How to put an end to antibiotic resistance
The discoverer of the first Antibiotic, Penicillin, Dr. Alexander Fleming, in his bouquet speech while receiving the Nobel prize in Dec 1945 predicted the issue of antibiotic resistance due to unethical and misuse of antibiotic . Now the time has come to see the effect which was predicted by him 75 years ago.
Antibiotic Residue
A residue indicates that traces of a substance are present in meat. Residue does not mean that the substance is harmful, and it can be one of many classes of compounds. For antibiotics in particular, if a residue is present, it is likely due to the producer not waiting long enough after the animal was given antibiotics to send it to market (not properly following the mandatory FDA withdrawal guidelines).
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| How to curb Antibiotic resistance |
Antibiotic Resistance
The presence of a residue in meat does not indicate antibacterial resistance. The two are separate issues. If resistance is detected, this means that there are bacteria on the meat that have tested resistant to one or more antibiotics. Resistance is measured and reported through the National Antimicrobial Resistance Monitoring System (NARMS). If resistance is detected, that does not mean there are residues; likewise, if a residue is found, that does not mean that there are resistant bacteria to that antibiotic.
The introduction of anti-bacterial was one of the most important developments in medicine. Their availability has facilitated increasingly complex care and, not surprisingly, microbial resistance to antibacterial has been identified as one of the greatest threats to animal and human health. A return to the “pre-antibiotic era” would render many routine infections untreatable and would seriously affect current practice in veterinary and human medicine through major increases in morbidity and mortality. Drug resistance occurs due to indiscriminate use of antibacterial in veterinary hospitals and practices. Veterinary practices involving the use of antibacterial for prophylaxis and growth promotion rather than treatment also contribute to this problem. The current situation is becoming serious with an increasing incidence of detection of resistance to all known drug treatments, especially amongst bacteria. For example, the incidence of Multi Drug Resistance (MDR) in Mycobacterium tuberculosis, which can result in untreatable tuberculosis infection, is rising steadily worldwide. According to a recent WHO report, an estimated 4,40,000 cases of MDR tuberculosis were notified worldwide in 2011. Furthermore, 84 countries have reported untreatable tubercular infection. The second example is that of common bacterial infections caused by Enterobacteria in human beings. Carbapenem-resistant Enterobacteriaceae (CRE) infections are on the rise, and have recently becomes resistant to ‘last-resort antibacterial’.
These bacteria are an increasing cause of mortality in many countries. The time to act is now – before we lose these “miracle” drugs for good.
What is antimicrobial resistance?
Resistance to antimicrobials is a natural biological phenomenon. The introduction of every antimicrobial agent into clinical practice has been followed by the detection in the laboratory of strains of microorganisms that are resistant, i.e. able to multiply in the presence of drug concentrations higher than the concentrations in animals receiving therapeutic doses. Such resistance may either be a characteristic associated with the entire species or emerge in strains of a normally susceptible species through mutation or gene transfer. Resistance genes encode various mechanisms which allow microorganisms to resist the inhibitory effects of specific antimicrobials. These mechanisms offer resistance to other antimicrobials of the same class and sometimes to several different antimicrobial classes.
Types of resistance
1. Natural Resistance: Inherently or genetically resistant due to lake of penetration of drug into bacterial cell, absence of metabolic pathway or target site or rapid inactivation of drug in bacterial cell.
2. Acquired resistance: Resistance against drug to which bacteria was previously sensitive. It is due to inappropriate use of antimicrobials. It is done by mutation or gene transfer.
Mechanism of resistance
1. Reduced drug accumulation: by decreasing drug permeability and/or increasing active efflux (pumping out) of the drugs across the cell surface.
2. Drug inactivation or modification: e.g., enzymatic deactivation of Penicillin in some penicillin-resistant bacteria through the production of β-lactamases
3. Alteration of target site: e.g., alteration of PBP — the binding target site of penicillin — in MRSA and other penicillin-resistant bacteria.
4. Alteration of metabolic pathway: e.g., some sulfonamide-resistant bacteria do not require para-aminobenzoic acid (PABA), an important precursor for the synthesis of folic acid and nucleic acids in bacteria inhibited by sulfonamides. Instead, like mammalian cells, they turn to utilizing preformed folic acid.
