Dissemination and prevalence of plasmid-mediated high-level tigecycline resistance gene tet (X4)

Molecular mechanisms of tigecycline-resistance among Enterobacterales

The global emergence of antimicrobial resistance to multiple antibiotics has recently become a significant concern. Gram-negative bacteria, known for their ability to acquire mobile genetic elements such as plasmids, represent one of the most hazardous microorganisms. This phenomenon poses a serious threat to public health. Notably, the significance of tigecycline, a member of the antibiotic group glycylcyclines and derivative of tetracyclines has increased. Tigecycline is one of the last-resort antimicrobial drugs used to treat complicated infections caused by multidrug-resistant (MDR) bacteria, extensively drug-resistant (XDR) bacteria or even pan-drug-resistant (PDR) bacteria. The primary mechanisms of tigecycline resistance include efflux pumps' overexpression, tet genes and outer membrane porins. Efflux pumps are crucial in conferring multi-drug resistance by expelling antibiotics (such as tigecycline by direct expelling) and decreasing their concentration to sub-toxic levels. This review discusses the problem of tigecycline resistance, and provides important information for understanding the existing molecular mechanisms of tigecycline resistance in Enterobacterales. The emergence and spread of pathogens resistant to last-resort therapeutic options stands as a major global healthcare concern, especially when microorganisms are already resistant to carbapenems and/or colistin.

Sub-MIC Antibiotics Modulate Productions of Outer Membrane Vesicles in Tigecycline-Resistant Escherichia coli

Antimicrobial resistance (AMR) has been recognized as one of the most important crises affecting global human health in the 21st century. Tigecycline is one of the last resort antibiotics for treating severe infections caused by multi-drug resistant Enterobacteriaceae. However, the mobile resistance gene tet(X4), which could mediate high-level tigecycline resistance, was discovered in 2019. The outer membrane vesicle (OMV) has been recognized as a new route for horizontal gene transfer; antimicrobial resistant bacteria also have the ability to secret OMVs, while little is known about the impact of antibiotics on the secretion and characteristics of OMVs from tigecycline resistant bacteria till now. This study aimed to investigate the effects of antibiotics on the production and traits of a tigecycline resistant Escherichia coli strain of 47EC. The results showed that sub-inhibitory (1/2 MIC or 1/4 MIC) concentrations of gentamicin, meropenem, ceftazidime, chloramphenicol, tigecycline, ciprofloxacin, polymycin, rifaximin and mitomycin C could significantly increase the secretion of OMVs (0.713 ± 0.05~6.333 ± 0.15 mg/mL) from E. coli 47EC compared to the respective untreated control (0.709 ± 0.03 mg/mL). In addition, the particle sizes of OMVs were generally larger, and the zeta potential were lower in the antibiotics-treated groups than those of the antibiotic-free group. The copy numbers of the tigecycline resistance gene of tet(X4) in the OMVs of most antimicrobial-treated groups were higher than that of the control group. Moreover, transcriptome analysis on ciprofloxacin-treated E. coli 47EC indicated that the SOS response and prophage activation might participate in the ciprofloxacin-induced OMV formation. In conclusion, the clinical application of antibiotics in treating bacterial infections, especially multi-drug resistant bacteria, might lead to the increased secretion of bacterial OMVs and the enrichment of antimicrobial-resistant genes in the OMVs.

Co-Occurrence of tet(X4) and blaNDM-5 in Escherichia coli Isolates of Inpatient Origin in Guangzhou, China

Tigecycline, one of the last-resort therapeutic options for complicated infections caused by multidrug-resistant pathogens, especially carbapenem-resistant Enterobacterales and Acinetobacter in recent years. The emergence of antibiotic-resistant bacteria and antibiotic-resistant genes has threatened the effectiveness of antibiotics and public health with the excessive use of antibiotics in clinics. However, the emergence and dissemination of high-level mobile tigecycline-resistance gene tet(X) is challenging for clinical effectiveness of antimicrobial agent. This study aimed to characterize an E. coli strain T43, isolated from an inpatient in a teaching hospital in China. The E. coli T43 was resistant to almost all antimicrobials except colistin and consisted of a 4,774,080 bp chromosome and three plasmids. Plasmids pT43-1 and pT43-2 contained tigecycline-resistance gene tet(X4). Plasmid pT43-1 had a size of 152,423 bp with 51.05% GC content and harbored 151 putative open reading frames. pT43-1 was the largest plasmid in strain T43 and carried numerous resistance genes, especially tigecycline resistance gene tet(X4) and carbapenemase resistance gene blaNDM-5. The tet(X) gene was associated with IS26. Co-occurrence of numerous resistance genes in a single plasmid possibly contributed to the dissemination of these genes under antibiotics stress. It might explain the presence of clinically crucial resistance genes tet(X) and blaNDM-5 in clinics. This study suggested the applicable use of antibiotics and continued surveillance of tet(X) and blaNDM-5 in clinics are imperative.

