Imipenem Resistance Research Articles

Antimicrobial resistance and metallo-beta-lactamase producing among commensal Escherichia coli isolates from healthy children of Khuzestan and Fars provinces; Iran

BackgroundThe emergence of metallo-β-lactamase (MBL)-producing isolates is alarming since they carry mobile genetic elements with great ability to spread; therefore, early detection of these isolates, particularly their reservoir, is crucial to prevent their inter- and intra-care setting dissemination and establish suitable antimicrobial therapies. The current study was designed to evaluate the frequency of antimicrobial resistance (AMR), MBL producers and identification of MBL resistance genes in Escherichia coli strains isolated from fecal samples of the healthy children under 3 years old. A total of 412 fecal E. coli isolates were collected from October 2017 to December 2018. The study population included healthy infants and children aged < 3 years who did not exhibit symptoms of any diseases, especially gastrointestinal diseases. E. coli isolates were assessed to determine the pattern of AMR. E. coli isolates were assessed to determine the pattern of AMR, the production of extended spectrum β-lactamase (ESBL) and MBL by phenotypic methods. Carbapenem-resistant isolates were investigated for the presence of MBL and carbapenemase genes, plasmid profiling, and the ability of conjugation.ResultsIn sum, AMR, multi-drug resistance (MDR) and ESBL production were observed in more than 54.9, 36.2 and 11.7% of commensal E. coli isolates, respectively. Out of six isolates resistant to imipenem and meropenem, four isolates were phenotypically detected as MBL producers. Two and one E. coli strains carried the blaNDM-1 and blaVIM-2 genes, respectively and were able to transmit imipenem resistance through conjugation.ConclusionOur findings showed that children not exposed to antibiotics can be colonized by E. coli isolates resistant to the commonly used antimicrobial compounds and can be a good indicator for the occurrence and prevalence of AMR in the community. These bacteria can act as a potential reservoir of AMR genes including MBL genes of pathogenic bacteria and lead to the dissemination of resistance mechanisms to other bacteria.

Emergence of Imipenem Resistance in a CpxA-H208P-Variant-Producing Proteus mirabilis Clinical Isolate

The Proteus mirabilis PmirS clinical isolate, which was susceptible to imipenem (0.5 μg/mL) and amikacin (1 μg/mL), was recovered from a bronchial aspirate of a patient who recently underwent lung transplantation. The P. mirabilis PmirR clinical isolate, which exhibited resistance to imipenem (16 μg/mL) and amikacin (24 μg/mL), was isolated 3 weeks later from the same patient and the same specimen type. Using short-read sequencing technology, these isolates appeared to be genetically identical except the cpxA gene of the PmirR isolate that was mutated leading to the His-208-Pro substitution. The structural alteration was localized in the histidine kinase, adenylate cyclase, methyl accepting protein, phosphatase (HAMP) domain, which is involved in the signal transduction between the sensor kinase and the regulator response of the CpxA/CpxR two-component system (TCS). No significant defect in the growth rate was found between the PmirS and PmirR isolates. This study suggests that alteration in CpxA might confer imipenem and amikacin resistance in P. mirabilis. This study brings new evidence that the TCS alteration could provide an adaptive capacity in a clinical context by conferring antibiotic resistance without fitness cost.

Activity of imipenem/relebactam against Pseudomonas aeruginosa producing ESBLs and carbapenemases.

ESBL- and carbapenemase-producing Pseudomonas aeruginosa are prevalent in, for example, the Middle East, Eastern Europe and Latin America, though rarer elsewhere. Because P. aeruginosa readily mutate to become carbapenem resistant via loss of OprD, isolates producing ESBLs are often as broadly resistant as those producing carbapenemases. We hypothesized that: (i) relebactam might overcome class A carbapenemases directly in P. aeruginosa; and (ii) relebactam's inhibition of AmpC, which gives a generalized potentiation of imipenem against the species, might restore imipenem susceptibility in OprD-deficient ESBL producers. MICs were determined using CLSI agar dilution for P. aeruginosa isolates producing ESBLs, principally VEB types, and for those producing GES-5, KPC and other carbapenemases. Relebactam potentiated imipenem by around 4-8-fold for most P. aeruginosa isolates producing VEB and other ESBLs; however, MICs were typically only reduced to 4-16 mg/L, thus mostly remaining above EUCAST's susceptible range and only partly overlapping CLSI's intermediate range. Strong (approx. 64-fold) potentiation was seen for isolates producing KPC carbapenemases, but only 2-fold synergy for those with GES-5. Predictably, potentiation was not seen for isolates with class B or D carbapenemase activity. Relebactam did potentiate imipenem against ESBL-producing P. aeruginosa, which are mostly imipenem resistant via OprD loss, but this potentiation was generally insufficient to reduce imipenem MICs to the clinical range. Imipenem resistance owing to KPC carbapenemases was reversed by relebactam in P. aeruginosa, just as for Enterobacterales.

