Counting STECs in poop: Medium matters

The isolation and quantification of non-O157 Shiga toxin–producing Escherichia coli (STEC) from cattle feces are challenging. The primary objective of this study was to evaluate the performance of selected agar media in an attempt to identify an optimal medium for the detection and quantification of non-O157 STEC in cattle feces.

medium.messageComparison studies were performed using CHROMagar STEC, Possé differential agar (Possé), Possé modified by the reduction or addition of antimicrobials, STEC heart infusion washed blood agar with mitomycin C (SHIBAM), and SHIBAM modified by the addition of antimicrobials. Fourteen STEC strains, two each belonging to serogroups O26, O45, O103, O111, O121, O145, and O157, were used to test detection in inoculated fecal suspensions at concentrations of 102 or 103 CFU/g. One STEC strain from each of these seven serogroups was used to estimate the concentration of recovered STEC in feces inoculated at 103, 104, or 105 CFU/g. Significantly more suspensions (P < 0.05) were positive for STEC when plated on Possé containing reduced concentrations of novobiocin and potassium tellurite compared with SHIBAM, but not SHIBAM modified by containing these same antimicrobials at the same concentrations. Numerically, more suspensions were positive for STEC by using this same form of modified Possé compared with Possé, but this difference was not statistically significant. More suspensions were positive for STEC cultured on CHROMagar STEC compared with those on Possé (P < 0.05) and on modified Possé (P = 0.05). Most inoculated fecal suspensions below 104 CFU/g of feces were underestimated or not quantifiable for the concentration of STEC by using CHROMagar STEC or modified Possé.

These results suggest that CHROMagar STEC performs better than Possé or SHIBAM for detection of STEC in bovine feces, but adjustments in the concentrations of novobiocin and potassium tellurite in the latter two media result in significant improvements in their performance.

Comparison of agar media for detection and quantification of Shiga toxin–producing Escherichia coli in cattle feces

Journal of Food Protection®, Number 6, June 2016, pp. 896-1055, pp. 939-949(11)

Stromberg, Zachary R.; Lewis, Gentry L.; Moxley, Rodney A.

Whole Foods still sucks at food safety; so does a Toronto newspaper and Cooks Illustrated

In the latest installment of Whole Foods Market has terrible food safety advice — blaming consumers for getting sick, selling raw milk in some stores, offering up fairytales about organic and natural foods – today’s grilling tip is that “chicken that is cooked enough will feel springy when pressed. If you’re uncertain, cut into the thickest part of one piece. The meat should still be juicy, but the juices should be clear, never reddish.”

Color is a lousy indicator.

Use a tip-sensitive digital thermometer.

Toronto’s Globe and Mail has gotten into the trend of using someone with what appears to be an Australian accent to flog food but seems to skimp on the food safety.

Stephen Alexander, owner of Cumbrae Meats, says in a video  that, “cooking a burger to medium is totally fine as long as you start with good quality fresh ground meat.”

I don’t know what medium means. How is good quality defined, by bacterial counts? And where’s the thermometer, the same one Alexander uses when cooking chicken on the grill but that Whole Foods doesn’t know exists.

Cook’s Illustrated likes its burgers “juicy and rosy throughout.” 

Hamburger Habits: Is Medium Safe?

I’m a reformed medium-rare hamburger eater. Before I met Doug, I always wanted my hamburgers pink in the middle and frankly had no clue that this was a potentially risky habit. Now that I’ve learned hamburger needs to be cooked to 160 F to be safe, however, I rarely eat hamburger unless Doug cooks it at home. That’s the only way I can assure that the cook is using a meat thermometer and knows how to properly do so.

Tonight, though, I’m in Buffalo, NY and I had dinner with two British friends in a rowdy Irish pub. While I intended to order salad, the pickings were few on the menu and I settled on a cheeseburger with fries. The waitress asked me, “How do you want that cooked.” Somewhat startled and without my food safety arsenal beside me, I said, “Medium.” I hate well-done hamburger because of the texture, but I wanted my burger safe. How could I tell her that?

My burger came and was very medium rare looking … very pink in the middle and done on the outside. I ate it. The whole thing. And it tasted good. And now I’m thinking about my foolish behavior and wondering if I’ll get e. coli. I know that color is a lousy indicator and I know it’s not likely I’ll get sick. But without the thermometer, how can you be sure?