Metallo-β-lactamases in Gram-negative bacteria: introducing the era of pan-resistance?

In silico designing and immunoinformatics analysis of a novel peptide vaccine against metallo-beta-lactamase (VIM and IMP) variants

The rapid spread of acquired metallo-beta-lactamases (MBLs) among gram negative pathogens is becoming a global concern. Improper use of broad-spectrum antibiotics can trigger the colonization and spread of resistant strains which lead to increased mortality and significant economic loss. In the present study, diverse immunoinformatic approaches are applied to design a potential epitope-based vaccine against VIM and IMP MBLs. The amino acid sequences of VIM and IMP variants were retrieved from the GenBank database. ABCpred and BCPred online Web servers were used to analyze linear B cell epitopes, while IEDB was used to determine the dominant T cell epitopes. Sequence validation, allergenicity, toxicity and physiochemical analysis were performed using web servers. Seven sequences were identified for linear B cell dominant epitopes and 4 sequences were considered as dominant CD4+ T cell epitopes, and the predicted epitopes were joined by KK and GPGPG linkers. Stabilized multi-epitope protein structure was obtained using molecular dynamics simulation. Molecular docking showed that the designed vaccine exhibited sustainable and strong binding interactions with Toll-like receptor 4 (TLR4). Finally, codon adaptation and in silico cloning studies were performed to design an effective vaccine production strategy. Immune simulation significantly provided high levels of immunoglobulins, T helper cells, T-cytotoxic cells and INF-γ. Even though the introduced vaccine candidate demonstrates a very potent immunogenic potential, but wet-lab validation is required to further assessment of the effectiveness of this proposed vaccine candidate.

Uropathogenic Escherichia coli endeavors: an insight into the characteristic features, resistance mechanism, and treatment choice

Uropathogenic Escherichia coli (UPEC) are the strains diverted from the intestinal status and account mainly for uropathogenicity. This pathotype has gained specifications in structure and virulence to turn into a competent uropathogenic organism. Biofilm formation and antibiotic resistance play an important role in the organism's persistence in the urinary tract. Increased consumption of carbapenem prescribed for multidrug-resistant (MDR) and Extended-spectrum-beta lactamase (ESBL)-producing UPECs, has added to the expansion of resistance. The World Health Organization (WHO) and Centre for Disease Control (CDC) placed the Carbapenem-resistant Enterobacteriaceae (CRE) on their treatment priority lists. Understanding both patterns of pathogenicity, and multiple drug resistance may provide guidance for the rational use of anti-bacterial agents in the clinic. Developing an effective vaccine, adherence-inhibiting compounds, cranberry juice, and probiotics are non-antibiotical approaches proposed for the treatment of drug-resistant UTIs. We aimed to review the distinguishing characteristics, current therapeutic options and promising non-antibiotical approaches against ESBL-producing and CRE UPECs.

Effectiveness of a Self-Decontaminating Coating Containing Usnic Acid in Reducing Environmental Microbial Load in Tertiary-Care Hospitals

Surfaces have been implicated in the transmission of pathogens in hospitals. This study aimed to assess the effectiveness of an usnic-acid-containing self-decontaminating coating in reducing microbial surface contamination in tertiary-care hospitals. Samples were collected from surfaces 9 days before coating application, and 3, 10, and 21 days after its application (phases 1, 2, 3, and 4, respectively). Samples were tested for bacteria, fungi, and SARS-CoV2. In phase 1, 53/69 (76.8%) samples tested positive for bacteria, 9/69 (13.0%) for fungi, and 10/139 (7.2%) for SARS-CoV-2. In phase 2, 4/69 (5.8%) samples tested positive for bacteria, while 69 and 139 samples were negative for fungi and SARS-CoV-2, respectively. In phase 3, 3/69 (4.3%) samples were positive for bacteria, 1/139 (0.7%) samples tested positive for SARS-CoV-2, while 69 samples were negative for fungi. In phase 4, 1/69 (1.4%) tested positive for bacteria, while no fungus or SARS-CoV-2 were detected. After the coating was applied, the bacterial load was reduced by 87% in phase 2 (RR = 0.132; 95% CI: 0.108-0.162); 99% in phase 3 (RR = 0.006; 95% CI: 0.003-0.015); and 100% in phase 4 (RR = 0.001; 95% CI: 0.000-0.009). These data indicate that the usnic-acid-containing coating was effective in eliminating bacterial, fungal, and SARS-CoV-2 contamination on surfaces in hospitals.Our findings support the benefit ofan usnic-acid-containing coating in reducing the microbial load on healthcare surfaces.

Detection by metagenomic functional analysis and improvement by experimental evolution of β-lactams resistance genes present in oil contaminated soils

The spread of antibiotic resistance genes has become a global health concern identified by the World Health Organization as one of the greatest threats to health. Many of antimicrobial resistance determinants found in bacterial pathogens originate from environmental bacteria, so identifying the genes that confer resistance to antibiotics in different habitats is mandatory to better understand resistance mechanisms. Soil is one of the most diverse environments considered reservoir of antimicrobial resistance genes. The aim of this work is to study the presence of genes that provide resistance to antibiotics used in clinical settings in two oil contaminated soils by metagenomic functional analysis. Using fosmid vectors that efficiently transcribe metagenomic DNA, we have selected 12 fosmids coding for two class A β-lactamases, two subclass B1 and two subclass B3 metallo-β-lactamases, one class D β-lactamase and three efflux pumps that confer resistance to cefexime, ceftriaxone, meropenem and/or imipenem. In some of them, detection of the resistance required heterologous expression from the fosmid promoter. Although initially, these environmental genes only provide resistance to low concentrations of antibiotics, we have obtained, by experimental evolution, fosmid derivatives containing β-lactamase ORFs with a single base substitution, which substantially increase their β-lactamase activity and resistance level. None of the mutations affect β-lactamase coding sequences and are all located upstream of them. These results demonstrate the presence of enzymes that confer resistance to relevant β-lactams in these soils and their capacity to rapidly adapt to provide higher resistance levels.

Flagellotropic Bacteriophages: Opportunities and Challenges for Antimicrobial Applications

Bacteriophages (phages) are the most abundant biological entities in the biosphere. As viruses that solely infect bacteria, phages have myriad healthcare and agricultural applications including phage therapy and antibacterial treatments in the foodservice industry. Phage therapy has been explored since the turn of the twentieth century but was no longer prioritized following the invention of antibiotics. As we approach a post-antibiotic society, phage therapy research has experienced a significant resurgence for the use of phages against antibiotic-resistant bacteria, a growing concern in modern medicine. Phages are extraordinarily diverse, as are their host receptor targets. Flagellotropic (flagellum-dependent) phages begin their infection cycle by attaching to the flagellum of their motile host, although the later stages of the infection process of most of these phages remain elusive. Flagella are helical appendages required for swimming and swarming motility and are also of great importance for virulence in many pathogenic bacteria of clinical relevance. Not only is bacterial motility itself frequently important for virulence, as it allows pathogenic bacteria to move toward their host and find nutrients more effectively, but flagella can also serve additional functions including mediating bacterial adhesion to surfaces. Flagella are also a potent antigen recognized by the human immune system. Phages utilizing the flagellum for infections are of particular interest due to the unique evolutionary tradeoff they force upon their hosts: by downregulating or abolishing motility to escape infection by a flagellotropic phage, a pathogenic bacterium would also likely attenuate its virulence. This factor may lead to flagellotropic phages becoming especially potent antibacterial agents. This review outlines past, present, and future research of flagellotropic phages, including their molecular mechanisms of infection and potential future applications.

