Initial Lung Infection Research Articles

Lung infection with classical Klebsiella pneumoniae strains establishes robust macrophage-dependent protection against heterologous reinfection

At present, there is no approved vaccine for prevention of infection by the opportunistic bacterium Klebsiella pneumoniae (Kp); success in treating these infections is increasingly challenged by the spread of antibiotic resistance. Preclinical investigation of adaptive immunity elicited by lung infection with live classical Kp may reveal host mechanisms of protection against this pathogen. Here, we utilize multiple virulent classical Kp strains to demonstrate that following lung infection, surviving wild-type mice develop protective immunity against both homologous and heterologous (heterotypic) reinfection. For Kp strains with low capacity to disseminate from the lung, this immunity is B-cell-independent. We further demonstrate that this immune protection is also effective against subsequent challenge with hypervirulent Kp if the strains share the same capsule type. Systemic inoculation fails to elicit the same protective effect as lung inoculation, revealing a lung-specific immune effector function is responsible for this protection. We therefore utilized clodronate-loaded liposomes to substantially deplete both alveolar macrophages and lung interstitial macrophages, finding that simultaneous depletion of both subsets entirely ablates protection. These findings indicate that following initial lung infection with Kp, lung macrophages mediate protection against ensuing Kp challenge.

What Spanish consensus meant for the treatment of Pseudomonas aeruginosa infection in patients with cystic fibrosis in the initial lung infection?

What Spanish consensus meant for the treatment of Pseudomonas aeruginosa infection in patients with cystic fibrosis in the initial lung infection?

Effect of antibiotic treatment in preweaned Holstein calves after experimental bacterial challenge with Pasteurella multocida

The primary objective of this randomized controlled challenge study was to investigate the effect of ampicillin on ultrasonographic (US) lung consolidation after experimental challenge with Pasteurella multocida in preweaned dairy calves. The secondary objectives were to determine whether ampicillin affected respiratory score, gross consolidation, or the detection of P. multocida in lung tissue at postmortem exam (PME). Holstein bull calves (n = 39) were transported to the University of Wisconsin-Madison School of Veterinary Medicine isolation facility at the mean (±SD) age of 52 ± 6 d. After a 7-d acclimation period, 30 calves were inoculated intratracheally with 1010 cfu of ampicillin-sensitive P. multocida. Lung US and respiratory scoring were performed 2, 6, 12, and 24 h post-challenge, then US once daily and respiratory scoring twice daily until d 14. Calves were randomized to receive ampicillin [n = 17, treatment (TX), 6.6 mg/kg i.m. once daily for 3 d] or placebo [n = 11, control (CON), saline, equal volume, i.m. once daily for 3 d] when ≥1 cm2 of lung consolidation was observed and ≥6 h had elapsed since challenge. Lung lesions ≥1 cm2 were considered positive for consolidation. Calves were respiratory score positive if ≥2 in 2 or more categories based on the Wisconsin respiratory health score chart. Area under the curve (AUC) was calculated for US score and respiratory score as a proxy for time with consolidation and clinical respiratory disease, respectively. Gross lung lesions and pathogens were quantified following PME. At the time of first treatment, consolidation had developed in 28/30 calves (TX, n = 17; CON, n = 11) and 6% (1 out of 17) of TX and 9% (1 out of 11) of CON calves had a positive respiratory score. The TX calves had a significantly lower median (interquartile range given in parentheses) AUC for US score [TX: 23 (20, 29), CON: 47 (33, 53)], whereas mean AUC for respiratory score was not different between groups (TX: 93 ± 28, CON: 96 ± 17). On d 14, 70% (12 out of 17) of TX and 100% (11 out of 11) of CON calves had lung consolidation, and 24% (4 out of 17) of TX and 27% (3 out of 11) of CON calves had clinical respiratory disease. On PME, median consolidation was 10% (6, 15) for TX and 10% (2, 28) for CON calves. Lung cultures were positive for P. multocida in 77% (13 out of 17) of TX and 91% (10 out of 11) of CON calves. Lung health benefited from a 3-d ampicillin therapy, but benefits were short-lived. Treatment failures might be due to incomplete resolution of the initial lung infection. Future studies are needed to optimize TX strategies to improve long-term lung health.

