Mechanical ventilation enhances Acinetobacter baumannii-induced lung injury through JNK pathways.

BACKGROUND: Patients in intensive care units (ICUs) often received broad-spectrum antibiotic treatment and Acinetobacter baumannii (A.b.) and Pseudomonas aeruginosa (P.a.) were the most common pathogens causing ventilator-associated pneumonia (VAP). This study aimed to examine the effects and mechanism of mechanical ventilation (MV) on A.b.-induced lung injury and the involvement of alveolar macrophages (AMs). METHODS: C57BL/6 wild-type (WT) and c-Jun N-terminal kinase knockout (JNK1-/-) mice received MV for 3 h at 2 days after nasal instillation of A.b., P.a. (1 × 106 colony-forming unit, CFU), or normal saline. RESULTS: Intranasal instillation of 106 CFU A.b. in C57BL/6 mice induced a significant increase in total cells and protein levels in the bronchoalveolar lavage fluid (BALF) and neutrophil infiltration in the lungs. MV after A.b. instillation increases neutrophil infiltration, interleukin (IL)-6 and vascular cell adhesion molecule (VCAM) mRNA expression in the lungs and total cells, IL-6 levels, and nitrite levels in the BALF. The killing activity of AMs against A.b. was lower than against P.a. The diminished killing activity was parallel with decreased tumor necrosis factor-α production by AMs compared with A.b. Inducible nitric oxide synthase inhibitor, S-methylisothiourea, decreased the total cell number in BALF on mice receiving A.b. instillation and ventilation. Moreover, MV decreased the A.b. and P.a. killing activity of AMs. MV after A.b. instillation induced less total cells in the BALF and nitrite production in the serum of JNK1-/- mice than those of WT mice. CONCLUSION: A.b. is potent in inducing neutrophil infiltration in the lungs and total protein in the BALF. MV enhances A.b.-induced lung injury through an increase in the expression of VCAM and IL-6 levels in the BALF and a decrease in the bacteria-killing activity of AMs. A lower inflammation level in JNK1-/- mice indicates that A.b.-induced VAP causes lung injury through JNK signaling pathway in the lungs.

γ-Glutamyltransferase as a Novel Virulence Factor of Acinetobacter baumannii Inducing Alveolar Wall Destruction and Renal Damage in Systemic Disease.

A thorough understanding of Acinetobacter baumannii pathogenicity is the key to identifying novel drug targets. In the current study, we characterize the γ-glutamyltransferase enzyme (GGT) as a novel virulence factor. A GGT assay showed that the enzyme is secreted via the type II secretion system and results in higher extracellular activity for the hypervirulent AB5075 than the laboratory-adapted strain American Type Culture Collection 17978. Enzyme-linked immunosorbent assay revealed that the former secretes larger amounts of GGT, and a rifampicin messenger RNA stability study showed that one reason for this could be the longer AB5075 ggt transcript half-life. Infection models confirmed that GGT is required for the virulence of A. baumannii. Finally, we show that clinical isolates with significantly higher extracellular GGT activity resulted in more severe infections, and assay of immune response and tissue damage markers confirm this correlation. The current findings establish for the first time the role of the GGT in the pathogenicity of A. baumannii.

Caspase-11 Plays a Protective Role in Pulmonary Acinetobacter baumannii Infection.

Activation of caspase-11 by some Gram-negative bacteria triggers the caspase-1/interleukin 1ß (IL-1ß) pathway, independent of canonical inflammasomes. Acinetobacter baumannii is a Gram-negative, conditionally pathogenic bacterium that can cause severe pulmonary infection in hospitalized patients. A. baumannii was revealed to activate canonical and noncanonical inflammasome pathways in bone marrow-derived macrophages (BMDMs). Pulmonary infection of caspase-11-/- mice with A. baumannii showed that caspase-11 deficiency impaired A. baumannii clearance, exacerbated pulmonary pathological changes, and enhanced susceptibility to A. baumannii These data indicate that the caspase-11-mediated innate immune response plays a crucial role in defending against A. baumannii.

Structure of the extended-spectrum class C ß-lactamase ADC-1 from Acinetobacter baumannii.

