Combined effect of Polymyxin B and Tigecycline to overcome Heteroresistance in Carbapenem-Resistant Klebsiella pneumoniae

Hypervirulent and carbapenem-resistant Klebsiella pneumoniae: A global public health threat

The evolution of hypervirulent and carbapenem-resistant Klebsiella pneumoniae can be categorized into three main patterns: the evolution of KL1/KL2-hvKp strains into CR-hvKp, the evolution of carbapenem-resistant K. pneumoniae (CRKp) strains into hv-CRKp, and the acquisition of hybrid plasmids carrying carbapenem resistance and virulence genes by classical K. pneumoniae (cKp). These strains are characterized by multi-drug resistance, high virulence, and high infectivity. Currently, there are no effective methods for treating and surveillance this pathogen. In addition, the continuous horizontal transfer and clonal spread of these bacteria under the pressure of hospital antibiotics have led to the emergence of more drug-resistant strains. This review discusses the evolution and distribution characteristics of hypervirulent and carbapenem-resistant K. pneumoniae, the mechanisms of carbapenem resistance and hypervirulence, risk factors for susceptibility, infection syndromes, treatment regimens, real-time surveillance and preventive control measures. It also outlines the resistance mechanisms of antimicrobial drugs used to treat this pathogen, providing insights for developing new drugs, combination therapies, and a "One Health" approach. Narrowing the scope of surveillance but intensifying implementation efforts is a viable solution. Monitoring of strains can be focused primarily on hospitals and urban wastewater treatment plants.

Monitoring of Klebsiella pneumoniae Infection and Drug Resistance in 17 Pediatric Intensive Care Units in China from 2016 to 2022

Objective

To investigate the characteristics and drug resistance patterns of Klebsiella pneumoniae (K. pneumoniae) infection in pediatric intensive care unit (PICU).

Methods

K. pneumoniae strains from 17 domestic PICUs were analyzed for overall condition and drug resistance using WHO-NET software.

Results

From 2016 to 2022, there was a linear increase in the detection rate of K. pneumoniae (P<0.05), with a total of 2591 (9.7%) strains detected. The primary sites of K. pneumoniae detection were the respiratory tract (71.1%), blood (8.6%), and urinary tract (7.1%). K. pneumoniae's resistance to penicillin drugs exceeded 90%, and are over 50% to cephalosporins. Resistance to cefoperazone-sulbactam decreased from 51.7% to 25.7%, and ranged from 9.1% to 20.8% for ceftolozane-tazobactam. Carbapenem-resistant K. pneumoniae strains constituted 32.3%. Resistance to imipenem and meropenem have decreased to 33.8% and 40.2%, while increased to 35.2% for ertapenem. Levofloxacin and amikacin resistance rates have decreased to 25.7% and 9.1%, but remain high at 63.8% for moxifloxacin and 44.6% for ciprofloxacin. K. pneumoniae demonstrated the lowest resistance rates to polymyxin B (0.9%), tigecycline (2.2%), and polymyxin E (3.1%). No strain of K. pneumoniae was resistant to both polymyxin B and meropenem. However, some strains showed co-resistance to meropenem with other antibiotics, including tigecycline (2%), imipenem (16%), amikacin (27%), colistin (37%), and levofloxacin (41%).

Conclusion

The rates of isolation and drug resistance of K. pneumoniae in PICU have significantly increased over 7 years. Careful antibiotic use, infection control strategies, and appropriate antibiotic combinations are crucial in addressing this problem.

High prevalence of polymyxin-heteroresistant carbapenem-resistant Klebsiella pneumoniae and its within-host evolution to resistance among critically ill scenarios

PURPOSE

We aimed to explore the prevalence and within-host evolution of resistance in polymyxin-heteroresistant carbapenem-resistant Klebsiella pneumoniae (PHR-CRKP) in critically ill patients.

METHODS

We performed an epidemiological analysis of consecutive patients with PHR-CRKP from clinical cases. Our study investigated the within-host resistance evolution and its clinical significance during polymyxin exposure. Furthermore, we explored the mechanisms underlying the dynamic evolution of polymyxin resistance at both subpopulation and genetic levels, involved population analysis profile test, time-killing assays, competition experiments, and sanger sequencing. Additionally, comparative genomic analysis was performed on 713 carbapenemase-producing K. pneumoniae strains.

RESULTS

We enrolled 109 consecutive patients, and PHR-CRKP was found in 69.7% of patients without previous polymyxin exposure. 38.1% of PHR-CRKP isolates exhibited polymyxin resistance and led to therapeutic failure in critically ill scenarios. An increased frequency of resistant subpopulations was detected during PHR-CRKP evolution, with rapid regrowth of resistant subpopulations under high polymyxin concentrations, and a fitness cost in an antibiotic-free environment. Mechanistic analysis revealed that diverse mgrB insertions and pmrB hypermutations contributed to the dynamic changes in polymyxin susceptibility in dominant resistant subpopulations during PHR evolution, which were validated by comparative genomic analysis. Several deleterious mutations (e.g. pmrBLeu82Arg, pmrBSer85Arg) were firstly detected during PHR-CRKP evolution. Indeed, specific sequence types of K. pneumoniae demonstrated unique deletions and deleterious mutations.

CONCLUSIONS

Our study emphasizes the high prevalence of pre-existing heteroresistance in CRKP, which can lead to polymyxin resistance and fatal outcomes. Hence, it is essential to continuously monitor and observe the treatment response to polymyxins in appropriate critically ill scenarios.

