media for organism growth

 Q: In laboratory, which media is used to detect Haemophilus influenzae? (select one) 

 A) Blood agar 

 B) Chocolate agar 

 C) MacConkey agar

Answer: B

The objective of this question is to emphasize the clinical relevance of ordering sputum culture. Laboratory personnel is usually trained to employ different media to grow different organisms but providing a little relevant history helps expedite the accurate result. For instance, Legionella pneumophila requires a specialized buffered charcoal-yeast extract (BCYE) agar media. 

Blood agar is used for gram-positive cocci (GPC) and for most of the gram-negative rods (GNR) useful.

Chocolate agar is used for Haemophilus influenzae and other fastidious organisms. 

MacConkey agar is used for gram-negative bacteria to allow further classification into lactose-positive or negative organisms.

References:

1. Muraki M, Kitaguchi S, Ichihashi H, Tsuji F, Ohmori T, Haraguchi R, Tohda Y. [Use of transport medium in sputum bacterial culture examination of lower airway infection]. Nihon Kokyuki Gakkai Zasshi. 2006 Jun;44(6):425-30. Japanese. PMID: 16841712. 

2. Rogers GB, Daniels TW, Tuck A, et al. Studying bacteria in respiratory specimens by using conventional and molecular microbiological approaches. BMC Pulm Med. 2009;9:14. Published 2009 Apr 15. doi:10.1186/1471-2466-9-14 

3. Recommendations of the Clinical Subcommittee of the Medical/Scientific Advisory Committee of the Canadian Cystic Fibrosis Foundation. Microbiological processing of respiratory specimens from patients with cystic fibrosis. Can J Infect Dis. 1993;4(3):166-169. doi:10.1155/1993/989086