Challenging the "gold standard" of colony-forming units - Validation of a multiplex real-time PCR for quantification of viable Campylobacter spp. in meat rinses

An Indirect Fluorescence Microscopy Method to Assess Vaginal Lactobacillus Concentrations

Lactobacillus species are the main colonizers of the vaginal microbiota in healthy women. Their absolute quantification by culture-based methods is limited due to their fastidious growth. Flow cytometry can quantify the bacterial concentration of these bacteria but requires the acquisition of expensive equipment. More affordable non-culturable methods, such as fluorescence microscopy, are hampered by the small size of the bacteria. Herein, we developed an indirect fluorescence microscopy method to determine vaginal lactobacilli concentration by determining the correlation between surface area bacterial measurement and initial concentration of an easily cultivable bacterium (Escherichia coli) and applying it to lactobacilli fluorescence microscopy counts. In addition, vaginal lactobacilli were quantified by colony-forming units and flow cytometry in order to compare these results with the indirect method results. The colony-forming-unit values were lower than the results obtained from the other two techniques, while flow cytometry and fluorescence microscopy results agreed. Thus, our developed method was able to accurately quantify vaginal lactobacilli.

Advances in Campylobacter: Molecular Epidemiology, Virulence Factors, Immune Responses and Drug Resistance

Campylobacter infections, caused by Campylobacter jejuni and Campylobacter coli, are a major global concern, particularly as they are the leading cause of bacterial enteritis [...].

Detection of Viable but Non-Culturable (VBNC)-Campylobacter in the Environment of Broiler Farms: Innovative Insights Delivered by Propidium Monoazide (PMA)-v-qPCR Analysis

Campylobacteriosis cases in humans are of global concern, with high prevalence rates in the poultry reservoir considered the most important source of infection. Research findings show Campylobacters' ability to enter a viable but non-culturable (VBNC) state, remaining "viable" but unable to grow on culture media. We explored the persistence of VBNC states in specific environments, particularly at broiler farms, as this state may lead to an underestimation of the present Campylobacter prevalence. For VBNC detection, a propidium monoazide PMA-dye viability qPCR (v-qPCR) was used in combination with cultivation methods. We examined samples collected from broiler farm barns and their surroundings, as well as chicken manure from experimental pens. In addition, the tenacity of culturable and VBNC-Campylobacter was studied in vitro in soil and water. In a total of three visits, Campylobacter was not detected either culturally or by v-qPCR (no Campylobacter DNA) in the environment of the broiler farms. In four visits, however, VBNC-Campylobacter were detected both inside and outside the barns. The overall prevalence in environmental samples was 15.9% for VBNC-Campylobacter, 62.2% for Campylobacter DNA, and 1.2% for culturable C. jejuni. In the experimental pens, no cultivable C. jejuni was detected in chicken manure after 24 h. Strikingly, "VBNC-Campylobacter" persisted even after 72 h. "VBNC-Campylobacter" were confirmed in barn surroundings and naturally contaminated chicken manure. Laboratory studies revealed that VBNC-Campylobacter can remain intact in soil for up to 28 days and in water for at least 63 days, depending on environmental conditions.

Nanomaterial interfaces designed with different biorecognition elements for biosensing of key foodborne pathogens

Foodborne diseases caused by pathogen bacteria are a serious problem toward the safety of human life in a worldwide. Conventional methods for pathogen bacteria detection have several handicaps, including trained personnel requirement, low sensitivity, laborious enrichment steps, low selectivity, and long-term experiments. There is a need for precise and rapid identification and detection of foodborne pathogens. Biosensors are a remarkable alternative for the detection of foodborne bacteria compared to conventional methods. In recent years, there are different strategies for the designing of specific and sensitive biosensors. Researchers activated to develop enhanced biosensors with different transducer and recognition elements. Thus, the aim of this study was to provide a topical and detailed review on aptamer, nanofiber, and metal organic framework-based biosensors for the detection of food pathogens. First, the conventional methods, type of biosensors, common transducer, and recognition element were systematically explained. Then, novel signal amplification materials and nanomaterials were introduced. Last, current shortcomings were emphasized, and future alternatives were discussed.

