Gram Positive Bacteria and Clinical Case Studies II

1. Gram Positive BacteriaandClinical Case Studies II

2. Introduction • Staphylococci and streptococci constitute the main group of medically important gram positive bacteria • There are also bacilli that are pathogenic such as Anthrax and the Clostridia group. These are also spore forming organisms • There are also some other gram positive rods such as Listeria, Lactobacillus,and Cornybacterium diptheria

3. Staphylococci • Staphylococci stain dark purple with the gram stain. • There are three medically important forms of staphylococci • Staphylococcus aureus – this causes many types of infections, food poisoning,and toxic shock • Staphylococcus epidermidis – this is a cause of infections in indwelling catheters • Staphylococcus saprophyticus that is an ongoing cause of cystitis in women

5. Staphylococci • Found in the air and on surfaces • Very resistant to drying and dehydration • They produce Catalase which is one of their distinguishing characteristics* this is an enzyme vital to the survival of many aerobic bacteria • The most virulent form of staphylococcus, SA also secretes coagulase, that causes citrated plasma to clot. These are referred to as coagulase positive • There are other staph that do not have this ability and are labeled coagulase negative

8. Staphylococcus aureus • Carried by 20-40 % of healthy individuals in their mouths or on their skin • It also found in their nasal mucosa • Carriers can serve as a source of infections as well as inanimate objects – these are called fomites

9. Staphylococci and virulence factors • Protein A – antiphagocytic effect • Exotoxins – Can cause cell lysis and destruction • Enterotoxins – Occurs when bacteria release toxin and cause vomiting • Toxic shock • Exfoliative –skin eruption and destruction

12. Infections • Erythema • Cellulitis • Boils and carbuncles • Septicemia • Toxic shock • Food Poisoning • Indwelling catheters • Cystitis

16. Streptococcus • Gram positive • Non motile • Ovoid to spherical in shape • Occur in pairs, short chains, or long chains

18. Biochemistry • Many are facultative anaerobes • Ferment even in the presence of oxygen • Require nutrient rich environments • Identified by their growth patterns on blood agar

19. Streptococci • Group A streptococcus – Streptococcus pyogenes – strep throat • Group B – streptococcus- genital infections Endocarditis – viridans group Otitis, and meningitis by Streptococcus pneumonia

20. Blood agar – Alpha hemolysis

21. Hemolytic bacteria • Cause a biochemical change in the hemoglobin of red blood cells – alpha hemolysis – green around the colonies • Cause gross hemolysis of the red blood cells in blood agar – beta hemolysis • Gamma – no hemolysis or change in the blood agar

22. Serologic • Lancefields groupings This is based upon a carbohydrate, C, in the cell wall of the bacteria Bacteria are typed according to the variant

23. Streptococcus pyogenes • Gram positive, non motile • Requires a low inoculum for infections • It does not survive well in the environment • Invades mucous membranes • Rapid progression of infection • Post infection sequelae can lead to glomerulonephritis

24. Transmission • Present in nasopharyngeal region • Spread via aerosol droplets Like sneezing and coughing

25. Pathogenic features • Fimbriae – for attachment- M protein • Exotoxins – cause rashes and other skin effects • Cytolytic toxins • Streptolysins – lyse white blood cells and red blood cells • Hyaluronidase – breaks down connective tissue to spread infection

26. Infections • Strep throat • Rheumatic fever • Acute glomerulonephritis • Impetigo • Pharyngitis

27. Summary of differences between staphylococci and streptococci • Gram stain and morphology • Both Gram + • Staphylococci: bunched cocci • Streptococci: chained cocci (S. pneumoniae form diplococcus) • Enzyme tests • Staphylococci: catalase + • Streptococci: catalase - • Growth • Staph.: large colonies (non-fastidious), some hemolytic • Strep.: small colonies (fastidious), many hemolytic (a or b)

28. Serological Techniques • Lancefield classified the streptococci into 20 serotypes designated A through V. • This is based upon an antigeninc substance called C • Streptococcus pyogenes belongs to Group A • These are also beta hemolytic

29. Bacitracin • A filter paper disc impregnated with the antibiotic Bacitracin is placed on a blood agar plate containing bacteria • If there is a zone of inhibition around the disk it is indicative of a Group A streptococci

30. Serological technique • Directigen test – A rapid nongrowth dependent immunological procedure • The bacteria are mixed with reagents that extract the Group A antigen and produce positive test results

31. Novobiocin Test • Differentiates between staphylococci based upon senesitivity to the antibiotic Novobiocin.

32. Molecular Methods - PCR

33. PCR Results