Medical Microbiology Lecture 1 PDF

Faculty of Pharmacy – Ahram Canadian University Vision and Mission Vision: Leadership in the pharmaceutical field on the national level with international recognition of excellence. Mission: The Faculty of Pharmacy - Ahram Canadian University, is committed to provide a...

Faculty of Pharmacy – Ahram Canadian University Vision and Mission Vision: Leadership in the pharmaceutical field on the national level with international recognition of excellence. Mission: The Faculty of Pharmacy - Ahram Canadian University, is committed to provide an up-to- date learning environment within a framework of advanced programs that enable the graduate to acquire professional ethics and have the competencies required for the job market. The Faculty, through distinguished calibers, supports effective collaboration with the community and encourages scientific research.  Medical Microbiology Lecture-1 Microbiology and Immunology Department  Introduction Micro-organisms can be multicellular, unicellular or acellular. Some microbes are ‘pathogenic’ which means that they have the ability to cause disease. Whilst bacteria and viruses cause the greatest number of healthcare associated infections. Environmental survival times for various common pathogens can range from a few hours to months or even years. Different microbial classes vary in their susceptibility to chemical disinfectants.  Terminology A pathogen: is a micro-organism that has the potential to cause disease. An infection: is the invasion and multiplication of pathogenic microbes in an individual or population. Disease: is when the infection causes damage to the individual’s vital functions or systems. An infection does not always result in disease. Virulence: The degree of pathogenicity. i.e. virulent or avirulent. Toxin production: Endotoxin, Exotoxin. Item Exotoxin Endotoxin 1 Secreted by living cell. Integral part of cell wall of Gram negative bacteria. 2 Found in both Gram positive Found only in Gram negative and Gram negative bacteria. Bacteria. 3 It is polypeptide. It is lipopolysaccharide complex. 4 Relatively unstable, heat Relatively stable, heat tolerant. labile (60°C). 5 Highly antigenic. Weakly immunogenic. 6 Highly toxic. Moderately toxic. 7 Specific in their action. Not specific. Endotoxins are part of the outer membrane of the cell wall of Gram negative bacteria. An exotoxin is a toxin secreted by bacteria; G+ or G-  CLINICAL MICROBIOLOGY Bacteriology Mycology Virology  Bacteriology Gram Gram Acid Fast Other Positive negative bacilli Types Cocci Rods 1- Staphylococci 2- Streptococci Non spore Forming Spore forming Diphtheria Listeria Aerobic Anaerobic Bacillus Clostridium  Staphylococci Morphology: Gram-positive cocci arranged in grape-like irregular clusters (bunches), facultative anaerobe. All are catalase positive (it is used to differentiate between Staphylococci (+ve) and Streptococci (-ve). Staphylococci are classified according to coagulase production into: 1. Coagulase positive: Staphylococcus aureus (S. aureus). 2. Coagulase negative (CoNS): Staphylococcus epidermidis and Staphylococcus saprophyticus. The enzyme, catalase, is produced by bacteria that respire using oxygen, and protects them from the toxic by-products of oxygen metabolism. Coagulase is a protein enzyme produced by several microorganisms that enables the conversion of fibrinogen to fibrin.  S. aureus S. epidermidis S. saprophyticus Pathogenicity Pathogenic Opportunistic Opportunistic pathogen pathogen Coagulase Enzyme + - - Mannitol + - - fermentation Blood hemolysis + ꞵ-hemolytic non-hemolytic non-hemolytic Growth in 9% NaCl + - - Novobiocin Sensitive Sensitive Resistant sensitivity test  1. Staphylococcus aureus Transmission: It is a normal flora in (skin and nose) where 20-50% of humans are carriers. It is also present in the environment e.g. clothing, bed linens. Virulence factors: I. Invasive factors: a) Adherence factors: Protein A and Clumping factor (Bound coagulase). b) Enzymes: Coagulase enzyme, Staphylokinase and DNase. II. Toxins: a) Super antigen exotoxins b) Other exotoxin: Virulence factors: I. Invasive factors: a) Adherence factors: ▪ Protein A: binds to the Fc portion of IgG at the complement-binding site so, prevent complement activation (inhibition of opsonization and protection of the organism from phagocytosis). ▪ Clumping factor (Bound coagulase). It converts fibrinogen into fibrin, which gets deposited on the cell surface rendering the organism resistant to phagocytosis. b) Enzymes: 1. Coagulase enzyme (free coagulase): Convert fibrinogen to fibrin which deposit on Staphylococcus surface so protect microorganism from phagocytosis. 2. Staphylokinase: fibrinolysin. 3. DNase: depolymerizes DNA in exudates or necrotic tissue. II. Toxins: a) Super antigen exotoxins (non-specific stimulation of T cells): A. Exfoliative toxin: Cause skin desquamation which resulted in SSSS (Staphylococcus Scalded Skin Syndrome). B. TSST (Toxic Shock Syndrome Toxin): Cause fever, hypotension and rash. C. Enterotoxin (6 heat stable toxins): Cause food poisoning (vomiting – diarrhea). b) Other exotoxin: Leukocidin: kill WBCs. Cytolytic exotoxin (hemolysin): Toxic to various cells and RBCs so causing necrosis and haemolysis.  Pathogenesis I. Invasive infections (Suppurative diseases): 1) Localized superficial skin infections with pus (pyogenic) e.g. Folliculitis, boils, carbuncles and abscesses. 2) Localized deep infections e.g. Arthritis, osteomyelitis, acute endocarditis. 