The use of carbapenems in the treatment of serious infections

Antimicrobial Treatment Challenges in the Management of Infective Spondylodiscitis Associated with Hemodialysis: A Comprehensive Review of Literature and Case Series Analysis

Infective spondylodiscitis (ISD), the infection of vertebral bodies and surrounding tissues, is a rare complication with major impact on the long-term survival of hemodialysis (HD) patients. Although the most frequent etiology is staphylococcal, identifying these pathogens in blood cultures and biopsy cultures is often difficult. This paper aims to present suitable antibiotic combinations for the treatment of these patients, which is usually challenging in the case of an unidentified pathogen. We presented the therapies applied for 13 HD patients and 19 patients without chronic kidney disease (CKD), diagnosed with ISD between 2013 and 2023 in Bihor County. The percentage of positive blood cultures was low in both groups (30.78% HD vs. 15.78% non-HD). The average length of antibiotic therapy was 5.15 weeks in HD patients and 6.29 weeks in non-HD patients. The use of Carbapenem alone (e.g., Meropenem) for an average of 19.6 days for patients in HD when the pathogen was not identified has proven to be efficient in most cases, similarly to using Vancomycin and Fluoroquinolone/Cephalosporines in combination. Regarding the non-CKD patients, the use of Clindamycin in various combinations for an average of 30.3 days has proven to be efficient in more than 90% of cases of ISD with a nonidentified pathogen. Within 2 years after ISD was diagnosed, 12 of the 13 HD patients passed away, mainly due to cardiovascular causes. Unfortunately, there are no guidelines in the literature concerning the empiric treatment of ISD in the particular case of HD patients. Upon checking the literature on PubMed and Google Scholar, only 10 studies provided relevant data regarding ISD treatment for HD patients. More data about the treatment and evolution of these patients is needed in order to elaborate a truly relevant metanalysis.

Carbapenem resistance in Enterobacterales from agricultural, environmental and clinical origins: South Africa in a global context

Carbapenem agents are regarded as last-resort antibiotics, however, bacterial resistance towards carbapenems has been reported in both clinical and agricultural settings worldwide. Carbapenem resistance, defined as the resistance of a bacteria towards one or more carbapenem drugs, can be mediated in either of, or a combination of, three mechanisms-although, the mechanism mediated through the production of carbapenemases (β-lactamases that are able to enzymatically degrade carbapenems) is of most significance. Of particular concern is the occurrence of carbapenemase producing Enterobacterales (CPE), with literature describing a dramatic increase in resistance globally. In South Africa, increases of carbapenemase activity occurring in Enterobacter species, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa have recently been reported. CPE can also be found in agricultural environments, as global studies have documented numerous instances of CPE presence in various animals such as pigs, cattle, seafood, horses and dogs. However, most reports of CPE occurrence in agricultural settings come from Northern America, Europe and some parts of Asia, where more extensive research has been conducted to understand the CPE phenomenon. In comparison to clinical data, there are limited studies investigating the spread of CPE in agricultural settings in Africa, highlighting the importance of monitoring CPE in livestock environments and the food chain. Further research is necessary to uncover the true extent of CPE dissemination in South Africa. This review will discuss the phenomenon of bacterial antibiotic resistance (ABR), the applications of the carbapenem drug and the occurrence of carbapenem resistance globally.

High Prevalence of GES-5 Variant and Co-Expression of VIM-2 and GES-45 among Clinical Pseudomonas aeruginosa Strains in Tunisia

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) are a global health concern. The antimicrobial resistance, virulence, and molecular typing of 57 CRPA isolated from 43 patients who attended a specific Tunisian hospital from September 2018 to July 2019 were analyzed. All but one were multidrug-resistant CRPA, and 77% were difficult-to-treat-resistant (DTR) isolates. The blaVIM-2 gene was detected in four strains (6.9%), and among the 36 blaGES-positive CRPA (62%), the blaGES-5 gene was the predominant variant (86%). Three strains co-harbored the blaVIM-2 and blaGES-45 genes, and seven CRPA carried the blaSHV-2a gene (14%). OprD alterations, including truncations by insertion sequences, were observed in 18 strains. Regarding the 46 class 1 integron-positive CRPA (81%), the blaGES-5 gene was located in integron In717, while the blaGES-29 and blaGES-45 genes were found in two new integrons (In2122 and In4879), and the blaVIM-2 gene was found in In1183 and the new integron In2142. Twenty-four PFGE patterns and thirteen sequence types (three new ones) were identified. The predominant serotype O:11 and exoU (81%) were mostly associated with ST235 and the new ST3385 clones. The seven blaSHV-2a-CRPA from different patients belonged to ST3385 and the same PFGE pattern. The blaGES-5- and blaVIM-2 + blaGES-45-positive CRPA recovered mostly from ICU patients belonged to the high-risk clone ST235. Our results highlight the alarming prevalence of blaGES-5- and ST235-CRPA, the co-existence of blaGES-45 and blaVIM-2, and their location within integrons favoring their dissemination.

From Batch to the Semi-Continuous Flow Hydrogenation of pNB, pNZ-Protected Meropenem

Meropenem is currently the most common carbapenem in clinical applications. Industrially, the final synthetic step is characterized by a heterogeneous catalytic hydrogenation in batch mode with hydrogen and Pd/C. The required high-quality standard is very difficult to meet and specific conditions are required to remove both protecting groups [i.e., p-nitrobenzyl (pNB) and p-nitrobenzyloxycarbonyl (pNZ)] simultaneously. The three-phase gas-liquid-solid system makes this step difficult and unsafe. The introduction of new technologies for small-molecule synthesis in recent years has opened up new landscapes in process chemistry. In this context, we have investigated meropenem hydrogenolysis using microwave (MW)-assisted flow chemistry for use as a new technology with industrial prospects. The reaction parameters (catalyst amount, T, P, residence time, flow rate) in the move from the batch process to semi-continuous flow were investigated under mild conditions to determine their influence on the reaction rate. The optimization of the residence time (840 s) and the number of cycles (4) allowed us to develop a novel protocol that halves the reaction time compared to batch production (14 min vs. 30 min) while maintaining the same product quality. The increase in productivity using this semi-continuous flow technique compensates for the slightly lower yield (70% vs. 74%) obtained in batch mode.

