Module 11: Streptococcus Flashcards
What is the clinical significance of Aerococcus viridans?
Opportunistic organism, rarely causes infections
Does Steptococcus ferment carbohydrates?
Yes and primarily produces lactic acid
Name some examples of Strep species for each Lancefield group
A - S. pyogenes
B. S. agalactiae
C. S. equisimilis
D. Enterococcus: E. faecalis, E. facium Non-Enterococcus: S. euinus, S. bovis
What are some streps that do not have a Lancefield grouping?
S. pneumoniae, S. viridans, S. anginosus/milleri
What do S. anginosus/milleri colonies look like?
Small/pinpoint
Alpha, beta, or gamma
What is a nutritionally variant Streptococcus?
Group with S. viridans but differ in that a thiol compound (cystine) or vitamin B (pyridoxal) is required for growth
What does most strep look like in a gram? What species is different and what does it look like?
Mostly gram positive cocci in chains, may be oval
S. pneumoniae is different, usually in pairs, elongated “lancet” shapes
How do most strep (A, B, C, F, G) colonies look?
Small-large colonies, gray, opaque or translucent, buttery, beta hemolysis (usually)
What are the growth requirements for most strep?
Mostly facultative, may grow better anaerobically, usually increased CO2 is not necessary
35 degrees
Blood or serum enrichment usually required for good growth
What causes hemolysis on blood plates?
Streptolysin S and/or Streptolysin O
What is Streptolysin S?
Produces beta hemolysis
Oxygen stable, acid labile - if agar has fermentable carbohydrates acid is produced and Steptolysin S may be destroyed
What is Steptolysin O?
Produces beta hemolysis
Oxygen labile, acid labile - exposure to oxygen and acid from carbohydrate fermentation may destroy Streptolysin O
What are the genus tests for Streptococcus?
Catalase - negative
Nitrate reduction - negative (red after zinc salts)
What are 2 tests that can give a presumptive ID for GAS?
Bacitracin susceptibility and PYR positive
What are the 2 tests that can give a definitive ID of GAS?
Latex/co-agglutination tests for specific cell-wall antigen (carbohydrate residue) and GAS-D, DNA probe
How does the GAS DNA probe work?
Bacteria is lysed off the original swab and the DNA is amplified, usually takes 4 hours
What are some advantages of GAS DNA probes?
The bacteria do not have to be living, a large number of tests can be done a day, and is it much faster than growing the organism up
What is the susceptibility of GAS?
Universally susceptible to penicillin
If a patient is allergic erythromycin and tetracycline are considered
Susceptibility not routinely done
What are the 4 major infections GAS causes?
- Upper respiratory (strept throat)
- Cutaneous
- Invasive infections
- Post-streptococcal disease
What infection does GAS cause in the upper respiratory tract? What are some symptoms and complications?
Acute pharyngitis and strept throat
Symptoms - sudden sore throat, swollen lymph nodes, fever, headache
Complications - ear and sinus infections, meningitis (rare)
What can acute pharyngitis develop into?
Scarlet fever if the strain of GAS produces a pyrogenic exotoxin
Causes a rash on upper chest which spreads, and strawberry/beefy tongue
What does GAS cause with cutaneous infections?
Pustular lesions, impetigo, eysipelas (strep infection in dermis, red and thick skin)
Usually disseminate into bacteremia/septicemia (invasive infection)
What does GAS cause with invasive infections?
Pneumonia, flesh eating disease/necrotizing fascitis
May be called Streptococcal toxic shock, fulminant group A infection, or invasive GAS disease
What are common symptoms of flesh eating disease?
Cellulitis w/ pain, fever, septic shock, decreased blood pressure, respiratory distress, renal dysfunction, liver dysfunction
30-50% mortality
What are the 2 post-streptococcal diseases?
Rheumatic fever and acute glomerulonephtitis
What is rheumatic fever?
Caused by GAS with specific M antigens which are similar to myosin in the heart
Anti-streptococcal antibodies attach to heart muscle causing inflammation and scarring of the valves
May require replacement of valves
What is acute glomerulonephritis?
Antigen-antibody complexes are deposited on the kidney glomerular membranes, activating complement, resulting in membrane damage which allows blood and protein to enter the urine
May follow pharyngitis or cutaneous infection
What lab test can determine possible post-streptococcal disease?
Test for antibodies, most frequently Anti-Streptolysin O (ASO)
High level = recent infection and possible post-streptococcal disease
How many people may carry GAS in their respiratory tract without infection?
