Research Accomplishment Reports 2011

Enteric Diseases of Swine and Cattle: Prevention, Control and Food Safety

M.C. Newman
Department of Animal and Food Sciences

 

Non-Technical Summary

1) Most food-borne illness events are of undefined etiology, stressing the need for identification and characterization of novel, emerging, or previously unrecognized agents, which undoubtedly account for many of these cases.

2) Most of the known bacterial, viral and parasitic food-borne disease agents are primarily zoonotic in nature.

3) Several of these agents are also severe pathogens of animals or have close relatives that are animal pathogens, such that investigation of the host-parasite relationship in animal models or in fact in the animal populations themselves will be informative regarding the host-parasite interactions in humans.

- Focus on emerging or currently unrecognized agents that result in food-borne human illness or enteric diseases of domestic animals, proposing research on the identification, characterization and development of diagnostics for emerging or currently unrecognized agents.

- Development of effective and practical interventions to reduce prevalence of agents already characterized to be of major importance in food safety and / or animal health, based on research on the ecology of the agents and their epidemiology and population dynamics in animal reservoirs.

- Provide training and continuing education to disseminate knowledge regarding new and emerging agents and interventions effective at reducing enteric disease agent incidence and prevalence.

2011 Project Description

The long-term use of subtherapeutic levels of antibiotics to promote growth in the U.S. animal livestock industry has contributed to the development of antibiotic resistance in gastrointestinal tract (GIT) microflora. As a result there has been increased pressure to implement restrictions on the use of antimicrobials in animal livestock production. The major concern is related to the use of antibiotics which are either directly used in human medicine or might contribute to cross-resistance to antibiotics use in human medicine.

The potential for increased restrictions on the use of antibiotics for growth promotion has encouraged the exploration of alternatives to antibiotics, such as probiotics. Probiotic feed supplements consist of live beneficial bacteria (e.g., lactobacilli) that function to protect the GIT from potential pathogens and to maintain the commensal GIT microflora. This focus on alternatives to antibiotic use in the animal livestock industry has highlighted the importance of commensal bacteria and it has subsequently become more important to understand the characteristics of this population.

Among the most significant bacterial types in the diverse GIT environment are Lactobacilli, which can be isolated from all regions of the GIT including the stomach, small intestine, and large intestine. Lactobacilli are also of great interest because they are considered an important and beneficial component of a balanced GIT microflora that contributes to the protective role of commensal bacteria as competitive exclusion of pathogens.These beneficial bacteria are usually nonpathogenic and are only recently being studied with regard to potential human health impacting characteristics such as the presence of acquired antibiotic resistance.

The impact of different animal management practices (i.e., extent of antibiotic exposure) on the presence of phenotypic or genotypic antibiotic resistance in commensal GIT bacteria has been minimally studied. To begin to establish an understanding of the nonpathogenic commensal bacteria, specifically Lactobacilli, a thorough evaluation of culturable Lactobacilli populations associated with different histories of antibiotic exposure is warranted. In addition, the environmental impact on genotypic antibiotic resistance will be evaluated using samples collected from respective farms.

2011 Impact

Phenotypic and genotypic antibiotic resistance characteristics of fecal Lactobacilli and the distribution of tetracycline resistance (TET-R) genes were evaluated for samples collected from an antibiotic-free and a conventional (antibiotic-receiving) swineherd. The majority (97%) of both farms' fecal lactobacilli isolates were resistant to tetracycline. The percentage of antibiotic-free farm isolates resistant to penicillin (32.4%) and ampicillin (31.4%) was significantly (p<0.01) higher than the percentage of isolates from the conventional swineherd. The percentage of the conventional farm isolates resistant to erythromycin (99.3%), lincomycin (100%), and clindamycin (97.8%) was significantly (p<0.01) higher than the percentages of resistant isolates from the antibiotic-free swineherd. Approximately 87% of the isolates from the antibiotic-free swineherd were resistant to lincomycin.

The majority (84.7%) of isolates from the conventional swineherd were resistant to four antibiotics. The majority (67.6%) of isolates from the antibiotic-free swineherd were resistant to two or less antibiotics.

The mean number of antibiotics in the multi-resistance pattens for isolates from the conventional swineherd (4.11) was significantly (p<0.01) greater than the average (2.49) for the antibiotic-free swineherd. Swine fecal lactobacilli demonstrated tetracycline minimum inhibitory concentrations from 12.5 to 400 μg/ml. The TET-R efflux genes (tetB, tetC, tetG, tetH, tetY, and tetZ) were detected in fecal, soil, and waste samples from both farms with variable frequencies. The TET-R ribosomal protection genes (tetM, tetO, tetQ, tetS, and tetW) were detected in fecal, soil, and waste samples from both farms with variable frequencies.

All of the ribosomal protection genes were detected in isolates from the antibiotic-free swineherd while only tet(M), tet(O), and tet(W) were detected in isolates from the conventional swineherd.