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Microbiology lec5

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Microbiology lec5

  1. 1. Medical Microbiology Lecture 6 Dr. Saleh M Y OTH PhD Medical Molecular Biotechnology and Infectious Diseases 11/10/2010 IMS - MSU Systemic bactreiology
  2. 2. Streptococci and its Diseases Systemic bactreiology
  3. 3. Staphylococci <ul><li>Coagulase-negative staphylococcus; frequently involved in nosocomial and opportunistic infections </li></ul><ul><li>S. epidermidis – lives on skin and mucous membranes; endocarditis , bacteremia , UTI </li></ul><ul><li>- S. saprophyticus – infrequently lives on skin, intestine, vagina; UTI </li></ul>
  4. 4. Staphylococci are gram positive cocci arranged in grape like clusters. The genus Staphylococcus includes 3 species of medical importance; Staph. aureus, Staph. epidermidis and Staph. saprophyticus .
  5. 5. General Characteristics of the Staphylococci <ul><li>Common inhabitant of the skin and mucous membranes </li></ul><ul><li>Spherical cells arranged in irregular clusters </li></ul><ul><li>Gram-positive </li></ul><ul><li>Lack spores and flagella </li></ul><ul><li>May have capsule </li></ul>
  6. 6. Staphylococcus aureus morphology
  7. 7. S. aureus <ul><li>- Grows in large, round, opaque colonies </li></ul><ul><li>- Optimum temperature of 37 o C </li></ul><ul><li>- Facultative anaerobe </li></ul><ul><li>- Withstands high salt, extremes in pH, and high temperatures </li></ul><ul><li>- Produces many virulence factors </li></ul>
  8. 8. S. aureus <ul><li>Major human pathogen </li></ul><ul><li>Habitat - part of normal flora in some humans and animals </li></ul><ul><li>Source of organism - can be infected human host, carrier, fomite or environment </li></ul>
  9. 9. Natural history of disease <ul><li>Many neonates, children, adults -intermittently colonised by S. aureus </li></ul><ul><li>Usual sites; skin, nasopharynx, perineum </li></ul><ul><li>Breach in mucosal barriers; can enter underlying tissue </li></ul><ul><li>- Characteristic abscesses; Disease due to toxin production </li></ul>
  10. 10. Grouping for Clinical Purposes <ul><li>1. Coagulase positive Staphylococci </li></ul><ul><ul><li>- Staphylococcus aureus </li></ul></ul><ul><li>2. Coagulase negative Staphylococci </li></ul><ul><ul><li>- Staphylococcus epidermidis </li></ul></ul><ul><ul><li>- Staphylococcus saprophyticus </li></ul></ul>
  11. 11. Diseases <ul><li>- Due to direct effect of organism </li></ul><ul><ul><li>- Local lesions of skin </li></ul></ul><ul><ul><li>- Deep abscesses </li></ul></ul><ul><ul><li>- Systemic infections </li></ul></ul><ul><li>- Toxin mediated </li></ul><ul><ul><li>- Food poisoning </li></ul></ul><ul><ul><li>- toxic shock syndrome </li></ul></ul><ul><ul><li>- Scalded skin syndrome </li></ul></ul>
  12. 12. Factors predisposing to S. aureus infections <ul><li>Host factors </li></ul><ul><ul><li>- Breach in skin </li></ul></ul><ul><ul><li>- Chemotaxis defects </li></ul></ul><ul><ul><li>- Opsonisation defects </li></ul></ul><ul><ul><li>- Neutrophil functional defects </li></ul></ul><ul><ul><li>- Diabetes mellitus </li></ul></ul><ul><ul><li>- Presence of foreign bodies </li></ul></ul><ul><li>Pathogen Factors </li></ul><ul><ul><li>- Catalase (counteracts host defences) </li></ul></ul><ul><ul><li>- Coagulase </li></ul></ul><ul><ul><li>- Hyaluronidase </li></ul></ul><ul><ul><li>- Lipases (Imp. in disseminating infection) </li></ul></ul><ul><ul><li>- B lactasamase(ass. With antibiotic resistance) </li></ul></ul>
  13. 13. Skin Lesions <ul><li>- Boils تقرح وخراج </li></ul><ul><li>- Styes دمامل </li></ul><ul><li>- Furuncles (infection of hair follicle) </li></ul><ul><li>- Carbancles (infection of several hair follicles) </li></ul><ul><li>- Wound infections ( progressive appearance of swelling and pain in a surgical wound after about 2 days from the surgery) </li></ul><ul><li>- Impetigo (skin lesion with blisters that break and become covered with crusting exudate) </li></ul>
  14. 15. Deep abscessses <ul><li>- Can be single or multiple </li></ul><ul><li>- Breast abscess can occur in 1-3% of nursing mothers in puerperiem </li></ul><ul><li>- Can produce mild to severe disease </li></ul><ul><li>- Other sites - kidney, brain from septic foci in blood </li></ul>
