Investigation of Colistin Susceptibility in Carbapenem-Resistant Gram-Negative Bacteria

Öz

Objective: We evaluated colistin susceptibility in carbapenem-resistant isolates and compared the automated microbiology system (VITEK 2 Compact, bioMérieux, France) with the broth microdilution (BMD) reference method. Materials and Methods: A total of 174 carbapenem-resistant Gram-negative isolates collected from various clinical specimens during 2022–2023 were included in the study. Identification and antimicrobial susceptibility testing were performed using conventional methods and the VITEK 2 Compact automated system (bioMérieux, France). Colistin susceptibility was confirmed by the BMD reference method. Results: Among 90 Enterobacterales isolates tested with BMD, 39 (43.3%) were susceptible and 51 (56.7%) were resistant. In the non-fermentative group, 67 (79.8%) of 84 isolates were susceptible, and 17 (20.2%) were resistant. When compared with BMD, VITEK 2 demonstrated an essential agreement (EA) of 68.8%, a categorical agreement (CA) of 80%, a very major error (VME) rate of 7.8%, and a major error (ME) rate of 35.9% for Enterobacterales. For non-fermentative isolates, EA and CA were markedly lower (54.7% and 73.8%, respectively), while VME (47%) and ME (20.9%) rates exceeded acceptable ISO performance thresholds. Conclusion: Although automated systems such as VITEK 2 streamline laboratory workflow, their colistin susceptibility results show poor concordance with the BMD reference method, particularly for non-fermentative isolates. The high error rates observed in this study highlight the critical importance of confirming automated colistin results with BMD to avoid misclassification and inappropriate antimicrobial therapy.

Anahtar Kelimeler

• Antimicrobial susceptibility testing
• automated system
• broth microdilution
• carbapenem resistance
• colistin

Etik Beyan

This study was conducted in accordance with the principles of the Declaration of Helsinki and relevant international guidelines. Ethical approval was obtained from the Bolu Abant İzzet Baysal University Clinical Research Ethics Committee (Date: 11.04.2023, decision no: 2023/106).

Karbapeneme Dirençli Gram-Negatif Bakterilerde Kolistin Duyarlılığının Araştırılması

Öz

Amaç: Karbapenem dirençli izolatlarda kolistin duyarlılığını değerlendirdik ve VITEK 2 Compact Otomatik Mikrobiyoloji Sistemi'ni sıvı mikrodilüsyon (BMD) referans yöntemi ile karşılaştırdık. Materyal ve Metot: Çalışmaya 2022–2023 yılları arasında çeşitli klinik örneklerden izole edilen toplam 174 karbapeneme dirençli Gram-negatif bakteri dâhil edildi. İzolatların tanımlanması ve antibiyotik duyarlılık testleri konvansiyonel yöntemler ve VITEK 2 Compact sistemi kullanılarak gerçekleştirildi. Kolistin duyarlılığı, BMD referans yöntemiyle doğrulandı. Bulgular: BMD yöntemiyle test edilen 90 Enterobacterales izolatının 39’u (%43,3) kolistine duyarlı, 51’i (%56,7) dirençli bulundu. Non-fermentatif gruptaki 84 izolattan 67’si (%79,8) duyarlı, 17’si (%20,2) dirençliydi. VITEK 2 sonuçları BMD ile karşılaştırıldığında, Enterobacterales grubunda esas uyum (EA) %68,8, kategorik uyum (CA) %80, çok büyük hata (VME) %7,8 ve büyük hata (ME) %35,9 olarak saptandı. Non-fermentatif bakterilerde EA %54,7, CA %73,8 olup VME (%47) ve ME (%20,9) oranları ISO performans kriterlerinin belirgin şekilde üzerindeydi. Sonuç: Kolistin direncinin belirlenmesinde VITEK 2 gibi otomatize sistemler laboratuvar iş akışını kolaylaştırsa da referans yöntem olan BMD’ye kıyasla daha düşük uyum ve daha yüksek hata oranlarına sahiptir. Bu çalışmada saptanan uyumsuzluk ve hata oranlarının ISO standartlarının altında kalması, özellikle non-fermentatif türlerde kolistin duyarlılık sonuçlarının BMD ile doğrulanmasının klinik açıdan kritik önem taşıdığını göstermektedir.

