Burkholderia pseudomallei multi-centre study to establish EUCAST MIC and zone diameter distributions and epidemiological cut-off values

OBJECTIVES

Melioidosis, caused by Burkholderia pseudomallei, requires intensive antimicrobial treatment. However, standardized antimicrobial susceptibility testing (AST) methodology based on modern principles for determining breakpoints and ascertaining performance of methods are lacking for B. pseudomallei. This study aimed to establish MIC and zone diameter distributions on which to set epidemiological cut-off (ECOFF) values for B. pseudomallei using standard EUCAST methodology for non-fastidious organisms.

METHODS

Non-consecutive, non-duplicate clinical B. pseudomallei isolates (9-70 per centre) were tested at eight study centres against eight antimicrobials by broth microdilution (BMD) and the EUCAST disc diffusion method. Isolates without and with suspected resistance mechanisms were deliberately selected. The EUCAST Development Laboratory ensured the quality of study materials, and provided guidance on performance of the tests and interpretation of results. Aggregated results were analysed according to EUCAST recommendations to determine ECOFFs.

RESULTS

MIC and zone diameter distributions were generated using BMD and disc diffusion results obtained for 361 B. pseudomallei isolates. MIC and zone diameter ECOFFs (mg/L; mm) were determined for amoxicillin-clavulanic acid (8; 22), ceftazidime (8; 22), imipenem (2; 29), meropenem (2; 26), doxycycline (2; none), tetracycline (8; 23), chloramphenicol (8; 22) and trimethoprim-sulfamethoxazole (4; 28).

CONCLUSIONS

We have validated the use of standard BMD and disc diffusion methodology for AST of B. pseudomallei. The MIC and zone diameter distributions generated in this study allowed us to establish MIC and zone diameter ECOFFs for the antimicrobials studied. These ECOFFs served as background data for EUCAST to set clinical MIC and zone diameter breakpoints for B. pseudomallei.

Role of Burkholderia pseudomallei biofilm formation and lipopolysaccharide in relapse of melioidosis

We examined whether quantitative biofilm formation and/or lipopolysaccharide type of Burkholderia pseudomallei was associated with relapsing melioidosis. We devised a 1:4 nested case-control study in which both cases and controls were drawn from a cohort of patients with primary melioidosis. Paired isolates from 80 patients with relapse and single isolates from 184 patients without relapse were tested. Relapse was associated with biofilm formation of the primary infecting isolate (conditional OR 2.03; 95% CI 1.27-3.25; p 0.003), but not with lipopolysaccharide type (p 0.74). This finding highlights the importance of biofilm formation in relapsing melioidosis.

Application of carbohydrate microarray technology for the detection of Burkholderia pseudomallei, Bacillus anthracis and Francisella tularensis antibodies

We developed a microarray platform by immobilizing bacterial 'signature' carbohydrates onto epoxide modified glass slides. The carbohydrate microarray platform was probed with sera from non-melioidosis and melioidosis (Burkholderia pseudomallei) individuals. The platform was also probed with sera from rabbits vaccinated with Bacillus anthracis spores and Francisella tularensis bacteria. By employing this microarray platform, we were able to detect and differentiate B. pseudomallei, B. anthracis and F. tularensis antibodies in infected patients, and infected or vaccinated animals. These antibodies were absent in the sera of naïve test subjects. The advantages of the carbohydrate microarray technology over the traditional indirect hemagglutination and microagglutination tests for the serodiagnosis of melioidosis and tularemia are discussed. Furthermore, this array is a multiplex carbohydrate microarray for the detection of all three biothreat bacterial infections including melioidosis, anthrax and tularemia with one, multivalent device. The implication is that this technology could be expanded to include a wide array of infectious and biothreat agents.

Differential patterns of endothelial and leucocyte activation in 'typhus-like' illnesses in Laos and Thailand

Scrub typhus is responsible for a large proportion of undifferentiated fevers in south-east Asia. The cellular tropism and pathophysiology of the causative agent, Orientia tsutsugamushi, remain poorly understood. We measured endothelial and leucocyte activation by soluble cell adhesion molecule enzyme-linked immunosorbent assays in 242 Lao and Thai patients with scrub or murine typhus, leptospirosis, dengue, typhoid and uncomplicated falciparum malaria on admission to hospital. Soluble E-selectin (sE-selectin) levels were lowest in dengue, sL-selectin highest in scrub typhus with a high sE-selectin to sL-selectin ratio in leptospirosis patients. In scrub typhus patients elevated sL-selectin levels correlated with the duration of skin rash (P = 0.03) and the presence of eschar (P = 0.03), elevated white blood cell (WBC) count (P = 0.007), elevated lymphocyte (P = 0.007) and neutrophil counts (P = 0.015) and elevated levels of sE-selectin correlated with the duration of illness before admission (P = 0.03), the presence of lymphadenopathy (P = 0.033) and eschar (P = 0.03), elevated WBC (P = 0.005) and neutrophil counts (P = 0.0003). In comparison, soluble selectin levels in murine typhus patients correlated only with elevated WBC counts (P = 0.03 for sE-selectin and sL-selectin). Soluble intercellular adhesion molecule-1 and soluble vascular adhesion molecule-1 levels were not associated significantly with any clinical parameters in scrub or murine typhus patients. The data presented suggest mononuclear cell activation in scrub typhus. As adhesion molecules direct leucocyte migration and induce inflammatory and immune responses, this may represent O. tsutsugamushi tropism during early dissemination, or local immune activation within the eschar.

