Insights on carbapenem-resistant Acinetobacter baumannii:  phenotypic characterization of relevant isolates

Matthew Gavino Donadu; Stefania Zanetti; Ádám László Nagy; Ibrahim Barrak; Márió Gajdács

doi:10.14232/abs.2021.1.85-92

Authors

Matthew Gavino Donadu Department of Biomedical Sciences, University of Sassari, Sassari, Italy, Department of Chemistry and Pharmacy, University of Sassari, Sassari, Italy https://orcid.org/0000-0001-7681-6194
Stefania Zanetti Department of Biomedical Sciences, University of Sassari, Sassari, Italy https://orcid.org/0000-0002-7958-2490
Ádám László Nagy Department of Prosthodontics, Faculty of Dentistry, University of Szeged, Szeged, Hungary https://orcid.org/0000-0002-8468-1717
Ibrahim Barrak Department of Periodontology, Faculty of Dentistry, University of Szeged, Szeged, Hungary https://orcid.org/0000-0001-8808-1762
Márió Gajdács Department of Pharmacodynamics and Biopharmacy, Faculty of Pharmacy, University of Szeged, Szeged, Hungary, Institute of Medical Microbiology, Faculty of Medicine, Semmelweis University, Budapest, Hungary https://orcid.org/0000-0003-1270-0365

DOI:

https://doi.org/10.14232/abs.2021.1.85-92

Keywords:

Acinetobacter, antibiotic, bioﬁlm, carbapenem, carbapenem-resistance, eﬄux pump, phenotypic assay

Abstract

Acinetobacter baumannii (A. baumannii) is an important nosocomial pathogen, which may be a causative agent in a wide-range of human pathologies. Carbapenems are usually considered the last safe and eﬀective choice of drugs for the treatment of Gram-negative infections. The emergence of carbapenem-resistant A. baumannii (CRAB) is a critical public health issue as they leave clinicians with limited therapeutic options. In this study, phenotypic methods were used to characterize sixty-two (n = 62) A. baumannii isolates, which were included based on their suspected non-susceptibility to meropenem. Minimum inhibitory concentrations (MICs) of meropenem, levofloxacin, gentamicin, sulfamethoxazole/trimethoprim, tigecycline were determined using E-tests, while colistin MICs were determined using broth microdilution. The isolates were subjected to the modiﬁed Hodge test (MHT), the modiﬁed carbapenem-inactivation method (mCIM) and the imipenem/EDTA combined disk test (CDT). Eﬄux pump overexpression was studied using agar plates containing phenylalanine-arginine β-naphthylamide (PAβN). Assessment of bioﬁlm-formation was carried out using the crystal violet tube-adherence method. 64.5% of the strains showed meropenem MICs in the resistant range (>8 mg/L), resistance rates were similarly high to the other tested antibiotics. The MHT and mCIM assay were positive in 79.0% and 67.7% of cases, respectively; the presence of an MBL was suggested for 29.0% of isolates. Eﬄux-pump overexpression was seen in 12.9% of isolates. 54.8% of the isolates were characterized as strong bioﬁlm-producers. Microbiology laboratories have an important role in diﬀerentiating the distinct mechanisms by which these pathogens develop the CRAB phenotype, as plasmid-borne carbapenemases are signiﬁcant from the standpoint of public health microbiology.