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Numerous researches have shown that antibiotics increase the rate and efficiency of growth in animals. Figure 1 shows that antibiotics are effective in pigs of all growth stages, but they are the most effective when the pigs are young and weanling.  The growth rate of pigs in starting phase (7-25kg) improved by an average of 16.4% and reduced the amount of feed required by 6.9%. However, the experiments are controlled and performed at clean and disease-free research facilities. Thus, the antibiotics are predicted to be more beneficial when used at the farm, where it is less clean, and thus, easier to catch diseases. (Cromwell, 2000). The exact mechanisms by which antibiotics favor growth are not known; however, researches propose that they possibly promote growth by depressing  the growth of microbes that are toxic or steal nutrients from the host, leading to the increased nutrition utilization and reduced energy investment in maintaining immune responses in the GI tract (Gaskins et al., 2002).  
 
Numerous researches have shown that antibiotics increase the rate and efficiency of growth in animals. Figure 1 shows that antibiotics are effective in pigs of all growth stages, but they are the most effective when the pigs are young and weanling.  The growth rate of pigs in starting phase (7-25kg) improved by an average of 16.4% and reduced the amount of feed required by 6.9%. However, the experiments are controlled and performed at clean and disease-free research facilities. Thus, the antibiotics are predicted to be more beneficial when used at the farm, where it is less clean, and thus, easier to catch diseases. (Cromwell, 2000). The exact mechanisms by which antibiotics favor growth are not known; however, researches propose that they possibly promote growth by depressing  the growth of microbes that are toxic or steal nutrients from the host, leading to the increased nutrition utilization and reduced energy investment in maintaining immune responses in the GI tract (Gaskins et al., 2002).  
 
  
 
  
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==Debate regarding Resistance==
 
==Debate regarding Resistance==
  
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Since antibiotics have been introduced as growth promoters, there have been concerns about antimicrobial resistance. Frequent use of antibiotics leads to increasing resistance in enteric bacteria that can infect people or transfer their resistance to other pathogenic bacteria (OMAFRA, 2005). When infected by multi-drug resistant bacteria, treatment options are limited, recovery is slow, and treatment is more costly (WHO, 2012). The concerns especially involve resistance against penicillin and tetracycline because they are used in human medicine as well (Cromwell, 2000). Antibiotic resistance is controlled by decreasing the use of unnecessary antibiotics. For example, the use of antibiotics in the livestock and poultry industries is completely banned in the European Union (EU) (OMAFRA, 2005). 
  
  
Since antibiotics have been introduced as growth promoters, there have been concerns about antimicrobial resistance. Frequent use of antibiotics leads to increasing resistance in enteric bacteria that can infect people or transfer their resistance to other pathogenic bacteria (OMAFRA, 2005). When infected by multi-drug resistant bacteria, treatment options are limited, recovery is slow, and treatment is more costly (WHO, 2012). The concerns especially involve resistance against penicillin and tetracycline because they are used in human medicine as well (Cromwell, 2000). Antibiotic resistance is controlled by decreasing the use of unnecessary antibiotics. For example, the use of antibiotics in the livestock and poultry industries is completely banned in the European Union (EU) (OMAFRA, 2005). 
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[[Image:Anti route.gif|thumb|300px|left|[http://momentscount.com/wp-content/uploads/2012/04/antibiotics-for-agriculture.gif Route of Antibiotic from Farm Animals to Humans.]]]
  
 
However, there has been no concrete evidence that shows that use of antibiotics in animal food production poses a threat to human health, and studies are still under way to find the direct linkage (OMAFRA, 2005). The process involving the transfer of antibiotic resistance plasmid between animal and human bacteria is not well known yet (Cromwell, 2002). Also, there is a study which shows that the amount of antibiotic resistance transfer from resistant E.coli to E.coli in the GI tract is small, and animal strains are poor at colonizing the human intestinal tract (Smith, 1969).  The question whether the use of antibiotics in animals presents a potential threat to human health will continue to be controversial.
 
