Gram-Positive Bacilli: Anthrax and Corynebacterium Diphtheriae PDF

Gram-Positive Bacilli: Anthrax Anthrax and Corynebacterium Corynebacterium Diphtheriae Diphtheriae by Heba Rashed  Characteristics of Gram-Positive Bacilli Thick Peptidoglycan Layer Capsule Formation Spore Formation Metachromatic Granules G...

Gram-Positive Bacilli: Anthrax Anthrax and Corynebacterium Corynebacterium Diphtheriae Diphtheriae by Heba Rashed  Characteristics of Gram-Positive Bacilli Thick Peptidoglycan Layer Capsule Formation Spore Formation Metachromatic Granules Gram-positive bacteria Some species, like Bacillus Certain gram-positive Corynebacterium possess a thick anthracis, have a capsule, a bacteria, such as Bacillus diphtheriae, the causative peptidoglycan layer, which protective layer that helps species, are capable of agent of diphtheria, has retains the crystal violet stain them evade the host's forming endospores, characteristic during the Gram staining immune system. resistant structures that can metachromatic granules, procedure. survive harsh environmental which appear as dark- conditions. staining bodies within the cells.  Corynebacterium ▪ Some species are part of normal flora of skin and mm. ▪ Medically important species is Corynebacterium diphtheriae  Morphology ▪ Gram-positive bacilli ▪ Club-shaped ▪ Arranged at acute angles or parallel to each other (Chinese letters). ▪ Meta-chromatic granules. ▪ Non-spore forming Methylene blue stain: Beaded appearance Meta-chromatic granules.  Culture Characters ▪ Aerobic. ▪ Growth on: 1. Blood agar 2. Loeffler’s serum: Best morphology 3. Blood tellurite agar: Selective & differential Grey to black colonies  Virulence factors Diphtheria Exotoxin  Disease: Diphtheria ▪ Upper respiratory tract infection. ▪ Transmitted by droplets. ▪ Characterized by: ▪ 1- Local pseudomembrane. ▪ 2- Toxemia. ▪ Complications: ▪ Airway obstruction ▪ Toxic myocarditis and heart failure ▪ Nerve paralysis  Diagnosis Mainly clinical Laboratory confirmation: A- Specimen: Throat swab from the pseudomembrane.  B- Direct Detection: Microscopic examination (Gram stain): Gram-positive bacilli Chinese letters appearance  B- Direct Detection: Microscopic examination (Methylene Blue stain): Meta-chromatic granules  C- Cultivation: 1- Loeffler’s serum: Best morphology 2- Blood tellurite agar: grey/black colonies 3- Blood agar to exclude S. pyogenes D- Identification: Microscopic examination: 1- Gram stained smear: Gram-positive club-shaped bacilli (Chinese letters). 2- MB stained smear: showing meta-chromatic granules.  The isolated organism is Corynebacterium diphtheriae Is it Toxigenic or Not?  E- Toxigenicity Tests: a) Elek’s test: most common assay. b) PCR: detection of toxin gene. c) ELISA: detection of toxin from culture.  Elek’s test: An antigen-antibody reaction in which the Ag is soluble “Precipitation”. Elek’s Test  Diphtheroids Corynebacteria that resemble C.diphtheriae in morphology. They are mainly commensals. It is normal flora of the mucous membrane of the throat, skin and respiratory tract. Gram-positive bacilli, Non–spore-forming , Non motile arranged in angles or in palisade Diseases caused by Diphtheroid 1. Urinary tract infection 2. Bacteraemia 3. Osteomylitis Listeria  Listeria monocytogenes Microscopic examination: Gram-positive rods (coccobacilli) Listeria resembles Corynebacteria in morphology but is MOTILE.  Morphology & Culture ❑Gram positive bacilli arranged in short chain ❑Non- capsulated ❑ Motile ❑ Non- spore forming ❑Listeria is cold-tolerant and can grow in refrigerated drink and food  Diseases Abortion, premature delivery or sepsis during the peripartum period. Neonatal meningitis Septicaemia and meningitis (in immunocompromised adults). Food poisoning (dairy products or undercooked meat)  Neonatal meningitis ▪ Meningitis caused by Listeria is almost always seen in neonates. ▪ Causes of Neonatal Meningitis: 1. Group B Streptococci 2. E. coli K1 3. Listeria monocytogenes  Case A one month old girl was admitted to hospital with acute meningitis. The Gram stain of CSF revealed Gram-positive short rods. What is the cause of neonatal meningitis? a. N. meningitidis, group A b. N. meningitidis, group C c. Listeria monocytogenes d. S. pneumoniae  How did the mother contract it? ▪ Listeriosis is a food-borne infection. ▪ Listeria resists drying, heating and freezing without forming spores. ▪ Commonly contaminated food items: 1. Dairy products (esp. unpasteurized milk and soft cheeses). 2. Undercooked meat (chicken, hot-dogs). 3. Refrigerated food. Review Questions 1- C.diphtheriae is cultured on: a- Nutrient agar. b- Chocolate agar. c- Loffler’s serum. d- Lowenstein-Jensen medium. e- MacConkey’s agar. c- Loffler’s serum. 