Spore-Forming Gram-Positive Bacilli PDF

Spore-Forming Gram- Positive Bacilli Department of Microbiology School of medicine Tehran University of Medical Science Fereshteh Jabalameli Professor...

Spore-Forming Gram- Positive Bacilli Department of Microbiology School of medicine Tehran University of Medical Science Fereshteh Jabalameli Professor in Microbiology  Spore-Forming Gram-Positive Bacilli Diverse collection of bacteria Grow aerobically or anaerobically Form endospores Two clinically important genera Bacillus (aerobic & facultative anaerobic spore formers) Clostridium (the strict, anaerobic spore formers) Bacillus Learning Objective ❖Describe the general characteristics of the genus Bacillus. ❖Distinguish between cutaneous, inhalation, and pulmonary anthrax. ❖ Describe how anthrax is controlled. ❖Explain human disease associated with Bacillus cereus. ❖Explain which Bacillus cereus infections are important to treat  Bacillus There are almost 300 species in this genus Bacillus anthracis Agent of anthrax Bacillus cereus An opportunist Causes food poisoning B.anthracis Large (l x 3 to 8 μm) Arranged as single or paired rods or as long, serpentine chains Spores (in 2- to 3-day-old cultures, not in clinical specimens) Virulence factor Capsule Toxins Virulence factor Polypeptide capsule In clinical specimens Consisting of poly-D-glutamic acid Plasmid pX02 Transfer of gene by Plasmid Inhibits phagocytosis Virulence factor Exotoxin Protective antigen (PA) Lethal factor (LF) Edema factor (EF) (are nontoxic individually) Plasmid pXO1 (carries genes for three toxin protein components) Edema toxin: PA + EF Lethal toxin: PA + LF Lethal Factor (LF) Zinc-dependent protease Cell death – tissue necrosis Edema factor (EF) Adenylate cyclase Conversion of adenosine triphosphate (ATP) to (cAMP) Increases intracellular cyclic adenosine mono phosphate (cAMP) results in Edema Fluid accumulation observed in anthrax Epidemiology Primarily infects herbivores Humans are infected through exposure to contaminated animals or animal products Human B. anthracis disease is acquired by Inoculation (95%) Ingestion (herbivores) Inhalation Clinical Diseases 1- Cutaneous Inoculation of Bacillus spores through exposed skin from either contaminated soil or infected animal products. 2- Gastrointestinal Is very rare in humans 3- Inhalation anthrax )wool-sorters' disease) From inhalation of B. anthracis spores during the processing of goat hair Injection anthrax Cutaneous anthrax At the site of inoculation subcutaneous inoculation of spores through incidental skin abrasions Painless papule Rapidly progresses to an ulcer surrounded by vesicles Necrotic eschar (Ulcer with a black center) ✓ Systemic signs ✓ Painful lymphadenopathy ✓ Massive edema Gastrointestinal anthrax Contaminated raw meat Clinical symptoms are determined by the site of the infection Upper intestinal tract Ulcers form in mouth or esophagus Leading to regional lymphadenopathy Edema, & sepsis Cecum or terminal ileum Nausea, vomiting, Malaise Rapidly progress to systemic disease Inhalation anthrax 16 Inhalation of spore-containing dust (animal hair or hides ) Incubation period is prolonged (2 months or more) During latent period spores can remain latent in nasal passages or reach lower airways Inhalation anthrax The initial clinical symptoms Nonspecific Fever, Myalgias, Nonproductive cough, Malaise The second stage of disease Fever, Edema, Massive enlargement of mediastinal lymph nodes, Respiratory failure, Sepsis Pneumonia (rarely develops) Meningeal symptoms (half of patients) Laboratory Diagnosis Microscopic morphology Organisms present in wounds, involved lymph nodes, and blood. Organisms can be seen when peripheral blood is Gram stained Laboratory Diagnosis Microscopic morphology Long, thin, gram-positive rods arranged singly or in long chain Organisms present in wounds, involved lymp nodes, blood Spores are not observed in clinical specimens Capsule of B. anthracis is produced in vivo Special spore stain Laboratory Diagnosis Colonial morphology Nonhemolytic Grow rapidly Firmly adherent to the agar "medusa head” Epidemiology Anthrax is primarily a disease of herbivores; humans are infected through exposure to contaminated animals or animal products. The disease is a serious problem in countries where animal vaccination is not practiced or is impractical Treatment, Prevention, Control Although penicillin was the drug of choice for B. anthracis Resistance to Penicillin Sulfonamides Extended-spectrum cephalosporins has been observed The current empiric treatment recommendation is use of ciprofloxacin or doxycycline combined with one or two additional antibiotics (e.g., rifampin, vancomycin, penicillin, imipenem, clindamycin, clarithromycin) Treatment, Prevention, Control Control of animal disease ✓ Vaccination of animal herds in endemic regions and burning of animals that die of anthrax Vaccination has also been used to protect 1- Animals 2- People who live in endemic areas 3- People who work with animal products 4- Military personnel Bacillus cereus Bacillus cereus Spore-forming, motile gram-positive rods Opportunistic pathogens Gastroenteritis Ocular infections