Metallo-beta-lactamases as emerging resistance determinants in Gram-negative pathogens: open issues

Redirecting pantoprazole as a metallo-beta-lactamase inhibitor in carbapenem-resistant Klebsiella pneumoniae

The development of resistance to carbapenems in Klebsiella pneumoniae due to the production of metallo-β-lactamases (MBLs) is a critical public health problem because carbapenems are the last-resort drugs used for treating severe infections of extended-spectrum β-lactamases (ESBLs) producing K. pneumoniae. Restoring the activity of carbapenems by the inhibition of metallo-β-lactamases is a valuable approach to combat carbapenem resistance. In this study, two well-characterized clinical multidrug and carbapenem-resistant K. pneumoniae isolates were used. The sub-inhibitory concentrations of pantoprazole and the well-reported metallo-β-lactamase inhibitor captopril inhibited the hydrolytic activities of metallo-β-lactamases, with pantoprazole having more inhibiting activities. Both drugs, when used in combination with meropenem, exhibited synergistic activities. Pantoprazole could also downregulate the expression of the metallo-β-lactamase genes bla NDM and bla VIM. A docking study revealed that pantoprazole could bind to and chelate zinc ions of New Delhi and Verona integron-encoded MBL (VIM) enzymes with higher affinity than the control drug captopril and with comparable affinity to the natural ligand meropenem, indicating the significant inhibitory activity of pantoprazole against metallo-β-lactamases. In conclusion, pantoprazole can be used in combination with meropenem as a new strategy for treating serious infections caused by metallo-β-lactamases producing K. pneumoniae.

Frequency and diversity of carbapenemase-producing Enterobacterales recovered from untreated wastewater impacted by selective media containing cefotaxime and meropenem in Ohio, USA

As safe agents of last resort, carbapenems are reserved for the treatment of infections caused by multidrug-resistant organisms. The impact of β-lactam antibiotics, cefotaxime, and meropenem on the frequency and diversity of carbapenemase-producing organisms recovered from environmental samples has not been fully established. Therefore, this methodological study aimed at determining β-lactam drugs used in selective enrichment and their impact on the recovery of carbapenemase-producing Enterobacterales (CPE) from untreated wastewater. We used a longitudinal study design where 1L wastewater samples were collected weekly from wastewater treatment plant (WWTP) influent and quarterly from contributing sanitary sewers in Columbus, Ohio USA with 52 total samples collected. Aliquots of 500 mL were passed through membrane filters of decreasing pore sizes to enable all the water to pass through and capture bacteria. For each sample, the resulting filters were placed into two modified MacConkey (MAC) broths, one supplemented with 0.5 μg/mL of meropenem and 70 μg/mL of ZnSO4 and the other supplemented with 2 μg/mL cefotaxime. The inoculated broth was then incubated at 37° C overnight, after which they were streaked onto two types of correspondingly-modified MAC agar plates supplemented with 0.5 μg/mL and 1.0 μg/mL of meropenem and 70 μg/mL of ZnSO4 and incubated at 37°C overnight. The isolates were identified based on morphological and biochemical characteristics. Then, up to four distinct colonies of each isolate's pure culture per sample were tested for carbapenemase production using the Carba-NP test. Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) MALDI-TOF MS was used to identify carbapenemase-producing organisms. In total 391 Carba-NP positive isolates were recovered from the 52 wastewater samples: 305 (78%) isolates had blaKPC, 73 (19%) carried blaNDM, and 14 (4%) harbored both blaKPC and blaNDM resistance genes. CPE genes of both blaKPC and blaNDM were recovered in both types of modified MAC broths, with 84 (21%) having a blaKPC gene, 22 (6%) carrying blaNDM and 9 (2%) harbored both a blaKPC and blaNDM of isolates recovered from MAC medium incorporated with 0.5ug/mL meropenem and 70ug/mL ZnSO4. The most prevalent isolates were Klebsiella pneumoniae, Escherichia coli, and Citrobacter spp.

A nomogram for predicting the risk of mortality in patients with acute pancreatitis and Gram-negative bacilli infection

OBJECTIVE

Gram-negative bacilli (GNB) are common pathogens of infection in severe acute pancreatitis (SAP), and their occurrence increases the mortality of SAP. Early identification of SAP severity and prognosis is of great significance to SAP treatment. This study explored risk factors for mortality in patients with SAP and GNB infection and established a model for early prediction of the risk of death in GNB-infected SAP patients.

METHODS

Patients diagnosed with SAP from January 1, 2016, to March 31, 2022, were included, and their baseline clinical characteristics were collected. Univariate logistic regression analysis was performed to screen for death related variables, and concurrently, a Boruta analysis was performed to identify potentially important clinical features associated with mortality. The intersection of the two results was taken for further multivariate logistic regression analysis. A logistic regression model was constructed according to the independent risk factor of death and then visualized with a nomogram. The performance of the model was further validated in the training and validation cohort.

RESULTS

A total of 151 patients with SAP developed GNB infections. Univariate logistic regression analysis identified 11 variables associated with mortality. The Boruta analysis identified 11 clinical features, and 4 out of 9 clinical variables: platelet counts (odds ratio [OR] 0.99, 95% confidence interval [CI] 0.99-1.00; p = 0.007), hemoglobin (OR 0.96, 95% CI 0.92-1; p = 0.037), septic shock (OR 6.33, 95% CI 1.12-43.47; p = 0.044), and carbapenem resistance (OR 7.99, 95% CI 1.66-52.37; p = 0.016), shared by both analyses were further selected as independent risk factors by multivariate logistic regression analysis. A nomogram was used to visualize the model. The model demonstrated good performance in both training and validation cohorts with recognition sensitivity and specificity of 96% and 80% in the training cohort and 92.8% and 75% in the validation cohort, respectively.

CONCLUSION

The nomogram can accurately predict the mortality risk of patients with SAP and GNB infection. The clinical application of this model allows early identification of the severity and prognosis for patients with SAP and GNB infection and identification of patients requiring urgent management thus allowing rationalization of treatment options and improvements in clinical outcomes.

Characterization of the novel plasmid-encoded MBL gene blaAFM-1, integrated into a blaIMP-45-bearing transposon Tn6485e in a carbapenem-resistant Pseudomonas aeruginosa clinical isolate

OBJECTIVES

To characterize the novel subclass B1 MBL AFM-1, encoded by a blaIMP-45-bearing megaplasmid from a carbapenem-resistant Pseudomonas aeruginosa (CRPA) clinical isolate.

METHODS

CRPA HS17-127 and its transconjugant were discovered to carry blaAFM-1 in our previous study. blaAFM-1 and blaNDM-1 were cloned and expressed in Escherichia coli TOP10 and P. aeruginosa PAO1, respectively, to test the resistance phenotype. Kinetic studies were performed to elucidate the biochemical characteristics of the AFM-1 enzyme. Comparative genomic analysis was applied to investigate the genetic context of blaAFM-1.

RESULTS

PAO1 transconjugant TcHS17-127 exhibited carbapenem resistance with an imipenem MIC of 64 mg/L. E. coli transformants with cloned blaAFM-1 or blaNDM-1 had increased MICs of all β-lactams tested (except aztreonam) and imipenem MICs of 4-8 mg/L. Kinetic studies showed that AFM-1 had greater catalytic efficiency against cephalosporins than carbapenems. blaAFM-1 was located on a 486 963 bp IncP-2 plasmid, pHS17-127, containing a 57.3 kb MDR Tn1403-derivative transposon, Tn6485e, which is genetically closest to the blaIMP-45-bearing Tn6485 transposon but has acquired an extra ISCR27n3-blaAFM-1 module. Multicentre surveillance of 605 P. aeruginosa clinical isolates identified three blaAFM carriers from different STs. Two of them co-carried blaAFM-1 and blaIMP-45. A BLAST search against the NCBI database showed six blaAFM carriers on various plasmids and the chromosomes of different Gram-negative species.