Comparative genomics of the sequential Pseudomonas aeruginosa isolates obtained from the continuous imipenem stress evolution.

Pseudomonas aeruginosa is a major opportunistic human pathogen that causes nosocomial infections, and the proportion of carbapenem resistance has recently dramatically increased in P. aeruginosa due to the overuse of them. In this study, strains G10 and G20, with minimum inhibitory concentration (MIC) of imipenem of 16μg/ml and more than 32μg/ml, were isolated during continuous subculture of cells exposed to stepwise increasing concentrations of imipenem, respectively. The genomes of G10 and G20 were sequenced and compared with parental strain (P. aeruginosa ATCC 27853, G0). There were 59, 59, and 58 genes involved in antibiotic resistance which were predicted in G0, G10, and G20, respectively, while 374, 366, and 363 genes involved in virulence factors were identified among these three strains. Due to the significantly different MICs of imipenem and highly similar profiles of antibiotic resistance and virulence factors related genes among three strains, the specific genetic variations that occurred were identified and compared, including single nucleotide polymorphisms (SNPs), insertions and deletions (InDels), and structural variations (SVs). The increase in the MIC of imipenem was proposed to be linked to mutations involved in polyamine biosynthesis, biofilm formation, OprD, and efflux pump functions. This study aims to clarify the underlying mechanism of imipenem resistance and provide alternative strategies for reducing resistance in P. aeruginosa. KEY POINTS: • Strains with different imipenem MIC were obtained via laboratory selection evolution. • Whole genomes of two strains with different MIC of imipenem were sequenced. • Underlying mechanism of imipenem resistance was clarified via comparative genomics.

Evaluation of the Resistance Profile of Bacteria Obtained From Infected Sites of Dogs in a Veterinary Teaching Hospital in Brazil: A Retrospective Study

The aim of this study was to evaluate the prevalence and antimicrobial resistance profile of bacterial species isolated from infected sites of canines. All samples were collected from canine patients who received clinical or surgical care at the veterinary teaching hospital between March 2016 and November 2017. The samples were analyzed in a private pathology laboratory. A descriptive analysis of 295 antimicrobial susceptibility test reports was performed. Staphylococcus spp. (104/295 [35.25%]), Escherichia coli (100/295 [33.90%]), Proteus spp. (44/295 [14.92%]), Pseudomonas spp. (25/295 [8.47%]), and Klebsiella spp. (20/295 [6.78%]) were more frequently isolated, and a high incidence of multidrug resistance was observed (69,83% [206/295]). Methicillin-resistant Staphylococcus spp. accounted for 33% (33/100) of the Staphylococcus strains. Enterobacteriaceae cefotaxime resistance constituted 22.82 ± 4.49% and Enterobacteriaceae imipenem resistance constituted 5% (1/20) for Klebsiella spp., 5% (5/100) for E coli, and 6.82% (3/44) for Proteus spp. Pseudomonas spp. strains accounted for 8% (2/25) of imipenem resistance and 45.45% (10/22) of polymyxin B resistance. Our findings revealed a high rate of multidrug-resistant bacteria involvement in the infectious process of dogs. From the perspective of the One Health scenario, our results showed alarming data, given the high risk of resistant-strain dissemination between animals, owners, and healthcare professionals. There is an urgent need for strategies to control and prevent the evolution of new multidrug-resistant bacteria in veterinary hospitals. It is also crucial to understand and emphasize the role of veterinary professionals in this public health battle.

