Infectious Diseases and C.difficile Quiz

Gram Positive Rods

• Bacillus, Clostridia, Listeria, Corynebacterium are gram-positive rods.
• Bacillus includes species like B. anthracis.
• Clostridia species encompass C. tetani, C. botulinum, C. perfringens, and C. difficile.
• Listeria includes L. monocytogenes.
• Corynebacterium includes C. diphtheriae.

Bacillus

• Gram-positive rods, large, arranged singly or in long chains.
• Endospore-formers and toxin-producers.
• Aerobic or facultative anaerobic, nonmotile or motile, nonhemolytic rods.
• Ubiquitous in nature (vegetation, water, soil).
• Involved in biological cycles of carbon/nitrogen.
• The family Bacillaceae is diverse, including some strains commensal to herbivores, and some that infect humans.
• Clinically relevant strains for humans include Bacillus anthracis and Bacillus cereus.
• Spore diameter does not exceed the bacterial cell diameter in this genus.

Bacillus anthracis

• Gram-positive rod, spore-forming.
• Virulent strains have a polypeptide capsule (poly-D-glutamic acid) encoded by a plasmid (pXO2).
• Virulent strains carry genes for three toxic protein components on a large plasmid (pXO1) : PA (protective antigen), EF (edema factor), and LF (lethal factor).

Anthrax (Charcoal)

• Zoonotic disease affecting herbivores (cattle, sheep, goats, deer) primarily.
• Humans are infected by ingesting contaminated vegetation, water, or soil or through exposure to contaminated animals or animal products (meat, wool).
• Anthrax has three types: cutaneous, inhalational, and intestinal.
• The disease is characterized by symptoms that depend on how anthrax spores enter the body.

Anthrax Transmission

• Human disease acquired through one of three routes: inoculation of spores through exposed skin, ingestion of spores, inhalation of spores.
• Inhalation is the most likely route for biological weapons.

Cutaneous Anthrax

• Painless papule at site of inoculation.
• Rapidly progresses to ulcer then necrotic eschar.
• Extensive surrounding edema/inflammation is hallmark.
• Case fatality: 20% without treatment; less than 2% with antimicrobial therapy.

Gastrointestinal Anthrax

• Ulcers form at the site of invasion (mouth, esophagus, intestine).
• First symptoms: nausea, vomiting, malaise, which progress to systemic disease.
• Almost 100% fatal without treatment.

Inhalation Anthrax

• Spores reach lower airways and mediastinal lymph nodes.
• Initial symptoms nonspecific: fever, myalgia, nonproductive cough, malaise.
• Second stage dramatic; rapidly worsening fever, edema, massive enlargement of mediastinal lymph nodes, respiratory failure, sepsis.
• Almost all cases progress to shock and death within 3 days of initial symptoms, unless treatment is initiated immediately.
• Virulence is very high in absence of treatment.

Laboratory Diagnosis

• Microscopy: Gram stain with observation of rods arranged singly or in long chains in biological specimens (skin lesions, oropharyngeal ulcers, blood, respiratory secretions).
• Culture: Colonies readily grow in blood agar plates, large, nonpigmented, with a dry "ground-glass" surface and irregular edges.
• B. anthracis colonies have a characteristic "Medusa Head" appearance with irregular edges and comma projections.

Treatment of B. anthracis infection

• Prior to 2001, penicillin was the first-line treatment.
• Current recommendation: ciprofloxacin or doxycycline combined with other antibiotics (rifampin, vancomycin, penicillin, imipenem, clindamycin, clarithromycin).
• Exposure to antibiotics should last the full 60 day course.

Clostridium

• Anaerobic Gram-positive rods capable of forming endospores.
• Ubiquitous in soil, water, and sewage.
• Part of the normal microbial population in the gastrointestinal tracts of animals and humans.
• Most are harmless saprophytes, some are recognized pathogens.

Clostridium tetani

• Large, motile, spore-forming rod.
• Vegetative form extremely susceptible to oxygen toxicity, but sporulates (forms spores) readily and survives in the environment for a long time.
• Virulence factor: production of two toxins: tetanolysin (oxygen-labile hemolysin; unknown clinical significance); and tetanospasmin (plasmid-encoded, heat-labile neurotoxin→ tetanus).
• The disease is characterized by muscle spasm and involvement of the autonomous nervous system.

