https://hdl.handle.net/10259/7437 Mon, 27 Apr 2026 18:22:08 GMT 2026-04-27T18:22:08Z https://hdl.handle.net/10259/7438 Listeria monocytogenes survives better at lower storage temperatures in regular and low-salt soft and cured cheeses Possas, Arícia; Hernández Pérez, Marta; Esteban Carbonero, Óscar; Valero, Antonio; Rodríguez Lázaro, David The behaviour of Listeria monocytogenes was investigated in soft pasteurized milk cheese elaborated with different salt concentrations (1.17 and 0.30% w/w) and in cured raw sheep milk cheese over storage up to 189 days at different isothermal conditions. Commercial 25-g cheese samples were inoculated with a 4-strain cocktail of L. monocytogenes (serovars 4b, 1/2a, 1/2b and 1/2c) at approximately 104 CFU/g. The inoculated samples were stored at 4 and 22 ◦C and withdrawn at proper intervals for L. monocytogenes enumeration. The prevalence of the different serovar strains of L. monocytogenes was characterized on soft cheese samples over storage at 4 ◦C using multiplex PCR. Salt reduction did not affect the survival of L. monocytogenes in soft cheeses and a maximum of 1- log reduction was observed in both regular and low-salt cheeses after 189 days of storage at 4 ◦C. The pathogen showed greater survival capacity in both soft and cured cheeses during storage at 4 ◦C compared to the storage at 22 ◦C, where more than 2.5 log reductions were computed. The fate of L. monocytogenes was described through a Weibull model fitted to survival data. The time required for a first tenfold reduction of the L. monocytogenes population (δ) at 4 ◦C is around 150 days in soft and 72 days in cured cheeses. At 22 ◦C, the estimated δ values are at least 60% lower in both cheese types. Among the four L. monocytogenes serovars present in the inoculated cocktail, the serovar 4b strain was the most sensitive to refrigerated storage, while the prevalence of serovar 1/2c strain increased over time in soft cheeses. Overall, the data obtained in this study help to deepen knowledge into factors affecting L. monocytogenes behaviour on cheeses and evidenced the variability between serovars in terms of survival capacity, which may be considered when performing microbial risk assessments. Wed, 01 Jun 2022 00:00:00 GMT https://hdl.handle.net/10259/7438 2022-06-01T00:00:00Z https://hdl.handle.net/10259/4864 Modelling the fate and serogroup variability of persistent Listeria monocytogenes strains on grated cheese at different storage temperatures Valero, Antonio; Hernández Pérez, Marta; Esteban Carbonero, Óscar; Rodríguez Lázaro, David Processed cheese from cow's milk is one of the most consumed dairy products worldwide. Since this product is defined as ready-to-eat, foodborne pathogens such as Listeria monocytogenes can represent a health concern for susceptible populations. In this study, the individual and combined kinetic behaviour of four L. monocytogenes serogroups (namely, 1/2a, 1/2b, 1/2c and 4b) persistently isolated from a Spanish cheesemaking factory was modelled on grated cheese at different isothermal conditions (4 and 12 °C) during a 120-days period. The serogroup variability was characterized over the storage time by the isolation and identification of the different serogroups in the cocktail containing the four strains. This processed cheese did not support the growth of L. monocytogenes during storage. Survival patterns described by the log-linear type model indicated a high variability of L. monocytogenes serotypes at the tested temperatures: L. monocytogenes serogroup 4b showed a more rapid decrease rate at 4 °C than at 12 °C, while the opposite trend was found for the rest of serogroups and the L. monocytogenes cocktail containing all the strains. Survival rate of L. monocytogenes serogroup 1/2c at 4 °C was 0.007 log CFU/d being the most resistant serotype while at 12 °C, serogroup 1/2a showed the lowest survival rate (0.011 log CFU/d), thus showing a prolonged survival at this temperature. This study highlights the potential implications of L. monocytogenes contamination in processed cheese and shows that serogroup variability should be considered when evaluating survival patterns in contaminated products. Finally, the predictive models developed here could be useful to assist food operators to set specific storage conditions and formulations to avoid L. monocytogenes growth and survival in grated cheeses. Sat, 01 Dec 2018 00:00:00 GMT https://hdl.handle.net/10259/4864 2018-12-01T00:00:00Z https://hdl.handle.net/10259/4411 Molecular Investigation of Tularemia Outbreaks, Spain, 1997–2008 Ariza Miguel, Jaime; Johansson, Anders; Fernández Natal, Isabel; Martínez Nistal, Carmen; Orduña, Antonio; Rodríguez Ferri, F.; Hernández Pérez, Marta; Rodríguez Lázaro, David Tularemia outbreaks occurred in northwestern Spain in 1997–1998 and 2007–2008 and affected >1,000 persons. We assessed isolates involved in these outbreaks by using pulsed-field gel electrophoresis with 2 restriction enzymes and multilocus variable number tandem repeat analysis of 16 genomic loci of Francisella tularensis, the cause of this disease. Isolates were divided into 3 pulsotypes by pulsed-field gel electrophoresis and 8 allelic profiles by multilocus variable number tandem repeat analysis. Isolates obtained from the second tularemia outbreak had the same genotypes as isolates obtained from the first outbreak. Both outbreaks were caused by genotypes of genetic subclade B.Br:FTNF002–00, which is widely distributed in countries in central and western Europe. Thus, reemergence of tularemia in Spain was not caused by the reintroduction of exotic strains, but probably by persistence of local reservoirs of infection. Thu, 01 May 2014 00:00:00 GMT https://hdl.handle.net/10259/4411 2014-05-01T00:00:00Z https://hdl.handle.net/10259/4410 Molecular Epidemiology of Invasive Listeriosis due to Listeria monocytogenes in a Spanish Hospital over a Nine-Year Study Period, 2006–2014 Ariza Miguel, Jaime; Fernández Natal, Isabel; Soriano, F.; Hernández Pérez, Marta; Stessl, Beatrix; Rodríguez Lázaro, David We investigated the pathogenicity, invasiveness, and genetic relatedness of 17 clinical Listeria monocytogenes stains isolated over a period of nine years (2006–2014). All isolates were phenotypically characterised and growth patterns were determined. The antimicrobial susceptibility of L. monocytogenes isolates was determined in E-tests. Invasion assays were performed with epithelial HeLa cells. Finally, L. monocytogenes isolates were subtyped by PFGE and MLST. All isolates had similar phenotypic characteristics (β-haemolysis and lecithinase activity), and three types of growth curve were observed. Bacterial recovery rates after invasion assays ranged from 0.09% to 7.26% (1.62 ± 0.46). MLST identified 11 sequence types (STs), and 14 PFGE profiles were obtained, indicating a high degree of genetic diversity. Genetic studies unequivocally revealed the occurrence of one outbreak of listeriosis in humans that had not previously been reported. This outbreak occurred in October 2009 and affected three patients from neighbouring towns. In conclusion, the molecular epidemiological analysis clearly revealed a cluster (three human cases, all ST1) of not previously reported listeriosis cases in northwestern Spain. Our findings indicate that molecular subtyping, in combination with epidemiological case analysis, is essential and should be implemented in routine diagnosis, to improve the tracing of the sources of outbreaks. Thu, 01 Jan 2015 00:00:00 GMT https://hdl.handle.net/10259/4410 2015-01-01T00:00:00Z