Role of Flies in the Maintenance of Antimicrobial Resistance in Farm Environments

Steady existence of Escherichia coli co-resistant to carbapenem and colistin in an animal breeding area even after the colistin forbidden

Carbapenem- and colistin-resistant Escherichia coli (CCREC) cause high mortality rates and health costs, and have become serious health concerns. Total 1764 samples were collected from 60 animal farms in 2019 and 2021, including worker and animal faeces, wastewater, well water, air, vegetables, human hands, object surfaces, throat swabs, soil, and flies to investigate the prevalence and potential transmission pathways of CCREC. Eleven CCREC were detected: 9 (5 in 2019 and 4 in 2021) from 5 worker faeces, 3 animal faeces, 1 wastewater, and 2 from 1 flies sample. Chicken farms had the highest number of CCREC (n = 9). The detection rate was low (<1.1%) overall, and there was no significant difference in both years, indicating that CCREC existed stably after 4 years of colistin ban. The combinations of chromosomes and plasmids harbouring blaNDM and mcr-1.1 were divided into 4 patterns: IncX3 plasmid-blaNDM & chromosome-mcr.1.1 (n = 5); IncX3 plasmid-blaNDM & IncHI2 plasmid-mcr.1.1 (n = 3); IncFII plasmid-blaNDM & IncI2 plasmid-mcr.1.1 (n = 2); both chromosome (n = 1). The blaNDM located on plasmids was surrounded by similar genetic structures: Tn3-IS-blaNDM-bleMBL-TrpF-DsbD-IS. The genetic contexts of mcr-1.1 were highly similar, with 'ISApl1-mcr-1.1-PAP2' and 'mcr-1.1-PAP2'. All plasmids can be successfully transferred into E. coli J53, except for the IncHI2 plasmids with the transfer rate of 33.3%. The IncFII and IncI2 plasmids from same strain of flies could be co-transferred. The clonal spread of CCREC from humans to humans occurred on the same pig farm (P4) or different chicken farms (BC9 and LH7). This study suggested that flies, chromosomes, and plasmids jointly contribute to the steady existence of CCREC.

Antibiotics and Pesticides Enhancing the Transfer of Resistomes among Soil-Bayberry-Fruit Fly Food Chain in the Orchard Ecosystem

While substantial amounts of antibiotics and pesticides are applied to maintain orchard yields, their influence on the dissemination and risk of antibiotic resisitome in the orchard food chain remains poorly understood. In this study, we characterized the bacterial and fungal communities and differentiated both antibiotic resistance genes (ARGs) and virulence factor genes (VFGs) in the soil, Chinese bayberry (matured and fallen), and fruit fly gut, collected from five geographic locations. Our results showed that fruit fly guts and soils exhibit a higher abundance of ARGs and VFGs compared with bayberry fruits. We identified 112 shared ARGs and 75 shared VFGs, with aminoglycoside and adherence factor genes being among the most abundant. The co-occurrence network revealed some shared microbes, such as Bacillus and Candida, as potential hosts of ARGs, highlighting the vector risks for both above- and below-ground parts of the orchard food chain. Notably, the elevated levels of antibiotics and pesticide residues in orchard soils increase ARGs, mobile genetic elements (MGEs), and VFGs in the soil-bayberry-fruit fly food chain. Our study highlighted that agricultural management, including the overuse of antibiotics and pesticides, could be the key factor in accumulating resistomes in the orchard food chain.

Short-chain fatty acids inhibit bacterial plasmid transfer through conjugation in vitro and in ex vivo chicken tissue explants

The animal gut acts as a potent reservoir for spreading and maintaining conjugative plasmids that confer antimicrobial resistance (AMR), fitness, and virulence attributes. Interventions that inhibit the continued emergence and expansion of AMR and virulent strains in agricultural and clinical environments are greatly desired. This study aims to determine the presence and efficacy of short-chain fatty acids (SCFA) inhibitory effects on the conjugal transfer of AMR plasmids. In vitro broth conjugations were conducted between donor Escherichia coli strains carrying AMP plasmids and the plasmid-less Escherichia coli HS-4 recipient strain. Conjugations were supplemented with ddH2O or SCFAs at 1, 0.1, 0.01, or 0.001 molar final concentration. The addition of SCFAs completely inhibited plasmid transfer at 1 and 0.1 molar and significantly (p < 0.05) reduced transfer at 0.01 molar, regardless of SCFA tested. In explant models for the chicken ceca, either ddH2O or a final concentration of 0.025 M SCFAs were supplemented to the explants infected with donor and recipient E. coli. In every SCFA tested, significant decreases in transconjugant populations compared to ddH2O-treated control samples were observed with minimal effects on donor and recipient populations. Finally, significant reductions in transconjugants for plasmids of each incompatibility type (IncP1ε, IncFIβ, and IncI1) tested were detected. This study demonstrates for the first time the broad inhibition ability of SCFAs on bacterial plasmid transfer and eliminates AMR with minimal effect on bacteria. Implementing interventions that increase the concentrations of SCFAs in the gut may be a viable method to reduce the risk, incidence, and rate of AMR emergence in agricultural and human environments.

