Presence of fecal coliforms does not mean “there’s poop here”, but for aspiring poop-hunters is there an alternative?

Image created by Austin Bouck. Dear god let there be no egregious mistakes…

Recently a podcast I often listen to has discussed several articles with a similar note in their conclusions.

Nearly half of the 90 beverages from soda fountain machines in one area in Virginia tested positive for coliform bacteria — which could indicate possible fecal contamination

The study, conducted over six months at six licensed day-care centers in California, found high levels of coliform contamination, particularly in kitchen areas and on the hands of day-care workers. Coliform bacteria are transmitted through feces.

But recent reports reveal that the coffee or tea you’re sipping  – and even the cash you used to pay for it –  also carry bacteria found in feces.

Seven out of 10 samples of Costa ice were found to be contaminated with bacteria found in faeces.

40 percent of office coffee mugs contain coliform bacteria, which can be found in feces.

I don’t need to rehash arguments that have already been made here. Fecal coliform is a group of organisms historically used to identify whether drinking water could be contaminated with sewage or fecal material. Because it’s still a valid test to determine if water has been contaminated (they don’t survive forever in clean water, so if they’re present it’s because there’s a likely a failure in the system), the CDC and tons of state regulations still falsely state that these organisms are only found in fecal material.

Part of the issue is that coliforms as an indicator in general were extrapolated to environmental samples and food. NACMCF summarized the most recent scientific conclusion:

…whether coliforms, fecal coliforms, Enterobacteriaceae or E. coli. Kornacki and others (Kornacki et al., 2013) provide an historical evaluation of these criteria for foods and their utility based on current knowledge. None of these criteria accurately and consistently reflect fecal contamination of raw and processed foods nor are they useful or reliable as index organisms predicting the presence of pathogens.

The Kornacki reference is from the Compendium of methods for the Microbiological Examination of foods, which while expensive is an excellent reference for any food micro lab:

The debunking of the coliform=feces absolute conclusion was well covered by Doyle and Erickson in 2006, and more recently some thoughts were posted by barfblog.

But I’m writing this post today because I have a follow up question,

How exactly would someone actually test for fecal material?

Apparently, this is actually a problem in forensics, as an article published as recently as 2013 stated”no sensitive and simple fecal identification method using molecular biological techniques has been reported.” (Nakanishi et al., 2013). Here were the methods I was able to find with a cursory review of the literature.

1. Direct (macro) observation

A.k.a, the stain on the tighty-whities. Feces can be identified from it’s characteristic green-brown color from bile digestion and characteristic odor…this detection method isn’t really worth going into and I apologize for the mental image/odor.

2. Microscopy

Now we’re getting sciencey. Fecal material is a hodgepodge of various microscopic indicators. An experienced eye would be able to find bacteria (the bulk of the dry weight), but also undigested food particles and cellulose cell walls from plant material. Some epithelial and mucousal cells from the GI tract would also be visible. Interestingly, one way to determine if the fecal material was from a person or animal would be to look for excess hair in the sample, either from digesting prey or from grooming. The hair has to go somewhere, and I’m really curious if you would see a difference in hair mass between bearded and clean shaven men…

3. Chemical Indicators

Urobilinogen is a byproduct of bilirubin metabolism, and will be found in animals which consume meat and/or are otherwise digesting blood.  This appears to be a fairly classic test to discriminate fecal material from other bodily fluids like sweat or saliva and can be performed on site using a fluorescence indicator solution. Unfortunately, urobilinogen can also be found in urine since it is also returned to the kidneys for excretion.

4. Microbiological Profile

Well, crap. Here we come full circle. The most recent research on this subject seems to be using newer sequencing techniques to identify the unique organisms in the microbiome of feces. The goal is to find specific organisms or genes that would allow forensic scientists to discriminate between fecal material and other bodily fluids.

Here’s the thing though, none of the research identifies coliforms as a group of interest. It’s too broad and unhelpful! Rather than traditional “fecal bacteria”, the Bacteriodes genus has been identified as the predominant organism group in feces. Specific organisms identified were B. uniformis, B. vulgatus, and B. thetaiotaomicron. However, the state of California has specifically identified these organisms thriving in marshlands, yet still attribute them directly to feces. It would seem that again we can infer that fecal material is likely to contain these organisms, but it seems improper to assume that the presence of the organisms means that fecal material was the source.

I’d love to hear from some forensic scientists on what I got right and wrong here. From what I can tell from the literature it seems like there isn’t as much forensic interest in fecal material. The authors referenced how it is hard to isolate DNA due to interference from bile enzymes and microorganisms, which would reduce its value as evidence.

It seems like at this time a definitive test for “there is poop on this plate/ice/food/hand” doesn’t exist.

Much to the chagrin of PCRM, who would like us to declare the invisible feces on our meat.

Maybe we can just stop making the correlation between feces and food hygiene and instead focus on pathogen detection/prevention/pervasiveness as a means to evaluate foods on the market. While we talk about the fecal-oral route a lot, we’ve known for a long time that pathogens can be found almost anywhere if you start looking, so let’s look for them instead of fecal coliform clickbait (which this post totally is).



Resources for fecal identification forensics:

Drexler, Judith Z., et al. “Marsh Soils as Potential Sinks for Bacteroides Fecal Indicator Bacteria, Waccamaw National Wildlife Refuge, Georgetown, SC, USA.” Water, Air, & Soil Pollution 225.2 (2014): 1861.

Forensic Resources.Serology – Blood and other Bodily Fluids.

James, Stuart H., Jon J. Nordby, and Suzanne Bell, eds. Forensic science: an introduction to scientific and investigative techniques. CRC press, 2002.

Li, Richard. Forensic biology. CRC Press, 2015.

Nakanishi, Hiroaki, et al. “Identification of feces by detection of Bacteroides genes.” Forensic Science International: Genetics7.1 (2013): 176-179.

Virkler, Kelly, and Igor K. Lednev. “Analysis of body fluids for forensic purposes: from laboratory testing to non-destructive rapid confirmatory identification at a crime scene.” Forensic Science International 188.1 (2009): 1-17.

Zou, Kai-Nan, et al. “Identification of vaginal fluid, saliva, and feces using microbial signatures in a Han Chinese population.” Journal of forensic and legal medicine 43 (2016): 126-131.