Effect of Stress and Resuscitation on Recovery of Indicator Bacteria from Foods Using Hydrophobic Grid-Membrane Filtration

Comparative evaluation of two methods of enumerating enterococci in foods: collaborative study

Two methods of enumerating enterococci in foods were compared in a collaborative study. Thirteen laboratories tested four blind duplicate samples containing different levels of enterococci and two negative control samples. Freeze-dried mixtures of bacteria were used as simulated food samples. The freeze-dried samples were reconstituted and either spread directly on the surface of Slanetz and Bartley medium (SB) and incubated at 44 degrees C for 48 h or preincubated in tryptone soya agar at 37 degrees C for 2 h before being overlaid by SB and incubated at 37 degrees C for a further 46 h. The numbers CFU of enterococci recovered by the two methods were not significantly different except for one sample where the 37 degrees C method gave a somewhat higher recovery. The 44 degrees C method was less time-consuming and less laborious.

The effect of resuscitation and the incubation-temperature on recovery of uninjured, heat injured and freeze injured enterococci

Five strains of enterococci were inoculated on the Slanetz and Bartley enterococcus agar (EA), and incubated at 37 degrees C and 44 degrees C following: no injury, heat-injury and freeze-injury. The experiments were repeated introducing a 2 h resuscitation step in Tryptic Soy Agar (TSA) at 37 degrees C and subsequent overlay with EA (TSA/EA) followed by incubation at both 37 degrees C and 44 degrees C. The TSA/EA method gave a significantly better recovery (1% confidence level) than the EA method at both 37 degrees C and 44 degrees C. The effect of incubation-temperature was only significant for two strains of Enterococcus durans, as one strain showed no growth at 44 degrees C and the other strain was recovered significantly (5% confidence level) better at 37 degrees C that at 44 degrees C when employing the EA method. Interpretation of the results using TSA/EA method was easier than that of the EA. Different lactic streptococci and lactobacilli commonly employed in the dairy industry did not develop false positive colonies in TSA/EA incubated at 37 degrees C.

Survival and transport of bacteria in egg washwater

An evaluation of methods for monitoring the quality of water used to wash eggs at grading stations was undertaken to improve maintenance of bacterial viability during overnight sample transport. Bacterial content of samples at analysis would then better reflect conditions at the time eggs were washed. The interactive effects of temperature and the highly alkaline water conditions upon viability were the subjects of this study. Nine transport methods were examined for their efficacy in recovering total and coliform bacteria from recycled water used to wash eggs, and these were compared with samples analyzed at two commercial egg grading stations. Samples were shipped under test to the laboratory for analysis the following day. The survival of Staphylococcus aureus and Escherichia coli was also examined, but in a synthetic washwater matrix under various combinations of temperature (6 to 32 degrees C) and pH (9.5 to 10.5) to determine whether there was likely to be a different response to variations in transport treatment among gram-positive and -negative bacteria. S. aureus was much more resistant to the lethal effects of high pH and moderate temperature than E. coli. These results indicated that samples of high pH should be held (transported) at less than or equal to 13 degrees C to optimize bacterial survival. Considering cost, ease of manipulation, and the ability to protect both coliforms and the bacterial population as a whole, the method of choice for transport of industrial samples was the direct addition of washwater to containers in which powdered KH2PO4 and Na2S2O3 had been placed to yield final concentrations, when dissolved, of 0.2 and 0.05% (wt/vol), respectively.