Antimicrobial Resistance Pattern against E. coli and Salmonella in Layer Poultry

Mohammad Mahmudul Hassan^1*, Khaled Bin Amin1, Muhammad Ahaduzzaman², Mahabub Alam³, Muhammad Shohel Al Faruk¹, Inkeyas Uddin⁴

*Corresponding author:miladhasan@yahoo.com

ARTICLE CITATION: Hassan MM, Amin KB, Ahaduzzaman M, Alam M, Faruk MSA, Uddin I (2014). Antimicrobial resistance pattern against E. coli and Salmonella in layer poultry. Res. j. vet. pract. 2 (2): 30 – 35.
Received: 2013–12–24, Revised: 2014–01–18, Accepted: 2014–01–20
The electronic version of this article is the complete one and can be found online at ( http://dx.doi.org/10.14737/journal.rjvp/2014/2.2.22.27 ) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

ABSTRACT

E. coli and Salmonella are leading cause of illness in layer farms. The emergence of antimicrobial–resistant E. coli and Salmonella are associated with the indiscriminate use of antibiotics in poultry farming. The present study aimed at determination of antimicrobial resistance pattern of E. coli and Salmonella strains isolated from commercial layer from different layer farms under Chittagong district of Bangladesh, during the period of September to December, 2012. Isolation and identification of E. coli and Salmonella were done by using standard methods. A total of 13 isolates of E. coli and 8 isolates of Salmonella were studied. Isolated E. coli and Salmonella were tested for resistance to 10 different antimicrobial agents, using disc diffusion method. The E. coli were found 100% resistant to Tetracycline, Ciprofloxacin, Enrofloxacin and Pefloxacin followed by Amoxicillin (84.62%), Kanamycin (69.24%), Colistin (63.75%), Doxycycline (53.75%) and Neomycin (23.08%). Conversely, E. coli isolates show high sensitivity to Gentamicin (100%) and Neomycin (76.92%). Among the Salmonella isolates, 100% were found resistant to Amoxicillin and Tetracycline followed by Enrofloxacin (87.5%), Ciprofloxacin (87.5%), Pefloxacin (87.5%), Doxycycline (50%), Colistin (50%) and Kanamycin (50%). Salmonella isolates showed high sensitivity (100%) to Gentamicin and Neomycin. All of the isolates showed multiple antimicrobial resistances. Rational use of antibiotics need to be adopt in commercial poultry farming system of Bangladesh to prevent the emergence of drug resistance E. coli and Salmonella. Moreover, Gentamicin might be the drug of choice for both avian colibacillosis and salmonellosis.

INTRODUCTION

Poultry farming is recognized profitable business in Bangladesh and getting popularity as employment opportunities. Over the 80% of the country’s people live in the rural sector and highly dependent on agricultural system (BBS, 2000). This reflection has got in the recent years due to the raising of commercial poultry farms to meet the demand of poultry meat and egg resulted from the establishment poultry belt in Dhaka, Chittagong, Gazipur, and Narshingdi district. The poultry farming has dramatically increased in recent years in Bangladesh but disease is one of the main constrains for their development.

Avian Colibacillosis and Salmonellosis has been found to be major infectious diseases of all ages of birds. E. coli are one of the common microbial floras of gastrointestinal tract of poultry and human being (Jawetz et al., 1984). Although most isolates of E. coli are nonpathogenic but they are considered as indicator of fecal contamination in food and about 10 to 15% of intestinal coliforms are opportunistic and pathogenic serotypes (Barnes et al., 1997) and cause a variety of lesions in immune–compromised hosts as well as in poultry. Infection with bacteria genus Salmonella are responsible for a variety of acute and chronic disease in poultry reported in Bangladesh (Bhattacharjee et al., 1996).

Escherichia coli are the primary causative agent of cellulitis, septicemia, and airsacculitis in poultry and Salmonella are the causative agent of pullorum disease, fowl typhoid and fowl paratyphoid (Gomis et al., 1997). Therefore, these are the most significant poultry bacterial pathogen. Antimicrobial resistance is a global problem, and emerging antimicrobial resistance has become a public health fact worldwide (Kaye et al., 2004). A variety of foods and environmental sources harbor bacteria that are resistant to one or more antimicrobial drugs used in human or veterinary medicine and in food–animal production (Schroeder et al., 2004). Though many bacteria recovered from poultry or poultry–related samples have been monitored, few published studies have reported on antimicrobial resistance in bacteria, particularly Salmonella and E. coli (Antunes et al., 2003).