CONCLUSIONS

The blaAFM-1 gene confers carbapenem resistance and has been captured in distinct species of non-fermenters. Co-carriage of blaAFM-1 and blaIMP-45 in an MDR transposon on a conjugative plasmid can be expected to promote further dissemination of blaMBLs.

Prevalence and molecular characterization of β-lactamase producers and fluoroquinolone resistant clinical isolates from North East India

INTRODUCTION

The rapid emergence and variations of antibiotic resistance among common gram negative bacteria cause a significant concern specially in India and all over the world because of high mortality and morbidity rates.

METHODS

In our study, we screened 189 bacterial isolates from Assam Medical College & Hospital, Dibrugarh for antibiotic resistance pattern and tried to identify the resistant genes causing responsible for β-lactam and fluoroquinolones resistance.

RESULTS

More than 80% and 45% strains were resistant to all the 3rd generation cephalosporins, fluoroquinolones respectively. Among the 3rd generation cephalosporin resistant strains, 38% and 24% isolates were only ESBL and MBL producers respectively and 11% were reported to have both ESBL and MBL genes. The ESBL positive isolates have shown the dominance of CTX-M3 gene. VIM-1 gene was mostly reported in MBL producers. Our study probably for the first time reporting SIM-1 and SPM-1 MBL gene from India. Mutations in QRDR is found to be the primary cause of fluoroquinolone resistance along with efflux pump and PMQR presence.

CONCLUSION

The study represents the first detailed study on antibiotic resistance from NE India this could help to take control measures for the emerging antibiotic resistance in hospital and community based infections in North East India.

Treatment of severe infections due to metallo-β-lactamases-producing Gram-negative bacteria

In the last decades, there was an important paucity of agents for adequately treating infections due to metallo-β-lactamases-producing Gram-negative bacteria (MBL-GNB). Cefiderocol, a novel siderophore cephalosporin showing in vitro activity against MBL-GNB, has been recently marketed, and a combination of aztreonam and ceftazidime/avibactam has shown a possible favorable effect on survival of patients with severe MBL-GNB infections in observational studies. Other agents showing in vitro activity against MBL-GNB are currently in clinical development (e.g., cefepime/taniborbactam, LYS228, cefepime/zidebactam) that could be an important addition to our future armamentarium for severe MBL-GNB infections. Nonetheless, we should not discontinue our efforts to optimize the use of non-β-lactams agents, since they could remain an essential last-resort or alternative option in selected cases.

Emergence and Persistence over Time of Carbapenemase-Producing Enterobacter Isolates in a Spanish University Hospital in Madrid, Spain (2005-2018)

Carbapenemase production is constantly increasing among different Enterobacterales species. We analyzed the microbiological characteristics and population structure of all carbapenemase-producing Enterobacter spp. (CP-Ent) isolates recovered at the Ramón y Cajal Hospital between 2005 and 2018. Overall, 178 CP-Ent isolates (60.7% colonization, 39.3% clinical) were recovered from 165 hospitalized patients (165/176, 93.7%; medical [102/165], surgical [34/165], and intensive care unit [29/165] areas), emergency unit (4/176, 2.3%), and ambulatory patients (7/176, 4.0%). In addition, three CP-Ent were found in environmental sources. Clinical samples were mainly urine (37.1%). The most frequent matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-identified species were Enterobacter cloacae (n = 85) and Enterobacter asburiae (n = 49). hsp60 gene sequencing showed a higher species diversity than MALDI-TOF: 70 Enterobacter hormaechei-clusters III, VI, VIII; 69 Enterobacter roggenkampii-IV; 15 Enterobacter kobei-II; 9 E. asburiae-I; 3 Enterobacter ludwigii-V; and 1 E. cloacae subsp. dissolvens-XII. Nine Klebsiella aerogenes were also identified. Overall, a high clonal diversity (Simpson Diversity Index >0.90) was found among CP-Ent-clusters. Environmental isolates were clonally related to clinical ones. Amikacin and tigecycline showed the highest susceptibility (>93%). VIM-1 (n = 133/181, 73.5%) and OXA-48 (n = 34/181, 18.8%) carbapenemases were predominant, followed by KPC-2 (n = 9/181, 5.0%), KPC-3 (n = 2/181, 1.1%), VIM-2 (n = 1/181, 0.6%), and two coproducers (VIM-1+KPC-2 and VIM-1+KPC-3). Extended-spectrum beta-lactamase (ESBL) coproduction (14.4%) emerged in 2012, mainly associated with bla_SHV-12 (p < 0.001), E. roggenkampii (p < 0.001), and colonization (p = 0.03). VIM-1- and OXA-48-CP-Ent fecal carriers increased in our hospital, particularly between 2011 and 2018 (p < 0.001). Moreover, KPC and OXA-48 producers emerged in 2010 and 2012, respectively. They superimposed over VIM producers, which were persistently recovered since first detection in 2005. These results depict increased complexity over time of CP-Ent.

Does the presence of multiple β-lactamases in Gram-negative bacilli impact the results of antimicrobial susceptibility tests and extended-spectrum β-lactamase and carbapenemase confirmation methods?

OBJECTIVES

Many multidrug-resistant Gram-negative bacilli (MDR-GNB) harbour multiple β-lactamases. The aim of this study was to assess the impact of multiple β-lactamase carriage on the accuracy of susceptibility tests and extended-spectrum β-lactamase (ESBL) and carbapenemase confirmation methods.

METHODS

A total of 50 MDR-GNB, of which 29 carried multiple β-lactamases, underwent broth microdilution (BMD) and disk diffusion (DD) testing as well as confirmation tests for ESBLs and carbapenemases. Whole-genome sequencing (WGS) was used for β-lactamase gene identification.

RESULTS

Categorical agreement of BMD and DD testing results ranged from 86.5 to 97.7% for 10 β-lactam agents. BMD and DD algorithms for ESBL detection were highly variable; 6 of 8 positive strains carried an ESBL plus a carbapenemase or an AmpC enzyme, which may confound antimicrobial selection. The sensitivity and specificity of the modified carbapenem inactivation method (mCIM) were both 100%, whilst mCIM and EDTA-modified carbapenem inactivation method (eCIM) when used together to differentiate serine from metallo-β-lactamase carriage were both 96%. Xpert® Carba-R results (in vitro diagnostic test) were consistent with WGS results. Predicting phenotypic carbapenem resistance from WGS data overall showed 100% specificity but only 66.7% sensitivity for Enterobacterales isolates that were non-susceptible to imipenem and meropenem.

CONCLUSIONS

Multiple β-lactamases in MDR-GNB does not impact DD results, the utility of mCIM/eCIM tests, or Xpert Carba-R results. However, ESBL algorithms produced inconsistent results and predicting carbapenem resistance from WGS data was problematic in such strains.

