Ability of Shiga toxin-producing Escherichia coli and Salmonella spp. to survive in a desiccation model system and in dry foods.
In order to determine desiccation tolerances of bacterial strains, the survival of 58 diarrheagenic strains (18 salmonellae, 35 Shiga toxin-producing Escherichia coli [STEC], and 5 shigellae) and of 15 nonpathogenic E. coli strains was determined after drying at 35 degrees C for 24 h in paper disks. At an inoculum level of 10(7) CFU/disk, most of the salmonellae (14/18) and the STEC strains (31/35) survived with a population of 10(3) to 10(4) CFU/disk, whereas all of the shigellae (5/5) and the majority of the nonpathogenic E. coli strains (9/15) did not survive (the population was decreased to less than the detection limit of 10(2) CFU/disk). After 22 to 24 months of subsequent storage at 4 degrees C, all of the selected salmonellae (4/4) and most of the selected STEC strains (12/15) survived, keeping the original populations (10(3) to 10(4) CFU/disk). In contrast to the case for storage at 4 degrees C, all of 15 selected strains (5 strains each of Salmonella spp., STEC O157, and STEC O26) died after 35 to 70 days of storage at 25 degrees C and 35 degrees C. The survival rates of all of these 15 strains in paper disks after the 24 h of drying were substantially increased (10 to 79 times) by the presence of sucrose (12% to 36%). All of these 15 desiccated strains in paper disks survived after exposure to 70 degrees C for 5 h. The populations of these 15 strains inoculated in dried foods containing sucrose and/or fat (e.g., chocolate) were 100 times higher than those in the dried paper disks after drying for 24 h at 25 degrees C.
Hiramatsu
Reiji
R
Aichi Prefectural Institute of Public Health, 7-6 Nagare Tsuji-machi, Kita-ku, Nagoya 462-8576, Japan. reiji_hiramatsu@pref.aichi.lg.jp
Matsumoto
Masakado
M
Sakae
Kenji
K
Miyazaki
Yutaka
Y
D000818:Animals; D015169:Colony Count, Microbial; D003890:Desiccation; D004926:Escherichia coli / Q000145:classification / Q000254:growth & development* / Q000502:physiology; D000431:Ethanol; D005511:Food Handling / Q000379:methods; D005519:Food Preservation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D010209:Paper; D012034:Refrigeration; D012475:Salmonella / Q000145:classification / Q000254:growth & development* / Q000502:physiology; D022621:Shiga Toxin / Q000096:biosynthesis*; D012965:Sodium Chloride; D013395:Sucrose; D013696:Temperature
D000431:Ethanol; D012965:Sodium Chloride; D013395:Sucrose; D022621:Shiga Toxin