String of pearl appearance is seen in:-

String of pearl appearance is seen in Bacillus anthracis. Laboratory Diagnosis of Anthrax: McFadyean reaction: Polypeptide capsule is seen as amorphous purple material surrounding blue bacilli when stained with polychrome methylene blue. Gram staining: chain of bacilli arranged in bamboo stick appearance (Refer to the image below). On Agar plate: Medusa head appearance colony (under low power microscope)(Refer to the image below). Gelatin stab: Appear as inveed fir tree appearance(Refer to the image below). Solid media with penicillin:String of pearl appearance in culture smear. Selective medium: PLET medium.