Vancomycin-resistance phenotypes, vancomycin-resistance genes, and resistance to antibiotics of enterococci isolated from food of animal origin

Antibiotic resistance spectrums of Escherichia coli and Enterococcus spp. strains against commonly used antimicrobials from commercial meat-rabbit farms in Chengdu City, Southwest China

Antimicrobial resistance (AMR) is commonly associated with the inappropriate use of antibiotics during meat-rabbit production, posing unpredictable risks to rabbit welfare and public health. However, there is limited research on the epidemiological dynamics of antibiotic resistance among bacteria indicators derived from local healthy meat-rabbits. To bridge the knowledge gap between antibiotic use and AMR distribution, a total of 75 Escherichia coli (E. coli) and 210 Enterococcus spp. strains were successfully recovered from fecal samples of healthy meat-rabbits. The results revealed that diverse AMR phenotypes against seven commonly used antimicrobials, including ampicillin (AMP), amoxicillin-clavulanic acid (A/C), doxycycline (DOX), enrofloxacin (ENR), florfenicol (FFC), gentamicin (GEN), and polymycin B (PMB), were observed among most strains of E. coli and Enterococcus spp. in two rabbit farms, although the distribution pattern of antibiotic resistance between young and adult rabbits was similar. Among them, 66 E. coli strains showed resistance against 6 antimicrobials except for PMB. However, 164 Enterococcus spp. strains only exhibited acquired resistance against DOX and GEN. Notably, the DOX-based AMR phenotypes for E. coli and Enterococcus spp. strains were predominant, indicating the existing environmental stress conferred by DOX exposure. The MICs tests suggested elevated level of antibiotic resistance for resistant bacteria. Unexpectedly, all GEN-resistant Enterococcus spp. strains resistant high-level gentamicin (HLGR). By comparison, the blaTEM, tetA, qnrS and floR were highly detected among 35 multi-resistant E. coli strains, and aac[6']-Ie-aph[2']-Ia genes widely spread among the 40 double-resistant Enterococcus spp. strains. Nevertheless, the presence of ARGs were not concordant with the resistant phenotypes for a portion of resistant bacteria. In conclusion, the distribution of AMR and ARGs are prevalent in healthy meat-rabbits, and the therapeutic antimicrobials use in farming practice may promote the antibiotic resistance transmission among indicator bacteria. Therefore, periodic surveillance of antibiotic resistance in geographic locations and supervisory measures for rational antibiotic use are imperative strategies for combating the rising threats posed by antibiotic resistance, as well as maintaining rabbit welfare and public health.

Molecular detection and occurrence of vancomycin resistance genes (van A, B, C1, C2/C3) among Enterococcus species isolated from farm ostriches

BACKGROUND

Evaluating the prevalence of vancomycin resistance genes (van genes) in enterococcal isolates from food-producing animals is an important public health issue because of the possibility of resistance genes spread to human.

OBJECTIVES

The present study aimed to determine the occurrence of vancomycin resistance genes among Enterococcus species obtained from ostrich faecal samples.

METHODS

One hundred and twenty-five faecal samples of apparently healthy ostriches from five different farms were investigated. Genes encoding vancomycin resistance were studied by multiplex-PCR, and susceptibility to six antibiotics was evaluated by disk-diffusion method.

RESULTS

In total, 107 Enterococcus spp. isolates were obtained and confirmed by biochemical and molecular tests. Enterococcus faecium was the prevailing species (56 isolates of 107; 52.3%), followed by E. hirae (24 isolates; 22.4%) and E. gallinarum (12 isolates; 11.2%). Of the 107 recovered isolates, 44% harboured at least a type of van genes. vanA, vanC2/3 and vanC1 were identified in 34 (31.7%), 13 isolates (12.1%) and 4 (3.7%) isolates respectively. Additionally, four isolates (E. gallinarum, E. rafinosus) co-harboured the the vanA and vanC1 or vanA and vanC2/3. Enterococcus faecium and Enterococcus hirae strains with the vanA genotype were the most frequent van-carrying enterococci from ostrich faecal samples. Among van-carrying enterococcal isolates, 23.4% were phenotypically resistant to vancomycin. This study revealed a relatively high prevalence (44%) of van-carrying enterococci in ostrich faecal samples.

