Food Safety and Feeding: Antibiotic Resistant Campylobacter

Foodborne illnesses afflicts 4.2 million people each year in the United States, resulting in approximately 1,600 deaths and costing an estimated 9.2 billion dollars. Two foodborne pathogens that are often associated with poultry meat include Salmonella and Campylobacter jejuni. Salmonella was found to be the one of the enteric pathogens with higher mortality rates followed by C. jejuni and E. coli 0157:H7 according to a Food Protection Report (1998).

Campylobacter is the leading cause of diarrhea affecting between 2 and 8 million individuals each year resulting in approximately 800 deaths (Maharaj, 1997). More alarming is the increased frequency with which antibiotic resistant campylobacter has been isolated. Because immunocompromised people are the primary recipients of antibiotic therapy to treat campylobacteriosis, antibiotic resistant campylobacter represents an emerging food safety issue.

Treating human illnesses caused by antibiotic resistant organisms becomes extremely difficult because the typical antibiotic therapy used to treat these infections becomes ineffective. The CDC estimated that of the 40 million patients hospitalized each year in the United States, approximately 13,300 die annually from infections caused by antibiotic resistant strains of bacteria. The number of deaths related to non-treatable infections is increasing each year. Therefore, the emergence of antibiotic resistant bacteria represents an enormous health threat.

The emergence of antibiotic resistant organisms is generally thought to stem from the broad use of antibiotics in human and veterinary medicine. Repeated exposure to antibiotics can lead to the selective emergence of antibiotic resistance that may be acquired or evolved. As a result, the use of antibiotics in livestock production to enhance growth and promote production continues to be a controversial issue.

In a recent report, it has been estimated that 80% of farm animal diets including swine, cattle and poultry are being supplemented with subtherapeutic levels of antibiotics to enhance growth (Hileman, 1999). According to the CDC, nineteen classes of antibiotics are approved for use in animals to promote growth rates and production. Of these antibiotics, six are important in the treatment of human illnesses. This represents a significant health risk because animal foods are thought to represent a transfer mechanism for the resistant bacteria to humans (Wegner et al., 1999).

A recent report links the use of antibiotics, particularly, fluoroquinolones in poultry to the increased fluoroquiolone resistant C. jejuni isolated from humans having C. jejuni infections. Specifically, the report indicated levels of fluoroquinolone resistant organisms isolated from humans increased from 1.3 percent in 1992 to 10.2 percent in 1998 (Smith et al., 1999). In 1995, the US approved the use of fluoroquinolones in poultry which temporally corresponds to the increase in fluoroquinolone resistant organisms found in humans in this particular study. When retail chicken products in the US were tested for antibiotic resistant campylobacter, poultry products had high rates of antibiotic resistant C. jejuni (Smith et al., 1999).

Furthermore, using molecular subtyping, antibiotic resistant C. jejuni isolates were found to be related to the isolates from humans having infections from antibiotic resistant C. jejuni indicating the resistant organisms were transferred from poultry to humans. Several other studies have also shown a substantial increase in fluoroquinolone resistant campylobacter isolated from humans (Rautelin et al., 1991 and Slavin et al., 1996).

This is a concern because erythromycin and fluoroquinolones such as ciprofloxacin are the two drugs most often used in the treatment of human campylobacteriosis when drug therapy is utilized. Other researchers also suggest that the veterinary use of fluoroquinolones, particularly enrofloxacin, is facilitating selective pressure for emergence of fluoroquinolone resistance to ciprofloxacin in humans (Endtz et al., 1990, 1991).

The findings of Gaunt and coworkers (1996) support this theory. Specifically, these researchers found that prevalence of fluoroquinolone resistant campylobacter was very low in poultry from the UK where enrofloxacin was not licensed for used during that time compared to imported poultry from neighboring countries where enrofloxacin was licensed for use. More importantly, risk factors identified in cases of human antibiotic resistant campylobacter infections were travel abroad and consumption of imported poultry products (Gaunt et al., 1996). Because of the possible epidemiological links, in September of 2005 FDA banned the use of enroflaxacin (veterinary flouroquinolone marketed as Baytril™) in the US.

There has been considerable dispute as to the extent of the relationship between human illness and antibiotic use in livestock. While fluoroquinolones were used primarily to treat E. coli infections, other antibiotics used as growth promoters have been linked to the development of antibiotic resistant organisms (Wegner et al., 1999). Specifically, Denmark and other European countries banned the feeding of avoparcin in poultry as a growth promoter after observing an increase in vancomycin-resistant Enterococci faecium, an organism having the ability to cause serious infections in hospital patients. More importantly, genetic ribotyping revealed a relationship between vancomycin-resistant Enterococci faecium in poultry and in human patients indicating a transfer of resistant organisms from poultry to humans (Wegner et al., 1999).

