Pathogens in meat and milk products: surveillance and impact on human health in France

Simultaneous Detection of Four Main Foodborne Pathogens in Ready-to-Eat Food by Using a Simple and Rapid Multiplex PCR (mPCR) Assay

The increasing consumption of organic or ready-to-eat food may cause serious foodborne disease outbreaks. Developing microbiological culture for detection of food-borne pathogens is time-consuming, expensive, and laborious. Thus, alternative methods such as polymerase chain reaction (PCR) are usually employed for outbreaks investigation. In this work, we aimed to develop a rapid and simple protocol for the simultaneous detection of Escherichia coli (E coli), Listeria monocytogenes (L. monocytogenes), Staphylococcus aureus (S. aureus) and Salmonella enterica (S. enterica), by the combination of an enrichment step in a single culture broth and a multiplex PCR (mPCR) assay. The effectiveness of several enrichment media was assessed by culture and PCR. Buffered peptone water (BPW) was selected as the optimum one. Then, mPCR conditions were optimized and applied both to pure co-cultures and artificially inoculated food samples (organic lettuce and minced meat). In the culture medium inoculated at 10⁰ CFU/mL, mPCR was able to detect the four microorganisms. When performed on artificially food samples, the mPCR assy was able to detect E. coli, S. enterica, and L. monocytogenes. In conclusion, BPW broth can effectively support the simultaneous growth of E. coli, S. aureus, L. monocytogenes, and S. enterica and could be, thus, used prior to a mPCR detection assay in ready-to-eat food, thereby considerably reducing the time, efforts and costs of analyzes.

Microbial quality and associated health risks of raw milk marketed in the Tanga region of Tanzania

OBJECTIVE

To evaluate microbial quality and associated health risks of raw milk marketed in the Tanga region of Tanzania.

METHODS

A microbial quality assessment of marketed raw milk was undertaken by evaluating 59 samples of milk from selling points (collecting centres =15), bicycle boys (12) and kiosks/restaurants (32) in Tanga city during April-May 2005. Quality and milk-borne hazards were assessed using a combination of tests in order to quantify the occurrence of Brucellosis (milk ring test), Escherichia coli (E. coli) O157:H7 (culture), the coliform bacteria as well as standard plate count (SPC). Specific gravity (SG) determination was used as an indicator of adulteration.

RESULTS

The mean coliform plate count (c.f.u/mL) of milk handled by bicycle boys (4.2×10(6)) was significantly higher than that handled by collecting centres (3.0×10(6)) and kiosk/ restaurants (1.4×10(6)), respectively (P < 0.05). Of the 59 milk samples collected, 33 (56%) were Brucella milk ring test (MRT)-positive and 78% and 17% of the samples graded satisfactorily based on SG and coliform plate counts as prescribed by East African Community standards for raw milk. There was no verocytotoxigenic E. coli (VTEC) O157: H7 in any of the milk samples collected and analysed during the present study.

CONCLUSIONS

It can be concluded that raw market milk in the study area is of poor bacteriological quality and hazardous for human consumption. This highlights the need to implement good hygiene practices and effective monitoring from production through the delivery chain to the consumer. Further studies are needed for detection of toxins that are produced by E. coli, other pathogenic spore forming bacteria (Bacillus spp. and Clostridium spp.) and other harmful microorganisms.

Response surface methodology to design a selective co-enrichment broth of Escherichia coli, Salmonella spp. and Staphylococcus aureus for simultaneous detection by multiplex PCR

Escherichia coli, Salmonella spp. and Staphylococcus aureus are frequent co-visitors of contaminated foods to cause food-borne diseases. To achieve rapid detection of three organisms by multiplex PCR, a selective co-enrichment broth was considered to design using response surface methodology (RSM) in this work. NaCl, LiCl and KSCN as selective bacterial inhibitors were selected to optimize their concentrations for a matched composition of bacterial biomass with uniform amplification of three targets. Central composite design was employed to collect the data and fit the responses. Three quadratic polynomial models were derived by computer simulation. A statistical analysis was carried out to explore the effects of the variables on the composition of bacterial biomass and PCR amplification yields. In the end, a novel broth (ESS-3 broth) of NaCl 1.60%, LiCl 0.70%, KSCN 0.10% was formulated to allow co-enrichment of the target pathogens and suppress growth of some non-target pathogens. The simultaneous detection of E. coli, Salmonella spp. and S. aureus was developed on a rapid, convenient and sensitive method consisting of selective co-enrichment in ESS-3 broth, DNA extraction with the boiling method and robust test by multiplex PCR. Our work provided broader application of RSM for the simultaneous detection of other combinations of multiple pathogens.