Bacteria Resistance to Reference
Streptococcus pneumoniae —–Penicillin, cotrimoxazole, tetracycline,
erythromycin, ciprofloxacin Goyal et al., 2007 Chawala et al., 2010
S. pyogenes ——-Penicillin, erythromycin, trimethoprim Capoor et al., 2009 Bergmann et al., 2012
Staphylococcus aureus–Clindamycin, Vancomycin Gupta et al., 2009
Thati et al., 2011 E. Coli —Ampicillin, tetracycline, co-trimazole,
trimethoprime, carbenicillin Sukumaran et al., 2012
Salmonella spp.———- Nalidixic acid, ciprofloxacin, ampicillin,
chloramphenicol, ampicillin and trimethoprim Rowe et al., 1997 Nagshetty et al., 2010
K. pneumoniae———- Ceftizoxime , cefotaxime, carbenicillin Sikarwar & Batra, 2011
Nagaraj et al., 2012
Shigella spp.——— Newer gen. fluoroquinolones, 3rd gen. cephalosporins Bhattacharya et al., 2012
Pseudomonas spp——–. Ciprofloxacin, ceftazidime, cefepime, gentamicin, amikacin Chaudhary et al., 2013
Mechanisms of Antibiotic Resistance
When bacteria are first exposed to an antibiotic, those most susceptible die, leaving surviving bacteria to pass on their resistant features to the succeeding generations. Antibiotics cause a selective pressure by killing susceptible bacteria, allowing antibiotic resistant bacteria to survive and multiply. Selective pressure is the influence exerted by the antibiotics to promote one group of organisms over another. In this process natural selection follows the rule of survival of the fittest. The indiscriminate use of antibiotics in animals and humans has accelerated the pace of resistance against both pathogenic and non-pathogenic bacteria.
Bacteria develop resistance in two ways: (i) by genetic mutations (vertical evolution), and (ii) by acquiring resistance genes from other bacteria (horizontal gene transfer).
(i) Through Genetic Mutations (Vertical Gene Transfer or Vertical Evolution)
Susceptible bacteria can become resistant through mutations in their genes. Mutations are spontaneous changes in the genetic material (DNA). They are thought to occur in about one in one million to one in ten million cells. Through mutations bacteria acquire defense mechanisms against antibiotics. Different genetic mutations result in different types of resistance. For example, some bacteria have developed biochemical “pumps” that can remove an antibiotic before it reaches its target, while others have evolved to produce enzymes to inactivate the antibiotic.
Bacteria reproduce rapidly, sometimes in as little as 20 minutes. Therefore, it does not take long for the antibiotic resistant bacteria to comprise a large proportion of a bacterial population.
Once the resistance genes have developed, they are transferred to all the bacterial progeny during DNA replication. The phenomenon is known as “vertical gene transfer” or “vertical evolution”.
(ii) Acquiring Resistance from Other Bacteria (Horizontal Gene Transfer)
Susceptible bacteria can become resistant also by acquiring antibiotic resistance genes from resistant bacteria. Development of resistance occurs by the exchange of small pieces of DNA called plasmids. Plasmids are extra-chromosomal circular molecules of DNA that replicate independently of the bacterial chromosome. Plasmids carry antibiotic resistance genes and have the ability to transfer themselves to other bacteria. They are called “resistance (R) plasmids” and act as vectors to transfer resistance genes.
Bacteria readily exchange plasmids among both related and unrelated species. This way the antibiotic resistance genes from one type of bacteria are incorporated into other bacteria. Non-resistant bacteria acquire resistance genes in three ways: (a) conjugation, (b) transduction, and (c) transformation.
a. Conjugation
Conjugation is the mechanism by which genetic material is transferred through plasmids between two bacterial cells. It requires cell-to-cell contact. A bacterial cell, containing an R plasmid, forms a mating pair with a bacterial cell that does not contain an R-plasmid. They undergo a mating process called “conjugation”. By a complex mechanism, plasmid containing resistant genes is transferred from the plasmid-containing bacterial cell (the donor) to the recipient. This enables the antibiotic susceptible bacteria express resistance as coded by the newly acquired resistance genes. Most antibiotic resistance in Gram-negative bacteria is acquired through horizontal gene transfer. Genes, encoding antibiotic resistance, are transferred between bacteria via plasmids. Plasmids are often capable of self-movement (conjugation) from one bacterium to another. They are also highly stable once established in a bacterium. Among E. coli and Salmonella enterica alone, there are more than 30 plasmid types identified and this number continues to grow. Plasmids associated with multidrug resistance are primarily a concern among E. coli, S. enterica, and Klebsiella pneumoniae, although numerous other Gram negative bacteria have been shown to possess multi-drug resistance-encoding plasmids.
