PURPOSE:The aim of this study was to characterize the genomic structure of the first isolated ST152 Klebsiella pneumoniae strain carrying blaNDM-1 in China. METHODS:Antimicrobial susceptibility was determined by broth microdilution method. Whole-genome sequencing was conducted using the Illumina HiSeq and Oxford Nanopore GridION X5 platforms, and the genomic features were analyzed using a range of bioinformatics tools. RESULTS:The strain HZKP1 demonstrated resistance to cefepime, ceftazidime, amoxicillin-clavulanic acid, amikacin, ciprofloxacin, meropenem, imipenem, and ertapenem, while showing sensitivity to tigecycline and colistin. It was classified as sequence type (ST) 152, K locus (KL) 105 and OC locus (OCL) O3b, respectively. The blaNDM-1 gene was identified on the IncX3 plasmid pHZKP1-NDM (54,035 bp), located downstream of the ISKox3-IS3000-ISAba125-IS5 segment and upstream of the bleMBL-IS26-blaSHV-69-IS26 segment. Phylogenetic analysis indicated its closest relative to be a strain isolated from a wound swab sample in Tanzania in 2013, differing by 598 alleles. CONCLUSION:We characterized genomic features of the first ST152 K. pneumoniae strain isolated in China. Our findings provide insights into the current status of resistance in new lineages within the region and enhance comprehension of K. pneumoniae carbapenem resistance transmission from a genetic structure perspective.

The aim of this study was to investigate in vitro activity of imipenem-relebactam alone and in combination with fosfomycin against carbapenem-resistant Gram-negative pathogens. A total of 100 Gram-negative bacteria resistant to carbapenem were collected. Among collected 25 carbapenem-resistant Klebsiella pneumoniae strains, 24 (96%) were KPC producers and none of them displayed NDM-1, NDM-5, and IMP carbapenemase. Among 25 carbapenem-resistant Escherichia coli strains, 3(12%), 1(4%), 17(68%), 25(100%) and 20(80%) harbored KPC, NDM-1, NDM-5, ESBLs, and membrane porin OmpC or OmpF mutations, respectively. Among all the carbapenem-resistant strains, 40% (40/100) were resistant to imipenem-relebactam. The FICI revealed the synergistic (60%, 6/10) and additive (40%, 4/10) effects of imipenem-relebactam in combination with fosfomycin, wherein synergistic activity was found against all tested Klebsiella pneumoniae and Acinetobacter baumannii. Imipenem-relebactam may be a new alternative for carbapenem-resistant Gram-negative pathogens infections and the combination of imipenem-relebactam and fosfomycin warrants further exploration.

Chinese dragon's blood (CDB), a characteristic red resin, is an important traditional Chinese medicine (TCM), and empiric therapy of infected wounds with CDB is performed in clinical settings. For the first time, we herein report the antibacterial and anti-biofilm efficacy of CDB against Staphylococcus aureus (S. aureus). Antimicrobial susceptibility testing, growth curve assay, time-kill curve assay, crystal violet biofilm assay, scanning electron microscope (SEM) analysis, cell membrane tests, and quantitative real-time polymerase chain reaction (qRT-PCR) were used for this purpose. The results suggested that the minimum inhibitory concentration (MIC) values of CDB against S. aureus ranged from 32 to 128 μg/mL. Growth curves and time-kill curves confirmed that CDB could inhibit the growth of S. aureus. The biofilm formation ability and the expression levels of saeR, saeS, and hla of S. aureus in the presence and absence of CDB were statistically significant (P < 0.01). The results of SEM analysis and cell membrane tests revealed that exposure to CDB had some destructive effects on S. aureus cells. In conclusion, CDB exhibits positive antibacterial activity against S. aureus. Moreover, CDB could reduce the biofilm formation and the virulence factors of S. aureus by downregulating the expression levels of saeR, saeS, and hla genes. These findings indicated that CDB has immense potential to serve as a viable alternative for the treatment of infected wounds caused by S. aureus in clinical settings.

