1. Gram Positive Bacteria and Clinical 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 % 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