Impact of AbaI mutation on virulence, biofilm development, and antibiotic susceptibility in Acinetobacter baumannii.

The quorum sensing (QS) system mediated by the abaI gene in Acinetobacter baumannii is crucial for various physiological and pathogenic processes. In this study, we constructed a stable markerless abaI knockout mutant (ΔabaI) strain using a pEXKm5-based allele replacement method to investigate the impact of abaI on A. baumannii. Proteomic analysis revealed significant alterations in protein expression between the wild type (WT) and ΔabaI mutant strains, particularly in proteins associated with membrane structure, antibiotic resistance, and virulence. Notably, the downregulation of key outer membrane proteins such as SurA, OmpA, OmpW, and BamA suggests potential vulnerabilities in outer membrane integrity, which correlate with structural abnormalities in the ΔabaI mutant strain, including irregular cell shapes and compromised membrane integrity, observed by scanning and transmission electron microscopy. Furthermore, diminished expression of regulatory proteins such as OmpR and GacA-GacS highlights the broader regulatory networks affected by abaI deletion. Functional assays revealed impaired biofilm formation and surface-associated motility in the mutant strain, indicative of altered colonization capabilities. Interestingly, the mutant showed a complex antibiotic susceptibility profile. While it demonstrated increased susceptibility to membrane-targeting antibiotics, its response to beta-lactams was more nuanced. Despite increased expression of metallo-beta-lactamase (MBL) superfamily proteins and DcaP-like protein, the mutant unexpectedly showed lower MICs for carbapenems (imipenem and meropenem) compared to the wild-type strain. This suggests that abaI deletion affects antibiotic susceptibility through multiple, potentially competing mechanisms. Further investigation is needed to fully elucidate the interplay between quorum sensing, antibiotic resistance genes, and overall antibiotic susceptibility in A. baumannii. Our findings underscore the multifaceted role of the abaI gene in modulating various cellular processes and highlight its significance in A. baumannii physiology, pathogenesis, and antibiotic resistance. Targeting the abaI QS system may offer novel therapeutic strategies for this clinically significant pathogen.

Type VI Secretion System Accessory Protein TagAB-5 Promotes Burkholderia pseudomallei Pathogenicity in Human Microglia.

Central nervous system (CNS) melioidosis caused by Burkholderia pseudomallei is being increasingly reported. Because of the high mortality associated with CNS melioidosis, understanding the underlying mechanism of B. pseudomallei pathogenesis in the CNS needs to be intensively investigated to develop better therapeutic strategies against this deadly disease. The type VI secretion system (T6SS) is a multiprotein machine that uses a spring-like mechanism to inject effectors into target cells to benefit the infection process. In this study, the role of the T6SS accessory protein TagAB-5 in B. pseudomallei pathogenicity was examined using the human microglial cell line HCM3, a unique resident immune cell of the CNS acting as a primary mediator of inflammation. We constructed B. pseudomallei tagAB-5 mutant and complementary strains by the markerless allele replacement method. The effects of tagAB-5 deletion on the pathogenicity of B. pseudomallei were studied by bacterial infection assays of HCM3 cells. Compared with the wild type, the tagAB-5 mutant exhibited defective pathogenic abilities in intracellular replication, multinucleated giant cell formation, and induction of cell damage. Additionally, infection by the tagAB-5 mutant elicited a decreased production of interleukin 8 (IL-8) in HCM3, suggesting that efficient pathogenicity of B. pseudomallei is required for IL-8 production in microglia. However, no significant differences in virulence in the Galleria mellonella model were observed between the tagAB-5 mutant and the wild type. Taken together, this study indicated that microglia might be an important intracellular niche for B. pseudomallei, particularly in CNS infection, and TagAB-5 confers B. pseudomallei pathogenicity in these cells.

In Vitro Roles of Burkholderia Intracellular Motility A (BimA) in Infection of Human Neuroblastoma Cell Line.