The changing pattern of bloodstream infections associated with the rise in HIV prevalence in northeastern Thailand

A survey of bloodstream infections was conducted in the large regional hospital in Ubon Ratchatani, northeastern Thailand between 1989 and 1998, during the onset of the HIV epidemic. The incidence of Staphylococcus aureus, Escherichia coli, Klebsiella/Enterobacter and Pseudomonas aeruginosa bacteraemias remained constant whereas infections caused by Burkholderia pseudomallei, non-typhoid Salmonellae, Cryptococcus neoformans, Penicillum marneffei and to a lesser extent Streptococcus pneumoniae all rose. Burkholderia pseudomallei infections were unrelated to HIV, whereas the other infections were associated directly with HIV. Group D non-typhoid Salmonellae bloodstream infections (mainly Salmonella enteritidis) rose coincident with the increase in HIV seroprevalence, and preceded the increase in the other HIV-associated infections. Other non-typhoid Salmonella bacteraemias increased two years after the rise in group D infections, and invasive yeast infections increased four years later, coincident with the increase in AIDS. Increasing Group D non-typhoid Salmonella bloodstream infections are an early warning signal of an impending rise in AIDS.

Cellular fatty acid profile distinguishes Burkholderia pseudomallei from avirulent Burkholderia thailandensis

Burkholderia pseudomallei, the cause of melioidosis, can be distinguished from the closely related but nonpathogenic Burkholderia thailandensis by gas chromatography (GC) analysis of fatty acid derivatives. A 2-hydroxymyristic acid derivative (14:0 2OH) was present in 95% of B. pseudomallei isolates and no B. thailandensis isolates. GC mass spectrophotometry confirmed that 2-hydroxymyristic acid was present in B. pseudomallei. GC-fatty acid methyl ester analysis may be useful in distinguishing these two closely related species.

Value of throat swab in diagnosis of melioidosis

Throat swab (TS) cultures were performed for 1,011 patients with melioidosis and 3,524 healthy subjects or patients with other diseases. The specificity of TS culture for the diagnosis of melioidosis was 100%, and the overall sensitivity was 36% (24% for sputum-negative patients and 79% for sputum-positive patients). Direct plating of the TS specimen on Ashdown's medium was rapid (colonies were usually evident within 24 h) but only 63% sensitive compared to the results of primary culture in a selective broth. A throat swab should be cultured in all cases of suspected melioidosis.

Melioidosis and Pandora's box in the Lao People's Democratic Republic

Melioidosis has not been recognized previously in Laos, but within months of starting a prospective study of community acquired septicemia in Vientiane, 2 patients with melioidosis were identified. One was a previously healthy, 44-year-old female rice farmer who presented with supraclavicular lymphadenitis and the other was a 74-year-old man with diabetes and renal calculi who was receiving corticosteroids and had septicemia and septic arthritis.

Pharmacokinetic-pharmacodynamic evaluation of ceftazidime continuous infusion vs intermittent bolus injection in septicaemic melioidosis

AIMS

Experimental studies have suggested that constant intravenous infusion would be preferable to conventional intermittent bolus administration of beta-lactam antibiotics for serious Gram-negative infections. Severe melioidosis (Burkholderia pseudomallei infection) carries a mortality over 40% despite treatment with high dose ceftazidime. The aim of this study was to measure the pharmacokinetic and pharmacodynamic effects of continuous infusion of ceftazidime vs intermittent bolus dosing in septicaemic melioidosis.

METHODS

Patients with suspected septicaemic melioidosis were randomised to receive ceftazidime 40 mg kg(-1) 8 hourly by bolus injection or 4 mg kg(-1) h(-1) by constant infusion following a 12 mg kg(-1) priming dose and pharmacokinetic and pharmacodynamic parameters were compared.

RESULTS

Of the 34 patients studied 16 (59%) died. Twenty patients had cultures positive for B. pseudomallei of whom 12 (60%) died. The median MIC90 of B. pseudomallei was 2 mg l(-1), giving a minimum target concentration (4*MIC) of 8 mg l(-1). The median (range) estimated total apparent volume of distribution, systemic clearance and terminal elimination half-lives of ceftazidime were 0.468 (0.241-0. 573) l kg(-1), 0.058 (0.005-0.159) l kg(-1) h(-1) and 7.74 (1.95-44.71) h, respectively. Clearance of ceftazidime and creatinine clearance were correlated closely (r = 0.71; P < 0.001) and there was no evidence of significant nonrenal clearance.

