Lecture 6 Human Pathogen note.docx

**Lecture 6 Human Pathogen Part 3** Three different types of bacteria: Primary pathogens (capable of causing disease) -- Salmonella, Shigella, Yersinia, Klebsiella pneumoniae, Escherichia coli -- Most of the species within the genus are considered pathogens, for some it's just...

**Lecture 6 Human Pathogen Part 3** Three different types of bacteria: Primary pathogens (capable of causing disease) -- Salmonella, Shigella, Yersinia, Klebsiella pneumoniae, Escherichia coli -- Most of the species within the genus are considered pathogens, for some it's just 1 or 2. Opportunistic Pathogens -- under particular conditions Non-pathogenic General characteristics - Gram -ve rods with no specific arrangement - Non-spore forming - Aerobic and facultative anaerobic - Motile by peritrichous flagella or non-motile - Capsulated with ill-defined slime later or non-capsulated - Fimbriae or pili present is most species - Lactose fermenter - Catalase +ve - Reduce nitrate to nitrite - Grow on peptone or meat extract media without the addition of sodium chloride or other supplements. **Antigenic structure** O antigens -- in the polysaccharide of cell wall (LPS) H antigens -- flagellar protein Type 1 pilli -- the most common one CFA, BFP, P- pili K antigen -- polysaccharide capsule (only for some species) Not all have capsules Vi antigen -- virulence - Salmonella species only O, H, K -- the most common ones **Escherichia coli** \>150 serotypes All typed by O and H Example: O157:H7 (EHEC) **Shigella** -- just looking at O for Serogroups 4 different species -- S. dysenteriae, S.flexneri, S. boydi, S. sonnei Each have different serogroups: A -- 10 types, B -- 6 types, C -- 15 types, D -- just 1. Salmonella \>2000 serotypes Typhoidal vs non-typhoidal are the main ones to distinguish between \+ Yersinia - Pseudotuberculosis -- cause diseases similar to tuberculosis - Enteracalitica -- diarrheal disease **Epidemiology of Enterobacteriaceae** Molecular pathogenesis of Enterobacteriaceae Fecal-oral spread -- contaminated food goes into a person (Salmonella with typhi serotype & Shigella) or from an animal (Salmonella & E.coli) can come into a person Through Gastrointestinal tract Once it gets into the colon (generally) =\> different types of problems =\> get into the bloodstream (UTI), urinary tract, fever. Stays in the colon =\> causing diarrhea ***Escherichia*** - *E.albertii* - *E.coli* - *E.fergusonii* - *E. hermannii* - *E. vulneris*  ***Escherichia coli*** - Gram -ve bacilli - Motile; facultative anaerobe Grow in both aerobic and anaerobic - \ this is how they cause diseases. **Transmission:** Fecal-oral transmission in general -- contaminated stools =\> into water, food, unwashed hands =\> into the person orally =\> gets to intestines and stomach =\> cause illness It has to get out the lumen and into the cells in order to cause the symptoms. Shiga toxin +ve symptoms: bloody stools/diarrhea and fever, causing the bad excretion of the pathogen to come back out and restart the transmission cycle.  This is proteobacteria but not Enterobacteriaceae -- the symptoms that it causes are very similar to Enterobacteriaceae. Campylobacter jejuni -- jejunum is a part of the GI tract -- where the name comes from ***Campylobacter spp.*** - Gram -ve - Slender, curved, Long spiral-shaped rods, maybe coccoid in really old culture (a bit more round) - Motile (single polar unsheathed flagellum at one or both ends) - Non-spore former - Microaerophilic & capnophilic Different to Enterobacteriaceae - Have to grow them at reduced oxygen and increased CO~2~ - Fastidious - Temperature -- grows at 42°C -- adapted to chickens with higher body temp. - Unable to use sugars either oxidatively or fermentatively; derive energy from amino acids; Not grow on MAC or NA; Should grow them on chocolate agar. - Virulence factors - Motility Allow them to burrow(dig) down through the mucus layer - Heat-labile enterotoxin = heat sensitive **Transmission:** Intestinal colonisation in Chicken -- does not cause any problems to chickens. Not cooked enough, contaminated =\> eat =\> infection OR Contamination of faeces from chickens =\> water, other animals, particularly into milk =\> unpasteurised milk that's contaminated with campylobacter **\ ** ***Campylobacter spp.