Antimicrobial susceptibilities of enterococci isolated from faeces of broiler and layer chickens

Enterococci as a One Health indicator of antimicrobial resistance

The rapid increase of antimicrobial-resistant bacteria in humans and livestock is concerning. Antimicrobials are essential for the treatment of disease in modern day medicine, and their misuse in humans and food animals has contributed to an increase in the prevalence of antimicrobial-resistant bacteria. Globally, antimicrobial resistance is recognized as a One Health problem affecting humans, animals, and environment. Enterococcal species are Gram-positive bacteria that are widely distributed in nature. Their occurrence, prevalence, and persistence across the One Health continuum make them an ideal candidate to study antimicrobial resistance from a One Health perspective. The objective of this review was to summarize the role of enterococci as an indicator of antimicrobial resistance across One Health sectors. We also briefly address the prevalence of enterococci in human, animal, and environmental settings. In addition, a 16S RNA gene-based phylogenetic tree was constructed to visualize the evolutionary relationship among enterococcal species and whether they segregate based on host environment. We also review the genomic basis of antimicrobial resistance in enterococcal species across the One Health continuum.

Dissemination, virulence characteristic, antibiotic resistance determinants of emerging linezolid and vancomycin-resistant Enterococcus spp. in fish and crustacean

Enterococci are emerging nosocomial pathogens. Their widespread distribution causes them to be food contaminants. Furthermore, Enterococci can colonize various ecological niches and diffuse into the food chain via contaminated animals and foods because of their remarkable tolerance to unfavorable environmental circumstances. Due to their potential dissemination to humans, antimicrobial-resistant Enterococci in fish are a worldwide health issue. This study characterized AMR, ARGs, VAGs, gelatinase activity, and biofilm formation in Enterococcus spp. recovered from fish and seafood and evaluated potential correlations. 54 Enterococcus spp. strains(32.73 %)were isolated from 165 samples (75 Oreochromis niloticus, 30 Argyrosomus regius, and 60 Shrimp), comprising 30 Enterococcus faecalis (55.6 %) and 24 Enterococcus faecium (44.4 %) with total 32.73 % (54/165), The maximum prevalence rate of Enterococcus spp. was observed in Nile tilapia (34/54; 63 %), followed by shrimp (14/54; 25.9 %) and Argyrosomus regius (6/54; 11.1 %). The maximum prevalence rate of E. faecalis was observed in Nile tilapia (22/30; 73.3 %), followed by shrimp (8/30; 26.7 %) with significant differences. The prevalence rate of E. faecium was observed in Nile tilapia (12/24; 50 %), followed by shrimp (6/24,25 %). E. faecium is only isolated from Argyrosomus regius (6/24,25 %). Isolates exhibited high resistance against both tetracycline (90.7 %) and erythromycin(88.9 %), followed by gentamycin (77.8 %), ciprofloxacin (74.1 %), levofloxacin (72.2 %), penicillin (44.4 %), vancomycin (37 %), and linezolid (20.4 %). 50 strains (92.6 %) exhibited resistance to more than two antibiotics, 5 strains (10 %) were XDR, and the remaining 45 strains (90 %) were classified as MDR. 92.6 % of the isolates had MARindices >0.2, indicating they originated in settings with a high risk of contamination. Additionally, ten ARGs were identified, with tet(M) 92.6 %, followed by erm(B) (88.9 %), aac(6')-Ie-aph(2″)-Ia(77.8 %), tet(K) (75.9 %), gyrA (74.1 %), blaZ (48.1 %), vanA (37 %), vanB (31.5 %), optrA (20.4 %), and catA(3.7 %). Biofilm formation and gelatinase activity were observed in 85.2 %, and 61.1 % of the isolates, respectively. A total of 11 VAGs were detected, with gelE as the most prevalent (83.3 %) followed by agg(79.6 %), pil (74.1 %), both sprE and asa1 (72.2 %), hyl (70.4 %), eps(68.5 %), EF3314 (57.4 %), ace (50 %), and cylA (35.2 %) with no detection of cylB. In conclusion, the emergence of linezolid-resistant -vancomycin-resistant enterococci recovered from Egyptian fish and shrimp, suggests that fish and seafood might participate a fundamental part in the emergence of antimicrobial resistance among humans.

