Thin Agar Layer Research Articles

Evaluation of a Double Layer Agar Plate For Direct Enumeration of Vibrio parahaemolyticus

ABSTRACTA double layer agar plate (DLAP) was developed according to the thin agar layer (TAL) method as a 1‐step procedure for direct enumeration of injured Vibrio parahaemolyticus cells based on the formation of unique purple colonies by V. parahaemolyticus. The DLAP was prepared by overlaying an equal volume (10 mL) of a nonselective medium (tryptic soy agar supplemented with 1.5% NaCl) onto a selective medium (Bio‐Chrome Vibrio medium). The DLAP was capable of detecting V. parahaemolyticus in mixed cultures containing non‐Vibrio bacteria. Production of purple colonies by V. parahaemolyticus on DLAP was not affected by the growth of other bacteria, even when V. parahaemolyticus was only a small fraction (5%) of the entire bacterial population. Direct plating on DLAP was found as effective as the most probable number (MPN) method for recovering heat‐and cold‐injured V. parahaemolyticus cells, which could not be detected by direct plating on Bio‐Chrome Vibrio medium or thiosulfate‐citrate‐bile salts‐sucrose agar. The DLAP offers an alternative to the MPN method for detecting injured V. parahaemolyticus cells and can be used as a simple 1‐step procedure for quick screening of V. parahaemolyticus in foods.

A Solid Agar Overlay Method for Recovery of Heat-Injured Listeria monocytogenes

A solid agar overlay method was developed for recovery of heat-injured Listeria monocytogenes. Presolidified nonselective tryptic soy agar with 0.6% yeast extract (TSAYE, 2% agar) was overlaid on top of solidified modified Oxford agar (MOX). Heat injury of L. monocytogenes was conducted at 58°C for 6 min in a jacketed flask filled with tryptic soy broth. Both noninjured and heat-treated L. monocytogenes cells were plated onto TSAYE, MOX, and TSAYE-MOX plates. No significant differences (P > 0.05) in recovery were found among the three media for noninjured bacterial cells. Recovery of heat-injured L. monocytogenes cells on TSAYE-MOX overlay plates was equivalent to that on the nonselective TSAYE medium, whereas recovery on the selective MOX medium was significantly lower (P < 0.05) compared with both TSAYE and the overlay plates. There were no significant differences (P > 0.05) among the overlay plates prepared 0, 2, 4, 6, 8, 16, and 24 h prior to plating heat-injured bacterial cells. The TSAYE-MOX overlay also allowed differentiation of L. monocytogenes from a mixture of four other types of foodborne pathogens. This solid agar overlay method for recovery of heat-injured L. monocytogenes cells is less time-consuming and less complicated than the conventional overlay-underlay technique and the double overlay modification of the thin agar layer method and may allow for greater laboratory plating efficiencies.

Effects of Recovery, Plating, and Inoculation Methods on Quantification of Escherichia coli O157:H7 and Listeria monocytogenes from Strawberries

Effects of different recovery and inoculation methods on quantification of Escherichia coli O157:H7 and Listeria monocytogenes from strawberries were studied. Strawberries were spot or dip inoculated with 7 to 8 log CFU per strawberry of each pathogen, air dried for 2 h, and stored for 1, 3, and 7 days at 4°C. The inoculated samples were stomached or washed with phosphate-buffered saline (PBS; pH 7.2) or with modified PBS (pH 8.4). Bacterial levels were determined using a direct selective plating, thin agar layer plating, or membrane-transferring plating (MTP) with tryptic soy agar and sorbital MacConkey agar (E. coli O157:H7) or modified Oxford agar (L. monocytogenes). Under most test conditions, washing with PBS followed by MTP had significantly higher (P < 0.05) recovery for both bacteria compared with other tested methods. Within a 7-day storage period for spot-inoculated strawberries, a stomaching step resulted in an injury of 0.9 to 1.4 log CFU for E. coli O157: H7 and 1.4 to 1.7 log CFU for L. monocytogenes. When a washing step was used instead, this resulted in an injury of only 0.2 to 0.6 log CFU for E. coli O157:H7 and 0.2 to 0.7 log CFU for L. monocytogenes. Both bacteria could survive on strawberry surfaces, but their recovered levels decreased with the increase of storage time at 4°C for both spot and dip inoculation methods. Dip inoculation generally had a lower recovery than spot inoculation. An ideal protocol to recover and enumerate E. coli O157:H7 and L. monocytogenes from strawberries involved shaking and washing samples with 100 ml of PBS for 15 min at 22°C coupled with a MTP enumeration method.

