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Trimethoprim/sulfamethoxazole resistance in clinical isolates of Burkholderia pseudomallei from Thailand.

Saiprom N, Amornchai P, Wuthiekanun V, Day NP, Limmathurotsakul D, Peacock SJ, Chantratita N - Int. J. Antimicrob. Agents (2015)

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.

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Subsequent studies have reported much lower rates of SXT resistance for isolates from Laos (0.8%), Australia (0.4%) and Cambodia (0%)... Here we report the results of a re-evaluation of SXT resistance in Thailand... Second-line oral treatment in patients infected with SXT-resistant B. pseudomallei or in whom SXT is contraindicated is amoxicillin/clavulanic acid (AMC), thus we also evaluated the susceptibility of SXT-resistant isolates to AMC and doxycycline (DOX), which is used less frequently as an alternative to SXT... Interpretative standards for the Etest were based on Clinical and Laboratory Standards Institute (CLSI) guidelines for broth microdilution, which classifies SXT MICs of ≤2/38 mg/L as susceptible and ≥4/76 mg/L as resistant... Susceptibility testing to AMC and DOX was also performed using the Etest, in which the MIC was read at the point of no visible growth... Escherichia coli ATCC 35218 was used as a control for AMC, and E. coli ATCC 25922 was used as a control for TMP, SMX and DOX... The Etest SXT MIC ranged from 0.016 mg/L to ≥32 mg/L [MIC50 (concentration that inhibits 50% of bacterial isolates) = 0.19 mg/L and MIC90 (concentration that inhibits 90% of bacterial isolates) = 0.75 mg/L; interquartile range 0.094–0.25 mg/L] (Fig. 1)... This demonstrated complete concordance of results between broth dilution and Etest performed in this study, confirming that the previous study had overestimated resistance... The most likely explanation for the erroneous results in the original study is error in reading the 80% inhibition point... This is inherently subjective and a minor difference in the interpretation of MIC results that are close to the breakpoint can lead to false classification as resistance... Inhibition zones frequently have diffuse edges, and reading against a black background aided technical observation in this study... Our finding that 99.7% of clinical B. pseudomallei isolates were susceptible to SXT is comparable with rates reported from Laos (99.2%), Australia (99.6%) and Cambodia (100%), which indicate that primary SXT resistance in B. pseudomallei is uncommon... Our study also confirmed that SXT-resistant B. pseudomallei were susceptible to AMC, the current second-line drug of choice.

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Trimethoprim/sulfamethoxazole minimum inhibitory concentrations (MICs) for Burkholderia pseudomallei from 3038 patients with primary melioidosis presenting to a hospital in northeast Thailand between 2004 and 2012. MICs were determined using the Etest. The numbers above each column represent the number of isolates with the corresponding MIC. The table shows the total and annual number of B. pseudomallei isolates tested, the MIC50 (concentration that inhibits 50% of bacterial isolates) and the percentage resistant.
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fig0005: Trimethoprim/sulfamethoxazole minimum inhibitory concentrations (MICs) for Burkholderia pseudomallei from 3038 patients with primary melioidosis presenting to a hospital in northeast Thailand between 2004 and 2012. MICs were determined using the Etest. The numbers above each column represent the number of isolates with the corresponding MIC. The table shows the total and annual number of B. pseudomallei isolates tested, the MIC50 (concentration that inhibits 50% of bacterial isolates) and the percentage resistant.

Mentions: Two isolate collections were evaluated. The first was drawn from a retrospective study of 3270 patients with culture-proven melioidosis at Sappasithiprasong Hospital in northeast Thailand between 2004 and 2012. A single isolate was used per patient (the first positive culture). All isolates had been stored at −80 °C and subculture recovered isolates from 3038 patients. The Etest SXT MIC ranged from 0.016 mg/L to ≥32 mg/L [MIC50 (concentration that inhibits 50% of bacterial isolates) = 0.19 mg/L and MIC90 (concentration that inhibits 90% of bacterial isolates) = 0.75 mg/L; interquartile range 0.094–0.25 mg/L] (Fig. 1). Ten isolates (0.33%) were resistant to SXT, with an annual resistance rate ranging from 0% to 0.7%. As this is considerably lower than that reported by us previously for B. pseudomallei isolated from patients presenting to the same hospital between 1992 and 2003 [3], we re-evaluated this original collection. Previously, 258/1976 isolates were assigned as SXT-resistant based on the Etest [3], of which 255 could be recovered from frozen stocks. Etest could only confirm SXT resistance in 13 (5.1%) of these 255 isolates (Supplementary Table S1). The 23 SXT-resistant isolates from both collections were resistant to TMP and SMX when tested as separate agents (Supplementary Table S1). All SXT-resistant isolates were susceptible to AMC, but only 21 isolates (91%) were susceptible to DOX.


