Emergence of Neisseria gonorrhoeae Clone with Reduced Susceptibility to Sitafloxacin in China: An In Vitro and Genomic Study.

Drug-resistant Neisseria gonorrhoeae poses an urgent threat to public health. Recently, sitafloxacin, a new-generation fluoroquinolone, has shown high in vitro activity against drug-resistant N. gonorrhoeae. However, data on its effectiveness in clinical isolates remains limited. In this study, we collected 507 N. gonorrhoeae isolates from 21 hospitals in Shanghai, China, during 2020 and 2021. Antimicrobial susceptibility testing revealed that sitafloxacin minimum inhibitory concentrations (MICs) exhibited a bimodal distribution, ranging from <0.004 to 2 mg/L. The MIC50 and MIC90 for sitafloxacin were 0.125 mg/L and 0.5 mg/L, respectively, which are 32 and 16 times lower than those for ciprofloxacin (4 mg/L and 8 mg/L, respectively). Sitafloxacin demonstrated high in vitro activity against isolates resistant to either ceftriaxone, azithromycin, or both. Notably, among the isolates with reduced sitafloxacin susceptibility (MIC ≥ MIC90), 83.7% (36/43) were identified as sequence type (ST) 8123. Further phylogenetic analysis showed that ST8123 has evolved into two subclades, designated as subclade-I and subclade-II. A majority of the isolates (80%, 36/45) within subclade-I exhibited reduced susceptibility to sitafloxacin. In contrast, all isolates from subclade-II were found to be susceptible to sitafloxacin. Subsequent genomic investigations revealed that the GyrA-S91F, D95Y, and ParC-S87N mutations, which were exclusively found in ST8123 subclade-I, might be linked to reduced sitafloxacin susceptibility. Our study reveals that sitafloxacin is a promising antibiotic for combating drug-resistant N. gonorrhoeae. However, caution is advised in the clinical application of sitafloxacin for treating N. gonorrhoeae infections due to the emergence of a clone exhibiting reduced susceptibility.

Quantitative and Qualitative Parameters of DCE-MRI Predict CDKN2A/B Homozygous Deletion in Gliomas.

RATIONALE AND OBJECTIVES: Homozygous deletion (HD) of CDKN2A/B holds important prognostic value in gliomas. This study aimed to explore the predictive potential of conventional MRI characteristics combined with dynamic contrast-enhanced MRI parameters in predicting CDKN2A/B HD status in gliomas. MATERIALS AND METHODS: Preoperative MRI data of 105 patients (69 without CDKN2A/B HD, and 36 with CDKN2A/B homozygous deletion) with gliomas were retrospectively collected. Conventional MRI features and dynamic contrast-enhanced-MRI qualitative parameter time-intensity curve type, quantitative parameters Ktrans, Kep, Ve, Vp, and iAUC were obtained. Logistic regression models for prediction of CDKN2A/B HD status were constructed in all types of gliomas and both subtypes of IDH-mutant and IDH-wild gliomas. RESULTS: Multivariate analysis for all patients demonstrated that age (OR=1.103, p = 0.002) and Ktrans (OR=1.051, p < 0.001) independently predicted CDKN2A/B HD. In IDH-mutant subgroup, multivariate analysis results indicated that Ktrans (OR=1.098, p = 0.031) emerged as autonomous predictors of CDKN2A/B HD. In IDH-wild subgroup, age (OR=1.111, p = 0.002) and Ktrans (OR=1.032, p = 0.001) were independent predictors of CDKN2A/B HD according to the multivariate analysis. The areas under the receiver operating characteristic curve of the corresponding models were 0.90, 0.95 and 0.84, respectively. CONCLUSION: Ktrans can serve as valuable predictive parameters for identifying CDKN2A/B HD status in all types of gliomas and both subtypes of IDH-mutant and IDH-wild gliomas. These findings provide a foundation for precise preoperative non-invasive diagnosis and personalized treatment approaches for glioma patients.

Clinical parameter-based prediction model for neurosyphilis risk stratification.