Antibiotic heteroresistance in Klebsiella pneumoniae: Definition, detection methods, mechanisms, and combination therapy

Klebsiella pneumoniae is a common opportunistic pathogen that presents significant challenges in the treatment of infections due to its resistance to multiple antibiotics. In recent years, K. pneumoniae has been reported for the development of heteroresistance, a phenomenon where subpopulations of the susceptible bacteria exhibit resistance. This heteroresistance has been associated with increased morbidity and mortality rates. Complicating matters further, its definition and detection pose challenges, often leading to its oversight or misdiagnosis. Various mechanisms contribute to the development of heteroresistance in K. pneumoniae, and these mechanisms differ among different antibiotics. Even for the same antibiotic, multiple mechanisms may be involved. However, our current understanding of these mechanisms remains incomplete, and further research is needed to gain a more comprehensive understanding of heteroresistance. While the clinical recommendation is to use combination antibiotic therapy to mitigate heteroresistance, this approach also comes with several drawbacks and potential adverse effects. In this review, we discuss the definition, detection methods, molecular mechanisms, and treatment of heterogenic resistance, aiming to pave the way for more effective treatment and management in the future. However, addressing the problem of heteroresistance in K. pneumoniae represents a long and complex journey that necessitates comprehensive research efforts.

sRNA expression profile of KPC-2-producing carbapenem-resistant Klebsiella pneumoniae: Functional role of sRNA51

The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) has significant challenges to human health and clinical treatment, with KPC-2-producing CRKP being the predominant epidemic strain. Therefore, there is an urgent need to identify new therapeutic targets and strategies. Non-coding small RNA (sRNA) is a post-transcriptional regulator of genes involved in important biological processes in bacteria and represents an emerging therapeutic strategy for antibiotic-resistant bacteria. In this study, we analyzed the transcription profile of KPC-2-producing CRKP using RNA-seq. Of the 4693 known genes detected, the expression of 307 genes was significantly different from that of carbapenem-sensitive Klebsiella pneumoniae (CSKP), including 133 up-regulated and 174 down-regulated genes. Both the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment and Gene Ontology (GO) analysis showed that these differentially expressed genes (DEGs) were mainly related to metabolism. In addition, we identified the sRNA expression profile of KPC-2-producing CRKP for the first time and detected 115 sRNAs, including 112 newly discovered sRNAs. Compared to CSKP, 43 sRNAs were differentially expressed in KPC-2-producing CRKP, including 39 up-regulated and 4 down-regulated sRNAs. We chose sRNA51, the most significantly differentially expressed sRNA in KPC-2-producing CRKP, as our research subject. By constructing sRNA51-overexpressing KPC-2-producing CRKP strains, we found that sRNA51 overexpression down-regulated the expression of acrA and alleviated resistance to meropenem and ertapenem in KPC-2-producing CRKP, while overexpression of acrA in sRNA51-overexpressing strains restored the reduction of resistance. Therefore, we speculated that sRNA51 could affect the resistance of KPC-2-producing CRKP by inhibiting acrA expression and affecting the formation of efflux pumps. This provides a new approach for developing antibiotic adjuvants to restore the sensitivity of CRKP.

Synergistic Activity and Mechanism of Sanguinarine with Polymyxin B against Gram-Negative Bacterial Infections

Compounds that potentiate the activity of clinically available antibiotics provide a complementary solution, except for developing novel antibiotics for the rapid emergence of multidrug-resistant Gram-negative bacteria (GNB). We sought to identify compounds potentiating polymyxin B (PMB), a traditional drug that has been revived as the last line for treating life-threatening GNB infections, thus reducing its nephrotoxicity and heterogeneous resistance in clinical use. In this study, we found a natural product, sanguinarine (SA), which potentiated the efficacy of PMB against GNB infections. The synergistic effect of SA with PMB was evaluated using a checkerboard assay and time-kill curves in vivo and the murine peritonitis model induced by Escherichia coli in female CD-1 mice in vivo. SA assisted PMB in accelerating the reduction in bacterial loads both in vitro and in vivo, improving the inflammatory responses and survival rate of infected animals. The subsequent detection of the intracellular ATP levels, membrane potential, and membrane integrity indicated that SA enhanced the bacterial-membrane-breaking capacity of PMB. A metabolomic analysis showed that the inhibition of energy metabolism, interference with nucleic acid biosynthesis, and the blocking of L-Ara4N-related PMB resistance may also contribute to the synergistic effect. This study is the first to reveal the synergistic activity and mechanism of SA with PMB, which highlights further insights into anti-GNB drug development.

Cefiderocol: Clinical application and emergence of resistance

Antibacterial drug resistance of gram-negative bacteria (GNB) results in high morbidity and mortality of GNB infection, seriously threaten human health globally. Developing new antibiotics has become the critical need for dealing with drug-resistant bacterial infections. Cefiderocol is an iron carrier cephalosporin that achieves drug accumulation through a unique "Trojan horse" strategy into the bacterial periplasm. It shows high antibacterial activity against multidrug-resistant (MDR) Enterobacteriaceae and MDR non-fermentative bacteria. The application of cefiderocol offers new hope for treating clinical drug-resistant bacterial infections. However, limited clinical data and uncertainties about its resistance mechanisms constrain the choice of its therapeutic use. This review aimed to summarize the clinical applications, drug resistance mechanisms, and co-administration of cefiderocol.

High prevalence of heteroresistance in Staphylococcus aureus is caused by a multitude of mutations in core genes

Heteroresistance (HR) is an enigmatic phenotype where, in a main population of susceptible cells, small subpopulations of resistant cells exist. This is a cause for concern, as this small subpopulation is difficult to detect by standard antibiotic susceptibility tests, and upon antibiotic exposure the resistant subpopulation may increase in frequency and potentially lead to treatment complications or failure. Here, we determined the prevalence and mechanisms of HR for 40 clinical Staphylococcus aureus isolates, against 6 clinically important antibiotics: daptomycin, gentamicin, linezolid, oxacillin, teicoplanin, and vancomycin. High frequencies of HR were observed for gentamicin (69.2%), oxacillin (27%), daptomycin (25.6%), and teicoplanin (15.4%) while none of the isolates showed HR toward linezolid or vancomycin. Point mutations in various chromosomal core genes, including those involved in membrane and peptidoglycan/teichoic acid biosynthesis and transport, tRNA charging, menaquinone and chorismite biosynthesis and cyclic-di-AMP biosynthesis, were the mechanisms responsible for generating the resistant subpopulations. This finding is in contrast to gram-negative bacteria, where increased copy number of bona fide resistance genes via tandem gene amplification is the most prevalent mechanism. This difference can be explained by the observation that S. aureus has a low content of resistance genes and absence of the repeat sequences that allow tandem gene amplification of these genes as compared to gram-negative species.

