In vitro activity of antibiotics potentially effective against difficult-to-treat strains of Gram-negative rods: retrospective study

Bacterial resistance surveillance is one of the main outputs of microbiological laboratories and its results are important part of antimicrobial stewardship (AMS). In this study, the susceptibility of specific bacteria to selected antimicrobial agents was tested. The susceptibility of 90 unique isolates of pathogens of critical priority obtained from clinically valid samples of ICU patients in 2017-2021 was tested. 50% of these fulfilled difficult-to-treat resistance (DTR) criteria and 50% were susceptible to all antibiotics included in the definition. 10 Enterobacterales strains met DTR criteria, and 2 (20%) were resistant to colistin (COL), 2 (20%) to cefiderocol (FCR), 7 (70%) to imipenem/cilastatin/relebactam (I/R), 3 (30%) to ceftazidime/avibactam (CAT) and 5 (50%) to fosfomycin (FOS). For Enterobacterales we also tested aztreonam/avibactam (AZA) for which there are no breakpoints yet. The highest MIC of AZA observed was 1 mg/l, MIC range in the susceptible cohort was 0.032-0.064 mg/l and in the DTR cohort (incl. class B beta-lactamase producers) it was 0.064-1 mg/l. Two (13.3%) isolates of Pseudomonas aeruginosa (15 DTR strains) were resistant to COL, 1 (6.7%) to FCR, 13 (86.7%) to I/R, 5 (33.3%) to CAT, and 5 (33.3%) to ceftolozane/tazobactam. All isolates of Acinetobacter baumannii with DTR were susceptible to COL and FCR, and at the same time resistant to I/R and ampicillin/sulbactam. New antimicrobial agents are not 100% effective against DTR. Therefore, it is necessary to perform susceptibility testing of these antibiotics, use the data for surveillance (including local surveillance) and conform to AMS standards.

Influence of PhoPQ and PmrAB two component system alternations on colistin resistance from non-mcr colistin resistant clinical E. Coli strains

BACKGROUND

The current understanding of acquired chromosomal colistin resistance mechanisms in Enterobacterales primarily involves the disruption of the upstream PmrAB and PhoPQ two-component system (TCS) control caused by mutations in the regulatory genes. Interestingly, previous studies have yielded conflicting results regarding the interaction of regulatory genes related to colistin resistance in Escherichia coli, specifically those surrounding PhoPQ and PmrAB TCS.

RESULTS

In our study, we focused on two clinical non-mcr colistin-resistant strains of E. coli, TSAREC02 and TSAREC03, to gain a better understanding of their resistance mechanisms. Upon analysis, we discovered that TSAREC02 had a deletion (Δ27-45) in MgrB, as well as substitutions (G206R, Y222H) in PmrB. On the other hand, TSAREC03 exhibited a long deletion (Δ84-224) in PhoP, along with substitutions (M1I, L14P, P178S, T235N) in PmrB. We employed recombinant DNA techniques to explore the interaction between the PhoPQ and PmrAB two-component systems (TCSs) and examine the impact of the mutated phoPQ and pmrB genes on the minimum inhibitory concentrations (MICs) of colistin. We observed significant changes in the expression of the pmrD gene, which encodes a connector protein regulated by the PhoPQ TCS, in the TSAREC02 wild-type (WT)-mgrB replacement mutant and the TSAREC03 WT-phoP replacement mutant, compared to their respective parental strains. However, the expressions of pmrB/pmrA, which reflect PmrAB TCS activity, and the colistin MICs remained unchanged. In contrast, the colistin MICs and pmrB/pmrA expression levels were significantly reduced in the pmrB deletion mutants from both TSAREC02 and TSAREC03, compared to their parental strains. Moreover, we were able to restore colistin resistance and the expressions of pmrB/pmrA by transforming a plasmid containing the parental mutated pmrB back into the TSAREC02 and TSAREC03 mutants, respectively.

CONCLUSION

While additional data from clinical E. coli isolates are necessary to validate whether our findings could be broadly applied to the E. coli population, our study illuminates distinct regulatory pathway interactions involving colistin resistance in E. coli compared to other species of Enterobacterales. The added information provided by our study contribute to a deeper understanding of the complex pathway interactions within Enterobacterales.

Ceftazidime-avibactam alone or in combination with Aztreonam versus Polymyxins in the management of carbapenem-Resistant Klebsiella pneumoniae nosocomial Infections (CAPRI study): a retrospective cohort study from South India

INTRODUCTION

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections commonly cause hospital-acquired infections. The study aimed to compare the outcomes of CRKP infections between patients receiving ceftazidime avibactam +/- aztreonam and polymyxins in a hospital setting with a high prevalence of New Delhi Metallo Beta Lactamase production.

METHODS

We conducted a retrospective cohort study from January 2020 to September 2022 in critically ill adult patients admitted to a non-COVID-19 medical intensive care unit with CRKP infection. The patients were followed up for a total of 30 days or death, whichever was later.

RESULTS

Of a total of 106 patients included in the study, 65 patients received polymyxins and 41 patients received ceftazidime-avibactam +/- aztreonam. Higher 30-day mortality was noted in the polymyxin group (56.9% vs. 29.2%, P = 0.005). The mean time to event (mortality) in ceftazidime-avibactam +/- aztreonam was 23.9 + 1.5 days which was significantly higher compared to polymyxins (17.9 + 1.2 days, p = 0.006). On Cox regression analysis, after adjusting for the covariates, the hazard ratio for time to event with the use of polymyxin was 2.02 (95% CI: 1.03-3.9).

