Other Pathogens of Concern

Salmonella, E. coli, and shigella can survive but are unable to grow at temperatures lower than 4°C; however, growth can resume if temperature abuse occurs. At higher refrigeration temperatures, growth may be possible, and atmospheres used in MAP will differently influence growth parameters of these pathogens. Amanatidou and others [12] found that 8°C and 10 to 20% CO2 in N2 reduced the growth rate of Salmonella enteritidis but had no effect on the growth rate of S. typhimurium or E. coli. Combined atmospheres of high O2 and CO2 increased X and decreased ^ax and Nmax for S. enteritidis and E. coli, but had no effect on S. typhimurium. High O2 alone reduced ^ax or Nmax for S. typhimurium and S. enteritidis, but had little effect on E. coli. Another study found that Shigella sonnei and S. flexneri growth was not affected by atmospheres of 3% O2 and 5 to 10% CO2 at 7 and 12°C. Growth and survival was predominantly affected by the type of vegetable tested (grated carrot, chopped bell pepper, mixed lettuce) [47] as well as by temperature. Francis and O'Beirne [49] determined that survival and growth of E. coli O157:H7 under MAP was dependent upon type of vegetable (swedes, lettuce, soybean sprouts, dry coleslaw mix), temperature, atmosphere, and strain; the pathogen grew better under atmospheres of 30% CO2 and 5% O2 compared to air, and 9 to 12% CO2 and 2 to 4% O2 were not inhibitory at 8°C. Reduction of storage temperatures from 8 to 4° C prevented growth and reduced survival of E. coli. Others [58] have shown that E. coli O157:H7 can survive on fresh-cut apples under >15% CO2 at abusive temperatures (15 and 20°C). These studies emphasize the important effect of temperature in maintaining MAP produce safety.

Campylobacter jejuni requires 5% O2, 10% CO2, and 85% N2 for optimal growth, atmospheres that may commonly occur in MAP systems. Even under refrigeration temperatures, MAP atmospheres may create conditions more hospitable to the survival of this pathogen than under air; populations of C. jejuni on cilantro, green pepper, and romaine lettuce packaged under MAP for 15 days at 4°C were reported to be reduced by 2 log10 CFU/g by day 9 while a much greater reduction of 3 to 4 log10 CFU/g occurred under air and vacuum storage [15]. Campylobacter spp. have a low infective dose (100 to 500 CFU); while they do not typically grow below 30°C, they can survive. Thus, if the pathogen was initially present on the commodity upon packaging, only short intervals of temperature abuse in a typical MAP atmosphere might be needed to allow enough growth of the pathogen to cause food poisoning. Phillips [59] reported that 22.2% of mixed salad vegetable MAP products tested were contaminated with between 80 and 170 CFU/g Campylobacter spp., levels that could potentially produce illness, particularly if several grams of salad were ingested.

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