Klebsiella pneumoniae carbapenemase variants: the new threat to global public health

Klebsiella pneumoniae carbapenemase (KPC) variants, which refer to the substitution, insertion, or deletion of amino acid sequence compared to wild blaKPC type, have reduced utility of ceftazidime-avibactam (CZA), a pioneer antimicrobial agent in treating carbapenem-resistant Enterobacterales infections. So far, more than 150 blaKPC variants have been reported worldwide, and most of the new variants were discovered in the past 3 years, which calls for public alarm. The KPC variant protein enhances the affinity to ceftazidime and weakens the affinity to avibactam by changing the KPC structure, thereby mediating bacterial resistance to CZA. At present, there are still no guidelines or expert consensus to make recommendations for the diagnosis and treatment of infections caused by KPC variants. In addition, meropenem-vaborbactam, imipenem-relebactam, and other new β-lactam-β-lactamase inhibitor combinations have little discussion on KPC variants. This review aims to discuss the clinical characteristics, risk factors, epidemiological characteristics, antimicrobial susceptibility profiles, methods for detecting blaKPC variants, treatment options, and future perspectives of blaKPC variants worldwide to alert this new great public health threat.

Synergistic effects of polymyxin and vancomycin combinations on carbapenem- and polymyxin-resistant Klebsiella pneumoniae and their molecular characteristics

IMPORTANCE

This study provides insights into the mechanisms of polymyxin resistance in K. pneumoniae clinical isolates and demonstrates potential strategies of polymyxin and vancomycin combinations for combating this resistance. We also identified possible mechanisms that might be associated with the treatment of these combinations against carbapenem- and polymyxin-resistant K. pneumoniae clinical isolates. The findings have significant implications for the development of alternative therapies and the effective management of infections caused by these pathogens.

An effective antimicrobial strategy of colistin combined with the Chinese herbal medicine shikonin against colistin-resistant Escherichia coli

IMPORTANCE

Infections caused by multidrug-resistant Escherichia coli (MDR E. coli) have become a major global healthcare problem due to the lack of effective antibiotics today. The emergence of colistin-resistant E. coli strains makes the situation even worse. Therefore, new antimicrobial strategies are urgently needed to combat colistin-resistant E. coli. Combining traditional antibiotics with non-antibacterial drugs has proved to be an effective approach of combating MDR bacteria. This study investigated the combination of colistin and shikonin, a Chinese herbal medicine, against colistin-resistant E. coli. This combination showed good synergistic antibacterial both in vivo and in vitro experiments. Under the background of daily increasing colistin resistance in E. coli, this research points to an effective antimicrobial strategy of using colistin and shikonin in combination against colistin-resistant E. coli.

Carbapenem resistant Enterobacterales in the United Arab Emirates: a retrospective analysis from 2010 to 2021

Background

Carbapenem-resistant Enterobacterales (CRE) are spreading in the United Arab Emirates (UAE) where their dissemination is facilitated by international travel, trade, and tourism. The objective of this study is to describe the longitudinal changes of CRE as reported by the national AMR surveillance system of the UAE.

Methods

In this study, we retrospectively describe CRE isolated from 317 surveillance sites, including 87 hospitals and 230 centers/clinics from 2010 to 2021. The associated clinical, demographic, and microbiological characteristics are presented by relying on the UAE national AMR surveillance program. Data was analyzed using WHONET microbiology laboratory database software (http://www.whonet.org).

Results

A total of 14,593 carbapenem resistant Enterobacterales were analyzed, of which 48.1% were carbapenem resistant Klebsiella pneumoniae (CRKp), 25.1% carbapenem resistant Escherichia coli (CREc), and 26.8% represented 72 other carbapenem resistant species. Carbapenem resistant strains were mostly associated with adults and isolated from urine samples (36.9% of CRKp and 66.6% of CREc) followed by respiratory samples (26.95% for CRKp) and soft tissue samples (19.5% for CRKp). Over the studied period carbapenem resistance rates remained high, especially in K. pneumoniae, and in 2021 were equivalent to 67.6% for imipenem, 76.2% for meropenem, and 91.6% for ertapenem. Nevertheless, there was a statistically significant decreasing trend for imipenem and meropenem resistance in Klebsiella species (p < 0.01) while the decrease in ertapenem resistance was non-significant. Concerning E. coli, there was a statistically significant decreasing trend for meropenem and imipenem resistance over the 12 years, while ertapenem resistance increased significantly with 83.8% of E. coli exhibiting ertapenem resistance in 2021. Resistance rates to ceftazidime and cefotaxime remained higher than 90% (in 2021) for CRKp and cefotaxime rates increased to 90.5% in 2021 for CREc. Starting 2014, resistance to colistin and tigecycline was observed in carbapenem resistant Enterobacterales. CRE were associated with a higher mortality (RR: 6.3), admission to ICU (RR 3.9), and increased length of stay (LOS; 10 excess inpatient days per CRE case).

Conclusion

This study supports the need to monitor CRE in the UAE and draws attention to the significant increase of ertapenem resistance in E. coli. Future surveillance analysis should include a genetic description of carbapenem resistance to provide new strategies.

Characterization of the Novel Leaderless Bacteriocin, Bawcin, from Bacillus wiedmannii

The rise of drug-resistant bacteria is a major threat to public health, highlighting the urgent need for new antimicrobial compounds and treatments. Bacteriocins, which are ribosomally synthesized antimicrobial peptides produced by bacteria, hold promise as alternatives to conventional antibiotics. In this study, we identified and characterized a novel leaderless bacteriocin, bawcin, the first bacteriocin to be characterized from a Bacillus wiedmannii species. Chemically synthesized and purified bawcin was shown to be active against a broad range of Gram-positive bacteria, including foodborne pathogens Staphylococcus aureus, Bacillus cereus, and Listeria monocytogenes. Stability screening revealed that bawcin is stable over a wide range of pH (2.0-10.0), temperature conditions (25-100 °C), and against the proteases, papain and pepsin. Lastly, three-dimensional structure homology modeling suggests that bawcin contains a saposin-fold with amphipathic helices and a highly cationic surface that may be critical for membrane interaction and the subsequent cell death of its targets. This study provides the foundational understanding of the activity and properties of bawcin, offering valuable insights into its applications across different antimicrobial uses, including as a natural preservative in food and livestock industries.

Mobilization of the blaKPC-14 gene among heterogenous plasmids in extensively drug-resistant hypervirulent Klebsiella pneumoniae

Introduction

Ceftazidime/avibactam (CZA) is an effective alternative for the treatment of infections caused by KPC-producing carbapenem-resistant Klebsiella pneumoniae (CRKP). However, KPC variants with CZA resistance have been observed in clinical isolates, further limiting the treatment options of clinical use.

