Introduction

Klebsiella pneumoniae (K. pneumoniae) is a Gram-negative bacillus and is currently one of the most common nosocomial pathogens worldwide. Based on its phenotypic and genotypic characteristics, it can be classified into classical Klebsiella pneumoniae (cKP) and hypervirulent Klebsiella pneumoniae (hvKP).1 HvKP is more toxic and is a major cause of K. pneumoniae-related liver abscess (KLA).2 Due to the widespread use of antibiotics, CRKP is increasing globally. Notably, in sequence typing (ST), ST11 is the predominant strain among CRKP in China, accounting for the vast majority of CRKP isolates.3 The multidrug resistance and high mortality of CRKP pose significant challenges to clinical management.4 Notably, CRKP infections are often more difficult to treat and cure in patients with diabetes.5

Diabetes is a group of metabolic disorder diseases characterized by hyperglycemia.6 Past studies have shown diabetes is mainly related to the occurrence of non-infectious metabolic diseases.7 However, recent studies have shown that diabetes is also a key risk factor for the poor prognosis of infectious diseases.8,9 Diabetes can be diagnosed by detecting the patient’s HbA1c level or blood glucose levels, including the fasting plasma glucose (FPG) value, the 2-hour glucose (2-h PG) value during a 75-g oral glucose tolerance test (OGTT), or random blood glucose levels. HbA1c directly reflects the patient’s average blood glucose level over nearly three months. Compared to blood glucose detection, HbA1c offers several advantages, such as greater sensitivity and less variation during periods of stress, dietary changes, or illness.6

Studies have pointed out that diabetes increases the colonization and susceptibility of K. pneumoniae.10 In patients with primary liver abscesses caused by hvKP, glycemic control significantly affect disease progression. Compared to non-diabetic infected patients, those with diabetes are more prone to metastatic infections, often have longer hospital stays, and are at a higher risk of death.5,11,12 However, most of these previous studies focused on exploring the relationship between glycemic control and hvKP-related infections. Currently, there is insufficient discussion on the relationship between blood glucose levels and drug-resistant K. pneumoniae infections. Regarding whether blood glucose levels affect the susceptibility to drug-resistant K. pneumoniae, some studies suggest that patients with hyperglycemia are more likely to carry drug-resistant bacteria, particularly multidrug-resistant K. pneumoniae.13–15 In this context, we need to further understand the impact of blood glucose levels on the epidemiological characteristics of patients infected with CRKP.

Capsular polysaccharide is one of the most important virulence factors of K. pneumoniae. Studies have shown that glucose can influence the synthesis of bacterial CPS, thereby affecting bacterial virulence. This process is regulated by the global regulator, the cyclic adenosine monophosphate (cAMP) receptor protein (CRP).16 Additionally, it has been found that a hyperglycemic environment enhances bacterial resistance to neutrophil phagocytosis and leukocyte killing by stimulating the production of K. pneumoniae CPS and the expression of related genes, thereby further promoting the development of invasive syndromes.17 In the process of controlling bacterial invasive infections, the clearance of pathogens by serum is also a crucial step.1 However, few studies currently exist on how bacterial resistance to serum killing changes under hyperglycemic conditions.

Polymyxin is a cationic antimicrobial peptide that exerts bactericidal activity by disrupting the stability of the bacterial outer membrane, serving as a last line of defense in the treatment of CRKP. Among the polymyxin family, polymyxin B (PB) and polymyxin E are clinically used to treat drug-resistant Gram-negative bacilli due to their minimal nephrotoxicity. Unfortunately, polymyxin-resistant carbapenem-resistant Klebsiella pneumonia (PR-CRKP) has emerged18 Both the CPS and lipopolysaccharide (LPS) are negatively charged outer membrane structures of K. pneumoniae, while the positively charged polymyxin exerts its effect primarily by binding to LPS. Lipopolysaccharide modification is the primary mechanism of polymyxin resistance in PR-CRKP. However, studies also suggest that the amount of capsule synthesis largely affects polymyxin resistance, as free capsules can neutralize polymyxin and decrease its binding to LPS.19,20K. pneumoniae with reduced capsule synthesis exhibits a lower survival rate in the presence of polymyxin,21 while the addition of purified CPSs can enhance its resistance.20 There are also studies pointing out that the hyperglycemic environment may affect polymyxin resistance by changing bacterial capsule expression. Fan et al found in alcohol-producing K. pneumoniae that glucose can enhance bacterial resistance to polymyxin by inducing capsule synthesis.22 However, the specific effects of glucose on CRKP capsule synthesis and polymyxin resistance remain unclear.