An Improved Method for a Hydrophobic Grid‐membrane Filter System to Detect Heat‐injured Foodborne Pathogens in Ground Beef

ABSTRACT: Recovery of heat‐injured pathogens (Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium, and Yersinia enterocolitica) in ground beef samples was studied by the thin agar layer (TAL) and TAL = Oxyrase® (TALO) methods in conjunction with the ISO‐GRID® hydrophobic grid‐membrane filter (HGMF). This new combination using ISO‐GRID HGMFs with the TAL and TALO methods improved the efficiency (P &lt; 0.05) of recovery of pathogens. In addition, the TALO method showed a higher percentage increase of recovery than the TAL method because of stimulation of Oxyrase in growth of pathogens. The combination allows the detection of very low numbers of pathogens in food.

Inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 in Apple Juice by a Combination of Nisin and Cinnamon

Pasteurized apple juice with nisin (0, 25, 50, 100, and 200 ppm, wt/vol) and cinnamon (0 and 0.3%, wt/vol) was inoculated with Salmonella Typhimurium and Escherichia coli O157:H7 at 104 CFU/ml and stored at 5 and 20°C. Counts on tryptic soy agar (TSA), selective medium (xylose lysine desoxycholate agar for Salmonella Typhimurium, and MacConkey sorbitol agar for E. coli O157:H7), and thin agar layer (TAL) were determined at 1 h and 1, 3, 7, and 14 days. The TAL method (selective medium overlaid with TSA) was used for recovery of sublethally injured cells. The pathogens were gradually inactivated by the acidic pH of apple juice. Nisin and cinnamon greatly contributed to the inactivation. The killing effect was more marked at 20°C, with counts in all treated samples being undetectable by direct plating in 3 days for Salmonella Typhimurium and 7 days for E. coli O157:H7. Thus, several factors influenced the decrease in counts: low pH, addition of nisin and cinnamon, and storage temperature. The TAL method was as effective as TSA in recovering injured cells of the pathogens. The combination of nisin and cinnamon accelerates death of Salmonella Typhimurium and E. coli O157:H7 in apple juice and so enhances the safety of the product.

Evaluation of a 5′ -Nuclease (TaqMan) Assay with the Thin Agar Layer Oxyrase Method for the Detection of Yersinia enterocolitica in Ground Pork Samples

A 5′-nuclease (TaqMan) assay was evaluated for its capability to recover and detect stressed Yersinia enterocolitica. Sensitivity studies of a 5′-nuclease assay for detecting Y. enterocolitica O:8 in a pure culture system and spiked ground pork samples demonstrated that the assay has reliable sensitivity with a detection limit of 3 to 4 log CFU/ml or CFU/g. The PCR 5′-nuclease (TaqMan) assay was evaluated with the Thin Agar Layer Oxyrase method (TALO, overlaying 14 ml of Trypticase soy agar with a 1:30 dilution of “Oxyrase® for Agar” onto a prepoured pathogen-specific, selective medium), and it was compared against the selective medium cefsulodin-irgasan-novobiocin (CIN) for recovering and detecting Y. enterocolitica from inoculated nonfrozen and frozen (−15°C, 2 days) ground pork samples. The TALO method showed more sensitivity (detection limit, 2 log CFU/ml), and it has greater recovery capability (0.5 to 1 log CFU/ml) than CIN (P < 0.05). The 5′-nuclease assay provided rapid detection processing (5 versus 24 h after an 18-h enrichment). The sensitivity per PCR was calculated to as low as 0 to 1 log CFU per PCR reaction; however, in the method's current developmental stage, target pathogens should be enriched to 3 to 4 log CFU/ml or CFU/g to show consistent results. In a survey of 100 ground pork samples using TALO, CIN, and PCR methods, no Y. enterocolitica was recovered. A combined cultivation and an automated PCR TaqMan could be used as a presumptive screening test for detecting Y. enterocolitica in food samples.

