Mariza Landgraf

Minimally processed vegetable salads: microbial quality evaluation.

The increasing demand for fresh fruits and vegetables and for convenience foods is causing an expansion of the market share for minimally processed vegetables. Among the more common pathogenic microorganisms that can be transmitted to humans by these products are Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella. The aim of this study was to evaluate the microbial quality of a selection of minimally processed vegetables. A total of 181 samples of minimally processed leafy salads were collected from retailers in the city of Sao Paulo, Brazil. Counts of total coliforms, fecal coliforms, Enterobacteriaceae, psychrotrophic microorganisms, and Salmonella were conducted for 133 samples. L. monocytogenes was assessed in 181 samples using the BAX System and by plating the enrichment broth onto Palcam and Oxford agars. Suspected Listeria colonies were submitted to classical biochemical tests. Populations of psychrotrophic microorganisms >10(6) CFU/g were found in 51% of the 133 samples, and Enterobacteriaceae populations between 10(5) and 106 CFU/g were found in 42% of the samples. Fecal coliform concentrations higher than 10(2) CFU/g (Brazilian standard) were found in 97 (73%) of the samples, and Salmonella was detected in 4 (3%) of the samples. Two of the Salmonella-positive samples had <10(2) CFU/g concentrations of fecal coliforms. L. monocytogenes was detected in only 1 (0.6%) of the 181 samples examined. This positive sample was simultaneously detected by both methods. The other Listeria species identified by plating were L. welshimeri (one sample of curly lettuce) and L. innocua (2 samples of watercress). The results indicate that minimally processed vegetables had poor microbiological quality, and these products could be a vehicle for pathogens such as Salmonella and L. monocytogenes.

Growth potential of Salmonella spp. and Listeria monocytogenes in nine types of ready-to-eat vegetables stored at variable temperature conditions during shelf-life.

Growth potential (δ) is defined as the difference between the population of a microorganism at the end of shelf-life of specific food and its initial population. The determination of δ of Salmonella and Listeria monocytogenes in RTE vegetables can be very useful to determine likely threats to food safety. However, little is known on the behavior of these microorganisms in several RTE vegetables. Therefore, the aim of this study was to determine the δ of both pathogens in nine different types of RTE vegetables (escarole, collard green, spinach, watercress, arugula, grated carrot, green salad, and mix for yakisoba) stored at refrigeration (7°C) and abuse temperature (15°C). The population of aerobic microorganisms and lactic acid bacteria, including those showing antimicrobial activity has been also determined. Results indicated that L. monocytogenes was able to grow (δ≥0.5 log(10)) in more storage conditions and vegetables than Salmonella. Both microorganisms were inhibited in carrots, although a more pronounced effect has been observed against L. monocytogenes. The highest δ values were obtained when the RTE vegetables were stored 15°C/6days in collard greens (δ=3.3) and arugula (δ=3.2) (L. monocytogenes) and arugula (δ=4.1) and escarole (δ=2.8) (Salmonella). In most vegetables and storage conditions studied, the counts of total aerobic microorganisms raised significantly independent of the temperature of storage (p<0.05). Counts of lactic acid bacteria were higher in vegetables partially or fully stored at abuse temperature with recovery of isolates showing antimicrobial activity. In conclusion, the results of this study show that Salmonella and L. monocytogenes may grow and reach high populations in RTE vegetables depending on storage conditions and the definition of effective intervention strategies are needed to control their growth in these products.

Prevalence, populations and pheno- and genotypic characteristics of Listeria monocytogenes isolated from ready-to-eat vegetables marketed in Sao Paulo, Brazil