This study aims to explore the impact of glycemic control on the epidemiological characteristics of patients infected with CRKP and to analyze the risk factors for infection-related mortality during hospitalization. Additionally, this study will detect the effect of high-glucose environment on CRKP capsule production in vitro and further explore how CRKP resistance to polymyxin and serum killing changes under high glucose concentration.

Materials and Methods Research Design

A single-center retrospective cohort study design was adopted. A total of 218 clinically isolated CRKP strains which were collected from a large tertiary grade A hospital in Anhui Province between January 2019 and June 2024 were analyzed. Duplicate strain isolates were excluded. Clinical information on patients was obtained through the hospital’s case system, and strain identification and antimicrobial susceptibility testing were performed in the microbiology laboratory. Ethical approval for the study was obtained from the hospital’s institutional review board (approval numbers: KYLL20240200, LLSC20240703).

Data Collection

This study collected data on gender, age, specimen type, comorbidities, complications, invasive procedures, surgical history, clinical outcomes, and laboratory tests from the medical record system for patients. Notably, chronic obstructive pulmonary disease (COPD) encompasses chronic bronchitis and emphysema in this study. The laboratory tests conducted included assessments of HbA1c, C-reactive protein (CRP), white blood cells (WBC), neutrophils (Neut), lymphocytes (Lymph), and platelets (PLT). Patients were categorized into two groups based on HbA1c levels: those with HbA1c less than 7% and those with HbA1c 7% or greater.

Identification of Isolates and Drug Susceptibility Testing

All isolated strains were identified using the Microflex-LT/SH mass spectrometer (BRUKER, Germany). Use the VITEK 2 Compact automatic bacterial analyzer (with card numbers AST-N334 and AST-N335) from BioMérieux, France, or the Kirby-Bauer Disk Diffusion method from Oxoid, UK to detect the antimicrobial susceptibility of CRKP. Antimicrobial susceptibility results were analyzed in accordance with the guidelines of the Clinical and Laboratory Standards Institute (CLSI) issued in 2019. According to the guidelines of the CLSI, Klebsiella pneumoniae identified as resistant to any carbapenem antibiotic is confirmed as a CRKP strain.23

Capsular Serotype, MLST and Virulence Genotype Testing

According to the method of Sylvain Brisse and others,24 bacteria were cultured on blood agar plates and isolated and purified. A single colony was picked and suspended in 200μL of PBS, heated at 94°C for 10 minutes, and then centrifuged at 7500×g for 5 minutes. The supernatant was aspirated to prepare a DNA template and stored at −20°C. Capsular serotyping of CRKP was performed using wzi gene sequencing. The PCR products were detected by 1% agarose gel electrophoresis. Once the sample quality was confirmed, it was sent to Sangon Biotech (Shanghai, China) for sequencing. The sequencing results were compared on the website (https://bigsdb.pasteur.fr/klebsiella/). Multilocus sequence typing (MLST) was employed to determine the ST of CRKP, following the K. pneumoniae MLST protocol published on the MLST website of the Institut Pasteur, France (http://bigsdb.pasteur.fr/). The virulence genes of CRKP, including rmpA, rmpA2, and iucA, were detected by PCR combined with agarose gel electrophoresis. The primers were synthesized according to relevant literature reports25 (see Table 1 for details).

Table 1 The Primer Sequences Used in This Study

Glucuronic Acid Quantification

The hypervirulent Klebsiella pneumoniae strain ATCC43816 and three CRKP strains isolated from participants were selected as representative strains for subsequent experiments. The three clinically isolated strains, all belonging to ST11, were named CRKP28, CRKP70, and CRKP214, respectively. Among them, CRKP28 and CRKP70 were from the group with HbA1c ≥ 7%, while CRKP214 was from the group with HbA1c < 7%. The main component (glucuronic acid) of the capsule of K. pneumoniae was extracted by the hot phenol water bath method. The research method is essentially similar to previously described methods.24 The bacteria were centrifuged at high speed for 5–10 minutes, and the resulting bacterial pellet was resuspended in sterile water and incubated at 68°C for 2 minutes. Simultaneously, the bacterial suspension was continuously diluted and the concentration was determined. Then an equal volume of 75% phenol was added and incubation was continued for 30 minutes. After the sample was allowed to return to room temperature, chloroform was added, and the mixture was centrifuged to obtain the supernatant. CPS was then precipitated with anhydrous ethanol at −20°C. A standard curve was generated by the phenol sulfuric acid method. The concentrated sulfuric acid and 5% phenol solution were ice-bathed and mixed at a ratio of 5:1 as a chromogenic solution. The glucose standard solution and the samples to be tested were each reacted with the chromogenic solution at high temperature. The standard curve was drawn by measuring the OD490 value, and the capsule concentration was calculated.

