GRAM POSITIVE BACILLI Flashcards
What are the two types of Gram-positive rods?
- Spore-forming: Bacillus and Clostridium
- Non-spore-forming: Listeria monocytogenes and Corynebacterium diphtheriae
What is the key difference between Bacillus and Clostridium?
- Bacillus: Aerobic (grows in oxygen)
- Clostridium: Anaerobic (grows without oxygen)
What is unique about the capsule of Bacillus anthracis?
Made of poly-D-glutamic acid, which prevents phagocytosis
What are the two pathogenic Bacillus species and their diseases?
- Bacillus anthracis: Anthrax
- Bacillus cereus: Gastroenteritis (food poisoning)
What toxins are produced by Bacillus anthracis, and what do they do?
- Edema factor (EF): Disrupts water balance
- Protective antigen (PA): Helps EF enter cells
- Lethal factor (LF): Inactivates protein kinase
How do Bacillus cereus spores cause food poisoning?
Spores survive cooking, germinate, and release enterotoxins
- Symptoms: Nausea, vomiting, diarrhea
- Types of toxins: Heat-labile and heat-stable
What diseases are caused by Clostridium species?
- Botulism
- Tetanus
- Gas gangrene
- Pseudomembranous colitis
What is the main symptom of Clostridium botulinum poisoning?
Flaccid muscle paralysis
- Symptoms: Double vision, difficulty swallowing, muscle weakness
What causes infant botulism, and what are its symptoms?
Caused by spores in contaminated honey
- Symptoms: Constipation, muscle weakness, “floppy baby”
What is the effect of Clostridium tetani on the body?
- Tetanospasmin causes muscle contraction (tetany)
- Leads to spasms, lockjaw, and respiratory paralysis
How is Clostridium difficile related to antibiotic use?
Overuse of antibiotics destroys normal gut flora, allowing C. difficile to overgrow
- Symptoms: Severe diarrhea, abdominal cramps, fever
- Treatment: Discontinue antibiotics, administer metronidazole or vancomycin
What is unique about Listeria monocytogenes?
- Can cross blood-brain, gastrointestinal, and feto-placental barriers
- Can cause meningitis, stillbirth, and death in severe cases
What disease does Corynebacterium diphtheriae cause, and what is its pathogenesis?
- Causes diphtheria
- Colonizes the pharynx, forming a grayish pseudomembrane
- Exotoxin released into the bloodstream damages heart and neural cells by inhibiting protein synthesis
What is Listeria monocytogenes known for, and how is it treated?
Facultative intracellular organism (can live both inside and outside cells)
- High-risk individuals: immunosuppressed, young, elderly, AIDS, transplant patients
- Treatment: Ampicillin or trimethoprim-sulfamethoxazole
- No significant antimicrobial resistance
How is Corynebacterium diphtheriae treated?
1st step: Antitoxin to neutralize toxin
2nd step: Penicillin or erythromycin to kill bacteria
3rd step: DPT vaccine (Diphtheria component)
Bacteriophage is required for exotoxin production
What are the two species of Salmonella and how are they categorized?
- Salmonella enterica and Salmonella bongori
- S. enterica has many serovars like Typhimurium and Enteriditis
- Over 2,541 serovars of Salmonella exist
What is the difference between Enterocolitis and Enteric Fever caused by Salmonella?
- Enterocolitis: Gastroenteritis with nausea, vomiting, diarrhea, fever; caused by many S. enterica serovars
- Enteric Fever (Typhoid): Caused by S. enterica serovar Typhi; involves systemic infection and can cause intestinal ulceration, hemorrhage, and perforation
What is the principal feature of enteric fever caused by S. enterica serovar Typhi?
- Invasion of intestinal epithelium followed by multiplication in mesenteric lymph nodes and bloodstream
- Can result in chronic carrier state (1-2% of cases)
What is the treatment for uncomplicated Salmonella enterocolitis?
- Antibiotics not recommended as they can prolong stool excretion
- Treatment mainly supportive
What is the main symptom and mode of transmission of Shigella infections?