ADC-type class C ß-lactamases comprise a large group of enzymes that are encoded by genes located on the chromosome of Acinetobacter baumannii, a causative agent of serious bacterial infections. Overexpression of these enzymes renders A. baumannii resistant to various ß-lactam antibiotics and thus severely compromises the ability to treat infections caused by this deadly pathogen. Here, the high-resolution crystal structure of ADC-1, the first member of this clinically important family of antibiotic-resistant enzymes, is reported. Unlike the narrow-spectrum class C ß-lactamases, ADC-1 is capable of producing resistance to the expanded-spectrum cephalosporins, rendering them inactive against A. baumannii. The extension of the substrate profile of the enzyme is likely to be the result of structural differences in the R2-loop, primarily the deletion of three residues and subsequent rearrangement of the A10a and A10b helices. These structural rearrangements result in the enlargement of the R2 pocket of ADC-1, allowing it to accommodate the bulky R2 substituents of the third-generation cephalosporins, thus enhancing the catalytic efficiency of the enzyme against these clinically important antibiotics.

First Report of NDM-1-Producing Acinetobacter guillouiae.

BACKGROUND: Acinetobacter spp. is an opportunistic pathogen that has demonstrated increasing relevance in nosocomial infections. Carbapenem-resistant strains have been reported worldwide. METHODS: Since 2014, screening for metallo-ß-lactamases (MBLs) in all Acinetobacter spp. isolates using phenotypic methods and PCR has been implemented at the University Hospital Center Zagreb. RESULTS: The bacterial strain was isolated from the drain of a child hospitalized in a paediatric intensive care unit and identified as Acinetobacter guillouiae using a MALDI TOF automated system. The strain was resistant to meropenem, ceftazidime, cefotaxime, ceftriaxone, cefepime, sulbactam/ampicillin, gentamicin and ciprofloxacin, intermediately susceptible to piperacillin/tazobactam and imipenem, and susceptible to amikacin and colistin. The Hodge test and combined disk test with EDTA were positive. The MICs of meropenem and imipenem were not reduced by cloxacillin, but a small reduction of two dilutions was observed following the addition of sodium chloride, which indicated that OXA-58 was produced. PCR and sequencing of chromosomal DNA from boiled colonies revealed blaOXA-58 and blaNDM-1 genes. CONCLUSION: This is the first report of NDM-1 in Acinetobacter spp. in Croatia. The early detection of these genes will aid in the prevention and in the achievement of adequate infection control by limiting the spread of these organisms.

Acinetobacter calcoaceticus-baumannii complex strains induce caspase-dependent and caspase-independent death of human epithelial cells.

We investigated interactions of human isolates of Acinetobacter calcoaceticus-baumannii complex strains with epithelial cells. The results showed that bacterial contact with the cells as well as adhesion and invasion were required for induction of cytotoxicity. The infected cells revealed hallmarks of apoptosis characterized by cell shrinking, condensed chromatin, and internucleosomal fragmentation of nuclear DNA. The highest apoptotic index was observed for 4 of 10 A. calcoaceticus and 4 of 7 A. baumannii strains. Moreover, we observed oncotic changes: cellular swelling and blebbing, noncondensed chromatin, and the absence of DNA fragmentation. The highest oncotic index was observed in cells infected with 6 A. calcoaceticus isolates. Cell-contact cytotoxicity and cell death were not inhibited by the pan-caspase inhibitor z-VAD-fmk. Induction of oncosis was correlated with increased invasive ability of the strains. We demonstrated that the mitochondria of infected cells undergo structural and functional alterations which can lead to cell death. Infected apoptotic and oncotic cells exhibited loss of mitochondrial transmembrane potential (ΔΨ(m)). Bacterial infection caused generation of nitric oxide and reactive oxygen species. This study indicated that Acinetobacter spp. induced strain-dependent distinct types of epithelial cell death that may contribute to the pathogenesis of bacterial infection.

Outer membrane protein a in Acinetobacter baumannii induces autophagy through mTOR signalling pathways in the lung of SD rats.

