L14 Blood stream infections (1).pdf

Level 2 Semester 3 Module (Blood and Lymphatic system BMS201)  Lecture Title Blood Stream Infections (BSI)  Instructor information Contact: Professor Doctor/ Mohammed Mahmoud El-Naggar Department. Medical Microbiology and Immun...

Level 2 Semester 3 Module (Blood and Lymphatic system BMS201)  Lecture Title Blood Stream Infections (BSI)  Instructor information Contact: Professor Doctor/ Mohammed Mahmoud El-Naggar Department. Medical Microbiology and Immunology Official email: [email protected] Mobile (optional): 01126625177 Academic hours:  Sunday : 10:00-12:00 AM  Learning outcomes By the end of this lecture student will be able to: 1. Distinguish terms of blood stream infection; bacteremia, Septicemia and toxemia 2. Classify bacteremia and enumerate associated specific organisms. 3. Discuss the methods for the detection of bacteremia 4. Identify the characters of Staphylococci and laboratory diagnosis of Staphylococcal infections.  Lecture Outline Definitions: blood stream infections, bacteremia, toxemia. Classification and Diagnosis of bacteremia Characters of Staphylococci and laboratory diagnosis of Staphylococcal infections.  Case scenario, Clinical Correlate, Practice points - A young female aged 17 years usually use tampons, admitted to hospital with fever, vomiting, diarrhea, desquamation of skin & hypotension. Doctors were studying if she eats some food but the diagnosis was not food poisoning. - What is your probable diagnosis for this case? - Name the product responsible for this symptoms?  Terms Bacteremia Presence of viable bacteria in the blood, irrespective of clinical symptoms Septicemia Septicemia is the presence and multiplication of bacteria in the blood (blood poisoning) Sepsis A life threatening organ dysfunction caused by a dysregulated host response to infection. Septic shock Subset of sepsis in which profound circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than with sepsis alone. Toxemia Bacteria remain fixed at a site of infection but release toxins into the blood Viremia Presence of virus in the blood fungemia Presence of fungi in the blood  Classification of BSI Classification by Site of Origin Classification by Place of Acquisition Classification by Causative Agent Classification by Duration  Classification by Site of Origin Primary BSI: A laboratory confirmed BSI that is not secondary to an infection at another body site. Secondary BSI: BSI that is seeded from a site specific infection at another body site. such as the lung in patients with pneumonia.  Classification by Place of Acquisition Community-acquired BSI – Onset of symptoms within the first 48 h after admission Nosocomial BSI – Signs and symptoms detected after 48 hrs of admission  Classification by Duration Transient bacteremia: Manipulation/Surgery in infected/colonized area Intermittent bacteremia: Abdominal/Pelvic abscess Continuous bacteremia: Endocarditis/Intravascular infections/ First week of Typhoid , Brucellosis  Classification of Bacteremia by Causative Agent Gram-Positive Organisms Gram-Negative Organisms Staphylococcus Escherichia coli Staphylococcus aureus Klebsiella pneumoniae Staphylococcus epidermidis Enterobacter Streptococcus Pseudomonas aeruginosa Enterococcus Brucella Streptococcus pneumoniae Salmonella Streptococcus pyogenes N. meningitidis Streptococcus viridans Bacteroides fragilis Anaerobic Streptococci Listeria monocytogenes  Methods for detection of bacteremia BLOOD CULTURE The primary means for establishing a diagnosis of sepsis is by blood culture. Molecular diagnosis PCR  There are 3 species of Staphylococci S. aureus: pathogenic and is responsible for most of the Staphylococcal infections. S. epidermidis: members of the normal flora of skin and mucous membranes and can cause disease. S. saprophyticus: non-pathogenic  Classification Coagulase positive: only S aureus. Coagulase negative: all other species.  Staphylococcus aureus Gram positive cocci arranged in clusters No spore non motile. form microcapsule, Slime layer may be produced by other species. Staphylococci in culture. Gram stain. Gram stain of Staphylococcus aureus in pus  Culture characters facultative anaerobes. Optimum temperature: 37 C Normal atmospheric Co2. Media: »Ordinary media, Produce golden yellow endopigment. »blood agar ,Complete hemolysis »Mannitol salt agar (selective medium as mannitol inhibits other normal flora)  Enzymes and toxins a- Enzymes Coagulase and clumping factor Coagulase is an extracellular protein which binds to prothrombin →its activation to thrombin →conversion of fibrinogen to fibrin →coat the bacterial cell with fibrin , so interfere of opsonization & phagocytosis. Staphylokinase causes lyses of fibrin. Catalase : inactivate toxic hydrogen peroxide within phagocytic cells that enhance staph survival in phagocytes. Other enzymes: protease , lipase, DNase  b- Toxins 1- Membrane-damaging toxins: as haemolysins and leukocidin 2-Enterotoxins 6 antigenic types (A, B, C, D, E and G) Heat stable ,resist boiling for 30 minutes. Resist the action of gut enzymes (acid stable). Cause food poisoning when ingested. Cause toxic shock syndrome. 