Accurately predicting neurosyphilis prior to a lumbar puncture (LP) is critical for the prompt management of neurosyphilis. However, a valid and reliable model for this purpose is still lacking. This study aimed to develop a nomogram for the accurate identification of neurosyphilis in patients with syphilis. The training cohort included 9,504 syphilis patients who underwent initial neurosyphilis evaluation between 2009 and 2020, while the validation cohort comprised 526 patients whose data were prospectively collected from January 2021 to September 2021. Neurosyphilis was observed in 35.8% (3,400/9,504) of the training cohort and 37.6% (198/526) of the validation cohort. The nomogram incorporated factors such as age, male gender, neurological and psychiatric symptoms, serum RPR, a mucous plaque of the larynx and nose, a history of other STD infections, and co-diabetes. The model exhibited good performance with concordance indexes of 0.84 (95% CI, 0.83-0.85) and 0.82 (95% CI, 0.78-0.86) in the training and validation cohorts, respectively, along with well-fitted calibration curves. This study developed a precise nomogram to predict neurosyphilis risk in syphilis patients, with potential implications for early detection prior to an LP.

Gut Microbiota Alternation in Disease Progression of Neurosyphilis.

Background: The gut microbiota plays an important role in the development of neurological disorders such as Parkinson's disease and Alzheimer's disease. However, studies on the gut microbiota of patients with neurosyphilis (NS) were rarely reported. Methods: In this study, we collected fecal samples from 62 syphilis patients, including 39 with NS and 23 with non-NS. Among the NS patients, 18 were general paresis (GP). The white blood cell counts, protein concentrations, and Venereal Disease Research Laboratory test positive rates of cerebrospinal fluid from patients in NS or GP group were significantly higher than those from patients in non-NS group. 16S ribosomal RNA sequencing results revealed that the alpha and beta diversities of the gut microbiota were similar between NS and non-NS patients or GP and non-NS patients. Results: Linear discriminant analysis with effect size (LEfSe) analysis showed that some taxa, such as Coprobacter, were increased in both NS group and GP group, compared with non-NS group. Besides, the clade of Akkermansia was also overrepresented in GP Patients. Meanwhile, some taxa such as Clostridia_UCG-014 and SC-I-84 were underrepresented in NS patients. The abundances of class Bacilli and genus Alloprevotella were decreased in GP patients. Among them, the abundances of some taxa such as Coprobacter and Akkermansia have been reported to be associated with other neuropsychiatric disorders. Conclusion: Our findings suggest that the alternation of the gut microbiota in NS patients may contribute to the course of NS, which will deepen our understanding of NS.

Predicting MGMT Promoter Methylation in Diffuse Gliomas Using Deep Learning with Radiomics.

This study aimed to investigate the feasibility of predicting oxygen 6-methylguanine-DNA methyltransferase (MGMT) promoter methylation in diffuse gliomas by developing a deep learning approach using MRI radiomics. A total of 111 patients with diffuse gliomas participated in the retrospective study (56 patients with MGMT promoter methylation and 55 patients with MGMT promoter unmethylation). The radiomics features of the two regions of interest (ROI) (the whole tumor area and the tumor core area) for four sequences, including T1 weighted image (T1WI), T2 weighted image (T2WI), apparent diffusion coefficient (ADC) maps, and T1 contrast-enhanced (T1CE) MR images were extracted and jointly fed into the residual network. Then the deep learning method was developed and evaluated with a five-fold cross-validation, where in each fold, the dataset was randomly divided into training (80%) and validation (20%) cohorts. We compared the performance of all models using area under the curve (AUC) and average accuracy of validation cohorts and calculated the 10 most important features of the best model via a class activation map. Based on the ROI of the whole tumor, the predictive capacity of the T1CE and ADC model achieved the highest AUC value of 0.85. Based on the ROI of the tumor core, the T1CE and ADC model achieved the highest AUC value of 0.90. After comparison, the T1CE combined with the ADC model based on the ROI of the tumor core exhibited the best performance, with the highest average accuracy (0.91) and AUC (0.90) among all models. The deep learning method using MRI radiomics has excellent diagnostic performance with a high accuracy in predicting MGMT promoter methylation in diffuse gliomas.

Corrigendum: Deep Learning-Enabled Clinically Applicable CT Planbox for Stroke With High Accuracy and Repeatability.

[This corrects the article DOI: 10.3389/fneur.2022.755492.].

Deep Learning-Enabled Clinically Applicable CT Planbox for Stroke With High Accuracy and Repeatability.