However, there has been no concrete evidence that shows that use of antibiotics in animal food production poses a threat to human health, and studies are still under way to find the direct linkage (OMAFRA, 2005). The process involving the transfer of antibiotic resistance plasmid between animal and human bacteria is not well known yet (Cromwell, 2002). Also, there is a study which shows that the amount of antibiotic resistance transfer from resistant E.coli to E.coli in the GI tract is small, and animal strains are poor at colonizing the human intestinal tract (Smith, 1969).  The question whether the use of antibiotics in animals presents a potential threat to human health will continue to be controversial.
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==Current Research==
 
1. <b>A study of the microbial community composition and functional genes in oil contaminated soil </b>
 
  
In order to compare microbial functional diversity in different oil contaminated soils, and to find the relationship between the contamination and environmental factors, Liang et al. analyses soil samples from 5 different oil filed and used GeoChip to evaluate the microbial functional genes. Results showed that the samples were clustered by geographic locations and the contaminant degradations genes presented similar patterns under oil contaminant stress. Canonical analysis results also indicated that the local environmental variables significantly affect the microbial functional patterns (Liang et al. 2011).
 
  
2. <b>A case study of the environmental condition after Exxon Valdez oil spill</b>
 
  
In order to evaluate the long-term environmental effect of Exxon Valdez oil spill in 1989, a series of measurements of the background concentration of nutrients, dissolved oxygen (DO), and salinity were obtained from a contaminated beach. Results showed that both nutrients and DO are limiting factors for biodegradation. Also, the lowest nitrate and DO values were found in the oiled pits, implying that the microbial oil degradation was probably under anoxic conditions associated with denitrification (Boufadel et al. 2010).
 
  
3. <b>The application of bioautmentation</b>
 
  
The feasibility of a bioaugmentation strategy based on use of microbial formula tailored with selected native strains to remediate diesel contaminated site was assessed. The biodegradation process of diesel oil was assessed by monitoring the DO composition, CO<sub>2</sub> evolution rate, microbial load and composition of the community by T-RFLP, physiological profile in Biolog® ECOplates and ecotoxicity. The mixture of microbes that combines 10 bacterial strains selected for resistance to heavy metals was found to efficiently facilated and speed up the bioremediation of diesel hydrocarbons and heavey metals (Alisi et al. 2009)
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==References==
 
==References==

Revision as of 18:31, 12 December 2012

This student page has not been curated.

Introduction

The use of antibiotics has become common in the livestock production around the world. The growth-promotic effects of antibiotics are undisputed, but the collateral and long-term effect are a cause for a heated debate and banning in the European Union in 2005(OMAFRA, 2005.) Antibiotics increase the efficiency of animal growth by inhibiting the growth of microbes in the gastrointestinal tract which triggers immune responses in the host (Gaskins et al., 2002). They have been shown to improve the health of animals raised in close quarters in conventional operations and also reduce microbes on the meat that cause foodborne illnesses (OMAFRA, 2005). However, there is much concern regarding the development of antibiotic resistance associated with the use of drugs. It is important to study the microbial system within the host organism to carry out further studies related to the controversy.


Host Microbial Community

All livestock harbor a intestinal microbes in a dense and highly diverse community, which are engaged in complex interactions with one another. Despite the diversity, specific animals have innate microbial communities. For example, in swine, major groups include Bacteroides, Peptostreptococcus, Bifidobacterium, Selenomonas, Clostridium, Butyrivibrio, and Escherichia (Moore et al., 1987). Most of the microbes are found in the large intestine because of slow digesta turnover.  A low number of microbes occupy the small intestine because of low pH and the rapid digesta flow which results in bacterial washout (Gaskins, 2000). Gut flora benefits the host in a variety of ways including digestion of unutilized energy substrates, stimulating cell growth, repressing the growth of harmful microorganisms, training the immune system to respond to pathogens, and defending against some diseases (Guarner et al.,2003). The gut flora and the host form an important mutualistic relationship.


Immunological Interactions

The non-pathogenic microbes benefit their host by stimulating the development of immune responses. The host organism develops defensive responses such as the constant mucus production and high cell turnover of the GI tract (Gaskins et al., 2002). The immune responses result in bacterial washout, controlling the growth rate of the enteric bacteria (Gaskins et al., 2002). The washout leads to the prevention of  the pathogen growth, defending against diseases.  Also, indigenous bacteria are proposed to prevent the colonization of nonindigenous bacteria via competition for nutrients and mucosal attachment sites, or alteration of the growth environment by producing antimicrobial compounds and modified bile acids (Rolfe, 1997). Studies with germfree animals show that the absence of indigenous bacteria leads to an underdeveloped immune system and less effective response to pathogens (Gaskins, 2000). Thus, the normal intestinal microbes provide the host with important defense by outcompeting pathogenic bacteria and preventing enteric diseases (Nisbet, 1998). 


