Fundamental Food Microbiology, Third Edition - Fuad Fathir

366 FUNDAMENTAL FOOD MICROBIOLOGY
Although there are more than 2000 serotypes of Salmonella, only some of them
have been frequently associated with foodborne illnesses. This can be because of
geographical distribution of the serotypes as well as pathogenicity of a serovar or a
strain. In the U.S., Salmonella Typhimurium has been considered the major causative
agent of foodborne salmonellosis (more than 20% of the total cases). However, since
the 1980s, foodborne salmonellosis from Salmonella Enteritidis has increased,
mainly from contaminated Grade A shell eggs. In recent years, it has been involved
in the same number of cases as Salmonella Typhimurium. The exact cause of the
predominance of Salmonella Enteritidis is not yet clearly understood. 6,7 The methods
used in raising food of animals and birds and in processing of foods of animal origin
are suspected to have an important role.
G. Prevention and Control
Raw foods of animal origin that are heat treated before consumption can have
Salmonella. However, in the U.S. (and other developed countries), as per regulatory
requirements, heat-treated and ready-to-eat foods that contain Salmonella in portions
(samples) tested are considered to be adulterated and should not be sold. Many foodprocessing
industries have in-house Salmonella (as well as several other pathogens)
surveillance programs to control the presence of Salmonella in their products. Regulatory
agencies also have programs to educate consumers at home and food handlers
in food service places to control Salmonella contamination in foods. These include
proper cooking of foods (minimum to pasteurization temperature and time, such as
71.7�C for 15 sec or equivalent) and prompt cooling (to 3 to 4�C or freezing, if not
used in 2 h); preventing cross-contamination of ready-to-eat food with a raw food
through cutting boards, equipment, utensils, and hands; using proper sanitation and
personal hygiene; sick people not handling a food; and properly reheating a food
refrigerated for a long time. 6,7
H. Detection Method
The methods involve preenrichment of a sample of food in a nutrient broth, followed
by selective enrichment, streaking on a selective-differential agar medium, and
biochemical and serological confirmation (see Appendix E). Several rapid methods,
based on specific immunological characteristics and nucleotide base sequence in
nucleic acids, have been developed.
I. Case Study
In July 1989, 21 out of 24 people who attended a baby shower at a home in New
York had gastroenteritis, with severe diarrhea, vomiting, fever, and cramps 6 to 57
h after the party. 8 Twenty people needed medical help, of which 18 were hospitalized;
one at 38 weeks of pregnancy delivered while ill and the infant developed septicemia.
Salmonella Enteritidis was isolated from all 21 people (rectal swab) and the infant.
All 21 ill attendees, but not the 3 who remained well, ate a homemade baked ziti
pasta dish consisting of one raw egg, ricotta cheese, cooked tomato, and meat sauce,