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In vitro efficacy of N-acetylcysteine on bacteria associated with chronic suppurative otitis media Lea, Jane; Conlin, Anne E; Sekirov, Inna; Restelli, Veronica; Ayakar, Komathi G; Turnbull, LeeAnn; Doyle, Patrick; Noble, Michael; Rennie, Robert; Schreiber, William E; Westerberg, Brian D Jul 7, 2014

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ORIGINAL RESEARCH ARTICLEIn vitro efficacy of N-acetyucaEized by chronic inflammation of the middle ear or mas-toid, a non-intact tympanic membrane, and otorrheainflammatory (corticosteroid) topical otic drop. Thesafety and efficacy of Ciprodex® (ciprofloxacin 0.3%/Lea et al. Journal of Otolaryngology - Head and Neck Surgery 2014, 43:20 this coupled with recent evidence of P. aeruginosaVancouver V5Y 2B8, CanadaFull list of author information is available at the end of the articlevariably defined as lasting longer than two weeks to lon-ger than three months [1-3]. The most common bacter-ial isolates in CSOM are P. aeruginosa (18-67% ofisolates) and S. aureus (14-33%) [1-4].dexamethasone 0.1%; Bayer AG, licensed to Alcon La-boratories, Inc., Fort Worth, TX) has been demonstratedin both children and adults with CSOM [5]. However,symptoms fail to resolve in 9-15% of patients [5]. Thetreatment of refractory otorrhea remains a clinical chal-lenge for otolaryngologists.P. aeruginosa resistance to quinolones has been docu-mented to be as high as 18% in suppurative otitis [6]* Correspondence: bwesterberg@providencehealth.bc.ca1Division of Otolaryngology – Head & Neck Surgery, University of BritishColumbia, Vancouver, BC, Canada5St. Paul’s Hospital Rotary Hearing Clinic, Providence 2, 1081 Burrard St,Background: The safety and efficacy of Ciprodex® has been demonstrated for treatment of chronic suppurative otitismedia (CSOM). However, symptoms fail to resolve in 9-15% of patients. The objective of this study is to evaluate theefficacy of N-acetylcysteine (NAC) on S. aureus, and planktonic and sessile (biofilm forming) P. aeruginosa in vitro usingclinical isolates from patients with CSOM.Methods: 1) Stability was assessed using liquid chromatography-mass spectrometry for each component in a preparedmixture of Ciprodex® and NAC over 15 days. Sterility was assessed by measuring bacterial growth on a blood agarplate. Efficacy was assessed using a disc diffusion method by inoculating plates with S. aureus ATCC 29513 andP. aeruginosa ATCC 27853, and measuring the clearance zone.2) Fifteen P. aeruginosa strains were isolated from patients with CSOM and tested in vitro using the bioFILM PA™antimicrobial susceptibility assay. Treatment solutions included Ciprodex® & ciprofloxacin +/- NAC, and NAC alone(0.25%, 0.5% & 1.25%).Results: 1) NAC combined with Ciprodex® demonstrated stability, sterility, and efficacy over a two-week period2) P. aeruginosa strains in the sessile (33%-40%) and planktonic (13%) state demonstrated resistance to Ciprodex® andciprofloxacin. When NAC ≥0.5% was used in isolation or as an adjunct to either of these medications, no resistance wasfound in the sessile or planktonic state among all 15 strains.Conclusion: 1) Ciprodex® combined with NAC has a shelf life of at least two weeks given the documentedpreservation of stability, sterility, and clinical efficacy of the mixed compounds.2) P. aeruginosa strains demonstrated resistance to both Ciprodex® and ciprofloxacin. NAC ≥0.5% overcomes issueswith resistance and shows promise in the treatment of CSOM.Keywords: Otitis media, suppurative, Antibacterial agents, Microbial sensitivity tests, N-acetylcysteine, Ciprodex®,Ciprofloxacin, Administration, topical, Pseudomonas aeruginosa, Staphylococcus aureusIntroductionChronic suppurative otitis media (CSOM) is