Antibiotic resistance is the ability of a microorganism to withstand the effects of an antibiotic.
It is a specific type of drug resistance.
Antibiotic resistance evolves naturally via natural selection through random mutation, but it could also be engineered by applying an evolutionary stress on a population.
Once such a gene is generated, bacteria can then transfer the genetic information in a horizontal fashion (between individuals) by plasmid exchange.
If a bacterium carries several resistance genes, it is called multiresistant or, informally, a superbug.
Causes Antibiotic resistance can also be introduced artificially into a microorganism through transformation protocols.
This can be a useful way of implanting artificial genes into the microorganism.
Antibiotic resistance is a consequence of evolution via natural selection.
The antibiotic action is an environmental pressure; those bacteria which have a mutation allowing them to survive will live on to reproduce.
They will then pass this trait to their offspring, which will be a fully resistant generation.
Several studies have demonstrated that patterns of antibiotic usage greatly affect the number of resistant organisms which develop.
Overuse of broad-spectrum antibiotics, such as second- and third-generation cephalosporins, greatly hastens the development of methicillin resistance.
Other factors contributing towards resistance include incorrect diagnosis, unnecessary prescriptions, improper use of antibiotics by patients, and the use of antibiotics as livestock food additives for growth promotion.
Researchers have recently demonstrated the bacterial protein LexA may play a key role in the acquisition of bacterial mutations.
Resistant pathogens Staphylococcus aureus (colloquially known as "Staph aureus" or a Staph infection) is one of the major resistant pathogens.
Found on the mucous membranes and the skin of around a third of the population, it is extremely adaptable to antibiotic pressure.
It was the first bacterium in which penicillin resistance was found—in 1947, just four years after the drug started being mass-produced.
Methicillin was then the antibiotic of choice, but has since been replaced by oxacillin due to significant kidney toxicity.
MRSA (methicillin-resistant Staphylococcus aureus) was first detected in Britain in 1961 and is now "quite common" in hospitals.
MRSA was responsible for 37% of fatal cases of blood poisoning in the UK in 1999, up from 4% in 1991.
Half of all S. aureus infections in the US are resistant to penicillin, methicillin, tetracycline and erythromycin.
This left vancomycin as the only effective agent available at the time.
However, strains with intermediate (4-8 ug/ml) levels of resistence, termed GISA (glycopeptide intermediate Staphylococcus aureus) or VISA (vancomycin intermediate Staphylococcus aureus), began appearing the the late 1990s.
The first identified case was in Japan in 1996, and strains have since been found in hospitals in England, France and the US.
The first documented strain with complete (>16ug/ml) resistence to vancomycin, termed VRSA (Vancomycin-resistant Staphylococcus aureus) appeared in the United States in 2002.
A new class of antibiotics, oxazolidinones, became available in the 1990s, and the first commercially available oxazolidinone, linezolid, is comparable to vancomycin in effectiveness against MRSA.
Linezolid-resistance in Staphylococcus aureus was reported in 2003.
CA-MRSA (Community-acquired MRSA) has now emerged as an epidemic that is responsible for rapidly progressive, fatal diseases including necrotizing pneumonia, severe sepsis and necrotizing fasciitis.
Methicillin-resistant Staphylococcus aureus (MRSA) is the most frequently identified antimicrobial drug-resistant pathogen in US hospitals.
The epidemiology of infections caused by MRSA is rapidly changing.
In the past 10 years, infections caused by this organism have emerged in the community.
The 2 MRSA clones in the United States most closely associated with community outbreaks, USA400 (MW2 strain, ST1 lineage) and USA300, often contain Panton-Valentine leukocidin (PVL) genes and, more frequently, have been associated with skin and soft tissue infections.
Outbreaks of community-associated (CA)-MRSA infections have been reported in correctional facilities, among athletic teams, among military recruits, in newborn nurseries, and among active homosexual men.
CA-MRSA infections now appear to be endemic in many urban regions and cause most CA-S. aureus infections.
Enterococcus faecium is another superbug found in hospitals.
Penicillin-Resistant Enterococcus was seen in 1983, Vancomycin-Resistant Enterococcus (VRE) in 1987, and Linezolid-Resistant Enterococcus (LRE) in the late 1990s.
Streptococcus pyogenes (Group A Streptococcus: GAS) infections can usually be treated with many different antibiotics.
Early treatment may reduce the risk of death from invasive group A streptococcal disease.
However, even the best medical care does not prevent death in every case.
For those with very severe illness, supportive care in an intensive care unit may be needed.
For persons with necrotizing fasciitis, surgery often is needed to remove damaged tissue.
Strains of S. pyogenes resistant to macrolide antibiotics have emerged, however all strains remain uniformly sensitive to penicillin.
Resistance of Streptococcus pneumoniae to penicillin and other beta-lactams is increasing worldwide.
The major mechanism of resistance involves the introduction of mutations in genes encoding penicillin-binding proteins.