Background Staphylococcus aureus (S. aureus) is a major contributor to nosocomial and community-acquired infections. S. aureus small colony variants (SCVs) which changed in relevant phenotype have made more limited and difficult for therapeutic options against S. aureus infections increasingly. Rifampicin is considered as the “last-resort” antibiotic against S. aureus. Our study investigated resistance profiles and biological characteristics of rifampicin-resistant S. aureus SCVs. Methods We collected S. aureus SCVs that were selected from 41 rifampicin-resistant clinical isolates. Then, biological characteristics, resistance spectrum, and rifampicin resistance mechanisms of tested S. aureus SCVs and corresponding parental strains were investigated by classic microbiological methods, agar dilution method, polymerase chain reaction (PCR). Moreover, the fitness cost of S. aureus SCVs, including growth, biofilm formation ability, and virulence profile, was also determined by bacterial growth curve assay, biofilm formation assay, and Galleria mellonella infection model. Results There were three S. aureus SCVs (JP310 SCVs, JP1450 SCVs, JP1486 SCVs) that were selected from 41 rifampicin-resistant S. aureus. S. aureus SCVs colonies were tiny, with decreased pigmentation, and the hemolysis circle was not obvious compared with corresponding parental strains. And SCVs could not be restored to normal-colony phenotype after hemin, menaquinone, or thymidine supplementation. Different rpoB mutations occurred in JP1486 SCVs. Antimicrobial susceptibility testing revealed MICs of SCVs were higher than corresponding parental strains. Besides, the growth ability and virulence of SCVs were lower, and biofilm formation ability of which increased compared with parental strains. Conclusion S. aureus SCVs share the rifampicin resistance mechanisms with parental strains, although there were some differences in the position of rpoB mutations. Moreover, we found that the biological characteristics of SCVs were significantly different from corresponding parental strains. In contrast, decreased susceptibility to other antibiotics of SCVs was observed during phenotype switch. Furthermore, SCVs incur the fitness cost.

BACKGROUND:The emergence of carbapenem-resistant and colistin-resistant ECC pose a huge challenge to infection control. The purpose of this study was to clarify the mechanism of the carbapenems and colistin co-resistance in Enterobacter cloacae Complex (ECC) strains.RESULTS:This study showed that the mechanisms of carbapenem resistance in this study are: 1. Generating carbapenemase (7 of 19); 2. The production of AmpC or ESBLs combined with decreased expression of out membrane protein (12 of 19). hsp60 sequence analysis suggested 10 of 19 the strains belong to colistin hetero-resistant clusters and the mechanism of colistin resistance is increasing expression of acrA in the efflux pump AcrAB-TolC alone (18 of 19) or accompanied by a decrease of affinity between colistin and outer membrane caused by the modification of lipid A (14 of 19). Moreover, an ECC strain co-harboring plasmid-mediated mcr-4.3 and blaNDM-1 has been found.CONCLUSIONS:This study suggested that there is no overlap between the resistance mechanism of co-resistant ECC strains to carbapenem and colistin. However, the emergence of strain co-harboring plasmid-mediated resistance genes indicated that ECC is a potential carrier for the horizontal spread of carbapenems and colistin resistance.

Abstract Background The study aimed to elucidate the species taxonomy, clinical manifestations, virulence gene profiles and antimicrobial susceptibilities of Aeromonas strains isolated from life-threatening bacteremia in southeastern China. Methods Clinical samples of Aeromonas causing bacteremia were isolated from a teaching hospital in Wenzhou from 2013 to 2018 and a retrospective cohort study was performed. Aeromonas strains were identified at species level by housekeeping gene gyrB. Virulence and drug resistance-associated genes were screened by polymerase chain reaction (PCR) and antimicrobial susceptibility testing (AST) was performed by the VITEK 2 Compact system. Results A total of 58 Aeromonas isolated from patients with bacteremia were collected during 6 years (2013–2018). 58 isolates were identified to five different species, where Aeromonas dhakensis appeared to be the predominant species (26/58), followed by Aeromonas veronii (13/58), Aeromonas caviae (10/58), Aeromonas hydrophila (7/58) and Aeromonas jandaei (2/58). 16 of 58 patients had poor prognosis. Poor prognosis was significantly associated with liver cirrhosis and inappropriate empirical antimicrobials therapy. The progression of bacteremia caused by Aeromonas was extremely fast, especially in A. dhakensis infections. Virulence genes aer, lip, hlyA, alt, ast, and act, were detected at ratios of 24.1% (14/58), 62.1% (36/58), 65.5% (38/58), 58.6% (34/58), 15.5% (9/58) and 65.5% (38/58), respectively. Antimicrobial susceptibility testing exhibited that 9 out of 58 isolates were identified as multi-drug resistant (MDR) organism. The bla TEM gene was identified in all 9 MDR isolates. bla SHV, bla AQU-1, bla MOX, bla CepH, bla CphA and aac(6′)-Ib-cr were detected in 4 isolates, 2 isolates, 1 isolate, 3 isolates, 8 isolates, and 3 isolates, respectively. The majority of Aeromonas strains maintained susceptible to 3rd generation cephalosporins, aminoglycosides, fluoroquinolones and furantoin. Conclusions The prevalence and dangerousness of Aeromonas infections, especially A. dhakensis, are underestimated in clinic. Continuous monitoring is essential to keep track of MDR Aeromonas due to the increasing prevalence recently and a more effective measure is required to control the spread of resistance determinants.