CONCLUSION

Ceftazidime-avibactam + aztreonam is possibly associated with better clinical outcomes in patients infected with CRKP.

Colistin heteroresistance in Citrobacter freundii clinical isolates from Republic of Korea

We investigated colistin heteroresistance in Citrobacter freundii isolates from Korean hospitals. Using population analysis profiling (PAP), we detected colistin heteroresistance in 31.3% of isolates. Among these, ST217 was the most prevalent clone (58.5%), particularly within colistin-heteroresistant isolates (80.0%). Interestingly, the second most common clone, ST248, was not found in heteroresistant isolates. We identified amino acid changes in PhoQ, PmrA, and PmrB, along with mRNA overexpression in pmrB and arnD. Colistin monotherapy showed no efficacy, but a combination of colistin and ciprofloxacin successfully eradicated all five isolates, even at 0.5 × minimum inhibitory concentrations. This study underscores the high prevalence of colistin heteroresistance in C. freundii isolates, limiting the effectiveness of colistin monotherapy. Combining colistin with ciprofloxacin may offer a viable treatment option for C. freundii infections.

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.

Comparison of in vitro synergy between polymyxin B or colistin in combination with 16 antimicrobial agents against multidrug-resistant Acinetobacter baumannii isolates

PURPOSES

This study determined the synergy of polymyxin B (POLB) and colistin (COL) with 16 other tested antimicrobial agents in the inhibition of multidrug-resistant Acinetobacter baumannii (MDR-AB).

METHODS

We used chequerboard assays to determine synergy between the drugs against 50 clinical MDR-AB from a tertiary hospital in the Zhejiang province in 2019, classifying combinations as either antagonistic, independent, additive, or synergistic. The efficacy of hit combinations which showed highest synergistic rate were confirmed using time-kill assays.

RESULTS

Both POLB and COL displayed similar bactericidal effects when used in combination with these 16 tested drugs. Antagonism was only observed for a few strains (2%) exposed to a combination of POLB and cefoperazone/sulbactam (CSL). A higher percentage of synergistic combinations with POLB and COL were observed with rifabutin (RFB; 90%/96%), rifampicin (RIF; 60%/78%) and rifapentine (RFP; 56%/76%). Time-kill assays also confirmed the synergistic effect of POLB and rifamycin class combinations. 1/2 MIC rifamycin exposure can achieve bacterial clearance when combined with 1/2 MIC POLB or COL.

CONCLUSION

Nearly no antagonism was observed when combining polymyxins with other drugs by both chequerboard and time-kill assays, suggesting that polymyxins may be effective in combination therapy. The combinations of POLB/COL with RFB, RIF, and RFP displayed neat synergy, with RFB showing the greatest effect.

Hyaluronan/B12-chitosan polyelectrolyte complex for oral colistin administration

Polyelectrolyte complexes (PECs) based on polysaccharides, including hyaluronic acid (HA) and chitosan (CS), are promising delivery systems for antimicrobial agents, including oral administration of the peptide antibiotic colistin (CT). Modification of CS with different targeting ligands to improve intestinal permeability is a suitable way to improve the oral bioavailability of polyelectrolyte particles. This study describes the procedure for obtaining CT-containing PECs based on HA and CS modified with cyanocobalamin (vitamin B12). In this case, vitamin B12 is used as a targeting ligand because it is absorbed in the ileum via specific transporter proteins. The resulting PECs had a hydrodynamic size of about 284 nm and a positive ζ-potential of about 26 mV; the encapsulation efficiency was 88.2 % and the CT content was 42.2 μg/mg. The developed systems provided a two-phase drug release: about 50 % of the CT was released in 0.5-1 h, and about 60 % of the antibiotic was cumulatively released in 5 h. The antimicrobial activity of encapsulated CT was maintained at the same level as the pure drug for at least 24 h (minimum inhibitory concentration against Pseudomonas aeruginosa was 2 μg/mL for both). In addition, the apparent permeability coefficient of CT in the PEC formulation was 2.4 × 10-6 cm/s. Thus, the incorporation of CT into HA- and vitamin B12-modified CS-based PECs can be considered as a simple and convenient method to improve the oral delivery of CT.

Sub-inhibitory concentrations of colistin and imipenem impact the expression of biofilm-associated genes in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen that is responsible for nosocomial infections. Imipenem and colistin are drugs that are commonly used to treat severe infections caused by A. baumannii, such as sepsis, ventilator-associated pneumonia, and bacteremia. However, some strains of A. baumannii have become resistant to these drugs, which is a concern for public health. Biofilms produced by A. baumannii increase their resistance to antibiotics and the cells within the inner layers of biofilm are exposed to sub-inhibitory concentrations (sub-MICs) of antibiotics. There is limited information available regarding how the genes of A. baumannii are linked to biofilm formation when the bacteria are exposed to sub-MICs of imipenem and colistin. Thus, this study's objective was to explore this relationship by examining the genes involved in biofilm formation in A. baumannii when exposed to low levels of imipenem and colistin. The study found that exposing an isolate of A. baumannii to low levels of these drugs caused changes in their drug susceptibility pattern. The relative gene expression profiles of the biofilm-associated genes exhibited a change in their expression profile during short-term and long-term exposure. This study highlights the potential consequences of overuse and misuse of antibiotics, which can help bacteria become resistant to these drugs.

