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STAPHYLOCOCCUS

STAPHYLOCOCCUS. Staphylococci are gram positive cocci, Occur in grape like clusters, In Greek; staphyle - Bunch of grapes Kokkus - Berry. CLASSIFICATION: A) Based on coagulase production: 1. Coagulase positive: Eg- S. aureus 2. Coagulase negative: Eg- S. epidermidis

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STAPHYLOCOCCUS

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  1. STAPHYLOCOCCUS .

  2. Staphylococci are gram positive cocci, • Occur in grape like clusters, • In Greek; staphyle -Bunch of grapes Kokkus - Berry

  3. CLASSIFICATION: A) Based on coagulase production: 1. Coagulase positive: Eg- S. aureus 2. Coagulase negative: Eg- S. epidermidis S. saprophyticus B) Based on pathogenicity: 1. Common pathogen: Eg- S. aureus 2. Opportunistic pathogens: Eg- S. epidermidis S. saprophyticus 3. Non pathogen: Eg- S. homonis

  4. STAPHYLOCOCCUSAUREUS MORPHOLOGY: • These are spherical cocci. • Approximately 1μm in diameter. • Arranged characteristically in grape like clusters. • They are non motile and non sporing. • A few strains possess capsules.

  5. CULTURE: Media used :- i) Non selective media: Nutrient agar, Blood agar, MacConkey’s agar. ii) Selective media: Salt-milk agar, Ludlam’s medium

  6. Cultural Characteristics: i) On nutrient agar- The colonies are large, circular, convex, smooth, shiny, opaque and easily emulsifiable. Most strains produce golden yellow pigments.

  7. ii) On MacConkey’s agar- The colonies are small & pink in colour. iii) On blood agar- Most strains produce β- haemolytic colonies.

  8. Biochemical reactions: 1) Catalase test- Positive.

  9. 2) Coagulase test- i) Slide coagulase test- Positive. ii) Tube coagulase test- Positive. SLIDE COAGULASE TEST TUBE COAGULASE TEST

  10. PATHOGENICITY: Source of infection: A) Exogenous: patients or carriers B) Endogenous: From colonized site Mode of transmission: A) Contact: direct or indirect( through fomites) B) Inhalation of air borne droplets

  11. Disease: Diseases produced by Staphylococcus aureus is studied under 2 groups: A) Infections B) Intoxications

  12. A) INFECTIONS: Mechanism of pathogenesis: Cocci gain access to damaged skin, mucosal or tissue site Colonize by adhering to cells or extracellular matrix Evade the host defense mechanisms and multiply Cause tissue damage

  13. Common Staphylococcal infections are: 1) Skin and soft tissue: Folliculitis, furuncle (boil), carbuncle, styes, abscess, wound infections, impetigo, paronychia and less often cellulitis. Folliculitis

  14. Furuncle (boil) Carbuncle

  15. Styes Abscess

  16. Impetigo Paronychia Wound infection Cellulitis

  17. 2) Musculoskeletal: Osteomyelitis, arthritis, bursitis, pyomyositis. osteomyelitis 3) Respiratory: Tonsillitis, pharyngitis, sinusitis, otitis, bronchopneumonia, lung abscess, empyema, rarely pneumonia.

  18. 4) Central nervous system: Abscess, meningitis, intracranial thrombophlebitis. 5) Endovascular: Bacteremia, septicemia, pyemia, endocarditis. Endocarditis 6) Urinary: Urinary tract infection.

  19. B) INTOXICATIOINS: The disease is caused by the bacterial exotoxins, which are produced either in the infected host or preformed in vitro. There are 3 types- • Food poisoning • Toxic shock syndrome • Staphylococcal scalded skin syndrome

  20. 1) Food poisoning: • Enterotoxin is responsible for manifestations of staphylococcal food poisoning. • Eight types of enterotoxin are currently known, named A, B, C1-3, D, E, and H. • It usually occurs when preformed toxin is ingested with contaminated food. • The toxin acts directly on the autonomic nervous system to cause the illness, rather than gut mucosa.

  21. The common food items responsible are - milk and milk products, meat, fish and ice cream. • Source of infection- food handler who is a carrier. • Incubation period- 2 to 6 hours. • Clinical symptoms- nausea, vomiting and diarrhoea. • The illness is usually self limited, with recovery in a day or so.

  22. 2) Staphylococcal Toxic shock syndrome (STSS): • STSS is associated with infection of mucosal or sequestered sites by TSST( formerly known as enterotoxin type F) producing S.aureus. • It is fatal multisystem disease presenting with fever, hypotension, myalgia, vomiting, diarrhoea, mucosal hyperemia and erythematous rash which desquamates subsequently.