*** Comma-shaped (curved) \- **Common Cause**: One of the most common causes of bacterial gastroenteritis worldwide. \- **Common Sources**: Found in foods like poultry and unpasteurised milk. **Anatomy and Physiology:** \- Cell Wall: Thin peptidoglycan cell wall; appears pink/red when gram-stained (gram-**negative** bacteria). \- Motility: Has a flagellum at one end, making it motile. \- Oxidase Test: Oxidase positive (can use oxygen to create ATP). \- Growth Conditions: \- Microaerophile (thrives in low oxygen environments). \- Optimal temperature: 42°C. \- Grows on blood agar varieties like Skirrow, butzler, and Campy-BAP. Chocolate agar (fastidious) **Transmission:** \- Route: Fecal-oral transmission. \- Common Carriers: \- Birds (particularly in the gastrointestinal tract of poultry). \- Cows (risk from unpasteurised milk). \- Infected pets (notably puppies). **Pathogenesis and Virulence Factors:** \- Attachment: Uses fimbri-like filaments and cell surface proteins like PEV-1 and CADF to attach to the mucosa of the small intestine and colon. \- Invasion: \- Drills into mucosa using its spiral shape and long flagella. \- Releases cytotoxins like cytolethal distending toxins (CDT), causing cell damage and inflammation. \- Complications: \- Toxic Megacolon: Extensive inflammation can lead to colon dilation. \- Bacteremia: Bacteria can enter the bloodstream. \- Guillain-Barré Syndrome: The immune system produces antibodies that attack peripheral nerves, causing paralysis. \- Reactive Arthritis: Autoimmune reaction causing joint inflammation. **Symptoms:** \- Incubation Period: 1-7 days. \- Initial Symptoms: Fever, muscle pain, malaise, headache. \- Gastrointestinal Symptoms: \- Crampy abdominal pain. \- Watery diarrhea initially, which may turn bloody. \- Bloody diarrhea is more common in children. \- Complication Symptoms: \- Toxic Megacolon: Bloating, tachycardia, loss of bowel sounds. \- Guillain-Barré Syndrome: Ascending paralysis (starting at the feet and moving upwards). \- Reactive Arthritis: Pain in large joints. **Diagnosis:** \- Clinical Manifestations: Based on symptoms. \- Stool Sample Examination: \- Gram-negative, comma-shaped bacteria. \- Presence of white and red blood cells. \- Cultures: Isolating the bacteria on specific media. **Treatment:** \- General Treatment: Hydration and correcting electrolyte imbalances. \- Severe Infection: Antibiotics like erythromycin. **Distinguishing from Other Bacteria:** \- Gram Staining: Both Campylobacter and Enterobacteriaceae are gram-negative. \- Microscopy: Campylobacter is comma-shaped, while Enterobacteriaceae are rod-shaped. \- Motility: Campylobacter is motile (distinguishing it from non-motile Shigella). \- Incubation Conditions: \- Campylobacter grows in low oxygen and warmer temperatures. \- Enterobacteriaceae do not have such specific growth requirements. \- Growth Requirements: \- Campylobacter requires specialised media (e.g., chocolate agar). \- Enterobacteriaceae grow on a wider range of media. \- Oxidase Test: \- Campylobacter is oxidase positive. \- Enterobacteriaceae are oxidase negative. ***Shigella* spp*.*** **General Information:** \- Family: Enterobacteriaceae \- Species: \- Shigella dysenteriae \- Shigella flexneri \- Shigella boydii \- Shigella sonnei \- All species can cause **shigellosis**, a contagious intestinal infection, which can progress to dysentery. **Anatomy and Physiology:** \- Gram-negative (appears red or pink). \- Rod-shaped. \- Facultative anaerobe (can survive with or without oxygen). \- Motility: Non-motile (lacks flagella). \- Non-spore former \- Non-lactose fermenter. \- Urease and oxidase negative. \- H~2~S negative **Identification:** \- Culture Medium: Grows on selective media like MacConkey agar. \- Forms white, non-lactose fermenting, non-hydrogen sulfide-producing colonies. \- Microscopy: Stool stains with methylene blue may show polymorphonuclear leukocytes. \- PCR Testing: Direct identification of Shigella DNA. **Pathogenesis:** 1\. Ingestion and Initial Infection: \- Shigella is ingested and multiplies in the small intestine before passing into the colon. \- Targets epithelial cells of the mucosal lining, particularly M-cells. 