scholarly journals INHIBITION OF BACTERIA ISOLATED FROM NINH THUAN GRAPES BY ORGANIC ACIDS

2018 ◽  
Vol 54 (4A) ◽  
pp. 290
Author(s):  
Nguyen Thi Hanh
Keyword(s):  
Ascorbic Acid ◽  
Lactic Acid ◽  
Citric Acid ◽  
Bacillus Thuringiensis ◽  
Organic Acids ◽  
Bacillus Cereus ◽  
Minimal Inhibitory Concentration ◽  
Inhibitory Concentration ◽  
Dilution Method ◽  
Minimal Bactericidal Concentration

Ninh Thuan grapes are famous specialty of Vietnam. After harvesting, they are very susceptible to damage if not preserved in time. This study aimed to find the minimal inhibitory concentration and minimal bactericidal concentrations of organic acids, such as lactic acid, citric acid, and ascorbic acid towards seven bacteria previously isolated from Ninh thuan grapes (Empedobacter  brevis, Citrobacter sp. Enterobacterium ludwigii, Bacillus cereus, Flavobacterium sp., Pseudomonas oryzihabitans and Bacillus thuringiensis) in order to apply in pretreatment of grapes prior to storage. The Minimal Inhibitory Concentration (MIC) was determined by the binary dilution method. 0.1 ml of each dilution of test acids with initial concentration of 3 % was mixed with 0.1 ml of bacteria (c.a. 5.105 CFU/ml), in 96-culturing-well plate. Innoculated plate was incubated for 24 hours at temperature of 37 °C. Optical density was measured at 620 nm wavelength by a Microplate reader device. For Minimal Bactericidal Concentration (MBC) determination, 0.1 ml of bacteria (c.a.5.105 CFU/ml) was mixed with 0.4 ml liquid medium of Tryptone Glucose Agar (TGA) and of 0.5 ml acid at above concentrations, culturing within 24 hours at temperature of 37 °C. After 24 hours, they were dropped onto TGA agar plates, and cultured for 24 hours at 37 °C. The results showed that, the MIC and MBC of citric acid toward Empedobacter brevis were 0.12 mg/ml and 0.12 mg/ml; Citrobacter sp. were 0.9 mg/ml and 3.8 mg/ml; Enterobacterium ludwigii were 0.45 mg/ml and 1.9 mg/ml; Bacillus cereus were  0.9 mg/ml and 0.9 mg/ml; Flavobacterium sp. were 0.12 mg/ml  and 0.45 mg/ml; Pseudomonas oryzihabitans were 0.12 mg/ml and 0.45 mg/ml and Bacillus thuringiensis were 0.12 mg/ml  and 0.9 mg/ml, respectively. Similarly, MIC and MBC of  lactic acid toward: Empedobacter brevis were 0.12 mg/ml and 0.23 mg/ml;Citrobacter sp. were 0.9 mg/ml and 1.9 mg/ml; Enterobacterium ludwigii were 0.45 mg/ml and 0.9 mg/ml; Bacillus cereus were 0.23 mg/ml and 0.45 mg/ml; Flavobacterium sp. were 0.12 mg/ml and 1.9 mg/ml;  Pseudomonas oryzihabitans  were 0.23 mg/ml and 1.9 mg/ml and Bacillus thuringiensis were 0.12 mg/ml and 1.9 mg/ml, respectively. Ascorbic acid was found to be inefficient for use as antimicrobial agent against isolated bacteria. The above results suggested that citric and lactic acids could be used at maximal concentrations of 3.8 mg/ml and 1.9 mg/ml, respectively to suppress bacteria from grapes. This finding would contribute to develop method for pretreatment of grapes in fresh grape preservation techniques. 

scholarly journals Uji aktivitas antibakteri ekstrak biji petai cina (Leucaena leucocephala) terhadap Staphylococcus aureus

2020 ◽  
Vol 20 (2) ◽  
Author(s):  
Vivi Permata Sari ◽  
Wiwin Retnowati ◽  
Yuani Setiawati
Keyword(s):  
Staphylococcus Aureus ◽  
Antibacterial Activity ◽  
Minimal Inhibitory Concentration ◽  
Leucaena Leucocephala ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Inhibitory Concentration ◽  
Seed Extract ◽  
Dilution Method ◽  
Minimal Bactericidal Concentration ◽  
Vancomycin Resistant