CONCLUSIONS

Results of the present study suggest that ostrich faeces could be considered as a reservoir of vancomycin resistance genes, especially vanA containing enterococci that could be potentially transferred to human through the food chain.

Methicillin- and Vancomycin-Resistant Staphylococcus aureus and Vancomycin-Resistant Enterococci Isolated from Hospital Foods: Prevalence and Antimicrobial Resistance Patterns

This study aimed to investigate the prevalence of Methicillin- and Vancomycin-Resistant Staphylococcus aureus (MRSA, VRSA) and Vancomycin-Resistant Enterococcus (VRE) of hospital food samples in Mashhad, Iran. A total of 357 hospital food samples were collected from 13 hospitals. Enterococcus spp. and Staphylococcus aureus were identified using conventional cultural techniques following genotypic confirmation by PCR. The antibiotic resistance patterns of MRSA, VRSA, and VRE strains were analyzed using the disk diffusion methods. The prevalence of S. aureus and MRSA were 24.37% (87/357) and 22.98% (20.87), respectively. In addition, the vanB gene involved in vancomycin resistance was detected in 1.14% of the S. aureus strains. Enterococci and VRE had a prevalence of 15.4% (55/357) and 21.81% (12/55), respectively. Meat, chicken barbecues, and salad were the most commonly contaminated samples with S. aureus, MRSA, Enterococci, and VRE. PCR detected two vancomycin resistance genes, including vanA (1.81%, 1.55) and vanC2 (20%, 11.55) genes. MRSA strains revealed the highest resistance against penicillin, erythromycin, clindamycin, azithromycin, tetracycline, and gentamicin. The VRSA isolates were resistant to penicillin, ampicillin, oxacillin, cefoxitin, clindamycin, erythromycin, gentamicin, and trimethoprim-sulfamethoxazole. Furthermore, VRE isolates exhibited the highest resistance against quinupristin-dalfopristin, erythromycin, and tetracycline. The results of this study indicated that hospital foods might act as a reservoir of Enterococci spp. and S. aureus strains, which can transfer antibiotic resistance. Moreover, multidrug resistance (MDR) in some MRSA, VRSA, and VRE isolates represents a serious threat to susceptible persons in hospitals.

Electrospun Nanofiber Films Suppress Inflammation In Vitro and Eradicate Endodontic Bacterial Infection in an E. faecalis-Infected Ex Vivo Human Tooth Culture Model

Treatment failure of endodontic infections and their concurrent inflammations is commonly associated with microbial persistence and reinfection, also stemming from the anatomical restrictions of the root canal system. Aiming to address the shortcomings of current treatment options, a fast-disintegrating nanofibrous film was developed for the intracanal coadministration of an antimicrobial (ZnO nanoparticles) and an anti-inflammatory (ketoprofen) agent. The electrospun films were fabricated based on polymers that dissolve rapidly to constitute the actives readily available at the site of action, aiming to eliminate both microbial infection and inflammation. The anti-inflammatory potency of the nanofiber films was assessed in an in vitro model of lipopolysaccharide (LPS)-stimulated RAW 264.7 cells after confirming their biocompatibility in the same cell line. The nanofiber films were found effective against Enterococcus faecalis, one of the most prominent pathogens inside the root canal space, both in vitro and ex vivo using a human tooth model experimentally infected with E. faecalis. The physical properties and antibacterial and anti-inflammatory potency of the proposed electrospun nanofiber films constitute a promising therapeutic module in the endodontic therapy of nonvital infected teeth. All manuscripts must be accompanied by an abstract. The abstract should briefly state the problem or purpose of the research, indicate the theoretical or experimental plan used, summarize the principal findings, and point out major conclusions.

