Evaluation of the petrifilm plate method for the enumeration of aerobic microorganisms and coliforms in retailed meat samples

Precise Photothermal Treatment of Methicillin-Resistant S. aureus Infection via Phage Lysin-Cell Binding Domain-Modified Gold Nanosheets

The increasing spread of antibiotic resistance in bacterial pathogens poses a huge threat to global human health. Precise targeting of bacterial pathogens while avoiding collateral damage to healthy tissues has become the overriding goal for bacterial infection treatment. Inspired by the host specificity of bacteriophages, a biomimetic intelligent platform was designed for highly precise photothermal treatment herein. As proof-of-concept, the lysin cell-binding domain (CBD) from a newly discovered virulent methicillin-resistant S. aureus (MRSA) phage Z was applied to the functionalization of gold nanosheets. Our results demonstrated that the bionanocomposite gold particles (Au@PEG-CBDz) could be effectively delivered directly to MRSA and kill them effectively under near infrared irradiation in vitro, while displaying good in vivo biocompatibility. This work is the first to report the combination of phage lysin navigatory function with photothermal effect-induced bactericidal activity from Au nanosheets, providing a novel therapeutic mode for the precision treatment of antibiotic-resistant bacterial infections.

The Effect of Stachy sieboldii MIQ. Supplementation on Modulating Gut Microflora and Cytokine Expression in Mice

AIMS AND OBJECTIVES

The intake of Stachys sieboldii MIQ. has been associated with relieving inflammation and maintaining optimal gut health function. We investigated the diversity and composition of microflora in feces of S. sieboldii MIQ.-fed mice. In addition, we evaluated the production of major cytokines (Interleukin-6 and -10) related to inflammation and fatty acid composition of several tissues.

MATERIALS AND METHODS

16S ribosomal DNA sequencing-based microbiome taxonomic profiling analysis was performed using EzBioCloud data base. The total RNA from the mesenteric lymph node was isolated and then synthesized with prime script 1st strand cDNA synthesis kit. Quantitative real-time PCR was performed on cDNA samples using the SYBR™ Green PCR Master Mix.

RESULTS

Mice fed on S. sieboldii MIQ. showed significantly reduced counts of aerobic and coliform in the feces compared with control. 16S rDNA sequencing analysis of fecal samples showed that supplementation with S. sieboldii MIQ. increased beneficial intestinal microflora (Ruminococcaceae and Akkermansia muciniphila) and decreased the community of harmful microflora (Enterobacteriaceae, including Escherichia coli and Bacteroides sp.) in feces compared with that in the control (P<0.05 for all). Mice showed a significantly lower mRNA expression of cytokines IL-6 and IL-10 in mesenteric lymph node compared with that in control (P<0.05). The fecal fatty acid composition in the S. sieboldii MIQ. group showed a higher percentage of 6:0 and 18:2n-6 compared with that in the control group (P<0.05). The percentages of 6:0 and 20:3n-6 fatty acids were also significantly higher in the intestines of S. sieboldii MIQ. group (P<0.05). No differences were revealed between the two groups in terms of the percentages of total saturated, monounsaturated, n-6 and n-3 polyunsaturated fatty acids found in feces and tissues.

CONCLUSION

The present results showed that supplementation of mice with S. sieboldii MIQ. increased beneficial gut microflora and decreased harmful microflora. Moreover, lower mRNA expression of pro-inflammatory cytokine IL-6, and anti-inflammatory cytokine IL-10 in the mesenteric lymph node of supplemented mice might be associated with the lower abundances of harmful fecal microflora.

The application of the lytic domain of endolysin from Staphylococcus aureus bacteriophage in milk