 Abstract. Staphylococcus aureus merupakan flora normal kulit manusia yang bisa menyebabkan infeksi ketika sistem imun tubuh manusia sedang lemah. Pengobatan Staphylococcus aureus tergolong sulit karena Staphylococcus aureus mudah resisten terhadap beberapa antibiotik sehingga dikenal istilah Methicillin-resistant Staphylococcus aureus (MRSA), Vancomycin-intermediate Staphylococcus aureus (VISA), dan Vancomycin-resistant Staphylococcus aureus (VRSA) yang menunjukkan resistensi tersebut. Pertumbuhan Staphylococcus aureus dapat dihambat ekstrak daun petai cina (Leucaena leucocephala). Tanaman petai cina (Leucaena leucocephala) digunakan masyarakat Indonesia sebagai obat tradisional untuk menyembuhkan luka, mengobati cacingan, dan mengobati jerawat. Tujuan penelitian ini adalah untuk mengetahui aktivitas antibakteri ekstrak biji petai cina (Leucaena leucocephala) dalam menghambat pertumbuhan Staphylococcus aureus.Penelitian ini merupakan eksperimental laboratorium dengan metode dilusi sebanyak 6 replikasi. Setiap replikasi menggunakan konsentrasi ekstrak biji petai cina (Leucaena leucocephala) sebesar 3,125%, 6,25%, 12,5%, 25%, 50%, dan 100% untuk mencari konsentrasi hambat minimal dan konsentrasi bunuh minimal terhadap Staphylococcus aureus.Hasil penelitian tidak dapat menentukan konsentrasi hambat minimal (KHM) ekstrak biji petai cina (Leucaena leucocephala) terhadap Staphylococcus aureus karena warna ekstrak yang gelap. Sedangkan konsentrasi bunuh minimal (KBM) ekstrak biji petai cina (Leucaena leucocephala) terhadap Staphylococcus aureus ditemukan pada konsentrasi 50%, yang menunjukkan bahwa konsentrasi 50% adalah konsentrasi terkecil dimana tidak terdapat pertumbuhan bakteri Staphylococcus aureus.Sebagai simpulan, ekstrak biji petai cina (Leucaena leucocephala) memiliki aktivitas antibakteri terhadap Staphylococcus aureus. Kata kunci: Staphylococcus aureus, Leucaena leucocephala, metode dilusi  Abstract. Staphylococcus aureus is a normal human skin flora that can cause infection when human immune system is weak. Staphylococcus aureus treatment is difficult because Staphylococcus aureus is easily resistant to some antibiotics so several terms such as Methicillin-resistant Staphylococcus aureus (MRSA), Vancomycin-intermediate Staphylococcus aureus (VISA), and Vancomycin-resistant Staphylococcus aureus (VRSA) are known to indicate the resistance. The growth of Staphylococcus aureus can be inhibited by Leucaena leucocephala leaf extract. Leucaena leucocephala is used by Indonesian people as traditional medicine to heal wounds, treat worm infection, and treat acne. The objective of this study was to identify the antibacterial activity of Leucaena leucocephala seed extract against Staphylococcus aureus.This was a laboratory experimental study using dilution method as many as five replications. Each replication used Leucaena leucocephala seed extract in concentrations of 3.125%, 6.25%, 12.5%, 25%, 50%, and 100% to determine the minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) against Staphylococcus aureus. The results were not able to determine the minimal inhibitory concentration (MIC) of Leucaena leucocephala seed extract against Staphylococcus aureus due to dark color of the extract. While the minimal bactericidal concentration (MBC) of Leucaena leucocephala seed extract against Staphylococcus aureus was 50%. This showed that the concentration of 50% was the lowest concentration where there was no growth of the bacteria Staphylococcus aureus.In conclusion, the extract of Leucaena leucocephala seed has antibacterial activity against Staphylococcus aureus. Keywords: Staphylococcus aureus, Leucaena leucocephala, dilution method

scholarly journals Nisin and ε-poly-L-lysine as natural antimicrobials towards spoilage-associated Lactobacillus plantarum

2021 ◽  
Vol 51 (2) ◽  
Author(s):  
Fernanda Cristina Kandalski Bortolotto ◽  
Maria Helena da Rosa Farfan ◽  
Nathalia Cristina Kleinke Jede ◽  
Gabriela Maia Danielski ◽  
Renata Ernlund Freitas de Macedo
Keyword(s):  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Inhibitory Concentration ◽  
Inhibitory Effect ◽  
Minimal Bactericidal Concentration ◽  
Natural Antimicrobials ◽  
Food Preservatives ◽  
Spoilage Bacteria ◽  
Mass Spectrometry Identification