Genomic Analysis of Multidrug-Resistant Enterococcus faecium Harboring vanA Gene from Wastewater Treatment Plants

The emergence of vancomycin-resistant Enterococcus faecium (Efm) harboring vanA gene and multidrug-resistant determinants is a relevant public health concern. It is an opportunistic pathogen responsible for nosocomial infections widely distributed in the environment, including wastewater treatment plants (WWTPs). Our study addresses a genomic investigation of vanA-carrying Efm from WWTPs in Brazil. Samples from five WWTPs supplied with sewage from different sources were evaluated. Here we present whole-genome sequencing of eight vanA-Efm isolates performed on Illumina MiSeq platform. All these isolates presented multidrug-resistant profile, and five strains were from treated wastewater. Multiple antimicrobial resistance genes (ARGs) were found, such as aph(3')-IIIa, ant(6')-Ia, erm(B), and msrC, some of them being allocated in plasmids. The virulence profile was predominantly constituted by efaAfm and acm genes and all isolates, except for one, were predicted as human pathogens. Multilocus sequence typing analysis revealed a new allele and five different STs, three previously described (ST32, ST168, and ST253) and two novel ones (ST1893 and ST1894). Six strains belonged to CC17, often associated with hospital outbreaks. As far as our knowledge, no genomic studies of vanA-Efm recovered from WWTPs revealed isolates belonging to CC17 in Brazil. Therefore, our findings point to the environmental spread of Efm carrying multiple ARGs.

Genotyping of enterotoxigenic methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Staphylococcus aureus (VRSA) among commensal rodents in North Sinai, Egypt

AIM

This study aimed to identify genotype enterotoxigenic antimicrobial-resistant Staphylococcus aureus species, mainly methicillin-resistant S. aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) among commensal rodents.

METHODS AND RESULTS

A total of 280 samples were collected from nasal and mouth swabs, heart blood, intestinal content, and lung tissues of 56 commensal rodents trapped from North Sinai, Egypt. Antimicrobial susceptibility testing was performed to bacteriologically identified S. aureus isolates against 15 antimicrobial agents by disc diffusion method. Detection was conducted for identifying coagulase gene (coA), antimicrobial-resistant genes (mecA and vanA/B), enterotoxigenic, and virulence determinant genes (hlg, seb, sed, and see) among the MRSA and VRSA isolates.

RESULTS

S. aureus species were isolated from 24 (42.86%) out of 56 rodents. Phenotypic examination revealed that all the isolates were multidrug-resistant, whereas two isolates were multiple antibiotic resistant (MAR). Out of 33 examined isolates, 33 (100%) were resistant to oxacillin and amoxicillin, 31 (93.93%) to cefoxitin, and 12 (36.36%) to vancomycin. PCR assay revealed that 24 isolates revealed (100%) positivity to coA gene, 17 (70.83%) to mecA gene, and 12 (50%) to vanA/B genes. Enterotoxin genes and hemolysin genes were detected among MRSA and VRSA isolates. There was a strong positive correlation between the tested antimicrobial-resistant genes and virulence genes (P>0.05).

CONCLUSIONS

This study demonstrated the occurrence of MRSA and VRSA strains among commensal rodents in North Sinai, Egypt. The detection of enterotoxigenic and virulence genes of the isolated MRSA and VRSA strains indicated the health hazards of food contamination and zoonotic infections.

SIGNIFICANCE AND IMPACTS OF THE STUDY

This study emphasizes the role of commensal rodents in maintaining and disseminating multidrug-resistant MRSA and VRSA strains to the environment, animals, and human beings.

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.

Evaluation of commercial veterinary probiotics containing enterococci for transferrable vancomycin resistance genes

Objective

Vancomycin resistant enterococci (VRE) are of significant public health concern. The identification of VRE in livestock and food has increased. The objective of this study was to determine if the transferrable vancomycin resistance genes vanA and vanB were present in probiotics marketed for use in animals that claimed to contain Enterococcus spp.