About 65 years ago, from the time when antibiotics became widely available, they have been acclaimed as miracle drugs talented to destroy disease–causing bacteria. But with each transitory decade, bacteria that resist not only single, but multiple, antibiotics making some diseases particularly troublesome to control have become progressively more prevalent. Antimicrobial resistance take place when bacteria adjust or adapt in a way that permits them to stay alive in the presence of antibiotics designed to kill them, bacteria evolve resistance to these drugs, typically by acquiring chromosomal mutations and multidrug resistant plasmid (Finch et al., 2003; Nichol et al., 2003).

Antibiotics are extensively used as growth promoters in poultry production or to control infectious disease and abuse are considered to be the most vital selecting force to antimicrobial resistance of bacteria (Moreno et al., 2000). Due to enormous use of antibiotics in the field of veterinary medicine, an increased number of resistant bacterial strains were developed in recent years. In different parts of the world, multi drug resistant strains of E. coli are ubiquitous in both human and animal isolates (Amara et al., 1995) and multiple drug resistant, nonpathogenic E. coli found in the intestine are probably an important reservoir of resistance genes (Osterblad et al., 2000) and momentarily drug–resistant E. coli of animal origin may colonize the human intestine (Marshall et al., 1990).

Acquired multi drug resistance to antimicrobial agents creates an extensive trouble in case of the management of intra and extra intestinal infections caused by E. coli, which is a major source of illness, death, and increased healthcare costs (Gupta et al., 2001). There only little scattered work on antimicrobial sensitivity testing was performed in Chittagong region. Therefore, the present study was designed to detect the antimicrobials that are no longer active against avian colibacillosis and salmonellosis in Chittagong, Bangladesh. The present study was targeted to isolate the E. coli and Salmonella strain from poultry sample and determine the antibiotic resistance patterns against E. coli and Salmonella.

MATERIALS AND METHODS

Study Area and Duration
The study was conducted on layer poultry at Chittagong District, which is one of the most concentrated poultry areas of Bangladesh, during the period of September to December, 2012. A total of 30 dead birds from different layer farms of Chittagong were subjected to postmortem during the study period at PRTC laboratory, Chittagong.

Questionnaire Design and Data collection
Diagnosis of disease was made on the basis of post mortem examination and standard microbiological examination, using standard methods for bacterial isolation and identification described by OIE (2000).

Isolation and Identification
The liver and spleen sample was collected aseptically and used for microbiological test. Isolation and identification of bacteria were done by using the method described by Collins and Lyne (1976). Culturing on various selective media, examination of colony characteristics, observation of the organisms under microscope and various biochemical tests were done to isolation and identification of E. coli and Salmonella organisms.

Culturing on Agar Media
For Suspected cases of Colibacillosis, after collections of samples were inoculated into peptone broth for primary enrichment, then incubate the broth 24 hours at 370C and from broth streaked on MacConkey Agar and Eosin Methylene Blue (EMB) agar plate. The plate was incubated at 370C examined after 24 hours for growth and change in the color of the medium. After overnight incubation the bacterial growth was observed as large pink colonies at MacConkey and mid night blue metallic sheen colonies at EMB agar. Both lactose fermenting and non lactose fermenting colonies were found. Salmonella pullorum and Salmonella gallinarum both the organisms will grow on differential plating media such as MacConkey and SS Agar. It has been shown that Salmonella pullorum occasionally fails to grow on certain selective media such as Briliant Green agar or Salmonella–Shigella agar but grows satisfactorily on Bismuth Sulfite and McConkey agars (Carlson et al., 1974). Confirmation of Salmonella was done by culturing on selective media such as Xylose lysine deoxycholate (XLD) Agar and Brilliant Green Agar (BGA) Agar and observation of colony characteristics such as black centered pale pink colony and red–pink–white opaque colored colonies surrounded by brilliant red zones, respectively.

Biochemical Tests
For confirmation of E. coli and Salmonella various biochemical tests were done for confirmation of the isolates as described by Cruickshank et al. (1995).

