Co-Existence of Carbapenemase-Encoding Genes in Acinetobacter baumannii from Cancer Patients

Acinetobacter baumannii is an opportunistic pathogen, which can acquire new resistance genes. Infections by carbapenem-resistant A. baumannii (CRAB) in cancer patients cause high mortality.

CRAB isolates from cancer patients were screened for carbapenemase-encoding genes that belong to Ambler classes (A), (B), and (D), followed by genotypic characterization by enterobacterial-repetitive-Intergenic-consensus-polymerase chain reaction (ERIC-PCR) and multilocus-sequence-typing (MLST).

A total of 94.1% of CRAB isolates co-harbored more than one carbapenemase-encoding gene. The genes bla_NDM, bla_OXA-23-like, and bla_KPC showed the highest prevalence, with rates of 23 (67.7%), 19 (55.9%), and 17 (50%), respectively. ERIC-PCR revealed 19 patterns (grouped into 9 clusters). MLST analysis identified different sequence types (STs) (ST-268, ST-195, ST-1114, and ST-1632) that belong to the highly resistant easily spreadable International clone II (IC II). Genotype diversity indicated the dissemination of carbapenem-hydrolyzing, β-lactamase-encoding genes among genetically unrelated isolates. We observed a high prevalence of metallo-β-lactamase (MBL)-encoding genes (including the highly-resistant bla_NDM gene that is capable of horizontal gene transfer) and of isolates harboring multiple carbapenemase-encoding genes from different classes.

The findings are alarming and call for measures to prevent and control the spread of MBL-encoding genes among bacteria causing infections in cancer patients and other immunocompromised patient populations.