Transcriptional responses of toxigenic and atoxigenic isolates of Aspergillus flavus to oxidative stress in aflatoxin-conducive and non-conducive media

Aflatoxin production by isolates of Aspergillus flavus varies, ranging from highly toxigenic to completely atoxigenic. Several mechanisms have been identified which regulate aflatoxin production including medium carbon source and oxidative stress. In recent studies, aflatoxin production has been implicated in partially ameliorating oxidative stress in A. flavus. To better understand the role of aflatoxin production in oxidative stress responses, a selection of toxigenic and atoxigenic isolates of A. flavus with moderate to high oxidative stress tolerance were exposed to increasing concentrations of H2O2 in both aflatoxin-conducive and non-conducive media. Mycelial mats were collected for global transcriptome sequencing followed by differential expression, functional prediction, and weighted co-expression analyses. Oxidative stress and medium carbon source had a significant effect on the expression of several secondary metabolite gene clusters including those for aflatoxin, aflatrem, aflavarin, cyclopiazonic acid, and kojic acid. Atoxigenic biological control isolates showed less differential expression under stress than other atoxigenic isolates suggesting expression profiles may be useful in screening. Increasing stress also resulted in regulation of SakA/Hog1 and MpkA MAP kinase signalling pathways pointing to their potential roles in regulating oxidative stress responses. Their expression was also influenced by medium carbon source. These results suggest that aflatoxin production along with that of other mycotoxins may occur as part of a concerted coping mechanism for oxidative stress and its effects in the environment. This mechanism is also regulated by availability of simple sugars and glycolytic compounds for their biosynthesis.

Transcriptional responses of toxigenic and atoxigenic isolates of Aspergillus flavus to oxidative stress in aflatoxin-conducive and non-conducive media

Aflatoxin production by isolates of Aspergillus flavus varies, ranging from highly toxigenic to completely atoxigenic. Several mechanisms have been identified which regulate aflatoxin production including medium carbon source and oxidative stress. In recent studies, aflatoxin production has been implicated in partially ameliorating oxidative stress in A. flavus. To better understand the role of aflatoxin production in oxidative stress responses, a selection of toxigenic and atoxigenic isolates of A. flavus with moderate to high oxidative stress tolerance were exposed to increasing concentrations of H2O2 in both aflatoxin-conducive and non-conducive media. Mycelial mats were collected for global transcriptome sequencing followed by differential expression, functional prediction, and weighted co-expression analyses. Oxidative stress and medium carbon source had a significant effect on the expression of several secondary metabolite gene clusters including those for aflatoxin, aflatrem, aflavarin, cyclopiazonic acid, and kojic acid. Atoxigenic biological control isolates showed less differential expression under stress than other atoxigenic isolates suggesting expression profiles may be useful in screening. Increasing stress also resulted in regulation of SakA/Hog1 and MpkA MAP kinase signalling pathways pointing to their potential roles in regulating oxidative stress responses. Their expression was also influenced by medium carbon source. These results suggest that aflatoxin production along with that of other mycotoxins may occur as part of a concerted coping mechanism for oxidative stress and its effects in the environment. This mechanism is also regulated by availability of simple sugars and glycolytic compounds for their biosynthesis.

Identifying and developing maize germplasm with resistance to accumulation of aflatoxins

Efforts to identify maize germplasm with resistance to Aspergillus flavus infection and subsequent accumulation of aflatoxins were initiated by the US Department of Agriculture, Agricultural Research Service at several locations in the late 1970s and early 1980s. Research units at four locations in the south-eastern USA are currently engaged in identification and development of maize germplasm with resistance to A. flavus infection and accumulation of aflatoxins. The Corn Host Plant Resistance Research Unit, Mississippi State, MS, developed procedures for screening germplasm for resistance to A. flavus infection and accumulation of aflatoxins. Mp313E, released in 1990, was the first line released as a source of resistance to A. flavus infection. Subsequently, germplasm lines Mp420, Mp715, Mp717, Mp718, and Mp719 were released as additional sources of resistance. Quantitative trait loci associated with resistance have also been identified in four bi-parental populations. The Crop Protection and Management Research Unit and Crop Genetics and Breeding Research Unit, Tifton, GA, created a breeding population GT-MAS:gk. GT601, GT602, and GT603 were developed from GT-MAS:gk. The Food and Feed Safety Research Unit, New Orleans, LA, in collaboration with the International Institute for Tropical Agriculture used a kernel screening assay to screen germplasm and develop six germplasm lines with resistance to aflatoxins. The Plant Science Research Unit, Raleigh, NC, through the Germplasm Enhancement of Maize (GEM) Project provides to co-operators diverse germplasm that is a valuable source of resistance to A. flavus infection and accumulation of aflatoxins in maize.

