Effect of Simulated Spray Chilling with Chemical Solutions on Acid-Habituated and Non–Acid-Habituated Escherichia coli O157:H7 Cells Attached to Beef Carcass Tissue

2004 ◽  
Vol 67 (10) ◽  
pp. 2099-2106 ◽  
Author(s):  
J. D. STOPFORTH ◽  
Y. YOON ◽  
K. E. BELK ◽  
J. A. SCANGA ◽  
P. A. KENDALL ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Lactic Acid ◽  
Cold Water ◽  
Phase 1 ◽  
Sodium Chlorite ◽  
Escherichia Coli O157 ◽  
Phase 2 ◽  
E Coli ◽  
Chemical Solutions ◽  
Beef Carcass

Samples (10 by 20 by 2.5 cm) of beef carcass tissue were inoculated (104 to 105 CFU/cm2) with Escherichia coli O157: H7 that was either non–acid habituated (prepared by incubating at 15°C for 48 h in inoculated filter-sterilized composite [1:1] of hot and cold water meat decontamination runoff fluids, pH 6.05) or acid habituated (prepared in inoculated water fluids mixed with filter-sterilized 2% lactic acid [LA] runoff fluids in a proportion of 1/99 [vol/vol], pH 4.12). The inoculated surfaces were exposed to conditions simulating carcass chilling (−3°C for 10 h followed by 38 h at 1°C). Treatments applied to samples (between 0 and 10 h) during chilling included the following: (i) no spraying (NT) or spraying (for 30 s every 30 min) with (ii) water, (iii) cetylpyridinium chloride (CPC; 0.1 or 0.5%), (iv) ammonium hydroxide (AH; 0.05%), (v) lactic acid (LA; 2%), (vi) acidified sodium chlorite (ASC; 0.12%), (vii) peroxyacetic acid (PAA; 0.02%), (viii) sodium hydroxide (SH; 0.01%), or (ix) sodium hypochlorite (SC; 0.005%) solutions of 4°C. Samples were taken at 0, 10, 24, 36, and 48 h of the chilling process to determine changes in E. coli O157:H7 populations. Phase 1 tested water, SH, PAA, LA, and 0.5% CPC on meat inoculated with non–acid-habituated pathogen populations, whereas phase 2 tested water, SC, AH, ASC, LA, and 0.1% CPC on meat inoculated with acid- and non–acid-habituated populations. Reductions in non–acid-habituated E. coli O157:H7 populations from phase 1 increased in the order NT = water = SH < PAA < LA < CPC. Reductions from phase 2 for acid-habituated cells increased in the order NT = water = SC < ASC = LA = AH < CPC, whereas on non–acid-habituated cells the order observed was NT = water = SC < AH = ASC < LA < CPC. Previous acid habituation of E. coli O157:H7 inocula rendered the cells more resistant to the effects of spray chilling, especially with acid; however, the trend of reduction remained spray chilling with water = non–spray chilling < spray chilling with chemical solutions.

Reduction of Escherichia coli O157:H7 and Salmonella Typhimurium on Beef Carcass Surfaces Using Acidified Sodium Chlorite

1999 ◽  
Vol 62 (6) ◽  
pp. 580-584 ◽  
Author(s):  
A. CASTILLO ◽  
L. M. LUCIA ◽  
G. K. KEMP ◽  
G. R. ACUFF
Keyword(s):  
Escherichia Coli ◽  
Salmonella Typhimurium ◽  
Room Temperature ◽  
Surface Region ◽  
Sodium Chlorite ◽  
Escherichia Coli O157 ◽  
Method Detection Limit ◽  
E Coli ◽  
Better Than ◽  
Beef Carcass