Synergistic antibacterial and anti-biofilm activity of nisin like bacteriocin with curcumin and cinnamaldehyde against ESBL and MBL producing clinical strains

Bacteriocins are small peptides that can inhibit the growth of a diverse range of microbes. There is a need to identify bacteriocins that are effective against biofilms of resistant clinical strains. The present study focussed on the efficacy of purified nisin like bacteriocin-GAM217 against extended spectrum β-lactamase (ESBL) and metallo-beta-lactamase (MBL) producing clinical strains. Bacteriocin-GAM217 when combined with curcumin and cinnamaldehyde, synergistically enhanced antibacterial activity against planktonic and biofilm cultures of Staphylococcus epidermidis and Escherichia coli. Bacteriocin-GAM217 and phytochemical combinations inhibited biofilm formation by >80%, and disrupted the biofilm for selected ESBL and MBL producing clinical strains. The anti-adhesion assay showed that these combinatorial compounds significantly lowered the attachment of bacteria to Vero cells and that they elicited membrane permeability and rapid killing as viewed by confocal microscopy. This study demonstrates that bacteriocin-GAM217 in combination with phytochemicals can be a potential anti-biofilm agent and thus has potential for biomedical applications.

Label-Free Electrochemical Microfluidic Chip for the Antimicrobial Susceptibility Testing

The emergence and spread of antibiotic-resistant bacteria is a global threat to human health. An accurate antibiotic susceptibility test (AST) before initiating the treatment is paramount in the treatment and bacterial resistance control. However, the current AST methods either are complex, use chemical and biological labels, lack multiplexing, are expensive, or are too slow to be used for routine screening. The primary objective of the current study is to develop an automated electrochemical microfluidic chip (EMC) for simple and rapid AST. The microfluidic channels and gold microelectrodes were designed for the automation of antibiotic mixing and distribution in multiple test chambers and for electrical signal measurements. The designed chip was tested for AST with E. coli samples, and the results were compared with conventional broth microdilution. The presented EMC provided rapid bacterial count and AST in 170 and 150 min, respectively, while the conventional broth microdilution evaluates in 450 and 240 min, respectively. The rapid AST capability of the EMC was further demonstrated with the artificial urine samples, and the results were obtained in 270 min, which was 90 min faster than the broth microdilution method. Additionally, the minimum inhibitory concentration (MIC) was evaluated on the EMC and compared with the results from an AlamarBlue assay. The experimental results indicate the sensitivity of the chip, minimum loss of antibiotics, and eventually, reduction in the evolution of antibiotic resistance. Cumulatively, we have developed an automated, label-free, economical, rapid, robust, and user-friendly EMC for the evaluation of AST in urine samples.

Prevalence of plasmid-encoded carbapenemases in multi-drug resistant Escherichia coli from patients with urinary tract infection in northern Iran

OBJECTIVES

Resistance to carbapenems as the last line for controlling resistant bacteria is increasing due to production of carbapenemase. The aim of this study was to detect the plasmid-encoded carbapenemases using phenotypic methods and multiplex PCR among the multi-drug resistant (MDR) isolates from patients with urinary tract infection (UTI) in northern Iran.

MATERIALS AND METHODS

Antimicrobial susceptibility testing and extended spectrum β-lactamase (ESBL) production test were performed for 91 MDR Escherichia coli strains by disc diffusion and double disk synergy tests (DDST), respectively. Carbapenemases production was confirmed using Hodge test, EDTA double disk synergy test (EDST) and combined disk test (CDT). The isolates were subjected to PCR targeting bla IMP, bla VIM, bla KPC and bla OXA-48 β-Lactamase genes.

RESULTS

Resistance of isolates to 1st, 2nd, 3rd, and 4th generations of cephalosporins, carbapenems, and penicillins were 73%, 84.5%, 62%, 37.5%, 17.5%, and 76%, respectively. Based on CDT and Hodge test, 1 (3%) and based on EDST, 2 (6%) of 33 ESBL producers synthesize a type of carbapenemase. The frequency of bla IMP, bla VIM, bla KPC, and bla OXA-48 genes was 8.7%, 9.8%, 2.1%, and 15.3%, respectively. Existence of bla IMP conferred more resistance to cephalotin, fosfomycin, and piperacillin (P≤0.01) and carrying bla VIM caused more resistance to cephalotin, cefepime, and ceftazidime (P≤0.01). The presence of bla KPC conferred more resistance to cephalotin and presence of bla OXA-48 caused more resistance to chloramphenicol and piperacillin (P≤0.05).

CONCLUSION

Identification and controlling of this nearly low frequent ESBL and carbapenemase producing strains are important due to the presence of plasmid genes encoding carbapenemase.

Whole-genome analysis of the potentially zoonotic Elizabethkingia miricola FL160902 with two new chromosomal MBL gene variants

Objectives

Elizabethkingia is an emerging life-threatening pathogen in both humans and animals. We describe the whole-genome analysis of an Elizabethkingia miricola strain isolated from a diseased frog in China and investigate the molecular mechanism of carbapenem resistance in this pathogen.

Methods

WGS of E. miricola FL160902 was performed using single-molecule, real-time technology. A phylogenetic tree was generated by SNP analysis, comparing the genome of our strain with other E. miricola isolates of amphibian and human origins. Antimicrobial resistance genes and virulence-related genes were identified using the Comprehensive Antibiotic Resistance Database (CARD) and the Virulence Factor Database (VFDB). Two putative carbapenemase genes were expressed in Escherichia coli to evaluate their contribution to antimicrobial resistance.

Results

The genome of E. miricola FL160902 consists of a 4 249 586 bp circular chromosome with 27 putative resistance genes and 38 predicted virulence-associated genes. Comparative genomic analysis demonstrated that the E. miricola strains of human and amphibian origins have similar virulence-associated gene profiles. In addition, all the amphibian isolates clustered together with one of the human isolates in the phylogenetic analysis. WGS revealed the presence of two novel MBL genes, designated blaBlaB-16 and blaGOB-19. Cloning of blaBlaB-16 and blaGOB-19 into E. coli DH5α resulted in increased MICs of most β-lactams, including imipenem, meropenem and ampicillin.

Conclusions

We identified two chromosomal MBL gene variants, named blaBlaB-16 and blaGOB-19 in an amphibian E. miricola isolate, which was considered potentially zoonotic based on phylogenetic analysis and virulence-associated gene comparison. This study highlights the importance of E. miricola as a potential zoonotic pathogen and a reservoir of MDR genes.

VIM/IMP carbapenemase-producing Enterobacteriaceae in Poland: epidemic Enterobacter hormaechei and Klebsiella oxytoca lineages

Objectives

To analyse VIM/IMP-type MBL-producing Enterobacteriaceae isolates identified in Poland during 2006-12.

Methods

Isolates were typed by PFGE, followed by MLST. blaVIM/IMP genes were amplified and sequenced within class 1 integrons. Their plasmidic versus chromosomal location was assessed by nuclease S1 and I-CeuI plus hybridization experiments. Plasmids were characterized by transfer assays and PCR-based replicon typing.

