02 Gram-Positive Cocci Flashcards
What are the Gram-Positive Cocci?
Staphylococci (grapelike clusters). Streptococci (Spherical cocci in chains or pairs)
How does Staphylococci cause disease?
Cause disease by producing toxins and by multiplying in tissues –> inflammation
What are the diseases of S. aureus?
Abscesses. Endocarditis. Osteomyelitis. Food poisoning. Toxic shock syndrome (TSS)
What are the diseases of S. epidermidis?
Endocarditis. Infected foreign bodies
What are the diseases of S. saprophyticus?
UTIs
Which Staphylococci will test positive in a coagulase test?
S. aureus
How are staphylococci transmitted?
Normal human flora. S. epidermidis = skin, mucous membranes. S. aureus = nose, skin (Diarlysis, DM, IVDA, surgical pts, AIDS. Colonized pts have increased risk of becoming infected)
What are the clinical findings from Staphylococci?
Inflammatory. Toxin-mediated
What are the inflammatory clinical findings from Staphylococci?
Skin infections (impetigo, furuncles, cellulitis, surgical wound infections). Bacteremia from localized lesion. Endocarditis. Osteomyelitis and arthritis (hematogenous or traumatic). Pneumonia. Abscesses after bacteremia
What are the Toxin-Mediated clinical findings from Staphylococci?
Food poisoning due to ingestion of enterotoxin preformed in foods, incubation period (1-8 hours). TSS in menstruating women using tampons or those with wound infections. Scalded skin syndrome in young children - sloughing of the superficial layers of the epidermis in response to the presence of exfoliation
What are some common causes of Streptococci?
Pharyngitis. Skin and soft tissue infections (impetigo, cellulitis, necrotizing fasciitis). Pneumonia. UTI. Intraabdominal infection. Endocarditis
What are the two types of bacteria that should always be considered with tissue infections?
Staph or Strep
How are Streptococci classified?
Alpha-Hemolytic (partial lysis of RBC in the agar). Beta-Hemolytic (complete lysis)
What Streptococci group is S. pneumoniae?
Alpha-hemolytic
What Streptococci group is Viridans Streptococci?
Alpha-hemolytic
What Streptococci group is S. pyogenes?
Group A (beta-hemolytic)
What Streptococci group is S. agalactiae?
Group B (beta-hemolytic). GBS
What Streptococci group is Enterococci?
Group D (beta-hemolytic)
What Streptococci group is S. bovis?
Group D (beta-hemolytic)
How is Streptococci commonly transmitted?
Normal flora of throat, skin, intestines. Oropharynx: viridans strep, S. pneumoniae. Skin: S. pyogenes. Female genital tract: S. agalatiae. Lower intestinal tract: enterococci, anaerobic streptococci
Where is S. pyogenes found?
Skin
Where is S. agalactiae found?
Female genital tract
Where is Viridans Strep found?
Oropharynx
Where is S. pneumoniae found?
Oropharynx
What are some common causes of Group A Strep - S. pyogenes?
Pharyngitis (fever, tender cervical lymph nodes, inflammation, exudate, fever), if untreated, recovery in 10 days; rheumatic fever may follow (may extend to otitis, sinusitis, mastoiditis, meningitis). Cellulitis, necrotizing fasciitis - exotoxin B rapidly destroys tissue. Pyoderma (impetigo) - communicable superficial infection of abraded skin that forms pus or crusts (acute glomerulonephritis may follow)
What are immunologic disorders from Streptococci?
Inflammation in an organ that was NOT infected by the streptococci. NOT benefit from PCN treatment after onset. Occurs 2-3 weeks after infection. Acute glomerulonephritis (AGN). Rheumatic fever
What is Acute Glomerulonephritis (AGN)?
Typically occurs 2-3 weeks after skin infection with Group A Strep. HTN, facial edema (periorbital) and ankles, “smokey” urine (rbcs) –> complete recovery in most pts. Initiated by antigen-antibody complexes on the glomerular basement membrane
How is AGN prevented?
By eradication of nephritogenic streptococci from skin colonization
What is Rheumatic Fever?
Occurs ~2 weeks after Group A Strep pharyngitis. Fever, migratory polyarthritis, carditis may damage mitral and aortic valves. Resulting from cross-reactions b/w strep antigens and antigens of joint and heart tissue. “Autoimmune” disease greatly exacerbated by recurrence of strep infection –> long term PCN prophylaxis
How is Rheumatic Fever prevented?
By treatment of strep infection within 8 days after onset
For laboratory diagnosis, why are gram-stain smears in pharyngitis useless for streptococci?
Cannot distinguish S. pyogenes from normal flora (viridans strep). Useful from skin lesions or wounds
What is the “Rapid Strep Test”?
Direct detection of Group A polysaccharide antigen in throat swabs, 10-15 minutes, highly specific (>95%), 80-90% sensitive
What is a common cause of Group B Strep (S. agalactiae)?
Neonatal sepsis and meningitis. Infected in utero or during passage thru birth canal. Early-onset (1st 3 days): 75% of neonatal infection (pneumonia, prolonged membrane ruptures (>18 hours) in colonized women; low-birth-weight. Late-onset (10-14 days, up to 3 months): meningitis more common; full-term infants
How is S. agalactiae in DM?
14x higher risk - Bacteremia from infected foot ulcers or cellulitis
What are some risks of getting S. agalactiae infection in adults?
DM. CVD. Solid cancers. Alcoholism. Cirrhosis
What is done to prevent GBS is pregnant women?
Found in 2-7% of patients urine. Screen by culture at 35-37 weeks. Infection causes septic abortion, stillbirth, chorioamnionitis, endometritis
What is Viridans Strep?
Part of mouth flora. Infective endocarditis (organism enters bloodstream from the oropharynx as a result of poor oral hygiene or after dental surgery)
What are the Group D Streptococci?
Enterococci. S. bovis
What can Enterococci cause?
UTIs in catheterized pts. Endocarditis following GI or GU surgery or instrumentation. Intraabdominal and pelvic infections
What is most commonly associated with S. bovis?
Bacteremia or endocarditis is strongly associated with colon cancer
What can Strep pneumoniae (pneumococcus) cause?
Respiratory tract infections: otitis, sinusitis, pneumonia. Bacteremia. Meningitis
What are the characteristics of S. pneumoniae?
Polysaccharide capsules (virulence factors which interfere with phagocytosis. Infection or administration of vaccine elicit specific antibody formation which helps opsonizes the organism –> phagocytosis)
What is done for prevention of S. pneumoniae?
Vaccines. Pneumococcal vaccine (23-type): immunocompromized, elderly. 7-valent conjugate vaccine in children
What is the Transmission/Pathogenesis of S. pneumoniae?
5-50% of the healthy population harbor virulent organisms in oropharynx. Produce IgA protease enhance the organisms ability to colonize the mucosa of the upper respiratory tract. NO toxins
What are the predisposing host factors to infection?
Compromised gag reflex (CNS depression, alcohol or drug intoxication). Abnormality of the respiratory tract (pooling of mucus, bronchial obstruction). Pulmonary congestion, HF. Splenectomy. Sickle cell anemia, nephrosis
What is the laboratory diagnosis for S. pneumoniae?
Predominant organism in sputum smears. Alpha-hemolytic colonies on blood agar. Antimicrobial susceptibility testing - important for therapeutic decision. Can detect by urin antigen from first voided clean catch urine (> 90% specificity in adults, 21-54% false positive in children with nasopharyngeal carriage and no evidence of pneumonia)
