PetrifilmTM Aerobic Count Research Articles

Validation of the diagnostic accuracy of the 3M™ Petrifilm™ coliform and aerobic count plates to measure colostrum bacterial contamination on Scottish dairy farms

A calf should receive 10–12 % of its bodyweight in high quality colostrum ( >50 g/L immunoglobulin) shortly after birth in order to confer passive immunity, with calves ideally receiving their first feed of colostrum in the first 1–2 hours of life (Godden et al., 2019). It is recommended (not validated) that total counts for bacteria and coliforms in colostrum should not exceed 100,000 colony forming units per mL (CFU/mL) and 10,000 CFU/mL, respectively. This study was conducted between March and September 2023. Eighty-five colostrum samples from 5 commerical dairy farms in Dumfries and Galloway in Scotland were purposively selected. Samples were collected from various stages during the colostrum harvest, storage and feeding process to provide multiple samples with variable (low, medium and high) bacterial contamination. The objective of this study was to validate the diagnostic accuracy of the 3 M Petrifilm™ Coliform Count Plate (CCP) and Aerobic Count Plate (ACP) for colostrum bacteriology. The Petrifilm™ Aerobic Count Plates were compared to 5 % sheep blood agar (SBA) (total bacteria counts, TBC), and the Petrifilm™ Coliform Count Plates were compared to MacConkey plates (MAC) (total coliform counts, TCC) and test sensitivity and specificity were calculated.Colostrum bacterial contamination was highly variable between farms (TBC median and interquartile range= 50,000CFU/mL and 546000CFU/mL; TCC median and interquartile range=100,750CFU/mL and 188,500CFU/mL). Overall correlation between the Petrifilms™ and reference plate measures was moderate (Spearman rho=0.38–0.47). The statistical accuracy of the Petrifilm™ systems and the test sensitivity were improved by lowering the bacterial cutpoint from 100,000CFU/mL to 91,000 CFU/mL for the aerobic counts plates and from 10,000CFU/mL to 1500 CFU/mL for the coliform count plates. The Petrifilm™ system could be used as a monitoring tool to provide quick and statistically accurate results for TBC and TCC but should not be seen as a comprehensive solution for poor colostrum hygiene.

CONTROL OF BACTERIAL CONTAMINATION OF DENTAL UNIT WATER USING SODIUM HYPOCHLORITE

Objective: To evaluate bacterial load of water using and not using sodium hypochlorite aiming at bacterial control of dental unit water. Method: Dental unit reservoirs from a dental clinic from School of Dentistry of Ribeirão Preto -USP were filled with public-supply water with and without sodium hypochlorite solution at 0.0003%, and water samples were collected and evaluated by Petrifilm™ AC (Aerobic Count) system from 2014 to 2017. Results: No bacterial contamination was observed in the water samples using sodium hypochlorite solution. However, bacterial contamination was detected in water from reservoirs, air-water syringes and high-speed outputs (without handpieces) without the disinfectant. Conclusion: The use of sodium hypochlorite solution controlled bacterial load of all the dental unit water samples as established by Brazilian legislation (<500CFU/mL).

Comparison of conventional plating methods and PetrifilmTM for the recovery of aerobic bacteria and mold from hatchery fluff samples

SUMMARY The enumeration and evaluation of bacteria and mold are important elements in the evaluation of hatchery sanitation programs. However, detection of bacteria and mold in fluff samples is time consuming and cumbersome. The PetrifilmTM aerobic count plate (ACP) and the Petrifilm yeast/mold count plate are ready-to-use alternatives to the traditional enumeration media used for bacteria and mold associated with environment and food. The purpose of this study was to evaluate the usefulness of Petrifilms for enumeration of aerobic bacteria and mold from hatchery fluff samples. Comparisons of ACP and mold counts were performed in 25 fluff samples. These samples were from 2 commercial hatcheries. ACP comparisons were made by evaluating the standard for pour plating with plate count agar versus aerobic count plate Petrifilm. Mold comparisons were made by evaluating Sabouraud dextrose agar versus yeast/mold plate count Petrifilm. Overall equivalent bacterial counts and mold counts were obtained by both enumeration methods. Because the Petrifilm method is convenient and gave comparative results, it offers a good alternative for fluff aerobic bacteria and mold counts.

