Modelling the interactions between Pseudomonas putida and Escherichia coli O157:H7 in fish-burgers: use of the lag-exponential model and of a combined interaction index.
OBJECTIVE
The objective of the current study was to examine the interactions between Pseudomonas putida and Escherichia coli O157:H7 in coculture studies on fish-burgers packed in air and under different modified atmospheres (30 : 40 : 30 O(2) : CO(2) : N(2), 5 : 95 O(2) : CO(2) and 50 : 50 O(2) : CO(2)), throughout the storage at 8 degrees C.


RESULTS
The lag-exponential model was applied to describe the microbial growth. To give a quantitative measure of the occurring microbial interactions, two simple parameters were developed: the combined interaction index (CII) and the partial interaction index (PII). Under air, the interaction was significant (P < 0.05) only within the exponential growth phase (CII, 1.72), whereas under the modified atmospheres, the interactions were highly significant (P < 0.001) and occurred both in the exponential and in the stationary phase (CII ranged from 0.33 to 1.18). PII values for E. coli O157:H7 were lower than those calculated for Ps. putida.


CONCLUSIONS
The interactions occurring into the system affected both E. coli O157:H7 and pseudomonads subpopulations. The packaging atmosphere resulted in a key element.


CONCLUSIONS
The article provides some useful information on the interactions occurring between E. coli O157:H7 and Ps. putida on fish-burgers. The proposed index describes successfully the competitive growth of both micro-organisms, giving also a quantitative measure of a qualitative phenomenon.
Speranza
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 Department of Food Science, Faculty of Agricultural Science, University of Foggia, via Napoli 25, 71100, Foggia, Italy.
Bevilacqua
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 Department of Food Science, Faculty of Agricultural Science, University of Foggia, via Napoli 25, 71100, Foggia, Italy.| Istituto per la Ricerca e le Applicazioni Biotecnologiche per la Sicurezza e la Valorizzazione dei Prodotti Tipici e di Qualità (BIOAGROMED), University of Foggia, via Napoli 25, 71100, Foggia, Italy.
Mastromatteo
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 Department of Food Science, Faculty of Agricultural Science, University of Foggia, via Napoli 25, 71100, Foggia, Italy.
Sinigaglia
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 Department of Food Science, Faculty of Agricultural Science, University of Foggia, via Napoli 25, 71100, Foggia, Italy.| Istituto per la Ricerca e le Applicazioni Biotecnologiche per la Sicurezza e la Valorizzazione dei Prodotti Tipici e di Qualità (BIOAGROMED), University of Foggia, via Napoli 25, 71100, Foggia, Italy.
Corbo
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 Department of Food Science, Faculty of Agricultural Science, University of Foggia, via Napoli 25, 71100, Foggia, Italy.| Istituto per la Ricerca e le Applicazioni Biotecnologiche per la Sicurezza e la Valorizzazione dei Prodotti Tipici e di Qualità (BIOAGROMED), University of Foggia, via Napoli 25, 71100, Foggia, Italy.
D000818:Animals; D002245:Carbon Dioxide; D019453:Escherichia coli O157 / Q000254:growth & development*; D005396:Fish Products / Q000382:microbiology*; D005516:Food Microbiology; D056265:Microbial Interactions; D015233:Models, Statistical; D016958:Pseudomonas putida / Q000254:growth & development*; D013696:Temperature
D002245:Carbon Dioxide