Reliably colonising broiler chickens with Campylobacter spp. using a litter-based method.

1. Chicken-associated Campylobacter spp. are the cause of most food poisoning cases in Europe. In order to study the host-pathogen interactions, a reliable and reproducible method of colonising chickens with the bacteria is required. 2. This study aimed to identify a more appropriate and less invasive method of colonisation (cf. gavaging) by seeding bedding material (litter) that commercial chickens are kept on with a mixture of Campylobacter spp., broth and faeces. 3. The first phase of the study tested the longevity of Campylobacter spp. recovery in seeded litter over 24 h: significantly more Campylobacter spp. was recovered at 0 or 3 h post-seeding than at 6 and 24 h post-seeding, indicating that the pathogen can survive to detectable levels for at least 3 h in this environment. 4. In the second phase, three groups of 10 broiler chickens (negative for Campylobacter spp. prior to exposure) were exposed at 21 days of age to one of three different Campylobacter jejuni and C. coli mixes (A, B, C), using the method above. At 28 days of age, birds were euthanised by overdose of barbiturate or cervical dislocation, and livers and caeca removed for Campylobacter spp. assessment. 5. All liver and 28/30 caeca samples tested positive for Campylobacter spp., with mix A and C giving higher counts in the caeca than mix B. The method of euthanasia did not affect Campylobacter spp. counts. 6. In conclusion, a successful method for reliably colonising broiler chickens with Campylobacter spp. has been developed which negates the need for gavaging and is more representative of how contamination occurs in the field.

Infection of chickens with antimicrobial-resistant Salmonella enterica Typhimurium DT193 and monophasic Salmonella Typhimurium-like variants: an emerging risk to the poultry industry?

Antimicrobial-resistant Salmonella enterica poses a particular risk to public health, and in particular isolates belonging to clonal lineages such as Salmonella Typhimurium DT104 cause epidemics across species including poultry. In recent years, antimicrobial-resistant S. Typhimurium DT193 and specifically the monophasic S. Typhimurium-like variants of this phage type, serotypes 4,12:i:- and 4,5,12:i:-, have become an increasing risk to public health in Europe and the USA and now account for nearly one-half of human S. Typhimurium infections in the UK. Unlike S. Typhimurium that possesses two forms of flagella which can vary between phase 1 and phase 2 during infection, monophasic variants possess only phase 1 flagella. These monophasic antimicrobial-resistant variants have become a major problem in pig production but human cases have also been associated with poultry consumption and have been found in UK flocks through surveillance schemes since 2010. In this study we determined the ability of antimicrobial-resistant DT193 serotype 4,12:i:- and 4,5,12:i:- isolates from pigs to infect chickens. All isolates were found to colonize the caeca and liver. All but one isolate of serotype 4,5,12:i:- also infected the spleen. Levels of infection and pathology were comparable with those found with the virulent S. Typhimurium isolate 4/74. These findings indicate that both S. Typhimurium DT193 and monophasic variants of this phage type usually associated with pigs are capable of colonizing the chicken. This shows that both S. Typhimurium DT193 and monophasic variants represent a significant and potential emerging threat to poultry production from "spill-over" of these isolates from the pig industry or other sources.

Campylobacter infection has different outcomes in fast- and slow-growing broiler chickens.

Campylobacter spp. are frequently carried by poultry, but they are not believed to cause significant disease in these animals. Modern poultry breeds have been selected to grow rapidly under intensive conditions, but recently, consumers have moved toward purchasing birds produced in higher welfare, free-range or organic systems. Birds reared in these systems tend to be a slower growing breed and are fed a different diet. Birds reared in such systems are stocked at a lower density compared with the standard conventional broilers, and they have access to environmental enrichment, such as perches. In previous research, these slower growing birds have been shown to have different levels of Campylobacter carriage in commercial rearing conditions, but the reasons for, and effect of, these different levels are unknown; is it the bird breed, diet, or environmental conditions? In this study, experimental flocks of fast- and slow-growing breeds of broiler chickens were reared to a standard commercial slaughter weight, with their weight gain being measured during the growing period. At 21 days, birds were either infected with Campylobacter jejuni or given a placebo as control. Cohorts of birds were euthanatized at various intervals, and samples were taken for examination for Campylobacter. The fast-growing birds gained weight more rapidly than the slow-growing birds. By 2 days postinfection (dpi), C. jejuni was detected in the caeca and by enrichment from the liver and spleen samples from both breeds of birds. Low-level colonization persisted in the spleen and liver samples but was undetectable by 28 dpi. Fast- and slow-growing birds did not show detectably different levels of Campylobacter carriage. Infection with C. jejuni affected the incidence of hock marks and pododermatitis in both breeds of birds, but the differences were greater with the fast-growing breed compared with the uninfected control birds. In addition, the incidence of pododermatitis was significantly higher in Campylobacter-positive fast-growing birds than in their slower-growing counterparts. The results show that infection with Campylobacter can have an indirect welfare effect on birds via increased incidence of hock marks and pododermatitis.