Methods

In this study, we isolated three KPC-14-producing CRKP from two patients in intensive care units without CZA therapy. The antimicrobial susceptibility was determined using the broth microdilution method. Three CRKP were subjected to whole-genome sequencing to analyze the phylogenetic relatedness and the carriage of antimicrobial resistance genes and virulence factors. Long-read sequencing was also performed to obtain the complete sequences of the plasmids. The horizontal transfer of the blaKPC-14 gene was evaluated by conjugation experiments.

Results

Three CRKP displayed resistance or reduced susceptibility to ceftazidime/avibactam, colistin, and tigecycline. Single-nucleotide polymorphism (SNP) analysis demonstrated the close phylogenetic distance between these strains. A highly similar IncFII/IncR plasmid encoding blaKPC-14 was shared by three CRKP, with blaKPC-14 located in an NTEKPC-Ib element with the core region of ISKpn27- blaKPC-14-ISKpn6. This structure containing blaKPC-14 was also observed in another tet(A)-carrying plasmid that belonged to an unknown Inc-type in two out of three isolates. The horizontal transferability of these integrated plasmids to Escherichia coli EC600 was confirmed by the cotransmission of tet(A) and blaKPC-14 genes, but the single transfer of blaKPC-14 on the IncFII/IncR plasmid failed. Three CRKP expressed yersiniabactin and carried a hypervirulence plasmid encoding rmpA2 and aerobactin-related genes, and were thus classified as carbapenem-resistant hypervirulent K. pneumoniae (hvKP).

Discussion

In this study, we reported the evolution of a mosaic plasmid encoding the blaKPC-14 gene via mobile elements in extensively drug-resistant hvKP. The blaKPC-14 gene is prone to integrate into other conjugative plasmids via the NTEKPC-Ib element, further facilitating the spread of ceftazidime/avibactam resistance.

Virulence, antimicrobial resistance, and molecular characteristics of carbapenem-resistant Klebsiella pneumoniae in a hospital in Shijiazhuang City from China

Carbapenem-resistant Klebsiella pneumoniae (CRKP), as one of the most common drug-resistant bacteria threatening human health, is hyper-resistant to multiple antimicrobial drugs and carbapenems, which can be dealt with only limited clinical treatment options. This study described the epidemiological characteristics of CRKP in this tertiary care hospital from 2016 to 2020. Specimen sources included blood, sputum, alveolar lavage fluid, puncture fluid, secretions from a burn wound, and urine. Among the 87 carbapenem-resistant strains, ST11 was the predominant isolate, followed by ST15, ST273, ST340, and ST626. These STs were in broad agreement with the STs defined by pulsed-field gel electrophoresis clustering analysis in discriminating clusters of related strains. Most CRKP isolates contained the blaKPC-2 gene, some isolates carried the blaOXA-1, blaNDM-1, and blaNDM-5 genes, and the isolates carrying carbapenem resistance genes were more resistant to the antimicrobials of β-lactams, carbapenems, macrolides, and fluoroquinolone. The OmpK35 and OmpK37 genes were detected in all CRKP strains, and the Ompk36 gene was detected in some CRKP strains. All detected OmpK37 had 4 mutant sites, and OmpK36 had 11 mutant sites, while no mutant sites were found in OmpK35. More than half of the CRKP strains contained the OqxA and OqxB efflux pump genes. The virulence genes were most commonly combined with urea-wabG-fimH-entB-ybtS-uge-ycf. Only one CRKP isolate was detected with the K54 podoconjugate serotype. This study elucidated the clinical epidemiological features and molecular typing of CRKP, and grasped the distribution of drug-resistant genotypes, podocyte serotypes, and virulence genes of CRKP, providing some guidance for the subsequent treatment of CRKP infection.

Virulence, antimicrobial resistance, and molecular characteristics of carbapenem-resistant Klebsiella pneumoniae in a hospital in Shijiazhuang City from China

Carbapenem-resistant Klebsiella pneumoniae (CRKP), as one of the most common drug-resistant bacteria threatening human health, is hyper-resistant to multiple antimicrobial drugs and carbapenems, which can be dealt with only limited clinical treatment options. This study described the epidemiological characteristics of CRKP in this tertiary care hospital from 2016 to 2020. Specimen sources included blood, sputum, alveolar lavage fluid, puncture fluid, secretions from a burn wound, and urine. Among the 87 carbapenem-resistant strains, ST11 was the predominant isolate, followed by ST15, ST273, ST340, and ST626. These STs were in broad agreement with the STs defined by pulsed-field gel electrophoresis clustering analysis in discriminating clusters of related strains. Most CRKP isolates contained the blaKPC-2 gene, some isolates carried the blaOXA-1, blaNDM-1, and blaNDM-5 genes, and the isolates carrying carbapenem resistance genes were more resistant to the antimicrobials of β-lactams, carbapenems, macrolides, and fluoroquinolone. The OmpK35 and OmpK37 genes were detected in all CRKP strains, and the Ompk36 gene was detected in some CRKP strains. All detected OmpK37 had 4 mutant sites, and OmpK36 had 11 mutant sites, while no mutant sites were found in OmpK35. More than half of the CRKP strains contained the OqxA and OqxB efflux pump genes. The virulence genes were most commonly combined with urea-wabG-fimH-entB-ybtS-uge-ycf. Only one CRKP isolate was detected with the K54 podoconjugate serotype. This study elucidated the clinical epidemiological features and molecular typing of CRKP, and grasped the distribution of drug-resistant genotypes, podocyte serotypes, and virulence genes of CRKP, providing some guidance for the subsequent treatment of CRKP infection.

Polymyxin B and fusidic acid, a novel potent synergistic combination against Klebsiella pneumoniae and Escherichia coli isolates with polymyxin B resistance

The increasing prevalence of multidrug-resistant (MDR) Gram-negative bacteria and comparatively limited options of antibiotics pose a major threat to public health worldwide. Polymyxin B is the last resort against extensively resistant Gram-negative bacterial infections. However, a large number of Gram-negative bacteria exhibited high-level resistance to Polymyxin B, bringing challenges for antimicrobial chemotherapy. Combination therapies using polymyxins and other antibiotics are recommended to treat multidrug-resistant pathogens. In this study, we selected Gram-negative bacterial strains, including Klebsiella pneumoniae and Escherichia coli, to explore whether fusidic acid and polymyxin B have a synergistic killing effect. Through broth microdilution, we observed that minimum inhibitory concentrations (MICs) against polymyxin B in the isolates tested were significantly reduced by the addition of fusidic acid. Notably, chequerboard analysis indicated a synergistic effect between polymyxin B and fusidic acid. In addition, subsequent time-kill experiments showed that the combination of polymyxin B and fusidic acid was more effective than a single drug in killing bacteria. Finally, our investigation utilizing the murine model revealed a higher survival rate in the combination therapy group compared to the monotherapy group. Our research findings provide evidence of the synergistic effect between polymyxin B and fusidic acid. Fusidic acid was shown to increase the sensitivity of multi-drug resistant E. coli and K. pneumoniae to polymyxin B, thereby enhancing its bactericidal activity. This study provides new insights into a potential strategy for overcoming polymyxin B resistance, however, further investigations are required to evaluate their feasibility in real clinical settings.

