Author's response to reviews Title: Comparison between bacteremia caused by carbapenem resistant Acinetobacter baumannii and Acinetobacter nosocomialis Authors: Ya-Sung Yang (ysyoung4097@gmail.com) Yi-Tzu Lee (s851009@yahoo.com.tw) Wen-Chiuan Tsai (drtsaiwenchuan@mail2000.com.tw) Shu-Chen Kuo (ludwigvantw@gmail.com) Jun-Ren Sun (sun3342@yahoo.com.tw) Chin-Hsuan Yang (maddieyang@hotmail.com) Te-Li Chen (tecklayyy@gmail.com) Jung-Chung Lin (linjungchung1@yahoo.com.tw) Chang-Phone Fung (cpfung@vghtpe.gov.tw) Feng-Yee Chang (fychang@ndmctsgh.edu.tw) Version: 3 Date: 22 April 2013 Author's response to reviews: see over
22 April 2013 The Editor BMC Infectious Disease To the Editor, We wish to re-submit the revised manuscript (MS: 7273645318745088; Comparison between bacteremia caused by carbapenem resistant Acinetobacter baumannii and Acinetobacter nosocomialis). The invaluable comments and suggestions are highly appreciated. We have addressed the reviewers queries and suggestions, item by item, as shown below. The changes we made in the manuscript are highlighted in bold type. All the authors have read and agreed to the re-submitted version of the manuscript. REVIEWER 1: The paper is well-written and clear. It is also important. It would have been helpful for the referee to insert continuous line numbers throughout the paper. Thank you for your precious comments. The line numbers have been inserted.
Major compulsory revisions: Comment 1: In general, citations should be excellent and correspond to the current state-of-knowledge, for example: P5, line: ref. 3-6: reference 6 is not a good example and there are other and better ones. It has been removed. We have re-edited the references (page 5, line 3). Comment 2: P5, line 8-10: 'account for...80%': this is too absolute. Where? when? Definitely, other reports exist with other results (Karah et al., JAC 2011, 66:738-744 and van den Broek et al., JCM 2009, 47, 3593-3599). We have revised the description (page 5, lines 8-11). Comment 3:
P5, bottom line-p6, top line: Delete part of the sentence 'as it has been... multidrug resistance [16,17]': these citations are biased in an attempt to emphasize the importance of the study (citation 16 is very general with no evidence of this phenomenon on Acinetobacter and citation 17 is on a particular environmental strain not representative for clinical relevant acinetobacters. We have rewritten the sentences and applied new references to address the issues (page 5, lines 16-17). Comment 4: Page 16: line 4 from bottom: 'A pittii is...'. The authors should use the past tense (e.g. was found to be) and state where (type of samples, clinical or not) and when. It has been clarified (page 15, lines 13-14). Thanks for your remind. Comment 5: Finally, it would have been interesting to assess the diversity of the organisms at the strain level, to know whether for each species the organisms were epidemiologically related or not. A high resolution typing method would have been
necessary for that since A nosocomialis strains can be highly similar (clonal species). Perhaps antibiotic susceptibility profiles might be used as an indication of the possible epidemic spread of particular strains. There is then the question as to whether this would affect the conclusions of the study (strain or species effect). Thanks for your suggestion. Pulsed-field gel electrophoresis (PFGE) of 20 randomly selected isolates from each Acinetobacter species was performed to identify the clonal relationship of the isolates. As shown below (figure 1 and 2), there were 7 (A-G) and 14 (A-N) pulsotypes of carbapenem resistant A. baumannii and A. nosocomialis isolates, respectively. According to the result of PFGE, we believe the differences between patients of CARB and CRAN bacteremia are majorly species effect (page 8, lines 9-11; page 11, lines 9-10; page 15, lines 8-11). Comment 6: The study underscores that species identification can be important. rpob sequence analysis is very useful for this purpose and this should be mentioned (Gundi et al., 2009) Thank you for the kind remind, the comprehensive reference has been added
(page 15, lines 9-11). REVIEWER 2: The manuscript is well prepared, but I have two major concerns. Comment 1: Nine years is a long time, new antimicrobial resistance mechanisms are constantly being introduced especially to these genetically versatile acinetobacters. Lumping all the carbapenem-resistant isolates together within such long period in one analysis, may not represent the current picture. It would be interesting to see how the incidence rate of CRAB and CRAN varied over period. The incidence rates of CRAB and CRAN were shown as below (figure 3). As demonstrated by the diverse pattern of pulsotypes and the incidence rates of both acinetobacters over years, we believe the differences between patients of CRAB and CRAN bacteremia are majorly species effect.
Comment 2: The importance of species delineation in prescribing treatment as well as predicting clinical outcome in Acinetobacter has been shown by several previous studies as the authors have pointed out. Focusing on carbapenem resistance and see if that may make a difference between two well-known Acinetobacter species in clinical outcome is of limited novelty. It has been demonstrated that the virulence of A. baumannii resistant to certain drugs is impaired [1, 2]. So, it is unknown whether the more severe clinical outcomes of A. baumannii bacteremia compared to A. nosocomialis bacteremia will be the same if both the pathogens are carbapenem resistant. Our study addresses an important clinical issue that emphasizes the need to identify the carbapenem resistant Acinetobacters into genomic species. We have tried our best to respond appropriately to each of the reviewer s comments. We believe that the manuscript is much improved based on changes made in response to their invaluable recommendations. We hope that you will find the revised manuscript suitable for publication in your esteemed journal.
Sincerely, Te-Li Chen, M.D. Ph.D. Institute of Clinical Medicine, School of Medicine, National Yang-Ming University. No.155, Sec.2, Linong Street, Taipei, 112, Taiwan. Telephone: +886 2 28757494 Fax: +886 2 28730052 Email: tecklayyy@gmail.com
References 1. Lopez-Rojas R, Dominguez-Herrera J, McConnell MJ, Docobo-Perez F, Smani Y, Fernandez-Reyes M, Rivas L, Pachon J: Impaired virulence and in vivo fitness of colistin-resistant Acinetobacter baumannii. J Infect Dis 2011, 203(4):545-548. 2. Smani Y, Lopez-Rojas R, Dominguez-Herrera J, Docobo-Perez F, Marti S, Vila J, Pachon J: In vitro and in vivo reduced fitness and virulence in ciprofloxacin-resistant Acinetobacter baumannii. Clin Microbiol Infect 2012, 18(1):E1-4.
Figure 1. Pulsed-field gel electrophoresis of 20 randomly selected isolates of carbapenem resistant Acinetobacter baumannii from patients with bacteremia.
Figure 2. Pulsed-field gel electrophoresis of 20 randomly selected isolates of carbapenem resistant Acinetobacter nosocomialis from patients with bacteremia.
Figure 3. Annual incidences of carbapenem resistant isolates among Acinetobacter baumannii and Acinetobacter nosocomialis. 50 50 Incidence of carbapenem resistance (%) 40 30 20 10 40 30 20 10 Number of patients 0 2000 2001 2002 2003 2004 2005 2006 2007 2008 Year 0 Acinetobacter baumannii Acinetobacter nosocomialis Carbapenem resistant Incidence of carbapenem resistance among Acinetobacter baumannii Incidence of carbapenem resistance among Acinetobacter nosocomialis