Molecular vs culture methods for the detection of bacterial faecal indicators in groundwater for human use.
OBJECTIVE
The current standard culture methods are unable to detect nongrowing bacteria and, thus, might not be sufficient for precise monitoring of the microbiological quality of waters. The use of a molecular method such as PCR could be a valid alternative to detect bacterial faecal contamination indicators such as Escherichia coli and Enterococcus faecalis and reveal the presence of culturable and nonculturable bacterial forms.


RESULTS
The presence of E. coli and Ent. faecalis cells in 30 groundwater samples was evaluated with the standard culture method and compared with a specific PCR protocol. A substantial percentage (50%) of the samples not containing culturable cells proved positive in the search for Ent. faecalis DNA by PCR. Quantification by competitive PCR (cPCR) of the DNA detected allowed us to calculate the number of nonculturable cells present in water samples: the number varied from 2 to 120 cells ml(-1). Only four samples were positive for E. coli DNA and the corresponding nonculturable cells varied from 24 to 70 ml(-1).


CONCLUSIONS
This study demonstrates that the standard culture methods in use are unable to detect a substantial proportion of the bacterial population which is nonculturable but, as previously demonstrated, potentially still viable and able to express those pathogenic factors needed for causing infections in humans.


CONCLUSIONS
To protect human health it is necessary to develop and use methods which detect the nonculturable as well as culturable bacteria present in water.
Lleo
M M
MM
Dipartimento di Patologia, Sezione di Microbiologia, Università di Verona, Verona, Italy. mlleo@univr.it
Bonato
B
B
Tafi
M C
MC
Signoretto
C
C
Pruzzo
C
C
Canepari
P
P
D001431:Bacteriological Techniques; D015169:Colony Count, Microbial; D004269:DNA, Bacterial / Q000032:analysis; D013293:Enterococcus faecalis / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D005618:Fresh Water / Q000382:microbiology*; D015336:Molecular Probe Techniques; D016133:Polymerase Chain Reaction; D014871:Water Microbiology
D004269:DNA, Bacterial