2\. Invasion and Immune Response: \- M-cells phagocytose Shigella and release it into mucosa-associated lymphoid tissues (MALT). \- Macrophages in MALT gobble up Shigella, but Shigella induces apoptosis in macrophages. \- Release of cytokines (e.g., interleukin-1-beta) triggers intense inflammation, attracting more immune cells, damaging epithelial cells, and causing ulcerations and abscesses. 3\. Spread within the Host: \- Disrupts cellular junctions, allowing Shigella to enter enterocytes. \- Uses type III secretory system to inject proteins into enterocytes, inducing phagocytosis. \- Inside enterocytes, Shigella escapes the phagosome into the cytoplasm, uses actin-based motility to move and spread infection. 4\. Shiga Toxin (specific to Shigella dysenteriae serotype 1): \- An AB toxin (two subunits: A and B). \- B subunit binds to the host cell membrane; toxin engulfed into the phagosome. \- Acidic environment in phagosome breaks disulfide bond, separating subunits. \- A subunit diffuses into the cytoplasm, and cleaves 28S rRNA in ribosomes, halting protein synthesis and causing cell death. \- Can reach the bloodstream and cause hemolytic uremic syndrome (HUS). **Symptoms:** \- Symptoms last about seven days. \- infected person can be a carrier for infection up to 4 weeks after the onset of symptoms. \- Typical Symptoms: \- Severe abdominal and rectal cramping and pain. \- High fever, vomiting, loss of appetite. \- Watery, mucus-like diarrhea, potentially containing **blood** or pus. Bloody diarrhea \- Complications: \- Hemolytic Uremic Syndrome (HUS): Hemolytic anemia, kidney failure, thrombocytopenia. \- Tonic-Clonic Seizures: Particularly in children. \- Sepsis: Mostly in neonates, malnourished children, and people with S. dysenteriae serotype 1 infection. \- Reactive Arthritis: Pain and swelling in knee joints. **Transmission:** \- Fecal-oral transmission. \- Sources: \- Contaminated water or food. \- Flies carrying stool particles. \- Contact with contaminated objects or hands. \- Sexual contact (occasionally). **- Virulence: Extremely virulent; as few as 10 bacteria can cause an infection.** **- Survival: Can survive the acidic environment of the stomach.** **Diagnosis:** \- Fecal Sample: Cultured on selective media like MacConkey agar. \- Stool Stains: Methylene blue may show polymorphonuclear leukocytes. \- PCR Testing: For direct identification of Shigella DNA. **Treatment:** \- General Treatment: Fluid and electrolyte replenishment. \- Antibiotics: Beta-lactams (penicillins and cephalosporins), macrolides, quinolones. ***Salmonella typhoidal (Salmonella typhi)*** **General Information** \- Family: Enterobacteriaceae \- Species: Salmonella bongori and Salmonella enterica (with 6 subspecies) \- Encapsulated gram-negative rod bacteria (appear red or pink on gram stain) \- Characteristics: \- Facultative intracellular pathogens \- Motile with flagella \- Non-spore former \- Facultative anaerobes (can undergo respiratory and fermentative metabolism) \- Can ferment glucose but not lactose \- Oxidase negative \- H~2~S positive \- Specific to Humans: Only infects humans and causes enteric fever (typhoid fever) **Pathogenesis** \- Ingestion and Targeting: \- Reaches distal ileum of the small intestine \- Targets epithelial layer of the mucosal lining \- Adheres to and is phagocytosed by M cells \- Spit into underlying Peyer\'s patches \- Immune Evasion: \- Vi capsular polysaccharide antigen protects against antibody tagging \- Suppresses neutrophil recruitment \- Induces recruitment of monocytes and macrophages \- Can cause hypertrophy, necrosis, and potentially ileal perforation \- Survival and Replication: \- Phagocytosed by macrophages, forming a salmonella-containing vacuole \- Type III secretion system injects effector proteins, preventing vacuole-lysosome fusion \- Survives and replicates within the vacuole **- Systemic Spread:** \- Uses macrophages to enter lymphatic vessels and systemic lymphatic circulation \- Reaches reticuloendothelial tissues (liver, spleen, bone marrow, gallbladder) \- Induces macrophage apoptosis, causing bacteremia \- Can lead to sepsis **- Complications:** \- Osteomyelitis in individuals with spleen issues \- Chronic infection and carrier state (gallbladder reservoir) **Transmission** \- Routes: Fecal-oral, poor sanitation, poor hygiene, contaminated water/food, particularly endemic to Asia, Africa, Latin America, and the Caribbean \- Inoculum: Requires about 100,000 microorganisms to cause infection **Symptoms** \- Onset: 