| Background and aims:Acinetobacter baumannii is a clinically important non-fermentative conditional pathogens in China.It can widely exist and survive for a long time in natural and hospital environment.A.baumannii causes the infections via invasive medical operations such as arteriovenous catheterization and tracheal intubation,especially for patients with immune deficiency,hypoimmunity or critical illness,in which patients with bloodstream infections have the highest mortality rate.Also,A.baumannii is one of the main pathogens causing biofilm-related infections in the hospital,while biofilm is an important virulence factor of A.baumannii.However,the relationship and mechanism between biofilm formation and drug-resistance of A.baumannii are still controversial.The effect of biofilm formation on disease progression and prognosis of patients and the related mechanism are also worthy of further research and discussion.This research will discuss biofilm formation characterization and related mechanism of A.baumannii in bloodstream.Methods:1.We collected 83 strains of A.baumannii infected by bloodstream in the first Affiliated hospital of Nanchang university during 2015-2017.The biofilm formation ability was evaluated through using crystal violet staining.Two strains which biofilm forming negative strain and biofilm forming strong positive were selected as representative strains,respectively.Scanning electron microscopy was used to observe the biofilm formation and structure.We compared and analyzed the growth curve of A.baumannii and the forming growth curve of biofilm under different biofilm forming abilities.2.We collected the clinical data of 83 patients with bloodstream infection of A.baumannii.Meanwhile,to explore the correlation between biofilm forming ability of A.baumannii and clinical manifestations of patients,we analyzed the drug resistance,department distribution,disease manifestations,progression and prognosis of different strains with different biofilm forming ability.3.To investigate the carrying situation of biofilm-associated genesin 83 A.baumannii infected by bloodstream infection,we selected 10 biofilm-forming related genes reported to verify and analyze the formation of A.baumannii biofilm.The PFGE and MLST molecular typing methods were used to systematically classify A.baumannii.Two strains of A.baumannii with the same PFGE typing and MLST typing but obvious difference in biofilm formation ability were selected for the whole genomes sequencing,we will explore the mechanism of A.baumannii biofilm formation by bloodstream infection from a genetic level.Relusts:1.62 strains(74.7%)in the 83 strains of A.baumannii infected with bloodstream were able to form biofilms,of which 17 strains(27.4%)showed strongly positive expression while 45 were weak positive.Scanning electron microscopy showed that the biofilm formation strongly positive of flora was surrounded by a large amount of flocculent mucous material and formed a cloud-like biofilm structure,while the biofilm formation negative specimens almost only showed the exposed microbial clusters.There was no significant difference in the growth rate of strains with different biofilm formation ability,but the difference in biofilm formation measured by strain culture for 24 hours was obvious,and it can most reflect the ability of the biofilm formation.2.Among 83 strains of A.baumannii infected by bloodstream,49 strains(59.0%)were extensively drug resistant(XDR)bacteria(13 of them were full-resistant bacteria,accounting for 15.7%),and 16strains(19.3%)were multidrug resistant(MDR).XDR and MDR bacteria accounted for the vast majority of all strains(78.3%),and the remaining 18 strains(21.7%)were sensitive bacteria.The biofilm formation rate of sensitive strains was 94.4%,which was higher than 69.2% of the drug-resistant strains,and the difference was statistically significant(P<0.05).However,there was no significant difference in biofilm forming ability between the XDR strains and the MDR strains.We collected 83 strains which were mainly distributed in ICU(49 strains)and burn department(11 strains),and studied their resistance to 19 kinds of commonly used clinical antibiotics from 8 categories.The drug resistance rates of all strains were almost above70%.To ceftazidime,ceftriaxone,cefepime,cefotaxime,cefuroxime and meropenem,the drug resistance rates of negative biofilm formation strains were higher than those of positive biofilm formation strains,the difference was statistically significant Significance(P<0.05).For the other 13 antibiotics,the biofilm forming ability of the strain had no significant effect on the drug resistance,and the difference was not statistically significant(P>0.05).83 strains of A.baumannii were divided into two groups : good prognosis and poor prognosis.It was found that central venous catheterization,ICU,platelet,complications(malignant tumor,respiratory failure,renal failure)had an impact on the prognosis of patients.The difference was statistical significance(P <0.05).These six factors in the binary logistic regression analysis showed no significant effect on the prognosis of the patients,and the difference was not statistically significant(P>0.05).The 83 strains A.baumannii were divided into biofilm negative and biofilm positive groups.A variety of clinical data were included for comparative analysis.The final results showed that biofilm formation ability was positively correlated with hospitalization days,and the difference was statistically significant(P< 0.05).3..The carrier rate of bap,csuC,csuD,csuE and ompA genes of biofilm formation positive A.baumannii by bloodstream infected was higher than that of biofilm formation negative bacteria(P<0.05).There was no significant difference in the biofilm formation-related gene rate between the weakly positive and strong positive A.baumannii(P>0.05).There was no significant difference in related gene carrying rate between biofilm formation weakly positive and strong positive of A.baumannii(P>0.05).A.baumannii were systematically classified by PFGE and MLST molecular typing methods,and two strains of A.baumannii with the same PFGE typing and different MLST typing in the spects of biofilm formation ability were selected: Samples 516(biomembrane negative)and 632(biomembrane strongly positive)showed that there were base differences between them through three generations of sequencing.By analyzing the non-synonymous mutation differential genes and their respective functions,it was maybe due to the functional differences of LysR family transcription regulator,histone acetyltransferase,DNA binding protein and transcription regulator lead to obvious differences in biomembrane formation ability,and there are non-synonymous mutation differential genes which other gene functions are unknown or COG classification is unknown.Conclusion:1.In this study,most of A.baumanniiin blood stream infecction have strong biofilm formation ability.The growth of A.baumannii does not affect biofilm formation.2.The study demonstrate that the drug resistance of A.baumannii in bloodstream infection is really serious,and it is negatively correlated with biofilm formation ability.When analyzing the factors affecting the prognosis of patients,we haven't found any statistically significant independent risk factor that were related to the prognosis.The biofilm formation ability of A.baumannii only affected the hospitalization days of patients.3.Gene differences among different strains of Acinetobacter baumannii may lead to functional differences,which result in differencet biofilm formation ability of A.baumannii.Biofilm formation is a dynamic process.Any factor involved in biofilm formation process of A.baumannii can affect biofilm formation,and its mechanisms needmore studies going on. |
PDF Full Text Request