Background: Computed tomography (CT) plays an essential role in classifying stroke, quantifying penumbra size and supporting stroke-relevant radiomics studies. However, it is difficult to acquire standard, accurate and repeatable images during follow-up. Therefore, we invented an intelligent CT to evaluate stroke during the entire follow-up. Methods: We deployed a region proposal network (RPN) and V-Net to endow traditional CT with intelligence. Specifically, facial detection was accomplished by identifying adjacent jaw positions through training and testing an RPN on 76,382 human faces using a preinstalled 2-dimensional camera; two regions of interest (ROIs) were segmented by V-Net on another training set with 295 subjects, and the moving distance of scanning couch was calculated based on a pre-generated calibration table. Multiple cohorts including 1,124 patients were used for performance validation under three clinical scenarios. Results: Cranial Automatic Planbox Imaging Towards AmeLiorating neuroscience (CAPITAL)-CT was invented. RPN model had an error distance of 4.46 ± 0.02 pixels with a success rate of 98.7% in the training set and 100% with 2.23 ± 0.10 pixels in the testing set. V-Net-derived segmentation maintained a clinically tolerable distance error, within 3 mm on average, and all lines presented with a tolerable angle error, within 3° on average in all boundaries. Real-time, accurate, and repeatable automatic scanning was accomplished with and a lower radiation exposure dose (all P < 0.001). Conclusions: CAPITAL-CT generated standard and reproducible images that could simplify the work of radiologists, which would be of great help in the follow-up of stroke patients and in multifield research in neuroscience.

Platelet Indices Are the Promising Biomarkers in Monitoring Disease Activities in Patients with Syphilis.

OBJECTIVES: To uncover the role of the platelet indices in patients with syphilis. METHODS: A total of 2061 patients with syphilis and 528 healthy controls were enrolled in this retrospective cohort study. The data of platelet count (PLT), mean platelet volume (MPV), platelet distribution width (PDW), and indicators of syphilis activities were collected. The correlations between the platelet indices and disease activities were analyzed. RESULTS: A total of 425 (20.6%) of the 2061 patients were of primary and secondary syphilis, 433 (21.0%) latent, 463 (22.5%) serofast, 350 (17.0%) asymptomatic neurosyphilis, and 390 (18.9%) symptomatic neurosyphilis. Compared with the healthy controls, PLT was significantly increased in the primary and secondary syphilis group; whereas, MPV and PDW were significantly decreased in all stages of syphilis. These changes of platelet indices were reversed after anti-treponemal therapy. Further correlation analysis showed that PLT was positively associated with the syphilis activity indicators [rapid plasma reagin (RPR) titer, cerebrospinal fluid white blood cell (CSF-WBC), CSF-protein, and CSF-VDRL (venereal disease research laboratory)] and inflammatory markers [WBC, C-reaction protein (CRP), and erythrocyte sedimentation rate (ESR)]. Conversely, PDW was negatively correlated with all of these parameters. MPV had an inverse relationship with RPR, ESR, and CRP. CONCLUSIONS: Platelet indices are associated with syphilis activities.

Reduced Virulence and Enhanced Host Adaption during Antibiotics Therapy: a Story of a Within-Host Carbapenem-Resistant Klebsiella pneumoniae Sequence Type 11 Evolution in a Patient with a Serious Scrotal Abscess.

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has disseminated globally and threatened human life. The sequence type (ST) 11 CRKP is a dominant clone in Asia, but how this clone evolves in vivo then adapts to the host and facilitates dissemination remains largely unknown. Here, the genomic dynamics of 4 ST11-CRKP isolates, which were sequentially collected from the urine of a patient with initial serious scrotal abscess and finally recovered without effective medication, were analyzed. Genomic differences were identified and their implications for pathogenesis and host adaptation were investigated. The related transcriptional pathways were further explored by RNA-Seq. Genomic analysis identified 4 to 24 mutations, among which 94% to 100% of them were synonymous or intergenic mutations. During 47 days of antibiotics therapy, CRKP underwent adaptive evolution, including tigecycline resistance and virulence attenuation. Tigecycline resistance was caused by a deletion within the ramR ribosomal binding site, which has been described by us previously. On the other hand, mutations associated with two genes, acyltransferase (act) and ompK26, resulted in the attenuation phenotype of ST11-CRKP. act deficiency reduced the capsular polysaccharide (CPS) production, enhanced biofilm formation, weakened capsular protection, and decreased induction of proinflammatory cytokines. Further RNA-Seq analysis revealed that act influenced the expression of ldhA, bglX, mtnK, and metE which likely participate in capsular synthesis and biofilm formation. ompK26 affected the virulence by its overexpression caused by the deletion of the upstream repressor binding site. This study presents a within-host adaption of ST11-CRKP and suggests an important role of CPS in the adaptive evolution of virulence and persistence of CRKP. IMPORTANCE Carbapenem-resistant Klebsiella pneumoniae (CRKP) has disseminated worldwide and can cause life-threatening infections, including pneumonia, bloodstream infections, urinary tract infections, intraabdominal infection, liver abscess, and meningitis. CRKP infection is the leading cause of high mortality in hospitals. The sequence type (ST) 11 CRKP is a dominant clone and accounts for 60% of CRKP infections in China. Recently, the ST11-CRKP with high transmissibility is increasingly identified. Understanding how this clone has evolved is crucial for developing strategies to control its further dissemination. The significance of our research is the identification of the in vivo genomic dynamics of ST11-CRKP and the genetic basis for ST11-CRKP that facilitate persistence and dissemination. Furthermore, our study also highlights the importance of monitoring the within-host evolution of pathogens during the treatment and developing interventions to minimize the potential impact of host adaptation on human health.