Object: To analyze the difference in biofilm formation between carbapenem-resistant and carbapenem-sensitive Klebsiella pneumoniae based on analysis of mrkH distribution and to further explore the function of mrkH for biofilm formation from the perspective of gene regulation. Methods: 40 imipenem-resistant strains and 40 imipenem-sensitive strains were selected to conduct experiments. Carbapenem (imipenem) susceptibility test was performed by the agar-dilution method. blaKPC resistance gene, type 3 fimbriae-related coding genes (mrkA and mrkD) and regulation gene (mrkH) were screened by PCR. Biofilm formation assay was performed using crystal violet staining method in MHB. The relative expression of genes that critically involved in biofilm formation (mrkA, luxS, pgaA) and carbapenem resistance (ompk35, ompk36, acrB) were measured by quantitative real-time PCR (qRT-PCR). Furthermore, the mrkH cassette was cloned into pGEM-T Easy plasmid to yield pGEM:pmrkH and expressed in Escherichia coli DH5 alpha and K. pneumoniae FK1911, and the biofilm formation assay after transformation was further tested. Results: The MICs of imipenem were all more than 16 mu g/mL in 40 imipenem-resistant strains and ranged from 0.125 mu g/mL to 0.5 mu g/mL in 40 imipenem-sensitive strains. Moreover, the blaKPC was identified in the 40 imipenem-resistant K. pneumoniae strains. All 80 K. pneumoniae strains were found to carry mrkA and mrkD genes. Interestingly, the mrkH gene was detected in 43 strains, of which 32 were carbapenem-sensitive strains. The biofilm formation capacity of strains carried mrkH cassette was significantly higher than other 37 strains in MHB media. The relative expression of mrkA in K. pneumoniae carrying mrkH gene was significantly up-regulated. Importantly, the biofilm formation ability of FK1911-pGEM:pmrkH strain was more higher than the strain of FK1911 in MHB medium. Conclusions: Our data demonstrated that MrkH played a crucial role in the regulation of biofilm formation by K. pneumoniae. In contrast to carbapenem-sensitive K. pneumoniae, carbapenem-resistant K. pneumoniae was less likely to have strong biofilm-forming capacity because it does not carry the mrkH gene.

In this study, we report a clinical isolate of a carbapenem-, colistin-, and fosfomycin-resistant Escherichia coli isolate DC-3737 co-harboring bla NDM-1 , mcr-1 , and fosA3 from an inpatient in China. Antimicrobial susceptibility testing, polymerase chain reaction, multi-locus sequence typing, conjugation experiment, and Southern blot hybridization were performed on E. coli DC-3737 isolated from the wound. Plasmid analysis is presented and the locations of bla NDM-1 , mcr-1 , fosA3 , and other resistance genes were identified as well. E. coli DC-3737 was resistant to ampicillin, ceftriaxone, ceftazidime, ciprofloxacin, levofloxacin, gentamicin, tobramycin, trimethoprim–sulfamethoxazole, imipenem, meropenem, ertapenem, fosfomycin and colistin, and with intermediate susceptibility to amikacin. It was typed as sequence type 27. The isolate possessed bla NDM-1 , mcr-1 , fosA3 , bla CTX-M-9 , bla TEM-1 , aac (6 ′ )-Ib-cr and sul1 simultaneously. In addition, the mutations in quinolone resistance-determinant regions (QRDRs) such as Ser83Leu and Asp87Asn in gyrA , and Ser80Ile in parC were detected. Conjugation assays revealed that bla NDM-1 , fosA3 , sul1 , mcr-1 , and bla CTX-M-9 genes could successfully transfer their resistance phenotype to E. coli strain J53. Plasmid analysis and Southern hybridization showed that DC-3737 possessed Z-type self-transmissible plasmid bearing bla NDM-1 , fosA3 , and sul1 . Moreover, mcr-1 , bla CTX-M-9 , and bla TEM-1 were located on a ~60-kb IncFIB type self-transmissible plasmid. This is the first report of bla NDM-1 , mcr-1 and fosA3 co-harboring in E. coli in China. Moreover, it is also the first description of the co-harboring of bla NDM and fosA3 in a single Z plasmid in Enterobacteriaceae species. The identification of E. coli DC-3737 co-harboring bla NDM-1 , mcr-1 , and fosA3 in this study highlights the need to increase epidemiologic surveillance and the need for new classes of antibiotics to address multidrug-resistant bacteria.