Particle-size stratification of airborne antibiotic resistant genes, mobile genetic elements, and bacterial pathogens within layer and broiler farms in Beijing, China

The particle-size distribution of antimicrobial resistant (AMR) elements is crucial in evaluating their environmental behavior and health risks, and exposure to the fecal microbiome via particle mass (PM) is an important route of transmission of AMR from livestock to humans. However, few studies have explored the association between air and fecal AMR in farm environments from the perspective of particle-size stratification. We collected feces and PMs of different sizes from layer and broiler farms, quantified antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and human pathogenic bacteria (HPB) using Droplet digital PCR (ddPCR), and analyzed the bacterial communities based on 16S rRNA sequencing. The particle-size distributions of 16S rRNA and AMR elements were similar and generally increased with larger particle sizes in chicken farms. In broiler farms, we observed a bimodal distribution with two peaks at 5.8-9.0 μm and 3.3-4.7 μm. The dominant airborne bacterial phyla were Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. The dominant phyla in the feces were the same as those in the air, but the order of relative abundance varied. The particle-size distributions of specific bacterial genera differed between the animal-farm types. Overall, the degree of association between feces and different particulates increased with increasing particle size. The microbial communities in the coarse particles were similar to those in fecal samples. Escherichia coli, Staphylococcus spp., Campylobacter spp., and sul 2 (sulfonamide ARGs) tended to attach to small particles. We highlight the particle size-specific relationship between fecal and air microbes involving ARGs, MGEs, and HPB and provide valuable information for comprehensively assessing the transmission of fecal microorganisms through the airpath and its environmental and occupational health risks.

Determination of the Prevalence and Antimicrobial Resistance of Enterococcus faecalis and Enterococcus faecium Associated with Poultry in Four Districts in Zambia

The presence of antimicrobial-resistant Enterococci in poultry is a growing public health concern worldwide due to its potential for transmission to humans. The aim of this study was to determine the prevalence and patterns of antimicrobial resistance and to detect drug-resistant genes in Enterococcus faecalis and E. faecium in poultry from four districts in Zambia. Identification of Enterococci was conducted using phenotypic methods. Antimicrobial resistance was determined using the disc diffusion method and antimicrobial resistance genes were detected using polymerase chain reaction and gene-specific primers. The overall prevalence of Enterococci was 31.1% (153/492, 95% CI: 27.1–35.4). Enterococcus faecalis had a significantly higher prevalence at 37.9% (58/153, 95% CI: 30.3–46.1) compared with E. faecium, which had a prevalence of 10.5% (16/153, 95% CI: 6.3–16.7). Most of the E. faecalis and E. faecium isolates were resistant to tetracycline (66/74, 89.2%) and ampicillin and erythromycin (51/74, 68.9%). The majority of isolates were susceptible to vancomycin (72/74, 97.3%). The results show that poultry are a potential source of multidrug-resistant E. faecalis and E. faecium strains, which can be transmitted to humans. Resistance genes in the Enterococcus species can also be transmitted to pathogenic bacteria if they colonize the same poultry, thus threatening the safety of poultry production, leading to significant public health concerns.

High prevalence of vancomycin non-susceptible and multi-drug resistant enterococci in farmed animals and fresh retail meats in Bangladesh

The emergence of antimicrobial resistant Enterococcus spp., a main cause of untreatable nosocomial infection, in food animals and dissemination to humans is a public health risk. The study was performed to determine the prevalence and antimicrobial resistance, and virulence characteristics of Enterococcus faecalis and Enterococcus faecium in food animals and meats in Bangladesh. Enterococcus spp., were confirmed using sodA gene specific PCR, and antimicrobial resistance and virulence properties were characterized by PCR. Enterococcus spp. were recovered from 57% of the collected samples (n = 201/352). Farm samples yielded significantly higher (p ≤ 0.05) prevalence (62%) than that of retail meat samples (41%). E. faecalis (52%) is most frequently isolated species. Greater proportions of isolates exhibited resistance to tetracycline (74%), erythromycin (65%) and ciprofloxacin (34%). Fifty-one isolates are vancomycin non-susceptible enterococci (VNSE), of which forty-seven are MDR and twenty are linezolid resistant, a last line drug for VNSE. Virulence factors such as gelatinase (gelE), aggregation factor (asa1) and sex pheromone (cpd) are detected along with vancomycin resistance gene (vanA, vanB and vanC2/C3) in VNSE isolates. The high prevalence of MDR enterococci in food animals and retail meats may cause consumers infections with concomitant reduction of available therapeutic options.