Low-frequency transmission and persistence of antimicrobial-resistant bacteria and genes from livestock to agricultural soil and crops through compost application

Livestock excrement is composted and applied to agricultural soils. If composts contain antimicrobial-resistant bacteria (ARB), they may spread to the soil and contaminate cultivated crops. Therefore, we investigated the degree of transmission of ARB and related antimicrobial resistance genes (ARGs) and, as well as clonal transmission of ARB from livestock to soil and crops through composting. This study was conducted at Rakuno Gakuen University farm in Hokkaido, Japan. Samples of cattle feces, solid and liquid composts, agricultural soil, and crops were collected. The abundance of Escherichia coli, coliforms, β-lactam-resistant E. coli, and β-lactam-resistant coliforms, as well as the copy numbers of ARG (specifically the bla gene related to β-lactam-resistant bacteria), were assessed using qPCR through colony counts on CHROMagar ECC with or without ampicillin, respectively, 160 days after compost application. After the application of the compost to the soil, there was an initial increase in E. coli and coliform numbers, followed by a subsequent decrease over time. This trend was also observed in the copy numbers of the bla gene. In the soil, 5.0 CFU g-1 E. coli was detected on day 0 (the day post-compost application), and then, E. coli was not quantified on 60 days post-application. Through phylogenetic analysis involving single nucleotide polymorphisms (SNPs) and using whole-genome sequencing, it was discovered that clonal blaCTX-M-positive E. coli and blaTEM-positive Escherichia fergusonii were present in cattle feces, liquid compost, and soil on day 0 as well as 7 days post-application. This showed that livestock-derived ARB were transmitted from compost to soil and persisted for at least 7 days in soil. These findings indicate a potential low-level transmission of livestock-associated bacteria to agricultural soil through composts was observed at low frequency, dissemination was detected. Therefore, decreasing ARB abundance during composting is important for public health.

Persistence of Marine Bacterial Plasmid in the House Fly (Musca domestica): Marine-Derived Antimicrobial Resistance Genes Have a Chance of Invading the Human Environment

The house fly is known to be a vector of antibiotic-resistant bacteria (ARB) in animal farms. It is also possible that the house fly contributes to the spread of ARB and antibiotic resistance genes (ARGs) among various environments. We hypothesized that ARB and ARGs present in marine fish and fishery food may gain access to humans via the house fly. We show herein that pAQU1, a marine bacterial ARG-bearing plasmid, persists in the house fly intestine for 5 days after fly ingestion of marine bacteria. In the case of Escherichia coli bearing the same plasmid, the persistence period exceeded 7 days. This interval is sufficient for transmission to human environments, meaning that the house fly is capable of serving as a vector of marine-derived ARGs. Time course monitoring of the house fly intestinal microflora showed that the initial microflora was occupied abundantly with Enterobacteriaceae. Experimentally ingested bacteria dominated the intestinal environment immediately following ingestion; however, after 72 h, the intestinal microflora recovered to resemble that observed at baseline, when diverse genera of Enterobacteriaceae were seen. Given that pAQU1 in marine bacteria and E. coli were detected in fly excrement (defined here as any combination of feces and regurgitated material) at 7 days post-bacterial ingestion, we hypothesize that the house fly may serve as a vector for transmission of ARGs from marine items and fish to humans via contamination with fly excrement.

Distribution and associations for antimicrobial resistance and antibiotic resistance genes of Escherichia coli from musk deer (Moschus berezovskii) in Sichuan, China