Background The emergence and spread of carbapenem-resistant Escherichia coli (E. coli) pose a serious threat to human health worldwide. This study aimed to investigate the molecular mechanisms underlying carbapenem resistance and their prevalence among E. coli in China. Methods A collection of 5796 E. coli clinical isolates were collected from the First Affiliated Hospital of Wenzhou Medical University from 2002 to 2017. Sensitivity to antibiotics was determined using the agar dilution method. The detection of carbapenemases production and the prevalence of resistance-associated genes were investigated through modified carbapenem inactivation method (mCIM), PCR and sequencing. The mutations in outer membrane porins genes (ompC and ompF) were also analyzed by PCR and sequencing assays. The effect of efflux pump mechanism on carbapenem resistance was also tested. E. coli were typed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Results A total of 58 strains (1.0%) of carbapenem-resistant E. coli were identified. The strains carrying blaKPC-2 and blaNDM accounted for 22.4% (13/58) and 51.7% (30/58), respectively. Among blaNDM- positive strains, 27 blaNDM genes were assigned to blaNDM-5, while the remaining three strains were blaNDM-1, whereas blaVIM, blaIMP, blaOXA-48, and blaSHV were not found. The CTX-M-type β-lactamase genes accounted for 96.6% (56/58). In addition, blaTEM-1 genes were identified in 58.6% of tested strains. In carbapenem-resistant isolates, mutations in OmpC (the majority of mutated sites were D192G and Q104_F141del, accounting for 54.5%) and OmpF (large deletions S75_V127del, W83_D135del and Q88_D135del) were detected. Of note, the antibiotic resistance was not associated with overexpression of efflux pump. Moreover, MLST categorized the 58 carbapenem-resistant isolates into 19 different sequence types. PFGE analysis revealed that homology among the carbapenem-resistant isolates was low and sporadic. Conclusion The blaNDM was the principal resistance mechanism of carbapenem-resistant E. coli in the hospital. blaNDM-5 is becoming a new threat to public health and the alteration of outer membrane porins might help further increase the MIC of carbapenem.

OBJECTIVE:To characterize the evolutionary pathways of tigecycline (TGC) resistance and alterations in the biological characteristics of hospital-derived Staphylococcus aureus isolates under selective pressure.METHODS:Three clinical S. aureus strains and one standard S. aureus strain, ATCC 29213, were used for the in vitro selection of TGC-resistant S. aureus variants with gradient concentrations of TGC. Changes in drug resistance and genetic alterations in resistance-related genes (operon mepRAB and rpsJ) in mutant strains were determined. The efflux inhibitor assay for MepA and the fitness cost, determined by comparing the growth and virulence of parental and mutant strains, were also investigated.RESULTS:Mutants induced in vitro showed a 64- to 128-fold increase in the minimum inhibitory concentration (MIC) of TGC. Substitution mutations were detected in the transcriptional repressor mepR and the efflux pump gene mepA. A K57M amino acid substitution occurred in the ribosomal S10 protein-encoding gene rpsJ. The MICs of TGC in the final mutants were significantly decreased in the presence of efflux pump inhibitors. It was worth noting that growth was unaffected by TGC resistance selection in vitro, with the exception of one strain, and the MICs of other antibiotics and virulence were also unaffected.CONCLUSIONS:The evolution of TGC resistance in S. aureus in vitro is associated with a loss-of-function mutation in the efflux pump transcriptional repressor mepR and a missense mutation in the efflux pump-encoding gene mepA. Our work further validated the resistance mechanisms of S. aureus to TGC and reported previously undiscovered mutations.

