Abstract
Background Burkholderia pseudomallei (Bps) is a Gram-negative bacterium that causes frequently lethal melioidosis, with a particularly high prevalence in the north and northeast of Thailand. Bps is highly resistant to many antimicrobial agents and this resistance may result from the low drug permeability of outer membrane proteins, known as porins.Principal FindingsMicrobiological assays showed that the clinical Bps strain was resistant to most antimicrobial agents and sensitive only to ceftazidime and meropenem. An E. coli strain defective in most porins, but expressing BpsOmp38, exhibited considerably lower antimicrobial susceptibility than the control strain. In addition, mutation of Tyr119, the most prominent pore-lining residue in BpsOmp38, markedly altered membrane permeability, substitution with Ala (mutant BpsOmp38Y119A) enhanced uptake of the antimicrobial agents, while substitution with Phe (mutant BpsOmp38Y119F) inhibited uptake. Channel recordings of BpsOmp38 reconstituted in a planar black lipid membrane (BLM) suggested that the higher permeability of BpsOmp38Y119A was caused by widening of the pore interior through removal of the bulky side chain. In contrast, the lower permeability of BpsOmp38Y119F was caused by introduction of the hydrophobic side chain (Phe), increasing the ‘greasiness’ of the pore lumen. Significantly, liposome swelling assays showed no permeation through the BpsOmp38 channel by antimicrobial agents to which Bps is resistant (cefoxitin, cefepime, and doripenem). In contrast, high permeability to ceftazidime and meropenem was observed, these being agents to which Bps is sensitive.Conclusion/SignificanceOur results, from both in vivo and in vitro studies, demonstrate that membrane permeability associated with BpsOmp38 expression correlates well with the antimicrobial susceptibility of the virulent bacterium B. pseudomallei, especially to carbapenems and cephalosporins. In addition, substitution of the residue Tyr119 affects the permeability of the BpsOmp38 channel to neutral sugars and antimicrobial agents.
Highlights
Burkholderia pseudomallei (Bps) is a Gram-negative bacterium that causes melioidosis, a highly infectious disease that is endemic to areas that include south and southeast Asia and northern Australia [1,2,3,4]
When compared with the most recently updated breakpoints recommended for pseudomonas spp. by EUCAST (Table 1), most antimicrobial agents tested against Bps had MIC values higher than the breakpoint values for resistance
Ceftazidime and meropenem are the only two antibiotics with MIC values lower than the breakpoint values, indicting that this Bps strain is sensitive to these two antibiotics
Summary
Burkholderia pseudomallei (Bps) is a Gram-negative bacterium that causes melioidosis, a highly infectious disease that is endemic to areas that include south and southeast Asia and northern Australia [1,2,3,4]. Patients infected with Bps usually develop skin ulcers, visceral abscesses, pneumonia and septicaemia and require urgent antimicrobial treatment to avoid fatal progression of the disease [7,8]. This is difficult, since Bps is highly resistant to most classes of antimicrobial agent. A combination of cefoperazone and sulbactam may be administered, but the survival rate is relatively low at 60%, though a combination of ceftazidime and cotrimoxazole may help to increase this to 70–75% [9,10,11,12] If these drugs are unavailable, amoxicillin-clavulanate (co-amoxiclav) may be used, but is often ineffective [13]. Bps is highly resistant to many antimicrobial agents and this resistance may result from the low drug permeability of outer membrane proteins, known as porins
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
