The increasing frequency of bacteria showing antimicrobial resistance (AMR) raises the menace of entering into a postantibiotic era. Horizontal gene transfer (HGT) is one of the prime reasons for AMR ...acquisition. Acinetobacter baumannii is a nosocomial pathogen with outstanding abilities to survive in the hospital environment and to acquire resistance determinants. Its capacity to incorporate exogenous DNA is a major source of AMR genes; however, few studies have addressed this subject. The transformation machinery as well as the factors that induce natural competence in A. baumannii are unknown. In this study, we demonstrate that naturally competent strain A118 increases its natural transformation frequency upon the addition of Ca(2+)or albumin. We show that comEA and pilQ are involved in this process since their expression levels are increased upon the addition of these compounds. An unspecific protein, like casein, does not reproduce this effect, showing that albumin's effect is specific. Our work describes the first specific inducers of natural competence in A. baumannii Overall, our results suggest that the main protein in blood enhances HGT in A. baumannii, contributing to the increase of AMR in this threatening human pathogen.
In the past few decades Acinetobacter baumannii has emerged as a notorious nosocomial pathogen because of its ability to acquire genetic material and persist in extreme environments. Recently, human ...serum albumin (HSA) was shown to significantly increase natural transformation frequency in A. baumannii. This observation led us to perform transcriptomic analysis of strain A118 under HSA induction to identify genes that are altered by HSA. Our results revealed the statistically significant differential expression of 296 protein-coding genes, including those associated with motility, biofilm formation, metabolism, efflux pumps, capsule synthesis, and transcriptional regulation. Phenotypic analysis of these traits showed an increase in surface-associated motility, a decrease in biofilm formation, reduced activity of a citric acid cycle associated enzyme, and increased survival associated with zinc availability. Furthermore, the expression of genes known to play a role in pathogenicity and antibiotic resistance were altered. These genes included those associated with RND-type efflux pumps, the type VI secretion system, iron acquisition/metabolism, and ß-lactam resistance. Together, these results illustrate how human products, in particular HSA, may play a significant role in both survival and persistence of A. baumannii.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Our previous data show that serum albumin can trigger natural transformation in
Acinetobacter baumannii
. However, extracellular matrix/basal membrane components, norepinephrine, and mucin did not ...have a significant effect on this process. Therefore, the effect of human products appears to be albumin specific, as both BSA and HSA have been shown to increase of natural transformation.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
ABSTRACT
The increasing frequency of bacteria showing antimicrobial resistance (AMR) raises the menace of entering into a postantibiotic era. Horizontal gene transfer (HGT) is one of the prime ...reasons for AMR acquisition.
Acinetobacter baumannii
is a nosocomial pathogen with outstanding abilities to survive in the hospital environment and to acquire resistance determinants. Its capacity to incorporate exogenous DNA is a major source of AMR genes; however, few studies have addressed this subject. The transformation machinery as well as the factors that induce natural competence in
A. baumannii
are unknown. In this study, we demonstrate that naturally competent strain A118 increases its natural transformation frequency upon the addition of Ca
2+
or albumin. We show that
comEA
and
pilQ
are involved in this process since their expression levels are increased upon the addition of these compounds. An unspecific protein, like casein, does not reproduce this effect, showing that albumin's effect is specific. Our work describes the first specific inducers of natural competence in
A. baumannii
. Overall, our results suggest that the main protein in blood enhances HGT in
A. baumannii
, contributing to the increase of AMR in this threatening human pathogen.
Acinetobacter baumannii is a multidrug resistant nosocomial pathogen that shows an outstanding ability to undergo genetic exchange, thereby acquiring different traits that contribute to its success. ...In this work, we identified genetic features of an indigo-pigmented A. baumannii strain (Ab33405) that belongs to the clonal complex CC113
/CC79
. Ab33405 possesses a high number of genes coding for antibiotic resistance and virulence factors that may contribute to its survival, not only in the human host, but also in the hospital environment. Thirteen genes conferring resistance to different antibiotic families (trimethoprim, florfenicol, β-lactams, aminoglycosides and sulfonamide) as well as the adeIJK genes and the capsule locus (KL) and outer core locus (OCL) were identified. Ab33405 includes 250 unique genes and a significant number of elements associated with Horizontal Gene Transfer, such as insertion sequences and transposons, genomic islands and prophage sequences. Also, the indigo-pigmented uncommon phenotype that could be associated with the monooxygenase or dioxygenase enzyme coded for by the iacA gene within the iac cluster was probably conferred by insertion of a 18-kb DNA fragment into the iacG gene belonging to this cluster. The Ab33405 genome includes all type VI secretion system genes and killing assays showed the ability of Ab33045 to kill Escherichia coli. In addition, Ab33405 can modulate susceptibility antibiotics when exposed to blue light.
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Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Acinetobacter baumannii has emerged over the last few decades as a major nosocomial pathogen. Its ability to acquire genetic material and survive in extreme environments has positioned it as a ...paradigm of multidrug resistance. Horizontal genetic transfer, specifically natural transformation, has played a key role in its evolution. However, little is known about how competence for natural transformation is induced or regulated in A. baumannii and, therefore, our research focuses on identifying inducers of competence and characterizing genes involved in this process. To identify inducers of competence, A. baumannii cells were grown in the presence of host human products or antibiotics and transformation frequencies were assessed. Human serum albumin (HSA) was the only host human product that significantly increased transformation frequencies, suggesting that an albumin-specific mechanism exists in this species. In addition, all three antibiotics tested increased transformation frequencies, likely via different pathways. To better understand induction of competence, RNA sequencing was performed under HSA induction and 167 genes were identified as being significantly differentially expressed. Twenty-three genes were analyzed in depth, including putative transcriptional regulators and those associated with two component regulatory systems and type IV pili. This analysis led to the identification of a number of genes that were not explored before and whose roles in competence development are suitable for further analysis.
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