An Ancient Drug for a Modern Era: Minocycline for the Treatment of Multi-Drug-Resistant Acinetobacter baumannii.

INTRODUCTION: Infections caused by Acinetobacter baumannii are a major cause of health concerns in the hospital setting. Moreover, the presence of extreme drug resistance in A. baumannii has made the scenario more challenging due to limited treatment options thereby encouraging the researchers to explore the existing antimicrobial agents to combat the infections caused by them. This study focuses on the susceptibility of multi-drug-resistant A. baumannii (MDR-AB) strains to minocycline and also to colistin. METHODOLOGY: A cross-sectional study was conducted from June 2022 to June 2023. One hundred isolates of​​​​​​ A. baumannii â€‹â€‹â€‹obtained from various clinical samples were sent to Central Laboratory, Department of Microbiology, Sree Balaji Medical College and Hospital, Chrompet, Chennai, India. The antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines, 2022. For the standard antibiotics, the disc diffusion method was performed. For minocycline and colistin, the minimum inhibitory concentration (MIC) was determined using an epsilometer strip (E-strip) test. RESULTS: In this study, 100 isolates of A. baumannii were obtained, and 83% of the isolates were multi-drug-resistant. Among the MDR-AB, 50 (60%) were susceptible to minocycline and 40 (48%) were susceptible to colistin. Out of the 40 colistin-susceptible A. baumannii strains, 29 (73%) were susceptible to minocycline with a statistically significant P-value of <0.05. Among the 43 colistin-resistant A. baumannii strains, 21 (53%) were susceptible to minocycline with a statistically significant P-value of <0.05. CONCLUSIONS: When taking into account the expense of treating carbapenemase-producing Gram-negative bacteria, colistin and minocycline can be used as an alternative drug as they have fewer side effects and are more affordable. Minocycline can be used as an alternative to colistin because it is feasible to convert from an injectable to an oral formulation.

Global epidemiology and genetic diversity of mcr-positive Klebsiella pneumoniae: A systematic review and genomic analysis.

The rapid increase of mcr-positive Klebsiella pneumoniae (K. pneumoniae) has received considerable attention and poses a major public health concern. Here, we systematically analyzed the global distribution of mcr-positive K. pneumoniae isolates based on published articles as well as publicly available genomes. Combining strain information from 78 articles and 673 K. pneumoniae genomes, a total of 1000 mcr-positive K. pneumoniae isolates were identified. We found that mcr-positive K. pneumoniae has disseminated widely worldwide, especially in Asia, with a higher diversity of sequence types (STs). These isolates were disseminated in 57 countries and were associated with 12 different hosts. Most of the isolates were found in China and were isolated from human sources. Moreover, MLST analysis showed that ST15 and ST11 accounted for the majority of mcr-positive K. pneumoniae, which deserve sustained attention in further surveillance programs. mcr-1 and mcr-9 were the dominant mcr variants in mcr-positive K. pneumoniae. Furthermore, a Genome-wide association study (GWAS) demonstrated that mcr-1- and mcr-9-producing genomes exhibited different antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), thereby indicating a distinct evolutionary path. Notably, the phylogenetic analysis suggested that certain mcr-positive K. pneumoniae genomes from various geographical areas and hosts harbored a high degree of genetic similarities (<20 SNPs), suggesting frequent cross-region and cross-host clonal transmission. Overall, our results emphasize the significance of monitoring and exploring the transmission and evolution of mcr-positive K. pneumoniae in the context of "One health".

Investigation of Plasmid-Mediated Colistin Resistance Genes (mcr-1-8) in Enterobacterales Isolates.