Anahtar Kelimeler

• Antibiyotik duyarlılık testi
• karbapenem direnci
• kolistin
• otomatize sistem
• sıvı mikrodilüsyon

Etik Beyan

Bu çalışma, Helsinki Bildirgesi ilkeleri ve ilgili uluslararası kılavuzlar doğrultusunda yürütülmüştür. Bolu Abant İzzet Baysal Üniversitesi Klinik Araştırmalar Etik Kurulu'ndan etik onay alınmıştır (Tarih: 11.04.2023, karar no: 2023/106).

Kaynakça

1. 1. Hoşbul T, Aydoğan CN, Kaya S, Bedir O, Gümral R, Albay A. In vitro activity of ceftazidime-avibactam and colistin against carbapenem-resistant Klebsiella pneumoniae clinical isolates. Mikrobiyol Bul. 2022;56(2):218-229. doi:10.5578/mb.20229803
2. 2. Altınkanat Gelmez G, Sayın E, Hasdemir U, Söyletir G. Kolistin duyarlılık testi için Diagnostics colistin MIC-strip testinin değerlendirilmesi. ANKEM Derg. 2021;35(1):9-13. doi:10.5222/ankem.2021.009
3. 3. Poirel L, Jayol A, Nordmann P. Polymyxins: antibacterial activity, susceptibility testing, and resistance mechanisms encoded by plasmids or chromosomes. Clin Microbiol Rev. 2017;30(2):557-596. doi:10.1128/cmr.00064-16
4. 4. Koyuncu Özyurt Ö, Özhak B, Öğünç D, et al. Evaluation of the BD Phoenix 100 system and colistin broth disk elution method for antimicrobial susceptibility testing of colistin against Gram-negative bacteria. Mikrobiyol Bul. 2019;53(3):254-261. doi:10.5578/mb.68066
5. 5. Tüzemen NÜ, Işık Ö, Akça B, Özakın C. Determination of colistin resistance in Gram-negative bacteria by modified broth disk elution method. Turk Mikrobiyol Cemiy Derg. 2022;52(3):184-191. doi:10.54453/TMCD.2022.37167
6. 6. Lo-Ten-Foe JR, de Smet AMGA, Diederen BMW, Kluytmans JAJW, van Keulen PHJ. Comparative evaluation of the VITEK 2, disk diffusion, Etest, broth microdilution, and agar dilution susceptibility testing methods for colistin in clinical isolates, including heteroresistant Enterobacter cloacae and Acinetobacter baumannii strains. Antimicrob Agents Chemother. 2007;51(10):3726-3730. doi:10.1128/aac.01406-06
7. 7. European Committee on Antimicrobial Susceptibility Testing. Breakpoint tables for interpretation of MICs and zone diameters. Version 13.0. 2023.
8. 8. Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing. 33rd ed. CLSI supplement M100. Wayne, PA; 2023.