character-First line pharmacologic treatment for patients withCSOM usually entails a combination antibiotic anti-associated with chronic sJane Lea1, Anne Elizabeth Conlin1, Inna Sekirov2,3, VeroniPatrick Doyle2,3, Michael Noble2,3, Robert Rennie4, WilliamAbstract© 2014 Lea et al.; licensee BioMed Central LtdCommons Attribution License (http://creativecreproduction in any medium, provided the orDedication waiver (http://creativecommons.orunless otherwise stated.Open Accesslcysteine on bacteriappurative otitis mediaRestelli2,3, Komathi G Ayakar2,3, LeeAnn Turnbull4,Schreiber5 and Brian D Westerberg1,5*. This is an Open Access article distributed under the terms of the, which permits unrestricted use, distribution, andiginal work is properly credited. The Creative Commons Public Domaing/publicdomain/zero/1.0/) applies to the data made available in this article,Lea et al. Journal of Otolaryngology - Head and Neck Surgery 2014, 43:20 Page 2 of 7 formation in otology [7,8] could explain manytreatment failures. Biofilm formation may sustain the in-flammatory response that promotes persistent drainagefrom the ear [9,10].N-acetylcysteine (NAC) is best known as an antidote toreduce liver toxicity following acetaminophen overdose[11]. However, research in the field of otolaryngology withthis agent is not new. Prior studies have explored the util-ity of intra-tympanic NAC in the prevention of Cisplatinototoxicity, and noise-induced hearing loss [12-15]. NACalso exhibits important mucolytic and antibacterial prop-erties, including inhibition of P. aeruginosa biofilm forma-tion [16]. A recent case series of patients with refractoryotorrhea showed promising clinical results utilizing topical2% NAC as an adjunct to Ciprodex® [17].We deemed the combination of NAC and ciprofloxa-cin warranted further study. The objectives of thecurrent study were to:1. Delineate the in vitro stability, sterility and efficacyof a mixture of ciprofloxacin and dexamethasone(Ciprodex®) with added NAC over a two-weekperiod to ensure safety and preservation of bacterialefficacy against P. aeruginosa and S. aureus; and2. Assess the efficacy of NAC in combination withCiprodex® and ciprofloxacin, and NAC alone, on P.aeruginosa clinical isolates from patients withCSOM with a specific focus on biofilm susceptibilityin vitro.Materials and methodsInstitutional Clinical Ethics Board approval was obtained(University of British Columbia-Providence Health CareResearch Ethics Board approval number H09-00953).Stability, sterility and efficacy of ciprodex® in combinationwith 1.25% NACStudy solutionA 1.25% NAC solution (12.5 mg/mL) was created by add-ing 50 μL of a commercially available 20% NAC solutionto 750 μL of Ciprodex® (ciprofloxacin 0.3%/dexametha-sone 0.1%). This solution was prepared on day 0, stored ina refrigerator at 4°C and used throughout the study tomeasure stability, sterility and efficacy. A 15 day studyperiod was chosen as this corresponds to the upper limitof a typical treatment course with topical antibiotic dropsfor CSOM, and is the timeframe for which a standardCiprodex® bottle will be depleted if used as directed.StabilityThe concentrations of ciprofloxacin, dexamethasone (inCiprodex®) and NAC in the 1.25% NAC solution were mea-sured on days 0, 1, 2, 7 and 15 by liquid chromatography-mass spectrometry (LC-MS).Sterility dataOne drop (10 uL) of the above solution was placed on ablood agar plate on days 0, 7, and 14. The plates wereincubated at 35°C for 48 hours, at which time they wereassessed visually for bacterial growth.Efficacy dataUsing a disc diffusion method, 10 μL of the 1.25% NACand Ciprodex® mixture was inoculated onto plain discs andtested on plates containing S. aureus ATCC 29513 or P.aeruginosa ATCC 27853. The same 1.25% NAC Ciprodex®mixture