| 1The significance of quantitative culture, total cell counts and of trachealaspirate in patients with invasive mechanical ventilation for positiveculture of Acinetobacter baumanniiObjective: To investigate the value of quantitative culture, total cellcounts and Gram staining of tracheal aspirate in patients with invasivemechanical ventilation for the positive tracheal aspirate culture findings of A.baumannii in the diagnosis of lower airway bacterial colonization andinfection．Methods: From October2011to January2012, a prospectiveobservational cohort survey was carried out in patients on mechanicalventilation (MV) for more than48hours with positive tracheal aspirate culturefindings for A. baumannii admitted to the ICU of four teaching hospitals.Quantitative culture, total cell counts examined in a hemocytometer and Gramstaining of tracheal aspirate (TA) were performed. Based on the ClinicalPulmonary Infection Score (CPIS) and results of quantitative culture, allsubjects were divided into two groups: the infection group and thecolonization group. Then the quantification of infected cells (IC),polymorphonuclear leukocytes (PMNL), number of bacteria in Gram stainmethod (GRAM), total cell counts and absolute neutrophils percentages of TAwere compared to evaluate the value of them in diagnosis of infection andcolonization. When the findings of qualitative cultures and quantitativecultures of TA were inconsistent, a change or not in antibiotic agents based onnumerically dominant bacteria of quantitative cultures was at the discretion ofthe attending physician. If changed, serial monitoring with surveillance cultures using quantitative TA specimens was conducted to analysis the effectof the change.Results:30patients on MV for>48h prospectively were enrolled in thisstudy. Among them25patients were diagnosed of ventilator-associatedrespiratory infection(VARI), and5were colonization. In the qualitativeanalysis of TA, none presented epithelial cell numbers higher than10/field.Cytological analysis of TA showed that VARI patients presented higher valuesin those Gram stain parameters that are suggestive of infection. In addition, ofthe25VARI group,55%presented with infected cell percentages＞2%in TAand whereas no infected cells were identified in the colonization group.Furthermore, among the VARI patients, leukocyte counts were higher than25/field in80%of the TA in contrast to20%among patients in thecolonization group. Moreover,68%patients in the VARI group presented withbacterial counts were above10/field in comparison with20%in thecolonization group. If it was used at least2of the positive parameters forinfection, the sensitivity and specificity in the diagnosis of VARI was64%and80%. Considering the3positive parameters, sensitivity was44%, andspecificity was100%. In the colonization group the mean total cell count ofthe TA was2.31±0.47×106/g (mean±sd) with proportion of neutrophils48.2%,in the VARI group it was11.27±6.06×106/g (mean±sd) with proportion ofneutrophils86.1%and had a significant difference. Between Gram stainresults and the quantitative culture results for TA, there was total agreement in80%of cases, partial agreement in16.6%and no agreement in3.3%, and therewas moderate agreement (kappa coefficient=0.412). In this study,64%A.baumannii infections were polymicrobial infections, and44%infections werecaused by polymicrobial A. baumannii and Pseudomonas aeruginosa. In3cases, the findings of qualitative cultures and quantitative cultures of TA wereinconsistent, numerically dominant Gram-positive bacteria considered ascontamination by oropharyngeal colonization was ignored by qualitativecultures, and a change in antibiotic agents was effective.Conclusions:(1) If the Gram stain procedure is carefully performed and the quality of the sample is guaranteed, it may help diagnose of lower airwaybacterial colonization and infection until the results of the quantitative culturesare available.(2) Total cell counts and neutrophil percentages of trachealaspirate in mechanically ventilated patients in the infection group and thecolonization group have a significant difference.(3) Most of VARI caused byA. baumannii is polymicrobial infection; there could be a symbioticrelationship between it and the other bacteria. Gram-positive bacteria found byqualitative cultures of tracheal aspirate should not be ignored.2In vitro activities of carbapenems combined with sulbactam andtigecycline against XDR Acinetobacter baumanniiObjective: A. baumannii has emerged as one of the most troublesomeinfectious pathogens for health care institutions globally, for its remarkableacquired and cumulative resistance determinants. As the emergence andfrequent outbreaks of XDR (extensive-drug resistant)/PDR (pan-drug resistant)A. baumannii, and the fact they are resistant to all commercially availableantibiotics, clinical and social problems in controlling XDR/PDR A.baumannii are serious and urgent to be solved. Though it was reported that invitro other carbapenems combined with sulbactam and tigecycline againstXDR A. baumannii showed synergistic activities, none had focused on thebiapenem/sulbactam and biapenem/tigecycline combinations, and there is noreport about imipenem combined with sulbactam and tigecycline in thedomestic. So we state the study of in vitro activities of carbapenems combinedwith sulbactam and tigecycline against XDR A.baumannii to evaluate theactivities of combinations and provide the basis for combination therapy.Methods:22clinical isolates of XDR A. baumannii had been collectedand susceptibility testing was performed by the disk diffusion method. Allbacterial isolates were isolated from tracheal aspirate, stored inMueller-Hinton broth with15%glycerol and frozen at-80°C. MICs forbiapenem, imipenem, sulbactam and tigecycline alone were determined bybroth microdilution method. The checkerboard microdilution panel method,performed in96-well broth microdilution plates containing two antimicrobial agents in two-fold dilutions dispensed in a checkerboard format, was used forthe MIC determination of biapenem, imipenem combined with sulbactam andtigecycline. FICI was calculated for each combination based on the MICs andtime-kill assays at0.5×MIC were performed on the biapenem/sulbactam andbiapenem/tigecycline combinations found synergistic or antagonistic bycheckerboard microdilution panel method.Results： The checkerboard microdilution panel method withbiapenem/sulbactam combination demonstrated36.4%(8/22) synergism,40.9%(9/22) partial synergism,4.5%(1/22) additive,18.1%(4/22)indifference, and no antagonism. For the combination of imipenem/sulbactam,31.8%(7/22) synergism,45.5%(10/22) partial synergism,4.5%(1/22)additive,18.1%(4/22) indifference, and no antagonism was found. The XDRA. baumannii isolates of low-levels resistance to biapenem or imipenem,combined with sulbactam, demonstrated MIC90for biapenem or imipenemwas8μg/ml and within the susceptible range. Biapenem/tigecyclinecombination demonstrated the following interactions13.6%(3/22) synergism,50%(11/22) partial synergism,18.1%(4/22) additive,18.1%(4/22)indifference, and no antagonism and imipenem/tigecycline suggested similarresult. For8isolates for which biapenem/sulbactam showed synergism and3isolates for which biapenem/tigecycline showed synergism by checkerboardmicrodilution panel method, time-kill assays confirmed the synergisticinteraction between biapenem and sulbactam (3/8), and no antagonism wasconfirmed by time-kill assays.Conclusions: Biapenem/sulbactam and imipenem/sulbactamcombinations show synergism or partial synergism against most XDR A.baumannii isolates. For the XDR A. baumannii isolates of low-levelsresistance to the biapenem or imipenem, biapenem/sulbactam orimipenem/sulbactam combinations may be as a choice of combinationtherapies. Biapenem/tigecycline and imipenem/tigecycline combinationsshow synergism or partial synergism against most XDR A. baumanniiisolates, no antagonism found. The results from checkerboard microdilution panel method may disagree with the time depending on theconcentration studied in the time-kill test. |
PDF Full Text Request