Listeria monocytogenes is a foodborne pathogen of great concern due to the high fatality rates of listeriosis. The consumption of RTE vegetables has increased in Brazil over the last two decades, but little is known about the risks associated to the consumption of these products. This study evaluated the prevalence and counts of L. monocytogenes in 512 packages of ready-to-eat vegetables marketed in São Paulo. The isolates were characterized for their serotypes, ribotypes, positivity for virulence genes inlA, inlC and inlJ, resistance to chlorine, growth rate variability and capability to form biofilm on stainless steel (AISI 304, #4) coupons. L. monocytogenes was detected in 3.1% of the samples. Only five samples presented countable levels, with counts between 1.0×10(1) and 2.6×10(2)CFU/g. Isolates belonged to serotypes 1/2b or 4b and most were positive for genes inlC and inlJ. Ribotypable isolates were grouped into four groups: 1038 (69.4%), 19175 (11.3%), 19191 (17.7%) and 18604 (one isolate). Most isolates survived to exposure to 125 ppm of a chlorine-based disinfectant for 3 min. All isolates were capable to attach to the coupons, reaching counts above 4 log(10) CFU/cm(2) and the growth rate (μ) at 25°C of the majority of the isolates varied between 0.1 and 0.2 log OD/h, but for few strains the μ was as high as 0.26 log OD/h. Results of this survey indicate that RTE vegetables may be vehicles of L. monocytogenes strains with limited variation in serotype, ribotype and virulence factors but varying significantly in resistance to chlorine disinfectants, capability of forming biofilm and growth rate. Data obtained is of foremost importance to serve as baseline for the development of scientific-based policies to control the incidence of L. monocytogenes in RTE vegetables in Brazil.

Inactivation by ionizing radiation of Salmonella Enteritidis, Salmonella Infantis, and Vibrio parahaemolyticus in oysters (Crassostrea brasiliana)

Irradiation is considered one of the most efficient technological processes for the reduction of microorganisms in food. It can be used to improve the safety of food products, and to extend their shelf lives. Oysters are considered one of the most important vehicles for pathogenic bacteria because of their feeding characteristics. The aim of this study was to evaluate the influence of a gamma radiation process on high levels of Salmonella Enteritidis, Salmonella Infantis, and Vibrio parahaemolyticus incorporated by oysters (Crassostrea brasiliana), as well as the effects of the process on the survival of the oysters and on their sensory attributes. The oysters were exposed to gamma radiation (60Co) in doses ranging from 0.5 to 3.0 kGy. A dose of 3.0 kGy was generally sufficient to reduce the level of Salmonella serotypes by 5 to 6 log10 units. A dose of 1.0 kGy was sufficient to produce a 6-log10 reduction in the level of V. parahaemolyticus. The highest irradiation dose did not kill the oysters or affect their sensory attributes. Hence, a dose of 3.0 kGy can be considered effective in inactivating Salmonella and V. parahaemolyticus in oysters without changing their odor, flavor, or appearance.

Parameters determining the quality of charqui, an intermediate moisture meat product

Charqui is a typical Brazilian meat product obtained by salting and sun-drying beef samples. The chemical, physical and microbiological characteristics of the charqui were evaluated throughout processing and storage. The results confirm charqui is an intermediate moisture meat product (A(w) = 0·70-0·75). A close relationship between moisture, pretein and ash vaiues was found, suggesting the possibility of using the resulting charqui A(w) value as a parameter to define the product instead of the official moisture and mineral residue contents. The TBA determination, which expresses the state of lipid oxidation, rapidly reached the maximum value, corroborating the previous observations on the salt pro-oxidant role, and then decreased gradually. A gradual decrease in microorganism count during processing and storage of charqui was also observed. These results indicate the feasibility of obtaining a final product with a low level of microbial count when raw materials of good quality, and adequate handling conditions, are used for charqui production.

Silent dissemination of colistin-resistant Escherichia coli in South America could contribute to the global spread of the mcr-1 gene.

During a Brazilian multicentric antimicrobial resistance surveillance study, colistin resistance was investigated in 4,620 Enterobacteriaceae isolated from human, animal, food and environmental samples collected from 2000 to 2016. We present evidence that mcr-1-positive Escherichia coli has been emerging in South America since at least 2012, supporting a previous report on the possible acquisition of mcr-1-harbouring E. coli by European travellers visiting Latin American countries.

Foodborne outbreak caused by Staphylococcus aureus: phenotypic and genotypic characterization of strains of food and human sources.

