Lethal Systemic Infections Research Articles

Novel Phenol-soluble Modulin Derivatives in Community-associated Methicillin-resistant Staphylococcus aureus Identified through Imaging Mass Spectrometry

Staphylococcus aureus causes a wide range of human disease ranging from localized skin and soft tissue infections to potentially lethal systemic infections. S. aureus has the biosynthetic ability to generate numerous virulence factors that assist in circumventing the innate immune system during disease pathogenesis. Recent studies have uncovered a set of extracellular peptides produced by community-associated methicillin-resistant S. aureus (CA-MRSA) with homology to the phenol-soluble modulins (PSMs) from Staphylococcus epidermidis. CA-MRSA PSMs contribute to skin infection and recruit and lyse neutrophils, and truncated versions of these peptides possess antimicrobial activity. In this study, novel CA-MRSA PSM derivatives were discovered by the use of microbial imaging mass spectrometry. The novel PSM derivatives are compared with their parent full-length peptides for changes in hemolytic, cytolytic, and neutrophil-stimulating activity. A potential contribution of the major S. aureus secreted protease aureolysin in processing PSMs is demonstrated. Finally, we show that PSM processing occurs in multiple CA-MRSA strains by structural confirmation of additional novel derivatives. This work demonstrates that IMS can serve as a useful tool to go beyond genome predictions and expand our understanding of the important family of small peptide virulence factors.

Lower Respiratory Tract Infection Induced by a Genetically Modified Picornavirus in Its Natural Murine Host

Infections with the picornavirus, human rhinovirus (HRV), are a major cause of wheezing illnesses and asthma exacerbations. In developing a murine model of picornaviral airway infection, we noted the absence of murine rhinoviruses and that mice are not natural hosts for HRV. The picornavirus, mengovirus, induces lethal systemic infections in its natural murine hosts, but small genetic differences can profoundly affect picornaviral tropism and virulence. We demonstrate that inhalation of a genetically attenuated mengovirus, vMC0, induces lower respiratory tract infections in mice. After intranasal vMC0 inoculation, lung viral titers increased, peaking at 24 h postinoculation with viral shedding persisting for 5 days, whereas HRV-A01a lung viral titers decreased and were undetectable 24 h after intranasal inoculation. Inhalation of vMC0, but not vehicle or UV-inactivated vMC0, induced an acute respiratory illness, with body weight loss and lower airway inflammation, characterized by increased numbers of airway neutrophils and lymphocytes and elevated pulmonary expression of neutrophil chemoattractant CXCR2 ligands (CXCL1, CXCL2, CXCL5) and interleukin-17A. Mice inoculated with vMC0, compared with those inoculated with vehicle or UV-inactivated vMC0, exhibited increased pulmonary expression of interferon (IFN-α, IFN-β, IFN-λ), viral RNA sensors [toll-like receptor (TLR)3, TLR7, nucleotide-binding oligomerization domain containing 2 (NOD2)], and chemokines associated with HRV infection in humans (CXCL10, CCL2). Inhalation of vMC0, but not vehicle or UV-inactivated vMC0, was accompanied by increased airway fluid myeloperoxidase levels, an indicator of neutrophil activation, increased MUC5B gene expression, and lung edema, a sign of infection-related lung injury. Consistent with experimental HRV inoculations of nonallergic, nonasthmatic human subjects, there were no effects on airway hyperresponsiveness after inhalation of vMC0 by healthy mice. This novel murine model of picornaviral airway infection and inflammation should be useful for defining mechanisms of HRV pathogenesis in humans.

The relevance of the migration inhibitory factor (MIF) for peripheral tissue response in murine sublethal systemicAspergillus fumigatusinfection

We recently demonstrated that macrophage migration inhibitory factor deficient (MIF (- / -)) mice exhibited a higher susceptibility to lethal systemic Aspergillus fumigatus infections than genetically matched, wild-type (WT) C57BL/6 mice, and displayed altered cytokine profiles in the spleen when challenged by sublethal infections. In this report we focused on the potential involvement of MIF in the response of mice to sublethal systemic A. fumigatus infections in tissues other than spleen. Impaired fungal clearance from lungs, kidneys, liver and brain in MIF (- / -) mice was noted and was associated with histologically-evident differences in signs of inflammation in these organs. Higher values of some indicators of pathologic changes in urine parameters (increases in bilirubin, glucose and ketones), as well as a greater degree of brain tissue damage, pointed to multiple organs being affected in MIF (- / -) mice. Analysis of the lung response revealed differences in the composition of infiltrated cells between MIF-sufficient and MIF-deficient mice. MPO activity and reactive oxygen species production were impaired, as well as production of IL-17 and IFN-γ in MIF (- / -) mice as compared to WT counterparts. Lower systemic IL-1β and IL-6 levels in infected MIF (- / -) mice coincided with reduced blood neutrophil counts and organ infiltration. Collectively, this study identifies MIF as a resistance factor that orchestrates events in several non-lymphoid areas which provide a milieu that accomplishes anti-fungal A. fumigatus defense.