5-15%
What tests can be used for presumptive ID of GBS?
Positive CAMP and positive hippurate hydrolysis
What is the test that can definitively ID GBS?
Latex or co-agglutinaton test to detect specific group B antigens
What bacteria may give a false positive with GBS latex typing? How can it be determined if the organism is GBS or not?
Listeria monocytogenes
Gram stain - GBS are GPC, Listeria are GPB
How does GBS affect neonates?
Can cause serious general infection, neonatal sepsis (rapid or late onset)
Most common cause of neonatal sepsis and death
What is rapid onset of GBS sepsis in neonates?
Infection occurs in utero or during birth from a colonized vagina
Usually born critically ill with respiratory distress, sepsis, and meningitis
High mortality rate
What is late onset of GBS sepsis in neonates?
Occurs weeks after birth (average = 4 weeks)
Meningitis is usual
Lower mortality
What can GBS cause in adults?
Eye, ear, upper respiratory tract, surgical incision, and other body infections
Usually opportunistic and may colonize without infection, commonly in the vagina/rectum (Noraml in feces)
What do GDS colonies look like?
Small-large, gray, buttery, usually non-hemolytic
May grow on MAC without crystal violet (small, deep pink)
What genus test may have a false positive against GDS?
Enterococcus may be catalase pseudopositive
What tests can be used to identify GDS?
Positive BEA (Bile esculin), PYR, 6.5% sodium chloride, and latex/co-agglutination
What type of GDS is PYR positive?
Enterococcus (ex: faecalis, faecium)
What type of GDS is 6.5% sodium chloride positive?
Enterococcus will grow (ex: faecalis, faecium)
What is the pathogenicity of GDS Enterococcus?
Normal fecal and intestinal flora
Commonly urinary tract, wound, and miscellaneous infections
E. faecium is important nosocomial pathogen due to vancomycin resistance
E. faecalis is the most common isolate
What is the pathogenicity of GDS Non-Enterococcus?
S. bovis is the most common isolate
Presence in blood cultures is associated with GI carcinoma/neoplasm
What is the susceptibility of GDS Enterococcus?
Sometimes resistant to low dose penicillin and ampicillin (good for UTI, concentrates in urine) Serious infections (endocarditis) treated with aminoglycoside and penicillin combo Aminoglycoside resistance emerging
What is the susceptibility of GDS Non-Enterococcus?
S. bovis susceptible to penicillin, combination therapy usually used
What is the susceptibility of GBS?
Susceptible to penicillin (G or amp)
Ampicillin and gentamicin combo sometimes used
Erythromycin and vancomycin are alternatives for penicillin allergies
What is the significance of GCS and GFS?
Animal pathogens
May cause pharyngitis, pneumonia, septicemia, meningitis, and others
What is the significance of GGS?
Animal pathogens
May cause pharyngitis, otitis media, neonate sepsis, endocarditis, and meningitis
What is VRE?
Vancomycin Resistant Enterococcus Important nosocomial pathogen Usually resistant to all antibiotics Mostly affects immunocompromised, may colonize others Normal gut flora Usually E. faecium
How is VRE screened for?
Rectal swabs on agar containing vancomycin (agar dilution, 6ug/mL)
Growth in 72 hours = VRE if identified as Enterococcus
What organisms could an alpha hemolytic Streptococcus be?
S. pneumoniae or S. viridans
What feature may S. pneumoniae have that other Streptococcus species do not?
A capsule
What does a typical S. pneumoniae colony look like?
Alpha hemolytic, “dimpled”/”life-saver” shaped
May flatten out later due to autolysis from H2O2 accumulation
What tests are used to speciate S. pneumoniae?
Positive/soluble bile solubility, sensitive to optochin (>/= 14mm ZOI), and latex/co-agglutination reactions (pneumoslide)
What is the pathogenicity of S. pneumoniae?
Most common cause of adult lobar pneumoniae usually sudden and with septicemia
May also cause otitis media, sinusitis, conjunctivitis, and meningitis (in children spinal fluid is full of neutrophils)
Most common cause of death in old people
Can be found in the upper respiratory tract without infection
What is the antimicrobial susceptibility for S. pneumoniae?
Drug of choice is penicillin, resistance emerging
Susceptibility testing is essential
Screening done with oxacillin disc on Mueller Hinton in CO2, >20mm is susceptible
What is the pathogenicity of S. viridans?
