Surface-Related Features and Virulence Among Acinetobacter baumannii Clinical Isolates Belonging to International Clones I and II

Abstract

Acinetobacter baumannii currently represents one of the most important nosocomial infection agent due to its multidrug-resistance and a propensity for the epidemic spread. The A. baumannii strains belonging to the international clonal lineages I (IC I) and II (IC II) are associated with the hospital outbreaks and a high virulence. However, the intra and inter lineage-specific features of strains belonging to these most worldwide spread A. baumannii clones are not thoroughly explored. In this study we have investigated a set of cell surface-related features of A. baumannii IC I (n = 20) and IC II (n = 16) lineage strains, representing 30 distinct pulsed-field gel electrophoresis types in the collection of clinical isolates obtained in Lithuanian tertiary care hospitals. We show that A. baumannii IC II strains are non-motile, do not form pellicle and display distinct capsular polysaccharide profile compared with the IC I strains. Moreover, in contrast to the overall highly hydrophobic IC I strains, IC II strains showed a greater variation in cell surface hydrophobicity. Within the IC II lineage, hydrophilic strains demonstrated reduced ability to form biofilm and adhere to the abiotic surfaces, also possessed twofold thicker cell wall and exhibited higher resistance to desiccation. Furthermore, these strains showed increased adherence to the lung epithelial cells and were more virulent in nematode and mouse infection model compared with the hydrophobic IC II strains. According to the polymerase chain reaction-based locus-typing, the reduction in hydrophobicity of IC II strains was not capsule or lipooligosaccharide locus type-dependent. Hence, this study shows that the most widespread A. baumannii clonal lineages I and II markedly differ in the series of cell surface-related phenotypes including the considerable phenotypic diversification of IC II strains at the intra-lineage level. These findings suggest that the genotypically related A. baumannii strains might evolve the features which could provide an advantage at the specific conditions outside or within the host.

Wza gene knockout decreases Acinetobacter baumannii virulence and affects Wzy-dependent capsular polysaccharide synthesis

“…These results suggest that Wza affects the formation of bacterial capsules. Russo et al constructed the wza mutant and found that the wza mutants were capsule deficient [18], Skerniškytė J et al also constructed a wza mutant and found it was a CPSnegative phenotype [26]. These studies were consistent with the results of the cell wall we assessed by TEM.…”

“…Based on the bacterial toxicity test results of our study, Russo et al 2010 [18] and Skerniskyte et al 2019 [26], we found that after wza knockout, bacteria couldn't form capsule layer, which was easily killed by the immune system of the host, and what effect does wza have on the wzy pathway? whether the absence of Wza affects the expression of other molecules involved in the synthesis of Wzy capsular polysaccharides has not been reported.…”

“…The wza mutants showed significantly decreased survival in human ascites fluid, human serum and in a rat soft tissue model compared to that of WT strains [18]. Similarly, Skerniškytė J et al constructed a wza mutant and showed that the wza mutant displayed an increase in serum-sensitivity and an impairment in CPS synthesis compared with the parent strain [26]. A study from our group reported finding the wza gene in the highly virulent strain Lac-4 and other highly virulent strains, and that the wza gene is an important toxic factor of AB [27].…”

Thioredoxin Modulates Cell Surface Hydrophobicity in Acinetobacter baumannii

“…In A. baumannii, hydrophobicity has previously been correlated with increased adherence to abiotic surfaces but not to buccal epithelial cells (Costa et al, 2006;Pour et al, 2011). Furthermore, a recent study analyzed 16 clinical isolates of A. baumannii in the International Clone Lineage II (IC-II) and found the more hydrophobic strains produced increased biofilms, adhered more readily to abiotic surfaces, and had decreased virulence compared to the more hydrophilic isolates (Skerniskyte et al, 2018). Our laboratory has recently suggested the previously unidentified role of thioredoxin in surface hydrophobicity of an A. baumannii clinical isolate Ci79 (May et al, 2019).…”

“…Ci79 was genome sequenced (Ketter et al, 2014a), and largescale whole genome phylogenic analysis indicates a closer genetic relationship with AYE (IC-I) and ATCC strains 19606, 17978 than ACICU strain (IC-II). Twitching motility and pellicle formation are strongly associated with IC-I lineage strains (Eijkelkamp et al, 2011;Skerniskyte et al, 2018). Deletion of the thioredoxin A gene in Ci79 (ΔtrxA) greatly reduced twitching motility and surface type IV pili (T4P), but increased biofilm formation and cell surface hydrophobicity (CSH) as measured by Congo Red binding (May et al, 2019).…”