Evolution and epidemiology of extended-spectrum beta-lactamases (ESBLs) and ESBL-producing microorganisms

A plasmid with the bla CTX-M gene enhances the fitness of Escherichia coli strains under laboratory conditions

Antimicrobial resistance (AMR) is a major threat to global public health that continues to grow owing to selective pressure caused by the use and overuse of antimicrobial drugs. Resistance spread by plasmids is of special concern, as they can mediate a wide distribution of AMR genes, including those encoding extended-spectrum β-lactamases (ESBLs). The CTX-M family of ESBLs has rapidly spread worldwide, playing a large role in the declining effectiveness of third-generation cephalosporins. This rapid spread across the planet is puzzling given that plasmids carrying AMR genes have been hypothesized to incur a fitness cost to their hosts in the absence of antibiotics. Here, we focus on a WT plasmid that carries the bla CTX-M 55 ESBL gene. We examine its conjugation rates and use head-to-head competitions to assay its associated fitness costs in both laboratory and wild Escherichia coli strains. We found that the wild strains exhibit intermediate conjugation levels, falling between two high-conjugation and two low-conjugation laboratory strains, the latter being older and more ancestral. We also show that the plasmid increases the fitness of both WT and lab strains when grown in lysogeny broth and Davis-Mingioli media without antibiotics, which might stem from metabolic benefits conferred on the host, or from interactions between the host and the rifampicin-resistant mutation we used as a selective marker. Laboratory strains displayed higher conjugation frequencies compared to WT strains. The exception was a low-passage K-12 strain, suggesting that prolonged laboratory cultivation may have compromised bacterial defences against plasmids. Despite low transfer rates among WT E. coli, the plasmid carried low fitness cost in minimal medium but conferred improved fitness in enriched medium, indicating a complex interplay between plasmids, host genetics and environmental conditions. Our findings reveal an intricate relationship between plasmid carriage and bacterial fitness. Moreover, they show that resistance plasmids can confer adaptive advantages to their hosts beyond AMR. Altogether, these results highlight that a closer study of plasmid dynamics is critical for developing a secure understanding of how they evolve and affect bacterial adaptability that is necessary for combating resistance spread.

Antimicrobial resistance and prevalence of extended-spectrum beta-lactamase-producing Klebsiella species in East Tennessee dairy farms

Klebsiella species commonly reside in dairy cattle guts and are consistently exposed to beta-lactam antibiotics, including ceftiofur, which are frequently used on the U.S. dairy farms. This may impose selection pressure and result in the emergence of extended-spectrum beta-lactamase (ESBL)-producing strains. However, information on the status and antimicrobial resistance (AMR) profile of ESBL-Klebsiella spp. in the U.S. dairy farms is largely unknown. This study aimed to determine the prevalence and AMR profile of ESBL-Klebsiella spp. and the factors affecting their occurrence in dairy cattle farms. Rectal fecal samples (n = 508) and manure, feed, and water samples (n = 64) were collected from 14 dairy farms in Tennessee. Samples were directly plated on CHROMagar ESBL, and presumptive Klebsiella spp. were confirmed using matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Antimicrobial susceptibility testing was performed on the isolates against panels of 14 antimicrobial agents from 10 classes using minimum inhibitory concentration. Of 572 samples, 57 (10%) were positive for ESBL-Klebsiella spp. The fecal prevalence of ESBL-Klebsiella spp. was 7.2% (95% CI: 6.5-8.0). The herd-level fecal prevalence of ESBL-Klebsiella spp. was 35.7% (95% CI: 12.7-64.8). The fecal prevalence of ESBL-Klebsiella spp. was significantly higher in calves than in cows and higher in cows with higher parity (≥3) as compared to cows with low parity (P < 0.001). Most (96.5%, n = 57) ESBL-Klebsiella spp. were resistant to ceftriaxone. The highest level of acquired co-resistance to ceftriaxone in ESBL-Klebsiella spp. was to sulfisoxazole (66.7%; 38/57). About 19% of ESBL-Klebsiella spp. were multidrug resistant. The presence of ESBL-producing Klebsiella spp. in dairy cattle, feed, and water obtained from troughs could play a crucial epidemiological role in maintaining and spreading the bacteria on farms and serving as a point source of transmission.

IMPORTANCE

We collected 572 samples from dairy farms, including rectal feces, manure, feed, and water. We isolated and identified extended-spectrum beta-lactamase (ESBL)-Klebsiella spp. and conducted an antimicrobial susceptibility test and analyzed different variables that may be associated with ESBL-Klebsiella spp. in dairy farms. The results of our study shed light on how ESBL-Klebsiella spp. are maintained through fecal-oral routes in dairy farms and possibly exit from the farm into the environment. We determine the prevalence of ESBL-Klebsiella spp. and their antimicrobial susceptibility profiles, underscoring their potential as a vehicle for multiple resistance gene dissemination within dairy farm settings. We also collected data on variables affecting their occurrence and spread in dairy farms. These findings have significant implications in determining sources of community-acquired ESBL-Enterobacteriaceae infections and designing appropriate control measures to prevent their spread from food animal production systems to humans, animals, and environments.

Multi-drug resistant (MDR) Gram-negative pathogenic bacteria isolated from poultry in the Noakhali region of Bangladesh

Rapidly increasing antibiotic-resistant bacterial strains in Bangladesh's food and farm animals stem from the excessive and inappropriate use of antibiotics. To assess the prevalence of multi-drug resistant (MDR) Gram-negative bacteria in poultry chicks, we sought to isolate and identify strains carrying antimicrobial resistance genes. Isolation and identification involved biochemical tests, 16S rRNA sequencing, and PCR screening of species-specific genes. MDR patterns were evaluated using CLSI guidelines with seventeen antibiotics across twelve classes. Targeted gene sequences were amplified for the detection of Extended-spectrum β-Lactamase (ESBL), carbapenem, tetracycline, sulfonamide, and colistin resistance genes. Common isolates, such as Escherichia coli, Klebsiella pneumoniae, Proteus penneri, and Enterobacter hormaechei, exhibited average Multiple Antimicrobial Resistance (MAR) indices of 0.66, 0.76, 0.8, 0.84, and 0.81, 0.76, 0.84, 0.41 for broiler and layer chicken, respectively. Providencia stuartii and Salmonella enterica, exclusive to broiler samples, had MAR indices of 0.82 and 0.84, respectively. Additional isolates Morganella morganii, Aeromonas spp., and Wohlfahrtiimonas chitiniclastica were found in layers (Average MAR indices: 0.73, 0.71, and 0.91). Notably, M. morganii, E. hormaechei and W. chitiniclastica were identified for the first time in Bangladeshi poultry chicken, although their evolution is yet to be understood. In this study, Pan-drug resistance was observed in one P. stuartii (broiler) and one Aeromonas spp. (layer) with a MAR index 1, while all isolates exhibited MAR indices >0.2, indicating MDR. Antimicrobial resistance (AMR) gene screening identified blaTEM, blaSHV, tetA, and sul1 in a majority of the MDR strains. Interestingly, E. coli (lactose positive and negative) and E. hormaechei were exclusively found to possess the tetB gene. In addition, E. coli (lactose negative), Klebsiella pneumoniae, Enterobacter hormaechei, M. morganii, and P. stuartii were observed to carry the colistin-resistant mcr-1 gene, whereas sul2 was detected in E. coli (lactose positive and negative), E. hormaechei, P. stuartii, and P. penneri. These findings emphasize the health risk of our consumers of both broiler and layer chickens as they have turned into a potent reservoir of various AMR gene carrying MDR and Pan-drug resistant bacteria.

Extended Spectrum beta-Lactamase Bacteria and Multidrug Resistance in Jordan are Predicted Using a New Machine-Learning system

Background

The incidence of microorganisms with extended-spectrum beta-lactamase (ESBL) is on the rise, posing a significant public health concern. The current application of machine learning (ML) focuses on predicting bacterial resistance to optimize antibiotic therapy. This study employs ML to forecast the occurrence of bacteria that generate ESBL and demonstrate resistance to multiple antibiotics (MDR).

Methods

Six popular ML algorithms were initially trained on antibiotic resistance test patient reports (n = 489) collected from Al-Hussein/Salt Hospital in Jordan. Trained outcome models predict ESBL and multidrug resistance profiles based on microbiological and patients' clinical data. The results were utilized to select the optimal ML method to predict ESBL's most associated features.

Results

Escherichia coli (E. coli, 82%) was the most commonly identified microbe generating ESBL, displaying multidrug resistance. Urinary tract infections (UTIs) constituted the most frequently observed clinical diagnosis (68.7%). Classification and Regression Trees (CART) and Random Forest (RF) classifiers emerged as the most effective algorithms. The relevant features associated with the emergence of ESBL include age and different classes of antibiotics, including cefuroxime, ceftazidime, cefepime, trimethoprim/ sulfamethoxazole, ciprofloxacin, and gentamicin. Fosfomycin nitrofurantoin, piperacillin/tazobactam, along with amikacin, meropenem, and imipenem, had a pronounced inverse relationship with the ESBL class.

Conclusion

CART and RF-based ML algorithms can be employed to predict the most important features of ESBL. The significance of monitoring trends in ESBL infections is emphasized to facilitate the administration of appropriate antibiotic therapy.