Trimethoprim/sulfamethoxazole resistance in clinical isolates of Burkholderia pseudomallei from Thailand.

Saiprom N, Amornchai P, Wuthiekanun V, Day NP, Limmathurotsakul D, Peacock SJ, Chantratita N - Int. J. Antimicrob. Agents (2015)

Trimethoprim/sulfamethoxazole minimum inhibitory concentrations (MICs) for Burkholderia pseudomallei from 3038 patients with primary melioidosis presenting to a hospital in northeast Thailand between 2004 and 2012. MICs were determined using the Etest. The numbers above each column represent the number of isolates with the corresponding MIC. The table shows the total and annual number of B. pseudomallei isolates tested, the MIC50 (concentration that inhibits 50% of bacterial isolates) and the percentage resistant.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4537509&req=5

fig0005: Trimethoprim/sulfamethoxazole minimum inhibitory concentrations (MICs) for Burkholderia pseudomallei from 3038 patients with primary melioidosis presenting to a hospital in northeast Thailand between 2004 and 2012. MICs were determined using the Etest. The numbers above each column represent the number of isolates with the corresponding MIC. The table shows the total and annual number of B. pseudomallei isolates tested, the MIC50 (concentration that inhibits 50% of bacterial isolates) and the percentage resistant.
Mentions: Two isolate collections were evaluated. The first was drawn from a retrospective study of 3270 patients with culture-proven melioidosis at Sappasithiprasong Hospital in northeast Thailand between 2004 and 2012. A single isolate was used per patient (the first positive culture). All isolates had been stored at −80 °C and subculture recovered isolates from 3038 patients. The Etest SXT MIC ranged from 0.016 mg/L to ≥32 mg/L [MIC50 (concentration that inhibits 50% of bacterial isolates) = 0.19 mg/L and MIC90 (concentration that inhibits 90% of bacterial isolates) = 0.75 mg/L; interquartile range 0.094–0.25 mg/L] (Fig. 1). Ten isolates (0.33%) were resistant to SXT, with an annual resistance rate ranging from 0% to 0.7%. As this is considerably lower than that reported by us previously for B. pseudomallei isolated from patients presenting to the same hospital between 1992 and 2003 [3], we re-evaluated this original collection. Previously, 258/1976 isolates were assigned as SXT-resistant based on the Etest [3], of which 255 could be recovered from frozen stocks. Etest could only confirm SXT resistance in 13 (5.1%) of these 255 isolates (Supplementary Table S1). The 23 SXT-resistant isolates from both collections were resistant to TMP and SMX when tested as separate agents (Supplementary Table S1). All SXT-resistant isolates were susceptible to AMC, but only 21 isolates (91%) were susceptible to DOX.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

Subsequent studies have reported much lower rates of SXT resistance for isolates from Laos (0.8%), Australia (0.4%) and Cambodia (0%)... Here we report the results of a re-evaluation of SXT resistance in Thailand... Second-line oral treatment in patients infected with SXT-resistant B. pseudomallei or in whom SXT is contraindicated is amoxicillin/clavulanic acid (AMC), thus we also evaluated the susceptibility of SXT-resistant isolates to AMC and doxycycline (DOX), which is used less frequently as an alternative to SXT... Interpretative standards for the Etest were based on Clinical and Laboratory Standards Institute (CLSI) guidelines for broth microdilution, which classifies SXT MICs of ≤2/38 mg/L as susceptible and ≥4/76 mg/L as resistant... Susceptibility testing to AMC and DOX was also performed using the Etest, in which the MIC was read at the point of no visible growth... Escherichia coli ATCC 35218 was used as a control for AMC, and E. coli ATCC 25922 was used as a control for TMP, SMX and DOX... The Etest SXT MIC ranged from 0.016 mg/L to ≥32 mg/L [MIC50 (concentration that inhibits 50% of bacterial isolates) = 0.19 mg/L and MIC90 (concentration that inhibits 90% of bacterial isolates) = 0.75 mg/L; interquartile range 0.094–0.25 mg/L] (Fig. 1)... This demonstrated complete concordance of results between broth dilution and Etest performed in this study, confirming that the previous study had overestimated resistance... The most likely explanation for the erroneous results in the original study is error in reading the 80% inhibition point... This is inherently subjective and a minor difference in the interpretation of MIC results that are close to the breakpoint can lead to false classification as resistance... Inhibition zones frequently have diffuse edges, and reading against a black background aided technical observation in this study... Our finding that 99.7% of clinical B. pseudomallei isolates were susceptible to SXT is comparable with rates reported from Laos (99.2%), Australia (99.6%) and Cambodia (100%), which indicate that primary SXT resistance in B. pseudomallei is uncommon... Our study also confirmed that SXT-resistant B. pseudomallei were susceptible to AMC, the current second-line drug of choice.

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Related in: MedlinePlus