Polymyxin B Time-Bactericidal Curve Assay and Serum Bactericidal Assay

To investigate the effect of glucose on Klebsiella pneumoniae polymyxin resistance, we selected polymyxin B (Sangon Biotech, Shanghai, China) as a representative polymyxin drug. Polymyxin B time-bactericidal curve experiments were conducted following the method described by Fan et al.22 Briefly, the purified bacteria were incubated in Luria-Bertani (LB) medium with or without glucose, until logarithmic growth phase. The bacterial solution was then diluted into fresh medium to achieve a glucose concentration of 0.5% and a polymyxin concentration of 1 × MIC. The cultures were incubated in a constant temperature shaker at 37°C. At 0, 1, 2, 3, and 4 hours, equal volumes of bacterial suspensions were removed, serially diluted, and inoculated onto Mueller-Hinton (MH) plates. The plates were then incubated overnight for colony counting. To evaluate Klebsiella pneumoniae resistance to serum killing under hyperglycemic conditions, we collected sera from eight healthy males and eight healthy females at the clinic and mixed them to serve as bacterial media. The bacterial suspension, cultured with or without glucose, was diluted to a concentration of 5 x 10^5 CFU/mL. We then took 25μL of the diluted bacterial solution and 75μL of donor serum, mixed them, and co-incubated the mixture at 37°C. Bacterial survival was assessed consecutively at each hour for the first 3 hours.26

Data Analysis

Data were analyzed and figures were plotted using SPSS 26.0 and Graphpad Prism 10.0 software. Statistical comparisons were performed using the chi-square test, Fisher’s exact test, or Mann–Whitney U-test, depending on the data type. Univariate and multivariate Logistic regression analyses were employed to identify risk factors. The P value less than 0.05 was used to determine whether there was a statistically significant difference between groups.

Results Clinical Characteristics of Patients With CRKP Infection in the Good and Poor Glycemic Control Groups

Among all CRKP-infected patients, 68.3% were male and 31.7% were female. The median age was 65 (50.0~77.25) years. The main underlying diseases were hypertension (43.1%) and diabetes mellitus (23.4%), followed by coronary artery disease (15.1%) and tumors (14.2%). Patients with poor glycemic control had a higher prevalence of comorbid CKD (16.0% vs 5.4%, P<0.05) and acute renal insufficiency (30.0% vs 15.5%, P<0.05) compared to those with good glycemic control. Among patients receiving deep vein catheterization, those with poor glycemic control had a higher likelihood of CRKP infection (78.0% vs 61.3%, P=0.030). Laboratory tests showed significantly higher levels of CRP, WBC, and NE in patients with poor glycemic control (P<0.01). Patients with poor glycemic control were more likely to develop sepsis subsequent to CRKP infection compared to those with good glycemic control (32.0% vs 23.8%, P>0.05). Furthermore, patients had a significantly higher mortality rate with poor glycemic control (48.0% vs 23.8%, P=0.001). (For detailed results, see Table 2).

Table 2 General Demographic and Clinical Characteristics of 218 CRKP Infected Patients

Microbial Capsular Serotyping, Virulence Gene Detection and Drug Susceptibility Test Results

Among the 218 collected CRKP strains, we detected the K64 capsular serotype with the highest current prevalence and three major virulence genes (rmpA, rmpA2, and iucA) of CRKP. As shown in Table 3, the carrying rates of the virulence genes were highest for iucA (68.8%), followed by rmpA2 (45.4%). No significant differences were observed in the distribution of carrying rates for the three virulence genes or the K64 capsular serotype between the two groups. The susceptibility test results in Table 4 indicate that all clinically isolated bacteria exhibited broad resistance to carbapenems, penicillins, cephalosporins, cephamycin, and quinolones. Resistance rates to amikacin and compound sulfamethoxazole also exceeded 50%. In contrast, resistance rates to ceftazidime/avibactam, tigecycline, and polymyxin were relatively low, at 30.3%, 19.3%, and 4.6%, respectively. Studies have suggested a potential link between high-glucose environments and polymyxin resistance. Consistent with these findings, our study found that patients with poor glycemic control had a higher probability of infection with PR-CRKP than those with good glycemic control (8.0% vs 3.6%, P > 0.05). However, this difference did not reach statistical significance. This may be attributed to the relatively low overall detection rate of PR-CRKP, which resulted in a non-significant difference.