Analysis on Bacterial Distribution and Change of Drug Resistance Rate in ICUs Across Southwest China from 2018 to 2022

Purpose

To analyze the distribution of bacteria and their drug resistance changes in Intensive Care Units (ICUs) across Southwest China from 2018 to 2022 and establish the antibiogram in this region to provide a basis for early empirical antimicrobial use.

Methods

Non-repetitive pathogens isolated from 109 member units with qualified data were obtained from the Antimicrobial Resistance Surveillance System in Sichuan Province, southwest China. The results obtained were interpreted with reference to CLSI M100-31th, and analyzed with WHONET 5.6 software.

Results

A total of 46,728 clinical isolates in ICUs were collected from 2018 to 2022, of which gram-negative organisms accounted for 76.1%, and gram-positive were 23.9%. The top 5 were Klebsiella pneumoniae, Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, respectively. From 2018 to 2022, the resistance rates of Klebsiella pneumoniae to imipenem and meropenem changed from 14.5% and 17.8% to 14.0% and 14.4%, showing a steady downward trend. Escherichia coli was always highly sensitive to carbapenems, with a total resistance rate of 3.8%. Among non-fermented gram-negative bacteria, the resistance rates of Pseudomonas aeruginosa to imipenem and meropenem decreased significantly, changed from 25.3% and 22.9% in 2018 to 20.0% and 15.1% in 2022. However, Acinetobacter baumannii showed high resistance rates of 76.2% and 76.9% to imipenem and meropenem, respectively. MRSA and MRCNS accounted for 31.7% and 82.7%, respectively. No vancomycin and linezolid-resistant Staphylococcus aureus was isolated. Enterococcus faecalis maintained high activity to vancomycin, teicoplanin, and linezolid; no vancomycin or teicoplanin-resistant Enterococcus faecium strains were detected.

Conclusion

From 2018 to 2022, the isolated bacteria in ICU were mainly gram-negative bacteria, and the growth of some multidrug-resistant bacteria was effectively controlled. All levels of medical institutions should continue to strengthen bacterial resistance surveillance, promote the establishment of antimicrobial stewardship program, and enhance restrictions on outpatient antimicrobial use.

Ceftolozane/tazobactam heteroresistance in cystic fibrosis-related Pseudomonas aeruginosa infections

Objectives

Cystic fibrosis (CF) patients are often colonized with Pseudomonas aeruginosa. During treatment, P. aeruginosa can develop subpopulations exhibiting variable in vitro antimicrobial (ABX) susceptibility patterns. Heteroresistance (HR) may underlie reported discrepancies between in vitro susceptibility results and clinical responses to various ABXs. Here, we sought to examine the presence and nature of P. aeruginosa polyclonal HR (PHR) and monoclonal HR (MHR) to ceftolozane/tazobactam in isolates originating from CF pulmonary exacerbations.

Methods

This was a single-centre, non-controlled study. Two hundred and forty-six P. aeruginosa isolates from 26 adult CF patients were included. PHR was defined as the presence of different ceftolozane/tazobactam minimum inhibitory concentration (MIC) values among P. aeruginosa isolates originating from a single patient specimen. Population analysis profiles (PAPs) were performed to assess the presence of MHR, defined as ≥4-fold change in the ceftolozane/tazobactam MIC from a single P. aeruginosa colony.

Results

Sixteen of 26 patient specimens (62%) contained PHR P. aeruginosa populations. Of these 16 patients, 6 (23%) had specimens in which PHR P. aeruginosa isolates exhibited ceftolozane/tazobactam MICs with categorical differences (i.e. susceptible versus resistant) compared to results reported as part of routine care. One isolate, PSA 1311, demonstrated MHR. Canonical ceftolozane/tazobactam resistance genes were not found in the MHR isolates (MHR PSA 1311 or PHR PSA 6130).

Conclusions

Ceftolozane/tazobactam PHR exists among P. aeruginosa isolates in this work, and approximately a quarter of these populations contained isolates with ceftolozane/tazobactam susceptibiilty interpretations different from what was reported clinically, supporting concerns surrounding the utility of traditional susceptibility testing methodology in the setting of CF specimens. Genome sequencing of isolates with acquired MHR to ceftolozane/tazobactam revealed variants of unknown significance. Future work will be centred on determining the significance of these mutations to better understand these data in clinical context.

The Etiological and Drug Resistance Characteristics of Multidrug-Resistant Pathogens in Patients Requiring Extracorporeal Membrane Oxygenation: A Retrospective Cohort Study

Purpose

Infections induced by multidrug-resistant (MDR) pathogens are one of the most common and serious complications in extracorporeal membrane oxygenation (ECMO) patients. However, there is currently little research about "ECMO and MDR bacteria". The purpose of our study was to clarify the epidemiological characteristics of MDR bacteria and provide references for empiric antibiotic treatments according to the drug susceptibility tests for ECMO patients.

Patients and Methods

There were 104 patients admitted to our department and receiving ECMO treatments between January 2014 and December 2022. Altogether, 61 veno-arterial ECMO (VA-ECMO) and 29 veno-venous ECMO (VV-ECMO) patients enrolled. The data on other intensive care unit (ICU) patients in our department in the same period are summarized.

Results

A total of 82 MDR bacteria were detected from ECMO patients, and most of these were MDR Gram-negative bacteria (MDR-GNB). There were also 5559 MDR-GNB collected from other patients in our department in the same period. We found that the distribution of MDR-GNB in ECMO patients was different from other critical patients. The proportion of Klebsiella pneumoniae (MDR-KP) in VV-ECMO patients was higher than other critical patients (35.1% and 21.3%, respectively). Moreover, the proportions of MDR Acinetobacter baumannii (MDR-AB) of VA-ECMO and VV-ECMO were higher than other critical patients (54.6%, 43.2% and 30.5%, respectively). In addition, MDR-AB and MDR-KP in ECMO patients exhibited higher percentages of drug resistance to possibly appropriate antibiotics for other critical patients, but showed better sensitivity to colistin.