The efficacy of a phosphoric acid–activated acidified sodium chloride (PASC) spray and a citric acid–activated acidified sodium chlorite (CASC) spray applied at room temperature (22.4 to 24.7°C) in combination with a water wash was compared with that of a water wash only treatment for reduction of Escherichia coli O157:H7 and Salmonella Typhimurium inoculated onto various hot-boned individual beef carcass surface regions (inside round, outside round, brisket, flank, and clod). Initial counts of 5.5 and 5.4 log CFU/cm2 were obtained after inoculation with E. coli O157:H7 and Salmonella Typhimurium, respectively. Initial numbers for both pathogens were reduced by 3.8 to 3.9 log cycles by water wash followed by PASC spray and by 4.5 to 4.6 log cycles by water wash followed by CASC spray. The sprays consisted of applying 140 ml of the appropriate sanitizing solution for 10 s at 69 kPa. Corresponding reduction values obtained by water wash alone were 2.3 log. The performance of CASC appeared to be consistently better than that of PASC. In general, no effect of the carcass surface region was observed on the log reductions for either pathogen, except for the inside round, which consistently had lower reductions. Both PASC and CASC were capable of effectively reducing pathogens spread to areas beyond the initial contaminated area of the cuts to levels close to or below the counting method detection limit (0.5 log CFU/cm2). However, 30 to 50% of the carcasses treated by these antimicrobial solutions still yielded countable colonies. Results of this study indicate that acidified sodium chlorite sprays are effective for decontaminating beef carcass surfaces.

Identification of Escherichia coli O157:H7 Meat Processing Indicators for Fresh Meat through Comparison of the Effects of Selected Antimicrobial Interventions

2005 ◽  
Vol 68 (12) ◽  
pp. 2580-2586 ◽  
Author(s):  
K. M. MARSHALL ◽  
S. E. NIEBUHR ◽  
G. R. ACUFF ◽  
L. M. LUCIA ◽  
J. S. DICKSON
Keyword(s):  
Escherichia Coli ◽  
Lactic Acid ◽  
Beef Cattle ◽  
Tissue Sample ◽  
Tissue Type ◽  
Escherichia Coli O157 ◽  
Fresh Meat ◽  
E Coli ◽  
The Mean ◽  
Beef Carcass

Fresh meat products can become contaminated with the pathogen Escherichia coli O157:H7 during the slaughter process; therefore, an E. coli O157:H7 indicator to verify the effectiveness of process controls in slaughter establishments would be extremely useful. The hides of 20 beef cattle were sampled, and 113 bacterial isolates were obtained. Thirteen of these isolates representing four genera, Escherichia, Enterobacter, Providencia, and Serratia, were selected based on growth and biochemical characteristics similar to those of five clinical strains of E. coli O157:H7. The temperature sensitivity was determined for the individual isolates and the five E. coli O157:H7 strains at 55 and 65°C. D65-values for all 13 isolates were not significantly different from D65-values of the E. coli O157:H7 strains. E. coli isolates were the only isolates whose D55-values were not significantly different from those of the E. coli O157:H7 strains. E. coli isolates P3 and P68 were more resistant to the effects of 55°C than were the other E. coli isolates but were not significantly different from E. coli O157:H7 WS 3331 (P > 0.05). The remaining E. coli isolates (P1, P8, and P14) were not significantly different from E. coli O157:H7 strains ATCC 35150, ATCC 43894, ATCC 43895, and WS 3062 (P > 0.05). Prerigor lean and adipose beef carcass tissue was artificially contaminated with stationary-phase cultures of the five E. coli beef cattle isolates or a cocktail of five E. coli O157:H7 strains in a fecal inoculum. Each tissue sample was processed with the following microbial interventions: 90°C water; 90°C water followed by 55°C 2% lactic acid; 90°C water followed by 20°C 2% lactic acid; 20°C water followed by 20°C 2% lactic acid; 20°C water followed by 20°C 20 ppm chlorine; and 20°C water followed by 20°C 10% trisodium phosphate. The appropriateness of the E. coli isolates as potential E. coli O157:H7 indicators was dependent upon the microbial intervention utilized. For all microbial intervention methods applied irrespective of tissue type, the mean log reductions of at least two E. coli isolates were not significantly different from the mean log reduction of the E. coli O157:H7 cocktail (P > 0.05). Because of the frequent employment of multiple microbial interventions in the cattle industry, no single isolate can realistically represent the effectiveness of all microbial interventions for reduction of E. coli O157:H7. Thus, the use of a combination of E. coli isolates may be required to accurately predict the effectiveness of microbial intervention methods on the reduction of E. coli O157: H7 in beef carcass tissue.