Table 3 The Capsular Serotypes and Virulence Factors of the Two Groups of CRKP Strains

Table 4 The Antibiotic Resistance of 218 Clinical Isolates of CRKP Strains

Analysis of Risk Factors for Death in Patients With CRKP Infection

Univariate Logistic regression analysis identified several independent risk factors for death in patients with CRKP infection, including age, HbA1c ≥7%, CKD, tumor, glucocorticoid treatment, mechanical ventilation, flexible fiberoptic bronchoscopy (FFB), deep vein catheterization, gastric tube insertion, urinary catheterization, ICU admission, and sepsis. (The detailed results are presented in Table 5). After adjusting for confounding factors, multivariate Logistic regression analysis identified independent risk factors for death in patients with CRKP infection. These included age (OR=1.024, 95% CI=1.003–1.044, P=0.021), HbA1c ≥7% (OR=2.417, 95% CI=1.155–5.055, P=0.019), CKD (OR=8.322, 95% CI=2.534–27.326, P< 0.001), tumor (OR = 4.562, 95% CI=1.811–11.492, P=0.001), mechanical ventilation (OR=4.586, 95% CI=2.000–10.517, P<0.001), and sepsis (OR=2.270, 95% CI=1.110–4.642, P=0.025). (See Figure 1).

Table 5 Univariate Logistic Regression Analysis of Mortality Risk Factors for CRKP Infection

Figure 1 Multivariable Logistic regression analysis of mortality risk factors for CRKP infection.

The Influence of Glucose and cAMP on the Production of Capsule of CRKP

To evaluate the impact of a high-glucose environment on the capsule synthesis of Klebsiella pneumoniae, this study performed quantitative capsule assessments on the hypervirulent Klebsiella pneumoniae ATCC43816 and three clinically isolated CRKP strains (ST11). Initially, bacterial suspensions in the logarithmic growth phase were subjected to low-speed centrifugation (3000×g for 10 minutes). Figure 2A–D illustrates the state of the centrifuged suspensions of ATCC43816 and three clinically isolated CRKP strains. Compared to the suspensions cultured in LB medium alone, those co-incubated with glucose were more viscous and resistant to sedimentation at the bottom of the centrifuge tubes. The addition of cAMP facilitated the sedimentation of the suspensions. Subsequent quantitative polysaccharide extraction experiments demonstrated that exogenous glucose significantly enhanced capsular polysaccharide synthesis in ATCC43816 and the three clinical CRKP isolates (P < 0.05). Moreover, this increase in bacterial capsular polysaccharide synthesis was inhibited by cAMP (2 mm) (Figure 3A–D).

Figure 2 ATCC43816 (A), CRKP28 (B), CRKP70 (C), and CRKP214 (D) were separately cultured in LB broth, LB broth supplemented with 0.5% glucose (LB + 0.5% Glu), and LB broth with 0.5% glucose and 2 mm cyclic adenosine monophosphate (LB + 0.5% Glu + 2 mm cAMP) to the logarithmic phase of growth. Subsequently, the cultures were centrifuged at 3000 rpm for 10 minutes to obtain the bacterial pellets.

Figure 3 A high-glucose environment can stimulate the synthesis of CRKP capsules. ATCC43816 (A), clinical isolates CRKP28 (B), CRKP70 (C), and CRKP214 (D) were cultured in media with or without 0.5% glucose or with or without 2mM cAMP until they reached the logarithmic growth phase, after which the capsule polysaccharides of the bacteria were quantitatively extracted according to the hot phenol water bath method. *, P<0.05, ***, P<0.001, ****, P<0.0001.

Abbreviation: n.s., not significant.

Glucose Enhances the Resistance of CRKP to Polymyxin and Serum Killing

This study explored the influence of elevated glucose concentration on the resistance of Klebsiella pneumoniae to polymyxin and serum killing through bactericidal curve experiments. Polymyxin showed bactericidal activity against the experimental strains, and bacterial counts at different time points indicated that the survival rate of bacteria decreased over time. As shown in Figure 4A–D, there was no significant difference in the bacterial growth curves between the presence and absence of 0.5% glucose. However, the survival rate of ATCC43816 and the three clinical CRKP isolates in polymyxin was significantly higher in the presence of 0.5% glucose than in its absence (P < 0.001). The serum bactericidal assay results indicated that the survival rate of ATCC43816 was enhanced when cultured in LB broth with 0.5% glucose compared to LB broth alone (Figure 5A). In contrast to the hypervirulent Klebsiella pneumoniae strain ATCC43816, the clinical strains (CRKP28, CRKP70, and CRKP214) showed weaker resistance to serum killing. However, the survival rates of the CRKP strains were significantly higher when grown in LB medium with 0.5% glucose compared to glucose-free medium (Figure 5B–D).