Results

Of the 40 products selected, Enterococcus spp. DNA was successfully extracted from 36 products. Of these 36 products with enterococcal DNA, 2 (6%) had a PCR product consistent with vanA which was confirmed by sequencing. None of the products appeared to contain vanB.

Antimicrobial resistance genes in bacteria from animal-based foods

Antimicrobial resistance is a worldwide public health threat. Farm animals are important sources of bacteria containing antimicrobial resistance genes (ARGs). Although the use of antimicrobials in aquaculture and livestock has been reduced in several countries, these compounds are still routinely applied in animal production, and contribute to ARGs emergence and spread among bacteria. ARGs are transmitted to humans mainly through the consumption of products of animal origin (PAO). Bacteria can present intrinsic resistance, and once antimicrobials are administered, this resistance may be selected and multiply. The exchange of genetic material is another mechanism used by bacteria to acquire resistance. Some of the main ARGs found in bacteria present in PAO are the bla, mcr-1, cfr and tet genes, which are directly associated to antibiotic resistance in the human clinic.

Surveillance of Enterococcus spp. reveals distinct species and antimicrobial resistance diversity across a One-Health continuum

For a One-Health investigation of antimicrobial resistance (AMR) in Enterococcus spp., isolates from humans and beef cattle along with abattoirs, manured fields, natural streams, and wastewater from both urban and cattle feedlot sources were collected over two years. Species identification of Enterococcus revealed distinct associations across the continuum. Of the 8430 isolates collected, Enterococcus faecium and Enterococcus faecalis were the main species in urban wastewater (90%) and clinical human isolates (99%); Enterococcus hirae predominated in cattle (92%) and feedlot catch-basins (60%), whereas natural streams harbored environmental Enterococcus spp. Whole-genome sequencing of E. faecalis (n = 366 isolates) and E. faecium (n = 342 isolates), revealed source clustering of isolates, indicative of distinct adaptation to their respective environments. Phenotypic resistance to tetracyclines and macrolides encoded by tet(M) and erm(B) respectively, was prevalent among Enterococcus spp. regardless of source. For E. faecium from cattle, resistance to β-lactams and quinolones was observed among 3% and 8% of isolates respectively, compared to 76% and 70% of human clinical isolates. Clinical vancomycin-resistant E. faecium exhibited high rates of multi-drug resistance, with resistance to all β-lactam, macrolides, and quinolones tested. Differences in the AMR profiles among isolates reflected antimicrobial use practices in each sector of the One-Health continuum.

Identification of antimicrobial resistant bacteria from plant-based food products imported into Canada

The role of plant-based foods in the epidemiology of antimicrobial resistance has been inadequately studied. In this investigation, resistant organisms from vegetables, fruits and spices imported into Canada were identified and characterized. A total of 143 products imported from primarily Asian and African countries were purchased from international markets in Saskatoon, Saskatchewan. Samples were selectively cultured for bacterial species where resistance is known to be emerging. The proportions of samples positive for each organism were as follows: E. coli (n = 13, 9.1%), Salmonella spp. (n = 2, 1.4%), ESBL producing Enterobacter spp. (n = 2, 1.4%) and K. pneumoniae (n = 2, 1.4%), S. aureus (n = 7, 4.9%) and Enterococcus spp. (n = 66, 46.2%). Antimicrobial minimum inhibitory concentrations were determined by broth micro-dilution and agar-dilution. Based on the susceptibility of each organism, isolates were screened for resistance genes (β-lactamases and plasmid mediated quinolones resistance determinants) by PCR. Extended-spectrum β-lactamase producing Enterobacteriaceae and methicillin resistant S. aureus (MRSA) were identified from 6/143 (4.2%) and 2/143 (1.4%) of samples respectively. The qnrB, qnrS and aac(6')-Ib-cr plasmid mediated quinolone resistance determinants were identified in 2/143 (1.4%) of samples tested. None of the Enterobacteriaceae isolates were resistant to meropenem or colistin. Similarly, all Enterococcus isolates remained susceptible to ampicillin, penicillin and vancomycin. Finding multi-drug resistant bacteria which are frequently isolated from human infections is concerning, although the contribution of the global food trade to the dissemination of resistance remains cryptic. These results suggest that imported plant-based foods may be an underappreciated source of clinically relevant resistant organisms. Further study is required to address these gaps in our understanding of the epidemiology of resistance, and the magnitude of the risk posed to human health by these organisms.

