NOTES NOTES AEROBIC RODS MICROBE OVERVIEW ▪ Gram-positive, rod-shaped, aerobes/ facultative anaerobes BACILLUS ANTHRACIS (ANTHRAX) osms.it/bacillus-anthracis PATHOLOGY & CAUSES ▪ Etiologic agent of anthrax; nonmotile, nonhemolytic; potential biological weapon ▪ Endospore-forming (centrally located) ▫ Highly adaptable to extreme environmental conditions ▪ Surrounded by protein capsule (composed of poly-D-gamma-glutamic acid) ▫ Prevents phagocytosis 310 OSMOSIS.ORG ▪ Transmission (4 Is) ▫ Ingestion ▫ Inhalation ▫ skin Invasion ▫ direct Injection ▪ Anthrax toxin composed of three proteins ▫ Protective antigen (PA): essential for binding, entry to cell ▫ Lethal factor (LF): alteration of signaling pathways → cell death; ↑
Chapter 55 Aerobic Rods proinﬂammatory cytokines production → inﬂammation ▫ Edema factor (EF): ↑ cyclic adenosine monophosphate (cAMP) → disordered water, electrolyte balance → edema RISK FACTORS ▪ Occupational ▫ People who work with animals/ animal products (e.g. veterinarians, livestock producers, butchers); possible bioterrorism (e.g. military personnel); laboratory professionals ▪ Injecting drug users (e.g. heroin contaminated with anthrax spores) COMPLICATIONS ▪ Hemorrhagic meningitis, mediastinitis; pleural effusion; pneumonia; shock SIGNS & SYMPTOMS ▪ Respiratory infection ▫ Prodromal phase: ﬂu-like symptoms (e.g. fever, malaise, myalgia), hemoptysis, dyspnea, nausea, chest pain ▫ Fulminant phase: severe dyspnea, hypoxemia, cyanosis, shock, coma ▪ Gastrointestinal (GI) infection ▫ Severe abdominal pain; nausea; vomiting; ascites; ulcerations → GI hemorrhage ▪ Cutaneous infection ▫ Painless, pruritic papule → enlarges, forms central black-colored necrotic ulceration → black eschar ▫ Surrounding edema ▫ Regional lymphadenopathy, lymphadenitis Figure 55.1 A lesion on the neck caused by Bacillus anthracis. DIAGNOSIS LAB RESULTS ▪ Identify microbe ▫ Gram stain, culture, direct ﬂuorescent antibody (DFA), polymerase chain reaction (PCR) OTHER DIAGNOSTICS ▪ History, physical examination TREATMENT MEDICATIONS ▪ Antibiotics OTHER INTERVENTIONS ▪ Vaccine (people at high risk of exposure, post-exposure prophylaxis) OSMOSIS.ORG 311
BACILLUS CEREUS (FOOD POISONING) osms.it/bacillus-cereus PATHOLOGY & CAUSES ▪ Common foodborne pathogen; also associated with contaminated medical equipment (e.g. ventilators, dialysis machines), opportunistic infections ▪ Endospore-forming (centrally located) ▫ Highly adaptable to extreme environmental conditions ▪ Motile, catalase positive, beta-hemolytic ▪ Can be transient component of GI microﬂora Pathogenesis of food poisoning ▪ Production of enterotoxins ▫ Diarrheal toxin (thermolabile) → ↑ cAMP → disordered function of ion pumps → ↑ efﬂux of ions, water from infected enterocytes → diarrhea ▫ Emetic toxin, cereulide (thermostable) → ↑ afferent vagus nerve stimulation → nausea, vomiting ▪ Two types of food poisoning ▫ Diarrheal syndrome (meat, vegetables, sauces) → toxicoinfection → ingestion of bacteria, production of toxins in digestive tract ▫ Emetic syndrome (rice) → alimentary intoxication → direct ingestion of toxin RISK FACTORS ▪ Consumption of improperly cooked food 312 OSMOSIS.ORG SIGNS & SYMPTOMS ▪ Abdominal cramps, diarrhea, nausea, vomiting DIAGNOSIS LAB RESULTS ▪ ▪ ▪ ▪ Stool/contaminated food sample Gram stain Culture (blood agar) PCR TREATMENT OTHER INTERVENTIONS ▪ Intravenous (IV) ﬂuid, electrolyte replacement