Antimicrobial Resistance, Biofilm Formation, and Virulence Genes in Enterococcus Species from Small Backyard Chicken Flocks

Backyard birds are small flocks that are more common in developing countries. They are used for poultry meat and egg production. However, they are also implicated in the maintenance and transmission of several zoonotic diseases, including multidrug-resistant bacteria. Enterococci are one of the most common zoonotic bacteria. They colonize numerous body sites and cause a wide range of serious nosocomial infections in humans. Therefore, the objective of the present study was to investigate the diversity in Enterococcus spp. in healthy birds and to determine the occurrence of multidrug resistance (MDR), multi-locus sequence types, and virulence genes and biofilm formation. From March 2019 to December 2020, cloacal swabs were collected from 15 healthy backyard broiler flocks. A total of 90 enterococci strains were recovered and classified according to the 16S rRNA sequence into Enterococcus faecalis (50%); Enterococcus faecium (33.33%), Enterococcus hirae (13.33%), and Enterococcus avium (3.33%). The isolates exhibited high resistance to tetracycline (55.6%), erythromycin (31.1%), and ampicillin (30%). However, all of the isolates were susceptible to linezolid. Multidrug resistance (MDR) was identified in 30 (33.3%) isolates. The enterococci AMR-associated genes ermB, ermA, tetM, tetL, vanA, cat, and pbp5 were identified in 24 (26.6%), 11 (12.2%), 39 (43.3%), 34 (37.7%), 1 (1.1%), 4 (4.4%), and 23 (25.5%) isolates, respectively. Of the 90 enterococci, 21 (23.3%), 27 (30%), and 36 (40%) isolates showed the presence of cylA, gelE, and agg virulence-associated genes, respectively. Seventy-three (81.1%) isolates exhibited biofilm formation. A statistically significant correlation was obtained for biofilm formation versus the MAR index and MDR. Multi-locus sequence typing (MLST) identified eleven and eight different STs for E. faecalis and E. faecium, respectively. Seven different rep-family plasmid genes (rep1–2, rep3, rep5–6, rep9, and rep11) were detected in the MDR enterococci. Two-thirds (20/30; 66.6%) of the enterococci were positive for one or two rep-families. In conclusion, the results show that healthy backyard chickens could act as a reservoir for MDR and virulent Enterococcus spp. Thus, an effective antimicrobial stewardship program and further studies using a One Health approach are required to investigate the role of backyard chickens as vectors for AMR transmission to humans.

Nationwide Surveillance on Antimicrobial Resistance Profiles of Enterococcus faecium and Enterococcus faecalis Isolated from Healthy Food Animals in South Korea, 2010 to 2019

Intestinal commensal bacteria are considered good indicators for monitoring antimicrobial resistance. We investigated the antimicrobial resistance profiles and resistance trends of Enterococcus faecium and Enterococcus faecalis isolated from food animals in Korea between 2010 and 2019. E. faecium and E. faecalis, isolated from chickens and pigs, respectively, presented a relatively high resistance rate to most of the tested antimicrobials. We observed high ciprofloxacin (67.9%), tetracycline (61.7%), erythromycin (59.5%), and tylosin (53.0%) resistance in E. faecium isolated from chickens. Similarly, more than half of the E. faecalis isolates from pigs and chickens were resistant to erythromycin, tetracycline and tylosin. Notably, we observed ampicillin, daptomycin, tigecycline and linezolid resistance in a relatively small proportion of enterococcal isolates. Additionally, the enterococcal strains exhibited an increasing but fluctuating resistance trend (p < 0.05) to some of the tested antimicrobials including daptomycin and/or linezolid. E. faecalis showed higher Multidrug resistance (MDR) rates than E. faecium in cattle (19.7% vs. 8.6%, respectively) and pigs (63.6% vs. 15.6%, respectively), whereas a comparable MDR rate (≈60.0%) was noted in E. faecium and E. faecalis isolated from chickens. Collectively, the presence of antimicrobial-resistant Enterococcus in food animals poses a potential risk to public health.

Antimicrobial use through consumption of medicated feeds in chicken flocks in the Mekong Delta of Vietnam: A three-year study before a ban on antimicrobial growth promoters

Antimicrobials are included in commercial animal feed rations in many low- and middle-income countries (LMICs). We measured antimicrobial use (AMU) in commercial feed products consumed by 338 small-scale chicken flocks in the Mekong Delta of Vietnam, before a gradual nationwide ban on prophylactic use of antimicrobials (including in commercial feeds) to be introduced in the country over the coming five years. We inspected the labels of commercial feeds and calculated amounts of antimicrobial active ingredients (AAIs) given to flocks. We framed these results in the context of overall AMU in chicken production, and highlighted those products that did not comply with Government regulations. Thirty-five of 99 (35.3%) different antimicrobial-containing feed products included at least one AAI. Eight different AAIs (avilamycin, bacitracin, chlortetracycline, colistin, enramycin, flavomycin, oxytetracycline, virginamycin) belonging to five classes were identified. Brooding feeds contained antimicrobials the most (60.0%), followed by grower (40.9%) and finisher feeds (20.0%). Quantitatively, chlortetracycline was consumed most (42.2 mg/kg SEM ±0.34; 50.0% of total use), followed by enramycin (18.4 mg/kg SEM ±0.03, 21.8%), bacitracin (16.4 mg/kg SEM ±0.20, 19.4%) and colistin (6.40 mg/kg SEM ± 4.21;7.6%). Other antimicrobials consumed were virgianamycin, avilamycin, flavomycin and oxytetracycline (each ≤0.50 mg/kg). Antimicrobials in commercial feeds were more commonly given to flocks in the earlier part of the production cycle. A total of 10 (9.3%) products were not compliant with existing Vietnamese regulation (06/2016/TT-BNNPTNT) either because they included a non-authorised AAI (4), had AAIs over the permitted limits (4), or both (2). A number of commercial feed formulations examined included colistin (polymyxin E), a critically important antimicrobial of highest priority for human medicine. These results illustrate the challenges for effective implementation and enforcement of restrictions of antimicrobials in commercial feeds in LMICs. Results from this study should help encourage discussion about policies on medicated feeds in LMICs.