Figure 4 ATCC43816 and CRKP strains exhibited enhanced resistance to polymyxins under glucose-rich conditions. ATCC43816 (A) and CRKP strains CRKP28 (B), CRKP70 (C), and CRKP214 (D) were first pre-cultured in LB medium with and without 0.5% glucose, and then treated with polymyxin B at a concentration of 1×MIC in the presence and absence of 0.5% glucose. Viable bacterial counts were assessed hourly from 0 to 4 hours through serial dilution and plating. **, P<0.01, ****, P<0.0001.

Abbreviation: n.s., not significant.

Figure 5 Klebsiella pneumoniae strains cultured under high-glucose conditions exhibit enhanced resistance to serum killing. Serum samples from 16 healthy individuals were incubated with strains ATCC43816 (A), CRKP28 (B), CRKP70 (C), and CRKP214 (D), which had been pre-cultured in LB broth with and without the addition of 0.5% glucose. The incubation lasted for 3 hours, with bacterial survival rates determined every hour. *, P<0.05, ****, P<0.0001.

Abbreviation: n.s., not significant.

Discussion

Diabetes is a disease of carbohydrate metabolism disorder. The primary pathogenic mechanism involves elevated blood glucose levels due to excessive endogenous glucose production and an impaired ability to utilize glucose effectively.8 Studies have pointed out that patients with hyperglycemia are more prone to colonization and infection by K. pneumoniae and have a higher mortality rate.5,12–14 In this study, we used HbA1c levels of ≥7% as the criterion for grouping to investigate the correlation between glycemic control and the clinical features as well as pathogen drug resistance in patients infected with CRKP. Utilizing in vitro experiments, we assessed the impact of glucose on bacterial capsule synthesis and its underlying mechanisms. Additionally, we further explored the resistance changes of bacteria to polymyxin and serum killing under a high glucose environment.

We observed that patients with poor glycemic control typically exhibit a stronger inflammatory response upon infection. Patients with HbA1c ≥ 7% presented with elevated levels of CRP, WBC, and NE at the initial stage of infection (P<0.01), which is consistent with the findings of previous studies.26 When HbA1c is ≥7%, patients exhibit chronically elevated blood glucose levels. This sustained hyperglycemia can impair the function of white blood cells, including a reduction in phagocytic capacity. Consequently, the immune system’s ability to eliminate pathogens is compromised, leading to chronically elevated inflammation in affected patients.27 The heightened inflammatory response observed in patients with poor HbA1c control may also be associated with dysregulated lipid metabolism. Previous studies have shown that hyperglycemia can interfere with the normal metabolism of lipids through multiple ways. Lipid substances can trigger the secretion of multiple cytokines and inflammatory mediators, thereby exacerbating the systemic inflammatory response.28 Hyperglycemia is correlated with the absolute value of neutrophils. Patients with poor glycemic control exhibit higher neutrophil counts. This elevation may stem from the impairment of neutrophil extracellular trap (NET) pathogen-killing functions in patients with chronic hyperglycemia, leading to a pronounced increase in neutrophils upon pathogen infection.29

In recent years, K. pneumoniae strains with high virulence and carbapenem resistance have become widely prevalent,2 posing significant challenges to clinical treatment. Even worse, studies have indicated that diabetic patients are more likely to be infected by these superbugs.30 Among these bacteria, the CRKP-K64 is predominant and has been confirmed to possess virulence equivalent to that of the K1 and K2 capsular serotypes of K. pneumoniae.31 The presence of rmpA, rmpA2 and iucA genes is commonly used to assess the virulence level of these bacteria.32 Our study revealed no significant differences in the detection rates of CRKP-K64 and major virulence genes (rmpA, rmpA2, iucA) between the groups with poor and good glycemic control. Consequently, we conclude that hyperglycemia does not appear to influence susceptibility to CRKP-K64.

Our study shows that the mortality rate of patients infected with CRKP is relatively high, at 29.4%. Therefore, we tried to find risk factors associated with mortality in these patients. In this study, after adjusting for potential confounders, multivariate regression analysis identified independent risk factors for mortality in CRKP-infected patients, which include age, HbA1c ≥7%, CKD, tumor, sepsis, and mechanical ventilation. Traditional risk factors such as underlying diseases and invasive treatments are predictable and understandable, which is basically consistent with previous studies.6 It should still be noted that regarding the relationship between blood glucose level and the mortality rate of K. pneumoniae infection, studies have shown that in patients with KLA, the glycemic control level is not related to the patient’s mortality rate.11 However, our study indicates that among patients with CRKP infection, those with HbA1c≥7% have a 2.417-fold higher risk of mortality compared to those with HbA1c <7% (OR=2.417,95% CI=1.155–5.055,P=0.019). Therefore, increased vigilance is warranted for patients with poor glycemic control who are infected with CRKP. In addition to the heightened mortality rate from infections attributable to hyperglycemia-induced impairment of the immune system, chronic complications arising from long-term hyperglycemia, such as chronic kidney disease, may also contribute to increased patient mortality (16% vs 5.4%, P<0.05). In the advanced stages of CKD, renal dysfunction ensues, often progressing to end-stage renal disease (ESRD). With severely impaired renal function, patients often rely on dialysis or transplantation as treatment options, which increases the risk of death associated with CKD.33

