What is the probable pathogen responsible for yellow colonies on XLD agar from a burger-related illness?

What is the probable pathogen responsible for yellow colonies on XLD agar from a burger-related illness?

• A. Salmonella spp.
• B. Shigella spp.
• C. E. coli O157:H7
• D. Yersinia enterocolitica

Answer: (C)

Yellow colonies on XLD (Xylose Lysine Deoxycholate) agar usually indicate the presence of certain lactose fermenting bacteria, which can include E. coli, particularly strains that are pathogenic, such as E. coli O157:H7. This strain is notable for causing gastrointestinal illness, often linked to undercooked or contaminated beef, such as in burgers. In the context of a burger-related illness, E. coli O157:H7 is a common pathogen associated with foodborne outbreaks, and its presence can be detected on XLD agar through the characteristic yellow colonies. These yellow colonies result from the fermentation of xylose and/or lactose present in the medium, leading to acid production which causes a color change in the agar. Other pathogens listed may be involved in gastrointestinal illnesses but are more associated with different characteristics on XLD agar. For example, Salmonella typically produces red colonies, Shigella does not ferment xylose and will appear as colorless colonies, and Yersinia enterocolitica may also produce red colonies depending on its sugar fermentation profile. Thus, in the context of the question focusing on a pathogen linked specifically to burger-related illness and the resulting colony color on XLD agar, E. coli O157:H7

Yellow colonies on XLD (Xylose Lysine Deoxycholate) agar usually indicate the presence of certain lactose fermenting bacteria, which can include E. coli, particularly strains that are pathogenic, such as E. coli O157:H7. This strain is notable for causing gastrointestinal illness, often linked to undercooked or contaminated beef, such as in burgers.

In the context of a burger-related illness, E. coli O157:H7 is a common pathogen associated with foodborne outbreaks, and its presence can be detected on XLD agar through the characteristic yellow colonies. These yellow colonies result from the fermentation of xylose and/or lactose present in the medium, leading to acid production which causes a color change in the agar.

Other pathogens listed may be involved in gastrointestinal illnesses but are more associated with different characteristics on XLD agar. For example, Salmonella typically produces red colonies, Shigella does not ferment xylose and will appear as colorless colonies, and Yersinia enterocolitica may also produce red colonies depending on its sugar fermentation profile. Thus, in the context of the question focusing on a pathogen linked specifically to burger-related illness and the resulting colony color on XLD agar, E. coli O157:H7