Inactivation and sublethal injury of foodborne pathogens by high pressure processing: Evaluation with conventional media and thin agar layer method

The recovery of seven pathogens was determined in tryptone soya agar (TSA), selective medium and with the thin agar layer (TAL) method, to evaluate inactivation and sublethal injury caused by high pressure at 20 °C. The TAL method consists of selective medium overlaid with TSA. Cell suspensions were treated by combining different pressures (100-MPa increments) and times (1 and 5 min), until complete inactivation. Vibrio parahaemolyticus and Bacillus cereus were totally inactivated at 300 MPa for 5 min and 400 MPa for 1 min; Salmonella typhimurium, Escherichia coli and Yersinia enterocolitica, at 400 MPa for 1 min; and Listeria monocytogenes, at 400 MPa for 5 min and 500 MPa for 1 min. Staphylococcus aureus was the most resistant, being totally inactivated at 700 and 800 MPa for 5 min and 900 MPa for 1 min. Regarding recovery of injured cells, in most cases, counts on the three media were not different. The TAL method may allow differentiation of pathogens from background microbiota of foods.

Use of Conventional Media and Thin Agar Layer Method for Recovery of Foodborne Pathogens from Pressure‐treated Poultry Products

ABSTRACT: The recovery of 5 pathogens from minced chicken (MC) and liquid whole egg (LWE) was determined with tryptone soya agar (TSA), selective medium, and thin agar layer (TAL; selective medium overlaid with TSA) to evaluate high‐pressure effects at 200, 300, 400, and 500 MPa for 1 and 5 min at 20 °C. At 400 MPa for 5 min, Escherichia coli inactivation was 4 log in MC and 5.5 log in LWE, whereas no Salmonella Typhimurium, Yersinia enterocolitica, or Listeria monocytogenes were detected in either product. Staphylococcus aureus was the most pressure‐resistant. In general, counts on the 3 media were not different. The TAL method allows differentiation of the inoculated pathogens from background microbiota.

Reduction of Bacteria on Pork Carcasses Associated with Chilling Method

In addition to reducing the temperature of pork carcasses immediately after slaughter and before fabrication, blast chilling (snap chill) or conventional chilling can reduce bacterial populations associated with fresh meats. However, there is little information on bacteria survival resulting from the freeze or chill injury of meat products. In this study, porcine fecal slurries with and without pathogens (Listeria monocytogenes, Salmonella Typhimurium, and Campylobacter coli) were inoculated onto skin-on and skin-off pork surfaces and subjected to industry-specific blast or conventional chilling conditions. A thin agar layer method was used for the recovery of freeze- or chill-injured cells. Test results indicated that there were no statistically significant (P > 0.05) differences between blast and conventional chilling treatments with respect to the reduction of high and low inoculation levels of mesophilic aerobic bacteria, total coliforms, or Escherichia coli on either skin-on or skin-off surfaces. Chilling treatments did not differ significantly (P > 0.05) with respect to their ability to reduce low (3 log10 CFU/cm2) levels of L. monocytogenes and Salmonella Typhimurium. However, C. coli was reduced to undetectable levels, even after enrichment, on pork surfaces inoculated with low levels (3 log10 CFU/cm2) and subjected to blast chilling. Blast and conventional chilling treatments were more effective against all pathogenic bacterial populations when pork surfaces where inoculated at high levels (5 log10 CFU/cm2). The effects of chilling techniques on microbial populations could provide pork processors with an additional intervention for pork slaughter or information to modify and/or improve the chilling process. The information obtained from this study has the potential to serve as a means of producing a microbiologically safer product.

Comparison of Recovery Methods for Freeze-Injured Listeria monocytogenes, Salmonella Typhimurium, and Campylobacter coli in Cell Suspensions and Associated with Pork Surfaces

Cells injured as a result of freezing, heating, and acidification treatments may not grow during conventional microbiological procedures owing to the presence of selective agents, compounds, or dyes in the media, impairing the cell's ability to repair itself and grow. Injured cells can be recovered by combining selective and nonselective media into a single system. With such combinations, the diffusion of the selective compounds or dyes is controlled, allowing for the resuscitation of injured cells of interest while also inhibiting the growth of undesirable background microflora. In this study, Listeria monocytogenes, Salmonella Typhimurium, and Campylobacter coli suspended in buffer or associated with pork surfaces were subjected to a freeze-thaw cycle (−15°C for 24 h, 4°C for 4 h). Following treatments, freeze-injured cells were plated on appropriate media for the overlay (OV), thin agar layer (TAL), and Lutri plate (LP) recovery methods. The levels of L. monocytogenes and Salmonella Typhimurium recovered from cell suspensions and pork surfaces by the TAL, OV, and LP methods following freeze treatments were not statistically different (P > 0.05) from recovery levels associated with nonselective media. Conversely, levels of pathogens on selective media were significantly reduced compared with those for the other methods employed. The TAL method's recovery of C. coli was not significantly different from that achieved with the nonselective media. Overall, the results presented in this study demonstrate that the TAL method not only was easier to perform, but also allowed improved isolation of single colonies for further characterization. This study may provide researchers with better methods to determine the effectiveness of industry-employed chilling processes in reducing pathogenic bacteria associated with red meat surfaces.

