Comparative Evaluation of Quantitative Polymerase Chain Reaction Methods for Routine Enumeration of Specific Bacterial DNA in Aquatic Samples

Quantification of Vibrio species in oysters from the Gulf of Mexico with two procedures based on MPN and PCR

Oysters can accumulate potentially pathogenic water bacteria. The objective of this study was to compare two procedures to quantify Vibrio species present in oysters to determine the most sensitive method. We analyzed oyster samples from the Gulf of Mexico, commercialized in Mexico City. The samples were inoculated in tubes with alkaline peptone water (APW), based on three tubes and four dilutions (10^-1 to 10^-4). From these tubes, the first quantification of Vibrio species was performed (most probable number (MPN) from tubes) and bacteria were inoculated by streaking on thiosulfate-citrate-bile salts-sucrose (TCBS) petri dishes. Colonies were isolated for a second quantification (MPN from dishes). Polymerase chain reaction (PCR) was used to determine species with specific primers: ompW for Vibrio cholerae, tlh for Vibrio parahaemolyticus, and VvhA for Vibrio vulnificus. Simultaneously, the sanitary quality of oysters was determined. The quantification of V. parahaemolyticus was significantly higher in APW tubes than in TCBS dishes. Regarding V. vulnificus counts, the differences among both approaches were not significant. In contrast, the MPNs of V. cholerae obtained from dishes were higher than from tubes. The quantification of MPNs through PCR of V. parahaemolyticus and V. vulnificus obtained from APW was sensitive and recommendable for the detection of both species. In contrast, to quantify V. cholerae, it was necessary to isolate colonies on TCBS prior PCR. Culturing in APW at 42 °C could be an alternative to avoid colony isolation. The MPNs of V. cholerae from dishes was associated with the bad sanitary quality of the samples.

Quantification of anammox populations enriched in an immobilized microbial consortium with low levels of ammonium nitrogen and at low temperature

Anaerobic ammonium oxidizing (anammox) bacteria present in microbial communities in two laboratory-scale upflow anoxic reactors supplied with small amounts of ammonium (<3 mg/l) at low temperature were detected and quantified. The reactors, operated at 20 degrees C, were seeded with an immobilized microbial consortium (IMC) and anaerobic granules (AG) from an upflow anaerobic sludge blanket (UASB) treating brewery wastewater. Our results showed that complete ammonium and nitrite removal with greater than 92% total nitrogen removal efficiency was achieved in the reactor inoculated with both the IMC and AG, while that of the reactor inoculated with only the IMC was lower than 40%; enrichment was successful after the addition of AG. Quantitative fluorescence in situ hybridization (FISH) analysis confirmed that anammox bacteria were present only in the reactor inoculated with an IMC and AG. The copy number of the 16S-rRNA gene of the anammox bacteria calculated by most probable number-polymerase chain reaction (MPN-PCR) from the total DNA extracted from both reactors (2.5 x 10(4) copies/mug of DNA) was two orders lower than that of the domain bacteria (2.5 x 10(6) copies/mug of DNA). The results revealed that immobilized multiple seed sludges were optimal for anammox enrichment at low temperature and ammonium concentrations.