Human listeriosis is a severe foodborne disease caused by Listeria monocytogenes. It is a zoonosis that represents a significant concern for the food industry due to the high mortality rate it causes and the fact that the organism is capable of growing at refrigeration temperatures. Dairy products and ready-to-eat meats are among the foods most often involved in listeriosis outbreaks. Listeria is a common contaminant in the dairy environment, both on the farm and in the processing plant. The main sources of L. monocytogenes in dairy farms are manure and improperly fermented silage. If silage crops are grown on contaminated land, a new cycle of silage contamination and faecal shedding by ruminants that consume such silage may ensue. High loads of L. monocytogenes produced in farm environments may thus represent a primary source for the introduction of this pathogen into the human food supply chain; dairy cows would represent a reservoir for the bacterium, and raw milk and beef would represent the main vehicles for its transmission from dairy farms to humans. Even if contamination originates in post-processing environments, contaminated raw foods may still represent a vehicle for introducing L. monocytogenes into food processing plants. Molecular typing methods have confirmed that common strains of L. monocytogenes are present in dairy farm-associated isolates and isolates from both human epidemic and sporadic cases. Pre-harvest (on-farm) control of listeriosis should be based mainly on the control of manure, silage, herd health and milking practices.Additional key words: animal reservoir; dairy primary production; environmental sources; food vehicles; listeriosis. ResumenRevisión. Tipos de gestión y producción de las granjas de ganado vacuno lechero relacionados con la presencia de Listeria monocytogenes en la leche y la carne La listeriosis humana es una grave enfermedad transmitida por alimentos y causada por Listeria monocytogenes. Se trata de una zoonosis que supone una gran preocupación para la industria alimentaria debido a su alta tasa de mortalidad y al hecho de que el microorganismo es capaz de crecer a temperaturas de refrigeración. Listeria es un contaminante habitual en las granjas y plantas de productos lácteos. En las granjas las fuentes principales de L. monocytogenes son el estiércol y los ensilados mal fermentados. Si la cosecha utilizada para producir ensilados procede de campos contaminados, puede comenzar un nuevo ciclo de contaminación de los ensilados y liberación del patógeno en las heces de los animales. El ganado vacuno lechero representa uno de los principales reservorios de este microorganismo y la leche y la carne representarían los principales vehículos para su transmisión desde la granja de producción de leche al ser humano. Incluso cuando la contaminación del alimento procede de etapas posteriores al procesado, los alimentos crudos contaminados también representan uno de los vehículos de entrada de L. monocytogenes en las plan-
Listeria monocytogenes is an opportunistic pathogen that is widely distributed in the environment. Here we show the prevalence and transmission of L. monocytogenes in dairy farms in the Cantabria region, on the northern coast of Spain. A total of 424 samples was collected from 14 dairy farms (5 organic and 9 conventional) and 211 L. monocytogenes isolates were recovered following conventional microbiological methods. There were no statistically significant differences in antimicrobial resistance ratios between organic and conventional farms. A clonal relationship among the isolates was assessed by pulsed field gel electrophoresis (PFGE) analysis and 64 different pulsotypes were obtained. Most isolates (89%, n = 187) were classified as PCR serogroup IVb by using a multiplex PCR assay. In this case, 45 isolates of PCR serogroup IVb were whole genome-sequenced to perform a further analysis at genomic level. In silico MLST analysis showed the presence of 12 sequence types (ST), of which ST1, ST54 and ST666 were the most common. Our data indicate that the environment of cattle farms retains a high incidence of L. monocytogenes, including subtypes involved in human listeriosis reports and outbreaks. This pathogen is shed in the feces and could easily colonize dairy products, as a result of fecal contamination. Effective herd and manure management are needed in order to prevent possible outbreaks.
The aim of this study was the examination of the genetic diversity and antimicrobial susceptibility of C. jejuni isolates obtained from dairy farms situated in Cantabria. The presence of Campylobacter jejuni was scrutinized in dairy farms situated in the Cantabria region (Atlantic coast, North of Spain). A total of 520 samples were collected from 12 dairy farms and 62 C. jejuni isolates were achieved. Sixty-one (61) of the isolates proceeded from fresh feces and only one from the stable (soil). Characterization of the isolates was conducted by Pulsed Field Gel Electrophoresis (PFGE) analysis. Antimicrobial susceptibility testing was carried out by standardized disk diffusion test. The PFGE analysis showed a high genetic diversity. From the 62 C. jejuni isolates, 27 different PFGE types were obtained with 70% similarity. The results of the antimicrobial susceptibility tests showed that 21 out of 27 strains were resistant to ciprofloxacin (78%), and 15 of them were also resistant to tetracycline (55%), whereas none of the 27 strains analyzed were resistant to erythromycin. C. jejuni was capable of surviving in livestock waste for at least 20–25 days, whereas the maximum detectable survival time on crops was of six days. This study reveals the high genetic diversity and ciprofloxacin resistance of C. jejuni in dairy cattle farms in Northern Spain, a fact that highlights the urgent need for the surveillance and control of this foodborne pathogen.
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