1 / 37

STAPHYLOCOCCI

STAPHYLOCOCCI. INTRODUCTION. Staphylococci are Gram-positive spherical bacteria arranged in microscopic clusters resembling grapes Staphyloccocci – Greek word “stapyle” = bunch of grapes and “kokkos”= a berry. This group includes a major human pathogen and skin commensals.

honea
Download Presentation

STAPHYLOCOCCI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. STAPHYLOCOCCI

  2. INTRODUCTION • Staphylococci are Gram-positive spherical bacteria arranged in microscopic clusters resembling grapes • Staphyloccocci – Greek word “stapyle” =bunch of grapes and “kokkos”= a berry. • This group includes a major human pathogen and skin commensals

  3. Grouping for Clinical Purposes • Coagulase positive Staphylococci • Staphylococcus aureus- major pathogen • Coagulase negative Staphylococci • Staphylococcus epidermidis • Staphylococcus saprophyticus • Staphylococcus hemolyticus

  4. Staphylococcus aureus • Major human pathogen • Habitat - S. aureus colonizes mainly the nasal passages, but it may be found regularly in most other anatomical sites, including skin, oral cavity and gastrointestinal tract • Source of organism - can be infected human host, carrier, fomite or environment

  5. Culture: S.aureus forms a fairly large golden yellow colony on rich medium • Often hemolytic on blood agar • S.aureus- golden yellow colonies • S.albus- white colonies • S.citreus-lemon yellow colonies

  6. Biochemical reactions: • Staphylococci are facultative anaerobes that grow by aerobic respiration or by fermentation that yields principally lactic acid • Catalase-positive

  7. Nearly all strains of S. aureus produce the enzyme coagulase • S.aureus should always be considered a potential pathogen

  8. Important phenotypic characteristics of S.aureus • Gram-positive, cluster-forming cocci • facultative anaerobe -fermentation of glucose produces mainly lactic acid • Catalase positive, Coagulase positive • Golden yellow colony on agar • Normal flora of humans found on nasal passages, skin and mucous membranes • Pathogen of humans: causes suppurative infections, food poisoning, toxic shock syndrome

  9. Virulence factors of S.aureus

  10. Natural history of disease • Neonates, children, adults -intermittently colonised by S. aureus • Usual sites - skin, nasopharynx, perineum • Breach in mucosal barriers - can enter underlying tissue- Characteristic abscesses • Disease due to toxin production

  11. DISEASES Due to direct effect of organism • Local lesions of skin • Deep abscesses • Systemic infections Toxin mediated • Food poisoning • Toxic shock syndrome • Scalded skin syndrome

  12. Factors predisposing to S. aureus infections Host factors • Breach in skin • Chemotaxis defects • Opsonisation defects • Neutrophil functional defects • Diabetes mellitus • Presence of foreign bodies Pathogen Factors • Catalase (counteracts host defences) • Coagulase • Hyaluronidase • Lipases • B –lactasamase (antibiotic resistance)

  13. SKIN LESIONS • Boils, Styes • Furuncles (infection of hair follicle) • Carbuncles (infection of several hair follicles) • Wound infections • Impetigo (skin lesion with blisters that break and become covered with crusting exudate)

  14. DEEP ABSCESSSES • Can be single or multiple • Breast abscess can occur in 1-3% of nursing mothers in puerperium • Other sites - kidney, brain from septic foci in blood

  15. Systemic Infections • Osteomyelitis, septic arthritis • Heart (infective endocarditis) • Brain(brain abscesses) • With predisposing factors • multiple abscesses, septicaemia (IV drug users) • Staphylococcal pneumonia (Post viral)

  16. B. TOXIN MEDIATED DISEASES Staphylococcal food poisoning • Due to production of entero toxins- heat stable entero toxin acts on gut • Produces severe vomiting following a very short incubation period • Resolves on its own within about 24 hours

  17. Toxic shock syndrome • High fever, diarrhoea, shock and erythematous skin rash which desquamate • Mediated via ‘toxic shock syndrome toxin’ • 10% mortality rate • Described in two groups of patients • Young women using tampones during menstruation • Described in young children and men

  18. Scalded skin syndrome • Disease of young children • Mediated through minor Staphylococcal infection by ‘epidermolytic toxin’ producing strains • Mild erythema and blistering of skin followed by shedding of layers of epidermis

  19. Antibiotic sensitivity pattern • Very imp. In Pt. Management • Antibiotic resistance mechanisms • Β-lactamase production - plasmid mediated • Has made S. aureus resistant to penicillin group of antibiotics - 90% of S. aureus • B lactamase stable penicillins (cloxacillin, oxacillin, methicillin) used

  20. Alteration of penicillin binding proteins- (Chromosomal mediated) • Has made S. aureus resistant to β-lactamase stable penicillins (MRSA) • 10-20% S. aureus are resistant to all Penicillins and Cephalasporins • Vancomycin is the drug of choice

  21. MRSA detected in the lab using methicillin • In Japan emergence of VIRSA(vancomycin intermediate resistant S. aureus) • No effective antibiotics for successful treatment

  22. DIAGNOSIS • In all pus forming lesions • Gram stain and culture of pus • In all systemic infections • Blood culture • In infections of other tissues • Culture of relevant tissue or exudate

  23. Staphylococcal Lab Identification & Diagnostic Tests • Microscopic • Lab isolation • Coagulase positive • S. aureus

  24. Mannitol Salt Agar (MSA) Staphylococcus aureus

  25. Differential Characteristics Catalase 2H2O2 O2 + 2H2O Streptococcivs. Staphylococci

  26. Catalase POS Catalase NEG Staphylococcus

  27. S. aureus Differential Characteristics Coagulase Fibrinogen  Fibrin

  28. Staphylococcus aureus Coagulase POS Coagulase NEG

  29. Treatment • Drain infected area • Deep/metastatic infections • Semi-synthetic penicllins • Cephalosporins • Erythromycin, Clindamycin • Endocarditis • semi-synthetic penicillin + an aminoglycoside • MRSA: Vancomycin

  30. Prevention • Carrier status prevents complete control • Proper hygiene, segregation of carrier from highly susceptible individuals • Good aseptic techniques when handling surgical instruments • Control of nosocomial infections

  31. 2. Staphylococcus epidermidis • Skin commensal • Has predilection for plastic material • Ass. With infection of IV lines, prosthetic heart valves, shunts • Causes urinary tract infection in cathetarised patients • Has variable ABS pattern • Treatment should be aided with ABST

  32. 3. Stapylococcus saprophyticus • Skin commensal • Imp. Cause of UTI in sexually active young women • Usually sensitive to wide range of antibiotics

More Related