Prevalence and Molecular Characterization of Metallo β-Lactamase Producing Gram-Negative Pathogens Causing Eye Infections

Purpose:

Metallo β-lactamases (MβL) production is a worldwide problem, particularly in gram-negative bacteria. As scanty data is available on the prevalence of MBL, the present study is being undertaken to determine the prevalence, antibacterial sensitivity patterns, and molecular characterization of MβL associated resistant genes in gram-negative bacteria isolated from ocular infections.

Material and Methods

At a tertiary eye care center in south India, 359 gram-negative pathogens, 200 isolates from eye infections, and 159 isolates from normal flora of the eye were studied. A gold standard microbiology method was used to identify the isolates. An antibiotic double disc synergy test and a combination disc test were used to detect MβL production. Multiplex PCR was used to investigate the molecular characteristics of the MβL encoding genes blaVIM, blaIMP, and blaNDM.

Results

Of the 359 gram-negative bacterial pathogens, Pseudomonas aeruginosa 108 (30.1%) and Enterobacter agglomerans 46 (12.8%) were commonly isolated. High prevalence of P. aeruginosa 81% (17 strains) was detected as an MβL producer and it shows 100% resistance to 2nd and 3rd generation cephalosporins and meropenem. Multiplex PCR detected only the blaVIM gene in 56 (28%) of various eye infections and 27 (17%) of normal flora of the gram-negative bacteria (GNB). The blaVIM gene is detected predominantly in 51.8% of keratitis and 21.4% of postoperative endophthalmitis. High prevalence of the gene was detected in P. aeruginosa 42.9% (24 of 56) and Alcaligens denitrificans 10.7% (6 of 56) from eye infections. Whereas, in the control group, P. aeruginosa and E. coli each had 14.8% (4 of 27) that were shown positive.

Conclusion

The emerging MβLs mediated resistance among P. aeruginosa is a challenging task for ophthalmologists, especially in patients with endophthalmitis and bacterial keratitis. This local knowledge will aid in advising appropriate antibiotic use and avoiding unnecessary antibiotic prescriptions, which are highly warranted.

Emergence of a Hypervirulent Tigecycline-Resistant Klebsiella pneumoniae Strain Co-producing blaNDM–1 and blaKPC–2 With an Uncommon Sequence Type ST464 in Southwestern China

Emergence of bla_NDM–1 and bla_KPC–2 co-producing Klebsiella pneumoniae strains is currently attracting widespread attention, but little information is available about their tigecycline resistance, virulence, and prevalence in Southwest China. In July 2021, an extensively drug-resistant K. pneumoniae strain AHSWKP25 whose genome contained both bla_NDM–1 and bla_KPC–2 genes was isolated from the blood of a patient with the malignant hematological disease in Luzhou, China. We investigated the resistance profiles of AHSWKP25 using microbroth dilution, agar dilution, modified carbapenemase inactivation (mCIM), and EDTA-modified carbapenemase inactivation methods (eCIM). The virulence of AHSWKP25 was assessed through string tests, serum killing assays, and a Galleria mellonella larval infection model. Conjugation and plasmid stability experiments were conducted to determine the horizontal transfer capacity of plasmids. And efflux pump phenotype test and real-time quantitative reverse transcription-PCR (RT-PCR) were used to determine its efflux pump activity. Sequencing of AHSWKP25 determined that AHSWKP25 belonged to ST464, which is resistant to antibiotics such as carbapenems, tetracycline, fluoroquinolones, tigecycline, and fosfomycin. The efflux pump phenotype tests and RT-PCR results demonstrated that efflux pumps were overexpressed in the AHSWKP25, which promoted the tigecycline resistance of the bacteria. AHSWKP25 also showed hypervirulence and serum resistance in vitro model. AHSWKP25 carried several different plasmids that contained bla_NDM–1, bla_KPC–2, and mutated tet(A) genes. Sequence alignment revealed that the plasmids carrying bla_NDM–1 and bla_KPC–2 underwent recombination and insertion events, respectively. We demonstrated that an X3 plasmid carrying bla_NDM–1 was transferred from pSW25NDM1 to E. coli J53. We also identified missense mutations in the ramR, rcsA, lon, and csrD genes of AHSWKP25. Our results highlighted the potential of bla_NDM–1 and bla_KPC–2 co-producing K. pneumoniae strains to further develop antimicrobial resistance and hypervirulent phenotypes, but measures should be taken to closely monitor and control the spread of superbugs with multidrug-resistant phenotypes and hypervirulence.

Why Do Antibiotics Exist?

In the struggle with antibiotic resistance, we are losing. There is now a serious threat of moving into a postantibiotic world. High levels of resistance, in terms of both frequency and strength, have evolved against all clinically approved antibiotics worldwide. The usable life span of new clinically approved antibiotics is typically less than a decade before resistance reaches frequencies so high as to require only guarded usage. However, microbes have produced antibiotics for millennia without resistance becoming an existential issue. If resistance is the inevitable consequence of antibiotic usage, as has been the human experience, why has it not become an issue for microbes as well, especially since resistance genes are as prevalent in nature as the genes responsible for antibiotic production? Here, we ask how antibiotics can exist given the almost ubiquitous presence of resistance genes in the very microbes that have produced and used antibiotics since before humans walked the planet. We find that the context of both production and usage of antibiotics by microbes may be key to understanding how resistance is managed over time, with antibiotic synthesis and resistance existing in a paired relationship, much like a cipher and key, that impacts microbial community assembly. Finally, we put forward the cohesive, ecologically based "secret society" hypothesis to explain the longevity of antibiotics in nature.

Molecular Epidemiological Surveillance of CTX-M-15-producing Klebsiella pneumoniae from the patients of a teaching hospital in Sindh, Pakistan

Background 

The presence of Extended-spectrum β-lactamase positive bacteria in hospital setting is an aggravating influential factor for hospitalized patients, and its consequences may be hazardous. Therefore, there is a need for rapid detection methods for newly emerging drug-resistant bacteria. This study was aimed at the molecular characterization of Extended-spectrum β-lactamase -positive  Klebsiella pneumoniae isolates recovered from the patients of a teaching hospital in Sindh, Pakistan.  

Methods 

A total of 513  K. pneumoniae isolates were obtained from various clinical samples during June 2019 to May 2020. The collected isolates were investigated for antimicrobial susceptibility (antibiogram), and PCR and DNA sequencing were performed to analyse the ESBL genes.  

Results 

Among the 513 isolates, as many as 359 (69.9%) were Extended-spectrum β-lactamase producers and 87.5% were multi-drug resistant, while none had resistance to imipenem. PCR scored 3% blaTEM, 3% blaSHV, and 60% blaCTX-M-15 genes for the tested isolates.  