Major discrepancy between factual antibiotic resistance and consumption in South of France: analysis of 539,037 bacterial strains

The burden of antibiotic resistance is currently estimated by mathematical modeling, without real count of resistance to key antibiotics. Here we report the real rate of resistance to key antibiotics in bacteria isolated from humans during a 5 years period in a large area in southeast in France. We conducted a retrospective study on antibiotic susceptibility of 539,107 clinical strains isolated from hospital and private laboratories in south of France area from January 2014 to January 2019. The resistance rate to key antibiotics as well as the proportion of bacteria classified as Difficult-to-Treat (DTR) were determined and compared with the Mann–Whitney U test, the χ2 test or the Fisher’s exact test. Among 539,037 isolates, we did not observe any significant increase or decrease in resistance to key antibiotics for 5 years, (oxacillin resistance in Staphylococcus aureus, carbapenem resistance in enterobacteria and Pseudomonas aeruginosa and 3rd generation cephalosporin resistance in Escherichia coli and Klebsiella pneumoniae). However, we observed a significant decrease in imipenem resistance for Acinetobacter baumannii from 2014 to 2018 (24.19–12.27%; p = 0.005) and a significant increase of ceftriaxone resistance in Klebsiella pneumoniae (9.9–24.03%; p = 0.001) and Enterobacter cloacae (24.05–42.05%; p = 0.004). Of these 539,037 isolates, 1604 (0.3%) had a DTR phenotype. Over a 5-year period, we did not observe a burden of AR in our region despite a high rate of antibiotic consumption in our country. These results highlight the need for implementation of real-time AR surveillance systems which use factual data.

Molecular Detection of blaOXA-51 in Carbapenem-resistant Acinetobacterbaumannii Isolated from Different Clinical Sources

Carbapenems are the drugs of choice against serious infections caused by Gram-negative bacteriaCarbapenem-resistant. Acinetobacterbaumannii (CRAB) represents one of the important causing agentsof nosocomial infections especially in immunocompromised and Intensive Care Units (ICUs) patients. Theaim of this work was to identify the Carbapenem-Resistant genes in Acinetobacterbaumannii isolated fromBaghdad and Ramadi hospitals. Among 48A. baumannii isolates, 33 isolates (68.75%) were resistant toimipenem and meropenem. One gene for carbapenem resistance (blaOXA-51 like) were amplified by PCR.The presence of blaOXA-51-like genes in 100% of CRAB isolates indicated that the blaOXA-51-like genesare the predominant mechanism for imipenem resistance in our isolates.

High Frequency of AdeA, AdeB and AdeC Genes among Acinetobacter baumannii Isolates.

Background:Efflux pumps are involved in resistance of Acinetobacter baumannii isolates to antimicrobial agents. AdeABC efflux pump is one of the RND superfamily efflux pump and consists of adeA (membrane fusion), adeB (multidrug transporter) and adeC (outer membrane) genes. In this study, the frequency of adeA, adeB and adeC genes among A. baumannii isolates with resistance to erythromycin, trimethoprim, meropenem and imipenem was investigated.Methods:Overall, 79 strains of A. baumannii were isolated from patients admitted to two major hospitals in Tehran during 2016. Antibiotic susceptibility testing was determined by disc diffusion and microdilution methods according to Clinical and Laboratory Standards Institute (CLSI) guideline. The presence of adeA, adeB and adeC genes was also determined using Multiplex PCR assay.Results:The highest and the lowest resistance among A. baumannii isolates were to trimethoprim (93%) and erythromycin (53%), respectively. The frequency of adeA, adeB and adeC genes was 96.2%, 96.2% and 91.1 % respectively. There was a significant relationship between imipenem resistance and presence of efflux pump genes (P<0.05).Conclusion:According to the high prevalence of the AdeABC efflux system genes, it may involve in resistance of clinical isolates of A. baumannii to imipenem, especially.