Conclusion

Infections induced by MDR-GNB in ECMO patients were serious and exhibited higher degrees of drug resistance compared with other ICU patients. Colistin might be an option to consider if there is no medical contraindication. However, widespread use of broad spectrum antibiotics is something that should be discouraged, and alternative options are being explored.

Insight into Antibiotic Synergy Combinations for Eliminating Colistin Heteroresistant Klebsiella pneumoniae

Colistin heteroresistance has been identified in several bacterial species, including Escherichia coli and Klebsiella pneumoniae, and may underlie antibiotic therapy failures since it most often goes undetected by conventional antimicrobial susceptibility tests. This study utilizes population analysis profiling (PAP) and time-kill assay for the detection of heteroresistance in K. pneumoniae and for evaluating the association between in vitro regrowth and heteroresistance. The mechanisms of colistin resistance and the ability of combination therapies to suppress resistance selection were also analysed. In total, 3 (18%) of the 16 colistin-susceptible strains (MIC ≤ 2 mg/L) were confirmed to be heteroresistant to colistin by PAP assay. In contrast to the colistin-susceptible control strains, all three heteroresistant strains showed regrowth when exposed to colistin after 24 h following a rapid bactericidal action. Colistin resistance in all the resistant subpopulations was due to the disruption of the mgrB gene by various insertion elements such as ISKpn14 of the IS1 family and IS903B of the IS5 family. Colistin combined with carbapenems (imipenem, meropenem), aminoglycosides (amikacin, gentamicin) or tigecycline was found to elicit in vitro synergistic effects against these colistin heteroresistant strains. Our experimental results showcase the potential of combination therapies for treatment of K. pneumoniae infections associated with colistin heteroresistance.

The Efficacy and Influencing Factors of Polymyxin B in High-Level Carbapenem-Resistant Klebsiella pneumoniae Infections

Background

Polymyxin B (PMB) is a remedial treatment for carbapenem-resistant Klebsiella pneumoniae (CRKP) infection; however, there is a paucity of reports on the treatment of high-level CRKP infections with polymyxin B. Studies are needed to explore its treatment efficacy and associated influencing factors.

Methods

Patients with high-level CRKP infections treated with PMB during hospitalization from June 2019 to June 2021 in a hospital were retrospectively studied, and risk factors affecting the efficacy were explored by subgroup analysis.

Results

A total of 92 patients were enrolled, and the results showed that the PMB-based regimen had a bacterial clearance rate of 45.7%, an all-cause discharge mortality rate of 22.8%, and an incidence of acute kidney injury (AKI) of 27.2% for high-level CRKP treatment. The combination of β-lactams other than carbapenems facilitated bacterial clearance, and the combination of electrolyte disturbances and higher APACHE II scores was detrimental to microbial clearance. Risk factors for all-cause discharge mortality were advanced age, concomitant antifungal drugs, concomitant tigecycline and incidence of AKI.

Conclusion

PMB-based regimens are an effective option for the treatment of high-level CRKP infections. However, the optimal dose of treatment and the choice of combination regimens need to be explored in further studies.

Multiple heteroresistance to tigecycline and colistin in Acinetobacter baumannii isolates and its implications for combined antibiotic treatment

BACKGROUND

We investigated the presence of heteroresistance against both tigecycline and colistin in Acinetobacter baumannii and then evaluated the effectiveness of combined antibiotic treatment given the existence of discrete tigecycline- and colistin-resistant subpopulations.

METHODS

We performed population analysis profiling (PAP) to evaluate the degree of composite heteroresistance in A. baumannii isolates, with the extent of this resistance quantified using subsequent antibiotic susceptibility testing. We then evaluated the amino acid sequence of PmrBAC and the relative mRNA expression levels of pmrB. Finally, we investigated the combined antibiotic efficacy of tigecycline and colistin in multiple-heteroresistant isolates using dual PAP and in vitro time-killing assays.

RESULTS

All tigecycline-heteroresistant A. baumannii isolates, with the exception of one colistin-resistant isolate, were also heteroresistant to colistin. Evaluations of the colistin-resistant subpopulations revealed amino acid alterations in PmrA and PmrB and increased expression of pmrB. All tigecycline-resistant subpopulations were susceptible to colistin, and all colistin-resistant subpopulations were susceptible to tigecycline. Dual PAP analysis using tigecycline and colistin showed no heteroresistance, and in vitro time-killing assays revealed that a combination of these two antibiotics effectively eliminated the bacterial cells.

CONCLUSION

Our results suggest that multiple heteroresistance to tigecycline and colistin is highly prevalent among A. baumannii clinical isolates and that these resistant subpopulations exist independently in single multiple heteroresistant isolates. Therefore, our findings may explain the success of combined antibiotic therapies in these infections.

Secondary bacterial infection caused by ST16 NDM-1 and OXA-48-producing colistin and carbapenem-resistant Klebsiella pneumoniae treated with tigecycline in a pregnant woman with COVID-19

During the COVID-19 pandemic, the rapid emergence of carbapenem and colistin-resistant Klebsiella pneumoniae has resulted in an alarming situation worldwide. We aimed to describe secondary infections and antimicrobial use, in a pregnant woman admitted to hospital with COVID-19. A 28-year-old pregnant woman was admitted to the hospital due to COVID-19. According to the clinical conditions, the patient was transferred to the ICU on the second day. She was empirically treated with ampicillin and clindamycin. Mechanical ventilation through an endotracheal tube was started on the 10th day. During her hospitalization in the ICU, she was infected with ESBL-producing K. pneumonia, Enterobacter spp and carbapenemase-producing colistin-resistant Klebsiella pneumoniae isolates. Finally, the patient was treated with tigecycline monotherapy that was associated with ventilator-associated pneumonia clearance. Bacterial co-infection is relatively infrequent in hospitalized patients with COVID-19. Treatment of infections caused by carbapenemase-producing colistin-resistant K. pneumoniae isolates is challenging, with limited antimicrobials available in Iran. In order to prevent the spread of extensively drug-resistant bacteria, infection control programs must be implemented more seriously.

