Abstract
BackgroundBurkholderia mallei is a Gram-negative bacterium that causes glanders, a zoonotic disease, especially in equine populations (e.g. horses, donkeys, and mules). B. mallei usually grows slowly on most culture media, and this property makes it difficult to isolate from clinical specimens. One of the problems is that B. mallei is easily overgrown by other bacteria, especially in animal specimens collected from non-sterile sites. The aim of this study was to develop a new selective agar for the laboratory diagnosis of glanders. We formulated a new agar, named BM agar, to enrich B. mallei growth, but inhibit the growth of other bacteria and fungi based on their antimicrobial profiles. We compared the growth of B. mallei on BM with Xie’s and PC agars, the two previously described selective agars for B. mallei.ResultsBM agar could sufficiently grow almost all of the tested B. mallei strains within 72 h: only one out of the 38 strains grew scantly after 72 h of incubation. BM agar was further tested with other Burkholderia species and various bacterial species commonly found in the nasal cavities and on the skin of horses. We have found that other Burkholderia species including B. pseudomallei and B. thailandensis can grow on BM agar, but non-Burkholderia species cannot. Furthermore, the specificities of the three selective agars were tested with or without spiking B. mallei culture into clinical specimens of non-sterile sites collected from healthy horses. The results showed that BM agar inhibited growths of fungi and other bacterial species better than PC and Xie’s agars. We have also found that growth of B. mallei on BM agar was equivalent to that on 5% horse blood agar and was significantly greater than those on the other two agars (P < 0.05).ConclusionsWe believe that BM agar can be used to efficiently isolate B. mallei from mixed samples such as those typically collected from horses and other contaminated environments.
Highlights
Burkholderia mallei is a Gram-negative bacterium that causes glanders, a zoonotic disease, especially in equine populations
All strains of B. pseudomallei, B. thailandensis, and Burkholderia cepacia complex (Bcc) grew on BM agar within 24 h, whereas growths of all 24 non-Burkholderia species were completely inhibited during the 72 h incubation period
The following bacterial species were identified on the different agars: Xie’s agar, Chryseobacterium gleum, Bacillus cereus, Arthrobacter histidinolovorans, Paenibacillus species, Bacillus species, Enterobacter cloacae, Rhizobium radiobacter, Staphylococcus saprophyticus, Enterococcus casseliflavus, Pantoea ananatis, Pantoea agglomerans, Staphylococcus species, Staphylococcus haemolyticus, Sphingomonas species, Rhizobium species, and Escherichia coli; Pseudomonas cepacia agar (PC agar), Fig. 1 Representative growth of B. mallei Gifu Type Culture Collection (GTC) 3P0003T (a) plate view and (b) colony view, on BM agar after 72 h incubation at 37 °C
Summary
Burkholderia mallei is a Gram-negative bacterium that causes glanders, a zoonotic disease, especially in equine populations (e.g. horses, donkeys, and mules). B. mallei usually grows slowly on most culture media, and this property makes it difficult to isolate from clinical specimens. B. mallei can be grown on most enriched media, including sheep blood agar and trypticase soy agar, but grows very slowly, requiring up to 72 h of incubation [3]. This property makes it difficult to isolate B. mallei from clinical and environmental specimens because B. mallei is overgrown by other bacteria, especially in animal specimens collected from non-sterile sites [4, 5]. B. mallei is often overgrown by other bacteria even in fresh samples obtained under sterile conditions [8]
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