was used throughout this portion of the study, withseparate testing occurring on day 0, 7, and 14. The plateswere incubated for 24 hours at which time they wereassessed for efficacy by measuring and photo-documentingthe clearance zone around each disc.Susceptibility of P. aeruginosa isolates in the planktonicand sessile stateInoculum preparationFifteen strains of P. aeruginosa isolated from clinical speci-mens of patients with CSOM were tested. P. aeruginosaATCC 35032 was used as the quality control organism.Treatment solutionsTwenty seven study solutions were prepared under ster-ile conditions consisting of ciprofloxacin or Ciprodex®alone (3, 1, and 0.5 μg/mL) and in combination withNAC at 0.25% (2.5 mg/mL), 0.5% (5 mg/mL) and 1.25%(12.5 mg/mL). NAC alone (no added ciprofloxacin orCiprodex®) was also prepared at concentrations of0.25%, 0.5% and 1.25%. Each solution was tested in du-plicate. Concentrations of ciprofloxacin were chosenbased on Clinical and Laboratory Standards Institute(CLSI) guidelines [18].Biofilm formationFor each tested strain, a 0.5 McFarland bacterial suspen-sion was prepared from a fresh subculture grown onblood agar plates (BAP); 300 μL of the suspension wasfurther diluted with 19.7 mL of trypticase soy broth(TSB). The diluted suspension was used to inoculate a96 well microtiter plate with a 95 peg inoculation lid(bioFILM PA™ antimicrobial susceptibility device; Inno-votech, Edmonton, AB). One column was inoculatedwith sterile TSB alone for sterility control. The micro-plates were incubated at 35 ± 1°C on a platform shakerset at 110 rpm for 5 hours to allow biofilms to form onall pegs at a standard concentration of bacterial cells.bioFILM PA™ has received regulatory approval by HealthCanada and meets all current standards of the CLSI forreproducibility and consistency. Standard protocols fortesting were followed.corresponding to a resistance rate of 13%. Greater resist-(Figure 2).All 15 planktonic and sessile P. aeruginosa strains wereinhibited when NAC ≥0.5% was used alone (Figure 3) or asan adjunct to either Ciprodex or ciprofloxacin. Interestinglyhowever, NAC 0.25% alone, or in combination with Cipro-dex® or ciprofloxacin yielded inferior results in the sessilepopulation. Growth occurred in all but one P. aeruginosastrain when NAC 0.25% was used in isolation, yielding a re-sistance rate of 93% (Figure 3). Thirteen strains demon-strated growth when NAC 0.25% was used in combinationwith either Ciprodex® or ciprofloxacin for a resistance rateof 87%. NAC 0.25% alone and in combination with eitherLea et al. Journal of Otolaryngology - Head and Neck Surgery 2014, 43:20 Page 3 of 7 susceptibility testing of P. aeruginosa strainsIsolates and control strain response to treatment solu-tions was assessed by quantifying the optical density as agauge of bacterial growth. Optical density (OD) valuesof ≥0.1 using a microreader at 620 nm were consideredas growth or resistance. As each solution was tested induplicate incongruent OD values were possible; these in-congruent data were excluded from the analysis and cat-egorized as non-reproducible duplicates.a) Planktonic state: After removing the microplatesfrom the incubator, the pegged lids were carefully liftedand transferred onto the “challenge plate” containingthe treatment solutions outlined above. Eachconcentration and combination was tested induplicate. Immediately after transferring the pegged lidto the challenge plate, an inoculum check wasperformed from the growth-control wells to ensure anacceptable bacterial load of colony forming units(CFU) with a minimum goal of 5×105CFU/mL. Theplates were then incubated at 35 ± 1°C for 18-24 hours.Bacterial density (growth) of the planktonic populationwas assessed after incubation using measured