Pharmacokinetics of benapenem for injection in subjects with mild to moderate renal impairment

OBJECTIVE

This study evaluated the pharmacokinetic (PK) characteristics of benapenem in subjects with mild to moderate renal impairment to provide a reference for benapenem dosing regimens in this patient population.

METHODS

Eighteen subjects were enrolled in this study. Each subject received a single dose of benapenem intravenously (1.0 g in 100 ml of 0.9% saline) followed by blood and urine collection to measure the concentrations of benapenem and its major metabolite. PK analysis was performed to evaluate the effect of varying degrees of renal impairment on the PK characteristics of benapenem. The safety of benapenem was also evaluated.

RESULTS

In subjects with normal renal function, mild renal impairment, and moderate renal impairment, the maximum plasma benapenem concentrations were 163 ± 6.58 mg/L, 138 ± 17.4 mg/L, and 134 ± 0.11 mg/L, respectively (15.3% and 17.8% lower in subjects with mild and moderate renal impairment, respectively, than in subjects with normal renal function). The areas under the plasma concentration-time curve (AUC_0-inf) were 1153.67 ± 143.2 mg·h/L, 1129.17 ± 241.41 mg·h/L, and 1316.46 ± 229.83 mg·h/L, respectively (P > 0.05); the cumulative urinary excretion rates at 72 h after dosing were 52.61 ± 8.58%, 39.42 ± 8.35%, and 29.84 ± 9.15%, respectively; and the metabolic ratio (AUC_0-inf__KBP-3331/AUC_0-inf__benapenem) were 3.96 ± 0.35%, 5.56 ± 0.82%, and 8.24 ± 0.85%, respectively. No drug-related adverse events (AEs), serious AEs, or AEs leading to withdrawal occurred in this study.

CONCLUSION

No adjustment to benapenem dosing is needed in patients with mild to moderate renal impairment.

CLINICAL TRIAL REGISTRATION

Drug clinical trial registration and information publicity platform: http://www.chinadrugtrials.org.cn/index.html .

REGISTRATION NUMBER

CTR20190760.

Genetic Characterization of Carbapenem-Resistant Klebsiella spp. from Municipal and Slaughterhouse Wastewater

Currently, human and veterinary medicine are threatened worldwide by an increasing resistance to carbapenems, particularly present in opportunistic Enterobacterales pathogens (e.g., Klebsiella spp.). However, there is a lack of comprehensive and comparable data on their occurrence in wastewater, as well as on the phenotypic and genotypic characteristics for various countries including Germany. Thus, this study aims to characterize carbapenem-resistant Klebsiella spp. isolated from municipal wastewater treatment plants (mWWTPs) and their receiving water bodies, as well as from wastewater and process waters from poultry and pig slaughterhouses. After isolation using selective media and determination of carbapenem (i.e., ertapenem) resistance using broth microdilution to apply epidemiological breakpoints, the selected isolates (n = 30) were subjected to WGS. The vast majority of the isolates (80.0%) originated from the mWWTPs and their receiving water bodies. In addition to ertapenem, Klebsiella spp. isolates exhibited resistance to meropenem (40.0%) and imipenem (16.7%), as well as to piperacillin-tazobactam (50.0%) and ceftolozan-tazobactam (50.0%). A high diversity of antibiotic-resistance genes (n = 68), in particular those encoding β-lactamases, was revealed. However, with the exception of bla_GES-5-like, no acquired carbapenemase-resistance genes were detected. Virulence factors such as siderophores (e.g., enterobactin) and fimbriae type 1 were present in almost all isolates. A wide genetic diversity was indicated by assigning 66.7% of the isolates to 12 different sequence types (STs), including clinically relevant ones (e.g., ST16, ST252, ST219, ST268, ST307, ST789, ST873, and ST2459). Our study provides information on the occurrence of carbapenem-resistant, ESBL-producing Klebsiella spp., which is of clinical importance in wastewater and surface water in Germany. These findings indicate their possible dissemination in the environment and the potential risk of colonization and/or infection of humans, livestock and wildlife associated with exposure to contaminated water sources.

Dosing strategies of imipenem in neonates based on pharmacometric modelling and simulation

OBJECTIVES

Imipenem is a broad-spectrum antibacterial agent used in critically ill neonates after failure of first-line treatments. Few studies have described imipenem disposition in this population. The objectives of our study were: (i) to characterize imipenem population pharmacokinetics (PK) in a cohort of neonates; and (ii) to conduct model-based simulations to evaluate the performance of six different dosing regimens aiming at optimizing PK target attainment.

METHODS

A total of 173 plasma samples from 82 neonates were collected over 15 years at the Lausanne University Hospital, Switzerland. The majority of study subjects were preterm neonates with a median gestational age (GA) of 27 weeks (range: 24-41), a postnatal age (PNA) of 21 days (2-153) and a body weight (BW) of 1.16 kg (0.5-4.1). PK data were analysed using non-linear mixed-effect modelling (NONMEM).