This study aimed to investigate the antimicrobial resistance (AMR), antibiotic resistance genes (ARGs) and integrons in 157 Escherichia coli (E. coli) strains isolated from feces of captive musk deer from 2 farms (Dujiang Yan and Barkam) in Sichuan province. Result showed that 91.72% (144/157) strains were resistant to at least one antimicrobial and 24.20% (38/157) strains were multi-drug resistant (MDR). The antibiotics that most E. coli strains were resistant to was sulfamethoxazole (85.99%), followed by ampicillin (26.11%) and tetracycline (24.84%). We further detected 13 ARGs in the 157 E. coli strains, of which blaTEM had the highest occurrence (91.72%), followed by aac(3')-Iid (60.51%) and blaCTX-M (16.56%). Doxycycline, chloramphenicol, and ceftriaxone resistance were strongly correlated with the presence of tetB, floR and blaCTX-M, respectively. The strongest positive association among AMR phenotypes was ampicillin/cefuroxime sodium (OR, 828.000). The strongest positive association among 16 pairs of ARGs was sul1/floR (OR, 21.667). Nine pairs positive associations were observed between AMR phenotypes and corresponding resistance genes and the strongest association was observed for CHL/floR (OR, 301.167). Investigation of integrons revealed intl1 and intl2 genes were detected in 10.19% (16/157) and 1.27% (2/157) E. coli strains, respectively. Only one type of gene cassettes (drA17-aadA5) was detected in class 1 integron positive strains. Our data implied musk deer is a reservoir of ARGs and positive associations were common observed among E. coli strains carrying AMRs and ARGs.

Antimicrobial Resistant Coagulase-Negative Staphylococci Carried by House Flies (Musca domestica) Captured in Swine and Poultry Farms

House flies (Musca domestica) are very diffuse insects attracted by biological materials. They are abundantly present in farm environments and can frequently come in contact with animals, feed, manure, waste, surfaces, and fomites; consequently, these insects could be contaminated, carry, and disperse several microorganisms. The aim of this work was to evaluate the presence of antimicrobial-resistant staphylococci in house flies collected in poultry and swine farms. Thirty-five traps were placed in twenty-two farms; from each trap, 3 different kinds of samples were tested: attractant material present in the traps, the body surface of house flies and the body content of house flies. Staphylococci were detected in 72.72% of farms, 65.71% of traps and 43.81% of samples. Only coagulase-negative staphylococci (CoNS) were isolated, and 49 isolates were subjected to an antimicrobial susceptibility test. Most of the isolates were resistant to amikacin (65.31%), ampicillin (46.94%), rifampicin (44.90%), tetracycline (40.82%) and cefoxitin (40.82%). Minimum Inhibitory concentration assay allowed to confirm 11/49 (22.45%) staphylococci as methicillin-resistant; 4 of them (36.36%) carried the mecA gene. Furthermore, 53.06% of the isolates were classified as multidrug-resistant (MDR). Higher levels of resistance and multidrug resistance were detected in CoNS isolated from flies collected in poultry farms than in swine farms. Therefore, house flies could carry MDR and methicillin-resistant staphylococci, representing a possible source of infection for animals and humans.

House Flies (Musca domestica) from Swine and Poultry Farms Carrying Antimicrobial Resistant Enterobacteriaceae and Salmonella

The house fly (Musca domestica) is a very common insect, abundantly present in farm settings. These insects are attracted by organic substrates and can easily be contaminated by several pathogenic and nonpathogenic bacteria. The aim of this survey was to evaluate the presence of Salmonella spp. and other Enterobacteriaceae in house flies captured in small-medium size farms, located in Northwest Tuscany, Central Italy, and to evaluate their antimicrobial resistance; furthermore, isolates were tested for extended spectrum β-lactamase and carbapenems resistance, considering the importance these antimicrobials have in human therapy. A total of 35 traps were placed in seven poultry and 15 swine farms; three different kinds of samples were analyzed from each trap, representing attractant substrate, insect body surface, and insect whole bodies. Enterobacteriaceae were isolated from 86.36% of farms, 82.87% of traps, and 60.95% of samples; high levels of resistance were detected for ampicillin (61.25% of resistant isolates) and tetracycline (42.5% of resistant isolates). One extended spectrum β-lactamase producer strain was isolated, carrying the blaTEM-1 gene. Salmonella spp. was detected in 36.36% of farms, 25.71% of traps, and 15.24% of samples. Five different serovars were identified: Kentucky, Kisarawe, London, Napoli, and Rubislaw; some isolates were in R phase. Resistance was detected mainly for ampicillin (31.21%) and tetracycline (31.21%). House flies could represent a serious hazard for biosecurity plans at the farm level, carrying and sharing relevant pathogenic and antimicrobial resistant bacteria.