Sensitive and rapid detection of tet(X2) ~ tet(X5) by loop-mediated isothermal amplification based on visual OTG dye

The emergence of tigecycline-resistant tet(X2/X3/X4/X5) genes poses a new threat to the efficacy of anti-infective therapy and the safety of our food and environment. To control the transfer of such genes, a sensitive and rapid molecular method is warranted to detect tet(X2/X3/X4/X5) genes in clinical isolates. Herein, we established a loop-mediated isothermal amplification (LAMP) assay to rapidly detect tet(X2/X3/X4/X5) genes, and the results were assessed by chromogenic visualization. The specificity and sensitivity of the primers during the LAMP assay for the simultaneous detection of tet(X2/X3/X4/X5) genes were determined in this study. All 48 clinical strains without tet(X2/X3/X4/X5) genes yielded negative results during the LAMP assay, substantiating the high specificity of the LAMP primers. The detection thresholds of this assay were 1.5 × 102 CFU/ml and 0.2 fg/uL corresponding to a 10 to 100-fold and 100-fold increase in sensitivity compared to polymerase chain reaction (PCR) assays. Out of 52 bacterial strains tested, using PCR as a reference, our research revealed that the LAMP assay demonstrated a sensitivity and specificity of 100%. To sum up, our novel approach has huge prospects for application in the simultaneous detection of tet(X2/X3/X4/X5) genes and can be applied to detect other drug-resistance genes.

Detection of tetracycline resistance genes and their diversity in Escherichia coli isolated from pig farm waste in Banten province, Indonesia

Background and Aim

Livestock waste in the form of feces and liquid represents an important reservoir of antibiotic resistance genes (ARGs). Because many ARGs can be horizontally transferred to other pathogens, livestock waste plays an essential role in the emergence and transmission of various ARGs in the environment. Therefore, this study aimed to detect and assess the diversity of tet genes in Escherichia coli isolated from pig farm waste in Banten province, Indonesia.

Materials and Methods

Solid waste (feces) and wastewater were collected from 44 pig farms in Banten province. The isolation and identification of E. coli referred to the Global Tricycle Surveillance extended-spectrum beta-lactamase E. coli World Health Organization (2021) guidelines. tet genes were detected using quantitative real-time polymerase chain reaction after dividing pig farms in the province into four clusters based on their adjacent areas and characteristics.

Results

tetA, tetB, tetC, tetM, tetO, and tetX were detected in solid waste and wastewater from pig farms, whereas tetE was not detected in either sample type. tetX (100%) and tetO (75%) were the most dominant genes in solid waste, whereas wastewater samples were dominated by tetA, tetM, tetO, and tetX (prevalence of 50% each). Furthermore, eight tet gene patterns were found in pig farm waste (prevalence of 12.5% each).

Conclusion

The results showed a high prevalence of tetO and tetX in solid waste and wastewater from pig farms in Banten province. This significant prevalence and diversity indicated the transmission of tet genes from pigs to the environment, posing a serious threat to public health.

Genomic traits of multidrug resistant enterotoxigenic Escherichia coli isolates from diarrheic pigs