2- Blood tellurite agar is a(n): a- Enriched medium b- Enrichment medium c- Simple medium d- Selective and differential medium e- Indicator medium only – d- Selective and differential medium 3- Which of the following is a toxigenicity test for C.diphtheriae ? a- Elek’s test b- Coagulase c- Catalase test d- Culture on blood tellurite e- ELISA test for antibody detection a- Elek’s test 4- C. diphtheriae has the following morphology: a- Gram negative cocci arranged in pairs b- Gram positive cocci arranged in chains c- Gram positive club-shaped bacilli d- Gram positive cocci in clusters e- Gram positive capsulated diplococci  Gram positive club-shaped bacilli 6- A 1-week old newborn develops meningitis. Short gram-positive rods are isolated. The mother had eaten unpasteurized cheese during pregnancy. What is the most likely etiological diagnosis? a- C. diphtheriae. b- S. pyogenes. c- L. monocytogenes. d- S. pneumoniae. e- S. agalactiae – c- L. monocytogenes. THANK YOU  Characteristics of Gram-Positive Bacilli Thick Peptidoglycan Layer Capsule Formation Spore Formation Metachromatic Granules Layer Gram-positive bacteria Some species, like Bacillus Certain gram-positive Corynebacterium possess a thick anthracis, have a capsule, a bacteria, such as Bacillus diphtheriae, the causative peptidoglycan layer, which protective layer that helps species, are capable of agent of diphtheria, has retains the crystal violet stain them evade the host's forming endospores, characteristic during the Gram staining immune system. resistant structures that can metachromatic granules, procedure. survive harsh environmental which appear as dark- conditions. staining bodies within the cells. This genus includes large aerobic, Gram positive , spore-forming bacilli that have Pathogenic : Bacillus anthracis, which causes diseases mainly in animals, but it can affect man and lead to anthrax Saprophytic : Anthracoids , which are widely spread in nature water, soil, and air). Some strains of Anthracoids are pathogenic such as B. cereus cause food poisoning Bacillus cereus is Gram positive bacilli , non-capsulated, motile, spore forming  Bacillus species Bacillus anthracis Bacillus cereus Bacillus anthracis is the causative agent of Bacillus cereus is a common foodborne anthrax, a serious infectious disease that pathogen that can cause food poisoning. can affect humans and animals. Anthrax is primarily a disease of It produces toxins that can cause vomiting, diarrhea, and other gastrointestinal herbivores, but it can be transmitted to symptoms. humans through contact with infected animals or their products. Bacillus anthracis: the Causative Agent of Anthrax Bacillus anthracis is a facultative anaerobic, Gram-positive, rod-shaped bacterium that forms spores. Anthrax is a zoonotic disease, meaning it can be transmitted from animals to humans. The bacterium is found in soil and can infect animals such as cattle, sheep, goats, and horses. Humans can contract anthrax through contact with infected animals, their products, or contaminated soil. Bacillus anthracis: the Causative Agent of Anthrax Bacillus anthracis is a facultative anaerobic, Gram- positive, rod-shaped bacterium that forms spores. Anthrax is a zoonotic disease, meaning it can be transmitted from animals to humans. Anthrax: Clinical Manifestations Cutaneous Anthrax Inhalation Anthrax Most common form. Begins as Rare but deadly. Flu-like a painless skin lesion that symptoms initially, followed by progresses into a black eschar. severe respiratory distress. Gastrointestinal Anthrax Injection Anthrax Results from ingesting Rare form associated with contaminated meat. Causes injection drug use. Symptoms severe abdominal pain, nausea, similar to cutaneous anthrax, and vomiting. but may spread quickly.  Anthrax: Diagnosis Clinical Presentation Microscopic Examination Anthrax diagnosis is often based on Gram staining reveals large, square- clinical signs and symptoms, ended, spore-forming bacilli, depending on the type of infection. confirming a presumptive diagnosis. Culture Serological Tests Isolation of Bacillus anthracis on Detection of specific antibodies blood agar or other suitable media against anthrax toxin can aid provides definitive identification. diagnosis, especially in cases of cutaneous anthrax. Potential Bioterrorism Concerns Anthrax Diphtheria Bacillus anthracis spores are highly stable and can Corynebacterium diphtheriae is a highly contagious survive for extended periods. bacteria. Anthrax can be weaponized and dispersed as an aerosol. The toxin produced by C. diphtheriae can cause severe illness and death.