Understanding the role of insects in the acquisition and transmission of antibiotic resistance

Antibiotic resistance (AR) is a global healthcare threat that requires a comprehensive assessment. Poorly regulated antibiotic stewardship in clinical and non-clinical settings has led to a horizontal dissemination of AR. A variety of often neglected elements facilitate the circulation of AR from antibiotic sinks like concentrated animal feeding operations and healthcare settings to other environments that include healthy human communities. Insects are one of those elements that have received underwhelming attention as vectors of AR, despite their well-known role in transmitting clinically relevant pathogens. We here make an exhaustive attempt to highlight the role of insects as zoonotic reservoirs of AR by discussing the available literature and deriving realistic inferences. We review the AR associated with insects housing various human-relevant environments, namely, animal farm industry, edible-insects enterprise, healthcare institutes, human settlements, agriculture settings and the wild. We also provide evidence-based accounts of the events of the transmission of AR from insects to humans. We evaluate the clinical threats associated with insect-derived AR and propose the adoption of more sophisticated strategies to understand and mitigate future AR concerns facilitated by insects. Future works include a pan-region assessment of insects for AR in the form of AR bacteria (ARB) and AR determinants (ARDs) and the introduction of modern techniques like whole-genome sequencing, metagenomics, and in-silico modelling.

The Emergence of Colistin- and Imipenem-Associated Multidrug Resistance in Escherichia coli Isolates from Retail Meat

To determine the prevalence of Escherichia coli and their drug resistance profiles in fresh pork sold at two retail outlets (open-air market and closed retail stores) in Alice, South Africa. Retail meat samples (n = 176) collected from four shops (two from open-air markets and two from closed stores) were analyzed by conventional biochemical and PCR-based molecular confirmatory tests. The confirmed isolates were profiled for antimicrobial susceptibility to a panel of 12 commercial antibiotics: tetracycline, ampicillin, sulphamethoxazole trimethoprim, erythromycin, gentamycin, colistin sulphate, cefotaxime, chloramphenicol, norfloxacin, ciprofloxacin, cefuroxime, and imipenem. Colistin, ampicillin, and erythromycin resistance genes were profiled with the gene-specific primers. Multidrug resistance (MDR) and the association of imipenem and colistin in the MDR profile were determined. A total of 68 (39.08%) E. coli isolates were confirmed by PCR analysis. Resistance was most common to erythromycin (100%), followed by cefotaxime (95.58%), ampicillin (88.23%), cefuroxime (88.23%), trimethoprim-sulphamethoxazole (88.23%), and tetracycline (60.29%). Overall, 27/68 (39.70%) were MDR (≥ 3antibiotics classes). MDR E. coli isolates associated with imipenem resistance (50.00%) and colistin resistance (33.82%) were detected. The resistance genes were detected among the isolates though not in all the phenotypically resistant isolates. The detection of colistin resistance among MDR E. coli isolates from retail meat is troubling as the drug is a last resort antibiotic. Overall, the epidemiological implications of the findings are of public health importance.

Current status and future perspective of antimicrobial-resistant bacteria and resistance genes in animal-breeding environments

The emergence and spread of antimicrobial-resistant bacteria (ARB) and antimicrobial resistance genes (ARGs) are a global public health concern. ARB are transmitted directly or indirectly from animals to humans. The importance of environmental transmission of ARB and ARGs has recently been demonstrated, given the relationships between compost, livestock wastewater, insects, and wildlife. In addition, companion animals and their surrounding environments (veterinary hospitals and homes with companion animals) should be considered owing to their close relationship with humans. This review discusses the current status and future perspectives of ARB and ARGs in animal-breeding environments.

Models for Gut-Mediated Horizontal Gene Transfer by Bacterial Plasmid Conjugation

The emergence of new antimicrobial resistant and virulent bacterial strains may pose a threat to human and animal health. Bacterial plasmid conjugation is a significant contributor to rapid microbial evolutions that results in the emergence and spread of antimicrobial resistance (AR). The gut of animals is believed to be a potent reservoir for the spread of AR and virulence genes through the horizontal exchange of mobile genetic elements such as plasmids. The study of the plasmid transfer process in the complex gut environment is limited due to the confounding factors that affect colonization, persistence, and plasmid conjugation. Furthermore, study of plasmid transfer in the gut of humans is limited to observational studies, leading to the need to identify alternate models that provide insight into the factors regulating conjugation in the gut. This review discusses key studies on the current models for in silico, in vitro, and in vivo modeling of bacterial conjugation, and their ability to reflect the gut of animals. We particularly emphasize the use of computational and in vitro models that may approximate aspects of the gut, as well as animal models that represent in vivo conditions to a greater extent. Directions on future research studies in the field are provided.

Flies as Vectors and Potential Sentinels for Bacterial Pathogens and Antimicrobial Resistance: A Review

The unique biology of flies and their omnipresence in the environment of people and animals makes them ideal candidates to be important vectors of antimicrobial resistance genes. Consequently, there has been increasing research on the bacteria and antimicrobial resistance genes that are carried by flies and their role in the spread of resistance. In this review, we describe the current knowledge on the transmission of bacterial pathogens and antimicrobial resistance genes by flies, and the roles flies might play in the maintenance, transmission, and surveillance of antimicrobial resistance.