Conclusion 

The study showed that CTX-M-15 was the major prevalent Extended-spectrum β-lactamase type among the isolates. Additionally, all the isolates were susceptible to carbapenems. Screening and detection of Extended-spectrum β-lactamase tests are necessary among all isolates from the enterobacteriaceae family in routine microbiology laboratory to prevent associated nosocomial infections. A larger study is essential to understand molecular epidemiology of Extended-spectrum β-lactamase producing organisms to minimize morbidities due to these multidrug resistant organisms.

In vitro comparative activity of the new beta-lactamase inhibitor taniborbactam with cefepime or meropenem against Klebsiella pneumoniae and cefepime against Pseudomonas aeruginosa metallo-beta-lactamase-producing clinical isolates

Metallo-beta-lactamase (MBL)-producing Gram-negative bacteria are increasing worldwide and very few agents are active against these pathogens. Taniborbactam (formerly VNRX-5133) is a newly developed bicyclic boronate beta-lactamase inhibitor that directly inhibits all four Ambler classes of beta-lactamases. In the present study the in vitro activity of cefepime or meropenem combined with taniborbactam against 100 Klebsiella pneumoniae and cefepime combined with taniborbactam against 100 Pseudomonas aeruginosa molecularly characterized MBL-producing strains were investigated using ISO standard broth microdilution assays and compared with a panel of antimicrobial agents that are used in clinical practice (amikacin, aztreonam, ciprofloxacin, levofloxacin, gentamicin, piperacillin/tazobactam, imipenem, tigecycline, ceftolozane-tazobactam, cefepime-tazobactam, meropenem-vaborbactam, ceftazidime-avibactam). For K. pneumoniae isolates, the MIC₉₀ values were ≥64 mg/L for all drugs except cefepime-taniborbactam (16 mg/L; 87% inhibited at ≤8/4 mg/L), meropenem-taniborbactam (4 mg/L; 94% inhibited at ≤8/4 mg/L) and tigecycline (8 mg/L), with high levels of resistance (≥65%) found for all approved comparator antimicrobials tested. For P. aeruginosa, the MIC₉₀ values were ≥64 mg/L for all drugs except aztreonam (32 mg/L), cefepime-taniborbactam (32 mg/L; 88% inhibited at ≤16/4 mg/L) and ciprofloxacin (32 mg/L), with high levels of resistance (≥73%) for all approved drugs except aztreonam (27%). Taniborbactam reduced cefepime and meropenem MICs by a median 5 and 7 two-fold dilutions to ≤8 mg/L in 87% and 94% of MBL-producing K. pneumoniae isolates, and cefepime MICs by a median 5 two-fold dilutions to ≤16 mg/L in 86% of MBL-producing P. aeruginosa, respectively. The combinations cefepime-taniborbactam and meropenem-taniborbactam are promising alternative treatment options for infections by MBL-producing isolates.

Detection of NDM-1 and VIM Genes in Carbapenem-Resistant Klebsiella pneumoniae Isolates from a Tertiary Health-Care Center in Kathmandu, Nepal

BACKGROUND

Klebsiella pneumoniae is one of the leading causes of nosocomial infections. Carbapenems are used as the last resort for the treatment of multidrug resistant Gram-negative bacterial infections. In recent years, resistance to these lifesaving drugs has been increasingly reported due to the production of carbapenemase. The main objective of this study was to detect the carbapenem-resistant genes blaNDM-1 and blaVIM in K. pneumoniae isolated from different clinical specimens.

METHODS

A total of 585 clinical specimens (urine, pus, sputum, blood, catheter tips, and others) from human subjects attended at Annapurna Neurological Institute and Allied Sciences, Kathmandu were obtained in the period between July 2018 and January 2019. The specimens were isolated and identified for K. pneumoniae. All K. pneumoniae isolates were processed for antimicrobial susceptibility testing (AST) using the disk diffusion method. The isolates were further phenotypically confirmed for carbapenemase production by the modified Hodge test (MHT) using imipenem (10 μg) and meropenem (10 μg) discs. Thus, confirmed carbapenemase-producing isolates were further screened for the production of blaNDM-1 and blaVIM using conventional polymerase chain reaction (PCR).

RESULTS

Among the clinical isolates tested, culture positivity was 38.29% (224/585), and the prevalence of K. pneumoniae was 25.89% (58/224). On AST, K. pneumoniae exhibited resistance toward carbapenems including ertapenem, meropenem, and imipenem, while it showed the highest susceptibility rate against to tigecycline (93.1%; 54/58). Overall, AST detected 60.34% (35/58) carbapenem-resistant isolates, while the MHT phenotypically confirmed 51.72% (30/58) isolates as carbapenemase-producers and 48.28% (28/58) as carbapenemase nonproducers. On subsequent screening for resistant genes among carbapenemase-producers by PCR assay, 80% (24/30) and 3.33% (1/30) isolates were found to be positive for blaNDM-1 and blaVIM, respectively. In the same assay among 28 carbapenem nonproducing isolates, 9 (32.14%) isolates were positive for blaNDM-1 gene while none of them were tested positive for blaVIM gene.

CONCLUSIONS

Molecular detection of resistant genes provides greater specificity and sensitivity than those with conventional techniques, thus aiding in accurate identification of antimicrobial resistance and clinical management of the disease.

Carbapenemase-producing Gram-negative bacteria in aquatic environments: a review

Antibiotic resistance is one of the greatest public-health challenges worldwide, especially with regard to Gram-negative bacteria (GNB). Carbapenems are the β-lactam antibiotics of choice with the broadest spectrum of activity and, in many cases, are the last-resort treatment for several bacterial infections. Carbapenemase-encoding genes, mainly carried by mobile genetic elements, are the main mechanism of resistance against carbapenems in GNB. These enzymes exhibit a versatile hydrolytic capacity and confer resistance to most β-lactam antibiotics. After being considered a clinical issue, increasing attention is being giving to the dissemination of such resistance mechanisms in the environment and especially through water. Aquatic environments are among the most significant microbial habitats on our planet, known as a favourable medium for antibiotic gene transfer, and they play a crucial role in the huge spread of drug resistance in the environment and the community. In this review, we present current knowledge regarding the spread of carbapenemase-producing isolates in different aquatic environments, which may help the implementation of control and prevention strategies against the spread of such dangerous resistant agents in the environment.

Emerging carbapenem-resistant Klebsiella pneumoniae sequence type 16 causing multiple outbreaks in a tertiary hospital in southern Vietnam

The emergence of carbapenem resistance in Klebsiella pneumoniae represents a major global public health concern. Nosocomial outbreaks caused by multidrug-resistant K. pneumoniae are commonly reported to result in high morbidity and mortality due to limited treatment options. Between October 2019 and January 2020, two concurrent high-mortality nosocomial outbreaks occurred in a referral hospital in Ho Chi Minh City, Vietnam. We performed genome sequencing and phylogenetic analysis of eight K. pneumoniae isolates from infected patients and two environmental isolates for outbreak investigation. We identified two outbreaks caused by two distinct lineages of the international sequence type (ST) 16 clone, which displayed extensive drug resistance, including resistance to carbapenem and colistin. Carbapenem-resistant ST16 outbreak strains clustered tightly with previously described ST16 K. pneumoniae from other hospitals in Vietnam, suggesting local persistence and transmission of this particular clone in this setting. We found environmental isolates from a hospital bed and blood pressure cuff that were genetically linked to an outbreak case cluster, confirming the potential of high-touch surfaces as sources for nosocomial spread of K. pneumoniae. Further, we found colistin resistance caused by disruption of the mgrB gene by an ISL3-like element, and carbapenem resistance mediated by a transferable IncF/blaOXA-181 plasmid carrying the ISL3-like element. Our study highlights the importance of coordinated efforts between clinical and molecular microbiologists and infection control teams to rapidly identify, investigate and contain nosocomial outbreaks. Routine surveillance with advanced sequencing technology should be implemented to strengthen hospital infection control and prevention measures.