CONCLUSIONS

Simulations based on these data and the ceftazidime sensitivity of the B. pseudomallei isolates indicated that administration by constant infusion would allow significant dose reduction and cost saving. With conventional 8 h intermittent dosing to patients with normal renal function, plasma ceftazidime concentrations could fall below the target concentration but this would be unlikely with a constant infusion. Correction for renal failure, which is common in patients with meliodosis is Clearance = k(*) creatinine clearance where k = 0.72. Calculation of a loading dose gives median (range) values of loading dose, DL of 18.7 mg kg(-1) (9.5-23) and infusion rate I = 3.5 mg k(-1) h(-1) (0.4-13) (which equals 84 mg kg(-1) day(-1)). A nomogram for adjustment in renal failure is given.

Pharmacokinetic-pharmacodynamic evaluation of ceftazidime continuous infusion vs intermittent bolus injection in septicaemic melioidosis

AIMS

Experimental studies have suggested that constant intravenous infusion would be preferable to conventional intermittent bolus administration of beta-lactam antibiotics for serious Gram-negative infections. Severe melioidosis (Burkholderia pseudomallei infection) carries a mortality of 40% despite treatment with high dose ceftazidime. The aim of this study was to measure the pharmacokinetic and pharmacodynamic effects of continuous infusion of ceftazidime vs intermittent bolus dosing in septicaemic melioidosis.

METHODS

Patients with suspected septicaemic melioidosis were randomised to receive ceftazidime 40 mg kg-1 8 hourly by bolus injection or 4 mg kg-1 h-1 by constant infusion following a 12 mg kg-1 priming dose to perform estimation of pharmacokinetic and pharmacodynamic parameters.

RESULTS

Of the 34 patients studied 16 (59%) died. Twenty patients had cultures positive for B. pseudomallei of whom 12 (60%) died. The median MIC90 of B. pseudomallei was 2 mg l-1, giving a target concentration CT, of 8 mg l-1. The median (range) estimated total apparent volume of distribution, systemic clearance and terminal elimination half-lives of ceftazidime were 0.468 (0.241-0.573) l kg-1, 0.058 (0.005-0.159) l kg-1 h-1 and 7.74 (1.95-44.71) h, respectively. Clearance of ceftazidime and creatinine clearance were correlated closely (r = 0. 71; P < 0.001) and there was no evidence of significant nonrenal clearance.

CONCLUSIONS

Simulations based on these data and the ceftazidime sensitivity of the B. pseudomallei isolates indicated that administration by constant infusion would allow significant dose reduction and cost saving. With conventional 8 h intermittent dosing to patients with normal renal function, plasma ceftazidime concentrations could fall below the target concentration but this would be unlikely with a constant infusion. Correction for renal failure which is common in these patients is Clearance = k * creatinine clearance where k = 0.072. Calculation of a loading dose gives median (range) values of loading dose, DL of 3.7 mg kg-1 (1. 9-4.6) and infusion rate I = 0.46 mg kg h-1 (0.04-1.3) (which equals 14.8 mg kg-1 day-1). A nomogram for adjustment in renal failure is given.

Interaction of insulin with Burkholderia pseudomallei may be caused by a preservative

AIM

To re-examine the previously reported in vitro interaction of insulin with Burkholderia pseudomallei, in the light of a suggestion that the interaction may have resulted from the presence of the preservative m-cresol in commercial preparations.

METHODS

Broth culture studies of B pseudomallei were performed with and without the addition of m-cresol and various preparations of insulin.

RESULTS

Growth of B pseudomallei was inhibited by m-cresol at the concentrations found in pharmaceutical insulin preparations, and by the insulin preparation Humulin R, but not by pure insulin.

CONCLUSIONS

The results of previous experiments may have been confounded by the presence of the preservative m-cresol.

Serum bactericidal and inhibitory titres in the management of melioidosis

A retrospective evaluation of the relationship between serum bactericidal and inhibitory titres and treatment outcome in 195 adult Thai patients with severe melioidosis was conducted. Drug regimens included ceftazidime (52% of patients), co-amoxiclav (24%), imipenem (11%) or the conventional four-drug combination (11%). Pre- and 1 h post-dose serum samples were collected after 48-72 h of therapy, and serum inhibitory and bactericidal titrations determined. Median post-dose titres were: bactericidal 1:8 (range 0-1:128) and inhibitory 1:16 (range 0-1:128). Overall mortality was 26% and outcome was not influenced by either inhibitory or bactericidal titres. Pre-dose titres correlated with renal function; renal function was the most important predictor of mortality. Determination of serum inhibitory or bactericidal titres is unhelpful in the management of severe melioidosis.

Stable marker on flagellin gene sequences related to arabinose non-assimilating pathogenic Burkholderia pseudomallei

Using PCR-based isolation and sequence analysis of the flagellin gene from two distinct biotypes of Burkholderia pseudomallei, a 15-bp deletion was found within the variable domain of the gene in isolates capable of assimilating arabinose (Ara+). This finding led to the development of a PCR-based method in order to differentiate and identify pathogenic B. pseudomallei for epidemiological study. A pair of specific primers was designed covering the 15-bp deletion region at the variable domain. PCR-amplification products of 176 and 191 bp in size were detected from 41 Ara+ isolates and 39 Ara - isolates of B. pseudomallei, respectively. Moreover, flagellin gene fragments of other bacterial species tested in this study were not amplified using these primers. The results suggest that the flagellin gene sequences of both B. pseudomallei biotypes in this region are stable and distinct. This method can be applied and useful for the epidemiological study of B. pseudomallei.