Results

One hundred and nineteen VIM/IMP-positive Enterobacteriaceae cases were reported in Poland from the first case in 2006 until 2012. The patients were in 54 hospitals and were infected or colonized by 121 organisms, including Enterobacter cloacae complex (n = 64), Klebsiella oxytoca (n = 23), Serratia marcescens (n = 20) and Klebsiella pneumoniae (n = 11). The isolates represented numerous pulsotypes and mainly original STs, and carried eight integrons with blaVIM-1-like genes (blaVIM-1/-4/-28/-37/-40; n = 101), three with blaVIM-2 variants (blaVIM-2/-20; n = 17) and one with blaIMP-19 (n = 3). Six integrons were new, and five and two formed prevalent families of In238-like (n = 96) and In1008-like (n = 16) elements, respectively. In238 (aacA4-blaVIM-4rpt) and In1008 (blaVIM-2-aacA4) had been originally observed in Polish Pseudomonas aeruginosa, suggestive of their transfer to enterobacteria, followed by spread and diversification. Four organisms have disseminated inter-regionally, i.e. Enterobacter hormaechei ST90 with plasmidic In238/In238a integrons (n = 36), K. oxytoca ST145 with a chromosomal In237-like element (n = 18) and two subclones of E. hormaechei ST89 with In1008- or In238-type variants (n = 8 and n = 7, respectively).

Conclusions

The epidemiology of VIM/IMP-producing Enterobacteriaceae in Poland has revealed a remarkable number of specific or novel characteristics of the organisms, with some possible links to other mid-southern European countries.

Emerging carbapenem-resistant Aeromonas spp. infections in Cali, Colombia

INTRODUCTION

Aeromonas species are renowned enteric pathogens with virulence determinants linked to human diseases, such as gastroenteritis, skin, soft-tissue and muscle infections, and septicemia. A recent concern of resistance in this organism has emerged, especially the presence carbapenemases. Herein we describe a case series of emerging carbapenem-resistant Aeromonas species infection in our hospital in Cali, Colombia.

MATERIALS AND METHODS

Cases from 2012 to 2018 are reported. Clinical data was abstracted from the clinical charts and laboratory information. Phenotypic detection of resistance was identified using the VITEK®2 system (BioMérieux) and broth microdilution MicroScan WalkAway plus System (Beckman Coulter). CARBA NP-test and multiplex qPCR assay was performed in 11 isolates to identify genes encoding carbapenemases (bla_KPC, bla_VIM, bla_IMP and bla_NDM).

RESULTS

21 cases of Aeromonas infection in hospitalized patients with phenotypic resistance to carbapenems were studied. The median age was 50 years, 55% (12/21) were male, and 67% (14/21) were healthcare-associated infections (HAI). Aeromonas hydrophila was the most common species (19/21). Forty-three percent (9/21) of the patients were immunocompromised. The mortality was 33% (7/21), and in patients with bacteremia was 100%. Most patients received empirical treatment with meropenem and failed to this treatment. PCR amplification tests showed negative results for the carbapenemases analyzed.

CONCLUSION

Emerging phenotypic carbapenem-resistant infection has been seen in our hospital, most as HAI. High mortality was found, especially in immunocompromised patients and in those who failled empirical treatment with carbapenems. As the main carbapenemases tested were negative, carbapenem-resistant could be attributed to an intrinsic metallo-β-lactamase, CphA encoded by the cphA gene, possible hyperproduction of ampC β-lactamase and/or porins expression.

Impact of specific inhibitors on metallo-β-carbapenemases detected in Escherichia coli and Klebsiella pneumoniae isolates

Carbapenems are widely regarded as the drugs of choice for the treatment of severe infections caused by extended-spectrum beta lactamases producing Enterobacteriaceae. The emergence of carbapenem-resistant organisms is worrisome due to the limited treatment options. Detection of carbapenemase-producing bacteria is critical for the choice of appropriate therapy. However, Inhibition of carbapenemases is an alternative approach to combat resistance to carbapenms. In this study, Escherichia coli and Klebsiella pneumoniae carbapenem resistant isolates were recovered from 300 clinical isolates. They were subjected phenotypically for detection of class B metallo-carbapenemase (MBL) producers (by carbapenem disks with or without EDTA), and were subjected for confirmation genotypically by PCR. In addition, the synergistic activities of MBL-inhibitors in combination with carbapenems were elucidated. Two E. coli and 15 K. pneumoniae isolates were carbapenem resistant. The genes encoding blaNDM-1 carbapenemase were detected in 16/17 isolates solely, or collaboratively with either blaVIM, or blaIMP or both in all carbapenem resistant isolates, by PCR method. The VIM-carbapenemase was encoded by one isolate. In pre-clinical trials for development of MBL-specific inhibitors, Sub-inhibitory concentrations of citric acid, malic acid, ascorbic acid and ciprofloxacin in combination with imipenem or meropenem exerted synergistic activities against metallo-carbapenemases. Their activities are probably attributed to the chelation of zinc ions in the active site of carbapenemase. Conclusively, these promising combined therapies might represent a new strategy for combating such serious infections caused by metallo-B-carbapenemase producers of K. pneumoniae and E. coli isolates.

Imipenem resistance in clinical Escherichia coli from Qom, Iran

Objective

The emergence of metallo-β-lactamase-producing Enterobacteriaceae is a worldwide health concern. In this study, the first evaluation of MBL genes, bla_IMP and bla_VIM, in Escherichia coli resistant to imipenem isolated from urine and blood specimens in Qom, Iran is described. Three hundred urine and blood specimens were analysed to detect the presence of E. coli. Resistance to imipenem and other antimicrobials was determined by disk diffusion and MIC. MBL production was screened using CDDT. PCR was also carried out to determine the presence of bla_IMP and bla_VIM genes in imipenem-resistant isolates.

Results

In total, 160 E. coli isolates were collected from March to May 2016. According to disk diffusion, high-level of resistance (20%) to cefotaxime was observed, whereas the lowest (1%) was detected for tetracycline. In addition, five isolates showed resistance to imipenem with a MIC ≥ 4 µg/mL. CDDT test confirmed that five isolates were MBL-producing strains, but no bla_IMP and bla_VIM genes were detected. Results of this study show a very low level of resistance to imipenem in our geographical area.

Molecular Characterization of Pseudomonas putida Group Isolates Carrying blaVIM-2 Disseminated in a University Hospital in Korea

Pseudomonas putida group are Gram-negative bacilli with polar flagellation, which are ubiquitous in the environment, although they are rarely involved in human infections. The aim of this study was to identify the dissemination of VIM-2-producing P. putida group in clinical isolates from a hospital in Korea. Thirteen strains were collected from 2014 to 2015 for the study. The isolates were recovered from urine cultures of both inpatients and outpatients at the hospital. Minimum inhibitory concentrations of antibiotics were determined by Etest. Carbapenemase genes were amplified by polymerase chain reaction and sequenced. Pulsed-field gel electrophoresis was performed for strain typing. Whole-genome sequencing was carried out randomly for two strains chosen from each year of the study to analyze the plasmid structure carrying the bla_VIM-2 genes. The 13 isolates carried nine different class I integrons harboring VIM-2 and were resistant to meropenem and imipenem (minimum inhibitory concentrations, ≥32 μg/ml), thus exhibiting a multidrug-resistant phenotype. The bla_VIM-2 gene was located on a plasmid in seven of the isolates and on the chromosome in six isolates. Each case of the bla_VIM-2 gene was disseminated by clonal spread, horizontal transfer, and was mostly an occasional occurrence. In this study, we demonstrated that multidrug-resistant P. putida group carrying VIM-2 has reemerged in human specimens in Korea.

A hospital based surveillance of metallo-beta-lactamase producing gram negative bacteria in Nepal by imipenem-EDTA disk method

BACKGROUND

A rising threat of the rapid spread of acquired metallo-beta-lactamases (MBLs) among major Gram-negative pathogens is a matter of public health concern worldwide. Hence, for a low income nation like Nepal, surveillance data on MBL producing clinical isolates via a cost effective technique is necessary to prevent their dissemination as well as formulation and regulation of antimicrobial stewardship policy.

