The reason we should all study microbiology

During the first day of class, I stated that I perceive society today as  facing two critical epidemics.  For those of us living in developed societies, disease due to inadequate exercise, tobacco use, and poor dietary choices has led to alarming numbers of people facing issues of all forms of cardiovascular disease and other conditions such as diabetes. In that lecture, I made the assertion that although health care workers may have some influence over the choices of their patients, changes in the lifestyle of the patient enabling resolution of these diseases are ultimately in the hands of those patients. The other epidemic we face is that due to infectious agents, including emerging infectious disease which have not been previously associated with significant human disease, and the emergence of multiply drug resistant isolates of existing infectious agents. I further asserted that point of contact health care workers will be a significant force in helping to curb this epidemic.

Which brings us to today’s Microbes in the News offering. It may not be immediately obvious why we face an epidemic of emerging infectious disease, but many of them are due to the conveniences of modern society and the way we live our lives.  Two important concepts in infectious disease are reservoirs (where a microorganism can survive outside of a human host), and vectors for transmission of infectious agents. The linked article from WebMD article discusses evidence that antibiotic resistant strains of bacteria can arise due to the high levels of antibiotics that are used in farming to promote animal growth and health. The high levels of exposure in agriculture puts selective pressure on microbes in the environment, resulting in acquisition of antibiotic resistance broadly in microbial populations.

This is not a new finding; modern agriculture has been known to be a factor in the emergence of antibiotic resistant strains of infectious agents, and is one that we will discuss in class later in the term, along with other inappropriate uses of antibiotics. What is novel in this report is the description of the role that common insects can play in the spread of infectious agents. Authors at Kansas State and North Carolina State Universities found that flies and cockroaches recovered adjacent to pig farms were able to transmit many organisms associated with gastrointestinal disease, including Enterococcus faecalis. The isolates of these bacteria that were recovered from the insects were identical to strains found in pig manure. The conclusions of the studies were that the insects were serving as mechanical vectors of transmission to neighboring residential areas. So merely ensuring that your pork chops are cooked to an appropriate internal temperature is no longer enough; you now need to ensure that your Caesar Salad hasn’t been touched by flies which have visited from the farm next door!

Bonus opportunity: Based on what we are learning in Chapter 6, what can you conjecture about the growth requirements or the nutritional requirements of the organisms that this article mentions? How do you think they might be isolated or studied in the laboratory?


About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on February 1, 2011, in Bonus!, Lecture, Microbes in the News. Bookmark the permalink. 6 Comments.

  1. Enterococcus faecalis lives in the intestines of animals so basically all of it’s nutritional sources could be fulfilled from the food as it passes through there. It’s need for carbon could be met from organic compounds like glucose in the intestines making it a chemoheterotroph.
    It could be studied in the lab by taking a stool sample from a pig and by killing off other non antibiotic resistant organisms with an antibiotic. Then a quadrant streak plane method could be used to culture the organism.

    • Stool samples are typically cultured exactly with this method. Aaron’s suggestion of using an antibiotic in the culture media is a technique called selection or enrichment organisms that might be in the minority of the sample. This is necessary, as the vast majority of the organisms in the sample will NOT be E. faecalis.

      Temperature requirements?

  2. While reading related articles about the study of antibiotic resistance in the farming industry, I came across information on the E. hirae, a pathogenic bacteria. The article, published in the Journal of Clinical Microbiology stated that E. hirae has recently become antibiotic resistant, and that it is a Gram positive bacteria. The article explains how E. hirae has been the cause of some cases of native valve endocarditis, a heart condition where the valves and lining of the heart are infected. According to one of the linked studies, E. hirae was the second most prominent pathogen found predominately in pig feces. Such as bacteria could cause harm to humans because of its antibiotic resistant properties. Since the bacteria is Gram positive, it has a thick layer of peptidoglycan, and no outer membrane, however the thicker layer of peptidoglycan helps give the bacteria more resistance against physical and environmental forces that it could face during its life. Collecting a stool sample would be an easy way to collect the bacteria. The bacteria could be cultured by giving it similar nutrients found in a pig’s digestive system. Furthermore, once the sample is collected, Gram staining could be used to help differentiate it from other Gram negative bacteria. Other tests such as nucleic acid testing (DNA testing) could help prove its relations with previously non-pathogenic forms of the bacteria.

    • Good find! E. hirae infections rarely cause infection in humans although they are encountered to some degree in animals as you have found. As we get into the next several chapters, we will begin to learn about the normal microbial flora, or those organisms that we can find living in and on us, in the absence of disease. E. hirae is apparently a member of the porcine intestinal flora, but I would guess that it is not frequently found in humans. Infections of people apparently occur extremely infrequently, and the linked article cites a case in someone who had other very significant medical issues (end-stage renal disease, dialysis) when he developed septicemia due to this organism. E. faecalis on the other hand, is very well adapted to living in humans, and when it gets someplace in the body that it doesn’t belong, serious disease can be the result. Since the bacteria is found in us to begin with, disease happens with alarming frequency.

  3. I missed this post earlier, hence my late comment. Resistance works at the “macro” as well as the “micro” level. Many years ago I had the “pleasure” of studying DDT resistance in roaches. The Entomology Lab down the hall from my Chemistry Lab had several strains of roaches that were resistant to several hundred times the amount of DDT that would kill most similar organisms (levels high enough to be dangerous to human health). The founder organisms for these strains were not bred in a lab but rather were isolated from a number of natural sources. Once they were brought into the lab, they were maintained with high levels of DDT in their cages in order to prevent their loss of resistance.

    All of these observations are explained by Charles Darwin’s notion of natural selection. An organism, micro or macro, resistant to an environmental stress (antibiotic, insecticide, etc.) will be more “fit” and will survive when a lot of those substances are around to kill off their less fit relatives.

    • There is no such thing as a “late” comment in this discussion! This is a highly appropriate comment for where we are in the course. Antimicrobial resistance (and I am using this term as broadly as possible, to include the compounds we think of when we think of antibiotics, and antiseptics/disinfectants, and other non-chemotherapy agents) is on the rise, and the spread of this property is due to the natural (or artificial in this case) selection of random mutants which happen to acquire resistance and pass on this trait to their offspring.

      Now, an antibiotic resistance gene obviously confers a benefit on an organism when that antibiotic is present in the environment. It is able to survive after all. What about an organism that has a gene, and is making a special enzyme or protein to combat the antibiotic and confer resistance, in the absence of the antibiotic? In this case, the antibiotic resistance trait is not helping the organism, and may actually be a detriment to the organism. Consider: if an organism is wasting time and wasting energy on making something it doesn’t actually require, it is doing so at the expense of something else it might need to maximize its growth rate. So, microorganisms that have acquired antimicrobial resistance actually tend to rather rapidly lose that ability when they do not require it. This is one strategy we can use to fend off our microbial adversaries!

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