&lt;p&gt;Zinc Chelator N,N,N′,N′-Tetrakis(2-Pyridylmethyl)Ethylenediamine Reduces the Resistance of &lt;em&gt;Mycobacterium abscessus&lt;/em&gt; to Imipenem&lt;/p&gt;

PurposeImipenem is one of the very few effective options for treating Mycobacterium abscessus (M. abscessus) infections; the development of imipenem resistance is a major health concern.Materials and MethodsThe susceptibility of 194 clinical M. abscessus isolates to imipenem was determined. The ability of imipenem to synergize with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), a zinc chelator and a metallo-β-lactamases (MBLs) inhibitor, to inhibit M. abscessus growth was also assessed.ResultsM. abscessus exhibited an elevated resistance to imipenem (MIC50 = 16 mg/L, MIC90 = 64 mg/L). A combination of TPEN and imipenem synergized to inhibit the growth of 100% of imipenem-resistant and 79.2% of imipenem-resistance intermediate isolates; no synergy was observed treating imipenem-sensitive isolates. A remarkable decrease in the MIC50 (from 16 to 4 mg/L) and MIC90 (from 64 to 8 mg/L) of imipenem was observed when it was combined with TPEN; the portion of imipenem-resistant isolates also decreased (from 48.4% to 0%). Consistent with these results demonstrating synergy, a time-kill assay showed the addition of TPEN significantly improved the bactericidal activity of imipenem toward M. abscessus. Similarly, EDTA (a potent MBLs inhibitor) promoted the anti-M. abscessus activity of imipenem in a disk assay, corroborating the effect of TPEN and supporting the role of MBLs in imipenem resistance exhibited by some isolates.ConclusionThese findings demonstrate that TPEN can reduce the resistance of M. abscessus to imipenem and suggest that the inhibition of MBLs activity is the underlying mechanism.

BlaNDM-1, blaKPC, blaOXA-181- as the major mediators of carbapenem resistance in carbapenemase producing Escherichia coli and Klebsiella species isolated from a tertiary care hospital in Bangladesh

Background and objectives: Carbapenem resistance is an emerging problem worldwide. Detection of carbapenem resistance genes is important to institute appropriate therapy and to initiate preventive measures. This study was conducted to determine the presence of carbapenemase enzyme producing Escherichia coli and Klebsiella species in a tertiary care hospital of Bangladesh, as well as to observe the patterns of antibiotic resistance and carbapenem resistance genes among them.&#x0D; Methodology: Total 166 Escherichia coli, Klebsiella pneumoniae and Klebsiella oxytoca were isolated from urine, wound swab, pus, sputum and blood samples of patients of Dhaka Medical College Hospital. Antibiotic susceptibility test was performed by disk-diffusion technique. Carbapenemase producers were detected phenotypically by Double-disk synergy (DDS) test, Modified Hodge test (MHT) and Combined disk (CD) assay. Minimum inhibitory concentration (MIC) of imipenem was done by agar dilution method among carbapenemase producing strains. Genotypically carbapenemase genes (blaNDM-1, blaVIM, blaIMP, blaKPC, blaOXA-48/blaOXA-181) among the imipenem resistant Escherichia coli and Klebsiella species were detected by polymerase chain reaction (PCR). Sequencing was done to differentiate blaOXA-181 gene from blaOXA-48 gene. Class 1 integron were also detected by PCR using specific primer among carbapenemase producers.&#x0D; Results: Thirty seven (22.29%) imipenem resistant isolates were detected during disk-diffusion technique, among them 16 (43.24%) carbapenemase producers were detected by MHT, 20 (54.05%) by DDS test, 22 (59.46%) by CD assay and 23 (62.16%) by PCR. Out of 23 carbapenemase producing strains, MIC of imipenem ranged from 4 μg/ml up to ≥128 μg/ml. NDM-1 (43.24%) was the dominant genotype in imipenem resistant strains followed by KPC (21.62%) and OXA-181 (18.92%). Class 1 integron were present in 16 (69.57%) of the genotypically identified carbapenemase producers.&#x0D; Conclusion: The results of this study showed high proportion of carbapenemase enzyme producing Escherichia coli and Klebsiella species in Bangladesh. Genes encoding carbapenemase enzymes including blaNDM-1, blaKPC, blaVIM, blaIMP and blaOXA-181 were responsible for imipenem resistance. blaNDM-1 producers are increasing and blaKPC and blaOXA-181 producers are emerging in Bangladesh. Regular surveillance of antibiotic resistance should be done in every tertiary care hospital to prevent spread of these strains.&#x0D; Bangladesh J Med Microbiol 2020; 14 (2): 25-29

Overexpression of bla OXA-58 Gene Driven by ISAba3 Is Associated with Imipenem Resistance in a Clinical Acinetobacter baumannii Isolate from Vietnam.

