Background: Antibibacteria,fungi,and actinomycetes,which have inhibitory effect against other bacteria and fungi.With the discovary of the first antibiotic penicillin by Alexzander fleming in 1920 and subsequent use for the treatment of bacterial infections antibiotics were hailed as magic bullets for their ability to control infections and true to that they successfully cured many dreadful infectious diseases thus increasing human life expectancy.
Since the discovery of penicillin,many other anbiotics with inhibitory actions against a wide variety of microorganizms have been discovered.In addition to natural antibiotics many semi-synthetic deravatives and synthetic antimicrobial agents have been developed for the treatment of of infections.Antibiotics acts on bacteria by a variety of mechanisms like inhibition of cell wall synthesis,inhibition of protien synthesis,interfering with DNA replication to distrupt the microbial metabolism.
Antibiotics are not used only in humen but also in animal health and production.Widespreas use of antibiotic has led to the emergence of antibiotic resistant bacteria in the environment which is a matter of great concern for public health workers.Emergence of antibiotic resistant bacteria is a global problem and this is increasing so fast that there is a real threat to going back to the pre-antibiotic era.
Use of Antibiotics in animal health and production: Soon after the use of antibiotic in human health it was introduced into veterinary medicine to treat microbial infections of animals.Now a days antibiotics have formed a formidable part of the veterinarian’s arsenal for the treatment of of various infectious or even noninfectious diseases and enabling in part to meet the food requirements of the increasing human population.Almost all the major antibiotics that are prescribed for humans are also used in veterinary practics.In animals antibiotics are used not only to treat the infectious diseases,but also to augment animal production like growth promotors.As growth promotors antibiotics help in rapid weight gain up to 50% or more without increase in feed consumption enabling animals to reach market weight early.How antibiotic exactly help in weight gain is not clear but it is assumed that these compound interfere with gut microflora leading to better absorption of food.
For use as growth promotors antibiotics are administered to animals quite below recomended therapeutic levels and are supplied mainly through feed,occasionally through water.When administered as feed more than 80% of the antibiotic is excreted out through the faeces or urine.This sub-therapeutic use of antibiotics as growth promotors has emerged as a major factor contributing towards development and spread of antibiotic resistant bacteria.This commensal microflora of food animals serving as a reservoir of resistance traits spreading to commensals and pathogenic microbs of human being.
Emergence and spread of antibiotic resistance bacteria: When administered at sub-therapeutic levels antibiotics are not at a concentration high enough to inhibit disease causing bacteria but rather by selection prrssure this leads to emergence of antibiotic resistant bacteria.Selective pressure for resistance as well as spread of resistance among bacterial population is influenced by a purpose,dose,duration and rout of administration of antibiotics.Development of resistance by selective pressuer is because bacteria are capable of servival in adverse physiological conditions by changing their genetic make-up to adjust to a new environment employing a variety of mechanisms like production of antibiotic degrading enzyme,overproduction of target molecule;efflux pump to drain out antibiotics;altered permeability.In this way antibiotics select only antibiotic resistant bacteria which divide rapidly and outgrow sensitive and useful bacteria in gut.
Antibiotic resistance genes could be present on bacterial chromosomes or on plasmids.Once acquired antibiotic resistance genes spread very fast to other bacteria through all known means of genetic exchang like commonly by conjugation,naked gene uptake,mobile genetic elements.These genetic exchanges among bacteria are fairly common and it could be inter-species,inter or intra-genetic.From animals antibiotic resistant bacteria find their way to the environment when manure from farms using antibiotics as growth promotors is applied to agricultural land.Once in the soil antibiotic resistant bacteria exchange their genetic information with native soil microflora including pathogenic ons where as residual antibiotics in manure provide an environment for enrichment of antibiotic resistant bacteria.From such agricultural lands often these antibiotics and antibiotic resistant bacteria find their way to nearby streams or river by leaching or through surface runoff because of rain.Such soils,contaminated water and agricultural produce from these lands are the major sources of antibiotic resistant bacteria finding their way to the our food chain.Many pathogenic bacteria previously sensetive to an antibiotic could acquire resistance by these means posing threat to human and animal health.