Melioidosis in Southern Vietnam: clinical surveillance and environmental sampling

From 1992-1998, Burkholderia pseudomallei was isolated from only 9 (0.25%) of 3653 cultures of blood from febrile patients admitted to the Centre for Tropical Diseases in Ho Chi Minh City, an infectious disease referral center for southern Vietnam. Soil was sampled from 407 sites in 147 rice fields along the 5 major roads radiating from Ho Chi Minh City. B. pseudomallei was isolated from 73 sites (18%) in 39 rice fields (27%), but only 15 (21%) of the 71 isolates from 9 (6%) of 147 fields were the virulent l-arabinose (ara)-negative biotype. All except 1 of the fields with the ara-negative biotype were close to the homes of the patients with melioidosis. The low incidence of melioidosis in the provinces around Ho Chi Minh City may be explained by the restricted distribution of ara-negative B. pseudomallei in the soil in this area.

A comparison of lysis centrifugation, pour plate, and conventional blood culture methods in the diagnosis of septicaemic melioidosis

AIMS

To determine whether quantitative blood culture methods could improve the diagnosis of septicaemic melioidosis.

METHODS

A comparison of conventional broth based blood cultures, a pour plate method, and a commercial lysis centrifugation (Isolator 10) blood culture system was conducted in 71 Thai patients with severe melioidosis. The time to identification of B pseudomallei was recorded for each method.

RESULTS

42 patients (59%) were septicaemic. Compared with conventional blood culture, the Isolator and pour plate methods had sensitivities of 81% and 61%, respectively. The median times to a positive culture were: Isolator 39.3 hours, pour plates 45.5 hours, broth culture 61.8 hours (p < 0.001 Isolator v broth). There was a significant inverse correlation between Isolator tube or pour plate quantitative counts and time to detection (r = -0.44 and -0.57, respectively). Mortality was higher in patients who were septicaemic.

CONCLUSIONS

Routine use of one of these quantitative methods, in addition to conventional broth culture, may lead to earlier diagnosis of septicaemic melioidosis.

Comparison of imipenem and ceftazidime as therapy for severe melioidosis

An open, prospective, randomized, comparative treatment trial was conducted to compare the therapeutic efficacy of high-dose intravenous imipenem and ceftazidime for acute severe melioidosis. Adult Thai patients with suspected acute, severe melioidosis were randomized to receive either imipenem, at a dosage of 50 mg/(kg x d), or ceftazidime, at a dosage of 120 mg/(kg x d), for a minimum of 10 days. The main outcome measures were death or treatment failure. Of the 296 patients enrolled, 214 had culture-confirmed melioidosis, and 132 (61.7%) of them had positive blood cultures. Mortality among patients with melioidosis was 36.9% overall. There were no differences in survival overall (P = .96) or after 48 hours (P = .3). Treatment failure after 48 hours was more common among patients treated with ceftazidime (P = .011). Both treatments were well tolerated. Imipenem is a safe and effective treatment for acute severe melioidosis and may be considered an alternative to ceftazidime.

Risk factors for melioidosis and bacteremic melioidosis

A case-control study was conducted in four hospitals in northeastern Thailand to identify risk factors for melioidosis and bacteremic melioidosis. Cases were patients with culture-proven melioidosis, and there were two types of controls (those with infections, i.e., with community-acquired septicemia caused by other bacteria, and those without infection, i.e., randomly selected patients admitted with noninfectious diseases to the same hospitals). Demographic data, clinical presentations, and suspected risk factors were analyzed. Diabetes mellitus, preexisting renal diseases, thalassemia, and occupational exposure, classified by the soil and water risk assessment, were confirmed to be significant risk factors for melioidosis and bacteremic melioidosis. Only diabetes mellitus was a significant factor associated with bacteremic melioidosis, as compared with nonbacteremia. A significant interaction was found between diabetes mellitus and occupational exposure. Thus, diabetic rice farmers would be the most appropriate population group for targeted control measures such as vaccination in the future.

Antigenic differences between clinical and environmental isolates of Burkholderia pseudomallei

Burkholderia pseudomallei is a free-living organism that causes the potentially lethal tropical infection melioidosis. The disease is endemic in many parts of eastern Asia and northern Australia. The presence of two distinct biotypes in soil can be reliably distinguished by their ability to assimilate L-arabinose. Whereas some soil isolates could utilize this substrate (Ara+), the remaining soil isolates and all clinical isolates tested so far could not (Ara-). Only the Ara- isolates were virulent in animal models. We have raised a murine monoclonal antibody (MAb) that can readily distinguish Ara- from Ara+ biotypes. The MAb reacted with a high molecular weight component present only on the Ara- biotype. With this MAb, clinical and soil Ara- isolates gave identical positive reactions in agglutination, immunofluorescence, ELISA and immunoblot assays. Using these same assay systems, the soil Ara+ biotype did not react with the MAb. Similar but distinct immunoblot patterns were also noted when these two Ara biotypes were probed with sera from patients with melioidosis or with polyclonal immune rabbit sera. These data showed that the Ara- biotype from both clinical and environmental isolates is antigenically different from its Ara+ environmental counterpart. The SDS-PAGE protein and lectin-binding profiles of both groups of Ara- isolates were also found to be different from those of the Ara+ biotype.