A comparison of antibiotics, antibiotic resistance genes, and bacterial community in broiler and layer manure following composting

Animal manure is an important source of antibiotics and antibiotic resistance genes (ARGs) in the environment. However, the difference of antibiotic residues and ARG profiles in layer and broiler manure as well as their compost remains unexplored. In this study, we investigated the profiles of twelve antibiotics, seventeen ARGs, and class 1 integrase gene (intI1) in layer and broiler manure, and the corresponding compost at large-scale. Compared with layer manure, broiler manure exhibited approximately six times more residual tetracyclines, especially chlortetracycline. The relative abundances of qnrS and ermA genes in broiler manure were significantly higher than those in layer manure. The concentration of tetracyclines not only had a significantly positive correlation with tetracycline resistance genes (tetA and tetC) but was also positively correlated with quinolone resistance (qepA, qnrB, and qnrS) and macrolide resistance (ermA and ermT). Most ARGs in manure were reduced after composting. However, the relative abundance of sulfonamide resistance gene sul1 increased up to 2.41% after composting, which was significantly higher than that of broiler (0.41%) and layer (0.62%) manure. The associated bacterial community was characterized by high-throughput 16S rRNA gene sequencing. The relative abundances of thermophilic bacteria had significant positive correlations with the abundance of sul1 in compost. The composting has a significant impact on the ARG-associated gut microbes in poultry manure. Variation partitioning analysis indicated that the change of bacterial community compositions and antibiotics contributed partially to the shift in ARG profiles. The results indicate that at industry-scale production broiler manure had more antibiotics and ARGs than layer manure did, and composting decreased most ARG abundances in poultry manure except for sulfonamide resistance genes.

Susceptibility of chicken Lactobacillus bacteria to coccidiostats

The aim of this study was to determine the susceptibility of Lactobacillus bacteria to selected coccidiostats. Seventy-five Lactobacillus isolates obtained from chickens were classified by MALDI-TOF mass spectrometry and 16S rDNA restriction analysis into seven species, among which L. salivarius (33%) and L. johnsonii (24%) were dominant. Susceptibility of lactobacilli to coccidiostats was determined by broth microdilution method. The ranges of minimum inhibitory concentrations (MICs) were 0.5-≥128 µg/ml for monensin, 0.125-8 µg/ml for salinomycin, ≤0.03-2 µg/ml for lasalocid A, and 4-16 µg/ml for robenidine. Coccidiostats in low concentrations inhibited in vitro growth of most lactobacilli and therefore there is a high probability that administration of this drugs to chickens would reduce the number of lactobacilli in the gut.

Enterococci isolated from farm ostriches and their relation to enterocins

The present study focuses on the detection of enterococci in ostrich faeces. Forty-six bacterial colonies from 140 ostriches were identified at the species level using the MALDI-TOF MS identification system. According to the score value evaluation, they were allotted to the species Enterococcus hirae, Enterococcus faecium and Enterococcus mundtii confirmed also by phenotypic testing. Dominated species E. hirae (34 strains) were submitted to more detailed testing. Those strains E. hirae produced either no or only slight amount of the enzymes related to disorders (N-acetyl-β-glucosaminidase, β-glucuronidase, α-chymotrypsin, trypsin). Most of the strains were not hemolytic. They did not harbour the hiracin-producing gene. Five E. hirae strains harboured virulence factor gene gelE; however, they were phenotypically gelatinase negative. They also harboured other virulence factor genes such as esp, efaAfm and ccf. E. hirae strains were mostly sensitive to antibiotics and those resistant at least to one antibiotic were sensitive to enterocins (200-25,600 AU/mL). This study represents original and novel results concerning the enterococcal microflora in ostriches; enterococci in ostriches have not been described in detail up to now; sensitivity to enterocins of E. hirae strains harbouring virulence factor genes to enterocins is also new.