RESULTS

A one-compartment model best characterized imipenem disposition. Population PK parameters estimates of CL and volume of distribution were 0.21 L/h and 0.73 L, with an interpatient variability (CV%) of 20.1% on CL in a representative neonate (GA 27 weeks, PNA 21 days, BW 1.16 kg, serum creatinine, SCr 46.6 μmol/L). GA and PNA exhibited the greatest impact on PK parameters, followed by SCr. These covariates explained 36% and 15% of interindividual variability in CL, respectively.Simulated regimens using a dose of 20-25 mg/kg every 6-12 h according to postnatal age led to the highest PTA (T>MIC over 100% of time).

CONCLUSIONS

Dosing adjustment according to BW, GA and PNA optimizes imipenem exposure in neonates.

Antibiotic resistance of non-fermenting Gram-negative bacilli isolated at a large Infectious Diseases Hospital in North-Eastern Romania, during an 11-year period

Introduction

Increased antibiotic resistance of non-fermenting Gram-negative bacilli (NFGNB) associated with increased morbidity and mortality makes the infections they produce a major public health problem. This study aims to assess the evolution of antibiotic susceptibility and the level of NFGNB antibiotic resistance.

Methods

We carried out a retrospective study on 994 NFGNB strains which had been isolated in the Clinical Laboratory of the "Sf. Parascheva" Clinical Hospital of Infectious Diseases, Iaşi, during a period of 11 years (2008-2018).

Results

Of the 994 NFGNB analyzed, 322 were Acinetobacter spp. and 672 Pseudomonas aeruginosa. Also, 882 NFGNB were isolated from non-sterile sites, in which there was a higher burden of P. aeruginosa strains (n=617). Acinetobacter spp. presented over 70% resistance to the majority of antibiotics. Three pandrug-resistant P. aeruginosa strains were identified. The rate of colistin resistance was 2.91% for P. aeruginosa and 3.33% for Acinetobacter spp. A comparative analysis of the antibiotic susceptibility of strains isolated from non-sterile sites versus sterile sites revealed statistically significant differences only for Acinetobacter spp. The percentage of resistant strains was significantly higher in tracheobronchial aspirate compared to sputum.

Conclusions

The results show that Acinetobacter spp. is substantially more resistant to antibiotics compared to P. aeruginosa and that the use of medical devices can favor the occurrence of infections with multidrug-resistant strains.

Whole Genome Sequencing of a Citrobacter freundii Strain Isolated from the Hospital Environment: An Extremely Multiresistant NDM-1 and VIM-48 Coproducing Isolate

Citrobacter freundii has acquired resistance to several antimicrobial drugs, including last-resort antibiotics affecting, therefore, clinical efficacy and causing high rates of mortality. In this study, we investigate the whole genome sequence of a carbapenem-resistant C. freundii strain isolated from the hospital environment in Tunisia. A total of 210 samples were taken using sterile swabs, from inanimate surfaces, medical devices, and care staff, during the period extended between March and April 2019. After the microbiological analysis of samples and antimicrobial susceptibility testing, only one strain identified as C. freundii showing resistance to carbapenems was selected for the whole genome sequencing. The genome analysis revealed a high-level resistance to most antibiotics. Interestingly, we have noted the coexistence of bla_NDM-1 and bla_VIM-48 metallo-β-lactamase (MBL) encoding genes conferring resistance to carbapenems. Other β-lactamases encoding genes have also been detected, including bla_TEM-1, bla_CMY-48, and bla_OXA-1. Moreover, genes conferring resistance to aminoglycoside [aac(3)-IId, ant(3″)-Ia, aadA, aac(6')-Ib], macrolide [mph(A)], sulfonamide (sul1), trimethoprim (dfrA1), tetracycline [tet(D)], chloramphenicol [cat(B3)], rifamycin (arr-3), and quinolone (qnrB) have been revealed. The multi-locus sequence typing analysis showed that this isolate could not be assigned to an existing sequence type (ST), but it is almost identical to ST22. The plasmid investigation revealed the presence of five plasmids belonging to diverse incompatibility groups (IncFII, IncHI1A, IncHI1B, IncN, and IncX3). To the best of our knowledge, our findings report the first detection of NDM-1 and VIM-48 coproducing C. freundii in Tunisia and the second detection in the world of the bla_VIM-48.

Carbapenem Therapeutic Drug Monitoring in Critically Ill Adult Patients and Clinical Outcomes: A Systematic Review with Meta-Analysis

Drug monitoring is one strategy of antibiotic stewardship to face antimicrobial resistance. This strategy could have a determinant role in critically ill patients treated with carbapenems to overcome pharmacokinetic variability, reduce the risk of subtherapeutic dosage or toxicity, and reduce the risks inherent to treatment. However, the effectiveness of therapeutic drug monitoring (TDM) is unknown. This paper aims to identify TDM effectiveness in critically ill patients treated with carbapenems. English and ClinicalTrials.gov databases were searched to identify relevant studies evaluating carbapenem TDM. Randomized controlled trials (RCTs) and comparative cohort studies were selected for inclusion if they compared carbapenem TDM to standard care in adult critically ill or sepsis/septic shock patients. The primary outcome was mortality. Secondary outcomes included morbidity, clinical cure, microbiological eradication, antimicrobial resistance, drug-related side effects, and achievement of target plasma concentrations. Overall, performing carbapenem TDM was not associated with a decrease in mortality. However, it could be evidence for a relationship with clinical cure as well as target attainment. Some studies found favorable outcomes related to clinical and microbiological responses, such as lower procalcitonin levels at the end of the monitored therapy compared to standard care. For the primary and secondary outcomes analyzed, strong evidence was not identified, which could be due to the size, risk of bias, and design of selected studies.

