Use of Epidemiologic and Food Survey Data To Estimate a Purposefully Conservative Dose-Response Relationship for Listeria monocytogenes Levels and Incidence of Listeriosis

Reis

Rev. Soc. Bras. Med. Trop.

2006

A análise fenotípica de 255 amostras do gênero Listeria isoladas de material clínico humano, tanto de indivíduos doentes (220-86,3%), como de aparentemente normais (35-13,7%) de várias regiões do país e colecionadas no período de 1969 a 2000, permitiu caracterizar a distribuição de sorovares de Listeria monocytogenes. Nas faixas etárias de 0 a 10 e de 41 a 60 anos, predominaram os isolamentos de líquido cefalorraquidiano sobre os de sangue, incluindo dos transplantados renais. Somente dos hemocultivos foi possível detectar os sete sorovares de Listeria monocytogenes. No cômputo geral, o sorovar 4b foi o mais incidente (154-60,3%) secundado por ¹/2 a (74-29%) nos três decênios considerados, além de ocorrerem em quase todas as regiões do país. Os dados deste estudo evidenciaram a circulação de L. monocytogenes na espécie humana, provocando quadros graves de meningite e septicemia, bem como, revelando a figura do portador assintomático, razão pela qual são recomendadas novas investigações bacteriológicas, subsidiadas por análises clínico-patológicas e epidemiológicas.

Section: Methodsunclassified

Sorovares de Listeria monocytogenes e espécies relacionadas, isoladas de material clínico humano

Reis

Rev. Soc. Bras. Med. Trop.

2006

International Journal of Food Microbiology

“…Epidemiologic data indicate that foods involved in listeriosis outbreaks are those in which the organism has multiplied and in general have contained levels significantly higher than 100 cfu/g (Buchanan et al,1997;Ross et al, 2000;ICMSF, 2002). Based on risk assessment for L. monocytogenes in RTE foods, the Codex Alimentarius recommended that the maximum contamination level for L. monocytogenes in food at consumption should be less than 100/g (Codex Alimentarius, 2002).…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a challenge testing protocol to assess the stability of ready-to-eat cooked meat products against growth of Listeria monocytogenes

Uyttendaele¹

2004

Challenge testing of ready-to-eat (RTE) foods with Listeria monocytogenes is recommended to assess the potential for growth. The present study was undertaken to evaluate a protocol for challenge testing applied to RTE cooked meat products. In order to choose L. monocytogenes strains with a representative behaviour, initially, the variability of the response of multiple L. monocytogenes strains of human and food origin to different stress and growth conditions was established. The strains were not inhibited in their growth at moderate acid pH (5.25) and the four strains tested in particular showed a similar acid-adaptive response. Growth of the various strains under four different combined stress conditions indicated that no L. monocytogenes strain had consistently significant longer or shorter lag phase or higher or lower maximum specific growth rates. The effect of choice of strain and history (pre-incubation temperature 7 or 30 jC) on growth of L. monocytogenes under optimum conditions (Brain Heart Infusion, BHI) and modified BHI simulating conditions of cooked ham and paté was studied. In general, all four L. monocytogenes strains behaved similarly. In BHI, no difference in lag phase was observed for the cold-adapted and standard inoculum, whereas in BHI adjusted to ham and pâté conditions, a ca. 40-h reduction of the lag phase was noted for the coldadapted inoculum. Subsequently, microbial challenge testing of L. monocytogenes in modified atmosphere packaged sliced cooked ham and paté was performed. A mixed inoculum of four L. monocytogenes strains and an inoculum level of ca. 1 -10 cfu/g was used. On vacuum packed sliced cooked ham, the concentration of 100 cfu/g, the safety limit considered as low risk for causing listeriosis, was exceeded after 5 days whereas ca. 10 5 cfu/g were obtained after 14 days when also LAB spoilers reached unacceptable numbers (ca. 10 7 cfu/g) whether standard or cold-adapted inoculum was used. The concentration of sodium lactate determined the opportunities for growth of L. monocytogenes in pâté. If growth of L. monocytogenes in pâté was noticed, the threshold of 100 cfu/ml was crossed earlier for the cold-adapted inoculum compared to the standard inoculum. D

“…However, a leading hypothesis is that a range of doses as opposed to an infectious dose threshold can cause an infection with various probabilities. More specifically, as the dose of L. monocytogenes consumed by an individual increases, the likelihood that an infection will occur also increases (3,8,42). Existing L. monocytogenes risk assessments assume some heterogeneity in virulence (8,42,50); however, they do not mechanistically relate strain-specific genetic characteristics to virulence and, as a result, may overestimate the virulence of strains carrying a PMSC in inlA and underestimate the virulence of epidemic clone strains.…”

mentioning

confidence: 99%

Significant Shift in Median Guinea Pig Infectious Dose Shown by an Outbreak-AssociatedListeria monocytogenesEpidemic Clone Strain and a Strain Carrying a Premature Stop Codon Mutation ininlA

Stelten

Simpson

Chen

et al. 2011

Appl Environ Microbiol

Listeria monocytogenes contains (i) epidemic clone (EC) strains, which have been linked to the majority of listeriosis outbreaks worldwide and are overrepresented among sporadic cases in the United States, and (ii) strains commonly isolated from ready-to-eat foods that carry a mutation leading to a premature stop codon (PMSC) in inlA, which encodes the key virulence factor internalin A (InlA). Internalin A binds certain isoforms of the cellular receptor E-cadherin to facilitate crossing the intestinal barrier during the initial stages of an L. monocytogenes infection. Juvenile guinea pigs, which express the human isoform of E-cadherin that binds InlA, were intragastrically challenged with a range of doses of (i) an EC strain associated with a listeriosis outbreak or (ii) a strain carrying a PMSC mutation in inlA. Recovery of L. monocytogenes from tissues (i.e., liver, spleen, mesenteric lymph nodes, and ileum) was used to develop strain-specific dose-response curves on the basis of individual and combined organ data. Modeling of individual and combined organ data revealed an approximate 1.2 to 1.3 log 10 increase in the median infectious dose for the strain carrying a PMSC in inlA relative to that for the EC strain. Inclusion of the strain parameter significantly improved the goodness of fit for individual and combined organ models, indicating a significant shift in median infectious dose for guinea pigs challenged with an inlA PMSC strain compared to that for guinea pigs challenged with an EC strain. Results from this work provide evidence that the L. monocytogenes dose-response relationship is strain specific and will provide critical data for enhancement of current risk assessments and development of future risk assessments.