Validation of Lactic Acid Bacteria, Lactic Acid, and Acidified Sodium Chlorite as Decontaminating Interventions To Control Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 in Mechanically Tenderized and Brine-Enhanced (Nonintact) Beef at the Purveyor

2010 ◽  
Vol 73 (12) ◽  
pp. 2169-2179 ◽  
Author(s):  
ALEJANDRO ECHEVERRY ◽  
J. CHANCE BROOKS ◽  
MARKUS F. MILLER ◽  
JESSE A. COLLINS ◽  
GUY H. LONERAGAN ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Salmonella Typhimurium ◽  
Control Point ◽  
Meat Products ◽  
Sodium Chlorite ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Critical Control Point

After three different outbreaks were linked to the consumption of nonintact meat products contaminated with Escherichia coli O157:H7, the U.S. Food Safety and Inspection Service published notice requiring establishments producing mechanically tenderized and moisture-enhanced beef products to reassess their respective hazard analysis and critical control point systems, due to potential risk to the consumers. The objective of this study was to validate the use of lactic acid bacteria (LAB), acidified sodium chlorite (ASC), and lactic acid (LA) sprays when applied under a simulated purveyor setting as effective interventions to control and reduce E. coli O157:H7 and Salmonella Typhimurium DT 104 in inoculated U.S. Department of Agriculture (USDA) Choice strip loins (longissimus lumborum muscles) pieces intended for either mechanical blade tenderization or injection enhancement with a brine solution after an aging period of 14 or 21 days at 4.4°C under vacuum. After the mechanical process, translocation of E. coli O157:H7 and Salmonella Typhimurium DT 104 from the surface into the internal muscles occurred at levels between 1.00 and 5.72 log CFU/g, compared with controls. LAB and LA reduced internal E. coli O157:H7 loads up to 3.0 log, while ASC reduced the pathogen 1.4 to 2.3 log more than the control (P < 0.05), respectively. Salmonella Typhimurium DT 104 was also reduced internally 1.3 to 2.8, 1.0 to 2.3, and 1.4 to 1.8 log after application of LAB, LA, and ASC, respectively. The application of antimicrobials by purveyors prior to mechanical tenderization or enhancement of steaks should increase the safety of these types of products.

Validation of Intervention Strategies To Control Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 in Mechanically Tenderized and Brine-Enhanced Beef

2009 ◽  
Vol 72 (8) ◽  
pp. 1616-1623 ◽  
Author(s):  
ALEJANDRO ECHEVERRY ◽  
J. CHANCE BROOKS ◽  
MARKUS F. MILLER ◽  
JESSE A. COLLINS ◽  
GUY H. LONERAGAN ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Salmonella Typhimurium ◽  
Intervention Strategies ◽  
Sodium Chlorite ◽  
Point System ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Beef Products

After three different outbreaks were linked to the consumption of nonintact meat products contaminated with Escherichia coli O157:H7, the U.S. Department of Agriculture, Food Safety and Inspection Service published notice requiring establishments producing mechanically tenderized and moisture-enhanced beef products to reassess their respective hazard analysis and critical control point system, due to potential risk to the consumers. The purpose of this study was to determine the effectiveness of different intervention strategies (lactic acid, lactic acid bacteria, and acidified sodium chlorite) to control E. coli O157:H7 and Salmonella enterica serotype Typhimurium definitive phage type 104 in mechanically tenderized and brine-enhanced beef strip loins when applied to the steaks prior to packaging and shipment for processing. After the mechanical process, translocation of E. coli O157:H7 and Salmonella Typhimurium DT 104 from the surface into the internal muscles occurred at levels between 2.0 and 4.0 log CFU/g (from an initial inoculation level of 5.0 log) after mechanical tenderization, and at levels of 1.0 to 3.0 log CFU/g after injection, with all the interventions consistently presenting lower microbial counts (P < 0.05) than did the controls. Lactic acid bacteria reduced internal E. coli O157:H7 loads 1.2 to >2.2 log cycles, while the acidified sodium chlorite and lactic acid reduced them between 0.8 and 3.0 log, respectively. Salmonella Typhimurium DT 104 was also reduced internally after application of all interventions between 0.9 and 2.2 log. The application of antimicrobials to the steaks prior to packaging and shipment on day 0 was effective in reducing internalization of both pathogens in nonintact beef products stored for both 14 and 21 days.