b. Transduction
Transduction involves transfer of DNA from one bacterial cell (donor) to another (recipient) by bacteria-specific viruses (bacteriophages). It occurs between two closely related bacteria.
c. Transformation
Transformation occurs from the uptake of short fragments of free DNA from the surrounding medium by non-resistant bacteria. The free DNA is normally present in the surrounding medium from the death and lysis of other bacteria. Bacteria like Streptococcus are capable of natural transformation.
Obstacles in the Way
No new effective antibiotic has been developed in the past more than 20 years. Perhaps pharmaceutical companies are not investing required financial resources for antibiotic drug discovery, because the profit margins have declined. Apparently the antibiotics are becoming ineffective at faster rate due to the emergence of antibiotic resistance, largely from abuse of these drugs. It takes almost 15-20 years to bring a new antibiotic in the market, and the return on investment is uncertain due to the development of new resistance.
Antibiotic Resistance in Livestock
Numerous studies have demonstrated that routine use of antibiotics on the farm promotes drug-resistant superbugs. This is because there are always some bacteria the drug can’t kill, and these survive and proliferate.
A simple way to overcome the health problems caused by antibiotic resistance is to stop adding antibiotics to animal feed. It was found that when poultry and beef are produced without antibiotics, bacterial resistance quickly declines. Feeding antibiotics to livestock creates an ever-increasing number of antibiotic-resistant bacteria, including many that cause disease in humans.
The US Food and Drug Administration (FDA) say that 80% of all antibiotics sold in the US are fed to food animals. Meat animals are fed antibiotics because doing so increases their weight gain, prevents disease, and makes meat production cheaper.
Many countries have already acted to curb antibiotic feeding to livestock. Most notably, the European Union banned feeding of all medically important antibiotics to livestock in 1998.
This was followed with a total ban on all antibiotics in 2006.
Threat to public health from the overuse of antibiotics in food animals is real and growing. Humans are at risk both due to potential presence of superbugs in meat and poultry and to their migration into the environment, where they can transmit their genetic immunity against antibiotics to other bacteria, including those that make people sick.
Cost of resistance
The emergence of antimicrobial resistance has an impact on the cost of animal and human health care worldwide. Ineffective therapy due to antimicrobial resistance is
associated with increased animal and human suffering, loss of productivity and often death (WHO, 2001).
Resistant strains of bacteria are found around the world.
Organisms that are resistant to one drug are more likely to become resistant to others. The bacteria Streptococcus pneumonia has become resistant to penicillin and now demonstrates some resistance to several other antibacterial.
Resistant pathogens are expensive to control and extremely difficult to eradicate.
Ineffective therapy can seriously affect the progress and outcome of disease
Significantly impact the cost of treating disease.
Limited clinical effectiveness of readily available cheap antimicrobials in many regions which results in difficult to choice and to use more effective but more expensive drugs to treat.
Resistant animal pathogens in food products may cause infections in humans that are difficult to treat.
Loss of public confidence in the safety of food which affects the demand for products, with potentially serious economic effects on the farming sector
Why an Antimicrobial Therapy fails?
Improper diagnosis (Viral not Bacterial infection)
Improper selection of drug (Causative organisms are not sensitive to drug).
The microorganisms have developed resistance to drug.
Mixed infection & narrow spectrum drug
Penetration of drug into site infection is not proper due to pus, debris, exudates etc.
The host defense mechanism is impaired
Improper route of administration with inadequate duration of treatment Interaction of drug with other administered drugs.
Late administration of antimicrobial drug
Use of expired drug
The owner or attendant of animal does not comply with therapeutic regimen
Improper nursing and feeding
Selection of an Antimicrobial Agent
Requires clinical judgment and detailed knowledge of pharmacological and
microbiological factors.
Antibacterial : empirical therapy, definitive therapy, and prophylactic therapy.
