The Molecular Detection of Class B and Class D Carbapenemases in Clinical Strains of Acinetobacter calcoaceticus-baumannii Complex: The High Burden of Antibiotic Resistance and the Co-Existence of Carbapenemase Genes

The emergence of carbapenem-resistant Acinetobacter calcoaceticus-baumannii complex (CRACB) in clinical environments is a significant global concern. These critical pathogens have shown resistance to a broad spectrum of antibacterial drugs, including carbapenems, mostly due to the acquisition of various beta-lactamase genes. Clinical samples (n = 1985) were collected aseptically from multiple sources and grown on blood and MacConkey agar. Isolates and antimicrobial susceptibility were confirmed with the VITEK-2 system. The modified Hodge test confirmed the CRACB phenotype, and specific PCR primers were used for the molecular identification of bla(OXA) and bla(NDM) genes. Of the 1985 samples, 1250 (62.9%) were culture-positive and 200 (43.9%) were CRACB isolates. Of these isolates, 35.4% were recovered from pus samples and 23.5% from tracheal secretions obtained from patients in intensive care units (49.3%) and medical wards (20.2%). An antibiogram indicated that 100% of the CRACB isolates were resistant to beta-lactam antibiotics and beta-lactam inhibitors, 86.5% to ciprofloxacin, and 83.5% to amikacin, while the most effective antibiotics were tigecycline and colistin. The CRACB isolates displayed resistance to eight different AWaRe classes of antibiotics. All isolates exhibited the bla(OXA-51) gene, while bla(OXA-23) was present in 94.5%, bla(VIM) in 37%, and bla(NDM) in 14% of the isolates. The bla(OXA-51), bla(OXA-23), and bla(OXA-24) genes co-existed in 13 (6.5%) isolates. CRACB isolates with co-existing bla(OXA-23), bla(OXA-24), bla(NDM), bla(OXA-51) and bla(VIM) genes were highly prevalent in clinical samples from Pakistan. CRACB strains were highly critical pathogens and presented resistance to virtually all antibacterial drugs, except tigecycline and colistin.

Automated summary

The emergence of carbapenem-resistant Acinetobacter calcoaceticus-baumannii complex (CRACB) in clinical environments is a significant global concern. These critical pathogens have shown resistance to a broad spectrum of antibacterial drugs, including carbapenems. CRACB isolates displayed resistance to most antibiotics, except tigecycline and colistin.