Media Evaluation and Behavior of Clostridium Perfringens as an Adjunct Indicator of Quality in Shellfish Growing Areas

In numerous studies of estuaries of the West Coast of the United States, we have recovered C.perfringens, total and fecal coliforms, and fecal streptococci from shellfish, sediments and water. In some areas closed to shellfish harvest and known to be subject to fecal contamination, C.perfrinqens were recovered regularly from shellfish and sediments. For example, in one estuary, prior to sampling, a local sewage treatment plant (STP) with a design capacity of 1 million gallons per day (MGD) was receiving high flows of raw sewage of 3.02 MGD. This resulted in an overflow or bypass of raw sewage into the estuary. Fecal coliform and fecal streptococci levels measured in impacted oysters showed an increase during the initial stages of the bypass and decreased to baseline levels by the 5th day of sampling. C.perfringens levels increased from 36 MPN/100 g and reached maximum levels in oysters (4600 MPN/100 g) on the 6th day when the sewage flow was returning to normal, but still over capacity (1.8 MGD) and sewage was being discharged into the bay. At this time, fecal coliforms and fecal streptococci counts were near baseline levels (120 and 50 organisms/100 g respectively). Therefore, at the later stages of the sewage bypass, C.perfrinqens was a useful indicator of fecal contamination in oysters. The most recent and promising method for the enumeration of C.perfrinqens in all types of environmental samples is the Iron Milk Method (IMM). The method has been tested with water, marine and freshwater sediments, soil, fish gut contents and foods, and has been shown to enumerate C.perfrinqens without the need for confirmation. The IMM uses a 3 tube MPN procedure with each tube containing 10 ml of homogenized milk plus 0.2 g iron powder per tube. Inoculated tubes are incubated for 16-18 hrs at 45 °C. The presence of the classical stormy fermentation signifies a positive tube. Numbers of C.perfrinqens in samples are rapidly measured.