02 Gram-Positive Cocci

Question 1

What are the Gram-Positive Cocci?

Answer 1

Staphylococci (grapelike clusters). Streptococci (Spherical cocci in chains or pairs)

Question 2

How does Staphylococci cause disease?

Answer 2

Cause disease by producing toxins and by multiplying in tissues –> inflammation

Question 3

What are the diseases of S. aureus?

Answer 3

Abscesses. Endocarditis. Osteomyelitis. Food poisoning. Toxic shock syndrome (TSS)

Question 4

What are the diseases of S. epidermidis?

Answer 4

Endocarditis. Infected foreign bodies

Question 5

What are the diseases of S. saprophyticus?

Answer 5

UTIs

Question 6

Which Staphylococci will test positive in a coagulase test?

Answer 6

S. aureus

Question 7

How are staphylococci transmitted?

Answer 7

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)

Question 8

What are the clinical findings from Staphylococci?

Answer 8

Inflammatory. Toxin-mediated

Question 9

What are the inflammatory clinical findings from Staphylococci?

Answer 9

Skin infections (impetigo, furuncles, cellulitis, surgical wound infections). Bacteremia from localized lesion. Endocarditis. Osteomyelitis and arthritis (hematogenous or traumatic). Pneumonia. Abscesses after bacteremia

Question 10

What are the Toxin-Mediated clinical findings from Staphylococci?

Answer 10

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

Question 11

What are some common causes of Streptococci?

Answer 11

Pharyngitis. Skin and soft tissue infections (impetigo, cellulitis, necrotizing fasciitis). Pneumonia. UTI. Intraabdominal infection. Endocarditis

Question 12

What are the two types of bacteria that should always be considered with tissue infections?

Answer 12

Staph or Strep

Question 13

How are Streptococci classified?

Answer 13

Alpha-Hemolytic (partial lysis of RBC in the agar). Beta-Hemolytic (complete lysis)

Question 14

What Streptococci group is S. pneumoniae?

Answer 14

Alpha-hemolytic

Question 15

What Streptococci group is Viridans Streptococci?

Answer 15

Alpha-hemolytic

Question 16

What Streptococci group is S. pyogenes?

Answer 16

Group A (beta-hemolytic)

Question 17

What Streptococci group is S. agalactiae?

Answer 17

Group B (beta-hemolytic). GBS

Question 18

What Streptococci group is Enterococci?

Answer 18

Group D (beta-hemolytic)

Question 19

What Streptococci group is S. bovis?

Answer 19

Group D (beta-hemolytic)

Question 20

How is Streptococci commonly transmitted?

Answer 20

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

Question 21

Where is S. pyogenes found?

Answer 21

Skin

Question 22

Where is S. agalactiae found?

Answer 22

Female genital tract

Question 23

Where is Viridans Strep found?

Answer 23

Oropharynx

Question 24

Where is S. pneumoniae found?

Answer 24

Oropharynx

Question 25

What are some common causes of Group A Strep - S. pyogenes?

Answer 25

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)

Question 26

What are immunologic disorders from Streptococci?

Answer 26

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

Question 27

What is Acute Glomerulonephritis (AGN)?

Answer 27

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

Question 28

How is AGN prevented?

Answer 28

By eradication of nephritogenic streptococci from skin colonization

Question 29

What is Rheumatic Fever?

Answer 29

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

Question 30

How is Rheumatic Fever prevented?

Answer 30

By treatment of strep infection within 8 days after onset

Question 31

For laboratory diagnosis, why are gram-stain smears in pharyngitis useless for streptococci?

Answer 31

Cannot distinguish S. pyogenes from normal flora (viridans strep). Useful from skin lesions or wounds

Question 32

What is the "Rapid Strep Test"?

Answer 32

Direct detection of Group A polysaccharide antigen in throat swabs, 10-15 minutes, highly specific (>95%), 80-90% sensitive

Question 33

What is a common cause of Group B Strep (S. agalactiae)?

Answer 33

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

Question 34

How is S. agalactiae in DM?

Answer 34

14x higher risk - Bacteremia from infected foot ulcers or cellulitis

Question 35

What are some risks of getting S. agalactiae infection in adults?

Answer 35

DM. CVD. Solid cancers. Alcoholism. Cirrhosis

Question 36

What is done to prevent GBS is pregnant women?

Answer 36

Found in 2-7% of patients urine. Screen by culture at 35-37 weeks. Infection causes septic abortion, stillbirth, chorioamnionitis, endometritis

Question 37

What is Viridans Strep?

Answer 37

Part of mouth flora. Infective endocarditis (organism enters bloodstream from the oropharynx as a result of poor oral hygiene or after dental surgery)

Question 38

What are the Group D Streptococci?

Answer 38

Enterococci. S. bovis

Question 39

What can Enterococci cause?

Answer 39

UTIs in catheterized pts. Endocarditis following GI or GU surgery or instrumentation. Intraabdominal and pelvic infections

Question 40

What is most commonly associated with S. bovis?

Answer 40

Bacteremia or endocarditis is strongly associated with colon cancer

Question 41

What can Strep pneumoniae (pneumococcus) cause?

Answer 41

Respiratory tract infections: otitis, sinusitis, pneumonia. Bacteremia. Meningitis

Question 42

What are the characteristics of S. pneumoniae?

Answer 42

Polysaccharide capsules (virulence factors which interfere with phagocytosis. Infection or administration of vaccine elicit specific antibody formation which helps opsonizes the organism --> phagocytosis)

Question 43

What is done for prevention of S. pneumoniae?

Answer 43

Vaccines. Pneumococcal vaccine (23-type): immunocompromized, elderly. 7-valent conjugate vaccine in children

Question 44

What is the Transmission/Pathogenesis of S. pneumoniae?

Answer 44

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

Question 45

What are the predisposing host factors to infection?

Answer 45

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

Question 46

What is the laboratory diagnosis for S. pneumoniae?

Answer 46

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)