Clinical and pathological observations on goats experimentally infected with Pseudomonas pseudomallei

Disseminated melioidosis in early pregnancy - an unproven cause of foetal loss

Background

Melioidosis is a potentially life-threatening infection caused by the Gram-negative bacterium Burkholderia pseudomallei. Melioidosis is difficult to diagnose due to its diverse clinical manifestations, which often delays administration of appropriate antibiotic therapy.

Case presentation

Melioidosis is uncommon in pregnancy but both spontaneous abortion and neonatal melioidosis have been reported. We report a case of bacteraemic melioidosis in a young woman with a subsequent spontaneous abortion, with B. pseudomallei cultured from a high vaginal swab as well as blood.

Conclusion

It remains unclear in this and previously reported cases as to whether the maternal melioidosis was sexually transmitted.

Case Report: Chorioamnionitis and Premature Delivery due to Burkholderia pseudomallei Infection in Pregnancy

We report a case of placental infection leading to preterm delivery in a mother diagnosed with septicemia and pneumonia due to Burkholderia pseudomallei in pregnancy. Placental infection occurred despite prolonged ceftazidime therapy.

Detection of Burkholderia pseudomallei toxin-mediated inhibition of protein synthesis using a Caenorhabditis elegans ugt-29 biosensor

Toxins are believed to play a crucial role in Burkholderia pseudomallei pathogenicity, however to date, only a few have been identified. The discovery of additional toxic molecules is limited by the lack of a sensitive indicator of B. pseudomallei toxicity. Previously, from a whole genome transcriptome analysis of B. pseudomallei-infected Caenorhabditis elegans, we noted significant overexpression of a number of worm genes encoding detoxification enzymes, indicating the host's attempt to clear bacterial toxic molecules. One of these genes, ugt-29, a family member of UDP-glucuronosyltransferases, was the most robustly induced phase II detoxification gene. In this study, we show that strong induction of ugt-29 is restricted to infections by the most virulent species among the pathogens tested. We also noted that ugt-29 is activated upon disruption of host protein synthesis. Hence, we propose that UGT-29 could be a promising biosensor to detect B. pseudomallei toxins that compromise host protein synthesis. The identification of bactobolin, a polyketide-peptide hybrid molecule, as a toxic molecule of B. pseudomallei further verifies the utilization of this surveillance system to search for bacterial toxins. Hence, a ugt-29 based reporter should be useful in screening for other molecules that inhibit host protein synthesis.

Pathogenesis of percutaneous infection of goats with Burkholderia pseudomallei: clinical, pathologic, and immunological responses in chronic melioidosis

Melioidosis is a severe suppurative to granulomatous infection caused by Burkholderia pseudomallei. The disease is endemic to South-East Asia and Northern Australasia and is also of interest as a potential biological weapon. Natural infection can occur by percutaneous inoculation, inhalation or ingestion, but the relative importance of each route is unknown. Experimental infection models using mice have shown inhalation to be the most lethal route of exposure, but few studies have examined the pathogenesis of percutaneous infection despite its presumptive importance in natural disease. Caprine models are useful in the study of melioidosis because goats are susceptible to natural infection by B. pseudomallei, display similar epizootiology/epidemiology to that of humans within the endemic range and develop similar pathologic lesions. Percutaneous inoculation with 10(4)  CFU of B. pseudomallei produced disease in all experimental animals with rapid dissemination to the lungs, spleen and kidneys. Initial fever was brief, but temperatures did not return to pre-infection levels until day 18, concurrent with a dramatic lymphocytosis and the transition to chronic disease. Distribution and appearance of gross pathologic and radiographic lesions in goats were similar to caprine aerosol infection and to reported human disease. The similarities seen despite different routes of infection suggest that host or bacterial factors may be more important than the route of infection in disease pathogenesis. The nature of melioidosis in goats makes it amenable for modelling additional risk factors to produce acute clinical disease, which is important to the study of human melioidosis.