Structure and Function of L,D- and D,D-Transpeptidase Family Enzymes from Mycobacterium tuberculosis

Peptidoglycan, the exoskeleton of bacterial cell and an essential barrier that protects the cell, is synthesized by a pathway where the final steps are catalysed by transpeptidases. Knowledge of the structure and function of these vital enzymes that generate this macromolecule in M. tuberculosis could facilitate the development of potent lead compounds against tuberculosis. This review summarizes the experimental and computational studies to date on these aspects of transpeptidases in M. tuberculosis that have been identified and validated. The reported structures of L,D- and D,D-transpeptidases, as well as their functionalities, are reviewed and the proposed enzymatic mechanisms for L,D-transpeptidases are summarized. In addition, we provide bioactivities of known tuberculosis drugs against these enzymes based on both experimental and computational approaches. Advancing knowledge about these prominent targets supports the development of new drugs with novel inhibition mechanisms overcoming the current need for new drugs against tuberculosis.

Molecular epidemiology and resistance patterns of blaOXA-48Klebsiella pneumoniae and Escherichia coli: A nationwide multicenter study in Taiwan

BACKGROUND

We describe the molecular epidemiology and resistance patterns of bla_OXA-48Klebsiella pneumoniae and Escherichia coli in Taiwan.

METHODS

In this multicenter surveillance study from January 2012 to August 2015, the identified bla_OXA-48Enterobacteriaceae isolates were subjected to antibiotics susceptibility testing. PCR method was used for detecting concomitant other beta-lactamases. Outer membrane porins were analyzed. Genetic relatedness and molecular epidemiology of the isolates were determined through pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Plasmid incompatibility was determined using PCR-based replicon typing.

RESULTS

Forty-three bla_OXA-48K. pneumoniae and two E. coli isolates were analyzed. The annual incidence of bla_OXA-48K. pneumoniae isolates from 2012 to 2015 were 0%, 1.1%, 2.4%, and 7.6%, respectively. Forty-three (95.5%) of 45 isolates were non-susceptible to broad-spectrum beta-lactams (ceftriaxone, ceftazidime, cefepime, piperacillin/tazobactam), Forty-two (93.3%) of the 45 isolates showed resistance against all tested carbapenems (imipenem, meropenem, doripenem, and ertapenem). Molecular characterization revealed that they co-produced at least one extended-spectrum beta-lactamases or AmpC beta-lactamases, with at least one outer membrane porin loss. Thirty-eight (88.3%) of the 43 K. pneumoniae isolates belonged to ST11. PFGE analysis of 43 K. pneumoniae isolates revealed dissemination of multiple clones. Six of the 12 tested K. pneumoniae representatives of different pulso-types belonged to IncA/C.

CONCLUSION

Concomitant loss of porins and production of other beta-lactamases renders the bla_OXA-48-producing isolates in Taiwan a high-level carbapenem resistance and broad resistance against many beta-lactam antibiotics. Following dissemination of multiple clones of bla_OXA-48 K pneumoniae ST 11, a trend of increased bla_OXA-48 prevalence was noted.

Comparison of Four Commercial Screening Assays for the Detection of blaKPC, blaNDM, blaIMP, blaVIM, and blaOXA48 in Rectal Secretion Collected by Swabs

The spread of carbapenem-resistant Enterobacteriaceae (CRE) has been enabled by the lack of control measures directed at carriers of multidrug-resistant organisms in healthcare settings. Screening patients for asymptomatic colonization on the one hand, and implementation of contact precautions on the other hand, reduces patient-to-patient transmission. Screening plates represents a relatively low-cost method for isolating CRE from rectal swabs; however, molecular assays have become widely available. This study compared the performance of four commercial molecular platforms in detecting clinically significant carbapenemase genes versus routine screening for CRE. A total of 1015 non-duplicated rectal swabs were cultured on a chromogenic carbapenem-resistant selective medium. All growing Enterobacteriaceae strains were tested for carbapenemase-related genes. The same specimens were processed using the following molecular assays: Allplex™ Entero-DR, Amplidiag^® CarbaR + MCR, AusDiagnostics MT CRE EU, and EasyScreen™ ESBL/CPO. The prevalence of Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae detected by swab culture was 2.2%, while organisms producing oxacillinase (OXA)-48 and metallo-β-lactamases were infrequent. The cost of CRE-related infection control precautions, which must be kept in place while waiting for screening results, are significant, so the molecular tests could become cost-competitive, especially when the turnaround time is decreased dramatically. Molecular assays represent a powerful diagnostic tool as they allow the rapid detection of the most clinically relevant carbapenemases.

In vitro activities of colistin, imipenem and ceftazidime against drug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii isolates in the south of Iran

OBJECTIVE

The present study aimed to determine in vitro activity of colistin and other agents against drug-resistant isolates of Pseudomonas aeruginosa and Acinetobacter baumannii.

RESULTS

This in vitro study performed on a collection of non-fermenting Gram-negative bacilli (NFB) consist of 18 A. baumannii and 21 P. aeruginosa isolates. Non-duplicated isolates (one per patient) were isolated from blood, endotracheal tube and sputum samples of hospitalized patients in the south of Iran. The minimum inhibitory concentrations (MICs) of each isolate was determined using Epsilometer (E)-test strips containing colistin, imipenem, and ceftazidime. In overall, all A. baumannii isolates were non-susceptible to imipenem and ceftazidime. In contrast, all isolates were susceptible to colistin with MIC50 and MIC90 of 0.75/1.5 µg/mL, respectively. Antibiotic susceptibility results showed that 81% and 23.8% of P. aeruginosa isolates were susceptible to ceftazidime and imipenem, respectively. While, all of the P. aeruginosa isolates were susceptible to colistin with MIC50 and MIC90 of 0.5/1 µg/mL, respectively. In summary, colistin showed the promising in vitro activity against drug-resistant strains of two clinically important NFB in our region. However, investigation on a larger collection of drug-resistant strains demands to support these observations in the near future.

