1. Pathogenic Gram-Positive Cocci19
Pathogenic Gram-Positive Cocci

2. Staphylococcus Normal flora of every human
Gram-positive cocci in clusters
Catalase positive
Facultative anaerobe
Tolerant of:
Salt
Dessication

3. Staphylococcus species
Two species are commonly associated with staphylococcal diseases in humans:
Staphylococcus aureus
More virulent strain
Some people are “carriers” in nose and on skin
Staphylococcus epidermidis
Normal microbiota of human skin
Can cause opportunistic infections

4. Pathogenicity
“Staph” infections result when staphylococci break through the body’s physical barriers
Low “Infectious Dose”:
Entry of only a few hundred bacteria can result in disease
Pathogenicity results from three virulence factors
Evades phagocytosis by capsule production
Produces Enzymes
Produces Exotoxins

5. Defenses Against Phagocytosis
Protein A coats the cell surface
Binds to class G antibodies
Inhibits the complement cascade
Slime layer
Inhibits chemotaxis of leukocytes
Helps Staphylococcus attach to artificial surfaces

6. Enzymes Coagulase Hyaluronidase Staphylokinase
Converts fibrinogen into fibrin to form blood clots
Fibrin clots hide the bacteria from phagocytic cells
Hyaluronidase
Breaks down hyaluronic acid, enabling the bacteria to spread between cells
Staphylokinase
Dissolves fibrin threads in blood clots, allowing S.aureus to free itself from clots

7. Enzymes 4. Lipases 5. -lactamase
Digest lipids, allowing staphylococcus to grow on the skin’s surface and in oil glands
5. -lactamase
Breaks down penicillin
Allows the bacteria to survive treatment with -lactam antimicrobial drugs
Methicillin –Derivative of penicillin that is resistant to beta-lactamase
MRSA- Methicillin resistant Staphylococcus aureus

8. Toxins Cytolytic toxins Exfoliative toxins Toxic-shock-syndrome toxin
Disrupt host’s cell membrane
Leukocidins lyse leukocytes
Exfoliative toxins
Causes skin cells to separate and slough off
Toxic-shock-syndrome toxin
Enterotoxins
Stimulate intestinal muscle contractions, nausea, and intense vomiting associated with staphylococcal food poisoning
Toxin is heat-stable; resistant to boiling

9. Table 19.1

10. Staphylococcal Diseases
Cutaneous Diseases
Folliculitis – hair follicle infection
Furuncle – boil
Carbuncle – involves connective tissue
Impetigo – red patches; pus-filled crust
impetigo
furuncle

11. Staphylococcal Diseases
Systemic disease
Bacteremia – presence of bacteria in the blood from wound infections
50% are nosocomial infections
Endocarditis – occurs when bacteria attack the lining of the heart; 50% mortality rate
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; from wound or bacteremia

12. Diagnosis, Treatment, and Prevention
Detection of Gram-positive bacteria in grapelike arrangements isolated from pus, blood, or other fluids
Treatment
Methicillin is the drug of choice
Is a semisynthetic form of penicillin and is not inactivated by -lactamase
MRSA- methicillin-resistant Staph. aureus
Vancomycin – drug of choice for moderate to severe infections

13. Ceftaroline (brand nameTeflaro®)
Treatment for MRSA
Ceftaroline (brand nameTeflaro®)  
the first commercially available cephalosporin with activity against
methicillin-resistantStaphylococcus aureus(MRSA)
penicillin-resistantStreptococcus pneumoniae.
In addition, ceftaroline is active against most non-ESBL Enterobacteriaceae.

14. Prevention of MRSA Spread in ICU
All patients in ICU bathed daily with a 2% chlorhexidine containing cloth, and had an antibiotic ointment of mupirocin applied twice daily inside their nose (the body site most commonly colonized with S. aureus) for 5 days.
44% reduction in all septicemias including those caused by MRSA. The incidence of MRSA colonization on these patients was reduced by 37%.  
There are about 80,000 cases of invasive MRSA infections per year, resulting in about 11,000 deaths annually. MRSA, and Staphylococcus in general, account for approximately one-quarter of the 80,000 deaths from hospital-acquired infections in the U.S.