Antibiotic Sensitivity
The antibiotic sensitivity of the isolated strain at different concentration was performed by using standard paper disc diffusion method described by NCCLS, (2009). The following antibiotics and disc potencies were used: GEN: Gentamicin (10μg), DO: Doxycycline (30μg), CIP: Ciprofloxacin (5μg), ENR: Enrofloxacin (5μg), AMC: Amoxicillin (10μg), N: Norfloxacin (10µg), CL: Colistin (10μg), TE: Tetracycline (30µg), Pf: Pefloxacin (10µg), K: Kanamycin (30µg) from HIMEDIA Ltd (Mombai, India).

Data Analysis
Data obtained was imported to the Microsoft Office Excel–2007 and transferred to the software STATA/IC–11 for analysis. Descriptive statistics was done by using the STATA/IC–11 software and expressed as percentages of different variables like resistance, intermediate and sensitivity pattern of antimicrobials.

RESULTS

A total of 13 individual colonies of E. coli and 8 individual colonies of Salmonella were isolated from poultry liver samples through different test. Table 1 presented antimicrobial resistant pattern against E. coli. Among the 13 isolates, all were sensitive to Gentamicin and all were resistant to Ciprofloxacin, Enrofloxacin, Pefloxacin and Tetracycline. In case of Colistin and Doxycycline 7 isolates were resistant and 6 were sensitive. Antimicrobial resistant pattern in Norfloxacin showed 3 isolates were resistant and 10 were sensitive. Seven isolates were resistant, 2 were sensitive and 4 were intermediate sensitive to kanamycin. In case of Amoxicillin 11 isolates were resistant, 1 was sensitive and 1 was intermediate sensitive.

Antibiotic susceptibility pattern and prevalence of antimicrobial resistance of E. coli isolates from samples of layer farms has been outlined in table 1 and table 2, respectively. Resistance spectrum of E. coli for 10 antibiotics tested in descending order were respectively, Ciprofloxacin (100%), Enrofloxacin (100%), Pefloxacin (100%), Tetracycline (100%), Amoxicillin (84.62%), Kanamycin (69.24%), Colistin (53.75%), Doxycycline (53.75%), Neomycin (23.08%) and Gentamicin (0%). In this study is revealed that no isolate were found sensitive to Ciprofloxacin, Enrofloxacin, Pefloxacin and Tetracycline. On the other hand no isolate were found resistant to Gentamicin. Intermediate sensitivity was only found to two antibiotics (Amoxicillin and Kanamycin). All the isolates of E. coli showed multiple drug resistance (up to against 9 antibiotics out of 10 used in the test).

Antimicrobial resistant pattern of Salmonella isolates were shown in table 3. Among the 8 isolates, all were sensitive to Gentamicin and Neomycin and all were resistant to Tetracycline and Amoxicillin. In case of Ciprofloxacin, Enrofloxacin and Pefloxacin 7 isolates were resistant and 1 isolate was sensitive. Antimicrobial resistant pattern in Kanamycin showed 4 isolates were resistant, 3 were sensitive and 1 was intermediate sensitive. In case of Colistin 4 isolates were resistant and 4 isolates were sensitive. Four isolates were resistant, 2 were sensitive and 2 were intermediate sensitive to Doxycycline.

Antibiotic susceptibility pattern and prevalence of antimicrobial resistance of Salmonella isolates from samples of layer farms has been outlined in Table 3 and Table 4, respectively. Resistance spectrum of Salmonella for 10 antibiotics tested in descending order were respectively Tetracycline (100%), Amoxicillin (100%), Ciprofloxacin (87.5%), Enrofloxacin (87.5%), Pefloxacin (87.5%), Kanamycin (50%), Colistin (50%), Doxycycline (50%), Neomycin (0%) and Gentamicin (0%). In this study it was revealed that no isolate were found sensitive to Tetracycline and Amoxicillin. On the other hand no isolate were found resistant to Neomycin and Gentamicin. Intermediate sensitivity was only found to two antibiotics (Kanamycin and Doxycycline). All the isolates of Salmonella showed multiple drug resistance (up to against 8 antibiotics out of 10 used in the test).