Pathogen Distribution, Drug Resistance Risk Factors, and Construction of Risk Prediction Model for Drug-Resistant Bacterial Infection in Hospitalized Patients at the Respiratory Department During the COVID-19 Pandemic

Objective

To investigate the distribution and drug resistance of pathogens among hospitalized patients in the respiratory unit during the COVID-19 pandemic, analyze the risk factors of drug resistance, construct a risk prediction model.

Methods

This study isolated 791 strains from 489 patients admitted to the Affiliated Hospital of Chengdu University, who were retrospectively enrolled between December 2019 and June 2021. The patients were divided into training and validation sets based on a random number table method (8:2). The baseline information, clinical characteristics, and culture results were collected using an electronic database and WHONET 5.6 software and compared between the two groups. A risk prediction model for drug-resistant bacteria was constructed using multi-factor logistic regression.

Results

K. pneumoniae (24.78%), P. aeruginosa (17.19%), A. baumannii (10.37%), and E. coli (10.37%) were the most abundant bacterial isolates. 174 isolates of drug-resistant bacteria were collected, ie, Carbapenem-resistant organism-strains, ESBL-producing strains, methicillin-resistant S. aureus, multi-drug resistance constituting 38.51%, 50.57%, 6.32%, 4.60%, respectively. The nosocomial infection prediction model of drug-resistant bacteria was developed based on the combined use of antimicrobials, pharmacological immunosuppression, PCT>0.5 ng/mL, CKD stage 4-5, indwelling catheter, and age > 60 years. The AUC under the ROC curve of the training and validation sets were 0.768 (95% CI: 0.624-0.817) and 0.753 (95% CI: 0.657-0.785), respectively. Our model revealed an acceptable prediction demonstrated by a non-significant Hosmer-Lemeshow test (training set, p=0.54; validation set, p=0.88).

Conclusion

K. pneumoniae, P. aeruginosa, A. baumannii, and E. coli were the most abundant bacterial isolates. Antimicrobial resistance among the common isolates was high for most routinely used antimicrobials and carbapenems. COVID-19 did not increase the drug resistance pressure of the main strains. The risk prediction model of drug-resistant bacterial infection is expected to improve the prevention and control of antibacterial-resistant bacterial infection in hospital settings.

Ceftazidime/Avibactam, Polymyxin or Tigecycline as a Rescue Strategy for the Treatment of Carbapenem-Resistant Klebsiella pneumoniae in Bloodstream Infection: A Retrospective Cohort Study

Objective

To analyze the clinical characteristics, outcomes, and risk factors of patients treated with ceftazidime/avibactam, polymyxin, or tigecycline (CPT) compared with those receiving a conventional therapy (CT) (ie, imipenem, levofloxacin, or gentamicin).

Methods

A single-center retrospective cohort study included patients with carbapenem-resistant Klebsiella pneumoniae bloodstream infection (CRKP-BSI) treated at one Chinese tertiary hospital between March 2012 and November 2022 was performed. Clinical characteristics, outcomes, and risk factors of patients treated with CPT or CT were compared. Predictors of 30-day mortality of patients with CRKP-BSI were also analysed in our study.

Results

Among 184 recruited patients with CRKP-BSI, 39.7% (73/184) were treated with CPT, while 60.3% (111/184) were treated with CT. Compared to patients treated with CT, patients treated with CPT had worse conditions, as evidenced by a higher rate of underlying diseases and invasive procedures; however, they also had a better prognosis and lower rates of 14-day treatment failure (p = 0.024). In addition, univariate analysis and multivariate analysis showed that SOFA score [odds ratio (OR) = 1.310, 95% confidence interval (CI) 1.157-1.483; p < 0.001] and cold weather (OR = 3.658, 95% CI 1.474-9.081; p = 0.005) were independent risk factors for 30-day mortality.

Conclusion

Compared to CRKP-BSI patients treated with CT, patients treated with CPT had worse conditions but better prognoses. CRKP-BSI occurred more frequently in hot weather; however, higher 30-day mortality was associated with cold weather. A randomized trial is needed to confirm these observational results.

Lumbar Cistern Drainage and Gentamicin Intrathecal Injection in the Treatment of Carbapenem-Resistant Klebsiella Pneumoniae Intracranial Infection After Intracerebral Hemorrhage craniotomy: A Case Report

Background

Intracranial infection is a common complication caused by craniotomy. In particular, patients in Intensive Care Units (ICU) are prone to intracranial infection with multiple drug-resistant bacteria. Due to the lack of sensitive antibiotics for the treatment of multiple drug-resistant bacteria, there are few literatures focusing on the treatment of intracranial infection, and patients often fail to receive unified and standardized treatment. Consequently, patients with Carbapenem-resistant bacteria intracranial infection report poor prognosis and high mortality. It is very important to discuss how to treat patients with intracranial infection caused by multidrug resistant bacteria.

Case Presentation

We reported a case of intracranial infection of Carbapenem-resistant Klebsiella pneumoniae(CRKp) due to high flap tension, poor wound healing and CSF leakage caused by subcutaneous fluid accumulation after intracerebral hemorrhage craniotomy. Since the patient was exposed to intracranial infection resulted from subcutaneous fluid accumulation, we adopted the method of continuous drainage with subcutaneous tube. When subcutaneous effusion disappeared, the subcutaneous drainage tube was pull out, while patients exhibited high fever again, the waist big pool drainage catheter and continuous drainage were carried out. According to the result of Subcutaneous effusion and CSF culture indicated multiple drug resistant Klebsiella pneumoniae intracranial infection and drug susceptibility, The treatment of gentamicin intrathecal injection, intravenous use amikacin and oral Paediatric Compound Sulfamethoxazole Tablets was adopted, the condition of intracranial infection was eventually controlled, with the consciousness restored. This patient was characterized by intracranial infection with Carbapenem-resistant Klebsiella pneumoniae(CRKp).

Conclusions

Subcutaneous effusion is a high-risk factor for poor wound healing and interventions are required to be conducted to promote healing as early as possible to contribute to decreasing the menace of CSF leakage. In this case, Continuous drainage and intrathecal injection of sensitive antibiotics serve as critical process to determine the best strategy for clinical treatment of intracranial infection.