Immunity vs. Growth efficiency

However, those innate immune responses are offered at the expense of the growth efficiency (Gaskins et al., 2002). Building the defense against the microbial community in the GI tract requires disproportionate amounts of energy and resources. For example, in swine, although the GI tissues only represent 5% of the total body weight, they receive 15 to 35% of the whole body oxygen consumption and protein turnover because of high metabolic rate (Gaskins, 2000). Germfree organisms do not have to develop such immune responses, and instead, they can make effective use of their energy by investing it in weight growth.





Efficacy and Mechanism of Antibiotics

Figure 1. Efficacy of antibiotics as Growth promoters for pigs at different growth stages. The pigs in the starting phase is between 7-25kg, the growing phase is between 17-49kg, and growing finishing phase is between 24-89kg. It summarizes the data from Table 18.3 (Cromwell, 2000), acquired from 1194 experiments performed in the US from 1950 to 1985.

Numerous researches have shown that antibiotics increase the rate and efficiency of growth in animals. Figure 1 shows that antibiotics are effective in pigs of all growth stages, but they are the most effective when the pigs are young and weanling.  The growth rate of pigs in starting phase (7-25kg) improved by an average of 16.4% and reduced the amount of feed required by 6.9%. However, the experiments are controlled and performed at clean and disease-free research facilities. Thus, the antibiotics are predicted to be more beneficial when used at the farm, where it is less clean, and thus, easier to catch diseases. (Cromwell, 2000). The exact mechanisms by which antibiotics favor growth are not known; however, researches propose that they possibly promote growth by depressing  the growth of microbes that are toxic or steal nutrients from the host, leading to the increased nutrition utilization and reduced energy investment in maintaining immune responses in the GI tract (Gaskins et al., 2002).     








Debate regarding Resistance

Since antibiotics have been introduced as growth promoters, there have been concerns about antimicrobial resistance. Frequent use of antibiotics leads to increasing resistance in enteric bacteria that can infect people or transfer their resistance to other pathogenic bacteria (OMAFRA, 2005). When infected by multi-drug resistant bacteria, treatment options are limited, recovery is slow, and treatment is more costly (WHO, 2012). The concerns especially involve resistance against penicillin and tetracycline because they are used in human medicine as well (Cromwell, 2000). Antibiotic resistance is controlled by decreasing the use of unnecessary antibiotics. For example, the use of antibiotics in the livestock and poultry industries is completely banned in the European Union (EU) (OMAFRA, 2005). 


However, there has been no concrete evidence that shows that use of antibiotics in animal food production poses a threat to human health, and studies are still under way to find the direct linkage (OMAFRA, 2005). The process involving the transfer of antibiotic resistance plasmid between animal and human bacteria is not well known yet (Cromwell, 2002). Also, there is a study which shows that the amount of antibiotic resistance transfer from resistant E.coli to E.coli in the GI tract is small, and animal strains are poor at colonizing the human intestinal tract (Smith, 1969).  The question whether the use of antibiotics in animals presents a potential threat to human health will continue to be controversial.













References

1. Alisi C, Musella R, Tasso F, Ubaldi C, Manzo S, Cremisini C, Sprocati AR (2009) Bioremediation of diesel oil in a co-contaminated soil by bioaugmentation with a microbial formula tailored with native strains selected for heavy metals resistance. Sci Total Environ 407:3024-3032

2. Atlas R (1981) Microbial-degradation of petroleum-hydrocarbons-an environmental perspective. Microbiol Rev 45:180-209

3. Atlas R, Horowitz A, Busdosh M (1978) Prudhoe crude-oil in Arctic Marine ice, water, and sediment ecosystems-degradation and interactions with microbial and benthic communities. Journal of the Fisheries research board of Canada 35:585-590

4. Atlas R (1991) Microbial hydrocarbon degradation-bioremediation of oil spills. Journal of Chemical Technology & Biotechnology 52:149-156