Empirical therapy: infecting organism has not been identified – Combination
therapy/broad-spectrum agent
Infecting microorganism is identified : Narrow-spectrum AB Select an antibacterial based on indication
The diagnosis may be masked if therapy is started before cultures are obtained.
Antibacterial may be used immediately if disease is severe
Initiation of optimal empiric antibacterial therapy: knowledge of most likely infecting
organisms and their antibacterial susceptibilities.
Simple and rapid laboratory tests may permit more rational selection of initial
antibacterial therapy.
Blood should be taken prior to the institution of drug therapy.
For definitive therapy, Use specific & narrow-spectrum antibacterial once an
organism has been identified & its susceptibility is known.
Successful Antimicrobial Therapy
For definitive therapy, recommend a narrow-spectrum drug
Keep the broad spectrum drug reserve for life threatening infection Prefer bactericidal over bacteriostatic drug with less toxicity
Prefer drug requires administration at long interval
For less severe infections prefer an oral administration in small animals
For severe infection
parenteral administration
Always use antimicrobial agent in proper dose
Proper duration of time
Do not combine antimicrobials without valid cause
Do not use antimicrobial indiscriminately
Avoid overuse of newer agent if older is effective
Use drug manufactured by reliable pharmaceutical firm.
Do not use antimicrobials to treat slight, self-limiting or unbeatable infections. How can we fight back?
Maintain good hygiene and infection control measures – particularly hand washing.
Strict infection control measures should be monitor in hospitals
Don’t use antibacterial in minor or self limiting viral infections
Farmers should not use antibacterial of previous prescription
Educate farmers: help them to understand about cost of unnecessary use of antibacterial
Communicate with farmers about progression of disease after initiation of therapy
Use laboratory tests to support your diagnosis & select the right antibacterial.
Record of vaccinations must be generated.
Develop and implement guidelines, protocols and drug utilization reviews to ensure
that use of antibacterial drug is optimized
Ensure surveillance for changes in the occurrence and pattern of antimicrobial
resistance in different bacteria.
Emphasize good animal husbandry practices (adequate and clean quarters)
Work with governments to move away from using antibacterial as growth promoters.
Collaborate in monitoring of antibacterial use and resistant pattern with institutes
Educate the public and health professionals about the antibacterial resistance
Coordinate the development and implementation of regional programs to optimize
antibacterial use and to prevent the spread of resistant organisms.
Develop the rapid affordable systems for diagnosis and susceptibility testing.
Ensure that antibacterials remain available through prescription only, rather than as over-the-counter medications.
Prevention and Control of Antibiotic Resistance
A simple way to overcome the emergence of antibiotic resistance in bacteria is to stop adding antibiotics to animal feed. Ban on the use of antibiotics for growth promotion in some countries has indicated that they could be avoided without any significant impact in livestock production. The experiences from different countries suggest that major reductions can be achieved without significant negative effects on animal health or productivity, and for the long-term benefit of public, environmental, and animal health.
However, the veterinarians should still be allowed to use antibiotics to treat animals in case of diseases, but only drugs which are not used for humans; and all treatments should be documented to allow retrospective analysis of field data.
Alternatives to antibiotics to treat or control infections are other important areas that need attention. This may include acidifiers, enzymes, prebiotics and probiotics, boosting host’s immune system, and certain other approaches to control infectious agents.
The feed industry, in the meantime, must offer other options to keep animals as healthy as possible.
Improving hygiene and sanitation counter infectious diseases, and is crucial to reducing the rise in drug resistance. The less people get infected, the less they need to use medicines such as antibiotics, and the less drug resistance arises. Improving the general hygiene in all stages of production and thereby reducing the microbial load on food products will also reduce the antimicrobial resistance load. Sensitivity tests should be done to make sure the right antibiotic is prescribed. Also, antibiotics should be administered exactly as prescribed by the veterinarian. Doses should not be skipped and the prescribed course of treatment be completed even when the flocks start feeling better.
Certain essential oils can prevent the transmission of some drug resistance strains of pathogens, especially Staphylococcus, Streptococcus, and also Candida. Essential oils are extracted from different parts of plants such as eucalyptus, clove, tea tree, and lavender.
Herbal medicines have been and should be further explored as alternatives to antibiotics.
Reference available-on request
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Microbiology