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Darkfield microscopy for routine microbiological observation.

Darkfield microscopy is not utilized to a great extent today in hospital microbiology laboratories. Some reasons may be that staff are not trained in the use of darkfield, as brightfield microscopy has been used exclusively in clinical laboratories. Personnel are therefore not aware of the useful information that can be obtained quickly when darkfield microscopy is incorporated into microbiological procedures.

This correspondence concerns a recommendation to implement darkfield microscopy as a routine procedure in a hospital microbiology laboratory to observe specimens such as blood, cerebrospinal fluid, urine for UTI, minced tissue in fluid, and exudates from lesions, as well as other specimens such as stools. (1) Photomicrographs may be obtained for the record. After receipt of a specimen and darkfield observation of microorganisms, a clinician could be alerted quickly about a possible infection, and a report could be made within minutes rather than the hours or days required for stains, cultures, and instrumental procedures. For instance, if microorganisms are observed in an uncontaminated urine specimen by darkfield microscopy, it may be deduced very quickly that a patient has a UTI.

Two actual clinical cases (personal communications) are presented as examples of how darkfield microscopy could have been or was instrumental in reporting serious infections:

Case #1: A patient was admitted to a hospital clinic on a Friday complaining of weakness, fatigue, and lethargy. Following gross examination, the patient was advised by the attending physician that if symptoms persisted he should return to the hospital the following Monday. The patient returned to the hospital on Monday, blood was drawn, and the patient was diagnosed with septicemia. Had blood been drawn and observed by darkfield microscopy the previous Friday, septicemia could have been determined immediately rather than two days later and intravenous antimicrobial agents administered.

Case #2: A patient was admitted to a public health hospital complaining of vaginal discharge, pain, and burning. A vaginal specimen was obtained and submitted to the microbiology laboratory that utilized a darkfield microscope. Trichomonads were observed and reported to the physician within minutes of receipt of the specimen, and the patient was treated immediately.

Darkfield microscopy is usually not used for identification of microorganisms, but rather to alert personnel of their presence. Moreover, some microorganisms, such as leptospira and other spirochetes, are observed easily by darkfield (2,3) but cannot be resolved by brightfield because spirochetes are very thin. Additionally, both morphology and motility of microorganisms are discernible readily by darkfield microscopy, (3,4) and counts of microorganisms may be made by using appropriate devices. Also, motility of sperm may be made by, e.g., urologists, pathologists, veterinarians, and other staffs requiring this capability.

A brightfield microscope may be modified to darkfield by replacing the Abbe condenser with an oil immersion darkfield condenser.

References

(1.) Paisley JW, Mirrett S, Laurer BA, Reller RB. Microscopy of human feces for presumptive diagnosis of Camplyobacter fetus subsp jejuni enteritis. J. Clin. Microbiol. 1982;15(1):61-63.

(2.) Pierce EF, KatzKA. Darkfield microscopy for point-of-care syphilis diagnosis./WLO. 2011.43(1):30-31.

(3.) Rajasuo A, Leppanen J, Savolaininen S, Mieurman JH. Pericoronitis and tonsillitis:Clinical and darkfield microscopyfindings. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1996; 81(51:526-532.

(4.) Listgarten MA, Helliden L. Relative distribution of bacteria at clinically healthy and periodontally diseased sites in humans. J. Clin. Periodont. 1978;5(2):115-132.

--Jerry Abramson, PhD Fellow (AAA)
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Title Annotation:Readers respond
Author:Abramson, Jerry
Publication:Medical Laboratory Observer
Geographic Code:1USA
Date:Jun 1, 2014
Words:561
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