Adequacy of Petrifilm™ Aerobic Count plates supplemented with de Man, Rogosa & Sharpe broth and chlorophenol red for enumeration of lactic acid bacteria in salami

The present study aimed to assess the performance of alternative protocols to enumerate lactic acid bacteria (LAB) in salami. Fourteen cultures and two mixed starter cultures were plated using six protocols: 1) Petrifilm™ Aerobic Count (AC) with MRS broth and chlorophenol red (CR), incubated under aerobiosis or 2) under anaerobiosis, 3) MRS agar with CR, 4) MRS agar with bromocresol purple, 5) MRS agar at pH5.7, and 6) All Purpose Tween agar. Samples of salami were obtained and the LAB microbiota was enumerated by plating according protocols 1, 2, 3 and 5. Regression analysis showed a significant correlation between the tested protocols, based on culture counts (p<0.05). Similar results were observed for salami, and no significant differences of mean LAB counts between selected protocols (ANOVA, p>0.05). Colonies were confirmed as LAB, indicating proper selectivity of the protocols. The results showed the adequacy of Petrifilm™ AC supplemented with CR for the enumeration of LAB in salami.

KONSENTRASI MINIMUM SISTEM LAKTOPEROKSIDASE UNTUK MENEKAN PERTUMBUHAN Escherichia coli PADA SUSU SAPI SEGAR

Fresh milk production in Central Java has increased every year resulting in the requirement of the rapid and good process for fresh milk handling to keep the quality against bacteria. Lactoperoxidase system (LPOS) was well documented as a strategy to extend the shelf life of fresh milk but it hasn’t been known yet for the minimum level of lactoperoxidase (LPO) utilization to activate LPOS in the milk. The purpose of this study was to analyze minimum concentration of LPO and its components by calculating minimum inhibitory concentration (MIC) against Escherichia coli and total bacteria in fresh milk. LPO was obtained from bovine whey and its purity was analyzed using SDS-PAGE. To activate the LPO performance, two substates namely H 2 O 2 and KSCN were used with various concentrations. The MIC was analyzed 3 times using 3M™ Petrifilm™ Aerobic Count Plates. The result showed that 3.11 unit/mL LPO, 0.03 mM subs-trates have been found as MIC of LPOS against bacteria and Escherichia coli in milk. This result might provide benefit to the utilization of minimal LPOS in fresh milk to safe the amount of LPO.

Evaluation of Petrifilm™ aerobic count plates as an equivalent alternative to drop plating on R2A agar plates in a biofilm disinfectant efficacy test.

This paper compares Petrifilm™ aerobic count (AC) plates to drop plating on R2A agar plates as an alternative method for biofilm bacteria enumeration after application of a disinfectant. A Pseudomonas aeruginosa biofilm was grown in a Centers for Disease Control and Prevention biofilm reactor (ASTM E2562) and treated with 123 ppm sodium hypochlorite (as free chlorine) according to the Single Tube Method (ASTM E2871). Aliquots from the same dilution tubes were plated on Petrifilm™ AC plates and drop plated on R2A agar plates. The Petrifilm™ AC and R2A plates were incubated for 48 and 24 h, respectively, at 36 ± 1 °C. After nine experimental runs performed by two technicians, the mean difference in biofilm log densities [log biofilm density (LD) = log10(CFU/cm(2))] between the two methods for control coupons, treated coupons, and log reduction (LR) was 0.052 (p = 0.451), -0.102 (p = 0.303), and 0.152 (p = 0.313). Equivalence testing was used to assess equivalence of the two plating methods. The 90 % confidence intervals for the difference in control and treated mean LDs between methods were (-0.065, 0.170) and (-0.270, 0.064), both of which fall within a (-0.5, +0.5) equivalence criterion. The 90 % confidence interval for the mean LR difference (-0.113, 0.420) also falls within this equivalence criterion. Thus, Petrifilm™ AC plates were shown to be statistically equivalent to drop plating on R2A agar for the determination of control LDs, treated LDs, and LR values in an anti-biofilm efficacy test. These are the first published results that establish equivalency to a traditional plate counting technique for biofilms and for a disinfectant assay.