The role of Musca domestica and milk in transmitting pathogenic multidrug-resistant Escherichia coli and associated phylogroups to neonatal calves

Escherichia coli, as a global source of antimicrobial resistance, is a serious veterinary and public health concern. The transmission of pathogenic multidrug-resistant (MDR) E. coli within diarrheic calves and its correlation with Musca domestica and milk strains have been investigated. In total, 110, 80, and 26 E. coli strains were obtained from 70 rectal swabs from diarrheic calves, 60 milk samples and 20 M. domestica, respectively. Molecular pathotyping of E. coli revealed the presence of pathogenic E. coli with a higher percentage of shigatoxigenic strains within diarrheic calves and M. domestica at 46.4% and 34.6%, respectively. Phenotypic antimicrobial resistance revealed higher β-lactams resistance except for cefquinome that exhibited low resistance in M.domestica and milk strains at 30.8% and 30%, respectively. The extended-spectrum cephalosporin (ESC) resistant strains were detected within fecal, M. domestica, and milk strains at 69.1%, 73.1%, and 71.3%, respectively. All E. coli strains isolated from M. domestica exhibited MDR, while fecal and milk strains were harboring MDR at 99.1% and 85%, respectively. Molecular detection of resistant genes revealed the predominance of the bla_TEM gene, while none of these strains harbored the bla_OXA gene. The highest percentages for bla_CTXM and bla_CMYII genes were detected in M. domestica strains at 53.8% and 61.5%, respectively. Regarding colistin resistance, the mcr-1 gene was detected only in fecal and milk strains at 35.5% and 15%, respectively. A high frequency of phylogroup B2 was detected within fecal and M. domestica strains, while milk strains were mainly assigned to the B1 phylogroup. Pathogenic E. coli strains with the same phenotypic and genotypic antimicrobial resistance and phylogroups were identified for both diarrheic calves and M. domestica, suggesting that the possible role of M. domestica in disseminating pathogenic strains and antimicrobial resistance in dairy farms.

Transmission routes of antibiotic resistant bacteria: a systematic review

Background

Quantification of acquisition routes of antibiotic resistant bacteria (ARB) is pivotal for understanding transmission dynamics and designing cost-effective interventions. Different methods have been used to quantify the importance of transmission routes, such as relative risks, odds ratios (OR), genomic comparisons and basic reproduction numbers. We systematically reviewed reported estimates on acquisition routes’ contributions of ARB in humans, animals, water and the environment and assessed the methods used to quantify the importance of transmission routes.

Methods

PubMed and EMBASE were searched, resulting in 6054 articles published up until January 1st, 2019. Full text screening was performed on 525 articles and 277 are included.

Results

We extracted 718 estimates with S. aureus (n = 273), E. coli (n = 157) and Enterobacteriaceae (n = 99) being studied most frequently. Most estimates were derived from statistical methods (n = 560), mainly expressed as risks (n = 246) and ORs (n = 239), followed by genetic comparisons (n = 85), modelling (n = 62) and dosage of ARB ingested (n = 17). Transmission routes analysed most frequently were occupational exposure (n = 157), travelling (n = 110) and contacts with carriers (n = 83). Studies were mostly performed in the United States (n = 142), the Netherlands (n = 87) and Germany (n = 60). Comparison of methods was not possible as studies using different methods to estimate the same route were lacking. Due to study heterogeneity not all estimates by the same method could be pooled.

Conclusion

Despite an abundance of published data the relative importance of transmission routes of ARB has not been accurately quantified. Links between exposure and acquisition are often present, but the frequency of exposure is missing, which disables estimation of transmission routes’ importance. To create effective policies reducing ARB, estimates of transmission should be weighed by the frequency of exposure occurrence.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07360-z.