Enrichment culture can bias the isolation of Campylobacter subtypes.

Enrichment culture is often used to isolate Campylobacter. This study compared isolation of Campylobacter spp. from 119 broiler chicken environments from two farms, using Preston and modified Exeter (mExeter) and modified Bolton (mBolton) enrichments. mExeter was significantly more effective in isolating Campylobacter spp. from the environmental samples compared to Preston (P<0.001) and mBolton (P<0.04) broths but there was no significant difference between the latter two methods (P>0.05). Enrichment broth type did not affect isolation from chicken faecal or soil and litter samples. C. jejuni was isolated from significantly more environmental samples using mExeter broth compared to Preston (P<0.01) and mBolton (P<0.003) broths; there was no difference between the latter two methods or between all methods for detection of C. coli (P>0.05). Only C. coli was isolated from the soil and litter samples and although both C. jejuni and C. coli were recovered from the faecal samples there was no effect of using different enrichment broths. The majority of samples where the same species had been isolated yielded the same or closely related genotypes as defined by pulsed-field gel electrophoresis. Isolates recovered using Preston and mBolton broths were less genetically diverse than those from mExeter broth. We conclude that the enrichment method used affects both the number and species of Campylobacter isolated from naturally contaminated samples.

Influence of season and geography on Campylobacter jejuni and C. coli subtypes in housed broiler flocks reared in Great Britain.

Geographical and seasonal variation in the incidence and prevalence of Campylobacter jejuni and C. coli in housed broiler flocks reared in Great Britain in 2004 to 2006 was investigated in this study. Ceca (30) from 797 flocks, not subject to prior partial depopulation and reared on 211 farms, were examined individually for the presence of Campylobacter spp. The best-fitting climatic factors explained approximately 46% of the prevalence of Campylobacter-colonized flocks at slaughter and consisted of a combination of temperature at slaughter, number of sunshine hours in placement month, and millimeters of rainfall in placement month. Positive flocks were more likely to be slaughtered between June and November than during the rest of the year and to be reared in northern Great Britain than in central or southern Great Britain. C. jejuni was identified in approximately 90% of flocks, and C. coli was present in 10% of flocks. The most common clonal complexes identified in 226 isolates typed by multilocus sequence typing (MLST) were ST-45, ST-21, ST-574, ST-443, and ST-828. Flocks slaughtered at the same time were more likely to have similar complexes, and ST-45 had a seasonal pattern, with the highest prevalence in June, and was also more likely to be present in flocks reared in northern Great Britain.

SulA-induced filamentation in Salmonella enterica serovar Typhimurium: effects on SPI-1 expression and epithelial infection.

AIMS: Salmonella enterica serovar Typhimurium is capable of adopting a filamentous phenotype in response to damage. How this adaptive response affects bacterial virulence is unclear. We have examined the hypothesis that filamentation affects the ability of Salmonella to infect host cells. METHODS AND RESULTS: Expression of the cell division inhibitor SulA in Salm. Typhimurium SL1344 from an arabinose-inducible plasmid resulted in filamentation. We examined expression of the type 3 secretion system (T3SS) encoded by Salmonella pathogenicity island 1 (SPI-1) using SL1344 expressing a chromosomal PprgH-gfp reporter. Single cell analysis of SulA-induced SL1344 PprgH-gfp revealed a relationship between increasing cell length and decreasing propensity for prgH expression, but there was no evidence of a significant change in prgH expression evident at the whole population level. Filamentous Salm. Typhimurium were capable of initiating membrane ruffling on MDCK epithelial cells, but only nonfilamentous bacteria (< 6 µm) invade. CONCLUSIONS: Induction of SulA expression in Salmonella inhibits septation. Increasing filament length is associated with down-regulation of SPI-1 gene expression, but a significant proportion of filaments retain the ability to produce SPI-1 T3SS and induce membrane ruffles on epithelia. Despite an active SPI-1 T3SS, filamentous Salmonella are unable to invade epithelial cells. SIGNIFICANCE AND IMPACT OF THE STUDY: Our findings that filamentous Salmonella can express an invasive phenotype but fail to invade cells suggest that their presence in food does not constitute an immediate risk of infection until septation occurs. The described SulA expression model provides a convenient model for studying the impact of filamentation in the absence of additional stresses.

