With this statement in mind, and considering that prompt action is needed to reduce
the overall misuse of antibiotics in all areas human medicine, veterinary medicine,
animal production and plant protection the Fish Utilization and Marketing Service,
Fisheries Division, FAO, took the initiative to develop this review, with the aim of
raising awareness of the antibiotic resistance problem in fish farming and related sectors,
promoting prudent use of these drugs according to the FAO Code of Conduct for
Aspects such as the toxicity and allergic effects of antibiotic residues, the mechanism of transmission of antimicrobial resistance and environmental impact were also taken into account. As the terms antibiotic and antimicrobial are often used indiscriminately, it should be noted that, for the purposes of this document, discussion is limited to just those antibiotics as defined in the glossary, although many aspects of the topic may be common to other antimicrobials used in animal husbandry or aquaculture.
Information regarding antibiotics in use, authorized or banned should be read in relation to the data and other information of the reference. Since the status of veterinary regulations varies very often in many countries, the interested reader should reconfirm/ update the specific information. Information given in this review is mainly for didactic purposes and in support of responsible use of antibiotics in aquaculture.
Antibiotics are drugs of natural or synthetic origin that have the capacity to kill or to
inhibit the growth of micro-organisms. Antibiotics that are sufficiently non-toxic to
the host are used as chemotherapeutic agents in the treatment of infectious diseases of
humans, animals and plants. They have long been present in the environment and have
played a crucial role in the battle between man and microbe.
Many bacterial species multiply rapidly enough to double their numbers every 20-30 minutes, so their ability to adapt to changes in the environment and survive unfavourable conditions often results in the development of mutations that enable the species to survive changing external conditions.
Another factor contributing to their adaptability is that individual cells do not rely on their own genetic resources. Many, if not all, have access to a large pool of itinerant genes that move from one bacteria cell to another and spread through bacterial populations through a variety of mobile genetic elements, of which plasmids and transposable elements are two examples. The capacity of bacteria to adapt to changes in their environment and thus survive is called resistance.
Drug choices for the treatment of common infectious diseases are becoming increasingly limited and expensive and, in some cases, unavailable due to the emergence of drug resistance in bacteria and fungi resistance that is threatening to reverse much medical progress of the past 50 years.
Dissemination of resistant micro-organisms may occur in both hospitals and communities. It is recognized that a major route of transmission of resistant microorganisms from animals to humans is through the food chain.
In aquaculture, antibiotics have been used mainly for therapeutic purposes and as prophylactic agents. The contribution to antimicrobial resistance of antibiotics used in aquaculture is reviewed here, using a risk analysis framework. Some recommendations on responsible conduct in this context are proposed, aimed at diminishing the threat of build up of antimicrobial resistance.
- Definition of antibiotics
- Mechanism of action of antibiotics
- Anti-infectious agents
- Growth promotion
- Classification of antibiotics for veterinary use
- Spectinomycin (Aminocyclitol)
- Florfenicol (Fluorinated derivative of thiamphenicol)
- Antibiotics banned for animals intended for food production
- Antibiotics authorized for use in aquaculture
- Risk assessment
- Hazard identification
- Antimicrobial resistance
- Epidemiology of antibiotic resistance
- Antimicrobial resistance in aquaculture
- Mechanism of resistance transfer
- Hazard characterization
- Human health risks associated with the use of antibiotics in aquaculture
- Environmental risks
- Exposure assessment
- Guidelines on the establishment of MRLs
- Assessing the effects of antimicrobial residues in food on the human intestinal microflora
- Hazard identification
- Risk management options
- At regulatory level
- Considerations from international forums
- Laboratory methods for the detection and quantification of antimicrobial resistance
- Methods of analysis and sampling for antibiotics residues
- At industrial level
- Approaches to minimizing antibiotics use in food-animal production
- At regulatory level
- Risk communication
- Promoting the prudent use of antibiotics in human medicine
- Promoting the prudent use of antibiotics in veterinary medicine and animal production
With the development and widespread application of antibiotics and vaccines, and
through improvements in urban sanitation and water quality, death from infectious
diseases has reduced dramatically. Progress was so great that, three decades ago, some
experts predicted the end of infectious diseases.
However, this optimism was premature. There is a global resurgence of infectious diseases, with both newly identified infectious agents and a re-emergence of older infectious diseases associated with the rapid spread of antimicrobial resistance. Antibiotic resistance is a serious clinical and public health problem on a global basis. Drug choices for the treatment of common infectious diseases are becoming increasingly limited, expensive and, in some cases, useless, due to the emergence of drug resistance in bacteria and fungi, and this loss of treatment options is threatening to reverse much of the medical progress of the past 50 years (HHS, 1999a).