目的 评价快速多黏菌素NP法检测肠杆菌科(大肠埃希菌和肺炎克雷伯菌)多黏菌素耐药性的性能,并初步探究其在鲍曼不动杆菌多黏菌素耐药性检测中的应用价值.方法 收集2010年至2019年温州医科大学附属第一医院临床分离多黏菌素耐药株42株,其中大肠埃希菌14株、肺炎克雷伯菌20株、鲍曼不动杆菌8株;同期多黏菌素敏感株120株,其中大肠埃希菌与肺炎克雷伯菌各50株、鲍曼不动杆菌20株.采用微量肉汤稀释法确认多黏菌素E最低抑菌浓度(MIC),同时使用快速多黏菌素NP试剂(含1％葡萄糖)检测肠杆菌科细菌对多黏菌素E的耐药性,并评价分别含1％、2％、4％葡萄糖浓度的快速多黏菌素NP试剂对检测鲍曼不动杆菌多黏菌素E耐药性的效果.结果 以微量肉汤稀释法检测结果为标准,快速多黏菌素NP法检测肠杆菌科细菌多黏菌素E耐药性的灵敏度、特异度和准确率分别为100％(34/34)、99％(99/100)和99.3％(133/134);采用4％葡萄糖浓度的快速多黏菌素NP试剂,培养至16 h时对鲍曼不动杆菌多黏菌素耐药性检测的灵敏度、特异度和准确率也可达到100％(8/8)、90％(18/20)和92.9％(26/28).结论 快速多黏菌素NP法具有快速、简便、准确的优点,在肠杆菌科细菌的多黏菌素耐药性检测方面具有良好的应用价值,经改良后也可应用于鲍曼不动杆菌的多黏菌素耐药性检测,为当前临床快速可靠检测病原菌对多黏菌素耐药性提供了新的策略.

Purpose To investigate transitions in resistance mechanisms, virulence characteristics and molecular epidemiology of carbapenem-resistant Klebsiella pneumoniae (CRKP) during 2003–2016 in a major Eastern Chinese medical center. Patients and Methods From a total of 2299 K. pneumoniae clinical strains collected from 2003 to 2016, 214 were found to be CRKP isolates and were selected for further study. Characterization of these was conducted by molecular detection of antibiotic resistance markers and virulence determinants, modified carbapenem inactivation method and multilocus sequence typing (MLST). Results In this study, the prevalence of CRKP was increasing over the 14-year period, mirroring a national trend. These CRKP strains were resistant to most of the tested, clinically relevant drugs. The majority of these CRKP strains were positive for carbapenemases, with the Klebsiella pneumoniae carbapenemase (KPC) found to be the dominant type (207/210, 98.6%). The carrier rates of virulence genes uge, entB, fimH, mrkD and ureA increased in 2016, while the ybtA, iucA and irp2 showed a relatively constant trend. From MLST data, ST11 (88.8%, 190/214) was the preponderant sequence type (ST), followed by ST15 (1.9%, 4/214) and ST656 (1.4%, 3/214). Several strains with less common STs (ST690, ST895, ST1823 and ST1384) were also detected, and these too showed high levels of antimicrobial resistance. Conclusion The average national rise in CRKP across China is mirrored in this in-depth analysis of a single hospital, while the prevalence of hypervirulent CRKP (such as ST15) was relatively low as of 2016. Continuous monitoring is necessary to keep track of CRKP and should include the prospect of newly emerging strains with less common STs and the prospect of detecting carbapenem-resistant, carbapenemase-negative Klebsiella pneumoniae.

