Transferable plasmid-mediated antibiotic resistance in Acinetobacter.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Acinetobacter calcoaceticus strain BM2500 exhibits resistance to several clinically relevant antibiotics, including ampicillin, aminoglycoside-aminocyclitols, chloramphenicol, sulfonamides, and trimethoprim.
• Antibiotic resistance mechanisms in bacteria are often mediated by mobile genetic elements like plasmids, facilitating their spread.

Purpose of the Study:

• To characterize the genetic basis of antibiotic resistance in Acinetobacter calcoaceticus strain BM2500.
• To identify and analyze the plasmid responsible for conferring multiple drug resistance.
• To investigate the transferability and potential origin of the resistance plasmid.

Main Methods:

• Phenotypic characterization of antibiotic resistance.
• Identification and molecular analysis of the resistance plasmid (pIP1031) using restriction endonuclease digestion, nucleic acid hybridization, and CsCl density gradient ultracentrifugation.
• Conjugation experiments to assess plasmid transfer to Escherichia coli.

Main Results:

• Ampicillin resistance is attributed to beta-lactamase (TEM-1), while aminoglycoside-aminocyclitol resistance is due to phosphotransferase (APH(3")(5")I) and adenylyltransferase (AAD(3)(9]) activities.
• A 167 kb plasmid, designated pIP1031 (incompatibility group 6-C), carries these resistance genes.
• Plasmid pIP1031 is self-transferable at very low frequency to Escherichia coli via conjugation.

Conclusions:

• Plasmid pIP1031 is the sole carrier of the identified antibiotic resistance genes in Acinetobacter calcoaceticus strain BM2500.
• The plasmid's ability to transfer suggests potential for dissemination of antibiotic resistance.
• The data supports the hypothesis of a recent acquisition of plasmid pIP1031 by strain BM2500.