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.

Predictive value of α-amylase in tracheal aspirates for ventilator-associated pneumonia in elderly patients.

OBJECTIVE: This study aims to investigate the correlation between α-amylase in tracheal aspirates and risk factors of aspiration, as well as ventilator-associated pneumonia (VAP), in elderly patients undergoing mechanical ventilation and explore the clinical value of α-amylase for predicting VAP. METHODS: Tracheal aspirates were collected from elderly patients within 2 weeks after tracheal intubation in mechanical ventilation, and α-amylase was detected. Patients were grouped according to the presence of VAP. The correlation between α-amylase and risk factors of aspiration before intubation, as well as VAP, were analyzed. RESULTS: The sample of this study comprised 147 patients. The average age of these patients was 86.9 years. The incidence of VAP was 21% during the study period. Tracheal aspirate α-amylase level increased with the increase in the number of risk factors for aspiration before intubation, α-amylase level was significantly higher in the VAP group than in the non-VAP group, the area under the receiver operating characteristic curve (ROC) of the diagnostic value of α-amylase for VAP was 0.813 (95% CI: 0.721-0.896), threshold value was 4,681.5 U/L, sensitivity was 0.801 and specificity was 0.793. Logistic multivariate analysis revealed the following risk factors for VAP: a number of risk factors before intubation of ≥3, a Glasgow score of <8 points, the absence of continuous aspiration of subglottic secretion and a tracheal aspirate α-amylase level of >4681.5 U/L. CONCLUSION: Tracheal aspirate α-amylase can serve as a biomarker for predicting VAP in elderly patients undergoing mechanical ventilation.

Ventilator-associated pneumonia is characterized by excessive release of neutrophil proteases in the lung.

BACKGROUND: Ventilator-associated pneumonia (VAP) is characterized by neutrophils infiltrating the alveolar space. VAP is associated with high mortality, and accurate diagnosis remains difficult. We hypothesized that proteolytic enzymes from neutrophils would be significantly increased and locally produced inhibitors of human neutrophil elastase (HNE) would be decreased in BAL fluid (BALF) from patients with confirmed VAP. We postulated that in suspected VAP, neutrophil proteases in BALF may help identify "true" VAP. METHODS: BAL was performed in 55 patients with suspected VAP and in 18 control subjects. Isolation of a pathogen(s) at > 104 colony-forming units/mL of BALF dichotomized patients into VAP (n = 12) and non-VAP (n = 43) groups. Matrix metalloproteinases (MMPs), HNE, inhibitors of HNE, and tissue inhibitors of matrix metalloproteinases (TIMPs) were quantified. Plasminogen activator (PA) activity was estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and zymography. RESULTS: Neutrophil-derived proteases HNE, MMP-8, and MMP-9 were significantly increased in cell-free BALF from patients with VAP as compared with those without VAP (median values: HNE, 2,708 ng/mL vs 294 ng/mL, P < .01; MMP-8, 184 ng/mL vs 5 ng/mL, P < .01; MMP-9, 310 ng/mL vs 11 ng/mL, P < .01). HNE activity was also significantly increased in VAP (0.45 vs 0.01 arbitrary units; P < .05). In contrast, no significant differences were observed for protease inhibitors, TIMPs, or PAs. HNE in BALF, at a cutoff of 670 ng/mL, identified VAP with a sensitivity of 93% and specificity of 79%. CONCLUSIONS: Neutrophil proteases are significantly elevated in the alveolar space in VAP and may contribute to pathogenesis. Neutrophil proteases appear to have potential in suspected VAP for distinguishing true cases from "non-VAP" cases.

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.