title: Inactivation of Escherichia coli and Staphylococcus aureus by pulsed electric fields increases with higher bacterial population and with agitation of liquid medium.
abstract: Inactivation of Escherichia coli, E. coli O157:H7, and Staphylococcus aureus in liquid media by pulsed electric fields (PEF) was conducted at varying bacterial populations with and without sample agitation. A laboratory-scale PEF batch unit with a rectangular electric pulse was used, operating under the following conditions: 25 kV/cm (E. coli, E. coli O157:H7) and 30 kV/cm (S. aureus) electric field strengths, 1-μs pulse width, 1-Hz pulse repetition rate, and 20 to 350 pulses for all samples. Not surprisingly, bacterial inactivation (for all three strains) increased with increasing pulse number, achieving the highest reduction at 350 pulses. Log CFU per milliliter microbial inactivation increased commensurately with increasing bacterial population (P < 0.05) but only when samples were treated with more than 200 pulses. For example, when E. coli was treated with 200 pulses at 10(5) CFU/ml, inactivation was only 3.0 Log versus 4.8 Log at the 10(10) inoculation level. When E. coli O157:H7 was treated with 200 pulses at 10(5) CFU/ml, inactivation was only 2.5 Log versus 4.6 Log at the 10(10) inoculation level. When S. aureus was treated with 200 pulses at 10(6) CFU/ml, inactivation was only 2.6 Log versus 4.8 Log at the 10(10) inoculation level. Inactivation of populations was also found to be statistically greater (P < 0.05) when liquid samples were agitated, in comparison to nonagitated samples. Because PEF inactivation activity is influenced by bacterial population and sample agitation, future studies should carefully consider these factors in experimental designs and/or scaled-up industry application.
authors.affiliation: Dipartimento di Scienze ed Innovazione Tecnologica, Università del Piemonte Orientale A. Avogadro, Viale T. Michel 11, 15121 Alessandria, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Bonetta
authors.affiliation: Dipartimento di Scienze della Sanità Pubblica e Pediatriche, Università di Torino, Piazza Polonia 94, 10126 Torino, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Bonetta
authors.affiliation: Dipartimento di Scienze ed Innovazione Tecnologica, Università del Piemonte Orientale A. Avogadro, Viale T. Michel 11, 15121 Alessandria, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Bellero
authors.affiliation: Dipartimento di Fisica G. Occhialini, Università di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Pizzichemi
authors.affiliation: Dipartimento di Scienze della Sanità Pubblica e Pediatriche, Università di Torino, Piazza Polonia 94, 10126 Torino, Italy. elisabetta.carraro@unito.it.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Carraro
mesh_terms: D000818:Animals; D003470:Culture Media / Q000737:chemistry; D004560:Electricity; D055664:Electrochemical Techniques / Q000295:instrumentation / Q000379:methods*; D004926:Escherichia coli / Q000737:chemistry* / Q000254:growth & development*; D051379:Mice; D050296:Microbial Viability; D013211:Staphylococcus aureus / Q000737:chemistry* / Q000254:growth & development*
chemical_list: D003470:Culture Media