DISCUSSION

Organisms were isolated based on colony characteristics and biochemical tests. The present study revealed that all of the isolates of E. coli from commercial chicken were resistance to multiple antibiotics (> =4) which coincided with the findings of Zhao et al. (2005), Guerra et al. (2003) and Islam et al. (2008). Multiple antimicrobial resistance might happened due to indiscriminate use of antibiotics, chemotherapeutics and or disperse of drug resistant microorganism in the environment (Van de Boogard and Stobberingh, 2000). All E. coli isolates were found resistant (100%) to Ciprofloxacin which is higher than the earlier report (Saenz, et al., 2001; Kang et al., 2005). In present study there were found no isolate of E. coli was sensitive to Enrofloxacin, this finding agree with Cooke et al. (2002) who reported Enrofloxacin resistance in E. coli isolated from dogs with urinary tract infections. Resistances that observed against Tetracycline is more or less similar with Islam et al. (2008), they showed 96.6% resistance to Tetracycline of E. coli isolated from poultry farm at Chittagong District in Bangladesh. Schroeder et al. (2001) stated comparatively lower resistance (71%) to Tetracycline of E. coli isolated from turkey. In present study it was revealed higher value of resistance (84.62%) of E. coli to Amoxicillin than reported by Schroeder et al. 2001 (28%) where E. coli are isolated from turkey. Resistance that was observed to Kanamycin (69.24%) is more or less agree with Akond et al. (2009) in a study on chicken collected from different poultry markets of Dhaka, Bangladesh (76%). It was revealed that 53.75% sensitive isolates of E. coli to Colistin and this finding have similarity with Catchpole et al. (1997) who observed Colistin is active against most strains of E. coli in a study on reassessment of the in–vitro activity of Colistin sulphate sodium. The resistance of E. coli against Doxycycline was 53.75% isolates which agree with Raum et al. (2008) who stated 29–58% resistance of E. coli to Doxycycline isolated from stool sample in a study in Germany. E. coli showed resistance against Neomycin (23.08%), Stephan and Schumacher (2001) observed O100: H–STEC strains isolated from healthy slaughter pigs were resistant to neomycin. In this study it was observed that all the isolated E. coli were sensitive to gentamicin and this finding is in agreement with Alam et al. (2006) who reported that most of the environmental strains were (97%) sensitive to Gentamicin. However, Schroeder et al. (2001) and Saenz et al. (2001) showed 24% resistance in turkey isolates and 38% resistance in broiler isolates of E. coli to Gentamicin.

eSalmonella were found resistant to multiple antibiotics (≥4) which is coincided with the findings of Weill et al. (2006) who reported 67% of Salmonella enterica serotype Typhimurium isolates of humans in France. There were no isolate of Salmonella found sensitive to Tetracycline which corroborate with the findings of Musgrove et al. (2006) who stated 63.4% and Zhao et al. (2008) who reported 39.9%, respectively. Resistance of Salmonella to Amoxicillin that revealed in this study (100%) is higher than reported by Siemon et al. (2007) isolated from conventionally reared poultry (62%) but similar finding was observed by Ahaduzzaman et al. (2014) in environmental effluents. Salmonella showed resistance against Ciprofloxacin (87.5%), however, Musgrove et al. (2006) found no resistance of Salmonella against Ciprofloxacin in isolates obtained from commercial chicken and Gay et al. (2006) also showed 0.1% resistant isolates from human. In this study 87.5% Salmonella isolates showed resistance against Enrofloxacin and this finding is higher than the findings of Antunes et al. (2003) who reported 50%. Resistance of Salmonella to Pefloxacin was almost 88% in the current study which does not correlate with the findings of Ajayi et al. (2011) who found 20% resistant Salmonella in cattle fecal isolates. Nearly 50% isolates of Salmonella were resistant to Kanamycin, Colistin and Doxycycline which are supported by the findings of Musgrove et al. (2006) and Murugkar et al. (2005). In this study it was observed that all the isolated Salmonella were sensitive to Neomycin and Gentamicin. However, Carmrainana et al. (2004) reported 53.4% resistant isolates of Salmonella to Neomycin in a findings where organisms were isolated from a poultry slaughterhouse in Spain. Our findings demonstrate that multidrug–resistant strains of E. coli and Salmonella isolates were frequently present in layer poultry farm of Chittagong District. The high prevalence of multidrug–resistant E. coli and Salmonella in layer poultry reflects a reservoir of resistance in birds that can be transmitted to humans. If these resistance organisms to antimicrobial persist, there will be a great problem of antimicrobial choice in near future. Proper efforts should be needed to reduce the prevalence of resistant E. coli and Salmonella in layer farms, including the adoption of guidelines for the prudent use of antimicrobial agents in animals used for food.