Sur7 promotes plasma membrane organization and is needed for resistance to stressful conditions and to the invasive growth and virulence of Candida albicans.

ABSTRACTThe human fungal pathogen Candida albicans causes lethal systemic infections because of its ability to grow and disseminate in a host. The C. albicans plasma membrane is essential for virulence by acting as a protective barrier and through its key roles in interfacing with the environment, secretion of virulence factors, morphogenesis, and cell wall synthesis. Difficulties in studying hydrophobic membranes have limited the understanding of how plasma membrane organization contributes to its function and to the actions of antifungal drugs. Therefore, the role of the recently discovered plasma membrane subdomains termed the membrane compartment containing Can1 (MCC) was analyzed by assessing the virulence of a sur7Δ mutant. Sur7 is an integral membrane protein component of the MCC that is needed for proper localization of actin, morphogenesis, cell wall synthesis, and responding to cell wall stress. MCC domains are stable 300-nm-sized punctate patches that associate with a complex of cytoplasmic proteins known as an eisosome. Analysis of virulence-related properties of a sur7Δ mutant revealed defects in intraphagosomal growth in macrophages that correlate with increased sensitivity to oxidation and copper. The sur7Δ mutant was also strongly defective in pathogenesis in a mouse model of systemic candidiasis. The mutant cells showed a decreased ability to initiate an infection and greatly diminished invasive growth into kidney tissues. These studies on Sur7 demonstrate that the plasma membrane MCC domains are critical for virulence and represent an important new target for the development of novel therapeutic strategies.

Efficacy of Piperacillin Combined with the Penem β-Lactamase Inhibitor BLI-489 in Murine Models of Systemic Infection

The in vivo efficacy of piperacillin in combination with the penem inhibitor BLI-489 was determined using acute lethal systemic infections in mice. On the basis of preliminary results with various ratios, a dosing ratio of 8:1 was found to be optimal for retention of enhanced efficacy. Piperacillin-BLI-489 dosed at an 8:1 ratio was efficacious against murine infections caused by class A (including extended-spectrum beta-lactamases), class C (AmpC), and class D beta-lactamase-expressing pathogens.

Integrin αDβ2 Is Dynamically Expressed by Inflamed Macrophages and Alters the Natural History of Lethal Systemic Infections

The leukocyte integrins have critical roles in host defense and inflammatory tissue injury. We found that integrin alphaDbeta2, a novel but largely uncharacterized member of this family, is restricted to subsets of macrophages and a small population of circulating leukocytes in wild-type mice in the absence of inflammatory challenge and is expressed in regulated fashion during cytokine-induced macrophage differentiation in vitro. alphaDbeta2 is highly displayed on splenic red pulp macrophages and mediates their adhesion to local targets, identifying key functional activity. In response to challenge with Plasmodium berghei, a malarial pathogen that models systemic infection and inflammatory injury, new populations of alphaD+ macrophages evolved in the spleen and liver. Unexpectedly, targeted deletion of alphaD conferred a survival advantage in P. berghei infection over a 30-day observation period. Mechanistic studies demonstrated that the increased survival of alphaD-/- animals at these time points is not attributed to differences in magnitude of anemia or parasitemia or to alterations in splenic microanatomy, each of which is a key variable in the natural history of P. berghei infection, and indicated that an altered pattern of inflammatory cytokines may contribute to the difference in mortality. In contrast to the outcome in malarial challenge, death of alphaD-/- animals was accelerated in a model of Salmonella sepsis, demonstrating differential rather than stereotyped roles for alphaDbeta2 in systemic infection. These studies identify previously unrecognized and unique activities of alphaDbeta2, and macrophages that express it, in host defense and injury.