Inhalable Antimicrobials for Treatment of Bacterial Biofilm-Associated Sinusitis in Cystic Fibrosis Patients: Challenges and Drug Delivery Approaches.

Bacterial biofilm-associated chronic sinusitis in cystic fibrosis (CF) patients caused by Pseudomonas aeruginosa infections and the lack of available treatments for such infections constitute a critical aspect of CF disease management. Currently, inhalation therapies to combat P. aeruginosa infections in CF patients are focused mainly on the delivery of antimicrobials to the lower respiratory tract, disregarding the sinuses. However, the sinuses constitute a reservoir for P. aeruginosa growth, leading to re-infection of the lungs, even after clearing an initial lung infection. Eradication of P. aeruginosa from the respiratory tract after a first infection has been shown to delay chronic pulmonary infection with the bacteria for up to two years. The challenges with providing a suitable treatment for bacterial sinusitis include: (i) identifying a suitable antimicrobial compound; (ii) selecting a suitable device to deliver the drug to the sinuses and nasal cavities; and (iii) applying a formulation design, which will mediate delivery of a high dose of the antimicrobial directly to the site of infection. This review highlights currently available inhalable antimicrobial formulations for treatment and management of biofilm infections caused by P. aeruginosa and discusses critical issues related to novel antimicrobial drug formulation design approaches.

Role of Alanine Dehydrogenase of Mycobacterium tuberculosis during Recovery from Hypoxic Nonreplicating Persistence.

Mycobacterium tuberculosis can maintain a nonreplicating persistent state in the host for decades, but must maintain the ability to efficiently reactivate and produce active disease to survive and spread in a population. Among the enzymes expressed during this dormancy is alanine dehydrogenase, which converts pyruvate to alanine, and glyoxylate to glycine concurrent with the oxidation of NADH to NAD. It is involved in the metabolic remodeling of M. tuberculosis through its possible interactions with both the glyoxylate and methylcitrate cycle. Both mRNA levels and enzymatic activities of isocitrate lyase, the first enzyme of the glyoxylate cycle, and alanine dehydrogenase increased during entry into nonreplicating persistence, while the gene and activity for the second enzyme of the glyoxylate cycle, malate synthase were not. This could suggest a shift in carbon flow away from the glyoxylate cycle and instead through alanine dehydrogenase. Expression of ald was also induced in vitro by other persistence-inducing stresses such as nitric oxide, and was expressed at high levels in vivo during the initial lung infection in mice. Enzyme activity was maintained during extended hypoxia even after transcription levels decreased. An ald knockout mutant of M. tuberculosis showed no reduction in anaerobic survival in vitro, but resulted in a significant lag in the resumption of growth after reoxygenation. During reactivation the ald mutant had an altered NADH/NAD ratio, and alanine dehydrogenase is proposed to maintain the optimal NADH/NAD ratio during anaerobiosis in preparation of eventual regrowth, and during the initial response during reoxygenation.

Clinical features of post-infectious bronchiolitis obliterans in children undergoing long-term azithromycin treatment.

The aim of the present study was to outline any predisposing factors and clinical and radiological features of post-infectious bronchiolitis obliterans (PIBO) in pediatric patients, and to determine the effect of long-term azithromycin treatment on these factors. In total, 16 cases of children with PIBO were retrospectively reviewed. Adenovirus and Mycoplasma pneumoniae were the most common etiological agents (12/16) in the children with PIBO. The patients presented with persistent dyspnea, a chronic cough, sputum production and wheezing following the initial lung infection. Chest X-rays indicated pulmonary overinflation and patchy ground-glass opacity. In addition, high-resolution computed tomography (HRCT) scans revealed patchy ground-glass opacity, bronchiectasis, bronchial wall thickening and mosaic perfusion in all 16 cases. A unilateral hyperlucent lung was observed in two cases. All the patients underwent treatment with low-dose azithromycin and prednisone. Follow-up examinations of the 16 cases, varying in duration between 7 and 31 months, showed that the disease condition had improved in 10 cases. However, no significant improvements were identified from the HRCT scans or were observed in the patient condition in the additional six cases. The diagnosis of BO is primarily based on a typical clinical presentation and HRCT observations. Therefore, a typical clinical history and patchy ground-glass opacity features on HRCT scans are screening indices that predict BO development. Steroids are the cornerstone of BO treatment; however, long-term azithromycin treatment can improve the condition of the patients. In summary, PIBO is a disease with a high morbidity rate and should be treated by a multidisciplinary team. Patients should receive follow-up examination for an extended period. Patchy ground-glass opacity features on HRCT scans indicate that clinical suspicion of BO is necessary in children with persistent and severe wheezing.