9. 9. International Organization for Standardization. ISO 20776-1:2019. Susceptibility testing of infectious agents and evaluation of performance of antimicrobial susceptibility test devices—Part 1. Geneva; 2019.
10. 10. International Organization for Standardization. ISO 20776-2:2007. Clinical laboratory testing and in vitro diagnostic test systems—Susceptibility testing of infectious agents and evaluation of performance of antimicrobial susceptibility test devices—Part 2. Geneva; 2007.
11. 11. Mukhopadhyay K, Yadav D. A review on colistin resistance: an antibiotic of last resort. Microorganisms. 2024;12(4):772. doi:10.3390/microorganisms12040772
12. 12. Özkaya E, Buruk CK, Tosun İ, Toraman B, Kaklıkkaya N, Aydın F. Investigation of plasmid-mediated mcr colistin resistance gene in clinical Enterobacterales isolates. Mikrobiyol Bul. 2020;54(2):191-202. doi:10.5578/mb.69021
13. 13. Mermer S, Çağlayan E. Prevalence, clinical characteristics, and antibiotic resistance of carbapenem-resistant Klebsiella pneumoniae in a tertiary hospital in Türkiye (2023–2025). Research Square. 2025. doi:10.21203/rs.3.rs-7291198/v1
14. 14. Gürbüz M, Çimke P, Altunkara H, et al. Evaluation of pathogens and antibiotic resistance profiles isolated from lower respiratory tract samples. Kocaeli Üniversitesi Sağlık Bilimleri Dergisi. 2023;9(1):14-19. doi:10.30934/kusbed.1083430
15. 15. Vincent JL, Sakr Y, Singer M, et al. Prevalence and outcomes of infection among patients in intensive care units in 2017. JAMA. 2020;323(15):1478-1487. doi:10.1001/jama.2020.2717
16. 16. Yürüyen C, Daldaban Dinçer Ş, Yanılmaz Ö, Boz ES, Aksaray S. Yoğun bakım ünitelerinde kümülatif antibiyogram ile antibiyotik direncinin izlenmesi. Mikrobiyol Bul. 2018;52(4):329-339. doi:10.5578/mb.67408
17. 17. Latifi F, Pakzad R, Asadollahi P, Hematian A, Pakzad I. Worldwide prevalence of colistin resistance among Enterobacteriaceae: a systematic review and meta-analysis. Clin Lab. 2023;69(4):657-669. doi:10.7754/Clin.Lab.2022.220646
18. 18. World Health Organization. Antimicrobial resistance surveillance in Europe: 2023–2021 data. 2023
19. 19. Lagadinou M, Amerali M, Michailides C, et al. Antibiotic resistance trends in carbapenem-resistant Gram-negative pathogens and eight-year surveillance of XDR bloodstream infections in a Western Greece tertiary hospital. Pathogens. 2024;13(12):1136. doi:10.3390/pathogens13121136
20. 20. Ananda T, Vandana KE, Mukhopadhyay C. Comparative evaluation of VITEK® 2 and broth microdilution method for colistin susceptibility testing of Gram-negative isolates from intensive care unit in a tertiary care hospital. Indian J Med Microbiol. 2024;48:100559.
21. 21. Khurana S, Malhotra R, Mathur P. Evaluation of VITEK®2 performance for colistin susceptibility testing for Gram-negative isolates. JAC Antimicrob Resist. 2020;2(4):dlaa101. doi:10.1093/jacamr/dlaa101
22. 22. Şafak B, Tombak Ö, Eren-Topkaya A. Comparative evaluation of VITEK 2 and broth microdilution methods for colistin antimicrobial susceptibility testing. Namık Kemal Tıp Dergisi. 2020;8(1):73-78. doi:10.37696/nkmj.581622
23. 23. Çiftçi N, Arslan PDU, Türk Dağı H. Comparison of colistin susceptibility tests. Health Academy Kastamonu. 2024;9(1):38-45. doi:10.25279/sak.1274681
24. 24. Aydın Uysal A. Klebsiella pneumoniae suşlarında kolistin direncinin araştırılması ve yöntem karşılaştırılması. Ege Üniversitesi, Tıp Fakültesi, Tıbbi Mikrobiyoloji Anabilim Dalı, Uzmanlık Tezi. İzmir, Türkiye. 2023.
25. 25. Chew KL, La MV, Lin RTP, Teo JWP. Colistin and polymyxin B susceptibility testing for carbapenem-resistant and mcr-positive Enterobacteriaceae: comparison of sensititre, microscan, vitek 2, and etest with broth microdilution. J Clin Microbiol. 2017;55(9):2609-2616.