Antimicrobial Susceptibility Patterns of Enterococcus faecalis and Enterococcus faecium Isolated from Poultry Flocks in Germany

Between 2010 and 2011, 145 Enterococcus isolates (Enterococcus faecalis, n = 127; Enterococcus faecium, n = 18) were collected during routine bacteriologic diagnostics from broilers, layers, and fattening turkeys in Germany showing various clinical signs. The susceptibility to 24 antimicrobial agents was investigated by broth microdilution test to determine minimum inhibitory concentrations (MICs). All E. faecalis isolates (n = 127) were susceptible to the beta-lactam antibiotics ampicillin, amoxicillin-clavulanic acid, and penicillin. Corresponding MIC with 50% inhibition (MIC50) and MIC with 90% inhibition (MIC90) values of these antimicrobial agents were at the lower end of the test range (≤ 4 μg/ml). In addition, no vancomycin-resistant enterococci (VRE) were found. High resistance rates were identified in both Enterococcus species for lincomycin (72%-99%) and tetracycline (67%-82%). Half or more than half of Enterococcus isolates were resistant to gentamicin (54%-72%) and the macrolide antibiotics erythromycin (44%-61%) and tylosin-tartate (44%-56%). Enterococcus faecalis isolated from fattening turkeys showed the highest prevalence of antimicrobial resistance compared to other poultry production systems. Eighty-nine out of 145 Enterococcus isolates were resistant to three or more antimicrobial classes. Again, turkeys stood out with 42 (8 1%) multiresistant isolates. The most-frequent resistance patterns of E. faecalis were gentamicin, lincomycin, and tetracycline in all poultry production systems.

Antimicrobial resistance in Enterococcus spp. isolated from environmental samples in an area of intensive poultry production

Enterococcus spp. from two poultry farms and proximate surface and ground water sites in an area of intensive poultry production were tested for resistance to 16 clinical antibiotics. Resistance patterns were compared to assess trends and possible correlations for specific antimicrobials and levels of resistance. Enterococci were detected at all 12 surface water sites and three of 28 ground water sites. Resistance to lincomycin, tetracycline, penicillin and ciprofloxacin in poultry litter isolates was high (80.3%, 65.3%, 61.1% and 49.6%, respectively). Resistance in the surface water to the same antibiotics was 87.1%, 24.1%, 7.6% and 12.9%, respectively. Overall, 86% of litter isolates, 58% of surface water isolates and 100% of ground water isolates were resistant to more than one antibiotic. Fifty-four different resistance patterns were recognised in isolates obtained from litter and environmental samples and several E. faecium and E. faecalis isolates from litter and environment samples shared the same resistance pattern. Multiple antibiotic resistant (MAR) indices calculated to assess health risks due to the presence of resistant enterococci suggested an increased presence of antibiotics in surface water, likely from poultry sources as no other wastewater contributions in the area were documented.

National monitoring for antimicrobial resistance among indicator bacteria isolated from food-producing animals in Japan

The antimicrobial susceptibilities of 2,205 isolates of Escherichia coli and 1,181 isolates of Enterococcus faecalis (n=610) and E. faecium (n=571) from apparently healthy cattle, pigs and broiler and layer chickens collected from 2000 to 2003 were examined using an agar dilution method. Overall, the isolates from cattle and layer chickens showed a lower incidence of resistance to almost all antimicrobials studied compared with those from pigs and broiler chickens. Fluoroquinolone resistance was found at a low level in isolates of E. coli from four animal species and in E. faecalis from pigs and broiler and layer chickens. Resistance to cephalosporin was identified in isolates of E. coli from broiler chickens in 2000-2002 and from four animal species in 2003. Incidence of antimicrobial resistance in the bacteria did not vary from year to year during the investigation period.

Distribution of drug resistance among enterococci and Salmonella from poultry and cattle in Ethiopia

Enterococci and Salmonella were isolated from feces of chicken in intensive poultry farms and cattle which are maintained following traditional practices. Their resistance to different antibiotics was also determined. A total of 298 enterococcal isolates consisting of Enterococcus faecium (49.6%), Enterococcus durans (26.9%), Enterococcus hirea (11.9%), and Enterococcus faecalis (11.5%) were obtained. Among the enterococci, resistance to erythromycin (Ery), clindamicin (Cli), amoxicillin (Amo), ampicillin (Amp), and cephalothin (Cep) was high. Resistance to vancomycin (Van) was detected in all enterococcal species. Over 80% of the isolates showed multiple drug resistance. The most dominant patterns in poultry were Amo/Amp/Cep/Pen and Amo/Amp/Cep/Cli/Pen/Van. Among isolates from cattle, Amo/Amp/Cep/Cli/Ery/Pen/Van and Amo/Amp/Cli/Ery/Pen/Van constituted the most dominant multiple resistance patterns. A total of 51 Salmonella isolates were obtained from poultry (43/280) and cattle (8/450). About 70% of the isolates had varying resistance to the tested antibiotics. Multiple drug resistance was observed in over 30% of the Salmonella isolates. The most frequent resistance pattern was Amo/Amp/Cip/Gen/Str in cattle and Amo/Amp/Cep/Cip/Gen/Kan/Str in poultry. Enteroccoccal and Salmonella isolates showed multiple resistance to those antibiotics used in human and veterinary medicine. The high frequency of isolation of resistant enterococci is indicative of the wide dissemination of antibiotic resistant bacteria in the farm environment.