METHODS

The prospective study was conducted at Nepal Medical College, Kathmandu from May to October, 2014 to assess the prevalence of MBL production among ceftazidime-resistant Gram-negative rods (GNRs) isolates. The samples were processed according to standard microbiological procedure following the Manual of clinical Microbiology. Isolated GNRs were subjected to susceptibility testing against the selected panel of antibiotics by Kirby- Bauer disc diffusion method and interpretation made in conformity with the Clinical and Laboratory Standards Institute (CLSI) guidelines. Ceftazidime-resistant isolates were subjected to the detection of MBL production by imipenem-EDTA combined disc (CD) method.

RESULTS

Among the Gram-negative isolates, 5.80% (21/362) were found to be MBL positive with Acinetobacter spp. showing the highest prevalence i.e. 85.71% (18/21), followed by P. aeruginosa i.e. 14.29% (3/21). None of the other cefazidime resistant gram negative bacteria tested were found to be positive for MBL production with all the positive isolates determined to be Multidrug resistant (MDR) strains.

CONCLUSION

This study demonstrated a higher rate of resistance among P. aeruginosa and Acinetobacter spp. to a wide variety of antibiotic categories with an additional burden of MBL production within them, warranting a need for strict surveillance and rapid detection of MBL production among the GNRs.

Lateral Antimicrobial Resistance Genetic Transfer is active in the open environment

Historically, the environment has been viewed as a passive deposit of antimicrobial resistance mechanisms, where bacteria show biological cost for maintenance of these genes. Thus, in the absence of antimicrobial pressure, it is expected that they disappear from environmental bacterial communities. To test this scenario, we studied native IntI1 functionality of 11 class 1 integron-positive environmental strains of distant genera collected in cold and subtropical forests of Argentina. We found natural competence and successful site-specific insertion with no significant fitness cost of both aadB and bla_VIM-2 antimicrobial resistance gene cassettes, in a model system without antibiotic pressure. A bidirectional flow of antimicrobial resistance gene cassettes between natural and nosocomial habitats is proposed, which implies an active role of the open environment as a reservoir, recipient and source of antimicrobial resistance mechanisms, outlining an environmental threat where novel concepts of rational use of antibiotics are extremely urgent and mandatory.

Carbapenem-Resistant Enterobacteriaceae: A Strategic Roadmap for Infection Control

The incidence of carbapenem-resistant Enterobacteriaceae (CRE) has increased worldwide with great regional variability. Infections caused by these organisms are associated with crude mortality rates of up to 70%. The spread of CRE in healthcare settings is both an important medical problem and a major global public health threat. All countries are at risk of falling victim to the emergence of CRE; therefore, a preparedness plan is required to avoid the catastrophic natural course of this epidemic. Proactive and adequate preventive measures locally, regionally, and nationally are required to contain the spread of these bacteria. The keys to success in preventing the establishment of CRE endemicity in a region are early detection through targeted laboratory protocols and containment of spread through comprehensive infection control measures. This guideline provides a strategic roadmap for infection control measures based on the best available evidence and expert opinion, to enable preparation of a multifaceted preparedness plan to abort epidemics of CRE. Infect Control Hosp Epidemiol 2017;38:580-594.

Expanding the Repertoire of Carbapenem-Hydrolyzing Metallo-ß-Lactamases by Functional Metagenomic Analysis of Soil Microbiota

Carbapenemases are bacterial enzymes that hydrolyze carbapenems, a group of last-resort β-lactam antibiotics used for treatment of severe bacterial infections. They belong to three β-lactamase classes based amino acid sequence (A, B, and D). The aim of this study was to elucidate occurrence, diversity and functionality of carbapenemase-encoding genes in soil microbiota by functional metagenomics. Ten plasmid libraries were generated by cloning metagenomic DNA from agricultural (n = 6) and grassland (n = 4) soil into Escherichia coli. The libraries were cultured on amoxicillin-containing agar and up to 100 colonies per library were screened for carbapenemase production by CarbaNP test. Presumptive carbapenemases were characterized with regard to DNA sequence, minimum inhibitory concentration (MIC) of β-lactams, and imipenem hydrolysis. Nine distinct class B carbapenemases, also known as metallo-beta-lactamases (MBLs), were identified in six soil samples, including two subclass B1 (GRD23-1 and SPN79-1) and seven subclass B3 (CRD3-1, PEDO-1, GRD33-1, ESP-2, ALG6-1, ALG11-1, and DHT2-1). Except PEDO-1 and ESP-2, these enzymes were distantly related to any previously described MBLs (33 to 59% identity). RAIphy analysis indicated that six enzymes (CRD3-1, GRD23-1, DHT2-1, SPN79-1, ALG6-1, and ALG11-1) originated from Proteobacteria, two (PEDO-1 and ESP-2) from Bacteroidetes and one (GRD33-1) from Gemmatimonadetes. All MBLs detected in soil microbiota were functional when expressed in E. coli, resulting in detectable imipenem-hydrolyzing activity and significantly increased MICs of clinically relevant ß-lactams. Interestingly, the MBLs yielded by functional metagenomics generally differed from those detected in the same soil samples by antibiotic selective culture, showing that the two approaches targeted different subpopulations in soil microbiota.

New Delhi metallo-β-lactamase and extended spectrum β-lactamases co-producing isolates are high in community-acquired urinary infections in Assam as detected by a novel multiplex polymerase chain reaction assay

BACKGROUND

The ability of microorganisms to evade antibiotic pressure is challenging in healthcare as patients have little or no drug treatment options. Detection of the prevalence of antibacterial resistance pattern helps towards improved antibiotic policy and empirical treatment.

OBJECTIVES

We carried out antibiogram profiling and documented the prevalence and co-prevalence of New Delhi metallo-β-lactamase (NDM) and extended spectrum β-lactamases (ESBL) encoding genes in urinary Escherichia coli and Klebsiella pneumonia isolates.

MATERIALS AND METHODS

Antibiotic susceptibilities were tested for 241 isolates of E. coli and K. pneumoniae from urine samples collected from out- and hospitalised patients. Polymerase chain reaction (PCR) was carried out on isolates tested positive for phenotypic production of metallo-β-lactamase and ESBL. A multiplex PCR assay was designed to detect the genes.

RESULTS

Multiplex PCR assay designed had a limit of detection of 10 3 CFU/mL in vitro. NDM detected was significantly higher among K. pneumoniae compared to E. coli (69.2% vs. 18.2%; P = 0.001). Of 17, 14 NDM positive isolates also harboured ESBL genes. The co-production of CTX-M + TEM + NDM (3/9; 33.3% and 5/8; 62.5%) was most common in K. pneumoniae and E. coli, respectively while CTX-M + TEM + SHV + NDM was found in one isolate. Of the 156 phenotypically ESBL producing isolates, CTX-M, TEM and SHV was detected by PCR in 85, 53 and 24 isolates, respectively.

CONCLUSION

NDM and ESBL co-producing isolates were both community (64.7%) and hospital (35.29%) acquired among E. coli. Antibiotic resistance can be effectively evaluated by a cost and time effective molecular method, such as the multiplex PCR used in this study, which complement culture and sensitivity tests.