Sub-clinical infection with Salmonella in chickens differentially affects behaviour and welfare in three inbred strains.

1. Much evidence exists detailing how animals respond to pathogen challenge, yet information explaining how the various behavioural, immunological, and physiological systems in chickens interplay during such challenges remains limited. 2. To gain an understanding of this interplay while controlling for genetic variation, the current study collected a variety of behavioural, physiological and immunological measures from three inbred lines (P, O and N) of laying hens before and after a sub-clinical infection with Salmonella enterica Typhimurium at 56 d of age. For comparison, an equal number of control birds were inoculated with a Salmonella-free broth. To identify an underlying profile, which might result in reduced susceptibility to infection, data were also collected in the pre-infection period. Post-infection blood and faeces were collected at 1-d post infection (dpi) and faeces again at 8 dpi. Animals were killed 15 d after infection and faeces, caecal contents, and spleen were examined for the presence of Salmonella. 3. Statistical analysis was performed to identify pre- and post-infection differences between genetic lines, changes in bird behavioural patterns between the two periods, and associations between a positive test for Salmonella and the various response measures. 4. Tissues from Line P birds were more often negative for Salmonella than those from birds of other lines, though this was inconsistent and tissue-dependent. The P line was also characterised by relatively greater serum concentrations of immunoglobulins at 1 dpi and α(1)-acid glycoprotein at 15 dpi. In addition, P line birds were more timid and their growth was reduced during the pre-infection period suggesting the possibility of a profile with reduced susceptibility to the bacterial challenge. 5. The current work has identified correlations between attributes of chicken strains and improved clearance. Future work using hypothesis-based testing will be required to determine whether the identified correlations are causally related.

Persistence of Campylobacter species, strain types, antibiotic resistance and mechanisms of tetracycline resistance in poultry flocks treated with chlortetracycline.

OBJECTIVES: The aim of this study was to investigate the persistence of Campylobacter species, strain types, antibiotic resistance and mechanisms of tetracycline resistance in poultry flocks treated with chlortetracycline. METHODS: Three commercially reared broiler flocks, naturally colonized with Campylobacter, were treated with chlortetracycline under experimental conditions. The numbers of Campylobacter isolated, and the species, flaA short variable region allele, and antimicrobial resistance of isolates were determined. RESULTS: For two of three flocks, tetracycline-resistant strains predominated prior to chlortetracycline exposure. Presence of the antibiotic had no discernible effect on the numbers or types of Campylobacter and the tetracycline-resistant strains persisted in numbers similar to those observed before treatment. With all flocks, some faecal samples were obtained that contained no Campylobacter, irrespective of exposure to chlortetracycline; this was more common as the birds grew older. For the third flock, tetracycline-resistant Campylobacter were in the minority of samples before and during exposure to chlortetracycline, but at sampling times after this, no resistant strains were found in the treated (or untreated) birds, irrespective of exposure to the antibiotic. All tetracycline-resistant isolates (MICs 16 to >128 mg/L) contained tet(O) and, for some isolates, this was transferable to Campylobacter jejuni 81116. The efflux pump inhibitor PAbetaN reduced the MICs of tetracycline for these isolates by 4-fold, suggesting that an intact efflux pump, presumably CmeABC, is required for high-level tetracycline resistance. CONCLUSIONS: Our data indicate that chlortetracycline treatment does not eradicate tetracycline-resistant Campylobacter spp. from poultry. However, if a low number of resistant isolates are present, then the antibiotic pressure appears insufficient to select such strains as the dominant population.

Effects of repeated cycles of acid challenge and growth on the phenotype and virulence of Salmonella enterica.

AIMS: The aim of the study was to investigate how stresses like low pH, which may be encountered in farms or food preparation premises, shape populations of Salmonella enterica by the selection of stress-resistant variants. METHODS AND RESULTS: Stationary-phase cultures of S. enterica serovar Enteritidis and serovar Typhimurium (one strain of each) were exposed to pH 2.5 for up to 4 h, followed by growth at pH 7 for 48 h. This process was repeated 15 times in two separate experiments, which increased the acid resistance of the three out of four populations we obtained, by three- to fourfold. Sustainable variants derived from the populations showed changes in colony morphology, expression of SEF17 fimbriae, growth, increased heat resistance and reduced virulence. CONCLUSIONS: The study demonstrates that low pH environments can select for populations of S. enterica with persistent phenotypic changes such as increased acid resistance and occasionally increased SEF17 expression and lower virulence. SIGNIFICANCE AND IMPACT OF THE STUDY: There is a common belief that increased acid resistance coincides with increased virulence. This study demonstrates for the first time that increased acid resistance often impairs virulence and affects the general phenotype of S. enterica.

