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Published Date: 2012-09-19 11:22:34
Subject: PRO/AH/EDR> Antibiotic resistance, Campylobacter: swine, environ. persistence
Archive Number: 20120919.1300101

ANTIBIOTIC RESISTANCE, CAMPYLOBACTER: SWINE, ENVIRONMENTAL PERSISTENCE
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Date: Mon 17 Sep 2012
Source: Phys.Org [edited]
http://phys.org/news/2012-09-antibiotic-resistant-pathogens-persist-antibiotic-free-pigs.html

Researchers from North Carolina State University have found identical strains of antibiotic-resistant _Campylobacter coli_ (_C. coli_) in both antibiotic-free (ABF) and conventionally raised pigs. This finding may indicate that these antibiotic-resistant pathogens can persist and thrive in the environment, regardless of antimicrobial usage by pork producers.

Dr Siddhartha Thakur, assistant professor of population health and pathobiology, had previously found that antibiotic-resistant _C. coli_, a leading cause of foodborne illness in the US, was present in both ABF-certified and conventionally raised pigs. The pathogen was present in both groups in all facilities from breeding to processing. Thakur wanted to determine whether the _C. coli_ that he found in each group was genetically the same, in order to see if the presence or absence of antimicrobial usage had an effect on the pathogen's genetic makeup.

The rise of antibiotic-resistant pathogens like _C. coli_ is a concern for the food animal industry. Some pig farms have switched to raising ABF pigs in an attempt to get away from the conditions that facilitated antibiotic resistance in the 1st place. The hope is that once the selection pressure -- in the form of antimicrobial use -- on _C. coli_ to retain antibiotic resistance decreases, the pathogen will lose its resistance. Over several years, Thakur and PhD student Macarena Quintana-Hayashi collected thousands of samples from pigs and their surrounding environments, and performed a genetic analysis on 200 representative isolates of _C. coli_, to see if these strains were similar. They found that the _Campylobacter_ populations in the 2 swine production systems (conventional and ABF) were in fact the same. Since the different pig populations never came into contact, the researchers concluded that the environment must be playing a large role in the continuing survival of antibiotic-resistant _C. coli_.

Thakur's findings appear online in PLoS One. "In the case of ABF pigs, the environment plays an important role in their exposure to these resistant strains," Thakur says. "If the environment itself, and not the pig, is serving as a reservoir for _C. coli_, then we will most probably continue to find resistant bacterial populations, regardless of a producer's antimicrobial use."

[Reference]: "Phylogenetic Analysis Reveals Common Antimicrobial Resistant _Campylobacter coli_ Population in Antimicrobial-Free (ABF) and Commercial Swine Systems" PLoS One, 2012 (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0044662).

Abstract
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The objective of this study was to compare the population biology of antimicrobial resistant (AR) _Campylobacter coli_ isolated from swine reared in the conventional and antimicrobial-free (ABF) swine production systems at farm, slaughter, and environment. A total of 200 _C. coli_ isolates selected from fecal, environmental, and carcass samples of ABF (n = 100) and conventional (n = 100) swine production systems were typed by multilocus sequence typing (MLST). Sequence data from seven housekeeping genes was analyzed for the identification of allelic profiles, sequence types (STs) and clonal complex determination. Phylogenetic trees were generated to establish the relationships between the genotyped isolates. A total of 51 STs were detected including 2 novel alleles (glnA 424 and glyA 464) and 14 novel STs reported for the 1st time. The majority of the _C. coli_ isolates belonged to ST-854 (ABF: 31, conventional: 17), and were grouped in clonal complex ST-828 (ABF: 68 percent, conventional: 66 percent). The mean genetic diversity (H) for the ABF (0.3963+/20.0806) and conventional (0.4655+/20.0714) systems were similar. The index of association (IsA) for the ABF (IsA= 0.1513) and conventional (IsA= 0.0991) _C. coli_ populations were close to linkage equilibrium, indicative of a freely recombining population. Identical STs were detected between the pigs and their environment both at farm and slaughter. A minimum spanning tree revealed the close clustering of _C. coli_ STs that originated from swine and carcass with those from the environment. In conclusion, our study reveals a genotypic diverse _C. coli_ population that shares a common ancestry in the conventional and ABF swine production systems. This could potentially explain the high prevalence of antimicrobial resistant _C. coli_ in the ABF system in the absence of antimicrobial selection pressure.