ATP-Bioluminescence as a method to evaluated microbiological quality of UHT milk

New approaches are needed to quickly indicate possible contamination of UHT milk, among them the technique of ATP-Bioluminescence. Therefore, the aim of this study was to compare the results of culture methods with the results of ATP-Bioluminescence technique of 102 UHT whole milk samples incubated at 48, 72, and 168 hours. UHT milk samples were analyzed for the presence of mesophilic and psychrotrophic aerobic microorganisms using Plate Count Agar (PCA), Brain-Heart Infusion (BHI) media and PetrifilmTM Aerobic Count (AC) plates. The ATP-Bioluminescence technique was applied through the Microbial Luminescent Screening (MLS) system. Significant correlations were found between counts of aerobic mesophilic microorganisms on PCA, PetrifilmTM AC, BHI and results of ATP bioluminescence technique (P≤0.05). The ATP-Bioluminescence technique had higher correlation with counting method in PCA than BHI media. At lower pass/fail limits of Relative Light Units (60, 50, 45 and 40 RLU), the number of samples identified as positive increased and statistically agreed with aerobic mesophilic microorganism counts (P&gt;0.05). For the dairy industry, the ATP-Bioluminescence technique may become an important tool that assists the official methods to quickly monitor the microbiological quality of UHT milk though this will likely require a threshold below 150 RLU.

Development of a selective culture medium for bifidobacteria, Raffinose-Propionate Lithium Mupirocin (RP-MUP) and assessment of its usage with Petrifilm™ Aerobic Count plates

This study aimed to develop a selective culture media to enumerate bifidobacteria in fermented milk and to assess this medium when used with Petrifilm™ AC plates. For this purpose, Bifidobacterium spp., Lactobacillus spp. and Streptococcus thermophilus strains were tested to verify their fermentation patterns for different carbohydrates. All bifidobacteria strains were able to use raffinose. Based on these characteristic, a selective culture medium was proposed (Raffinose-Propionate Lithium Mupirocin, RP-MUP), used with Petrifilm™ AC plates, and was used to enumerate bifidobacteria in fermented milk. RP-MUP performance was assessed by comparing the results with this medium to reference protocols and culture media for bifidobacteria enumeration. RP-MUP, whether used or not with Petrifilm™ AC, presented similar performance to TOS-MUP (ISO 29981), with no significant differences between the mean bifidobacteria counts (p < 0.05) and with high correlation indices (r = 0.99, p < 0.05). As an advantage, reliable results were obtained after just 48 h of incubation when RP-MUP was used with Petrifilm™ AC, instead of the 72 h described in the ISO 29981 protocol.

Comparison of 3M™ Petrifilm™ Aerobic Count Plates to Standard Plating Methodology for Use with AOAC Antimicrobial Efficacy Methods 955.14, 955.15, 964.02, and 966.04 as an Alternative Enumeration Procedure: Collaborative Study

