Microbiology Lecture Notes PDF

Dr/Ahmed Mostafa_Microbiology I G -ve Cocci Neisseria Neisseria are commensals of the upper respiratory tract, mouth, throat & pharynx and in vagina. Two highly pathogenic members: - 1. Neisseria...

Dr/Ahmed Mostafa_Microbiology I G -ve Cocci Neisseria Neisseria are commensals of the upper respiratory tract, mouth, throat & pharynx and in vagina. Two highly pathogenic members: - 1. Neisseria gonorrhea (Gonococcus) 2. Neisseria meningitidis (Meningococcus) Morphology: gram-negative cocci arranged in pairs, the pathogenic members occur intracellular in pus cells & extracellular. Cultural characters: - – It requires enriched media (heated blood agar) e.g. chocolate agar “Enriched” & Thayer Martin agar medium(MTM) “Selective” with 5-10% CO2. 1- Neisseria gonorrhea= Gonococcus Pathogenicity: 1- Venereal diseases: a. Male infection of mucus membrane of anterior urethra (Urethritis) with yellow creamy pus and painful urination, the chronic cases are asymptomatic. b. Female: endocervical infection causing vaginal discharge and 50% are asymptomatic. 2-Non venereal a. Ophthalmia neonatorum b. Vulvovaginitis c. Oral infection which varies from pharyngitis to painful erythema, ulceration of soft palate, gingival and buccal mucosa. Laboratory Diagnosis Specimen: urethral discharge, conjunctival discharge & pharyngeal swab. Urogenital gonorrhea can be diagnosed by testing urine or urethral discharge (for men), or endocervical or vaginal discharge (for women) using the very accurate test: 1-nucleic acid amplification testing (NAAT) 2-gonorrhea culture, which requires endocervical or urethral swab specimens. Gram stain: Neisseria are gram-ve cocci, capsulated and arranged in pairs found Intracellular “inside the pus cells of the inflammatory exudate-urethral discharge” and Extracellular. Treatment Penicillin. If resistant, Ciprofloxacin or streptomycin is recommended  Dr/Ahmed Mostafa_Microbiology I 2- Neisseria meningitis= Meningococcus Cause Epidemic Cerebrospinal Meningitis. Also, can cause pharyngitis and rarely myocarditis. It’s a droplet infection from case or carrier, the main harbor of the organism is in nasopharynx. Pathogenesis & disease Organism in nasopharynx to lymphatic then to-blood, to the meninges causing (meningococcemia) Which manifested by: fever, skin rash, stiffness in the neck, back pain, severe headache and projectile vomiting. Diagnosis: Specimen is cerebrospinal fluid (CSF) which is obtained by lumber puncture under complete aseptic precaution is subjected to: Direct examination: 1- CSF is examined microscopically by using Gram & Zeihl-Neelsen stain. 2- Latex to detect antigen in csf. 3- Culture on chocolate agar(enriched) & Thayer Martin agar media(selective). 4- blood culture. Treatment: 1- Penicillin G is the drug of choice. 2- Third – generation Cephalosporin is used in persons allergic to penicillin. 3- Chloramphenicol “Penicillin & chloramphenicol have antagonistic effect” Prevention & Control 1- Refampicin for 2 days to contacts. 2- Vaccination CDC recommends routine MenACWY vaccination for all teens at 11-12 years with booster dose at 16..  Dr/Ahmed Mostafa_Microbiology I Aerobic Spore-forming Gram-positive bacilli (Bacillus group) The most important pathogenic member in this genus is Bacillus anthracis. Most of other members are saprophytes in water, soil & air and are collectively termed anthracoids. Ø Of these, B. cereus and B. subtillis may act as opportunistic pathogens in debilitated persons in whom they cause bacteremia, meningitis, endocarditis or endophthalmitis. Ø Bacillus cereus causes food poisoning after consumption of cooked rice (Koshary) in which the spores grow profusely & produce enterotoxin. 1- Bacillus anthracis It causes anthrax (a disease of animals that can infect man in direct contact with infected animals). Clinical types are: Cutaneous anthrax (malignant pustule). Pneumonic anthrax (wool sorter disease) due to inhalation of spores. Intestinal anthrax due to ingestion of infected meat is rare. 2- Anthracoids They are saprophytes present in environment (soil & water): - 1. B. cereus which causes food poisoning à “Cooked rice (Koshary)” 2. Antibiotic producer e.g. polymyxin. 3. To test the efficiency of some sterilization procedures e.g.: a. Spores of B. stearothermophilus to test efficiency of the autoclave. b. Spores of B. subtilis to test ethylene oxide gas sterilizer. c. Spores of B. pumilis for ionizing irradiation.  Dr/Ahmed Mostafa_Microbiology I Aerobic Non-Spore forming Gram-positive bacilli Corynebacterium The genus Corynebacterium includes, important man pathogens and many commensals (diphteroids) found in upper respiratory tract, vagina, urethra and skin. These commensals are short gram positive bacilli arranged in angled pairs or parallel rows. Corynebacterium diphtheriae – The most pathogenic member of Corynebacterium. Morphology: – Gram +ve non spore forming slender bacilli have club shaped ends and contain metachromatic phosphate granules called volutin (which give green beaded appearance) by Methylene Blue stain. Culture: – On Loffler's Serum “Enriched with case” and Blood Tellurite “Selective with carrier”. Diphtheria exotoxin: – Lysogenic strains Only producing a powerful exotoxin. Diphtheria Disease – It is URT illness characterized by sore throat, low-grade fever & adherent pseudomembrane on pharynx, tonsils. – This is a serious infectious disease, affecting mainly children 5-15 years. Incubation Period: 2-5 days. Mode of transmission: Droplet infection from a case or carrier. It affects man only. Tonsillar or pharyngeal diphtheria is the commonest type. Clinical Pictures – Upper respiratory tract illness which is caused by droplet infection from case or carrier, characterized by sore throat, low-grade fever & adherent grey-black pseudo membrane covering the tonsils & pharynx.  