Intravenous catheter-related sepsis Rare cases of severe pneumonia Gastroenteritis Bacillus cereus Food Poisoning Emetic Form Diarrheal Form Implicated Food Rice Meat, vegetables Incubation period (h) < 6 (mean, 2) > 6 (mean, 9) Vomiting, nausea, Diarrhea, nausea Symptoms abdominal cramps abdominal cramps Duration (h) 8-10 (mean, 9) 20-36 (mean, 24) Enterotoxin Heat-stable Heat-labile The mechanism of cAMP action - E. coli, V. cholerae Ocular infections After traumatic, penetrating injuries of the eye with a soil contaminated object Necrotic toxin (a heat-labile enterotoxin) Cereolysin (a potent hemolysin) Phospholipase C (a potent lecithinase) ✓ Rapid destruction of the eye infections results from the interaction of these toxins ✓ Is a rapidly aggressive disease that almost results in complete eye loss within 48 hours of the injury Other common infections ✓Intravenous catheter and Central nervous system shunt infections ✓Endocarditis (most common in drug abusers) One rare disease of B. cereus Severe pneumonia (Immunosuppressed patients) ▪ The strains contained B. anthracis pXO1 toxin genes ▪ Transferring B. anthracis virulence genes into the ubiquitous B. cereus Laboratory Diagnosis B. cereus gastroenteritis ▪ Are diagnosed by epidemiologic criteria ▪ The implicated food (rice, meat, vegetables) must be cultured for confirmation of the existence of foodborne disease. Treatment Gastroenteritis Symptomatic treatment is adequate. Other Bacillus infections Treatment is complicated Penicillins and cephalosporins are ineffective (B. cereus carries genes for resistance to penicillins and cephalosporins). Vancomycin, clindamycin, ciprofloxacin, and gentamicin can be used Eye infections must be treated rapidly Anaerobic Gram-Negative Bacteria Learning Objective What are the most likely anaerobic bacteria in this infection? What infections are typically caused by Bacteroides fragilis? Which antibiotics are usually active against B. fragilis? What are the important points in diagnosing anaerobic infections? Anaerobic Gram-Negative Bacteria Most important gram-negative anaerobes colonize human Upper respiratory Gastrointestinal tracts Genitourinary tracts Bacteroides Fusobacterium Parabacteroides Porphyromonas Prevotella Veillonella (cocci ) Physiology & Structure Very small or elongated Stain weakly with the Gram stain Bacteroides fragilis Gram-negative cell wall surrounded by a polysaccharide capsule LPS has little or no endotoxin activity Pathogenesis Capsule Fimbriae - can adhere to epithelial cells and extracellular molecules Succinic acid - The short chain fatty acids produced during anaerobic metabolism inhibit phagocytosis and intracellular killing IgA, IgM, IgG proteases ✓Tolerate exposure to oxygenSOD Catalase ✓Toxin Enterotoxigenic toxin B. fragilis (BFT) -a heat-labile zinc metalloprotease toxin Clinical Diseases Respiratory Tract Infections ~ half of the chronic infections of the sinuses & ears & all periodontal infections involve mixtures of gram-negative anaerobes ✓ Prevotella ✓ Porphyromonas ✓ Fusobacterium ✓ Non-fragilis Bacteroides Clinical Diseases Brain Abscess Anaerobic infections of the brain are typically associated with a history of chronic sinusitis or otitis Prevotella Porphyromonas Fusobacterium Peptostreptococcus Multiple abscesses are present Clinical Diseases Intraabdominal Infections B. fragilis , most common organism Gastroenteritis Strains of enterotoxin-producing B. fragilis Self-limited watery diarrhea In children younger than 5 years Clinical Diseases Gynecologic Infections ✓ Infections of the female genital tract (e.g., pelvic inflammatory disease, abscesses, endometritis) ✓ Mixtures of anaerobes Most important Prevotella B. fragilis is commonly responsible for abscess formation. Clinical Diseases Skin & soft Tissue Infections Most common organism is B. fragilis Bacteremia ✓ less than 5 % of all clinically significant cases of bacteremia ✓ B. fragilis is most commonly isolated in blood cultures Are not part of the normal flora of the skin they can be introduced by a bite or through contamination of a traumatized surface. Epidemiology Colonize human body in large numbers Prevent colonization by pathogenic organisms from exogenous sources, Digestion of food, Stimulate host immunity Disease These normal protective organisms produce disease when they Move from their endogenous homes to normally sterile sites Endogenous infections are polymicrobial Laboratory diagnosis Microscopy Bacteria may stain faintly and irregularly pleomorphic rods Culture Most endogenous infections then collect specimens are not contaminated with the normal bacteria Drying causes significant bacterial loss then Specimens should also be kept in a moist environment Polymicrobial infections & different organisms present Require long incubation (only Bacteroides grow rapidly ) Treatment Antibiotic therapy combined with surgical intervention Many species produce β-lactamases Then resistant to penicillin & many cephalosporins Metronidazole Carbapenems (imipenem, meropenem), β-lactam–β-lactamase inhibitors (piperacillin tazobactam) Prophylactic treatment with antibiotics Thank you for your attention