A multilaboratory study was conducted to determine the equivalence of the 3M Petrifilm Aerobic Count Plate and standard plating methodology for measuring viable bacteria and spores recovered from hard-surface carriers (stainless steel and porcelain), also known as "control carrier counts," used in AOAC antimicrobial efficacy test methods. Six laboratories participated in the study in which carriers inoculated with Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella enterica, and spores of Bacillus subtilis were evaluated using 3M Petrifilm Aerobic Count (AC) plates and standard plating side-by-side. The data were analyzed using a matched-pair t-test to determine the between-method effect with confidence intervals. For all test organisms pooled across all laboratories, the mean difference in log10 concentration between the standard plate count method and 3M Petrifilm AC Plates was -0.012, with a 95% confidence interval of (-0.090, +0.066), which was well within the -0.5, +0.5 interval established as the acceptance criterion. The between-carrier SD averaged 0.139; the between-replicate SD was 0.050. The carrier reproducibility, given that a single replicate per carrier is done, was estimated to be 0.148. Although differences were seen in the final concentrations of the test organisms among laboratories, there were no statistical differences between the enumeration methods. Based on the results from this study, 3M Petrifilm AC Plates are equivalent to standard plating methodology and can be used as an alternative procedure for the enumeration of test organisms used in AOAC Methods 955.14, 955.15, 964.02, and 966.04.

Selective enumeration of propionibacteria in Emmental-type cheese using Petrifilm™ Aerobic Count plates added to Lithium Glycerol broth

Propionibacteria derived from dairy products are relevant starter cultures for the production of Swiss and Emmental-type cheeses, and the monitoring of which is mandatory for proper quality control. This study aimed to evaluate an alternative procedure to enumerate propionibacteria, in order to develop a reliable and practical methodology to be employed by dairy industries. 2,3,5-triphenyltetrazolium chloride (TTC) inhibitory activity was tested against five reference strains (CIRM 09, 38, 39, 40 and 116); TTC at 0·0025% (w/v) was not inhibitory, with the exception of one strain (CIRM 116). Subsequently, the four TTC-resistant strains, three commercial starter cultures (PS-1, PB-I, and CHOO) and twelve Emmental-type cheese samples were subjected to propionibacteria enumeration using Lithium Glycerol (LG) agar, and Petrifilm™ Aerobic Count (AC) plates added to LG broth (anaerobic incubation at 30 °C for 7 d). Petrifilm™ AC added to LG broth presented high counts than LG agar (P<0·05) for only two reference strains (CIRM 39, and 40) and for all commercial starter cultures. Cheese sample counts obtained by both procedures did not show significant differences (P<0·05). Significant correlation indexes were observed between the counts recorded by both methods (P<0·05). These results demonstrate the reliability of Petrifilm™ AC plates added to LG broth in enumerating select Propionibacterium spp., despite some limitations observed for specific commercial starter cultures.

Efficacy of 3M™ Petrifilm™ aerobic count plates for enumerating Bacillus sporothermodurans and Geobacillus stearothermophilus in UHT milk

The effectiveness of the 3M™ Petrifilm™ aerobic count plate for determining the amount of Bacillus sporothermodurans and Geobacillus stearothermophilus in ultra high temperature milk was determined and its efficacy was compared with the pour-plate agar and one-streak nutrient agar methods. Tubes containing milk were inoculated with spore suspensions, heat shocked and incubated. Aliquots were collected after 0, 24, 48, and 72h of incubation, inoculated using the three different plate methods, and incubated at 55°C. B. sporothermodurans was detected at 9h on the Petrifilm plate, compared with 18h for both the pour plate and one-streak methods. Depending on the strain, G. stearothermophilus was detected between 6 and 12h by the Petrifilm plate method and between 9 and 12h by the other methods. The Petrifilm plates gave reproducible results compared with the traditional methods and are compatible with industrial requirements for milk quality control.

A randomized trial to evaluate a launderable bed protection system for hospital beds