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.

Treatment of Staphylococcus aureus skin infection in vivo using rifampicin loaded lipid nanoparticles

We have previously reported on a novel nanoparticle formulation that was effective at killing Staphylococcus aureus in vitro. Here, we report for the first time, the antibacterial effects of a lipidic nano-carrier containing rifampicin (NanoRIF) which can be used to successfully treat Methicillin-Resistant S. aureus (MRSA) infection at a reduced antibiotic dosage compared to the free drug in a skin wound model in mice. The formulation used contains the lipid monoolein, a cationic lipid N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl-sulfate (DOTAP) and the antibiotic. We have shown that rifampicin-loaded nanoparticles are more effective at treating infection in the skin wound model than the antibiotic alone. Cryo-TEM was used to capture for the first time, interactions of the formed nanoparticles with the cell wall of an individual bacterium. Our data strongly indicate enhanced binding of these charged nanoparticles with the negatively charged bacterial membrane. The efficacy we have now observed in vivo is of significant importance for the continued development of nanomedicine-based strategies to combat antibiotic resistant bacterial skin infections.

Analysis of Metallo-β-lactamases, oprD Mutation, and Multidrug Resistance of β-lactam Antibiotic-Resistant Strains of Pseudomonas aeruginosa Isolated from Southern China

The purpose of this study was to analyze the metallo-β-lactamases (MBLs) genotype and oprD mutations of the β-lactam antibiotic-resistant Pseudomonas aeruginosa (PA) strains isolated from southern China. We collected 110 strains of β-lactam antibiotic-resistant PA from 2 hospitals during January 2016–December 2017 from Dongguan, South China. MBLs were detected, amplified, and typed using EDTA disc synergy test, PCR, and Sanger gene sequencing. The mutations and expression levels of oprD were detected using Sanger gene sequencing and qPCR. A total of 16.36% (18/110) β-lactam antibiotic-resistant PA strains produced MBLs, and the main genotypes of MBLs were IMP-25, VIM-2, and SIM-2. Sanger gene sequencing results showed that 107 of the 110 strains harbored mutations in oprD sequence, while 3 strains were negative for oprD amplification (2.73%). Among the 107 strains with positive amplification (97.27%), the rate of intentional mutations (including deletions, insertions, and premature stop codons) was 93.46% (100/107) and that of no disrupted mutation was 6.54% (7/107). qPCR analysis confirmed that the expression level of the OprD protein in the 7 strains of no disrupted mutation was significantly reduced. Among the β-lactam antibiotic-resistant PA strains in southern China, 16.36% were positive for MBLs. The loss rate of oprD was 2.73%, and almost all PA strains showed oprD amplification variation or transcription downregulation. Thus, impaired oprD expression and MBLs production may be some of the mechanisms of β-lactam antibiotic-resistance of PA strains in southern China.

The Molecular Mechanisms Underlying Hidden Phenotypic Variation among Metallo-β-Lactamases

Genetic variation among orthologous genes has been largely formed through neutral genetic drift while maintaining the functional role of these genes. However, because the evolution of gene occurs in the context of each host organism, their sequence changes are also associated with adaptation to a specific environment. Thus, genetic variation can create critical phenotypic variation, particularly when genes are transferred to a new host by horizontal gene transfer. Unveiling "hidden phenotypic variation" is particularly important for genes that confer resistance to antibiotics. However, our understanding of the molecular mechanisms that underlie phenotypic variation remains limited. Here we sought to determine the extent of phenotypic variation in the B1 metallo-β-lactamase (MBL) family and its molecular basis by systematically characterizing eight MBL orthologs, including NDM-1 and VIM-2 and IMP-1. We found that these MBLs confer diverse levels of resistance. The phenotypic variation cannot be explained by variation in catalytic efficiency alone; rather, it is the combination of the catalytic efficiency and abundance of functional periplasmic enzyme that best predicts the observed variation in resistance. The level of functional periplasmic expression varied dramatically between MBL orthologs. This was the result of changes at multiple levels of each ortholog's: (1) quantity of mRNA, (2) amount of MBL expressed, and (3) efficacy of functional enzyme translocation to the periplasm. Overall, it is the interaction between each gene and the host's underlying cellular processes (transcription, translation, and translocation) that determines MBL genetic incompatibility through horizontal gene transfer. These host-specific processes may constrain the effective spread and deployment of MBLs to certain host species and could explain the current observed distribution bias.

Prevalence of metallo-β-lactamase acquired genes among carbapenems susceptible and resistant Gram-negative clinical isolates using multiplex PCR, Khartoum hospitals, Khartoum Sudan

Background

The increased prevalence of carbapenem-resistant Gram-negative isolates caused by Metallo-β-lactamase (MBL) is worrisome in clinical settings worldwide. The mortality rate associated with infections caused by MBLs producing organisms ranging from 18 to 67%.

This study aimed to determine the prevalence of Metallo-β-lactamase genes among some Gram-negative clinical isolates (Carbapenems susceptible and resistant).

Methods

This paper describes a descriptive cross-sectional study carried out to detect MBL genes such as (blaVIM, blaIMP and blaNDM) by multiplex PCR mixture reaction among 200 Gram-negative clinical isolates (Citrobacter spp, Escherichia coli, Enterobacter spp, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, Proteus valgaris). Khartoum hospitals during 2015 to 2016.

Limitation: The study organisms were not evaluated for non-MBL carbapenemases, such as KPC and OXA-48.

Results

The prevalence of MBL genes by multiplex PCR assays among 200 Gram-negative clinical isolates was 72(36.1%). MBL positive genes among 100 carbapenems sensitive and 100 resistant isolates were 27(27%) and 45(45%) respectively. There was a statistically, significant association between the antimicrobial susceptibility and the presences of MBL genes (P.value = 0.008).

E.coli was the predominant species possessing MBL genes 26(36.1%), with 22(30.7%) species having a combination of MBL genes.

Verona integron Metallo beta-lactamase (VIM) was the most frequent genes 28(38.9%) out of 72 MBL detected genes, followed by imipenemase (IMP) was 19(26.4%), and consequently, New Delhi Metallo beta lactamase was 3(4.2%).

Conclusion

This study revealed a high prevalence of MBL genes in some Gram-negative isolates from Khartoum State Hospitals which were not previously established in these hospitals.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3581-z) contains supplementary material, which is available to authorized users.

Multidrug-Resistant Acinetobacter baumannii Ventriculostomy-Related Infection, Treated by a Colistin, Tigecycline, and Intraventricular Fibrinolysis

BACKGROUND

Acinetobacter baumannii meningitis and ventriculitis are difficult issues, because of the low diffusion of antibiotics in the cerebrospinal fluid and bacterial multidrug resistance. The presence of an infected intraventricular hematoma, constituting an equivalent of undrained abscess, may promote biofilm formation and failure of medical treatment.

