Analysis Of Epidemiological And Natural Competence Related Genes Of Acinetobacter Baumannii

bjective: To analyze the clinical distribution and drugresistance characteristics of Acinetobcter baumannii, so as to providescientific basis for clinical medication. To study the expression ofcompetence genes in A.baumannii, contributing to an improvedunderstanding of the mechanism of uptaking exogenous DNA elements,and providing a new thought to control multidrug-resistant A.baumanniiinfections. Methods: The distribution and drug resistance of A.baumanniiisolated from the infectious specimens of the inpatients during2009to2012were analyzed retrospectively. Competence related genes ofA.baumannii were obtained by comparative genomics, the whole genomesequences of A.baumannii were compared with Acinetobacter sp. strainBD413and Thermus thermophilus strain HB27, the latter two organismwere well-established models for natural transformation studies. Therelateness between the expression of comB and growth phases ofA.baumannii were studied by RT-PCR. The expression character ofcomB、comP、pilC、pilU、comM and comEA, under different stimulusconditions（exogenous DNA, Antimicrobial agents and iron deficiency）,were analyzed by Reverse transcription PCR and Real-time PCR. Results:The main infection departments of A.baumannii isolates were neurologydepartment, ICU, geriatrics and respiratory department with detectionrates of28.2%、23.6%、16.8%and9.8%, respectively；the isolation rateof1140strains of A.baumannii from sputum（94.9%） was the highest; theresistance rate of A.baumannii against amikacin（14.1%） remained stableand low, the drug resistance rates to other commonly used antibioticsincluding carbapenems increased rapidly during2009to2011, though dropping a little in2012than in2011, which were still high.18competence genes were obtained, including pilus related genes,A1S₃166（comE）、A1S₃167（comC）、A1S₃165（comF）、A1S₃168（comB）and A1S₃177（comP）; type Ⅳ prepilin peptidase genes,A1S₀327（pilD）、A1S₀328（pilC）and A1S₀329（pilB）; twitchingmotility protein encoding genes, A1S₀896（pilU）and A1S₀897（pilT）;DNA receportor genes, A1S₀582（comEA）; inner membrane channelencoding gene, A1S₂610（comEC）; and inner membrane integratedtransporter encoding genes, A1S₃195（comM）、A1S₃004（pilN）andA1S₃193（pilO）. The competence gene comB expression was agrowth-phase-dependent manner. Foreign DNA was unable to induce theexpression of competence genes. Competence genes expression increasedobviously in response to Mitomycin C stimulation; under chlorhexdinestimulating, however, these genes were not induced. In iron limitingculture, competence genes expression had raised, but the expressiondegree not so as MMC. Conclusion: A.baumannii drug resistance is veryserious in our hospital, and raised year by year. The main infectiondepartments of A.baumannii isolates are neurology department and ICU,and a large number of A.baumannii strains are isolated from sputum. Weshould attach great importance to the dynamic monitoring of nosocomialinfection and drug resistacne of A.baumannii, it is necessary to conductthe anti-infection treatment according to drug susceptibility texting so asto effectively control the outbreak of multidrug-resistant A.baumannii.A.baumannii may be a natural transformation organism, there arecompetence genes in its genome, the expression of these competencegenes depend on growth phase. Natural transformation is strictlyregulated by bacterial inherent genes, and has nothing to do with theexistence of exogenous DNA. DNA-damaging antimicrobial agents induce expression of competence genes of A.baumannii, however, not soas to other physical fungicides. Nutrient limiting conditions are also ableto enhance competence genes expression.