Early acquisition of Pneumocystis carinii in neonatal rats as evidenced by PCR and oral swabs

Detection of Pneumocystis and Morphological Description of Fungal Distribution and Severity of Infection in Thirty-Six Mammal Species

Pneumocystis spp. are thought to adapt to the lungs of potentially all mammals. However, the full host range, fungal burden and severity of infection are unknown for many species. In this study, lung tissue samples originating from 845 animals of 31 different families of eight mammal orders were screened by in situ hybridization (ISH) using a universal 18S rRNA probe for Pneumocystis, followed by hematoxylin and eosin (H&E) staining for determining histopathological lesions. A total of 216 (26%) samples were positive for Pneumocystis spp., encompassing 36 of 98 investigated mammal species, with 17 of them being described for the first time for the presence of Pneumocystis spp. The prevalence of Pneumocystis spp. as assessed by ISH varied greatly among different mammal species while the organism load was overall low, suggesting a status of colonization or subclinical infection. Severe Pneumocystis pneumonia seemed to be very rare. For most of the Pneumocystis-positive samples, comparative microscopic examination of H&E- and ISH-stained serial sections revealed an association of the fungus with minor lesions, consistent with an interstitial pneumonia. Colonization or subclinical infection of Pneumocystis in the lung might be important in many mammal species because the animals may serve as a reservoir.

Pneumocystis spp. in Pigs: A Longitudinal Quantitative Study and Co-Infection Assessment in Austrian Farms

While Pneumocystis has been recognized as both a ubiquitous commensal fungus in immunocompetent mammalian hosts and a major opportunistic pathogen in humans responsible for severe pneumonias in immunocompromised patients, in pigs its epidemiology and association with pulmonary diseases have been rarely reported. Nevertheless, the fungus can be quite abundant in porcine populations with up to 51% of prevalence reported so far. The current study was undertaken to longitudinally quantify Pneumocystis carinii f. sp. suis and other pulmonary pathogens in a cohort of 50 pigs from five Austrian farms (i.e., 10 pigs per farm) with a history of respiratory disease at five time points between the first week and the fourth month of life. The fungus was present as early as the suckling period (16% and 26% of the animals in the first and the third week, respectively), yet not in a high amount. Over time, both the organism load (highest 4.4 × 10⁵ copies/mL) and prevalence (up to 88% of positive animals in the third month) increased in each farm. The relative prevalence of various coinfection patterns was significantly different over time. The current study unravelled a complex co-infection history involving Pneumocystis and other pulmonary pathogens in pigs, suggesting a relevant role of the fungus in the respiratory disease scenario of this host.

Update on invasive fungal infections in the Middle Eastern and North African region

In the recent years, the epidemiology of invasive fungal infections (IFIs) has changed worldwide. This is remarkably noticed with the significant increase in high-risk populations. Although surveillance of such infections is essential, data in the Middle Eastern and North African (MENA) region remain scarce. In this paper, we reviewed the existing data on the epidemiology of different IFIs in the MENA region. Epidemiological surveillance is crucial to guide optimal healthcare practices. This study can help to guide appropriate interventions and to implement antimicrobial stewardship and infection prevention and control programs in countries.

A Molecular Window into the Biology and Epidemiology of Pneumocystis spp

Pneumocystis, a unique atypical fungus with an elusive lifestyle, has had an important medical history. It came to prominence as an opportunistic pathogen that not only can cause life-threatening pneumonia in patients with HIV infection and other immunodeficiencies but also can colonize the lungs of healthy individuals from a very early age. The genus Pneumocystis includes a group of closely related but heterogeneous organisms that have a worldwide distribution, have been detected in multiple mammalian species, are highly host species specific, inhabit the lungs almost exclusively, and have never convincingly been cultured in vitro, making Pneumocystis a fascinating but difficult-to-study organism. Improved molecular biologic methodologies have opened a new window into the biology and epidemiology of Pneumocystis. Advances include an improved taxonomic classification, identification of an extremely reduced genome and concomitant inability to metabolize and grow independent of the host lungs, insights into its transmission mode, recognition of its widespread colonization in both immunocompetent and immunodeficient hosts, and utilization of strain variation to study drug resistance, epidemiology, and outbreaks of infection among transplant patients. This review summarizes these advances and also identifies some major questions and challenges that need to be addressed to better understand Pneumocystis biology and its relevance to clinical care.

High transient colonization by Pneumocystis jirovecii between mothers and newborn

The aim of the study was to explore the frequency and dynamics of acquisition and colonization of Pneumocystis jirovecii among neonates, as well as the epidemiological and genotypic characteristics in mother-child binomial. In a prospective enrolled cohort of women in their third trimester of pregnancy, nasopharyngeal swabs (NPS) and clinical and epidemiological data were collected at four different times: 17 days, 2nd, 4th, and 6th month of life of the newborn. P. jirovecii was detected by nested-PCR for the mtLSU-rRNA gene in each NPS; the genotypes were determined amplifying four genes. Forty-three pairs and 301 NPS were included. During the third trimester, 16.3% of pregnant women were colonized. The rate of colonization in mothers at delivery was 16, 6, 16, and 5% and in their children 28, 43, 42, and 25%, respectively. Within pregnant women, 53% remained negative throughout follow-up, and among these, 91% of their children were positive in at least one of their samples. In both, mothers and children, the most frequent genotype of P. jirovecii was 1.