ABSTRACT: Sausages are highly susceptible to microbial spoilage. Lactic acid bacteria (LAB) is the main group of spoilage bacteria in vacuum packed cooked sausages. To control microbial growth natural antimicrobials have been used as food preservatives. The aim of this study was to identify strains of lactic acid bacteria isolated from spoiled commercial Calabresa sausages and use them in an in vitro challenge with the natural antimicrobials, nisin (NI) and ε-poly-L-lysine (ε-PL). Mass spectrometry identification of LAB isolated from sausages using MALDI-TOF revealed a predominance of L. plantarum in the LAB population. RAPD-PCR of L. plantarum strains showed four different genetic profiles. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of NI and ε-PL, alone and in combination, against a pool of different profiles L. plantarum were determined. MIC of NI and ε-PL were 0.468 mg/ L and 75 mg/ L; respectively, whereas MBC of NI and ε-PL were 12.48 mg/L and 150 mg/L, respectively. The combined effect of NI and ε-PL was determined using concentrations at 1/4 and 1/8 of individual MICs. Synergistic effect was confirmed at both concentrations showing a fractional inhibitory concentration index of 0.5 and 0.2, respectively. The combination of NI and ε-PL at a small concentration of 0.05 mg/L and 9.375 mg/L, respectively, showed inhibitory effect towards spoilage L. plantarum Results show the potential of the combined use of NI and ε-PL to control sausage spoilage-associated with lactobacilli.

Survival of Escherichia coliO157:H7 in Synthetic Gastric Fluid after Cold and Acid Habituation in Apple Juice or Trypticase Soy Broth Acidified with Hydrochloric Acid or Organic Acids

1998 ◽  
Vol 61 (8) ◽  
pp. 939-947 ◽  
Author(s):  
HEIDI E. ULJAS ◽  
STEVEN C. INGHAM
Keyword(s):  
Lactic Acid ◽  
Citric Acid ◽  
Organic Acids ◽  
Apple Juice ◽  
Acid Tolerance ◽  
Storage Conditions ◽  
Gastric Fluid ◽  
E Coli ◽  
Storage Media ◽  
Strain Storage

Extreme acid tolerance of Escherichia coli O157:H7 has raised doubts about the safety of acidic foods. This study examined whether prior storage in acidic and/or cold conditions enhanced survival of E. coli O157 :H7 in synthetic gastric fluid (SGF). Three E. coli O157:H7 strains were stored in trypticase soy broth (TSB; acidified with HCl, malic acid, citric acid, or lactic acid) or pH 3.5 and 6.5 (nonacidic control) apple juice at 4 and 21°C for ≤7 days and then were incubated in pH 2.5 SGF at 37°C for 4 h. Cells survived better in apple juice than in TSB containing organic acids, suggesting that juice constituents other than organic acids protect E. coli O157:H7. Refrigeration combined with low pH best protected cells in apple juice and acidified TSB, but, compared to the nonacidic control, only acidified TSB enhanced subsequent survival in pH 2.5 SGF. Equal survival in SGF occurred after storage in pH 3.5 or 6.5 apple juice at 4°C, suggesting that low temperature alone in apple juice enhanced acid tolerance. Two strains stored at 4°C in TSB containing malic or citric acid subsequently survived better in SGF than cells stored in nonacidified TSB but poorer than cells stored in the presence of HCl. These differences reflect the higher pKa of these organic acids. However, subsequent survival of these strains in SGF was poorer after refrigerated storage in apple juice than in TSB containing citric or malic acids. Cells stored in lactic acid were most likely to be completely eliminated upon transfer to SGF. Differences in survival in storage media or SGF related to strain, storage conditions, or acidifier were consistent and often statistically significant (P < 0.05). Although the survival of E. coli O157:H7 in refrigerated acidic beverages may not be affected by the type of acidifier used, the subsequent survival in SGF of this pathogen may be critically dependent on this factor.

scholarly journals Some Pomological Properties of Promising Seed Propagated Walnut Genotypes from Inner Turkey