目的 研究黏菌素分别与氯霉素、左氧氟沙星、头孢他啶、米诺环素及复方磺胺甲噁唑联用对多重耐药嗜麦芽寡养单胞菌的体外抗菌活性.方法 收集2015-2018年分离自温州医科大学附属第一医院的431株嗜麦芽寡养单胞菌;采用微量肉汤稀释法检测黏菌素对嗜麦芽寡养单胞菌的最低抑菌浓度(minimal inhibitory concentration,MIC),计算逐年耐药率;通过棋盘法和微量肉汤稀释法检测黏菌素分别与氯霉素、左氧氟沙星、头孢他啶、米诺环素与复方磺胺甲噁唑联用及各自单用时对多重耐药嗜麦芽寡养单胞菌的MIC值,并通过计算部分抑菌浓度指数(FICI)评价联合抑菌效果.结果 2015-2018年间,我院嗜麦芽寡养单胞菌对黏菌素的耐药率呈现逐年上升趋势;黏菌素与氯霉素、左氧氟沙星及米诺环素联用后均表现为协同或相加作用;与头孢他啶及复方磺胺甲噁唑联用都存在无关作用,未发现拮抗作用.结论 黏菌素与氯霉素、左氧氟沙星、米诺环素联合对多重耐药嗜麦芽寡养单胞菌具有较好的体外抗菌活性,将对临床联合用药治疗多重耐药嗜麦芽寡养单胞菌的选择更具指导意义.

OBJECTIVES:The aim of this study was to investigate the mechanisms of fosfomycin resistance and epidemiological characteristics in fosfomycin-resistant enterococci in China.METHODS:A collection of 761 enterococcal clinical isolates from a teaching hospital in Wenzhou, China were studied. The fosfomycin susceptibility of the isolates was investigated by the agar dilution method. The isolates were also analysed for mechanisms of re fosfomycin resistance by PCR and quantitative real-time PCR. Furthermore, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were performed to analyse the molecular epidemiological characteristics of the fosfomycin-resistant isolates.RESULTS:In this study, 0.3% (1/372) of Enterococcus faecalis and 4.9% (19/389) of Enterococcus faecium clinical isolates were found to be resistant to fosfomycin. Among the 20 fosfomycin-resistant isolates, 5 harboured the fosB gene, 10 carried multiple amino acid substitutions in MurA, and 6 showed high-level expression of the fosX gene; of note, 1 isolate simultaneously carried fosB and amino acid mutation in MurA. Furthermore, a high degree of homology in the fosfomycin-resistant enterococci was confirmed using MLST and PFGE.CONCLUSION:These finding demonstrate that the fosB gene, mutations in the fosfomycin target enzyme MurA, and a high expression level of fosX were the resistance mechanisms in these fosfomycin-resistant enterococci.

Objective:To study the in vitro antibacterial activity of three carbapenems in combination with colistin against Enterobacter cloacae complex resistant to both carbapenems and colistin. Methods:Strains of the Enterobacter cloacae complex were isolated from various clinical specimens in the First Affiliated Hospital of Wenzhou Medical University from 2011 to 2018. Their susceptibility to common antimicrobials was detected by Vitek 2-Compact automatic microbial analyzer. A total of 19 isolates of the Enterobacter cloacae complex that were resistant to carbapenems and colistin were screened out. The minimum inhibitory concentrations of carbapenems and colistin to the 19 isolates were detected with agar dilution method. Checkerboard method was used to evaluate the in vitro antibacterial activity of three combination therapy strategies to the co-resistant Enterobacter cloacae complex. Results:The resistance rates of the 19 strains to the first- and third-generation cephalosporins were higher than 90%. Their resistance rates to ertapenem, meropenem and imipenem were 100%, 26.3% and 31.6%, respectively. The combined effect of colistin with imipenem, meropenem or ertapenem on the Enterobacter cloacae complex was mainly synergistic or additive. Both meropenem and imipenem combined with colistin showed unrelated effect to one strain. Conclusions:The combination of carbapenems with colistin had better antibacterial effects on the Enterobacter cloacae complex resistant to both carbapenems and colistin, suggesting a potential treatment strategy for infections caused by multidrug-resistant Enterobacter cloacae complex.

