Antimicrobial Resistance Gene Transfer in Drug Resistant Acinetobacter Species

Authors: CRIPPEN, CLAY - University Of Georgia; PALTRY, ROBERT - University Of Georgia; Rothrock, Michael; SANCHEZ, SUSAN - University Of Georgia; SZYMANSKI, CHRISTINE - University Of Georgia

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/13/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: Abstract: Antibiotic resistance is rapidly developing into one of the most formidable challenges for healthcare providers and researchers alike. To combat the rapid evolution of resistance, it will be important to uncover different mechanisms that bacteria use to acquire drug resistance genes. Acinetobacter baumannii is an emergent pathogen that effectively acquires multidrug resistances from its surroundings and has recently been observed in the feces of food-chain animals. In this study, we isolated several multi-drug resistant Acinetobacter species from feces of free-range chickens, ducks, and turkeys. These isolates showed a broad spectrum of resistances including cephalosporins, nitrofurantion, chloramphenicol, a carbapenem derivative, tetracycline, ß-lactams, among others, with one isolate classifying as XDR. MALDI-TOF mass spectrometry together with sequencing of the 16S ribosomal RNA subunit and rpoB, identified isolates as A. lwoffii, A. radioresistens and A. johnsonii. We simultaneously isolated bacteriophages that could only propagate on A. radioresistens and focused on characterizing two differing plaque morphologies, a “halo” and “non-halo” phenotype. Examination of the Acinetobacter resistance patterns indicated that the trends were not species-specific, but rather correlated to the bird type. This suggested that the resistances can be exchanged within the respective hosts via known mechanisms for DNA exchange. To elucidate whether this genetic material could serve as an environmental reservoir for the acquisition of resistance determinants for pathogenic microbes such as A. baumannii, we determined whether the A. baumannii type VI secretion system (T6SS) is sufficient to release detectable amounts of the plasmid-borne kanamycin resistance gene when co-incubated with the isolated species. In all cases, A. baumannii released the kanamycin resistance gene in a contact-dependent manner. We also compared the efficiency of the two bacteriophages to release genetic material after host cell lysis. Our results demonstrate that both phage mediated lysis and interspecies T6SS killing can significantly contribute to the spread of antimicrobial resistance genes in bacterial communities.

Technical Abstract: Abstract: Antibiotic resistance is rapidly developing into one of the most formidable challenges for healthcare providers and researchers alike. To combat the rapid evolution of resistance, it will be important to uncover different mechanisms that bacteria use to acquire drug resistance genes. Acinetobacter baumannii is an emergent pathogen that effectively acquires multidrug resistances from its surroundings and has recently been observed in the feces of food-chain animals. In this study, we isolated several multi-drug resistant Acinetobacter species from feces of free-range chickens, ducks, and turkeys. These isolates showed a broad spectrum of resistances including cephalosporins, nitrofurantion, chloramphenicol, a carbapenem derivative, tetracycline, ß-lactams, among others, with one isolate classifying as XDR. MALDI-TOF mass spectrometry together with sequencing of the 16S ribosomal RNA subunit and rpoB, identified isolates as A. lwoffii, A. radioresistens and A. johnsonii. We simultaneously isolated bacteriophages that could only propagate on A. radioresistens and focused on characterizing two differing plaque morphologies, a “halo” and “non-halo” phenotype. Examination of the Acinetobacter resistance patterns indicated that the trends were not species-specific, but rather correlated to the bird type. This suggested that the resistances can be exchanged within the respective hosts via known mechanisms for DNA exchange. To elucidate whether this genetic material could serve as an environmental reservoir for the acquisition of resistance determinants for pathogenic microbes such as A. baumannii, we determined whether the A. baumannii type VI secretion system (T6SS) is sufficient to release detectable amounts of the plasmid-borne kanamycin resistance gene when co-incubated with the isolated species. In all cases, A. baumannii released the kanamycin resistance gene in a contact-dependent manner. We also compared the efficiency of the two bacteriophages to release genetic material after host cell lysis. Our results demonstrate that both phage mediated lysis and interspecies T6SS killing can significantly contribute to the spread of antimicrobial resistance genes in bacterial communities.