Transport Medium Evaluated for Gut Bacterium

An alternative transport medium supplemented with a cyanobacterial extract (CE) has been evaluated for the preservation and viability of Helicobacter pylori strains.

The transport medium was free of animal derivatives, and was compared with other media during long-term transportation and the recovery of H. pylori from biopsy samples.

Microbiologists at the Universidad Nacional de San Luis (Argentina), collected four gastric antral biopsy specimens from 134 patients with gastroduodenal disease and were positive H. pylori infection. The transport media were based on an agar soft medium prepared with Mueller–Hinton broth 0.3% agar (MH) and 0.3% of CE (MH-CE). MH 5% fetal calf serum (FCS) was used as the reference medium (MH-FCS). Two gastric biopsy samples were placed into MH-CE or MH-FCS transport media and stored at 4 °C and at room temperature. Another biopsy sample was used for the urease test and polymerase chain reaction (PCR) identification. The remainder of the biopsy specimen was Gram stained. The diagnosis of H. pylori infection was established when two of three diagnostic methods, urease test, Gram or culture) were positive, followed by confirmation with PCR.

The recovery rate of H. pylori at 4 °C was similar among MH-CE and MH-FCS transport media between 24 to 72 hours, whereas a higher recovery was obtained with MH-CE after 96 and 120 hours. Only MH-CE allowed recovery after 120 hours. The H. pylori recovery at room temperature after 96 hour was higher in MH-CE than in MH-FCS. Similar survival rates were observed in biopsy samples conserved in MH-CE and MH-FCS at 4 °C. The recovery after 48 hours at room temperature in MH-CE was higher than MH-FCS and was the only medium allowing recovery after 72 hours. The viability of H. pylori strains stored within agar plugs in transport media and from biopsy specimens was assessed by viable count determinations (colony-forming units) on Mueller–Hinton agar supplemented with 7% horse blood (MHA-B) and direct fluorescence microscopy with the LIVE/DEAD BacLight Bacterial Viability Kit (Invitrogen Corporation, Eugene, OR, USA).

The authors concluded that MH-CE could be used as a transport medium to minimize the loss of bacterial viability when immediate culture or cool shipping is not possible. The transport medium proposed is simple to handle, inexpensive and complies with the present tendency of avoiding the use of animal derivatives. The study was published in the February 2012 edition of the European Journal of Clinical Microbiology and Infectious Diseases.

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Universidad Nacional de San Luis
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