Primary ocular melioidosis due to a single genotype of Burkholderia pseudomallei in two cats from Arnhem Land in the Northern Territory of Australia

Melioidosis was diagnosed in two domestic crossbred cats presented for unilateral ocular disease. One patient was born and bred in Nhulunbuy, Arnhem Land, while the other had moved there 6 months previously from Townsville, Queensland. Both patients were presented with sudden onset of a 'red eye' and blepharospasm, which progressed to an enlarged, painful, firm globe with loss of pupillary light reflexes and vision. An obvious primary focus of infection outside the eye was not detected in either cat. In both patients, the affected eye was surgically removed and vitreal culture revealed a pure growth of Burkholderia pseudomallei. In each instance, the infection had penetrated the sclera to produce retrobulbar cellulitis, and in one case frank retrobulbar abscessation. Histologically, there was a pyogranulomatous uveitis with extensive destruction of intraocular structures. The first case was still alive approximately 1 year following enucleation and limited antimicrobial therapy using amoxicillin clavulanate and doxycycline. The second was euthanased when a localised abscess developed on the same side of the face as the healed surgical incision, despite appropriate antimicrobial therapy. Both cases were caused by the same multilocus sequence type of B pseudomallei (ST 116), which had only been isolated previously from two human patients, both living in the same isolated geographical area as the cats of this report. Apart from the geographical clustering, no epidemiological links were evident between the two cats and/or the two people. The presumptive pathogenesis of these infections is discussed in relation to current knowledge about melioidosis in northern Australia.

Experimental Burkholderia pseudomallei infection of pigs

Experimental infection with Burkholderia pseudomallei was successfully produced after a single intravenous challenge of 2-month-old pigs with a dose of 5.0 x 10(9) bacterial cells. Clinical, paraclinical and morphological findings of the infectious process and post-infectious immunity were examined up to day 30 post infection (p.i.). A transient and short hyperthermia accompanied by enhanced and longer demonstrated pulse frequency. An increased erythrocyte sedimentation rate and tachypnea were observed too after clinical examination. The infection starts with significant leucopenia, and a reduced number of alveolar and peritoneal macrophages which have been overcome in the latest intervals of infection. In contrast, the phagocytic activity of leucocytes was statistically increased during the course of infection and up to day 15 p.i. in the case of alveolar macrophages. Burkholderia pseudomallei was able to colonize the lungs during the whole experiment and was only present 3 days in the spleen and mesenterial lymph nodes (MLN). Significant antibody response was developed as early as day 7 p.i. Hyperaemia, haemorrhages and necrotic foci were found in the brain, liver spleen and MLN. Lung tissue was also hyperaemic, with formation of small abscesses and signs of catarrhal pneumonia. Data obtained in this study revealed that B. pseudomallei causes a chronic generalized infection in pigs, even after intravenous challenge.

Disseminated melioidosis in two cats

Melioidosis was diagnosed in two cats at necropsy. The first cat presented with jaundice and anaemia but died of overwhelming sepsis soon after admission, despite blood transfusion and other supportive measures. The second cat died several days after developing neurological signs; an infected digital wound may have been the primary focus of infection in this patient. The cats had presumably acquired the infection in Malaysia and northern Australia, respectively, and in both cases disease may have represented reactivation of a latent infection brought on by the stress of relocation. The epidemiology, clinical presentation, diagnosis and treatment of melioidosis are discussed from a feline perspective.

Causes of caprine abortion: diagnostic assessment of 211 cases (1991-1998)

In an 8-year period, 1991-1998, 217 accessions of caprine abortions were submitted to the California Veterinary Diagnostic Laboratory System. Of these 217 submissions, 211 were suitable for examination in this study (6 had insufficient data). Infectious agents as the cause of abortions were found in 37% of the cases: bacterial agents were identified in 30.5%, viral agents in 2%, fungal agents in 0.5%, and protozoal agents in 4% of the cases submitted. The most common causes of abortions were Chlamydia psittaci and Coxiella burnetii infection, which accounted for 23% of all goat abortions. Mineral deficiencies were observed in 4%, fetal anomalies accounted for 3%, and leukoencephalomalacia of the brain (probable oxygen deprivation) accounted for 3% of the submissions. No diagnosis was made in 112 of the 211 submissions (53%). No lesions were noted in 104 of the submissions (49%). The other 8 submissions (4%) had histologic lesions suggestive of a bacterial agent; however, no infectious agents were identified in these cases.