Staphylococcus aureus is a widespread foodborne pathogen that threatens human health. In particular, multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) are emerging problems in modern health care, food safety, and animal health, which require the development of new antimicrobials to replace overused conventional antibiotics. Dairy products can potentially act as vehicles for the transmission of S. aureus and other antibiotic-resistant strains from the farm into the general human population, and should be controlled during the production and storage process. Recently, bacteriophage endolysins, which degrade the cell wall that is indispensable for bacteria, have been deemed promising antimicrobial agents. In this study, one endolysin, LysGH15, demonstrated prominent antimicrobial efficacy against S. aureus, as did its catalytic domain, cysteine, histidine-dependent amidohydrolase/peptidases (CHAP)_LysGH15 alone. The LysGH15 and CHAP_LysGH15 exhibited different characteristics in one MRSA strain (MRSA 2701), reaching the highest activity under different conditions (35°C and pH 6.0 for LysGH15, 40°C and pH 9.0 for CHAP_LysGH15). A difference in the sensitivity of LysGH15 and CHAP_LysGH15 to NaCl concentration was found, where the lytic activity of LysGH15 depends strongly on its binding domain's binding capacity, which is positively correlated with the NaCl concentration, whereas the CHAP_LysGH15 activity showed a negative correlation with the NaCl concentration. When the NaCl concentration was 450 mM, the lytic activity of LysGH15 reached its peak, whereas the lytic activity of CHAP_LysGH15 was the highest in the absence of NaCl. The difference in NaCl sensitivity between LysGH15 and CHAP_LysGH15 may be due to the sensitivity of the SH3b binding protein of LysGH15 to NaCl. The CHAP_LysGH15 was tested as a biopreservative in whole and skim milk and exerted effective control against S. aureus (declined by approximately 2.5 log₁₀ cfu/mL when incubated at 4°C for 8 h), which suggests promise for application in dairy products.

3M Petrifilm Lactic Acid Bacteria Count Plate Is a Reliable Tool for Enumerating Lactic Acid Bacteria in Bacon

ABSTRACT

This study aimed to evaluate the behavior of Petrifilm Lactic Acid Bacteria Count Plates (PLAB) as an alternative methodology to enumerate lactic acid bacteria (LAB) in bacon. Bacon samples (n = 40) were obtained from retail sale, 10-fold diluted with buffered peptone water (BPW, 0.2% [w/v]) and Letheen broth, and subjected to LAB enumeration according to four protocols: (i) de Man Rogosa Sharpe (MRS) agar, pH 5.7, 30°C; (ii) MRS, pH 5.7, 30°C, anaerobiosis; (iii) all-purpose Tween agar (APT), 25°C; and (iv) PLAB, 30°C. Colonies were enumerated at 24, 48, and 72 h, and the results expressed as log CFU per gram for comparison by analysis of variance and regression (P < 0.05). Furthermore, colonies were randomly selected and characterized as LAB (Gram staining and catalase). Mean LAB counts from MRS and PLAB did not present significant differences independently of incubation time or diluent (P > 0.05), whereas counts in APT with BPW after 24 h were significantly lower (P < 0.05). PLAB counts with BPW (24, 48, and 72 h) presented significant correlation with MRS (r ranging from 0.87 to 0.89; in anaerobiosis, r ranging from 0.94 to 0.95) and APT (r ranging from 0.84 to 0.86). With Letheen broth, PLAB (24, 48, and 72 h) presented significant correlation with MRS (r ranging from 0.92 to 0.94; in anaerobiosis, r ranging from 0.93 to 0.96) and APT (r ranging from 0.77 to 0.79). In total, 1,032 colonies (97%) from 1,063 colonies were characterized as LAB. Thus, PLAB can be considered as an alternative tool for enumerating LAB in bacon, with reliable results even after 24 h of incubation.

HIGHLIGHTS

Impact of Mannanase-Producing Bacillus spp. on the Accuracy of the 3M Petrifilm Aerobic Count Method

Consistent deviations of the 3M Petrifilm aerobic counts (AC) from the standard pour plate aerobic plate count (APC) were observed with dehydrated onion and garlic products. A large study was designed to determine the relationship of these two methods and the root cause for the deviations. A total of 3,800 dehydrated onion and garlic samples were analyzed by both the Petrifilm AC and the standard pour plate APC method. Large spreader-like liquefied areas were observed on numerous Petrifilm plates. These liquefied areas made enumeration inaccurate. "Liquefier" microorganisms from Petrifilm plates were isolated and identified to species level by 16S rRNA and gyrB gene sequencing. Enzyme diffusion assay was performed to determine potential enzymatic degradation of guar gum, the gelling agent used in Petrifilm plates. The results indicated that the correlation between Petrifilm AC and standard APC is relatively low. Paired t test results suggested that the Petrifilm AC method produced significantly different results compared with standard APC. The discrepancies were attributable at least partly to a liquefier organism that hydrolyzed guar gum, leading to liquefaction. Liquefaction of Petrifilm plates seems to have two effects on accuracy: (i) liquefied areas may allow motile organisms to move and multiply in the liquefied area during the incubation period, yielding more than one colony from one cell and, as a result, leading to overestimation of the microbial load and (ii) the blurred areas obscure other colonies, leading to potential underestimation. The liquefier organism was identified as Bacillus amyloliquefaciens , a potent mannanase producer and heat-resistant spore former. Enzyme diffusion assay confirmed that mannanase contained in the cell-free supernatant of B. amyloliquefaciens can hydrolyze the 1,4-β-mannopyranosyl bond, the backbone of guar gum. This is the first report of the role of B. amyloliquefaciens in the liquefaction of Petrifilm plates and its negative impact on accuracy.