opticaldensity with a microreader at 620 nm.b) Biofilm (sessile) state: After removing the challengeplates with the pegged lid from the incubator, thepegged lids were transferred to a 96-well microplatecontaining sterile water for 30 seconds to remove thetreatment solutions from the pegs. The pegged lid wasthen transferred on to a 96-well microplate containingcation-adjusted Mueller-Hinton broth (CAMHB) andincubated at 35 ± 1°C for 18-24 hours to recover sessilebacteria. Bacterial density was similarly assessed afterincubation using measured optical density with amicroreader at 620 nm.ResultsStability, sterility and efficacy of ciprodex® in combinationwith 1.25% NACStabilityEach component of the mixture of Ciprodex® and NACdemonstrated stability over a 15 day period. NAC con-centrations varied from 1.12-1.25%, ciprofloxacin from0.27%-0.321%, and dexamethasone from 0.0922%-0.0976% (Table 1).SterilityThe solutions remained sterile with no evidence of bac-terial growth throughout the 15-day study period.EfficacyAntimicrobial effect against both S. aureus ATCC29513 and P. aeruginosa ATCC 27853 remained stablebased on a constant zone of inhibition around the diskance was seen when the bacteria were in the sessile (bio-film) state; five (33%) and six (40%) strains showedgrowth with Ciprodex® and ciprofloxacin, respectivelycontaining the solution of Ciprodex and 1.25% NACon days 0, 7 and 14.Susceptibility of P. aeruginosa isolates in the planktonicand sessile stateAll strains grew in the control wells. One strain was slowto grow with final OD levels four times lower versus otherstrains, however growth was still substantial enough todemonstrate resistance to treatment with Ciprodex andciprofloxacin (OD > 0.1), and therefore we included thisstrain in the analysis. Inoculum control for the challengeplates was between 6 × 10^4 and 1.7 × 10^6 cfu/mL (tar-get: 5× 10^5 cfu/mL). Five percent of our data (42/840)was excluded from analysis as OD values were non-reproducible. The majority of the 42 non-reproducible du-plicates occurred in 0.25% NAC group; the 0.25% NACsolution accounted for 23 of the 42 non-reproducible du-plicates, primarily an issue in the planktonic population.Detailed resistance rates for each concentration ofCiprodex® and ciprofloxacin are shown in Figure 1, withcombined results highlighted in Figure 2. Among the 15P. aeruginosa strains, two showed growth when treatedwith Ciprodex® or ciprofloxacin in the planktonic state,Table 1 Stability data of N-acetylcysteine, ciprofloxacinand dexamethasone (Ciprodex combined with 1.25%N-acetylcysteine)Day N-Acetylcysteine (%) Ciprofloxacin (%) Dexamethasone (%)0 1.12 0.27 0.09531 1.25 0.259 0.09762 1.2 0.258 0.09767 1.16 0.315 0.092215 1.19 0.321 0.0953Ciprodex® or ciprofloxacin effectively inhibited growth inthe planktonic population.DiscussionN-acetylcysteine holds promise as an adjunct in theThis study highlights the issue of in vitro antibiotic re-sistance of P. aeruginosa to Ciprodex® and ciprofloxacinFigure 1 P. aeruginosa resistant strains to Ciprodex or ciprofloxacin at various concentrations.Lea et al. Journal of Otolaryngology - Head and Neck Surgery 2014, 43:20 Page 4 of 7 of patients with chronic otitis media andpersistent otorrhea that is refractory to treatment withstandard topical antibiotic preparations. The addition ofNAC to Ciprodex® maintained a combination that wasstable, sterile and efficacious in vitro against P. aerugi-nosa and S. aureus, up to two weeks after mixing. Fur-thermore, in vitro testing indicated improved efficacyagainst biofilm forming P. aeruginosa when NAC ≥ 0.5%was used alone or in combination with Ciprodex® or cip-rofloxacin, overcoming the resistance observed to solu-tions containing ciprofloxacin alone.Figure 2 P. aeruginosa