CONCLUSION

The frequency of colonization by P. jirovecii was higher in newborns than in their respective progenitors. Colonization of both mothers and children is transitory; however, the mother of the newborn is not necessarily the source of primary infection. What is Known: • We did not find studies comparing P. jirovecii colonization between mothers and children simultaneously, yet the frequency of colonization by serologic and molecular methods in pregnant women has been reported. What is New: • According to our findings, 3/4 of the children had transient colonization during the first 6 months of life, in only half in the mothers, without proof of mother-to-child transmission or vice versa.

Progression of Type 2 Helper T Cell-Type Inflammation and Airway Remodeling in a Rodent Model of Naturally Acquired Subclinical Primary Pneumocystis Infection

Subclinical primary Pneumocystis infection is the most common pulmonary infection in early infancy, making it important to determine whether it damages the lung. Pneumocystis peaks at 2 to 5 months of age, when respiratory morbidity coincidently increases. We have documented that Pneumocystis increases mucus production in infant lungs, and animal models reveal lung lesions that warrant characterization. Herein, immunocompetent rats infected at birth with Pneumocystis by cohabitation, to resemble community-acquired infection, underwent lung assessments at 45, 60, and 75 days of age. Lungs fixed by vascular perfusion to prevent collapse during necropsy were used for morphometry evaluations of mucus production, airway epithelial thickening, perivascular and peribronchiolar inflammation, and structural airway remodeling. Changes in these histologic features indicate lung disease. Selected immune markers were assessed in parallel using fresh-frozen lung tissue from sibling rats of the same cages. Sequential activation of NF-κB and an increased Gata3/T-bet mRNA level ratio, consistent with a type 2 helper T-cell-type inflammatory response, and subacute fibrosis were recognized. Therefore, documenting subclinical Pneumocystis infection induces lung disease in the immunocompetent host. Taken together with the peak age of primary Pneumocystis infection, results warrant investigating the clinical impact of this often subclinical infection on the severity of respiratory diseases in early infancy. This model can also be used to assess the effects of airway insults, including coinfections by recognized respiratory pathogens.

Infections in the immunosuppressed host

The interaction between host immunity and infections in the context of a suppressed immune system presents an opportunity to study the interaction of colonization and infection with the development of acute and chronic pulmonary morbidity and mortality. This article summarizes presentations at the Pittsburgh International Lung Conference about comorbid consequences in two categories of immunosuppressed hosts: HIV-infected individuals and lung transplant recipients. Specifically, chronic obstructive pulmonary disease, pulmonary hypertension, and chronic lung rejection after transplant are three diseases that may be consequences of colonization or infection by viruses or fungi, whether HIV itself or the opportunistic infections Pneumocystis and cytomegalovirus. In the fourth section, we discuss unique aspects of infections after lung transplant as well as the battle against multidrug-resistant organisms in this population and theorize that the immunosuppressed population may provide a unique group of patients in which to study ways to overcome nosocomial pathogenic challenges. These host-pathogen interactions serve as models for developing new strategies to reduce acute and chronic morbidity due to colonization and subclinical infection, and potential therapeutic avenues, which are often overlooked in the clinical arena.

The Prevalence of Pneumocystis jiroveci in Bronchoalveolar Lavage Specimens of Lung Transplant Recipients Examined by the Nested PCR

BACKGROUND

The use of immune suppressive drugs for organ transplant recipients predisposes them to opportunistic infections, especially by fungal agents. Pneumocystis jiroveci, as an opportunistic pathogen, endangers the patients' life in those with immune system disorders. Early detection of latent Pneumocystis infection in susceptible patients may help choose the optimal treatment for these patients.

OBJECTIVES

The aim of this study was to identify and determine the colonization of latent P. jiroveci infection among lung transplant recipients.

PATIENTS AND METHODS

This cross-sectional descriptive study was conducted on lung transplant recipients. Bronchoalveolar lavage (BAL) specimens were collected from 32 patients undergoing bronchoscopy. The samples were aseptically homogenized by 10 mM dithiothreitol, and their DNA was extracted. The mtLSUrRNA gene of P. jiroveci was amplified using nested PCR in two stages. Nested PCR was performed using external primers of pAZ-102-E and pAZ102-H followed by using the PCR product of the first stage and internal primers of pAZ-102-E and pAZ102-L2.

RESULTS

The genome of P. jiroveci was revealed by a 346 bp PCR product in the initial amplification and a 120 bp product in the nested PCR. The results showed that seven BAL specimens (21.9%) from lung transplant recipients were positive for P. jiroveci.