Background The escalating global rise in multidrug-resistant gram-negative bacteria presents an increasingly substantial threat to patient safety. Over the past decade, carbapenem-resistant Enterobacterales (CRE) have emerged as one of the most critical pathogens in hospital-acquired infections, notably within intensive care units. Colistin has become one of the last-resort antimicrobial agents utilized to combat infections caused by CRE. However, the use of colistin has been accompanied by a notable increase in the prevalence of colistin-resistant bacteria. This study aimed to investigate plasmid-mediated colistin resistance genes ranging from mcr-1 to mcr-8 among members of the Enterobacterales order. Materials and methods This prospective study was conducted in the microbiology laboratory of Afyonkarahisar Health Sciences University Health Research and Practice Center between May 1, 2021 and July 31, 2022. A total of 2,646 Enterobacterales isolates were obtained from all culture-positive clinical samples sent from various clinics. Of these, 79 isolates exhibiting resistance to carbapenem antibiotics were included in the study. Among the 79 isolates, the presence of mcr-1 to mcr-8 genes was investigated in 27 isolates that were shown to be resistant to colistin. The identification of bacteria at the species level and antibiotic susceptibility tests were conducted using the VITEK 2 automated system (bioMérieux, USA). Colistin resistance among Enterobacterales strains exhibiting carbapenem resistance was evaluated using the broth microdilution technique (ComASP™ Colistin, Liofilchem, Italy), in accordance with the manufacturer's instructions. Results In our in vitro investigations, the minimum inhibitory concentration (MIC) values for meropenem were determined to be >8 µg/ml, whereas for colistin, the MIC50 value was >16 µg/ml and the MIC90 value was 8 µg/ml. A total of 27 colistin-resistant strains were identified among the 79 carbapenem-resistant Enterobacterales strains analyzed. The most prevalent agent among colistin-resistant strains was Klebsiella pneumoniae (K. pneumoniae), representing 66.7% of the isolates. This was followed by Proteus mirabilis (P. mirabilis) with 29.6% and Escherichia coli (E. coli) with 3.7%. The colistin resistance rate among carbapenem-resistant strains was found to be 34.2%, with colistin MIC values in strains tested by the broth microdilution method ranging from 4 to >16 µg/ml concentrations. In polymerase chain reaction (PCR) studies, the mcr-1 gene region was successfully detected by real-time PCR in the positive control isolate. Nevertheless, none of the gene regions from mcr-1 to mcr-8 were identified in our study investigating the presence of plasmid-mediated genes using a multiplex PCR kit. Conclusion Although our study demonstrated the presence of increased colistin resistance rates in carbapenem-resistant Enterobacterales isolates, it resulted in the failure to detect genes from mcr-1 to mcr-8 by the multiplex PCR method. Therefore, it is concluded that the colistin resistance observed in Enterobacteriaceae isolates in our region is not due to the mcr genes screened, but to different resistance development mechanisms.

Emergence of mcr-4.3 genes in a novel Shewanella specie isolated from the Arctic environment.

Mobile colistin resistance (mcr) genes are pivotal contributors to last-line of antimicrobial resistance in human infections. Shewanella, historically recognized as a natural environmental bacterium with metal reduction capabilities, recently has been observed in clinical settings. However, limited knowledge has been explored on genetic differences between strains from non-clinical and clinical strains. In this study, we conducted the whole genome sequencing on six Arctic strains, illustrated the phylogenetic relationships on published 393 Shewanella strains that categorized the genus into four lineages (L1 to L4). Over 86.4% of clinical strain group (CG) strains belonged to L1 and L4, carrying mcr-4 genes and a complete metal-reduction pathways gene cluster. Remarkably, a novel Arctic Shewanella strain in L3, exhibits similar genetic characteristics with CG strains that carried both mcr-4 genes and a complete metal reduction pathway gene cluster. It raised concerns about the transmission ability from environment to clinic setting causing in the potential infections, and emphasized the need for monitoring the emerging strains with human infections.

Analysis of mcr family of colistin resistance genes in Gram-negative isolates from a tertiary care hospital in India.