Following the discovery of the growth promoting and disease fighting capabilities of antibiotics, fish farmers and livestock producers began using such drugs in animal feeds. Antibiotics routinely used for treatment of human infections are also used for animals, for either therapy, prophylactic reasons or growth promotion. For the lastnamed purpose, subtherapeutic doses of antibiotics usually have been used, and this has contributed to promoting resistance.
The accumulated scientific evidence is that certain uses of antibiotics in foodproducing animals can lead to antibiotic resistance in intestinal bacteria, and this resistance can then be transmitted to the general population, causing treatment-resistant illness. These uses of antibiotics can also create antibiotic resistance in non-pathogenic bacteria, the resistance genes of which can be transferred to disease-causing bacteria, resulting in antibiotic-resistant infections for humans.
The report from the invitational European Union conference on The Microbial Threat (EU, 1998) recognized that the major route of transmission of resistant microorganisms from animals to humans is through the food chain. This trend is confirmed by other authors (Nawaz et al., 2001).
There have been significant increases in developed countries in the occurrence of resistance in non-typhoidal Salmonella enterica and in Campylobacter spp., and to a lesser extent in Vero cytotoxin-producing Escherichia coli 0157 (VTEC 0157). There is also an increase in the occurrence of resistance in non-typhoidal S. enterica in developing countries, but, in contrast to the situation observed in developed countries, these increases have been almost entirely associated with the use of antimicrobials in human medicine (Threlfall et al., 2000).
According to a study by the European Federation of Animal Health (FEDESA), farm animals in 1999 consumed 4 700 tonne (35 percent) of all the antibiotics administered in the European Union, while humans consumed 8 500 tonne (65 percent). Of the antibiotics that were given to animals, 3 900 tonne (29 percent of total usage) were administered to help sick animals recover from disease, while 786 tonne (6 percent of total usage) were fed to farm animals as growth promoters. The survey estimated that the amount of antibiotics used as growth promoters had fallen by half since 1997, when animals consumed around 1 600 tonne as feed additives (EU, 2002b).
At the same time, the drug resistance problem has an economic cost. A study conducted in New York estimated that resistant infections due to Staphylococcus aureus cost an additional US$ 2 500 per infected patient, or US$ 7 million annually, in New York City alone. Another report estimated that the emergence of antimicrobial resistance among six common bacteria in hospitals added approximately US$ 661 million per year in hospital charges. This estimate did not include indirect costs or costs of infections caused by other resistant pathogens. If the spread of resistance continues, this cost will almost certainly increase. The foregoing points to great potential for economic savings by preventing antibiotic-resistant infections in human beings (HHS, 1999a).
The indiscriminate use of antibiotics for veterinary purposes has increasingly become a matter of public concern, and legal requirements are being reinforced. Regulatory authorities license antibiotics for use if the agents meet scientific criteria for quality, efficacy and safety. The authorities have to consider safety in relation to the treated animal, to the consumer and to the individuals handling the product during treatment.
In the fish farming (aquaculture, mariculture, etc.) sector, the widespread use of antibiotics for treating bacterial diseases has been associated with development of antibiotic resistance in Aeromonas hydrophila, A. salmonicida, Edwardsiella tarda, E. icttaluri, Vibrio anguillarum, V. salmonicida, Pasteurella piscida and Yersinia ruckeri (De Paola, Peeler and Rodrick, 1995), and controlled studies are needed to determine the effect of antimicrobial therapy on the ecology of aquaculture ponds, particularly at the micro-organism level.
The contribution to antimicrobial resistance of antibiotics used in the aquaculture industry is reviewed in this work, using a risk analysis framework. Some recommendations on responsible conduct in this context are proposed, aimed at diminishing the antimicrobial resistance threat.
The author wishes to express her special gratitude to Mr Hector Lupn for his various suggestions during the preparation of this document. Many thanks go to the Consejo de Desarrollo Cientfico y Humanstico (Council for Scientific and Humanistic Development) of the Universidad Central de Venezuela, which co-supported Professor Pilar Hernndez during her period of study in Rome. The author is also grateful to Mrs Wilma van Kessel and Ms Cristina Zuccaroli for their patience and diligence in editing and document layout. Final language editing and preparation of the publication were by Thorgeir Lawrence.
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Source: Food and Agriculture Organization of the United Nations (FAO) - April 2006