Non-spore-forming Gram-positive Bacilli Flashcards
Specimen for Corynebacterium diphtheriae
Swabs from the
oropharynx
nasopharynx
cutaneous lesions
If a pseudomembrane is present, swab specimens from [?] the membrane should be collected.
beneath
Gram staining: [?] that occur in angular arrangements (commonly referred to as Chinese letters or palisades) and whose ends may be swollen, producing a club shape.
Pleomorphic gram-positive rods
Pleomorphic beaded rods, reddish purple metachromatic granules or bars of polyphosphates are apparent.
Loeffler’s alkaline methylene blue (LAMB), e.g., Albert’s staining:
C. ulcerans and C. pseudotuberculosis resemble C. diphtheriae, producing [?] cells containing metachromatic granules.
distinctive, clubshaped, diphtheroidal
Used to screen and rule out group A β-hemolytic streptococci from throat specimen.
5% sheep BAM, Columbia CNA agar
AKA Cystine-sodium thiosulfate-tellurite
medium
Tinsdale agar (TIN)
High concentration of potassium tellurite is inhibitory to most [?] (other than Corynebacterium species) and majority of [?]
upper respiratory tract normal flora
gram-negative bacteria
organisms capable of growing on the
medium are differentiated based on the [?], resulting in the reduction to tellurium, thus will grow as [?].
tellurite reductase activity
black colonies
[?] and [?] provide essential growth factors.
Bovine serum and horse serum
provide sulfur for H2S production; and cystine detects cystinase activity producing brown halos around the colonies.
Sodium thiosulfate
A heart infusion agar supplemented with [?].
5% rabbit blood, tellurite, and Lcystine
A selective and differential medium for Corynebacterium species similar
to TIN.
Cystine-tellurite blood agar (CTBA)
Contains [?] and [?], rather than agar, to coagulate to produce a solid medium.
eggs and beef serum
Stimulates the growth of distinctive, [?] cells of C. diphtheriae and the production of metachromatic granules in the cells.
club-shaped, diphtheroidal
colonies show no characteristic differential features to distinguish from other gram-positive bacilli.
“Poached egg”
Contains coagulated egg in distilled water and glycerin.
Pai medium
Specimens should be inoculated to a [?] and a selective medium such as a [?] (eg, CTBA or TIN)
blood agar
tellurite plate
Incubate at either in ambient air or in
5% to 10% CO2 for 24 - 48 h
C. diphtheriae may appear as four distinct colony types (biotypes) designated [?]
These biotypes also differ slightly in Gram’s stain morphology, certain biochemical reactions, and historically, in the severity of the disease processes they produce.
gravis, mitis, intermedius, and belfanti
On
C. diphtheriae produce colonies ranging from
small, gray, and translucent - [?]
to medium, white, and opaque
C. diphtheriae [?] may be βhemolytic.
BAM
- biotype intermedius
- biotypes mitis, belfanti, and gravis
- biotype mitis
On
Colonies of C. diphtheriae appear
CTBA
black or gray.
Large (2-4 mm), flatter, dark gray with radial striations and irregular edges.
“DAISY HEAD” colonies.
Short, coccoid, or pyriform.
C. diphtheriae biotype gravis
Small (0.5 mm), sometime pinpoint, flat, and gray.
“FROG’S EGGS” colonies.
Highly pleomorphic, from very long to very short rods.
C. diphtheriae biotype intermedius
Medium-sized (1-2 mm), convex, very black with regular edges.
“COOLIE HAT” colonies.
May be weakly βhemolytic
Long, pleomorphic, rigid clubshaped rods.
C. diphtheriae biotype mitis
C. diphtheriae biotype belfanti
On
All four biotypes of C. diphtheriae grow as [?] surrounded by [?].
TIN
- black colonies
- dark brown halos
C. ulcerans and C. pseudotuberculosis resemble C. diphtheriae, producing [?] that are surrounded by brown halos on TIN.
black colonies
Other diphtheroids, S. aureus and some streptococci which can also grow in the presence of tellurite will develop black colonies due to tellurite reduction although [?] around the colonies are NOT present.
brown halos
is based on the production by the organism of phospholipase C or D that inhibits the staphylococcal β-hemolysin.
The reverse CAMP reaction
An arrowhead zone of [?] is formed at the junction of the organism being tested with the staphylococci.
NO hemolysis
Once an organism is biochemically identified as a possible C. diphtheriae, the isolate must be tested for the ability to produce diphtheria toxin.
Toxigenicity test
For demonstration of toxin production by C. diphtheriae.
Elek Test
A filter paper strip impregnated with [?] is buried just beneath the surface of a [?] before the agar hardens.
Strains to be tested and known positive and negative toxigenic strains are streaked on the agar’s surface in a line across the plate and at a right angle to the antitoxin paper strip.
After 24 hours of incubation at 37°C, the plates are examined with transmitted light for the presence of fine [?] at a 45-degree angle to the streaks.
The presence of precipitin lines indicates that the strain produced toxin that reacted with the [?].
Line 1 is the negative control.
Line 2 is the positive control.
Line 3 is a test organism that is a nontoxigenic strain.
Line 4 is a test organism that is a toxigenic strain.
diphtheria antitoxin
rabbit serum agar plate
precipitin lines
homologous antitoxin
Specimens for Listeria monocytogenes
CSF, blood, amniotic fluid/placenta
Gram staining: Short, gram-positive bacilli (coccobacilli) may occur intracellularly or extracellularly, at times, may occur in pairs and be mistaken for pneumococci; it tends to appear gram-negative when overdecolorized.
Listeria monocytogenes
In wet mounts observed at 25oC, it exhibits “tumbling” or “head over heels” motility.
Listeria monocytogenes
Recovery of the organism from clinical samples is enhanced by inoculation in broth medium and incubation at 4°C for 4 \ hours prior to incubation on primary culture plates.
Cold enrichment technique: Listeria monocytogenes
Requires 5% to 10% CO2 for growth.
Listeria monocytogenes
L. monocytogenes has a narrow zone of beta-hemolysis on
5% sheep BAM
can be used as a plating medium with or without supplementation of blood
McBride Agar
Partial selectivity is provided by [?], which aid in suppressing both G+ and G-bacteria other than Listeria
lithium chloride, glycine and phenylethanol
develops into small, blue-green colonies, with small zone of hemolysis around and under colonies.
L. monocytogenes on McBride Agar
In semi-solid medium, the identification can be made by observing for a thin, umbrella-like growth from the stab line.
Motility test
This is a pathogenicity test that differentiates pathogenic from non-pathogenic strains of L. moncytogenes.
It Involves instillation of a 24hr broth culture of L. monocytogenes in the conjunctiva of a lab animal.
Development of purulent conjunctivitis within 24 to 36 hours constitutes a positive result.
Anton Test