Detection of Enterobacterales resistant to polymyxins using Rapid Polymyxins NP test

Two hundred isolates of Enterobacterales were tested by Rapid Polymyxins NP for the detection of polymyxin resistance and compared to the reference test broth microdilution (BMD). The sensitivity and specificity of the NP test were 98% and the results are faster than the BMD, decreasing from approximately 24 to 2 h.

Carbapenem Resistance: A Review

Carbapenem resistance is a major and an on-going public health problem globally. It occurs mainly among Gram-negative pathogens such as Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii, and may be intrinsic or mediated by transferable carbapenemase-encoding genes. This type of resistance genes are already widespread in certain parts of the world, particularly Europe, Asia and South America, while the situation in other places such as sub-Saharan Africa is not well documented. In this paper, we provide an in-depth review of carbapenem resistance providing up-to-date information on the subject.

β-Lactams and β-Lactamase Inhibitors: An Overview

β-Lactams are the most widely used class of antibiotics. Since the discovery of benzylpenicillin in the 1920s, thousands of new penicillin derivatives and related β-lactam classes of cephalosporins, cephamycins, monobactams, and carbapenems have been discovered. Each new class of β-lactam has been developed either to increase the spectrum of activity to include additional bacterial species or to address specific resistance mechanisms that have arisen in the targeted bacterial population. Resistance to β-lactams is primarily because of bacterially produced β-lactamase enzymes that hydrolyze the β-lactam ring, thereby inactivating the drug. The newest effort to circumvent resistance is the development of novel broad-spectrum β-lactamase inhibitors that work against many problematic β-lactamases, including cephalosporinases and serine-based carbapenemases, which severely limit therapeutic options. This work provides a comprehensive overview of β-lactam antibiotics that are currently in use, as well as a look ahead to several new compounds that are in the development pipeline.

Prevalence and Fate of Carbapenemase Genes in a Wastewater Treatment Plant in Northern China

Carbapenemase-producing strains of bacteria, which were primarily found in the medical field, have increasingly been found in the environment, thus posing potential risks to public health. One possible way for carbapenemase genes to enter the environment is via wastewater. Therefore, the goal of this study was to determine the occurrence and fate of five high-risk carbapenemase genes in a wastewater treatment plant (WWTP) in northern China using real-time qPCR. Results showed that the bla_KPC-2, bla_GES-1, and bla_IMP-1 genes prevailed throughout all processing stages (even in the chlorination disinfection unit) in the WWTP, whereas the bla_VIM-2 and bla_OXA-48 genes were not detected in all samples. Worryingly, considerable amounts of carbapenemase genes ((1.54 ± 0.61) × 10³ copies/mL to (2.14± 0.41) × 10⁵ copies/mL) were detected in WWTP effluent samples, while the majority of the carbapenemase genes were transported to the dewatered sludge with concentrations from (6.51 ± 0.14) × 10⁹ copies/g to (6.18 ± 0.63) × 10¹⁰ copies/g dry weight. Furthermore, a total of 97 KPC-2-producing strains, belonging to 8 bacterial genera, were isolated from the WWTP. Sequencing of 16S rRNA revealed that most of KPC-2 producing isolates were opportunistic pathogens, including Klebsiella spp. (10.3%), Enterococcus spp. (11.3%), Acinetobacter spp. (19.6%), Escherichia spp. (12.4%), Shigella spp. (17.5%), Stenotrophomonas spp. (10.3%) and Wautersiella spp. (9.3%). Moreover, bla_KPC-2 genes were identified for the first time in Paenibacillus spp. isolates (an indigenous bacteria), indicating an increased risk of horizontal transfer between clinical pathogens and environmental bacteria. Indeed, a conjugation experiment demonstrated transfer of the bla_KPC-2 gene to an E.coli J53 strain from a Klebsiella strain isolated from the WWTP. To our knowledge, this is the first study to obtain Paenibacillus spp. isolates carrying the carbapenemase gene and to quantify the abundance of carbapenemase genes in the environment.

Evaluation of peptide nucleic acid-mediated multiplex real-time PCR kits for rapid detection of carbapenemase genes in gram-negative clinical isolates

The emergence of clinical isolates of carbapenemase-producing microbes confers multidrug-resistance to these bacteria and renders them difficult to treat. This study was performed to evaluate peptide nucleic acid (PNA) probe-based multiplex real-time PCR kits used to detect carbapenemase genes. In total, 324 carbapenemase genes, collected from 318 gram-negative clinical isolates in 36 different hospital laboratories, were assayed to evaluate multiplex real-time PCR kits (PANAGENE; Daejeon, Korea). The nine most prevalent carbapenemase genes (KPC, OXA-48, GES, IMP, VIM, NDM, ISAba1-OXA-51, OXA-23, and OXA-58) were included in this study. The sensitivity and specificity of the multiplex real-time PCR assay to all of the carbapenemase genes were above 99.0%, except for ISAba1-OXA-51. The detection limit of the assay was 100 target copies per 25 μL of reaction volume for all of the nine genetic types of carbapenemases, and the genes were all detected in a single three-hour PCR. The assay also showed considerable efficiency (above 80.0%), stable reproducibility (coefficient of variation, below 5.0%) and a long shelf-life (more than eight months) with no cross reactivity. The developed PNA-mediated multiplex real-time PCR assay was useful for the rapid, accurate and simultaneous identification of nine carbapenemase genes in gram-negative clinical isolates, suggesting its potential to help choose the appropriate antibiotics and aid the control of carbapenemase genes.