Post-infectious bronchiolitis obliterans in children: clinical features and bronchoalveolar lavage therapy.

Objective To investigate the clinical features and bronchoalveolar lavage （BAL）therapy of postinfectious bronchiolitis obliterans （BO） in children. Method Ten children, who had post-infectious BO from February 2009 to February 2010, received BAL therapy, and were retrospectively analyzed. The data included pathology,chnical feature,chest HRCT scan, BALF cellular, levels of blood T cell subtypes and outcome of BAL therapy. Results Adenoviruses or mycoplasma pneumoniae were the most common etiologic agents （4/10, respectively）. All patients presented persistent or recurrent dyspneic respirations and wheezing since the initial lung infection. The findings of HRCT included mosaic pattern of perfusion （6/10）, accompanied by gas retention,bronchiectasis, atelectasis and bronchial wall thickening. The percentage of neutrophils in BALF was significantly increased in all cases （10/10）. There were predominance of CD8^＋ T cell subtype （9/10） and lower ratio of CD4 ^＋/CD8^＋ （ 10/10）in blood. Reduced symptoms and shortened hospital stay of BO in 9 of all 10 cases were observed after BAL therapy. Conclusions Severe adenovirus or mycoplasma pneunoniae bronchiolitis and/or pneumonia has higher risk for developing BO in children. Increased percentage of neutrophils in BALF and predominance of CD8^ ＋T cell subtype may play an important role in the mechanism of BO. BAL therepy can reduce the respiratory symptoms of BO in children. Key words: Bronchiolitis obliterans; Infection; Bronchoalveolar lavage; Neutrophils; T cell

Early Pseudomonas aeruginosa infection in individuals with cystic fibrosis: is susceptibility testing justified?

To test the presumption that Pseudomonas aeruginosa isolates responsible for initial lung infection in individuals with cystic fibrosis (CF) are invariably susceptible to antipseudomonal agents. Antibiotic susceptibility was determined (MIC and Etest) in two populations of P. aeruginosa associated with initial lung infection. Population 1: environmental isolates (n=78). Population 2: clinical isolates responsible for first infection in previously non-infected patients (85 isolates from 85 patients). Susceptibility or resistance was determined using current BSAC guidelines; ninth version (2009). The majority (≥ 90%) of isolates in both bacterial populations were susceptible to the front-line antipseudomonal agents; colistin, ciprofloxacin, tobramycin, ceftazidime, amikacin and meropenem. Up to 10% of isolates were resistant to one or more antibiotics. A single isolate from each population would be defined as resistant to tobramycin based on a breakpoint (>128 mg/L) that has been suggested for use in patients receiving inhaled therapy. The high prevalence of susceptibility found in P. aeruginosa isolates associated with initial infection contrasts with the high prevalence of resistance found in isolates from chronic CF lung infection. However, susceptibility in early isolates cannot be presumed. Until further data are obtained from clinically based studies, susceptibility tests should continue to be performed to assist the choice of antibiotics for treatment of early infection.

Bronchiolitis obliterans in children: Clinical presentation, therapy and long‐term follow‐up

To delineate the predisposing factors, clinical, radiological features and outcomes of bronchiolitis obliterans (BO) in children for minimising morbidity and mortality. Ten children who had BO from July 1995 to July 2005 were retrospectively reviewed at a tertiary paediatric facility in northern Taiwan. Bronchiolitis obliterans complicated by infections, Stevens-Johnson syndrome was found in eight and two patients, respectively. In children with post-infectious BO, adenoviruses were the most common etiologic agents (7/8). Among them, six patients needed intensive management and five patients needed mechanical ventilation. All patients presented persistent dyspneic respirations and wheezing since the initial lung infection. Initial focal atelectasis (n = 3) on chest radiographs progressed to atelectasis/lobar collapse (n = 8) when the diagnosis of BO was made. After adequate supportive management, atelectatic bronchiectasis was the most common complication (n = 5). Severe adenovirus bronchiolitis and/or pneumonia appear to have higher risk of development of BO in children. In order to minimise associated complications of BO, meticulous respiratory care for preventing pulmonary collapse may be considered in such instances.