Inactivation of Escherichia coli O157:H7, Salmonella enterica Serotype Enteritidis, and Listeria monocytogenes on Lettuce by Hydrogen Peroxide and Lactic Acid and by Hydrogen Peroxide with Mild Heat

2002 ◽  
Vol 65 (8) ◽  
pp. 1215-1220 ◽  
Author(s):  
CHIA-MIN LIN ◽  
SARAH S. MOON ◽  
MICHAEL P. DOYLE ◽  
KAY H. McWATTERS
Keyword(s):  
Escherichia Coli ◽  
Hydrogen Peroxide ◽  
Lactic Acid ◽  
Listeria Monocytogenes ◽  
Salmonella Enterica ◽  
Salmonella Enteritidis ◽  
Sensory Characteristics ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Log Reduction

Iceberg lettuce is a major component in vegetable salad and has been associated with many outbreaks of foodborne illnesses. In this study, several combinations of lactic acid and hydrogen peroxide were tested to obtain effective antibacterial activity without adverse effects on sensory characteristics. A five-strain mixture of Escherichia coli O157:H7, Salmonella enterica serotype Enteritidis, and Listeria monocytogenes was inoculated separately onto fresh-cut lettuce leaves, which were later treated with 1.5% lactic acid plus 1.5% hydrogen peroxide (H2O2) at 40°C for 15 min, 1.5% lactic acid plus 2% H2O2 at 22°C for 5 min, and 2% H2O2 at 50°C for 60 or 90 s. Control lettuce leaves were treated with deionized water under the same conditions. A 4-log reduction was obtained for lettuce treated with the combinations of lactic acid and H2O2 for E. coli O157:H7 and Salmonella Enteritidis, and a 3-log reduction was obtained for L. monocytogenes. However, the sensory characteristics of lettuce were compromised by these treatments. The treatment of lettuce leaves with 2% H2O2 at 50°C was effective not only in reducing pathogenic bacteria but also in maintaining good sensory quality for up to 15 days. A ≤4-log reduction of E. coli O157:H7 and Salmonella Enteritidis was achieved with the 2% H2O2 treatment, whereas a 3-log reduction of L. monocytogenes was obtained. There was no significant difference (P > 0.05) between pathogen population reductions obtained with 2% H2O2 with 60- and 90-s exposure times. Hydrogen peroxide residue was undetectable (the minimum level of sensitivity was 2 ppm) on lettuce surfaces after the treated lettuce was rinsed with cold water and centrifuged with a salad spinner. Hence, the treatment of lettuce with 2% H2O2 at 50°C for 60 s is effective in initially reducing substantial populations of foodborne pathogens and maintaining high product quality.

Influence of Sodium Chloride on Growth of Lactic Acid Bacteria and Subsequent Destruction of Escherichia coli O157:H7 during Processing of Lebanon Bologna

2001 ◽  
Vol 64 (8) ◽  
pp. 1145-1150 ◽  
Author(s):  
NAVEEN CHIKTHIMMAH ◽  
RAMASWAMY C. ANANTHESWARAN ◽  
ROBERT F. ROBERTS ◽  
EDWARD W. MILLS ◽  
STEPHEN J. KNABEL
Keyword(s):  
Escherichia Coli ◽  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Low Ph ◽  
Escherichia Coli O157 ◽  
Quality Changes ◽  
E Coli ◽  
Fermented Product ◽  
Nacl Concentration ◽  
Different Levels

