Carbapenemase and ESBL Genes Found Across Iranian Acinetobacter baumannii Isolates

A study of 180 Acinetobacter baumannii isolates recovered from clinical specimens in Iran between 2018 and 2022 has documented how commonly these hospital pathogens produce the enzymes that break down beta-lactam antibiotics. The research, published in Molecular Biology Reports, combined phenotypic screening with polymerase chain reaction (PCR) confirmation of the genes involved, and fingerprinting of the most resistant isolates.

The team used three phenotypic methods, each targeted at a different enzyme class. The Modified Hodge Test (MHT) was applied to detect carbapenemase production, the Disc Potentiation Test (DPT) to identify extended-spectrum beta-lactamase (ESBL) producers, and the Double Disc Test (DDT) to flag AmpC beta-lactamase producers. PCR was then used to confirm the presence of carbapenemase, ESBL, and AmpC encoding genes.

The phenotypic results showed extensive enzyme production across the collection. Of the 180 isolates, 44.5 percent, or 80 isolates, tested positive for carbapenemase production in the MHT. A larger share, 98 percent or 177 isolates, were positive in the metallo-beta-lactamase phenotypic test. AmpC production was detected in 17.5 percent of isolates, corresponding to 32 isolates, while ESBL production was found in 4.5 percent, or 8 isolates.

Resistance levels were also measured directly. 44.44 percent of the isolates showed a minimum inhibitory concentration (MIC) of at least 8 micrograms per milliliter for imipenem, a carbapenem antibiotic.

Molecular testing identified which resistance genes were present. The most frequently detected genes were OXA51, found in 96 percent of isolates, OXA24 in 53.3 percent, CTX in 41.5 percent, OXA23 in 36.6 percent, and TEM in 31.5 percent. PCR thus confirmed the presence of carbapenemase, ESBL, and AmpC encoding genes among the isolates.

To differentiate the highly resistant isolates from one another, the team applied enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) fingerprinting to approximately 80 isolates with high imipenem MICs. This method generates DNA banding patterns that distinguish strains within a collection. Five ERIC types were detected among these isolates.

The authors conclude that ESBL-, AmpC-, and carbapenemase-producing A. baumannii isolates represent a serious threat to human public health, and that identifying these organisms is critical for the proper management of the infections they cause.

The study is a cross-sectional characterization of isolates from clinical specimens in Iran covering 2018 to 2022, and its findings describe this particular collection. The reported figures, from the 44.5 percent carbapenemase positivity in the MHT to the 96 percent detection rate of OXA51, provide phenotypic and molecular data on the enzyme production and resistance gene content of these isolates, together with fingerprint evidence showing five ERIC types among the most imipenem-resistant strains.

Subject of Research: Phenotypic and molecular characterization of ESBL, AmpC, and carbapenemase-producing Acinetobacter baumannii isolates from clinical specimens in Iran

Article Title: Phenotypic and molecular characterization of ESBL, AmpC, and carbapenemase-producing Acinetobacter baumannii isolates from clinical specimens in Iran

Article References: Rahimzadeh, R., Babazadeh, F., Mohammadshahi, J., teimourpour, A., Sadigh, A., Nabavinia, M., Erfanirad, M., Sardari, M., Ashouri, P., & Teimourpour, R. (2026). Phenotypic and molecular characterization of ESBL, AmpC, and carbapenemase-producing Acinetobacter baumannii isolates from clinical specimens in Iran. Molecular Biology Reports, 53(1), Article 1821. https://doi.org/10.1007/s11033-026-13018-9

Image Credits: AI Generated

DOI: 10.1007/s11033-026-13018-9

Keywords: Phenotypic, molecular, characterization, ESBL, AmpC, carbapenemase-producing, Acinetobacter, baumannii, isolates, clinical, specimens, Iran