Effect of Hcp Iron Ion Regulation on the Interaction Between Acinetobacter baumannii With Human Pulmonary Alveolar Epithelial Cells and Biofilm Formation

Abstract

Acinetobacter baumannii is a type of bacterial nosocomial infection with severe drug resistance. Hemolysin co-regulated protein (Hcp) is a marker of activated type VI secretion system (T6SS), a key secretory system that promotes Gram-negative bacteria colonization, adhesion, and invasion of host cells. Hcp is also regulated by iron ions (Fe). In this study, an ATCC17978 hcp deletion strain (ATCC17978Δhcp), an hcp complement strain (ATCC17978Δhcp+), and an A. baumannii–green fluorescent protein (GFP) strain were constructed and used to investigate the role of hcp in bacterial adhesion to cells (human pulmonary alveolar epithelial cells (HPAEpiC)) and biofilm formation. Our results indicate that the inhibitory concentrations of the three A. baumannii strains (ATCC17978 wild type, ATCC17978Δhcp, and ATCC17978Δhcp+) were drug-sensitive strains. A. baumannii hcp gene and iron ions might be involved in promoting the formation of a biofilm and host–bacteria interaction. Iron ions affected the ability of A. baumannii to adhere to cells, as there was no significant difference in the bacterial numbers when assessing the adhesion of the three strains to HPAEpiC in the presence of iron ion concentrations of 0 μM (F = 3.1800, p = 0.1144), 25 μM (F = 2.067, p = 0.2075), 100 μM (F = 30.52, p = 0.0007), and 400 μM (F = 17.57, p = 0.0031). The three strains showed significant differences in their ability to adhere to HPAEpiC. The numbers of bacteria adhesion to HPAEpiC were ATCC17978Δhcp>ATCC17978Δhcp+>ATCC17978 in descending order. Hcp gene was positively regulated by iron ions in the bacteria–cells’ co-culture. It is speculated that the effect of iron ions on the interaction between A. baumannii and HPAEpiC might be related to the transport function of hcp and bacterial immune escape mechanisms.

Impact of Gene Repression on Biofilm Formation of Vibrio cholerae

“…T6SS has been demonstrated to impact biofilm formation in several bacteria, such as Pseudomonas aeruginosa , Acinetobacter baumannii , and Burkholderia spp. ( Aubert Daniel et al, 2008 ; Schwarz et al, 2010 ; Moscoso et al, 2011 ; Pan et al, 2022 ). In V. cholerae , T6SS and biofilm formation are also connected as both negatively controlled by quorum sensing ( Hammer and Bassler, 2003 ; Zheng et al, 2010 ).…”

Utility of Strem-1 Biomarker and HCP Gene for Identification of Acinetobacter Baumannii Colonization and Infection in Lung

“…Variation among infection and colonization found at different hospitals has been reported ( 20 ). Martín-Aspas et al ( 21 ) reported a 40% (49/122) Ab infection rate and a 60% (73/122) colonization rate while Rodríguez-Baño et al ( 22 ) found Ab colonization to be approximately 50% in some Spanish hospitals. Differences may be attributed to local socioeconomic conditions, hospital management, epidemiological differences, and patients’ basic conditions.…”

“…The T6SS is a gram-negative bacteria virulence system, which enables bacterial competition in the host, enhances invasiveness and adhesion, and improves bacterial viability within macrophages. T6SS is central to the pathogenesis of Ab infection (18)(19)(20)22,32,33). The T6SS marker, Hcp, shows different presence and expression levels in clinical isolates (11,14,15).…”

H3-T6SS of Pseudomonas aeruginosa PA14 contributes to environmental adaptation via secretion of a biofilm-promoting effector

“…However, few effectors associated with secretion systems, especially in T6SS, have been found to promote biofilm formation. Only VgrG and Hcp, which are both components and effectors of the T6SS, have been found to play positive roles in biofilm formation in bacteria (Sha et al 2013 ; Fei et al 2022 ; Pan et al 2022 ). TepB is the first identified enzymatic effector of T6SS that promotes biofilm formation during acute and chronic infections of P. aeruginosa PA14.…”