resistant strains: combined results for Ciprodeotic solutions, with resistance levels as high as 13% and40% for planktonic and sessile states respectively. Bac-teria in biofilm (sessile) states exhibit exopolysaccharide-cellular towers separated by open channels that delivernutrients and remove waste, a complex process requir-ing cellular communication and modification of generegulation, but one that renders bacteria 10-1000 timesmore resistant to antibiotic therapy versus geneticallyidentical planktonic forms [19]. However, NAC at con-centrations ≥0.5% revealed universal susceptibility of allP. aeruginosa strains from clinical isolates of patientsx and ciprofloxacin.iatiLea et al. Journal of Otolaryngology - Head and Neck Surgery 2014, 43:20 Page 5 of 7 CSOM in both planktonic and sessile states. Ourfindings are consistent with other in vitro studies show-ing that NAC significantly inhibits the formation of bac-terial biofilms when used alone. However, we failed toduplicate the beneficial synergistic effect of NAC withantimicrobial drugs that has previously been docu-mented in the literature [16,20,21]. If the prior treatmentfailure rates of 9-15% in patients with CSOM [5] are at-tributed in whole or in part to biofilm formation, theutilization of NAC alone or as an adjunct to ciprofloxa-cin/dexamethasone (Ciprodex®) may culminate in im-proved symptom resolution and patient benefit.Paradoxically, 0.25% NAC alone, or as an adjunct toCiprodex® or ciprofloxacin yielded inferior susceptibilityin the sessile population when compared to eitherCiprodex® or ciprofloxacin alone. NAC 0.25% appearedFigure 3 P. aeruginosa resistant strains to NAC alone. Figure abbrevto maintain efficacy in the planktonic state, both aloneand in combined solutions with Ciprodex® and ciproflox-acin. We hypothesize that this low concentration ofNAC (0.25%) may destabilize the outer surface of thebiofilms to allow some viable bacteria from the innerlayers to escape and grow. However, the true explanationfor this finding requires further study. The biofilm is adynamic biological complex, which may explain, in part,issues of in-vitro reproducibility.The identification of an agent such as NAC that eradi-cates biofilms has potential for a significant clinical im-pact in the management of patients with infectiousconditions in otolaryngology-head and neck surgery. Ahigh rate of Pseudomonas biofilms have been identifiedon tympanostomy tubes in patients with persistent otor-rhea despite treatment with ciprofloxacin otic drops [8].Jang, in a case series of 12 infected tympanostomytubes revealed ciprofloxacin resistant P.aeruginosa as thesole organism with a high rate of tympanostomy tubebiofilm formation as shown by EM [8]. The topicalapplication of 20% NAC to the middle ear in patientswith tympanostomy tubes has been shown to increasetube longevity, and to decrease the need for replacementof tubes, and subsequent physician visits [22]. In a re-cent case series of seven patients with CSOM and refrac-tory otorrhea, use of Ciprodex® augmented with NAC(0.5% or 2%) showed resolution of symptoms in 86% (6/7) of patients within 4 weeks [17]. Compliance issueswere noted in the one subject with persistent otorrhearefractory to treatment. No adverse effects were identi-fied in treated patients with follow-up ranging from 14-19 months. In particular, serial audiometry revealed nochanges in pure tone averages or speech discriminationscores, thus supporting an absence of clinically signifi-cant ototoxicity [17].However, despite these promising findings regardingon: NAC: N-acetylcysteine.the efficacy and safety of NAC, some prudence is war-ranted with respect to the safety of intratympanicadministration of NAC. In our study, the low concentra-tions of 0.5% and 