ACKNOWLEDGEMENTS

Authors are grateful to the Poultry Research and Training Centre (PRTC), Chittagong Veterinary and Animal Sciences University, Bangladesh for giving laboratory support to the present research project.

COMPETING INTERESTS

Authors declare that they have no competing interests.

REFERENCES

Ahaduzzaman M, Hassan MM, Alam M, Islam SKMA and Uddin I (2014). Antimicrobial resistance pattern against Staphylococcus aureus in environmental effluents. Res. J. Vet. Pract. 2(1): 13–16
http://dx.doi.org/10.14737/journal.rjvp/2014/2.1.13.16

Ajayi A, Olowe OA and Famurewa O (2011). Plasmid Analysis of Fluoroquinolone Resistant Commensal E. coli from Faecal Samples of Apparently Healthy Cattle in Ado–Ekiti, Ekiti–State. J. Anim. Vet. Adv. 10(2): 180–184.
http://dx.doi.org/10.3923/javaa.2011.180.184

Akond MA, Alam S, Hassan SMR and Shirin M (2009). Antibiotic Resistance of Escherichia Coli Isolated From Poultry and Poultry Environment of Bangladesh. Int. J. Food. Safety. 11: 19–23.

Alam M, Nur–A–Hasan, Ahasan S, Pazhani G P, Tamura K, Ramamurthy T, Gomes D J, Rahman S R, Islam A, Akhtar F, Shinoda S, Watanabe H, Faruque SM and Nair B (2006). Phenotypic and molecular characteristics of Escherichia coli isolated from Aquatic Environment of Bangladesh. Microbiol. Immunol. 50 (5): 359–370.
http://dx.doi.org/10.1111/j.1348-0421.2006.tb03802.x
PMid:16714843

Amara A, Ziani Z and Bouzoubaa K (1995). Antibiotic resistance of Escherichia coli strains isolated in Morocco from chickens with colibacillosis. Vet. Microbiol. 43: 325–330.
http://dx.doi.org/10.1016/0378-1135(94)00101-2

Antunes P, Reu C, Sousa JC, Peixe L and Pestana N (2003). Incidence of Salmonella from poultry products and their susceptibility to antimicrobial agents. Int. J. Food. Microbiol. 82:97–103.
http://dx.doi.org/10.1016/S0168-1605(02)00251-9

Bangladesh Bureau of Statistics (BBS) (2000). Agriculture sample Survey of Bangladesh–2005. Planning Division, Ministry of Planning, and Government of peoples Republic of Bangladesh.

Barnes H J and Gross WB (1997). Colibacillosis. In: Diseases of poultry, 10th ed. Calnek, B.W.B. Barnes, H.J., Beard, C.W., McDougald, L.R. and Saif, Y.M. Iowa State University Press, Ames, IA. 131–141.

Bhattacharjee PS, Kundu RL, Biswas RK, Mazumder JU, Hossain E and Miah AH (1996). A retrospective analysis of chicken diseases diagnosed at the Central Disease Investigation Laboratory, Dhaka. Bangladesh Vet. J. 30 (3 – 4): 105 – 113.

Carlson HC, Itakura C and Lang GN (1974). Experimental transmission of haemorrhagic enteritis of turkeys. Avian Pathol. (3): 279–292.
PMid:18777283

Carraminana JJ, Rota C, Agustin I and Herrera A (2004). High prevalence of multiple resistance to antibiotics in Salmonella serovars isolated from a poultry slaughterhouse in Spain. Vet. Microbiol. 104(1–2): 133–139.
http://dx.doi.org/10.1016/j.vetmic.2004.08.010
PMid:15530748

Catchpole CR, Andrews JM, Brenwald N and Wise R (1997). A reassessment of the in–vitro activity of colistin sulphomethate sodium. J. Antimicrob. Chemother. 39: 255–260.
http://dx.doi.org/10.1093/jac/39.2.255
PMid:9069549

Colins CH and Lyne PM (1976). In Microbiological Methods. 4th ed. Laboratory Techniques Series. Buttenworths, London.

Cooke CL, Randall BS, Singer S, Jang SS and Hirsh DC (2002). Enrofloxacin resistance in Escherichia coli isolated from dogs with urinary tract infections. J. Am. Vet. Med. Assoc. 220(2): 190–192.
http://dx.doi.org/10.2460/javma.2002.220.190
PMid:12126128

Cruickshank R, Duguid JH, Marimion BP and Swain RHA (1995). In Medical Microbiology, 12th ed. Vol–II, Churchill Livingstone, London.