1-2 weeks after infection \- Duration: 4-6 weeks \- Typical Symptoms: \- High sustained fever \- Abdominal pain \- Constipation followed by diarrhea \- Rose or salmon-coloured spots on chest and abdomen \- Hepatomegaly and splenomegaly \- Dehydration, weakness, headaches, and cloudy mental state in advanced cases **Diagnosis** \- Methods: Blood culture, stool culture, intestinal secretions (vomit or duodenal aspirate), and gallbladder bile culture for carriers **Treatment** \- Symptomatic Management: Fluid and electrolyte replenishment, NSAIDs for pain and fever \- Antibiotics: Broad-spectrum antibiotics like fluoroquinolones or cephalosporins (ceftriaxone) \- Carriers: Combination of antibiotics and gallbladder removal **Prevention** \- Vaccines: Oral live attenuated vaccine and intramuscular vaccine containing VI capsular polysaccharide \- Hygiene: Proper sanitation and hygiene practices ***Non-typhoidal Salmonella*** **General Characteristics** \- Serotypes: Over 2,500 serotypes within subspecies enterica \- Common Serotype: Salmonella enteritidis **Pathogenesis** \- Ingestion and Targeting: \- Reaches the distal ileum of the small intestine \- Targets epithelial layer of the mucosal lining \- Adheres to and is phagocytosed by M cells \- Spit into underlying Peyer\'s patches \- Immune Response: \- Strong pro-inflammatory cytokine response \- Recruitment of immune cells (especially neutrophils) \- Causes enterocolitis (inflammation of the small intestine and colon) \- Can lead to mucosal damage and ulcers \- Potential Spread: \- Usually limited to the mucosa and destroyed by local immune cells \- In some cases, can become invasive and cause bacteremia **Transmission** \- Reservoirs: Infected humans and animals (birds, reptiles, mammals, amphibians) \- Routes: Fecal-oral, foodborne (contaminated raw/undercooked animal products, water, fruits, vegetables, peanut butter), direct contact with infected animals **Symptoms** \- Onset: 24-48 hours after infection \- Typical Symptoms: \- Watery diarrhea (sometimes bloody) \- Abdominal cramps \- Nausea and vomiting \- Headache, chills, low-grade fever \- Dehydration **Diagnosis** \- Methods: Stool culture on selective media, additional cultures for invasive infections **Treatment** \- Symptomatic Management: Fluid and electrolyte replenishment, suppressing nausea, alleviating pain \- Antibiotics: Typically not indicated for uncomplicated infections; used for invasive infections based on sensitivity of the strain ***Escherichia coli*** **Characteristics:** \- Gram-negative: Thin peptidoglycan layer, stains pink with safranin dye. \- Rod-shaped bacteria. \- Catalase-positive: Produces catalase enzyme. \- Lactose fermenter: Produces beta-galactosidase and cleaves lactose into glucose and galactose. **Tests and Cultivation** \- Catalase Test: Adding hydrogen peroxide to a colony; the presence of catalase results in foaming. \- Lactose Fermentation Test: Cultivation on lactose-containing media (e.g., phenol lactose), resulting in acid production and colour change from red to yellow. \- Eosin Methylene Blue (EMB) Agar: Grows into black colonies with a greenish-black metallic sheen. **Physical Properties** \- Encapsulation: Covered by a polysaccharide layer called a capsule. \- Motility: Has flagella for movement. \- Facultative Anaerobe: Can live with or without oxygen. **Pathogenic Strains** \- Attachment: Uses fimbriae to attach to host cells. \- Serotype Classification: Based on antigens: \- Somatic (O) antigens: On the cell membrane. \- Capsular (K) antigens: On the capsule. \- Fimbrial (F) antigens: On the fimbriae. \- Flagellar (H) antigens: On the flagella. **Serotypes and Diseases** \- Examples: \- K1 antigen: Causes neonatal meningitis. \- O157:H7: Associated with hemorrhagic colitis, hemolytic uremic syndrome, and diarrheal outbreaks. \- Numerous Serotypes: Up to 200 serotypes. **Pathotype Classification** \- Pathotypes: Based on the disease-causing mechanism and virulence factors: 1\. Shiga-like toxin-producing E. coli (STEC) \- Produces Shiga toxin, causes bloody diarrhea, and can lead to hemolytic uremic syndrome (HUS). 2\. Enterotoxigenic E. coli (ETEC) \- Produces heat-labile and heat-stable enterotoxins, causing watery diarrhea. 3\. Enteroinvasive E. coli (EIEC) \- Invades and destroys intestinal epithelial cells, causing bloody diarrhea. 