Campylobacter spp. contamination of chicken carcasses during processing in relation to flock colonisation.

The presence and numbers of campylobacters on chicken carcasses from 26 slaughter groups, originating from 22 single-house flocks and processed in four UK plants, were studied in relation to the level of flock colonisation determined by examining the caecal contents of at least ten birds per group. The prevalence of campylobacters on carcasses from five campylobacter-negative flocks processed just after other negative flocks was low (8.0 log(10) cfu) than carcasses originating from low prevalence flocks (average of 2.3 log(10) cfu; range: <1.1 to 4.1 log(10) cfu). There was a reduction in the numbers of campylobacters on carcasses between plucking and chilling in eight of ten fully colonised flocks. In another eight flocks, a significant (P<0.001) decrease (0.8 log(10) cfu) in the number of campylobacters on carcasses from just before to after chilling was detected. Campylobacter spp. could be isolated from aerosols, particles and droplets in considerable numbers in the hanging-on, defeathering and evisceration areas but not in the chillers. This was the case even when campylobacters were not isolated from the target flock. Campylobacters on carcasses from two partly colonised flocks were either the same subtype, as determined by speciation, Multi-Locus Sequence Typing (MLST) and flaA Restricted Fragment Length Polymorphism (RFLP) typing, as those in the fully colonised flocks processed previously, although not necessarily the most prevalent ones; or were the same subtypes as those found in the caeca of the flock itself. The prevalences of the different campylobacter subtypes found on carcasses from two fully colonised flocks did not closely reflect those found in the caeca. MLST combined with flaA RFLP provided a good method for ascertaining the relatedness of strains isolated from carcasses and caecal contents. This study showed that carcass contamination is related to the within-flock prevalence of campylobacter colonisation, but that contamination from previously processed flocks was also significant, especially on carcasses from low prevalence flocks. Forced dry air cooling of carcasses reduced contamination levels.

Inter-relationships between sodium and potassium intake and the blood pressure effects of ACTH in sheep.

These studies examine the effect of sodium (Na) and potassium (K) intake on the pressor and metabolic actions of ACTH (20 micrograms/kg/day) in sheep. After 21 days on each of five regimens in which Na and K intake varied from 0 to 100 mmol/day, no simple relationship between Na and K intake and blood pressure was found. After five days of ACTH treatment, mean arterial pressure (MAP) rose + 5 mmHg in sheep on 0 mmol Na, 0 mmol K (expressed as 0 Na 0 K); + 13 mmHg on 10 Na 100 K; + 5 mmHg on 0 Na 100 K; + 20 mmHg on 100 Na 0 K and + 24 mmHg on 100 Na 100 K. Plasma [K] was unchanged by ACTH on 0 Na 0 K but fell in sheep on the other electrolyte regimens. Water intake increased with ACTH on all regimens except 100 Na 0 K. Blood aldosterone concentration was high in sheep maintained on 0 Na regimens but lower after five days of ACTH treatment in all groups. Blood cortisol and corticosterone concentrations increased with ACTH on all regimens studied.

Survival of Escherichia coli O157 in a soil protozoan: implications for disease.

Intra-protozoal growth of bacterial pathogens has been associated with increased environmental survival, virulence and resistance to biocides and antibiotics. Using laboratory microcosms we have shown that Escherichia coli O157 survives and replicates in a common environmental protozoan, Acanthamoeba polyphaga. As protozoa are widely distributed in soils and effluents, they may constitute an important environmental reservoir for transmission of E. coli O157 and other pathogens.

Aerosol route enhances the contamination of intact eggs and muscle of experimentally infected laying hens by Salmonella typhimurium DT104.

Commercial laying hens were infected with Salmonella typhimurium DT104 strain 16 alternatively via the crop (10(7) cfu per bird) or by an aerosol delivered directly to the beaks using a Collison nebuliser and Henderson apparatus (2 x 10(2) or 2 x 10(4) cfu per bird). Infection by both routes caused systemic infection and prolonged contamination of faeces. Contamination rates of eggs and muscle were much higher following the aerosol challenges despite the much lower doses given by this route. The frequency of Salmonella isolation from eggs rose from 1.7% following oral challenge to 14% and 25%, for each of the aerosol challenges respectively, and the frequency of isolation from muscle rose from 0% following the oral challenge to 27% following each of the aerosol challenges.

