Respiratory Mycoplasmas

Published on September 30, 2015   32 min

Other Talks in the Series: Respiratory Infection

0:00
It's a pleasure for me to talk to you today about respiratory mycoplasmas. My name's Stephen Gillespie. I'm the Sir James Black Professor of Medicine at the University of St. Andrews.
0:12
In this talk, I'm going to describe these elusive, interesting, but enigmatic organisms. I first of all will give you a definition of what a mycoplasma is, and then a quick overview of the human mycoplasmas that are a challenge to clinicians. I'm going to focus most of this talk on two important respiratory pathogens, mycoplasma pneumoniae and mycoplasma amphoriforme. Then I'll speak a little bit about the future of mycoplasma research, and hopefully come to some conclusions.
0:45
Mycoplasmas and related organisms are ubiquitous in nature, and such organisms are found widely in humans, animals, and plants. We don't think much about them as clinicians because they're very difficult to diagnose because of their slow growth. Their small cells were the first to have a whole genome sequenced and indeed the first organism to be synthesized synthetically. So they're very small bacteria and the smallest capable of extracellular existence. Their genome is also small, ranging from 0.5 of a megabit to 2.2. They closely adhere to cells, and they lack a typical bacterial cell wall. They have no peptidoglycan. They have an interesting evolutionary past. Mycoplasmas are thought to have evolved from gram positive bacteria, probably clostridia, through reductive evolution. Both pathogens and commensals are found in human samples. And it can be often challenging to differentiate whether the organisms are acting as commensals or pathogens.
1:50
The small genome size of a mycoplasma means it has to depend on the host for many of its metabolic factors. It has very few genes for the biosynthesis of cofactors, nucleic acids, and metabolic precursors. Indeed they do not synthesize their own amino acids and their fatty acids. All mycoplasmas require cholesterol for membrane function, except, of course, the acula plasmas, which in general are not human pathogens. They use glucose as a carbon source or arginine, they are facultative anaerobes, and their optimal growth temperature is 37 degrees Celsius. A major challenge of these fastidious requirements is that they do not grow on normal laboratory media. This means that they fall out of the normal diagnostic pathway and are often unrecognized by bacteriologists.
2:45
In this slide I show you a list of many of the organisms and mycoplasmas that have been isolated from human samples. I've divided the slide to two halves, respiratory organisms found in respiratory samples and the organisms that are often found in urogenital samples. You can see that I've highlighted two organism names in bold, and these are two organisms that are respiratory pathogens. Among the urogenital organisms, I've noted three with an asterisk. These represent organisms that are probably pathogens, although it remains a matter of some debate. So in this talk, I'm going to concentrate predominantly on mycoplasma pneumoniae and mycoplasma amphoriforme.
3:31
Mycoplasma pneumoniae is an important respiratory pathogen. Infections are found at all times throughout the year, and there is a relative peak in the late summer that may be due to the absence of other respiratory infections, making mycoplasma infections appear more prominent. So seems that the climate, season, and geography do not appear to affect the incidence of mycoplasma pneumoniae infection. And indeed, this organism has been found throughout the world and in all climates. There is a periodicity associated with mycoplasma infections. Approximately every 4 to 5 years, there will be a peak of incidence. Infection occurs in all ages, but is highest in children and especially in young adults. To emphasize its importance as a cause of respiratory infection, mycoplasma pneumoniae is the second most common bacterial respiratory pathogen isolated in high quality reviews of etiology.
4:28
How does it cause disease? Well, essentially there are two important components of mycoplasma pathogenicity. There is the very close adhesion that the organism has to the respiratory tract, and this is mediated primarily through the P1 antigen. But there are a number of other accessory adhesions, such as P30. In addition to this, and recently recognized, mycoplasma pneumoniae produces a toxin known as the Community Acquired Respiratory Distress Syndrome, or CARDS toxin. This is a 68 kiloDalton antigen which demonstrates a very high affinity binding to human surfactant protein A and exhibits specific biological activities, including mono ADP right oscillation and vacuolization. These properties lead to an inflammatory process in the airway and a range of cytopathologies, including ciliostasis, loss of tissue integrity and injury, and cell death. So this is an important new discovery in the area of mycoplasma infection.
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Respiratory Mycoplasmas

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