The bacterial pathogen Burkholderia pseudomallei causes human melioidosis, which can infect the brain, leading to encephalitis and brain abscesses. Infection of the nervous system is a rare condition but is associated with an increased risk of mortality. Burkholderia intracellular motility A (BimA) was reported to play an important role in the invasion and infection of the central nervous system in a mouse model. Thus, to gain insight of the cellular mechanisms underlying the pathogenesis of neurological melioidosis, we explored the human neuronal proteomics to identify the host factors that are up- and downregulated during Burkholderia infection. When infected the SH-SY5Y cells with B. pseudomallei K96243 wild-type (WT), 194 host proteins showed a fold change of >2 compared with uninfected cells. Moreover, 123 proteins showed a fold change of >2 when infected with a knockout bimA mutant (ΔbimA) mutant compared with WT. The differentially expressed proteins were mainly associated with metabolic pathways and pathways linked to human diseases. Importantly, we observed the downregulation of proteins in the apoptosis and cytotoxicity pathway, and in vitro investigation with the ΔbimA mutant revealed the association of BimA with the induction of these pathways. Additionally, we disclosed that BimA was not required for invasion into the neuron cell line but was necessary for effective intracellular replication and multinucleated giant cell (MNGC) formation. These findings show the extraordinary capacity of B. pseudomallei in subverting and interfering with host cellular systems to establish infection and extend our understanding of B. pseudomallei BimA involvement in the pathogenesis of neurological melioidosis. IMPORTANCE Neurological melioidosis, caused by Burkholderia pseudomallei, can result in severe neurological damage and enhance the mortality rate of melioidosis patients. We investigate the involvement of the virulent factor BimA, which mediates actin-based motility, in the intracellular infection of neuroblastoma SH-SY5Y cells. Using proteomics-based analysis, we provide a list of host factors exploited by B. pseudomallei. The expression level of selected downregulated proteins in neuron cells infected with the ΔbimA mutant was determined by quantitative reverse transcription-PCR and was consistent with our proteomic data. The role of BimA in the apoptosis and cytotoxicity of SH-SY5Y cells infected by B. pseudomallei was uncovered in this study. Additionally, our research demonstrates that BimA is required for successful intracellular survival and cell fusion upon infection of neuron cells. Our findings have significant implications for understanding the pathogenesis of B. pseudomallei infections and developing novel therapeutic strategies to combat this deadly disease.

Cycle-Inhibiting Factor Is Associated with Burkholderia pseudomallei Invasion in Human Neuronal Cells.

Burkholderia pseudomallei is a pathogenic bacterium that causes human melioidosis, which is associated with a high mortality rate. However, the underlying mechanisms of B. pseudomallei pathogenesis are largely unknown. In this study, we examined the infection of human neuronal SH-Sy5y cells by several clinically relevant B. pseudomallei strains. We found that all tested B. pseudomallei strains can invade SH-Sy5y cells, undergo intracellular replication, cause actin-tail formation, and form multinucleated giant cells. Additionally, a deletion mutant of B. pseudomallei cycle-inhibiting factor (cif) was constructed that exhibited reduced invasion in SH-Sy5y cells. Complementation of cif restored invasion of the B. pseudomallei cif-deleted mutant. Our findings enhance understanding of B. pseudomallei pathogenicity in terms of the virulence factor Cif and demonstrate the function of Cif in neurological melioidosis. This may eventually lead to the discovery of novel targets for treatment and a strategy to control the disease.

Burkholderia pseudomallei pathogenesis in human skin fibroblasts: A Bsa type III secretion system is involved in the invasion, multinucleated giant cell formation, and cellular damage.

Burkholderia pseudomallei-a causative agent of melioidosis that is endemic in Southeast Asia and Northern Australia-is a Gram-negative bacterium transmitted to humans via inhalation, inoculation through skin abrasions, and ingestion. Melioidosis causes a range of clinical presentations including skin infection, pneumonia, and septicemia. Despite skin infection being one of the clinical symptoms of melioidosis, the pathogenesis of B. pseudomallei in skin fibroblasts has not yet been elucidated. In this study, we investigated B. pseudomallei pathogenesis in the HFF-1 human skin fibroblasts. On the basis of co-culture assays between different B. pseudomallei clinical strains and the HFF-1 human skin fibroblasts, we found that all B. pseudomallei strains have the ability to mediate invasion, intracellular replication, and multinucleated giant cell (MNGC) formation. Furthermore, all strains showed a significant increase in cytotoxicity in human fibroblasts, which coincides with the augmented expression of matrix metalloproteinase-2. Using B. pseudomallei mutants, we showed that the B. pseudomallei Bsa type III secretion system (T3SS) contributes to skin fibroblast pathogenesis, but O-polysaccharide, capsular polysaccharide, and short-chain dehydrogenase metabolism do not play a role in this process. Taken together, our findings reveal a probable connection for the Bsa T3SS in B. pseudomallei infection of skin fibroblasts, and this may be linked to the pathogenesis of cutaneous melioidosis.

