Medical Bacteriology Chapters 1820

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Medical Bacteriology Chapters 18-20

• Review characteristics of bacteria
• Mechanisms of pathogenesis chapter 18
• Virulence factors
• Lab Dx of bacterial diseases chapter 19
• Antibacterial agents chapter 20

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Unique Characteristics of Bacteria

• cell wall with peptidoglycan
• G bacteria have lipoteichoic acids (LTA)
• G- have outer membrane with LPS
• cell walls contain important antigens
• e.g. O Ags of G- bacteria
• many bact. have capsules (K), flagella (H), pili

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Pathogenic Mechanisms of Bacteria

• Inoculum size - MID (minimum infectious dose)
• Bacterial virulence factors (VF)
• Genes for VF grouped in pathogenicity islands
• Portals of entry / mode of transmission
• Adhesins
• Invasiveness
• Tissue destruction
• Toxins
• Immunopathology
• Evasive mechanisms

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Portals of Entry / XMT

• Ingestion foodborne, waterborne diseases
• Fecal-oral route
• Inhalation respiratory route
• Trauma
• Needles parenteral route
• Bug bite vector XMT
• Direct contact STD, etc.

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Adhesins

• pili / fimbriae
• gonorrhea, UTI
• LTA Staphylococcus, Streptococcus
• capsule / biofilm pneumonia, tooth decay
• Quorum sensing

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Invasiveness Tissue Destruction

• Spreading factors
• Invasive enzymes
• hyaluronidase, fibrinolysin, hemolysins,
  proteases, etc.
• Type III secretion system

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Bacterial Toxins

• Exotoxins many have A-B structure
• Cytotoxins kill cells
• Neurotoxins inhibit neurotransmitters
• Enterotoxins target gut
• Superantigens activate T cells cytokine storm
• Endotoxin G- lipopolysaccharide (LPS)
• Pyrogen, stimulates acute-phase responses
• Septic shock, disseminated intravascular
  coagulation (DIC), cytokine storm

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Effects of Bacterial Endotoxin
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Immunopathogenesis

• harmful inflammation
• granuloma formation
• Complement activation
• Acute phase response / cytokine storm
• Autoimmune disease

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Bacterial Evasive Mechanisms

• Inhibit or interfere with host defenses
• Capsules inhibit phagocytosis
• Survive / multiply in macrophages
• Intracellular growth
• Antigenic variation

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Interfering with Phagocytosis
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Dx of Bacterial Diseases

• Culture
• Identification
• biochemical tests (fermentation, indole, etc.)
• multitest kits
• automated ID systems
• serological tests (Ag agglutination, FA stain)
• antimicrobial susceptibility testing (AST)

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Specimens

• septicemia / bacteremia / endocarditis
• blood cultures need special processing
• meningitis lumbar puncture
• STAT gram stain
• other fluids peritoneal, synovial
  (arthrocentesis)
• URT pharyngitis, sinusitis, diphtheria,
  whooping cough
• pneumonia (LRT)
• Otitis media (tympanocentesis)
• keratitis, conjunctivitis, endophthalmitis,
  retinitis, blepharitis

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Specimens

• cellulitis, fasciitis, pyoderma
• superficial swab specimens ng
• wound need anaerobic culture for deep wound
• peritonitis, appendicitis
• cystitis, UTI quantitative culture
• STD urethritis (gonorrhea, NGU), vaginitis
• Chlamydia requires cell culture virus
• syphilis Dx by serology wont grow on media
• colitis, enteritis, enterocolitis,
  gastroenteritis, cholera

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Specimens

• See tables in Chapter 19 for specimen processing
  instructions and Dx methods by organism

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Antibacterial Agents

• bacteriostatic / bacteriocidal
• broad spectrum
• susceptible / resistant
• Mechanism of action
• resistance mechanisms
• inactivate drug beta-lactamase
• alter target mutated penicillin-binding protein
• alter drug transport MDR pumps
• PPNG, MRSA, MDR-TB, etc.