Research Article In Vitro Antibacterial Interaction of Doripenem and Amikacin against Multidrug-Resistant Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae Isolates Tonny Loho , Ninik Sukartini, Dalima A. W. Astrawinata, Suzanna Immanuel, Diana Aulia, and Ika Priatni Infectious Diseases Division, Department of Clinical Pathology, Faculty of Medicine, Universitas Indonesia, Jakarta, Indonesia CorrespondenceshouldbeaddressedtoTonnyLoho;tonnyloho@yahoo.com Received 23 February 2018; Revised 21 May 2018; Accepted 29 May 2018; Published 3 July 2018 AcademicEditor:JorgeGarbino Copyright©2018TonnyLohoetal.isisanopenaccessarticledistributedundertheCreativeCommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited. Evaluationoftheinvitrointeractionofdoripenemandamikacinagainst Acinetobacter baumannii, Pseudomonas aeruginosa,and Klebsiella pneumoniae was done by classifying them into four groups: doripenem and amikacin sensitive (DOR-S/AMK-S), doripenemsensitiveandamikacinresistant(DOR-S/AMK-R),doripenemresistantandamikacinsensitive(DOR-R/AMK-S),and bothdoripenemandamikacinresistant(DOR-R/AMK-R).eMICofeachantibioticandtheircombinationwasobtainedusing the Etest method. e fractional inhibitory concentration index was calculated to classify the results as synergistic, additive, indifferent,orantagonisticinteraction.IntheDOR-S/AMK-Sclass,1isolateof A. baumannii showedsynergyandtheother5 showed additive results, 5 isolates of P. aeruginosa showed additive and 1 isolate showed indifferent result, and 2 isolates of K. pneumoniae showedadditiveandtheother4showedindifferentresults.IntheDOR-S/AMK-Rclass,3isolatesof A. baumannii showedadditiveandtheother3showedindifferentresults,2isolatesof P. aeruginosa showedindifferentresults,and1isolateof K. pneumoniae showedadditiveandtheother5showedindifferentresults.IntheDOR-R/AMK-Sclass,1isolateof A. baumannii showedadditiveandtheother5showedindifferentresults,1isolateof P. aeruginosa showedadditiveandtheother5showed indifferent results, and 4 isolates of K. pneumoniae showed additive and the other 2 showed indifferent results. In the DOR- R/AMK-Rclass,6isolatesof A. baumannii showedindifferentresults,1isolateof P. aeruginosa showedadditiveandtheother5 showedindifferentresults,and1isolateof K. pneumoniae showedadditiveandtheother5showedindifferentresults.Synergy occurredinonly1(1.5%)isolate.Additiveinteractionoccurredin24(35.3%)isolates,andindifferentinteractionoccurredin43 (63.2%)isolates.DoripenemsensitivecombinedwithamikacinsensitivereducedMICsignificantlyinallbacterialisolateswhen comparedtosingleMICofeachantibiotic. 1. Background ewideoveruseormisuseofantibioticshasbeenfollowed by the emergence of resistant bacteria causing healthcare- associated and community-acquired infections worldwide [1].Manyofthepathogensrelatedtotheepidemicinfectious diseases in humans have evolved into multidrug-resistant (MDR) bacteria [2]. Some isolates change further and be- come extended drug-resistant (XDR) or pandrug-resistant (PDR) pathogens. Antibiotic resistance pattern in Cipto MangunkusumoHospital(CMH),Jakarta,showedthatthe most prevalent PDR bacteria last year were Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa [3,4]. Empirical treatment with antibiotics combination has been recommended in severe sepsis and septic shock to reduce mortality such as meropenem and amikacin, mer- openem and levofloxacin, and carbapenem (meropenem, imipenem, and doripenem) and polymyxin [5, 6]. In vitro studies showed that combining antimicrobial agents could bemoreeffectiveagainstresistantpathogensthanthesingle antibiotic. It can be used to evaluate the efficacy of an Hindawi Canadian Journal of Infectious Diseases and Medical Microbiology Volume 2018, Article ID 1047670, 6 pages https://doi.org/10.1155/2018/1047670