In vitro passage alters virulence, immune activation and proteomic profiles of Burkholderia pseudomallei.

Serial passage is a problem among many bacterial species, especially those where strains have been stored (banked) for several decades. Prior to banking with an organization such as ATCC, many bacterial strains were passaged for many years, so the characteristics of each strain may be extremely different. This is in addition to any differences in the original host environment. For Burkholderia pseudomallei, the number of serial passages should be carefully defined for each experiment because it undergoes adaptation during the course of serial passages. In the present study, we found that passaged B. pseudomallei fresh clinical isolates and reference strain in Luria-Bertani broth exhibited increased plaque formation, invasion, intracellular replication, Galleria mellonella killing abilities, and cytokine production of host cells. These bacteria also modulated proteomic profiles during in vitro passage. We presume that the modulation of protein expression during in vitro passage caused changes in virulence and immunogenicity phenotypes. Therefore, we emphasize the need for caution regarding the use of data from passaged B. pseudomallei. These findings of phenotypic adaptation during in vitro serial passage can help researchers working on B. pseudomallei and on other species to better understand disparate findings among strains that have been reported for many years.

Altered proteome of a Burkholderia pseudomallei mutant defective in short-chain dehydrogenase affects cell adhesion, biofilm formation and heat stress tolerance.

Burkholderia pseudomallei is a Gram-negative bacillus that causes melioidosis and is recognized as an important public health problem in southeast Asia and northeast Australia. The treatment of B. pseudomallei infection is hampered by resistance to a wide range of antimicrobial agents and no vaccine is currently available. At present, the underlying mechanisms of B. pseudomallei pathogenesis are poorly understood. In our previous study, we reported that a B. pseudomallei short-chain dehydrogenase (SDO; BPSS2242) mutant constructed by deletion mutagenesis showed reduced B. pseudomallei invasion and initial intracellular survival. This indicated that SDO is associated with the pathogenesis of melioidosis. In the present study, the role of B. pseudomallei SDO was further investigated using the SDO deletion mutant by a proteomic approach. The protein profiles of the SDO mutant and wild-type K96243 were investigated through gel-based proteomic analysis. Quantitative intensity analysis of three individual cultures of the B. pseudomallei SDO mutant revealed significant down-regulation of five protein spots compared with the wild-type. Q-TOF MS/MS identified the protein spots as a glutamate/aspartate ABC transporter, prolyl-tRNA synthetase, Hsp70 family protein, quinone oxidoreductase and a putative carboxypeptidase. Functional assays were performed to investigate the role of these differentially expressed proteins in adhesion to host cells, biofilm induction and survival under heat stress conditions. The SDO deletion mutant showed a decreased ability to adhere to host cells. Moreover, biofilm formation and the survival rate of bacteria under heat stress conditions were also reduced in the mutant strain. Our findings provide insight into the role of SDO in the survival and pathogenesis of B. pseudomallei at the molecular level, which may be applied to the prevention and control of B. pseudomallei infection.

Mass spectrometry-based identification and whole-genome characterisation of the first pteropine orthoreovirus isolated from monkey faeces in Thailand.

