Survival, isolation and characterization of a psychrotrophic Bacillus cereus strain from a mayonnaise-based ready-to-eat vegetable salad.
Incidence and population levels of Bacillus cereus in American salad, an industrially manufactured, packaged and refrigerated deli salad containing vegetables and mustard, were determined. Of 12 ready-to-eat samples examined, one (8.3%) was positive for B. cereus at less than 5 x 10(3)cfu g(-1). According to the ISO confirmation procedure, a strain was isolated and further characterized and identified as B. cereus EPSO-35AS by API 50CH/20E phenotypic system, combined with additional tests of motility, oxidase activity and anaerobic growth. This strain produced diarrhoeal enterotoxin in tryptic soy broth culture as detected by BCET-RPLA test, hydrolysed starch and had a low D(90)-value (2.1 min), with an estimated z-value of 6.79 degrees C. After a lengthy lag phase (9-12 days of incubation), the strain was able to grow at 8 degrees C in both nutrient broth and tyndallized carrot broth with specific growth rates from 0.009 to 0.037 h(-1), respectively. In the vegetable substrate, lag time was approximately 3 days (66 h) shorter than in laboratory medium. The effect of temperature abuses on the safety of the product during the time of use or consumption is discussed.
Valero
M
M
Departamento de Producción Vegetal y Microbiología, Escuela Politécnica Superior de Orihuela, Universidad Miguel Hernández-Campus de Orihuela, Carretera de Beniel, Orihuela, Alicante, Spain. m.valero@umh.es
Hernández-Herrero
L A
LA
Giner
M J
MJ
D001409:Bacillus cereus / Q000145:classification / Q000302:isolation & purification* / Q000378:metabolism; D015373:Bacterial Typing Techniques; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004768:Enterotoxins / Q000096:biosynthesis; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D006801:Humans; D007700:Kinetics; D013696:Temperature; D013997:Time Factors; D014675:Vegetables / Q000382:microbiology*
D004768:Enterotoxins