2019 ◽  
Vol 47 (4) ◽  
pp. 1094-1099
Author(s):  
Aysen KOC ◽  
Hakan KELES ◽  
Sezai ERCISLI
Keyword(s):  
Fatty Acids ◽  
Ascorbic Acid ◽  
Linoleic Acid ◽  
Citric Acid ◽  
Organic Acids ◽  
Fumaric Acid ◽  
Juglans Regia ◽  
Kernel Weight ◽  
Digital Object Identifier ◽  
Digital Object

In this study, fruits from seed propagated walnut (Juglans regia L.) trees were collected two consecutive years in harvest seasons in Yozgat province in Turkey.  Considering two years results, promising five genotypes were determined as cultivar candidate. In the promising genotypes, nut weight ranged from 12.55 (Y11) to 15.08 g (Y15), kernel weight ranged from 5.23 (Y11) to 7.34 g (Y15) and kernel ratio varied between 41.67 (Y11) to 50.84% (Y1), respectively. Linoleic acid was the only polyunsaturated fatty acids and oleic, palmitoleic and gondoic acids determined as major monounsaturated acids ranged from 30.36 to 48.43%, 0.05 to 0.14% and 0.22 to 0.29%, respectively. Propylparaben was the major phenolic acid among the determined phenolic acids in fruits of all five promising genotypes and Y16 had the highest amount of propylparaben (128.08 mg per kg) in its kernel. Malic and tartaric acid were the major organic acids in walnut kernels ranged from 47.88 to 78.51 mg per 100 g and 30.27 to 49.60 mg per 100 g, respectively. L-ascorbic acid was the another organic acids in walnut kernels ranged from 10.71 to 19.71 mg per 100 g. Citric acid was non-determined in kernels of Y1, Y14 and Y15 but determined at kernels of Y11 and Y16 as 4.51 and 7.55 mg per 100 g, respectively. It was determined that the oxalic, malonic, succinic, maleic and fumaric acid contents varied between 8.39-12.08 mg per 100 g, 6.02-9.19 mg per 100 g, 2.86-5.32 mg per 100 g, 0.26-3.00 mg per 100 g and 0.26-0.58 mg per 100 g, respectively.   ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********

Uji konsentrasi hambat minimum (KHM) ekstrak daun binahong (Anredera cordifolia Steenis) sebagai antibakteri terhadap pertumbuhan Streptococcus mutans

e-GIGI ◽  
2016 ◽  
Vol 4 (2) ◽  
Author(s):  
Klaudya E. Warokka ◽  
Jane Wuisan ◽  
Juliatri .
Keyword(s):  
Minimal Inhibitory Concentration ◽  
Streptococcus Mutans ◽  
Leaf Extract ◽  
Inhibitory Concentration ◽  
Test Methods ◽  
Control Group ◽  
Dilution Method ◽  
Control Group Design ◽  
Study Program ◽  
Group Design

Abstract: Inadequate oral and dental hygiene can cause plaques containing various kinds of bacteria; one of them is Streptococcus mutans which is the main cause of dental caries. Binahong leaf (Anredera cordifolia Steenis) is a medicinal herb that contains antibacterial compounds namely flavonoids, alkonoid, terpanoid, and saponins. This study aimed to determine the minimal inhibitory concentration (MIC) of binahong leaf extract to the growth of Streptococcus mutans. This was a true experimental study with a randomized pretest-posttest control group design. The method used in this study was serial dilution method with turbidimetry and spectrophotometry as the test methods. Binahong leaves were taken from Tempok village and were extracted with maceration method using ethanol 96%. Streptococcus mutans bacteria were obtained from a pure bacterial stock in Microbiology Laboratory of Pharmacy Study Program, Faculty of Mathematics and Natural Science University of Sam Ratulangi Manado. The result showed that the minimal inhibitory concentration (MIC) of binahong leaf extract (Anredera cordifolia steenis) to the growth of Streptococcus mutans was 6.25%.Keywords: Streptococcus mutans, binahong leaf, MIC, tooth cariesAbstrak: Kebersihan gigi dan mulut yang buruk dapat menyebabkan terbentuknya plak yang mengandung berbagai macam bakteri, salah satu diantaranya Streptococcus mutans yang menjadi penyebab utama terjadinya karies gigi. Daun binahong (Anredera cordifolia steenis) merupakan tanaman herbal yang mengandung senyawa antibakteri yaitu flavonoid, alkonoid, terpanoid dan saponin. Penelitian ini bertujuan untuk mengetahui konsentrasi hambat minimum (KHM) dari daun binahong terhadap pertumbuhan Streptococcus mutans. Jenis penelitian ini ialah eksperimental murni dengan randomized pretest-posttest control group design. Penelitian ini menggunakan metode serial dilusi dengan metode pengujian turbidimetri dan spektrofotometri. Daun binahong diperoleh di desa Tempok, dan diekstraksi dengan metode maserasi menggunakan etanol 96%. Bakteri Streptococcus mutans diambil dari stok bakteri murni Laboratorium Mikrobiologi Program Studi Farmasi Fakultas MIPA Universitas Sam Ratulangi Manado. Hasil penelitian mendapatkan bahwa KHM daun binahong terhadap pertumbuhan streptococcus mutans ialah pada konsentrasi 6,25%.Kata kunci: Streptococcus mutans, daun binahong, KHM, karies gigi