Diagnosis of Penicillium marneffei infection by quantitation of urinary antigen by using an enzyme immunoassay

Penicillium marneffei is a major cause of opportunistic infection in patients with AIDS in north and northeastern Thailand. A method for the quantitation of P. marneffei antigen in urine was developed by using fluorescein isothiocyanate-labelled purified rabbit hyperimmune immunoglobulin G in an enzyme-linked immunosorbent assay. This method was evaluated with 33 patients with culture-proven penicilliosis and 300 controls (52 healthy subjects, 248 hospitalized patients without penicilliosis) from the same area in which penicilliosis is endemic. Urinary antigen was found in all 33 (100%) patients with penicilliosis, with a median titer of 1:20,480. With undiluted samples, 67 (27%) of 248 hospital patients and 3 (6%) of 52 healthy controls were reactive. At a cutoff titer of 1:40, the urine antigen detection assay had a diagnostic sensitivity of 97% and specificity of 98% (positive predictive value, 84%; negative predictive value, 99.7%). This test offers a valuable and rapid method for the diagnosis of penicilliosis in patients with AIDS and could be a useful addition to conventional diagnostic methods in areas in which penicilliosis is endemic.

Lipopolysaccharide from nonvirulent Ara+ Burkholderia pseudomallei isolates is immunologically indistinguishable from lipopolysaccharide from virulent Ara- clinical isolates

Different lines of evidence suggest that a discrepancy between the distribution of Burkholderia (Pseudomonas) pseudomallei in the environment and the distribution of the disease melioidosis is attributable, at least in part, to phenotypic differences between clinical and some environmental isolates. Two antigenically and biochemically distinct biotypes have been described, only one of which is virulent. In this study, lipopolysaccharides (LPSs) were extracted by the proteinase K digestion method from a total of 214 B. pseudomallei isolates, and their immunoreactivities with sera from patients with different clinical spectra and with other infections were evaluated. With the exception of4 isolates from a total of 214 tested, the sodium dodecyl sulfate-polyacrylamide gel electrophoresis silver-staining profiles of the LPSs from the two biotypes showed identical ladder patterns that were typical for smooth LPSs from other gram-negative bacteria. The 210 isolates with typical LPS patterns (119 Ara- clinical, 13 Ara- soil, 70 Ara+ soil, and 8 reference National Type Culture Collection strains) also exhibited similar immunoblot profiles against pooled sera from patients with melioidosis and hyperimmune mouse sera. Concordant findings were noted in the indirect enzyme-linked immunosorbent assay with Ara- and Ara+ LPSs to coat the microtiter plates. The LPSs of the different B. pseudomallei biotypes appear antigenically indistinguishable. It is, therefore, unlikely that this component is related to the virulence and pathogenicity of B. pseudomallei.

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.

Biochemical characteristics of clinical and environmental isolates of Burkholderia pseudomallei

The biochemical characteristics of 213 isolates of Burkholderia pseudomallei from patients with melioidosis and 140 isolates from the soil in central and northeastern Thailand were compared. Whereas the biochemical profiles of all the clinical isolates were similar, all soil isolates from the central area and 25% of isolates from northeastern Thailand comprised a different phenotype. This was characterised by the ability to assimilate L-arabinose (100%), adonitol (100%), 5-keto-gluconate (90%) and D-xylose (84%), but failure to assimilate dulcitol (0%), erythritol (0%) and trehalose (10%). Compared with clinical isolates, these organisms had similar antibiotic susceptibility profiles and were also recognised by a specific polyclonal antibody against B. pseudomallei. As melioidosis is rare in central Thailand, but common in the northeast, this raises the possibility that this biochemical phenotype may be less virulent, or may even represent a different species.

The laboratory diagnosis of melioidosis

The recognition of unusual, but important, pathogens such as Burkholderia pseudomallei is essential for the rapid implementation of appropriate antimicrobial therapy--delays can be fatal. Melioidosis should be considered as a potential diagnosis for any patient with exposure to areas of endemicity, and thus laboratories should be aware of the differential features of the disease and the causative organism. Isolation of B. pseudomallei is readily achieved using standard culture media such as blood, MacConkey or cystine-lactose-electrolyte-deficient (CLED) agars, and routine blood culture broths. Selective media, Ashdown's agar and selective broth, are required for respiratory tract specimens to ensure reliable isolation from amongst the normal or contaminating flora. These media are easily prepared from common media constituents. Colonial morphology and simple biochemical tests will suggest the identity of the organism, which can then be confirmed by additional tests for 'non-fermenters', such as the API 20NE.