Isolation and Characterization of Acinetobacter baumannii Recovered from Campylobacter Selective Medium

Acinetobacter baumannii, a Gram-negative opportunistic pathogen, is known to cause multidrug resistant infections. This organism has primarily been isolated from clinical environments and its environmental reservoirs remain largely unknown. In the present study, we recovered seven isolates of A. baumannii growing under conditions selective for Campylobacter spp. (microaerophilic at 42°C and in the presence of antibiotics) from dairy cattle manure storage tank or surface water impacted by livestock effluents. Antibiotic susceptibility tests revealed that all of these isolates were less susceptible to at least two different clinically relevant antibiotics, compared to the type strain A. baumannii ATCC17978. Expression of resistance-nodulation-division efflux pumps, an important mechanism of intrinsic resistance in these organisms, was analyzed, and adeB was found to be overexpressed in one and adeJ was overexpressed in three isolates. Comparison of these isolates using genomic DNA Macro-Restriction Fragment Pattern Analysis (MRFPA) revealed relatively low relatedness among themselves or with some of the clinical isolates from previous studies. This study suggests that A. baumannii isolates are capable of growing under selective conditions for Campylobacter spp. and that this organism can be present in manure and water.

Primer Evaluation for PCR and its Application for Detection of Carbapenemases in Enterobacteriaceae

BACKGROUND

During the last decade, the prevalence of carbapenem-resistant Enterobacteriaceae in human patients has increased. Carbapenemase-producing bacteria are usually multidrug resistant. Therefore, early recognition of carbapenemase producers is critical to prevent their spread.

OBJECTIVES

The objective of this study was to develop the primers for single and/or multiplex PCR amplification assays for simultaneous identification of class A, class B, and class D carbapenem hydrolyzing β-lactamases in Enterobacteriaceae and then to evaluate their efficiency.

MATERIALS AND METHODS

The reference sequences of all genes encoding carbapenemases were downloaded from GenBank. Primers were designed to amplify the following 11 genes: bla KPC, bla OXA, bla VIM, bla NDM, bla IMP, bla SME, bla IMI, bla GES , bla GIM, bla DIM and bla CMY . PCR conditions were tested to amplify fragments of different sizes. Two multiplex PCR sets were created for the detection of clinically important carbapenemases. The third set of primers was included for detection of all known carbapenemases in Enterobacteriaceae. They were evaluated using six reference strains and nine clinical isolates.

RESULTS

Using optimized conditions, all carbapenemase-positive controls yielded predicted amplicon sizes and confirmed the specificity of the primers in single and multiplex PCR.

CONCLUSIONS

We have reported here a reliable method, composed of single and multiplex PCR assays, for screening all clinically known carbapenemases. Primers tested in silico and in vitro may distinguish carbapenem-resistant Enterobacteriaceae and could assist in combating the spread of carbapenem resistance in Enterobacteriaceae.

Molecular surveillance for carbapenemase genes in carbapenem-resistant Pseudomonas aeruginosa in Australian patients with cystic fibrosis

The aim of this study was to assess the prevalence of acquired carbapenemase genes amongst carbapenem non-susceptible Pseudomonas aeruginosa isolates in Australian patients with cystic fibrosis (CF). Cross-sectional molecular surveillance for acquired carbapenemase genes was performed on CF P. aeruginosa isolates from two isolate banks comprising: (i) 662 carbapenem resistant P. aeruginosa isolates from 227 patients attending 10 geographically diverse Australian CF centres (2007-2009), and (ii) 519 P. aeruginosa isolates from a cohort of 173 adult patients attending one Queensland CF clinic in 2011. All 1189 P. aeruginosa isolates were tested by polymerase chain reaction (PCR) protocols targeting ten common carbapenemase genes, as well the Class 1 integron intI1 gene and the aadB aminoglycoside resistance gene. No carbapenemase genes were identified among all isolates tested. The intI1 and aadB genes were frequently detected and were significantly associated with the AUST-02 strain (OR 24.6, 95% CI 9.3-65.6; p < 0.0001) predominantly from Queensland patients. Despite the high prevalence of carbapenem resistance in P. aeruginosa in Australian patients with CF, no acquired carbapenemase genes were detected in the study, suggesting chromosomal mutations remain the key resistance mechanism in CF isolates. Systematic surveillance for carbapenemase-producing P. aeruginosa in CF by molecular surveillance is ongoing.

Detection of expanded-spectrum β-lactamases in Gram-negative bacteria in the 21st century

Emerging β-lactamase-producing-bacteria (ESBL, AmpC and carbapenemases) have become a serious problem in our community due to their startling spread worldwide and their ability to cause infections which are difficult to treat. Diagnosis of these β-lactamases is of clinical and epidemiological interest. Over the past 10 years, several methods have been developed aiming to rapidly detect these emerging enzymes, thus preventing their rapid spread. In this review, we describe the range of screening and detection methods (phenotypic, molecular and other) for detecting these β-lactamases but also whole genome sequencing as a tool for detecting the genes encoding these enzymes.

Carbapenemases: A worldwide threat to antimicrobial therapy

Carbapenems are potent β-lactams with activity against extended-spectrum cephalosporinases and β-lactamases. These antibiotics, derived from thienamycn, a carbapenem produced by the environmental bacterium Streptomyces cattleya, were initially used as last-resort treatments for severe Gram-negative bacterial infections presenting resistance to most β-lactams but have become an empirical option in countries with high prevalence of Extended Spectrum β-lactamase-producing bacterial infections. Imipenem, the first commercially available carbapenem, was approved for clinical use in 1985. Since then, a wide variety of carbapenem-resistant bacteria has appeared, primarily Enterobacteriaceae such as Escherichia coli or Klebsiella pneumoniae (K. pneumoniae), Pseudomonas aeruginosa and Acinetobacter baumannii, presenting different resistance mechanisms. The most relevant mechanism is the production of carbapenem-hydrolyzing β-lactamases, also known as carbapenemases. These enzymes also inactivate all known β-lactams, and some of these enzymes can be acquired through horizontal gene transfer. Moreover, plasmids, transposons and integrons harboring these genes typically carry other resistance determinants, rendering the recipient bacteria resistant to almost all currently used antimicrobials, as is the case for K. pneumoniae carbapenemase - or New Delhi metallo-β-lactamases-type enzymes. The recent advent of these enzymes in the health landscape presents a serious challenge. First, the emergence of carbapenemases limits the currently available treatment options; second, these enzymes pose a risk to patients, as some studies have demonstrated high mortality associated with carbapenemase-producing bacterial infections; and third, these circumstances require an extra cost to sanitary systems, which are particularly cumbersome in developing countries. Therefore, emphasis should be placed on the early detection of these enzymes, the prevention of the spread of carbapenemase-producing bacteria and the development of new drugs resistant to carbapenemase hydrolysis.

Molecular detection of metallo-β-lactamase gene blaVIM-1 in imipenem-resistant Pseudomonas aeruginosa strains isolated from hospitalized patients in the hospitals of Isfahan

BACKGROUND

Pseudomonas aeruginosa is an opportunistic human pathogen that causes serious problems, especially in people, who have immunodeficiency. In recent times, metallo-β-lactamase (MBLs) resistance in this bacterium has led to some difficulties in treating bacterial infections. The metallo-beta-lactamase family of genes, including blaVIM-1, is being reported with increasing frequency worldwide. The aim of this study is the detection of the metallo-β-lactamase gene blaVIM-1 in imipenem-resistant P. aeruginosa (IRPA) strains isolated from hospitalized patients.