CONCLUSIONS

In molecular epidemiology studies, nested PCR has higher sensitivity than PCR. Results of this study support the colonization of P. jiroveci in patients receiving lung transplantation. Patients who are carriers of P. jiroveci are at a higher risk of P. jiroveci pneumonia.

Pneumocystis

Since its initial misidentification as a trypanosome some 100 years ago, Pneumocystis has remained recalcitrant to study. Although we have learned much, we still do not have definitive answers to such basic questions as, where is the reservoir of infection, how does Pneumocystis reproduce, what is the mechanism of infection, and are there true species of Pneumocystis? The goal of this review is to provide the reader the most up to date information available about the biology of Pneumocystis and the disease it produces.

Detection of Pneumocystis in the nasal swabs of immune-suppressed rats by use of PCR and microscopy

BACKGROUND

Detection of Pneumocystis jiroveci colonization in lungs or oral samples due to high sensitivity of PCR methods results in undue treatment of patients without any symptoms of Pneumocystis pneumonia. The aim of the present study is to demonstrate Pneumocystis carinii in rats, immune suppressed by oral and subcutaneous administration of dexamethasone.

MATERIAL/METHODS

Blood, oral, nasal and eye swabs were collected prior to immune suppression and 2, 6, 12 weeks after administration of dexamethasone. Also, samples were collected from lung, heart, liver, kidney, diaphragm, brain, spleen, tongue, muscle, eye, intestine, and feces. Cysts and trophozoites were investigated in stained slides and MSG gene was detected by PCR.

RESULTS

The results showed that weight loss is significantly higher in rats administered oral dexamethasone (P<0.05). Microscopy was positive only in lungs of rats orally administered dexamethasone. PCR was positive in lungs and oral swabs of rats prior to the administration of dexamethasone. After the administration of dexamethasone, the MSG gene was detected in oral swabs, lungs, spleen, kidney and (for the first time) in nasal swabs. PCR was positive in nasal swabs during the second and sixth weeks of oral and subcutaneous administration of dexamethasone, respectively.

CONCLUSIONS

Presence of P. jiroveci in nasopharyngeal aspirate, oropharyngeal wash, oral swab, induced sputum or BAL, and absence in nasal swab in a patient without symptoms of PCP may support clinician's decision regarding colonization. Overall, detection of P. carinii in nasal swabs of rats by PCR demonstrated that nasal sampling can be used for the diagnosis of Pneumocystis pneumonia.

Near-universal prevalence of Pneumocystis and associated increase in mucus in the lungs of infants with sudden unexpected death

BACKGROUND

Pneumocystis without obvious accompanying pathology is occasionally reported in autopsied infant lungs. Its prevalence and significance are unknown. Interestingly, this mild infection induces a strong activation of mucus secretion-related genes in young immunocompetent rodents that has not been explored in infants. Excess mucus is induced by multiple airway offenders through nonspecific pathways and would explain a cofactor role of Pneumocystis in respiratory disease. We undertook characterization of the prevalence of Pneumocystis and associated mucus in infant lungs.

METHODS

Samples from 128 infants (mean age, 101 days) who died suddenly and unexpectedly in Santiago during 1999-2004 were examined for Pneumocystis using nested polymerase chain reaction (nPCR) amplification of the P. jirovecii mtLSU ribosomal RNA gene and immunofluorescence microscopy (IF). Pneumocystis-negative infants 28 days and older and their age-closest positives were studied for MUC5AC expression and Pneumocystis burden by Western blot and quantitative PCR, respectively.

RESULTS

Pneumocystis DNA was detected by nPCR in 105 of the 128 infants (82.0%) and Pneumocystis organisms were visualized by IF in 99 (94.3%) of the DNA-positive infants. The infection was commonest at 3-4 months with 40 of 41 (97.6%) infants of that age testing positive. MUC5AC was significantly increased in Pneumocystis-positive tissue specimens (P = .013). Death was unexplained in 113 (88.3%) infants; Pneumocystis was detected in 95 (84.0%) of them vs 10 of 15 (66.7%) with explained death (P = .28).

CONCLUSIONS

A highly focal Pneumocystis infection associated to increased mucus expression is almost universally present in the lungs of infants dying unexpectedly in the community regardless of autopsy diagnosis.

Microbial antigenic variation mediated by homologous DNA recombination

Pathogenic microorganisms employ numerous molecular strategies in order to delay or circumvent recognition by the immune system of their host. One of the most widely used strategies of immune evasion is antigenic variation, in which immunogenic molecules expressed on the surface of a microorganism are continuously modified. As a consequence, the host is forced to constantly adapt its humoral immune response against this pathogen. An antigenic change thus provides the microorganism with an opportunity to persist and/or replicate within the host (population) for an extended period of time or to effectively infect a previously infected host. In most cases, antigenic variation is caused by genetic processes that lead to the modification of the amino acid sequence of a particular antigen or to alterations in the expression of biosynthesis genes that induce changes in the expression of a variant antigen. Here, we will review antigenic variation systems that rely on homologous DNA recombination and that are found in a wide range of cellular, human pathogens, including bacteria (such as Neisseria spp., Borrelia spp., Treponema pallidum, and Mycoplasma spp.), fungi (such as Pneumocystis carinii) and parasites (such as the African trypanosome Trypanosoma brucei). Specifically, the various DNA recombination-based antigenic variation systems will be discussed with a focus on the employed mechanisms of recombination, the DNA substrates, and the enzymatic machinery involved.

