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Retail poultry products are known sources of antibiotic-resistant Escherichia coli, a major human health concern. Consumers have a range of choices for poultry, including conventional, organic, kosher, and raised without antibiotics (RWA)-designations that are perceived to indicate differences in quality and safety. However, whether these categories vary in the frequency of contamination with antibiotic-resistant E. coli is unknown. We examined the occurrence of antibiotic-resistant E. coli on raw chicken marketed as conventional, organic, kosher and RWA. From April – June 2012, we purchased 213 samples of raw chicken from 15 locations in the New York City metropolitan area. We screened E. coli isolates from each sample for resistance to 12 common antibiotics. Although the organic and RWA labels restrict the use of antibiotics, the frequency of antibiotic-resistant E. coli tended to be only slightly lower for RWA, and organic chicken was statistically indistinguishable from conventional products that have no restrictions. Kosher chicken had the highest frequency of antibiotic-resistant E. coli, nearly twice that of conventional products, a result that belies the historical roots of kosher as a means to ensure food safety. These results indicate that production methods influence the frequency of antibiotic-resistant E. coli on poultry products available to consumers. Future research to identify the specific practices that cause the high frequency of antibiotic-resistant E. coli in kosher chicken could promote efforts to reduce consumer exposure to this potential pathogen.


Jack M. Millman;  Kara Waits;  Heidi Grande;  Ann R. Marks;  Jane C. Marks;  Lance B. Price;  Bruce A. Hungate

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  • The article reports the frequency of resistance phenotypes in chicken collected at retail level. The title of the article is appropriate.

    The abstract is clearly written although the consequences of the findings are not clearly referred to. The findings are not really surprising as production methods are bound to impact on the level of resistance among bacteria such as E. coli. Also, I think the reference being made to consumers may be misleading as it may imply consumer risk. It would be helpful to provide more details on specific husbandry practices used for kosher chicken as readers may not be familiar with them.

    Regarding the statistical method; I am not clear what the dependent variable for the ANOVA was. It should typically be a numerical not categorical variable, so I assume it was percentage? I understand that analysis was done by brand. So we have a multi-level clustering here (sample-brand-production system). Data should therefore be analysed in this way.

    I assume that resistance was established as a binary variable. Note that it is recommended to move towards more quantitative measurement of resistance. The description of the statistical analysis is too superficial to conclude on validity of results. The number of samples was low.

    It has been demonstrated that the extent and type of antimicrobial usage is hugely variable between farms even within one production type (e.g. among conventional producers). It is therefore recommended to use data that allow for linking of resistance status in the product to the true exposure of the animal, i.e. to link retail back to pre-harvest. I know that this is difficult, but else evidence will remain weak.

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  • The study is of interest as this type of data is necessary to fully understand the use of antibiotics in animal production. The manuscript is well written and easy to understand. There are a few points that the authors need to address:


    Please list the number of brands per category that were sampled as in Table 1. Also, please list the number of samples collected per brand. This information would be helpful and may have some impact on the data.

    The total number of E. coli isolates collected per type or brand is not stated. It would be helpful to know what percentage of each were positive.


    The first sentence of the discussion section is very inflammatory to the industry and is not absolutely true. I would suggest refining this greatly or deleting it.

    Similarly, the second sentence is quite definitive and implies that antibiotic usage always creates antibiotic resistance which may not be true. I suggest modifying this sentence with a qualifying word such as “may select for” or “can select for”.

    One variable the authors did not address is the fact that chickens produced by the same brand most likely came from different farms. Because there seems to be a large number of brands sampled, this further adds to the total number of farms that were likely to be sampled. The farm environment does have some impact on the quality of the food. Further, birds from multiple farms may be processed within the same processing plant and this too can impact the microbiological quality of the carcass due to cross-contamination. These are confounding variables that may have impacted the author’s data.

    I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above. Competing Interests: No competing interests were disclosed. - See more at:

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  • This paper is of interest because it compares chickens raised by conventional, organic, raised without antibiotics, and kosher chickens for the prevalence of antibiotic resistant E. coli.

    The finding that organic and conventionally raised chickens were statically indistinguishable while chickens raised without antibiotics tended to be slightly lower once again raises the question of the tangible and potential health advantages to the consumer of eating organically raised/raised without antibiotic vs. conventionally raised poultry. Why kosher products had higher prevalence of antibiotic resistant E. coli and E. coli which were multi-resistant is a new finding and certainly needs further study.

    Whether statistical differences in the raised without antibiotic animals would have been found if larger numbers were tested is not clear. However this study continues to fuel the debate on whether the use of antibiotics as growth promoters in poultry production leads to selection of antibiotic resistant and multi-resistant bacteria; which ultimately may have consequences for treatment of diseases in both man and animals. This issue has been settled in the EU which has banned the practice, but is of major discussion currently in the US Congress where “The Strategies to Address Antimicrobial Resistance (STAAR)” (which would take important steps to strengthen the US federal response to the public health crisis of antimicrobial resistance) is currently being considered.

    I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard. Competing Interests: No competing interests were disclosed. - See more at:

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