Phylogenetic Analysis of Bacillus cereus Isolates from Severe Systemic Infections Using Multilocus Sequence Typing Scheme

Bacillus cereus strains from cases of severe or lethal systemic infections, including respiratory symptoms cases, were analyzed using multilocus sequence typing scheme of B. cereus MLST database. The isolates were evenly distributed between the two main clades, and 60% of them had allele profiles new to the database. Half of the collection's strains clustered in a lineage neighboring Bacillus anthracis phylogenetic origin. Strains from lethal cases with respiratory symptoms were allocated in both main clades. This is the first report of strains causing respiratory symptoms to be identified as genetically distant from B. anthracis. The phylogenetic location of the presented here strains was compared with all previously submitted to the database isolates from systemic infections, and were found to appear in the same clusters where clinical isolates from other studies had been assigned. It seems that the pathogenic strains are forming clusters on the phylogenetic tree.

Lethality to Ferrets of H5N1 Influenza Viruses Isolated from Humans and Poultry in 2004

The 2004 outbreaks of H5N1 influenza viruses in Vietnam and Thailand were highly lethal to humans and to poultry; therefore, newly emerging avian influenza A viruses pose a continued threat, not only to avian species but also to humans. We studied the pathogenicity of four human and nine avian H5N1/04 influenza viruses in ferrets (an excellent model for influenza studies). All four human isolates were fatal to intranasally inoculated ferrets. The human isolate A/Vietnam/1203/04 (H5N1) was the most pathogenic isolate; the severity of disease was associated with a broad tissue tropism and high virus titers in multiple organs, including the brain. High fever, weight loss, anorexia, extreme lethargy, and diarrhea were observed. Two avian H5N1/04 isolates were as pathogenic as the human viruses, causing lethal systemic infections in ferrets. Seven of nine H5N1/04 viruses isolated from avian species caused mild infections, with virus replication restricted to the upper respiratory tract. All chicken isolates were nonlethal to ferrets. A sequence analysis revealed polybasic amino acids in the hemagglutinin connecting peptides of all H5N1/04 viruses, indicating that multiple molecular differences in other genes are important for a high level of virulence. Interestingly, the human A/Vietnam/1203/04 isolate had a lysine substitution at position 627 of PB2 and had one to eight amino acid changes in all gene products except that of the M1 gene, unlike the A/chicken/Vietnam/C58/04 and A/quail/Vietnam/36/04 viruses. Our results indicate that viruses that are lethal to mammals are circulating among birds in Asia and suggest that pathogenicity in ferrets, and perhaps humans, reflects a complex combination of different residues rather than a single amino acid difference.

In vivo antibacterial activity of FK041, a new orally active cephalosporin.

The therapeutic activities of orally administered FK041 were evaluated in mouse models of systemic and local infections with a variety of bacteria and were compared with those of cefdinir (CFDN) and cefditoren pivoxil (CDTR-PI). FK041 exhibited potent therapeutic activity against lethal systemic infections induced by intraperitoneally inoculated Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae with 50% effective doses (ED50) in the range of 0.20 to 0.36 mg/kg and was more active than CFDN and CDTR-PI. This result correlated well with its in vitro activity. The therapeutic effects of FK041 and reference drugs on murine local infections were evaluated in an in vivo pharmacokinetic model simulating human plasma concentrations for oral administration of 50 mg, 100 mg, and 200 mg. Against murine subcutaneous abscess induced by S. aureus, FK041 was as effective as CFDN and significantly more effective than CDTR-PI in reducing the number of recoverable viable bacteria in the skin at the infection sites. The efficacy of FK041 against murine pneumonia with H. influenzae was comparable to that of CDTR-PI and was superior to that of CFDN in reducing viable bacteria activity in the lungs. These results strongly suggest that FK041 has potential for clinical use against various bacterial infections.

Influenza viruses, cell enzymes, and pathogenicity.

Proteolytic cleavage of the influenza virus hemagglutinin glycoprotein (HA) by cellular proteases is a prerequisite for virus infectivity, spread of the virus in the infected organism, tissue tropism, and viral pathogenicity. Production of infectious virus depends upon the structure at the HA cleavage site as well as the substrate specificity and the distribution of appropriate enzymes. Differences exist in the specificities of the endoproteases that recognize the different sequence motifs at the cleavage site. With avian influenza viruses that cause lethal systemic infections, the cleavage site consists of multibasic amino acids. Furin, which activates this type of HA, is a member of the subtilisin family and represents the prototype of ubiquitously occurring membrane-bound proteases. On the other hand, serine proteases secreted from a restricted number of cell types and some bacterial enzymes recognize a monobasic cleavage signal at HA of the mammalian and the apathogenic avian influenza viruses. The limited occurrence of these proteases results in only localized infection. Implementation of these defined conditions for virus activation may represent a novel type of disease control.