Internal Migration and Leprosy in Shanghai from 2000 to 2019: an Epidemiological Study of New Cases.

Leprosy is a chronic infectious disease caused by Mycobacterium leprae. Massive internal migration from rural to urban areas poses new challenges for leprosy control in Shanghai, China. This retrospective epidemiological study examined new cases of leprosy diagnosed in Shanghai from 2000 to 2019, with emphasis on internal migration cases. There were 145 cases of leprosy in the study period; the majority of cases (89.0%) were internal migrants. Migrant cases had a mean of 25.4 months lag time from onset of symptoms to diagnosis, which was significantly longer than that of resident cases (mean 10.8 months, p < 0.001). Greater lag time from the first visit to diagnosis was observed in migrant cases (mean 23.2 months) compared with resident cases (mean 9.4 months, p < 0.001). A large majority of cases (91.0%) had been misdiagnosed. Internal migrant cases were responsible for most incidences of leprosy in Shanghai. They often did not receive timely diagnosis and treatment, which may have an adverse impact on the prevention of epidemic leprosy.

A New Specimen for Syphilis Diagnosis: Evidence by High Loads of Treponema pallidum DNA in Saliva.

BACKGROUND: DNA from many pathogens can be detected in saliva. However, the presence and quantity of Treponema pallidum DNA in patients with syphilis in saliva is unknown. METHODS: 234 patients with syphilis with different stages and 30 volunteers were enrolled. Paired saliva and plasma samples were collected from all participants. Consecutive saliva samples from 9 patients were collected every 4 hours following treatment. Treponema pallidum DNA in samples was determined by nested polymerase chain reaction (PCR) and droplet digital PCR targeting polA and Tpp47. RESULTS: Treponema pallidum DNA detection rates in saliva and plasma were 31.0% (9/29) and 51.7% (15/29) in primary syphilis (P = .11), 87.5% (63/72) and 61.1% (44/72) in secondary syphilis (P < .001), 25.6% (21/82) and 8.5% (7/82) in latent syphilis (P = .004), and 21.6% (11/51) and 5.9% (3/51) in symptomatic neurosyphilis (P = .021), respectively. Median (range) loads of Tpp47 and polA in saliva were 627 (0-101 200) and 726 (0-117 260) copies/mL, respectively, for patients with syphilis. In plasma, however, loads of Tpp47 and polA were low: medians (range) of 0 (0-149.6) and 0 (0-176) copies/mL, respectively. Loads of T. pallidum DNA in saliva during treatment fluctuated downward; the clearance time was positively correlated with the loads of T. pallidum DNA before treatment. CONCLUSIONS: Collection of saliva is noninvasive and convenient. The high loads of T. pallidum DNA in saliva and reduction after treatment indicated that saliva can be not only a diagnostic fluid for syphilis but also an indicator of therapeutic effectiveness.

RamA upregulates multidrug resistance efflux pumps AcrAB and OqxAB in Klebsiella pneumoniae.

Overexpression of the acrAB genes regulated by RamA and overexpression of oqxAB regulated by RarA have been reported to mediate multidrug resistance in Gram-negative bacilli. In this study, regulation of acrAB and oqxAB simultaneously by the global regulator RamA was investigated in a multidrug-resistant Klebsiella pneumoniae clinical isolate (KP22) resistant to tigecycline and other antimicrobials. KP22 overexpressed ramA due to a ramR mutation, along with an unexpected overexpression of oqxB. Deletion of ramA led to a 16-fold decrease in the tigecycline minimum inhibitory concentration (MIC) with decreased expression of acrB (4.3-fold) and oqxB (7.1-fold) compared with KP22. Transcomplementation of KP22ΔramA with the wild-type ramA gene restored the tigecycline MIC and upregulation of the acrB (3.9-fold) and oqxB (4.0-fold) genes compared with KP22. When oqxB was knocked out, MICs of ciprofloxacin, olaquindox and nitrofurantoin were considerably decreased, while deletion of acrB led to MIC decreases for cefepime, piperacillin/tazobactam and tigecycline in addition to the above three antimicrobials. The results of electrophoretic mobility shift assay showed that RamA could bind the promoter regions of both the acrAB and oqxAB operons. This study demonstrates for the first time that RamA can directly regulate multidrug resistance efflux pumps AcrAB and OqxAB in K. pneumoniae.

