Effects of Short-Term Alkaline Adaptation on Surface Properties of Listeria monocytogenes 10403S (original) (raw)

Morphological changes in Listeria monocytogenes subjected to sublethal alkaline stress

International Journal of Food Microbiology, 2007

Scanning electron microscopy (SEM) studies revealed that exposure to 4lethal alkaline stress induced statistically significant (P b 0.05) changes in mean cell length, radius and volume in Listeria monocytogenes and a derived σ B deficient mutant. Bacterial morphology was altered at pH values above 9.0, to include single filamentous or elongated chain forms. Such filamentation and chain formation was observed in the parent strain and in the σ B deficient strain, and in buffered and non-buffered media. Giemsa staining revealed that the filaments were multi-nucleate, with nucleoids spaced along the length of the atypical cells. In buffered media, longer alkaline exposure was associated with increases in the frequency and length of filamentation. In non-buffered medium, longer exposure was associated with gradual decline in length and the frequency of observation of filaments. Transfer of alkaline treated cells to neutral conditions was associated with the formation of septa within filaments, cell division, and a rapid return to normal morphology, i.e. within 3 h. The observed effects, and their reversibility, may be important in increasing the alkaline tolerance of this pathogen during phagocytosis within the innate human immune system response, and in adaptation/survival in food environments treated with alkali detergents and/or sanitisers. Such atypical cells may be associated with increased survival of L. monocytogenes in adverse environments and may also contribute to qualitative and quantitative underestimation of this important pathogen in food processing environments, with potential implications in public health.

Transcriptome Analysis of Alkali Shock and Alkali Adaptation in Listeria monocytogenes 10403S

Foodborne Pathogens and Disease, 2010

Alkali stress is an important means of inactivating undesirable pathogens in a wide range of situations. Unfortunately, Listeria monocytogenes can launch an alkaline tolerance response, significantly increasing persistence of the pathogen in such environments. This study compared transcriptome patterns of alkali and nonalkalistressed L. monocytogenes 10403S cells, to elucidate the mechanisms by which Listeria adapts and=or grows during short-or long-term alkali stress. Transcription profiles associated with alkali shock (AS) were obtained by DNA microarray analysis of midexponential cells suspended in pH 9 media for 15, 30, or 60 min. Transcription profiles associated with alkali adaptation (AA) were obtained similarly from cells grown to midexponential phase at pH 9. Comparison of AS and AA transcription profiles with control cell profiles identified a high number of differentially regulated open-reading frames in all tested conditions. Rapid (15 min) changes in expression included upregulation of genes encoding for multiple metabolic pathways (including those associated with Na + =H + antiporters), ATP-binding cassette transporters of functional compatible solutes, motility, and virulence-associated genes as well as the s B controlled stress resistance network. Slower (30 min and more) responses to AS and adaptation during growth in alkaline conditions (AA) involved a different pattern of changes in mRNA concentrations, and genes involved in proton export.

Genomic and proteomic analysis of the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes 10403S

BMC Microbiology, 2008

Background: Information regarding the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes is very limited. Treatment of alkali-adapted cells with the protein synthesis inhibitor chloramphenicol has revealed that the AlTR is at least partially protein-dependent. In order to gain a more comprehensive perspective on the physiology and regulation of the AlTR, we compared differential gene expression and protein content of cells adapted at pH 9.5 and un-adapted cells (pH 7.0) using complementary DNA (cDNA) microarray and two-dimensional (2D) gel electrophoresis, (combined with mass spectrometry) respectively.

Effects of pH or aw stress on growth of Listeria monocytogenes

International Journal of Food Microbiology, 1998

The growth of three strains of Listeria monocytogenes at 208C in a meat broth of different pH or water activity was investigated. At inoculation or at the beginning of the exponential phase, cells were exposed to stress by the addition of 1 NaOH or NH , acetic acid, NaCl or KCl, in order to reach a pH of either 9.0 or 5.6, or an a of 0.950 or 0.965, respectively.

Survival of acid stress adapted cells of Listeria monocytogenes serotypes 1/2a and 4b in commonly used disinfectants in broth and water models

LWT, 2019

The purpose of this study was to determine the survival of acid stress adapted Listeria monocytogenes Bug600 and ScottA cells in various lethal concentrations of disinfectants in broth and water models. Acid stress adapted cells had significantly greater survival than the non-adapted cells in lethal concentrations of hydrochloric acid, lactic acid, and acetic acid in tryptic soy broth containing yeast extract (TSBYE). Also, acid stress adaptation protected L. monocytogenes cells against lethal sodium hydroxide (NaOH), potassium hydroxide (KOH) and ammonium hydroxide (NH 4 OH). Increased tolerance to lethal concentrations of ethanol and isopropanol was also observed after acid stress adaptation. Acid stress adapted cells also exhibited higher survival in two quaternary ammonium compounds (QAC-1 and QAC-2). Acid stress adapted cells were more susceptible to hydrogen peroxide (H 2 O 2) inactivation. Similar survival patterns were observed for the acid stress adapted and non-adapted cells in both water and broth models, suggesting that the impact of acid adaptation on L. monocytogenes survival in disinfectants was not altered due to the presence of nutrients. Overall, these findings indicate that oxidative based agents are the best choice to decontaminate the food contact surface where acid stress adapted L. monocytogenes cells may be present.