MATERIALS AND METHODS

In this study, 106 P. aeruginosa samples were isolated from various nosocomial infections. The isolates were identified, tested for susceptibility to various antimicrobial agents by the Kirby-Bauer disk diffusion method, and all the imipenem-resistant isolates were screened for the presence of MBLs by using the combined disk (IMP-EDTA). The minimal inhibitory concentration (MIC) of imipenem was determined by E-test on the Mueller-Hinton agar. To detect the blaVIM-1 gene, the isolates were subjected to a polymerase chain reaction (PCR).

RESULTS

Of all the P. aeruginosa isolates, 62 (58.5%) were found to be imipenem-resistant P. aeruginosa (MIC ≥32 μg/ml). Twenty-six (42%) of the imipenem-resistant isolates were MBL positive. None of these isolates carried the blaVIM-1 gene using the PCR assay.

CONCLUSION

The results demonstrated the serious therapeutic threat of the MBL-producing P. aeruginosa populations. The rate of imipenem resistance due to MBL was increased dramatically. Early detection and infection-control practices are the best antimicrobial strategies for this organism. None of MBL-producing isolates in this study carry the blaVIM-1 gene; therefore, another gene in the MBL family should be investigated.

Crystal structure of human persulfide dioxygenase: structural basis of ethylmalonic encephalopathy

The ethylmalonic encephalopathy protein 1 (ETHE1) catalyses the oxygen-dependent oxidation of glutathione persulfide (GSSH) to give persulfite and glutathione. Mutations to the hETHE1 gene compromise sulfide metabolism leading to the genetic disease ethylmalonic encephalopathy. hETHE1 is a mono-iron binding member of the metallo-β-lactamase (MBL) fold superfamily. We report crystallographic analysis of hETHE1 in complex with iron to 2.6 Å resolution. hETHE1 contains an αββα MBL-fold, which supports metal-binding by the side chains of an aspartate and two histidine residues; three water molecules complete octahedral coordination of the iron. The iron binding hETHE1 enzyme is related to the ‘classical’ di-zinc binding MBL hydrolases involved in antibiotic resistance, but has distinctive features. The histidine and aspartate residues involved in iron-binding in ETHE1, occupy similar positions to those observed across both the zinc 1 and zinc 2 binding sites in classical MBLs. The active site of hETHE1 is very similar to an ETHE1-like enzyme from Arabidopsis thaliana (60% sequence identity). A channel leading to the active site is sufficiently large to accommodate a GSSH substrate. Some of the observed hETHE1 clinical mutations cluster in the active site region. The structure will serve as a basis for detailed functional and mechanistic studies on ETHE1 and will be useful in the development of selective MBL inhibitors.

Optimizing antimicrobial therapy in critically ill patients

Critically ill patients with infection in the intensive care unit (ICU) would certainly benefit from timely bacterial identification and effective antimicrobial treatment. Diagnostic techniques have clearly improved in the last years and allow earlier identification of bacterial strains in some cases, but these techniques are still quite expensive and not readily available in all institutions. Moreover, the ever increasing rates of resistance to antimicrobials, especially in Gram-negative pathogens, are threatening the outcome for such patients because of the lack of effective medical treatment; ICU physicians are therefore resorting to combination therapies to overcome resistance, with the direct consequence of promoting further resistance. A more appropriate use of available antimicrobials in the ICU should be pursued, and adjustments in doses and dosing through pharmacokinetics and pharmacodynamics have recently shown promising results in improving outcomes and reducing antimicrobial resistance. The aim of multidisciplinary antimicrobial stewardship programs is to improve antimicrobial prescription, and in this review we analyze the available experiences of such programs carried out in ICUs, with emphasis on results, challenges, and pitfalls. Any effective intervention aimed at improving antibiotic usage in ICUs must be brought about at the present time; otherwise, we will face the challenge of intractable infections in critically ill patients in the near future.

Detection of carbapenemases in Enterobacteriaceae: a challenge for diagnostic microbiological laboratories

Carbapenemase-producing bacteria have now spread all over the world. Infections caused by those bacteria are difficult to treat. Therefore, there is an urgent need for accurate and fast detection of carbapenemases in diagnostic laboratories. In this review, we summarize screening methods for suspected isolates, direct assays for confirmation of carbapenemase activity (e.g. the Carba NP test and matrix-assisted laser desorption ionization time-of-flight mass spectrometry carbapenem hydrolysis assay), inhibitor-based methods for carbapenemase classification, and molecular-genetic techniques for precise identification of carbapenemase genes. We also propose a workflow for carbapenemase identification in diagnostic laboratories.

Molecular and epidemiological characterization of IMP-type metallo-β-lactamase-producing Enterobacter cloacae in a Large tertiary care hospital in Japan

IMP-type metallo-β-lactamase enzymes have been reported in different geographical areas and in various Gram-negative bacteria. However, the risk factors and epidemiology pertaining to IMP-type metallo-β-lactamase-producing Enterobacter cloacae (IMP-producing E. cloacae) have not been systematically evaluated. We conducted a retrospective, matched case-control study of patients from whom IMP-producing E. cloacae isolates were obtained, in addition to performing thorough molecular analyses of the clinically obtained IMP-producing E. cloacae isolates. Unique cases with IMP-producing E. cloacae isolation were included. Patients with IMP-producing E. cloacae were matched to uninfected controls at a ratio of 1 to 3. Fifteen IMP-producing E. cloacae cases were identified, with five of the isolates being obtained from blood, and they were matched to 45 uninfected controls. All (100%) patients from whom IMP-producing E. cloacae isolates were obtained had indwelling devices at the time of isolation, compared with one (2.2%) uninfected control. Independent predictors for isolation of IMP-producing E. cloacae were identified as cephalosporin exposure and invasive procedures within 3 months. Although in-hospital mortality rates were similar between cases and controls (14.3% versus 13.3%), the in-hospital mortality of patients with IMP-producing E. cloacae-caused bacteremia was significantly higher (40%) than the rate in controls. IMP-producing E. cloacae isolates were frequently positive for other resistance determinants. The MICs of meropenem and imipenem were not elevated; 10 (67%) and 12 (80%) of the 15 IMP-producing E. cloacae isolates had a MIC of ≤ 1 μg/ml. A phylogenetic tree showed a close relationship among the IMP-producing E. cloacae samples. Indwelling devices, exposure to cephalosporin, and a history of invasive procedures were associated with isolation of IMP-producing E. cloacae. Screening for carbapenemase production is important in order to apply appropriate clinical management and infection control measures.

High-level and novel mechanisms of carbapenem resistance in Gram-negative bacteria from tertiary hospitals in Nigeria

To determine the occurrence and molecular basis of carbapenem resistance in Gram-negative bacteria from tertiary hospitals in Nigeria, 182 non-duplicate Gram-negative bacterial isolates were investigated for antimicrobial susceptibility, presence of carbapenemases (tested phenotypically and genotypically), random amplified polymorphic DNA (RAPD) typing, plasmid sizing and replicon typing. Minimum inhibitory concentrations of carbapenems showed a high degree of resistance, with 67 isolates (36.8%) being resistant to all carbapenems, of which 40 (59.7%) produced enzymes able to hydrolyse imipenem. PCR and sequencing identified only 10 isolates (5.5%) carrying known carbapenemase genes, including bla(NDM), bla(VIM) and bla(GES). The majority of phenotypically carbapenem-resistant and carbapenemase-producing isolates did not carry a known carbapenemase gene. Transconjugant or transformant plasmid sizes were estimated to be 115 kb for bla(NDM)- and 93 kb for bla(VIM)-carrying plasmids. These plasmids were untypeable for replicon/incompatibility and transferred various other genes including plasmid-mediated quinolone resistance (PMQR) genes and bla(CTX-M-15). Typing showed that the isolates in this study were not clonally related. There is a high level of carbapenem resistance in Nigeria. As well as the globally relevant carbapenemases (bla(NDM), bla(VIM) and bla(GES)), there are other unknown gene(s) or variant(s) in circulation able to hydrolyse carbapenems and confer high-level resistance.

