Subacute pulmonary melioidosis in a temperate climate

Correlates of immune protection following cutaneous immunization with an attenuated Burkholderia pseudomallei vaccine

Infections with the Gram-negative bacterium Burkholderia pseudomallei (melioidosis) are associated with high mortality, and there is currently no approved vaccine to prevent the development of melioidosis in humans. Infected patients also do not develop protective immunity to reinfection, and some individuals will develop chronic, subclinical infections with B. pseudomallei. At present, our understanding of what constitutes effective protective immunity against B. pseudomallei infection remains incomplete. Therefore, we conducted a study to elucidate immune correlates of vaccine-induced protective immunity against acute B. pseudomallei infection. BALB/c and C57BL/6 mice were immunized subcutaneously with a highly attenuated, Select Agent-excluded purM deletion mutant of B. pseudomallei (strain Bp82) and then subjected to intranasal challenge with virulent B. pseudomallei strain 1026b. Immunization with Bp82 generated significant protection from challenge with B. pseudomallei, and protection was associated with a significant reduction in bacterial burden in lungs, liver, and spleen of immunized mice. Humoral immunity was critically important for vaccine-induced protection, as mice lacking B cells were not protected by immunization and serum from Bp82-vaccinated mice could transfer partial protection to nonvaccinated animals. In contrast, vaccine-induced protective immunity was found to be independent of both CD4 and CD8 T cells. Tracking studies demonstrated uptake of the Bp82 vaccine strain predominately by neutrophils in vaccine-draining lymph nodes and by smaller numbers of dendritic cells (DC) and monocytes. We concluded that protection following cutaneous immunization with a live attenuated Burkholderia vaccine strain was dependent primarily on generation of effective humoral immune responses.

Detection of Burkholderia pseudomallei in blood samples using polymerase chain reaction

A highly sensitive, specific, rapid and simple method to detect Burkholderia pseudomallei in blood samples was developed. Two 22-base oligonucleotide primers, based on sequences from a specific DNA probe, were used for amplification of bacterial DNA by the polymerase chain reaction (PCR). Amplification with these primers yielded a 178-base pair product in 100 clinical isolates of B. pseudomallei. As little as 0.5 fg of B. pseudomallei DNA was detectable by this method. Experiments involving inoculation of the organism into uninfected blood samples showed that the method could be used to detect as few as 1 bacterial cell ml-1 of whole blood. Non-specific amplification of other bacterial DNAs from 18 samples of bacteria was not observed. Blood samples from seven patients proven to have melioidosis by haemoculture were positive using these primers. The total time required for sample processing, amplification and visualization was approximately 3.5 h. The high sensitivity, rapidity and simplicity of this method should make it valuable for diagnosis, monitoring of drug treatment and for epidemiological studies of the melioidosis.

Melioidosis: the tip of the iceberg?

For nearly 80 years clinical melioidosis has been considered a rare disease. This bacterial infection is caused by Pseudomonas pseudomallei, a saprophyte found in soil and surface water of endemic areas. Consequently, those who have most contact with soil, the rural poor, are likely to be at greatest risk of infection. Since the diversity of clinical manifestations necessitates the isolation and identification of the causative organism for a definitive diagnosis of melioidosis and the population at greatest risk within endemic areas rarely have access to an appropriate level of health care, the disease has probably been underrecognized. Melioidosis is now known to be an important cause of human morbidity and mortality in Thailand, and this may be true throughout Southeast Asia, which is usually regarded as the main endemic area for the disease. In Australia, melioidosis causes a smaller number of human infections, while disease among livestock has important economic and possible public health implications. Sporadic reports of the infection indicate its presence in several other tropical regions: in the Indian subcontinent, Africa, and Central and South America. Clinical melioidosis may be highly prevalent in these areas, but underdiagnosed as a result of a lack of awareness of the clinical and microbiological features of the disease, or simply because of a lack of health care facilities. Furthermore, during the last two decades the importation and transmission of melioidosis within nontropical zones have been documented. The causative organism is not difficult to grow, and modern antibiotics have improved disease prognosis. Further studies are needed to determine the true worldwide distribution and prevalence of melioidosis so that improved therapeutic and preventive measures can be developed and applied.

In vitro activities of the newer beta-lactam and quinolone antimicrobial agents against Pseudomonas pseudomallei

Imipenem was highly active and bactericidal against all 100 strains of Pseudomonas pseudomallei tested, followed in activity by piperacillin, carumonam, ceftazidime, cefotaxime, and ceftriaxone. The addition of clavulanic acid significantly increased the activities of both amoxicillin and ticarcillin. Ciprofloxacin and norfloxacin showed poor activity against test strains.