Chitinases in Pneumocystis carinii pneumonia

Pneumocystis pneumonia remains an important complication of immune suppression. The cell wall of Pneumocystis has been demonstrated to potently stimulate host inflammatory responses, with most studies focusing on β-glucan components of the Pneumocystis cell wall. In the current study, we have elaborated the potential role of chitins and chitinases in Pneumocystis pneumonia. We demonstrated differential host mammalian chitinase expression during Pneumocystis pneumonia. We further characterized a chitin synthase gene in Pneumocystis carinii termed Pcchs5, a gene with considerable homolog to the fungal chitin biosynthesis protein Chs5. We also observed the impact of chitinase digestion on Pneumocystis-induced host inflammatory responses by measuring TNFα release and mammalian chitinase expression by cultured lung epithelial and macrophage cells stimulated with Pneumocystis cell wall isolates in the presence and absence of exogenous chitinase digestion. These findings provide evidence supporting a chitin biosynthetic pathway in Pneumocystis organisms and that chitinases modulate inflammatory responses in lung cells. We further demonstrate lung expression of chitinase molecules during Pneumocystis pneumonia.

Pneumocystis carinii causes a distinctive interstitial pneumonia in immunocompetent laboratory rats that had been attributed to "rat respiratory virus"

A prevalent and distinctive infectious interstitial pneumonia (IIP) of immunocompetent laboratory rats was suspected to be caused by a putative virus, termed rat respiratory virus, but this was never substantiated. To study this disease, 2 isolators were independently populated with rats from colonies with endemic disease, which was perpetuated by the regular addition of naive rats. After Pneumocystis was demonstrated by histopathology and polymerase chain reaction (PCR) in the lungs of rats from both isolators and an earlier bedding transmission study, the relationship between Pneumocystis and IIP was explored further by analyzing specimens from 3 contact transmission experiments, diagnostic submissions, and barrier room breeding colonies, including 1 with and 49 without IIP. Quantitative (q) PCR and immunofluorescence assay only detected Pneumocystis infection and serum antibodies in rats from experiments or colonies in which IIP was diagnosed by histopathology. In immunocompetent hosts, the Pneumocystis concentration in lungs corresponded to the severity and prevalence of IIP; seroconversion occurred when IIP developed and was followed by the concurrent clearance of Pneumocystis from lungs and resolution of disease. Experimentally infected immunodeficient RNU rats, by contrast, did not seroconvert to Pneumocystis or recover from infection. qPCR found Pneumocystis at significantly higher concentrations and much more often in lungs than in bronchial and nasal washes and failed to detect Pneumocystis in oral swabs. The sequences of a mitochondrial ribosomal large-subunit gene region for Pneumocystis from 11 distinct IIP sources were all identical to that of P. carinii. These data provide substantial evidence that P. carinii causes IIP in immunocompetent rats.

Update on the diagnosis and treatment of Pneumocystis pneumonia

Pneumocystis is an opportunistic fungal pathogen that causes an often-lethal pneumonia in immunocompromised hosts. Although the organism was discovered in the early 1900s, the first cases of Pneumocystis pneumonia in humans were initially recognized in Central Europe after the Second World War in premature and malnourished infants. This unusual lung infection was known as plasma cellular interstitial pneumonitis of the newborn, and was characterized by severe respiratory distress and cyanosis with little or no fever and no pathognomic physical signs. At that time, only anecdotal cases were reported in adults and usually these patients had a baseline malignancy that led to a malnourished state. In the 1960-1970s additional cases were described in adults and children with hematological malignancies, but Pneumocystis pneumonia was still considered a rare disease. However, in the 1980s, with the onset of the HIV epidemic, Pneumocystis prevalence increased dramatically and became widely recognized as an opportunistic infection that caused potentially life-treating pneumonia in patients with impaired immunity. During this time period, prophylaxis against this organism was more generally instituted in high-risk patients. In the 1990s, with widespread use of prophylaxis and the initiation of highly active antiretroviral therapy (HAART) in the treatment of HIV-infected patients, the number of cases in this specific population decreased. However, Pneumocystis pneumonia still remains an important cause of severe pneumonia in patients with HIV infection and is still considered a principal AIDS-defining illness. Despite the decreased number of cases among HIV-infected patients over the past decade, Pneumocystis pneumonia continues to be a serious problem in immunodeficient patients with other immunosuppressive conditions. This is mostly due to increased use of immunosuppressive medications to treat patients with autoimmune diseases, following bone marrow and solid organ transplantation, and in patients with hematological and solid malignancies. Patients with hematologic disorders and solid organ and hematopoietic stem cell transplantation are currently the most vulnerable groups at risk for developing this infection. However, any patient with an impaired immunity, such as those receiving moderate doses of oral steroids for greater than 4 weeks or those receiving other immunosuppressive medications are at also at significant risk.