Glycopeptidolipid Genotype Correlates With the Severity of Mycobacterium abscessus Lung Disease.

BACKGROUND: Smooth and rough colony morphotypes of Mycobacterium abscessus are associated with virulence, but some isolates form both smooth and rough colonies, impeding successful morphotype identification. Reportedly, smooth/rough morphotypes are also related to the glycopeptidolipid (GPL) genotype. However, the accuracy of GPL genotyping to discriminate morphotypes and the relationship between GPL genotype and clinical characteristics of M abscessus lung disease have not been verified. METHODS: A retrospective analysis of colony morphology, GPL genotype, and clinical data from 182 patients with M abscessus lung disease was conducted. RESULTS: Of 194 clinical isolates, 126 (65.0%), 15 (7.7%), and 53 (27.3%) exhibited rough, smooth, and mixed colony morphotypes, respectively. Glycopeptidolipid genotyping indicated that 86.7% (13 of 15) of smooth isolates belonged to the GPL-wild type (WT) group, whereas 98.4% (124 of 126) of rough isolates belonged to the GPL-mutant type (MUT) group. Therefore, GPL genotyping accurately distinguished between smooth and rough morphotypes. Mixed colony morphotypes were also divided into GPL-WT (18.9%) and GPL-MUT (81.1%) groups. Further analysis revealed that patients infected with the GPL-MUT group presented with significantly worse baseline clinical characteristics and exacerbated episodes of lung disease. CONCLUSIONS: Glycopeptidolipid genotyping accurately distinguishes smooth and rough colony morphotypes. Patients infected with the GPL-MUT genotype exhibit worse clinical characteristics and are at a higher risk of exacerbated lung disease.

The Impact of Spatial Normalization Strategies on the Temporal Features of the Resting-State Functional MRI: Spatial Normalization Before rs-fMRI Features Calculation May Reduce the Reliability.

Previous resting-state functional magnetic resonance imaging (rs-fMRI) studies frequently applied the spatial normalization on fMRI time series before the calculation of temporal features (here referred to as "Prenorm"). We hypothesized that calculating the rs-fMRI features, for example, functional connectivity (FC), regional homogeneity (ReHo), or amplitude of low-frequency fluctuation (ALFF) in individual space, before the spatial normalization (referred to as "Postnorm") can be an improvement to avoid artifacts and increase the results' reliability. We utilized two datasets: (1) simulated images where temporal signal-to-noise ratio (tSNR) is kept a constant and (2) an empirical fMRI dataset with 50 healthy young subjects. For simulated images, the tSNR is constant as generated in individual space but increased after Prenorm and intersubject variability of tSNR was induced. In contrast, tSNR was kept constant after Postnorm. Consistently, for empirical images, higher tSNR, ReHo, and FC (default mode network, seed in precuneus) and lower ALFF were found after Prenorm compared to those of Postnorm. Coefficient of variability of tSNR and ALFF was higher after Prenorm compared to those of Postnorm. Moreover, the significant correlation was found between simulated tSNR after Prenorm and empirical tSNR, ALFF, and ReHo after Prenorm, indicating algorithmic variation in empirical rs-fMRI features. Furthermore, comparing to Prenorm, ALFF and ReHo showed higher intraclass correlation coefficients between two serial scans after Postnorm. Our results indicated that Prenorm may induce algorithmic intersubject variability on tSNR and reduce its reliability, which also significantly affected ALFF and ReHo. We suggest using Postnorm instead of Prenorm for future rs-fMRI studies using ALFF/ReHo.

Outbreak Of Klebsiella pneumoniae Carbapenemase-Producing Klebsiella aerogenes Strains In A Tertiary Hospital In China.