  15. 16. Systemic Infections <ul><li>1. With obvious focus بؤرة متقرحة </li></ul><ul><ul><li>Osteomyelitis, septic arthritis </li></ul></ul><ul><li>2. No obvious focus </li></ul><ul><ul><ul><li>- heart (infective endocarditis) </li></ul></ul></ul><ul><ul><ul><li>- Brain (brain abscesses) </li></ul></ul></ul><ul><li>3. Ass. With predisposing factors </li></ul><ul><ul><li>- multiple abscesses, septicaemia(IV drug users) </li></ul></ul><ul><ul><li>- Staphylococcal pneumonia (Post viral) </li></ul></ul>
  16. 17. Toxin Mediated Diseases <ul><li>1. Staphylococcal food poisoning </li></ul><ul><ul><li>- Due to production of entero toxins </li></ul></ul><ul><ul><li>- heat stable entero toxin acts on gut </li></ul></ul><ul><ul><li>- produces severe vomiting following a very short incubation period </li></ul></ul><ul><ul><li>- Resolves on its own within about 24 hours </li></ul></ul>
  17. 18. Toxic shock syndrome <ul><li>- High fever, diarrhoea, shock and erythematous skin rash which desquamate </li></ul><ul><li>- Mediated via ‘toxic shock syndrome toxin’ </li></ul><ul><li>- 10% mortality rate </li></ul><ul><li>- Described in two groups of patients </li></ul><ul><ul><li>- Ass. With young women using tampones during menstruation </li></ul></ul><ul><ul><li>- Described in young children and men </li></ul></ul>
  18. 20. Scalded skin syndrome <ul><li>- Disease of young children </li></ul><ul><li>- Mediated through minor Staphylococcal infection by ‘epidermolytic toxin’ producing strains </li></ul><ul><li>- Mild erythema and blistering of skin followed by shedding of sheets of epidermis </li></ul><ul><li>- Children are otherwise healthy and most eventually recover </li></ul>
  19. 21. Virulence factors of S. aureus <ul><li>Enzymes : </li></ul><ul><li>- Coagulase; coagulates plasma and blood; produced by 97% of human isolates; diagnostic </li></ul><ul><li>- Hyaluronidase; digests connective tissue </li></ul><ul><li>- Staphylokinase; digests blood clots </li></ul><ul><li>- DNase; digests DNA </li></ul><ul><li>- Lipases; digest oils; enhances colonization on skin </li></ul><ul><li>- Penicillinase; inactivates penicillin </li></ul>
  20. 22. Virulence factors of S. aureus <ul><li>Toxins : </li></ul><ul><li>- Hemolysins ( α , β , γ , δ ); lyse red blood cells </li></ul><ul><li>- Leukocidin; lyses neutrophils and macrophages </li></ul><ul><li>- Enterotoxin; induce gastrointestinal distress </li></ul><ul><li>- Exfoliative toxin; separates the epidermis from the dermis </li></ul><ul><li>- Toxic shock syndrome toxin (TSST); induces fever, vomiting, shock, systemic organ damage </li></ul>
  21. 23. Epidemiology and Pathogenesis <ul><li>- Present in most environments frequented by humans </li></ul><ul><li>- Readily isolated from fomites </li></ul><ul><li>- Carriage rate for healthy adults is 20-60% </li></ul><ul><li>- Carriage is mostly in anterior nares, skin, nasopharynx, intestine </li></ul><ul><li>- Predisposition to infection include: poor hygiene and nutrition, tissue injury, pre-existing primary infection, diabetes, immunodeficiency </li></ul><ul><li>- Increase in community acquired methicillin resistance - MRSA </li></ul>
  22. 24. Staphylococcal Disease <ul><li>Range from localized to systemic </li></ul><ul><li>Localized cutaneous infections; invade skin through wounds, follicles, or glands </li></ul><ul><ul><li>- Folliculitis; superficial inflammation of hair follicle; usually resolved with no complications but can progress </li></ul></ul><ul><ul><li>- Furuncle; boil; inflammation of hair follicle or sebaceous gland progresses into abscess or pustule بثرة </li></ul></ul><ul><ul><li>- Carbuncle; larger and deeper lesion created by aggregation and interconnection of a cluster of furuncles </li></ul></ul><ul><ul><li>- Impetigo; bubble-like swellings that can break and peel away; most common in newborns </li></ul></ul>
  23. 25. Bullous impetigo
  24. 26. Cutaneous lesions of S. aureus
  25. 27. <ul><li>Systemic infections </li></ul><ul><ul><li>Osteomyelitis; infection is established in the metaphysis; abscess forms </li></ul></ul><ul><ul><li>- Bacteremia; primary origin is bacteria from another infected site or medical devices; endocarditis possible </li></ul></ul>