Diarrhea caused by enterotoxigenic Escherichia coli (ETEC) infections poses a significant challenge in global pig farming. To address this issue, the study was conducted to identify and characterize 19 ETEC isolates from fecal samples of diarrheic pigs sourced from large-scale farms in Sichuan Province, China. Whole-genome sequencing and bioinformatic analysis were utilized for identification and characterization. The isolates exhibited substantial resistance to cefotaxime, ceftriaxone, chloramphenicol, ciprofloxacin, gentamicin, ampicillin, tetracycline, florfenicol, and sulfadiazine, but were highly susceptible to amikacin, imipenem, and cefoxitin. Genetic diversity among the isolates was observed, with serotypes O22:H10, O163orOX21:H4, and O105:H8 being dominant. Further analysis revealed 53 resistance genes and 13 categories of 195 virulence factors. Of concern was the presence of tet(X4) in some isolates, indicating potential public health risks. The ETEC isolates demonstrated the ability to produce either heat-stable enterotoxin (ST) alone or both heat-labile enterotoxin (LT) and ST simultaneously, involving various virulence genes. Notably, STa were linked to human disease. Additionally, the presence of 4 hybrid ETEC/STEC isolates harboring Shiga-like toxin-related virulence factors, namely stx2a, stx2b, and stx2e-ONT-2771, was identified. IncF plasmids carrying multiple antimicrobial resistance genes were prevalent, and a hybrid ETEC/STEC plasmid was detected, highlighting the role of plasmids in hybrid pathotype emergence. These findings emphasized the multidrug resistance and pathogenicity of porcine-origin ETEC strains and the potential risk of epidemics through horizontal transmission of drug resistance, which is crucial for effective control strategies and interventions to mitigate the impact on animal and human health.

Characteristics of tet(X4)-Producing Escherichia coli in Chicken and Pig Farms in Hunan Province, China

BACKGROUND

The plasmid-mediated tigecycline resistance gene tet(X4) confers a high level of resistance to tigecycline. The experiment aims to investigate the prevalence and characterization of tet(X4) in Escherichia coli isolates from chicken and pig farms in Hunan province, China.

METHODS

A total of six tet(X4) positive strains were identified in 257 E. coli derived from chicken samples in Xiangtan city (n = 2), pig samples in Xiangxiang city (n = 1), Chenzhou city (n = 2), and Zhuzhou city (n = 1). The presence of tet(X4) was directly detected by PCR assay, and then the broth dilution method determined the antimicrobial susceptibility profile of the tet(X4)-positive isolates. Genomic locations were identified by whole-genome sequencing (WGS) and bioinformatics.

RESULTS

Almost all tet(X4)-positive strains showed high resistance to multidrug, including tigecycline. Resistome analysis revealed many antibiotic resistance genes, including those with resistance to tetracyclines, β-lactams, phenicols, quinolones, lincosamides chloramphenicol, aminoglycosides and sulfamids. These tet(X4)-bearing strains exhibited six distract STs, such as ST10, 202, ST218, ST362, ST2077, ST7068. The plasmid replicon types carrying tet(X4) were the hybrid plasmid IncFIA(HI1)/IncHIA/IncHIB(R27) (5/6) and IncX1 (1/6).

CONCLUSIONS

The presence of similar genetic environments in E. coli from different cities suggests there may be horizontal transmission pathways promoting the broad spread of drug-resistant genes in Hunan Province, putting great pressure on multidrug resistance monitoring.

Comparison of Fitness Cost, Stability, and Conjugation Frequencies of tet(X4)-Positive Plasmids in Chicken and Pig Escherichia coli

The large-scale epidemic of the tet(X4) gene in the livestock and poultry industry is threatening public health; however, there is still a lack of comparative studies on tet(X4)-bearing plasmids in chicken and pig Escherichia coli. To evaluate the prevalence trend of tet(X4)-bearing plasmids and the factors influencing their persistence in the livestock and poultry industry, we examined the fitness cost, stability under tetracyclines pressure, and conjugation frequencies at various temperatures of six tet(X4)-bearing plasmids in four representative pig E. coli isolates and chicken E. coli isolates. Compared with pig E. coli, the plasmid in chicken E. coli showed lower fitness cost, and stronger ability to promote bacterial biofilm formation and motility. Meanwhile, the presence of tetracycline may favor the stability of tet(X4)-bearing plasmids, which was more common in chicken E. coli. Furthermore, the optimal temperature for IncX1 tet(X4)-bearing plasmid conjugation was 42 °C, and its conjugation frequency in chicken E. coli was higher than that in pig E. coli, whereas the optimal temperature for IncFII tet(X4)-bearing plasmid conjugation was 37 °C and it performed better in pig E. coli, suggesting the predominant plasmid types circulating in chicken E. coli and pig E. coli may be distinct. Collectively, although tet(X4) currently appears to be more prevalent in pig E. coli, this is probably independent of the fitness cost caused by tet(X4)-plasmids. To curb the future spread of the tet(X4) gene, reduced tetracyclines usage and tailored interventions should be applied in different breeding industries.