Diphtheria laboratory findings: Difference between revisions
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__NOTOC__ | __NOTOC__ | ||
{{Diphtheria}} | {{Diphtheria}} | ||
{{CMG}} {{AE}} {{ | {{CMG}}; {{AE}}{{DN}} | ||
==Overview== | ==Overview== | ||
==Laboratory Findings== | ==Laboratory Findings== | ||
A presumptive diagnosis is usually based on clinical features. | A presumptive diagnosis of [[diphtheria]] is usually based on clinical features. A definitive diagnosis is made by growing the specific [[Corynebacterium]] species on special cultures from the [[respiratory]] tract secretions or [[cutaneous]] lesions.<ref name="pmid10657205">{{cite journal |vauthors=Efstratiou A, Engler KH, Mazurova IK, Glushkevich T, Vuopio-Varkila J, Popovic T |title=Current approaches to the laboratory diagnosis of diphtheria |journal=J. Infect. Dis. |volume=181 Suppl 1 |issue= |pages=S138–45 |year=2000 |pmid=10657205 |doi=10.1086/315552 |url=}}</ref><ref name="pmid1740514">{{cite journal |vauthors=Colman G, Weaver E, Efstratiou A |title=Screening tests for pathogenic corynebacteria |journal=J. Clin. Pathol. |volume=45 |issue=1 |pages=46–8 |year=1992 |pmid=1740514 |pmc=495813 |doi= |url=}}</ref><ref name="pmid18017268">{{cite journal |vauthors=Widelock D |title=Laboratory Diagnosis of Diphtheria |journal=Am J Public Health Nations Health |volume=41 |issue=1 |pages=120 |year=1951 |pmid=18017268 |pmc=1525936 |doi= |url=}}</ref> | ||
===Culture and Staining=== | ===Culture and Staining=== | ||
Diagnosis of diphtheria is usually made on the basis of clinical presentation since it is imperative to begin presumptive therapy quickly. Culture of the lesion is done to confirm the diagnosis. It is critical to take a swab of the pharyngeal area, especially any discolored areas, ulcerations, and tonsillar crypts. Culture medium containing [[tellurite]] is preferred because it provides a selective advantage for the growth of this organism. A [[blood agar]] plate is also inoculated for detection of hemolytic [[streptococcus]]. If diphtheria bacilli are isolated, they must be tested for toxin production. [[Gram stain]] and [[Kenyon stain]] of material from the membrane itself can be helpful when trying to confirm the clinical diagnosis. The Gram stain may show multiple club-shaped forms that look like Chinese characters. Other Corynebacterium species (diphtheroids) that can normally inhabit the throat may confuse the interpretation of direct stain. However, treatment should be started if clinical diphtheria is suggested, even in the absence of a diagnostic Gram stain. | Diagnosis of diphtheria is usually made on the basis of clinical presentation since it is imperative to begin presumptive therapy quickly. Culture of the lesion is done to confirm the diagnosis. It is critical to take a swab of the pharyngeal area, especially any discolored areas, ulcerations, and tonsillar crypts. Culture medium containing [[tellurite]] is preferred because it provides a selective advantage for the growth of this organism. A [[blood agar]] plate is also inoculated for detection of hemolytic [[streptococcus]]. If diphtheria bacilli are isolated, they must be tested for toxin production. [[Gram stain]] and [[Kenyon stain]] of material from the membrane itself can be helpful when trying to confirm the clinical diagnosis. The Gram stain may show multiple club-shaped forms that look like Chinese characters. Other Corynebacterium species (diphtheroids) that can normally inhabit the throat may confuse the interpretation of direct stain. However, treatment should be started if clinical diphtheria is suggested, even in the absence of a diagnostic Gram stain. | ||
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[[PCR]] assays can also be performed on isolates, swabs, or [[membrane]] specimens to rapidly confirm the presence of the tox gene responsible for production of diphtheria toxin, but the test is available only in research or reference laboratories. | [[PCR]] assays can also be performed on isolates, swabs, or [[membrane]] specimens to rapidly confirm the presence of the tox gene responsible for production of diphtheria toxin, but the test is available only in research or reference laboratories. | ||
==References== | ==References== | ||
{{Reflist|2}} | {{Reflist|2}} | ||
[[Category:Infectious disease]] | [[Category:Infectious disease]] | ||
{{WikiDoc Help Menu}} | {{WikiDoc Help Menu}} | ||
{{WikiDoc Sources}} | {{WikiDoc Sources}} | ||
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dima Nimri, M.D. [2]
Overview
Laboratory Findings
A presumptive diagnosis of diphtheria is usually based on clinical features. A definitive diagnosis is made by growing the specific Corynebacterium species on special cultures from the respiratory tract secretions or cutaneous lesions.[1][2][3]
Culture and Staining
Diagnosis of diphtheria is usually made on the basis of clinical presentation since it is imperative to begin presumptive therapy quickly. Culture of the lesion is done to confirm the diagnosis. It is critical to take a swab of the pharyngeal area, especially any discolored areas, ulcerations, and tonsillar crypts. Culture medium containing tellurite is preferred because it provides a selective advantage for the growth of this organism. A blood agar plate is also inoculated for detection of hemolytic streptococcus. If diphtheria bacilli are isolated, they must be tested for toxin production. Gram stain and Kenyon stain of material from the membrane itself can be helpful when trying to confirm the clinical diagnosis. The Gram stain may show multiple club-shaped forms that look like Chinese characters. Other Corynebacterium species (diphtheroids) that can normally inhabit the throat may confuse the interpretation of direct stain. However, treatment should be started if clinical diphtheria is suggested, even in the absence of a diagnostic Gram stain.
Elek's test
It's worth noting that a low concentration of iron is required in the medium for toxin production; as at high iron concentrations, iron molecules bind to a repressor which shuts down toxin production[4]. This is most appreciated when performing Elek's test for toxogenecity, in order to know if the organism is able to produce the diphtheria toxin or not.
PCR
PCR assays can also be performed on isolates, swabs, or membrane specimens to rapidly confirm the presence of the tox gene responsible for production of diphtheria toxin, but the test is available only in research or reference laboratories.
References
- ↑ Efstratiou A, Engler KH, Mazurova IK, Glushkevich T, Vuopio-Varkila J, Popovic T (2000). "Current approaches to the laboratory diagnosis of diphtheria". J. Infect. Dis. 181 Suppl 1: S138–45. doi:10.1086/315552. PMID 10657205.
- ↑ Colman G, Weaver E, Efstratiou A (1992). "Screening tests for pathogenic corynebacteria". J. Clin. Pathol. 45 (1): 46–8. PMC 495813. PMID 1740514.
- ↑ Widelock D (1951). "Laboratory Diagnosis of Diphtheria". Am J Public Health Nations Health. 41 (1): 120. PMC 1525936. PMID 18017268.
- ↑ Microbiology: A Human Perspective. Fourth edition. McGraw Hill