  26. 28. Staphylococcal osteomyelitis in a long bone
  27. 29. Staphylococcal Disease <ul><li>Toxigenic disease </li></ul><ul><ul><li>- Food intoxication – ingestion of heat stable enterotoxins; gastrointestinal distress </li></ul></ul><ul><ul><li>- Staphylococcal scalded skin syndrome – toxin induces bright red flush, blisters, then desquamation of the epidermis </li></ul></ul><ul><ul><li>- Toxic shock syndrome – toxemia leading to shock and organ failure </li></ul></ul>
  28. 30. Effects of staphylococcal toxins on skin
  29. 31. Toxic Shock Syndrome Toxin <ul><li>- Superantigen </li></ul><ul><li>- Non-specific binding of toxin to receptors triggers excessive immune response </li></ul>
  30. 32. TSS Symptoms <ul><li>- 8-12 h post infection </li></ul><ul><li>- Fever </li></ul><ul><li>- Susceptibility to Endotoxins </li></ul><ul><li>- Hypotension </li></ul><ul><li>- Diarrhea </li></ul><ul><li>- Multiple Organ System Failure </li></ul><ul><li>- Erythroderma (rash) </li></ul>
  31. 33. TSS Treatment <ul><li>- Clean any obvious wounds and remove any foreign bodies </li></ul><ul><li>- Prescription of appropriate antibiotics to eliminate bacteria </li></ul><ul><li>- Monitor and manage all other symptoms, e.g. administer IV fluids </li></ul><ul><li>- For severe cases, administer methylprednisone, a corticosteriod inhibitor of TNF-a synthesis </li></ul>
  32. 34. Identification of Staphylococcus in Samples <ul><li>Frequently isolated from pus, tissue exudates, sputum, urine, and blood </li></ul><ul><li>- Cultivation, catalase, biochemical testing, coagulase </li></ul>
  33. 35. Catalase test
  34. 36. Clinical Concerns and Treatment <ul><li>- 95% have penicillinase and are resistant to penicillin and ampicillin </li></ul><ul><li>- MRSA – methicillin-resistant S. aureus; carry multiple resistance </li></ul><ul><ul><li>- Some strains have resistance to all major drug groups except vancomycin </li></ul></ul><ul><li>- Abscesses have to be surgically perforated </li></ul><ul><li>- Systemic infections require intensive lengthy therapy </li></ul>
  35. 37. Prevention of Staphylococcal Infections <ul><li>- Universal precautions by healthcare providers to prevent nosocomial infections </li></ul><ul><li>- Hygiene and cleansing </li></ul>
  36. 38. Antibiotic sensitivity pattern <ul><li>- Very variable and not predictable </li></ul><ul><li>- Very important In Patient Management </li></ul><ul><li>- Mechanisms </li></ul><ul><ul><li>1. B lactamase production - plasmid mediated </li></ul></ul><ul><ul><ul><li>- Has made S. aureus resistant to penicillin group of antibiotics - 90% of S. aureus (Gp A) </li></ul></ul></ul><ul><ul><ul><li>- β - lactamase stable penicillins (cloxacillin, oxacillin, methicillin) used </li></ul></ul></ul><ul><ul><li>2. Alteration of penicillin binding proteins </li></ul></ul><ul><ul><ul><li>- (Chromosomal mediated) </li></ul></ul></ul><ul><ul><ul><li>- Has made S. aureus resistant to β - lactamase stable penicillins </li></ul></ul></ul><ul><ul><ul><li>- 10-20% S. aureus Gp (B) GH Colombo/THP resistant to all Penicillins and Cephalasporins) </li></ul></ul></ul><ul><ul><ul><li>- Vancomycin is the drug of choice </li></ul></ul></ul>
  37. 39. DIAGNOSIS <ul><li>1. In all pus forming lesions </li></ul><ul><ul><li>- Gram stain and culture of pus </li></ul></ul><ul><li>2. In all systemic infections </li></ul><ul><ul><li>- Blood culture </li></ul></ul><ul><li>3. In infections of other tissues </li></ul><ul><ul><li>- Culture of relevant tissue or exudate </li></ul></ul>
  38. 40. S. epidermidis <ul><li>Skin commensal </li></ul><ul><li>Has predilection for plastic material </li></ul><ul><li>Ass. With infection of IV lines, prosthetic heart valves, shunts </li></ul><ul><li>Causes urinary tract infection in cathetarised patients </li></ul><ul><li>- Treatment should be aided with ABST </li></ul>
  39. 41. S. saprophyticus <ul><li>Skin commensal </li></ul><ul><li>Imp. cause of UTI in sexually active young women. </li></ul><ul><li>- Usually sensitive to wide range of antibiotics </li></ul>

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