SUSCEPTIBILITY OF Listeria monocytogenes STRAINS ISOLATED FROM FOOD TO ANTIMICROBIAL AGENTS

The objective of this study was to evaluate the susceptibility of 40 L. monocytogenes strains isolated from seafood and processing environments to 19 antibiotics currently used in veterinary and human therapy. Susceptibility tests were performed by the automated system VITEK2. Apart from Penicillin, Ampicillin and Trimethoprim-Sulfamethoxazole, for which clinical breakpoint for Listeria susceptibility testing are defined according to the Clinical and Laboratory Standard Institute (CLSI), in the present study the CLSI criteria for staphylococci were applied. This study shows that isolated L. monocytogenes strains are susceptible to the antibiotics commonly used in veterinary and human listeriosis treatment. Very few strains (7,5%) showed a resistance behaviour towards Oxacillin, whereas a variable pattern was showed for Ciprofloxacin and Moxifloxacin. Moreover, an increase in tetracycline resistance, reported by several authors, can not be confirmed in this study, probably due to the different sources of strains isolation. At last, the VITEK2 system represents a rapid and easy-to-use means for antimicrobial susceptibility test of Listeria monocytogenes. In conclusion, because of the increase of antimicrobial resistance showed by L. monocytogenes, a continuous surveillance of emerging antimicrobial resistance among this pathogen is important to ensure effective treatment of human listeriosis. These data can be used for improve background data on antibiotic resistance of strains isolated from food and food environment, even considering the lack of clinical breakpoint provided by the CLSI

Preliminary notes on invasion and proliferation of foodborne Listeria monocytogenes strains

In this study, virulence properties of L. monocytogenes strains isolated from food and food environments were evaluated. In particular, adhesion and invasion efficiencies were tested in a cell culture model (HeLa). Half of the isolates (9/18) exhibited a high invasion index. In particular, the strain isolated from smoked salmon had the highest invasion index. The remaining isolates showed an intermediate invasion index. All environmental isolates belonged to this group. Finally, no isolates revealed a low invasion index. Regarding intracellular growth, all tested isolates had a replication time between 2 and 6 hours. For this reason, they can be considered virulent. In spite of its capability to invade HeLa cells with a medium/high invasion index, a non-haemolytic rabbit isolate did not show any intracellular growth. In conclusion, differences in invasion efficiency and intracellular growth did not seem strictly related to the origin of the strains. Moreover, invasiveness of an organism is not the only requirement for establishing an infection. Virulence of L. monocytogenes also depends on ability to grow intracellularly and to spread from cell to cell. For these reasons, PCR detection of known virulence genes has the potential to gain additional insight into their pathogenic potential. A comprehensive comparative virulence characterization of different L. monocytogenes strains in studies that include tissue culture models and PCR detection of virulence genes will be necessary to investigate differences in human-pathogenic potentials among the subtypes of this bacterium

Listeria monocytogenes: biofilm in food processing

Contamination of food by Listeria monocytogenes (L.m) frequently occurs in food processing environments, where cells persist due to their ability to attach to surfaces. L.m is able to attach and colonize environmental surfaces by producing a three-dimensional matrix of extracellular polymeric substances (EPS) called biofilm; such structures are dynamic systems. Once established, biofilms can serve as a source of product contamination. Moreover, L.m in the biofilm state shows a reduced susceptibility to antimicrobial agents. The present review focuses on L.m biofilms in food processing environments. In addition, some aspects of biofilm control and eradication are highlighted

The Experience in Nicaragua: Childhood Leukemia in Low Income Countries—The Main Cause of Late Diagnosis May Be “Medical Delay”

Background. The event-free survival for pediatric leukemia in low-income Countries is much lower than in high-income countries. Late diagnosis, which is regarded as a contributing factor, may be due to “parental” or “medical” delay. Procedures. The present study analyses determinants of lag time from first symptoms to diagnosis of leukemia, comparing pediatric (0–16 years old) patients in two referral centers, one in Nicaragua and one in Italy. An observational retrospective study was conducted to assess factors influencing the time to diagnosis. Results. 81 charts of children diagnosed with acute myeloid leukemia or lymphoblastic leukemia were analyzed from each centre. Median lag time to diagnosis was higher in Nicaragua than in Italy (29 versus 14 days, P < 0.001) and it was mainly due to “physician delay” (16.5 versus 7 days, P < 0.001), whereas “patient delay” from symptoms to first medical assessment was similar in the two centers (7 versus 5 days, P = 0.27). Moreover, median lag time from symptoms to diagnosis was decreased in Nicaraguan districts were a specific training program upon childhood oncological diseases was carried out (20.5 versus 40 days, P = 0.0019). Conclusions. Our study shows that delay in diagnosis of childhood leukemia is mainly associated with “physician delay” and it may be overcome by programs of continuous medical education