Echinocandin treatment of pneumocystis pneumonia in rodent models depletes cysts leaving trophic burdens that cannot transmit the infection

Fungi in the genus Pneumocystis cause pneumonia (PCP) in hosts with debilitated immune systems and are emerging as co-morbidity factors associated with chronic diseases such as COPD. Limited therapeutic choices and poor understanding of the life cycle are a result of the inability of these fungi to grow outside the mammalian lung. Within the alveolar lumen, Pneumocystis spp., appear to have a bi-phasic life cycle consisting of an asexual phase characterized by binary fission of trophic forms and a sexual cycle resulting in formation of cysts, but the life cycle stage that transmits the infection is not known. The cysts, but not the trophic forms, express β -1,3-D-glucan synthetase and contain abundant β -1,3-D-glucan. Here we show that therapeutic and prophylactic treatment of PCP with echinocandins, compounds which inhibit the synthesis of β -1,3-D-glucan, depleted cysts in rodent models of PCP, while sparing the trophic forms which remained in significant numbers. Survival was enhanced in the echincandin treated mice, likely due to the decreased β -1,3-D-glucan content in the lungs of treated mice and rats which coincided with reductions of cyst numbers, and dramatic remodeling of organism morphology. Strong evidence for the cyst as the agent of transmission was provided by the failure of anidulafungin-treated mice to transmit the infection. We show for the first time that withdrawal of anidulafungin treatment with continued immunosuppression permitted the repopulation of cyst forms. Treatment of PCP with an echinocandin alone will not likely result in eradication of infection and cessation of echinocandin treatment while the patient remains immunosuppressed could result in relapse. Importantly, the echinocandins provide novel and powerful chemical tools to probe the still poorly understood bi-phasic life cycle of this genus of fungal pathogens.

Complexity of the MSG gene family of Pneumocystis carinii

Background

The relationship between the parasitic fungus Pneumocystis carinii and its host, the laboratory rat, presumably involves features that allow the fungus to circumvent attacks by the immune system. It is hypothesized that the major surface glycoprotein (MSG) gene family endows Pneumocystis with the capacity to vary its surface. This gene family is comprised of approximately 80 genes, which each are approximately 3 kb long. Expression of the MSG gene family is regulated by a cis-dependent mechanism that involves a unique telomeric site in the genome called the expression site. Only the MSG gene adjacent to the expression site is represented by messenger RNA. Several P. carinii MSG genes have been sequenced, which showed that genes in the family can encode distinct isoforms of MSG. The vast majority of family members have not been characterized at the sequence level.

Results

The first 300 basepairs of MSG genes were subjected to analysis herein. Analysis of 581 MSG sequence reads from P. carinii genomic DNA yielded 281 different sequences. However, many of the sequence reads differed from others at only one site, a degree of variation consistent with that expected to be caused by error. Accounting for error reduced the number of truly distinct sequences observed to 158, roughly twice the number expected if the gene family contains 80 members. The size of the gene family was verified by PCR. The excess of distinct sequences appeared to be due to allelic variation. Discounting alleles, there were 73 different MSG genes observed. The 73 genes differed by 19% on average. Variable regions were rich in nucleotide differences that changed the encoded protein. The genes shared three regions in which at least 16 consecutive basepairs were invariant. There were numerous cases where two different genes were identical within a region that was variable among family members as a whole, suggesting recombination among family members.

Conclusion

A set of sequences that represents most if not all of the members of the P. carinii MSG gene family was obtained. The protein-changing nature of the variation among these sequences suggests that the family has been shaped by selection for protein variation, which is consistent with the hypothesis that the MSG gene family functions to enhance phenotypic variation among the members of a population of P. carinii.

Epidemiology of Pneumocystis colonization in families

Whether Pneumocystis colonization is transmitted in families with human immunodeficiency virus (HIV)-infected members is unknown. Using nested polymerase chain reaction of oropharyngeal or nasopharyngeal samples, we detected colonization in 11.4% of HIV-infected adults and in 3.3% of their children, but there was no evidence of clustering.