Finch RG, Greenwood D, Norrby SR and Whitley RJ (2003). Antibiotic and chemotherapy Anti– infective agents and their use in therapy. 8th ed. Edinburgh: Churchill Livingstone. Page 964.

Gay K, Robicsek A, Strahilevitz J, Park CH, Jacoby G, Barrett TJ, Medalla F, Chiller TM and Hooper DC (2006). Plasmid–Mediated Quinolone Resistance in Non–Typhi Serotypes of Salmonella enterica. Clin. Infect. Dis. 43:297–304.
http://dx.doi.org/10.1086/505397
PMid:16804843

Gomis SM, Goodhope R, Kumor L, Caddy N, Riddell C, Petter AA and Allan JJ (1997). Experimental reproduction of Escherichia coli, cellulitis and septicemia in broiler chickens. Avian Dis. 41:234–240.
http://dx.doi.org/10.2307/1592464
PMid:9087341

Guerra B, Junker E, Schroeter A, Malorny B, Lehmann S and Helmuth R (2003). Phenotypic and genotypic characterization of antimicrobial resistance in German Escherichia coli isolates from cattle, swine and poultry. J.Antimicrob. Chemother. 52(3):489–92.
http://dx.doi.org/10.1093/jac/dkg362
PMid:12888584

Gupta K, Hooton TM and Stamm WE (2001). Increasing antimicrobial resistance and the management of uncomplicated communityacquired urinary tract infections. Ann. Intern. Med. 135: 41–50.
http://dx.doi.org/10.7326/0003-4819-135-1-200107030-00012
PMid:11434731

Islam MJ, Sultana S, Das KK, Sharmin N and Hasan MN (2008). Isolation of plasmid–mediated multidrug resistant Escherichia coli from poultry. Int. J. Sustain. crop production. 3(5):46–50.

Jawetz E, Melnick J and Adelberg EA (1984). Review of Medical Microbiology. 16th ed. Los Altos, California: Long Medical Publication. 122–144.

Kang HY, Jeong YS, Oh JY, Tae SH, Choi CH, Moon DC, Lee WK, Lee WC, Seol SY, Cho DT and Lee JC (2005). Characterization of antimicrobial resistance and class 1integrons found in Escherichia coli isolates from humans and animals in Korea. J. Antimicrob. Chemother. 55: 639–644.
http://dx.doi.org/10.1093/jac/dki076
PMid:15761064

Kaye KS, Engemann JJ, Fraimow HS and Abrutyn E (2004). Pathogens resistant to antimicrobial agents: Epidemiology, molecular mechanisms, and clinical management. Infect. Dis. Clin. North Am. 18:467–511.
http://dx.doi.org/10.1016/j.idc.2004.04.003
PMid:15308273

Marshall BD, Petrowski and Levy SB (1990). Inter– and intraspecies spread of Escherichia coli in a farm environmental in the absence of antibiotic usage. PNAS. 87: 6609–6613.
http://dx.doi.org/10.1073/pnas.87.17.6609
PMid:2204058 PMCid:PMC54586

Moreno MA, Dominguez L, Teshoger T, Herrero IA and Porrero ME (2000). Antibiotic resistances monitoring: The Spanish Programme. Int. J.Antimicro. Ag.14: 285–290.
http://dx.doi.org/10.1016/S0924-8579(00)00138-2

Murugkar HV, Rahman H, Kumar A and Bhattacharyya D (2005). Isolation, phage typing and antibiogram of Salmonella from man and animals in northeastern India. Indian J. Med. Res. 122: 237–242.
PMid:16251781

Musgrove MT, Jones DR, Northcutt JK, Cox NA, Harrison MA, Fedorka–Cray PJ and Ladely SR (2006). Antimicrobial Resistance in Salmonella and Escherichia coli Isolated from Commercial Shell Eggs. Poultry. Sci. 85:1665–1669.
http://dx.doi.org/10.1093/ps/85.9.1665
PMid:16977855

National Committee for Clinical Laboratory (NCCLS) (2009). Performance standards for antimicrobial disk susceptibility tests. Approved standard M2–A6. Wayne.