AIM: Colistin serves as the drug of last resort for combating numerous multidrug-resistant (MDR) Gram-negative infections. Its efficacy is hampered by the prevalent issue of colistin resistance, which severely limits treatment options for critically ill patients. Identifying resistance genes is crucial for controlling resistance spread, with horizontal gene transfer being the primary mechanism among bacteria. This study aimed to assess the prevalence of plasmid-mediated mcr genes associated with colistin resistance in Gram-negative bacteria, utilizing both genotypic and phenotypic tests. METHODS AND RESULTS: The clinical isolates (n=913) were obtained from a tertiary care center in Chennai, India. Colistin resistance was seen among Gram-negative isolates. These strains underwent screening for mcr-1, mcr-3, mcr-4, and mcr-5 genes via conventional PCR. Additionally, mcr-positive isolates were confirmed through Sanger sequencing and phenotypic testing. The bacterial isolates predominantly comprised Klebsiella pneumoniae (62.43%), Escherichia coli (19.71%), Pseudomonas aeruginosa (10.73%), Acinetobacter baumannii (4.81%), along with other species. All isolates exhibited multidrug resistance to three or more antibiotic classes. Colistin resistance, determined via broth microdilution (BMD) using CLSI guidelines, was observed in 13.08% of the isolates studied. Notably, mcr-5 was detected in K. pneumoniae in PCR, despite their absence in Sanger sequencing and phenotypic tests (including the combined-disk test, colistin MIC in the presence of EDTA, and Zeta potential assays). This finding underscores the importance of employing multiple diagnostic approaches to accurately identify colistin resistance mechanisms. CONCLUSION AND IMPACT: The study highlights a concerning prevalence of colistin resistance among Enterobacterales, especially those producing carbapenemase, thereby impacting mortality rates. Nonetheless, further investigations are warranted to elucidate common mechanisms of colistin resistance and to evaluate the efficacy of screening techniques in detecting isolates carrying mcr genes responsible for enzyme-mediated lipopolysaccharide (LPS) modification.

Genetic alterations in the pmrAB two-component system and lipid A biosynthesis genes of polymyxin-resistant Acinetobacter baumannii isolates.

The rate of pandrug-resistant Acinetobacter baumannii strains is on the rise in all continents. This bacterium can acquire resistance to all antibiotics, even to colistin. Alterations in the lipid A or/and the two-component pmrAB were earlier detected in colistin resistance. We investigated and analyzed two strains of A. baumannii (ABRC1 and ABRC2) isolated from two patients admitted to intensive care unit with a septic shock. Both strains were resistant to all tested antibiotics including colistin with a MIC >256 mg L-1. Colistin resistance genes (pmrA, pmrB, lpxA, lpxC, lpxD, and lpsB) of two strains (ABRC1 and ABRC2) were investigated by PCR and sequencing. Obtained nucleic acid sequences were aligned with reference sequences of ATCC 19606 and 17987. In this study two amino acid mutations, N287D in the lpxC gene and E117K in the lpxD gene, were detected in both ABRC1 and ABRC2 strains. ABRC1 had an additional H200L mutation in the pmrA gene. Both colistin resistant strains harbored the same A138T mutation in the pmrB gene. The ABRC2 strain also had an alteration in the kinase domain, specifically an R263S substitution of the histidine kinase domain. Three identical mutations were found in the lpsB gene of both A. baumannii strains: Q216K + H218G + S219E. As a result, a newly deduced protein sequence in both ABRC1 and ABRC2 strains differed from those described in ATCC 17978 and 19606 strains was determined. Colistin resistance is multifactorial in A. baumannii. In our study we detected novel mutations in colistin resistant A. baumannii clinical isolates.

Molecular characterization and epidemiological investigation of colistin resistance in carbapenem-resistant Klebsiella pneumoniae in a tertiary care hospital in Tehran, Iran.

BACKGROUND: Carbapenemase-producing Klebsiella pneumoniae (CRKP) presents a significant challenge to antimicrobial therapy, especially when compounded by resistance to colistin. The objective of this study was to explore molecular epidemiological insights into strains of clinical K. pneumoniae that produce carbapenemases and exhibit resistance to colistin. Eighty clinical isolates of CRKP were obtained from Milad Hospital in Tehran, Iran. Antimicrobial susceptibility and colistin broth disk elution were determined. PCR assays were conducted to examine the prevalence of resistance-associated genes, including blaKPC, blaIMP, blaVIM, blaOXA-48, blaNDM and mcr-1 to -10. Molecular typing (PFGE) was used to assess their spread. RESULTS: Colistin resistance was observed in 27 isolates (33.7%) using the Broth Disk Elution method. Among positive isolates for carbapenemase genes, the most frequent gene was blaOXA-48, identified in 36 strains (45%). The mcr-1 gene was detected in 3.7% of the obtained isolates, with none of the other of the other mcr genes detected in the studied isolates. CONCLUSION: To stop the spread of resistant K. pneumoniae and prevent the evolution of mcr genes, it is imperative to enhance surveillance, adhere rigorously to infection prevention protocols, and implement antibiotic stewardship practices.