Antigenic variation in pneumocystis

Pneumocystis is a genus containing many species of non-culturable fungi, each of which infects a different mammalian host. Pneumonia caused by Pneumocystis is a problem in immunodeficient humans, but not in normal humans. Nevertheless, it appears that Pneumocystis organisms cannot survive and proliferate outside of their mammalian hosts, suggesting that Pneumocystis parasitizes immunocompetent mammals. Residence in immunocompetent hosts may rely on camouflage perpetrated by antigenic variation. In P. carinii, which is found in rats, there exist three families of genes that appear to be designed to create antigenic variation. One gene family, which encodes the major surface glycoprotein (MSG), contains nearly 100 members. Expression of the MSG family is controlled by restricting transcription to the one gene that is linked to a unique expression site. Changes in the sequence of the MSG gene linked to the expression site occur and appear to be caused by recombination with MSG genes not at the expression site. Preliminary evidence suggests that gene conversion is the predominant recombination mechanism.

Upregulation of galectin-3 by Corynebacterium kutscheri infection in the rat lung

Corynebacterium (C) kutscheri and Staphylococcus aureus were isolated from two Sprague-Dawley (SD) rats with a hemisected spinal cord. Grossly, gray-white bulging foci and abscesses were distributed throughout the parenchyma of the lung. Pathologically, severe necrotizing lobar pneumonia with abscesses and fibrinous pleuritis were observed. Immunohistochemical analysis found accumulation of galectin-3 in alveolar macrophages and the alveolar interstitial region. No other viral or bacterial pathogens were detected in these animals. In addition, similar pathogenic changes and accumulation of galectin-3 were observed in the lungs of SD rats experimentally infected with C. kutscheri. Using northern blot analysis, the relative galectin-3 and GAPDH mRNA levels were 4.6 to 9.3 times higher in C. kutscheri-infected lung than in uninfected controls. These results demonstrate that a single C. kutscheri infection can induce the upregulation of galectin-3 in the lung and that this molecule may have an important pathogenic role in C. kutscheri infections in rats.

Transcriptome of Pneumocystis carinii during fulminate infection: carbohydrate metabolism and the concept of a compatible parasite

Members of the genus Pneumocystis are fungal pathogens that cause pneumonia in a wide variety of mammals with debilitated immune systems. Little is known about their basic biological functions, including life cycle, since no species can be cultured continuously outside the mammalian lung. To better understand the pathological process, about 4500 ESTS derived from sequencing of the poly(A) tail ends of P. carinii mRNAs during fulminate infection were annotated and functionally characterized as unassembled reads, and then clustered and reduced to a unigene set with 1042 members. Because of the presence of sequences from other microbial genomes and the rat host, the analysis and compression to a unigene set was necessarily an iterative process. BLASTx analysis of the unassembled reads (UR) vs. the Uni-Prot and TREMBL databases revealed 56% had similarities to existing polypeptides at E values of<or=10(-6), with the remainder lacking any significant homology. The most abundant transcripts in the UR were associated with stress responses, energy production, transcription and translation. Most (70%) of the UR had similarities to proteins from filamentous fungi (e.g., Aspergillus, Neurospora) and existing P. carinii gene products. In contrast, similarities to proteins of the yeast-like fungi, Schizosaccharomyces pombe and Saccharomyces cerevisiae, predominated in the unigene set. Gene Ontology analysis using BLAST2GO revealed P. carinii dedicated most of its transcripts to cellular and physiological processes ( approximately 80%), molecular binding and catalytic activities (approximately 70%), and were primarily derived from cell and organellar compartments (approximately 80%). KEGG Pathway mapping showed the putative P. carinii genes represented most standard metabolic pathways and cellular processes, including the tricarboxylic acid cycle, glycolysis, amino acid biosynthesis, cell cycle and mitochondrial function. Several gene homologs associated with mating, meiosis, and sterol biosynthesis in fungi were identified. Genes encoding the major surface glycoprotein family (MSG), heat shock (HSP70), and proteases (PROT/KEX) were the most abundantly expressed of known P. carinii genes. The apparent presence of many metabolic pathways in P. carinii, sexual reproduction within the host, and lack of an invasive infection process in the immunologically intact host suggest members of the genus Pneumocystis may be adapted parasites and have a compatible relationship with their mammalian hosts. This study represents the first characterization of the expressed genes of a non-culturable fungal pathogen of mammals during the infective process.

Primary pneumocystis infection in infants hospitalized with acute respiratory tract infection

Acquisition of Pneumocystis jirovecii infection early in life has been confirmed by serologic studies. However, no evidence of clinical illness correlated with the primary infection has been found in immunocompetent children. We analyzed 458 nasopharyngeal aspirates from 422 patients hospitalized with 431 episodes of acute respiratory tract infection (RTI) by using a real-time PCR assay. In 68 episodes in 67 infants, P. jirovecii was identified. The odds ratio (95% confidence interval) of a positive signal compared with the first quartile of age (7-49 days) was 47.4 (11.0-203), 8.7 (1.9-39.7), and 0.6 (0.1-6.7) for infants in the second (50-112 days), third (113-265 days), and fourth (268-4,430 days) age quartiles, respectively. Infants with an episode of upper RTI (URTI) were 2.0 (1.05-3.82) times more likely to harbor P. jirovecii than infants with a lower RTI. P. jirovecii may manifest itself as a self-limiting URTI in infants, predominantly those 1.5-4 months of age.