The aim of this study was to investigate genetic structures and expression of blaOXA-58 gene in five Acinetobacter baumannii clinical isolates recovered from two hospitals in southern Vietnam during 2012-2014. A. baumannii isolates were identified by automated microbiology systems and confirmed by PCR. All isolates were characterized as multidrug resistant by antimicrobial testing using the disk diffusion method. Four imipenem susceptible and one nonsusceptible isolates (MIC > 32 μg·ml−1) were identified by E-test. PCR amplification of blaOXA-58 gene upstream and downstream sequences revealed the presence of ISAba3 at both locations in one multidrug-resistant isolate. Semiquantitation of blaOXA-51 and blaOXA-58 gene expression was performed by the 2-ΔΔCt method. The blaOXA-51 gene expression of five isolates showed little difference, but the isolate bearing ISAba3-blaOXA-58-ISAba3 exhibited significantly higher blaOXA-58 mRNA level. Higher β-lactamases activity in periplasmic than cytoplasmic fraction was found in most isolates. The isolate overexpressing blaOXA-58 gene possessed very high periplasmic enzyme activity. In conclusion, the A. baumannii isolate bearing ISAba3-blaOXA-58 gene exhibited high resistance to imipenem, corresponding to an overexpression of blaOXA-58 gene and very high periplasmic β-lactamase activity.

Assessment of microbiological quality and contamination level of Hospital water samples collected from storage points

Drinking water contamination at the level of storage points poses a potential threat to the hospital environment as it can lodge some resistant pathogenic microorganisms that may cause hospital acquired infections. The study analyzed the physico-chemical and microbiological parameters of drinking water samples collected from the main water storage points from ten different local hospitals in and around Visakhapatnam using standard protocols. The samples were processed within 2 hours after collection and the identification of pathogenic bacteria was performed through Most Probable Number (MPN) method, cultural characteristics and biochemical reactions. Antimicrobial susceptibility test was carried out by Agar well diffusion method according to Clinical and Laboratory Standards Institute (CLSI) guidelines. In the current study, all the tested ten water samples cross the permissible MPN count indicating that the water samples were not potable for drinking purpose and needs further and better disinfection procedures. Among the isolated pathogens, Pseudomonas aeruginosa exhibited highest sensitivity to antibiotics imipenem (50%) and tetracycline (50%) and resistance towards other tested antibiotics, whereas E.coli showed 100% susceptibility to imipenem and 100% resistance to ampicillin. Out of ten isolated strains of Proteus species, majority have exhibited 80% resistance to ampicillin and Tetracycline and 80% sensitivity to imipenem. All the four isolated strains of Shigella species expressed 100% resistance to ampicillin and 75% sensitivity to imipenem, meropenem, azithromycin, linezolid, vancomycin and chloramphenicol. The five isolated strains of Vibrio species showed 100% resistance to ampicillin and 80% sensitivity to imipenem, doxycycline and tetracycline. Greater part of the isolates were multidrug resistant isolates.

Detection of blaSPM-1 and blaSIM-2 Metallo-β-Lactamases Genes in Imipenem-Resistant Pseudomonas aeruginosa Clinical Isolates Recovered from Two University Hospitals in Egypt

