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. 2020 Jun 17;9(6):328.
doi: 10.3390/antibiotics9060328.

Characterization of Extremely Drug-Resistant and Hypervirulent Acinetobacter baumannii AB030

Manu Singh  1 , P Malaka De Silva  1 , Yasser Al-Saadi  1 , Jacek Switala  1 , Peter C Loewen  1 , Georg Hausner  1 , Wangxue Chen  2 , Ismael Hernandez  3 , Santiago Castillo-Ramirez  3 , Ayush Kumar  1
Affiliations

Characterization of Extremely Drug-Resistant and Hypervirulent Acinetobacter baumannii AB030

Manu Singh et al. Antibiotics (Basel). .

Abstract

Acinetobacter baumannii is an important nosocomial bacterial pathogen. Multidrug-resistant isolates of A. baumannii are reported worldwide. Some A. baumannii isolates display resistance to nearly all antibiotics, making treatment of infections very challenging. As the need for new and effective antibiotics against A. baumannii becomes increasingly urgent, there is a need to understand the mechanisms of antibiotic resistance and virulence in this organism. In this work, comparative genomics was used to understand the mechanisms of antibiotic resistance and virulence in AB030, an extremely drug-resistant and hypervirulent strain of A. baumannii that is a representative of a recently emerged lineage of A. baumannii International Clone V. In order to characterize AB030, we carried out a genomic and phenotypic comparison with LAC-4, a previously described hyper-resistant and hypervirulent isolate. AB030 contains a number of antibiotic resistance- and virulence-associated genes that are not present in LAC-4. A number of these genes are present on mobile elements. This work shows the importance of characterizing the members of new lineages of A. baumannii in order to determine the development of antibiotic resistance and virulence in this organism.

Keywords: comparative genomics; gram-negative; insertion elements; multidrug resistance; virulence.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Whole genome alignment showing genomic rearrangements between the genomes of AB030 (top) and LAC-4 (bottom) (a); showing shared or unique CDS between AB030 and LAC-4 (b).
Figure 2
Figure 2
Functional categorization of the whole genomes of LAC-4 and AB030 using COG database.
Figure 3
Figure 3
Presence of the ~9 Kb resistance island present in AB030 genome (red) (a). This island, missing in LAC-4 (blue), contains two aminoglycoside resistance genes and a β-lactam resistance gene (underlined). Comparison of the ~9 kb resistance island found in AB030 with those reported in A. baumannii and K. pneumoniae clinical isolates (b).
Figure 4
Figure 4
Genome-wide antibiotic resistance genes prediction using CARD database. * A mutation (81S→L) was found in the GyrA of AB030 and LAC-4. Percent identity to the reference gene is indicated in the shades of beige to maroon and the categories of the resistance genes are color-coded. #ParC has 84S→L in AB030, 88E→K in LAC-4, and 467S→G in both AB030 and LAC-4. @ RpsJ contains a 57V→L mutation in AB030.
Figure 5
Figure 5
Genetic organization of AdeABC RND-efflux system and two-component system, AdeRS in AB030 (red) and LAC-4 (blue). The adeRS operon that encodes the regulator of the AdeABC system is missing in the LAC-4 genome.
Figure 6
Figure 6
Bacterial burdens in lung (a), spleen (b), and blood (c). Mice (n = 5/group) were intranasally inoculated with AB030 and the type strain ATCC17978. The clinical signs were scored as indicated (d). The mice were sacrificed at 24 hours and their blood, lung, and spleen collected for quantitative bacteriology. The dotted lines in red indicate the limit of detection. Data for AB030 and ATCC17978 were compared with pooled data from 18 mice for LAC-4 (shown as gray horizontal bars) from four independent experiments. The bacterial burden data were analyzed by one-way ANOVA followed by post hoc Dunnett’s multiple comparison test.
Figure 7
Figure 7
Biofilm formation by AB030 in comparison to LAC-4 and ATCC17978 (a). Organization of bap (biofilm-associated protein-encoding gene) in AB030 (red) and LAC-4 (blue) (b). There is insertion of an IS5 family transposases before the start codon of the bap gene in AB030 which may disrupt its transcription. Statistical analysis was carried out using one-way ANOVA with Tukey’s multiple comparison test. **** denotes p < 0.0001.
Figure 8
Figure 8
Motility of AB030 compared to that of LAC-4 and ATCC17978 (a). Organization of the csu operon in AB030 (red) and LAC-4 (blue) (b). Statistical analysis was carried out using the one-way (for motility assays) and two-way (for biofilm assays) analysis of variance (ANOVA) (****, p < 0.0001).
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