Study On The Antibacterial Activity Of Tigecyclline Combined With Sulbactam Against Pan-resistant Acinetobacter Baumannii In Vitro

ObjectiveAcinetobacter baumannii has become a troublesome pathogen with thedevelopment of medical technology and over-abuse of broad-spectrum drugs,glucocorticoids and immunosuppressant. Due to its capability of rapidly getingand spreading drug-resistance, the multi-drug resistant,pan-resistant and allresistant Acinetobacter baumannii has been worldwide epidemic, which alsocontributes to its being focus of scientific attention.We can see that the situationof Acinetobacter baumannii infection is very serious according to the datafrom2010China CHINET Bacterial Resistance Monitoring Network, Detectionrate of acinetobacter is just after Escherichia coli and Klebsiella pneumoniae inthe respiratory tract infection, and infection rate of Acinetobacter baumannii ishigher and higher year by year, however,Acinetobacter baumannii has been themain pathogen of pulmonary nosocomial infection. What is more, it also cancause urinary tract infections, secondary meningitis, septicemia and so on.In theICU Acinetobacter baumanniieasy is easy to cause the outbreak,which is a greatthreat to patients in the intensive care unit (ICU). Recently, it is also found thata lot of military and non-military personnel from the United Kingdom and theUnited States in Iraq and Afghanistan infected with drug-resistant Acinetobacterbaumannii, Further to say Acinetobacter baumannii infection severity. Inclinical infections of resistant strains, clinical treatment is very difficult, oreven no drugs available. For drug-resistant strains, clinical often choosetigecycline United sulbactam treatment, and achieved a certain effect, but forwhether both have a synergistic role is not yet clear.This study aims to provide scientific basis for the clinical use of drugs via observing different MIC fromtigecycline and sulbactam used alone and two-drug combination.Materials and methodsStrains: Material, that is32pan-resistant Acinetobacter baumannii (24came from sputum samples,4came from secretions,2came from drainage fluid,and2came from cerebrospinal fluid), collected in April2011to September2012, in the Jinan Military General Hospital, isolated from clinical specimins.Standard quality control strains:Escherichia coli ATCC25922, Escherichiacoli ATCC35218(for monitoringβ-lactam/beta-lactamase inhibitor paper) fromBacteria room of Jinan Military General Hospital.Antibiotics:(1)Ampicillin/sulbactam, ciprofloxacin, levofloxacin, mer-openem, Imipenem, gentamicin, tobramycin, amikacin, kanamycin, piperacillin,piperacillin/tazobactam, cefepime, ceftriaxone, cefotaxime, doxycycline, mino-cycline doxycycline, cotrimoxazole, cefoperazone/sulbactam susceptibility pap-ers are purchased from the Oxoid Thermo Fisher Biochemical Products Co,Ltd.(2)Import injection Tigecycline,50mg/branch, provided by Pfizer Pharm-aceutical Co.Ltd.(3)Import injection Sulbactam,0.5g/branch, provided by QiluPharmaceutical Co. Ltd.MethodsCollecting Clinical Infectious specimens from Jinan Military GeneralHospital, applying conventional cultivation methods, isolating bacterial, ident-ifying Acinetobacter baurnannii by VITE-2automatic Analyzer, using a varietyof antibioties to do susceptibility testing by the disk diffusion method, selecting32pan-resistant Acinetobacter baumanniis. Firstly add100ul broth separatelyinto96-well sterile polystyrene plate under asepsis operation, secondly addtigecycline and sulbactam separately into96-well plates and dilute propor-tionally continuously,thirdly put100ul bacterial suspension under concentrationof3×105CFU/ml into the wells until the concentration is1.5×105CFU/ml, thenmeasure MIC of tigecycline and sulbactam separately after overnight culture,next apply checkerboard micro broth dilution method (horizontal for thesulbactam down gradient direction, vertical for tigecycline down gradientdirection) to measure MIC of each drug based on MIC gotten before andcalculate FIC according to MIC measured before and after tigecycline combinedwith sulbactam.Lastly select strains presenting synergy as tigecycline combined with sulbactam to further evaluate the interaction of the two drugs through timekilling curve method.ResultSelecting32Acinetobacter baumannii identified by VITEK-2analyzer viaWHONET5.4software and doing susceptibility testing again by disk diffusionmethod, the32Acinetobacter baumanniithe are definately pan-resistant. Dete-ction results of17antimicrobial drugs against32pan-resistant Acinetobacterbaumannii: ampicillin/sulbactam, ciprofloxacin, levofloxacin, meropenem, imi-penem, gentamicin, properly cloth neomycin, amikacin, piperacillin, piperacillin/tazobactam, cefepime, ceftriaxone, cefotaxime, doxycycline, mino-cycline,co-trimoxazole and cefoperazone/sulbactam resistant rate are all100%.The MIC of Sulbactam against32XDRAB ranges32to128ug/ml, MIC90is128ug/ml.The MIC of tigecycline against32XDRAB ranges0.5to1ug/ml,MIC90is1ug/ml. Sulbactam combined with tigecycline: synergy is28.1%(9/32), the additive effect is62.3%(20/32), no correlation effect is9.3%(3/32),no antagonism. Selecting MIC of tigecycline and sulbactam being both0.5×MIC from9collaborative XDR Acinetobacter baumannii measured by thecheckerboard broth method to evaluate by time killing curve method,we can seethat nine XDR Acinetobacter baumannii showed synergy, and no antagonism asthe two drugs combined.ConclusionSulbactam combined with tigecycline often showed synergistic or additiveeffect against the XDR Acinetobacter baumannii. Therefore for the clinicaltreatment of severe infections caused by XDRAB, we can apply sulbactamcombined with tigecycline method based on susceptibility testing.