Dr/Ahmed Mostafa_Microbiology I Pathogenesis – The organism multiplies locally on the mucosal surface of pharynx & tonsils. – Lysogenic strains produce exotoxin with local inflammation &necrosis of epithelial cells and formation of fibrin network, all form an adherent grey-black pharyngeal pseudo membrane. – An adherent grey-black pharyngeal pseudo membrane is formed & any attempt to remove it leads to bleeding. – The membrane and oedema may compress the respiratory airway leading to asphyxia. – The absorbed exotoxins through the membrane is carried by blood to distant organs with tropism for Cardiac, Neural and Renal cells causing degenerative changes. Laboratory Diagnosis 1) Direct smear with gram stain and methylene blue stain. 2) Culture on Loffler's serum and blood tellurite. 3) Elek's test for Toxigenic or Virulence tests: isolated organism from carrier should be tested for the production of the exotoxin. Treatment Antitoxin: started as soon as the diagnosis is suspected clinically, to neutralize free exotoxin secreted. Patient should be tested for hypersensitivity à to avoid sensitivity to horse serum, Cortisone and antihistamines for treatment of anaphylaxis must be available. Antibiotics: erythromycin and ampicillin for at least 7 days to eradicate the organism and stop further toxin production. Prevention and control 1. Active immunization: Diphtheria toxoid combined with that of Tetanus and Pertussis vaccine called DPT is given to infants at 2, 4, 6 months. At 18 months &before going to school, booster DT doses are also given every 10 years. 2. Passive immunization: antitoxic serum is given. 3. Antibiotic is given to close contacts.  Dr/Ahmed Mostafa_Microbiology I Anaerobic Spore forming Gram-positive bacilli “Clostridium” – Most of the members of this genus are saprophytic in soil and water. – Some are commensals in the intestine of Man & Animals. – They produce diseases through their toxins and enzymes. Pathogenic species are: 1. Cl. perfringens causing gas gangrene. 2. Cl. tetani which cause tetanus. 3. Cl. botulinum causing botulism (food poisoning). 4. Cl. difficile causing enterocolitis. Gas Gangrene – The commonest cause is Cl. perfringens. Virulence factors: 1- a Toxin (lecithinase) that cause membrane lysis 2- Collagenase and hyaluronidase help in spreading of infection. Pathogenesis – Massive accident, Contamination of the wound with soil in addition to: Presence of foreign body, local ischemia, atherosclerosis, diabetes and pyogenic infection (all are predisposing factors). – The wound Contaminated with soil containing the spores of Cl. perfringenes, they germinate, giving vegetative forms which produce their toxins & enzymes that spread infection to adjacent tissues and muscles (the glycogen in muscles) are fermented with production of large amount of gases that press on blood supply, more ischemia & more necrosis. – The affected area becomes tense, edematous, red and odorless. – Proteolytic clostridia (Cl. histoliticum) start the process of putrefaction of dead tissues, so becomes black with foul odor due to H2S production. – Tissue necrosis extends providing an opportunity for increased bacterial growth, sever toxemia & death. Laboratory Diagnosis – The specimen is taken from wound discharge then the following will be done: Gram stain shows large gram+ve bacilli. Culture on blood agar anaerobically. Treatment 1. Surgical debridement 2. Penicillin and metronidazole 3. Polyvalent anti gas gangrene serum. 4. Hyperbaric oxygen.  Dr/Ahmed Mostafa_Microbiology I Clostridium tetani C. tetani occurs in the intestine of man and domestic animals from their stool, It reach the soil. Ways of infection: 1-The disease follows injury in which the wound is contaminated with soil or dust in which spores are present. 2-Infection of umbilical stump due to badly sterilized cat-gut lead to tetanus neonatorum. Pathogenesis The spores vegetate, the organism multiply locally at the site of entry producing exotoxin (tetanospasmin) which spreads via blood to the spinal cord and affects the motor nerves to produce convulsion and muscle stiffness in the jaw leading to trismus (lock jaw), dysphasia, and finally spasm of most of the body's muscles. Laboratory Diagnosis: On clinical evidences. It is done only for confirmation. Treatment 1. Sedation and mechanical ventilation if needed. 2. Antitoxic serum: intravenous dripping of human serum to neutralize the toxin in the blood before it reaches the CNS. 3. Penicillin and metronidazole to kill the organism so stop further production of toxin. 4. Cleaning the wound and surgical debridement: The wound is left open and washed with H2O2. Immunization a. Passive immunization: Antitetanic serum is given SC or I.M. to patients with wounds contaminated with soil and foreign bodies or deep puncture wounds. b. Active immunization: 1- Formol –toxoid: ½ ml 6w - 6m - 6 years as booster dose. 2- D.P.T. vaccine (Diphtheria, Pertussis and Tetanus).