In-vitro activity of carbapenem antibiotics against beta-lactam susceptible and resistant strains of Burkholderia pseudomallei

Four carbapenem antibiotics were tested for their in-vitro activities (MICs, MBCs and time-kill studies) against Burkholderia pseudomallei. The carbapenems were all more active than either ceftazidime or co-amoxiclav against strains of B. pseudomallei with a normal susceptibility pattern. Biapenem was the most active antibiotic tested. All four carbapenems retained bactericidal activity against 24 strains of B. pseudomallei with reduced susceptibility to ceftazidime and/or co-amoxiclav.

A prospective clinical and bacteriologic study of inguinal buboes in Thai men

One-hundred thirteen men (mean age, 23 years) who presented with inguinal buboes to a government-operated hospital for sexually transmitted diseases (STDs) in Bangkok were studied between February 1987 and February 1989. The median duration of preceding symptoms was 7 days (range, 1-62 days). The majority of patients (74; 65%) had received treatment previously; 31 (27%) were febrile, 13 (12%) had extrainguinal lymphadenopathy, and 31 (27%) had concurrent active genital ulcers. There was no history of genital ulceration in 66 (58%) of the patients. Pus was obtained from 51 of the 110 buboes aspirated for culture; 21 (41%) of these cultures yielded Haemophilus ducreyi, and 2 (3.9%) were positive for Chlamydia trachomatis on immunofluorescence microscopy. Saline (1 mL) was injected and reaspirated from the buboes of 35 of the other 59 patients; 3 buboes yielded H. ducreyi and 9 were positive for C. trachomatis. All cultures for other aerobic and anaerobic bacteria and viruses in intact buboes were negative. Syphilis serology was positive in only one case. Patients attending STD clinics in this region who have large, fluctuant, edematous inguinal buboes containing pus should receive presumptive treatment for chancroid. If there is no pus, then the bubo is more likely to be caused by lymphogranuloma venereum.

Prognostic significance of quantitative bacteremia in septicemic melioidosis

Pour-plate blood cultures were performed for 418 adult patients with suspected septicemic melioidosis in order to determine the relationship between quantitative bacterial counts in blood and mortality. Of 108 patients whose hemocultures yielded Burkholderia pseudomallei, 53% had < 10 cfu/mL and 24% had > 100 cfu/mL. High blood bacterial counts were more common than reported previously with regard to other gram-negative septicemias and were significantly associated with the development of hypotension (P = .008) and a fatal outcome (P = .0001). The overall mortality was 63% (95% CI, 53%-72%); however, counts of < or = 1 cfu/mL were associated with a mortality of 42% (95% CI, 28%-58%), compared with 96% (95% CI, 80%-100%) with counts of > 100 cfu/mL. Heavy bacteremia (> 50 cfu/mL) is common in septicemic melioidosis and is usually fatal.

Postantibiotic effects and Burkholderia (Pseudomonas) pseudomallei: evaluation of current treatment

The postantibiotic effects (PAEs) OF 16 antibiotics or antibiotic combinations currently used against Burkholderia (Pseudomonas) pseudomallei were determined. The beta-lactams had zero PAEs, while the carbapenems and ciprofloxacin induced median PAEs of 1 and 5 h, respectively. These results emphasize the need to maintain antibiotic levels above inhibitory concentrations in blood throughout the dosing interval in cases of severe melioidosis.

Quantitative recovery of Burkholderia pseudomallei from soil in Thailand

Melioidosis is common in north-eastern Thailand, but is reported rarely from the adjacent areas of central Thailand, although rice farming is common to both regions. Quantitative soil cultures for Burkholderia pseudomallei were therefore prepared on 12 rice farms in both regions. B. pseudomallei was isolated from a similar proportion of rice fields in the central region (6/12) and in the north-east (7/12). Within the culture-positive sites, the number of B. pseudomallei colony-forming units (cfu) per mL of soil/water supernatant was significantly higher in the north-east (median 230 cfu/mL; range 1-17,000) than in the central region (median 10 cfu/mL; range 1-600). As bacterial counts in the soil are probably related to the risk of developing melioidosis, differences in exposure to B. pseudomallei probably contribute to the considerable differences in the incidence of this disease between these 2 adjacent regions.

Latex agglutination for rapid detection of Pseudomonas pseudomallei antigen in urine of patients with melioidosis

A latex agglutination test for the detection of Pseudomonas pseudomallei antigen in urine was evaluated for the rapid diagnosis of melioidosis. With unconcentrated urine, antigen was detected in only 18% of patients with melioidosis overall. However, when urine was concentrated 100-fold, antigen was detected in 47% overall and in 67% of patients with septicaemia or disseminated infection, in whom a rapid diagnosis is most important. The specificity of the test was 100%. These results compared favourably with an enzyme immunoassay. This latex agglutination test is a simple, rapid and highly specific method of diagnosing melioidosis, and will be particularly useful in areas with limited laboratory facilities.