Campylobacter is commonly found in poultry production and processing. Cason et al. (1997) reported 94% of ready-to-eat chicken carcasses tested positive for campylobacter. On the farm, researchers have found that C. jejuni manifestation in poultry is evident by 34-45 days (Shanker et al., 1988). Furthermore, researchers suggest that once a farm has tested positive for the organism, it rapidly spreads so that 100% of the birds are contaminated by the time of slaughter (Genigerogis et al., 1986).

Common vectors responsible for cross contamination of the organism on farms include the birds, poultry litter and the drinking water. Because the birds digestive tract serves as a reservoir for campylobacter, cross contamination can occur at many points on the farm or during transport and processing where fecal matter is spread. In the processing plant much of the contamination of poultry occurs during picking, viscera removal, scalding and chilling (Lillard, 1989).

Scalding, picking and chilling are processing steps where cross contamination from carcass to carcass can occur; however, scalding usually decreases overall microbial levels (Gardner and Golan, 1976). Picking and viscera removal are processing steps generally associated with having higher microbial levels when compared to the processing steps immediately prior to picking and viscera removal (Izat et al., 1988). It is generally accepted that the emergence of antibiotic resistant C. jejuni is due, in part, to the broad use of antibiotics in human and veterinary medicine. However, there is relatively no information on the relationship between antibiotic resistance genotype and transmission and/or survival patterns on the farm or in the food production environment.

Because of the prevalence of campylobacter in retail poultry and the past use of fluorquinolones in poultry production, it is not too surprising that high rates of antibiotic resistant campylobacter were found in retail poultry (Smith et al., 1999). High rates of antibiotic resistant campylobacter in poultry is disturbing because they have been epidemiologically linked to humans having resistant infections. Moreover, this raises many questions. Most importantly, what farm management practices and steps during processing facilitate the distribution of antibiotic resistant campylobacter in the production and processing environment? Are there any niches in the food production environment that select of antibiotic resistant populations.

Furthermore, how do we correlate farm management practices with the levels of antibiotic resistant campylobacter that are observed in retail poultry so that we may offer intervention strategies? By examining the prevalence of antibiotic resistant campylobacter and the detailed population structure on the farm and in the food production environment, we can begin to understand what steps in poultry production and processing may facilitate the selection and suppression of specific subpopulations of campylobacter.



Data


A. Isolation of antibiotic resistant campylobacter from air-chilled and immersion-chilled poultry carcasses.

To date, we have obtained data from our study examining the prevalence of antibiotic resistant organisms in ready-to-market broilers from air-chilled and immersion-chilled facilities. Preliminary results from our study are illustrated below in figure 1. Briefly, a total of 60 carcasses were collected. Fifteen birds were collected on two separate days (n=30) from a commercial air-chill facility immediately after chilling and held overnight at 4°C prior to sampling. Similarly, 15 birds from an immersion-chill facility were randomly collected on two separate days (n=30) and held overnight.

Campylobacter spp. isolates were collected and tested for resistance against nalidixic acid using a disk diffusion assay. Nalidixic acid resistant isolates were further tested for resistance against fluoroquinolones. The majority of the isolates from both air-chill and immersion-chill facilities were Campylobacter coli/jejuni. Of the Campylobacter isolates from the immersion chill facility, 46% were resistant to nalidixic acid. Of those isolates, 55% were also resistant to ceprafloxacin, 44% to grepafloxacin, and 38% to tetracycline (Figure 1). Very few isolates were resistant to erythromycin and levofloxacin. Lower numbers of campylobacter islolates from the air-chill facility were resistant to nalidixic acid with only 15% of them showing a typical resistance pattern.

However, all were sensitive to cepraWhile these preliminary results are encouraging, there are many questions to be answered to explain the differences observed. Because we did not start at the farm and follow birds through the processing facility, we do not no whether these differences are related to farm practices, initial loads of campylobacter, or perhaps different processing methods (ie air-chill vs immersion chill). Floxacin, grepafloxacin, levofloxacin, tetracycline and erythromycin (Figure 1).




Figure 1. Antibiotic resistant profiles of Campylobacter spp. isolates from air-chill and immersionchill poultry facilities.



Summary of preliminary findings

The emergence of antibiotic resistant campylobacter represents a significant health risk, particularly, for those people who are immunocompromised requiring antibiotic therapy. Epidemiological studies indicate antibiotic resistant campylobacter isolates found in humans are related to poultry.

Intervention strategies are needed to reduce antibiotic resistant campylobacter on the farm and in the processing facility where distribution and/or selection of antibiotic resistant campylobacter may occur.



Literature cited

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