Normal upper respiratory tract flora
Major cause of subacute bacterial endocarditis, endogenous infection usually from break in oral mucosa after the dentist, predisposed by damaged/scarred heart valves
What is the antimicrobial susceptibility of S. viridans?
Must be performed on all significant isolate
Majority susceptible to penicillin, some resistance
What tests can be used to identify S. viridans?
Negative/insoluble bile solubility, resistant (<14mm) to optochin
Gram positive cocci may be
a. Staphylococcus
b. Streptococcus
c. Both
d. Neither
c. both
Organisms that reduce nitrate to nitrite may be
a. Staphylococcus
b. Streptococcus
c. Both
d. Neither
a. Staphylococcus
Catalase negative organisms may be
a. Staphylococcus
b. Streptococcus
c. Both
d. Neither
b. Streptococcus
Organisms that are facultative anaerobes may be
a. Staphylococcus
b. Streptococcus
c. Both
d. Neither
c. both
Organisms where lactic acid is the main end product of fermentation may be
a. Staphylococcus
b. Streptococcus
c. Both
d. Neither
b. Streptococcus
S. pneumoniae is
a. GAS
b. GBS
c. GDS
d. no group
d. no group
S. agalactiae is
a. GAS
b. GBS
c. GDS
d. no group
b. GBS
Enterococcus species is
a. GAS
b. GBS
c. GDS
d. no group
c. GDS
S. pyogenes is
a. GAS
b. GBS
c. GDS
d. no group
a. GAS
S. bovis is
a. GAS
b. GBS
c. GDS
d. no group
c. GDS
Which of the following would indicate an organism is a Streptococcus rather than a Staphylococcus?
a. oval cells
b. one micrometer in diameter
c. clusters
d. chain of four
a. oval cells
The following is required fro good growth of S. pyogenes
a. oxygen
b. carbon dioxide
c. enrichment of blood or serum
d. none of the above
c. enrichment of blood or serum
Typical colonies of S. pyogenes on blood agar are
a. 1mm, opaque, alpha hemolytic
b. 2mm, opaque, yellow, beta hemolytic
c. 1mm, opaque, white, non-hemolytic
d. 1mm, opaque, gray, beta-hemolytic
d. 1mm, opaque, gray, beta hemolytic
Which of the following would explain why a strain of S. pyogenes was beta hemolytic on anaerobic blood agar but non-hemolytic when incubated in air?
a. the strain is an obligate aerobe
b. the strain has streptolysin O but lacks streptolysin S
c. the stain has streptolysin S but lacks streptolysin O
d. the strain has neither streptolysin S or O
b. the strain has streptolysin O but lacks streptolysin S
When bacitracin susceptibility testing is being used to identify S. pyogenes
a. accuracy is between 98 and 100%
b. positive results due to other streptococci will be encountered
c. approximately 6% of S. pyogenes will test negative
d. results are most accurate when the test is done on the primary plate
b. positive results due to other streptococci will be encountered
Most isolates of S. pyogenes are
a. sensitive to penicillin and resistant to erythromycin
b. sensitive to penicillin and erythromycin
c. resistant to penicillin and sensitive to erythromycin
d. resistant to penicillin and erythromycin
b. sensitive to penicillin and erythromycin
Antimicrobial susceptibility testing for S. pyogenes is
a. required for all isolates
b. required when indicated by treatment failure
c. only required for hospital isolates
d. never requied
b. required when indicated by treatment failure
Categories of clinical disease caused by S. pyogenes includes all of the following except
a. urinary infection
b. upper respiratory infection
c. cutaneous infection
d. invasive infection
a. urinary infection
The most common cause of bacterial pharyngitis is
a. S. pneumoniae
b. S. pyogenes
c. S. agalactiae
d. S. aurues
b. S. pyogenes
The etiological agent of scarlet fever is
a. S. pyogenes
b. S. agalactiae
c. S. aureus
d. S. bovis
a. S. pyogenes
Most patients with “flesh eating disease” will have the following organism isolated from blood culture
a. S. aureus
b. E. faecium
c. S. agalactiae
d. S. pyogenes
d. S. pyogenes
Typical colonies of GBS are
a. 1mm, gray, beta hemolytic
b. 1-2mm, gray, alpha hemolytic
c. 1mm, gray, double zone of hemolysis
d. 1mm, gray, gamma hemolytic
a. 1mm, gray, beta hemolytic
A four hour old neonate is seriously ill with septicemia and meningitis. The most likely bacterial cause is
a. S. aurues
b. S. pyogenes
c. E. faecium
d. S. agalactiae
d. S. agalactiae
The most likely source infecting bacteria in a four hour old neonate with septicemia and meningitis is
