Isolation of Enterobacter sakazakii from Stable Flies, Stomoxys calcitrans L. (Diptera: Muscidae)†

Abstract

Enterobacter sakazakii is an opportunistic foodborne pathogen that causes meningitis, enterocolitis, and sepsis, primarily in immunocompromised infants. Previously, it was suggested that stable flies, Stomoxys calcitrans, were a vector or reservoir of this pathogen. In our study, by means of a culturing approach combined with 16S rDNA PCR–restriction fragment length polymorphism genotyping and sequencing, we screened 928 individual stable flies collected in Kansas and Florida. Two stable flies (0.2%) were positive for E. sakazakii. In addition, 411 (44%) stable flies carried bacteria-forming red colonies (presumably enterics) on a violet red bile glucose agar (mean count = 6.4 × 104 CFU per fly), and 120 (13%) stable flies carried fecal coliforms (mean count = 8.7 × 103 CFU per fly). Sequencing of 16S rDNA showed that enterics from violet red bile glucose agar were represented by several genera, including Escherichia, Shigella, Providencia, Enterobacter, Pantoea, Proteus, Serratia, and Morganella. Our study shows that stable flies carry bacteria typically present in animal manure (a developmental site of stable fly larvae), which indicates that the natural reservoir of E. sakazakii is the digestive tract or manure of domestic animals. The low prevalence of E. sakazakii associated with stable flies suggests that stable flies do not play a major role as a reservoir or vector of this pathogen.