Risk factors for third-generation cephalosporin-resistant and extended-spectrum β-lactamase-producing Escherichia coli carriage in domestic animals of semirural parishes east of Quito, Ecuador

Extended-spectrum β-lactamase (ESBL)-producing and other antimicrobial resistant (AR) Escherichia coli threaten human and animal health worldwide. This study examined risk factors for domestic animal colonization with ceftriaxone-resistant (CR) and ESBL-producing E. coli in semirural parishes east of Quito, Ecuador, where small-scale food animal production is common. Survey data regarding household characteristics, animal care, and antimicrobial use were collected from 304 households over three sampling cycles, and 1195 environmental animal fecal samples were assessed for E. coli presence and antimicrobial susceptibility. Multivariable regression analyses were used to assess potential risk factors for CR and ESBL-producing E. coli carriage. Overall, CR and ESBL-producing E. coli were detected in 56% and 10% of all fecal samples, respectively. The odds of CR E. coli carriage were greater among dogs at households that lived within a 5 km radius of more than 5 commercial food animal facilities (OR 1.72, 95% CI 1.15-2.58) and lower among dogs living at households that used antimicrobials for their animal(s) based on veterinary/pharmacy recommendation (OR 0.18, 95% CI 0.04-0.96). Increased odds of canine ESBL-producing E. coli carriage were associated with recent antimicrobial use in any household animal (OR 2.69, 95% CI 1.02-7.10) and purchase of antimicrobials from pet food stores (OR 6.83, 95% CI 1.32-35.35). Food animals at households that owned more than 3 species (OR 0.64, 95% CI 0.42-0.97), that used antimicrobials for growth promotion (OR 0.41, 95% CI 0.19-0.89), and that obtained antimicrobials from pet food stores (OR 0.47, 95% CI 0.25-0.89) had decreased odds of CR E. coli carriage, while food animals at households with more than 5 people (OR 2.22, 95% CI 1.23-3.99) and located within 1 km of a commercial food animal facility (OR 2.57, 95% CI 1.08-6.12) had increased odds of ESBL-producing E. coli carriage. Together, these results highlight the complexity of antimicrobial resistance among domestic animals in this setting.

First Report of Extended-Spectrum β-Lactamase (blaCTX-M1) and Colistin Resistance Gene mcr-1 in E. coli of Lineage ST648 from Cockroaches in Tunisia

The emergence of multidrug-resistant bacteria has become a major problem. Cockroaches may play an important role in the spread of those bacteria between the environment and humans. This study was designed to screen extended-spectrum β-lactamase (ESBL)-producing and colistin-resistant strains and to investigate the molecular support of multidrug-resistant Enterobacteriaceae in the external surface and gut homogenates of cockroaches collected from different locations in Tunisia. Between July 2017 and June 2018, 144 Enterobacteriaceae samples were isolated from 115 trapped cockroaches (collective catering, houses, and a hospital). Antibiotic susceptibility testing was performed using the disk diffusion method. Extended-spectrum β-lactamase-encoding genes and the mcr-1 gene were investigated by real-time PCR (RT-PCR) and standard PCR. The genetic relationship among isolates was studied with the help of multilocus sequence type (MLST) analysis. Of the 144 Enterobacteriaceae isolates, 22 strains exhibited a positive ESBL-screening test (73.3%), including 17 Escherichia coli isolates and 5 Klebsiella pneumoniae isolates. Among them, 9 Escherichia coli isolates were resistant to colistin, with an MIC ranging from 8 to16 μg/L, all of which harbored the mcr-1 gene. Eight bla_CTX-M-15 genes were detected; two among them were associated with bla_TEM-117 and bla_TEM-128, and seven bla_CTX-M-1 genes were detected that also harbored the mcr-1 gene. Genotyping analysis revealed 7 different sequence types already described in humans and animals. We report the first survey of mcr-1 in ESBL-producing E. coli isolates from cockroaches. Our findings highlight cockroaches as a source of nosocomial infections, and they are a reservoir of colistin-resistant E. coli, which is a carrier of other additional risk genes such as bla_ESBL, especially in hospitals.

IMPORTANCE Multidrug resistance in Enterobacteriaceae has become a major concern worldwide that is increasingly observed in human, animals, and also cockroaches. In our study, we found that cockroaches may play an important role as a potential vector of multidrug-resistant Enterobacteriaceae in the hospital environment and collective catering. Our study describes the first survey of mcr-1 in ESBL-producing E. coli isolates from hospital cockroaches. Our results further highlight the possibility that mcr-1 may enter humans via cockroach contamination and thereby threaten public health. Our results show that these cockroaches are an important reservoir of colistin-resistant E. coli and carriers of other additional risk genes such as bla_ESBL, hence the importance of strengthening prevention strategies and of strictly respecting hygiene measures in order to control their distribution and spread in Tunisia.