BackgroundHospital beds are potential reservoirs of bacteria in hospitals. Preventing contamination of the bed and providing a cleaner surface should help prevent hospital-acquired infections (HAIs). Most hospital beds are cleaned between patients (terminal cleaning) using quaternary ammonia compounds (quats).ObjectiveThe study had two objectives: identify levels of bacterial contamination on beds (including the mattress and bed deck) and evaluate a new launderable cover.MethodsHospital beds on a bariatric surgery ward were randomized to either receive or not receive a launderable cover (Trinity Guardion, Batesville, IN). Bacterial counts on the surface of the mattress, the bed deck, and the launderable cover were then collected using Petrifilm™ Aerobic Count Plates (Petrifilm™, 3M™, St. Paul, MN, USA) (Petrifilm™) at three time periods (before patient use, after discharge, and after terminal cleaning). Standard hospital linen was used in all rooms.ResultsThe launderable cover (n = 28) was significantly cleaner prior to patient use than were the cleaned mattresses (n = 38) (1.1 CFU/30 cm2 vs. 7.7 CFU/30 cm2; p = 0.0189). The mattresses without launderable covers became significantly contaminated during use (7.7 CFU/30 cm2 on admission vs. 79.1 CFU/30 cm2 after discharge; p < 0.001). The mattresses with launderable covers did not become contaminated (3.0 CFU/30 cm2 on admission vs. 2.5 CFU/30 cm2 at discharge; p = 0.703). After terminal cleaning, the mattress surface contamination decreased to 12.8 CFU/30 cm2 (median 3 CFU/30 cm2; SD 7.8), but the bed deck was more contaminated (6.7 CFU/30 cm2 after discharge compared to 30.9 CFU/30 cm2 after terminal cleaning; p = 0.031).ConclusionsTerminal cleaning fails to eliminate bacteria from the surface of the hospital mattress. The launderable cover provides a cleaner surface than does terminal cleaning with quats, and the cover protects the bed from contamination during use.

Enumeration of bifidobacteria using Petrifilm™ AC in pure cultures and in a fermented milk manufactured with a commercial culture of Streptococcus thermophilus

Bifidobacteria are probiotic microorganisms that are widely used in the food industry. With the aim of using of Petrifilm™ Aerobic Count (AC) plates associated with selective culture media, aliquots of sterile skim milk were inoculated separately with four commercial cultures of bifidobacteria. These cultures were plated by both the conventional method and Petrifilm™AC, using the culture media NNLP and ABC. The cultures were incubated under anaerobiosis at 37 °C for 24, 48 and 72 h. No significant differences (p > 0.05) were observed between the obtained counts at 48 and 72 h. Bifidobacteria counts in ABC were usually higher than in NNLP, independent of the plating method. Subsequently, fermented milk was prepared with a Streptococcus thermophilus strain, and aliquots were inoculated with the same bifidobacteria. Then, the fermented milks were submitted to microbiological analysis for bifidobacteria enumeration using the same culture media and methodologies previously described, incubated under anaerobiosis at 37 °C for 48 h. Again, bifidobacteria counts in ABC were higher than in NNLP, with significant differences for some cultures (p < 0.05). The counts obtained by both methodologies presented significant correlations (p < 0.05). The results indicate the viability of Petrifilm™AC as an alternative method for bifidobacteria enumeration when associated to specific culture media, specially the ABC.

Effect of Beef Product Physical Structure on Salmonella Thermal Inactivation

Numerous studies have assessed thermal inactivation of Salmonella in beef. However, the impact of muscle structure has been considered only recently, with several studies reporting enhanced thermal resistance in whole-muscle as compared to ground meat. The functional relationship between meat product physical structure and Salmonella thermal resistance has not been reported; therefore, it is not known whether thermal resistance is affected by the degree of grinding (that is, size of resulting particles). The objective of this study was to evaluate the relationship between thermal resistance of Salmonella and degree of grinding (whole-muscle, coarsely ground, finely ground, and beef puree). Each of the 4 product types was irradiated to sterility and inoculated with a marinade containing an 8-serovar Salmonella cocktail to achieve approximately 10(7.8) CFU/g. Samples (5 g each) were packed into sterile brass tubes, which were sealed, held at 60 degrees C in a water bath, and removed at 30 s intervals. Samples were then serially diluted and plated on Petrifilm aerobic count plates to enumerate surviving salmonellae. All samples had the same composition, thermal history, and initial Salmonella counts; therefore, differences in thermal resistance were due entirely to the degree of grinding. Overall, thermal resistance of Salmonella was highest (P < 0.0001) in whole-muscle (D = 2.7 min), but there were no differences among the 3 ground products (D(mean)= 1.2 min). Therefore, it would be prudent for Salmonella thermal inactivation models to consider whether a product is whole-muscle or ground, but not necessarily the degree of grinding. Practical Application: The results of this study suggest that thermal process validations for ready-to-eat meat products should also consider the structure of the product (which in this study was changed by the physical act of grinding). Salmonella was more resistant to heat in whole-muscle beef than in ground products; however, the degree of grinding did not affect the resistance.

