Abstract
BackgroundExtensive use of antibiotics as growth promoters in the livestock industry constitutes strong selection pressure for evolution and selection of antibiotic resistant bacterial strains. Unfortunately, the microbial ecology and spread of these bacteria in the agricultural, urban, and suburban environments are poorly understood. Insects such as house flies (Musca domestica) and German cockroaches (Blattella germanica) can move freely between animal waste and food and may play a significant role in the dissemination of antibiotic resistant bacteria within and between animal production farms and from farms to residential settings.ResultsEnterococci from the digestive tract of house flies (n = 162), and feces of German cockroaches (n = 83) and pigs (n = 119), collected from two commercial swine farms were isolated, quantified, identified, and screened for antibiotic resistance and virulence. The majority of samples (93.7%) were positive for enterococci with concentrations 4.2 ± 0.7 × 104 CFU/house fly, 5.5 ± 1.1 × 106 CFU/g of cockroach feces, and 3.2 ± 0.8 × 105 CFU/g of pig feces. Among all the identified isolates (n = 639) Enterococcus faecalis was the most common (55.5%), followed by E. hirae (24.9%), E. faecium (12.8%), and E. casseliflavus (6.7%). E. faecalis was most prevalent in house flies and cockroaches, and E. hirae was most common in pig feces. Our data showed that multi-drug (mainly tetracycline and erythromycin) resistant enterococci were common from all three sources and frequently carried antibiotic resistance genes including tet(M) and erm(B) and Tn916/1545 transposon family. E. faecalis frequently harbored virulence factors gelE, esp, and asa1. PFGE analysis of selected E. faecalis and E. faecium isolates demonstrated that cockroaches and house flies shared some of the same enterococcal clones that were detected in the swine manure indicating that insects acquired enterococci from swine manure.ConclusionsThis study shows that house flies and German cockroaches in the confined swine production environment likely serve as vectors and/or reservoirs of antibiotic resistant and potentially virulent enterococci and consequently may play an important role in animal and public health.
Highlights
Extensive use of antibiotics as growth promoters in the livestock industry constitutes strong selection pressure for evolution and selection of antibiotic resistant bacterial strains
A connection between antibiotic resistance in bacterial isolates from healthy food animals and clinical isolates of human and animal origins has been suggested; this is a controversial issue because the ecology of these bacteria and their genes in the agricultural and urban environment is not well understood [10,12,13,14,15,16]
Differences in species prevalence varied by sources, E. faecalis was the common enterococcal species in all samples (55.5%), followed by E. hirae (24.9%), E. faecium (12.8%), E. casseliflavus (6.7%)
Summary
Extensive use of antibiotics as growth promoters in the livestock industry constitutes strong selection pressure for evolution and selection of antibiotic resistant bacterial strains. The microbial ecology and spread of these bacteria in the agricultural, urban, and suburban environments are poorly understood Insects such as house flies (Musca domestica) and German cockroaches (Blattella germanica) can move freely between animal waste and food and may play a significant role in the dissemination of antibiotic resistant bacteria within and between animal production farms and from farms to residential settings. Organic waste in and around animal production facilities provide excellent habitats for the growth and development of these insects Because of their habitat preferences, unrestricted movement, mode of feeding, and attraction to residential areas, house flies and cockroaches have a great potential to disseminate fecal bacteria, including human and animal pathogens and antibiotic resistant strains [17,18]. With continuing urban expansion in agriculturally zoned areas in the last two decades, there is an increasing concern in the medical and public health community about insect pests directly associated with the spread of bacterial pathogens and antibiotic resistant microorganisms within animal production systems and to residential settings
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