Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Microbiology lec5


Published on

  • Be the first to comment

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>