Postinfectious Bronchiolitis obliterans in Children: Clinical and Radiological Profile and Prognostic Factors

Background: Postinfectious bronchiolitis obliterans (BO) designates a clinical syndrome of chronic airflow obstruction associated with inflammatory changes in the small airways. Objectives: The aim of this study was to determine the etiology, clinical and radiological features and define prognostic factors of postinfectious BO in children. Methods: We undertook a review of the medical records of 20 children with postinfectious BO, who were followed up between January 1994 and August 2001. Results: Postinfectious BO was diagnosed in 11 boys and 9 girls with a median age of 21.5 months (6–69 months) who were followed up for a median of 23 months. Cough and wheezing persisted since the initial lung infection in all patients. Postinfectious BO was diagnosed in an average of 6 months (1–42 months) after the acute illness. Adenoviruses were the most common etiologic agents identified serologically. The diagnoses of postinfectious BO was made by thoracic high-resolution computed tomography and clinical features. Corticosteroid therapy was used in 17 patients and supportive treatment was applied in all patients. Age at initial lung infection, gender, time of starting corticosteroid treatment, presence of bronchiectasis or atelectasis and etiologic agents identified on presentation did not predict severity in our study. Conclusions: Despite the prominent role of inflammation in the pathogenesis of postinfectious BO, the use of anti-inflammatory agents remains controversial. We could not identify any prognostic factors related to disease severity. In order to minimize associated complications, patients with postinfectious BO should be closely followed up and receive meticulous lung care.

Complementation of a capsule deficient Cryptococcus neoformans with CAP64 restores virulence in a murine lung infection.

Cryptococcosis is a systemic infection in humans caused by the opportunistic fungal pathogen, Cryptococcus neoformans. The infection usually presents as chronic meningoencephalitis, but infects via the respiratory tract. A polysaccharide capsule is a major virulence factor, which allows the yeast to resist host defenses. However, the essential role of the capsule in allowing it to resist host defenses during the initial lung infection has not been clearly shown. A mutant acapsular C. neoformans strain 602 was complemented with the CAP64 gene to obtain an encapsulated strain, TYCC38-602. TYCC38-602 persisted in the lungs of C.B-17 mice after intratracheal inoculation and disseminated to the brain, whereas the mutant acapsular 602 and the plasmid control transformant CIP3-602 strains grew less readily in the lung and were infrequently detected in the brain. T cell-mediated immunity, developed to the encapsulated organism, was required to control growth within the lungs and had a significant impact on numbers of yeasts detected in the brain. The parent acapsular strain, but not the transformant control, also required T cells for optimal inhibition of growth within the lung, but not for maintaining control of the colony-forming units (cfu) in the brain. In summary, the cryptococcal capsule plays an important role in lung virulence and dissemination to the brain, and intact immunity is required to control lung growth of the encapsulated yeast.

The invasive behaviour of Cryptococcus neoformans: a possibility of direct access to the central nervous system?

Cryptococcocal meningoencephalitis is always considered secondary to initial lung infection. Because of the unquestionable evidence of haematogenious spread from the lungs, few publications have reported about other possible primary sites of infection or other routes to the central nervous system. This study was designed to investigate the infiltrative pattern of C. neoformans in immunocompromised mice by treatment with dexamethasone. The infection was performed by nasal instillation (30 mice) or injection into the retro-orbital space (12 mice). From the group infected intranasally, 3 mice presented diffuse invasive fungal colonisation of the mucosa and submucosa. The histologic findings showed infiltrative growth along the periosteum, sometimes surrounded nervous endings of submucosa, invasion along the olfactory nerve and simultaneous meningeal involvement in 2 mice on the 6th and 8th day of infection. All mice infected into the retro-ocular space developed lesions containing numerous cryptococci in the local of the inoculum. Out of the main lesion we observed preferential growth along the perineural spaces with adherence to the perineurium, perivascular spaces and sometimes along aponeurosis. Simultaneous invasion of trigeminal ganglio and trigeminal branches was observed in 4 mice. These morphologic patterns suggest the hypothesis of direct infiltrative invasion of the central nervous system.