Mutant prevention concentrations of imipenem and meropenem against Pseudomonas aeruginosa and Acinetobacter baumannii

The aim of this study was to determine the usefulness of the MPC of carbapenems against clinical isolates of Pseudomonas spp. and Acinetobacter spp. and to assess its possible relationship with mechanisms of resistance. Detection of the mechanisms of resistance was performed using Antibiotic Susceptibility Testing, Double Disk Synergy, disk antagonism, addition of NaCl to the medium, addition of PBA or EDTA to Carbapenem disks, addition of PBA to Cefoxitin disks, and CCCP test for 10 Pseudomonas spp. and Acinetobacter baumannii strains. The MIC and MPC were determined using the broth macrodilution and plate dilution methods, respectively. Four Acinetobacter baumannii strains produced MBL. Two of them produced Oxacillinase and one produced ESBL. Two Pseudomonas spp. isolates produced both KPC and MBL. The resistant Acinetobacter spp. and Pseudomonas spp. strains had higher MPC values than susceptible ones. However, the Mutant Selection Window was found to be dependent on the degree of resistance but not on a particular mechanism of resistance. The usefulness of the MPC was found to be dependent on its value. Based on our data, we recommend determining the MPC for each isolate before using it during treatment. Furthermore, the use of T>MSW instead of T>MIC is suggested.

Comparison of in vitro activities of meropenem productions on Klebsiella pneumoniae isolated from hospitalized patients

PURPOSE

Antimicrobial activities of meropenem products on Klebsiella pneumoniae isolates were determined.

METHODS

212 non-duplicated Klebsiella pneumoniae isolates were examined for in vitro meropenem susceptibility test by using the following disks, which were made from Meronem (AstraZeneca, UK), Exipenem (Exir, Iran) and Meroxan (DAANA, Iran) powders. MIC50 and MIC90 for meropenem antibiotics were determined.

RESULTS

Meronem had good activities against most isolates of Klebsiella pneumoniae, and only a few strains had a rather high MIC. Exipenem and Meroxan showed a similar activity with Meronem.

CONCLUSION

Regarding the comparison of two internal generic meropenem products with the external Meronem product have shown that they are equivalents in terms of microbiological activity, as measured using the disk diffusion and MIC. In developing countries, we suggested preparing disks with antibiotic powders that can be an equivalent function in microbiological activity with standard disks. In addition, since it demonstrated significant antimicrobial activity against the Klebsiella pneumoniae. For use of Exipenem and Meroxan in vivo, it would be better to perform additional testing (activity against different species, stability etc.).

Acinetobacter baumannii: An emerging pathogenic threat to public health

Over the last three decades, Acinetobacter has gained importance as a leading nosocomial pathogen, partly due to its impressive genetic capabilities to acquire resistance and partly due to high selective pressure, especially in critical care units. This low-virulence organism has turned into a multidrug resistant pathogen and now alarming healthcare providers worldwide. Acinetobacter baumannii (A. baumannii) is a major species, contributing about 80% of all Acinetobacter hospital-acquired infections. It disseminates antibiotic resistance by virtue of its extraordinary ability to accept or donate resistance plasmids. The procedures for breaking the route of transmission are still proper hand washing and personal hygiene (both the patient and the healthcare professional), reducing patient’s biofilm burden from skin, and judicious use of antimicrobial agents. The increasing incidence of extended-spectrum beta-lactamases and carbapenemases in A. baumannii leaves almost no cure for these “bad bugs”. To control hospital outbreaks of multidrug resistant-Acinetobacter infection, we need to contain their dissemination or require new drugs or a rational combination therapy. The optimal treatment for multidrug-resistant A. baumannii infection has not been clearly established, and empirical therapy continues to require knowledge of susceptibility patterns of isolates from one’s own institution. This review mainly focused on general features and introduction to A. baumannii and its epidemiological status, potential sources of infection, risk factors, and strategies to control infection to minimize spread.

Epidemiology and antimicrobial resistance among commonly encountered bacteria associated with infections and colonization in intensive care units in a university-affiliated hospital in Shanghai

BACKGROUND/PURPOSE

The aim of this study was to classify intensive care unit (ICU) bacterial strains as either ICU-acquired or ICU-on-admission and to compare their epidemiological and antibiogram characteristics.

METHODS

The study was performed in a 1300-bed university-affiliated hospital from January 1, 2006 to December 31, 2010. Based on the time of ICU admission, ICU isolates were classified as ICU-acquired strains (appearing more than 48 hours after admission) or ICU-on-admission strains (appearing 48 hours or less from admission). The microbiological data before ICU admission, the microbiological data, and susceptibility testing were compared between the ICU-acquired and ICU-on-admission bacterial isolates.

RESULTS

The most common ICU-acquired strains were Acinetobacter baumannii (19.5%), Pseudomonas aeruginosa (15.6%), Stenotrophomonas maltophilia (11.5%), Staphylococcus aureus (10.7%), Enterococcus spp. (10.6%), and Klebsiella pneumoniae (9.7%). There were significant differences between ICU-acquired and ICU-on-admission isolates in the susceptibility rates of Gram-negative bacteria to antibiotics, especially the susceptibility of A. baumannii to imipenem [23.8% (ICU-acquired) vs. 44.4% (ICU-on-admission), p < 0.001] and meropenem (24.1% vs. 37.8%, p < 0.001), and the susceptibility of P. aeruginosa to imipenem (39.3% vs. 76.1%, p < 0.001) and meropenem (58.5% vs. 76.1%, p < 0.05). Furthermore, decreased susceptibility rates of A. baumannii and P. aeruginosa to carbapenems were correlated with an extended ICU stay (p < 0.05).

CONCLUSION

Because of decreasing susceptibility rates of pathogens (especially ICU-acquired strains) and a significant correlation with the length of ICU stay, intensivists should consider a patient's time of ICU admission and previous microbiological data and should distinguish ICU-acquired strains from non-ICU-acquired strains so as to initiate optimized empirical antibiotic therapy against ICU-acquired infections.