5. Boufadel M, Sharifi Y, Van Aken B, Wrenn B, Lee K (2010) Nutrient and Oxygen Concentrations within the Sediments of an Alaskan Beach Polluted with the Exxon Valdez Oil Spill. Environmental science technology 44:7418-7424

6. Chen YP, Lopez-de-Victoria G, Lovell CR (1993) Utilization of aromatic compounds as carbon and energy sources during growth and N2-fixation by free-living nitrogen fixing bacteria. Arch Microbiol 159:207

7. de Brito I, Swannell R, Head I, Roling W (2004) Response of archaeal communities in beach sediments to spilled oil and bioremediation. Appl Environ Microbiol 70:2614

8. Drozdowicz A, Leite S, Rosado A, Prantera M (2002) Degradation of gasoline aromatic hydrocarbons by two N-2-fixing soil bacteria. Biotechnol Lett 24:85

9. Eckford R (2002) Free-living heterotrophic nitrogen-fixing bacteria isolated from fuel-contaminated Antarctic soils. Appl Environ Microbiol 68:5181

10. Gibson D, Vanbaalen C, Cerniglia C (1980) Oxidation of naphthalene by cyanobacteria and microalgae. J Gen Microbiol 116:495

11. Hamnrick G, Delaune R, Patrick W (1980) Effect of estuarine sediment pH and oxidation-reduction potential on microbial hydrocarbon degradation. Appl Environ Microbiol 40:365-369

12. Ibrahim M, Gamila H (2004) Algal bioassay for evaluating the role of algae in bioremediation of crude oil: I-isolated strains. Bull Environ Contam Toxicol 73:883

13. Liang Y, Van Nostrand JD, Deng Y, He Z, Wu L, Zhang X, Li G, Zhou J (2011) Functional gene diversity of soil microbial communities from five oil-contaminated fields in China. ISME Journal 5:403-413

14. Mulkinsphillips G, Stewart J (1974) Effect of environmental parameters on bacterial-degradation of Bunker-C oil, and hydrocarbons. Appl Microbiol 28:915-922

15. Musat F (2006) Study of nitrogen fixation in microbial communities of oil-contaminated marine sediment microcosms. Environ Microbiol 8:1834

16. Naidu R, Juhasz A (2000) Bioremediation of high molecular weight polycyclic aromatic hydrocarbons: a review of the microbial degradation of benzo-a-pyrene. International biodeterioration biodegradation 45:57

17. Ollivier B, Patel B, Magot M (2000) Microbiology of petroleum reservoirs. Antonie Van Leeuwenhoek 77:103

18. Patin S (2004) Crude Oil Spills, Environmental Impact of. In: Cutler J. Cleveland (ed) Encyclopedia of Energy. Elsevier, New York, pp 737-748

19. Prince R (1993) Petroleum spill bioremediation in marine environments. Crit Rev Microbiol 19:217-242

20. Santos VD, Bartels D, Bekel T, Brecht M, Buhrmester J, Schneiker S (2006) Genome sequence of the ubiquitous hydrocarbon-degrading marine bacterium Alcanivorax borkumensis. Nat Biotechnol 24:997

21. Shin W, Pardue J (2001) Oxygen dynamics in crude oil contaminated salt marshes: I. Aerobic respiration model. Environ Technol 22:845-854

22. Teralmoto M, Suzuki M, Okazaki F, Hatmanti A, Harayama S (2009) Oceanobacter-related bacteria are important for the degradation of petroleum aliphatic hydrocarbons in the tropical marine environment. Microbiology 155:3362-3370

23. Tyagi M, da Fonseca M, de Carvalho C (2011) Bioaugmentation and biostimulation strategies to improve the effectiveness of bioremediation processes. Biodegradation 22:231-241

24. Vila J, Nieto J, Mertens J, Springael D, Grifoll M (2010) Microbial community structure of a heavy fuel oil-degrading marine consortium: linking microbial dynamics with polycyclic aromatic hydrocarbon utilization. FEMS Microbiol Ecol 73:362

25. Xu R, Obbard J (2004) Biodegradation of polycyclic aromatic hydrocarbons in oil-contaminated beach sediments treated with nutrient amendments. J Environ Qual 33:861-867



Edited by Yan Zhou, a student of Angela Kent at the University of Illinois at Urbana-Champaign.