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Heat as a disinfection method for poultry houses persistently infected with Salmonella – an outline of methods and results . Kim O. Gradel Danmarks Veterin æ rinstitut, Å rhus Reng ø ring og Desinfektion af Stalde Hotel Australia, Vejle, 11.-12. November 2003. Background.
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Heat as a disinfection method for poultry houses persistently infected with Salmonella– an outline of methods and results Kim O. Gradel Danmarks Veterinærinstitut, Århus Rengøring og Desinfektion af Stalde Hotel Australia, Vejle, 11.-12. November 2003
Background • In general, heat rather than chemical disinfection of contaminated items is recommended whenever possible. • It is difficult to clean animal houses and cover all areas by surface disinfection. • Hypothesis: heat can be evenly distributed and it can penetrate organic matter without damaging materials. • Environmental considerations.
Disposition • Laboratory tests • Materials and methods • Results • Conclusions • Field tests • Materials and methods • Results • Conclusions
Micro- organism Type ”State/condition” Disinfectant Surroundings Type Concentration Organic matter Temperature pH Biofilm Heat tests related to general disinfection factors Heat project
Laboratory tests • Aims: • To find a temperature-humidity-time treatment that kills Salmonella. • Investigate correlations between susceptibility of spiked Salmonella and naturally occurring E. coli. • Principles: • Simulation of real-life conditions. • Worst-case scenarios. • Full factorial design.
Laboratory tests:test protocol • Thirty gram test material (feed or faeces) were put in beakers, yielding a layer 2-2.5 cm thick. • Spiked with high numbers of Salmonella. • Beakers at 20 oC and 30% RH during10-day period, lidded (no drying) or un-lidded (drying). • 10-day samples checked microbiologically, other samples moved to cooled incubator. • Other samples checked microbiologically as for 10-day samples after varying time periods, cf. next slide.
Laboratory tests: overview of tests 24-hour samples 48-hour samples 0-hour samples 1 oC per hour Final heating temperature 20 oC 20 oC 72-hour samples 10-day samples
Laboratory tests:microbiological procedures • From each beaker, traditional Salmonella procedures: pre-enrichment, selective enrichment, plating on Rambach agar. • From all beakers with faeces: plating from pre-enrichment broth on MacConkey agar (presence/absence of E. coli).
Laboratory tests:replicate tests • For the ”gold” standard, i.e. a temperature-humidity-time scheme that killed all bacteria, replicate tests were made. • Only S. Enteritidis was used, as there were few differences between the three Salmonella serotypes. • Only samples dried in the 10-day period were used. • Crumbled feed and egg yolk as well as pelleted feed and faeces were used. • All tests were repeated four times. • Three different selective enrichment procedures were applied.
E. coli detected? Salmonella spp. detected on Rambach agar? SUM Yes No Pure culture of Salmonella Salmonella- and non-Salmonella Growth of non-Salmonella Sterile Yes 8 90 10 8 116 No 40 8 3 222 273 SUM 48 98 13 230 389 Laboratory tests:correlations between results for Salmonella and E. coli
Laboratory tests:conclusions • Humidity, both before and during heating, was an important factor in the bacterial killing. • In general, there was a higher survival in feed than in faeces. • There were high correlations between the survival of spiked Salmonella and naturally occurring E. coli. • No bacteria were detected at 60 oC and 100% RH after 24 hours of heating (i.e. ”gold” standard for field studies), including in replicate tests.
Field tests • Aim: To test if the gold standard (60 oC & 100% RH during 24 hours) was valid in the field. • Principles: • Salmonella samples before and after heating. • Salmonella results per se. • Non-sterile Rambach agar plates (i.e. coliforms as possible indicator bacteria). • Challenge samples, placed at sites where temperature was measured.
Field tests:correlations between Salmonella and coliforms on house level
Field tests:correlations between Salmonella and coliforms on site level
Field tests:”traditional” Danish heating procedure • Practised for years in Danish poultry houses. • Principle: a short steam and formaldehyde heating until the temperature reaches ca. 60 oC, after which the heating ceases. • The house remains sealed for ca. 24 hours.
Field tests:”traditional” Danish heating: a typical temperature curve
Field tests:”traditional” heating: challenge samples and peak temperatures
Field tests:Conclusions • In tight houses, 60 oC and 100% RH was achieved minimum 10 cm above floor level within one hour and was easily maintained during 24 hours. • 60 oC and 100% RH during 24 hours seemed effective in eliminating Salmonella and putative indicator bacteria. • The addition of 30 ppm formaldehyde at the beginning of the process seemed to lower the lethal temperature by 2-5 oC. • The occurrence of coliforms could be a guidance for the efficacy against Salmonella, although no cut-off values could be predicted. • The ”traditional” Danish steam and formaldehyde procedure is ineffective.
Future perspectives • Certification of heating procedures • Possible model: Danish Technological Institute has certified a heat treatment against Dry Rot in buildings. Companies that can document a time-temperature scheme with validated equipment are approved by this system. It also includes insurance against re-occurrence of Dry Rot. See www.vks-udvalget.dk
Acknowledgments • Kirsten Holm, DVI, Århus, Denmark. • Kirsten Christensen, DVI, Århus, Denmark. • Staff at Landskontoret for Fjerkrærådgivning, Århus, Denmark. • Staff at Danish Meat Research Institute, Roskilde, Denmark. • Participating farmers.