Selective pressure is thought to play an important role, and use of beta-lactam antibiotics has been implicated as a risk factor for infection and colonization.
Streptococcus pneumoniae is responsible for pneumonia, bacteremia, otitis media, meningitis, sinusitis, peritonitis and arthritis.
Researchers have found evidence of a banned antibiotic in chickens for sale in major supermarkets and butchers.
Scientists from the School of Biology from the Australian National University took 281 samples from three major supermarkets and a butcher around Canberra.
In those chicken samples contaminated with the common bacteria E.coli, almost two thirds of the bugs were resistant to some form of antibiotic.
Therefore if a human were to get sick from the contaminated chicken meat, doctors would find the illness difficult to treat.
Researchers were particularly concerned to find four samples resistant to fluoroquinolone antibiotics, which are banned from use in Australian food-producing animals.
The strong antibiotics have never been approved for such uses in Australia, and the country is highly regarded for having low levels of fluoroquinolone resistance.
Researchers Belinda Vangchhia and Professor David Gordon from the ANU says their findings suggest that the food people consume is a significant source of antibiotic resistance.
"E.coli is known to cause common infections like urinary tract and other blood stream infections like septicaemia," Ms Vangchhia said.
"Just by consuming the meat we can be exposed to the antibiotic as well."
They suspect the contamination is happening somewhere in the production process.
"It would be worth the relevant authorities going back through the steps of the processing to see where the introduction of antibiotic resistant bacteria might have occurred."
Is transmission happening on farms?
Generally, antibiotics are used widely on farms for both preventing and treating illness.
They are also used in some cases for "sub-therapeutic" treatments where farmers administer antibiotics to help fatten up animals.
The theory is the drugs affect microbes in the gut which allow the animals to absorb more of their food and get fatter.
University of Sydney academic Dr Stephen Page, a veterinarian and clinical pharmacologist who consults for the Australian chicken industry, says it is highly unlikely Australian chickens are being fed banned fluoroquinolones at farm level.
"I know nobody in the industry who would even contemplate an illegal practice, especially one that has only one outcome and that is undermining the world-class reputation of the chicken meat industry." Dr Stephen Page
Dr Page believes contamination with resistant E.coli is happening elsewhere, and says the specific drugs do not help fatten up produce and are expensive.
Fluoroquinolones are only available in Australia through veterinary prescription in tablet and injection form for cats and dogs. The antibiotic is not available in liquid form to be put in chickens' water supply.
Dr Page says fluroquinolines would have to be imported and would likely to be detected by the Australian Customs and Border Protection Service (ACBPS).
Australia's seven chicken producers tightly control about 800 chicken farms in Australia.
Stringent controls have also meant vets do not need to turn to strong antibiotics because existing drugs work.
"We have good management of poultry health in Australia so there would be no need to use them," Dr Page said.
"I know nobody in the industry who would even contemplate an illegal practice, especially one that has only one outcome and that is undermining the world-class reputation of the chicken meat industry.
"There would be no financial gain in using them, only pain."
Could it be harmful?
Most harmful bacteria, including antibiotic-resistant E.coli, are destroyed when chicken is cooked properly.
However, during food preparation chickens come into contact with humans and household surfaces.
There is also some evidence that some bacteria and antibiotic residues can remain at low levels in meat after cooking.
Ultimately, transmission depends on the method of cooking, the bacteria, the antibiotic and the meat.
A 2000 study from the Netherlands of cooked pork meat found most common antibiotic microbes were destroyed after temperatures passed 134 degrees Celsius.
"High temperature destruction process does not guarantee a full break-down of residues of veterinary drugs present in condemned animals," the study concluded.
Many farms ensure a delay between treating animals with antibiotics and sending them to the abattoir to ensure drugs leave the system.
Departments developing national antimicrobial resistance strategy
The ABC asked the federal Department of Health, the Department of Agriculture, the Australian Pesticides and Veterinary Medicines Authority (APVMA) and the NSW Department of Primary Industries about regulation of fluoroquinolones.
The NSW Department of Primary Industries says fluoroquinolone regulation is the responsibility of the APVMA.
The APVMA says it licenses the use of antibiotics in animals but was not responsible for compliance with use.
"State and territory governments are responsible for controlling the use of pesticides and veterinary medicines beyond the point of retail sale," a spokeswoman said.
"Veterinarians, as the prescribing professionals, play a key role in ensuring prudent use of antibiotics consistent with guidelines developed by the Australian Veterinary Association."
The spokeswoman said farmers also participated in on-farm programs that required them to declare the veterinary treatments their livestock had received.
"There is potential for exposure to E.coli throughout the food supply chain," she said.
The Department of Agriculture also said the responsibility to monitor imports and exports and responsibility fell to the states.
The Department of Agriculture together with the Department of Health are developing a national antimicrobial resistance strategy.
Do you know more about this story? Email investigations@abc.net.au
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