BACKGROUND: The pteropine orthoreovirus (PRV) was isolated from monkey (Macaca fascicularis) faecal samples collected from human-inhabited areas in Lopburi Province, Thailand. These samples were initially obtained to survey for the presence of hepatitis E virus (HEV). RESULTS: Two virus isolates were retrieved by virus culture of 55 monkey faecal samples. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was successfully used to identify the viruses as the segmented dsRNA orthoreovirus. Phylogenetic analysis of the Lopburi orthoreovirus whole-genomes revealed relationships with the well-characterised PRVs Pulau (segment L1), Cangyuan (segments L2, M3 and S3), Melaka (segments L3 and M2), Kampar (segments M1 and S2) and Sikamat (segments S1 and S4) of Southeast Asia and China with nucleotide sequence identities of 93.5-98.9%. RT-PCR showed that PRV was detected in 10.9% (6/55) and HEV was detected in 25.5% (14/55) of the monkey faecal samples. CONCLUSIONS: PRV was isolated from monkey faeces for the first time in Thailand via viral culture and LC-MS/MS. The genetic diversity of the virus genome segments suggested a re-assortment within the PRV species group. The overall findings emphasise that monkey faeces can be sources of zoonotic viruses, including PRV and HEV, and suggest the need for active virus surveillance in areas of human and monkey co-habitation to prevent and control emerging zoonotic diseases in the future.

Effects of sodium chloride on heat resistance, oxidative susceptibility, motility, biofilm and plaque formation of Burkholderia pseudomallei.

Burkholderia pseudomallei is an environmental saprophyte and the causative agent of melioidosis, a severe infectious disease prevalent in tropical areas, including southeast Asia and northern Australia. In Thailand, the highest incidence of melioidosis is in the northeast region, where saline soil and water are abundant. We hypothesized that B. pseudomallei develops an ability to thrive in saline conditions and gains a selective ecological advantage over other soil-dwelling microorganisms. However, little is known about how an elevated NaCl concentration affects survival and adaptive changes in this pathogen. In this study, we examined the adaptive changes in six isolates of B. pseudomallei after growth in Luria-Bertani medium containing different concentrations of NaCl at 37°C for 6 hr. The bacteria were then investigated for resistance to heat at 50°C and killing by hydrogen peroxide (H2 O2 ). In addition, flagellar production, biofilm formation, and the plaque formation efficiency of B. pseudomallei after culture in saline conditions were observed. In response to exposure to 150 and 300 mmol L-1 NaCl, all B. pseudomallei isolates showed significantly increased thermal tolerance, oxidative resistance, and plaque-forming efficiency. However, NaCl exposure notably decreased the number of B. pseudomallei flagella. Taken together, these results provide insight into the adaptations of B. pseudomallei that might be crucial for survival and persistence in the host and/or endemic environments with high salinity.

Genetic variations in regions of bovine and bovine-like enteroviral 5'UTR from cattle, Indian bison and goat feces.

BACKGROUND: Bovine enteroviruses (BEV) are members of the genus Enterovirus in the family Picornaviridae. They are predominantly isolated from cattle feces, but also are detected in feces of other animals, including goats and deer. These viruses are found in apparently healthy animals, as well as in animals with clinical signs and several studies reported recently suggest a potential role of BEV in causing disease in animals. In this study, we surveyed the presence of BEV in domestic and wild animals in Thailand, and assessed their genetic variability. METHODS: Viral RNA was extracted from fecal samples of cattle, domestic goats, Indian bison (gaurs), and deer. The 5' untranslated region (5'UTR) was amplified by nested reverse transcription-polymerase chain reaction (RT-PCR) with primers specific to BEV 5'UTR. PCR products were sequenced and analyzed phylogenetically using the neighbor-joining algorithm to observe genetic variations in regions of the bovine and bovine-like enteroviral 5'UTR found in this study. RESULTS: BEV and BEV-like sequences were detected in the fecal samples of cattle (40/60, 67 %), gaurs (3/30, 10 %), and goats (11/46, 24 %). Phylogenetic analyses of the partial 5'UTR sequences indicated that different BEV variants (both EV-E and EV-F species) co-circulated in the domestic cattle, whereas the sequences from gaurs and goats clustered according to the animal species, suggesting that these viruses are host species-specific. CONCLUSIONS: Varieties of BEV and BEV-like 5'UTR sequences were detected in fecal samples from both domestic and wild animals. To our knowledge, this is the first report of the genetic variability of BEV in Thailand.