They are small, they are microscopic and contain about a thousand genes, yet within a few days they can kill the larger animals and humans that they infect – these are the superbugs.
Superbugs, Who, What and Where are They?
Many bacteria live on and inside the bodies of living animals. Skin and mucocutaneous membranes sites are among the most common places where these bacteria are found. In most instances these bacteria subsist on food and byproducts of animal or human metabolism and they survive quite well as they multiply from just a few to hundreds of thousands or even millions. Often many of these bacteria are simply normal flora — they are recognized as helpful or not harmful. However, certain different species, varieties or types of the same genus may cause infectious disease. And superbugs are just those types of bacteria.
The intestinal tract contains many Gram-negative (red-staining) bacteria of the Enterobacteriaceae – a large family of enterics (intestinal bacteria). These bacteria include the genera Escherichia, Klebsiella, Enterobacter, Serratia, Proteus and the regularly-pathogenic Salmonella and Shigella.
Staphylococcus aureus is the most notorious of the Gram positive (purple-staining) superbugs. It is a Gram-positive, spherical (coccus) that survives well on the skin, inside the nose and mouth and sometimes even quite well within the gastrointestinal (GI) tract. These S. aureus bacterial cells produce a large number of potent factors that can damage infected animal host cells and tissues.
Superbugs – Antibiotics Discovered and Used – Resistance Appears Also
Early scientists who advanced antimicrobial therapy, including Ehrlich, Domagk, Fleming, Waksman and many others, discovered new antimicrobial agents. From the early 1940s until today dozens of different and useful antimicrobials were available to doctors for treatment of infections.
These antibiotics and antimicrobials were truly miracle and wonder drugs for a world racked with death and disease over centuries of misery. Soon abscesses, carbuncles, boils, pneumonia, skin infections, strep throat, cholera, diphtheria, whooping cough, and plague were treatable and controlled by antibiotics and the advances in immunology birthed protective vaccines for immunization against disease.
However, even when these antibiotics were first introduced some resistant types of bacteria appeared from time to time within a few months or years. First there was penicillin resistance, and then resistance to streptomycin or gentamicin, or this antibiotic or that antibiotic. Soon antibiotic resistance was as common as the antibiotics themselves. The bacteria turned the tide in their favor in the ongoing war of humankind vs microbe. Antibiotics were not always effective for control of microbes even a few decades ago. Now the fear is that microbes are not only winning the battle for their survival – they are threatening human survival.
Superbugs, How do they Happen?
Antibiotic resistance arises primarily by mutation and selection. Because bacteria grow rapidly and mutations of the DNA are common there arise mutant forms of this bacterium or that bacterium. Soon the bacteria become resistant to many antibiotics. Often these bacteria carry multiple-resistant genes on plasmids. Plasmids are circles of DNA that are extra-chromosomal units. The genes on these plasmids often code (have instructions) for enzymes or factors that protect these bacteria from being inhibited or killed by antibiotics.
In some cases as many as 10 resistance genes are present on a plasmid. Furthermore, these resistance genes can be passed from one bacterium to another by primitive mating (conjugation) among the same species and even different species of these bacteria. Resistance can spread quickly within the enteric population as a result of these mechanisms.
Kirby-Bauer-Sherris Antibiotic Disk Testing
The Kirby-Bauer-Sherris Antibiotic Susceptibility Test permits determinations of bacteria as S (Susceptible), R (Resistant) or I (Indeterminate or Intermediate) to the antibiotics that are tested. Concentrated antibiotic disks are placed onto special Mueller-Hinton covered with a standardized layer of a pure culture of the test bacterium. The inhibitory zone sizes on agar are measured after 24-hr incubation. The different zone sizes of each antibiotic correlate with the actual MICs (minimum inhibitory concentrations) of these antibiotics in liquid media. Therefore, S, R and I antibiotic zone values correlate with clinical levels of antibiotics that occur in patients' blood, plasma and tissues.
Superbugs – Metallo-beta-lactamase 1 (NDM-1) in India, Pakistan and UK
In New Delhi, India a carbapenemase called metallo-β-lactamase 1 first appeared among enteric bacteria and this problem - a new type of resistance - is seen also in Pakistan and the UK. The multi-city research is reported in The Lancet medical journal and the following findings are significant:
- The NDM-1 resistance gene is carried and passed by plasmids (extranuclear DNA) among enterics.
- The resitance plasmids can be isolated, characterized and identified.
- Escherichia, Klebsiella, Proteus are among the most common enteric genera which contain these plasmids.
- NDM-1 resistant strains of enterics are common in hospitals and also in the outside community.
- Overuse of many non-prescription antibiotics throughout the Indian population has contributed to this resistance.
- Worldwide alerts have been posted to mutiple medical communities for the possible appearance of these resistant strains.
The prudent and wise use of antibiotics is an important step that each individual can take to fight against the rise of antibiotic resistance among bacteria.
Sources
Dionisio, F. et al. "Plasmids Spread Very Fast in Heterogeneous Bacterial Communities." Genetics. 2002 December; 162(4): 1525–1532.
Frieden, T.R. "Antibiotic Resistance and the Threat to Public Health." U.S. House Hearings, Energy-Commerce Committee, Subcommittee on Health, Wednesday, 28 April 2010.
Kumarasamy, K. et al. "Emergence of a new antibiotic resistance mechanism in India, Pakistan, and the UK: a molecular, biological, and epidemiological study." The Lancet Infectious Diseases, Early Online Publication, 11 August 2010 doi:10.1016/S1473-3099(10)70143-2
Donald Reinhardt - Think, read, write & live well always. DJR has a PhD in Biology/Microbiology & is a Fellow & Diplomate, ASM Amer Acad Micro.
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