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[_Campylobacter_ are curved, Gram negative bacilli; the most frequently reported _Campylobacter_ species in human disease are _C. jejuni_ and _C. coli_. _Campylobacter_ are one of the most common bacteria that cause intestinal infection worldwide. They normally inhabit the intestinal tract of warm-blooded animals such as poultry and cattle, and are frequently detected in foods derived from these animals. Infection occurs mainly following consumption of contaminated undercooked poultry. Outbreaks have been associated with consumption of unpasteurized milk (ProMED-mail post Campylobacteriosis - USA (10): unpasteurized milk 20120301.1057870) or contaminated water (Clark CG, et al: Characterization of waterborne outbreak-associated _Campylobacter jejuni_, Walkerton, Ontario. Emerg Infect Dis 2003: 9(10); available from http://wwwnc.cdc.gov/eid/article/9/10/02-0584.htm).

_Campylobacter_ infections are generally mild, but can be fatal among very young children, elderly, and immunocompromised individuals. Intestinal _Campylobacter_ infections produce an inflammatory, sometimes bloody, diarrhea or dysentery syndrome. _Campylobacter_ organisms are also an important cause of traveler's diarrhea, such as, in Thailand where fluoroquinolone-resistant _Campylobacter_ species are prevalent (DuPont HL: Antimicrobial-resistant _Campylobacter_ species -- a new threat to travelers to Thailand. Clin Infect Dis. 1995; 21(3): 542-3; and Kuschner RA, et al: Use of azithromycin for the treatment of _Campylobacter_ enteritis in travelers to Thailand, an area where ciprofloxacin resistance is prevalent. Clin Infect Dis. 1995; 21(3): 536-41; abstract available from http://www.ncbi.nlm.nih.gov/pubmed/8527539). Severe complications include invasive infection and Guillain-Barre syndrome (ProMED-mail post Guillain-Barre syndrome - Mexico (SO), USA (AZ) post-diarrhea 20110708.2072).

Antibiotics can shorten the course of symptomatic infection and duration of fecal excretion of _Campylobacter_ species. However, most people with intestinal _Campylobacter_ infection will recover on their own and do not require antimicrobial therapy. Antibiotics (such as, azithromycin or a fluoroquinolone) are used to treat _Campylobacter_ infection in immunocompromised people and those with severe intestinal infection or invasive disease.

Acquisition of antimicrobial drug resistance can affect the adaptation of _Campylobacter_ in various environments. This topic has been reviewed by Q Zhang et al. (Fitness of antimicrobial-resistant _Campylobacter_ and _Salmonella_. Microbes Infect 2006; 8(7): 1972-8; abstract available from http://www.ncbi.nlm.nih.gov/pubmed/16714138). Some resistance genes can have a biological fitness cost, that is, reduced growth and persistence of resistant bacteria in the host and environment in the absence of antibiotic selection pressure; while other resistance genes, such as, fluoroquinolone resistance in _Campylobacter_, can have no cost or even enhanced fitness, that is, the resistant bacteria proliferate and maintain the resistance traits even in the absence of antibiotics (Luo N, et al: Enhanced in vivo fitness of fluoroquinolone-resistant _Campylobacter jejuni_ in the absence of antibiotic selection pressure. Proc Natl Acad Sci USA 2005; 102(3): 541-6; available from http://www.pnas.org/content/102/3/541.long). Enhanced fitness may facilitate the spread and persistence of antimicrobial-resistant _Campylobacter_ in the host and environment in the absence of selection pressure, thus creating a significant barrier for controlling this antibiotic-resistant foodborne pathogen. - Mod.ML]

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