CASE DESCRIPTION

In this case of ventriculostomy-related infection after ventricular hemorrhage, Acinetobacter baumannii was sensitive only to colistin and tigecycline. Despite a combination therapy involving intraventricular injections of colistin, we observed clinical and bacteriologic failure. Therefore, at day 4 of antibiotic therapy, we performed intraventricular fibrinolysis, which dissolved the clot, enabling sterilization of the cerebrospinal fluid after 48 hours.

CONCLUSION

This clinical case suggests the usefulness of intraventricular fibrinolysis to lyse the clot and optimize the action of antibiotics.

Molecular epidemiology of carbapenem-resistant Pseudomonas aeruginosa in an endemic area: comparison with global data

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is an endemic problem in certain countries including Greece. CRPA and multidrug-resistant P. aeruginosa (MDRPA) firstly emerged in our region during the 80s, right after the launch of imipenem and meropenem as therapeutic agents against P. aeruginosa infections. The role of outer membrane protein (Opr) inactivation has been known to contribute to imipenem resistance since many years, while efflux overexpression systems have been mainly associated with meropenem resistance. Among carbapenemases, metallo-β-lactamases (MBL) and mostly Verona integron-mediated (VIM) MBL's have played the most crucial role in CRPA emergence. VIM-2 and VIM-4 producing CRPA, usually belonging to clonal complexes (CC) 111 and 235 respectively, have most frequently been isolated. Bla_VIM-2 and bla_VIM-4 are usually associated with a class 1 integron. VIM-17 also has appeared in Greece. On the other hand, other VIM subtypes detected in a global level, such as VIM-3, VIM-5, VIM-6, VIM-7, VIM-11, VIM-14, VIM-15, VIM-16 and VIM-18 have not yet emerged in Greece. However, new VIM subtypes will probably emerge in the future. In addition, MBL carbapenemases other than VIM, detected worldwide have not yet appeared. A single CRPA isolate producing KPC has emerged in our region several years ago. The study of the molecular basis of Opr deficiency and efflux overexpression remains a challenge for the future. In this article, we review the molecular epidemiology of CRPA in an endemic area, compared to global data.

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

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

Biochemical and genetic characterization of a novel metallo-β-lactamase from marine bacterium Erythrobacter litoralis HTCC 2594

Metallo-β-lactamases (MBLs) are a group of enzymes that can inactivate most commonly used β-lactam-based antibiotics. Among MBLs, New Delhi metallo-β-lactamase-1 (NDM-1) constitutes an urgent threat to public health as evidenced by its success in rapidly disseminating worldwide since its first discovery. Here we report the biochemical and genetic characteristics of a novel MBL, ElBla2, from the marine bacterium Erythrobacter litoralis HTCC 2594. This enzyme has a higher amino acid sequence similarity to NDM-1 (56%) than any previously reported MBL. Enzymatic assays and secondary structure alignment also confirmed the high similarity between these two enzymes. Whole genome comparison of four Erythrobacter species showed that genes located upstream and downstream of elbla2 were highly conserved, which may indicate that elbla2 was lost during evolution. Furthermore, we predicted two prophages, 13 genomic islands and 25 open reading frames related to insertion sequences in the genome of E. litoralis HTCC 2594. However, unlike NDM-1, the chromosome encoded ElBla2 did not locate in or near these mobile genetic elements, indicating that it cannot transfer between strains. Finally, following our phylogenetic analysis, we suggest a reclassification of E. litoralis HTCC 2594 as a novel species: Erythrobacter sp. HTCC 2594.

Detection of metallo-β-lactamases-encoding genes among clinical isolates of Pseudomonas aeruginosa in a tertiary care hospital, Kathmandu, Nepal

Objectives

This study was carried out to determine the prevalence of metallo-β-lactamases (MBLs) producing Pseudomonas aeruginosa in imipenem-nonsusceptible isolates and to detect MBL-encoding genes among MBLs-positive isolates.

Results

Metallo-β-lactamases production was detected in 68.6% isolates of P. aeruginosa with reduced susceptibility to imipenem. The bla_VIM-2 gene was detected in 75% isolates and bla_IMP-1 was detected in 25% isolates. All MBLs-positive isolates were multidrug resistant with a high level of resistance to imipenem (MIC 16 to ≥ 32 µg/ml), meropenem (MIC 16 to ≥ 32 µg/ml), and ceftazidime (MIC 64 to ≥ 512 µg/ml). All MBL-positive isolates were susceptible (MIC ≤ 2 µg/ml) to colistin. We found high prevalence of MBL-producing P. aeruginosa. To our knowledge this is the first report of detection of bla_VIM-2 and bla_IMP-1 in P. aeruginosa from Nepal. This indicates the need for awareness to prevent the spreading of these resistant isolates in hospital setting.

Multiple Antibiotic-Resistant, Extended Spectrum-β-Lactamase (ESBL)-Producing Enterobacteria in Fresh Seafood

Members of the family Enterobacteriaceae include several human pathogens that can be acquired through contaminated food and water. In this study, the incidence of extended spectrum β-lactamase (ESBL)-producing enterobacteria was investigated in fresh seafood sold in retail markets. The ESBL-positive phenotype was detected in 169 (78.60%) isolates, with Escherichia coli being the predominant species (53), followed by Klebsiella oxytoca (27), and K. pneumoniae (23). More than 90% of the isolates were resistant to third generation cephalosporins, cefotaxime, ceftazidime, and cefpodoxime. Sixty-five percent of the isolates were resistant to the monobactam drug aztreonam, 40.82% to ertapenem, and 31.36% to meropenem. Resistance to at least five antibiotics was observed in 38.46% of the isolates. Polymerase Chain Reaction (PCR) analysis of ESBL-encoding genes detected bla_CTX, bla_SHV, and bla_TEM genes in 76.92%, 63.3%, and 44.37% of the isolates, respectively. Multiple ESBL genes were detected in majority of the isolates. The recently discovered New Delhi metallo-β-lactamase gene (bla_NDM-1) was detected in two ESBL⁺ isolates. Our study shows that secondary contamination of fresh seafood with enteric bacteria resistant to multiple antibiotics may implicate seafood as a potential carrier of antibiotic resistant bacteria and emphasizes an urgent need to prevent environmental contamination and dissemination of such bacteria.