New Agents Are Coming, and So Is the Resistance

Antimicrobial resistance is a global threat that requires urgent attention to slow the spread of resistant pathogens. The United States Centers for Disease Control and Prevention (CDC) has emphasized clinician-driven antimicrobial stewardship approaches including the reporting and proper documentation of antimicrobial usage and resistance. Additional efforts have targeted the development of new antimicrobial agents, but narrow profit margins have hindered manufacturers from investing in novel antimicrobials for clinical use and therefore the production of new antibiotics has decreased. In order to combat this, both antimicrobial drug discovery processes and healthcare reimbursement programs must be improved. Without action, this poses a high probability to culminate in a deadly post-antibiotic era. This review will highlight some of the global health challenges faced both today and in the future. Furthermore, the new Infectious Diseases Society of America (IDSA) guidelines for resistant Gram-negative pathogens will be discussed. This includes new antimicrobial agents which have gained or are likely to gain FDA approval. Emphasis will be placed on which human pathogens each of these agents cover, as well as how these new agents could be utilized in clinical practice.

Characterization of Extended-Spectrum β-Lactamase-Producing Escherichia coli in Animal Farms in Hunan Province, China

Multi-drug resistance of bacteria producing extended-spectrum β-lactamase (ESBL) is a public health challenge. Thus, this study aimed to investigate the antimicrobial susceptibility of ESBL-producing Escherichia coli (ESBL-EC) in Hunan Province, China. A total of 1366 fecal samples were collected from pig, chicken, and cattle farms over a six-year period, which were assessed using strain isolation, 16S rRNA identification, polymerase chain reaction, drug sensitivity testing, whole-genome sequencing, and bioinformatics analysis. The results showed an overall prevalence of 6.66% for ESBL-EC strains, with ESBL positivity extents for pigs, chickens, and cattle isolates at 6.77%, 6.54%, and 12.5%, respectively. Most ESBL-EC isolates were resistant to cefotaxime, tetracycline, and trimethoprim-sulfamethoxazole; however, all the isolates were susceptible to meropenem, with relatively low resistance to amikacin and tigecycline. Various multi-locus sequence types with different origins and similar affinities were identified, with ST155 (n = 16) being the most common subtype. Several types of resistance genes were identified among the 91 positive strains, with beta-lactamase blaCTX-M-55 being the most common ESBL genotype. IncFIB was the predominant plasmid type. Widespread use of antibiotics in animal farming may increase antibiotic resistance, posing a serious threat to the health of farmed animals and, thus, to human food security and health.

Prevalence of drug resistant Enterobacteriaceae in a Nepalese tertiary care hospital

Antimicrobial resistance in Enterobacteriaceae is an emerging global public health problem. Numerous studies have reported community-acquired AmpC beta-lactamase and extended spectrum beta-lactamase (ESBL) producing Enterobacteriaceae in Nepal. However, there are limited data on community-acquired Metallo-beta-lactamase (MBL) producing Enterobacteriaceae. A hospital-based descriptive cross-sectional study was conducted using 294 Enterobacteriaceae isolates from a total of 2,345 different clinical specimens collected from patients attending a tertiary care hospital in Nepal. Bacteria were isolated using standard microbiological growth media and identified using biochemical tests. For antimicrobial susceptibility testing, Kirby-Bauer disc diffusion technique was used. AmpC, ESBL, and MBL productions were detected by using combined disc method. AmpC, ESBL, and MBL productions were detected in 19.4%, 29.6%, and 8.5% of total Enterobacteriaceae isolates respectively. Higher rates of beta-lactamases production were seen among the isolates from in-patients in comparison with those from out-patients. However, 11.6%, 25%, and 3.7% of the total isolates from out-patients were AmpC, ESBL, and MBL producers respectively. The co-production of the beta-lactamases was also detected, with two Klebsiella pneumoniae isolates producing all three beta-lactamases. One MBL producing Proteus vulgaris isolate that was pan-resistant with no remaining treatment options was also isolated. Prevalence of drug resistant Enterobacteriaceae in our study was very high. Detection of AmpC, ESBL, and MBL positive isolates from out-patients, who did not have recent history of hospital visit, indicated the community dissemination of the drug resistant bacteria. This is a matter of great concern and an immediate attention to formulate strategies to prevent further development and spread of antibiotic resistance is required.

Prevalence and antimicrobial resistance profiles of extended-spectrum beta-lactamase-producing Escherichia coli in East Tennessee dairy farms

Introduction

The extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, such as Escherichia coli, are emerging as a serious threat to global health due to their rapid spread and their multidrug-resistant (MDR) phenotypes. However, limited information is available regarding the prevalence and antimicrobial resistance (AMR) profile of ESBL-E. coli in the United States dairy farms. This study aimed to determine the prevalence and AMR pattern of ESBL-E. coli in East Tennessee dairy cattle farms.

Methods

Rectal fecal samples from dairy cattle (n = 508) and manure (n = 30), water (n = 19), and feed samples (n = 15) were collected from 14 farms. The presumptive E. coli was isolated on CHROMagar™ ESBL and confirmed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Antimicrobial susceptibility testing was performed on the ESBL-E. coli isolates.

Results and discussion

From 572 fecal and farm environmental samples, a total of 233 (41%, n = 572) ESBL-E. coli were identified. The prevalence of fecal ESBL-E. coli was 47.5% (95% CI: 46.2-49.2). The within-farm prevalence of ESBL-E. coli ranged from 8 to 100%. Recent treatment history with third-generation cephalosporins (3GC), cow parity ≥3, and calves were the independent risk factors associated (P < 0.05) with fecal carriage of ESBL-E. coli. Overall, 99.6% (n = 231) ESBL-E. coli tested were phenotypically resistant to at least one of the 14 antimicrobial agents tested. The most common AMR phenotypes were against beta-lactam antibiotics, ampicillin (99.1%; n = 231 isolates), and ceftriaxone (98.7%, n = 231). Most ESBL-E. coli isolates (94.4%) were MDR (resistance to ≥3 antimicrobial classes), of which 42.6% showed co-resistance to at least six classes of antimicrobials. ESBL-E. coli isolates with concurrent resistance to ceftriaxone, ampicillin, streptomycin, tetracycline, sulfisoxazole, and chloramphenicol are widespread and detected in all the farms. The detection of MDR ESBL-E. coli suggests that dairy cattle can be a reservoir for these bacteria, highlighting the associated public health risk.

Domestic Pets in the United Arab Emirates as Reservoirs for Antibiotic-Resistant Bacteria: A Comprehensive Analysis of Extended-Spectrum Beta-Lactamase Producing Escherichia coli Prevalence and Risk Factors

Extended-spectrum β-lactamases resistant (ESBL-R) Escherichia coli (E. coli) has been reported from healthy and sick pets. However, data from Middle Eastern countries, including the United Arab Emirates (UAE), are minimal. This study provides the first evidence of ESBL-R E. coli carriage among pets in the UAE. A total of 148 rectal swabs were collected from domestic cats (n = 122) and dogs (n = 26) attending five animal clinics in the UAE. Samples were cultured directly onto selective agar, and suspected colonies were confirmed as ESBL-producing using phenotypic and molecular methods. Confirmed isolates were screened for their phenotypic resistance to twelve antimicrobial agents using the Kirby Bauer method. The owners of the pets completed a questionnaire at the time of sampling, and the data were used to identify risk factors. ESBL-R E. coli was detected in rectal swabs of 35 out of 148 animals (23.65%) (95% confidence interval [CI]: 17.06-31.32). Multivariable logistic regression analysis identified cats and dogs with access to water in ditches and puddles as 3.71 (p-value = 0.020) times more likely to be positive to ESBL-R E. coli than those without access to open water sources. Ciprofloxacin resistance was evident in 57.14% (44/77) of the ESBL-R E. coli isolates. The percentage of resistance to azithromycin and cefepime was 12.99% (10/77) and 48.05% (37/77), respectively. The bla_CTX-M gene was detected in 82% of the PCR-screened isolates (n = 50). Multidrug resistance (MDR) phenotypes were evident in 91% (70/77) of the isolates. In conclusion, ESBL-R E. coli was detected at a noticeable rate among healthy pet cats and dogs in the UAE, and the majority are MDR to clinically important antimicrobials such as fluoroquinolones and 3rd and 4th generation cephalosporins. Our results call for strengthening antimicrobial stewardship among companion animal veterinarians in the UAE to reduce the potential transmission of ESBL-R E. coli between pets, humans, and urban environments.

Genetic diversity and prevalence of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in aquatic environments receiving untreated hospital effluents

The spread of extended-spectrum beta-lactamase (ESBL)-producing bacteria in the environment has been recognized as a challenge to public health. The aim of the present study was to assess the occurrence of ESBL-producing Escherichia coli and Klebsiella pneumoniae from selected water bodies receiving hospital effluents in Kerala, India. Nearly 69.8% of Enterobacteriaceae isolates were multi-drug resistant by the Kirby-Bauer disc diffusion method. The double disc synergy test was used to detect the ESBL production and the genes responsible for imparting resistance were detected by PCR. Conjugation experiments confirmed the mechanism of plasmid-mediated transfer of resistance. The prevalence of ESBL production in E. coli and K. pneumoniae was 49.2 and 46.8%, respectively. Among the ESBL-encoding genes, bla_CTX-M was the most prevalent group followed by bla_TEM, bla_OXA, bla_CMY, and bla_SHV. The results suggest that healthcare settings are one of the key contributors to the spread of ESBL-producing bacteria, not only through cross-transmission and ingestion of antibiotics but also through the discharge of waste without a proper treatment, leading to harmful effects on the aquatic environment. The high prevalence of ESBL-producing Enterobacteriaceae with resistance genes in public water bodies even post-treatment poses a serious threat.

