Gram Positive Cocci, Catalase Negative Flashcards
The group is antigen is unique, placing the organism in Lancefield group A.
Streptococcus pyogenes
is attached to the peptidoglycan of the cell wall and extends to the cell
surface
is essential for virulence S. pyogenes colonizes the throat and skin
on humans making these sites primary sources of transmission
Strepococcus pyogenes- M Protein
M protein encoded by the
genes emm
molecule causes streptococcal cell to resist phagocytosis and
plays a role in adherence of the bacterial cell to mucosal cells.
Steptococcus pyogenes-M protein
is the most common serotype seen in pharyngitis
M1 serotype
are adhesion
molecules that mediate attachment to host epithelial cells.
Fibronectin-binding protein (Protein F) and Lipotechoic acid-
- it prevents opsonized phagocytosis by neutrophils or
macrophages. It also allows the bacterium to mask its antigens and remain
unrecognized by its host
Hyaluronic acid capsule
Responsible for hemolysis on Sheep Blood Agar plates incubated
anaerobically, oxygen labile
Streptolysin O
yses leukocytes and is non-immunogenic
Oxygen stable
Streptolysin S
- spreading factor is an enzyme that solubilizes the ground
substance of mammalian connective tissues.
Hyaluronidase
red spreading rash
Streptococcal pyrogenic endotoxins/erythrogenic toxins
It is the most common clinical manifestation of Group A Streptococcus
Bacterial pharyngitis
include impetigo, cellulitis, erysipelas, wound
infection, or arthritis
Skin or pyodermal infections
- 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
Erysipelas-
can develop following deeper invasion by streptococci.
cellulitis
An invasive infection characterized by rapidly progressing inflammation
and necrosis of the skin, subcutaneous fat, and fascia.
Necrotizing Fasciitis
Key tests are bacitracin susceptibility or pyrrolidonyl-alpha-naphtylamide (PYR)
hydrolysis
Streptococcus pyogenes
have the group B-specific antigen, an acid-stable
polysaccharide located in the cell wall.
Streptococcus agalactiae
There are 9 recognized capsular polysaccharide serotypes.
Serotypes Ia, IIb and II contain a terminal residue of sialic acid
prevents phagocytosis but is ineffective after opsonisation.
The capsule
appears to be the most significant component of the capsule
and a critical virulence determinant
Sialic acid
Early onset infection -
<7 days old
Late onset infection
- at least 7 days old to about 3 months old
Grows on Sheep Blood Agar as grayish white mucoid colonies surrounded by a
small zone of Beta hemolysis
Streptococcus agalactiae
Todd-Hewitt
broth containing
10 ug/mL colistin and 15 ug/mL nalidixic acid.
Also known as pneumococcus
Streptococcus pneumoniae
Virulence Factors of Streptococcus pneumoniae
Capsular polysaccharide
o Hemolysin
o Immunoglobulin A protease
o Neuraminidase
o Hyaluronidase
It is an important human pathogen that causes pneumonia, sinusitis, otitis media,
bacteremia, and meningitis.
Streptococcus pneumoniae
Atypical haemolytic uremic syndrome in children
Streptococcus pneumoniae
o Brain-heart infusion agar, trypticase soy agar with 5% sheep RBCs, or chocolate
agar are necessary for good growth
Streptococcus pneumoniae
S. pneumoniae is susceptible
Optochin susceptibility-
S. pneumoniae is bile soluble
Bile solubility test-
They are constituents of the normal microbiota of the upper respiratory tract
Viridans Streptococci
They were previously classified as group D streptococci.
Enterococcus
he commonly identified species in clinical specimens of enterococcus are
Enterococcus faecalis and Enterococcus faecium.
sometimes exhibit pseudocatalase reaction.
Enterococci
they can grow in
extreme conditions and are resistant to multiple antimicrobial agents.
Enterococcus
are thought to play a role in the colonization of the
species and adherence to heart valves and renal epithelial cells.
enterococcus
shows similarity to bacteriocins produced by gram-positive bacteria and
is expressed by quorum-sensing mechanism.
Cytolysin
Trypticase soy or brain-heart infusion agar supplemented with 5% sheep blood is
routinely used to culture
enterococci.
If the clinical specimen is obtained from a contaminated site or is likely to contain
gram-negative organisms, selective media containing
bile esculin azide, colistin
nalidixic acid, phenylethyl alcohol, chromogenic substrates, or cephalexinaztreonam-arabinose agar should be used
Enterococcus spp. are identified based on their
ability to produce acid in carbohydrate broth
ability to hydrolyze arginine
tolerance of 0.04% tellurite (tween 80)
utilization of pyruvate
ability to produce acid from methyl-α-D-glucopyranoside