staphylococcal infections

staphylococcal Species, Classification, Structure, morphology, Colony characteristics, Growth and biochemical Characterization,, Diagnosis and treatments of staphylococcal infections

1. Staphylococcal infection Bilal Nasir

2. Staphylococcus Staphylococcus is a genus of Gram-positive cause a wide variety of infections in humans and other animals Certain toxin are produced by different Species Staphylococcal toxins are a common cause of food poisoning Staphylococci are also known to be a cause of bacterial conjunctivitis. Staphylococcus aureus can cause a number of different skin diseases Among neurosurgical patients, it can cause community-acquired meningitis commonly found on the skin or in the nose of even healthy individuals Normally  cause no problems or result in relatively minor skin infections.

3. Staphylococcus Sir Alexander Ogston , a Scottish surgeon, first showed in 1880 that a number of human pyogenic diseases were associated with a cluster-forming micro-organism. He introduced the name 'staphylococcus' (Greek: staphyle =bunch of grapes; kokkos = grain or berry), now used as the genus name for a group of facultatively anaerobic, catalase-positive, Gram positive cocci Gram positive cocci ( from Greek staphyle , means bunch of grapes ) that occur singly and in pairs, short chains and irregular grape-like clusters

4. Staphylococcus

5. Classification Family : Micrococcaceae Genus : Micrococcus and Staphylococcus Species : S. aureus , S. saprophyticus , S. epidermidis More than 20 species

6. Species of genus Staphylococcus The genus Staphylococcus contains about forty species and subspecies today. Only some of them are important as human pathogens: –Staphylococcus aureus –Staphylococcus epidermidis –Staphylococcus hominis –Staphylococcus haemolyticus –Staphylococcus saprophyticus –others

7. Structure and Physiology Gram-positive cocci, non-motile, facultative anaerobes Cells occur in grapelike clusters Cells division occurs along different planes and the daughter cells remain attached to one another Salt-tolerant: allows them to tolerate the salt present on human skin Tolerant of desiccation: allows survival on environmental surfaces (fomites)

8. The species Staphylococcus aureus Morphology Gram-positive, spherical cells, mostly arranged in irregular grape like clusters. Polysaccharide capsule is only rarely found on cells. The peptidoglycan layer is the major structural component of the cell wall. It is important in the pathogenesis of staphylococcal infections. Other important component of cell wall is teichoic acid. Protein A is the major protein component of the cell wall. It is located on the cell surface but is also released into the culture medium during the cell growth. A unique property of protein A is its ability to bind to the Fc part of all IgG molecules except IgG3. It is not an antigen-antibody specific reaction.

9. S aureus A Unique Organism

10. Physiology and structure Capsule or polysaccharide slime layer Peptidoglycan layer Teichoic acid Protein A Cytoplasmatic membrane Clumping factor Cytoplasma

11. What is Capsule or polysaccharide slime layer? A loose-fitting, polysaccharide layer (slime layer) is only occasionally found in staphylococci cultured in vitro, but is believed to be more commonly present in vivo. Eleven capsular serotypes have been identified in S. aureus , with serotypes 5 and 7 associated with majority of infections.

12. Capsule helps Staphylococcus species The capsule protects the bacteria by inhibiting the chemotaxis and phagocytosis of staphylococci by polymorph nuclear leukocytes, as well as by inhibiting the proliferation of mononuclear cells. It is also facilitates the adherence of bacteria to catheters and other synthetic material.

13. Staphylococcal enzymes – Coagulase – Catalase – Hyaluronidase – Fibrinolysin – Lipases –Nuclease – Penicillinase

14. Enzymes Coagulase – Triggers blood clotting Hyaluronidase – Breaks down hyaluronic acid, enabling the bacteria to spread between cells Staphylokinase – Dissolves fibrin threads in blood clots, allowing Staphylococcus aureus to free itself from clots Lipases – Digest lipids, allowing staphylococcus to grow on the skin’s surface and in cutaneous oil glands  -lactamase – Breaks down penicillin – Allows the bacteria to survive treatment with  -lactam antimicrobial drugs

15. Protein A The surface of most S. aureus strains (but not the coagulase-negative staphylococci) is uniformly coated with protein A. This protein is covalently linked to the peptidoglycan layer and has a unique affinity for binding to the Fc receptor of immunoglobulin IgG . The presence of protein A has been exploited in some serological tests, Additionally , detection of protein A can be used as a specific identification test for S. aureus .

16. Peptidoglycan Half of the cell wall by weight is peptidoglycan, a feature common to gram-positive bacteria. The subunits of peptidoglycan are N- acetylmuramic acid and N- acetylglucosoamine . Unlike gram-negative bacteria, the peptidoglycan layer in gram-positive bacteria consists of many cross-linked layers, which makes the cell wall more rigid.

17. Teichoic acid Teichoic acid is species-specific, phosphate containing polymers that are bound covalently to the peptidoglycan layer or through lipophilic linkage to the cytoplasmic membrane ( lipoteichoic acid). Teichoic acid mediates the attachment of staphylococci to mucosal surfaces through its specific binding to fibronectin

18. surface proteins Other surface proteins that appear to be important for adherence to host tissues include: collagen-binding protein elastin-binding protein fibronectin -binding protein

19. Cytoplasmic membrane The cytoplasmic membrane is made up of a complex of proteins, lipids, and small amount of carbohydrates. It serve as an osmotic barrier for the cell and provides an anchorage for the cellular biosynthetic and respiratory enzymes.

