Research On The Epidemic Characteristics,Mechanisms Of Resistance And Antimicrobial Screening Of Acinetobacter Baumanii Isolates To Senile Patients

Background:Acinetobacter baumannii is one of the most common opportunistic pathogens associated with hospital acquired infections.Senile patients are at high risk of A.baumannii infection because of their characteristics of hypoimmunity and long-term hospitalization.Objective:?1?Cross-sectional and longitudinal study was done among the senile patients to summarize the clinical characteristics,risk factors and epidemic characteristics during a period of two years?2011-2012?.?2?To investigate the clonal relatedness of A.baumannii isolates in our gerontal wards by conducting cross-sectional and longitudinal studies on genomic diversity.?3?To detect carbapenemase genes in order to handle carbapenemase genotypes of A.baumannii isolates in our gerontal wards.?4?Combined antimicrobial sensitivity test was conducted to evaluate in vitro activities of antimicrobial combinations against MDR and XDR and provide the effective combinations for clinical treatments.Methods:?1?Cross-sectional study was done among the 170 non-repetitive A.baumannii isolates that were recovered from senile patients during a period of two years.Longitudinal study was conducted among 77 repetitive A.baumannii isolates recovered from 8 senile patients within longtime hospitalization.Clinical diagnosis and treatments,clinical features,predisposing factors and antimicrobial sensitivity of bacteria were analyzed.?2?The genomic diversity of 170 non-repetitive isolates and 77 repetitive A.baumannii were analyzed by PFGE respectively.?3?11 carbapenemases genes of 170 strains were detected by PCR:OXA-51,OXA-23,OXA-24,OXA-58,VIM,IMP,SIM,GIM,DIM,NDM-1,KPC.?4?Combined antimicrobial sensitivity tests of 114 MDR AB were done by agar dilution methods,and antimicrobial combinations were as follows:SCF combined with MH,SCF combined with PE,SCF combined with MEM,SCF combined with IMP,PE combined with MEM,MH combined with PE.Finally,the FIC indices were calculated to reflect the combination effects.Findings:?1?In Cross-sectional study,the quantities of A.baumannii were second in all kind of clinical isolates,and the drug resistance rates of AB were obviously higher than P.aeruginosa which was the top one for quantities.Most of the 170 isolates?128/170,75.3%?were non-susceptible to carbapenems,and all CRAB were XDR or MDR which spread evenly all over the different departments in senile wards.All the 170 senile patients had multiple fundamental illnesses related to multi-organism.The most commonly used medicines were broad spectrum antibiotics such as ?-lactamase inhibitor combinations,carbapenems and fluoroquinolone with a long period of treatment.In longitudinal study,all patients had prolonged or repeated infections,and all the 77 isolates were XDR phenotype.?2?The isolates belonged to 36 pulsotypes determined by PFGE.Groups I to IV?contain119,4,1,2 isolates respectively?were major epidemic strains with similar clonal relatedness?similarity>80%?,98.4%?124/126?of which were CRAB with XDR phenotype.In longitudinal study,comparison of pulsotypes was performed for each patient and all isolates were clustered into group I except one isolate which belonged to a new group.?3?OXA-51was detected in all 170 isolates,besides that,the most positive gene was OXA-23 in CRAB?122/128,95.3%?,others positive results were that:blaVIM?1?,blaDIM?1?,blaSIM?2?,blaNDM?3?,blaKPC?11?.Most CSAB was detected with the negative result of OXA-23?40/42,95.2%?,and IMP and GIM genes were not detected any more.?4?When SCF was combined with IMP,there were 62.3%isolates displayed synergism and addition effect,the major effect was addition;When SCF was combined with MEM,there were 70.2%displayed synergism and addition effect,the major effect was addition;When SCF was combined with MH,there were only 48.7%isolates displayed synergism and addition effect,the major effect was addition;When PE was combined with SCF,there were 94.7%isolates displayed synergism and addition effect,the major effect was addition;When PE was combined with MEM,there were 99.1%isolates displayed synergism and addition effect,and 40%of which were synergism;When PE was combined with MH,there were 99.1%isolates displayed synergism and addition effect,the major effect was synergism.There was no antagonism in all combinations.Conclusion:?1?Resistance rate against microbial of A.baumannii isolated from our gerontal wards was higher than the average level in China;Mechanical ventilation was one of the important risk factors of resistant AB strains infection;The CRAB infection group with poorer prognosis compared with CSAB group.?2?Extensive drug-resistance of A.baumannii was a serious problem in our gerontal wards.The pulsotype I was major epidemic strain,which had led to the widespread dissemination,regardless of time or space.Clone dissemination was the most important style of XDR strains spread.Horizontal infection control measures to interrupt person-to-person transmission should be reinforced to reduce the further spread of XDR A.baumannii.?3?bla_OXA-23 was the major epidemic resistant genotype in our gerontal wards,and which had a satisfactory relationship with the resistant phenotype of CRAB.The detection of bla_OXA-51 bla_OXA-23 may be a possible method for rapid screening CRAB.?4?When PE was combined with SCF or MEM or MH,the combination displayed predominance synergism and addition effect.While the effect was just moderately well when SCF was combined with IMP or MEM,and SCF had a middle result when combined with MH.