Characterization of Escherichia coli from Edible Insect Species: Detection of Shiga Toxin-Producing Isolate

Insects as novel foods are gaining popularity in Europe. Regulation (EU) 2015/2283 laid the framework for the application process to market food insects in member states, but potential hazards are still being evaluated. The aim of this study was to investigate samples of edible insect species for the presence of antimicrobial-resistant and Shiga toxin-producing Escherichia coli (STEC). Twenty-one E. coli isolates, recovered from samples of five different edible insect species, were subjected to antimicrobial susceptibility testing, PCR-based phylotyping, and macrorestriction analysis. The presence of genes associated with antimicrobial resistance or virulence, including stx1, stx2, and eae, was investigated by PCR. All isolates were subjected to genome sequencing, multilocus sequence typing, and serotype prediction. The isolates belonged either to phylogenetic group A, comprising mostly commensal E. coli, or group B1. One O178:H7 isolate, recovered from a Zophobas atratus sample, was identified as a STEC. A single isolate was resistant to tetracyclines and carried the tet(B) gene. Overall, this study shows that STEC can be present in edible insects, representing a potential health hazard. In contrast, the low resistance rate among the isolates indicates a low risk for the transmission of antimicrobial-resistant E. coli to consumers.

Role played by the environment in the emergence and spread of antimicrobial resistance (AMR) through the food chain

The role of food-producing environments in the emergence and spread of antimicrobial resistance (AMR) in EU plant-based food production, terrestrial animals (poultry, cattle and pigs) and aquaculture was assessed. Among the various sources and transmission routes identified, fertilisers of faecal origin, irrigation and surface water for plant-based food and water for aquaculture were considered of major importance. For terrestrial animal production, potential sources consist of feed, humans, water, air/dust, soil, wildlife, rodents, arthropods and equipment. Among those, evidence was found for introduction with feed and humans, for the other sources, the importance could not be assessed. Several ARB of highest priority for public health, such as carbapenem or extended-spectrum cephalosporin and/or fluoroquinolone-resistant Enterobacterales (including Salmonella enterica), fluoroquinolone-resistant Campylobacter spp., methicillin-resistant Staphylococcus aureus and glycopeptide-resistant Enterococcus faecium and E. faecalis were identified. Among highest priority ARGs bla CTX -M, bla VIM, bla NDM, bla OXA -48-like, bla OXA -23, mcr, armA, vanA, cfr and optrA were reported. These highest priority bacteria and genes were identified in different sources, at primary and post-harvest level, particularly faeces/manure, soil and water. For all sectors, reducing the occurrence of faecal microbial contamination of fertilisers, water, feed and the production environment and minimising persistence/recycling of ARB within animal production facilities is a priority. Proper implementation of good hygiene practices, biosecurity and food safety management systems is very important. Potential AMR-specific interventions are in the early stages of development. Many data gaps relating to sources and relevance of transmission routes, diversity of ARB and ARGs, effectiveness of mitigation measures were identified. Representative epidemiological and attribution studies on AMR and its effective control in food production environments at EU level, linked to One Health and environmental initiatives, are urgently required.

Insects, Rodents, and Pets as Reservoirs, Vectors, and Sentinels of Antimicrobial Resistance

This paper reviews the occurrence of antimicrobial resistance (AMR) in insects, rodents, and pets. Insects (e.g., houseflies, cockroaches), rodents (rats, mice), and pets (dogs, cats) act as reservoirs of AMR for first-line and last-resort antimicrobial agents. AMR proliferates in insects, rodents, and pets, and their skin and gut systems. Subsequently, insects, rodents, and pets act as vectors that disseminate AMR to humans via direct contact, human food contamination, and horizontal gene transfer. Thus, insects, rodents, and pets might act as sentinels or bioindicators of AMR. Human health risks are discussed, including those unique to low-income countries. Current evidence on human health risks is largely inferential and based on qualitative data, but comprehensive statistics based on quantitative microbial risk assessment (QMRA) are still lacking. Hence, tracing human health risks of AMR to insects, rodents, and pets, remains a challenge. To safeguard human health, mitigation measures are proposed, based on the one-health approach. Future research should include human health risk analysis using QMRA, and the application of in-silico techniques, genomics, network analysis, and ’big data’ analytical tools to understand the role of household insects, rodents, and pets in the persistence, circulation, and health risks of AMR.