Pneumocystis: newer knowledge about the biology of this group of organisms in laboratory rats and mice

This review is an update on some of the remarkable advances that have led to greater understanding of Pneumocystis, an important group of rodent pathogens. The author outlines the life cycle of these pulmonic fungi, their taxonomic position, and their nomenclature. He discusses how infections begin and spread in laboratory rodent colonies, and how those infections are inadvertently maintained in barriered breeding colonies. He also addresses the diagnosis of Pneumocystis infection and provides suggestions for the establishment of Pneumocystis-free animal colonies.

Surfactant protein D enhances Pneumocystis infection in immune-suppressed mice

To further determine the role of surfactant protein (SP)-D in the pathogenesis of Pneumocystis pneumonia, a mouse model of transgenic overexpression (OE) of SP-D was studied. These animals produce roughly 30- to 50-fold greater SP-D than their wild-type (WT) counterparts but show no other differences in lung morphology and function. Animals in both the SP-D OE and WT groups were depleted of CD4 lymphocytes with weekly injections of GK1.5 antibody, before Pneumocystis inoculation, and throughout the subsequent infection period. At various time points, mice were killed and analyzed for inflammatory parameters and organism burden. Proinflammatory cytokines in bronchoalveolar lavage fluid were elevated throughout the period of infection, with OE animals exhibiting significantly higher levels of TNF-alpha and macrophage inflammatory protein-2 compared with WT controls. The total number of cells in the lavage fluid was also increased significantly only in the OE group, whereas the cell differential composition demonstrated lymphocyte and eosinophil infiltration in both groups of animals. Significantly, the organism burden was markedly higher in the SP-D OE animals, whereas the WT mice demonstrated little alteration in organism number over the course of infection. These results further indicate that SP-D facilitates the development of Pneumocystis infection and related lung inflammation in an immunosuppressed mouse model.

Pneumocystis: not just pneumonia

Once known exclusively as the agents of severe pneumonia in immunocompromised individuals, Pneumocystis spp. are now being associated with asymptomatic carriage in hosts that do not have profound immune debilitation. In the absence of a cultivation system, polymerase chain reaction and histological studies have identified Pneumocystis in neonatal populations, in pregnant women and in other patients that have chronic underlying disease processes. These findings in humans and in experimental animal models indicate the presence of potential reservoirs of infection, and provide insights into the transmission of this fungus. Also, the role of Pneumocystis has been investigated as a possible co-morbidity factor.

Competitive coexistence of two Pneumocystis species

Pneumocystis are fungal pathogens of mammalian lungs that can cause lethal pneumonia in immunocompromised hosts. In some mammals, coinfections of genetically distinct Pneumocystis populations have been identified, but the nature of their interaction and its significance are unknown. Two species that infect rats, Pneumocystis carinii and Pneumocystis wakefieldiae, were studied over a 6-year period, representing approximately 700 generations of Pneumocystis. Population densities of each species were analyzed within the framework of the Lotka-Volterra competition model, which revealed the two species were in competition and predicted competitive exclusion of one species. However, stable coexistence was observed in 460 replicate populations. Selected extrinsic factors that might mitigate the extinction were evaluated. Logistic-regression analyses showed that higher relative humidity and higher organism lung burdens were associated with infections comprised of P. carinii alone, while lower temperatures and an increased rat census were associated with the presence of P. wakefieldiae. PCR and immunofluorescent analysis of rat lung tissue showed that both species were present within the same alveoli, excluding habitat heterogeneity as a mechanism of coexistence. These data suggest that P. carinii and P. wakefieldiae were in competitive coexistence, which was influenced in part by extrinsic factors. To our knowledge, this is the first report to evaluate interactions of pathogenic fungal species within a mammalian host using ecological models.

Comparative genomics of Pneumocystis carinii with other protists: implications for life style

Three protistan genomes were analyzed for differential genetic traits that may be associated with biological adaptations to their unique life styles. The microsporidian, Encephalitozoon cuniculi, an obligate intracellular parasite; the ascomycetes, Pneumocystis carinii, considered an opportunistic pathogen; and Saccharomyces cerevisiae, a model organism exhibiting a free-living life style, were used in comparisons of genomic architecture, reproductive strategies, and metabolic capacity predicted by the presence of signature genes. Genome size, gene number, and metabolic function decreased as the organisms became more dependent on their hosts. In contrast, gene density and the percentage of genes dedicated to cell growth and division were substantially increased in the genome of E. cuniculi. The obligate life style was associated with reductions in gene number, genome size, and reduced metabolic capacity while the free-living life style was coincident with gene duplications and duplication of large portions of the genome. The genomic characteristics and metabolic capacity of P. carinii were usually intermediate between those of the other two protistan genomes, but unique characteristics such as the presence of a single rDNA locus may indicate that these organisms could be in the process of becoming more host dependent.