Molecular Characterization of Extensively Drug Resistant Salmonella Enterica Serovar Typhi Clinical Isolates from Lahore, Pakistan

Background

The emergence of extensively drug-resistant (XDR) typhoid in Pakistan has endangered the treatment options available to manage this infection. Third generation cephalosporin were the empiric choice to treat typhoid fever in Pakistan, but acquisition of ESBLs have knocked them out of the arsenal. The current empiric choice is azithromycin which is vulnerable to resistance too. This study aimed to assess the burden of XDR typhoid and the frequency of resistance determinants in blood culture samples collected from different hospitals in Lahore, Pakistan.

Methods

A total of 835 blood cultures were collected from different tertiary care hospitals in Lahore during January 2019 to December 2021. Among 835 blood cultures, 389 Salmonella Typhi were identified, and 150 were XDR S. Typhi (resistant to all recommended antibiotics). Antibiotics resistance genes of the first-line drugs (bla_TEM-1, catA1, sul1, and dhfR7) and second line drugs (gyrB, gyrA, qnrS, ParC and ParE) were investigated among XDR S. Typhi. There were different CTX-M genes isolated using the specific primers, bla_CTX-M-U, bla_CTX-M-1, bla_CTX-M-15, bla_CTX-M-2, bla_CTX-M-8 and bla_CTX-M-9.

Results

Antibiotic resistant genes of the first-line drugs were isolated with different frequency, bla_TEM-1 (72.6%), catA1 (86.6%), sul1 (70%), and dhfR7 (56%). Antibiotics resistance genes of second-line drugs were isolated as: gyrB (60%), gyrA (49.3%), qnrS (32.6%), parC (44%) and parE (28%). Among CTX-M genes, bla_CTX-M-U (63.3%) was the most frequent followed by bla_CTX-M-15 (39.3%) and bla_CTX-M-1 (26%).

Conclusion

Our study concluded that XDR isolates circulating in Pakistan have acquired first-line and second-line antibiotic resistant genes quite successfully along with CTX-M genes (ESBLs) rendering them resistant to the third generation cephalosporins as well. Emergence of azithromycin resistance in XDR S. Typhi which is currently used as an empiric treatment option is worrisome and needs to be monitored carefully in endemic countries like Pakistan.

Multi-drug resistant bacteria isolates from lymphatic filariasis patients in the Ahanta West District, Ghana

Background

Antimicrobial resistance is associated with increased morbidity in secondary infections and is a global threat owning to the ubiquitous nature of resistance genes in the environment. Recent estimate put the deaths associated with bacterial antimicrobial resistance in 2019 at 4.95 million worldwide. Lymphatic filariasis (LF), a Neglected Tropical Disease (NTD), is associated with the poor living in the tropical regions of the world. LF patients are prone to developing acute dermatolymphangioadenitis (ADLA), a condition that puts them at risk of developing secondary bacterial infections due to skin peeling. ADLA particularly worsens the prognosis of patients leading to usage of antibiotics as a therapeutic intervention. This may result in inappropriate usage of antibiotics due to self-medication and non-compliance; exacerbating antimicrobial resistance in LF patients. In this perspective, we assessed the possibilities of antimicrobial resistance in LF patients. We focused on antibiotic usage, antibiotic resistance in Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa isolates and looked at genes (mecA and Extended-spectrum beta-lactamase [blaCTX-M, blaSHV and blaTEM]) coding for resistance in multi-drug resistant (MDR) bacterial isolates.

Results

Of the sixty (60) participants, fifty-four (n = 54, 90%) were within 31–60 years of age, twenty (n = 20, 33.33%) were unemployed and thirty-eight (n = 38, 50.67%) had wounds aged (in months) seven (7) months and above. Amoxicillin (54%) and chloramphenicol (22%) were the most frequently used antibiotics for self-medication. Staphylococcus aureus isolates (n = 26) were mostly resistant to penicillin (n = 23, 88.46%) and least resistant to erythromycin (n = 2, 7.69%). Escherichia coli isolates (n = 5) were resistant to tetracycline (n = 5, 100%) and ampicillin (n = 5, 100%) but were sensitive to meropenem (n = 5, 100%). Pseudomonas aeruginosa isolates (n = 8) were most resistant to meropenem (n = 3, 37.50%) and to a lesser ciprofloxacin (n = 2, 25%), gentamicin (n = 2, 25%) and ceftazidime (n = 2, 25%). Multi-drug resistant methicillin resistant Staphylococcus aureus (MRSA), cephalosporin resistant Escherichia coli. and carbapenem resistant Pseudomonas aeruginosa were four (n = 4, 15.38%), two (n = 2, 40%) and two (n = 2, 25%) respectively. ESBL (blaCTX-M) and mecA genes were implicated in the resistance mechanism of Escherichia coli and MRSA, respectively.

Conclusion

The findings show presence of MDR isolates from LF patients presenting with chronic wounds; thus, the need to prioritize resistance of MDR bacteria into treatment strategies optimizing morbidity management protocols. This could guide antibiotic selection for treating LF patients presenting with ADLA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02624-9.

Detection of β-Lactamase Resistance and Biofilm Genes in Pseudomonas Species Isolated from Chickens

Bacteria of the genus Pseudomonas are pathogens in both humans and animals. The most prevalent nosocomial pathogen is P. aeruginosa, particularly strains with elevated antibiotic resistance. In this study, a total of eighteen previously identified Pseudomonas species strains, were isolated from chicken. These strains were screened for biofilm formation and antibiotic resistance. In addition, we evaluated clove oil’s effectiveness against Pseudomonas isolates as an antibiofilm agent. The results showed that Pseudomonas species isolates were resistant to most antibiotics tested, particularly those from the β-lactamase family. A significant correlation (p < 0.05) between the development of multidrug-resistant isolates and biofilms is too informal. After amplifying the AmpC-plasmid-mediated genes (blaCMY, blaMIR, DHA, and FOX) and biofilm-related genes (psld, rhlA, and pelA) in most of our isolates, PCR confirmed this relationship. Clove oil has a potent antibiofilm effect against Pseudomonas isolates, and may provide a treatment for bacteria that form biofilms and are resistant to antimicrobials.

Succession in the caecal microbiota of developing broilers colonised by extended-spectrum β-lactamase-producing Escherichia coli

Background

Broilers are among the most common and dense poultry production systems, where antimicrobials have been used extensively to promote animal health and performance. The continuous usage of antimicrobials has contributed to the appearance of resistant bacteria, such as extended-spectrum β-lactamase-producing Escherichia coli (ESBL-Ec). Here, we studied the ESBL-Ec prevalence and successional dynamics of the caecal microbiota of developing broilers in a commercial flock during their production life cycle (0–35 days). Broilers were categorised as ESBL-Ec colonised (ESBL-Ec⁺) or ESBL-Ec non-colonised (ESBL-Ec⁻) by selective culturing. Using 16S rRNA gene sequencing, we i. compared the richness, evenness and composition of the caecal microbiota of both broilers’ groups and ii. assessed the combined role of age and ESBL-Ec status on the broilers’ caecal microbiota.

Results

From day two, we observed an increasing linear trend in the proportions of ESBL-Ec throughout the broilers' production life cycle, X² (1, N = 12) = 28.4, p < 0.001. Over time, the caecal microbiota richness was consistently higher in ESBL-Ec⁻ broilers, but significant differences between both broilers’ groups were found exclusively on day three (Wilcoxon rank-sum test, p = 0.016). Bray–Curtis distance-based RDA (BC-dbRDA) showed no explanatory power of ESBL-Ec status, while age explained 14% of the compositional variation of the caecal microbiota, F (2, 66) = 6.47, p = 0.001.

Conclusions

This study assessed the role of ESBL-Ec in the successional dynamics of the caecal microbiota in developing broilers and showed that the presence of ESBL-Ec is associated with mild but consistent reductions in alpha diversity and with transient bacterial compositional differences. We also reported the clonal spread of ESBL-Ec and pointed to the farm environment as a likely source for ESBLs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-022-00199-4.

OXA-244-Producing ST131 Escherichia coli From Surface and Groundwaters of Pavia Urban Area (Po Plain, Northern Italy)

The study aimed to investigate (i) the occurrence of third-generation cephalosporins and/or carbapenems non-sensitive Enterobacterales in Pavia surface and groundwaters, (ii) their resistance determinants, and (iii) the clonal features of the most relevant strains. During May 13 and 14, 2019, n = 18 water samples from n = 12 sampling sites in the urban/peri-urban area of Pavia (Po Plain, Northern Italy) have been evaluated. At first, hydrochemical analysis and bacterial plate counts were carried out on all the water samples. One milliliter of each water sample was then screened on both MacConkey agar (MC) added with cefotaxime (1 mg/L; 2 mg/L) and MC plus meropenem (0.25 mg/L; 4 mg/L). Species identification and antimicrobial susceptibilities were assessed by MicroScan autoSCAN-4. Double Disk Synergy (DD) test, CT103XL microarray, acc(6‘)-Ib-cr, qnrS, blaCTX-M-/MOX-/VEB-/OXA-type genes targeted PCR and sequencing, Pulsed-Field Gel Electrophoresis (PFGE), MultiLocus Sequence Typing (MLST), and Whole-Genome Sequencing on selected strains were performed. A total of n = 30 isolates grown on β-lactams enriched MC: Escherichia coli (n = 21; 70%), Klebsiella spp. (n = 5; 16.6%), Citrobacter freundii (n = 2; 6.7%), and Kluyvera intermedia (n = 2; 6.7%). All E. coli and K. pneumoniae were ESβL-producers by DD. The 66.6, 38.0, and 19.0% of E. coli were ciprofloxacin/levofloxacin, trimethoprim-sulfamethoxazole, and gentamicin resistant (EUCAST 2019 breakpoints), respectively. A blaCTX-M-type determinant was identified in E. coli (n = 20/21; 95.2%) and K. pneumoniae (n = 2/3; 66.7%). The remaining E. coli was blaVEB-1 and blaMOX-2 genes positive. The aac(6′)-Ib-cr determinant was found in n = 7 E. coli and n = 1 K. pneumoniae, while qnrS was found in n = 1 E. coli and n = 2 K. pneumoniae. PFGE showed clonal heterogeneity among ESβL-E. coli. Two out of four E. coli detected as blaOXA-244-positive, belonged to the pandemic ST131. One XDR K. pneumoniae from a stream sample, detected as blaKPC-2 positive, resulted of ST258. The epidemiological impact of blaOXA-244 ST131 E. coli and blaKPC-2 ST258 K. pneumoniae presence in surface waters of an urban area in Northern Italy must not be underestimated.