1.25% NAC were utilized due to con-cerns about NAC at higher concentrations [12,13].Although NAC has been shown to have protective prop-erties against ototoxicity related to Cisplatin [12,14], aswell as protection from noise induced hearing loss [15],it has paradoxically also been implicated in causing in-flammation and hearing loss.In a recent study of 20% intratympanic NAC in aguinea pig model, negative effects were seen includingincreased ABR thresholds, inflammation of the externalauditory canal and middle ear mucosa, and diffuse oste-itis with severe disruption of the organ of Corti on elec-tron microscopy [13]. Similar inflammatory effects werefound on the external and middle ear of guinea pigstreated with 4% intratympanic NAC [12]. In a guinea pigcochlear implant model [23], although preservation ofresidual hearing was found in the basal turn as well as aLea et al. Journal of Otolaryngology - Head and Neck Surgery 2014, 43:20 Page 6 of 7 in the chronic inflammatory response associ-ated with cochlear implantation, a transient increase inhearing thresholds and osseoneogenesis was also foundin animals treated with topical 4% NAC [23]. Topical0.6% NAC after myringotomy in a guinea pig modelshowed significant otorrhea in the NAC treated groupassociated with reduced healing of the tympanic mem-brane post-myringotomy; 40% had persistent TM perfo-rations in the NAC treated group versus 100% closure ofperforations in the control group [24]. Two guinea pigstudies on intratympanic NAC for the prevention of Cis-platin ototoxicity have demonstrated safety at NAC con-centrations ≤4% [12,14]. NAC at a concentration of 4%yields nuclear/cytoplasmic membrane and stereo-ciliapreservation on electron microscopy [12], and 2% NACleads to partial preservation of distortion product oto-acoustic emissions [14]. While an inflammatory reactionwas seen in the 4% NAC group [12], none was observedwith 2% NAC (personal communication with Chang,KW; unpublished data).Human studies have shown a more promising side ef-fect profile for intratympanic NAC compared to the ani-mal studies. Yoo et al. reported no adverse events with2% intratympanic NAC in patients receiving cisplatinchemotherapy [25]. Riga et al, demonstrated clinical oto-protective effects of 10% intratympanic NAC in a cohortof patients treated with cisplatin based regimens basedon pure tone thresholds, with the only reported adverseeffect being pain post injection lasting less than five mi-nutes (26). However, in the same study 20% intratympa-nic NAC was trialed in five patients but discontinueddue to transient (<2 weeks) middle ear and tympanicmembrane inflammation [26]. The case series by Choeet al. also demonstrates an absence of clinically signifi-cant ototoxicity based on audiometric data in seven pa-tients treated with intratympanic NAC ≤2% [17].The evidence appears to trend toward increased safetywith reduced concentrations of topical NAC. Based oncurrent literature, intratympanic NAC <10% appears tohave an acceptable side effect profile based on clinicalhuman studies to date. However, long-term safety profiledata is currently unknown.ConclusionThe combination of Ciprodex® with NAC has a shelf lifeof at least two weeks given the documented preservationof stability, sterility and clinical efficacy of the mixture. Re-sistance of P. aeruginosa clinical isolates to both Ciprodexand ciprofloxacin was demonstrated in this study, withsessile bacteria having a higher incidence of resistance.NAC at a concentration of ≥0.5% alone, or as an adjunctto Ciprodex® or ciprofloxacin completely inhibited thegrowth of both planktonic and sessile P. aeruginosa popu-lations. NAC 0.25% revealed paradoxical results withincreased resistance in the sessile population and requiresfurther