Characterization of a Listeria monocytogenes Scott A Isolate with High Tolerance towards High Hydrostatic Pressure

Abstract

An isolate of L. monocytogenes Scott A that is tolerant to high hydrostatic pressure (HHP), named AK01, was isolated upon a single pressurization treatment of 400 MPa for 20 min and was further characterized. The survival of exponential-and stationary-phase cells of AK01 in ACES [N-(2-acetamido)-2-aminoethanesulfonic acid] buffer was at least 2 log units higher than that of the wild type over a broad range of pressures (150 to 500 MPa), while both strains showed higher HHP tolerance (piezotolerance) in the stationary than in the exponential phase of growth. In semiskim milk, exponential-phase cells of both strains showed lower reductions upon pressurization than in buffer, but again, AK01 was more piezotolerant than the wild type. The piezotolerance of AK01 was retained for at least 40 generations in rich medium, suggesting a stable phenotype. Interestingly, cells of AK01 lacked flagella, were elongated, and showed slightly lower maximum specific growth rates than the wild type at 8, 22, and 30°C. Moreover, the piezotolerant strain AK01 showed increased resistance to heat, acid, and H 2 O 2 compared with the wild type. The difference in HHP tolerance between the piezotolerant strain and the wild-type strain could not be attributed to differences in membrane fluidity, since strain AK01 and the wild type had identical in situ lipid melting curves as determined by Fourier transform infrared spectroscopy. The demonstrated occurrence of a piezotolerant isolate of L. monocytogenes underscores the need to further investigate the mechanisms underlying HHP resistance of food-borne microorganisms, which in turn will contribute to the appropriate design of safe, accurate, and feasible HHP treatments.

Heat Shock Protein-Mediated Resistance to High Hydrostatic Pressure in Escherichia coli

“…Interestingly, some studies observed a correlation between heat and pressure resistance among natural isolates of E. coli (1,4). Other studies, in which HHP-resistant mutants of E. coli (16) and of L. monocytogenes (27) were isolated after selection, also found that HHP resistance coincided with increased heat resistance. In E. coli O157:H7, the natural variation in pressure resistance was suggested to be correlated to the activity of the stationary-phase sigma factor (47).…”

“…Most in vivo observations on living cells exposed to HHP can be linked to these two effects: inhibition of key enzymes (43,49); and inactivation of cellular structures and processes, including transcription (9), ribosomes (39), microtubules (33) and membrane proteins (46), and structural and functional disruption of the cell membrane (11,42). Remarkable differences exist in the pressure sensitivity among bacterial species and even strains (1,4), and several groups have reported the isolation of mutants with acquired HHP resistance (12,16,27). The bacterial response to high pressure has been studied mainly in deep-sea bacteria (20,21,29,30,59).…”

Exploration of the Effects of High Hydrostatic Pressure on Microbial Growth, Physiology and Survival: Perspectives from Piezophysiology

“…Some studies have found a correlation between heat and high-pressure resistance among natural isolates of E. coli 21) and mutant isolates of E. coli and Listeria monocytogenes screened after highpressure treatment. 33,34) Membrane damage is one of the main causes of high-pressure induced cell death, but the nature of the damage and its relation to cell death differ among species and phases of growth. 35) Using a promoterless alkaline phosphatase as a reporter of oxidative stress, high hydrostatic pressure was found to be analogous to cytoplasmic oxidative stress in E. coli.…”

Characterization of the CtsR Stress Response Regulon in Lactobacillus plantarum

“…This is a novel, unexpected finding, since CtsR inactivation generally causes derepression of heat stress genes, thus rendering cells more prepared to face stressful conditions. Indeed, in most Grampositive bacteria analyzed so far, ctsR mutations increased heat resistance and/or general stress tolerance (4,16,17,18,24,36). The cell morphology of wild-type L. plantarum and ⌬ctsR mutant strains was analyzed before and after heat stress exposure by scanning electron microscopy (SEM) (Fig.…”