Evaluation of Salmonella typhimurium, Yersinia enterocolitica and Staphylococcus aureus counts in apple juice with cinnamon, by conventional media and thin agar layer method

Pasteurized apple juice (pH 3.64) with cinnamon (0% and 0.3%) was inoculated with Salmonella typhimurium, Yersinia enterocolitica or enterotoxigenic Staphylococcus aureus at 10 4 cfu ml −1, and stored at 5°C and 20°C. Counts on tryptic soy agar (TSA), selective medium and thin agar layer (TAL) were determined at 1 h and 1, 3, 7 and 14 days. The TAL method (selective medium overlaid with TSA) was for recovery of injured cells. In general, the sensitivity of pathogens to cinnamon in descending order was Staph. aureus, Y. enterocolitica and S. typhimurium. Staph. aureus (1.2 log cfu ml −1 at 3 days) and Y. enterocolitica (0.3 log cfu ml −1 at 1 day) were the most acid-sensitive at 5°C and 20°C, respectively. At some points of storage, the killing effect was significantly ( P<0.05) more pronounced at 20°C for the three pathogens, with c. 4 log cfu ml −1 reductions in 1 day in Y. enterocolitica-inoculated samples with and without cinnamon, and in Staph. aureus-inoculated samples with cinnamon. Counts on TSA and TAL did not differ significantly ( P>0.05) in any case. So, both media showed similar effectiveness in recovering damaged cells of the three pathogens. Cinnamon inactivates important foodborne pathogens in apple juice and thus enhances the safety of this product.

Simultaneous Recovery of Four Heat‐injured Foodborne Pathogens from a Four‐compartment Thin Agar Layer Plate

ABSTRACT: We have developed and tested a 1‐step resuscitation thin agar layer (TAL) system (nonselective agar overlaid on selective agar) to effectively recover heat‐, acid‐, cold‐, and salt‐injured foodborne pathogens in liquid foods. Each TAL unit was designed for the recovery of one injured population. To improve operation efficiency we have developed a single 4‐compartment Petri dish to simultaneously recover heat‐injured Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium, and Yersinia enterocolitica. No significant difference occurred between the single recovery unit and the 4‐compartment unit for enumeration of 4 heat‐injured pathogens (P &gt; 0.05). This 4‐compartment TAL system is at least 4 times more efficient than the single TAL system.

Combination of Carbon Dioxide and Cinnamon to Inactivate Escherichia coli O157:H7 in Apple Juice

ABSTRACT: Pasteurized apple juice with CO2 (0, 1, and 4%) and cinnamon (0 and 0.3%) was inoculated with Escherichia coli O157:H7 at 104 CFU/mL, and stored at 5 and 20 °C. Counts on nonselective and selective media, and thin agar layer (TAL; selective medium overlaid with nonselective medium) were determined at 1 h and 1, 3, 7, and 14 d. Inactivation was greater at 20 °C. Samples with 1 and 4% CO2, alone and combined with cinnamon, presented &lt; 0.7 log CFU/mL in 3 d. Counts in apple juice inoculated at 102 CFU/mL, a low‐level E. coli O157:H7 contamination, were nondetectable at 3 d. The TAL method was as effective as nonselective medium to recover injured cells.