Microbial glycoside hydrolases as antibiofilm agents with cross-kingdom activity

Galactosaminogalactan and Pel are cationic heteropolysaccharides produced by the opportunistic pathogens Aspergillus fumigatus and Pseudomonas aeruginosa, respectively. These exopolysaccharides both contain 1,4-linked N-acetyl-d-galactosamine and play an important role in biofilm formation by these organisms. Proteins containing glycoside hydrolase domains have recently been identified within the biosynthetic pathway of each exopolysaccharide. Recombinant hydrolase domains from these proteins (Sph3_h from A. fumigatus and PelA_h from P. aeruginosa) were found to degrade their respective polysaccharides in vitro. We therefore hypothesized that these glycoside hydrolases could exhibit antibiofilm activity and, further, given the chemical similarity between galactosaminogalactan and Pel, that they might display cross-species activity. Treatment of A. fumigatus with Sph3_h disrupted A. fumigatus biofilms with an EC₅₀ of 0.4 nM. PelA_h treatment also disrupted preformed A. fumigatus biofilms with EC₅₀ values similar to those obtained for Sph3_h In contrast, Sph3_h was unable to disrupt P. aeruginosa Pel-based biofilms, despite being able to bind to the exopolysaccharide. Treatment of A. fumigatus hyphae with either Sph3_h or PelA_h significantly enhanced the activity of the antifungals posaconazole, amphotericin B, and caspofungin, likely through increasing antifungal penetration of hyphae. Both enzymes were noncytotoxic and protected A549 pulmonary epithelial cells from A. fumigatus-induced cell damage for up to 24 h. Intratracheal administration of Sph3_h was well tolerated and reduced pulmonary fungal burden in a neutropenic mouse model of invasive aspergillosis. These findings suggest that glycoside hydrolases can exhibit activity against diverse microorganisms and may be useful as therapeutic agents by degrading biofilms and attenuating virulence.

Prevalence and dissemination of antibiotic resistance genes and coselection of heavy metals in Chinese dairy farms

This study aims to explore prevalence and dissemination of antibiotic resistance genes (ARGs) in dairy farms. A variety of ARGs conferring resistance to most classes of antibiotics were detected in feces and soil samples obtained from dairy farms, using a high-throughput metagenomic sequencing approach. The ARGs observed in the feces and the soil samples were significantly correlated (p<0.01). The abundance of mobile genetics elements, such as transposase, was also examined to evaluate the potential risk of horizontal ARGs transfer. The positive correlation (p<0.001) between the total abundance of transposase genes and ARGs in the soil samples suggested strong dissemination capacity of ARGs in soil. In addition, the ARGs and metal resistance genes (MRGs) were significantly correlated with heavy metals in the feces (p<0.01), suggesting that the heavy metals promoted the emergence of metal resistance, and participated in the coselection processes for ARGs. The prevalence of ARGs with high levels of genetic mobile elements in the dairy farms suggests that cattle excrement is a major reservoir of ARGs with a high risk of dissemination, which increases the potential risk of environmental pollution and threatens public health.

Consumption of antibiotics for community-acquired infections by adults in Greece: A cross-sectional study

We studied the rates and characteristics of antibiotics consumption for community-acquired infections in 309 adult patients. Of them, 293 (94.8%) had received at least 1 course of antibiotics during the past year. In total, 419 courses of antibiotics were consumed during the past year, including 285 (68%) following medical examination, 72 (17.2%) following telephone consultation, 30 (7.2%) following suggestion by a pharmacist, and in 16 (3.8%) the antibiotic was available at home. Older age and asthma were significantly associated with a higher risk for antibiotics consumption.

IMP-27, a Unique Metallo-β-Lactamase Identified in Geographically Distinct Isolates of Proteus mirabilis

A novel metallo-β-lactamase gene, bla_IMP-27, was identified in unrelated Proteus mirabilis isolates from two geographically distinct locations in the United States. Both isolates harbor bla_IMP-27 as part of the first gene cassette in a class 2 integron. Antimicrobial susceptibility testing indicated susceptibility to aztreonam, piperacillin-tazobactam, and ceftazidime but resistance to ertapenem. However, hydrolysis assays indicated that ceftazidime was a substrate for IMP-27.

Resistance mechanisms

By definition, the terms sepsis and septic shock refer to a potentially fatal infectious state in which the early administration of an effective antibiotic is the most significant determinant of the outcome. Because of the global spread of resistant bacteria, the efficacy of antibiotics has been severely compromised. S. pneumonia, Escherichia coli (E. coli), Klebsiella, Acinetobacter, and Pseudomonas are the predominant pathogens of sepsis and septic shock. It is common for E. coli, Klebsiella, Acinetobacter and Pseudomonas to be resistant to multiple drugs. Multiple drug resistance is caused by the interplay of multiple resistance mechanisms those emerge via the acquisition of extraneous resistance determinants or spontaneous mutations. Extended-spectrum beta-lactamases (ESBLs), carbapenemases, aminoglycoside-modifying enzymes (AMEs) and quinolone resistance determinants are typically external and disseminate on mobile genetic elements, while porin-efflux mechanisms are activated by spontaneous modifications of inherited structures. Porin and efflux mechanisms are frequent companions of multiple drug resistance in Acinetobacter and P. aeruginosa, but only occasionally detected among E. coli and Klebsiella. Antibiotic resistance became a global health threat. This review examines the major resistance mechanisms of the leading microorganisms of sepsis.

High prevalence of extensively drug-resistant and metallo beta-lactamase-producing clinical Acinetobacter baumannii in Iran

Acinetobacter species particularly Acinetobacter baumannii (A. baumannii) have been widely reported as broad-spectrum antibiotic resistant pathogens. Expression of various types of metallo beta-lactamases (MBL), classified as Ambler class B, has been associated with carbapenem resistance. Here, we attempted to assess the frequency of extensively drug-resistant (XDR) and MBL-producing A. baumannii among clinical isolates. 86 clinical A. baumannii strains were collected from 2014 to 2015 and their susceptibility to meropenem (10 μg), imipenem (10 μg), azteronem (30 μg), pipracillin (100 μg) tazobactam (110 μg), tobramycin (10 μg), fosfomycin (200 μg), rifampicin (5 μg), colistin (10 μg), tigecycline (15 μg), sulbactam/ampicillin (10 μg + 10 μg) and polymixin B (300 U) was evaluated using disk diffusion method. The MBL-producing isolates were screened using combined disc diffusion method. Furthermore, the presence of blaVIM, blaIMP, blaSPM, blaGIM, blaSIM and blaNDM was detected by PCR. 34.9% of isolates were recovered from bronchoalveolar lavage (BAL). 81 (94.2%) and 62 (71.2%) isolates were multidrug resistance (MDR) and XDR, respectively. 44 (51.2%) and 65 (75.6%) isolates were MBL-producing strains with resistance to imipenem and meropenem, respectively. 2 (2.3%), 13 (15.1%), 2 (2.3%), 4 (4.7%) and 2 (2.3%) isolates carried blaVIM, blaIMP, blaSPM, blaGIM and blaSIM genes, respectively. Our data showed that the rate of XDR and MBL A. baumannii is on the rise.

Emergence of Multidrug Resistance and Metallo-beta-lactamase Producing Acinetobacter baumannii Isolated from Patients in Shiraz, Iran

BACKGROUND

Metallo-beta-lactamase (MβL) enzymes production is one of the most important resistance mechanisms against carbapenems in some bacteria including Acinetobacter baumannii.

AIMS

This study was aimed to determine the antimicrobial susceptibility and the prevalence of MβL among carbapenem-resistant isolates of A. baumannii.

MATERIALS AND METHODS

In this cross-sectional study from October 2012 to April 2013, 98 isolates were identified as A. baumannii using Microgen™ kits and confirmed by molecular method. These isolates were tested for antimicrobial susceptibilities by disk diffusion method according to the Clinical and Laboratory Standards Institute guidelines. Carbapenem-resistant isolates were further detected phenotypically by MβL minimal inhibitory concentration (MIC)-test strips, and subsequently positive MβL isolates were confirmed by polymerase chain reaction (PCR).