Outer membrane protein A (OmpA) of Acinetobacter baumannii (A. baumannii) is associated with autophagy, which plays an important role in its pathogenicity. However, its exact pathophysiological role in the process of lung tissue cell autophagy remains unclear. In this study, animal and cell infection models were established by wild A. baumannii strain and An OmpA knockout mutant (OmpA-/- A. baumannii) strain. The expression levels of markers autophagy, histological change, cell viability and protein expression levels of inflammatory cytokines were examined. OmpA-/-A. baumannii was successfully constructed. The capacities of bacterial adhesion and invasion to host cells increased more obviously in the AB group and the AB + Rapa group than in the OmpA-/- AB group and AB + CQ group. The AB group and AB + Rapa group could produce double membrane vacuoles, endoplasmic reticulum dilation, mitochondrial ridge rupture, and mitochondrial vacuoles. OmpA could lead to increased LC3, AMPK, and PAMPK protein release, and decreased levels of P62, mTOR and pmTOR proteins in vivo and in vitro. OmpA caused lung pathology and the release of inflammatory cytokines. A. baumannii OmpA promotes autophagy in lung cells through the mTOR signalling pathway, which increases the bacterial colonization ability in the double-layer membrane autophagosome formed by the autophagy reaction to escape the clearance of bacteria by the host, promote the release of inflammatory mediators and aggravate the damage to the host.

Outbreak of Multidrug-Resistant Acinetobacter baumannii ST208 Producing OXA-23-Like Carbapenemase in a Children's Hospital in Shanghai, China.

Aims: Acinetobacter baumannii is notorious for acquiring antibiotic resistance and causing nosocomial infections worldwide. This study aimed to investigate the prevalence and molecular characteristics of A. baumannii isolates obtained from inpatients and the intensive care unit (ICU) environment of a pediatric hospital in Shanghai, China. Methods: Between July 2017 and January 2018, a total of 88 A. baumannii isolates, including three obtained from ICU environmental specimens, were characterized by antibiotic susceptibility, multilocus sequence typing, and resistance genes. Results: Carbapenem-resistant A. baumannii (CRAB) isolates, which were resistant to all the antibiotics tested except colistin, accounted for 69.3% (61/88) of all isolates. Three sequence types (STs) were identified among the CRAB isolates, and the predominant clone was ST208 (93.4%, 57/61), which included three environmental isolates and 54 clinical isolates collected from ICU patients. Carbapenem-susceptible isolates, none of which was multidrug resistant (MDR), showed a more diverse genetic background with three known STs and 21 novel STs identified. Intrinsic blaOXA-51-like and blaAmpC were detected in all isolates, while blaOXA-23-like was only detected in all CRAB isolates. ISAba1-blaOXA-23-like, ISAba1-blaOXA-51-like, and ISAba1-blaAmpC were identified in 69.3% (all CRAB isolates), 0%, and 65.9% (58 CRAB isolates) of all isolates, respectively. Conclusions: A nosocomial outbreak of MDR A. baumannii ST208 producing OXA-23-like carbapenemase occurred, highlighting the necessity for strict infection control interventions in the ICU.

Role of NADPH phagocyte oxidase in host defense against acute respiratory Acinetobacter baumannii infection in mice.

Acinetobacter baumannii is an emerging bacterial pathogen that rapidly develops multiple-drug resistance and is responsible for many nosocomial pulmonary infections. This study investigated the role of the NADPH phagocyte oxidase (phox) and inducible nitric oxide synthase (NOS2) in the host defense against respiratory infection with A. baumannii in mouse models of intranasal A. baumannii infection. gp91(phox-/-) mice showed higher susceptibility to A. baumannii infection than wild-type (WT) C57BL/6 mice, with significantly greater bacterial counts in their lungs (1,000-fold) (P < 0.005) and spleens (10-fold) (P < 0.05). Moreover, all of the gp91(phox-/-) mice succumbed to infection within 48 h. In contrast, only a moderate increase in bacterial burdens was detected in the lungs of NOS2(-/-) mice, and all NOS2(-/-) mice survived infection. Compared to WT mice, the pulmonary influx of inflammatory cells and serum and local inflammatory cytokine/chemokine responses were not obviously impaired at 4 h and were significantly higher at 24 h (P < 0.05) in gp91(phox-/-) mice, but NADPH-deficient neutrophils were unable to control bacterial replication and extrapulmonary dissemination. Thus, NADPH phagocyte oxidase appears to play a crucial role in the neutrophil-mediated host defense against A. baumannii.