Background: The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a looming threat to human health. Although there are numerous studies regarding porin alteration in association with the production of ESBLs and/or AmpC β-lactamase, a systematic study on the treatment-emergence of porins alteration in antibiotic resistance does not yet exist. The aim of this study was to investigate the underlying mechanism of resistance of K. pneumoniae during carbapenem treatment. Results: Here, we report three strains (FK-2624, FK-2723 and FK-2820) isolated from one patient before and after imipenem treatment during hospitalization. Antibiotic susceptibility testing indicated that that the first isolate, FK-2624, was susceptible to almost all tested antimicrobials, being resistant only to fosfomycin. The subsequent isolates FK-2723 and FK-2820 were multidrug resistant (MDR). After imipenem therapy, FK-2820 was found to be carbapenem-resistant. PCR and Genome Sequencing analysis indicated that oqxA, and fosA5 , were identified in all three strains. In addition, FK-2624 also harbored bla SHV - 187 and bla TEM-116 . The bla SHV - 187 and bla TEM-116 genes were not detected in FK-2723 and FK-2820. bla DHA -1, qnrB4 , aac (6’)-IIc, and bla SHV - 12 , EreA2, CatA2, SulI, and tetD , were identified in both FK-2723 and FK-2820. Moreover, the genes bla DHA -1, qnrB4 , aac (6’)-IIc were co-harbored on a plasmid. Of the virulence factors found in this study, ybtA, ICEKp6, mrkD, entB, iroN, rmpA2-6, wzi16 and capsular serotype K57 were found in the three isolates. The results of pairwise comparisons, multi-locus sequencing typing (MLST) and pulsed-field gel electrophoresis (PFGE) revealed high homology among the isolates. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that isolate FK-2820 lacked OmpK36, with genome sequence data validating that there was a premature stop codon in the ompK36 gene and real-time RT-PCR suggesting high turnover of the ompK36 non-sense transcript in FK-2820, with the steady-state mRNA level 0.007 relative to the initial isolate. Conclusion: This study in China highlight that the alteration of outer membrane porins due to the 14-day use of imipenem play a potential role in leading to clinical presentation of carbapenem-resistance. This is the first description of increased resistance developing from a carbapenem-susceptible K. pneumoniae with imipenem treatment driven by outer membrane remodeling.

Objective:To investigate the role of type Ⅵ secretion system (T6SS) in the pathogenicity and antibiotic resistance of Acinetobacter baumanii. Methods:From January 1 to December 31, 2016, a total of 45 Acinetobacter baumanii isolates were collected from patients with bloodstream infection in the First Affiliated Hospital of Wenzhou Medical University. The susceptibilities to commonly used antimicrobial agents were determined by VITEK 2 Compact automatic microbiology analyzer. Detection of T6SS characteristic gene hemolysin coregulated protein ( hcp) was achieved by polymerase chain reaction. Biofilm formations, serum resistances and competition tests of T6SS-positive/negative Acinetobacter baumanii were performed in vitro. The clinical data of patients with bloodstream infection were collected and analyzed. Chi-square test, t test and Kruskal-Wallis test were conducted for statistical analysis. Results:The positive rate of T6SS in 45 Acinetobacter baumanii isolates was 53.3% (24/45). The resistance rates of T6SS-positive Acinetobacter baumanii to ceftazidime, ciprofloxdcin, gentamicin, imipenem, levofloxacin, piperacillin/tazobactam, tobramycin and cefepime (95.8%, 95.8%, 66.7%, 95.8%, 79.2%, 95.8%, 79.2%, 91.7%)were all higher than that of T6SS-negative Acinetobacter baumanii (28.6%, 28.6%, 28.6%, 28.6%, 9.5%, 23.8%, 23.8%, 28.6%), and the differences were all statistically significant ( χ2=22.12, 22.12, 6.51, 22.12, 21.83, 24.72, 13.79, 18.97, respectively, all P<0.05). The biofilm formation ability, serum resistance and competitive ability of T6SS-positive Acinetobacter baumanii were stronger than those of T6SS-negative Acinetobacter baumanii, and the differences were all statistically significant ( t=4.99, Z=-2.61 and -2.27, respectively, all P<0.05). The positive rate of T6SS isolated from intensive care unit (ICU) ward (80.0%, 16/20) was significantly higher than that from non-ICU ward (32.0%, 8/25; χ2=10.29, P<0.05). But T6SS had no effect on the prognosis of patients ( χ2=1.74, P=0.188). Conclusions:T6SS of Acinetobacter baumanii is associated with high pathogenicity, and the high drug resistance rate makes treatment extremely difficult. Physicians need to pay much attention, especially to the patients from ICU wards.

