Abstract: Cronobacter sakazakii is an emerging opportunistic Gram-negative pathogen, and it is associated with various neonatal infections such as meningitis, septicemia, bacteremia, and necrotizing enterocolitis. The aims of this work were to explore the contents of seed-borne C. sakazakii in lucerne, to determine its pathogenicity against animals and plants, and to understand its bacterial characteristics. Using the dilution plate method, three suspected C. sakazakii bacterial isolates were isolated from surface-sterilized seeds of six lucerne varieties. The representative bacterial isolate 1gF3 was used to prepare a bacterial suspension (about 10⁹ cfu·mL^-1), which was used in a germination test of alfalfa seeds in Petri dishes under controlled laboratory conditions. In addition, intraperitoneal injection (I/P) into pathogen-free Kunming mice was conducted to understand the animal pathogenicity of 1gF3. The results showed that 1gF3 was not pathogenic to lucerne under laboratory conditions. At 12 h after I/P injection, mice showed suppurative encephalitis, myocardial edema dilatation and local myocardial fiber rupture, partial liver necrosis, acute splenitis, and acute diffuse hemorrhage of the lungs and kidneys. These results indicated that 1gF3 showed significant pathogenicity to mice after I/P injection under laboratory conditions. The suspected C. sakazakii bacterial isolate TM2 was isolated from the blood of injected diseased mice. Using phenotypic and 16S rDNA identification methods, 1gF3 and TM2 were identified as C. sakazakii. The biological characteristics of 1gF3 were verified. The bacterium was in the logarithmic growth phase from 24 to 36 h, followed by a recession. Drought stress aggravated the decline of bacterial linear growth. Strain 1gF3 could grow at a wide range of temperatures (10-41 ℃) and pH (3-11). It grew well without salt, but its growth was inhibited by increased NaCl concentrations. A 12-h light:12-h dark photoperiod favored bacterial growth. This research has provided a theoretical basis and new ideas about bacteria that could be pathogenic to animals and plants and could be hidden in plant or animal materials, thus avoiding animal and plant quarantine measures. It also provides a theoretical basis for the prevention and control of the transport and spread of C. sakazakii.

Key words: Medicago sativa, seed-borne bacteria, Cronobacter sakazakii, pathogenicity, plant and animal quarantine