strep, entero, other catalase-neg, gram-pos cocci Flashcards
formerly known as groud D strep
enterococci
previously classified as group N strep
lactococci
17 genera of catalase-neg, gram-pos cocci including
streptococcus, aerococcus, lactococcus, leuconostoc, pediococcus spp.
weak false-pos catalase reactions can be seen when
growth is taken from media containing blood, owing to the peroxidase activity of hemoglobin
streptococcal cells are more likely to appear in chains when grown in
broth cultures
growth is poor on nutrient agar such as
trypticase soy agar
media enriched with blood or serum
growth is more pronounced
partial lysis of rbc; greenish discoloration
alpha
complete lysis of rbc; clear area around colony
beta
no lysis of rbc; no change in agar
nonmeolytic
some isolates belonging to the viridans group produce
wide-zone or a’ hemolysis
pyogenic streptococci isolated frequently from humans include
streptococcus pyogenes, strep. agalactiae, strep. dysgalactiae subsp. equisimilis, strep. anginosus group
attached to the peptidoglycan of the cell wall of pyogenes and extends to the cell surface
m protein
s. pyogenes colonizes
throat and skin on humans, making these sites the primary sources of transmission
most common serotype seen in pharyngitis
M1
adhesion molecules that mediate attachment to host epithelial cells
lipoteichoic acid, protein F
s.pyogenes secretes four diff. DNases
A, B, C, D (most common is DNase B)
responsible for hemolysis on SBA plates incubated anaerobically; lyses leukocytes, platelets, other cell as well as rbc
streptolysin O
oxygen stable, lyses leukocytes, and is nonimmunogenic; hemolysis seen around colonies that have been incubated aerobically
streptolysin S
spreading factor, is an enzyme that solubilizes the ground substance of mammalian connective tissues
hyaluronidase
cause a red spreadin rash referred to as scarlet fever, caused by
streptococcal pyrogenic exotoxins, formerly called erythrogenuc toxins
infections resulting from s.pyogenes include
pharyngitis, scarlet fever, skin or pyodermal infections
most common clinical manifests of GAS infection are
pharyngitis and tonsillitis
“strep throat” is most often seen in
children between 5 and 15 yrs of age
skin or pyodermal infections with GAS result in
impetigo, cellulitis, erysipelas, wound infection or arthritis
a localized skin disease, begins as small vesicles that progress to weeping lesions
impetigo
rare infection of the skin and subcutaneous tissues observed frequently in elderly patients; characterized by an acute spreading skin lesion that is intensely erythematous
erysipelas
can develop following deeper invasion by streptococci; can be serious or life-threatening with bacteremia or sepsis
cellulitis
patients with peripheral vacular disease or diabetes, cellulitis may lead to
gangrene
characterized by a diffuse red rash that appears in the upper chest and spreads to the trunk and extremities; rash disappears over the next 5 to 7 days and is followed by desquamation
scarlet fever
an invasive infection characterized by rapidly progressing inflammation and necrosis of the skin, subcutaneous fat and fascia
necrotizing fasciitis
polymicrobial infection from which aerobic and anaerobic bacteria are recovered is categorized as
type 1 NF
consists of only GAS
type 2 NF
gas gangrene or clostridial myonecrosis
type 3
other terms for NF aside from flesh-eating bacteria
suppurative fasciitis, hospital gangrene, necrotizing erysipelas
a condition in which the entire organ system collapses, leading to death
streptococcal toxic shock syndrome
most common strains associated with streptococcal TSS
isolates with M1 and M3
two serious complications, or sequelae, of GAS disease are
rheumatic fever, acute glomerulonephritis
more common in children than in adults; sometimes occur after cutaneous or pharyngeal infection
acute glomerulonephritis
drug of choice for GAS
penicillin
for patients allergic to penicillin this can be used
erythromycin
proper sampling for strep pharyngitis
tongue should be depressed and the swab rubbed over the posterior pharynx and each tonsillar area
is inoculated and streaked for isolation; incubation should be at 35 degrees C either in ambient air or under anaerobic conditions
SBA agar plate
important virulence factor in group b strep
capsule
most significant component of the capsule and critical virulence determinant
sialic acid
products produced by s.agalactiae include
hemolysin, CAMP factor, neuraminidase, DNase, hyaluronidase, protease
two clinical syndromes are associated with neonatal GBS disease
early-onset infection (< 7 days old)
late-onset infection (at least 7 days old to about 3 months old)
vertical transmission from the mother
early onset infection 80%
early-onset infection often manifests as
pneumonia and sepsisa
late-onset infection manifests as
meningitis and sepsis
in adults, the infection affects two types of patients
1st is a young, previusly healthy woman who becomes ill after childbirth or abortion; endometritis and wound infection
2nd is an elderly person with serious underlying disease or immunodeficiency
drug of choice for gbs
penicillin, tho less susceptible than gas
s.agalactiae is sensitive to
penicillin and cephalosporin
gbs grows on sba as
grayish white mucoid colonies surrounded by a small zone of b-hemolysis; forms short chains in clinical spx and longer chains in culture
most useful tests are
camp test and positive hippurate hydrolysis
detection of bgs in pregnant women is accomplished by
collecting vaginal and rectal material with swabs between 35 and 37 weeks of gestation
samples should be inoculated into selective broth such as
todd-hewitt broth containing 10ug/ml colistin and 15ug/ml nalidixic acid
the inoculated media are incubated ay
35 degrees C for 18to24 hrs before being subcultured to SBA
can be substituted for lim or transvag broth
strepb carrot broth
b-hemolytic gbs produce an orange or red pigment in scb after
incubation for 6 hrs
the large colony-forming isolates with group c and g belong to the
subspecies s.dysgalactiae subsp. equisimilis
the small-colony-forming b-hemolytic isolates with group c and g antigens belong to the
s. anginosus group
spectrum of infections resembles s.pyogenes and includes
upper respiratory tract infections, skin infections, soft tissue infections, invasive infections such as NF