Pituitary and peripheral thyroid hormone responses to thyrotropin-releasing hormone during sustained sleep deprivation in freely moving rats.

Sleep deprivation is associated with poor cognitive ability and impaired physical health, but the ways in which the brain and body become compromised are not understood. In sleep-deprived rats, plasma total T4 and T3 concentrations decline progressively to 78% and 47% below baseline values, respectively, brown adipose tissue 5'-deiodinase type II activity increases 100-fold, and serum TSH values are unknown. The progressive decline in plasma thyroid hormones is associated with a deep negative energy balance despite normal or increased food intake and malnutrition-like symptoms that eventuate in hypothermia and lethal systemic infections. The purpose of the present experiment was to evaluate the probable causes of the low plasma total T4 during sleep deprivation by measuring the free hormone concentration to minimize binding irregularities and by challenging the pituitary-thyroid axis with iv TRH to determine both 1) the pituitary release of TSH and 2) the thyroidal response of free T4 (FT4) and free T3 (FT3) release to the TSH increment. Sleep-deprived rats were awake 91% of the total time compared with 63% of the total time in yoked control rats and 50% of the total time during the baseline period. Cage control comparison rats were permitted to sleep normally. Sustained sleep deprivation resulted in a decline from baseline in plasma FT4 of 73 +/- 6% and FT3 of 45 +/- 12%, which were similar to the declines in total hormone concentrations observed previously; nonstimulated TSH was unchanged. In the yoked and cage control groups, FT4 also declined, but much less than that of the sleep-deprived group. The relative changes in free compared with total hormone concentrations over the study were also less parallel than those in the sleep-deprived group. The plasma TSH response to TRH was similar in all groups across experimental days. The plasma FT4 and FT3 concentrations in sleep-deprived rats increased after TRH-stimulated TSH release to an extent comparable to control values. Taken together, low basal FT4 and FT3 hormone concentrations and unchanged TSH and thyroidal responses to TRH suggest a pituitary or hypothalamic contribution to the hypothyroxinemia during sleep deprivation.

Efficacy of A-73209, a potent orally active agent against VZV and HSV infections

A-73209 is a novel oxetanocin derivative with potent in vitro and in vivo activity against VZV, HSV-1, and HSV-2. A-73209 was two logs more potent than acyclovir against five thymidine kinase positive (TK +) strains of VZV in vitro (mean EC 50 0.01 vs. 1.22 μg/ml). The activity of A-73209 was one log more potent than acyclovir against TK + HSV-1 strains in vitro (EC 50 = 0.03 vs. 0.32 μg/ml). A-73209 yielded a mean EC 50 of 2.2 μg/ml compared to a mean EC 50 of 0.37 μg/ml for acyclovir against a panel of TK + HSV-2 strains in vitro. The in vitro activity of A-73209 against thymidine kinase negative or deficient strains of VZV, HSV-1 and HSV-2 was much lower than for the corresponding TK + strains. A-73209 produced efficacy superior to acyclovir against lethal systemic or intracerebral HSV-1 infections in mice. The greater efficacy of A-73209 relative to acyclovir was especially apparent with oral dosing. Against HSV-2 infections in mice, the efficacy of A-73209 ranged from equal to 1.7 times less active relative to acyclovir with oral dosing. A-73209 was orally bioavailable in mice, with maximal serum concentrations well in excess of in vitro inhibitory concentrations. A-73209 appears to be a potent and selective agent against varicella-zoster virus and herpes simplex virus infections.

Bacterial Translocation from the Gut

Bacterial infection is a common and serious problem in burn victims who survive the shock phase of thermal injury. Our experimental work, plus the clinical studies of others, suggests that the gut can serve as a reservoir for systemic infections caused by bacteria that cross (translocate) the gastrointestinal (GI) epithelium. Bacterial translocation from the GI tract does not normally occur in the healthy animal owing to (1) the presence of an indigenous GI microflora preventing bacterial overgrowth, (2) an intact intestinal epithelial barrier, and (3) normal host immune defenses. However, a thermal injury, as well as other stressors, can result in the disruption or impairment of any of these protective mechanisms, potentially leading to lethal systemic infections with bacteria colonizing the gut.