Evaluation of volume-based flow cytometry as a potential primary method for quantification of bacterial reference material

Bacterial reference materials (RMs) play a crucial role in many analytical processes of microbiological detection. Currently, bacteria are typically counted using the traditional plate-based approach, which results in a higher uncertainty of bacterial RMs unfortunately. Therefore, novel methods are urgently required for the value assignment of RMs in the field of microbiology to derive measurement traceability and accuracy. A potential primary method for microbiological quantification based on flow cytometry (FCM) is described in this study using Escherichia coli O157 (E. coli O157) as an example. The proposed method was applied to determine the number of viable E. coli O157 cells in the RMs with a result of (5.48 ± 0.27) × 10⁸ cells mL^-1, which was in good agreement with the result obtained using the plate-based method (E_n = 0.47). Additionally, this method could be entirely described and understood by equations, and provides formal traceability to the SI for counts of viable bacterial cells, while the associated relative expanded uncertainty (4.93%, k = 2) was significantly lower in comparison to the plate-based method. Therefore, the FCM-based method might be a potential primary method for characterizing bacterial RMs. To our knowledge, this is the first description of FCM as a potential primary method for accurate and traceable quantification of viable bacterial cells with a comprehensive uncertainty statement in microbiological metrology.

Simultaneous Detection of Salmonella spp. and Quantification of Campylobacter spp. in a Real-Time Duplex PCR: Myth or Reality?

In Europe, there is a process hygiene criterion for Salmonella and Campylobacter on broiler carcasses after chilling. The criterion gives indicative contamination values above which corrective actions are required by food business operators. The reference methods for verifying compliance with the criterion for Salmonella and Campylobacter are international standards EN ISO 6579-1 (2017) and EN ISO 10272-2 (2017), respectively. These methods are time-consuming and expensive for food business operators. Therefore, it would be advantageous to simultaneously detect Salmonella spp. and quantify Campylobacter in the same analysis, using the same sample after the pre-enrichment step for Salmonella recovery. A duplex PCR for Salmonella detection and Campylobacter spp. enumeration was developed. Considering the method as a whole, the LOD and LOQ for Campylobacter enumeration were slightly over the limit of 3 log CFU/g set by the process hygiene criterion. A comparison of the duplex PCR method developed with the ISO method on artificially contaminated bacterial suspensions and on naturally contaminated samples demonstrated a good correlation of the results for Campylobacter enumeration when the duplex PCR was performed on samples taken before or after the pre-enrichment step, but revealed a slight bias with a large standard deviation resulting in widely spaced limits of agreement.

Prevalence and Characterization of Campylobacter Species from Chickens Sold at Informal Chicken Markets in Gauteng, South Africa

ABSTRACT

This study determined the prevalence, characteristics, and risk factors of Campylobacter species contamination of chicken carcasses sold at informal poultry outlets in Gauteng province, South Africa. Within six townships, 151 chicken carcasses were collected from 47 outlets. Carcass swab, cloacal swab, and carcass drip samples were collected from each chicken, along with a matched questionnaire on risk factors regarding Campylobacter contamination. Sample-inoculated Bolton broth (BB) was cultured to isolate Campylobacter species by bacteriological methods. Subsequent confirmation and characterization of Campylobacter were conducted using polymerase chain reaction (PCR). Isolated Campylobacter strains were evaluated for the presence of six virulence genes (ciaB, dnaj, pldA, racR, flaA, and flaB), three toxin genes (cdtA, cdtB, and cdtC), and one antimicrobial resistance gene (tetO). The overall prevalence of Campylobacter was 23.4% (106 of 453), with sample type-specific prevalence being 17.2% (26 of 151), 25.8% (39 of 151), and 27.2% (41 of 151) for the carcass swabs, cloacal swabs, and carcass drip, respectively, following bacteriological isolation and confirmation by PCR. The overall prevalence of Campylobacter species was 93.5% by PCR, which varied significantly (P = 0.000) by sample: 99.2, 98.4, and 82.8% for carcass swabs, cloacal swabs, and carcass drip, respectively, by using PCR to detect Campylobacter in BB. Important risk factors for carcass contamination by Campylobacter included the slaughter of culled breeders and spent chickens, the use of stagnant water, and poor sanitation. Virulence and toxin gene frequencies were higher in C. jejuni-positive (82.5%) than in C. coli-positive (71.4%) BB cultures, but tetracycline resistance gene (tetO) frequency was higher in C. coli (75.9%) than in C. jejuni (48.10%). The observed high frequencies in C. jejuni recovered from street-vended chickens may pose food safety and therapeutic concerns to consumers.