Causes of polymyxin treatment failure and new derivatives to fill the gap

Polymyxins are a class of antibiotics that were discovered in 1947 from programs searching for compounds effective in the treatment of Gram-negative infections. Produced by the Gram-positive bacterium Paenibacillus polymyxa and composed of a cyclic peptide chain with a peptide-fatty acyl tail, polymyxins exert bactericidal effects through membrane disruption. Currently, polymyxin B and colistin (polymyxin E) have been developed for clinical use, where they are reserved as "last-line" therapies for multidrug-resistant (MDR) infections. Unfortunately, the incidences of strains resistant to polymyxins have been increasing globally, and polymyxin heteroresistance has been gaining appreciation as an important clinical challenge. These phenomena, along with bacterial tolerance to this antibiotic class, constitute important contributors to polymyxin treatment failure. Here, we review polymyxins and their mechanism of action, summarize the current understanding of how polymyxin treatment fails, and discuss how the next generation of polymyxins holds promise to invigorate this antibiotic class.

Relationships between Efflux Pumps and Emergence of Heteroresistance: A Comprehensive Study on the Current Findings

Heteroresiatnce (HR) is the type of resistance toward one or more antibiotics appearing as a population of the bacterial load consisting of one or more subpopulations with lower antibiotic susceptibility levels than others. Due to the lack of appropriate diagnosis of HR isolates and their importance in resistance emergence to antibiotics, investigating the origins, emergence factors, and HR inhibitors is critical in combating antibiotic resistance. Efflux pumps (EPs) are bacterial systems that own an influential role in acquiring resistance toward anti-bacterial compounds. Studies on EPs revealed that they can affect HR emergence mechanisms and are competent to be introduced as a suitable bacterial target for diagnostic and therapeutic development in combating HR isolates. This review will consider the relations between EPs and the emergence of HR isolates and discuss their importance in confronting this type of antibiotic resistance.

Risk Factors for the Development of Colistin Resistance during Colistin Treatment of Carbapenem-Resistant Klebsiella pneumoniae Infections

Colistin is one of the last-resort options for carbapenem-resistant Klebsiella pneumoniae (CRKP) infections if novel antibiotics are unavailable, where the development of colistin resistance during treatment represents a major challenge for clinicians. We aimed to investigate the risk factors associated with the development of colistin resistance in patients with CRKP infections following colistin treatment. We conducted a retrospective case-control study of patients with CRKP strains available before and after colistin treatment at a medical center in Taiwan, between October 2016 and November 2020. Cases (n = 35) included patients with an initial colistin-susceptible CRKP (ColS-CRKP) strain and a subsequent colistin-resistant CRKP (ColR-CRKP) strain. Controls (n = 18) included patients with ColS-CRKP as both the initial and subsequent strains. The 30-day mortality rate after the subsequent CRKP isolation was not different between cases and controls (12/35 [34%] versus 5/18 [28%] [P = 0.631]). blaKPC (n = 38) and blaOXA-48 (n = 11) accounted for the major mechanisms of carbapenem resistance. Alterations in mgrB were found in 18/35 (51%) ColR-CRKP strains, and mcr-1 was not detected in any of the strains. More patients received combination therapy in the control group than in the case group (17/18 versus 21/35 [P = 0.008]). The logistic regression model indicated that combination therapy with tigecycline was protective against the acquisition of colistin resistance (odds ratio, 0.17; 95% confidence interval, 0.05 to 0.62 [P = 0.008]). We observed that the inclusion of tigecycline in colistin treatment mitigated the risk of acquiring colistin resistance. These results offer insight into using the combination of tigecycline and colistin for the treatment of CRKP infections in antimicrobial stewardship. IMPORTANCE Treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) infections is challenging due to the limited options of antibiotics. Colistin is one of the last-resort antibiotics if novel antimicrobial agents are not available. It is crucial to identify modifiable clinical factors associated with the emergence of resistance during colistin treatment. Here, we found that the addition of tigecycline to colistin treatment prevented the acquisition of colistin resistance. Colistin-tigecycline combination therapy is therefore considered a hopeful option in antimicrobial stewardship to treat CRKP infections.

Heteroresistance Is Associated With in vitro Regrowth During Colistin Treatment in Carbapenem-Resistant Klebsiella pneumoniae

Polymyxins including polymyxin B and colistin (polymyxin E) are considered the last resort for treating infections caused by carbapenem-resistant gram-negative bacteria. However, in vitro regrowth with the emergence of resistance during treatment is common. Polymyxin heteroresistance, particularly in Acinetobacter baumannii and Klebsiella pneumoniae, has been widely reported. This study was primarily performed to evaluate the prevalence of colistin heteroresistance in carbapenem-resistant K. pneumoniae (CR-KP) and the association between in vitro regrowth and heteroresistance. The mechanisms of colistin resistance and the ability of combination therapies to suppress resistance selection were further investigated. A population analysis profile (PAP) analysis showed that 69 (71.9%) of 96 CR-KP strains had colistin heteroresistance. Time-kill assays revealed that the colistin monotherapy could quickly eliminate the bacterial cells in strains without heteroresistance within the first 6 h. Conversely, it could initially reduce the number of cells in heteroresistant strains, but then regrowth occurred rapidly. Resistance screening at 12 and 24 h in the time-kill assays indicated that susceptible populations were killed, and regrowth was the exact result of the continued growth of resistant subpopulations. Colistin resistance in the regrowth subpopulations was mainly due to the overexpression of phoPQ and pmrD. Colistin combined with tetracyclines (tigecycline or minocycline) or aminoglycosides (amikacin or gentamicin) could effectively suppress the resistance selection and significantly elicit in vitro synergistic effects. These findings suggested that the combination therapy can be used to treat infections caused by CR-KP with colistin heteroresistance. Nevertheless, further in vivo studies considering drugs pharmacokinetics/pharmacodynamics are needed to confirm these findings.

Antibiotic Heteroresistance in Klebsiella pneumoniae

Klebsiella pneumoniae is one of the most common pathogens responsible for infections, including pneumonia, urinary tract infections, and bacteremias. The increasing prevalence of multidrug-resistant K. pneumoniae was recognized in 2017 by the World Health Organization as a critical public health threat. Heteroresistance, defined as the presence of a subpopulation of cells with a higher MIC than the dominant population, is a frequent phenotype in many pathogens. Numerous reports on heteroresistant K. pneumoniae isolates have been published in the last few years. Heteroresistance is difficult to detect and study due to its phenotypic and genetic instability. Recent findings provide strong evidence that heteroresistance may be associated with an increased risk of recurrent infections and antibiotic treatment failure. This review focuses on antibiotic heteroresistance mechanisms in K. pneumoniae and potential therapeutic strategies against antibiotic heteroresistant isolates.