Survival of Salmonella during Apple Dehydration as Affected by Apple Cultivar and Antimicrobial Pretreatment

2020 ◽  
Vol 83 (5) ◽  
pp. 902-909
Author(s):  
JOSHUA B. GURTLER ◽  
SUSANNE E. KELLER ◽  
XUETONG FAN ◽  
O. MODESTO OLANYA ◽  
TONY JIN ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Lactic Acid ◽  
Citric Acid ◽  
Fumaric Acid ◽  
Potassium Sorbate ◽  
Apple Cultivar ◽  
Sodium Bisulfate ◽  
Apple Slices ◽  
Apple Cultivars ◽  
Salmonella Survival

ABSTRACT Dehydrated fruits, including dried coconut (Cocos nucifera) and dried apple (Malus sp.) slices, have been the subject of manufacturer recalls due to contamination with Salmonella. A study was conducted to determine the survival of Salmonella on apple slices of six apple cultivars after dehydration and also following treatment with antimicrobial solutions (0.5%, w/w) and dehydration. Samples of six apple cultivars (Envy, Gala, Red Delicious, Fuji, Pink Lady, Granny Smith) were cored and sliced into 0.4-cm rings, halved, inoculated with a five-strain composite of desiccation-resistant Salmonella, and dehydrated at 60°C for 5 h. Subsequently, Gala apple slices were treated in 0.5% solutions of one of eight antimicrobial rinses for 2 min and then dehydrated at 60°C for 5 h. Antimicrobial solutions used were potassium sorbate, sodium benzoate, ascorbic acid, propionic acid, lactic acid, citric acid, fumaric acid, and sodium bisulfate. Reduction of Salmonella populations varied according to apple cultivar. Salmonella survival on Envy, Gala, Red Delicious, Fuji, Pink Lady, and Granny Smith was 5.92, 5.58, 4.83, 4.68, 4.45, and 3.84 log CFU, respectively. There was significantly greater (P < 0.05) Salmonella inactivation on Granny Smith, Pink Lady, and Fuji apples than on Gala and Envy. Survival of Salmonella on Gala apple slices following dehydration was 5.58 log CFU for the untreated control and 4.76, 3.90, 3.29, 3.13, 2.89, 2.83, 2.64, and 0.0 log CFU for those treated with potassium sorbate, sodium benzoate, ascorbic acid, propionic acid, lactic acid, citric acid, fumaric acid, and sodium bisulfate, respectively. Pretreatment of apple slices with either fumaric acid or sodium bisulfate before dehydration led to lower Salmonella survival than pretreatment with all other antimicrobial treatments. Lower apple pH was statistically correlated (P < 0.05) with decreasing survival of Salmonella following dehydration. These results may provide methodology applicable to the food industry for increasing the inactivation of Salmonella during the dehydration of apple slices. HIGHLIGHTS

scholarly journals Effect of Bagging on the Content of Sugar and Acid in Postharvest "Jinhuang" Mango Fruit

2020 ◽  
Vol 145 ◽  
pp. 01032
Author(s):  
Changbin Wei ◽  
Jian Qiao ◽  
Xinming Tang ◽  
Qingze Yan ◽  
Lizhu Tang ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Citric Acid ◽  
Organic Acids ◽  
Fruit Quality ◽  
Hplc Method ◽  
Postharvest Storage ◽  
Mango Fruit ◽  
Acid Ratio

The glucose, fructose, sucrose, and organic acids in the pulp of “Jinhuang” mango were analyzed using the HPLC method and the effect of bagging on fruit quality was researched during the postharvest storage. The results showed that there was a certain difference in the content of sugar and acid among the three treatments. The effect of bagging treatments on fructose, glucose, and sucrose in the fruit of “Jinhuang” mango was mainly reflected in sucrose. The treatments of white bagging (WB) and black bagging (BB) delayed the production of sucrose and the decomposition of citric acid, and increased the content of ascorbic acid and quinine. Based on sugar-acid ratio, the flavor of the three treatments was evaluated as: CK> WB> BB. The fruit quality of “Jinhuang” mango was affected by bagging treatments to a certain extent.