Animal melioidosis in Australia

Melioidosis was first diagnosed in Australia in sheep in 1949. While it has been considered endemic in tropical Australia, there have been animal outbreaks in southwest Western Australia and southern Queensland. Infection occurs in many species, with both latency and a wide range of clinical manifestations. Some species may develop melioidosis only if immunocompromised. Sheep and goats are particularly susceptible, resulting in the requirement for pasteurisation of tropical commercial goat's milk. Nine out of 43 (21%) goats had aortic lesions at autopsy and seven died from aortic aneurysm rupture. Transplacental transmission in goats has also been documented. Asymptomatic organ abscesses are common in pigs but bovine melioidosis is very rare. Camels moved north and an alpaca brought to Darwin have died from melioidosis. It also occurs in wildlife, including birds, crocodiles and kangaroos. Zoonotic transmission to humans is extremely unusual, but there are many similar epidemiological and clinical features of melioidosis in animals and humans. There have been three possible zoonotic cases in Australia. Molecular typing has found identical Burkholderia pseudomallei organisms from animals, humans and soil. The study of melioidosis in animals, especially the use of molecular genetic techniques for organism identification and typing, will continue to unravel aspects of the disease that remain unclear in humans.

Characterization of a murine model of melioidosis: comparison of different strains of mice

Melioidosis is an infectious disease caused by the saprophytic gram-negative rod Burkholderia pseudomallei. The aim of this study was to establish and characterize a murine model of melioidosis to provide a basis for further investigations on the pathogenesis of the disease. After intravenous infection with B. pseudomallei, C57BL/6 mice were found to be significantly more resistant than BALB/c mice. There was a marked organotropism of B. pseudomallei for the spleen and liver in both strains of mice, with the highest bacterial load in the spleen. Electron microscopic investigations of the spleen clearly demonstrated intracellular replication within membrane-bound phagosomes. Electron micrographs of the liver provided evidence that B. pseudomallei-containing phagosomes in hepatocytes fuse with lysosomes, leading to degradation of bacteria. In both strains of mice, the course of infection was highly dependent on the infective dose and the bacterial strain used, ranging from death within a few days to death after several weeks. In comparison with BALB/c mice, the bacterial counts in C57BL/6 mice were decreased 12 h after infection, which is suggestive of an innate immune mechanism against B. pseudomallei in this early phase of infection contributing to the lower susceptibility of C57BL/6 mice. BALB/c mice developed a more pronounced lymphopenia, granulocytosis, and splenomegaly at a lower infective dose compared to C57BL/6 mice. Analysis of the antibody response against B. pseudomallei 11 days after infection revealed a significantly higher immunoglobulin G2A (IgG2a)/IgG1 ratio in C57BL/6 mice than in BALB/c mice, indicating that a T helper type 1 immune response is associated with resistance to infection with B. pseudomallei.

Killing of Pseudomonas pseudomallei by polymorphonuclear leukocytes and peritoneal macrophages from chicken, sheep, swine and rabbits

Differences in the kinetics of Pseudomonas pseudomallei killing by peritoneal macrophages (PM) and polymorphonuclear leucocytes (PMNL) from chickens, sheep, swine and rabbits were found. P. pseudomallei was rapidly killed by porcine PM and PMNL. However the bacterial killing by ovine and lapine PM and PMNL proceeded at a slower rate. In contrast, chicken PM and PMNL ingested and killed the lowest number of P. pseudomallei bacteria. The differences in the bactericidal activity of PM and PMNL from different animal species correlated with the level of their acid phosphatase and glycolytic activity.

Arabinose assimilation defines a nonvirulent biotype of Burkholderia pseudomallei

Two distinct types of Burkholderia pseudomallei, differentiated by the ability to assimilate L-arabinose but with similar morphologies and antigenicities, can be isolated from soil in Thailand. Approximately 25% of soil isolates from northeast Thailand were arabinose assimilators (Ara+), but in 1,200 sequentially studied patients, only arabinose "nonassimilators" (Ara-) caused melioidosis (P < 0.0001). In a murine model, there was a striking difference in virulence between Ara- and Ara+ B. pseudomallei. The mean (standard deviation) 50% lethal dose (LD[50]) inoculum for Ara- isolates was 182 (111) CFU/mouse compared with approximately 10(9) CFU/mouse for Ara+ soil isolates. There was no significant difference between the LD(50)s for clinical and soil Ara- isolates. All attempts to convert the biochemical phenotype by selective culture failed, which suggests that the biotype is stable.