Risk factors for symptoms of gastrointestinal illness in rural town Isiolo, Kenya

This study assesses risk factors for food-borne gastrointestinal illness indicated by diarrhoea and/or vomiting using 14-day recalls among children and young adults. The study was set in Isiolo, a rural town of Kenya, inhabited mainly by pastoralists of different ethnic groups. The preparation methods of milk at the household level were also investigated. The study was cross-sectional and involved 900 participants from randomly selected households. They were interviewed using a structured questionnaire. An unmatched nested case-control study was constructed by randomly selecting three controls for each case. Potential risk factors for gastrointestinal illness were analysed using both univariate and multivariate logistic regression models with random effect on ethnic groups. The study results showed that consumption of mutton, carrots, Irish potatoes, raw camel milk, boiled camel milk and fermented camel milk were important risk factors for diarrhoea and/or vomiting, whereas the consumption of boiled goat milk, boiled cow milk, spinach, washing of hands with soap and the presence of proper drainage system had protective effects (odds ratio < 1). We conclude that in this setting, primarily vegetables and the camel milk market chain pose the greatest risks for symptoms of food-borne gastrointestinal illness.

Interference of raw milk autochthonous microbiota on the performance of conventional methodologies for Listeria monocytogenes and Salmonella spp. detection

Pathogen detection in foods by reliable methodologies is very important to guarantee microbiological safety. However, peculiar characteristics of certain foods, such as autochthonous microbiota, can directly influence pathogen development and detection. With the objective of verifying the performance of the official analytical methodologies for the isolation of Listeria monocytogenes and Salmonella in milk, different concentrations of these pathogens were inoculated in raw milk treatments with different levels of mesophilic aerobes, and then submitted to the traditional isolation procedures for the inoculated pathogens. Listeria monocytogenes was inoculated at the range of 0.2-5.2 log CFU/mL in treatments with 1.8-8.2 log CFU/mL. Salmonella Enteritidis was inoculated at 0.9-3.9 log CFU/mL in treatments with 3.0-8.2logCFU/mL. The results indicated that recovery was not possible or was more difficult in the treatments with high counts of mesophilic aerobes and low levels of the pathogens, indicating interference of raw milk autochthonous microbiota. This interference was more evident for L. monocytogenes, once the pathogen recovery was not possible in treatments with mesophilic aerobes up to 4.0 log CFU/mL and inoculum under 2.0 log CFU/mL. For S. Enteritidis the interference appeared to be more non-specific.

Listeria monocytogenes and Salmonella spp. in raw milk produced in Brazil: occurrence and interference of indigenous microbiota in their isolation and development

This study aimed to verify the occurrence of Listeria monocytogenes and Salmonella spp. in raw milk produced in Brazil. On account of the poor microbiological quality of this product, possible interference from the indigenous microbiota in these pathogens was also evaluated. Two-hundred and ten raw milk samples were collected in four important milk-producing areas in Brazil, tested for L. monocytogenes and Salmonella spp. presence, and for enumeration of indicator microorganisms: mesophilic aerobes, total coliforms and Escherichia coli. The interference of the indigenous microbiota in the isolation procedures was also tested, as well the frequency of naturally occurring raw milk strains with antagonistic activity against both pathogens. The pathogens were not isolated in any raw milk sample, but poor microbiological quality was confirmed by the high levels of indicator microorganisms. When present at high levels, the indigenous microbiota generated an evident interference in the methodologies of L. monocytogenes and Salmonella spp. isolation, mainly when the pathogens appeared at low levels. Three-hundred and sixty raw milk strains were tested for antagonistic activity against both pathogens, and 91 (25.3%) showed inhibitory activity against L. monocytogenes and 33 (9.2%) against Salmonella spp. The majority of the antagonistic strains were identified as Lactic Acid Bacteria species, mainly Lactococcus lactis subsp. lactis and Enterococcus faecium, known by antimicrobial substance production.

Evaluation of the hygienic quality and associated public health hazards of raw milk marketed by smallholder dairy producers in the Dar es Salaam region, Tanzania

A cross-sectional study was conducted to determine three parameters of the quality of the raw milk marketed by milk selling points (MSPs) in Dar es Salaam region. Total bacterial count (TBC) was used as an indicator of the microbial quality of the milk; antimicrobial residues were determined; and the California mastitis test (CMT) was used to screen for milk somatic cells as an indication of the mastitis level in the cows that provided the milk. Moreover, a water sample at each MSP was taken for bacteriological culturing. Finally, a questionnaire survey was conducted with the milk sellers at the MSPs to identify risk factors for poor milk hygiene. A total of 128 milk samples and corresponding water samples were collected from randomly selected milk selling points in Dar es Salaam region. The mean TBC was (8.2 +/- 1.9) x 10(6) cfu/ml, and major bacterial isolates from the milk samples were Escherichia coli (6.3%), Bacillus cereus (6.3%), Staphylococcus aureus (6.3%) and Streptococcus agalactiae (6.3%), Enterobacter aerogenes (5.6%) and Enterococcus faecalis (4.7%). In most cases, the organisms identified in milk corresponded to those isolated from the corresponding water samples. Of milk samples, 79.0% were positive to the CMT and 7.0% were positive for antimicrobial residues. TBC was normalized by log-transformation, and the possible predictors of TBC were identified by fitting two linear regression models. In a random effect model, water microbial quality, frequency of cleaning the milk containers, frequency of milk supply, milk storage time and the type of containers, and mixing of fresh and previous milk were significantly (p < 0.05) associated with the mean log TBC. In a fixed effect model, in addition to these indicators, water shortage, water source and the refrigerator condition were significantly (p < or = 0.01) associated with log TBC. It was concluded that the milk sold in Dar es Salaam region is of poor quality and is of public health significance.

