First isolation and identification of Serratia marcescens J (Enterobacterales: Yersiniaceae) in a commercial colony of Nauphoeta cinerea (Olivier, 1789) (Blattodea: Blaberidae)

The speckled cockroach, Nauphoeta cinerea (Olivier, 1789) (Blattodea: Blaberidae), is a common live feed source for reptiles, amphibians, insectivorous birds, and predatory invertebrates due to its high nutritional value. On 26 July 2025, adult individuals obtained from a pet shop in Ankara were brought to the laboratory, and shortly thereafter, they exhibited pink feces, signs of decomposition, and mass mortality. Light microscopy of suspensions prepared from the cadavers revealed bacterial cells, which were subsequently cultured on LB agar. The colonies appeared dark red, and Gram staining indicated that the bacterium was Gram-negative with a bacillus morphology. Blastn analysis of the 16S rRNA gene region of the isolated bacterium confirmed its identity as Serratia marcescens J (Enterobacterales: Yersiniaceae) with 100% similarity. Phylogenetic analysis placed it in the same cluster as another isolate reported from Türkiye (accession number: KX959982.1), supported by a bootstrap value of 80%. Adult female N. cinerea individuals were experimentally infected with five different doses of S. marcescens (1 × 105–1 × 109 cfu/mL). After fourteen days, the highest dose resulted in 80% mortality, and the LD₅₀ was calculated as 9.84 × 105 cfu/mL. This study demonstrates, for the first time, the isolation of S. marcescens from the live feed N. cinerea and its high virulence in these insects. The findings highlight potential mass mortality events in the live feed trade, emphasizing economic losses, zoonotic and pathogenic risks, and the critical importance of hygiene and biosecurity measures.