Screening and enumeration of lactic acid bacteria in milk using three different culture media in Petrifilm™ Aerobic Count plates and conventional pour plate methodology

This study aimed to compare Petrifilm Aerobic Count (AC) plates and the conventional pour plate methodology using de Mann-Rogosa-Sharpe (MRS), Kang-Fung (KF) and Kang-Fung-Sol (KFS) culture media for screening and enumeration of lactic acid bacteria (LAB) in milk. Suspensions of 10 LAB species in reconstituted powder skim milk and 30 raw milk samples, without experimental inoculation, were tested. For selective enumeration, all samples were previously diluted in MRS, KF and KFS broths and then plated in Petrifilm AC and conventional pour plate methodology, using the same culture media with added agar. All plates were incubated at 37 degrees C for 48 h in anaerobic conditions. Differences in the counts were observed only for raw milk samples using KFS in conventional methodology, when compared with the counts obtained from MRS and KF (P0.05). The results showed excellent correlation indexes between both methodologies using the three culture media for LAB suspensions (r=0.97 for MRS, KF and KFS). For raw milk samples, the correlation indexes were excellent (r=0.97, for MRS) and good (r=0.84 for KF, and r=0.82 for KFS), showing some interference in Petrifilm AC when supplements were added, especially lactic acid. These results indicate the possibility of using Petrifilm AC plates for enumeration of LAB in milk, even with the use of selective supplements.

Enumeration of heterotrophs, fecal coliforms and Escherichia coli in water: comparison of 3M™ Petrifilm™ plates with standard plating procedures

A total of 177 naturally contaminated water samples were analyzed by membrane filtration according to the Standard Methods for the Examination of Water and Wastewater published by the American Public Health Association. Filters were incubated in parallel on mHPC-agar and 3M™ Petrifilm™ Aerobic Count Plates (Petrifilm™ AC plates) for heterotrophic counts. Fecal coliforms and Escherichia coli were enumerated on mFC-agar and 3M™ Petrifilm™ E. coli/Coliform Count Plates (Petrifilm™ EC plates). Typical colonies on each media type were confirmed following standard procedures. Heterotrophic counts were between 10 3 and 10 4 CFU/mL and the average log 10 counts obtained on Petrifilm™ AC plates were about two-fold lower than on mHPC-agar. Counts for fecal coliforms and E. coli were between 10 2 and 10 3 CFU/mL. Average log 10 counts for confirmed fecal coliforms obtained on Petrifilm™ EC plates were slightly lower than on mFC agar with a correlation coefficient of 0.949. The average log 10 counts for confirmed E. coli on Petrifilm™ EC plates and on mFC agar were statistically not different ( P=0.126) with a correlation coefficient of 0.879. Specificity of Petrifilm™ EC plates and mFC agar was evaluated by comparing typical colony counts with confirmed counts. On mFC agar, counts for typical colonies were by 2 log 10 CFU higher than the actual confirmed counts. In contrast, on Petrifilm™ EC plates typical colony counts were almost identical to confirmed colony counts for both fecal coliforms and E. coli. This comparison illustrates the high specificity of Petrifilm™ EC plates for enumeration of both fecal coliforms and E. coli in water.