Prevalence of Campylobacter species in meat, milk and other food commodities in Pakistan

A surveillance study was carried out to determine the prevalence of Campylobacter in meat, milk and other food commodities in Pakistan. Over a period of 3 years (January 2002-December 2004), a total of 1636 food samples of meat, milk and other food commodities were procured from three big cities of Pakistan (Faisalabad, Lahore and Islamabad) and were analysed. Among meat samples, the highest prevalence (48%) of Campylobacter was recorded in raw chicken meat followed by raw beef (10.9%) and raw mutton (5.1%). Among other food commodities, the highest prevalence was observed in vegetable/fruit salad (40.9%), sandwiches (32%), cheese (11%) and raw bulk milk samples (10.2%). The overall prevalence of Campylobacter was found to be 21.5%, out of which 70.6% were identified as Campylobacter (C.) jejuni and 29.4% as C. coli. The study reported that the prevalence of Campylobacter spp. was significantly higher in the food commodities, which included raw/undercooked ingredients.

Further Characterization ofCampylobacterIsolated from U.S. Dairy Cows

The objective of the present study was to compare polymerase chain reaction (PCR) identification with ribotype results and to use pulsed field electrophoresis (PFGE) to correlate genotypic patterns with antibiotic resistance of Campylobacter isolated from lactating dairy cows in the United States. Thirty isolates were studied. Twenty-seven of the isolates were identified by PCR as Campylobacter jejuni and three were identified as Campylobacter coli. Genotypic patterns of 15 isolates were determined by PFGE, and although isolates originated from geographically separated regions of the United States, some were genotypically identical. In contrast to their genetic similarity, antibiotic sensitivity patterns differed within some genotypes. Under the conditions of our study, we concluded that ribotyping is not as discriminatory as PCR for speciation, and that a phenotypic trait such as antimicrobial resistance cannot always be predicted within the same genotype.

Occurrence of Campylobacter in retail foods in Ireland

A surveillance study was carried out to determine the prevalence of Campylobacter in a range of retail foods purchased in three Irish cities over a 20-month period between March 2001 and October 2002. In total 2391 food samples were analysed during this period. Campylobacter was isolated from 444 raw chicken (49.9%), 33 turkey (37.5%) and 11 duck samples (45.8%). Lower isolation rates of 7/221 (3.2%), 10/197 (5.1%) and 31/262 (11.8%) were observed for raw beef, pork and lamb, respectively. One sample of pork paté from 120 samples analysed (0.8%) was Campylobacter-positive. A total of three shellfish samples (oysters) from 129 raw specimens examined (2.3%) were found to contain Campylobacter. Low prevalences of the organism (0.9%) were also isolated from fresh mushrooms. Of 62 raw bulk tank milk samples analysed, Campylobacter was recovered in a single sample (1.6%). Campylobacter was not detected in any of the comminuted pork puddings, prepared vegetables and salads, retail sandwiches or cheeses made from unpasteurised milk. In total, 543 Campylobacter were isolated from all of the food samples analysed, of which 453 (83.4%) were confirmed as Campylobacter jejuni and the remaining 90 (16.6%) as Campylobacter coli.

Diarrhoea, vomiting and the role of milk consumption: perceived and identified risk in Bamako (Mali)

OBJECTIVES

To evaluate the public health impact of milk contamination in Bamako, Mali.

METHODS

A case-control study assessed the risk-factors for food-borne toxi-infections with diarrhoea and vomiting as main clinical picture. A total of 131 schoolchildren between 5 and 20 years of age were interviewed by trained interviewers in schools in Bamako. A structured questionnaire was used to record health problems, food and particularly milk consumption habits and socio-economic indicators.

RESULTS

Final multivariate logistic regression analysis identified regular consumption of boiled milk [odds ratio(OR) = 4.38; 95% CI = 1.15-16.71], age between 5 and 10 years (OR vs. age group 11-15 years = 3.28; 95% CI = 1.09-9.85) and the existence of dry latrines in the household (OR = 7.65; 95% CI = 1.92-30.55) as risk factors for diarrhoea and vomiting. Other milk products and the socio-economic level of the household were not significantly associated with the outcome. Many people were unaware of the potential risks of milk consumption.

CONCLUSIONS

Milk products may be a risk factor for food-borne toxi-infections. Attention has to be paid to products considered 'safe', such as boiled or pasteurized milk. The low awareness of potential risks of many people may increase the risk of milk consumption. To achieve a sustainable increase in local milk production in Africa, milk quantity and production and transformation quality should be improved simultaneously.