gram-positive bacilli part three
Post on 14-Feb-2016
64 Views
Preview:
DESCRIPTION
TRANSCRIPT
GRAM-POSITIVE BACILLIPART THREE
MLAB 2434: MicrobiologyKeri Brophy-Martinez
CORYNEBACTERIA
Significant Corynebacterium species C. diphtheriae C. xerosis C. pseudodiphtheriticum C. pseudotuberculosis C. jekeium C. ulcerans
CORYNEBACTERIUM SPECIES:GENERAL CHARACTERISTICS
Found as free-living saprophytes in fresh and salt water, in soil and in the air
Members of the usual flora of humans and animals(often dismissed as contaminants)
Often called “diphtheroids” or “corneforms” Corynebacterium diphtheriae is the most
significant pathogen Other species may cause infections in
immunocompromised hosts
CORYNEBACTERIUM SPECIES:GENERAL CHARACTERISTICS
Morphology
Gram-positive, non–spore-forming rods
Arrange in palisades:“L-V” shape; “Chinese characters”
Pleomorphic: “club-ends” or coryneform
Beaded, irregular staining
C. DIPHTHERIAE: AGENT OF DIPHTHERIA Toxigenic Corynebacterium diphtheriae
Worldwide distribution but rare in places where vaccination programs exist
Exotoxin, Diphtheria toxin, as the virulence factor Not all C. diphtheriae strains produce toxin Disrupts protein synthesis Triggers cell lysis
TOXIGENIC CORYNEBACTERIUM DIPHTHERIAE
Toxin consists of two fragments A: Active fragment
Inhibits protein synthesis Leads to cell/tissue death
B: Binding Binds to specific cell membrane receptors Mediates entry of fragment A into cytoplasm of host
cell
CLINICAL FORMS OF DIPHTHERIA Respiratory
Acquired by droplet spray or hand to mouth contact Non-immunized individuals are susceptible
Non-respiratory Systemic form
Toxin is absorbed in the blood stream and carried systemically
Affects the kidneys, heart, and nervous system Death occurs due to cardiac failure
Cutaneous form Seen in tropical geographic areas Infections occur at the site of abrasions Associated with animal contact & unpasteurized dairy
products
C. DIPHTHERIAE: CAUSATIVE AGENT OF DIPHTHERIA
Respiratory disease–diphtheria Incubation period–2 to 5 days
Symptoms: sore throat, fever, malaise
Toxin is produced locally, usually in the pharynx or tonsils
Toxin causes tissue necrosis, can be absorbed to produce systemic effects
Forms a tough grey to white pseudomembrane which may cause suffocation
C. DIPHTHERIAE: CAUSATIVE AGENT OF DIPHTHERIA C. diphtheriae pseudomembrane
WBC + organism
C. DIPHTHERIAE:TREATMENT
Infected patients treated with anti-toxin and antibiotics Anti-toxin produced in horses
Binds the circulating toxin Antibiotics have no effect on circulating toxin, but
prevent spread of the toxin Penicillin drug of choice
DPT Immunization
LABORATORY DIAGNOSIS: CULTURAL CHARACTERISTICS
Loeffler's slant or Pai's slant—Used to demonstrate pleomorphism and metachromatic granules ("Babes’ Ernst bodies“)
Growth on Serum Tellurite or modified Tinsdale exhibits brown or grayish→ to black halos around the colonies
LABORATORY DIAGNOSIS Microscopic morphology
Gram-positive, non–spore-forming rods, club-shaped
Appear in palisades and give
"Chinese letter" arrangement
Can be beaded From the production of
metachromatic granules Corynebacterium diphtheriae gram stain
LABORATORY DIAGNOSIS:CORYNEBACTERIUM DIPHTHERIA Identification
Confirm identification by fermentation reactions(glucose +)
Catalase positive Urease negative Non-motile
LABORATORY DIAGNOSIS Toxigenicity testing
Elek test Immunodiffusion test
Organisms are streaked on media with lox Fe content to maximize toxin production.