ENUMERATING 3MTM PETRIFILMTM AEROBIC COUNT PLATES USING THE PETRISCAN® AUTOMATED COLONY COUNTER

ABSTRACTIn the food and dairy industries, aerobic plate counts are determined by a time‐consuming and laborious hand‐counting method. The PetriScan ® automated colony counter was developed to improve efficiency in the microbiology laboratory. In this study, colony counts of food, dairy, and milk products plated on 3MTM PetrifilmTM Aerobic Count Plates were compared using both automated and manual count plate methods. For sample variation, 16 different food, dairy, and milk products were used. Samples were prepared and serially diluted using Butterfield's diluent according to approved AOAC methods and APHA's Standard Methods. Plates were inoculated, incubated, and counted according to AOAC methods. For data collection, plates with counts between 5 and 300 colonies were included. A total of 55 low (5–30), 29 medium (31–100), and 23 high (101–300) count plates were used. Duplicate results were recorded for both methods; hand counts were tallied by two scientists. The duplicates of the mean log values for manual counts varied by 0.0005 and 0.0007, and the duplicates for the automated counts varied by 0.0011. The mean log value difference between the automated and manual counts for pooled data was 0.035. The correlation coefficient for the regression line comparing the automated and manual count methods for pooled data was 0.98. The regression equation was y = 0.9257x + 0.0781. These results demonstrate that the PetriScan® automated colony counter is a comparable and practical alternative to the standard method of manually counting plates.

Comparison of the SimPlate™ Total Plate Count Method with Petrifilm™, Redigel™, and Conventional Pour-Plate Methods for Enumerating Aerobic Microorganisms in Foods

The SimPlate™ Total Plate Count (TPC) method, developed by IDEXX Laboratories, Inc., is designed to determine the most probable number of aerobic microorganisms in foods. The 24-h test was compared to the conventional plate count agar (PCA) method, the Petrifilm™ Aerobic Count plates, and the Redigel™ Total Count procedure for enumerating microflora in 751 food samples. Results using the SimPlate™ TPC method were highly correlated (r ≥ 0.96) with results from other test methods. Slopes (0.96–0.97) were not significantly different from 1, and y intercepts (−0.03–0.08) were not different from 0. The SimPlate™ has a high counting range (> 1600 most probable number per single dilution), thus requiring fewer dilutions of samples compared to other methods evaluated. Some foods, e.g., raw liver, wheat flour, and nuts, contain enzymes that gave false-positive reactions on SimPlates™. Overall, however, the SimPlate™ TPC method is a suitable alternative to conventional PCA, Petrifilm™, and Redigel™ methods for estimating populations of mesophilic aerobic microorganisms in a wide range of foods.

Influence of Processing Schemes on Indicative Bacteria and Quality of Fresh Aquacultured Catfish Filletst

Fresh aquacultured catfish fillets were obtained from three processors using different processing protocols in summer, autumn, winter, and spring and evaluated for microbial quality. Twenty freshly processed fillets were randomly selected and each fillet was placed in a sterile polyethylene bag. The fillets were transported on ice-pack overnight by air immediately after processing. Five fillets were randomly selected for microbial assays. Each fillet was weighed and an equal volume of sterile 0.1 % peptone water at 0 to 1°C was added aseptically. The fillet was massaged (or rinsed) for 120 s and the rinse was used to determine microbial quality. Aerobes (incubation at 35°C for 48 h) and psychrotrophs (incubation at 20°C for 96 h) were enumerated using 3M Petrifilm™ Aerobic Count plates. Escherichia coli (incubation at 35°C for 24 to 48 h) and total coliforms (incubation at 35°C for 24 to 48 h) were enumerated on 3M Petrifilm™ E. coli Count plates. Staphylococcus aureus counts were determined on Baird-Parker agar (incubation at 35°C for 48 h). Significant differences (P ≤ 0.05) in aerobic, psychrotrophic, total coliform, E. coli, and S. aureus counts due to temperature effects during production and variations in processing protocols were observed. E. coli and S. aureus counts were significantly different during the four seasons. E. coli and S. aureus counts were high during summer and low during winter weather. There was a significant difference (P ≤ 0.05) in aerobic, psychrotrophic, and total coliform counts among the three processors during warm weather; however, these differences were significantly (P≤ 0.05) reduced in cold weather.