3) Bacteremia and septicemia. Folliculitis Furuncle Carbuncle Scalded Skin Syndrome 18 II. Diseases due to toxin production: 1) SSS "Scalded Skin Syndrome": It is characterized by skin desquamation and generalized bullous formation. 2) TSS "Toxic Shock Syndrome": It is predominant in menstruating females who are using tampons. It is characterized by fever, skin desquamation (1 – 2 weeks later) and hypotension ending in shock with multisystem organ failure. 3) Food poisoning: ▪ It is a self-limiting disease (rapid recovery within 8 hours). ▪ Occurs following ingestion of preformed enterotoxin in contaminated food. ▪ The organism reaches the food from the hands or nose of Staphylococcus aureus shedders (nasal carriers or cases). ▪ Foods most commonly involved are carbohydrates as milk, milk products, cakes and pastry. ▪ Incubation period is short (1-6 hours). ▪ Abdominal colic, nausea, vomiting but without fever. III) Nosocomial infections = hospital acquired infections (due to use catheters and sutures inside hospitals). IV) Bacteremia and septicemia.  Laboratory diagnosis A- Specimen: Depends upon the site of infection: Pus from abscesses or wounds; blood for blood culture...etc. B- Microscopical Examination: Gram positive cocci, Non-motile, non- capsulated and non-spore forming. (3 non). C- Culture media: i. Nutrient agar: produces golden yellow colonies (endopigment) ii. Blood agar: produces beta hemolytic colonies iii. Mannitol salt agar (MSA)  Laboratory diagnosis D- Biochemical reactions: a- Catalase test. b- Coagulase test. c- DNase test. d- Phosphatase test. E- Typing methods: - Phage Typing  Treatment ❑Wound drainage: If you have a skin infection, an incision is made into the sore to drain fluid that has collected there. ❑Antibiotics: 1. Penicillin 2. If resistance to penicillin, Use Methicillin or Oxacillin 3. A combination therapy with a penicillinase-resistant penicillin or cephalosporin and clindamycin or a quinolone (in case the organism is methicillin-sensitive S. aureus [MSSA]). Others suggest use of clindamycin, trimethoprim-sulfamethoxazole (TMP-SMX), rifampin, doxycycline, or a quinolone. 25  Treatment 4. Because community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) causes more than one half of all staphylococcal infections. 5. Incase of MRSA infection: vancomycin or teicoplanin. 6. If resistance to vancomycin (VRSA), then Use Streptogramins and Linezolid are recommended. 7. For topical infection: muprocin can be used. 26  A Case of Staphylococcus aureus Enterocolitis In the 1950s and 1960s, S. aureus was implicated as a major pathogen in postoperative and antibiotic- associated enterocolitis. A case of a patient with hemorrhagic enterocolitis who was initially suspected of having inflammatory bowel disease, but, based upon the diagnostic evaluation, was found to have S. aureus enterocolitis. A 49-year-old male hospital plumber with a history of hemorrhoids presented to an outside hospital with abdominal cramps and diarrhea. He was diagnosed with a gastrointestinal infection and was started on levofloxacin, metronidazole, and proton pump inhibitor therapy. The patient was discharged 2 days later but returned within 24 hours with worsened symptoms and bloody diarrhea. 27  Computed tomography (CT) scan revealed thickening of the duodenum and jejunum, and enteroscopy revealed an ulcerated duodenum and jejunum with necrosis. Stool microscopic examination and culture were positive for many polymorphonuclear neutrophils and S. aureus. Stool culture was negative for Camplobacter, Shigella, Salmonella, and Yersinia. The patient was started on intravenous fluids and continued on fluoroquinolone, metronidazole, and proton pump inhibitor therapy. 28  Exploratory laparotomy revealed a toxic megacolon, and a gram stain from the surgical specimens revealed gram-positive cocci in clusters. Histo-pathology from the colon and ileum resections showed chronic active colitis with cryptitis and crypt abscesses, focal mucosal inflammation and transmural acute inflammation, and ulceration and necrosis. Postoperatively, the patient's symptoms resolved. He was discharged without antibiotic therapy and remained in clinical and endoscopic remission at the 6-and 12-month follow-up visits. 29  A Case of Staphylococcus aureus native mitral valve endocarditis associated with bed bug bites Staphylococcus aureus is a leading cause of community acquired bacteremia and infective endocarditis. S. aureus is a part of the normal skin flora in approximately one third of the human population. Infective endocarditis due to S. aureus can cause several complications and is associated with increased mortality. 30  A 48-year-old female with no significant medical history presented with S. aureus bacteremia and native mitral valve endocarditis. Multiple cutaneous skin lesions were identified, which she reported were due to recent bed bug bites. No source of infection was found except for the skin lesions. Her hospital course was complicated by pulmonary and cerebral septic emboli, left pleural empyema, and acute renal injury. We suspected the bed bug skin bites were the most likely source of bacteremia. 31  Test yourself 1. Compare between Exotoxin and Endotoxin. 2. Compare between Staphylococcus aureus and Staphylococcus epidermidis. 3. Toxins produced by Staphylococcus aureus and their role in pathogenicity. 4. Laboratory diagnosis of Staphylococcus aureus. 5. Treatment of Staphylococcus aureus. 6. Compare between food poisoning caused by Staphylococcus aureus and........... etc.