Antimicrobial resistance ofEnterococcus spp. isolates from raw beef and meat products

E. faecalis (67%) and E. faecium (13.7%) were most frequently isolated among enterococci that contaminate cooled and frozen processed meat, follow-up heat-treated meat products and unheated fermented dry salami. Most isolates of both species were resistant to cephalothin (95 and 83 %) and clindamycin (77 and 67%, respectively). Furthermore, E. faecalis and E. faecium isolates were resistant to erythromycin (44 and 72%), tetracycline (34.5 and 17.4%), and streptomycin (13.3 and 4.3%, respectively). Only a few of the isolates were resistant to ampicillin, ampicillin-sulbactam, chloramphenicol, and vancomycin while all isolates were susceptible to gentamicin, penicillin, and teicoplanin. During the production of heat-treated meat products, numbers of resistant isolates increased in spite of the decreasing enterococcal contamination of the samples. An opposite situation was found in the production of fermented dry salami.

Comparison of pulsed-field gel electrophoresis patterns of antimicrobial-resistant Escherichia coli and enterococci isolates from the feces of livestock and livestock farmers in Japan

Seven hundred thirty-nine animal strains and 662 livestock-farmer strains, consisting of Escherichia coli and enterococci, were examined for their pulsed-field gel electrophoresis (PFGE) and antimicrobial-resistance patterns. Two hundred fifty-eight and 203 PFGE patterns were found among 739 animal strains isolated from animals comprising broilers, pigs and cattle, and 662 human strains isolated from livestock farmers, respectively, from 27 farms in Japan. These results demonstrated that the PFGE patterns found among E. coli and enterococci strains from animals and livestock-farmers were heterogeneous and considerably diverse. The strains having both the identical PFGE pattern and the same drug-resistance pattern were defined as a single clone in this study. Seven types of E. coli and enterococci clones were shared among animals within the same farms and between the different farms housing the same animal species. The 25 strains (3.4%) of 739 E. coli and enterococci animal strains belonged to these seven types of clones. Only three types of E. coli clones were shared among animals between the different farms housing different animal species, but no identical E. faecalis or E. faecium clones were found between different animal species farms. The 15 strains (2.0%) of 739 E. coli and enterococci animal strains belonged to these three types of clones. Additionally, the 11 strains (1.5%) of 739 E. coli and enterococci strains isolated from animals were identical clones to strains isolated from livestock farmers of the same farm. These results suggest that the transmission of animal clones to livestock farmers or vice versa is less common.

In vitro study on bacteriocin production of Enterococci associated with chickens

In recent years, the approach of using innovative strategies such as probiotics or bacteriocins for the prevention or treatment of bacterial infections has come into focus. The present study was undertaken to check in vitro ability of Enterococci-isolated from the gastrointestinal tract of chickens-to produce a bacteriocin-like substance and to describe some further probiotic properties in five selected Enterococcus faecium strains. All strains (n=17) were found to produce bacteriocin-like substances against 14 out of 20 indicator bacteria of animal, food or environmental origin. Selected E. faecium strains expressed sufficient survival by pH 3.0 after 3h, in the presence of 1% bile after 24h and they were sensitive to most of antimicrobials tested. All tested strains adhere to the human, canine and porcine intestinal mucus (between 1.5% and 9.2%). However, better adhesion ability was observed for the canine mucus. PCR detection of enterocin structural genes determined presence of enterocins A and P genes in all selected strains. Characterization of bacteriocin substance in detail was performed in E. faecium EF55. The EF55 strain produced a bacteriocin-like substance (during the late logarithmic and early stationary growth phase) with inhibitory activity mostly against Gram-positive bacteria (100-51,200 AU/mL) including Listeria monocytogenes. Proteinaceous character of the bacteriocin substance was confirmed (its inhibitory activity was lost after its treatment with proteases), it was found to be stable after heating (100 degrees C 10 min) and during 12 months storage at -20 degrees C. The highest inhibitory activity of bacteriocin produced by EF55 strain (growing in MRS) broth was achieved between pH 7.0 and 9.0.

Influence of avilamycin administration and its subsequent withdrawal on emergence and disappearance of antimicrobial resistance in enterococci in the intestine of broiler chickens

AIMS

To investigate the influence of avilamycin (AVM) administration and its subsequent withdrawal on the emergence and disappearance of AVM-resistant enterococci in the intestine of broiler chickens.