Effect of Food Processing-Related Stresses on Acid Tolerance of Listeria monocytogenes

Applied and Environmental Microbiology, 2003

Stationary-phase cells of Listeria monocytogenes grown in glucose-free or glucose-containing media were exposed for 90 min to various stresses, including acid stress (pH 4.0 to 7.0), osmotic stress (10.5 to 20.5% NaCl), and various temperatures (؊5 to 50°C), and were further exposed to pH 3.5. Exposure to a mildly acidic (pH 5.0 to 6.0) environment provided protection of the pathogen against acid upon subsequent exposure. This adaptive response, however, was found to be strongly dependent on other environmental conditions during the shock, such as temperature or the simultaneous presence of a second stress factor (NaCl). Growth of L. monocytogenes in the presence of glucose resulted in enhanced survival of the pathogen at pH 3.5. Sublethal stresses other than acidic stresses, i.e., osmotic, heat, and low-temperature stresses, did not affect the acid resistance of L. monocytogenes (P > 0.5). More-severe levels of these stresses, however, resulted in sensitization of the pathogen to acid.

Adaptive acid tolerance response of Listeria monocytogenes strains under planktonic and immobilized growth conditions

International Journal of Food Microbiology, 2012

The acid resistance of Listeria monocytogenes was evaluated: (i) after short (shock) or long-term (adaptation during growth) exposure to reduced (5.5) or neutral (7.2) pH in a liquid (broth) medium or on a solid surface (agar), and (ii) after growth on the surface of ham and turkey slices or in homogenates of these products. Three L. monocytogenes strains (serotypes 1/2a, 1/2b and 4b) were individually inoculated at: (i) 10 4 -10 5 CFU/ml in tryptic soy broth with 0.6% yeast extract (TSBYE) or on tryptic soy agar with 0.6% yeast extract (TSAYE) at pH 7.2 with 1% (+G) or without (−G) glucose of or TSBYE and TSAYE with 0.25% glucose at pH 5.5 (lactic acid) and incubated at 20°C, and (ii) 10 2 -10 3 CFU/cm 2 on ham and turkey slices (pH 6.39-6.42; formulated with potassium lactate and sodium diacetate) or in their homogenates (1:4 and 1:9; representing viscous [slurry] and liquid residues [purge], respectively), and stored at 10°C. The acid resistance of each strain was assessed in TSBYE of pH 3.5 (lactic acid) for strains growing in broth or on agar surfaces, and in TSBYE of pH 1.5 (HCl) for strains growing on ham and turkey slices or in their homogenates. Habituation at pH 5.5 for 3 or 24 h at 20°C increased acid (pH 3.5) resistance of all strains compared to the control (pH 7.2). Cells grown on the surface of TSAYE-G (pH 7.2 or 5.5) showed higher resistance than cells grown in broth (TSBYE-G), whereas the opposite was observed for cells grown on TSAYE + G or in TSBYE + G. Growth of L. monocytogenes on meat product slices was markedly slower than in homogenates. Pathogen reductions following exposure to pH 1.5, after 10 and 27 days of storage were strain-dependent and in the ranges of 0.5-2.5, 1.3-4.5 and 4.0-7.6 log units for cells grown on product slices in 1:4 and 1:9 homogenates, respectively. The results suggest that L. monocytogenes cells growing on food surfaces or in viscous matrices may show higher resistance to lethal acid conditions than cells growing in liquid substrates.

MudPIT analysis of alkaline tolerance by Listeria monocytogenes strains recovered as persistent food factory contaminants

Food Microbiology, 2012

Alkaline solutions are used to clean food production environments but the role of alkaline resistance in persistent food factory contamination by Listeria monocytogenes is unknown. We used shotgun proteomics to characterise alkaline adapted L. monocytogenes recovered as persistent and transient food factory contaminants. Three unrelated strains were studied including two persistent and a transient food factory contaminant determined using multilocus sequence typing (MLST). The strains were adapted to growth at pH 8.5 and harvested in exponential phase. Protein extracts were analysed using multidimensional protein identification technology (MudPIT) and protein abundance compared by spectra counting. The strains elicited core responses to alkaline growth including modulation of intracellular pH, stabilisation of cellular processes and reduced cell-division, independent to lineage, MLST or whether the strains were transient or persistent contaminants. Alkaline adaptation by all strains corresponded to that expected in stringent-response induced cells, with protein expression supporting metabolic shifts concordant with elevated alarmone production and indicating that the alkaline-stringent response results from energy rather than nutrient limitation. We believe this is the first report describing induction of a stringent response in different L. monocytogenes strains by alkaline pH under non-limiting growth conditions. The work emphasises the need for early intervention to avoid persistent food factory contamination by L. monocytogenes.

Effect of osmotic, alkaline, acid or thermal stresses on the growth and inhibition of Listeria monocytogenes

Journal of Applied Microbiology, 1999

Five strains of Listeria monocytogenes (a, b, c, d and e) isolated from industrial plants have been subjected to different osmotic, alkaline, acid or thermal stresses. The effects of these treatments on lag-phase (L) and growth rate (mu) of cells in mid-log phase have been followed using an automated optical density monitoring system. Increasing the osmotic pressure by the addition of different amounts of NaCl increased the lag phase and decreased the growth rate. The same phenomena were observed after decreasing the pH of the medium to 5.8, 5.6 or 5.4 by addition of acetic, lactic or hydrochloric acids. The inhibitory effect was: acetic acid > lactic acid > hydrochloric acid. The addition of NaOH to attain pH values of 9.5, 10.0, 10.5 or 11.0 in the medium produced a dramatic increase of the lag phase at pH 10.5 and 11. Growth rates were also decreased while the maximal population increased with high pH values. These effects varied according to strains. Strains d and e were the most resistant to acidic and alkaline stresses, and e was the most affected by the addition of NaCl. A cold shock of 30 min at 0 degree C had limited effects on growth parameters. On the other hand, hyperthermal shocks (55 or 63 degrees C, 30 min) led to similar increased lag phases and to significant increases of the maximal population in all five strains.