Antibacterial Resistance in Patients with Hematopoietic Stem Cell Transplantation

Carbapenem-resistant Serratia marcescens bloodstream infection in hematopoietic stem cell transplantation patients: Will it be the next challenge?

Surveillance programs have been reporting decreasing rates of carbapenem-sensitivity in Serratia marcescens, leading to a concern regarding the few remaining therapeutic options to treat these multidrug-resistant (MDR) organisms. Here, we describe a case series of 11 stem cell hematopoietic transplantation patients infected (N = 6) or colonized (N = 5) by carbapenem-resistant S marcescens (CrSm) from 2010 to 2013. The comorbidities found were acute renal insufficiency (3/11), neutropenia (7/11), and mucositis (8/11), and the mortality rate was 64%. KPC was the most prevalent carbapenemase detected (8/11) and tigecycline and gentamicin were the antimicrobials used as treatment.

Is it time to reconsider prophylactic antimicrobial use for hematopoietic stem cell transplantation? a narrative review of antimicrobials in stem cell transplantation

INTRODUCTION

Hematopoietic Stem Cell Transplantation (HSCT) is a life-saving procedure for multiple types of hematological cancer, autoimmune diseases, and genetic-linked metabolic diseases in humans. Recipients of HSCT transplant are at high risk of microbial infections that significantly correlate with the presence of graft-versus-host disease (GVHD) and the degree of immunosuppression. Infection in HSCT patients is a leading cause of life-threatening complications and mortality.

AREAS COVERED

This review covers issues pertinent to infection in the HSCT patient, including bacterial and viral infection; strategies to reduce GVHD; infection patterns; resistance and treatment options; adverse drug reactions to antimicrobials, problems of antimicrobial resistance; perturbation of the microbiome; the role of prebiotics, probiotics, and antimicrobial peptides. We highlight potential strategies to minimize the use of antimicrobials.

EXPERT OPINION

Measures to control infection and its transmission remain significant HSCT management policy and planning issues. Transplant centers need to consider carefully prophylactic use of antimicrobials for neutropenic patients. The judicious use of appropriate antimicrobials remains a crucial part of the treatment protocol. However, antimicrobials' adverse effects cause microbiome diversity and dysbiosis and have been shown to increase morbidity and mortality.

Differentiation of Myositis-Induced Models of Bacterial Infection and Inflammation with T2-Weighted, CEST, and DCE-MRI

We used T₂ relaxation, chemical exchange saturation transfer (CEST), and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) to assess whether bacterial infection can be differentiated from inflammation in a myositis-induced mouse model. We measured the T₂ relaxation time constants, %CEST at 5 saturation frequencies, and area under the curve (AUC) from DCE-MRI after maltose injection from infected, inflamed, and normal muscle tissue models. We applied principal component analysis (PCA) to reduce dimensionality of entire CEST spectra and DCE signal evolutions, which were analyzed using standard classification methods. We extracted features from dimensional reduction as predictors for machine learning classifier algorithms. Normal, inflamed, and infected tissues were evaluated with H&E and gram-staining histological studies, and bacterial-burden studies. The T₂ relaxation time constants and AUC of DCE-MRI after injection of maltose differentiated infected, inflamed, and normal tissues. %CEST amplitudes at −1.6 and −3.5 ppm differentiated infected tissues from other tissues, but these did not differentiate inflamed tissue from normal tissue. %CEST amplitudes at 3.5, 3.0, and 2.5 ppm, AUC of DCE-MRI for shorter time periods, and relative K^trans and k_ep values from DCE-MRI could not differentiate tissues. PCA and machine learning of CEST-MRI and DCE-MRI did not improve tissue classifications relative to traditional analysis methods. Similarly, PCA and machine learning did not further improve tissue classifications relative to T₂ MRI. Therefore, future MRI studies of infection models should focus on T₂-weighted MRI and analysis of T₂ relaxation times.

Bacteremia in pediatric patients with hematopoietic stem cell transplantation

BACKGROUND

This study aimed to describe the incidence, microbiological profile, and risk factors associated with bacteremia in pediatric patients with hematopoietic stem cell transplantation (HSCT).