Nichol K, Zhanel GG and Hoban DJ (2003). Molecular epidemiology of penicillin–resistant and ciprofloxacin–resistant Streptoccocus pneumoniae in Canada. Antimicrob. Ag. Chemother. 47:804–808.
http://dx.doi.org/10.1128/AAC.47.2.804-808.2003
PMid:12543698 PMCid:PMC151757

Office International des Epizooties (OIE) (2000). Manual of standards for diagnostics tests and vaccines.

Osterblad M, Hakanen A, Manninen R, Leistevuo T, Peltonen R, Meurman O, Huovinen P and Kotilainen P (2000). A between–species comparison of antimicrobial resistance in enterobacteria in fecal flora. Antimicrob. Ag. Chemother. 44: 1479–1484.
http://dx.doi.org/10.1128/AAC.44.6.1479-1484.2000
PMid:10817696 PMCid:PMC89900

Raum E, Lietzau S, Baum VH, Marre R and Brenner H (2008). Changes in Escherichia coli resistance patterns during and after antibiotic therapy: a longitudinal study among outpatients in Germany. Clin. Microbiol. Infect. 14(1): 41–48.
http://dx.doi.org/10.1111/j.1469-0691.2007.01841.x
PMid:18005177

Saenz Y, Zarazaga M, Brinas L, Lantero M, Ruiz–Larrea F and Torres C (2001). Antibiotic resistance in Escherichia coli isolates obtained from animals, foods and humans in Spain. Int. J. Antimicrob. Ag. 18(4):353–358.
http://dx.doi.org/10.1016/S0924-8579(01)00422-8

Schroeder CM, White DG and Meng J (2004). Retail meat and poultry as a reservoir of antimicrobial–resistant Escherichia coli. Food. Microbiol. 21:249–255.
http://dx.doi.org/10.1016/S0740-0020(03)00074-1

Schroeder CM, Meng J, Zhao S, DebRoy C, Torcolini J, Zhao C, McDermott PF, Wagner DD, Walker RD and White DG (2001). Antimicrobial Resistance of Escherichia coli O26, O103, O111, O128, and O145 from Animals and Humans. Emerg. Infect. Disease. 8(12):1409–1414.
http://dx.doi.org/10.3201/eid0812.0200770

Siemon CE, Bahnson PB and Gebreyes WA (2007). Comparative Investigation of Prevalence and Antimicrobial Resistance of Salmonella between Pasture and Conventionally Reared Poultry. Avian. Dis. 51(1): 112–117.
http://dx.doi.org/10.1637/0005-2086(2007)051[0112:CIOPAA]2.0.CO;2

Stephan R and Schumacher S (2001). Resistance patterns of non– O157 Shiga toxin producing Escherichia coli (STEC) strains isolated from animals, food and asymptomatic human carriers in Switzerland. Lett. Appl. Microbiol. 32 (2): 114–117.
http://dx.doi.org/10.1046/j.1472-765x.2001.00867.x
PMid:11169054

Van de Boogard AE and Stobberingh EE (2000). Epidemiology of resistance to antibiotics links between animals and humans. Int. J. Antimicrob. Ag. 14: 327–335.
http://dx.doi.org/10.1016/S0924-8579(00)00145-X

Weill F, Guesnier F, Guibert V, Timinouni M, Demartin M, Polomack L and Grimont PAD (2006). Multidrug Resistance in Salmonella enterica Serotype Typhimurium from Humans in France (1993 to 2003). J. Clin. Microbiol. 44 (3): 700–708.
http://dx.doi.org/10.1128/JCM.44.3.700-708.2006
PMid:16517842 PMCid:PMC1393144

Zhao S, Maurer JJ, Hubert S, De Villena JF, McDermott PF, Meng J, Ayers S, English L and White DG (2005). Antimicrobial susceptibility and molecular characterization of avian pathogenic Escherichia coli isolates. Vet. Microbiol. 107 (3–4): 215–24.
http://dx.doi.org/10.1016/j.vetmic.2005.01.021
PMid:15863280

Zhao S, White DG, Friedman SL, Glenn A, Blickenstaff K, Ayers SL, Abbott JW, Hall–Robinson E and McDermott PF (2008). Antimicrobial resistance in Salmonella enterica serovar Heidelberg isolates from retail meats, including poultry, from 2002 to 2006. Appl. Environment. Microbiol. 74(21): 6656–62.
http://dx.doi.org/10.1128/AEM.01249-08
PMid:18757574 PMCid:PMC2576681