Implementation of Modern Therapeutic Drug Monitoring and Lipidomics Approaches in Clinical Practice: A Case Study with Colistin Treatment.

Nowadays, lipidomics plays a crucial role in the investigation of novel biomarkers of various diseases. Its implementation into the field of clinical analysis led to the identification of specific lipids and/or significant changes in their plasma levels in patients suffering from cancer, Alzheimer's disease, sepsis, and many other diseases and pathological conditions. Profiling of lipids and determination of their plasma concentrations could also be helpful in the case of drug therapy management, especially in combination with therapeutic drug monitoring (TDM). Here, for the first time, a combined approach based on the TDM of colistin, a last-resort antibiotic, and lipidomic profiling is presented in a case study of a critically ill male patient suffering from Pseudomonas aeruginosa-induced pneumonia. Implementation of innovative analytical approaches for TDM (online combination of capillary electrophoresis with tandem mass spectrometry, CZE-MS/MS) and lipidomics (liquid chromatography-tandem mass spectrometry, LC-MS/MS) was demonstrated. The CZE-MS/MS strategy confirmed the chosen colistin drug dosing regimen, leading to stable colistin concentrations in plasma samples. The determined colistin concentrations in plasma samples reached the required minimal inhibitory concentration of 1 µg/mL. The complex lipidomics approach led to monitoring 545 lipids in collected patient plasma samples during and after the therapy. Some changes in specific individual lipids were in good agreement with previous lipidomics studies dealing with sepsis. The presented case study represents a good starting point for identifying particular individual lipids that could correlate with antimicrobial and inflammation therapeutic management.

Validating the utility of heavy water (Deuterium Oxide) as a potential Raman spectroscopic probe for identification of antibiotic resistance.

The impact of microbial infections is increasing over time, and it is one of the major reasons for death in both developed and developing countries. colistin is considered as the antibiotic of last choice for infections brought by major multidrug-resistant (MDR), gram-negative bacteria such as Enterobacter species, Acinetobacter species, and Pseudomonas aeruginosa. Existing approaches to diagnose these resistant species are relatively slow and take up to 2 to 3 days. In this work, we propose a novel interdisciplinary method based on Raman spectroscopy and heavy water to identify colistin-resistant microbes. Our hypothesis is based on the fact that resistant bacteria will be metabolically active in the culture medium containing antibiotics and heavy water, and these bacteria will take up deuterium instead of hydrogen to newly synthesized lipids and proteins. This effect will generate a 'C - D' bond-specific Raman spectral marker. Successful identification of this band in the spectral profile can confirm the presence of colistin-resistant bacteria. We have validated the efficacy of this approach in identifying colistin-resistant bacteria spiked in artificial urine and have compared sensitivity at different bacterial concentrations. Overall findings suggest that heavy water can potentially serve as a suitable Raman probe for identifying metabolically active colistin-resistant bacteria via urine under clinically implementable time and can be used in clinical settings after validation.

Global prevalence of mutation in the mgrB gene among clinical isolates of colistin-resistant Klebsiella pneumoniae: a systematic review and meta-analysis.

Background: Colistin is used as a last resort for managing infections caused by multidrug-resistant bacteria. However, the high emergence of colistin-resistant strains has restricted the clinical use of this antibiotic in the clinical setting. In the present study, we evaluated the global prevalence of the mutation in the mgrB gene, one of the most important mechanisms of colistin resistance in Klebsiella pneumoniae. Methods: Several databases, including Scopus, Medline (via PubMed), and Web of Science, were searched (until August 2023) to identify those studies that address the mgrB mutation in clinical isolates of K. pneumoniae. Using Stata software, the pooled prevalence of mgrB mutation and subgroup analyses for the year of publication, country, continent, mgrB mutation types, and detection methods of mgrB mutation were analyzed. Results: Out of the 115 studies included in the analysis, the prevalence of mgrB mutations in colistin-resistant K. pneumoniae isolates was estimated at 65% of isolates, and mgrB variations with insertional inactivation had the highest prevalence among the five investigated mutations with 69%. The year subgroup analysis indicated an increase in mutated mgrB from 46% in 2014 to 61% in 2022. Europe had the highest prevalence of mutated mgrB at 73%, while Africa had the lowest at 54%. Conclusion: Mutations in the mgrB gene are reported as one of the most common mechanisms of colistin resistance in K. pneumoniae, and the results of the present study showed that 65% of the reported colistin-resistant K. pneumoniae had a mutation in this gene.