Treatment of Candida albicans pericarditis in a heart transplant patient

Pericarditis due to Candida species is a rare clinical entity, associated with thoracic surgery and immunosuppression. We report here the second case of pericarditis due to Candida albicans in a heart transplant patient, which presented as tamponade approximately 3 weeks post transplant, in the absence of evidence of sternal osteomyelitis. The patient was treated with pericardiocentesis and a combination of caspofungin and fluconazole, but the patient ultimately required the explantation of retained epicardial leads and the creation of a pericardial window. This case illustrates that Candida species must be considered in the differential diagnosis in post-transplant pericarditis, and that foreign body removal is, as always, key in helping to resolve such infections. This case also demonstrates the first use of caspofungin with fluconazole to treat Candida pericarditis. We discuss the conflicting data regarding the use of caspofungin, alone or in combination therapy, in treating infections involving biofilms, such as the infected pericardium.

Mycobacterium avium complex infection in kidney transplant patients

Mycobacterium avium complex (MAC) infections have been reported rarely in renal transplant patients. Consequently the clinical course and optimal treatment of these patients are not well understood. We present 3 patients with MAC infections after receiving a renal transplant (2 with generalized and 1 with localized infection). All patients were treated with combination antibiotic therapy and reduction of immunosuppression. One patient experienced clinical control of disease but a mild cellular rejection that was successfully treated with high-dose corticosteroids. One patient died of disseminated MAC infection. The patient with localized infection died of unrelated causes. In summary, MAC infection, although rare in renal transplant patients, may respond to combination antimicrobial therapy and reduction of immunosuppression.

An outbreak of Legionella micdadei pneumonia in transplant patients: evaluation, molecular epidemiology, and control

PURPOSE

To describe a nosocomial outbreak of Legionella micdadei pneumonia in transplant patients and to characterize the source of the outbreak and the control measures utilized.

SUBJECTS AND METHODS

We performed retrospective Legionella micdadei serologic testing to enhance case finding in transplant patients with pneumonia that lacked a documented microbial etiology, as well as prospective environmental surveillance of water sites and testing for Legionella in clinical specimens.

RESULTS

During a 3-month period, 12 cases of Legionella micdadei pneumonia were identified either by culture or serologic testing among 38 renal and cardiac transplant patients. Legionella micdadei isolates from hot water sources were found by pulsed-field gel electrophoresis to have a DNA banding pattern that was identical to the isolates from the first 3 culture-positive cases and from 2 cases that occurred 16 months later.

CONCLUSIONS

Hospitals caring for organ transplant recipients and other immunosuppressed patients must be aware of the possibility of environmental sources of outbreaks of Legionella infection. A first-line screen with the Legionella urine antigen test will identify Legionella pneumophila serogroup 1. However, specific cultures in outbreak situations should be considered to identify other Legionella pneumophila serotypes and the nonpneumophila Legionella species.

Pulmonary tuberculosis after lung transplantation

During a 5-year study period, we diagnosed pulmonary tuberculosis in two (2%) of 94 lung and heart-lung transplant recipients. Each infection occurred 3 months after bilateral lung transplantation in the presence of evidence implicating donor-to-recipient transmission of the pathogen. The radiographic patterns of pulmonary tuberculosis were subtle: narrowing of the middle lobe bronchus of the right lung caused by an endobronchial granulomatous mass (n = 1) and a focal cluster of small nodules in the upper lobe of the left lung and small bilateral pleural effusions (n = 1). Each patient achieved complete clinical and radiographic response after antituberculous therapy. We conclude that Mycobacterium tuberculosis may be transmitted directly by a donor lung and may involve bronchial mucosa, pulmonary parenchyma, and pleura.

Thrombocytosis: an acute-phase reactant, not an adverse reaction to the new beta-lactam antibiotics

Thrombocytosis has been described as an adverse drug reaction in up to 30% of patients treated with new beta-lactam antibiotics. We evaluated 350 patients with acute noninfectious conditions and infectious diseases treated with a variety of new and old agents. Results indicate that thrombocytosis is an acute-phase reactant and not an adverse reaction to any antimicrobial agent.

Pharmacokinetics of ceftriaxone in patients with renal failure and in those undergoing hemodialysis

The pharmacokinetic parameters of ceftriaxone in eight patients with end-stage renal disease were determined during dialysis and during the interdialysis period. The mean half-life, clearance, and apparent volume of distribution during dialysis were 16 h, 722 ml/h, and 16.7 liters, respectively. During the interdialysis period, the half-life was 14 h, clearance was 739 ml/h, and volume of distributions was 14 liters. Individual variability in plasma concentrations occurred even in patients with apparently normal hepatic function. Based on these parameters, a dose of 1 g every 24 h would yield concentrations in excess of the concentrations needed to inhibit most gram-positive and gram-negative aerobic species.

Simple adaptation of the Technicon SMAC system to operate 18 channels with reduced volumes of plasma

The Technicon SMAC system was adapted to function with much smaller volumes of plasma than those used in standard procedures. With only minimal operator-entered changes to the 7.6 computer program, and simple modifications of the glucose and alkaline phosphatase channels, the SMAC analyser performed equally well when the plasma volume was decreased from 235 microliter sequentially down through 176 microliter, 142 microliter, and 105 microliter. The basic principle employed was to maintain a constant flow rate of diluted sample plus diluent with decreasing sample size. The instrument proved to have the capability of operating successfully on all channels with lower signals than those encountered with the unmodified system.