Comparison of the Recovery of Escherichia coli from Frozen Foods and Nutmeats by Confirmatory Incubation in EC Medium at 44.5 and 45.5 C

Abstract

FISHBEIN, MORRIS (Food and Drug Administration, Washington, D.C.), AND BERNARD F. SURKIEWICZ. Comparison of the recovery of Escherichia coli from frozen foods and nutmeats by confirmatory incubation in EC medium at 44.5 and 45.5 C. Appl. Microbiol. 12:127-131. 1964.-The productivity of confirmatory EC broth for the isolation of fecal Escherichia coli was determined at 44.5 and 45.5 C. A variety of frozen precooked foods and an assortment of nutmeats were examined after primary incubation in Lauryl Sulfate Tryptose (LST) broth. In 85.3% of the cases, the parallel tubes of EC broth incubated for 24 hr at 44.5 and 45.5 C gave rise to identical E. coli responses of positive, false positive, and negative. The remaining 14.7% of the reactions represent the qualitative difference between the two temperatures. The EC test at 45.5 C was more specific for E. coli, since twoto threefold fewer false positives were produced at this temperature than at 44.5 C. However, fecal E. coli recoveries were slightly higher (4%Vc) at the lower temperature. Incubating the EC tubes from the interval of 24 to 48 hr gave rise to an additional 4.3% of E. coli recovery, but this was accompanied by an excessive production of false positives (75.9%), representing a 3.5-fold decrease in specificity. It is recommended that, in the confirmatory use of EC broth in the examination of frozen foods and nutmeats for the recovery of fecal E. coli, the test be made at 45.5 C in a water bath and limited to 24 hr of incubation only, to insure optimal specificity. During the study, a "fixed" productivity ratio was noted; E. coli+/LST+ equaled approximately one-fourth or 25%. The significance of this ratio is discussed.

Escherichia coli variants for gas and indole production at elevated incubation temperatures

“…Considerable emphasis is placed on the production of gas from lactose at elevated incubation temperature to determine fecal origin of F. c(oli, or E. c(oli biotype 1 (13). In North America, incubation temperatures of 44.5 to 45.5°C are used to reduce the incidence of false-positive results and because gas production from lactose has been shown to be more specific for fecal E. coli at these temperatures (12). In Europe, it is believed that specificity for E. coli as an indicator organism is obtained with an elevated incubation temperature of 44°C for gas production from lactose and indole production (10).…”

Rapid Method for Detection and Enumeration of Fecal Coliforms in Fresh Chicken

“…Our data show the improvement effected by the 1 C reduction in EC broth incubation temperature-both a 19% increase in verification for the rapid method, with an improved log variance, and a substantial increase in the verified standard MPN count. Fishbein (9,10), working with pure cultures of E. coli and Aerobacter strains and also with frozen foods and nutmeats, concluded that 44.5 C was too low a temperature for EC broth incubation. Many Aerobacter strains and a significant number of non-E. coli strains isolated from the food products studied were verified as positive.…”

Coliform Behavior in Frozen Foods

“…d Fishbein and Surkiewicz (3). e The number of positive tubes in the E C (45.5 C) confirmatory test.…”