a. hospital staff
b. vagina of the mother
c. hospital environment
d. contaminated intravenous fluid
b. vagina of the mother
The following Streptococcus grows on MAC agar without crystal violet
a. GAS
b. GBS
c. GDS
d. S. pneumoniae
c. GDS
A Streptococcus that is bile soluble may be
a. Group D Enterococcus
b. Group D Non-Enterococcus
c. both
d. neither
d. neither
A Streptococcus that grows in bile salts may be
a. Group D Enterococcus
b. Group D Non-Enterococcus
c. both
d. neither
c. both
A Streptococcus that hydrolyzes esculin may be
a. Group D Enterococcus
b. Group D Non-Enterococcus
c. both
d. neither
c. both
A Streptococcus that grows in 6.5% sodium chloride may be
a. Group D Enterococcus
b. Group D Non-Enterococcus
c. both
d. neither
a. Group D Enterococcus
A Group D Streptococcus that is PYR positive may be
a. Group D Enterococcus
b. Group D Non-Enterococcus
c. both
d. neither
a. Group D Enterococcus
Identification of GDS to the species level requires
a. series of biochemical tests
b. DNA hybridization tests
c. serological identification of subgroup antigens
d. testing for susceptibility to a battery of antimicrobials
a. series of biochemical tests
Which of the following tends to be the most resistant to antimicrobials?
a. S. viridans
b. GBS
c. Group D Non-Enterococcus
d. Group D Enterococcus
d. Group D Enterococcus
Antimicrobials often used in combination to treat enterococcal infections include
a. penicillin and tetracycline
b. penicillin and aminoglycoside
c. penicillin and vancomycin
d. erythromycin and tetracycline
b. penicillin and aminoglycoside
The recommended screen test for VRE is
a. an agar plate with 6ug/L vancomycin
b. a disc diffusion test
c. a broth with 6ug/L vancomycin
d. an agar plate with an oxacillin disc
a. an agar plate with 6ug/L vancomycin
The organism most likely to be found as normal fecal flora is
a. S. agalactiae
b. S. viridans
c. CNS
d. Enterococcus species
d. Enterococcus species
The isolation of the following organism from a blood culture may indicate GI carcinoma
a. E. faecalis
b. S. agalactiae
c. S. bovis
d. E. faecium
c. S. bovis
Mucoid, alpha hemolytic colonies that tend to be concave are likely
a. S. viridans
b. S. pneumoniae
c. S. agalactiae
d. E. faecalis
b. S. pneumoniae
The carbon dioxide requirements for S. pneumoniae are best described as
a. increased CO2 required for all strains
b. increased CO2 never required
c. increased CO2 required for some strains on primary isolation
d. increased CO2 only required if growing on chocolate agar
c. increased CO2 required for some strains on primary isolation
A blood culture broth grew S. pneumoniae on the first subculture but showed no growth on subculture done two days later. The best explanation is
a. the first subculture was contaminated
b. the bacteria have undergone autolysis
c. the blood culture broths have been mixed up
d. a hot loop was used for the second subculture
b. the bacteria have undergone autolysis
Bile esculin Streptococcus may be
a. S. pneumoniae
b. S. viridans
c. both
d. neither
d. neither
Bile soluble Streptococcus may be
a. S. pneumoniae
b. S. viridans
c. both
d. neither
a. S. pneumoniae
Alpha hemolytic Streptococcus may be
a. S. pneumoniae
b. S. viridans
c. both
d. neither
c. both
Optochin sensitive Streptococcus may be
a. S. pneumoniae
b. S. viridans
c. both
d. neither
a. S. pneumoniae
PYR positive Streptococcus may be
a. S. pneumoniae
b. S. viridans
c. both
d. neither
d. neither
The following test may be used for rapid identification of S. pneumoniae
a. latex agglutination
b. hemagglutination test
c. PYR test
d. hippurate hydrolysis
a. latex agglutination
The following best describes the susceptibility of S. pneumoniae to penicillin
a. all strains are resistant
b. all strains are susceptible
c. most strains are susceptible but some are resistant
d. most strains are resistant but some are susceptible
c. most strains are susceptible but some are resistant
Screening for penicillin resistance in S. pneumoniae requires
a. Mueller Hinton agar enriched with blood
b. the use of an oxacillin disc
c. preparation of inoculum by emulsifying colonies directly in broth
d. all of the above
d. all of the above
Which of the following statements does not apply to S. viridans
a. includes alpha and gamma hemolytic strains
