Evaluation of an improved MPN medium for recovery of stressed and nonstressed Staphylococcus aureus.

Two media used for recovery of foodborne Staphylococcus aureus were compared: trypticase soy broth with 10% salt (TSBS), used in the official AOAC method, and TSBS with 1% sodium pyruvate added (PTSB). Adding pyruvate increased recovery of 4 heat-stressed and nonstressed S. aureus foodborne strains from artificially contaminated mashed potato and ham salad substrates. The overall geometric means for the 2 media differed significantly at the alpha = 0.05 level. Recovery of S. aureus from 70 replicates of naturally contaminated Monterey Jack cheese was highest in PTSB. The overall geometric means/g were 63 in TSBS and 96 in PTSB.

Microbiological Quality of Cream-Type Pies During Processing.

In-line samples of crust, filling and topping were collected from pies being prepared by all U.S. firms making frozen cream-type pies for interstate distribution. All firms adhered to Good Manufacturing Practices, as determined by visual inspection. Geometric mean aerobic plate count values were generally low for crust, filling and topping, ranging from 49 CFU/g for topping containing dairy ingredients as it was deposited onto the pie filling to 2400 CFU/g for filling containing dairy ingredients as it was deposited into the crust of the pie. Geometric mean coliform, Escherichia coli and Staphylococcus aureus values were generally lower than the limits of detection, which were 3/g for coliforms and E. coli and 10/g for S. aureus .

ICMSF Methods Studies. XV. Comparison of Four Media and Methods for Enumerating Staphylococcus aureus in Powdered Milk.

Four media were examined for their usefulness in enumerating Staphylococcus aureus inoculated (a) into milk that was then dried or (b) directly into dried milk powder. In all, seven strains of S. aureus were inoculated individually into each preparation and were enumerated after two periods of storage (18 to 19 d and 60 to 61 d). Fourteen laboratories from twelve countries participated in the comparison which found that direct plating on agar medium in 14-cm petri dishes may be as useful as enrichment followed by streaking. Plating on Baird-Parker medium or on Hauschild pork plasma fibrinogen medium and a MPN method using Giolitti and Cantoni's broth with Tween 80 were equally sensitive for enumerating S. aureus in dried milk powder. The use of Hauschild medium may eliminate the need for supplementary tests to confirm colonies as S. aureus , but in some cases was found to fail in some laboratories. Giolitti and Cantoni's broth without Tween 80 generally was less useful than the three other media for enumerating S. aureus . S. aureus inoculated into milk that was then dried survived longer than when inoculated into dried milk.

Microbiological Quality of Breaded Shrimp During Processing.

Duplicate samples of shrimp or breading materials were collected four times a day for two consecutive days at 12 locations along the processing lines of 33 shrimp-breading firms in the United States during 63 inspections. All firms were using good manufacturing practices. For stock shrimp, the geometric mean aerobic plate count at 35°C incubation (APC 35) was reduced from 2.1 × 106 to 3.3 × 105 colony-forming units (CFU)/g for the frozen finished product. At 35°C, an APC 35 of ≤106 CFU/g was found for 78% of the finished samples. At 30°C incubation, the mean APC was reduced from 7.8 × 106 CFU/g for the stock shrimp to 7.6 × 105 CPU/g for the finished product. Coliform mean counts were virtually static (64 to 83/g) up to the batter-breading steps; however, these counts reached 148 to 160/g at the first batter-breading step and remained constant until the breaded shrimp were frozen. Mean Escherichia coli and Staphylococcus aureus counts were ≤3 and ≤10/g, respectively, for all 12 in-line sampling locations. Salmonella organisms were found in one of 118 finished product samples tested for this pathogen.

Microbiological Quality of Cocoa Powder, Dry Instant Chocolate Drink Mix, Dry Nondairy Coffee Creamer and Frozen Nondairy Topping Obtained at Retail Markets.

A national survey was conducted of the microbiological quality of three dry ingredients used in beverages and one frozen non-dairy topping obtained at retail markets. Geometric mean aerobic plate counts (APCs) of units examined at 35°C were as follows: 1,313 units of cocoa powder, 6,600 CFU/g; 1,552 units of dry instant chocolate drink mix, 290 CFU/g; 1,559 units of dry non-dairy coffee creamer, 37 CFU/g; and 1,532 units of frozen non-dairy topping, 34 CFU/g. At 30°C, the geometric mean APC was 34 CFU/g for frozen nondairy topping. Geometric means for most probable number determinations of coliform bacteria and Escherichia coli were <3/g for the four products. Geometric mean values for Staphylococcus aureus in three of the products were <10/g; no S. aureus was found in cocoa powder. Geometric mean values for yeasts and molds in dry instant chocolate drink mix and dry nondairy coffee creamer were 8 and 6 CFU/g, respectively.

Microbiological quality of five potato products obtained at retail markets.

The microbiological quality of frozen hash brown potatoes, dried hash brown potatoes with onions, frozen french fried potatoes, dried instant mashed potatoes, and potato salad was determined by a national sampling at the retail level. A wide range of results was obtained, with most sampling units of each products having excellent microbiological quality. Geometric mean aerobic plate counts were as follows: dried hash brown potatoes, 270/g; frozen hash brown potatoes with onions, 580/g; frozen french fried potatoes 78/g; dried instant mashed potatoes, 1.1 x 10(3)/g; and potato salad, 3.6 x 10(3)/g. Mean values of coliforms, Escherichia coli, and Staphylococcus aureus were less than 10/g.

Microbiological quality of some spices and herbs in retail markets.

The microbiological quality of 10 spices or herbs was determined by a national survey at the retail level. Aerobic plate count values for the 10 products ranged from less than 100 to 3.1 X 10(8) per g; mean values of the individual spices or herbs ranged from 1,400 to 820,000 per g. Coliform counts ranged from less than 3 to 1.1 X 10(6) per g; however, mean values were less than 20 per g for all products. Escherichia coli counts ranged from less than 3 to 2,300 per g. Except for celery seed, which had a mean value of 7 per g, all mean values were less than 3 per g. Yeast and mold counts were made for 5 of the 10 products. Mean values were generally low; the highest mean (290 per g) was obtained for cinnamon.