Antimicrobial Resistance in Bacterial Pathogens and Detection of Carbapenemases in Klebsiella pneumoniae Isolates from Hospital Wastewater

During a six-month period (October 2017–March 2018), the prevalence and susceptibility of important pathogenic bacteria isolated from 12 hospital raw sewage samples in North Western Greece was investigated. The samples were analyzed for methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), extended-spectrum beta-lactamase (ESBL) producing Escherichia coli, carbapenemase-producing Klebsiella pneumoniae (CKP), and multidrug-resistant Pseudomonas aeruginosa. Antimicrobial susceptibility testing was performed using the agar diffusion method according to the recommendations of the Clinical and Laboratory Standards Institute. The diversity of carbapenemases harboring K. pneumoniae was examined by two phenotyping screening methods (modified Hodge test and combined disk test), a new immunochromatographic rapid assay (RESIST-4 O.K.N.V.) and a polymerase chain reaction (PCR). The results demonstrated the prevalence of MRSA, vancomycin-resistant Staphylococcus aureus (VRSA), VRE, and CKP in the examined hospital raw sewage samples. In addition, the aforementioned methods which are currently used in clinical laboratories for the rapid identification and detection of resistant bacteria and genes, performed sufficiently to provide reliable results in terms of accuracy and efficiency.

Horizontal transfer of vanA between probiotic Enterococcus faecium and Enterococcus faecalis in fermented soybean meal and in digestive tract of growing pigs

Background

The aim of this study was to investigate the intergeneric transfer of vancomycin resistance gene vanA between probiotic enterococci in the fermentation progress of soybean meal and in the digestive tract of growing pigs. One vanA genotype vancomycin resistant E. faecium strain, Efm4, and one chloramphenicol-resistant E. faecalis strain, Efs2, were isolated from twenty-nine probiotic basis feed material / additive samples. For in vitro conjugation, Efm4 and Efs2 were used as starter to ferment soybean meal. For in vivo conjugation, thirty growing pigs were randomly assigned to five groups (n = 6), treated with a basic diet, or supplemented with 10% fermented soybean meal, 1% Efm4, 5% Efs2 or a combination of 1% Efm4 + 5% Efs2 for 7 d, respectively. Fecal samples of pigs in each group were collected daily for the isolation and dynamic analysis of Efm4, Efs2 and transconjugants. The sequence types (STs) of Efm4, Efs2 and transconjugants were analyzed by multilocus sequence typing (MLST). The vanA harboring plasmid in Efm4 and transconjugants was analyzed by S1-pulsed field gel electrophoresis (PFGE) and further verified by multiple alignments.

Results

The results showed that, in FSBM, transconjugants were detected 1 h after the fermentation, with a conjugation frequency of ~ 10^- 3 transconjugants / recipient. Transconjugants proliferated with Efm4 and Efs2 in the first 8 h and maintained steadily for 10 d till the end of the experiment. Additionally, in vivo experiment showed that transcojugants were recovered in one of six pigs in both FSBM and Efm4 + Efs2 groups, with conjugation frequency of ~ 10^- 5 and ~ 10^- 4, respectively. MLST revealed the ST of Efm4, Efs2 and transconjugants was ST1014, ST69 and ST69, respectively. S1-PFGE confirmed the existence of the vanA-harboring, 142,988-bp plasmid, which was also a multi-drug resistant plasmid containing Tn1546-like transposon.