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>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.

Comparison of baseline bacterial levels in retail ground beef originating from different regulatory, processing, and packaging environments

The objectives of this study were to collect baseline measures of bacteria present in retail ground beef offered for sale in Saskatchewan and to assess differences associated with the licensing or regulatory environment of the packaging and processing facilities as indicated by package labeling. Packages of ground beef (n = 309) were purchased from May 2011 to May 2012. Retail samples were categorized as originating from facilities regulated by the federal government or licensed by the provincial government (n = 126), originating from facilities licensed by local health regions (n = 80), or having no inspection or source information on the package label (n = 103). Total aerobic plate counts and total Escherichia coli plate counts were determined using 3M Petrifilm methods. Total bacterial load was estimated using real-time quantitative PCR. The data were analyzed on a log scale using multivariable linear regression, accounting for season and whether the samples were fresh or frozen at purchase. Total aerobic plate counts and Escherichia coli plate counts were lower in samples from federally regulated or provincially licensed facilities than in samples from locally licensed facilities (P < 0.001 and P = 0.002, respectively) or in samples with no inspection information on the label (P < 0.001 and P = 0.011, respectively). Frozen ground beef from federally regulated or provincially licensed facilities had the lowest total bacterial load. Samples clearly labeled as packaged at federally regulated or provincially licensed facilities consistently had the lowest estimated bacterial levels.

Evaluation of the petrifilm aerobic count plate for enumeration of aerobic marine bacteria from seawater and Caulerpa lentillifera

The enumeration and evaluation of the activity of marine bacteria are important in the food industry. However, detection of marine bacteria in seawater or seafood has not been easy. The Petrifilm aerobic count plate (ACP) is a ready-to-use alternative to the traditional enumeration media used for bacteria associated with food. The purpose of this study was to evaluate the usefulness of a simple detection and enumeration method utilizing the Petrifilm ACP for enumeration of aerobic marine bacteria from seawater and an edible seaweed, Caulerpa lentillifera. The efficiency of enumeration of total aerobic marine bacteria on Petrifilm ACP was compared with that using the spread plate method on marine agar with 80 seawater and 64 C. lentillifera samples. With sterile seawater as the diluent, a close correlation was observed between the method utilizing Petrifilm ACP and that utilizing the conventional marine agar (r=0.98 for seawater and 0.91 for C. lentillifera). The Petrifilm ACP method was simpler and less time-consuming than the conventional method. These results indicate that Petrifilm ACP is a suitable alternative to conventional marine agar for enumeration of marine microorganisms in seawater and C. lentillifera samples.

Enumeration of total aerobic bacteria and Escherichia coli in minced meat and on carcass surface samples with an automated most-probable-number method compared with colony count protocols

An automated most-probable-number (MPN) system for the enumeration of total bacterial flora and Escherichia coli was compared with plate count agar and tryptone-bile-glucuronide (TBX) and ColiID (in-house method) agar methodology. The MPN partitioning of sample aliquots was done automatically on a disposable card containing 48 wells of 3 different volumes, i.e., 16 replicates per volume. Bacterial growth was detected by the formation of fluorescent 4-methylumbilliferone. After incubation, the number of fluorescent wells was read with a separate device, and the MPN was calculated automatically. A total of 180 naturally contaminated samples were tested (pig and cattle carcass surfaces, n = 63; frozen minced meat, n = 62; and refrigerated minced meat, n = 55). Plate count agar results and MPN were highly correlated (r = 0.99), with log MPN = -0.25 + 1.05 x log CFU (plate count agar) (n = 163; range, 2.2 to 7.5 log CFU/g or cm2). Only a few discrepancies were recorded. In two samples (1.1%), the differences were > or = 1.0 log; in three samples (1.7%), the differences were > or = 0.5 log. For E. coli, regression analysis was done for all three methods for 80 minced meat samples, which were above the limit of detection (1.0 log CFU/g): log MPN = 0.18 + 0.98 x log CFU (TBX), r = 0.96, and log MPN = -0.02 + 0.99 x log CFU (ColiID), r = 0.99 (range, 1.0 to 4.2 log CFU/g). Four discrepant results were recorded, with differences of > 0.5 but < 1.0 log unit. These results suggest that the automated MPN method described is a suitable and labor-saving alternative to colony count techniques for total bacterial flora and E. coli determination in minced meat or on carcass surfaces.