Novel functions of o-cymen-5-ol nanoemulsion in reversing colistin resistance in multidrug-resistant Klebsiella pneumoniae infections.

Multidrug resistance (MDR) Klebsiella pneumoniae (K. pneumoniae) is a major emerging threat to human health, and leads to very high mortality rate. The effectiveness of colistin, the last resort against MDR Gram-negative bacteria, is significantly compromised due to the widespread presence of plasmid- or chromosome-mediated resistance genes. In this study, o-cymen-5-ol has been found to greatly restore colistin sensitivity in MDR K. pneumoniae. Importantly, this compound does not impact bacterial viability, induce resistance, or cause any noticeable cell toxicity. Various routes disclosed the potential mechanism of o-cymen-5-ol potentiating colistin activity against MDR K. pneumoniae. These include inhibiting the activity of plasmid-mediated mobile colistin resistance gene (mcr-1), accelerating lipopolysaccharide (LPS) - mediated membrane damage, and promoting the ATP-binding cassette (ABC) transporter pathway. To enhance the administration and bioavailability of o-cymen-5-ol, a nanoemulsion has been designed, which significantly improves the loading efficiency and solubility of o-cymen-5-ol, resulting in antimicrobial potentiation of colistin against K. pneumoniae infection. This study has revealed a new understanding of the o-cymen-5-ol nanoemulsion as a means to enhance the effectiveness of colistin against resistant factors. The finding also suggests that o-cymen-5-ol nanoemulsion could be a promising approach in the development of potential treatments for multidrug-resistant Gram-negative bacterial infections.

Glycine restores the sensitivity to antibiotics in multidrug-resistant bacteria.

The management of infections caused by multiresistant bacteria has become of fundamental importance for any medical practice. Glycine is the most common and the simplest non-essential amino acid in humans. Glycine is very effective in improving health and supporting growth and wellbeing of humans and animals. Instead, for many bacteria, high concentrations of glycine induce lysis or deep morphological alterations. The effect of glycine on multidrug resistant (MDR) microorganisms has not yet been extensively researched. The present study was conducted 1) to establish the effect of glycine on different nosocomial pathogens isolated during routine diagnostic investigations; 2) to determine the minimum inhibitory concentration of glycine and the type of activity performed (bacteriostatic or bactericidal) on representative isolates; 3) to test the interaction between glycine and meropenem, cefiderocol, or colistin. The data reported here show a dose-dependent activity of glycine on bacteria and its bactericidal activity on MDR bacteria. Furthermore, we found that the action of glycine restores in vitro the susceptibility of multiresistant nosocomial pathogens to the tested antibiotics.IMPORTANCEAntimicrobial resistance is a constantly growing concern throughout the world, and Italy is among the Western countries where antimicrobial resistance is most widespread. In Tuscany, carbapenemase-producing Enterobacterales are now even endemic. In this study, we challenged some resistant bacteria with a well-known molecule, glycine, the antibacterial properties of which have been known since the past century. This study could bring new insights into combining antibiotics with the simplest of all amino acids. The restoration of sensitivity to the aforementioned antibiotics by a natural compound, already used for clinical purposes, is of extreme importance in an era of proliferation of multiresistant bacteria. The in vivo use of this amino acid in evaluating its effectiveness against infections should be investigated. The low cost of this molecule can also make it easy to use even in low-income countries.

Genomic characterization of carbapenem and colistin-resistant Klebsiella pneumoniae isolates from humans and dogs.