Identification of C. diphtheriae does NOT mean the patient has dipheria. Must show the isolate produces the toxin.
CORYNEBACTERIUM JEKEIUM Clinical Infections
Septicemia Meningitis Bacteremia Pulmonary disease
Populations Affected Immunosuppressed IV drug users Recent invasive procedure
C. JEIKEIUMISOLATION & IDENTIFICATION BAP: 48-72 hours @ 35oC in ambient air or 5% CO2 small, gray-
white colony, nonhemolytic
Gram stain: pleomorphic, club-shaped GPR arranged in V forms or palisades
Key Biochemicals Catalase= positive Nitrate reduction= negative Urea= negative Sucrose= negative Glucose= positive
Resistant to most antibiotics Susceptible to vancomycin
LISTERIA MONOCYTOGENES:GENERAL CHARACTERISTICS Gram-positive, non–spore-forming rods
Only human pathogen in genus
Widespread in nature
Known to infect a wide variety of animals
Human exposure is limited; direct or indirect
Transient colonization occurs without disease
LISTERIA MONOCYTOGENES:CLINICAL INFECTIONS Adults
Septicemia/meningitis in the compromised/elderly Mild flu-like syndrome in pregnant women could be
fatal to fetus Ingestion of contaminated food (cottage cheese,
coleslaw, chicken, hot dogs, lunch meat) Neonatal
Early onset from intrauterine transmission results in sepsis; high mortality rate
Late onset manifests as meningitis; lower mortality rate
LISTERIA MONOCYTOGENES:VIRULENCE FACTORS
Hemolysin ( Listeriolysin O) damages host cell membrane
Superoxide dismutase Resists toxic effects of the host
P60 surface protein Induces phagocytosis thru adhesion and penetration
LABORATORY DIAGNOSIS: L. MONOCYTOGENES
Identification Microscopic morphology
Gram Positive non–spore-forming coccobacillary, pairs or short chains
Colony Morphology Grows well on blood agar;
colonies produce a narrow zone of hemolysis similar to Group B Streptococcus
Small, round and translucent
LABORATORY DIAGNOSIS: L. MONOCYTOGENES
Grows well at 0.5° C to 45° C Because of this temperature range,
especially the cooler end of the range, this organism grows well in refrigerated products, such as cream, cheese, deli meats, etc.
Can sometimes be isolated after “cold enrichment” (hold broth at 4° C for several weeks and subculture)
LABORATORY DIAGNOSIS: L. MONOCYTOGENES
Identification Catalase positive
Motility: Motile at 25o C;
"umbrella" type →
Tumbling motility in hanging drop preparations (this can be seen on Gram Stain Tutor at www.medtraining.org)
“Umbrella” motility pattern (Left) typical for L. monocytogenes
LABORATORY DIAGNOSIS: L. MONOCYTOGENES
Identification CAMP test
Produces a “block” type of hemolysis in contrast to “arrow”-shape produced by Group B Streptococcus
Positive CAMP test for Group B Streptococcus
CAMP test with Listeria monocytogenes
DIFFERENTIATING CHARACTERISTICS BETWEEN L. MONOCYTOGENES AND OTHER GRAM POSITIVE BACTERIA
Species Catalase Hemolysis Motility
At R. T.EsculinHydrolysis
Growth6.5% NaCl
L. monocytogenes
Corynebacterium sp.
S. agalactiae
Enterococcus sp.
+
+
=
=
Beta
None, alpha
Beta
None, alphabeta
+
=/+
=
=
+
=
=
+
+
+/=
=/+
+
REFERENCES Engelkirk, P. G., & Duben-Engelkirk, J. (2008).
Laboratory Diagnosis of Infectious Diseases: Essentials of Diagnostic Microbiology . Baltimore, MD: Lippincott Williams & Willkins.
http://en.wikipedia.org/wiki/Lactobacillus http://www.thefullwiki.org/Corynebacterium_diphtheriae http://quizlet.com/10262287/print/ Kiser, K. M., Payne, W. C., & Taff, T. (2011). Clinical
Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education, Inc.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.
top related