Inactivation of Listeria monocytogenes Scott A 49594 in Apple Juice Supplemented with Cinnamon

Normal (pH 3.7) and adjusted (pH 5.0) pasteurized apple juice containing cinnamon (0, 0.1, 0.2, and 0.3%) was inoculated with Listeria monocytogenes Scott A 49594 at 104 CFU/ml and stored at 5 and 20°C for 7 days. Counts on tryptic soy agar (TSA), modified Oxford (MOX) medium, and thin agar layer (TAL) were determined at 1 h and 1, 3, and 7 days. The TAL method (MOX medium overlaid with TSA) was used for the recovery of injured cells. In apple juice, both at normal and adjusted pH, with any doses of cinnamon, no L. monocytogenes (a 4.6-log CFU/ml reduction) was detected after 1 h of storage at both temperatures, and no growth occurred at any points of storage. Therefore, cinnamon by itself (regardless of pH) had a pronounced killing effect. A further enrichment step with brain heart infusion agar showed that L. monocytogenes was completely inactivated in apple juice stored at 20°C, except in pH 5.0 samples with 0.1% of cinnamon. The TAL method was as effective as TSA in recovering injured cells of L. monocytogenes. Cinnamon considerably inactivates L. monocytogenes in apple juice and thus enhances the safety of this product.

COMPARISON OF EGG‐YOLK‐FREE TRYPTOSE SULFITE CYCLOSERINE AND SHAHIDI‐FERGUSON‐PERFRINGENS MEDIA FOR ENUMERATION OF CLOSTRIDIUM PERFRINGENS IN MEAT PRODUCTS AND PEPTONE WATER USING FUNG'S DOUBLE TUBE METHOD1

This study compared the ability of Clostridium perfringens to recover in Fung's Double Tube (FDT) system using either tryptose‐sulfite‐cycloserine without egg yolk (TSC) or Shahidi‐Ferguson‐perfringens (SFP) agar both in three typical meat products and peptone water. A three‐strain cocktail of C. perfringens spores (ATCC 10388, NCTC 8238, and NCTC 8239) was inoculated in each food system at three inoculum levels: 102, 104, and 106 cfu/g or mL. FDT system consists of a smaller glass test tube inserted into a larger glass test tube in which sample and agar have been poured. By inserting the inner tube, the agar squeezes between the exterior wall of the small tube and the interior wall of the larger tube to form a thin agar layer, which creates an anaerobic environment. Tubes are then incubated in aerobic incubators. There were no significant differences in enumeration of C. perfringens between the two media in any of the meat products and peptone water at any inoculation level. Thus, the use of SFP, which is less expensive and easier to prepare than TSC, is recommended as an alternative agar for analyses of C. perfringens in FDT system. Compared to the petri dish method, the FDT method generates greater anaerobiosis, is easier to prepare, more compact, and eliminates the need for an overlay and an anerobic chamber or jar. Combined together, the use of SFP in the FDT system provides an efficient, easy‐to‐use method that is less expensive than the conventional method to detect and enumerate C. perfringens in foods.

Comparison of Recovery of Airborne Microorganisms in a Dairy Cattle Facility Using Selective Agar and Thin Agar Layer Resuscitation Media

Thin agar layer (TAL) medium was developed at Kansas State University to improve the resuscitation of injured cells and has been shown to result in higher recovery than is obtained with selective media alone for cold-, heat-, salt-, and acid-injured cells. The experiment presented here was designed to determine the effectiveness of the TAL method for the recovery of possibly injured organisms from air. Eleven agar media were used for the experiment: tryptic soy agar (TSA), MacConkey sorbitol agar (MSA), TAL-MSA, Baird-Parker (BP) agar, TAL-BP agar, modified Oxford (MOX) agar, TAL-MOX agar, xylose lysine sodium desoxycholate (XLD) agar, TAL-XLD agar, Yersinia-selective (CIN) agar, and TAL-CIN agar. The TAL plates were prepared by pipetting 6 ml of selective agar into a BBL Rodac plate (65 by 15 mm). Selective agar was allowed to solidify, and then each plate was overlaid with 6 ml of TSA. Selective agar plates were prepared by pipetting 12 ml of agar into BBL Rodac plates and allowing the agar to solidify. Samples were taken at an indoor cattle facility at five separate locations with a BioScience SAS air-sampling instrument. For each plate, 60 liters of air was sampled. Three replications of the experiment were performed. The TAL method resulted in higher counts of microorganisms on all media tested. In addition, 175 isolates were selected randomly and identified in order to test the selectivity of TAL and the selective media for target organisms. The data obtained in this study show that the TAL resuscitation method is effective and necessary for the recovery of airborne organisms that may be injured.

Immobilization of Aspergillus fumigatus colonies in a soft agar matrix allows visualization of A549 cell detachment and death.