Secondary plant metabolites as potent drug candidates against antimicrobial-resistant pathogens

Antibiotic resistance is a major public health threat of the twenty-first century and represents an important risk to the global economy. Healthcare-associated infections mainly caused by drug-resistant bacteria are wreaking havoc in patient care worldwide. The spread of such pathogens limits the utility of available drugs and complicates the treatment of bacterial diseases. As a result, there is an urgent need for new drugs with mechanisms of action capable of curbing resistance. Plants synthesize and utilize various metabolic compounds to deter pathogens and predators. Utilizing these plant-based metabolites is a promising option in identifying novel bioactive compounds that could be harnessed to develop new potent antimicrobial drugs to treat multidrug-resistant pathogens. The purpose of this review is to highlight medicinal plants as important sources of novel antimicrobial agents that could be developed to help combat antimicrobial resistance.

In Silico Analysis of Extended-Spectrum β-Lactamases in Bacteria

The growing bacterial resistance to available β-lactam antibiotics is a very serious public health problem, especially due to the production of a wide range of β-lactamases. At present, clinically important bacteria are increasingly acquiring new elements of resistance to carbapenems and polymyxins, including extended-spectrum β-lactamases (ESBLs), carbapenemases and phosphoethanolamine transferases of the MCR type. These bacterial enzymes limit therapeutic options in human and veterinary medicine. It must be emphasized that there is a real risk of losing the ability to treat serious and life-threatening infections. The present study aimed to design specific oligonucleotides for rapid PCR detection of ESBL-encoding genes and in silico analysis of selected ESBL enzymes. A total of 58 primers were designed to detect 49 types of different ESBL genes. After comparing the amino acid sequences of ESBLs (CTX-M, SHV and TEM), phylogenetic trees were created based on the presence of conserved amino acids and homologous motifs. This study indicates that the proposed primers should be able to specifically detect more than 99.8% of all described ESBL enzymes. The results suggest that the in silico tested primers could be used for PCR to detect the presence of ESBL genes in various bacteria, as well as to monitor their spread.

Characteristics of ESBL-Producing Enterobacterales Colonizing the Gastrointestinal Tract in Patients Admitted to the Oncological Hospital

We analyzed the prevalence and genetic characteristics of the extended-spectrum β-lactamases (ESBLs)-producing Enterobacterales isolated from adult patients hospitalized in the oncological center in 2019. Out of 9372 patients admitted to the hospital, 1373 had been in various medical facilities during the last year, which was an indication to perform a screening test for ESBL-producing Enterobacterales colonizing their gastrointestinal tract. In eighty-three patients (6.1%), 85 ESBL producers were detected. These isolates included the following: Escherichia coli (n = 67; 78.8%), Klebsiella pneumoniae (n = 14; 16.5%), Enterobacter cloacae cplx (n = 3; 3.5%), and Klebsiella oxytoca (n = 1; 1.2%). CTX-M-1-like enzymes were the most common ESBLs (n = 67; 78.8%). Two K. pneumoniae isolates (2/85; 2.4%) additionally produced New Delhi-metallo-β-lactamases (NDM). All isolates, except for K. oxytoca, were typed by pulsed-field gel electrophoresis (PFGE) and demonstrated high genetic diversity. The most prevalent phylogroups of E. coli were B2 group (n = 30; 44.8%), followed by A group (n = 25; 37.3%). These observations have motivated us to investigate the link between ESBL-E colonization and infection among patients with solid tumors.

Non-catalytic-Region Mutations Conferring Transition of Class A β-Lactamases Into ESBLs

Despite class A ESBLs carrying substitutions outside catalytic regions, such as Cys69Tyr or Asn136Asp, have emerged as new clinical threats, the molecular mechanisms underlying their acquired antibiotics-hydrolytic activity remains unclear. We discovered that this non-catalytic-region (NCR) mutations induce significant dislocation of β3-β4 strands, conformational changes in critical residues associated with ligand binding to the lid domain, dynamic fluctuation of Ω-loop and β3-β4 elements. Such structural changes increase catalytic regions’ flexibility, enlarge active site, and thereby accommodate third-generation cephalosporin antibiotics, ceftazidime (CAZ). Notably, the electrostatic property around the oxyanion hole of Cys69Tyr ESBL is significantly changed, resulting in possible additional stabilization of the acyl-enzyme intermediate. Interestingly, the NCR mutations are as effective for antibiotic resistance by altering the structure and dynamics in regions mediating substrate recognition and binding as single amino-acid substitutions in the catalytic region of the canonical ESBLs. We believe that our findings are crucial in developing successful therapeutic strategies against diverse class A ESBLs, including the new NCR-ESBLs.

Investigating the impact of hospital antibiotic usage on aquatic environment and aquaculture systems: A molecular study of quinolone resistance in Escherichia coli

Quinolones are one of the most important classes of antibacterials available for the treatment of infectious diseases in humans. However, there is a growing concern about bacterial resistance to antimicrobials including quinolones. The spread of antibiotic-resistant bacteria in the aquatic environment has been recognized as a growing threat to public health and hospitals appear to be a major contributor to this. The objective of this study was to investigate the prevalence of quinolone resistance in Escherichia coli from selected water bodies receiving direct hospital effluents in Kerala, India. Standard disc diffusion and E-test were used for antibiotic susceptibility testing. As antibiotic resistance can develop in bacterial isolates by different means, EtBr Agar Cartwheel method was used to detect the efflux pump activity and presence of resistant genes was detected by PCR. The mechanism of transfer of plasmid mediated resistance was confirmed by conjugation experiments. A total of 209 multidrug-resistant Escherichia coli were isolated from different hospital effluent discharge sites and aquaculture farms located in their vicinity. Among them, qnrB was found to be most prevalent followed by qnrS, OqxAB, qnrA and aac (6')-Ib-cr. The results suggested that the antibiotics present at sub-inhibitory concentrations in direct hospital effluents increases the selection pressure impacting the cell function of even normal microorganisms in the aquatic environment to change the genetic expression of virulence factors or acquire resistance genes by different transfer mechanisms, posing a serious threat to public health.

Bacterial profile, antibiotic susceptibility pattern and associated risk factors of urinary tract infection among clinically suspected children attending at Felege-Hiwot comprehensive and specialized hospital, Northwest Ethiopia. A prospective study

Background

Urinary tract infection is one of the most common bacterial infections in children. Understanding the characteristics of uropathogens and their antimicrobial susceptibility pattern in a particular setting can provide evidence for the appropriate management of cases. This study aimed to assess the bacterial profile of urinary tract infection, their antimicrobial susceptibility pattern and associated factors among clinically suspected children attending at Felege-Hiwot Comprehensive Specialized Hospital, Northwest Ethiopia.

Methods

A hospital-based cross-sectional study was conducted from February–April, 2019. A systematic sampling technique was employed. A mid-stream urine sample was inoculated on cystine lactose electrolyte deficient media and incubated for 24–48 h. Sub-culturing was done on Mac-Conkey and blood agar. Antimicrobial susceptibility test was done on Muller-Hinton agar. A binary logistic regression model was used to see the association between dependent and independent factors. A p-value< 0.05 at 95% CI was considered as statistically significant.

Results

The overall prevalence of urinary tract infection was 16.7% (95% CI 12.4–21.1). Both Gram-negative and Gram-positive bacterial isolates were recovered with a rate of 44/50 (88%) and 6/50 (12%) respectively. Among Gram-negative isolates, E. coli 28/44(63.6%) was predominant while S. saprophyticus 2/6(33.3%) was prevalent among Gram-positive bacterial isolates. Overall, a high level of resistance to ampicillin, augmentin, and tetracycline was shown by Gram-negative bacteria with a rate of 44/44(100%), 39/44(88.6%), and36/44 (81.8%) respectively. About 33/50(66%) of overall multidrug resistance was observed (95% CI 52–78). About six Gram-negative bacterial isolates were extended spectrum beta-lactamase (ESBL) producers. Having a history of urinary tract infection (P-0.003, AOR 1.86–22.15) and male uncircumcision (p-0.00, AOR 5.5–65.35) were the independent variables that associate for urinary tract infections.

Conclusion

In the present study, the prevalence of urinary tract infection among children was high and considerably a high proportion of multidrug resistance was observed. This result will have a significant impact on the selection of appropriate antimicrobial agents for the treatment of urinary tract infection.