Due to undesirable quality changes, Lebanon bologna is often processed at temperatures that do not exceed 48.8°C (120°F). Therefore, it is important to study parameters that influence the destruction of Escherichia coli O157:H7 in Lebanon bologna. The objective of the present study was to determine the influence of curing salts (NaCl and NaNO2) on the destruction of E. coli O157:H7 during Lebanon bologna processing. Fermentation to pH 4.7 at 37.7°C reduced populations of E. coli O157:H7 by approximately 0.3 log10, either in the presence or absence of curing salts. Subsequent destruction of E. coli O157:H7 during heating of fermented product to 46.1°C was significantly reduced by the presence of 3.5% NaCl and 156 ppm NaNO2, compared to product without curing salts (P < 0.01). The presence of a higher level of NaCl (5%) in Lebanon bologna inhibited the growth of lactic acid bacteria (LAB), which yielded product with higher pH (~5.0) and significantly reduced the destruction of E. coli O157:H7 even further (P < 0.05). Lower concentrations of NaCl (0, 2.5%) yielded Lebanon bologna with higher LAB counts and lower pHs, compared to product with 5% NaCl. When lactic acid was used to adjust pH in product containing different levels of NaCl, it was determined that low pH was directly influencing destruction of E. coli O157:H7, not NaCl concentration.

Decontamination of Beef Subprimal Cuts Intended for Blade Tenderization or Moisture Enhancement

2007 ◽  
Vol 70 (5) ◽  
pp. 1174-1180 ◽  
Author(s):  
C. E. HELLER ◽  
J. A. SCANGA ◽  
J. N. SOFOS ◽  
K. E. BELK ◽  
W. WARREN-SERNA ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Lactic Acid ◽  
Hot Water ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Low Concentrations ◽  
Blade Tenderization ◽  
Antimicrobial Interventions

The prevalence of Escherichia coli O157:H7 on beef subprimal cuts intended for mechanical tenderization was evaluated. This evaluation was followed by the assessment of five antimicrobial interventions at minimizing the risk of transferring E. coli O157:H7 to the interior of inoculated subprimal cuts during blade tenderization (BT) or moisture enhancement (ME). Prevalence of E. coli O157:H7 on 1,014 uninoculated beef subprimals collected from six packing facilities was 0.2%. Outside round pieces inoculated with E. coli O157:H7 at 104 CFU/100 cm2 were treated with (i) no intervention, (ii) surface trimming, (iii) hot water (82°C), (iv) warm 2.5% lactic acid (55°C), (v) warm 5.0% lactic acid (55°C), or (vi) 2% activated lactoferrin followed by warm 5.0% lactic acid (55°C) and then submitted to BT or ME. Prevalence (n = 196) of internalized (BT and ME) E. coli O157:H7 was 99%. Enumeration of E. coli O157:H7 (n = 192) revealed mean surface reductions of 0.93 to 1.10 log CFU/100 cm2 for all antimicrobial interventions. E. coli O157:H7 was detected on 3 of the 76 internal BT samples and 73 of the 76 internal ME samples. Internal ME samples with no intervention had significantly higher mean E. coli O157:H7 populations than did those internal samples treated with an intervention, but there were no significant differences in E. coli O157:H7 populations among internal BT samples. Results of this study demonstrate that the incidence of E. coli O157:H7 on the surface of beef subprimal cuts is low and that interventions applied before mechanical tenderization can effectively reduce the transfer of low concentrations of E. coli O157:H7 to the interior of beef subprimal cuts.

Validation of the Use of Organic Acids and Acidified Sodium Chlorite To Reduce Escherichia coli O157 and Salmonella Typhimurium in Beef Trim and Ground Beef in a Simulated Processing Environment

2006 ◽  
Vol 69 (8) ◽  
pp. 1802-1807 ◽  
Author(s):  
K. HARRIS ◽  
M. F. MILLER ◽  
G. H. LONERAGAN ◽  
M. M. BRASHEARS
Keyword(s):  
Escherichia Coli ◽  
Salmonella Typhimurium ◽  
Frozen Storage ◽  
Ground Beef ◽  
Sodium Chlorite ◽  
Escherichia Coli O157 ◽  
Refrigerated Storage ◽  
E Coli ◽  
Log Reduction ◽  
Antimicrobial Treatments