An outbreak of staphylococcal food poisoning involving approximately 180 people occurred in Brodowski, São Paulo State, Brazil, in April 1998. Strains of Staphylococcus aureus isolated from foods and food handlers, implicated as the etiologic agent, were characterized with phenotypic (phage typing, antibiotic susceptibility test, and enterotoxin production), and genotypic (random amplified polymorphic DNA) characterization. Strains isolated from vegetable salad with mayonnaise sauce, broiled chicken, pasta in tomato sauce, and from the oropharyngeal secretions of five food handlers--A, B, C, H, and I--showed the same phage profile and antibiotic resistance. Random amplified polymorphic DNA generated 17 combined profiles with primers OPE-20 and OPA-7. The similarity of strains was analyzed by generating a dendrogram that classified the 59 strains of S. aureus into four major clusters (I, II, III, and IV). Strains from four food handlers (A, B, H, and I) and from vegetable salad with mayonnaise, broiled chicken, and pasta in tomato sauce showing the same phage type profile and resistance to antibiotics belonged to the same cluster and produced staphylococcal enterotoxin A. Therefore, these foods and food handlers were incriminated in the outbreak.

Correlation between Environmental Factors and Prevalence of Vibrio parahaemolyticus in Oysters Harvested in the Southern Coastal Area of Sao Paulo State, Brazil

ABSTRACT The presence of Vibrio parahaemolyticus in 123 oyster samples collected from an estuary on the southern coast of Sao Paulo state, Brazil, was investigated. Of the 123 samples, 99.2% were positive with densities ranging from <3 to 105 most probable number (MPN)/g. Densities correlated significantly with water temperature (r = 0.48; P < 0.001) but not with salinity (r = −0.09; P = 0.34). The effect of harvest site on counts was not significant (P > 0.05). These data provide information for the assessment of exposure of V. parahaemolyticus in oysters at harvest.

Biochemical characteristics of typical and atypical Staphylococcus aureus in mastitic milk and environmental samples of Brazilian dairy farms

This study reports results on the biochemical characteristics of 274 Staphylococcus aureus strains isolated from mastitic milk, hands of milkmen and milking machines. Features included colony morphology on Baird Parker agar (BPA), catalase, coagulase and thermonuclease tests. API-Staph (bioMerieux, France) was used as reference identification system. 39.4% of the colonies on BPA identified as S.aureus were atypical. They were more frequent in milk samples (94.4%). All S.aureus strains were coagulase positive but intensity of the test varied according to the source: environmental strains were 3+ or 4+, while 17.1% of strains isolated from milk presented only 1+ or 2+ results. The majority of atypical S.aureus strains presented a 4+ coagulase result. 2.2% of S.aureus strains were thermonuclease negative. Sixteen thermonuclease positive and coagulase positive strains were identified as S.hyicus.

Evaluation of motility enrichment on modified semi-solid Rappaport–Vassiladis medium (MSRV) for the detection of Salmonella in foods

The detection and identification of Salmonella spp. is still troublesome and time consuming to the food industry. Employing the modified semi-solid Rappaport-Vassiliadis medium (MSRV), presumptive results for Salmonella can be obtained in 48 h, representing an interesting alternative to the standard methods. The specificity and sensitivity of the MSRV method were evaluated in this research. The efficiency of this method was also compared with the methodology recommended by the US Food and Drug Administration (FDA) using bismuth sulfite agar, XLT4 agar and Rambach agar. A total of 146 food samples comprised of 41 chicken thighs, 35 Brazilian fresh pork sausages, 35 samples of cocoa powder and/or granulated cocoa and 35 samples of grated fresh coconut, were examined. Overall, the rapid method (direct + indirect) and the standard culture detected 96.1% and 84.6% of the positive samples, respectively. No Salmonella was detected in the coconut or cocoa samples by any of the methods. Eighteen (43.9%) chicken thigh samples were contaminated with the microorganism. The rapid method (direct + indirect) and the standard culture detected 94.4% and 88.9% of these, respectively. Salmonella was detected in eight (22.8%) fresh pork sausage samples. The MSRV method detected Salmonella in all eight samples, while the standard gave positive results in six (75%). When compared with the standard method, the indirect method showed 86.4% sensitivity and 96.8% specificity, while the direct MSRV showed a sensitivity of 71.4% and specificity of 99.2%. Combined, both MSRV methods showed 95.5% sensitivity and 96.8% specificity. The MSRV medium also reduces the time necessary for the isolation of Salmonella from foods.