Synergistic Antilisterial Effects of Mixtures of Lysozyme and Organic Acids

2016 ◽  
Vol 79 (12) ◽  
pp. 2184-2189 ◽  
Author(s):  
MYEONGGEUN OH ◽  
JOONGJAE LEE ◽  
YOONHWA JEONG ◽  
MISOOK KIM
Keyword(s):  
Acetic Acid ◽  
Lactic Acid ◽  
Citric Acid ◽  
Organic Acids ◽  
Succinic Acid ◽  
Malic Acid ◽  
Synergistic Effects ◽  
The Other ◽  
Food Preservative ◽  
Time Kill

ABSTRACT We investigated the synergistic effects of lysozyme combined with organic acids to inhibit the growth of Listeria monocytogenes. The antilisterial effects of the combination of lysozyme and acetic acid, citric acid, lactic acid, malic acid, or succinic acid were evaluated using the checkerboard method and time-kill assay. The MIC was 25,000 mg/liter for lysozyme, 625 mg/liter for acetic acid, and 1,250 mg/liter for the other acids. The MBC was 10,000 mg/liter for all of the tested organic acids. The combination of lysozyme and each organic acid showed synergistic effects via the checkerboard method; however, the time-kill assay showed synergistic effects for only three combinations of 1,250 mg/liter lysozyme with succinic acid (312 and 625 mg/liter) or malic acid (625 mg/liter). The results of this study indicate that the combination of lysozyme and malic acid or succinic acid can be effectively used as a food preservative to control L. monocytogenes.

Behavior of Acid-Adapted and Unadapted Escherichia coli O157:H7 When Exposed to Reduced pH Achieved with Various Organic Acids

1999 ◽  
Vol 62 (5) ◽  
pp. 451-455 ◽  
Author(s):  
JEE-HOON RYU ◽  
YUN DENG ◽  
LARRY R. BEUCHAT
Keyword(s):  
Escherichia Coli ◽  
Acetic Acid ◽  
Lactic Acid ◽  
Citric Acid ◽  
Organic Acids ◽  
Malic Acid ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Ph Values ◽  
Acid Ph

A study was done to determine if various organic acids differ in their inhibitory or lethal activity against acid-adapted and unadapted Escherichia coli O157:H7 cells. E. coli O157:H7 strain E0139, isolated from venison jerky, was grown in tryptic soy broth (TSB) and in TSB supplemented with 1% glucose (TSBG) for 18 h at 37°C, then plated on tryptic soy agar (TSA) acidified with malic, citric, lactic, or acetic acid at pH 5.4, 5.1, 4.8, 4.5, 4.2, and 3.9. Regardless of whether cells were grown in TSB or TSBG, visible colonies were not formed when plated on TSA acidified with acetic, lactic, malic, or citric acids at pH values of ≤5.4, ≤4.5, ≤4.2, or ≤4.2, respectively. Cells not adapted to reduced pH did not form colonies on TSA acidified with lactic acid (pH 3.9) or acetic acid (pH 3.9 and 4.2); however, a portion of acid-adapted cells remained viable on TSA containing lactic acid (pH 3.9) or acetic acid (pH 4.2) and could be recovered in TSB. Inactivation of acid-adapted cells was less than that of unadapted cells in TSB acidified at pH 3.9 with citric, lactic, or acetic acid and at pH 3.4 with malic acid. Significantly (P ≤ 0.05) higher numbers of acid-adapted cells, compared with unadapted cells, were detected 12 h after inoculation of TSB acidified with acetic acid at pH 3.9; in TSB containing lactic acid (pH 3.9), the number of acid-adapted cells was higher than the number of unadapted cells after 5 h. In TSB acidified at pH 3.9 with citric acid or pH 3.4 with malic acid, significantly higher numbers of acid-adapted cells survived. This study shows that organic acids differ in their inhibitory or lethal activity against acid-adapted and unadapted E. coli O157:H7 cells, and acid-adapted cells are more tolerant than unadapted cells when subsequently exposed to reduced pH caused by these acids.

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