Dissemination of class I integron in Acinetobacter baumliannii isolated from ventilator-associated pneumonia patients and their environment.

Multidrug resistant Acinetobacter baumannii has become the most common cause of health care-associated infections at Maharaj Nakhon Si Thammarat Hospital, Thailand. The objective of the study was to detect integrons using PCR-based method from 96 A. baumannii isolates from ventilator-associated pneumonia (VAP) patients and their environment. Antibiotic susceptibility was determined using a disk diffusion technique. Forty-six isolates exhibited integrase genes, with only class I and class II integron detected in 43 and 3 A. baumannii isolates, respectively. Twenty-seven of 52 clinical and 19 of 44 environmental isolates were integron-positive. Detection rate of integron-positive A. baumannii isolated from VAP patients increased from 25% to 83% over the 4 month study period. The majority (91%) of integron-positive A. baumannii showed resistance to 6 or more of 11 antibiotics tested and 72% of class I integron-positive isolates were imipenem-resistant. Thus, class I integron-positive A. baumannii had spread among the VAP patients and into hospital environment, the latter acting as reservoirs of potential pathogens possessing drug resistance genes.

Rapid Blue-Carba test: reduction in the detection time of carbapenemases performed from a 4-hour bacterial lawn.

The increase in carbapenem-resistant gram-negative bacteria is a matter of concern due to the limited therapeutic options available. In severe infections caused by these isolates, the rapid detection of the mechanisms of resistance is vital. We described a slightly modified version of the Blue-Carba test, rapid Blue-Carba test, which allows the detection of carbapenemases at 4 h of incubation from a haze of bacterial growth obtained from a positive blood culture. It was able to detect carbapenemase-producing isolates (Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter baumannii) with a sensitivity and specificity of 98.1 and 100%, respectively. It is a rapid, easy-to-perform and an inexpensive technique that can be applied to routine laboratories, together with the simultaneous identification by mass spectrometry which would help to screen non-enzymatic carbapenem resistance; this method allows the detection of clinically relevant multidrug-resistant bacteria and the early implementation of accurate therapeutic interventions.

Iron-Regulated Phospholipase C Activity Contributes to the Cytolytic Activity and Virulence of Acinetobacter baumannii.

Acinetobacter baumannii is an opportunistic Gram-negative pathogen that causes a wide range of infections including pneumonia, septicemia, necrotizing fasciitis and severe wound and urinary tract infections. Analysis of A. baumannii representative strains grown in Chelex 100-treated medium for hemolytic activity demonstrated that this pathogen is increasingly hemolytic to sheep, human and horse erythrocytes, which interestingly contain increasing amounts of phosphatidylcholine in their membranes. Bioinformatic, genetic and functional analyses of 19 A. baumannii isolates showed that the genomes of each strain contained two phosphatidylcholine-specific phospholipase C (PC-PLC) genes, which were named plc1 and plc2. Accordingly, all of these strains were significantly hemolytic to horse erythrocytes and their culture supernatants tested positive for PC-PLC activity. Further analyses showed that the transcriptional expression of plc1 and plc2 and the production of phospholipase and thus hemolytic activity increased when bacteria were cultured under iron-chelation as compared to iron-rich conditions. Testing of the A. baumannii ATCC 19606T plc1::aph-FRT and plc2::aph isogenic insertion derivatives showed that these mutants had a significantly reduced PC-PLC activity as compared to the parental strain, while testing of plc1::ermAM/plc2::aph demonstrated that this double PC-PLC isogenic mutant expressed significantly reduced cytolytic and hemolytic activity. Interestingly, only plc1 was shown to contribute significantly to A. baumannii virulence using the Galleria mellonella infection model. Taken together, our data demonstrate that both PLC1 and PLC2, which have diverged from a common ancestor, play a concerted role in hemolytic and cytolytic activities; although PLC1 seems to play a more critical role in the virulence of A. baumannii when tested in an invertebrate model. These activities would provide access to intracellular iron stores this pathogen could use during growth in the infected host.