4\. Enteropathogenic E. coli (EPEC) \- Causes disease in children under two years old, leading to watery diarrhea. 5\. Uropathogenic E. coli (UPEC) \- Causes urinary tract infections (UTIs), including cystitis and pyelonephritis. **Pathogenesis of Each Pathotype** **1. Shiga-like Toxin-Producing E. coli (STEC)** - **Attachment**: STEC attaches to the host\'s intestinal cells using fimbriae. - **Toxin Production**: Produces Shiga-like toxins (Stx1 and Stx2). - **Intestinal Injury**: Toxins cause damage to the intestinal epithelium and blood vessels, resulting in inflammation. - **Bloody Diarrhea**: Inflammation and vessel damage lead to fluid and blood leaking into the intestinal lumen. - **Hemolytic Uremic Syndrome (HUS)**: - **Systemic Toxin Release**: Toxins enter the bloodstream, affecting the kidneys. - **Kidney Damage**: Toxins bind to endothelial cells in the glomeruli, causing apoptosis and gaps in the capillary walls, leading to proteinuria. - **Inflammatory Response**: Cytokines and chemokines are released, activating platelets and causing clot formation. - **Thrombocytopenia**: Decreased platelet count due to clot formation. - **Hemolytic Anemia**: Red blood cells are fragmented (schistocytes) as they pass through obstructed microvessels. - **Ischemic Kidney Damage**: Clots obstruct arterioles, leading to kidney ischemia, reduced filtration, and uremia. **2. Enterotoxigenic E. coli (ETEC)** - **Attachment**: ETEC uses fimbriae to adhere to the intestinal mucosa. - **Toxin Production**: - **Heat-labile Enterotoxin (LT)**: - **Mechanism**: Activates adenylate cyclase, increasing cAMP, leading to chloride and water secretion. - **Heat-stable Enterotoxin (ST)**: - **Mechanism**: Activates guanylate cyclase, increasing cGMP, leading to electrolyte and water secretion. - **Outcome**: Causes watery diarrhea without damaging the intestinal wall. **3. Enteroinvasive E. coli (EIEC)** - **Attachment and Invasion**: EIEC attaches to and invades intestinal epithelial cells. - **Intracellular Multiplication**: - **Invasion**: Invades and multiplies within epithelial cells, causing cell destruction. - **Inflammatory Response**: Triggers a strong inflammatory response, leading to widespread epithelial damage and bloody diarrhea. **4. Enteropathogenic E. coli (EPEC)** - **Attachment**: EPEC uses bundle-forming pili (BFP) to attach to intestinal epithelial cells. - **Effacement**: - **Mechanism**: Injects effector proteins via a Type III secretion system, causing actin cytoskeleton rearrangement. - **Effect**: Leads to pedestal formation and microvilli effacement. - **Outcome**: Impairs absorption, causing watery diarrhea, primarily in children under two years of age. **5. Uropathogenic E. coli (UPEC)** - **Colonization**: UPEC can colonize the periurethral area and ascend the urinary tract. - **Adhesion and Invasion**: - **Fimbriae**: Uses type 1 fimbriae and P fimbriae to adhere to uroepithelial cells. - **Invasion**: Invades and replicates within bladder cells. - **Toxin Production**: - **Hemolysins**: Produces alpha and beta hemolysins, causing lysis of urinary tract cells. - **Ascending Infection**: - **Cystitis**: Infection of the bladder, causing dysuria and frequent urination. - **Pyelonephritis**: Can ascend to the kidneys, causing flank pain and more severe symptoms. **Symptoms and Complications** \- General Symptoms: Diarrhea, abdominal cramps, vomiting. \- STEC: Bloody diarrhea, low-grade fever, potential HUS with symptoms like body swelling, confusion, and jaundice. \- ETEC: Watery diarrhea, possible fever, and bloating. \- EIEC: Bloody diarrhea and chills. \- EPEC: Severe dehydration in children, prolonged diarrhea leading to malnutrition. \- UPEC: UTI symptoms like dysuria, urinary frequency, and possible flank pain if kidneys are affected. **Diagnosis** \- General Diagnosis: \- Gram Staining: On stool or urine sample. \- Culture: On eosin methylene blue agar. \- HUS Diagnosis: Identifying Shiga toxin in the blood. **Treatment** \- Diarrhea: \- Hydration and rest. \- Antibiotics in severe cases (e.g., doxycycline, cotrimoxazole). \- Hemolytic Uremic Syndrome (HUS): \- Supportive care: Dialysis, corticosteroids, blood transfusions, plasmapheresis. \- UTIs: \- Antibiotics: Cotrimoxazole, nitrofurantoin, fluoroquinolones (e.g., ciprofloxacin).