Tetanospasmin

• Neurotoxin produced during the stationary phase of growth, released when the cell is lysed.
• Responsible for the clinical manifestations of tetanus.
• A-B toxin cleaved by endogenous proteases.
• The two parts remain together up to spinal cord transportation
• A (zinc-endopeptidase) portion inactivates proteins that regulate the release of glycine and GABA.
• This leads to unregulated excitatory synaptic activity in motor neurons → spastic paralysis.

Clostridium tetani Infection

• Spores penetrate through skin wounds, burns, animal bites (splinter wounds are particularly dangerous).
• Germination of spores and neurotoxin production occurs after 24-36 hours under anaerobic conditions.

Generalized Tetanus

• Most common form.
• Incubation period 3-21 days.
• Symptoms include headache, mild fever, irritability, pain near the wound, trismus (lockjaw), difficulty opening the mouth due to spastic paralysis of the masseter muscle ("risus sardonicus").
• In addition, painful contraction at level of cervical musculature and of the trunk with a hyperextension contracture and a typical postural attitude.
• Other symptoms include thoracic and laryngeal spasms, respiratory failure, cardiac arrhythmias, potentially leading to death.
• Mortality rate: 30% - 50%.

Neonatal Tetanus

• Typically associated with initial infection of the umbilical stump (following nonsterile delivery).
• Progresses to become generalized.
• Develops 4-14 days after birth.
• Mortality rate exceeding 90% in infants.

Clostridium botulinum

• Heterogeneous collection of fastidious, spore-forming anaerobic rods.
• C. botulinum includes various strains producing distinct botulinum toxins (at least 7).
• Spores/neurotoxins can be present in home-made preserves, bad food refrigeration, and honey.
• Spores are common in the environment and can contaminate foods.
• Anaerobic conditions allow spores to germinate and produce botulinum neurotoxin.

Botulinum Neurotoxin (A-B toxin)

• Present in contaminated food, absorbed in the intestine.
• Complexed with nontoxin proteins; not inactivated by proteolytic enzymes through the digestive tract..
• B subunit binds motor neurons; A subunit (zinc-endopeptidase) inactivates proteins that regulate the release of acetylcholine (ACh) in peripheral nervous system presynapses (neuromuscular junction) → flaccid paralysis.

Classic/Foodborne Botulism

• Associated with consumption of home-canned food contaminated with toxins.
• Symptoms begin 6–days after ingestion, depending on the dose of ingested toxin.
• Clinical manifestations range from mild symptomotaology to severe cases (fatal ~5%).
• Symptoms: diplopia, difficulty in speech and in swallowing; muscle weakness progressing from the shoulders to the trunk and lower limbs, respiratory paralysis.

Infant Botulism

• Associated with consumption of foods (honey, infant milk powder) contaminated with spores.
• Spores germinate and colonize the gastrointestinal tract; multiply and produce toxins in vivo.
• Proliferation is achieved because of competitors absence.
• Initial symptoms are nonspecific: constipation, weak cry.
• Then flaccid paralysis and respiratory arrest followed by mortality rate less than 2%.

Wound Botulism

• Rare disease with unknown incidence.
• Toxin produced by bacteria in contaminated wounds.
• Symptoms similar to foodborne botulism, but incubation period is longer (>4 days).

Inhalation Botulism

• Major concern in the era of bioterrorism.
• Aerosolization of the neurotoxin as a biological weapon.
• Rapid onset and potentially high mortality.

Botulism Diagnosis, Treatment, and Prevention

• Clinical diagnosis confirmed by toxin detection in implicated food or patient's serum/feces.
• Cultures of heated specimens on enriched anaerobic media allow spore germination.
• Treatment: adequate ventilatory support; elimination of the organism from the gastrointestinal tract.
• Use of penicillin or metronidazole to kill bacteria and reduce toxin production; passive immunization with trivalent botulinum antitoxins (A, B, and E) to neutralize unbound toxin.
• Prevention: Destroy spores in food (virtually impossible), prevent spore germination, destroy preformed toxin by heating food at 60–100°C for 10 min.

Listeria monocytogenes

• Facultatively anaerobic Gram-positive rod with flagella.
• Short rod (coccobacillus), sometimes in pairs or short chains.
• Grows in wide range of temperatures, pH, and high salt concentration.
• Facultative intracellular pathogen, ubiquitous in nature (soil, vegetation, water, and gastrointestinal tracts of animals).
• Not found in humans.
• Associated with diseases in: pregnant women/neonates, elderly, and patients with defective cellular immunity.
• Foodborne pathogen (contaminated food).
• Undercooked or processed meats, unpasteurized/contaminated milk or cheese, unwashed raw vegetables.

