Q&A: Optochin in Diagnosing Diseases

Optochin (ethylhydrocupreine hydrochloride), a quinine derivative, is a chemical and completely soluble in water. Optochin is an antibiotic that interferes with the ATPase and production of adenosine triphosphate (ATP) in microorganisms.

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In this article:
Sputum culture
MCQ exams: clinical scenario
MCQ exams: answer
MCQ exams: explanation

Sputum culture

A sputum culture is a test to detect and identify bacteria or fungi that has infected the lungs or breathing passages. Sputum is the thick fluid produced in the lungs and in the adjacent airways. Normally, fresh morning sample is preferred for the bacteriological examination of sputum.

A sample of sputum is collected in a sterile, wide-mouthed, dry, leak-proof and break-resistant plastic-container and sent to the laboratory for testing. Sampling may be performed by sputum being expectorated (produced by coughing), induced (saline is sprayed in the lungs to induce sputum production), or taken via an endotracheal tube with a protected specimen brush (commonly used on patients on respirators) in an intensive care setting.

Optochin is used in bacteriology for the differentiation of optochin-sensitive and optochin-resistant organisms. This allows identification of the organism. The growth of bacteria that are optochin-sensitive will show a zone of inhibition around an optochin disc, while the growth of bacteria that are resistant to optochin will not be affected.

MCQ exams: clinical scenario

A 35 year old man has a three day history of a productive cough. His x-ray shows evidence of bilateral consolidation. A sputum culture grows a gram positive organism that is lysed by ethyl hydrocupriene (Optochin).

These features are characteristic of (please choose one):

a) Streptococcus pneumoniae
b) Bacteroides fragilis
c) Coxiella burnetii
d) Escherichia coli
e) Haemophilus influenzae

MCQ exams: answer

The correct answer is A.
Streptococcus pneumoniae is the right choice.

MCQ exams: explanation

The Optochin test is a presumptive test that is used to identify strains of Streptococcus pneumoniae. Optochin (ethyl hydrocupreine) disks are placed on inoculated blood agar plates; and because S. pneumoniae is not optochin resistant, a zone of inhibition will develop around the disk where the bacteria have been lysed. This zone is typically 14 mm from the disk or greater.

Streptococcus pneumoniae is a gram-positive coccus that in clinical specimens often appears in pairs with tapered ends (lancet shaped), although it grows in short chains on nutrient broth media. It is a relatively fastidious facultative anaerobe and requires increased carbon dioxide for optimum recovery from clinical specimens.

Susceptibility to ethyl hydrocupriene hydrochloride (Optochin) distinguishes pneumococci from other streptococci in the clinical microbiology laboratory.

Reference(s)
1). UK Standards for Microbiology Investigations. Optochin test. Available online: https://www.gov.uk/government/publications/smi-tp-25-optochin-test
2). Centre for Disease Control and Prevention. Identification and Characterization of Streptococcus pneumonia. Available online: https://www.cdc.gov/meningitis/lab-manual/chpt08-id-characterization-streppneumo.pdf
3). D. Behera (2010). Textbook of Pulmonary Medicine. JP Medical Ltd. p. 284. ISBN 978-81-8448-749-7