Literature indicates that glucose stimulates CPS production in K. pneumoniae, thereby modulating bacterial pathogenicity.22 In this study, 0.5% glucose was used to simulate the hyperglycemic environment in the human body.26 The results showed that 0.5% glucose significantly enhanced the production of CRKP capsules. The capsules afford the bacteria protection within the host, including enhancing the resistance of bacteria to phagocytosis and serum killing,34,35 and inhibiting airway epithelial cells from expressing β-defensins to promote bacterial colonization in the lungs.36 Thus, we hypothesize that in vivo, a chronic hyperglycemic environment may stimulate the production of CPS, leading to enhanced bacterial invasiveness and virulence. This also provides another plausible explanation for our finding that patients with hyperglycemic infections have a higher mortality rate.

Although polymyxin is the antibiotic of last resort for the treatment of CRKP infections,18 the emergence of PR-CRKP has become a concern, and hyperglycemia may exacerbate the development of this resistance. Prior research has documented that glucose increases the resistance of Bacillus subtilis and alcohol-producing K. pneumoniae to polymyxin. The mechanisms include maintaining intracellular ATP content and producing a higher amount of CPS.22,37 In this context, our study confirmed that high-glucose environment increases capsule production in CRKP and enhances the bacteria’s resistance to polymyxin as well as its serum bactericidal resistance. By monitoring the bacterial growth curve, we found that the presence of glucose hardly affects the growth rate of bacteria. Consequently, the enhanced resistance of bacteria to polymyxin and serum killing in a glucose-rich environment is not related to the bacterial proliferation rate. Exogenous cAMP can inhibit the stimulatory effect of glucose on capsular polysaccharide synthesis but does not suppress the bacteria’s resistance to polymyxin. This may be due to the fact that capsular production does not entirely dominate the emergence of polymyxin resistance. Therefore, merely reducing capsular synthesis may not completely reverse the enhancing effect of a high-glucose environment on bacterial polymyxin resistance.

Conclusion

In this study, we found that long-term poor glycemic control is associated with more severe infections and significantly increases the risk of death in patients infected with CRKP. Our research also shows that high-glucose environment can enhance the resistance of CRKP to polymyxin and serum killing. Therefore, implementing strict blood glucose management during hospitalization is of crucial importance for improving the prognosis of patients infected with CRKP and effectively curbing the evolution and spread of bacterial drug resistance.

Ethics Approval and Informed Consent

This retrospective cohort study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Anhui Medical University, with the approval number KYLL20240200. The CRKP strains were derived from previously isolated clinical samples. The study posed no adverse effects or risks to participants, and the committee waived the requirement for informed consent.

Funding

This work was supported by the Scientific Research Fund of Anhui Medical University (2022xkj172), Research Fund of Anhui Provincial Natural Science Foundation (2408085MH233), Anhui Institute of Translational Medicine (2023zhyx-C78), Natural Science Research Project of Anhui Educational Committee (2023AH053175), the Youth Innovation Promotion Association, CAS, China (Y2023122), the Anhui Provincial Natural Science Foundation (2408085J020), and the HFIPS Director’s Fund (BJPY2021B08).

Disclosure

The authors report no conflicts of interest in this work.

References

1. Pu D, Zhao J, Chang K, Zhuo X, Cao B. ”Superbugs” with hypervirulence and carbapenem resistance in Klebsiella pneumoniae: the rise of such emerging nosocomial pathogens in China. Sci Bull. 2023;68(21):2658–2670. doi:10.1016/j.scib.2023.09.040

2. Siu LK, Yeh KM, Lin JC, Fung CP, Chang FY. Klebsiella pneumoniae liver abscess: a new invasive syndrome. Lancet Infect Dis. 2012;12(11):881–887. doi:10.1016/S1473-3099(12)70205-0

3. Hu F, Pan Y, Li H, et al. Carbapenem-resistant Klebsiella pneumoniae capsular types, antibiotic resistance and virulence factors in China: a longitudinal, multi-centre study. Nat Microbiol. 2024;9(3):814–829. doi:10.1038/s41564-024-01612-1