study. NAC shows promise as an agent in treat-ment of bacteria implicated in CSOM in the laboratorysetting. Further study is warranted to delineate its efficacywith topical administration in the clinical setting.Competing interestsThe authors declare that they have no competing interests.Authors’ contributionsJL: Conducted study literature review, contributed to study design, analysisand interpretation of study data, primary author responsible for drafting andrevising of manuscript. AEC: Contributed to study design, acquisition of data,analysis and interpretation of data, drafting and revising of manuscript. IS:Contributed in data aquisition, analysis and interpretation of data for biofilmstudies, drafting and revising of manuscript. VR: Carried out the susceptibilitytesting of P. aeruginosa strains to ciprofloxacin, Ciprodex® alone or incombination with NAC, under biofilm-forming conditions, drafting andrevising of manuscript. KGA: Contributed to study design, acquisition of data,analysis and interpretation of data, drafting and revising of manuscript. LT:Contributed to study design, acquisition of data, drafting and revising ofmanuscript. PD: Contributed to study design, acquisition of data, analysis andinterpretation of data, drafting and revising of manuscript. MN: Contributedto the collection of clinical isolates of Ps. aeruginosa as well as the design,performance and interpretation of biofilm susceptibility testing, drafting andrevising manuscript. RR: Contributed to development and experimentaldesign of biofilm assays, data interpretations, drafting and revising ofmanuscript. WS: Contributed to design of the stability studies, data analysis,drafting and revising of manuscript. BDW: Conceptualization of studyquestion and study design, primary coordinator of study fromconceptualization to completion, interpretation of data, drafting and revisingof manuscript. All authors’ read and approved the final manuscript.AcknowledgementsFinancial assistance was obtained from the William E. Ainsley EndowmentFund, Division of Otolaryngology-Head and Neck Surgery, UBC for researchin the field of otology. The authors acknowledge Dr. Amanda Wilmer for hercontributions in the study design and methods and the administrative assist-ance of Ms. Julie Pauwels and Ms. Rachelle Dar Santos, ResearchCoordinators.Author details1Division of Otolaryngology – Head & Neck Surgery, University of BritishColumbia, Vancouver, BC, Canada. 2Department of Pathology & LaboratoryMedicine, University of British Columbia, West Mall, Vancouver, BC, Canada.3Vancouver General Hospital, West 12th Avenue, Vancouver, BC, Canada.4Medical Microbiology Research Laboratory, University of Alberta Hospital,112 Street NW, Edmonton, AB, Canada. 5St. Paul’s Hospital Rotary HearingClinic, Providence 2, 1081 Burrard St, Vancouver V5Y 2B8, Canada.Received: 26 February 2014 Accepted: 11 June 2014Published: 7 July 2014References1. Bluestone CD: Efficacy of ofloxacin and other ototopical preparations forchronic suppurative otitis media in children. Pediatr Infect Dis J 2001,20:111–115.2. Kenna MA, Bluestone CD: Microbiology of chronic suppurative otitismedia in children. Pediatr Infect Dis 1986, 5(2):223–225.3. Verhoeff M, van der Veen EL, Rovers MM, Sanders EA, Schilder AG: Chronicsuppurative otitis media: a review. Int J Pediatr Otorhinolaryngol 2006,70:1–12.4. Kiris M, Berktas M, Egeli E, Kutluhan A: The efficacy of topical ciprofloxacinin the treatment of chronic suppurative otitis media. Ear Nose Throat J1998, 77:904–905.5. Wall GM, Stroman DW, Roland PS, Dohar J: Ciprofloxacin 0.3%/dexamethasone 0.1% sterile otic suspension for the topical treatment ofear infections: a review of the literature. Pediatr Infect Dis J 2009,28:141–144.Submit your next manuscript to BioMed Centraland take full advantage of: • Convenient online submission• Thorough peer review• No space constraints or color figure charges• Immediate publication on acceptance• Inclusion in PubMed, CAS, Scopus and Google Scholar• Research which is freely available for redistributionLea et al. 