Microbes That Span the Clinical Lab and Your Grocery List

Jan. 25, 2021

Humans and microorganisms have existed in a mutual balance for millions of years. While some microorganisms can cause disease if given the opportunity, these same microbes serve many other important functions, including the development of food products. What might cause disease in one person could be a sustainable food option for another.

Fusarium: Cause of Fusariosis and Protein-Rich Meat Substitute

There are more than 50 known species of Fusarium, a fungus that commonly causes diseases in plants, such as crown rot and head blight. While not all Fusarium species are pathogenic, some species can cause disease in immunocompromised patients, and these infections range from superficial skin infections to systemic, disseminated disease. Documented infections include keratitis in contact lens wearers, upper and lower respiratory infections and infections of the skin and joints. Acquisition of the fungus typically occurs as a result of environmental exposure to soil, water systems or spores transported in the air. 
Several sample types are acceptable for the diagnosis of fusariosis. Respiratory disease may be diagnosed through the analysis of bronchoalveolar lavage samples, or through the biopsy of lung or sinus samples. The collection of a skin biopsy and blood for culture can help diagnose disseminated disease, particularly since blood cultures are frequently positive in fusariosis patients due to the fungus’ ability to produce yeast-like structures that promote dissemination and growth in the blood. While blood culture is insensitive for most molds, Fusarium is an exception because it can readily spread through the blood.

While 12 species of Fusarium have been implicated in some very serious and potentially deadly diseases, the environmental mold is not all bad news. The development of mycoprotein, created by allowing Fusarium venenatum to ferment carbohydrates, began decades ago in the United Kingdom as the result of a systematic search for an organism that could turn starch into edible protein. After scientists collected and analyzed over 3,000 soil organisms from around the world, F. venenatum emerged as a sustainable source of protein. In 1983, the U.K. Administration of Agriculture, Fisheries and Food approved mycoprotein for use in food. The resulting commercial product, Quorn, is currently sold in 16 countries, including the U.S., as a meat substitute. 

'Quorn'-don bleu made with mycoprotein instead of chicken, with the fungus Fusarium growing on potato dextrose agar in the inset.
'Quorn'-don bleu made with mycoprotein instead of chicken, with the fungus Fusarium growing on potato dextrose agar in the inset.
Source: Wikimedia Commons
 Mycoprotein is now produced on an industrial scale by growing Fusarium venenatum in large fermentation tanks. The tanks contain products that encourage fungal growth, such as oxygen and glucose. Given the appropriate balance of pH and nutrients, the biomass of the fungus doubles every 2 hours. While mycoprotein has demonstrated positive effects on cholesterol and blood sugar, it is expensive and the environmental impact is higher than other meat substitutes — all things one might consider before switching to a mycoprotein product. Importantly, Fusarium venenatum is not considered to be a human pathogen. With the exception of a handful of case studies that have reported allergic reactions due to mycotoxins produced in minute quantities by the fungus, the product is generally considered safe to consume. 

For those who choose to flip to fungus, the selection of tasty meatless treats seems to be endless, with options for every palette. Choices include meatless nuggets, fishless sticks, meatless grounds (resembling ground beef), breakfast patties, turkey roast and steaks.

Saccharomyces: Opportunistic Pathogen and Beer Brewer’s Best Bud

Saccharomyces cerevisiae is commonly known as “Baker’s Yeast” and is a key component to brewing beer and wine. Historically, this organism is considered non-pathogenic,
S. cerevisiae colonies on yeast extract glucose chloramphenicol agar (YGC).
S. cerevisiae colonies on yeast extract glucose chloramphenicol agar (YGC).
with a strong food safety record. However, as identification technologies have improved over the years, S. cerevisiae has been implicated in a variety of infections, including fungemia (infection of the blood), respiratory, urinary and abdominal infections. In a comprehensive review of reported invasive Saccharomyces infections, all patients had at least one underlying condition, demonstrating the opportunistic nature of the organism. While the epidemiology of S. cerevisiae infection in humans is not well understood, the primary portal of invasive disease is believed to be the digestive tract. S. cerevisiae can be identified in the clinical laboratory through the use of biochemical identification systems (API) or Matrix-Assisted Laser Desorption/Ionization-Time Of Flight (MALDI-TOF) Mass Spectrometry. 