HIGHLIGHTS

A Technique for Rapid Bacterial-Density Enumeration through Membrane Filtration and Differential Pressure Measurements

In this article, we present a microfluidic technique for the rapid enumeration of bacterial density with a syringe filter to trap bacteria and the quantification of the bacterial density through pressure difference measurement across the membrane. First, we established the baseline differential pressure and hydraulic resistance for a filtration membrane by fully wetting the filter with DI water. Subsequently, when bacteria were infused and trapped at the pores of the membrane, the differential pressure and hydraulic resistance also increased. We characterized the infusion time required for the bacterial sample to achieve a normalized hydraulic resistance of 1.5. An equivalent electric-circuit model and calibration data sets from parametric studies were used to determine the general form of a calibration curve for the prediction of the bacterial density of a bacterial sample. As a proof of concept, we demonstrated through blind tests with Escherichia coli that the device is capable of determining the bacterial density of a sample ranging from 7.3 × 10⁶ to 2.2 × 10⁸ CFU/mL with mean and median accuracies of 87.21% and 91.33%, respectively. The sample-to-result time is 19 min for a sample with lower detection threshold, while for higher-bacterial-density samples the measurement time is further shortened to merely 8 min.

Chicken Skin Decontamination of Thermotolerant Campylobacter spp. and Hygiene Indicator Escherichia coli Assessed by Viability Real-Time PCR

Thermotolerant Campylobacter spp. are fecal contaminants of chicken meat with serious implications for human health. E. coli is considered as hygiene indicator since, in contrast to Campylobacter. spp., the bacterium is generally present in the avian gut. Stress exposure may transiently cease bacterial division. Therefore, colony forming units (CFU) may underestimate the infection risk of pathogens. We developed a viability real-time PCR (v-qPCR) for the quantification of viable E. coli targeting the uidA gene, encoding β-glucuronidase, which is usually detected for phenotypic species identification. The short- and long-term effects of decontaminating chicken skin on the survival of both C. jejuni and an ESBL-producing E. coli were evaluated by CFU and v-qPCR. The results showed that freezing and storage in cool conditions are potentially underestimated by CFU but not by v-qPCR. The effect of treatment with peroxyacetic acid on survival was consistently detected by CFU and v-qPCR. v-qPCR analysis detected bacterial survival upon the application of lactic acid, which awaits further analysis. Interestingly, both bacteria showed similar kinetics of inactivation upon the application of reduction strategies, suggesting that E. coli might be a complementary hygiene indicator. We conclude that v-qPCR can improve food safety under the consideration of some limitations.

Digital Droplet-PCR for Quantification of Viable Campylobacter jejuni and Campylobacter coli in Chicken Meat Rinses

The EU commission established Regulation (2017/1495) in 2017 to reduce Campylobacter on chicken skin and to decrease the number of human cases of campylobacteriosis attributable to the consumption of poultry meat. A Process Hygiene Criterion based on colony-forming unit data was set to a maximum of 1000 CFU Campylobacter spp. per gram chicken neck skin at slaughterhouses. Confronted with stressors, including cold, oxidative stress or antibiotic treatment, live cells may enter into a viable but non-cultivable state (VBNC) and lose the ability to grow, in reference to the plate count ISO 10272-2:2017 method, but still possess the potential to recover and cause infections under favorable conditions. In this study, a droplet digital PCR combined with the intercalating dye propidium monoazide (PMA) was established for quantification of C. coli and C. jejuni in chicken meat rinses. The PMA was used to inactivate DNA from dead cells in this technique. This method was successfully validated against the reference method according to ISO 16140-2:2016 for accuracy and relative trueness. Additionally, it presented a 100% selectivity for Campylobacter jejuni and C. coli. Moreover, the technical measurement uncertainty was determined according to ISO 19036:2019, and the applicability of ddPCR for quantifying C. coli and C. jejuni in chicken meat rinses was investigated on naturally contaminated samples from slaughterhouses and supermarkets. Results obtained from this study demonstrated a strong correlation to qPCR as well as the classical microbiological reference method.