20. Staphylococcal toxins S. aureus produces many virulence factors, including at least five cytolytic or membrane-damaging toxins: – alpha toxin – beta toxin – delta toxin – gamma toxin – Panton-Valentin toxin – two exfoliative toxins – eigth enterotoxins (A-E, G-I) – Toxic Shock Syndrome Toxin 1 (TSST-1)

21. Toxic shock syndrome toxin (TSST-1) Toxic shock syndrome toxin (TSST-1) is a super-antigen capable of activating large number of T cells • (TSST-1) Was associated with use of tampons but is also known to be associated with postoperative wound or soft tissue infections

22. TSST and other Toxins The enterotoxins and TSST-1 belong to a class of polypeptide known as super antigens. • Staphylococcus aureus strains produce several other extracellular, biologically active substances, including proteases, phosphatases, lipases, lysozyme etc.

23. Exfoliative toxins Staphylococcal scalded skin syndrome (SSSS), a spectrum of diseases characterized by exfoliative dermatitis, is mediated by exfoliative toxins. • The prevalence of toxin production in S. aureus strains varies geographically but is generally less than 5% to 10%.

24. Enterotoxins Eight serologically distinct staphylococcal enterotoxins (A-E, G-I) and three subtypes of enterotoxin C have been identified. • The enterotoxin are stable to heating at 100 C for 30 minutes and are resistant to hydrolysis by gastric and jejunal enzymes

25. Enterotoxins Thus, once a food product has been contaminated with enterotoxin-producing staphylococci and the toxin have been produced, neither reheating the food nor the digestive process will be protective. • These toxins are produced by 30% to 50% of all S. aureus strains. • Enterotoxin A is most commonly associated with disease . Enterotoxins C and D are found in contaminated milk products , and enterotoxin B causes staphylococcal pseudomembranous enterocolitis.

26. What is the role of Coagulase The role of coagulase in the pathogenesis of disease is speculative, but coagulase may cause the formation of fibrin layer around a staphylococcal abscess, thus localizing the infection and protecting the organisms from phagocytosis

27. Hyaluronidase Hyaluronidase hydrolyzes hyaluronic acid, the acidic mucopolysaccharides present in the acellular matrix of connective tissue. This enzyme facilitates the spread of S. aureus in tissues. More than 90% of S. aureus strains produce this enzyme.

28. Fibrinolysin Fibrinolysin , also called staphylokinase , is produced by virtually all S. aureus strains and can dissolve fibrin clots. Staphylokinase is distinct from the fibrinolytic enzymes produced by streptococci.

29. coagulase The genus Staphylococcus can be divided into two subgroups (on the basis of its ability to clot blood plasma by enzyme coagulase): coagulase-positive coagulase-negative.

30. Staphylococcal Diseases Systemic Disease • Toxic shock syndrome-TSS toxin is absorbed into the blood and causes shock • Bacteremia-presence of bacteria in the blood • Endocarditis-occurs when bacteria attack the lining of the heart • Pneumonia-inflammation of the lungs in which the alveoli and bronchioles become filled with fluid • Osteomyelitis-inflammation of the bone marrow and the surrounding bone

31. Boil (Furuncle )

32. Surgical wound infections: many causes including S. aureus

33. Diagnosis • Microscopy – smears of clinical materials are stained according to Gram stain • Cultivation on solid media (agar, usually blood agar) • Biochemical tests • Phage typing – susceptibility of S. aureus strains to various temperature phages

34. Diagnosis Specimen • Smear • Culture • Coagulase test • Biochemical Reactions • Antibiograms • Typing

35. Clinical Concerns and Treatment 95% have penicillinase and are resistant to penicillin and ampicillin • MRSA – methicillin-resistant S. aureus – carry multiple resistance – Some strains have resistance to all major drug groups except vancomycin • Abscesses have to be surgically perforated • Systemic infections require intensive lengthy therapy

36. Treatment • Antistaphylococcal antibiotics of the first choice: – vancomycin – oxacillin (methicillin) – cephalosporins of I. generation ( cefazolin , cephalotin ) • Antistaphylococcal antibiotics of the second choice: – lincosamides (e.g. clindamycin) – glycopeptides ( vancomycin , teicoplanin ) – linezolid – tigecyklin – daptomycin – and others

37. Antibiotic sensitivity pattern • Very variable and not predictable • Very imp. In Pt. Management • Mechanisms – 1.B lactamase production - plasmid mediated • Has made S. aureus resistant to penicillin group of antibiotics - 90% of S. aureus ( Gp A) • B lactamase stable penicillin's ( cloxacillin , oxacillin , methicillin) used – 2. Alteration of penicillin binding proteins • (Chromosomal mediated) • Has made S. aureus resistant to B lactamase stable penicillins • 10-20% S. aureus Gp (B) GH Colombo/THP resistant to all Penicillins and Cephalosporins ) • Vancomycin is the drug of choice

38. Prevention – Hand antisepsis is the most important measure in preventing nosocomial infections – Also important is the proper cleansing of wounds and surgical openings, aseptic use of catheters or indwelling needles, an appropriate use of antiseptics