  23. 2 types of STSS known: i) Menstrual associated STSS: Here colonization of S.aureus occurs in the vagina of menstruating woman who uses highly absorbent vaginal tampons. ii) Non menstrual associated STSS: Here colonization of S.aureus occurs in other sites like surgical wound.

  24. 3) Staphylococcal scalded skin syndrome (SSSS): • Exfoliative toxin produced by S.aureus is responsible for this. • It is a skin disease in which outer layer of epidermis gets separated from the underlying tissues.

  25. Types of SSSS: Severe formMilder form In new born - Ritter’s disease - Pemphigus neonatorum In older patients - Toxic epidermal - Bullous necrolysis impetigo

  26. Pemphigus neonatorum Ritter’s disease Toxic epidermal necrolysis Bullous impetigo

  27. LAB DIAGNOSIS: Specimens collected: Depends on the type of infection. • Suppurative lesion- Pus, • Respiratory infection- Sputum, • Bacteremia & septicemia- Blood, • Food poisoning- Feces, vomit & the remains of suspected food, • For the detection of carriers- Nasal swab.

  28. Methods of examination: I) Direct microscopy: • Direct microscopy with Gram stained smear is useful in case of pus, where cocci in clusters are seen. • This is of no value for specimen like sputum where mixed flora are normally present.

  29. II) Culture: a) Media used: b) Cultural Characteristics: c) Gram staining: Smears are examined from the culture plate and reveals Gram positive cocci(1μm in diameter) arranged in grape like clusters.

  30. d) Biochemical reactions: III) Antibiotic sensitivity tests done as a guide to treatment. IV) Bacteriophage typing is done for epidemiological purposes. V) Serological tests are not useful.

  31. TREATMENT: • Drug resistance is common. • Benzyl penicillin is the most effective antibiotic, if the strain is sensitive. • Cloxacillin or Methicillin is used against beta-lactamase producing strains. • Methicillin Resistant Staphylococcus aureus (MRSA) strains have become common. • Vancomycin is used in treatment of infections with MRSA strains.

  32. EPIDEMIOLOGY: • Staphylococci are primary parasites of human beings and animals. • Hospital infections caused by staphylococci deserve special attention because of their frequency & they are caused by strains resistant to various antibiotics. • Staphylococci are the common cause of postoperative wound infection and other hospital cross infections.

  33. PREVENTION: • Isolation & treatment of MRSA patients. • Detection of carriers among hospital staff, their isolation & treatment. • Avoid indiscriminate usage of antibiotics.

  34. Coagulase Negative Staphylococci( CoNS ): Two species of coagulase negative Staphylococci can cause human infections- 1. Staphylococcus epidermidis 2. Staphylococcus saprophyticus

  35. S. Epidermidis: • It is a common cause of stitch abscesses. • It has predilection for growth on implanted foreign bodies such as artificial valves, shunts, intravascular catheters and prosthetic appliances leading to bacteraemia. • In persons with structural abnormalities of urinary tract, it can cause cystitis. • Endocarditis may be caused, particularly in drug addicts.

  36. Streptococcal Diseases Streptococcus pyogenes

  37. Streptococcus pyogenesPyogenes means pus producing • One of the most important pathogens • Gram positive cocci in chains • Lancefield Serological Group A • Beta Hemolytic on blood agar

  38. Gram Stain of S. pyogenes

  39. Hemolysis on Blood Agar Plates • Alpha hemolysis-organism excretes hemolysins which partially break down rbc (incomplete hemolysis) thus a greenish zone appears around colony. S. pneumoniae • Beta hemolysis-organisms excretes potent hemoysins which completely lyse rbc (complete hemolysis) thus a clear zone appears around colony. S. pyogenes

  40. S.pyogenes S. pneumonia Beta hemolysis Alpha hemolysis

  41. Diseases caused by S. pyogenes • Strep throat • Impetigo • Erysipelas • Cellulitis • Invasive Strep A infections • Necrotizing fasciitis • Myositis • Toxic shock-like syndrome

  42. Erysipelas • Acute infection and imflammation of the dermal layer of skin. • Painful red patches which enlarge and thicken • Treatment -penicillin or erythromycin

  43. Erysipelas

  44. Strep Throat • Most common of all Strep diseases • Spread by saliva or nasal secretions • Incubation period 2-4 days • Sore throat, slight fever (101) • Important to treat immediately to avoid post strep diseases

  45. Diagnosis and treatment of Strep Throat • Tell tale symptoms are slight fever associated with sore throat and visual of pus in back of throat • Quick diagnostic tests (Molecular) available but must be confirmed by throat swab and growth on blood agar (beta hemolysis)

  46. Diagnosis and treatment of Strep Throat • If the strain of S. pyogenes is lysogenic for a particular phage which expresses an erythrogenic toxin the result is Scarlet fever • Rash appears and characteristic is the strawberry colored tongue

  47. Strawberry Tongue

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