Chapter 55 Aerobic Rods CORYNEBACTERIUM DIPHTHERIAE (DIPHTHERIA) osms.it/corynebacterium-diphtheriae PATHOLOGY & CAUSES ▪ Infectious agent of diphtheria ▪ Rods with widening at polar regions forming club-like shape ▪ Characteristic “Chinese-letter” arrangement ▪ Nonmotile, non-spore-forming ▪ Stain ▫ Albert’s/Ponder’s; metachromatic granules (e.g. Babes–Ernst, volutin) ▪ Culture ▫ Löfﬂer's medium ▪ Differentiation ▫ Hoyle’s tellurite agar ▪ Types of infection ▫ Respiratory (pharyngeal), cutaneous RISK FACTORS ▪ Absent/incomplete immunization ▪ Immunocompromised individuals ▪ Citizens, migrants, returning travellers from endemic areas (e.g. African, Asian, South American countries) COMPLICATIONS ▪ Myocarditis, nerve damage (e.g. demyelinating polyneuropathy, paralysis), renal failure, suffocation (due to pseudomembrane aspiration) Pathophysiology ▪ Diphtheria toxin → composed of two subunits ▫ A: active, catalytic ▫ B: binding; composed of R (receptor), T (translocation) domains ▪ Bacteria binds to host cell using R domain → endocytosis → acidiﬁcation inside endosome → T domain transfers to endosomal membrane → translocation of A subunit to cytosol ▪ Subunit A inactivates elongation factor EF2 → inhibition of protein synthesis → cell death ▪ Toxin expression regulated by level of iron ▫ ↑ Fe → ↓ production of toxin ▫ ↓ Fe → ↑ production of toxin Figure 55.2 A pharyngeal pseudomembrane in a child with diphtheria. OSMOSIS.ORG 313
SIGNS & SYMPTOMS ▪ Respiratory infection ▫ Sore throat; malaise; low-grade fever; dysphagia; thick, grey, isolated necrotic tissue → pseudomembrane; massive swelling of tonsils, cervical lymph nodes → “bull neck”; stridor ▪ Cutaneous infection ▫ Lesions, pain, rash, tenderness, erythema, ulceration DIAGNOSIS LAB RESULTS ▪ ▪ ▪ ▪ Gram stain Culture Elek test (differentiation of toxigenic strains) PCR OTHER DIAGNOSTICS ▪ History, physical examination TREATMENT MEDICATIONS ▪ Diphtheria antitoxin ▪ Antibiotic OTHER INTERVENTIONS ▪ Prophylaxis ▫ Young children: diphtheria-tetanusacellular pertussis (DTaP) vaccine ▫ Adolescents/adults: tetanus-diphtheria (Td)/tetanus-diphtheria-pertussis (Tdap) vaccine 314 OSMOSIS.ORG Figure 55.3 An ulcerating skin lesion on the leg caused by cutaneous diphtheria.
Chapter 55 Aerobic Rods LISTERIA MONOCYTOGENES osms.it/listeria-monocytogenes PATHOLOGY & CAUSES ▪ Facultative intracellular bacteria, anaerobe; beta-hemolytic ▪ Capable of growing at refrigeration temperatures (0–4°C/32–39.2°F) ▪ Motile ▫ ≤ 30°C/32°F (ﬂagella); body temperature (comet tail structures, polymerized host cells actin) ▪ Foodborne pathogen, common cause of bacterial neonatal meningitis Pathophysiology ▪ Listeria enters host cell via zipper mechanism → bacterial protein internalin binds onto cell membrane protein cadherin → releases listeriolysin O → disruption of vacuolar membrane → invasion of cytosol → actin assembling-inducing protein → polymerisation of cytoskeleton → bacteria gains motility → rapid movement through cytosol, between cells RISK FACTORS ▪ Mild febrile gastroenteritis ▫ Immunocompetent individuals, ingestion of contaminated food (e.g. raw meat, unpasteurized dairy, seafood) ▪ Cutaneous infection ▫ Direct inoculation of skin (e.g. veterinarians, farmers handling infected animals) ▪ Invasive listeriosis ▫ Immunocompromised individuals, age (neonates, elderly), pregnancy COMPLICATIONS ▪ Immunodeﬁcient, elderly individuals ▫ Sepsis, meningitis, encephalitis, pneumonia, corneal ulcer ▪ Pregnant individuals ▫ Neonatal meningitis, granulomatosis infantiseptica, miscarriage, stillbirth, premature delivery with chorioamnionitis SIGNS & SYMPTOMS ▪ Previously healthy individuals ▫ Fever, headache, diarrhea, vomiting, nausea, pustular skin lesions ▪ Individuals with weakened immune system ▫ Stiff neck, confusion, convulsions, loss of balance, cranial nerve palsies ▪ Pregnant individuals ▫ Nonspeciﬁc ﬂu-like illness ▪ Newborns ▫ Low birth weight, irritability, fever, poor feeding, circulatory/respiratory insufﬁciency, pyogranulomatous lesions DIAGNOSIS LAB RESULTS ▪ Culture ▫ Blood, cerebrospinal ﬂuid (CSF); cervix, amniotic ﬂuid in pregnant individuals; meconium, gastric aspirate, infected tissues (e.g. skin granulomatous lesions) in newborns OTHER DIAGNOSTICS ▪ History, physical examination TREATMENT MEDICATIONS ▪ Antibiotics (e.g. ampicillin, penicillin G, gentamicin) OSMOSIS.ORG 315