The use of combination therapy for the improvement of colistin activity against bacterial biofilm

Colistin is used as a last resort for the management of infections caused by multi-drug resistant (MDR) bacteria. However, the use of this antibiotic could lead to different side effects, such as nephrotoxicity, in most patients, and the high prevalence of colistin-resistant strains restricts the use of colistin in the clinical setting. Additionally, colistin could induce resistance through the increased formation of biofilm; biofilm-embedded cells are highly resistant to antibiotics, and as with other antibiotics, colistin is impaired by bacteria in the biofilm community. In this regard, the researchers used combination therapy for the enhancement of colistin activity against bacterial biofilm, especially MDR bacteria. Different antibacterial agents, such as antimicrobial peptides, bacteriophages, natural compounds, antibiotics from different families, N-acetylcysteine, and quorum-sensing inhibitors, showed promising results when combined with colistin. Additionally, the use of different drug platforms could also boost the efficacy of this antibiotic against biofilm. The mentioned colistin-based combination therapy not only could suppress the formation of biofilm but also could destroy the established biofilm. These kinds of treatments also avoided the emergence of colistin-resistant subpopulations, reduced the required dosage of colistin for inhibition of biofilm, and finally enhanced the dosage of this antibiotic at the site of infection. However, the exact interaction of colistin with other antibacterial agents has not been elucidated yet; therefore, further studies are required to identify the precise mechanism underlying the efficient removal of biofilms by colistin-based combination therapy.

Extensively drug-resistant Enterobacter ludwigii co-harbouring MCR-9 and a multicopy of blaIMP-1 in South Korea

In this study, we describe an Enterobacter ludwigii clinical isolate that is resistant to both carbapenems and colistin in South Korea. Antimicrobial susceptibility testing revealed that E. ludwigii CRE2104-31 was non-susceptible to all tested antibiotics except fosfomycin. Whole genome sequencing identified a 323-kbp IncHI2 plasmid, pCRE2104-31a, that was co-harbouring mobile colistin resistance (mcr)-9.1 and blaIMP-1. In comparison with other full plasmids, pCRE2104-31a exhibited the closest similarity to a plasmid from the Klebsiella pneumoniae strain CNR48 from France, with 19.9% query coverage and 99% identity. Notably, we observed five tandem repeats of blaIMP-1 and aac(6')-Il genes, accompanied by multiple attCs within a class I integron on the Tn402-like transposon. The unit of blaIMP-1-attC-aac(6')-Il-attC might have accumulated due to multiple convergent events. In addition to mcr-9.1 and blaIMP-1, various other antibiotic resistance-associated genes were identified in the plasmid, as follows: blaTEM-1B, aph(3')-I, aph(3')-Ia, aac(6')-Il, aac(6')-IIc, aac(6')-IIa, aph(6)-Id, aph(3'')-Ib, aadA2b, aac(6')-Ib3, sul, dfrA19, qnrB2, aac(6')-Ib-cr, ere(A), and qacE. A conjugation assay showed that the mcr-9.1/blaIMP-1-co-bearing plasmid was self-transmissible to E. coli J53. However, colistin and carbapenem resistance could not be transferred to E. coli due to high incompatibility. The convergence of mcr and carbapenemase genes is thought to be host-dependent among Enterobacteriaceae. The emergence of extensively drug-resistant E. ludwigii co-harbouring MCR-9.1 and a multicopy of blaIMP-1 would pose a significant threat within the compatible Enterobacteriaceae.

In vitro activity of the newly approved antimicrobial agent Cefiderocol against Carbapenem resistant Gram negative clinical isolates

INTRODUCTION

Carbapenem resistant Gram negative bacteria have emerged as priority pathogens in recent years. Cefiderocol is a siderophore cephalosporin licensed in 2019 with claimed activity against ESBL producing and carbapenem resistant bacteria with much better safety margin compared to colistin. The present study was undertaken to assess the in vitro activity of cefiderocol against carbapenem resistant clinical isolates, compared to some select antimicrobial agents including colistin.

MATERIALS AND METHODS

Seventy-seven isolates of Gram negative bacteria belonging to the three commonly encountered groups of Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter spp were included. Susceptibility testing for Cefiderocol was determined by Kirby-Bauer's disk diffusion technique as per CLSI guidelines using Cefiderocol disc (30 μg). Sensitivity for the other agents were determined using automated system.

RESULTS

Of the 77 isolates, 58.4% belonged to Enterobacterales, followed by P.aeruginosa (27.3%) and Acinetobacter spp (14.3%). Three out of 45 Enterobacterales isolates, one out of 21 P.aeruginosa and none in the Acinetobacter group were found resistant to cefiderocol. All the isolates were intermediate sensitive (I) for colistin since the "susceptible" interpretive category has been eliminated. Tigecycline showed good activity (80.0% sensitive) against Enterobacterales followed by aztreonam (71.1% sensitive).

CONCLUSION

Cefiderocol is not yet available in India and our study is possibly the second one from this country demonstrating in vitro resistance to this important antimicrobial agent. However, with a relatively better safety profile compared to colistin, cefiderocol can be an important agent to combat these highly resistant pathogens.

Assessment of in vitro colistin susceptibility of carbapenem-resistant clinical Gram-negative bacterial isolates using four commercially available systems & Whole-genome sequencing: A diagnostic accuracy study

AIM

To analyze the diagnostic utility of commercially available platforms and Whole-genome sequencing (WGS) for accurate determination of colistin susceptibility test results.