RESULTS

Overall, 98% (96/98) of A. baumannii isolates were detected as carbapenem-resistant by MIC test. Highest sensitivity to the tested antibiotic with 42.9% (42/98) was observed to colistin. Of 96 carbapenem-resistant isolates, 43 were phenotypically positive for MβL; out of 43 isolates, 37 were confirmed for the presence of MβL genes by PCR.

CONCLUSION

The frequency of drug resistance among the clinical samples of A. baumannii isolated in our study against most of the antibiotics was very high. Moreover, all MβL producing isolates were multidrug resistance. Therefore, systematic surveillance to detect MβL producing bacteria and rational prescription and use of carbapenems could be helpful to prevent the spread of carbapenem resistance.

Clonal Relatedness among Imipenem-Resistant Pseudomonas aeruginosa Isolated from ICU-Hospitalized Patients

Imipenem-resistant Pseudomonas aeruginosa (P. aeruginosa) has become an increasingly important problem in healthcare settings worldwide. The aim of the present study was to evaluate clonal spread among imipenem-resistant P. aeruginosa isolated from ICU-hospitalized patients. Totally, 150 wound specimens were analyzed. Antibiotic resistance profiles and clonal diversity were evaluated using Kirby-Bauer's disk diffusion method and Random Amplified Polymorphic DNA- (RAPD-) PCR, respectively. The isolates showed a high frequency of antibiotic resistance against meropenem, and imipenem (100%) followed by ciprofloxacin, and ceftazidime (90%); meanwhile resistance to polymyxin B was not observed. Eighteen (40%) of P. aeruginosa isolates were MBL-positive via ethylenediaminetetraacetic acid (EDTA) combined disk test. Our findings showed high genetic diversity, with 37 different RAPD types detected. RAPD typing results showed cross-acquisition of P. aeruginosa in investigated hospital, suggesting failure in infection control practices. Incidence of MBL-positive isolates is high and should be regarded as a threat to hospitalized patients.

β-Lactam antibiotic-degrading enzymes from non-pathogenic marine organisms: a potential threat to human health

Metallo-β-lactamases (MBLs) are a family of Zn(II)-dependent enzymes that inactivate most of the commonly used β-lactam antibiotics. They have emerged as a major threat to global healthcare. Recently, we identified two novel MBL-like proteins, Maynooth IMipenemase-1 (MIM-1) and Maynooth IMipenemase-2 (MIM-2), in the marine organisms Novosphingobium pentaromativorans and Simiduia agarivorans, respectively. Here, we demonstrate that MIM-1 and MIM-2 have catalytic activities comparable to those of known MBLs, but from the pH dependence of their catalytic parameters it is evident that both enzymes differ with respect to their mechanisms, with MIM-1 preferring alkaline and MIM-2 acidic conditions. Both enzymes require Zn(II) but activity can also be reconstituted with other metal ions including Co(II), Mn(II), Cu(II) and Ca(II). Importantly, the substrate preference of MIM-1 and MIM-2 appears to be influenced by their metal ion composition. Since neither N. pentaromativorans nor S. agarivorans are human pathogens, the precise biological role(s) of MIM-1 and MIM-2 remains to be established. However, due to the similarity of at least some of their in vitro functional properties to those of known MBLs, MIM-1 and MIM-2 may provide essential structural insight that may guide the design of as of yet elusive clinically useful MBL inhibitors.

A comparative analysis of methylome profiles of Campylobacter jejuni sheep abortion isolate and gastroenteric strains using PacBio data

Campylobacter jejuni is a leading cause of human gastrointestinal disease and small ruminant abortions in the United States. The recent emergence of a highly virulent, tetracycline-resistant C. jejuni subsp. jejuni sheep abortion clone (clone SA) in the United States, and that strain's association with human disease, has resulted in a heightened awareness of the zoonotic potential of this organism. Pacific Biosciences' Single Molecule, Real-Time sequencing technology was used to explore the variation in the genome-wide methylation patterns of the abortifacient clone SA (IA3902) and phenotypically distinct gastrointestinal-specific C. jejuni strains (NCTC 11168 and 81-176). Several notable differences were discovered that distinguished the methylome of IA3902 from that of 11168 and 81-176: identification of motifs novel to IA3902, genome-specific hypo- and hypermethylated regions, strain level variability in genes methylated, and differences in the types of methylation motifs present in each strain. These observations suggest a possible role of methylation in the contrasting disease presentations of these three C. jejuni strains. In addition, the methylation profiles between IA3902 and a luxS mutant were explored to determine if variations in methylation patterns could be identified that might explain the role of LuxS-dependent methyl recycling in IA3902 abortifacient potential.

Detection of Metallo-Beta Lactamases Among Carbapenem-Resistant Pseudomonas aeruginosa

Background:

Carbapenems are important drugs used for the treatment of Pseudomonas aeruginosa infections, however metallo-β-lactamases (MBL) are able to efficiently hydrolyze these classes of drugs. Immediate detection of the MBL-producing P. aeruginosa is necessary in order to accurately treat infections caused by this organism.

Objectives:

To determine the prevalence of MBL producing P. aeruginosa in burn and non-burn patients by two phenotypic tests and polymerase chain reaction (PCR) and to compare phenotypic tests with PCR.

Materials and Methods:

A total of 223 non-duplicate strains of P. aeruginosa were collected from three teaching hospitals of Ahvaz, Iran. Antimicrobial susceptibility and minimum inhibitory concentrations (MICs) of carbapenems (imipenem, meropenem, doripenem and ertapenem) were determined by the Kirby-Bauer and E-test methods. Combined disk (CD) test, MBL E-test and PCR were performed for carbapenem-resistant P. aeruginosa isolates.

Results:

Amongst all the P. aeruginosa isolates, 58.7% were resistant to imipenem while 31.8%, 13.5% and 74.4% were resistant to meropenem, doripenem and ertapenem, respectively. Amongst all the P. aeruginosa isolates, 44.4% were multidrug resistant and 13.45% were resistant to all of the carbapenems. The CD test with doripenem disk / 750 μg ethylene diamine tetra acetic acid (EDTA) had the highest efficiency compared to the other phenotypic tests. bla_IMP and bla_VIM genes were detected in 11.7% and 0.4% of isolates, respectively. bla_SPM and bla_NDM genes were not observed.

Conclusions:

Epidemiological and regional evaluation of MBL-producing P. aeruginosa through simple and inexpensive methods should be considered for effective treatment of carbapenem-resistant P.aeruginosa infections.

Phenotypic and enzymatic comparative analysis of the KPC variants, KPC-2 and its recently discovered variant KPC-15

Sixteen different variants (KPC-2 to KPC-17) in the KPC family have been reported, and most current studies are focusing on KPC-2 and KPC-3. The KPC-15 variant, which isolated from Klebsiella pneumoniae in a Chinese hospital, was a recently discovered KPC enzyme. To compare the characteristics of KPC-15 and KPC-2, the variants were determined by susceptibility testing, PCR amplification and sequencing, and study of kinetic parameters. The strain harboring the KPC-15 showed resistance to 18 conventional antimicrobial agents, especially to cabapenem antibiotics, and the strain involving the KPC-2 also indicated resistance to cabapenem antibiotics, but both strains were susceptible to polymyxin B and colistin. The conjugation experiments showed that the changes of MIC values to the antibiotics were due to the transferred plasmids. The differences of amino acids were characterised at sites of 119 leucine and 146 lysine with KPC-15 and KPC-2. The minimum evolution tree indicated the KPC alleles evolution, and showed that the KPC-15 appeared to be homogenous with KPC-4 closely. Steady-state kinetic parameters showed the catalytic efficiency of KPC-15 was higher than that of KPC-2 for all tested antibiotics in this study. The catalytic efficiency of KPC-15 caused resistance to β-lactam antibiotics was higher than that of KPC-2. Meanwhile, an evolutionary transformation changed KPC from an efficient carbapenemase to its variants (KPC-15) with better ceftazidimase catalytic efficiency, and the old antibiotics polymyxin B and colistin might play a role in the therapy for multi-resistant strains.

