This study was undertaken to investigate the prevalence, antimicrobial resistance, and virulence gene profiles of Bacillus cereus in different brands of infant formula in Beijing supermarkets. Eighty-eight Bacillus cereus isolates were recovered in sixty-eight infant formulas of five domestic brands and fourteen imported brands. The prevalence rate in domestic and imported samples were 70.6% and 52.9%, respectively. Lower mean prevalence level was found in domestic samples (1.17 MPN/g) compared with the imported samples (3.52 MPN/g). Twenty-four virulence gene profiles were found, and most strains carried at least one virulence gene. The prevalence of nheA, nheB, nheC, cytK, bceT, and entFM in domestic and imported brand samples was similar. The occurrence of enterotoxin genes hblA, hblC, and hblD in domestic samples were 22.2%, 27.8%, and 22.2%, respectively, which was significantly higher than imported samples. Antimicrobial drugs-susceptibility analysis showed that all isolates were susceptible to gentamincin, amikacin, and ciprofloxacin; 38%, 7%, and 2.3% were resistant to rifampin, tetracycline, and chloramphenicol, respectively; and only one isolate was resistant to trimethoprim-sulfamethoxazole. Moreover, the cell numbers of Bacillus cereus in prepared infant formula increased rapidly at room temperature. Thus, monitoring guidelines are needed for accepted levels of Bacillus cereus in infant formula.

A heterologous expression of Vitreoscilla hemoglobin (VHb) for improving cell growth and fermentation products has been successfully demonstrated in various hosts. To improve a commercially used strain for gellan, vgb gene was expressed in Sphingomonas paucimobilis JLJ under the control of the oxygendependent vgb gene promoter (P vgb ). The promoter was maximally induced under microaerobic conditions. Biochemical activity of expressed vgb was confirmed by PCR, SDS-PAGE, and the CO-difference spectra analysis which exhibited a characteristic absorption maximum near 420 nm. The results showed that the expression of vgb could enhance cell growth. The composition of fermentation medium and the physical conditions of cultivations were investigated. The optimum medium consists of (g/L): Sucrose 30, Soybean meal 5, NaNO 3 1, KH 2 PO 4 1, K 2 HPO 4 1.5, MgSO 4 0.6. The optimum fermentation conditions were confirmed: pH 6.0, seed age 16 h, inoculum volume 10 %, 200 rpm, 30°C, and the maximum gellan yield of vgb + recombinant was 1.713 % ± 0.02 % after cultivated 72 h, 21 % higher than that of the parental strain. VHb exhibited positive effect on cell growth and optimize gellan yield. The results provided potential applications of vgb gene in other industrially important strains to solve the increasing demand of aerobic processes in polysaccharides production.