目的 探究龙血竭对分离自伤口感染的铜绿假单胞菌的抗菌活性,为临床合理使用龙血竭抗感染治疗提供依据.方法 收集2017年温州医科大学附属第一医院分离自伤口标本的铜绿假单胞菌26株,琼脂稀释法检测龙血竭对铜绿假单胞菌的最低抑菌浓度(MIC);生长曲线试验、半定量结晶紫染色法和细菌泳动试验分别检测龙血竭对铜绿假单胞菌的生长、生物膜形成能力、泳动能力的影响;实时荧光定量PCR方法检测生物膜形成相关基因的表达情况.结果 龙血竭对铜绿假单胞菌的MIC值为＞5000μg/mL;512μg/mL龙血竭能降低铜绿假单胞菌的生长速率和最大生长量;各浓度的龙血竭能降低铜绿假单胞菌的生物膜形成能力;经龙血竭处理的铜绿假单胞菌的生物膜形成相关基因pslA、pelA、algD、algU的表达量有所降低;铜绿假单胞菌在含≥128μg/mL龙血竭的泳动平板表面的扩散直径减小.结论 龙血竭对铜绿假单胞菌的生长具有一定的抑制作用,并能通过降低slA、pelA、algD、algU基因的表达水平降低其生物膜形成能力,同时可以降低细菌的泳动能力,进而在治疗铜绿假单胞菌所致的伤口感染中发挥作用.

Background Colistin resistance is considered a serious problem due to a lack of alternative antibiotics. The Rapid ResaPolymyxin Acinetobacter/Pseudomonas NP test is a resazurin reduction-based technique that relies on the visual detection of bacterial growth in the presence of a defined concentration of colistin. The aim of this study was to evaluate the performance of the Rapid ResaPolymyxin Acinetobacter/Pseudomonas NP test in the detection of colistin susceptibility in common clinical Gram-negative bacteria. Results A total of 253 clinical isolates from a teaching hospital, including Acinetobacter baumanii (n = 58, 8 colistin-resistant), Pseudomonas aeruginosa (n = 61, 11 colistin-resistant), Klebsiella pneumoniae (n = 70, 20 colistin-resistant) and Escherichia coli (n = 64, 14 colistin-resistant) were tested in this study. The sensitivity and specificity of the Rapid ResaPolymyxin Acinetobacter/Pseudomonas NP test compared to Broth microdilution method was 100 and 99%, respectively. Conclusions Our results suggest that Rapid ResaPolymyxin Acinetobacter/Pseudomonas NP test could be used as an accurate detection method for colistin resistance.

The emergence of carbapenem-resistant Kelbsiella pneumoniae (CRKP) posed threats to human health. Although there are numerous studies regarding porin alteration in association with the production of ESBLs and/or AmpC β-lactamase, a systematic research about the treatment-emergence of porins alteration in antibiotic resistance does not exist yet. The aim of this study was to investigate the underlying mechanism and evolution of resistance of K. pneumoniae during carbapenem treatment. Here, we reported three strains (FK-2624, FK-2723 and FK-2820) isolated from one patient before and after imipenem treatment during hospitalization. Antibiotic susceptibility testing indicated that FK-2624 was susceptible to almost antimicrobials but fosfomycin; FK-2723 and FK-2820 were MDR. After imipenem therapy, FK-2820 was evolved to carbapenem-resistant. PCR and Whole-Genome sequencing ( WGS) indicated that resistance genes bla SHV , oqxA and fosA5 were detected in FK-2624, in addition, FK-2723 and FK-2820 harbored bla DHA , qnrB , aac (6’)-Ib . Virulence factors K57, ybtA, mrkD, entB and iroN were detected simultaneously in all of three strains. The results of pairwise comparisons , multi-locus sequencing typing (MLST) and pulsed-field gel electrophoresis (PFGE) revealed high homology among the isolates. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that isolate FK-2820 lacked OmpK 36 as there was a premature stop codon of the outer membrane porin encoding gene ompk36 confirmed by sequencing. Real-time RT-PCR revealed that the expression of ompK36 in FK-2820 was 0.093 times the control isolate ATCC 13883. Our study highlighted that the alteration of outer membrane porins due to the 14-day use of imipenem clinically play a potential role in leading to the carbapenems-resistance of FK-2820.