Carbapenem-resistant Enterobacteriaceae: biology, epidemiology, and management

Introduced in the 1980s, carbapenem antibiotics have served as the last line of defense against multidrug-resistant Gram-negative organisms. Over the last decade, carbapenem-resistant Enterobacteriaceae (CRE) have emerged as a significant public health threat. This review summarizes the molecular genetics, natural history, and epidemiology of CRE and discusses approaches to prevention and treatment.

Evaluation of tests to predict metallo-β-lactamase in cystic fibrosis (CF) and non-(CF) Pseudomonas

Double disks synergy test (DDST) and combined disks test (CD) were evaluated to predict the presence of metallo-β-lactamase in 70 Pseudomonas aeruginosa isolates recovered from cystic fibrosis and non-cystic fibrosis patients. DDST_{CAZ-EDTA 1 cm} and CD_IMP-EDTA tests showed the best accuracy (94.3%). Furthermore, for other combinations, accuracy unsatisfactory was obtained.

Characterization and plasmid elimination of NDM-1-producing Acinetobacter calcoaceticus from China

The presence of multidrug-resistant bacterial pathogens in the environment poses a serious threat to public health. The opportunistic Acinetobacter spp. are among the most prevalent causes of nosocomial infections. Here, we performed complete genome sequencing of the Acinetobacter calcoaceticus strain XM1570, which was originally cultivated from the sputum of a patient diagnosed with pneumonia in Xiamen in 2010. We identified carbapenem resistance associated gene bla_NDM-1 located on a 47.3-kb plasmid. Three methods – natural reproduction, sodium dodecyl sulfate treatment and nalidixic acid treatment – were used to eliminate the bla_NDM-1-encoding plasmid, which achieved elimination rates of 3.32% (10/301), 83.78% (278/332), and 84.17% (298/354), respectively. Plasmid elimination dramatically increased antibiotic sensitivity, reducing the minimum bacteriostatic concentration of meropenem from 256 µg/ml in the clinical strain to 0.125 µg/ml in the plasmid-eliminated strain. Conjugation transfer assays showed that the bla_NDM-1-containing plasmid could be transferred into Escherichia coli DH5α:pBR322 in vitro as well as in vivo in mice. The bla_NDM-1 genetic environment was in accordance with that of other bla_NDM-1 genes identified from India, Japan, and Hong-Kong. The multilocus sequence type of the isolate was identified as ST-70. Two novel genes encoding intrinsic OXA and ADC were identified and named as OXA-417 and ADC-72. The finding of bla_NDM-1 in species like A. calcoaceticus demonstrates the wide spread of this gene in gram-negative bacteria which is possible by conjugative plasmid transfer. The results of this study may help in the development of a treatment strategy for controlling NDM-1 bacterial infection and transmission.

Incidence of metallo-beta-lactamase producing clinical isolates of Escherichia coli and Klebsiella pneumoniae in central Nepal

Background

The increasing and rapid spread of metallo-beta-lactamase (MBL) producing Enterobacteriaceae, particularly Escherichia coli and Klebsiella pneumoniae represents an emerging public health threat. However, limited data is available on MBL production in clinical isolates of E. coli and K. pneumoniae from Nepal. We have therefore undertaken this study to ascertain the incidence of MBL production in clinical isolates of E. coli and K. pneumoniae at a tertiary care teaching hospital in central Nepal.

Methods

A total of 401 consecutive, non-duplicate isolates of E. coli (n = 216) and K. pneumoniae (n = 185) were recovered from various clinical samples between July and December, 2012. These isolates were screened for the detection of carbapenemase production on the basis of their reduced susceptibility to meropenem or ertapenem by the disc diffusion method. The screened isolates were further phenotypically studied for carbapenemase production by modified Hodge test (MHT). MBL production was detected by performing combined disc test by using imipenem discs with and without ethylenediaminetetraacetic acid (EDTA), which chelates zinc required for MBL activity.

Results

Out of 216 E. coli isolates, a total of 41 isolates (18.98%) and out of 185 K. pneumoniae isolates, a total of 39 isolates (21.08%) were suspected to be carbapenemase- producers on the basis of their reduced susceptibility to meropenem or ertapenem. Interestingly, all the initially suspected isolates of E. coli and K. pneumoniae for carbapenemase production were found to be positive in both MHT and combined disc test. However, few weakly positive reactions were observed in MHT. All the MBL producing isolates were multidrug-resistant (MDR). In addition, 75.60% E. coli and 71.79% of K. pneumoniae isolates producing MBL were found to be “pandrug- resistant”.

Conclusions

Our findings showed MBL production in a considerable number of E. coli and K. pneumoniae isolates with MDR and pandrug-resistant phenotypes. Combined disc method can provide a sensible choice for phenotypic detection of MBL production in clinical microbiology laboratories as detection of MBL in bacterial isolates is indispensable for establishing the effective antibiotic policies and infection control strategies in the hospital setting.

Comparison of phenotypic tests for the detection of metallo-beta-lactamases in clinical isolates of Pseudomonas aeruginosa

Metallo-β-lactamase (MBL)-producing gram-negative bacteria are an increasing public health concern worldwide. Screening tests for the rapid and specific identification of these pathogens are essential, and should be included among routine diagnostics in laboratories. This study aimed to determine the MBL frequency among carbapenem-resistant Pseudomonas aeruginosa isolates, and to evaluate the accuracy of different tests in screening for MBL production. From January 2001 to December 2008, a total of 142 imipenem-non-susceptible P. aeruginosa strains were isolated from distinct clinical samples from hospitalized patients. These isolates were examined by PCR, MBL E-test, double-disk synergy test (DDST), and combined disk (CD) test. The minimal inhibitory concentration (MIC; μg/mL) was determined by agar dilution, and pulsed field gel electrophoresis (PFGE) was performed on all samples. Sequencing was performed to confirm and define the MBL variant and subtype. Using PCR and DNA sequence analysis, 93 strains were confirmed positive for MBLs, 91 strains for the blaSPM-1 gene, 1 strain for the blaIMP-1 gene, and 1 strain for the blaIMP-16 gene. PFGE displayed a clonal pattern. The sensitivities, specificities, positive and negative predictive values were evaluated for all tests. The DDST assay (CAZ-MPA) was the optimal method for screening MBL production in P. aeruginosa strains. However, the results of the CD assay (IMP/EDTA) showed close agreement with those of the DDST. In addition, the CD assay allowed a more objective interpretation and did not require the use of a toxic substance.