Objectives: Unraveling mechanisms whereby Pseudomonas aeruginosa becomes resistant to carbapenems through testing 114 non-duplicate P. aeruginosa clinical isolates for their susceptibility to various classes of antibiotics and scrutinizing the production of metallo-β-lactamases (MBLs) by tested isolates. Methods: Susceptibility testing of P. aeruginosa to different antibiotics was determined by Kirby-Bauer disk diffusion method and MBLs production by tested isolates was studied phenotypically and genotypically and PCR products were confirmed by sequencing Results: All tested clinical isolates showed eminent resistance to the majority of tested antibiotics and 14 isolates were imipenem (IPM)-resistant. Furthermore, IPM-resistant isolates were verified to be MBLs-producers. MBLs-encoding genes blaSIM and blaSPM genes were detected by PCR where four isolates were found to harbor blaSPM gene while only one isolate harbored blaSIM gene. The correct size of PCR products of blaSIM and blaSPM genes were sequenced and sequences were submitted to the GenBank databases and assigned the accession numbers KX452682 and KX452683 for blaSIM-2 and blaSPM-1, respectively. Conclusion: Here, we report the emanation of P. aeruginosa clinical isolates harboring blaSPM-1 and blaSIM-2 genes. This may reflect the substantial increase in the rate of imipenem resistance due to MBL in P. aeruginosa clinical isolates from Egypt. Early detection and infection-control practices are of the best antimicrobial strategy for combating this organism.

Detection, Characterization and Antibiotic Susceptibility of Clostridioides (Clostridium) difficile in Meat Products.

Clostridioides (Clostridium) difficile is a Gram (+), anaerobic, spore forming, rod shaped bacterium that can produce toxin. The objective of this study is to reveal the presence of C. difficile in meat products, to analyze the ribotype diversity by PCR and to evaluate the antibiotic susceptibility of isolated strains. The organism was isolated in 22 out of 319 (6.9%) examined meat product samples and 9 out of 22 (40.9%) isolates were identified as RT027 and all isolates had the ability of toxin production. In terms of antibiotic susceptibility, all isolates were susceptive to amoxicillin-clavulanic acid, tetracycline and vancomycin and 21 (95.4%) isolates to metronidazole. On the other hand, imipenem and cefotaxim resistance was observed in all. In conclusion, the results of this comprehensive study conducted in Turkey deduced the presence of C. difficile in different meat products. Therefore, these products can be evaluated as a potential contamination source of C. difficile from animals to humans especially for elders, youngsters, long terms wide spectrum antibiotic used and immuno-suppressed individuals.

Antimicrobial Resistance Profiles and Clonal Relationship among Non-ESBL Avian Pathogenic Escherichia coli Isolates and ESBL Producing E. coli Isolates from Human Urinary Tract Infections

Background: We aimed to investigate antimicrobial resistance and clonal relationships among poultry Escherichia coli isolates from different broiler farms and their relationships with Extended-Spectrum Beta-Lactamase (ESBL) producing urinary pathogenic E. coli (UPEC) isolates from the same geographical area. Methods: Twenty four E. coli isolates from six broiler farms with colibacillosis and 97 ESBL producing human UPEC isolates were investigated for resistance to critically important antimicrobials in human medicine in Shiraz, central Iran in 2015-16. In addition, clonal relationships of these isolates were investigated with Pulse Field Gel Electrophoresis (PFGE). Results: As expected, cephalosporins and imipenem resistance were significantly higher in ESBL producing human E. coli isolates in comparison with non-ESBL avian pathogenic E. coli (APEC) isolates. In addition, significantly higher percentages of gentamycin and trimethoprim-sulfamethoxazole resistance were seen in human isolates. In contrast, nitrofurantoin resistance was significantly higher in APEC isolates. Based on PFGE patterns, five clusters were identified in APEC isolates. Isolates from each farm were closely related to each other by PFGE patterns. However, different PFGE restriction profiles were seen among the E. coli isolates from different broiler farms. Comparison of PFGE patterns among APEC and UPEC isolates showed two closely related PFGE patterns. Conclusion: There were clonally related E. coli isolates caused the outbreaks of colibacillosis within broiler farms. Some of these isolates had closely related PFGE patterns with human UPEC isolates which suggest avian pathogenic E. coli strains as a potential zoonosis.

In vitro dynamics and mechanisms of resistance development to imipenem and imipenem/relebactam in Pseudomonas aeruginosa.