Introduction: Carbapenem and colistin-resistant Enterobacteriaceae, including Klebsiella pneumoniae, have become a growing global concern, posing a significant threat to public health. Currently, there is limited information about the genetic background of carbapenem and colistin-resistant K. pneumoniae isolates infecting humans and dogs in Thailand. This study aimed to characterize carbapenem and colistin-resistant genes in six resistant K. pneumoniae clinical isolates (three from humans and three from dogs) which differed in their pulse field gel electrophoresis profiles. Methods: Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), antimicrobial susceptibility testing, and whole-genome sequencing were employed to identify and analyze the isolates. Results and discussion: All six isolates were carbapenemase-producing K. pneumoniae isolates with chromosomally carried blaSHV, fosA, oqxA and oqxB genes, as well as nine to 21 virulence genes. The isolates belonged to five multilocus sequence types (STs): one isolate from a human and one from a dog belonged to ST16, with the other two human isolates being from ST340 and ST1269 and the other two dog isolates were ST147 and ST15. One human isolate and two dog isolates harbored the same blaOXA-232 gene on the ColKP3 plasmid, and one dog isolate carried the blaOXA-48 gene on the IncFII plasmid. Notably, one human isolate exhibited resistance to colistin mediated by the mcr-3.5 gene carried on the IncFII plasmid, which co-existed with resistance determinants to other antibiotics, including aminoglycosides and quinolones. In conclusion, this study provides a comprehensive characterization of both chromosome- and plasmid-mediated carbapenem and colistin resistance in a set of K. pneumoniae clinical isolates from unrelated humans and dogs in Thailand. The similarities and differences found contribute to our understanding of the potential widescale dissemination of these important resistance genes among clinical isolates from humans and animals, which in turn may contribute to outbreaks of emerging resistant clones in hospital settings.

Antibiotic susceptibility profile of Pseudomonas species isolated from clinical specimens to access, watch and reserve drugs across various hospital settings at a tertiary care hospital of central India.

Background and Objectives: Over the last decade, hospital-acquired infections, particularly in the critical care setting, have become more common, with Gram-negative bacterial infections having the highest prevalence. This study aims to determine the prevalence and antibiotic susceptibility pattern of Pseudomonas species to WHO's, aware class of antibiotics, which are commonly prescribed across various ICU's, medical and surgical wards of our tertiary care teaching hospital. Materials and Methods: This prospective study conducted from January 2021 to June 2022 at a tertiary care centre of central India identified Pseudomonas species from clinical samples using standard procedures and antimicrobial susceptibility testing performed as per Clinical Laboratory Standards Institute (CLSI) guidelines (M100; 32th Edition). Results: A total of 1490 non duplicate Pseudomonas species isolates were grown from 21,019 culture positive clinical samples, of which 1247 were Pseudomonas aeruginosa. Out of these 1247 Pseudomonas aeruginosa 384 were MDR (30.7%). Pseudomonas aeruginosa were most commonly isolated from the pus samples (85%). ICU isolates were significantly more resistant to antibiotics than those from other units. P. aeruginosa strains from ICUs showed the highest rates of resistance to ceftazidime (93.9%). Reserve drug colistin showed good susceptibility (98.2%). All the 18 colistin resistant strains were found to be negative for plasmid mediated mcr-1,2,3 genes. Conclusion: The study shall help to generate and disseminate the data so that proper antibiotic policy can be made for judicious use of Access, Watch and Reserve antibiotics and antibiotic de-escalation plan can be put forth.

Genetic Alterations Associated with Colistin Resistance Development in Escherichia coli.

Background: The increased incidence of infections due to multidrug-resistant Gram-negative bacteria has led to the renewed interest in the use of 'forgotten' antibiotics such as colistin. In this work, we studied the chromosomal colistin resistance mechanisms among laboratory-induced colistin-resistant Escherichia coli isolates. Methods: Three colistin-susceptible (ColS) clinical isolates of E. coli assigning to ST131, ST405, and ST361 were exposed to successively increasing concentrations of colistin. The nucleotide sequences of pmrA, pmrB, pmrD, phoP, phoQ, and mgrB genes were determined. The fitness burden associated with colistin resistance acquisition was determined by measuring the in vitro growth rate. Results: Colistin resistance induction resulted in 16-64 times increase in colistin MICs in mutants (n = 8) compared with parental isolates. Analysis of chromosomal genes in colistin-resistant mutants compared with those of ColS ancestors revealed genetic alterations confined to PmrAB two-component system and included PmrA G53R/R81S/L105P and PmrB E121K/E121A/A159P/A159V/G302E changes. The PmrB E121 was found as a critical position for colistin resistance development being altered in three mutants with different ancestors. The acquired colistin-resistance phenotype was stable following 10 consecutive passages in the absence of selective pressure of colistin and it did not alter the susceptibility of mutants to other antimicrobial agents. All mutants exhibited growth rates similar to their respective ColS ancestors, except for one isolate, which revealed a significant growth defect. Conclusion: Our results revealed that colistin resistance in E. coli was more related to PmrAB alterations, which did not impose a fitness cost in most cases.