Dosing nomograms for attaining optimum concentrations of meropenem by continuous infusion in critically ill patients with severe gram-negative infections: a pharmacokinetics/pharmacodynamics-based approach

The worrisome increase in Gram-negative bacteria with borderline susceptibility to carbapenems and of carbapenemase-producing Enterobacteriaceae has significantly undermined their efficacy. Continuous infusion may be the best way to maximize the time-dependent activity of meropenem. The aim of this study was to create dosing nomograms in relation to different creatinine clearance (CL(Cr)) estimates for use in daily clinical practice to target the steady-state concentrations (C(ss)s) of meropenem during continuous infusion at 8 to 16 mg/liter (after the administration of an initial loading dose of 1 to 2 g over 30 min). The correlation between meropenem clearance (CL(m)) and CL(Cr) was retrospectively assessed in a cohort of critically ill patients (group 1, n = 67) to create a formula for dosage calculation to target C(ss). The performance of this formula was validated in a similar cohort (group 2, n = 56) by comparison of the observed and the predicted C(ss)s. A significant relationship between CL(m) and CL(Cr) was observed in group 1 (r = 0.72, P < 0.001). The application of the formula to meropenem dosing in group 2, infusion rate (g/24 h) = [0.078 × CL(Cr) (ml/min) + 2.85] × target C(ss) × (24/1,000), led to a significant correlation between the observed and the predicted C(ss)s (r = 0.92, P < 0.001). Dosing nomograms based on CL(Cr) were created to target the meropenem C(ss) at 8, 12, and 16 mg/liter in critically ill patients. These nomograms could be helpful in improving the treatment of severe Gram-negative infections with meropenem, especially in the presence of borderline susceptible pathogens or even of carbapenemase producers and/or of pathophysiological conditions which may enhance meropenem clearance.

Acinetobacter baumannii Septicemia in a Recipient of an Allogeneic Hematopoietic Stem Cell Transplantation

Acinetobacter baumannii is a gram-negative, nonfermentative coccobacillus that causes infections in immunocompromised and chronically ill patients and is associated with multidrug resistance. Two days before receiving her nonmyeloablative stem cell allograft, a patient with acute myeloid leukemia developed Acinetobacter baumannii bacteremia that caused septic shock which was successfully treated with imipenem and removal of the central venous catheter. To our knowledge, this is the first report of Acinetobacter baumannii septicemia in a hematopietic stem cell transplantation recipient.

Urinary tract infections in the elderly population

BACKGROUND

Urinary tract infections (UTIs) are a common problem in the elderly population. The spectrum of disease varies from a relatively benign cystitis to potentially life-threatening pyelonephritis.

OBJECTIVE

This review covers the management of asymptomatic bacteriuria, acute uncomplicated cystitis, acute uncomplicated pyelonephritis, antibiotic resistance, catheter-associated bacteriuria/symptomatic UTIs, and antibiotic prophylaxis for recurrent infections in elderly men and women.

METHODS

Literature was obtained from English-language searches of MEDLINE (1966-April 2011), Cochrane Library, BIOSIS (1993-April 2011), and EMBASE (1970-April 2011). Further publications were identified from citations of resulting articles. Search terms included, but were not limited to, urinary tract infections, asymptomatic bacteriuria, acute uncomplicated cystitis, acute uncomplicated pyelonephritis, antibiotic resistance, catheter associated urinary tract infections, recurrent urinary tract infections, and elderly.

RESULTS

The prevalence of UTIs in elderly women depends on the location in which these women are living. For elderly women living in the community, UTIs compromise the second most common infection, whereas in residents of long-term care facilities (LTCFs) and hospitalized subjects, it is the number one cause of infection. The spectrum of patient presentation varies from classic signs and symptoms in the independent elderly population to atypical presentations, including increased lethargy, delirium, blunted fever response, and anorexia. Although there are few guidelines specifically directed toward the management of UTIs in the elderly population, therapy generally mirrors the recommendations for the younger adult age groups. When choosing a treatment regimen, special attention must be given to the severity of illness, living conditions, existing comorbidities, presence of external devices, local antibiotic resistance patterns, and the ability of the patient to comply with therapy.

CONCLUSIONS

Improved guidelines for the diagnosis and management of UTIs in the elderly population are needed. Better techniques to evaluate and prevent catheter-associated bacteriuria and UTIs await improved diagnostic modalities and catheter technologies. Alternative methods for prophylaxis of patients who suffer from recurrent infections must be found while minimizing the risk of developing or propagating antibiotic resistance.

Identification of products of inhibition of GES-2 beta-lactamase by tazobactam by x-ray crystallography and spectrometry

The GES-2 β-lactamase is a class A carbapenemase, the emergence of which in clinically important bacterial pathogens is a disconcerting development as the enzyme confers resistance to carbapenem antibiotics. Tazobactam is a clinically used inhibitor of class A β-lactamases, which inhibits the GES-2 enzyme effectively, restoring susceptibility to β-lactam antibiotics. We have investigated the details of the mechanism of inhibition of the GES-2 enzyme by tazobactam. By the use of UV spectrometry, mass spectroscopy, and x-ray crystallography, we have documented and identified the involvement of a total of seven distinct GES-2·tazobactam complexes and one product of the hydrolysis of tazobactam that contribute to the inhibition profile. The x-ray structures for the GES-2 enzyme are for both the native (1.45 Å) and the inhibited complex with tazobactam (1.65 Å). This is the first such structure of a carbapenemase in complex with a clinically important β-lactam inhibitor, shedding light on the structural implications for the inhibition process.

Current challenges in the management of the infected patient

PURPOSE OF REVIEW

Management of hospital-associated infections (HAIs) has been made more challenging by the increasing proportion of immunocompromised or otherwise severely ill patients and increasing prevalence of antibiotic-resistant pathogens in this environment. This review examines strategies to optimize clinical outcomes and lower healthcare costs for patients with HAIs by focusing on patient-related, pathogen-related, and drug-related factors.