Experimental melioidosis in hens

Experimental intramuscular infection of hens with Pseudomonas pseudomallei, strain 2796 (1 x 10(9) CFU from a 24-h culture) was reproduced. Clinical, paraclinical and pathomorphological findings were followed from 1 to 30 days after challenge. Haemagglutinin titre, bacterial dissemination in the viscera, number of leucocytes, alveolar (aMa) and peritoneal (pMa) macrophages and their phagocytic activity in vitro were studied. During the course of infection a leucocytosis as well as an increased haemagglutinin titre (1:256) were established. The number of bacteria per gram tissue in the spleen and liver was highest at 1 day post-infection (p.i.). Melioidose bacteria from egg yolk were isolated at 15 and 30 days p.i. Leucocyte and pMa phagocytic activity was maximal at 3 days p.i. unlike the activity of aMa which increased gradually until the end of the study. Inflammatory-necrotic changes were found in the viscera and brain at 3 and 15 days p.i. The investigation of experimental melioidosis infection in hens showed that they are susceptible to P. pseudomallei and this disease takes a generalized subacute course.

Experimental melioidosis in inbred mouse strains

Experimental infection was induced in three inbred mouse strains (BALB/c, BDF1 hybrid and C57BL) by i. p. inoculation with Pseudomonas pseudomallei. The bacterial load in the viscera and the host response induced in different compartments (blood, peritoneal cavity and organs) were determined. Blood cell parameters and peritoneal exudative cell populations were evaluated during the infection with the aid of an automated haematology analyser Technicon H-1. It was found that all mouse strains produced a similar intraperitoneal inflammatory response with predominance of granulocytes at the early stage of infection and subsequent increase of macrophages especially in BDF1 hybrid and BALB/c mice. The highest bacterial count found in the liver and spleen of C57BL was associated with corresponding tissue damage (purulent pneumonia, abscesses in liver, karyorrhexis of hepatocytes and meningoencephalitis). The degree of bacterial load and histological changes found in BALB/c and BDF1 hybrid mice were lower than in C57BL mice. The results show that the variations in the infection magnitude among inbred mouse strains are host-dependent.

Experimental infection of normal and immunosuppressed pigs with Pseudomonas pseudomallei

A single dose of 5 x 10(8) bacilli of Pseudomonas pseudomallei by intratracheal injection resulted in acute (21 cases) or chronic (19 cases) melioidosis in 40 of 48 pigs. Fifteen (10 acute and 5 chronic) had been immunosuppressed by cyclophosphamide before inoculation. The major clinical signs were initial fever, marked neutrophilia and, in the acute cases, respiratory distress. There were no signs of the nasal and ocular discharge, paresis or diarrhoea seen in acute cases in south-east Asia. The cyclophosphamide treatment caused a significant decrease in the neutrophil count by 7 d after inoculation in all 15 immunosuppressed pigs, and all were culture positive at necropsy. Eight of the 33 non-treated pigs were culture negative at necropsy. Pigs overcoming the initial phase of infection had more abscess-like nodules that were bacteriologically sterile at necropsy than the pigs with acute cases of melioidosis. P. pseudomallei was isolated predominantly from the spleen, lungs and the injection site. Although only one strain was used in this study, it is likely that Australian strains of P. pseudomallei are not as virulent as the south-east Asian isolates.

Evaluation of four serological tests for the diagnosis of caprine melioidosis

A complement fixation (CF) test, 2 indirect haemagglutination (IHA-A; IHA-L) tests which differed in antigen preparation and technique, and a microtitre agglutination (MA) test were compared in the serodiagnosis of melioidosis in goats. One hundred and eighteen experimental serums and 3143 field serums from goats in endemic and non-endemic areas of north Queensland were used in the evaluation. Culture of samples for Pseudomonas pseudomallei from 112 goats provided substantiating evidence of infection. The IHA-A test was the most sensitive, and the CF test the most specific. We advocate the use of the IHA-A as a screening test followed by the CF test for confirmation of active melioidosis. The IHA-A test is the better indicator of past infection.