Conclusions

The findings revealed the potential safety hazard existing in the commercial probiotic enterococci in China, because the horizontal transfer from farm to fork could potentially pose a safety risk to the public.

Antimicrobial Resistance and Biofilm Formation in Enterococcus spp. Isolated from Humans and Turkeys in Poland

Enterococci are a natural component of the intestinal flora of many organisms, including humans and birds. As opportunistic pathogens, they can cause fatal infections of the urinary tract and endocarditis in humans, whereas in poultry symptoms are joint disease, sepsis, and falls in the first week of life. The study covered 107 Enterococcus strains—56 isolated from humans and 51 from turkeys. Among the isolates investigated Enterococcus faecalis was detected in 80.36% of human and 80.39% of turkey samples. Enterococcus faecium was identified in 8.93% of human and 17.65% of turkey strains. The highest percentage of the strains was resistant to tetracycline as follows: 48 (85.71%) and 48 (94.12%) of human and turkey strains, respectively. Resistance to erythromycin occurred in 37.50% of the human and in 76.47% of turkey strains, otherwise 27.10% of all strains showed resistance to ciprofloxacin. Our study revealed that 25% of human and 15.69% of turkey strains were resistant to vancomycin. Multidrug resistance showed in 32.14% and 43.14% of human and turkey strains, respectively. The tetracycline resistance gene, tetM, was detected in 82.24% of all strains analyzed, whereas the tetO gene was found in 53.57% of human but only in 7.84% of turkey strains. The vancomycin resistance gene (vanA) was detected in seven Enterococcus strains (six isolated from turkeys and one from humans). The ermB gene (resistance to macrolide) was detected in 55.14% of all isolates (42.86% of human and 68.63% of turkey strains), whereas the ermA gene was detected in 17.65% of turkey but only in 3.57% of human isolates. All the strains had the ability to form biofilms. A stronger biofilm was formed after 24-hour incubation by strains isolated from turkeys, whereas after 48 hours of incubation all examined strains produced strong biofilm.

Antimicrobial Resistance in Enterococcus spp. of animal origin

Enterococci are natural inhabitants of the intestinal tract in humans and many animals, including food-producing and companion animals. They can easily contaminate the food and the environment, entering the food chain. Moreover, Enterococcus is an important opportunistic pathogen, especially the species E. faecalis and E. faecium, causing a wide variety of infections. This microorganism not only contains intrinsic resistance mechanisms to several antimicrobial agents, but also has the capacity to acquire new mechanisms of antimicrobial resistance. In this review we analyze the diversity of enterococcal species and their distribution in the intestinal tract of animals. Moreover, resistance mechanisms for different classes of antimicrobials of clinical relevance are reviewed, as well as the epidemiology of multidrug-resistant enterococci of animal origin, with special attention given to beta-lactams, glycopeptides, and linezolid. The emergence of new antimicrobial resistance genes in enterococci of animal origin, such as optrA and cfr, is highlighted. The molecular epidemiology and the population structure of E. faecalis and E. faecium isolates in farm and companion animals is presented. Moreover, the types of plasmids that carry the antimicrobial resistance genes in enterococci of animal origin are reviewed.

