The Relation Between Biofilm Formation Ability Of Acinetobacter Baumanii And Hospital-acquired Pneumonia In The Elderly

1. Objective:(1) To probe the clinical features, risk factors and antibiotics-resistantphenotypes of Acinetobactor baumannii (A. baumannii) infections in the elderlypatients in PLA General Hospital, a retrospective analysis of hospital-acquiredpneumonia (HAP) caused by A. baumannii (AB) during2010-2012was performed.(2)The clinical strains of AB, isolated from the sputum specimens of elderly patients withHAP, were examined for biofilm formation on abiotic surfaces to clarify the relationbetween biofilm formation ability of AB and HAP.(3) To explore the correlationbetween cell adhesiveness and HAP caused by AB, the clinical strains of AB wereexamined for bacteria adhesion of human alveolar epithelial cells.(4) The genesassociated to biofilm formation were detected by using PCR to explore the mechanisms.2. Methods:(1)121cases of ABHAP in elderly were analyzed, including the generalcondition, medication history, commodity diseases, clinical manifestations, antibioticsusceptibility, and clinical outcomes, etc.(2) Quantitative estimation of bacterialbiomass in biofilms was assessed in96-well polystyrene microtiter plates, using thecrystal-violet staining method. A case-control study was conducted to compare theclinical factors and drug sensitivity among different biofilm-forming strains.(3) Thenumber of bacteria adhering to A549cells was determined by using Giemsa stainingmethod. ATCC19606Twas used for comparisons.(4) Biofilm-related genes of clinicalisolates were detected by using PCR.3. Results:(1) ABHAP often occurred in patients complicated with other diseases. Mostof the patients were conducted with mechanical ventilation and received broad-spectrumantibiotics before infected with AB. Non-fever accounted for57.9%, and the raise ofWBC accounted for41.3%, in which the increase of neutrophils was predominant(76.0%). The increase of CRP accounted for81.8%．MDR-AB and PDR-AB accountedfor79.3%and24.0%, respectively. Logistic regression analysis showed that APACHE II score was independent risk factor of death in the elderly patients with ABHAP.(2)The AB strains isolated from respiratory tract can form biofilm. The strains with thestrongly positive biofilm-forming ability accounted for27.3%. Biofilm-forming abilitywas inversely correlated with antibiotic resistance to gentamicin, minocycline andceftazidime. The strains that isolated from the patients with low APACHE II score ortreated in non-intensive care unit were associated with positive biofilm-forming ability.There was no correlation between the biofilm-forming ability and disease severity and30-day mortality.(3) In the cell adherence assay, the strains with strong adhesion abilityaccounted for33.9%. There was a significant correlation between biofilm-formingcapacity and cell adhesiveness. The cell adhesion ability was inversely correlated withantibiotic resistance. There was no correlation between the ability of cell adhesivenessand disease severity and30-day mortality.(4) The amplification rate of biofilm-relatedgenes was higher in the strongly positive biofilm formation strains, and there exitssignificant statistical difference in csuAB, csuC, and bfmS gene amplification.4. Conclusions:(1) The clinical manifestations of ABHAP in elderly is not typical. Theincreased proportion of neutrophils and CRP had higher sensitivity. Chest X-ray showedthe signs of bronchial pneumonia. The isolation rate of MDR-AB and PDR-AB areincreasing. APACHE II score was independent risk factor of death in the elderly patientswith ABHAP.(2) Biofilm-forming ability was inversely correlated with antibioticresistance. The strains that isolated from the patients with low APACHE II score ortreated in non-intensive care unit were associated with positive biofilm-forming ability.There was no correlation between the ability of biofilm formation and disease severityand mortality.(3) There was a highly significant correlation between biofilm-formingcapacity and cell adhesiveness. There was no correlation between the ability of celladhesiveness and disease severity and mortality.(4) The regulation of biofilm formationis multifactorial, biofilm related genes were prevalent in clinically strains of AB isolatedfrom the lower respiratory tract, but the amplification was higer in the strongly positivegroup than the weakly positve group.