What organism is suggested if gram stain shows sulfur granules containing gram-positive rods?

The presence of sulfur granules containing gram-positive rods in a gram stain is characteristic of Actinomyces israeli. This organism is part of the Actinobacteria class and is recognized for producing a distinct disease known as actinomycosis, which is often associated with the formation of abscesses and the presence of these recognizable sulfur granules.

Actinomyces species are typically filamentous and can be observed as branching gram-positive rods under the microscope. The granules in question are actually clusters of the bacteria surrounded by a matrix of polysaccharides and debris, which can resemble sulfur in color, particularly when stained. This distinguishing feature is key to diagnosing infections caused by this organism and is not seen with the other choices presented.

Other organisms listed, such as Propionibacterium acnes, Staphylococcus intermedius, and Peptostreptococcus anaerobius, do not produce sulfur granules or show the same characteristic morphology in gram staining, making them less likely to be involved in a scenario that presents with these specific signs.