Main symptom: Severe diarrhea with mucus, pus, and blood
- Transmission: Ingestion of small numbers of bacteria, common in children and areas with poor sanitation
What are the different pathotypes of Escherichia coli?
- EPEC (Enteropathogenic E. coli): Causes severe diarrhea in infants
- ETEC (Enterotoxigenic E. coli): Causes traveler’s diarrhea
- EIEC (Enteroinvasive E. coli): Causes bloody diarrhea, similar to Shigella
- EHEC (Enterohemorrhagic E. coli): Causes hemorrhagic colitis and Hemolytic Uremic Syndrome (HUS), most commonly E. coli O157:H7
What is the significance of Cronobacter sakazakii?
- Linked to outbreaks from contaminated powdered infant formula
- Can cause wound infections, bacteremia, and hospital-acquired pneumonia
What disease is caused by Vibrio cholerae and how does it cause symptoms?
- Causes cholera
- Produces cholera toxin, which causes the small intestine to secrete chlorides and reduce sodium absorption, resulting in watery diarrhea
What are the clinical features of Campylobacter jejuni and Campylobacter coli infections?
- Cause fever, abdominal pain, and bloody diarrhea
- Common in animals and birds, infections usually from contaminated food
What are the clinical situations where Pseudomonas aeruginosa is important?
- Respiratory infections in cystic fibrosis patients
- Infections related to skin burns
What is Pseudomonas cepacia and its significance?
- Can multiply in low-nutrient environments
- Common contaminant in saline and water
- Respiratory pathogen in cystic fibrosis patients
- Difficult to treat due to intrinsic resistance to many antibiotics
What does Haemophilus influenzae cause, and where is it found?
Found in normal nasopharyngeal flora of many individuals, especially children
- Causes invasive infections in children under 5 (meningitis, pneumonia, joint infections)
- Also associated with chronic bronchitis exacerbations in adults
What are the key characteristics of Legionella pneumophila?
Grows in water, often found in shower heads and water tanks
- Causes Legionnaires’ disease, a form of pneumonia
- Opportunistic pathogen, especially in individuals with deficient cell-mediated immunity
- Transmission through aerosol exposure, not person-to-person
What does Helicobacter pylori cause, and what are its treatment options?
- Causes duodenal ulcers and chronic gastritis
- Has urease to protect against stomach acidity
- Triple therapy treatment: Amoxicillin, Metronidazole, and Omeprazole (antibiotics + proton pump inhibitor)
What is the causative agent of whooping cough?
Bordetella pertussis
- Causes a violent cough by destroying ciliated cells in the trachea and bronchi
- Virulence factors: Pertussis toxin, adenylate cyclase, filamentous hemagglutinin, and tracheal cytotoxin
- Vaccine: DPT vaccine (includes killed organism and toxins)
What is the biochemical classification of Gram-negative bacteria?
- Ability to ferment lactose (e.g., E. coli and Enterobacteriaceae ferment lactose, while Salmonella, Shigella, and Pseudomonas do not)
- Growth media: EMB (Eosin-Methylene-Blue) and MacConkey agar
- EMB: Lactose fermenters turn purple/black
- MacConkey: Lactose fermenters turn pink/purple
What are the three major surface antigens in enteric Gram-negative bacteria?
O antigen: Outer component of LPS
K antigen: Capsule covering O antigen
H antigen: Part of flagella subunits (present in motile bacteria)
What are the types of diarrhea caused by Gram-negative bacteria?
- No cell invasion: Exotoxins cause watery diarrhea (e.g., Vibrio cholerae)
- With cell invasion: Invasion of epithelial cells causing bloody stools (e.g., E. coli O157:H7)
- With lymph node and bloodstream invasion: Abdominal pain, fever, white blood cell count increase, and bloody diarrhea (e.g., Salmonella Typhi, Yersinia enterocolitica)
What other infections are caused by enteric Gram-negative bacteria?
- Urinary tract infections, pneumonia, bacteremia, sepsis
- Common enteric pathogens include E. coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter, Serratia, and Pseudomonas aeruginosa