MATERIAL & METHODS

An exploratory diagnostic accuracy study was conducted in which sixty carbapenem-resistant Gram-negative bacteria were subjected to identification and AST using MALDI-TOF MS & MicroScan walkaway 96 Plus. Additional AST was performed using the BD Phoenix system and Mikrolatest colistin kit. The test isolates were subjected to Vitek-2 and WGS at CRL, Bengaluru.

RESULTS

There was no statistically significant agreement between the colistin susceptibility results obtained by WGS, with those of commercial phenotypic platforms. The MicroScan 96 Plus had the highest sensitivity (31 %) & NPV (77 %), and the BD Phoenix system had the highest specificity (97 %) and PPV (50 %), respectively, for determining colistin resistance.

CONCLUSION

The utility of WGS as a tool in AMR surveillance and validation of phenotypic AST methods should be explored further.

In vitro antimicrobial susceptibility data of global meropenem-resistant Acinetobacter baumannii isolates causing pneumonia: Data from the Antimicrobial Testing Leadership and Surveillance Program, 2014-2021, and re-estimations of susceptibility breakpoints and appropriate dosages of important antibiotics for pneumonia treatment

OBJECTIVES

To evaluate the susceptibility of globally pneumonia-causing meropenem-resistant (MEM-R) Acinetobacter baumannii isolates against important antibiotics and estimate appropriate dosages of indicated antibiotics.

METHODS

We extracted the 2014-2021 Antimicrobial Testing of Leadership Surveillance database regarding the susceptibility of MEM-R A. baumannii isolates causing pneumonia against important antibiotics. The susceptibility and carbapenemase-encoding gene (CPEG) data of pneumonia-causing MEM-R A. baumannii isolates from patients hospitalized in intensive care units of five major regions were analyzed. The susceptibility breakpoints (SBP) recommended by the Clinical and Laboratory Standards Institute (CLSI) in 2022, other necessary criteria [SBP of MIC for colistin, 2 mg/L, in the CLSI 2018; and cefoperazone-sulbactam (CFP-SUL), 16 mg/L], and the pharmacokinetic and pharmacodynamic data of indicated antibiotics were employed.

RESULTS

Applying the aforementioned criteria, we observed the susceptible rates of colistin, minocycline, and CFP-SUL against the pneumonia-causing MEM-R A. baumannii isolates globally (n = 2905) were 93.2%, 69.1%, and 26.3%, respectively. Minocycline was significantly more active in vitro (MIC ≤4 mg/L) against the pneumonia-causing MEM-R A. baumannii isolates collected from North and South America compared to those from other regions (>90% vs. 58-72%). Additionally, blaOXA-23 and blaOXA-72 were the predominant CPEG in pneumonia-causing MEM-R A. baumannii isolates.

CONCLUSIONS

After deliberative estimations, dosages of 200 mg minocycline intravenously every 12 h (SBP, 8 mg/L), 100 mg tigecycline intravenously every 12 h (SBP, 1 mg/L), and 160 mg nebulized colistin methanesulphonate every 8 h (SBP, 2 mg/L) are needed for the effective treatment of pneumonia-causing MEM-R A. baumannii isolates.

Comparative evaluation of Vitek®2 and broth microdilution method for colistin susceptibility testing of Gram-negative isolates from intensive care unit in a tertiary care hospital

INTRODUCTION

Colistin is the last resort treatment against resistant Gram-negative bacteria, necessitating reliable and rapid means for sensitivity testing of colistin. Automated systems like VITEK®2 are adopted to determine the minimum inhibitory concentration (MIC) due to easy usage. Broth microdilution (BMD) for colistin MIC was suggested by EUCAST and CLSI.

OBJECTIVE

To compare and evaluate colistin MIC by BMD and VITEK®2 against Gram-negative organisms from the ICU in a tertiary care hospital.

METHOD

Clinically significant organisms isolated from ICU patients were included. MIC was determined using BMD and VITEK®2. Very major error (VME), major error (ME), essential agreement (EA), categorical agreement (CA), positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity were analysed.

RESULT

533 isolates were obtained from blood (435,81.60%), respiratory samples (57,10.70%), pus and exudates (20,3.80%), urine (18,3.40%), and CSF (3,0.60%). The Enterobacterales were K. pneumoniae (185,34.70%) E. coli (73,13.70%) and E. cloacae (26,4.90%) while non-fermenters were A. baumannii (209,39.20%) and P. aeruginosa (40,7.50%). The VITEK®2 sensitivity was >99%; specificity ranged from 14.28 to 52.94%. PPV was 93.81% while NPV was 93.75%. VME ranged from 47 to 100% between isolates. ME was up to 20%. The highest VME was obtained in E. coli (100%). The total EA and CA observed were 68.5% and 99.79% respectively.

CONCLUSION

Automated system VITEK®2 failed to detect the resistance in 32 (60%) isolates. The obtained VME and ME values were >3%, which is unacceptable as per the standard guidelines. EA of ≥90% wasn't obtained. Sensitivity for VITEK®2 was >99%, but had low specificity (14.28%). Hence, VITEK®2 is not reliable for colistin susceptibility testing.