Isolation of Pseudomonas pseudomallei from soil in north-eastern Thailand

In order to optimize the recovery from soil of Pseudomonas pseudomallei, the cause of melioidosis, 3 selective broths were compared. A basal salt solution containing L-threonine (TBSS) performed significantly better than trypticase soy broth containing crystal violet and colistin 50 mg/L (CVC50), both in isolation rate and suppression of overgrowth of other organisms, but the addition of colistin to TBSS gave the best results overall. In a survey in north-eastern Thailand, P. pseudomallei was recovered from 114 (68%) of the 167 sites tested. A detailed study of a single rice farm showed that the isolation rate increased with depth of soil sample, and P. pseudomallei could still be isolated during the dry season, although only from moist soil in areas where other crops were cultivated and around the water source.

Ceftazidime vs. amoxicillin/clavulanate in the treatment of severe melioidosis

An open, paired, randomized, controlled trial of high-dose parenteral ceftazidime (120 mg/[kg.d]) vs. amoxicillin/clavulanate (160 mg/[kg.d]) for the treatment of severe melioidosis was conducted in Ubon Ratchatani in northeastern Thailand. Of 379 patients enrolled in the study, 212 (56%) had culture-proven melioidosis; 106 patients were in each treatment group. The overall mortality rate (47%) was similar for both treatment groups. However, 4 of 75 surviving patients in the ceftazidime group compared with 16 of 69 surviving patients in the amoxicillin/clavulanate group were switched to the alternate regimen because of an unsatisfactory clinical response after > or = 72 hours of treatment (P = .004). The overall therapeutic failure rate (i.e., treatment failure or death due to uncontrolled melioidosis) was significantly higher for the amoxicillin/clavulanate group than for the ceftazidime group (P = .02). Clinical and bacteriologic responses for successfully treated patients were similar in both groups, and both treatments were well tolerated. Parenteral amoxicillin/clavulanate is a safe and effective initial treatment, but parenteral ceftazidime remains the treatment of choice for severe melioidosis.

Detection of Pseudomonas pseudomallei antigen in urine for the diagnosis of melioidosis

An enzyme-linked immunosorbent assay using a fluorescein isothiocyanate (FITC)-anti-FITC amplification system, has been developed to detect Pseudomonas pseudomallei antigen in urine. The assay was evaluated in 135 patients with acute melioidosis, 194 hospitalized patients with other disorders, and 40 healthy controls. Antigen was detected in the urine of 123 (91%) patients with melioidosis. Urinary antigen was found in 85 (96%) of 89 patients with septicemic melioidosis, all six patients with P. pseudomallei urinary tract infection, and 32 (80%) of 40 patients with other localized infections. Antigen was not detected in the urine of 40 healthy individuals, but the urine of 16 (8%) of 194 hospitalized patients with diagnoses other than melioidosis gave a positive result. Of the false-positive results, 13 of 16 were associated with bacteriuria > or = 10(4) colony-forming units/ml. At a cutoff titer of 1:10, the sensitivity and specificity of the test were 81% and 96%, respectively. Enzyme immunoassay detection of urinary antigen is a valuable and rapid laboratory test for the early diagnosis of acute melioidosis.

Immunofluorescence microscopy for the rapid diagnosis of melioidosis

A direct immunofluorescent antibody test (DIF) was developed for the rapid diagnosis of melioidosis, a potentially fatal infection caused by Pseudomonas pseudomallei. In a clinical evaluation of 369 sputum, pus, or urine specimens from 272 patients with suspected melioidosis, the DIF had a sensitivity of 73% and a specificity of 99% compared with culture. Using this DIF, a confident diagnosis of melioidosis can now be made within two hours of admission to hospital, compared with the delay of two to four days required for culture results. Consequent early institution of specific antimicrobial therapy may help to save lives.

Latex agglutination test for identification of Pseudomonas pseudomallei

A latex agglutination test was developed and evaluated for the rapid presumptive identification of Pseudomonas pseudomallei, the causative organism of melioidosis. The test was 100% sensitive for 52 isolates of Ps pseudomallei and 100% specific when tested with other medically important Pseudomonas species and Enterobacteriaceae. A subsequent field trial, with clinical specimens from patients with suspected melioidosis, confirmed the sensitivity and specificity of the test.

A national hospital-based survey of snakes responsible for bites in Thailand

Snakes which had been killed and brought to hospital with the patients they had bitten were collected in 80 district and provincial hospitals throughout 67 provinces in Thailand in order to establish the geographical distribution and relative medical importance of the venomous species. Of the 1631 snakes collected, 1145 were venomous: Malayan pit vipers (Calloselasma rhodostoma), green pit vipers (Trimeresurus albolabris) and Russell's vipers (Daboia russelii) were the most numerous, while T. albolabris, C. rhodostoma and spitting cobras ('Naja atra') were the most widely distributed. In 22 cases, non-venomous species were mistaken for venomous ones and antivenom was used unnecessarily. The Malayan krait (Bungarus candidus) was confused with B. fasciatus in 5 cases and B. fasciatus antivenom was used inappropriately. The study extended the known ranges of most of the medically-important venomous species in Thailand. Correct identification of venomous snakes is especially important in Thailand because the locally-produced antivenoms are monospecific. The technique of hospital-based collection, labelling and preservation of dead snakes brought by bitten patients is recommended when rapid assessment of a country's medically important herpetofauna is required.