Optimizing a Screening Protocol for Potential Extended-Spectrum β-Lactamase Escherichia coli on MacConkey Agar for Use in a Global Surveillance Program

The increasing prevalence of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli is worrisome. Coordinated efforts to better understand global prevalence and risk factors are needed. Developing lower- and middle-income countries need reliable, readily available, and cost-effective solutions for detecting ESBL E. coli to contribute to global surveillance. We evaluated MacConkey agar supplemented with ceftriaxone or cefotaxime as a screening method for accurately detecting and quantifying potential ESBL E. coli MacConkey agar from eight manufacturers, representing seven countries, was prepared with 2 or 4 μg/ml ceftriaxone or cefotaxime. Four E. coli strains (NC11, ATCC 25922, CM-13457, and CM-10455) and one Klebsiella pneumoniae strain (CM-11073) were grown overnight, serially diluted, and plated in triplicate for enumeration on all medium combinations. After recovery was assessed, US-1 MacConkey agar with cefotaxime was used to further evaluate the reproducibility and detection of potential ESBL E. coli from poultry cecal (n = 30) and water (n = 30) samples. Results indicated the recovery of E. coli 13457 from four MacConkey agar manufacturers was reduced by up to 4 log CFU/ml, and phenotypic differences in colony size and color were apparent for each manufacturer for control E. coli strains. A true ESBL, NC11, was not reduced with 4 μg/ml cefotaxime. From ceca and water, potential ESBL E. coli isolates were only confirmed from MacConkey agar with 4 μg/ml cefotaxime, where 45% and 16.6% of E. coli isolates phenotypically expressed ESBL production. The quality and reproducibility of MacConkey agar varied by manufacturer, which suggests that a single manufacturer and medium type should be selected for global monitoring efforts so that training and interpretation can be standardized.

Detection of New Delhi Metallo-β-lactamase 1 and Cephalosporin Resistance Genes Among Carbapenem-Resistant Enterobacteriaceae in Water Bodies Adjacent to Hospitals in India

The prevalence of carbapenem resistance among bacterial isolates from selected water bodies receiving hospital effluents and adjoining aquaculture farms in Kerala, India, was studied. Klebsiella pneumoniae followed by Escherichia coli, Klebsiella oxytoca, Enterobacter aerogenes and Acinetobacter baumannii were the predominant isolates. Antibiotic sensitivity of these isolates was determined by Kirby-Bauer disc diffusion method. Nearly 60% of the Enterobacteriaceae isolates screened were multidrug resistant of which 16.6% were carbapenem resistant. The carbapenem-resistant Enterobacteriaceae were further screened for the presence of New Delhi metallo β-lactamase-1 and cephalosporin resistance encoding genes. All NDM-1 isolates were highly resistant to carbapenem, cephalosporin, aminoglycosides, quinolones, tetracycline, and sulphonamides. K. pneumoniae harboring bla_NDM-1 gene and E. coli isolates with bla_CTX-M-15 and bla_SHV-11 genes were detected in hospital discharge points. In aquaculture farms too, carbapenem-resistant K. pneumoniae with bla_NDM-1 gene and E. coli isolates with bla_CTX-M-15 were observed, although there was no use of antibiotics in these farms. However, other carbapenemase genes such as bla_TEM, bla_VIM, bla_IMP and bla_GIM were not detected in any of these isolates. The results suggest the increased prevalence of carbapenem-resistant Enterobacteriaceae in the water bodies receiving hospital effluent and its dissemination to adjacent aquaculture farms, posing a serious threat to public health.

Antibiotic resistant and extended-spectrum β-lactamase producing faecal coliforms in wastewater treatment plant effluent

Wastewater treatment plants (WWTPs) provide optimal conditions for the maintenance and spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). In this work we describe the occurrence of antibiotic resistant faecal coliforms and their mechanisms of antibiotic resistance in the effluent of two urban WWTPs in Ireland. This information is critical to identifying the role of WWTPs in the dissemination of ARB and ARGs into the environment. Effluent samples were collected from two WWTPs in Spring and Autumn of 2015 and 2016. The bacterial susceptibility patterns to 13 antibiotics were determined. The phenotypic tests were carried out to identify AmpC or extended-spectrum β-lactamase (ESBL) producers. The presence of ESBL genes were detected by PCR. Plasmids carrying ESBL genes were transformed into Escherichia coli DH5α recipient and underwent plasmid replicon typing to identify incompatibility groups. More than 90% of isolated faecal coliforms were resistant to amoxicillin and ampicillin, followed by tetracycline (up to 39.82%), ciprofloxacin (up to 31.42%) and trimethoprim (up to 37.61%). Faecal coliforms resistant to colistin (up to 31.62%) and imipenem (up to 15.93%) were detected in all effluent samples. Up to 53.98% of isolated faecal coliforms expressed a multi-drug resistance (MRD) phenotype. AmpC production was confirmed in 5.22% of isolates. The ESBL genes were confirmed for 11.84% of isolates (9.2% of isolates carried bla_TEM, 1.4% bla_SHV-12, 0.2% bla_CTX-M-1 and 1% bla_CTX-M-15). Plasmids extracted from 52 ESBL isolates were successfully transformed into recipient E. coli. The detected plasmid incompatibility groups included the IncF group, IncI1, IncHI1/2 and IncA/C. These results provide evidence that treated wastewater is polluted with ARB and MDR faecal coliforms and are sources of ESBL-producing, carbapenem and colistin resistant Enterobacteriaceae.

The Frequency and Antimicrobial Resistance of blaTEM and blaCTX-M Genes in Escherichia coli Isolated From Patients With a Urinary Tract Infection

Introduction: The production of β-lactamase in bacteria, especially in Escherichia coli as a prevalent opportunistic bacterium, has caused many problems in patient treatment. β-lactamases are encoded by extended-spectrum β-lactamase (ESBL) genes such as blaTEM and blaCTX-M. We aimed to assess the prevalence and antibiotic sensitivity of β-lactamases encoded by blaCTX-M and blaTEM in E. coli isolated from patients suffering from urinary tract infections (UTIs). Methods: Escherichia coli strains were isolated from the patients’ urine culture presented to medical diagnostic laboratories in Zabol, Iran. The agar disc-diffusion test was performed on Müller-Hinton agar to investigate the antibiotic resistance of these isolates using eight antimicrobial paper discs including gentamicin, tetracycline, co-trimoxazole, norfloxacin, cefuroxime, ampicillin, neomycin, and amoxicillin. A conventional polymerase chain reaction (PCR) was used to detect blaCTX-M and blaTEM. Results: The frequencies of resistance to cefuroxime, norfloxacin, co-trimoxazole, neomycin, amoxicillin, tetracycline, gentamicin, and ampicillin were found to be 45 (90%), 15 (30%), 33 (66%), 33 (66%), 44 (88%), 34 (68%), 4 (8%), and 50 (100%), respectively. Moreover, the prevalence of blaCTX-M was 25 (50%) while that of blaTEM was 16 (32%). Conclusion: Based on the results, gentamicin and norfloxacin can be recommended as effective antibacterials for treating UTI caused by E. coli in the study population. Moreover, the frequency of resistant genes including blaCTX-M and blaTEM was high in the isolated E. coli. Effective control systems including appropriate treatments for ESBL-producing strains are therefore required for humans and food animals.

A Genotype-Phenotype Correlation Study of SHV β-Lactamases Offers New Insight into SHV Resistance Profiles

The SHV β-lactamases (BLs) have undergone strong allele diversification that has changed their substrate specificities. Based on 147 NCBI entries for SHV alleles, in silico mathematical models predicted 5 positions as relevant for the β-lactamase inhibitor (BLI)-resistant (2br) phenotype, 12 positions as relevant for the extended-spectrum BL (ESBL) (2be) phenotype, and 2 positions as related solely to the narrow-spectrum (2b) phenotype. These positions and six additional positions described in other studies (including one promoter mutation) were systematically substituted and investigated for their substrate specificities in a BL-free Escherichia coli background, representing, to our knowledge, the most comprehensive substrate and substitution analysis for SHV alleles to date. An in vitro analysis confirmed the essentiality of positions 238 and 179 for the 2be phenotype and of position 69 for the 2br phenotype. The E240K and E240R substitutions, which do not occur alone in known 2br SHV variants, led to a 2br phenotype, indicating a latent BLI resistance potential of these substitutions. The M129V, A234G, S271I, and R292Q substitutions conferred latent resistance to cefotaxime. In addition, seven positions that were found not always to be associated with the ESBL phenotype resulted in increased resistance to ceftaroline. We also observed that coupling of a strong promoter (IS26) to an A146V mutant with the 2b phenotype resulted in highly increased resistance to BLIs, cefepime, and ceftaroline but not to third-generation cephalosporins, indicating that SHV enzymes represent an underestimated risk for empirical therapies that use piperacillin-tazobactam or cefepime to treat different infectious diseases caused by Gram-negative bacteria.

Shotgun proteomic analysis of ESBL-producing and non-ESBL-producing Klebsiella Pneumoniae clinical isolates

Klebsiella pneumoniae is a pathogenic bacterium that is responsible for a wide range of infections in humans. An increased rate of infections caused by multi-drug-resistant K. pneumoniae has been noted in the last two decades. The association between antimicrobial resistance and virulence is an important topic of study. Genomic tools have been used widely for the detection of virulence. In our study, we used proteomic analysis with mass spectrometry and bioinformatics tools to explore the virulence factors of both ESBL-producing and non-ESBL-producing K. pneumoniae and to determine the association between virulence and antimicrobial resistance in these clinical isolates. We have revealed different proteomic profiles and different pathways between the ESBL- and non-ESBL-producing groups. Many proteins involved in stress responses have been reported in the shared proteome between ESBL-and non-ESBL producers, such as ElaB protein, Lon protease, and universal stress proteins G and A. The virulence and pathogenicity of ESBL-producing bacteria were stronger than those of the non-ESBL-producing bacteria. Several unique virulence determinants were identified in ESBL-producing K. pneumoniae, such as proteins with lyase, catalase, isochorismatase, and oxidoreductase activity.