The impact of colistin-based regimens on mortality compared to other antimicrobials in patients with carbapenem-resistant Enterobacterales bacteremia in South African hospitals: a cross-sectional study.

BACKGROUND: Treatment of carbapenem-resistant Enterobacterales (CRE) infections in low-resource settings is challenging particularly due to limited treatment options. Colistin is the mainstay drug for treatment; however, nephrotoxicity and neurotoxicity make this drug less desirable. Thus, mortality may be higher among patients treated with alternative antimicrobials that are potentially less efficacious than colistin. We assessed mortality in patients with CRE bacteremia treated with colistin-based therapy compared to colistin-sparing therapy. METHODS: We conducted a cross-sectional study using secondary data from a South African national laboratory-based CRE bacteremia surveillance system from January 2015 to December 2020. Patients hospitalized at surveillance sentinel sites with CRE isolated from blood cultures were included. Multivariable logistic regression modeling, with multiple imputations to account for missing data, was conducted to determine the association between in-hospital mortality and colistin-based therapy versus colistin-sparing therapy. RESULTS: We included 1 607 case-patients with a median age of 29 years (interquartile range [IQR], 0-52 years) and 53% (857/1 607) male. Klebsiella pneumoniae caused most of the infections (82%, n=1 247), and the most common carbapenemase genes detected were blaOXA-48-like (61%, n=551), and blaNDM (37%, n=333). The overall in-hospital mortality was 31% (504/1 607). Patients treated with colistin-based combination therapy had a lower case fatality ratio (29% [152/521]) compared to those treated with colistin-sparing therapy 32% [352/1 086]) (p=0.18). In our imputed model, compared to colistin-sparing therapy, colistin-based therapy was associated with similar odds of mortality (adjusted odds ratio [aOR] 1.02; 95% confidence interval [CI] 0.78-1.33, p=0.873). CONCLUSION: In our resource-limited setting, the mortality risk in patients treated with colistin-based therapy was comparable to that of patients treated with colistin-sparing therapy. Given the challenges with colistin treatment and the increasing resistance to alternative agents, further investigations into the benefit of newer antimicrobials for managing CRE infections are needed.

Fingolimod synergizes and reverses K. pneumoniae resistance to colistin.

Klebsiella pneumoniae (K. pneumoniae) infection and the rapid spread of multi-drug resistant (MDR) bacteria pose a serious threat to global healthcare. Polymyxin E (colistin), a group of cationic antimicrobial polypeptides, is currently one of the last resort treatment options against carbapenem-resistant Gram-negative pathogens. The effectiveness of colistin has been compromised due to its intensive use. This study found that fingolimod (FLD), a natural product derivative, exhibited a significant synergistic bactericidal effect on K. pneumoniae when combined with colistin, both in vitro and in vivo. The checkerboard method was employed to assess the in vitro synergistic effect of FLD with colistin. FLD enhanced the susceptibility of bacteria to colistin and lowered effectively minimum inhibitory concentrations (MIC) when compared to colistin MIC, and the fractional inhibitory concentrations (FIC) value was less than 0.3. The time-kill curve demonstrated that the combination treatment of FLD and colistin had significant bactericidal efficacy. The in vitro concurrent administration of colistin and FLD resulted in heightening membrane permeability, compromising cell integrity, diminishing membrane fluidity, and perturbing membrane homeostasis. They also induced alterations in membrane potential, levels of reactive oxygen species, and adenosine triphosphate synthesis, ultimately culminating in bacterial death. Moreover, the combination of FLD with colistin significantly influenced fatty acid metabolism. In the mouse infection model, the survival rate of mice injected with K. pneumoniae was significantly improved to 67% and pathological damage was significantly relieved with combination treatment of FLD and colistin when compared with colistin treatment. This study highlights the potential of FLD in combining with colistin for treating infections caused by MDR isolates of K. pneumoniae.