Induction of proteome changes involved in the cloning of mcr-1 and mcr-2 genes in Escherichia coli DH5-α strain to evaluate colistin resistance

OBJECTIVES

Plasmid genes, termed mobile colistin resistance-1 (mcr-1) and mobile colistin resistance-2 (mcr-2), are associated with resistance to colistin in Escherichia coli (E. coli). These mcr genes result in a range of protein modifications contributing to colistin resistance. This study aims to discern the proteomic characteristics of E. coli-carrying mcr-1 and mcr-2 genes. Furthermore, it evaluates the expression levels of various proteins under different conditions (with and without colistin).

METHODS

Plasmid extraction was performed using an alkaline lysis-based plasmid extraction kit, whereas polymerase chain reaction was used to detect the presence of mcr-1 and mcr-2 plasmids. The E. coli DH5α strain served as the competent cell for accepting and transforming mcr-1 and mcr-2 plasmids. We assessed proteomic alterations in the E. coli DH5α strain both with and without colistin in the growth medium. Proteomic data were analysed using mass spectrometry.

RESULTS

The findings revealed significant protein changes in the E. coli DH5α strain following cloning of mcr-1 and mcr-2 plasmids. Of the 20 proteins in the DH5α strain, expression in 8 was suppressed following transformation. In the presence of colistin in the culture medium, 39 new proteins were expressed following transformation with mcr-1 and mcr-2 plasmids. The proteins with altered expression play various roles.

CONCLUSION

The results of this study highlight numerous protein alterations in E. coli resulting from mcr-1 and mcr-2-mediated resistance to colistin. This understanding can shed light on the resistance mechanism. Additionally, the proteomic variations observed in the presence and absence of colistin might indicate potential adverse effects of indiscriminate antibiotic exposure on treatment efficacy and heightened pathogenicity of microorganisms.

Co-transfer of IncFII/IncFIB and IncFII plasmids mediated by IS26 facilitates the transmission of mcr-8.1 and tmexCD1-toprJ1

PURPOSE

This study aimed to characterise the whole-genome structure of two clinical Klebsiella pneumoniae strains co-harbouring mcr-8.1 and tmexCD1-toprJ1, both resistant to colistin and tigecycline.

METHODS

K. pneumoniae strains TGC-02 (ST656) and TGC-05 (ST273) were isolated from urine samples of different patients hospitalised at separate times in 2021. Characterisation involved antimicrobial susceptibility testing (AST), conjugation assays, whole-genome sequencing (WGS), and bioinformatics analysis. Comparative genomic analysis was conducted on mcr-8.1-carrying and tmexCD1-toprJ1-carrying plasmids.

RESULTS

Both K. pneumoniae isolates displayed a multidrug-resistant phenotype, exhibiting resistance or reduced susceptibility to ampicillin, ampicillin/sulbactam, cefazolin, aztreonam, amikacin, gentamicin, tobramycin, ciprofloxacin, levofloxacin, nitrofurantoin, trimethoprim/sulfamethoxazole, apramycin, tigecycline and colistin. WGS analysis revealed that clinical strain TGC-02 carried the TmexCD1-toprJ1 gene on a 200-Kb IncFII/IncFIB-type plasmid, while mcr-8 was situated on a 146-Kb IncFII-type plasmid. In clinical strain TGC-05, TmexCD1-toprJ1 was found on a 300-Kb IncFIB/IncHI1B/IncR-type plasmid, and mcr-8 was identified on a 137-Kb IncFII/IncFIA-type plasmid. Conjugation experiments assessed the transferability of these plasmids. While transconjugants were not obtained for TGC-05 despite multiple screening with tigecycline or colistin, pTGC-02-tmex and pTGC-02-mcr8 from clinical K. pneumoniae TGC-02 demonstrated self-transferability through conjugation. Notably, the rearrangement of pTGC-02-tmex and pTGC-02-mcr8 via IS26-based homologous recombination was observed. Moreover, the conjugative and fusion plasmids of the transconjugant co-harboured the tmexCD1-toprJ1 gene cluster and mcr-8.1, potentially resulting from IS26-based homologous recombination.

CONCLUSION

The emergence of colistin- and tigecycline-resistant K. pneumoniae strains is concerning, and effective surveillance measures should be implemented to prevent further dissemination.

Colistin monotherapy or combination for the treatment of bloodstream infection caused by Klebsiella pneumoniae: a systematic review and meta-analysis

BACKGROUND

Bloodstream infection of Klebsiella pneumoniae (BSI-KP) were associated with increased mortality. Klebsiella pneumoniae was tested to susceptible to colistin by E-test and broth microdilution method in clinical laboratory. This study aimed to assess the efficacy of colistin versus tigecycline, carbapenem monotherapy and combination in the treatment of BSI-KP.

METHODS

Electronic databases such as PubMed, Web of Science and Embase were searched. The last search was in November 24th, 2022, addressing the colistin, carbapenems and tigecycline monotherapy and combination treatments in patients with BSI-KP. The primary outcomes were 30-day or 28-day mortality. OR where available with 95% CI were pooled in random-effects meta-analysis.