We analysed the dynamics and mechanisms of resistance development to imipenem alone or combined with relebactam in Pseudomonas aeruginosa WT (PAO1) and mutator (PAOMS; ΔmutS) strains. PAO1 or PAOMS strains were incubated for 24 h in Mueller-Hinton Broth with 0.125-64 mg/L of imipenem ± relebactam 4 mg/L. Tubes from the highest antibiotic concentration showing growth were reinoculated in fresh medium containing concentrations up to 64 mg/L of imipenem ± relebactam for 7 days. Two colonies per strain, replicate experiment and antibiotic from early (Day 1) and late (Day 7) cultures were characterized by determining the susceptibility profiles, WGS and determination of the expression of ampC and efflux-pump-coding genes. Virulence was studied in a Caenorhabditis elegans infection model. Relebactam reduced imipenem resistance development for both strains, although resistance emerged much faster for PAOMS. WGS indicated that imipenem resistance was associated with mutations in the porin OprD and regulators of ampC, while the mutations in imipenem/relebactam-resistant mutants were located in oprD and regulatoras of MexAB-OprM. High-level imipenem/relebactam resistance was only documented in the PAOMS strain and was associated with an additional specific (T680A) mutation located in the catalytic pocket of ponA (PBP1a) and with reduced virulence in the C. elegans model. Imipenem/relebactam could be a useful alternative for the treatment of MDR P. aeruginosa infections, potentially reducing resistance development during treatment. Moreover, this work deciphers the potential resistance mechanisms that may emerge upon the introduction of this novel combination into clinical practice.

Molecular epidemiology of imipenem resistance in invasive Haemophilus influenzae infections in Germany in 2016

The carbapenems imipenem and meropenem play an important role in the empirical anti-infective treatment of critically ill patients. Carbapenem resistance in Haemophilus influenzae (Hi) has rarely been reported. We provide prevalence data for resistance to carbapenems from laboratory surveillance of invasive Hi infections in Germany in 2016. Phenotypic susceptibility testing against ampicillin, amoxicillin/clavulanate, cefotaxime and imipenem was carried out on 474 isolates from blood and CSF. The isolates were collected as part of the national laboratory surveillance programme. Imipenem-resistant strains were further tested for meropenem susceptibility. Molecular analysis was done by ftsI sequencing to detect mutations in PBP3, by acrR sequencing to detect alterations in the regulatory protein of the AcrAB-TolC efflux pump and by MLST. No resistance to meropenem was detected. Cefotaxime resistance was rare (n = 3; 0.6%). Imipenem resistance was found in 64 strains (13.5%) using gradient agar diffusion and was confirmed in 26 isolates by broth microdilution (5.5%). Imipenem resistance occurred predominantly in Hi that were β-lactamase negative but ampicillin resistant and in those that were β-lactamase positive but nevertheless amoxicillin/clavulanate resistant. This finding suggested a β-lactamase-independent mechanism. Accordingly, sequence analysis of PBP3 identified previously described mutations. MLST of the imipenem-resistant strains, which were all non-typeable Hi, revealed a high diversity. We conclude that imipenem, but not meropenem, resistance is frequent in Hi. It is likely to be supported by PBP3 mutations.

Evaluation of type II Toxin-Antitoxin Systems, Antibiotic Resistance Profiles, and Biofilm Quorum Sensing Genes in Acinetobacter Baumannii Isolates in Iraq.

Bacterial Toxin-Antitoxin (TAs) systems are extensive two-component elements in the bacterial genome, which are involved in many key biological functions, including growth arrest, survival, biofilm formation, plasmid maintenance, defense against phages, persistence, and virulence. This study aimed to assess the molecular determinants involved in TAs, biofilm quorum sensing, and antibiotic resistance profiles in Acinetobacter baumannii isolated from Baghdad's hospitals in Iraq. A total of 127 A. baumannii isolates were collected from 2160 different clinical samples. The antimicrobial susceptibility test was performed using the disk diffusion test. All isolates were characterized for molecular determinants involved in TAs and biofilm formation using the wellknown PCR-based sequencing assay. A high multi-drug resistant (MDR) (96.06%; 122/127) and imipenem resistance (84.25%; 107/127) rates were observed from A.baumannii isolates. Results showed the presence of rhlIR gene in three isolates (2.36%), and lasIR gene appeared in two isolates (1.57%) isolates, whilst, mazEF, ccdAB, and relBE genes have not been detected among any of the isolates. A high MDR and imipenem resistance rates within a low prevalence of rhlIR, and lasIR genes could be found in clinical A. baumannii isolates from some of the Iraqi hospitals.