A model to examine the effects of proliferating Aspergillus fumigatus ATCC 26933 colonies embedded in a thin layer of soft agar on a monolayer of A549 cells was developed and enabled an investigation of the response of cultured cells to fungal growth. This model simulates the conditions on the respiratory surface in patients with invasive aspergillosis and also in the mucus secretions of cystic fibrosis patients with allergic bronchopulmonary aspergillosis. Conidia of A. fumigatus adhering to A549 cells were immobilized in a thin layer of soft agar (0.6% (w/v)) and allowed to germinate at 37 degrees C. Fungal colonies greater than 5 mm in diameter caused rounding-up and detachment of A549 cells underneath the colony and towards the hyphal tips. As the fungal colony diameter increased, cell detachment occurred ahead of the hyphal tips. Cells detached for short periods (less than 6 h) showed no annexin-V (AV) or propidium iodide (PI) staining, suggesting no externalization of phosphatidylserine and an intact plasma membrane. Cells that had detached for periods greater than 6 h were positive for AV and PI indicating the rupture of the plasma membrane and cell death by necrosis. Chemical extraction and separation by thin layer chromatography of agar from zones of cell detachment around fungal colonies revealed the presence of three compounds that may play a role in inducing cell death.

A zinc–air cell employing a porous zinc electrode fabricated from zinc–graphite-natural biodegradable polymer paste

Porous zinc anodes have been fabricated from a mixture of zinc and graphite powder using gelatinized agar solution as the binding agent. Agar is a biodegradable polysaccharide polymer extracted from marine algae. The graphite content and the agar solution concentration were varied to find the best electrode composition. Zinc–air cells were fabricated using the porous zinc anode, a commercially available air cathode sheet and KOH electrolyte in the form of elastic jelly granules. The electrode performance was evaluated from the zinc–air cell galvanostatic discharge capability. In the cell design, a thin agar layer was introduced between the electrode-gelled electrolyte interfaces, resulting in substantially improved cell discharge performance. The inclusion of particulate graphite into the electrode did not enhance the electrode performance due to the formation of a graphite-rich layer, which obscured the electrode porosity. A zinc–air cell employing the optimized porous zinc electrode demonstrated a capacity of 2066 mA h and specific energy density of 443 Wh kg−1.

Effects of preparation method, age, and plating technique of thin agar layer media on recovery of Escherichia coli O157:H7 injured by sodium chloride

The thin agar layer (TAL) method was experimentally tested to determine its ability to recover Escherichia coli O157:H7 injured by sodium chloride (NaCl). Cells grown in Brain Heart Infusion broth with 0%, 5%, or 7.5% (w/v) NaCl were spread and spiral plated onto Tryptic Soy agar (TSA), MacConkey Sorbitol agar (MSA), and TSA/MSA TAL combinations. Generally, TSA recovered more injured cells than TAL ( p≤0.05), and TAL recovered more cells than MSA ( p≤0.05). Preparation mode (two vs. three layers) and age (0, 1, or 7 days) of TAL had negligible effect on resuscitation of injured cells ( p>0.05). TAL, which is conventionally used to recover heat, cold, and acid-injured foodborne pathogens, may be used to recover NaCl-injured E. coli O157:H7.

Evaluation of Thin Agar Layer Method for Recovery of Acid-Injured Foodborne Pathogens

The thin agar layer (TAL) method of Kang and Fung was used to enumerate acid-injured foodborne pathogens. This method involves overlaying 14 ml of nonselective medium (tryptic soy agar [TSA]) onto a prepoured and solidified pathogen-specific, selective medium in a petri dish. After surface plating, injured cells resuscitated and grew on TSA during the first few hours of incubation; then, the selective agents from the selective medium diffused to the top layer, interacted with the recovered microorganisms, and started to produce typical reactions. Foodborne pathogens were exposed to 2% acetic acid for 1, 2, or 4 min, and the recovery rate with the TAL method was compared with the rate of TSA and pathogen-specific, selective media. No significant difference occurred between TSA and TAL (P > 0.05) for enumeration of acid-injured Escherichia coli O157:H7, Salmonella Typhimurium, Staphylococcus aureus, and Yersinia enterocolitica, and both recovered significantly higher numbers than the selective medium for each respective pathogen (P < 0.05). For recovery of acid-injured Listeria monocytogenes, no difference (P > 0.05) occurred among TSA, TAL, and selective media. However, fewer cells were recovered in the selective media. The TAL method is a one-step, convenient procedure for recovery of acid-injured cells.