Food Fighters: Revenge of the Lettuce

 Am I the only one who remembers the cartoon Fighting Foodons? Or the Food Fighters little action figures? I might be and don't even know why I remember them. All I remember from the cartoon was how the food would come alive and could be "seasoned" and made stronger. Yes, it was a real show and no, you can't judge me for watching it. Why would you any way? Major Munch, Private Pizza, and the Burgerdier General would disapprove. What was I going on about? This was going to start with a joke about E. coli and collies but I will save that for another time. 

Escherichia coli or E. coli for short is a Gram-negative, facultative anaerobic, rod shaped bacteria. For this post I will refer to it as EC because I said so. Unlike the C. diff I talked about last time, EC can use aerobic and anaerobic metabolism to stay alive but prefer the gut where the oxygen is less. For its hosts, EC strains can prevent the growth of more pathogenic bacteria and produce vitamin K2 among other things. EC is an interesting bug in that it has been so thoroughly studied and is now well understood. For example, under optimal conditions EC is able to replicate every 20 minutes, this allows for easier study of how adaptions may occur based on the environment and low cost production of recombinant proteins, vaccines, and many industrial and scientifically used enzymes. 

Started in 1988, evolutionary biologist Richard Lenski started the LTEE or E. coli long term evolution experiment where by 12 EC groups are kept and 1% taken from each and grown again in a new medium. This allowed the study of evolution over 35 years and over 78,000 generations. I wish I had the patience for that. You should really read more about it, there is a website for the LTEE I will put in the resources section that goes in more depth than I understand. But here are a few cools things found by the LTEE: after ~20,000 generations unused metabolic functions were lost or degraded, all EC groups grew bigger EC cells, increases in fitness as generations go on is related to the "fixing" of low benefit mutations. Finally, some EC developed specific mutations not seen before in other EC, leading to examples of possible speciation in just 35 short years. Super rad dude. 

Ok but you can read about that. I want to talk about how EC makes you sick. When our bodies fail to keep the EC in check, either by happenstance, trauma to the abdomen, immunosupression, etc... EC is able to get into all sorts of shenanigans. The most common I see is EC UTIs but they can cause meningitis, peritonitis, mastitis, sepsis, pneumonia, and hemolytic-uremic syndrome to name a few. The severity depends on the host of course but also the strain of EC doing the infecting. The one I had heard about was O157:H7 though others such as O104:H4 and O111 can be equally as virulent and deadly. Quick aside (yeah right), EC strains are classified by the antigens O, K, or H and this has stuff to do with the makeup of the cell wall. Thats all I will say on that. 

I mentioned EC coming from within and causing infection, but coming from outside the body, EC is most famously spread via contaminated food stuffs. An example is the 2006 North American EC outbreak from spinach with 199 confirmed cases, 141 hospitalizations, and 3 deaths over 3 weeks. Thank goodness for epidemiologists and the like who found the source, 3 weeks is a long time but image a longer outbreak. The spinach was grown on a farm where the cows shed EC into the water and onto the plants, when washed properly this is less of an issue. Other outbreaks involved mishandled meat and other foods. Cooking appropriately normally kills the EC, but low heat and post cooking contamination can still get you sick. 

Besides the antigens, EC can be classified based on virulence properties. A good chart going  more in depth can be found in a paper by Croxen et al., listed in the resources and it's worth checking out. Some types multiply intracellularly, some have shiga toxin from Shigella bacteria, some are invasive and others only infect intestinal tissues. The above mentioned shiga toxin is a cause of bloody diarrhea in EC infections through the ability to breakdown the lining of blood vessels causing hemorrhage. There is the idea that this may contribute to the development of colorectal cancer (CRC) in that certain toxins from EC damage DNA which usually kills the cell. It is speculated that if the damage is not bad enough to kill the cell, it may replicate with the defective DNA increasing its tendency to become malignant. So does anything that damage DNA cause cancer if the cells do not die? Probably but I don't have the brains for that. 

Since antibiotics are the treatment of choice, we can't not talk about resistance. A study of 100 EC strains in neonates at Beijing Children's Hospital found 85% resistance to amoxicillin, 65% to cefuroxime, 60% to ceftriaxone, 20% to gentamicin, and 33% to cipro to name a few. 26% of the isolated strains were multi-drug resistant. Of 14,548 EC bacteremias in Ontario between 2017-2020 resistance was 46% to aminopenicillins, 39% to first generation cephalosporins, 26.5% to fluoroquinolones, 11.7% to aminoglycosides, and 0.1% being classified as "difficult to treat resistance" which is resistance to cerbapenems, fluoroquinolone, and 3rd generation cephalosporins or beta-lactam/beta-lactamase inhibitors. That seems to be quite a difference between the two countries but a 10 year retrospective study by Wang et al., in southeast China found similar numbers to the first study. I didn't go hunting for more but I would suspect looser antibiotic use may contribute. To highlight the importance of resistance, if untreated, some strains of EC have as high as 10% mortality. 

I hope that was at least not terribly painful to read, but if it was, you probably deserved it and should have learned your lesson last time you read my blog. Regardless, I love you anyways and thanks for your time. 

References

A Brief Overview of Escherichia coli O157:H7 and Its Plasmid O157 by Youn Lim et al., in the Journal of Microbiology and Biotechnology 2010

Antibiotic resistance spectrum of E. coli strains from different samples and age-grouped patients: a 10-year retrospective study by Wang et al., in BMJ Open 2022

Antimicrobial Resistance Analysis of Clinical Escherichia coli Isolates in Neonatal Ward by Wu et al., in Frontiers in Pediatrics 2021

Antimicrobial resistance and mortality following E. coli bacteremia by Daneman et al., in the Lancet: eClinical Medicine 2022

Epidemiology of Escherichia coli O157:H7 Outbreaks, United States, 1982–2002 by Rangel et al., in Emerging Infectious Diseases 2005

Genotoxins: The Mechanistic Links between Escherichia coli and Colorectal Cancer by Wang & Fu in Cancers 2023

Image of E. coli from a scanning electron microscope on National Geographic's encyclopedia entry on the same

Mortality in Escherichia coli bloodstream infections: a multinational population-based cohort study by MacKinnon et al., in BMC Infectious Diseases 2021

Recent Advances in Understanding Enteric Pathogenic Escherichia coli by Croxen et al., in Clinical Microbiology Reviews 2013

The Long-Term Evolution Experiment at the-tee.org 

The MN Department of Health, FDA, NIH, and WHO websites on the topic of E. coli

Today's Online Textbook of Bacteriology sections on E. coli (super great resource)