Public Health Concern: Development of antibiotic resistant bacteria is a matter of cocern from both human as well as animal health points of view.Disease caused by antibiotic resistant bacteria are difficult to treat because of longer diagnosis time,high treatment costs and often prove to be life threatening.That’s why even after costly treatment in reputed nurshing home when patient dies off their relatives vandalize these establishment in our country.
Since most of antibiotics which are used as growth promotors in animals are structurelly related to those for use in human medication and development of resistance against these leads to cross-resistance against those antibiotics which are exclusively for human use.Beside cross-resistance microbes which cause diseases in humans are acquiring resistance genes from these environmental gene pools of bacteria.Already infections caused by these antibiotic resistant microbes are on the rise in human beings. For example hospital borne MARSA(Multidrug resistant Staphylococcus aureus)are now common even in developed countries where good post-oprative care is taken.In our own context last year’s hospital borne infection in Thapathali maternity hospital in delivary room had not created a havoc. Infections by Multidrug resistant Staphylococcus aureus are very difficult to treat as strain of S.aureus have reported to have high resistance levels to methicillin once which was used to be considered as most effective antibiotic against such infection.Similarly emergence of Vancomycin resistant Enterococci is causing cooncrn among scientefic communities as vancomycin is the last known antibiotic to treat infections by Enterococcus fecalis.According to one report its one isolate was found to be resistant to ciprofloxacin a wide spectrum antibiotic used in human medicine.Possible source of development of this resistance has been related to use of a structurally related antibiotic enrofloxacin commonly used as a growth promotor as well as for treatment of every kind of illness in poultry.Which is most common in our poultry farming.
Beside human pathogens many microbial pathogens causing diseases in animals like Salmonella,Compylobactor,E.coli,Pasturella have acquired resistance genes causijng difficulties in treatment of such infections posing a threat to livestock worldwide.Alarmed by the high levels of antibiotic resistane many preventive measures have been initiated around the globe to limit the use of antibiotics as growth oromotors.Since 2000 many member counties of Europian Union as well as United State of America have imposed ban on use of antibiotic like virginamycin and enrofloxacin as growth promotor in livestock and poultry thats why this antibiotics are abandently find in our country’s city to remote region located agrovets.
Conclusions: Emergence of antibiotic resistant bacteria that could infect humans directly or by transfer of resistant genes to human pathogenes is the main cause of concern regarding the use of antibiotics in animals.It is important therefor to have discussion among medical and veterinary practitioners for the proper use of antibiotics in animals as well as people.Education of farmers and veterinarians in this regard aswell as adherence to codes of practics is the need of hour.Also there is need to establish the use of antibiotics according to the species of animals in which they are used.It is also time to think about alternatives to use of antibiotics in food animals like improved management practices that reduce the likelihood ofspread of resistance from farm to field and spread of infectious diseases.The major thrust of such practics could be to follow quarantine and other biosecurity measures and vaccination particularly against the viral diseases that induces secondary bacterial infections.Other important factors could be like genetic selection to inhance disease resistance,use of antiseptics such as teat deeping to prevent mastitis,vector control and use of probiotics to exclude pathogens.Alarmed by the pace of spread of resistance developed countries have iniciated work to stop misuse of antibiotics in animal health and production.Many working groups and commities of scientists,lawmakers,and farmers have been formed to assess the threat posed by these antibiotic resistant bacteria and to suggest remedial actions.The need to improve antimicrobial use in agriculture;ecological and human health consequences following steps need to be undertaken:
1:Antibiotics should not be used in agriculture,livestock and poultry in the absence of diseases.
2:Antibiotics should be administered to animals only when prescribed by qualified veterinarians.
3:Quantitative data on antimicrobial use in agriculture, livestock and poultry should be made available to form public policy.
4:The ecology of antimicrobial resistance should be considered by regulatory agencies in assessing human health risk associated with antibiotic use in agriculture, livestock and poultry.
5:Serveillance programmes for antibiotic resistance should be improved and expanded.
6:The ecology of antibiotic resistance in agriculture, livestock and poultry should be a research priority in national programmes.
-By Dr.Kedar Karki.