Longitudinal Analysis of Antimicrobial Resistance among Enterococcus Species Isolated from Australian Beef Cattle Faeces at Feedlot Entry and Exit

Abstract

Enterococcus faecium are commensal bacteria inhabiting the gastrointestinal tract of animals and humans and an important cause of drug-resistant nosocomial infections. This longitudinal study aimed to determine whether changes in the antimicrobial resistance (AMR) phenotype and genotype occurred among Enterococcus spp. isolated from cattle rectal samples obtained at the entry to and exit from an Australian feedlot. The samples obtained at the feedlot induction yielded enterococci (104/150; 69.3%), speciated as E. hirae (90/104; 86.5%), E. faecium (9/104; 8.7%), E. mundtii (3/104; 2.9%), E. durans, and E. casseliflavus (1/104; 1.0% each). AMR was observed to lincomycin (63/104; 60.6%), daptomycin (26/104; 25.0%), nitrofurantoin (9/104; 8.7%), ciprofloxacin (7/104; 6.7%), tetracycline (5/104; 4.8%), tigecycline (4/104; 3.9%), and quinupristin/dalfopristin (3/104; 2.9%). From the rectal swab samples collected at the abattoir from the same animals (i.e., the feedlot exit), the enterococci recovery was significantly higher (144/150; 96.0%), with a marked shift in species distribution dominated by E. faecium (117/144; 81.3%). However, the prevalence of AMR to individual antimicrobials remained largely static between the entry and exit except for the increased resistance to nitrofurantoin (77/144; 53.5%) and quinupristin/dalfopristin (26/144; 18.1%). Overall, 13 AMR genes were observed among the 62 E. faecium isolates. These included aac(6’)Ii, aac(6’)-Iid, and ant(6)-Ia (aminoglycosides); eatAv, lnu(G), vat(E), msr(C), and erm(B) (macrolides, lincosamides, and streptogramins); efmA (fluoroquinolones); and tet(45), tet(L), tet(M), and tet(S) (tetracyclines). The results confirm the presence of fluoroquinolone- and streptogramin-resistant enterococci in cattle faeces at the feedlot entry in the absence of antimicrobial selection pressure. E. faecium, exhibiting increased nitrofurantoin resistance, became the dominant Enterococcus spp. during the feeding period.

Antimicrobial resistance in Enterococcus isolated from western Canadian cow-calf herds

“…Slightly higher recover rates were seen in the current publication compared to most of the existing literature [ 7 , 8 , 19 – 21 ]. The present study followed the same protocol as the new Canadian national surveillance program for both culture on selective media and identification of Enterococcus species [ 9 ].…”

“…has previously been reported for cow-calf herds in the United States from 2007 to 08 and 2017, and more recently from beef herds in California [ 8 , 10 , 20 ]. Finally, one Australian study examined resistance in Enterococcus recovered from cattle at the time of arrival in the feedlot [ 21 ].…”

Alternatives to conventional antibiotics for the prevention and treatment of commonly occurring diseases in feedlot cattle

“…in feedlot cattle remained stable between feedlot entry and feedlot exit except for increased resistance to nitrofurantoin and quinupristin/dalfopristin in the absence of antimicrobial selection pressure. 3 Nevertheless, in Australia, there is a theoretical possibility that antibiotic-resistant bacteria or their resistance determinants could be transferred from production animals to humans. Therefore, there is societal pressure on the production animal industries to carefully manage the use of antibiotics to minimise the risk of the development of antibiotic-resistant bacteria in these animals.…”

“…Antibiotic‐resistant bacteria are an existing and increasing problem within human medicine 1 . Recent Australian research has shown that antibiotic resistance genes in Enterococcus faecium from production animals differ from those found in E. faecium with antibiotic resistance isolated from humans 2 and research in this area is ongoing. The authors concluded that strict regulation of antibiotics in food animals is the likely reason for the low level of antibiotic resistance found in food animals in Australia.…”

“…Further, antibiotic resistance prevalence in Enterococcus spp . in feedlot cattle remained stable between feedlot entry and feedlot exit except for increased resistance to nitrofurantoin and quinupristin/dalfopristin in the absence of antimicrobial selection pressure 3 . Nevertheless, in Australia, there is a theoretical possibility that antibiotic‐resistant bacteria or their resistance determinants could be transferred from production animals to humans.…”