Molecular characteristics of carbapenem-resistant Acinetobacter spp. from clinical infection samples and fecal survey samples in Southern China.

Background: Carbapenem resistance among Acinetobacter species has become a life-threatening problem. As a last resort in the treatment of gram-negative bacteria infection, resistance to colistin is also a serious problem. The aim of study was to analyze the mechanism of resistance and perform genotyping of carbapenem-resistant Acinetobacter from clinical infection and fecal survey samples in Southern China.

Methods: One hundred seventy and 74 carbapenem-resistant Acinetobacter were isolated from clinical infection samples and fecal survey samples, respectively. We detected the related genes, including carbapenemase genes (bla, bla, bla, bla, bla, bla, bla, bla, and bla), colistin resistance-related genes (mcr-1, mcr-2, mcr-3, mcr-4, and mcr-5), a porin gene (carO), efflux pump genes (adeA, adeB, adeC, adeI, adeJ, and adeK), mobile genetic element genes (intI1, intI2, intI3, tnpU, tnp513, IS26, ISAba1, and ISAba125), and the integron variable region. Genotyping was analyzed by enterobacterial repetitive intergenic consensus (ERIC)-PCR and dendrogram cluster analysis.

Results: Among the 244 carbapenem-resistant Acinetobacter, the common carbapenemase-positive genes included the following: bla, 183 (75.00%); bla, 174 (71.30%); bla, 57 (23.40%); and bla, 30 (12.30%). The coexistence of mcr-1 and bla in five strains of A. junii was found for the first time. Eleven distinct carO gene variants were detected in 164 (67.20%) strains, and ten novel variants, which shared 92-99% identity with sequences in the Genbank database, were first reported. Efflux system genes were present in approximately 70% of the isolates; adeABC and adeIJK were observed in 76.23 and 72.13%, respectively. Class 1 integrons were detected in 180 (73.80%) strains and revealed that four gene cassette arrays contained 11 distinct genes. The genotyping by ERIC-PCR demonstrated a high genetic diversity of non-baumannii Acinetobacter, and greater than 90% similarity to A. baumannii.

Conclusions: The bla gene was identified in up to 77% of the carbapenem-resistant Acinetobacter isolated from fecal survey samples, indicating that the gut might be a reservoir of resistant opportunistic bacteria. Intestinal bacteria can be transmitted through the fecal-hand, which is a clinical threat, thus, the monitoring of carbapenem-resistant bacteria from inpatients' feces should be improved, especially for patients who have been using antibiotics for a long time.