3 - Toxic shock syndrome toxin (TSST-1) causing toxic shock syndrome. 4 - Epidermolytic (exfoliative) toxin Causes scalded skin syndrome in neonates.  Cell wall associated proteins and polymers 1-Capsular polysaccharide: inhibits phagocytosis. 2- Protein A. Major protein in cell wall. Binds to Fc portion of IgG so inhibits opsonization.  DISEASES CAUSED BY S.aureus A) Suppurative (pus-forming) Skin lesions : Impetigo, folliculitis, boils & styes. Invasive infections: Pneumonia, meningitis, urinary tract infections , …etc.  B) Toxogenic diseases 1.Scalded skin syndrome Affecting neonates. Due to exofoliative toxin. Results in widespread blistering & loss of the epidermis 2.Food poisoning (Enterotoxins) Food: diary milk products. Incubation period: 1-6 hours. Clinical picture : nausea, vomiting and diarrhea, but no fever. 3.Toxic shock syndrome (TSS ) Occurs in young females who use tampons Clinical picture: fever, vomiting, diarrhea, desquamation of skin & hypotension.  LABORATORY DIAGNOSIS OF DISEASES CAUSED BY S. aureus Specimen collection Pus aspiration in pyogenic lesions. Biopsy Blood culture in BSI sputum in respiratory infection Cerebrospinal fluid in meningitis. urine in urinary tract infection. Food, vomit or faeces from food poisoning.  1- microscopic examination 1-Gram stain gram positive. 2-Morphology Cocci (spherical). 3-Arrangement Grape like clusters No spore non motile. Microcapsule  2- Culture a) Culture requirements: Facultative anaerobes, optimum temperature: 37⁰C., normal atmospheric CO2. b) Culture media: – Ordinary media: S. aureus produce golden yellow endopigments. – Enriched media: S. aureus causes beta-hemolysis on blood agar – Selective media: mannitol salt agar, where S. aureus ferments mannitol and salt inhibits other normal flora. S. aureus  Golden yellow endopigment Selective media: Mannitol salt agar (S. aureus  ferment Mannitol  yellow  3- Biochemical reactions All staphylococci are catalase positive. – S. aureus is: Catalase: positive Coagulase: positive Dnase: positive ferment mannitol.  Biochemical tests -Catalase test: Is used to differentiate between staphylococci (catalase +ve) and streptococci (catalase –ve.)  -DNase TEST Deoxyribonucleic Acid enables the detection of DNase that depolymerize DNA. A zone of clearing around the spot or streak indicates DNase activity. -Coagulase test is used to differentiate Staphylococcus aureus from coagulase-negative staphylococci. coagulase fibrinogen fibrin (clot formation)  The term MRSA refers to methicillin resistance Staphylococci  Most methicillin-resistant strains are also multiple resistant.  can be treated with vancomycin. Coagulase Negative Staphyloccoci S. epidermedis is an inhabitant of the skin. Non-pathogenic May be a pathogen in the hospital environment , causing nosocomial bacteremia, endocarditis& peritonitis  S. saprophyticus Is a common cause of urinary tract infection in young females Novobiocin R  Staphylococcus epidermidis Staphylococcus saprophyticus No hemolysis (gamma reaction). No hemolysis (gamma reaction) sensitive to the antibiotic novobiocin resistant to the antibiotic novobiocin as shown by the zone of inhibition  Differences between staphylococcal species Test S.aureus S.epidermidis S.saprophyti Coaguolase + - - DNase + - - Mannitol + - - Protein A + - - Exotoxins + - - Haemolysin + - - novobiocin Resistance - - +  Case scenario, Clinical Correlate, Practice points - A young female aged 17 years usually use tampons, admitted to hospital with fever, vomiting, diarrhea, desquamation of skin & hypotension. Doctors were studying if she eats some food but the diagnosis was not food poisoning. - What is your probable diagnosis for this case? - Name the product responsible for this symptoms? - Scalded skin syndrome is caused by: a. Neisseria gonorrhea b. Staphylococcus aureus c. Streptococcus pyogens d. Group B Streptococci. e. streptococcus pneumonie - Blood stream infection means: a. Presence of virus in the blood. b. Presence of viable bacteria in the blood. c. Presence official in the blood. d. Presence of toxins in the blood e. Growth of microorganism from a blood culture from a patient with clinical signs of infection - The differentiating character of S. Aureus and S. Saprophyticus is: a. inulin fermentation b. grow on blood agar c. Novobiocin resistance d. grow on ordinary medium e. catalase test  References or further readings Brooks, G. F., Jawetz, E., Melnick, J. L., & Adelberg, E. A. (2013). Jawetz, Melnick, & Adelberg's medical microbiology. New York: McGraw Hill Medical. Topley and Wilson’s Microbiology and Microbial Infections: 10th edition.