RESULTS

Following the outlined search strategy, a total of 658 articles were identified from the initial database searching. Six studies, 17 comparisons were included. However, they all were observational design, lacking high-quality randomized controlled trials (RCTs). Moderate or low-quality evidences suggested that colistin monotherapy was associated with an OR = 1.35 (95% CI = 0.62-2.97, P = 0.45, Tau2 = 0.00, I2 = 0%) compared with tigecycline monotherapy, OR = 0.81 (95% CI = 0.27-2.45, P = 0.71, Tau2 = 0.00, I2 = 0%) compared with carbapenem monotherapy. Compared with combination with tigecycline or carbapenem, Colistin monotherapy resulted in OR of 3.07 (95% CI = 1.34-7.04, P = 0.008, Tau2 = 0.00, I2 = 0%) and 0.98 (95%CI = 0.29-3.31, P = 0.98, Tau2 = 0.00, I2 = 0% ), respectively.

CONCLUSIONS

Colistin, carbapenem and tigecycline monotherapy showed similar treatment effects in patients who suffered from BSI-KP. Compared with colistin monotherapy, colistin combined tigecycline therapy might play the synergism effects.

TRIAL REGISTRATION

retrospectively registered.

Low prevalence of mcr-1 in Escherichia coli from food-producing animals and food products in China

BACKGROUND

mcr-1-positive Escherichia coli has emerged as a significant threat to human health, veterinary health, and food safety in recent years. After the prohibition of colistin as a feed additive in animal husbandry in China, a noticeable reduction in both colistin resistance and the prevalence of mcr-1 was observed in E. coli from animals and humans.

OBJECTIVES

To assess the prevalence of the colistin resistance gene mcr-1 and characterize its genetic context in E. coli strains derived from fecal and meat samples from food-producing animals in China.

METHODS

A total of 1,353 fecal samples and 836 food samples were collected between 2019 and 2020 in China. E. coli isolates were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and their susceptibility to colistin were determined using the broth microdilution method. The colistin-resistant E. coli isolates were screened for the presence of mcr by PCR analysis and sequencing. The minimal inhibitory concentrations (MICs) of 15 antimicrobial agents against the mcr-1-positive strains were further tested using the agar dilution method, conjugation assays were performed, and whole genome sequencing was performed using Illumina HiSeq.

RESULTS

In total, 1,403 E. coli strains were isolated. Thirteen isolates from chicken meat (n = 7), chickens (n = 3), and pigs (n = 3) were resistant to colistin with MIC values of 4 to 16 mg/L, and carried mcr-1. All mcr-1-positive strains, except for isolate AH20PE105, contained multiple resistance genes and exhibited multidrug-resistant phenotypes. They belonged to 10 sequence types (STs), including a novel ST (ST14521). mcr-1 was located on IncI2 (n = 9), IncX4 (n = 2), and IncHI2 (n = 2) plasmids, which were highly similar to other mcr-1-carrying plasmids sharing the same incompatibility type. Seven mcr-1-carrying plasmids could be successfully conjugally transferred to E. coli C600.

CONCLUSIONS

While the low prevalence of mcr-1 (0.93%) identified in this study may not immediately seem alarming, the very emergence of this gene merits attention given its implications for colistin resistance and public health. Hence, ongoing surveillance of mcr-1 in E. coli remains crucial.

Synergistic effects of nano curcumin mediated photodynamic inactivation and nano-silver@colistin against Pseudomonas aeruginosa biofilms

BACKGROUND

Patients with burn injuries colonized by multidrug-resistant Pseudomonas aeruginosa face increased mortality risk. The efficacy of colistin, a last-resort treatment, is declining as resistance levels rise. P. aeruginosa's robust biofilm exacerbates antibiotic resistance. Photodynamic Inactivation (PDI) shows promise in fighting biofilm.

MATERIALS AND METHODS

Nano curcumin (nCur) particles were synthesized, and their chemical characteristics were determined using zeta potential (ZP), dynamic light scattering analysis (DLS), energy-dispersive X-ray (EDX) analysis, and fourier transform infrared (FTIR). We conducted an MTT assay to assess the cytotoxicity of nCur-mediated PDI in combination with nanosilver colistin. The fractional biofilm inhibitory concentration (FBIC) of two P. aeruginosa clinical isolates and P. aeruginosa ATCC 27853 during nCur-mediated PDI@AgNPs@CL was determined using a 3-dimensional (3-D) checkerboard assay. To study the effect of nCur-mediated PDI@AgNPs@CL on lasI, lasR, rhlI, rhlR, pelA, and pslA gene expression, Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was conducted at each isolate's FBIC. The impact of treatments was also investigated using scanning electron microscopy (SEM).

RESULTS

The ZP and mean DLS values of the nCur were 10.3 mV and 402.6 ± 24.6 nm, respectively. The distinct functional groups of nCur corresponded with the peaks of FTIR absorption. Moreover, the EDX analysis showed the ratios of different metals in nCur. Cell viability percentages of nCur-mediated PDI@AgNPs@CL at FBIC concentrations of clinical isolates Nos. 30, 354, and P. aeruginosa ATCC 27853 were 91.36 %, 83.20 %, and 92.48 %, respectively. nCur-mediated PDI@AgNPs@CL treatment showed synergistic effects in clinical isolates and P. aeruginosa ATCC 27853 in a 3-D checkerboard assay. All six of the investigated genes showed down-regulation after nCur-mediated PDI@AgNPs@CL treatment. The most suppressed gene during nCur-mediated PDI@AgNPs@CL treatment was the rhlR gene (-11.9-fold) of P. aeruginosa ATCC 27853. The SEM micrographs further proved the connecting cement reduction and biofilm mass mitigation following nCur-mediated PDI@AgNPs@CL treatments.