A study was conducted to determine if acidified sodium chlorite (1,200 ppm) and acetic and lactic acids (2 and 4%) were effective in reducing foodborne pathogens in beef trim prior to grinding in a simulated processing environment. The reduction of Salmonella Typhimurium and Escherichia coli O157:H7 at high (4.0 log CFU/g) and low (1.0 log CFU/g) inoculation doses was evaluated at various processing steps, including the following: (i) in trim just after treatment application, (ii) in ground beef just after grinding, (iii) in ground beef 24 h after refrigerated storage, (iv) in ground beef 5 days after refrigerated storage, and (v) in ground beef 30 days after frozen storage. All antimicrobial treatments reduced the pathogens on the trim inoculated with the lower inoculation dose to nondetectable numbers in the trim and in the ground beef. There were significant reductions of both pathogens in the trim and in the ground beef inoculated with the high inoculation doses. On the trim itself, E. coli O157:H7 and Salmonella Typhimurium were reduced by 1.5 to 2.0 log cycles, with no differences among all treatments. In the ground beef, the organic acids were more effective in reducing both pathogens than the acidified sodium chlorite immediately after grinding, but after 1 day of storage, there were no differences among treatments. Overall, in the ground beef, there was a 2.5-log reduction of E. coli O157:H7 and a 1.5-log reduction of Salmonella Typhimurium that was sustained over time in refrigerated and frozen storage. Very few sensory differences between the control samples and the treated samples were detected by a consumer panel. Thus, antimicrobial treatments did not cause serious adverse sensory changes. Use of these antimicrobial treatments can be a promising intervention available to ground beef processors who currently have few interventions in their process.

Effects of Plant-Derived Extracts, Other Antimicrobials, and Their Combinations against Escherichia coli O157:H7 in Beef Systems

2015 ◽  
Vol 78 (6) ◽  
pp. 1090-1097 ◽  
Author(s):  
KYUNG YUK KO ◽  
IFIGENIA GEORNARAS ◽  
HYUN-DONG PAIK ◽  
KEE-TAE KIM ◽  
JOHN N. SOFOS
Keyword(s):  
Escherichia Coli ◽  
Lactic Acid ◽  
Untreated Control ◽  
Sodium Tripolyphosphate ◽  
Model System ◽  
Surface Contamination ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Blade Tenderization ◽  
Sodium Diacetate

The antimicrobial effects of thyme oil (TO), grapefruit seed extract (GSE), and basil essential oil, alone or in combination with cetylpyridinium chloride (CPC), sodium diacetate, or lactic acid, were evaluated against Escherichia coli O157:H7 in a moisture-enhanced beef model system. The model system was composed of a nonsterile beef homogenate to which NaCl (0.5%) and sodium tripolyphosphate (0.25%) were added, together with the tested antimicrobial ingredients. Beef homogenate treatments were inoculated (ca. 3 log CFU/ml) with rifampin-resistant E. coli O157:H7 (eight-strain mixture) and incubated at 15°C (48 h). The most effective individual treatments were TO (0.25 or 0.5%) and GSE (0.5 or 1.0%), which immediately reduced (P < 0.05) pathogen levels by ≥3.4 log CFU/ml. Additionally, CPC (0.04%) reduced initial E. coli O157:H7 counts by 2.7 log CFU/ml. Most combinations of the tested plant-derived extracts with CPC (0.02 or 0.04%) and sodium diacetate (0.25%) had an additive effect with respect to antibacterial activity. In a second study, antimicrobial interventions were evaluated for their efficacy in reducing surface contamination of E. coli O157:H7 on beef cuts and to determine the effect of these surface treatments on subsequent internalization of the pathogen during blade tenderization. Beef cuts (10 by 8 by 3.5 cm) were inoculated (ca. 4 log CFU/g) on one side with the rifampin-resistant E. coli O157:H7 strain mixture and were then spray treated (20 lb/in2, 10 s) with water, GSE (5 and 10%), lactic acid (5%), or CPC (5%). Untreated (control) and spray-treated surfaces were then subjected to double-pass blade tenderization. Surface contamination (4.4 log CFU/g) of E. coli O157:H7 was reduced (P < 0.05) to 3.4 (5% CPC) to 4.1 (water or 5% GSE) log CFU/g following spray treatment. The highest and lowest transfer rates of pathogen cells from the surface to deeper tissues of blade-tenderized sections were obtained in the untreated control and CPC-treated samples, respectively.

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