Antimicrobial Resistance in Acinetobacter Ringing the Panic Alarm for Public Health: Focusing on Colistin and Minocycline as a Treatment Option

INTRODUCTION Acinetobacter baumannii has emerged as an important pathogen predominantly associated with hospital-acquired infections, particularly in intensive care units (ICUs).[1] It causes various infections, including pneumonia, septicemia, endocarditis, meningitis, wound infection, and urinary tract infections.[2] Treatment options for A. baumannii infections are limited, as it is frequently resistant to various commonly used antibiotics, including carbapenems. The prevalence of carbapenem-resistant A. baumannii (CRAB) varies in different geographical regions worldwide. A low prevalence of CRAB infections was observed in Japan (2.8%) and Australia (6.5%), although a high prevalence was found in India (87.2%) and South Korea (88%).[3] The World Health Organization categorized CRAB as the “top priority pathogen” in the critical group that urgently requires novel antimicrobial agents.[1] Carbapenems, which were once considered the drug of choice for the treatment of multidrug-resistant (MDR) and extensively drug-resistant (XDR) A. baumannii (XDR-AB), are no longer effective nowadays. Therefore, the appropriate use of existing antimicrobial agents showing promising results is important. Due to encouraging outcomes documented worldwide, colistin and minocycline have gained importance (despite their limitations) as alternative treatment options for drug-resistant A. baumannii.[1,3,4] Considering the current situation, it is crucial to know the local antibiotic susceptibility patterns of A. baumannii, particularly XDR-AB. Hence, this study was conducted to determine susceptibility patterns of XDR-AB, with special reference to colistin and minocycline. MATERIALS AND METHODS This cross-sectional observational study was conducted from March 2022 to June 2023 in the Department of Microbiology at a tertiary care teaching hospital in Western India after obtaining approval from the Institutional Ethics Committee. A total of 226 isolates of A. baumannii were collected from various clinical specimens using the nonprobability convenience sampling method. Of the total isolates, 148 (65.49%) XDR-AB resistant to carbapenem were included in this study, and repetitive isolates from a single patient were excluded. The isolation and identification of A. baumannii were done by conventional microbiological techniques and the VITEK 2 automated system (bioMérieux, France). The final identification was made by detecting the blaOXA-51 gene intrinsic to A. baumannii.[1] The antibiotic susceptibility testing was performed by the Kirby–Bauer disc diffusion method and VITEK 2, and the report interpretation was made according to the Clinical and Laboratory Standards Institute 2021 guidelines. Antibiotics included for testing are listed in Table 1. Minimum inhibitory concentration values of imipenem and meropenem ≥8 μg/ml were considered to determine carbapenem resistance. Colistin and minocycline susceptibility was further confirmed by the broth microdilution test. A. baumannii, non-susceptible to at least one agent in three or more (≥3) antimicrobial categories, was considered MDR-A. baumannii. A. baumannii, non-susceptible to at least one agent in all but two or fewer antimicrobial categories, which suggests that bacterial isolates remain susceptible to only one or two categories was considered XDR-A. baumannii.[5]Table 1: Antibiotic susceptibility pattern of extensively drug-resistant Acinetobacter baumannii isolates (n=148)Statistical analysis Data were entered in Microsoft Excel and analyzed using SPSS version 27.0 (IBM Corp., Chicago, IL, USA) statistical program for Microsoft Windows. Frequency and percentage were calculated for baseline data. The Chi-square test was applied to find significant associations between the two variables, and P < 0.05 was considered statistically significant. RESULTS A total of 148 nonrepetitive XDR-AB isolates were studied. Isolates recovered from respiratory specimens were 72 (48.65%), followed by pus/wound swabs 32 (21.62%), blood 30 (20.27%), urine 7 (4.73%), and body fluids 7 (4.73%) [Figure 1]. Among the isolates, 109 (73.65%) were obtained from ICUs and 39 (26.35%) from various wards. The median age of the study participants was 50 years (interquartile range: 30, 65 years), and the majority, 58 (39.10%), were observed at 60 years old or above. Of all study participants, 82 (55.40%) were male and 66 (44.60%) were female. Comorbidities were documented in 60 (40.54%) participants. The average duration of hospitalization was 31 days, and overall patient outcome was recorded as discharged 81 (54.73%), discharged against medical advice 21 (14.19%), and death 46 (31.08%), respectively. The antibiotic susceptibility pattern of XDR-AB is shown in Table 1. The comparison of susceptibility to colistin and minocycline for XDR-AB is depicted in Table 2.Figure 1: Frequency distribution of isolates in various clinical specimensTable 2: Comparison of susceptibility to colistin and minocycline for extensively drug-resistant Acinetobacter baumannii isolates (n=148)CONCLUSION “The last-resort antibiotic,” colistin, and “an ancient drug for the current era,” minocycline, can be used as alternative drugs for treating carbapenem-resistant XDR-AB infections. Due to toxicity caused by colistin monotherapy, it can be administered along with other drugs. Minocycline is bacteriostatic, but when taken in combination with colistin, it can have bactericidal outcomes. In addition, the rational use and regular susceptibility testing of these existing antimicrobial agents play a pivotal role in further resistance development. The findings of our study could be significant because it will help clinicians to formulate a suitable treatment strategy for drug-resistant Acinetobacter infections, and ultimately, public health will be benefited. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.