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Prescott LF, Illingworth RN, Critchley JA, Stewart MJ, Adam RD, ProudfootAT: Intravenous N-acetylcystine: the treatment of choice for paracetamolpoisoning. BMJ 1979, 2:1097–1100.12. Saliba I, El Fata F, Ouelette V, Robitaille Y: Are intratympanic injections ofN-acetylcysteine and methylprednisolone protective against cisplatin-induced ototoxicity? J Otolaryngol: Head Neck Surg 2010, 39:236–243.13. Nader M, Theoret Y, Saliba I: The role of intratympanic lactate injection inthe prevention of cisplatin-induced ototoxicity. Laryngoscope 2010,120:1208–1213.14. Choe WT, Chinosornvatana N, Chang KW: Prevention of cisplatinototoxicity using transtympanic N-acetylcysteine and lactate.Otol Neurotol 2004, 25:910–915.15. Fetoni AR, Ralli M, Sergi B, Parrilla C, Troiani D, Paludetti G: Protectiveeffects of N-acetylcysteine on noise-induced hearing loss in guinea pigs.Acta Otorhinolaryngol Ital 2009, 29:70–75.16. Zhao T, Liu Y: N-acetylcysteine inhibits biofilms produced bypseudomonas aeruginosa. BMC Microbiol 2010, 10:140.17. Choe WT, Murray MT, Stidham KR, Roberson JB: N-acetylcysteine as anadjunct for refractory ear infections. Otol Neurotol 2007, 28:1022–1025.18. Clinical and Laboratory Standards Institute: Performance Standards forAntimicrobial Susceptibility Testing; Twenty-first Informational SupplementM100-21. Wayne, Pennsylvania: CLSI; 2011.19. Post JC, Hiller NL, Mistico L, Stoodley P, Ehrlich GD: The role of biofilms inotolaryngologic infections: update 2007. Curr Opin Otolaryngol Head NeckSurg 2007, 15:347–351.20. Pérez-Giraldo C, Rodríguez-Benito A, Morán FJ, Hurtado C, Blanco MT,Gómez-García AC: Influence of N-acetylcysteine on the formation of biofilmby Staphylococcus epidermidis. J Antimicrob Chemother 1997, 39:643–646.21. Marchese A, Bozzolasco M, Gualco L, Debbia EA, Schito GC, Schito AM:Effect of fosfomycin alone and in combination with N-acetylcysteine onE. coli biofilms. Int J Antimicrob Agents 2003, 22(suppl 2):95–100.22. Ovesen T, Felding JU, Tommerup B, Schousboe LP, Petersen CG: Effect ofN-acetylcysteine on the incidence of recurrence of otitis media witheffusion and re-insertion of ventilation tubes. Acta Otolaryngol Suppl 2000,543:79–81.23. Eastwood H, Pinder D, James D, Chang A, Galloway S, Richardson R, O'Leary S:Permanent and transient effects of locally delivered n-acetyl cysteine in aguinea pig model of cochlear implantation. Hear Res 2010, 259:24–30.24. Sanli A, Eken M, Evren C, Ates G, Paksoy M: Does topical N-acetylcysteineapplication after myringotomy cause severe otorrhea? Journal of Ear.Nose Throat 2007, 17:22–25.25. Yoo J, Hamilton SJ, Angel D, Fung K, Franklin J, Parnes LS, Lewis D,Venkatesan V, Winquist E: Cisplatin otoprotection using transtympanic L-N-acetylcysteine: A pilot randomization study in head and neck cancerpatients. Laryngoscope in press.26. Riga MG, Chelis L, Kakolyris S, Papadopoulos S, Stathakidou S, Chalidou E,Xenidis N, Amarantidis K, Dimopoulos P, Danielides V: Transtympanicinjections of N-acetycysteine for the prevention of cisplatin-induced oto-toxicity: a feasible method with promising efficacy. Am J Clin Oncol 2013,36:1–6.doi:10.1186/1916-0216-43-20Cite this article as: Lea et al.: In vitro efficacy of N-acetylcysteine onbacteria associated with chronic suppurative otitis media. Journal ofOtolaryngology - Head and Neck Surgery 2014 43:20.Submit your manuscript at


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