Antibiotic Adjuvants: Make Antibiotics Great Again!

Multiple approaches have been developed to combat bacterial resistance. However, the combination of antibiotic resistance mechanisms by bacteria and the limited number of effective antibiotics available decreases the effective interventions for the treatment of current bacterial infections. This review covers the many ways that bacteria resist antibiotics including antibiotic target modification, the use of efflux pumps, and antibiotic inactivation. As a pertinent example, the use of beta lactamase inhibitors in combination with β-lactam containing antibiotics is discussed in detail. The solution to emerging antibiotic resistance may involve combination therapies of existing antibiotics and potentiating adjuvants, which re-empower the antibiotic agent to become efficacious against the resistant strain of interest. We report herein that a reasoned adjuvant design permits one to perform polypharmacy on bacteria by not only providing greater internal access to the codosed antibiotics but also by de-energizing the efflux pumps used by the bacteria to escape antibiotic action.

Rapid Detection of Extended-Spectrum β-Lactamases (ESBL) and AmpC β-Lactamases in Enterobacterales: Development of a Screening Panel Using the MALDI-TOF MS-Based Direct-on-Target Microdroplet Growth Assay

Introduction: Antibiotic resistant bacteria are a growing concern worldwide. Extended-spectrum β-lactamases (ESBL) represent the most common resistance mechanism of Gram-negative bacteria against β-lactams, underlining the need for adequate diagnostic methods that provide reliable information in the shortest time possible. AmpC, a less prevalent but increasingly relevant class of β-lactamases, pose an additional challenge as their detection is complex. Here, we present an ESBL and AmpC screening panel employing the MALDI-TOF MS-based direct-on-target microdroplet growth assay (DOT-MGA). Materials and Methods: Four reference strains recommended by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) were used to develop the panel, which was further validated on 50 clinical Enterobacterales isolates resistant to third generation cephalosporins. The panel relies on the synergistic effect between ESBL and/or AmpC β-lactamase inhibitors and cephalosporins, which indicates β-lactamase production. Microdroplets containing the tested microorganism, cephalosporins in different concentrations and inhibitors were pipetted onto an MBT Biotarget and incubated for 3 or 4 h at 35 ± 1°C. Afterward, the liquid medium was removed and the material adhered to the spots was analyzed by MALDI-TOF MS. Synergy was detected by determining and comparing the minimum inhibitory concentrations of the tested cephalosporins with and without β-lactamase inhibitors. Data were interpreted following a diagnostic algorithm proposed by EUCAST in order to establish a final diagnosis. In comparison, PCR, broth microdilution (BMD) and combination disk tests (CDT) were performed. Results: Compared to the PCR results, the following positive and negative percent agreement values (PPA/NPA) were obtained for each resistance mechanism: ESBL, 94.44/100%; AmpC, 94.44/93.75% and ESBL+AmpC, 100/100%. These results, obtained after 4 h of incubation, were comparable with those of BMD and showed a higher accuracy than CDT. Discussion: We propose a novel phenotypic method for detection of ESBL and AmpC β-lactamases in Enterobacterales that provides reliable results in a short time, representing a promising alternative to the diagnostic techniques currently available. This easy-to-perform approach has potential for being implemented in routine laboratories, contributing to the further diversification of mass spectrometry technology into other fields such as antibiotic resistance testing.

Subinhibitory concentrations of resveratrol reduce alpha-hemolysin production in Staphylococcus aureus isolates by downregulating saeRS

Resveratrol is a natural phytoalexin. In recent studies, it has been shown to have beneficial effects on cardiovascular disease and cancer and has been deemed to have effective antiviral and immunomodulatory activities. Methicillin-resistant Staphylococcus aureus is a multidrug-resistant pathogen associated with skin and soft tissue infections. Alpha-hemolysin is known to play a key role in the symptoms caused by S. aureus, and the saeRS two-component system has been shown to be a major regulatory system of S. aureus virulence. The present study was designed to determine the effect of subinhibitory concentrations of resveratrol on the production of alpha-hemolysin in S. aureus. The effect of resveratrol on the transcription of S. aureus was studied by transcriptome sequencing. A total of 760 genes with >2-fold changes in expression were selected, including 479 upregulated genes and 281 downregulated genes. On the basis of transcriptome sequencing, the expression of alpha-hemolysin in the S. aureus strains of the resveratrol-treated group was downregulated. Our results showed that resveratrol weakly inhibited the growth of S. aureus strains, and subinhibitory concentration of resveratrol decreased the expression of hla and inhibited the regulation of saeRS. Hemolysis testing confirmed that resveratrol had an inhibitory effect on the hemolysis of rabbit erythrocytes infected with S. aureus strains in a dose-dependent manner. Resveratrol also decreased the hemolytic capacity by reducing the production of alpha-hemolysin. We found that resveratrol could decrease the expression of hla and reduce the secretion of alpha-hemolysin by downregulating saeRS. These findings have provided more evidence of the potential of resveratrol as a drug for resisting S. aureus infections.

Antibiotic Hybrids: the Next Generation of Agents and Adjuvants against Gram-Negative Pathogens?

The global incidence of drug-resistant Gram-negative bacillary infections has been increasing, and there is a dire need to develop novel strategies to overcome this problem. Intrinsic resistance in Gram-negative bacteria, such as their protective outer membrane and constitutively overexpressed efflux pumps, is a major survival weapon that renders them refractory to current antibiotics. Several potential avenues to overcome this problem have been at the heart of antibiotic drug discovery in the past few decades. We review some of these strategies, with emphasis on antibiotic hybrids either as stand-alone antibacterial agents or as adjuvants that potentiate a primary antibiotic in Gram-negative bacteria. Antibiotic hybrid is defined in this review as a synthetic construct of two or more pharmacophores belonging to an established agent known to elicit a desired antimicrobial effect. The concepts, advances, and challenges of antibiotic hybrids are elaborated in this article. Moreover, we discuss several antibiotic hybrids that were or are in clinical evaluation. Mechanistic insights into how tobramycin-based antibiotic hybrids are able to potentiate legacy antibiotics in multidrug-resistant Gram-negative bacilli are also highlighted. Antibiotic hybrids indeed have a promising future as a therapeutic strategy to overcome drug resistance in Gram-negative pathogens and/or expand the usefulness of our current antibiotic arsenal.

Occurrence and characteristics of extended-spectrum β-lactamase- and carbapenemase- producing bacteria from hospital effluents in Singapore

One of the most important resistance mechanisms in Gram-negative bacteria today is the production of enzymes causing resistance to cephalosporin and carbapenem antibiotics. The spread of extended-spectrum β-lactamases (ESBL)- and carbapenemase- producing Gram-negative bacteria is an emerging global public health problem. The aim of the present study was to (i) assess the prevalence of carbapenem-resistant bacteria (CRB) and ESBL-producing strains in sewage effluents from two major hospitals in Singapore, (ii) characterize the isolated strains and (iii) identify some of the ESBL and carbapenemase genes responsible for the resistance. CHROMagar ESBL and KPC plates were used to rapidly screen for ESBL-producing bacteria and those expressing reduced susceptibility to carbapenems, respectively. The abundance of ESBL-producers and CRB in hospital wastewater ranged between 10³ and 10⁶CFU/mL. Out of the 66 isolates picked from ESBL and KPC plates, 95%, 82%, 82% and 76% were resistant to ceftriaxone, ceftazidime (3rd generation cephalosporin family), ertapenem and meropenem (carbapenem family), respectively. Among the resistant isolates, the most predominant taxa identified were Pseudomonas spp. (28.2%), Klebsiella spp. (28.2%), Enterobacter spp. (18.3%) and Citrobacter spp. (11.3%). PCR and sequencing analysis showed that the predominant β-lactamase genes were bla_SHV (41.1%) followed by bla_NDM-1 (35.6%), bla_CTX (35.6%) and bla_KPC (28.8%). The results of this study show a high prevalence of bacteria resistant to modern extended-spectrum cephalosporins and carbapenems and the presence of ESBL- and carbapenemase producers in hospital effluents. These findings support the need to improve management of hospital wastewater in order to minimize the spread of antimicrobial resistant microorganisms from this source.

Prevalence and characteristics of extended-spectrum β-lactamase-producing Escherichia coli in domestic and imported chicken meats in Japan

The purpose of this study was to investigate the prevalence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (ESBL-Ec) in retail chicken meats in Japan. Fifty-six domestic and 50 imported (Brazil, n=36; United States, n=8; Thailand, n=6) chicken meat samples were analyzed. The 162 ESBL-Ec included 111 from 43 (77%) domestic samples and 51 from 26 (52%) Brazilian samples. Fifty-three and 30 of 111 and 51 ESBL-Ec from domestic and Brazilian chickens, respectively, were selected for ESBL genotyping. The bla_CTX-M (91%), bla_TEM (36%) and bla_SHV (15%) genes were detected in ESBL-Ec isolated from domestic chickens, whereas bla_CTX-M (100%) and bla_TEM (20%) were detected in ESBL-Ec isolated from imported chickens. Among the bla_CTX-M group, bla_CTX-M-2 (45%) and bla_CTX-M-1 (34%) were prevalent in domestic chicken isolates, whereas bla_CTX-M-2 (53%) and bla_CTX-M-8 (43%) were prevalent in imported chicken isolates. Domestic chicken isolates were mostly resistant to tetracycline (83%), followed by streptomycin (70%) and nalidixic acid (62%). Imported chicken isolates were resistant to streptomycin (77%), followed by nalidixic acid (63%) and tetracycline (57%). Notably, extensive multidrug resistance was detected in 60% (32/53) and 70% (21/30) ESBL-Ec from domestic and imported chickens, respectively. Virulence genes associated with diarrheagenic and extra-intestinal pathogenic E. coli were detected in ESBL-Ec isolated from domestic and imported chickens. These data suggest that ESBL-Ec in retail chicken meats could be a potential reservoir for antimicrobial resistance determinants and that some are potentially harmful to humans.