15. Staphylococcus toxins
Toxic shock syndrome
TSS toxin produced by Staphylococcus aureus is absorbed into the blood and causes shock
Linked to many initiating Staph infections
Sunburn-like rash
Desquamation

16. Toxic Shock Syndrome Information
TSS was first described in children in 1978
Later TSS was associated with menstruating women using highly absorbent tampons.
Cases of menstrual TSS (1 case per 100,000) steadily declined after withdrawing these tampons from the market.
50% of cases of TSS are not associated with menstruation.
TSS usually are complications of surgical and postpartum wound infections, burns, cutaneous lesions, osteomyelitis, and arthritis.
Although most cases of TSS occur in women, about 25% of cases occur in men.

17. Toxic Shock Syndrome – CDC Case Definition
An illness with the following clinical manifestations:
Fever :greater than or equal to 102.0°F
Rash: diffuse macular erythroderma
Desquamation: 1-2 weeks after onset of illness, particularly on the palms and soles
Hypotension: systolic blood pressure less than or equal to 90 mm Hg for adults
Multisystem involvement (3 or more): examples-
Gastrointestinal: vomiting or diarrhea at onset
Muscular: severe myalgia (muscle pain)
Hematologic: platelets less than 100,000/mm3
Renal, Hepatic, Central Nervous System

18. Staphylococcus toxins
Staphylococcal Scalded Skin Syndrome
Caused by exfoliative toxins
(ETA & ETB) of Staph. aureus
Acute exfoliation of the skin typically after an erythematous cellulitis.
Severity varies:
few blisters localized to the site of infection
severe exfoliation affecting almost the entire body
Ritter von Ritterschein disease (in newborns)

19. Staphylococcus toxins
Food poisoning
From the ingestion of enterotoxin-contaminated food
Often this type of food poisoning occurs when cooked food is allowed to cool slowly and/or sit at room temperature for some.
Distinguish staphylococcal from other types of food poisoning:
short incubation period
brevity of illness
usual lack of fever

20. Staphylococcal Food Poisoning
Sequence of events

21. Diagnosis, Treatment, and Prevention
Prevention of “Staph” infections
Hand antisepsis is the most important measure in preventing nosocomial infections
Proper cleansing of wounds and surgical openings
Aseptic use of catheters or indwelling needles
Refrigerate food
Good hygiene

22. Streptococcus Gram-positive cocci, arranged in pairs or chains
Catalase negative
Facultative anaerobes
Categorized based on:
Hemolysis - Ability to lyse RBC’s
Beta, Alpha, Gamma
Lancefield Grouping
Divides the streptococci into serotype groups based on the bacteria’s cell wall antigens
Group A and B are pathogens

23. Group A Streptococcus = Streptococcus pyogenes
Beta-hemolytic
Infects the pharynx or skin
Often causes disease when normal microbiota are depleted
Spreads through respiratory droplets

24. Group A Strep- Virulence Factors
M protein of fimbriae
adheres to pharyngeal tissue
resists phagocytosis
80 serotypes
Toxins
Streptolysin O and S - hemolysis
Erythrogenic toxin - rash
Pyrogenic toxin - fever
Enzymes
Deoxynuclease
Hyaluronidase
Streptokinase – lyse platelets, WBC
Help spread bacteria through tissue
M protein

25. Group A Streptococcal Diseases
Pharyngitis (“strep throat”)
inflammation of the pharynx
Scarlet fever
rash that begins on the chest and spreads across the body
Pyoderma/Impetigo
confined, pus-producing lesion that usually occurs on the face, arms, or legs
Necrotizing fasciitis
toxin production destroys tissues and eventually muscle and fat tissue