b. a common cause of subacute bacterial endocarditis
c. resistant to optochin
d. soluble in bile salts
d. soluble in bile salts
Which of the following is most likely to be the cause of adult lobar pneumonia
a. S. pyogenes
b. S. agalactiae
c. S. bovis
d. S. pneumoniae
d. S. pneumoniae
S. pneumoniae seen in spinal fluid from patients with meningitis are often seen as
a. spherical cocci in pairs
b. spherical cocci in chains
c. elongated cocci in pairs
d. round cocci in clusters
c. elongated cocci in pairs
The most common cause of subacute bacterial endocarditis is
a. S. pyogenes
b. S. bovis
c. S. viridans
d. S. pneumoniae
c. S. viridans
There may be more than one correct answer:
Tests that may be used for presumptive identification of S. pyogenes include
a. bacitracin susceptibility
b. CAMP
c. PYR
d. hippurate hydrolysis
a and c
bacitracin susceptibility and PYR
There may be more than one correct answer:
The antigens identified in Streptoocci grouping are
a. cell wall antigens
b. proteins
c. carbohydrates
d. capsular antigens
a and c
cell wall antigens and carbohydrates
There may be more than one correct answer:
Direct detection of group A antigen from throat swabs
a. provides results within 1 hour
b. yields few false positives
c. may be negative when few bacteria are present
d. is suited for home testing
a, b, and c
provides results within 1 hour, yields few false positives, and may be negative when few bacteria are present
There may be more than one correct answer:
Post-Streptococcal diseases include
a. rheumatic fever
b. scarlet fever
c. glomerulonephritis
d. subacute bacterial endocarditis
a and c
rheumatic fever and glomerulonephritis
There may be more than one correct answer:
Presumptive identification tests for GBS include
a. CAMP
b. PYR
c. hippurate hydrolysis
d. esculin hydrolysis
a and c
CAMP and hippurate hydrolysis
There may be more than one correct answer:
The following clinical specimens give reliable results for direct testing for Group B antigen
a. urine
b. serum
c. spinal fluid
d. sputum
a and c
urine and spinal fluid
There may be more than one correct answer:
Streptococci with Group D antigens include
a. E. faecalis
b. S. bovis
c. E. faecium
d. S. equinus
a, b, c, and d
E. faecalis, S. bovis, E. faecium, and S. equinus
There may be more than one correct answer:
Group D antigen identification
a. lacks specificity and sensitivity
b. involves identification of teichoic acid antigens
c. requires specific extraction procedures
d. is the most accurate method of identifying GDS
a, b, and c
lacks specificity and sensitivity, involves identification of teichoic acid antigens, and requires specific extraction procedures
There may be more than one correct answer:
VRE
a. are usually E. faecium
b. can be screed for using an agar plate with vancomycin
c. are important nosocomial pathogens
d. are less common now than ten years ago
a, b, and c
are usually E. faecium, can be screened for using an agar plate with vancomycin, and are important nosocomial pathogens
Identify the organism:
Alpha hemolytic, translucent, 1mm Gram positive cocci Bile esculin - negative Optochin - resistant Bile solubility - insoluble
S. viridans
Identify the organism:
Non-hemolyric, translucent, 2mm Gram positive cocci Catalase - negative Bile esculin - positive 6.5% NaCl - positive
Group D Streptococcus Enterococcus species
Identify the organism:
Beta hemolytic, creamy, opaque Gram positive cocci Catalase - positive Bacitracin - resistant Esculin - positive Slide coagulase - positive
S. aureus
Identify the organism:
Alpha hemolyric, translucent, 2mm
Gram positive cocci
Optochin - sensitive
Bile solubility - soluble
S. pneumoniae
Identify the organism:
Beta hemolytic, opaque, 1mm Gram positive cocci Catalase - negative Bile esculin - negative PYR - positive
S. pyogenes
Identify the organism:
Alpha hemolytic, translucent, 1mm
Gram positive cocci
Bile esculin - positive
PYR - negative
Group D Streptococcus Non-Enterococcus species
Identify the organism:
Beta hemolyric, translucent, 2mm Gram positive cocci Catalase - negative Bacitracin - resistant Group A antigen - negative Bile esculin - negative
What is needed to definitively ID this bug?
Streptococcus not group A or D
Requires antigen typing, latex/co-agglutination