Extended spectrum beta-lactamase and metallo beta-lactamase production among Escherichia coli and Klebsiella pneumoniae isolated from different clinical samples in a tertiary care hospital in Kathmandu, Nepal

Background

Extended spectrum beta-lactamase (ESBL) and metallo beta-lactamase (MBL) production in Klebsiella pneumoniae and Escherichia coli are the commonest modes of drug resistance among these commonly isolated bacteria from clinical specimens. So the main purpose of our study was to determine the burden of ESBL and MBL production in E. coli and K. pneumoniae isolated from clinical samples. Further, the antimicrobial susceptibility patterns of E. coli and K. pneumoniae were also determined.

Methods

A cross-sectional study was conducted at Om Hospital and Research Centre, Kathmandu, Nepal by using the E. coli and K. pneumoniae isolated from different clinical samples (urine, pus, body fluids, sputum, blood) from May 2015 to December 2015. Antimicrobial susceptibility testing was performed by Kirby-Bauer disc diffusion technique. Extended spectrum beta-lactamase production was detected by combined disc method using ceftazidime and ceftazidime/clavulanic acid discs and cefotaxime and cefotaxime/clavulanic acid discs. Similarly, metallo beta-lactamase production was detected by combined disc assay using imipenem and imipenem/ethylenediaminetetracetate discs. Bacteria showing resistance to at least three different classes of antibiotics were considered multidrug resistant (MDR).

Results

Of total 1568 different clinical samples processed, 268 (17.1%) samples were culture positive. Among which, E. coli and K. pneumoniae were isolated from 138 (51.5%) and 39 (14.6%) samples respectively. Of the total isolates 61 (34.5%) were ESBL producers and 7 (4%) isolates were found to be MBL producers. High rates of ESBL production (35.9%) was noted among the clinical isolates from outpatients, however no MBL producing strains were isolated from outpatients. Among 138 E. coli and 39 K. pneumoniae, 73 (52.9%) E. coli and 23 (59%) K. pneumoniae were multidrug resistant. The lowest rates of resistance was seen toward imipenem followed by piperacillin/tazobactam, amikacin and cefoperazone/sulbactam.

Conclusions

High rate of ESBL production was found in the E. coli and K. pneumoniae isolated from outpatients suggesting the dissemination of ESBL producing isolates in community. This is very serious issue and can’t be neglected. Regular monitoring of rates of ESBL and MBL production along with multidrug resistance among clinical isolates is very necessary.

Occurrence of Clinically Important Lineages, Including the Sequence Type 131 C1-M27 Subclone, among Extended-Spectrum-β-Lactamase-Producing Escherichia coli in Wastewater

Contamination of environmental waters by extended-spectrum-β-lactamase (ESBL)-producing Escherichia coli (ESBLEC) is of great concern. Wastewater treatment plants (WWTPs) and hospitals release large amounts of ESBLEC into the environment. In the present study, we isolated ESBLEC strains from wastewater collected from a WWTP and a hospital in Japan and performed whole-genome sequencing to characterize these strains. Genomic analysis of 54 strains (32 from the WWTP and 22 from hospital wastewater) revealed the occurrence of clinically important clonal groups with extraintestinal pathogenic E. coli status in the WWTP and hospital wastewater. Fine-scale phylogenetic analysis was performed to further characterize 15 sequence type 131 (ST131) complex strains (11 from the WWTP and 4 from hospital wastewater). These ST131 complex strains were comprised of the following different subgroups: clade A (n = 2), C1-M27 (n = 8), and C1 (non-C1-M27) (n = 1) for strains from the WWTP and clade A (n = 2), C1-M27 (n = 1), and C1 (non-C1-M27) (n = 1) for strains from hospital wastewater. The results indicate that ESBLEC strains belonging to clinically important lineages, including the C1-M27 clade, may disseminate into the environment through wastewater, highlighting the need to monitor for antibiotic resistance in wastewater.

Types and prevalence of extended-spectrum beta-lactamase producing Enterobacteriaceae in poultry

For several billion years, bacteria have developed mechanisms to resist antibacterial substances. In modern time, antibiotics are frequently used in veterinary and human medicine for prevention and treatment of diseases, globally still also for their growth promoting effects as feed additives. This complex situation has evolved in accelerating development and prevalence of multi-drug resistant bacteria in livestock and people. Extended-spectrum beta-lactamase (ESBL) producing bacteria are resistant to a wide range of ß-lactam antibiotics. They are currently considered as one of the main threats for the treatment of infections in humans and animals. In livestock and animal products, poultry and poultry products show the highest prevalence of ESBL-producers with CTX-M-1, TEM-52 and SHV-12 being the most common ESBL-types in poultry. Escherichia coli and Salmonella spp. are the bacteria in poultry, which carry ESBL-genes most frequently. ESBL-producing bacteria are present at every level of the poultry production pyramid and can be detected even in the meconium of newly hatched chicks. The environment close to poultry barns shows high prevalence rates of these bacteria and contributes to an ongoing infection pressure with further ESBL-types. Probiotics have been shown to successfully reduce ESBL-producers in chicken, as well as ESBL-gene transfer. Other feed additives, such as zinc and copper, increase the prevalence of ESBL-producing bacteria when fed to animals. To our best knowledge, this is the first publication presenting a comparative overview of the prevalence of ESBL-types using data from different countries. To reduce the hazard for public health from poultry carrying high numbers of ESBL-producers, preventive measurements must include the surrounding environment and avoidance of antibiotic usage at all levels of the production pyramid. The first results, of the research on the impact of feed additives on the spread of ESBL-genes, indicate the diet as a further, possible magnitude of influence.

The growing threat of carbapenem resistant enterobacteriaceae (CRE) within in-patient spinal rehabilitation units

This case report highlights the present threat and challenges with treatment and transmission of infections caused by carbepenem-resistant enterobacteriaceae (CRE) within in-patient spinal rehabilitation units. The setting is within the Spinal Cord Injury Unit, Royal North Shore Hospital, Sydney, Australia. We report the case of a 45-year-old female with T9 complete paraplegia who developed CRE urinary tract infection (UTI) and sepsis 1 month post injury while in an in-patient spinal rehabilitation unit. We describe the challenges in treatment with colistin, the implications of infection on her rehabilitation and challenges in containing the spread of CRE to other patients in the unit. We present our experience with the management of CRE bactaeraemia in a spinal rehabilitation unit and the enhanced importance of infection control and surveillance strategies required to successfully contain risk of transmission.

Antimicrobial Resistance and Molecular Characterization of Extended-Spectrum β-Lactamases and Other Escherichia coli Isolated from Food of Animal Origin and Human Intestinal Isolates

Antibiotics have always appeared miraculous, saving innumerable lives. However, the unwise use of antimicrobial drugs has led to the appearance of resistant bacteria. The purpose of this study was to evaluate antimicrobial resistance in Escherichia coli (n =160) isolated from food of animal origin. The focus was on E. coli -producing extended-spectrum β-lactamases. E. coli was chosen because it is a part of the normal microbiota in mammals and can enter the food chain during slaughtering and food manipulation. Subsequently, its resistance genes can be transferred to pathogenic bacteria and human microbiota. Phenotypic and genotypic analyses of selected antimicrobial resistances were carried out together with a molecular analysis of virulence genes. E. coli isolates from food of animal origin were compared with clinical E. coli strains isolated from the human intestinal tract. Extended-spectrum β-lactamase-producing E. coli isolates were found in 9.4% of food isolates and in 1.8% of intestinal isolates. Phylogenetically, the majority of food (86.3%) and intestinal E. coli (58.1%) isolates were found to belong to the commensal phylogenetic groups A and B1. The distribution of 4 of 14 analyzed virulence factors was similar in the food and intestinal isolates. Strains isolated from food in Slovenia harbored resistance genes and virulence factors, which can constitute a problem for food safety if not handled properly.

Potential transfer of extended spectrum β-lactamase encoding gene, blashv18 gene, between Klebsiella pneumoniae in raw foods

This study investigated the transfer frequency of the extended-spectrum β-lactamase-encoding gene (blaSHV18) among Klebsiella pneumoniae in tryptic soy broth (TSB), pasteurized milk, unpasteurized milk, alfalfa sprouts and chopped lettuce at defined temperatures. All transconjugants were characterized phenotypically and genotypically. KP04(ΔKM) and KP08(ΔKM) isolated from seed sprouts and KP342 were used as recipients in mating experiments with K. pneumoniae ATCC 700603 serving as the donor. In mating experiments, no transconjugants were detected at 4 °C in liquid media or chopped lettuce, but detected in all media tested at 15 °C, 24 °C, and 37 °C. At 24 °C, the transfer of blaSHV18 gene occurred more frequently in alfalfa sprouts (5.15E-04 transconjugants per recipient) and chopped lettuce (3.85E-05) than liquid media (1.08E-05). On chopped lettuce, transconjugants were not detected at day 1 post-mating at 15 °C, but observed on day 2 (1.43E-05). Transconjugants carried the blaSHV18 gene transferred from the donor and the virulence gene harbored by recipient. More importantly, a class 1 integrase gene and resistance to tetracycline, trimethoprim/sulfamethoxazole were co-transferred during mating. These quantitative results suggest that fresh produce exposed to temperature abuse may serve as a competent vehicle for the spread of gene encoding for antibiotic resistance, having a potential negative impact on human health.