Genetic diversity and in vitro activity of ceftazidime/avibactam and aztreonam/avibactam against imipenem-resistant Enterobacteriaceae isolates in Southwest China: A single-centre study

ObjectivesThe aim of this study was to investigate the molecular mechanisms of imipenem resistance in Enterobacteriaceae and to assess the antimicrobial activities of ceftazidime/avibactam (CAZ/AVI) and aztreonam/avibactam (ATM/AVI) against imipenem-resistant clinical isolates in a tertiary hospital in China. MethodsA total of 91 imipenem-resistant Enterobacteriaceae were collected and genes encoding carbapenemases, ESBLs, AmpC β-lactamases and porins were detected using PCR. MICs and susceptibility were determined using in-house-prepared broth microdilution panels and were interpreted according to CLSI breakpoints. ResultsImipenem-resistant isolates comprising 54 Klebsiella pneumoniae, 18 Escherichia coli, 8 Enterobacter cloacae, 6 Serratia marcescens, 3 Klebsiella oxytoca and 2 Klebsiella aerogenes were collected independently. Five different carbapenemase genes were identified, namely blaKPC-2 (n = 60), blaNDM-5 (n = 14), blaNDM-1 (n = 11), blaKPC-3 (n = 4) and blaIMP-4 (n = 1). Among the 91 carbapenem-resistant Enterobacteriaceae (CRE), 85 isolates harboured at least one ESBL and/or AmpC gene, including 5 strains without carbapenemase-encoding genes. Moreover, 31 K. pneumoniae carried ompK35 and/or ompK36 mutations. MLST results showed that the K. pneumoniae belonged to 12 different STs, with ST11 being predominant (29/54; 53.7%). Overall, 17.6%, 25.3%, 41.8%, 65.9% and 100% of the CRE strains were susceptible to amikacin, trimethoprim/sulfamethoxazole, tetracycline, CAZ/AVI and ATM/AVI, respectively. ConclusionThis study revealed that CRE isolates differ significantly in their species, STs, porins and carbapenemase genes in a single Chinese hospital. ATM/AVI exhibited potent activity against CRE isolates, even for the most notorious double-carbapenemase-producers with porin defects, whereas CAZ/AVI was active against all the non-metallo-β-lactamase-producing isolates.

&lt;p&gt;Mechanisms of Heteroresistance and Resistance to Imipenem in &lt;em&gt;Pseudomonas aeruginosa&lt;/em&gt;&lt;/p&gt;

BackgroundHeteroresistance is a phenomenon that occurs in all bacteria and can cause treatment failure. Yet, the exact mechanisms responsible for heteroresistance still remain unknown. The following study investigated the mechanisms of imipenem-heteroresistance and -resistance in Pseudomonas aeruginosa clinical isolates from Wenzhou, China.MethodsImipenem resistance was detected by the agar dilution method; heteroresistance was determined by population analysis profiles. Biofilm formation assay and modified carbapenem inactivation methods were also performed. Polymerase chain reaction (PCR) was conducted to detect oprD, and quantitative real-time PCR was used to determine expression levels of oprD, ampC and four efflux pump coding genes (mexB, mexD, mexE and mexY).ResultsSix imipenem-heteroresistant and -resistant P. aeruginosa isolates were selected respectively. Deficient oprD was detected in all resistant isolates and two heteroresistant isolates. No strains produced carbapenemases. Expression levels of oprD were down-regulated in heteroresistant isolates. Transcription levels of the mexE and mexY were significantly increased in all heterogeneous subpopulations compared with their respective native ones. Compared with the susceptible group, increased mean relative expression levels of mexE and mexY or the decreased mean relative expression levels of oprD were observed in the resistant group (P < 0.05), whereas transcription levels of the mexB and mexD remained unchanged.ConclusionDown-regulation of oprD contributed to the resistance and heteroresistance of imipenem in our P. aeruginosa clinical isolates. In addition, the marginal up-regulation of efflux systems may indirectly affect imipenem resistance. Contrarily, defective oprD was less common in our experimental heteroresistant strains than resistant strains.