METHODS AND RESULTS

Five chicks each of C, L and H groups were given the basal diet, the basal diet supplemented with 5 g AVM/ton and the basal diet supplemented with 50 g AVM/ton, respectively. The AVM-resistant Enterococcus faecalis population did not emerge during 30 days of the AVM administration period, whereas the AVM-resistant Enterococcus faecium with a minimum inhibitory concentration of >512 microg ml(-1) in the faeces of chicks of the L and H groups emerged on 3 and 1 days after the AVM administration, respectively. Thereafter, the AVM-resistant Ent. faecium population density in both L and H groups maintained high levels during the AVM administration period. Twenty days after the AVM withdrawal, the AVM-resistant Ent. faecium population disappeared from the intestines of both four of five chicks of L group and three of five chicks of H group. The AVM-resistant Ent. faecium population density in one chick from each of the groups, L and H, did not change before and after the AVM removal.

CONCLUSIONS

The AVM-resistant Ent. faecium emerged during the AVM administration, and disappeared from the intestine of most chicks after the AVM withdrawal. However, the AVM-resistant Ent. faecium persisted in some chicks 20 days after AVM withdrawal.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results suggest that introducing an AVM withdrawal period could minimize the risk of AVM-resistant Ent. faecium becoming carcass contaminants, and that prudent antibiotic use alone is not sufficient to stem emergence of the AVM-resistant Ent. faecium.

Antimicrobial resistance in Enterococcus spp. strains isolated from organic chicken, conventional chicken, and turkey meat: a comparative survey

The mean counts of Enterococcus spp. were determined for 30 samples each of organic chicken meat, conventional chicken meat, and turkey meat, and differences for Enterococcus contamination in meat were determined. Two enterococci strains from each sample were isolated to obtain a total of 180 strains, and resistance to ampicillin, chloramphenicol, doxycycline, ciprofloxacin, erythromycin, gentamicin, nitrofurantoin, and vancomycin was determined by a disk diffusion method. Average counts obtained showed that Enterococcus mean counts from organic chicken meat (3.18 log CFU/g) were significantly higher than those obtained from conventional chicken meat (2.06 log CFU/g) or conventional turkey meat (1.23 log CFU/g). However, the resistance data obtained showed that isolates from organic chicken meat were less resistant than enterococci isolates from conventional chicken meat to ampicillin (P = 0.0067), chloramphenicol (P = 0.0154), doxycycline (P = 0.0277), ciprofloxacin (P = 0.0024), erythromycin (P = 0.0028), and vancomycin (P = 0.0241). In addition, isolates from organic chicken were less resistant than conventional turkey meat isolates to ciprofloxacin (P = 0.001) and erythromycin (P = 0.0137). Multidrug-resistant isolates were found in every group tested, but rates of multidrug-resistant strains were significantly higher in conventional chicken and turkey than those obtained from organic chicken meat. Enterococcus faecalis was the most common species isolated from organic chicken (36.67%), whereas Enterococcus durans was the most common species isolated from conventional chicken (58.33%) and turkey (56.67%). The rates obtained for antimicrobial resistance suggest that although organic chicken meat may have higher numbers of Enterococcus, these bacteria present a lower level of antimicrobial resistance.

Antimicrobial resistance in Enterococcus spp. and Escherichia coli isolated from poultry feed and feed ingredients

Poultry feed is at the start of the food safety chain in the "farm-to-fork" model, and might serve as a source of antimicrobial resistant bacteria present in poultry meat. Antimicrobial resistance was investigated in 1137 enterococci and 163 Escherichia coli strains recovered from 23 samples of commercial broiler feed and 66 samples of raw feeding materials taken over half a year timespan. Enumeration of enterococci and E. coli were also performed using traditional plating and fluorescent in situ hybridisation methods. Viable enterococci were detected in all feed samples and in 66% of samples of separate feed ingredients, while E. coli was present in 50% and 32% of feed and raw feeding materials, respectively. The median values (50th percentile) for plate and FISH counts for feeds were, respectively, 2.70 log CFU/g and 5.52 log cells/g for enterococci, and 0.15 log CFU/g and 6.00 log cells/g for E. coli. Among enterococci recovered from feed ingredients, resistance to rifampicin, erythromycin, nitrofurantoin, tetracycline, and ciprofloxacin was found in 59.8%, 21.6%, 21.2%, 18.0% and 6.9% of the isolates, respectively. A considerable proportion of the enterococci isolates obtained from broiler feed displayed resistance to tetracycline (69.1%), rifampicin (58.5%), erythromycin (52.9%) and nitrofurantoin (36.2%). Lower percentage of resistance was observed to chloramphenicol (4.6%), ciprofloxacin (3.9%), vancomycin (1.9%) and ampicillin (1.2%). Among E. coli recovered from feed ingredients and poultry feeds, resistance to ampicillin, tetracycline and streptomycin was found in 22.9%, 27.6% and 19.0% and in 22.4%, 41.4% and 17.0% of the isolates, respectively. These data show that feedstuffs and poultry feeds are extensively contaminated by resistant enterococci and, in a lesser extent, by E. coli, thus leading to their introduction in the farm environment.