Listeria monocytogenes Infection

• Enter gastrointestinal tract after contaminated food ingestion.
• Adhere to epithelial cells via internalin A (cell wall surface protein).
• Induce phagocytosis by epithelial cells.
• Inside the infected cells, listeriolysin O and two phospholipases C enzymes are produced.
• Release into the cytosol of infected cells.
• Replicates by intracellular spread (cell-to-cell).
• Enters macrophages.
• Spreads via lymph nodes blood vessels to splean and liver.
• Dissemination of disease.

Listeria monocytogenes: Life Cycle in Host Cells

• Bacteria undergo phagocytosis.
• Lysis of phagolysosome.
• Proliferation.
• Cell-to-cell spread via filopods.
• Repeated cycles.

Listeria monocytogenes: High-Risk Groups

• Pregnant women (nonspecific influenza-like symptoms), newborns (acquired during pregnancy; early or late onset disease) → abortion, stillbirth, premature birth, or formation of abscesses and granulomas in multiple organs.
• Elderly and immunocompromised patients: sepsis, meningitis, meningoencephalitis.
• Listeria infections in healthy adults are typically asymptomatic or mild influenza-like illness (self-limiting gastroenteritis, headache, myalgias, and arthralgias).

Listeria: Laboratory Diagnosis & Treatment

• Microscopy: Gram stain reveals short rods (coccobacilli).
• Culture: Grows on most conventional media; small colonies with beta-hemolysis on blood agar plates (distinguish from streptococci).
• Cold enrichment for culture from food.
• Treatment: Gentamicin with penicillin or ampicillin for serious infections (septicemia and meningitis).
• Trimethoprim-sulfamethoxazole.

Corynebacterium spp.

• Includes over 100 species.
• Gram-positive bacteria, irregular shape, clumps or short chains.
• Aerobic or facultatively anaerobic.
• Motile, non-spore-forming, and club-shaped.
• Commonly found in soil, water, human skin and respiratory tract.
• Most important is C. diphtheriae (etiologic agent of diphtheria) in which humans are the only reservoir.
• Corynebacteria often display metachromatic granules (containing phosphates, lipids, RNA) at the ends of the bacterial cell.
• Microscopy shows appearance resembling "Chinese letters".

Corynebacterium diphtheriae

• Major virulence factor: diphtheria toxin.
• Tox gene introduced by a lysogenic bacteriophage (β-phage).
• Diphtheria toxin inhibits protein synthesis.
• Receptor is heparin-binding epidermal growth factor (present in many cell types, especially heart and nerve cells).

Diphtheria: Respiratory Infection

• Bacteria enter through the respiratory tract, multiply locally on epithelial cells in the pharynx.
• Causes damage, malaise, sore throat, exudative pharyngitis, and low-grade fever.
• Exudate develops into thick pseudomembrane of bacteria, lymphocytes, plasma cells, fibrin and dead cells.
• Toxin spreads through the blood and noncontiguous anatomical sites, leading to severe systemic disease, primarily involving the heart (myocarditis) and nervous system (neuropathy, dysphagia, paralysis).

Diphtheria: Cutaneous Infection

• Involves invasion of organism from the patient's skin into subcutaneous tissue.
• Develops a papule at the site of contact; later covered by a greyish membrane.
• Similarly to respiratory diphtheria, a systemic response occurs, especially with fever.
• Also affects the heart and nervous system.

Diphtheria: Laboratory Diagnosis, Therapy, & Prevention

• Microscopy: Gram stain preparation on pseudomembrane, respiratory swabs, cutaneous lesions.
• Culture: Bacteria cultured on Loffler medium and selective agar plates (e.g., cysteine-tellurite blood agar, colistin-nalidixic agar).
• Treatment: Penicillin or erythromycin to eliminate C. diphtheriae, terminate toxin production.
• Early administration of diphtheria antitoxin to specifically neutralize the exotoxin before it binds to the epithelial cells.
• Prevention: Vaccination is the best way.

Test your knowledge on infectious diseases, focusing specifically on anthrax and C.difficile infections. This quiz covers transmission routes, symptoms, diagnostic methods, and treatment options associated with these diseases. Perfect for students and professionals in the medical field.