal flora of oropharynx – dental carries • Subacute bacterial endocarditis
Streptococcus sp. • Streptococcus pyogenes(GAS) • Causes • Pyogenic – pharyngitis, cellulitis, impetigo • Toxigenic – scarlet fever, toxic shock syndrome • Immunologic – rheumatic fever, acute glomerulonephritis • ASO titer detects recent S. pyogenesinfection • Streptococcus agalactiae (GBS) • β hemolytic, bacitracin resistance • Causes – pneumonia, meningitis, and sepsis mainly in babies
Group D Strep • Enteroccocus • E. faecalisand E. faecium • Normal colonic flora • Penicillin G resistant • Cause UTIs • VRE - important cause of nosocomial infections • Streptococcus bovis • Colonizes gut • Causes – bacteremia and subacuteendocarditis • Colonizes 15% of colon cancer patients
Diphtheria • Corynebacteriumdiphtheriae • Gram positive Rod • Exotoxin inhibits EF-2 • Pseudomembranouspharyngitis with lymphadenopathy • Lab Dx – Gram - rods with metachromatic granules • Toxoid vaccine
Clostridium sp. • Gram positive rods, spore forming, obligate anaerobes • C. tetani • Tetanospamin (tetanus exotoxin) tetanus, spastic paralysis • C. botulinum • Heat-labile toxin inhibits ACh release at neuromuscular junction botulism • In adults ingestion of preformed toxin • In babies ingestion of spores (floppy baby syndrome)
Clostridium sp. • C. perfringens • α-toxin myonecrosis (gas gangrene) and hemolysis • C. difficile • Cytotoxin kills enterocytespseudomembranous colitis • Often 2° to antibiotic use especially clindamycin or ampicillin • Dx: check for C. diff toxin in stool • Tx: metronidazole
Anthrax • Bacillus anthracis • Spore forming, gram positive rod, produces anthrax toxin • Capsule contains D-glutamate • Cutaneous anthrax – contact, black eschar formation; can progress to bacteremia, death • Pulmonary anthrax – inhalation of spores; flu-like symptoms rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock.
Listeriamonocytogenes • Gram positive rod, facultative intracellular • “actin rockets” to move cell to cell • Tumbling motility • The only Gram + with endotoxin • Ingestion of unpasteurized milk/cheese and deli meats (avoid in pregnancy) or by vaginal transmission • Dz: amnionitis, septicemia, spontaneous abortion, granulomatosisinfantiseptica; neonatal meningitis; meningitis in immune compromised; mildgastroenteritis in healthy individuals
Actinomyces vs. Nocardia • Gram positive rods in long branching filaments resembling fungi • Actinomycesisraelii • Anaerobe, normal oral flora • Oral/facial abscesses • Drain through sinus tracts in skin – yellow sulfur granules • Nocardiaasteroides • Weakly acid fast aerobes • In soil • Pulmonary infection in immunocompromised patients
TB • Mycobacterium tuberculosis • Primary TB – (non-immune host) • Ghon complex = Ghon focus (calcified scar in lower lobe) + lobar and perihilar node involvement • Healing with fibrosis (+ PPD), OR • Progressive lung disease (in HIV, etc) rarely death, OR • Severe bacteremia (miliary TB) Death, OR • Pre-allergic lymphatic or hematogenous dissemination dormant TB in organs reactivation TB • Secondary TB – Reactivation TB • Fibrocaseouscavitary lesion in upper lobes • Extrapulmonary TB • CNS, Vertebral body (Potts disease), lymphadenitis, Renal, GI
Leprosy • Mycobacterium leprae • Acid-fast bacillus • Likes cool temps – infects skin and superficial nerves • US reservoir in armadillos • 2 forms of disease • Lepromatous – leonine facies = loss of eyebrows, nasal collapse, lumpy earlobes • Tuberculous – diffusely over skin, is communicable; lose sensation in fingers and toes (spontaneous amputations) • Treatment – long term oral dapsone; or rifampin + clofazimine + dapsone • 6 months to 2 years of antibiotics
Other Mycobacteria • M. kansasii • Pulmonary TB-like symptoms • M. avium-intracellulare • Often multidrug resistant • Disseminated disease in AIDS
Gram Negatives H. flu Pasturella Brucella Bordatellapertussis Neisseria Moraxella N. gonorrhoeae N. meningitidis Shigella Salmonella Proteus Pseudamonas Citrobacter Serratia Klebsiella E. Coli Enterobacter
Neisseria sp. • Gram negative cocci – diplococci • Gonococci • No capsule, maltose non-fermenter, no vaccine, STD • Causes gonorrhea, septic arthritis, neonatal conjunctivitis (give erythromycin eye drops at birth), PID, and Fitz-Hugh-Curtis Syndrome • Meningococci • Capsule, maltose fermenter, vaccine, spread by respiratory and oral secretions • Causes meningococcemia and meningitis, Waterhouse Friderichsen syndrome
Legionellapneumophila • Gram negative rod • Silver stain • Grows on charcoal yeast extract w/ cystein • Dx: antigens in urine • Transmission: aerosol from water source • Legionnaire’s disease = severe pneumonia and fever • Pontiac fever = mild flu-like syndrome • Treatment - erythromycin
Pseudomonas aeruginosa • Gram – rod, aerobic, blue-green pigment, grapelike odor • Associated with wound and burn infections • Also causes: • Pneumonia (CF) • Sepsis • External otitis (swimmer’s ear) • UTI • Drug use (endocarditis) • Diabetic osteomyelitis • Hot tub folliculitis • Malignant otitisexterna (in DM) • Tx: Aminoglycoside + extended spectrum penicillin