Posttreatment temperature influences toxicity of insect growth regulators in Musca domestica

Musca domestica is one of the major cosmopolitan pests in livestock facilities because it can be both a nuisance and a vector of pathogens to animals. Currently, treatment of animal manure with insect growth regulator (IGR) insecticides is among major practices to control M. domestica throughout the year over wide-ranging environmental temperatures. Fluctuation in daily or seasonal temperature is one of the most established factors impacting toxicity of insecticides against insect pests. In this study, the effect of posttreatment temperature (range, 20-36 °C) on the toxicity of eight IGRs: five chitin synthesis inhibitors (cyromazine, diflubenzuron, lufenuron, novaluron, triflumuron), two juvenile hormone analogs (methoprene, pyriproxyfen), and one ecdysone agonist (methoxyfenozide), was investigated against M. domestica. The toxicity of lufenuron and novaluron increased by 1.78 times over the range of 20-28 °C, and 2.25 and 1.83 times, respectively, over the range of 28-36 °C, with an overall increase by 4.00 and 3.26 times, respectively (i.e., positive temperature coefficient). In contrast, the toxicity of diflubenzuron, pyriproxyfen, and triflumuron decreased by 1.43, 1.89, and 2.10 times, respectively, over the range of 20-28 °C, and 1.70, 2.00, and 1.95 times, respectively, over the range of 28-36 °C, with an overall decrease by 2.43, 3.78, and 4.10 times, respectively. The toxicity of cyromazine, methoprene, and methoxyfenozide did not change significantly. Overall, these data will help stakeholders to choose appropriate insecticides for M. domestica control depending on the prevailing environmental temperature and to avoid misuse of insecticides that ultimately lead to environmental safety.

The Stable Fly (Stomoxys calcitrans) as a Possible Vector Transmitting Pathogens in Austrian Pig Farms

This pilot study aimed to investigate stable flies from Austrian pig farms for the presence of defined swine pathogens, such as porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus 2 (PCV2), hemotrophic mycoplasmas in ingested blood and/or body parts and bacteria on the surface of the flies. Furthermore, the use of stable flies as a diagnostic matrix for the detection of pathogens in the ingested pig blood should be investigated. In total, 69 different microorganisms could be found on the surface of tested S. calcitrans from 20 different pig farms. Escherichia coli was the most common bacterium and could be found on flies from seven farms. In seven farms, hemotrophic mycoplasmas were detected in stable flies. PRRSV could not be found in any of the samples of these 20 farms but PCV2 was detected in six farms. Whether the stable fly can be used as a matrix to monitor the health status cannot be accurately determined through this study, especially in regard to PRRSV. Nevertheless, it might be possible to use the stable fly as diagnostic material for defined pathogens like Mycoplasma suis and PCV2.

Feeding Response to Select Monosaccharides, Sugar Alcohols, and Artificial Sweeteners Relative to Sucrose in Adult House Flies, Musca domestica (Diptera: Muscidae)

Use of insecticidal baits risks the evolution of resistance to the feeding stimulant in the bait, not just to the active ingredient (toxicant). Sucrose-based baits are widely used against house flies, Musca domestica L. The baits are applied as dry granules, but readily liquefy. The proboscis extension reflex (PER) and consumption of alternative sweeteners, dry or in solution, were examined. Fructose, glucose, and xylitol merit further study as alternatives to sucrose. Dry, fructose, glucose, and xylitol elicited PER much more than sucrose, although not when in solution. Furthermore, dry or in solution, females and males ate as much or more fructose as sucrose. In solution, flies ate as much glucose as sucrose; although when dry, consumption was much less for glucose than sucrose. Dry, xylitol elicited as much consumption as sucrose for females, though less for males. In solution, for both sexes, xylitol elicited less consumption than sucrose did. Acesulfame potassium, sodium cyclamate, and sucralose do not look promising as they did not often elicit PER, whether dry or in solution. Erythritol also does not look promising. Erythritol elicited PER no more than sucrose did when dry and elicited PER much less than sucrose when in solution. Flies ate much less erythritol than sucrose whether dry or in solution.

Larvicidal potential of the polyol sweeteners erythritol and xylitol in two filth fly species

The house fly, Musca domestica (L.) (Diptera: Muscidae), and the stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), are two filth flies responsible for significant economic losses in animal production. Although some chemical control products target adults of both species, differences in mouthpart morphology and behavior necessitates distinct modalities for each. For these reasons, larvicides are an attractive means of chemical control. We assessed the potential of the polyol sweeteners erythritol and xylitol as larvicides to the house fly and stable fly. LC₅₀ values of erythritol against 2^nd instar larvae were 34.94 mg/g media (house fly) and 22.10 mg/g media (stable fly). For xylitol, LC₅₀ values were 74.91 mg/g media (house fly) and 41.58 mg/g media (stable fly). When given a choice, neither species showed a preference for ovipositing in media treated with either sweetener at various concentrations or in media without sweetener. Significantly lower development from egg to adult was observed when the 2^nd instar LC₅₀ equivalent of each sweetener was present in the media compared to controls. Erythritol and xylitol both have larvicidal qualities, however their effective concentrations would necessitate creative product formulation and deployment methods to control all stages of developing flies.