THE MICROBIOLOGY 
OF FOOD MARKET SALAD AND SALAD BAR ITEMS

Copyright April 1997 by
O. Peter Snyder, Jr., Ph.D.
Hospitality Institute of Technology and Management
670 Transfer Road, Suite 21A
St. Paul, MN 55114

Summary
This past year in the Twin Cities, there have been a number of television news exposés on the microbiological quality of pre-packaged and salad bar salads in food markets. In order to determine the microbial condition salads from various operations in the Minneapolis-St. Paul, Minnesota area, samples of salads were collected from retail food stores in the Twin City area during February and March 1997, and were subjected to a microbial analysis. The only bacteria known to cause foodborne illness that was detected at levels of concern was Bacillus cereus. However, this microbial analysis did not determine what percentage of the population of B. cereus was pathogenic (Not all strains of B. cereus are pathogenic.) It is evident that B. cereus is present and is capable of multiplying at normal food market refrigeration temperatures.

The data indicate that the older the product (salad), the higher the microbial count. If pathogenic bacteria such as Aeromonas hydrophila, Yersinia enterocolitica, or Listeria monocytogenes, which begin to multiply at 29.3ºF, were present, these pathogens could grow at the temperatures at which the salads were displayed and held, and could become a potential problem. Finding these organisms, because they only sporadically contaminate food, will require extensive testing of a sufficiently large sample.

If you have any suggestions as to how to deal with the salad time-temperature problem so that salads sold in supermarkets and other retail food operations are fresher (not as old), I would be most interested in your comments.

Food Market Salad Bar Item Microbial Contamination (CFU/gram)

Source
Salad 
Type
APC
Coliform
E. coli
Lactics
Mold
Yeast
Bacillus 
cereus
Listeria 
mono-
cyt.
Staph.
(Coag)+
Salmonella
Store A Salad*
16,000,000
320,000
<10
60
230
8,700
39,000
NA
NA
NA
Store A Salad*
9,500,000
93,000
<10
10,000,000
20
110,000
28,000
NA
NA
NA
Store A Salad*
35,000,000
3,400
<10
4,500
<10
12,000,000
220,000
NA
NA
NA
Store A Salad*
650,000
160,000
<10
2,500
<10
22,000
31,000
NA
NA
NA
Store A Salad*
25,000,000
22,000
<10
50,000
400
500,000
48,000
NA
NA
NA
Store A Salad*
12,000,000
2,000
<10
4,300
700
60,000
300,000
NA
NA
NA
Store A Ingred.**
150,000
7,400
<10
1,000
<10
140
<100
NA
NA
NA
Store B Ingred.**
390,000
10
<10
110
30
190
1,000
NA
NA
NA
Store C Pkgd.
61,000
50
<10
1,100
100
900
<100
neg/25g
NA
NA
Nat'l 
brand 1		 Pkgd.
7,800,000
240,000
<10
1,000
<10
300
<100
neg/25g
NA
NA
Conven. 
store		 Pkgd.
6,700,000
11,000
<10
370,000
400
84,000
<100
neg/25g
NA
NA
Store D Pkgd.
5,600,000
80,000
<10
2,800
200
2,000
<100
neg/25g
NA
NA
Store B Pkgd.
220,000
6,000
<10
4,200
200
22,000
<100
neg/25g
NA
NA
Nat'l 
brand 2		 Pkgd.
17,000,000
40,000
<10
77,000
300
40,000
150,000
neg/25g
NA
NA
Store E Pkgd.
16,000,000
6,000
<10
NA
NA
NA
<100
neg/25g
<10
neg/25g
Store A Pkgd.
45,000,000
30,000
<10
NA
NA
NA
<100
neg/25g
<10
neg/25g
Store A Pkgd.
280,000,000
>560,000
<10
NA
NA
NA
<100
neg/25g
<10
neg/25g
Store F Pkgd.
10,000,000
180,000
<10
NA
NA
NA
<100
neg/25g
<10
neg/25g
Organic 
food store		 Pkgd.
19,000,000
28,000
<10
NA
NA
NA
<100
neg/25g
<10
neg/25g
Nat'l 
brand 1		 Pkgd.
55,000,000
>560.000
<10
NA
NA
NA
<100
neg/25g
<10
neg/25g
Nat'l 
brand 
pasta 
salad		 Pkgd.
700,000
5,000
<10
NA
NA
NA
<100
neg/25g
<10
neg/25g