Mobile Colistin-Resistant Genes mcr-1, mcr-2, and mcr-3 Identified in Diarrheal Pathogens among Infants, Children, and Adults in Bangladesh: Implications for the Future.

Colistin is a last-resort antimicrobial for treating multidrug-resistant Gram-negative bacteria. Phenotypic colistin resistance is highly associated with plasmid-mediated mobile colistin resistance (mcr) genes. mcr-bearing Enterobacteriaceae have been detected in many countries, with the emergence of colistin-resistant pathogens a global concern. This study assessed the distribution of mcr-1, mcr-2, mcr-3, mcr-4, and mcr-5 genes with phenotypic colistin resistance in isolates from diarrheal infants and children in Bangladesh. Bacteria were identified using the API-20E biochemical panel and 16s rDNA gene sequencing. Polymerase chain reactions detected mcr gene variants in the isolates. Their susceptibilities to colistin were determined by agar dilution and E-test by minimal inhibitory concentration (MIC) measurements. Over 31.6% (71/225) of isolates showed colistin resistance according to agar dilution assessment (MIC > 2 µg/mL). Overall, 15.5% of isolates carried mcr genes (7, mcr-1; 17, mcr-2; 13, and mcr-3, with co-occurrence occurring in two isolates). Clinical breakout MIC values (≥4 µg/mL) were associated with 91.3% of mcr-positive isolates. The mcr-positive pathogens included twenty Escherichia spp., five Shigella flexneri, five Citrobacter spp., two Klebsiella pneumoniae, and three Pseudomonas parafulva. The mcr-genes appeared to be significantly associated with phenotypic colistin resistance phenomena (p = 0.000), with 100% colistin-resistant isolates showing MDR phenomena. The age and sex of patients showed no significant association with detected mcr variants. Overall, mcr-associated colistin-resistant bacteria have emerged in Bangladesh, which warrants further research to determine their spread and instigate activities to reduce resistance.

In vitro assessment of newer colistin-sparing antimicrobial agents for clinical isolates of carbapenem-resistant organisms.

OBJECTIVES: Carbapenem-resistant organisms (CROs) are a significant public health threat globally, particularly in countries like India with high antibiotic resistance rates. The current study investigates the prevalence of CROs, detects resistance mechanisms using phenotypic methods and assesses the efficacy of newer antibiotics against CROs. METHODS: A prospective study conducted at a tertiary care hospital in India during 2021-23. Clinical specimens were processed and bacterial identification was performed using MALDI-TOF mass spectrometry followed by antimicrobial susceptibility testing using CLSI guidelines against a plethora of newer antibiotics for CROs. Carbapenemase production was detected using phenotypic methods, and the presence of the mcr-1 gene was assessed by real-time PCR. RESULTS: During the study period, predominantly (70 %) Gram-negative bacteria were isolated; amongst which 5692 strains were carbapenem-resistant, wherein resistance to different carbapenems ranged from 34.1% to 79 %. Majority of the carbapenemase producers were metallo-ß-lactamases (MBL) producers (75 %). Colistin resistance was noted in 5.4 % of selected carbapenem-resistant isolates. Among newer antibiotics, cefiderocol demonstrated the lowest resistance rates (0-14 %), while resistance to newer ß-lactam/ß-lactamase inhibitor combinations was very high in carbapenem-resistant isolates. Fosfomycin, minocycline and tigecycline, each showing variable efficacy depending on the site of infection. Moreover, newer ß-lactam/ß-lactamase inhibitor combinations offer restricted benefits due to widespread prevalence of MBL in the region. CONCLUSION: The escalating prevalence of CROs in India underscores the urgency for alternative treatment options beyond colistin. Hence, highlighting the critical importance of developing effective strategies to combat carbapenem resistance.