CONCLUSIONS

The combined effect of nCur-mediated PDI and AgNPs@CL synergistically reduce the formation of biofilm in P. aeruginosa. This may be attributable to the suppression of the genes responsible for regulating the production of biofilms.

Battle of polymyxin induced nephrotoxicity: Polymyxin B versus colistin

OBJECTIVES

Nephrotoxicity is the most serious and common adverse effect that limits the use of polymyxins. This study compared polymyxin E (colistin) and polymyxin B regarding drug-related nephrotoxicity.

METHODS

This study was conducted as a retrospective cohort study in a university hospital between January 2020 and July 2022. Patients older than 18 years and who received colistin or polymyxin B were identified using electronic hospital records. Kidney disease improving global outcome criteria were used for assessing nephrotoxicity.

RESULTS

A total of 190 patients, 95 in both groups, were evaluated. The incidence of acute kidney injury during the treatment was higher in the colistin group [52.6% (n = 50) and 34.7% (n = 33), P = 0.013]. In patients who were exposed to high-dose, the rate of nephrotoxicity was higher in patients receiving colistin [25% (n = 3) vs. 76.9% (n = 10); P = 0.017]. Nephrotoxicity was reversible in 64.4% (n = 38) of patients and the reversibility rate was similar (70% and 52.6% for colistin and polymyxin; P = 0.248). In the multivariable analysis, colistin treatment [odds ratio (OR): 3.882, 95% confidence interval (95% CI) = (1.829-8.241)], concomitant vasopressor use (OR = 2.08, CI: 1.036-4.179), and age (OR=1.036, CI: 1.014-1.058) were found to be independent markers of nephrotoxicity.

CONCLUSION

Nephrotoxicity was more common in patients receiving high-dose colistin than polymyxin B. Therefore, the use of appropriate doses of colistin is important in terms of preventing nephrotoxicity. In addition, advancing age and concomitant use of vasopressors contribute to polymyxin-related nephrotoxicity.

Roles of crrAB two-component regulatory system in Klebsiella pneumoniae: growth yield, survival in initial colistin treatment stage, and virulence

OBJECTIVES

Alternation of the colistin resistance-regulating two-component regulatory system (crrAB) is a colistin-resistance mechanism in Klebsiella pneumoniae (K. pneumoniae), but its role in bacteria is not fully understood.

METHODS

Twelve colistin-susceptible K. pneumoniae clinical isolates were included in this study: six crrAB-positive and six crrAB-negative. We deleted the crrAB genes from two crrAB-positive isolates and complemented them. We measured the growth yields by determining growth curves in lysogeny broth and minimal media with or without Fe2+. In vitro selection rates for colistin resistance were determined by exposure to colistin, and survival rates against high concentrations of colistin (20 mg/L) at the early stage of growth (20 min) were investigated. Virulence was determined using a serum bactericidal assay and Galleria mellonella larval infection.

RESULTS

The presence of crrAB was not associated with colistin resistance and did not increase the in vitro selection rate of colistin resistance after exposure. The growth yield of crrAB-positive isolates was higher in lysogeny broth media and increased when Fe2+ was added to minimal media. The crrAB-positive isolates showed higher survival rates in the early stages of exposure to high colistin concentrations. Decreased serum resistance was identified in the crrAB-deleted mutants. More G. mellonella larvae survived when infected by crrAB-deleted mutants, and higher survival rates of bacteria were identified within the larvae infected with wild-type than crrAB-deletant isolates.

CONCLUSION

Through rapid response to external signals, crrAB would provide advantages for K. pneumoniae survival by increasing the final growth yield and initial survival against colistin treatment. This may partly contribute to the bacterial virulence.

Phenotypic and genotypic characterization of extended spectrum beta-lactamase producing E. coli harboring carbapenem and colistin-resistant genes from poultry farms in Egypt

Background

eEscherichia coli (E. coli) bacteria that produce extended spectrum beta-lactamase (ESBL) is associated with a high prevalence of human illnesses worldwide. The emergence of resistance to carbapenem and colistin compounds poses further challenges to the treatment options for these illnesses. This study aimed to evaluate the phenotypic and genotypic pattern of resistance to carbapenem and colistin in ESBL-producing E. coli. Escherichia coli isolates collected from the respiratory tract of chickens in El-Sharkia government, Egypt.

Methods

A total of 250 lung samples were collected from 50 poultry farms. These samples were then subjected to isolation, identification, and serotyping of E. coli. The presence of antimicrobial resistance was identified by disc diffusion testing. The occurrence of ESBL phenotypes was also assessed using the double disc synergy method. PCR/sequencing techniques were employed to examine the presence of ESBL (β-lactamase (bla)-TEM, blaSHV, and blaCTX-M), colistin (mcr-1), and carbapenem (blaNDM, blaVIM, and blaKPC) resistance genes.

Results

The findings revealed that 140 out of 250 (56%) were identified as E. coli. All E. coli isolates had a high level of multi-antimicrobial resistance (MAR) with an index value greater than 0.2, and 65.7% of them were confirmed to produce ESBL. Out of the 92 ESBL phenotypes, 55 (59.7%), 32 (34.7%), 18 (19.6%), and 37 (40.2%) isolates harbor b laTEM-3, b laSHV-4, b laCTX-M-1, a nd blaCTX-M-14 genes, respectively. The blaNDM-1 gene was identified in all 40 phenotypes that exhibited resistance to carbapenem, accounting for 28.5% of all strains of E. coli and 43.4% of ESBL isolates. The VIM and KPC genes were not detected in any of the samples. Furthermore, there was a significant prevalence of the mobilized colistin resistance (mcr)-1 gene, with 64 (69.5%) of the ESBL isolates exhibiting this gene.

