Chap 16: Aerobic gram-pos bacilli Flashcards
positive aerobic bacilli spore-forming genus
bacillus
non-spore-forming bacteria include genera
corynebacterium, arcanobacterium, rhodococcus, listeria, erysipelothrix, gardnerella
branching, non-spore-forming aerobic actinomycetes
nocardia
non-spore-forming, nonbranching catalase-pos bacilli
corynebacterium
based on 16S rRNA, corynebacteria are closely related to
mycobacteria and nocardiae
corynebacteria can be divided into
nonlipophilic and lipophilic
type of corynebacteria that are often considered fastidious and grow slowly on standard culture media; culture must be incubated at least 48 hrs before growth is detected
lipophilic corynebacteria
on gram stain, corynebacteria are
slightly curved, gram-pos rods with unparallel sides and sligtly wider ends, producing the described “club-shaped”
most significant pathogen of the group
C. diphtheriae; which causes diphtheria
nondiphtheria corynebacterium spp. that produce disease in humans include, but are not limited to
corynebacterium amycolatum, corynebacterium pseudodiphtheriticum, corynebacterium pseudotuberculosis, corynebacterium jeikeium, corynebacterium striatum, corynebacterium ulcerans, corynebacterium urealyticum
major virulence factor of C. diphtheriae
diphtheria toxin
this toxin is produced by strains of C.diphtheriae infected with
lysogenic B-phage, which carries the tox gene for diphtheria toxin
diphtheria toxin is exceedingly potent and is lethal for humans in amounts of
130 ng/kg of body weight
toxicity is due to the
ability of diphtheria toxin to block protein synthesis in eukaryotic cells
toxin is secreted by the bacterial cell and nontoxic until
exposed to trypsin
trypsinization cleaves the toxin into
two fragments
this fragment is responsible for the cytotoxicity
fragment A
fragment that binds to receptors on the eukaryotic cells and mediates the entry of fragment A into the cytoplasm
fragment B
enzyme required for elongation of polypeptide chains on ribosomes
adenosine diphosphoribose (ADPR)
production of the toxin in vitro depends on environmental conditions
alkaline pH (7.8 tp 8.0), oxygen, iron concentration
C. diphtheriae causes two diff. forms of disease in humans
respiratory and cutaneous diphtheria
humans are the only natural hosts for c. diphtheriae
individuals vaccinated as children who have not revaccinated as adults are susceptible to infection
c.diphtheriae is carried in the upper respiratory tract and spread by droplet infection or hand-to-mouth contact
incubation period averages 2 to 5 days
illness begins gradually and characterized by
low-grade fever, malaise, and mild sore throat
most common site of infection
tonsils or pharynx
combination of cell necrosis and exudate forms a
tough gray-to-white pseudomembrane, which attaches to the tissues
there’s a potential for suffocation
if the membrane blocks the air passage or if it is dislodged, perhaps as the result of sampling for a throat culture
toxin is also absorbed and can produce various systemic effects involving the
kidneys, heart, and nervous system, altho all tissues possess the receptor for the toxin and may be affected
another effect of the toxin is
demyelinating peripheral neuritis, which can result in paralysis following the acute illness
cutaneous diphtheria consists of
nonhealing ulcers with a dirty gray membrane
commercial diphtheria antitoxin is producedin
horses
drug of choice is
penicillin; erythromycin is used for penicillin-sensitive individuals
c. diphtheriae is highly pleomorphic (many shapes) gram-pos bacillus that appears in palisades (cells lie in paraller rows) or as individual cells lying at sharp angles to another “V” and “L” formations
microscopy
organisms often stain irregularly, especially when stained with methylene blue,
giving them a beaded appearance
the metachromatic areas of the cell, which stain more intensely that other parts, are called
Babes-Ernst granules
c.diphtheriae is a facultative anaerobe
grows best under aerobic conditions and has an optimal growth temp of 37 degrees, altho multiplication occurs within the range of 15 to 40 degrees C
c. diphtheriae grows on nutrient agar, better growth is usually obtained on medium containing blood or serum, such as
loeffler serum or pai agars
the organism can have a very small zone of B-hemolysis in this media
SBA
a modification of Tinsdale medium, contains sheep blood rbs, bovine serum, cystine, and potassium tellurite
cystine-tellurite blood agar
cbta is both
selective and differential medium
when grown on cbta, corynebacteria form
black or brownish colonies from the reduction of tellurite
useful in differentiating feature of C.diphtheriae, c.ulcerans, c.pseudotuberculosis
brown halo surrounding the colony on CBTA, owing to cystinase activity
all medically important corynebacteria are
catalase-positive and nonmotile
the addition of iron too iron-starved cultures
inhibits production very quickly
in vivo toxin testing is rarely done because the in vitro methods are
reliable, less expensive, and free from animal use
the in vitro diphtheria toxin detection procedure is an immunodiffusion test first described by
elek
elek test requires that reagents and antisera be carefully
controlled and titrated
also available for detecting of the diphtheria toxin
rapid enzyme-linked immunosorbent assays and immunochromatographic strip assays
is the most frequently recovered corynebacterium species from human clinical material
c.amycolatum
part if the normal skin microbiota and has previously been misidentifies by clinical lab as
c.striatum, c.xerosis, c.minutissimum
often associated with prosthetic joint infection and has been reported to cause blood-stream infection and endocarditis
c.amycolatum
colonies of c.amycolatum are
flat, dry, have a matte or waxy appearance, and are nonlipophilic
most strains have been reported to be resistant to wide range of antimicrobials, including
B-lactams, fluoroquinolines, macrolides, clindamycin, aminoglycosides
named after johnson and kaye, who first linked this organism with human infections, appear to be part of the normal skin microbiota
c.jeikeium
also the most common cause of corynebacterium-associated prosthetic valve endocarditis in adults; causes septicemia, meningitis, prosthetic joint infections, skin complications such as rash and subcutaneous nodules
c.jeikeium
jeikeium resistant to wide range of antimicrobials, including
penicillins, cephalosporins, macrolides, aminoglycosides
drug of choice for jeikeium is
vancomycin
part of normal microbiota of human nasopharynx; an infrequent cause of infection
c. pseudodiphtheriticum
c.pseudodiphtheriticum has been reported to cause
endocarditis
uti
cutaneous wound infections
primarily a veterinary pathogen; infections are associated with contact with sheep and are rare
c. pseudotuberculosis
often considered a commensal or skin contaminant
c.striatum
most commonly associated with device-related infection; reported incases of endocarditis, septic arthritis, meningitis, pneumonia
c. striatum
also a veterinary pathogen, causing mastitis in cattle and other domestic and wild animals
c. ulcerans
most commonly associated with UTIs
c. urealyticum
are actually gram-pos cocci that can appear rod-like that belong to the family of micrococcaceae
rothia spp.
has been linked to bacteremia, endocarditis, pneumonia, other infections
rothia mucilaginosa
member of normal human oropharyngeal microbiota and may be found in saliva and supragingival plaque
rothia dentocariosa
