Antibiotic myths

By Siouxsie Wiles 10/09/2012 6


Dr Michael Addidle, a clinical microbiologist with Pathlab in Tauranga, has written a very nice article* in the Clinical Microbiology Journal, debunking some of the urban myths around antibiotic resistance. Alas the article is behind a pay wall so I thought I would summarise a few of the myths here.

Myth 1: Antibiotics were invented in the 1930s

Nope. We didn’t invent antibiotics, we merely ‘discovered’ them. Antibiotics are substances produced by microbes to kill other microbes and so its likely they have been around for almost as long as the microbes themselves have been. So unless you are a creationist, that is a very long time indeed.

One of my favourite examples is of the glowing bacterium Photorhabdus luminescens. This bug is part of a deadly duo: it pairs up with a small worm and together they kill various insect larvae. P. luminescens lives in the worms gut. When the worms are eaten by larvae, they regurgitate their bacterial passengers who then start to produce toxins which kill the insect, and enzymes which turn it into a soup of nutrients. P. luminescens also start to glow, possibly to attract other unsuspecting lavae to the show, as well as produce antibiotics, presumably to stop any other bacteria enjoying the delights of the rotting cadaver which the worms are now feeding on. Anyway, bacteria and worms multiply, re-associate and burst forth in search of new prey. I’ve often read that injured soldiers in the Crimean War (1853-1856) who had glowing wounds were more likely to survive their injuries than those whose wounds didn’t glow. If this is true, an explanation could be that the ‘glowing’ wounds contained P. luminescens and the antibiotics they produced stopped other much nastier bacteria contaminating the wounds and killing the soldiers.

Myth 2: Antibiotic Resistance Developed Soon After the Invention of Antibiotics

Nope. Its likely antibiotic resistance has been around for almost as long as bacteria have been producing antibiotics. In fact E. coli were found to produce an enzyme capable of degrading penicillin before penicillin went into clinical use.

Myth 3: Inappropriate Antibiotic Use Creates Antibiotic Resistance

Dr Addidle argues that this is a misleading statement and in fact all antibiotic use selects for resistant bacteria. While this is true, Dr Addidle is putting it in the context of treating a patient with a broad spectrum antibiotic when a narrow spectrum one might do. When I think of an inappropriate use, I’m thinking more of feeding broad spectrum antibiotics to poultry so they can be housed in less than ideal conditions and not all die from infection! Ideally these antibiotics could be removed completely by less intensive farming practices.

Myth 4: Finish Your Course of Antibiotics to Prevent Emergence of Resistance

I’m not sure I agree with this statement being a myth. Dr Addidle argues that a longer than necessary course of antibiotics prolongs the selective pressure for resistant organisms to thrive, promoting antibiotic resistance. Instead he says the real message should be that antibiotic courses should be long enough to deal with the infection at hand, but not so prolonged that they unnecessarily promote selection of resistant bacterial strains. My assumption has always been that the prescribing doctor is giving you the appropriate length course of antibiotics and that you should finish them else your course is too short! Not taking antibiotics for long enough is one of the factors that in my understanding has lead to the rise of antibiotic resistance in M. tuberculosis, which is a global health disaster.

Myth 5: No New Antibiotics Are Being Developed

Let’s end on this myth which is most definitely a myth. While the majority of big pharma are not interested in antibiotic development (too little reward for too little effort) there are still plenty of labs around the world trying to develop new treatments. Its clear though, that in order to limit resistance emerging, what we need are entirely synthetic antibiotics like nothing ever seen in nature. And that’s a big ask!

*Addidle M (2012). Antimicrobial resistance: urban myths. Clinical Microbiology Journal, 34 (18):147–150.


6 Responses to “Antibiotic myths”

  • Oooh, that glowing bacteria story is wonderful. I am so going to borrow it for the next round of ‘Biological curiosities’ 😉

  • Hi Siouxsie

    I spotted your blog about my article on the net. Many thanks, it is always good to challenge dogma! One point about Tuberculosis resistance I would like to make. The resistance here is prevented by taking muliple anti-mycobacterial drugs in synchrony, so any resistant strains/mutants to one anti-TB drug should be wiped out by one of the partner drugs. It is likely that the resistant strains in Mycobacterium tubercuosis are selected out by the drugs not being taken simultaneously, or at the wrong time, or at the wrong dosage, thus increasing the likelihood of resistant strains surviving. I believe it is unlikely that not taking the antibiotics for the correct duration has any bearing on increasing the MDR TB prevalence.

    My thoughts anyway!

    Cheers
    Michael

  • Re your assumption “. has always been that the prescribing doctor is giving you the appropriate length course of antibiotics and that you should finish them else your course is too short!” your faith is greatly misplaced. In the vast majority of instances the length of a course of antibiotics that a doctor prescribes is little better than guesswork, and errs far too much on the side of excessive caution by prescribing too much. I know, because I have been such a precriber!