PURPOSE: This study aimed to evaluate the molecular characteristics and prevalence of clinical carbapenem-resistant Klebsiella aerogenes (CRKA), collected during an outbreak in a Chinese tertiary hospital. METHODS: Antimicrobial susceptibility test, using 17 antibiotics, was performed on 14 CRKA isolates. The strains were examined for the presence of ß-lactamase genes by PCR, and efflux pump phenotype was determined by efflux pump inhibition test. Presence of outer-membrane porins was examined. Clonal relatedness among the isolates was investigated by pulsed-field gel electrophoresis (PFGE). S1 nuclease-PFGE and plasmid incompatibility group analysis were performed to determine plasmids, and the genetic environment of bla KPC-2 was analyzed. Epidemiological data were collected via chart review. RESULTS: The 14 CRKA isolates were all resistant to carbapenems; five distinct groups (PFGE types A-E) were observed. All 14 isolates carried the bla KPC-2 gene. S1 nuclease-PFGE indicated the size of bla KPC-2-carrying plasmids to range from 20 kb to 200 kb, and the 14 plasmids belonged to various incompatibility groups. The most frequent genetic environment of bla KPC-2 was Tn1721- bla KPC-2-ΔTn3-IS26. PFGE type A group, including 11 KPC-2-producing clinical isolates, was primarily responsible for dissemination. CONCLUSION: Our findings suggest both transposons and vertical transmission to contribute to the transformation of bla KPC-2. The results strongly suggest strict implementation of infection control of CRKA, in healthcare facilities.

Clinical Efficacy and Adverse Effects of Antibiotics Used to Treat Mycobacterium abscessus Pulmonary Disease.

Treatment of Mycobacterium abscessus pulmonary infection requires long-term administration of multiple antibiotics. Little is known, however, about the impact of each antibiotic on treatment outcomes. A retrospective analysis was conducted to evaluate the efficacy and adverse effects of antibiotics administered in 244 cases of M. abscessus pulmonary disease. Only 110 (45.1%) patients met the criteria for treatment success. The efficacy of treating M. abscessus pulmonary disease continues to be unsatisfactory especially for infections involving M. abscessus subsp. abscessus. Treatment with drug combinations that included amikacin [adjusted odds ratio (AOR), 3.275; 95% confidence interval (CI), 1.221-8.788], imipenem (AOR, 2.078; 95% CI, 1.151-3.753), linezolid (AOR, 2.231; 95% CI, 1.078-4.616), or tigecycline (AOR, 2.040; 95% CI, 1.079-3.857) was successful. Adverse side effects affected the majority of patients (192/244, 78.7%). Severe effects that resulted in treatment modification included: gastrointestinal distress (29/60, 48.3%) mostly caused by tigecycline, ototoxicity (14/60, 23.3%) caused by amikacin; and myelosuppression (6/60, 10%) caused mainly by linezolid. In conclusion, the success rate of treatment of M. abscessus pulmonary disease is still unsatisfactory. The administration of amikacin, imipenem, linezolid, and tigecycline correlated with increased treatment success. Adverse side effects are common due to long-term, combination antibiotic therapy. Ototoxicity, gastrointestinal distress, and myelosuppression are the most severe.

Efflux pumps AcrAB and OqxAB contribute to nitrofurantoin resistance in an uropathogenic Klebsiella pneumoniae isolate.

Klebsiella pneumoniae is a common cause of urinary tract infections (UTIs). Nitrofurantoin (NIT), with high therapeutic concentrations in urine, is recommended as the first-line drug for both empiric treatment and chemoprophylaxis of UTIs. Although NIT resistance in K. pneumoniae is relatively high, the resistance mechanism is not well understood. This study collected a NIT-resistant K. pneumoniae [NRKP, minimum inhibitory concentration (MIC)=128 mg/L] and investigated the resistance mechanism. Addition of efflux pump inhibitors increased the susceptibility of NRKP to NIT (MIC decreased from 128 to 32 mg/L), implying the important role of efflux pumps in NIT resistance. Quantitative reverse transcriptase polymerase chain reaction analysis showed that NRKP had >100-fold increased expression of ramA, which was demonstrated to be caused by ramR mutation. Deletion of ramA led to a four-fold decrease in the MIC of NIT, and the expression levels of efflux pumps acrB and oqxB were downregulated by four- to seven-fold. Complementation of ramA restored both the MIC value and the expression level of acrB and oqxB in the ramA mutant strain. In order to confirm the role of acrB and oqxB in NIT resistance, gene knockout strains were constructed. Deletion of acrB or oqxB alone led to a four-fold decrease in the MIC of NIT, and deletion of acrB and oqxB simultaneously led to a 16-fold decrease in the MIC of NIT. These results demonstrate that AcrAB and OqxAB contribute to NIT resistance in K. pneumoniae.