Antibacterial Efficacy of Commercially Available Essential Oils Tested Against Drug-Resistant Gram-Positive Pathogens

The potential antibacterial activity of basil (Ocimum basilicum), chamomile (Matricaria chamomilla), origanum (Thymus capitatus), tea tree (Melaleuca alternifolia) and thyme (Thymus vulgaris) essential oils, was investigated against 29 Gram-positive bacterial strains isolated from wastewater treatment plants, clinical samples (n = 25) and American Type Culture Collection (ATCC) reference strains (n = 4). Wild bacterial strains included methicillin-resistant Staphylococcus aureus (n = 16) and vancomycin-resistant Enterococcus spp. (n = 9). The antimicrobial activity of the selected oils was studied using the broth macrodilution method. The Minimal Inhibitory Concentration (MIC) values for S. aureus ranged from 0.06 to 0.5% (v/v) for origanum oil, 0.06 to 1% (v/v) for thyme oil, 0.12 to 1% (v/v) for tea tree oil, 0.25 to 4% (v/v) for basil oil and 2 to >4% (v/v) for chamomile oil. For enterococci the MIC values were significantly higher ranging from 0.25 to 1% (v/v), 0.5 to 2% (v/v), 1 to 4% (v/v), 4 to >4% (v/v) and >4% (v/v) for the above-mentioned oils, respectively. The main compounds of the tested essential oils were: estragole (Ocimum basilicum), bisabolol and trans-b-farnesene (Matricaria chamomilla), carvacrol and thymol (Thymus capitatus), terpinen-4-ol and p-cymene (Melaleuca alternifolia), thymol, linalool, and p-cymene (Thymus vulgaris). Origanum essential oil yielded the best antimicrobial results followed by thyme, tea tree, and basil oil, while chamomile oil exhibited weak antibacterial properties.

Genomic insights into the pathogenicity and environmental adaptability of Enterococcus hirae R17 isolated from pork offered for retail sale

Genetic information about Enterococcus hirae is limited, a feature that has compromised our understanding of these clinically challenging bacteria. In this study, comparative analysis was performed of E. hirae R17, a daptomycin‐resistant strain isolated from pork purchased from a retail market in Beijing, China, and three other enterococcal genomes (Enterococcus faecium DO, Enterococcus faecalis V583, and E. hirae ATCC^™9790). Some 1,412 genes were identified that represented the core genome together with an additional 139 genes that were specific to E. hirae R17. The functions of these R17 strain‐specific coding sequences relate to the COGs categories of carbohydrate transport and metabolism and transcription, a finding that suggests the carbohydrate utilization capacity of E. hirae R17 may be more extensive when compared with the other three bacterial species (spp.). Analysis of genomic islands and virulence genes highlighted the potential that horizontal gene transfer played as a contributor of variations in pathogenicity in this isolate. Drug‐resistance gene prediction and antibiotic susceptibility testing indicated E. hirae R17 was resistant to several antimicrobial compounds, including bacitracin, ciprofloxacin, daptomycin, erythromycin, and tetracycline, thereby limiting chemotherapeutic treatment options. Further, tolerance to biocides and metals may confer a phenotype that facilitates the survival and adaptation of this isolate against food preservatives, disinfectants, and antibacterial coatings. The genomic plasticity, mediated by IS elements, transposases, and tandem repeats, identified in the E. hirae R17 genome may support adaptation to new environmental niches, such as those that are found in hospitalized patients. A predicted transmissible plasmid, pRZ1, was found to carry several antimicrobial determinants, along with some predicted pathogenic genes. These data supported the previously determined phenotype confirming that the foodborne E. hirae R17 is a multidrug‐resistant pathogenic bacterium with evident genome plasticity and environmental adaptability.

Lipophilic teicoplanin pseudoaglycon derivatives are active against vancomycin- and teicoplanin-resistant enterococci

A selection of nine derivatives of teicoplanin pseudoaglycon were tested in vitro against clinical vancomycin-resistant Enterococcus strains possessing vanA, vanB or both genes. The bacteria were characterized by PCR for the identification of their resistance genes. The tested compounds contain lipoic acid, different carbohydrates and aryl groups as lipophilic moieties. About one-third of the teicoplanin-resistant strains were shown to be susceptible to one or more of the glycopeptide derivatives.

