&lt;p&gt;Capsule Thickness, Not Biofilm Formation, Gives Rise to Mucoid &lt;em&gt;Acinetobacter baumannii&lt;/em&gt; Phenotypes That are More Prevalent in Long-Term Infections: A Study of Clinical Isolates from a Hospital in China&lt;/p&gt;

Multidrug-resistant bacterial infections are becoming increasingly common, with only few last-resort antibiotics such as colistin available for clinical therapy. An alternative therapeutic strategy gaining momentum is phage therapy, which has the advantage of not being affected by bacterial resistance to antibiotics. However, a major challenge in phage therapy is the rapid emergence of phage-resistant bacteria. In this work, our main aim was to understand the mechanisms of phage-resistance used by the top priority pathogen Acinetobacter baumannii . We isolated the novel phage Phab24, capable of infecting colistin-sensitive and -resistant strains of A. baumannii . After co-incubating Phab24 with its hosts, we obtained phage-resistant mutants which were characterized on both genotypic and phenotypic levels. Using whole genome sequencing, we identified phage-resistant strains that displayed mutations in genes that alter the architecture of the bacterial envelope at two levels: the capsule and the outer membrane. Using an adsorption assay, we confirmed that phage Phab24 uses the bacterial capsule as its primary receptor, with the outer membrane possibly serving as the secondary receptor. Interestingly, the phage-resistant isolates were less virulent compared to the parental strains in a Galleria mellonella infection model. Most importantly, we observed that phage-resistant bacteria that evolved in the absence of antibiotics exhibited an increased sensitivity to colistin, even though the antibiotic resistance mechanism per se remained unaltered. This increase in antibiotic sensitivity is a direct consequence of the phage-resistance mechanism, and could potentially be exploited in the clinical setting.

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“…Biofilm assays were performed as described previously: [ 60 ]. Each sample was done five times, with 3 independent experiments.…”

Section: Methodsmentioning

confidence: 99%

Colistin-phage combinations decrease antibiotic resistance in Acinetobacter baumannii via changes in envelope architecture

Wang

Loh

Altamirano

et al. 2021

Emerging Microbes & Infections

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“…However, there have been observations that A. baumannii strains with thinner capsules do not display increased biofilm formation ( Hu et al, 2020 ), suggesting that such modulation of capsule structure might be more favorable under other conditions. Recent research conducted using opaque and translucent colonies formed by the same strain due to phenotypic switching, identified two-fold difference in capsule thickness between them ( Chin et al, 2018 ).…”

Section: Discussionmentioning

confidence: 99%

Capsule Protects Acinetobacter baumannii From Inter-Bacterial Competition Mediated by CdiA Toxin

et al. 2020

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Currently, Acinetobacter baumannii is considered as one of the most important infectious agents causing hospital acquired infections worldwide. It has been observed that many clinically important pathogens express contact-dependent growth inhibition (CDI) phenomenon, which modulates cell–cell and cell–environment interactions, potentially allowing bacteria to adapt to ever-changing conditions. Mainly, these systems are used for the inhibition of the growth of genetically different individuals within the same species. In this work, by performing cell competition assays with three genotypically different (as determined by pulse-field gel electrophoresis) clinical A. baumannii isolates II-c, II-a, and II-a1, we show that A. baumannii capsule is the main feature protecting from CDI-mediated inhibition. We also observed that for one clinical isolate, the two-component BfmRS system, contributed to the resistance against CDI-mediated inhibition. Moreover, we were able to demonstrate, that the effector protein CdiA is released into the growth media and exhibits its inhibitory activity without the requirement of a cell–cell contact. Lastly, by evaluating the remaining number of the cells pre-mixed with the CdiA and performing live/dead assay, we demonstrate that purified CdiA protein causes a rapid cell growth arrest. Our results indicate, that capsule efficiently protects A. baumannii from a CDI-mediated inhibition by a clinical A. baumannii V15 strain, which is able to secrete CdiA effector into the growth media and cause target cell growth arrest without a cell–cell contact.

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“…The role of capsules in virulence mechanisms and clinical outcomes is well known for K. pneumoniae [10,23,24], while data are limited for A. baumannii [5,11]. Only two studies linked A. baumannii mucosity and capsule formation to clinical severity and epidemic potential of the strains [12,25].…”

Section: Discussionmentioning

confidence: 99%

“…Overproduction of surface carbohydrates comprising the bacterial capsule may result in a mucoid phenotype [10][11][12]. This phenotype may vary, depending on the growth medium, incubation time, and conditions [10][11][12]. The observed phenotype is subjective and difficult to determine by simple examination, thus requiring further confirmation.…”

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confidence: 99%

Rapid identification of capsulated Acinetobacter baumannii using a density-dependent gradient test

et al. 2020

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Background Gram-negative bacterial capsules are associated with production of carbohydrates, frequently resulting in a mucoid phenotype. Infections caused by capsulated or mucoid A. baumannii are associated with increased clinical severity. Therefore, it is clinically and epidemiologically important to identify capsulated A. baumannii. Here, we describe a density-dependent gradient test to distinguish between capsulated and thin/non-capsulated A. baumannii. Results Thirty-one of 57 A. baumannii isolates displayed a mucoid phenotype. The density-dependent gradient test was comprised of two phases, with silica concentrations of 30% (top phase) and 50% (bottom phase). Twenty-three isolates migrated to the bottom phase, indicating thin or non-capsulated strains, and 34 migrated to the top phase, suggesting strains suspected to be capsulated. There was agreement between the mucoid and the non-mucoid phenotypes and the density-dependent gradient test for all but three isolates. Total carbohydrates extracted from strains suspected to be capsulated were significantly higher. Transmission electron microscopy confirmed the presence of a capsule in the six representative strains suspected to be capsulated. Conclusions The density-dependent gradient test can be used to verify capsule presence in mucoid-appearing A. baumannii strains. Identifying capsulated strains can be useful for directing infection control measures to reduce the spread of hypervirulent strains.

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<p>Capsule Thickness, Not Biofilm Formation, Gives Rise to Mucoid <em>Acinetobacter baumannii</em> Phenotypes That are More Prevalent in Long-Term Infections: A Study of Clinical Isolates from a Hospital in China</p>

Cited by 20 publications

References 24 publications

Colistin-phage combinations decrease antibiotic resistance in Acinetobacter baumannii via changes in envelope architecture

Colistin-phage combinations decrease antibiotic resistance in Acinetobacter baumannii via changes in envelope architecture

Capsule Protects Acinetobacter baumannii From Inter-Bacterial Competition Mediated by CdiA Toxin

Rapid identification of capsulated Acinetobacter baumannii using a density-dependent gradient test

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