Could chloramphenicol be used against ESKAPE pathogens? A review of in vitro data in the literature from the 21st century

The widespread use of antibiotics has been associated with the emergence of antimicrobial resistance among bacteria. 'ESKAPE' (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acintobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) pathogens play a major role in the rapidly changing scenario of antimicrobial resistance in the 21st century. Chloramphenicol is a broad spectrum antibiotic that was abandoned in developed countries due to its association with fatal aplastic anemia. However, it is still widely used in the developing world. In light of the emerging problem of multi-drug resistant pathogens, its role should be reassessed. Our paper reviews in vitro data on the activity of chloramphenicol against ESKAPE pathogens. Susceptibility patterns for Gram-positives were good, although less favorable for Gram-negatives. However, in combination with colistin, chloramphenicol was found to have synergistic activity. The risk-benefit related to chloramphenicol toxicity has not been analyzed. Therefore, extra precautions should be taken when prescribing this agent.

Tigecycline activity against metallo-β-lactamase-producing bacteria

Backgound:

Treatment of serious life-threatening multi-drug-resistant organisms poses a serious problem due to the limited therapeutic options. Tigecycline has been recently marketed as a broad-spectrum antibiotic with activity against both gram-positive and gram-negative bacteria. Even though many studies have demonstrated the activity of tigecycline against ESBL-producing Enterobacteriaceae, its activity is not well-defined against micro-organisms producing metallo-β-lactamases (MBLs), as there are only a few reports and the number of isolates tested is limited.

Aims:

The aim of the present study was to evaluate the activity of tigecycline against MBL-producing bacterial isolates.

Materials and Methods:

The isolates were tested for MBL production by (i) combined-disk test, (ii) double disc synergy test (DDST), (iii) susceptibility to aztreonam (30 μg) disk. Minimum inhibitory concentration to tigecycline was determined according to agar dilution method as per Clinical Laboratory Standards Institute (CLSI) guidelines. Disc diffusion susceptibility testing was also performed for all these isolates using tigecycline (15 μg) discs.

Results:

Among the total 308 isolates included in the study, 99 were found to be MBL producers. MBL production was observed mostly in isolates from pus samples (40.47%) followed by urine (27.4%) and blood (13.09%). MBL production was observed in E. coli (41.48%), K. pneumoniae (26.67%), Proteus mirabilis (27.78%), Citrobacter spp. (41.67%), Enterobacter spp. (25.08%), and Acinetobacter spp. (27.27%). The result showed that tigecycline activity was unaffected by MBL production and it was showed almost 100% activity against all MBL-producing isolates, with most of the isolates exhibiting an MIC ranging from 0.25-8 μg/ml, except 2 MBL-producing E. coli isolates who had an MIC of 8 μg/ml.

Conclusion:

To conclude, tigecycline was found to be highly effective against MBL-producing Enterobacteriaceae and acinetobacter isolates, but the presence of resistance among organisms, even before the mass usage of the drug, warrants the need of its usage as a reserve drug. The study also found that the interpretative criteria for the disc diffusion method, recommended by the FDA, correlates well with the MIC detection methods. So, the microbiology laboratories might use the relatively easier method of disc diffusion, as compared to the comparatively tedious method of MIC determination.

The potential of use basil and rosemary essential oils as effective antibacterial agents

The considerable therapeutical problems of persistent infections caused by multidrug-resistant bacterial strains constitute a continuing need to find effective antimicrobial agents. The aim of this study was to demonstrate the activities of basil (Ocimum basilicum L.) and rosemary (Rosmarinus officinalis L.) essential oils against multidrug- resistant clinical strains of Escherichia coli. A detailed analysis was performed of the resistance of the drug to the strains and their sensitivity to the tested oils. The antibacterial activity of the oils was tested against standard strain Escherichia coli ATCC 25922 as well as 60 other clinical strains of Escherichia coli. The clinical strains were obtained from patients with infections of the respiratory tract, abdominal cavity, urinary tract, skin and from hospital equipment. The inhibition of microbial growth by both essential oils, presented as MIC values, were determined by agar dilution. Susceptibility testing to antibiotics was carried out using disc diffusion. The results showed that both tested essential oils are active against all of the clinical strains from Escherichia coli including extended-spectrum β-lactamase positive bacteria, but basil oil possesses a higher ability to inhibit growth. These studies may hasten the application of essential oils in the treatment and prevention of emergent resistant strains in nosocomial infections.

Matrix-assisted laser desorption ionization-time of flight (maldi-tof) mass spectrometry for detection of antibiotic resistance mechanisms: from research to routine diagnosis

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been successfully applied as an identification procedure in clinical microbiology and has been widely used in routine laboratory practice because of its economical and diagnostic benefits. The range of applications of MALDI-TOF MS has been growing constantly, from rapid species identification to labor-intensive proteomic studies of bacterial physiology. The purpose of this review is to summarize the contribution of the studies already performed with MALDI-TOF MS concerning antibiotic resistance and to analyze future perspectives in this field. We believe that current research should continue in four main directions, including the detection of antibiotic modifications by degrading enzymes, the detection of resistance mechanism determinants through proteomic studies of multiresistant bacteria, and the analysis of modifications of target sites, such as ribosomal methylation. The quantification of antibiotics is suggested as a new approach to study influx and efflux in bacterial cells. The results of the presented studies demonstrate that MALDI-TOF MS is a relevant tool for the detection of antibiotic resistance and opens new avenues for both clinical and experimental microbiology.

Extraintestinal pathogenic Escherichia coli: an update on antimicrobial resistance, laboratory diagnosis and treatment

Escherichia coli remains one of the most frequent causes of nosocomial and community-acquired bacterial infections including urinary tract infections, enteric infections and systemic infections in humans. Extraintestinal pathogenic E. coli (ExPEC) had emerged during the 2000s as an important player in the resistance to antibiotics, especially to the cephalosporins and fluoroquinolones. Most importantly, among ExPEC is the increasing recognition of isolates producing 'newer β-lactamases' that consist of plasmid-mediated AmpC β-lactamases (e.g., CMY), extended-spectrum β-lactamases (e.g., CTX-M) and carbapenemases (e.g., New Delhi metallo-β-lactamase, Klebsiella pneumonaie carbapenemase and OXA-48). This review will highlight recent aspects on antimicrobial resistance in ExPEC, including the laboratory detection of these isolates, and describe some treatment options for infections due to antimicrobial-resistant isolates.

Identification of blaOXA-₅₁-like, blaOXA-₅₈, blaDIM-₁, and blaVIM carbapenemase genes in hospital Enterobacteriaceae isolates from Sierra Leone

We describe the results of a molecular epidemiological survey of 15 carbapenemase-encoding genes from a recent collection of clinical isolates from Mercy Hospital in Bo, Sierra Leone. The most salient findings revealed that (i) 60% of the isolates harbored multiple carbapenemase genes; (ii) the blaDIM-1 gene, which has previously only been reported in The Netherlands, is also circulating in this environment; and (iii) blaOXA-51-like and blaOXA-58 genes, which were thought to reside exclusively in Acinetobacter species, can also be found in members of the Enterobacteriaceae.