With respect to food production, Saccharomyces is commonly used in the beer brewing process.
Home beer brewing set up.
Home beer brewing set up.
The first step in the process is the conversion of barley to malt, which is a liquid that contains fermentable sugars, flavor and colors. Malt is then converted to a liquid called wort, which contains amino acids, carbohydrates, vitamins and lipids that serve as the nutrient source for the Saccharomyces yeast. Once the wort is cooled, strains of Saccharomyces are added. The yeast ferment the sugars present in the wort, converting them to ethanol and carbon dioxide, producing beer. While Saccharomyces is an essential part of the brewing process, beer would not be complete without help from a variety of gram-negative and gram-positive bacteria as well.

Enterococcus: Opportunistic Pathogen and Charcuterie Board Companion

The enterococci are gram-positive organisms that can be found in the environment, in food, as a part of normal human and animal gastrointestinal microbiota and as pathogens implicated in serious human infections. Clinically, enterococci are associated with urinary tract infections, bacteremia, endocarditis and surgical site infections. Most Enterococcus infections are hospital-acquired, with E. faecalis and E. faecium being most prevalent. Infections caused by enterococci can be particularly concerning due to their intrinsic antibiotic resistance and ability to acquire resistance traits. 

E. faecalis seen using scanning electron microscopy.
E. faecalis seen using scanning electron microscopy.
Enterococci play an important role in food production and are known to ripen and develop the aroma of various meats and cheeses, such as sausage, ham, minced meat, feta cheese and mozzarella. Cheeses that are produced in Mediterranean countries often contain significant amounts of enterococci, the source of which is believed to be dairy-cow feces, contaminated water or milking equipment. Because certain strains of Enterococcus seem to have a favorable impact on European cheeses, their use in starter cultures has been proposed. A study performed in 2002 demonstrated the effects of using E. faecium in a starter culture for feta cheese and determined that the addition of the bacteria positively affected the growth of other lactic-acid bacteria and improved the overall taste, color and aroma of the cheese. The presence of enterococci in meats is believed to be due to contamination from commensal intestinal flora that occurs during slaughter, and enterococci have been consistently isolated from beef, poultry and pig meats. These bacteria even contaminate processed meats, as the heating process used offers them a competitive advantage due to their thermophilic nature
There are positive and negative aspects to the presence of enterococci in food. Studies have demonstrated that several strains of enterococci are capable of producing bacteriocins, substances with antibiotic-like action on other strains of bacteria. Importantly, these strains produce a bacteriocin that has activity against Listeria monocytogenes, which has been linked to many outbreaks of potentially life-threatening illness associated with the consumption of contaminated meats and cheeses. On the other hand, enterococci found in food can colonize the human gastrointestinal tract via consumption. This can lead to serious infections in people who are, or become, immunosuppressed or immunocompromised, especially if the colonizing strain has acquired additional antibiotic resistance traits. 

You Are What You Eat

As strange as it may seem, many of the organisms that are in the environment are also used to make, enrich and preserve the food we eat. While introducing these organisms to our diets can occasionally result in opportunistic infections, they often serve as microbial friends. Importantly, the OneHealth concept reminds us that food safety is critically important, and that we should be mindful of how the lives of animals, microbes and humans intersect. 

Author: Andrea Prinzi, Ph.D., MPH, SM(ASCP)

Andrea Prinzi, Ph.D., MPH, SM(ASCP)
Andrea Prinzi, Ph.D., MPH, SM(ASCP) is a field medical director of U.S. medical affairs and works to bridge the gap between clinical diagnostics and clinical practice.