RECENT FINDINGS

Factors have converged to increase the risk of infection with antibiotic-resistant pathogens in the current hospital environment, including the increasing prevalence of resistant species and number of hospitalized patients with conditions increasingly susceptible to infection with drug-resistant bacteria. Although the list of bacterial pathogens associated with HAIs has been fairly constant over time, the prevalence and resistance profile of these individual species continues to evolve. Periodic antibiograms should be utilized to access local patterns of resistance within the different hospital wards. Outcomes for patients with HAIs are optimized with early empiric treatment with an appropriate regimen, selected on the basis of patient characteristics and local resistance patterns. Dosing strategies should be utilized to ensure that the efficacy of an appropriate antibiotic is optimized, by achieving the pharmacodynamic target predictive of its efficacy. Using these strategies improves quality of care and is associated with lower overall healthcare costs.

SUMMARY

Bacterial resistance is an increasing problem in the hospital environment, and has been associated with poorer clinical outcomes and elevated healthcare costs. By using patient characteristics, local antibiograms, and dosing strategies to achieve an optimal pharmacodynamic profile, early appropriate empiric therapy can be utilized to improve clinical outcomes, minimize the development of resistance, and reduce healthcare costs.

Management of complicated urinary tract infections in the era of antimicrobial resistance

Complicated urinary tract infections (cUTIs) are a major cause of hospital admissions and are associated with significant morbidity and health care costs. Patients presenting with a suspected UTI should be screened for the presence of complicating factors, such as anatomic and functional abnormalities of the genitourinary tract. In the setting of cUTIs, the etiology and susceptibility of the causative organism is not predictable; therefore, when infection is suspected, patients should undergo a urinalysis in addition to culture and sensitivity testing. Although not warranted in all cases of complicated pyelonephritis, blood cultures are appropriate in some clinical settings. With the increased prevalence of antimicrobial resistance, and the lack of well-designed clinical trials, treatment of cUTIs can be challenging for clinicians. Although resistant organisms are not always implicated as the causative agent, all patients with cUTIs should be assessed for predisposing risk factors. Consideration of an optimal antimicrobial agent should be based on local resistance patterns, patient-specific factors, including anatomic site of infection and severity of disease, pharmacokinetic and pharmacodynamic principles, and cost. Resistance to first-line antimicrobial agents, including fluoroquinolones, has become increasingly common in Escherichia coli. Fluoroquinolones should not be used as a first-line option for empiric treatment of serious cUTIs, especially when patients exhibit risk factors for harboring a resistant organism, such as previous or recent use of fluoroquinolones. Fluoroquinolones, trimethoprim-sulfamethoxazole, and nitrofurantoin are still appropriate empiric options for mild lower cUTIs. However, empiric treatment for serious cUTIs, where risk factors for resistant organisms exist, should include broad-spectrum antibiotics such as carbapenems or piperacillin-tazobactam. Once organisms and susceptibilities are identified, treatment should be targeted accordingly. Nitrofurantoin and fosfomycin have limited utility in the setting of cUTIs and should be reserved as alternative treatment options for lower cUTIs following confirmation of the causative organism. Aminoglycosides, tigecycline, and polymyxins can be used for the treatment of serious cUTIs when first-line options are deemed to be inappropriate or patients fail therapy. The duration of treatment for cUTIs has not been well established; however, treatment durations can range from 1 to 4 weeks based on the clinical situation.

Biochemical and structural characterization of Mycobacterium tuberculosis beta-lactamase with the carbapenems ertapenem and doripenem

Despite the enormous success of beta-lactams as broad-spectrum antibacterials, they have never been widely used for the treatment of tuberculosis (TB) due to intrinsic resistance that is caused by the presence of a chromosomally encoded gene (blaC) in Mycobacterium tuberculosis. Our previous studies of TB BlaC revealed that this enzyme is an extremely broad-spectrum beta-lactamase hydrolyzing all beta-lactam classes. Carbapenems are slow substrates that acylate the enzyme but are only slowly deacylated and can therefore act also as potent inhibitors of BlaC. We conducted the in vitro characterization of doripenem and ertapenem with BlaC. A steady-state kinetic burst was observed with both compounds with magnitudes proportional to the concentration of BlaC used. The results provide apparent K(m) and k(cat) values of 0.18 microM and 0.016 min(-1) for doripenem and 0.18 microM and 0.017 min(-1) for ertapenem, respectively. FTICR mass spectrometry demonstrated that the doripenem and ertapenem acyl-enzyme complexes remain stable over a time period of 90 min. The BlaC-doripenem covalent complex obtained after a 90 min soak was determined to 2.2 A, while the BlaC-ertapenem complex obtained after a 90 min soak was determined to 2.0 A. The 1.3 A diffraction data from a 10 min ertapenem-soaked crystal revealed an isomerization occurring in the BlaC-ertapenem adduct in which the original Delta(2)-pyrroline ring was tautomerized to generate the Delta(1)-pyrroline ring. The isomerization leads to the flipping of the carbapenem hydroxyethyl group to hydrogen bond to carboxyl O2 of Glu166. The hydroxyethyl flip results in both the decreased basicity of Glu166 and a significant increase in the distance between carboxyl O2 of Glu166 and the catalytic water molecule, slowing hydrolysis.

Side chain SAR of bicyclic beta-lactamase inhibitors (BLIs). 1. Discovery of a class C BLI for combination with imipinem

Bridged monobactam beta-lactamase inhibitors were prepared and evaluated as potential partners for combination with imipenem to overcome class C beta-lactamase mediated resistance. The (S)-azepine analog 2 was found to be effective in both in vitro and in vivo assays and was selected for preclinical development.