Combined antimicrobial resistance in Enterococcus faecium isolated from chickens

Nineteen E. faecium strains isolated from chicken caecum samples, collected in slaughterhouses and highly resistant to vancomycin or gentamicin, were coresistant to erythromycin, and/or tetracyclines, and/or streptogramins, and/or avilamycin. Multiple antibiotic resistance was related to the presence in various combinations of aac(6')-aph(2"), erm(B), emtA, mef(A), tet(L), tet(M), and vanA genes.

Multiple-antibiotic resistance of Enterococcus spp. isolated from commercial poultry production environments

The potential impact of food animals in the production environment on the bacterial population as a result of antimicrobial drug use for growth enhancement continues to be a cause for concern. Enterococci from 82 farms within a poultry production region on the eastern seaboard were isolated to establish a baseline of susceptibility profiles for a number of antimicrobials used in production as well as clinical environments. Of the 541 isolates recovered, Enterococcus faecalis (53%) and E. faecium (31%) were the predominant species, while multiresistant antimicrobial phenotypes were observed among all species. The prevalence of resistance among isolates of E. faecalis was comparatively higher among lincosamide, macrolide, and tetracycline antimicrobials, while isolates of E. faecium were observed to be more frequently resistant to fluoroquinolones and penicillins. Notably, 63% of the E. faecium isolates were resistant to the streptogramin quinupristin-dalfopristin, while high-level gentamicin resistance was observed only among the E. faecalis population, of which 7% of the isolates were resistant. The primary observations are that enterococci can be frequently isolated from the poultry production environment and can be multiresistant to antimicrobials used in human medicine. The high frequency with which resistant enterococci are isolated from this environment suggests that these organisms might be useful as sentinels to monitor the development of resistance resulting from the usage of antimicrobial agents in animal production.

Prevalence and antimicrobial resistance of enterococcus species isolated from retail meats

From March 2001 to June 2002, a total of 981 samples of retail raw meats (chicken, turkey, pork, and beef) were randomly obtained from 263 grocery stores in Iowa and cultured for the presence of Enterococcus spp. A total of 1,357 enterococcal isolates were recovered from the samples, with contamination rates ranging from 97% of pork samples to 100% of ground beef samples. Enterococcus faecium was the predominant species recovered (61%), followed by E. faecalis (29%), and E. hirae (5.7%). E. faecium was the predominant species recovered from ground turkey (60%), ground beef (65%), and chicken breast (79%), while E. faecalis was the predominant species recovered from pork chops (54%). The incidence of resistance to many production and therapeutic antimicrobials differed among enterococci recovered from retail meat samples. Resistance to quinupristin-dalfopristin, a human analogue of the production drug virginiamycin, was observed in 54, 27, 9, and 18% of E. faecium isolates from turkey, chicken, pork, and beef samples, respectively. No resistance to linezolid or vancomycin was observed, but high-level gentamicin resistance was observed in 4% of enterococci, the majority of which were recovered from poultry retail meats. Results indicate that Enterococcus spp. commonly contaminate retail meats and that dissimilarities in antimicrobial resistance patterns among enterococci recovered from different meat types may reflect the use of approved antimicrobial agents in each food animal production class.

Effect of MTAD on Enterococcus faecalis–Contaminated Root Canals of Extracted Human Teeth

The purpose of this investigation was to compare the antimicrobial effect of MTAD (a mixture of a tetracycline isomer, an acid, and a detergent) with that of NaOCl with and without EDTA. Eighty-five extracted human teeth were contaminated with Enterococcus faecalis for 4 weeks. After biomechanical instrumentation using 1.3% or 5.25% NaOCl as root canal irrigant, the root canal and the external surface of each tooth were exposed to a 5-min application of MTAD, 1.3% NaOCl, 5.25% NaOCl or a 1-min application of EDTA followed by irrigation with 5 ml of 1.3% NaOCl or 5.25% NaOCl. Teeth or dentin shavings were cultured to determine presence or absence of the test bacteria. Fisher's exact test showed that the combination of 1.3% NaOCl as a root canal irrigant and MTAD as a final rinse was significantly more effective against E. faecalis than the other regimens. The chi2 test showed no difference between the other regimens.