Incidences of problematic organisms on petrifilm aerobic count plates used to enumerate selected meat and dairy products

Petrifilm aerobic count plates are similar to or better than conventional pour plates. Petrifilm has its problems, however; some microorganisms can liquefy the Petrifilm gel and others do not produce the necessary color change with the indicator dye used. Petrifilm aerobic count plates were compared with the pour plates for determining the incidence and identification of problematic organisms in 329 meat and dairy products. Petrifilm plates produced higher mean counts with better repeatability than did pour plates. There was also close correlation between methods with coefficients of 0.97 to 1.0. Bacillus subtilis, Bacillus licheniformis, and a group D Streptococcus liquefied Petrifilm gels in 17.4% of the samples tested: dairy products accounted for 16.0%, and meats accounted for the remaining 1.4%. Liquefaction hindered enumeration in 3.2% of the Petrifilm plates used. Streptococcus viridans was not detectable on Petrifilm plates after the recommend incubation period, and this organism occurred in 0.3% of the Petrifilm plates used. These results indicate that Petrifilm plates would be unsuitable for samples with large numbers of these organisms. Knowledge of the contaminating flora may be an asset when utilizing Petrifilm aerobic count plates for the enumeration of microbes in food.

Menadione-catalyzed luminol chemiluminescence assay for the rapid detection of viable bacteria in foods under aerobic conditions

A menadione-catalyzed luminol chemiluminescence assay was developed for the rapid detection and estimation of viable bacteria in foods. The principle of this assay is based on the extracellular menadione-catalyzed active oxygen spieces (O2- and H2O2) generated by the activity of NAD(P)H:menadione oxidoreductase in viable cells. This luminol chemiluminescence assay requires 10 min for the incubation of cells with menadione and then 2 s for the measurement of chemiluminescence intensity after an injection of luminol solution without the treatment of cell lysis. This method was evaluated using liquid food samples of milk, vegetable juice, green tea, and coffee spiked with Escherichia coli ATCC 25922. The study result revealed that E. coli contamination at 1 to 10 CFU/ml in these foods could be detected after incubation at 37 degrees C for 7 h in an enrichment medium; however, the green tea and coffee samples requires filtration. This method could be a useful tool for the rapid evaluation of microbial food contamination.

A review of conventional detection and enumeration methods for pathogenic bacteria in food

With continued development of novel molecular-based technologies for rapid, high-throughput detection of foodborne pathogenic bacteria, the future of conventional microbiological methods such as viable cell enumeration, selective isolation of bacteria on commercial media, and immunoassays seems tenuous. In fact, a number of unique approaches and variations on existing techniques are currently on the market or are being implemented that offer ease of use, reliability, and low cost compared with molecular tools. Approaches that enhance recovery of sublethally injured bacteria, differentiation among species using fluorogenics or chromogenics, dry plate culturing, differentiation among bacteria of interest using biochemical profiling, enumeration using impedence technology, techniques to confirm the presence of target pathogens using immunological methods, and bioluminescence applications for hygiene monitoring are summarized here and discussed in relation to their specific advantages or disadvantages when implemented in a food microbiology setting.Key words: food pathogen, detection, enumeration methods, food safety.

Development of a PCR assay for detection of Enterobacteriaceae in foods

A broad-range PCR assay for the detection of bacteria belonging to the Enterobacteriaceae family was developed in this study. Primers targeting the bacterial 16S rRNA gene were newly designed and used in this PCR assay. To determine the specificity of the assay, 72 different bacterial species (of 49 genera), 2 fungi, 3 animals, and 4 plants were tested. Results were positive for every tested Vibrioaceae or Enterobacteriaceae strain except Proteus mirabilis. For all other bacterial strains and eukaryotes tested, results were negative. Bacterial DNA for PCR was prepared by a simple procedure with the use of Chelex 100 resin from culture after growth in brain heart infusion medium. To test this PCR assay for the monitoring of the Enterobacteriaceae family, either Escherichia coli or Salmonella Enteritidis was inoculated into various foods as an indicator. Prior to the PCR, the inoculation of 10 to 40 CFU of bacteria per g of food was followed by a 5-h enrichment culture step, and the PCR assay allowed the detection of bacterial cells. When actual examinations of the contamination of 15 noodle foods with Enterobacteriaceae by this PCR assay were conducted, 33% (5 of 15) of the samples tested positive. These results agreed with those of the Petrifilm Enterobacteriaceae Count Plate assay. Including the enrichment culture step, the entire PCR detection process can be completed within 7 h.