Conclusion

The prevalence of ESBL-producing E. coli, particularly those resistant to carbapenem and colistin, poses a significant public health risk in society.

Distinguishing Inducible and Non-Inducible Resistance to Colistin in Pseudomonas aeruginosa by Quantitative and Systems Pharmacology Modeling at Low and Standard Inocula

Colistin is a polymyxin and peptide antibiotic that can yield rapid bacterial killing, but also leads to resistance emergence. We aimed to develop a novel experimental and Quantitative and Systems Pharmacology approach to distinguish between inducible and non-inducible resistance. Viable count profiles for the total and less susceptible populations of Pseudomonas aeruginosa ATCC 27853 from static and dynamic in vitro infection models were simultaneously modeled. We studied low and normal initial inocula to distinguish between inducible and non-inducible resistance. A novel cutoff filter approach allowed us to describe the eradication and inter-conversion of bacterial populations. At all inocula, 4.84 mg/L of colistin (sulfate) yielded ≥4 log10 killing, followed by >4 log10 regrowth. A pre-existing, less susceptible population was present at standard but not at low inocula. Formation of a non-pre-existing, less susceptible population was most pronounced at intermediate colistin (sulfate) concentrations (0.9 to 5 mg/L). Both less susceptible populations inter-converted with the susceptible population. Simultaneously modeling of the total and less susceptible populations at low and standard inocula enabled us to identify the de novo formation of an inducible, less susceptible population. Inducible resistance at intermediate colistin concentrations highlights the importance of rapidly achieving efficacious polymyxin concentrations by front-loaded dosage regimens.

Conversion to colistin susceptibility by tigecycline exposure in colistin-resistant Klebsiella pneumoniae and its implications to combination therapy

OBJECTIVES

This study investigated the effect of tigecycline exposure on susceptibility of colistin-resistant Klebsiella pneumoniae isolates to colistin and explored the possibility of antibiotic combination at low concentrations to treat colistin-resistant K. pneumoniae isolates.

METHODS

Twelve tigecycline-resistant (TIR) mutants were induced in vitro from wild-type, colistin-resistant, and tigecycline-susceptible K. pneumoniae isolates. Antibiotic susceptibility was determined using the broth microdilution method. The deduced amino acid alterations were identified for genes associated with colistin resistance, lipid A biosynthesis, and tigecycline resistance. Expression levels of genes were compared between wild-type stains and TIR mutants using quantitative real-time polymerase chain reaction (PCR). Lipid A modification was explored using MALDI-TOF mass spectrometry. Time-killing assay was performed to assess the efficiency of combination therapy using low concentrations of colistin and tigecycline.

RESULTS

All TIR mutants except one were converted to be susceptible to colistin. These TIR mutants had mutations in the ramR gene and increased expression levels of ramA. Three genes associated with lipid A biosynthesis, lpxC, lpxL, and lpxO, were also overexpressed in TIR mutants, although no mutation was observed. Additional polysaccharides found in colistin-resistant, wild-type strains were modified in TIR mutants. Colistin-resistant K. pneumoniae strains were eliminated in vitro by combining tigecycline and colistin at 2 mg/L. In this study, we found that tigecycline exposure resulted in reduced resistance of colistin-resistant K. pneumoniae to colistin. Such an effect was mediated by regulation of lipid A modification involving ramA and lpx genes.

CONCLUSION

Because of such reduced resistance, a combination of colistin and tigecycline in low concentrations could effectively eradicate colistin-resistant K. pneumoniae strains.

Clinical Efficacy and Safety of Colistin Sulfate in the Treatment of Carbapenem-Resistant Organism Infections in Patients with Hematological Diseases

INTRODUCTION

Carbapenem-resistant organisms (CRO) have emerged as a significant worldwide issue. However, the availability of efficacious antibiotics for treating CRO infections remains limited. Polymyxins, including colistin sulfate, represent the last-line therapeutic option against CRO infections. This study aims to retrospectively evaluate the clinical effectiveness and safety of colistin sulfate in managing CRO infections among patients with hematological diseases.

METHODS

Between April 2022 and January 2023, a total of 118 hematological patients diagnosed with CRO infection were treated with colistin sulfate at Suzhou Hongci Hospital of Hematology. The assessment encompassed the clinical efficacy, bacterial clearance rate, adverse reactions, and 30-day all-cause mortality.

RESULTS

The study found that the total effective rate of colistin sulfate in the treatment of CRO infection was 74.6%, with a bacterial clearance rate of 72.6%. Throughout the treatment, nephrotoxicity occurred in 7.6% of cases, neurotoxicity in 2.5% of cases, and the 30-day all-cause mortality rate was 22.9%. Multivariate logistic analysis revealed that the treatment course and combination medication with other antimicrobials were independent factors affecting the clinical efficacy of colistin sulfate.

CONCLUSION

Our study demonstrates that the treatment of colistin sulfate can achieve high clinical efficacy and microbial responses, with a low risk of nephrotoxicity. This study provides evidence of the positive clinical efficacy and safety of colistin sulfate treatment in these patients. High-quality randomized controlled trials are still needed to further confirm the beneficial role of colistin sulfate.