Curing vector for IncI1 plasmids and its use to provide evidence for a metabolic burden of IncI1 CTX-M-1 plasmid pIFM3791 on Klebsiella pneumoniae

Using a sequence-based approach we previously identified an IncI1 CTX-M-1 plasmid, pIFM3791, on a single pig farm in the UK that was harboured by Klebsiella pneumoniae, Escherichia coli and Salmonella enterica serotype 4,5,12:i:-. To test the hypothesis that the plasmid had spread rapidly into these differing host bacteria we wished to assess whether the plasmid conferred a fitness advantage. To do this an IncI1 curing vector was constructed and used to displace the IncI1 CTX-M-1 plasmids from K. pneumoniae strain B3791 and several other unrelated IncI1-harbouring strains indicating the potential wider application of the curing vector. The IncI1 CTX-M-1 plasmid was reintroduced by conjugation into the cured K. pneumoniae strain and also a naturally IncI1 plasmid free S. enterica serotype 4,5,12:i:-, S348/11. Original, cured and complemented strains were tested for metabolic competence using Biolog technology and in competitive growth, association to mammalian cells and biofilm formation experiments. The plasmid-cured K. pneumoniae strain grew more rapidly than either the original plasmid-carrying strain or plasmid-complemented strains in competition experiments. Additionally, the plasmid-cured strain was significantly better at respiring with l-sorbose as a carbon source and putrescine, γ-amino-n-butyric acid, l-alanine and l-proline as nitrogen sources. By contrast, no differences in phenotype were found when comparing plasmid-harbouring and plasmid-free S. enterica S348/11. In conclusion, the IncI1 curing vector successfully displaced multiple IncI plasmids. The IncI1 CTX-M1 plasmid conferred a growth disadvantage upon K. pneumoniae, possibly by imposing a metabolic burden, the mechanism of which remains to be determined.

Emergence of blaCTX-M-15, blaTEM-169 and blaPER-1 extended-spectrum β-lactamase genes among different Salmonella enterica serovars from human faecal samples

BACKGROUND

Broad-spectrum β-lactams are used for empirical therapy of severe infections with non-typhoid Salmonella serotypes; however, activities of these drugs against the strains producing different β-lactamase is not so clear. This study investigated the prevalence of β-lactamase genes among isolates of S. enterica serovars from human faecal samples and determined their diversity in activity against different β-lactams.

METHODS

Antimicrobial resistance of faecal isolates of S. enterica to extended-spectrum cephalosporins was analysed and MIC values were determined for the strains presenting extended-spectrum β-lactamases (ESBLs) phenotypes. The β-lactamase genes were identified by PCR and sequencing. β-lactamase activity of the Salmonella strains exhibiting ESBL phenotype was detected by biological, iodometric, spectrophotometry and nitrocefin assays.

RESULTS

Out of 202 S. enterica isolates, ESBLs phenotype was detected among 3.4% (7/202) of the strains. blaTEM-1 and blaCTX-M-15 were among the frequent β-lactamase genes. Detection of blaTEM-169 in S. enterica serovar Typhimurium and S. enterica serovar Bredeney and blaPER-1 in S. enterica serovar Infantis was a new finding in this experiment. Location of blaCTX-M-15/blaTEM-169/blaPER-1 genes on plasmid was confirmed in a transformation experiment. While crude extracts of the enzymes from each strain showed higher activity against cephalothin and cefotaxime, the lowest activity was detected against ceftazidime. The greatest synergistic activity was seen in a strain of S. enterica that carried blaCTX-M-15 and blaPER-1 genes compared with those presenting blaCTX-M-15/blaTEM-169 or blaCTX-M-15/blaTEM-1 genotypes.

CONCLUSIONS

The results show dissemination of ESBLs encoding genes and their combined activity among different serovars of S. enterica that are a threat for future treatment options.

Prevalence and characteristics of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae isolated from rural well water in Taian, China, 2014

The production of extended-spectrum beta-lactamase (ESBL) is one of the major antimicrobial resistance mechanisms in Enterobacteriaceae, and the increasing number of ESBL-producing Enterobacteriaceae isolated from water environments has posed a serious threat to the public health. The study aimed to analyze prevalence and characterization of ESBL-producing Enterobacteriaceae from rural well waters in Taian, China. A total of 10 isolates expressing an ESBL phenotype, including 9 Escherichia coli (E. coli) and 1 Klebsiella pneumoniae (K. pneumoniae) was obtained from 4 (4%) out of the 100 sampled wells. ESBL genotype revealed that 9 expressed CTX-M-15 and 1 produced CTX-M-27. Five out of 8 ESBL-producing E. coli expressing CTX-M-15 belonged to ST10, which are mostly detected from human feces in China. Importantly, the only strain of CTX-M-27-producing E. coli belonged to multi-locus sequence type B2:131 (ST131), which may be related with severe infection in humans and animals.

Prevalence and characterization of extended-spectrum-β-lactamase-producing Escherichia coli and Klebsiella pneumoniae in ready-to-eat vegetables

The objective of this investigation was to determine the prevalence and characteristics of extended-spectrum-β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae in ready-to-eat (RTE) vegetables. A total of 189 RTE vegetable samples (91 sprouts and 98 mixed salads) were collected in a retail market in South Korea from October 2012 to February 2013. The prevalence of ESBL-producing E. coli and K. pneumoniae was 10.1%. Of these, 94.7% were from the sprout samples. All isolates were resistant to cefotaxime, and many of the ESBL producers were also resistant to non-β-lactam antibiotics, including gentamicin, trimethoprim/sulfamethoxazole, and ciprofloxacin (73.7%, 63.2%, and 26.3% respectively). TEM-1, SHV-1, -2, -11, -12, -27, -28 and -61, and CTX-M-14, -15 and -55 β-lactamases were detected alone or in combination. The genetic platforms of all CTX-M producing isolates were ISEcp1-blaCTX-M-orf477 and ISEcp1-blaCTX-M-IS903 in CTX-M groups 1 and 9, respectively. To our knowledge, this is the first report of the prevalence and characterization of ESBL-producing E. coli and K. pneumoniae isolated from RTE vegetables. The results of this study indicate that RTE vegetables, sprouts, in particular, may play a role in spreading antimicrobial resistant bacteria and ESBL genes to humans.

Enterobacteriaceae resistant to third generation cephalosporins upon hospital admission: risk factors and clinical outcomes

Objectives

Evaluate risk factors and clinical outcomes of infections caused by Enterobacteriaceae resistant to third-generation cephalosporins present in samples collected upon hospital admission.

Methods

Risk factors were evaluated using a 1:2 ratio case–control study. Influence of resistance on the appropriateness of antibiotic therapy, length of stay, and hospital mortality were prospectively evaluated. Characteristics independently associated with the presence of resistant enterobacteria were assessed by logistic regression.

Results

Enterobacteria resistant to third-generation cephalosporins were quite common (26.0%). Male gender (OR: 2.66; 95% CI, 1.17–5.06; p = 0.019), invasive prosthesis (OR: 3.79; 95% CI, 1.29–11.08; p = 0.015), previous use of cephalosporins (OR: 2.77; 95% CI, 1.10–6.97; p = 0.029) and hospitalization in the last 6 months (OR: 5.33; 95% CI, 2.29–12.44; p < 0.001) were independently associated with the presence of these microorganisms. These bacteria were associated with higher frequency of inappropriate antimicrobial therapy, worse clinical response, and longer length of stay. Finally, older age, admission to the ICU, and site of infection other than urinary tract were independently associated to higher hospital mortality.

Conclusions

Risk factors identified in this study may help in the choice of empirical antibiotic therapy for infected patients suspected of harboring these bacteria and in the early implementation of measures to avoid the spread of these bacteria in the hospital environment.

Factors that affect transfer of the IncI1 β-lactam resistance plasmid pESBL-283 between E. coli strains

The spread of antibiotic resistant bacteria worldwide presents a major health threat to human health care that results in therapy failure and increasing costs. The transfer of resistance conferring plasmids by conjugation is a major route by which resistance genes disseminate at the intra- and interspecies level. High similarities between resistance genes identified in foodborne and hospital-acquired pathogens suggest transmission of resistance conferring and transferrable mobile elements through the food chain, either as part of intact strains, or through transfer of plasmids from foodborne to human strains. To study the factors that affect the rate of plasmid transfer, the transmission of an extended-spectrum β-lactamase (ESBL) plasmid from a foodborne Escherichia coli strain to the β-lactam sensitive E. coli MG1655 strain was documented as a function of simulated environmental factors. The foodborne E. coli isolate used as donor carried a CTX-M-1 harboring IncI1 plasmid that confers resistance to β-lactam antibiotics. Cell density, energy availability and growth rate were identified as factors that affect plasmid transfer efficiency. Transfer rates were highest in the absence of the antibiotic, with almost every acceptor cell picking up the plasmid. Raising the antibiotic concentrations above the minimum inhibitory concentration (MIC) resulted in reduced transfer rates, but also selected for the plasmid carrying donor and recombinant strains. Based on the mutational pattern of transconjugant cells, a common mechanism is proposed which compensates for fitness costs due to plasmid carriage by reducing other cell functions. Reducing potential fitness costs due to maintenance and expression of the plasmid could contribute to persistence of resistance genes in the environment even without antibiotic pressure. Taken together, the results identify factors that drive the spread and persistence of resistance conferring plasmids in natural isolates and shows how these can contribute to transmission of resistance genes through the food chain.