Noninvasive method for monitoring Pneumocystis carinii pneumonia

The progression of Pneumocystis carinii pneumonia was temporally monitored and quantified by real-time polymerase chain reaction of P. carinii–specific DNA in oral swabs and lung homogenates from infected rats. DNA levels correlated with the number of P. carinii organisms in the rats’ lungs, as enumerated by microscopic methods. This report is the first of a noninvasive, antemortem method that can be used to monitor infection in a host over time.

Characterization of transmission of Pneumocystis carinii f. sp. muris through immunocompetent BALB/c mice

By using mouse models, it has been shown that Pneumocystis carinii f. sp. muris can be transmitted to immunocompetent mice that are exposed to immunosuppressed mice with active P. carinii pneumonia. We sought to determine whether P. carinii f. sp. muris could be transmitted between normal mice. The rationale for these experiments was to demonstrate whether the normal host could serve as the reservoir of organisms that produce Pcp when the organism is acquired by the immunosuppressed host. Under the conditions of these experiments, normal mice are able to be infected by brief cohousing with P. carinii-infected SCID mice. There was active replication of organisms in the normal host such that the organism could be transmitted to other normal mice, again with active replication. Mice that had seroconverted after exposure to P. carinii-infected SCID mice were more resistant to infection when reexposed. Infection in normal mice was well tolerated with minimal effects on dynamic lung compliance. We speculate, based on these results, that transmission from normal host to normal host, as an asymptomatic or minimally symptomatic infection, could be a way to maintain this opportunistic pathogen in the environment.

Exposure of immunocompetent adult mice to Pneumocystis carinii f. sp. muris by cohousing: growth of P. carinii f. sp. muris and host immune response

There has been emerging evidence that immunocompetent hosts can harbor Pneumocystis in their lungs. The purpose of this study was to determine the kinetics of Pneumocystis carinii f. sp. muris infection in adult immunocompetent mice and the host immune response to the organisms. To accomplish this, we exposed adult immunocompetent mice to SCID mice infected with P. carinii f. sp. muris by cohousing. We found that P. carinii f. sp. muris was detectable in the lungs of cohoused immunocompetent mice by PCR by 3 weeks after the beginning of cohousing. At about 4 weeks of cohousing, P. carinii f. sp. muris was readily detectable in the lungs of mice by microscopic techniques. Also at this time, P. carinii f. sp. muris-specific immunoglobulin G was found in the sera of the mice, and CD62(low) CD4- and CD8-positve T cells accumulated in the lungs. Shortly after this immune response, the P. carinii f. sp. muris organisms were cleared from the lungs. Adult mice cohoused for only 1 week also contained P. carinii f. sp. muris cysts detectable by silver staining at 5 and 6 weeks after the beginning of cohousing. We also found that the P. carinii f. sp. muris organisms grew to greater numbers in the lungs of BALB/c mice than in those of C57BL6 mice. This indicates that immunocompetent hosts develop a mild infection with P. carinii f. sp. muris which resolves in 5 to 6 weeks when there is a detectable immune response to the organism. Once an acquired immune response was initiated, the P. carinii f. sp. muris organisms were quickly eliminated without clinical signs of disease.

Genotypes at the internal transcribed spacers of the nuclear rRNA operon of Pneumocystis jiroveci in nonimmunosuppressed infants without severe pneumonia

The frequency of Pneumocystis jiroveci (human-derived Pneumocystis) in immunocompetent infants developing acute respiratory syndromes has recently been evaluated and has been shown to be close to 25%. Until now, there have been no data on the genomic characteristics of the fungus in these patients, while molecular typing of P. jiroveci organisms was mostly performed with samples from immunosuppressed patients with pneumocystosis (Pneumocystis carinii pneumonia [PCP]). The present report describes the genotypes of P. jiroveci organisms in 26 nonimmunosuppressed infants developing a mild Pneumocystis infection contemporaneously with an episode of bronchioloalveolitis. The typing was based on sequence analysis of internal transcribed spacers (ITSs) 1 and 2 of the rRNA operon, followed by the use of two typing scores. By use of the first score, 11 P. jiroveci ITS types were identified: 10 were previously reported in immunosuppressed patients with PCP, while 1 was newly described. By use of the second score, 13 types were identified, of which 2 were newly described. The most frequent type was identified as type B(1)a(3) (first score), which corresponds to type Eg (second score). Mixed infections were diagnosed in three infants. The occurrence of such diversity of P. jiroveci ITS types, an identical main type, and mixed infections has previously been reported in immunosuppressed patients with PCP. Thus, the P. jiroveci ITS genotypes detected in immunocompetent infants and immunosuppressed patients developing different forms of Pneumocystis infection share characteristics, suggesting that both groups of individuals make up a common human reservoir for the fungus. Finally, the frequency of P. jiroveci in nonimmunosuppressed infants with acute respiratory syndromes and the genotyping results provide evidence that this infant population is an important reservoir for the fungus.