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Objective: To compare biofilm formation in trimethoprim/sulfamethoxazole (SXT)- susceptible Escherichia coli (E. coli) (SSEC) and SXT-resistant E. coli (SREC) isolated from patients with urinary tract infections, and study the motile ability and physical characteristics of the isolates. Methods: A total of 74 E. coli isolates were tested for antimicrobial susceptibility with the disc diffusion assay. Based on the SXT-susceptibility test, the E. coli isolates were divided into SSEC (N = 30) and SREC(N = 44) groups. All E. coli isolates were examined for motile ability by using a motility test medium, and for checking biofilm formation a scanning electronmicroscope was used. Bacterial colony size was measured with a vernier caliper and bacterial cell length was measured under a light microscope. The bacterial growth rate was studied by plotting the cell growth (absorbance) versus the incubation time. Results: The frequencies of non-motility and biofilm formation in the SREC group were significantly higher than that in the SSEC group (P < 0.01). The SREC bacterial cell length was shorter than that in the SSEC group [(1.35 ± 0.05) vs. (1.53 ± 0.05) mm, P < 0.05)], whereas the bacterial colony size and mid-log phase of the growth curve were not significantly different. Conclusions: The present study indicated that biofilm formation and phenotypic change of uropathogenic E. coli can be attributed to the mechanism of E. coli SXT resistance.
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Haemophilus influenzae is a part of normal upper respiratory flora of human, which can cause a wide variety of infections. Other members of genus Haemophilus rarely cause human infection but are frequently isolated from clinical specimens, such as sputum. The pathogenicity between H. influenzae and other Haemophilus species is different therefore a reliable method for identification of H. influenzae is essential. The aim of this study was to compare the identification methods for Haemophilus by four phenotypic tests with that by a PCR-based method. A total of 101 Haemophilus isolates were identified by biochemical tests and the XV requirement test by using XV paper strip technique, porphyrin test and Staphylococcus streak technique. The PCR-based method was performed using specific primers for 16SrDNA, p6 genes of H. influenzae and sodA gene of H. parainfluenzae. Using the XV paper strip technique, porphyrin test and biochemical tests, 88 and 13 isolates were identified as H. influenzae and H. parainfluenzae respectively, whereas 54 H. influenzae and 47 H. parainfluenzae were identified by using Staphylococcus streak technique (66.4 % agreement with that of the three tests). The PCR-based method revealed that 83 H. influenzae and 12 H. parainfluenzae were identified, whereas 6 isolates could not be categorized into both species. This study showed that identification of Haemophilus by the XV paper strip technique, porphyrin test and biochemical test gave 93.1 % agreement with that of the PCR method, whereas the Staphylococcus streak technique gave only 71.3 % agreement.
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ABSTRACT
Carbapenem resistance mediated by acquired carbapenemase genes has been increasingly reported in Pseudomonas aeruginosa. Class B carbapenemases or metallo-b-lactamases (MBLs) are the most clinical concern. Currently, there is no recommendation available from the Clinical Laboratory Standards Institute (CLSI) for MBL detection. In this study, we attempted to evaluate the performance for phenotypic detection of MBLs in imipenem-nonsusceptible clinical isolates of P. aeruginosa from Srinagarind Hospital. Five MBL-positive control strains, each producing IMP-1, IMP-4, IMP-9, VIM-1, or VIM-2 enzyme, and 74 clinical isolates of P. aeruginosa were screened for the presence of MBLs by combined-disk test (CDT) and double-disk synergy test (DDST) on a single agar plate using imipenem (10 µg IPM) and meropenem (10 µg MEM) disks as substrates and 292 µg of EDTA as an MBL inhibitor. Multiplex PCR for detection of MBL genes was used as a gold standard. Genotypic confirmation revealed that 9 of the 74 clinical isolates (12.2%) carried MBL genes, blaVIM (6 isolates) and blaIMP (3 isolates). Comparison of the MBL phenotypic tests to the multiplex PCR revealed that the CDT using IPM+EDTA/IPM correctly differentiated all MBL-producing isolates (sensitivity of 100%) but gave three false-positive isolates (specificity of 95.4%), whereas that with MEM+EDTA/MEM showed sensitivity and specificity of 92.9% and 92.3% respectively. In addition, the DDST using either IPM or MEM with EDTA gave the same result for all isolates with sensitivity and specificity of 92.9% and 96.9% respectively. These methods are simple and accurate for detection of MBLs in imipenem-nonsusceptible P. aeruginosa isolates from this hospital. Early detection of MBL producers and strict infection control will contribute to prevent further spread of these resistant strains.
ABSTRACT
The performance of the electronic-filter air purifier that uses the principle of electrostatic field on airborne fungi(Aspergillus niger and Penicillium citrinum) and bacteria (Staphylococcus epidermidis and Bacillus subtilis)removals was tested in this study. The experiment was conducted in the 8-m3 chamber by injecting each type ofmicroorganism and sampling the bioaerosol at two height levels, 0.5 and 1.5 m. Since the air purifier was locatedat the floor with the height of 0.67 m, the microbe concentrations at these two height levels were observed for anydifference in its performance. However, the main objective was to compare the microbe concentrations whenturning on the air purifier and turning off for duration of 4 hours. The results were that the air purifier could removethe microbes from the initial concentrations of 34,000 - 80,000 cfu/m3 to comply with the recommended concentrationof 500 cfu/m3 within 30-40 min except for B. subtilis that needed longer time. The height level did not affectthe performance of the air purifier in this study at the level of confidence of 99 %.