4. Logan LK, Weinstein RA. The epidemiology of carbapenem-resistant Enterobacteriaceae: the impact and evolution of a global menace. J Infect Dis. 2017;215(suppl_1):S28–S36. doi:10.1093/infdis/jiw282

5. Qian Y, Bi Y, Liu S, Li X, Dong S, Ju M. Predictors of mortality in patients with carbapenem-resistant Klebsiella pneumoniae infection: a meta-analysis and a systematic review. Ann Palliat Med. 2021;10(7):7340–7350. doi:10.21037/apm-21-338

6. ElSayed NA, Aleppo G, Bannuru RR, American Diabetes Association Professional Practice Committee. 2 diagnosis and classification of diabetes: standards of care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S20–S42. doi:10.2337/dc24-S002

7. Antar SA, Ashour NA, Sharaky M, et al. Diabetes mellitus: classification, mediators, and complications; A gate to identify potential targets for the development of new effective treatments. Biomed Pharmacother. 2023;168:115734. doi:10.1016/j.biopha.2023.115734

8. Çölkesen F, Tarakçı A, Eroğlu E, et al. Carbapenem-resistant Klebsiella pneumoniae infection and its risk factors in older adult patients. Clin Interv Aging. 2023;18:1037–1045. doi:10.2147/CIA.S406214

9. Benfield T, Jensen JS, Nordestgaard BG. Influence of diabetes and hyperglycaemia on infectious disease hospitalisation and outcome. Diabetologia. 2007;50(3):549–554. doi:10.1007/s00125-006-0570-3

10. Todd K, Gunter K, Bowen JM, Holmes CL, Tilston-Lunel NL, Vornhagen J. Type-2 diabetes mellitus enhances Klebsiella pneumoniae pathogenesis. Preprint BioRxiv. 2024;596766. doi:10.1101/2024.05.31.596766

11. Wang HH, Tsai SH, Yu CY, et al. The association of haemoglobin A₁C levels with the clinical and CT characteristics of Klebsiella pneumoniae liver abscesses in patients with diabetes mellitus. Eur Radiol. 2014;24(5):980–989. doi:10.1007/s00330-014-3113-1

12. Lin YT, Wang FD, Wu PF, Fung CP. Klebsiella pneumoniae liver abscess in diabetic patients: association of glycemic control with the clinical characteristics. BMC Infect Dis. 2013;13(1):56. doi:10.1186/1471-2334-13-56

13. Yi H, Huang J, Guo L, Zhang Q, Qu J, Zhou M. Increased antimicrobial resistance among sputum pathogens from patients with hyperglycemia. Infect Drug Resist. 2020;13:1723–1733. doi:10.2147/IDR.S243732

14. Pattolath A, Adhikari P, Pai V. Carbapenemase-producing Klebsiella pneumoniae infections in diabetic and nondiabetic hospitalized patients. Cureus. 2024;16(1):e52468. doi:10.7759/cureus.52468

15. Luan CW, Liu CY, Yang YH, et al. The pathogenic bacteria of deep neck infection in patients with type 1 diabetes, type 2 diabetes, and without diabetes from chang gung research database. Microorganisms. 2021;9(10):2059. doi:10.3390/microorganisms9102059

16. Ou Q, Fan J, Duan D, et al. Involvement of cAMP receptor protein in biofilm formation, fimbria production, capsular polysaccharide biosynthesis and lethality in mouse of Klebsiella pneumoniae serotype K1 causing pyogenic liver abscess. J Med Microbiol. 2017;66(1):1–7. doi:10.1099/jmm.0.000391

17. Lee CH, Chen IL, Chuah SK, et al. Impact of glycemic control on capsular polysaccharide biosynthesis and opsonophagocytosis of Klebsiella pneumoniae: implications for invasive syndrome in patients with diabetes mellitus. Virulence. 2016;7(7):770–778. doi:10.1080/21505594.2016.1186315

18. Nang SC, Azad MAK, Velkov T, Zhou QT, Li J. Rescuing the last-line polymyxins: achievements and challenges. Pharmacol Rev. 2021;73(2):679–728. doi:10.1124/pharmrev.120.000020

19. Olaitan AO, Morand S, Rolain JM. Mechanisms of polymyxin resistance: acquired and intrinsic resistance in bacteria. Front Microbiol. 2014;5:643. doi:10.3389/fmicb.2014.00643

20. Campos MA, Vargas MA, Regueiro V, Llompart CM, Albertí S, Bengoechea JA. Capsule polysaccharide mediates bacterial resistance to antimicrobial peptides. Infect Immun. 2004;72(12):7107–7114. doi:10.1128/IAI.72.12.7107-7114.2004