Amoxycillin-clavulanic acid treatment of melioidosis

Melioidosis is a serious infection with high acute mortality, and a high rate of relapse despite protracted antimicrobial treatment. The current recommended conventional oral treatment regimen is a 4-drug combination of high-dose chloramphenicol, doxycycline and trimethoprim-sulphamethoxazole given for between 6 weeks and 6 months. We have evaluated prospectively the use of amoxycillin-clavulanic acid, to which Pseudomonas pseudomallei is consistently sensitive in vitro, for the oral maintenance treatment of melioidosis. Amoxycillin-clavulanic acid was used either as sole treatment of localized disease, or as maintenance therapy following either parenteral ceftazidime or the conventional 4-drug regime; 20 patients with localized infections and 26 with septicaemic melioidosis received a median of 7.5 (2-12) weeks treatment. After a mean follow-up period of 6 months (range 1-19), 31 patients (67%) remain free of disease. The drug was well tolerated. Three patients had fatal relapses, one other died suddenly at home, and another died from underlying promyelocytic leukaemia. The remaining 10 relapses were treated successfully. Resistance developed in one case. Amoxycillin-clavulanic acid is a safe alternative to the conventional 4-drug antimicrobial combination for the oral treatment of melioidosis. It may be of particular value in children, pregnant women, and in infections with Ps. pseudomallei resistant to the potentially toxic conventional regimen, but the optimum dose and duration of therapy need to be established.

The use of selective media for the isolation of Pseudomonas pseudomallei in clinical practice

Ashdown's selective-differential agar medium, with or without preenrichment in selective broth, was evaluated for the isolation of Pseudomonas pseudomallei from 1972 clinical specimens obtained from 643 subjects in Northeast Thailand; 226 patients proved to have meliodosis. The use of Ashdown's medium significantly increased the frequency of recovery of P. pseudomallei from sites or specimens with an extensive normal flora (throat, rectum, wounds and sputum) as compared to the recovery on blood and MacConkey agars (p less than 0.01). The isolation frequency from throat, rectal and wound swabs was further increased by the use of the broth pre-enrichment. The colonial morphology of P. pseudomallei on Ashdown's medium was sufficiently characteristic to allow presumptive identification. With the use of these selective media it was possible to culture P. pseudomallei from throat swabs taken from 87% of the patients from whom the organism could also be isolated from corresponding tracheal aspirates or sputum specimens. P. pseudomallei was isolated from rectal swabs taken from 51 patients, the first time that faecal excretion of the organism has been demonstrated in man. The diagnosis of melioidosis would not have been confirmed bacteriologically in eight patients (3.5%) without the use of the selective media. It is suggested that, in areas endemic for melioidosis, all sputum specimens should be cultured on selective media, such as Ashdown's. For the investigation of clinically suspected cases of melioidosis, and for follow-up during treatment of the disease, the use of broth pre-enrichment is recommended for specimens obtained from sites with an extensive normal flora.

Blood culture techniques for the diagnosis of melioidosis

The effects of variations in laboratory technique on the speed and sensitivity of isolation of Pseudomonas pseudomallei from blood were evaluated prospectively. Pseudomonas pseudomallei was isolated from 154 of 546 cultures from 325 patients with suspected or confirmed melioidosis. Subcultures after 12 to 24 and 36 to 48 hours of incubation were positive in 52.3% and 80.8% respectively. The yields from 20 ml (blood to broth ratio 1:4) and 50 ml (blood to broth ratio 1:10) brain heart infusion broth bottles were equivalent in patients not receiving treatment for melioidosis. During therapy, the 50 ml bottles grew Pseudomonas pseudomallei significantly faster than the 20 ml bottles (p less than 0.01), and gave a higher overall yield for cultures processed in antimicrobial removal devices (p less than 0.05). These devices themselves increased the speed of isolation of the organism from treated patients (p less than 0.01). In most cases, all bottles collected from a patient before treatment were positive, and a single 20 ml bottle had an estimated relative sensitivity of 85.7% (95% confidence interval 77.1-94.3%). Early subculture should be employed routinely for the laboratory diagnosis of septicaemic melioidosis. However, blood culture techniques do not need to be sophisticated. Culture of 5 ml blood in 20 ml broth is a simple and sensitive procedure suitable for regions where melioidosis is currently under-diagnosed.

The use of bone marrow culture for the diagnosis of melioidosis

We have evaluated prospectively the contribution of bone marrow culture to the diagnosis of melioidosis. Bone marrow (BMC) and blood cultures (BC) were collected concurrently from 105 patients with suspected acute, severe melioidosis. 67 patients were subsequently proved to have the disease whilst other significant organisms were isolated from these specimens in 5 cases. Overall, 67.2% of BC and 64.2% of BMC from melioidosis patients grew Pseudomonas pseudomallei. Time to positivity did not differ significantly in paired BC and BMC specimens. These results do not support the routine use of BMC in the diagnosis of acute, severe melioidosis. In one patient with pulmonary melioidosis, however, blood cultures were repeatedly negative, whilst bone marrow grew P. pseudomallei, and this preceded the development of a distant focus of infection. This suggests that culture of bone-marrow may be of value in certain blood culture-negative patients with melioidosis.