METHODS

A retrospective cohort study was performed on patients under 18 years old who underwent HSCT due to any indication, between January 2012 and January 2017. The patient data were collected from the first 100 days post-HSCT. Bacteremia was defined as the isolation of bacteria from at least one blood culture. The relation between bacteremia and associated risk factors was evaluated using univariate and multivariate analysis.

RESULTS

We enrolled a total of 111 pediatric patients who received HSCT during the period of study. The total number of patients who developed at least one episode of bacteremia was 46 (41.4%), and the total number of bacteremia episodes was 62. Rectal swabs were performed in 44 patients to detect prior colonization and this showed that 25% of them were positive, the main pathogen isolated being carbapenem-resistant enterobacteriaceae. The Gram-negative bacteria cases accounted for 60% of 62 events. The main Gram-negative bacteria isolated were Klebsiella pneumoniae and Escherichia coli and the majority were resistant strains. The mortality rate on day +100 for the whole cohort was 18% (n=20). Regarding the patients with bacteremia, the mortality rate on day +100 was 30% (n=14), and the cause of death was related to infection in 10 of them. We did not find any statistically significant risk factor for the development of bacteremia.

CONCLUSION

Bacteremia is common after HSCT, and there is a high frequency of resistant Gram-negative infections which is related to high mortality.

Genomic characterization of Citrobacter freundii strains coproducing OXA-48 and VIM-1 carbapenemase enzymes isolated in leukemic patient in Spain

Background

The emergence of carbapenemase-producing (CP) Citrobacter freundii poses a significant threat to public health, especially in high-risk populations. In this study, whole genome sequencing was used to characterize the carbapenem resistance mechanism of three C. freundii clinical isolates recovered from fecal samples of patients with acute leukemia (AL) from Spain.

Materials and methods

Twelve fecal samples, collected between 2013 and 2015 from 9 patients with AL, were screened for the presence of CP strains by selecting them on MacConkey agar supplemented with ertapenem (0.5 mg/L). Bacteria were identified by MALDI-TOF mass spectrometry and were phenotypically characterized. Whole genome sequencing of C. freundii isolates was performed using the MinION and MiSeq Illumina sequencers. Bioinformatic analysis was performed in order to identify the molecular support of carbapenem resistance and to study the genetic environment of carbapenem resistance encoding genes.

Results

Three carbapenem-resistant C. freundii strains (imipenem MIC≥32 mg/L) corresponding to three different AL patients were isolated. Positive modified Carba NP test results suggested carbapenemase production. The genomes of each C. freundii tested were assembled into a single chromosomal contig and plasmids contig. In all the strains, the carbapenem resistance was due to the coproduction of OXA-48 and VIM-1 enzymes encoded by genes located on chromosome and on an IncHI2 plasmid, respectively. According to the MLST and the SNPs analysis, all strains belonged to the same clone ST169.

Conclusion

We report in our study, the intestinal carrying of C. freundii clone ST169 coproducing OXA-48 and VIM-1 identified in leukemic patients.

Infection Complications in Hematopoietic Stem Cells Transplant Recipients: Do Genetics Really Matter?

Hematopoietic stem cell transplantation (HSCT) is a highly advanced technique that offers a potential cure for an increasing number of life-threatening diseases. Enormous progress achieved in the last decade, including the refinement of donor selection and advancements in patient supportive care, had significantly improved transplant outcomes; however, invasive infections, graft-vs.-host disease (GVHD) and other serious complications still represent a major source of morbidity and mortality in HSCT recipients. The damage of anatomical barriers due to pre-transplant conditioning, a severely damaged immune function and a profound disruption in the composition of gut microbial commensals (gut microbiota) are alterations inherent to the transplant procedure that are directly implicated in the development of invasive infections and other HSCT complications. Although HLA-matching represents the most important genetic predictor of transplant outcomes, genetic variants in non-HLA genes, especially single nucleotide polymorphisms (SNPs) of genes encoding proteins associated with the immune response to tissue injury and pathogen infection have also been proposed as additional risk factors implicated in the occurrence of HSCT complications. Furthermore, although the microbiota composition is affected by several factors, recent evidence suggests that certain host genetic variants are associated with an altered composition of the gut microbiome and may, therefore, predispose some individuals to invasive infectious complications. This article summarizes the current understanding of the influence that genetic variants in non-HLA genes have on the development of infectious complications in HSCT recipients.