21. Llobet E, Tomás JM, Bengoechea JA. Capsule polysaccharide is a bacterial decoy for antimicrobial peptides. Microbiology. 2008;154(Pt 12):3877–3886. doi:10.1099/mic.0.2008/022301-0

22. Fan Z, Fu T, Liu H, et al. Glucose induces resistance to polymyxins in high-alcohol-producing Klebsiella pneumoniae via increasing capsular polysaccharide and maintaining intracellular ATP. Microbiol Spectr. 2023;11(4):e0003123. doi:10.1128/spectrum.00031-23

23. Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. 20th Informational Supplement M100-S28. Wayne, PA: Clinical and Laboratory Standards Institute; 2018.

24. Brisse S, Passet V, Haugaard AB, et al. wzi gene sequencing, a rapid method for determination of capsular type for Klebsiella strains. J Clin Microbiol. 2013;51(12):4073–4078. doi:10.1128/JCM.01924-13

25. Turton JF, Payne Z, Coward A, et al. Virulence genes in isolates of Klebsiella pneumoniae from the UK during 2016, including among carbapenemase gene-positive hypervirulent K1-ST23 and ‘non-hypervirulent’ types ST147, ST15 and ST383. J Med Microbiol. 2018;67(1):118–128. doi:10.1099/jmm.0.000653

26. Tang L, Wang H, Cao K, et al. Epidemiological features and impact of high glucose level on virulence gene expression and serum resistance of Klebsiella pneumoniae causing liver abscess in diabetic patients. Infect Drug Resist. 2023;16:1221–1230. doi:10.2147/IDR.S391349

27. Szablewski L, Sulima A. The structural and functional changes of blood cells and molecular components in diabetes mellitus. Biol Chem. 2017;398(4):411–423. doi:10.1515/hsz-2016-0196

28. Kane JP, Pullinger CR, Goldfine ID, Malloy MJ. Dyslipidemia and diabetes mellitus: role of lipoprotein species and interrelated pathways of lipid metabolism in diabetes mellitus. Curr Opin Pharmacol. 2021;61:21–27. doi:10.1016/j.coph.2021.08.013

29. Jin L, Liu Y, Jing C, Wang R, Wang Q, Wang H. Neutrophil extracellular traps (NETs)-mediated killing of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) are impaired in patients with diabetes mellitus. Virulence. 2020;11(1):1122–1130. doi:10.1080/21505594.2020.1809325

30. Liang S, Cao H, Ying F, Zhang C. Report of a fatal purulent pericarditis case caused by ST11-K64 carbapenem-resistant hypervirulent Klebsiella pneumoniae. Infect Drug Resist. 2022;15:4749–4757. doi:10.2147/IDR.S379654

31. Zhou Y, Wu C, Wang B, et al. Characterization difference of typical KL1, KL2 and ST11-KL64 hypervirulent and carbapenem-resistant Klebsiella pneumoniae. Drug Resist Updat. 2023;67:100918. doi:10.1016/j.drup.2023.100918

32. Tian D, Liu X, Chen W, et al. Prevalence of hypervirulent and carbapenem-resistant Klebsiella pneumoniae under divergent evolutionary patterns. Emerg Microbes Infect. 2022;11(1):1936–1949. doi:10.1080/22221751.2022.2103454

33. Evans M, Lewis RD, Morgan AR, et al. A narrative review of chronic kidney disease in clinical practice: current challenges and future perspectives. Adv Ther. 2022;39(1):33–43. doi:10.1007/s12325-021-01927-z

34. Abe R, Ram-Mohan N, Yang S. Re-visiting humoral constitutive antibacterial heterogeneity in bloodstream infections. Lancet Infect Dis. 2024;24(4):e245–e251. doi:10.1016/S1473-3099(23)00494-2

35. Huang X, Li X, An H, et al. Capsule type defines the capability of Klebsiella pneumoniae in evading Kupffer cell capture in the liver. PLoS Pathog. 2022;18(8):e1010693. doi:10.1371/journal.ppat.1010693

36. Moranta D, Regueiro V, March C, et al. Klebsiella pneumoniae capsule polysaccharide impedes the expression of beta-defensins by airway epithelial cells. Infect Immun. 2010;78(12):5352. doi:10.1128/IAI.00940-09

37. Yu WB, Pan Q, Ye BC. Glucose-induced cyclic lipopeptides resistance in bacteria via ATP maintenance through enhanced glycolysis. iScience. 2019;21:135–144. doi:10.1016/j.isci.2019.10.009