Pathogenic Gram-Positive Cocci 19 Pathogenic Gram-Positive Cocci

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

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

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

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

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

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

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

Table 19.1

Staphylococcal Diseases Cutaneous Diseases Folliculitis – hair follicle infection Furuncle – boil Carbuncle – involves connective tissue Impetigo – red patches; pus-filled crust impetigo furuncle http://www.youtube.com/watch?v=gU7hrtxBWmA

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

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 http://www.kidsmeds.info/en/art/81/

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.

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.

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 http://emedicine.medscape.com/article/787407-overview

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.

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

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 http://emedicine.medscape.com/article/788199-overview Ritter von Ritterschein disease (in newborns)

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

Staphylococcal Food Poisoning Sequence of events

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

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

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

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

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

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 http://www.mayoclinic.com/health/rheumatic-fever/DS00250/DSECTION=causes

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

Group A Streptococcus Skin diseases Erysipelas Pyoderma (Impetigo) Necrotizing fasciitis “flesh-eating” bacteria http://www.youtube.com/watch?v=QJZxV1kcS_w

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

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

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

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

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

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)

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

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

Enterococcus http://www.medicinenet.com/vancomycin-resistant_enterococci_vre/article.htm

Table 19.2