Resistance to antimicrobial agents in campylobacter isolated from chickens raised in intensive and organic farms and its implications for the management of risk to human health

Soonthornchaikul, Nantika (2006) Resistance to antimicrobial agents in campylobacter isolated from chickens raised in intensive and organic farms and its implications for the management of risk to human health. PhD thesis, Middlesex University. [Thesis]

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Abstract

The use of antimicrobials in poultry may lead to the emergence of resistant micro-organisms that could cause additional health risk to humans through food consumption. This study aims to investigate the relative health risks from Campylobacter and its antimicrobial resistance
associated with chicken raised in organic and intensive rearing systems. Three groups of chicken were tested, pre-packaged intensively reared (PIC) and pre-packaged organically reared chickens (POC) both purchased from supermarkets and unwrapped intensively reared (BIC) chickens purchased from butcher' shops in London. Thirty chickens were randomly sampled for each group.

Campylobacter was isolated using three culture methods and enumerated using most probable number method (MPN). A modified MPN was also developed for the study. Resistance rates to three antimicrobials were determined using an agar dilution method. Numbers and antimicrobial resistance rates of campylobacter were used in consumer risk models to calculate health risks.

The BICs harboured significantly highest numbers of Campylobacter (8.0+0.81log₁₀MPN/g), followed by the POCs and PICs. All isolates from all groups of chickens were resistant to erythromycin and nalidixic acid. All isolates from the POCs were susceptible to ciprofioxacin, whereas 8.7% of the PICs and 26.7% of the BICs harboured resistant isolates.

The calculated risk of campylobacter associated illness related to the consumption of chicken meals using the dose response relationship model was found to be the highest for
the BICs group (33% probability). However, this is the worst case scenario. If elevated internal temperatures (63°C-72°C) are achieved for a sufficient length of time (1-5 minutes), this risk is reduced to <1 %. High resistance rates to antimicrobials may generate additional risk where levels of infection are high.

Potential intervention options for the reduction of campylobacter load in chickens and the control of antimicrobial resistance were considered. The most significant factors found were the initial number of organisms, personal hygiene practices and cooking procedures.

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