Acid adaptation and food poisoning microorganisms

Hill, Colin; O'driscoll, B.; Booth, Ian R.

doi:10.1016/0168-1605(95)00060-7

Cited by 105 publications

(50 citation statements)

References 15 publications

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“…5A and 6). This is somewhat surprising, as it is generally accepted that cells entering the stationary phase undergo radical changes which ensure that they can deal with physical stresses (30), and it is known that low pH ex values (such as the pH ex values in stationary phase) induce adaptation mechanisms that increase survival (5,8,9,27). The similarities in pH i regulation in stationary and exponentially growing cells may reveal a universal characteristic of these bacteria, but the influence of methodological artifacts needs to be investigated to confirm this observation.…”

Section: Discussionmentioning

confidence: 92%

Dynamic Changes of Intracellular pH in Individual Lactic Acid Bacterium Cells in Response to a Rapid Drop in Extracellular pH

Siegumfeldt

Rechinger

Jakobsen

2000

Appl Environ Microbiol

141

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We describe the dynamics of changes in the intracellular pH (pH i ) values of a number of lactic acid bacteria in response to a rapid drop in the extracellular pH (pH ex ). Strains of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, and Lactococcus lactis were investigated. Listeria innocua, a gram-positive, non-lactic acid bacterium, was included for comparison. The method which we used was based on fluorescence ratio imaging of single cells, and it was therefore possible to describe variations in pH i within a population. The bacteria were immobilized on a membrane filter, placed in a closed perfusion chamber, and analyzed during a rapid decrease in the pH ex from 7.0 to 5.0. Under these conditions, the pH i of L. innocua remained neutral (between 7 and 8). In contrast, the pH i values of all of the strains of lactic acid bacteria investigated decreased to approximately 5.5 as the pH ex was decreased. No pronounced differences were observed between cells of the same strain harvested from the exponential and stationary phases. Small differences between species were observed with regard to the initial pH i at pH ex 7.0, while different kinetics of pH i regulation were observed in different species and also in different strains of S. thermophilus.Bacteria have developed different ways to withstand stressful situations, such as a decrease in the pH ex . Neutrophilic bacteria like Escherichia coli maintain a pH i that is close to neutral when the pH ex is decreased and therefore generate large proton gradients (28). Among the gram-positive bacteria, strains of Enterococcus hirae which were originally identified as Streptococcus faecalis (12) have been studied extensively in order to examine pH homeostasis (14-16). These bacteria also grow at alkaline pH values, and they are considered neutrophiles (31), although they are phylogenetically related to streptococci and lactococci.Many acid-tolerant fermentative bacteria have developed another strategy; in these organisms the pH i decreases as the pH ex decreases during growth (4, 23) in order to maintain a constant pH gradient rather than a constant pH i . Generating a large proton gradient is disadvantageous for fermentative lactic acid bacteria, because proton translocation consumes energy (16), and anaerobic organisms gain significantly less energy from sugar metabolism than aerobes gain. Furthermore, a large proton gradient results in accumulation of organic acid anions in the cytosol (33).Food fermentations are often carried out by sequential microbial populations; this occurs in dairy fermentations, such as yogurt fermentation (32), as well as in indigenous spontaneous fermentations of cereals and vegetables (7,10,20). Lactic acid bacteria, particularly lactobacilli, which are considered the most acid-tolerant bacteria, are often dominant at the end of these fermentations (13, 34). The acid tolerance of these organisms is advantageous, as they have a competitive advantage over known pathogens and other undesirable bacteria when the concent...

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Section: Discussionmentioning

confidence: 92%

Dynamic Changes of Intracellular pH in Individual Lactic Acid Bacterium Cells in Response to a Rapid Drop in Extracellular pH

Siegumfeldt

Rechinger

Jakobsen

2000

Appl Environ Microbiol

141

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“…For each trial, the cells were adapted to pH 4 before inoculation to trigger the acid tolerance response known to enhance cell survival in acidic foods (9,11,13,14,17). In this way, we tried to reproduce a worst-case scenario, in which the product is contaminated with acid-tolerant cells.…”

Section: Resultsmentioning

confidence: 99%

Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella in Cranberry, Lemon, and Lime Juice Concentrates

Nogueira

Oyarzábal²,

Gombas³

2003

Journal of Food Protection

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The production of thermally concentrated fruit juices uses temperatures high enough to achieve at least a 5-log reduction of pathogenic bacteria that can occur in raw juice. However, the transportation and storage of concentrates at low temperatures prior to final packaging is a common practice in the juice industry and introduces a potential risk for postconcentration contamination with pathogenic bacteria. The present study was undertaken to evaluate the likelihood of Escherichia coli O157: H7, Listeria monocytogenes and Salmonella surviving in cranberry, lemon, and lime juice concentrates at or above temperatures commonly used for transportation or storage of these concentrates. This study demonstrates that cranberry, lemon, and lime juice concentrates possess intrinsic antimicrobial properties that will eliminate these bacterial pathogens in the event of postconcentration recontamination. Bacterial inactivation was demonstrated under all conditions; at least 5-log Salmonella inactivation was consistently demonstrated at −23°C (−10°F), at least 5-log E. coli O157:H7 inactivation was consistently demonstrated at −11°C (12°F), and at least 5-log L. monocytogenes inactivation was consistently demonstrated at 0°C (32°F).

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“…If the bacteria that have become adapted to moderately acidic pH in acidified foods, sewage, or acid rain-affected water come to infect animals or humans by the oral route, they will have a better chance of surviving in the lower pH of the mammalian gastrointestinal tract. Similarly, L. monocytogenes in mildly acidic foods can resist better subsequent severe acidic treatment or even thermal treatment, since cross-protection between acid and heat stress has been demonstrated in Listeria (Farber and Pagotto, 1992;Hill et al, 1995).…”

mentioning

confidence: 99%

Physiological and biochemical aspects of the acid survival of Listeria monocytogenes.

Phan‐Thanh

Montagne

1998

J. Gen. Appl. Microbiol.

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Acid adaptation and food poisoning microorganisms

Cited by 105 publications

References 15 publications

Dynamic Changes of Intracellular pH in Individual Lactic Acid Bacterium Cells in Response to a Rapid Drop in Extracellular pH

Dynamic Changes of Intracellular pH in Individual Lactic Acid Bacterium Cells in Response to a Rapid Drop in Extracellular pH

Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella in Cranberry, Lemon, and Lime Juice Concentrates

Physiological and biochemical aspects of the acid survival of Listeria monocytogenes.

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