Nosocomial infection and its molecular mechanisms of antibiotic resistance

Nosocomial infection is a kind of infection, which is spread in various hospital environments, and leads to many serious diseases (e.g. pneumonia, urinary tract infection, gastroenteritis, and puerperal fever), and causes higher mortality than community-acquired infection. Bacteria are predominant among all the nosocomial infection-associated pathogens, thus a large number of antibiotics, such as aminoglycosides, penicillins, cephalosporins, and carbapenems, are adopted in clinical treatment. However, in recent years antibiotic resistance quickly spreads worldwide and causes a critical threat to public health. The predominant bacteria include Methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Acinetobacter baumannii. In these bacteria, resistance emerged from antibiotic resistant genes and many of those can be exchanged between bacteria. With technical advances, molecular mechanisms of resistance have been gradually unveiled. In this review, recent advances in knowledge about mechanisms by which (i) bacteria hydrolyze antibiotics (e.g. extended spectrum β-lactamases, (ii) AmpC β-lactamases, carbapenemases), (iii) avoid antibiotic targeting (e.g. mutated vanA and mecA genes), (iv) prevent antibiotic permeation (e.g. porin deficiency), or (v) excrete intracellular antibiotics (e.g. active efflux pump) are summarized.

Human health risks associated with antimicrobial-resistant enterococci and Staphylococcus aureus on poultry meat

Enterococci and staphylococci are frequent contaminants on poultry meat. Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus are also well-known aetiological agents of a wide variety of infections resulting in major healthcare costs. This review provides an overview of the human health risks associated with the occurrence of these opportunistic human pathogens on poultry meat with particular focus on the risk of food-borne transmission of antimicrobial resistance. In the absence of conclusive evidence of transmission, this risk was inferred using data from scientific articles and national reports on prevalence, bacterial load, antimicrobial resistance and clonal distribution of these three species on poultry meat. The risks associated with ingestion of antimicrobial-resistant enterococci of poultry origin comprise horizontal transfer of resistance genes and transmission of multidrug-resistant E. faecalis lineages such as sequence type ST16. Enterococcus faecium lineages occurring in poultry meat products are distantly related to those causing hospital-acquired infections but may act as donors of quinupristin/dalfopristin resistance and other resistance determinants of clinical interest to the human gut microbiota. Ingestion of poultry meat contaminated with S. aureus may lead to food poisoning. However, antimicrobial resistance in the toxin-producing strains does not have clinical implications because food poisoning is not managed by antimicrobial therapy. Recently methicillin-resistant S. aureus of livestock origin has been reported on poultry meat. In theory handling or ingestion of contaminated meat is a potential risk factor for colonization by methicillin-resistant S. aureus. However, this risk is presently regarded as negligible by public health authorities.

Agriculture and food animals as a source of antimicrobial-resistant bacteria

One of the major breakthroughs in the history of medicine is undoubtedly the discovery of antibiotics. Their use in animal husbandry and veterinary medicine has resulted in healthier and more productive farm animals, ensuring the welfare and health of both animals and humans. Unfortunately, from the first use of penicillin, the resistance countdown started to tick. Nowadays, the infections caused by antibiotic-resistant bacteria are increasing, and resistance to antibiotics is probably the major public health problem. Antibiotic use in farm animals has been criticized for contributing to the emergence of resistance. The use and misuse of antibiotics in farm animal settings as growth promoters or as nonspecific means of infection prevention and treatment has boosted antibiotic consumption and resistance among bacteria in the animal habitat. This reservoir of resistance can be transmitted directly or indirectly to humans through food consumption and direct or indirect contact. Resistant bacteria can cause serious health effects directly or via the transmission of the antibiotic resistance traits to pathogens, causing illnesses that are difficult to treat and that therefore have higher morbidity and mortality rates. In addition, the selection and proliferation of antibiotic-resistant strains can be disseminated to the environment via animal waste, enhancing the resistance reservoir that exists in the environmental microbiome. In this review, an effort is made to highlight the various factors that contribute to the emergence of antibiotic resistance in farm animals and to provide some insights into possible solutions to this major health issue.