26. Streptococcus pyogenes - Strep throat
Symptoms:
sore throat, cough
high fever
swollen lymph nodes
“beefy” red throat
Treatment:
penicillin
Autoimmune Complications:
Rheumatic fever – inflammation that leads to damage of heart valves muscle
Glomerulonephritis – inflammation of the glomeruli and nephrons obstruct blood flow through the kidneys

27. Group A Streptococcal Diseases Scarlet Fever
Accompanies strep throat if strain releases erythrogenic toxins
Symptoms:
strep throat
“strawberry” tongue
skin rash due to
erythrogenic toxins
Treatment:
Penicillin

28. Group A Streptococcus Skin diseases
Erysipelas
Pyoderma
(Impetigo)
Necrotizing fasciitis
“flesh-eating” bacteria

29. Group B Streptococcus = Streptococcus agalactiae
Normally colonizes the lower gastrointestinal, genital, and urinary tracts
Diseases
Most often associated with neonatal bacteremia, meningitis, and pneumonia
Immunocompromised older patients are at risk

30. Group B Streptococcus = Streptococcus agalactiae
Pathogenicity
Often infects newborns who have not yet antibodies and whose mothers do not provide passive immunity
Prevention
Culture the vaginal tract at 37 weeks to check for colonization of Group B Streptococcus. If positive, prophylactic administration of penicillin.
Prophylactic administration of penicillin at birth to children whose mothers’ urinary tracts are colonized with group B streptococci

31. Alpha-Hemolytic Streptococci: Streptococcus pneumoniae
Gram-positive diplococcus
Alpha-hemolytic
Normally colonizes the mouths and pharynx
Can cause disease if travels to the lungs
Disease is highest in children and the elderly

32. Alpha-Hemolytic Streptococci: Streptococcus pneumoniae
Virulence Factors:
Phosphorylcholine –
stimulates cells to phagocytize the bacteria
Polysaccharide capsule
protects the bacteria from digestion after endocytosis
Protein adhesin –
binds the cells to pharynx epithelial cells
Secretory IgA protease – destroys IgA
Pneumolysin – lyses epithelial cells and suppresses the digestion of the endocytized bacteria

33. Diseases caused by S. pneumoniae
Pneumococcal pneumonia –
bacteria multiply in the lower lung; cause damage to the alveolar lining; produce an inflammatory response
High fever; chest pain; SOB; sputum production
85% occur after viral disease
Sinusitis and otitis media –
bacteria invade the sinuses or middle ear, often following a viral infection
Bacteremia and endocarditis –
bacteria in the bloodstream or in the lining of the heart
Pneumococcal meningitis –
bacteria that have spread to the meninges

34. Streptococcus pneumoniae
S. pneumoniae accounts for 25-35% of cases of community-acquired bacterial pneumonia leading to 40,000 deaths/year in the US (Merck)
Treatment – Penicillin
Up to 35% of strains are resistant to penicillin (as well as erythromycin, Bactrim, cephalosporins)
Prevention - Pneumovax
Vaccine from purified capsular polysaccharides
Provides long lasting immunity in normal adults; (not as effective in children, the elderly, or AIDS patients)

35. Alpha-Hemolytic Streptococci: The Viridans Group
Alpha-hemolytic (“viridans = green”)
No Lancefield group
Lack group-specific carbohydrates
Normal microbiota
mouth, pharynx, GI tract, GU tract
Opportunistic Disease:
One of the causes of dental caries and dental plaques; produces dextran; leads to biofilm formation
Can cause meningitis and endocarditis

36. Enterococcus E. faecalis and E. faecium
Previously classified as group D streptococci but reclassified as a separate genus
Normal microbiota of the human colon
Opportunistic disease:
Urinary Tact Infection
Endocarditis
Common cause of nosocomial infections
Treatment: Difficult to treat due to resistance
Ampicillin and ceftriaxone
VRE - Vancomycin Resistant Enterococcus

37. Enterococcus

38. Table 19.2