Microbial contamination of hospital showers and shower water: the effect of an automatic drain valve.

The installation of a valve to drain away water on the completion of showering was found to have no significant effect on the numbers of microorganisms in shower water and on the internal surfaces of shower fittings.

Contamination of egg shell and contents with Salmonella enteritidis: a review.

Salmonella enteritidis can contaminate the contents of clean, intact shell eggs as a result of infections of the reproductive tissue of laying hens. The principal site of infection would appear to be the upper oviduct. In egg contents the most important sites of contamination are either the outside of the vitelline membrane or the albumen surrounding it. In fresh eggs, only few salmonellas are present and as albumen is an iron-restricted environment, growth will only occur once storage-related changes to vitelline membrane permeability, which allow salmonellas to invade yolk contents, have taken place. When this happens high populations are achieved in both yolk contents and albumen. Some eggs from naturally infected hens have been found to contain large numbers of S. enteritidis. The rate of change in membrane permeability is temperature-dependent. In eggs stored at 20 degrees C, yolk invasion is uncommon until eggs have been stored for 3 weeks. In stimulated kitchen conditions where temperatures reached 30 degrees C, salmonellas could grow rapidly after a few days.

Growth of Salmonella enteritidis in artificially contaminated eggs: the effects of inoculum size and suspending media.

Growth profiles of two isolates of Salmonella enteritidis phage type (PT) 4 inoculated into either the albumen of whole shell eggs or into separated albumen were found to be markedly affected by the size of the inoculum and the composition of the medium used to suspend the cells prior to inoculation. Using our model with an inoculum of two cells, multiplication of the Salmonella was not seen in 93% of eggs held at 20 degrees C for 8 days. In approximately 7% of eggs, however, growth occurred during the 8 days of storage. If the inoculum equaled or exceeded 25 cells per egg when eggs were subsequently stored at 20 degrees C, or 250 cells per egg when eggs were stored at 30 degrees C, high levels of growth of Salmonella in the egg occurred significantly more frequently than when the inoculum was two cells. High levels of growth were also seen more frequently if the inoculum was suspended in buffered peptone water or maximal recovery diluent rather than in phosphate buffered saline. Growth of Salmonella in separated albumen occurred very infrequently (1.1% of samples) at low inoculum levels and did not become significant until the inoculum was 250 cells or greater. Growth in the albumen was unaffected by the composition of the suspending medium. Provided that the inoculum was approximately 2 cells per egg and the bacteria were suspended in PBS, observed growth profiles of S. enteritidis inoculated into the albumen of whole eggs resembled those in naturally contaminated eggs.

Prevalence and numbers of Salmonella and Campylobacter spp. on raw, whole chickens in relation to sampling methods.

Salmonella and Campylobacter continue to be major foodborne pathogens and raw poultry is considered to be an important source of these bacteria. In this study, the prevalence and numbers of Salmonella and Campylobacter spp. in relation to isolation/sampling methods were determined in 241 whole raw chickens purchased from retail outlets in England during the winters of 1998/1999 (101 chickens) and 1999/2000 (140 chickens). The packaging of the 140 chickens was also examined for the presence of the above pathogens. The prevalence and numbers of enterococci were examined in 21 of the 101 chickens. In total, Salmonella and Campylobacter spp. were present in 25% and 83% of the chickens, respectively. Salmonella were isolated from a sample representing both the inside and outside of the packaging in 19% of the chickens, while the corresponding figure for Campylobacter spp. was 56%. Both of these pathogens were isolated from the outside of the packaging in 6% of the chickens. Salmonella was more frequently isolated from samples containing chicken skin in comparison with those containing carcass-rinse fluid only. Two chickens (0.8%) were positive for Salmonella by direct enumeration methods with contamination levels of log10 3.8 and 4.5 colony forming units (cfu) per carcass, respectively. The most prevalent serotypes were S. Hadar, S. Enteritidis and S. Indiana and two different serotypes were identified in 5/20 salmonella-positive chickens. Resistance to at least one antibiotic was found in 70% of the strains, 46% were multiresistant (resistant to > or = four drugs) and 52% showed a lowered susceptibility to ciprofloxacin. The likelihood of isolating Campylobacter spp. from neck-skin, carcass-rinse or carcass-rinse plus whole skin samples was similar, Campylobacter spp. were found in higher levels in carcass-rinse or carcass-rinse plus whole skin samples than in neck-skin. The log10 cfu of Campylobacter spp. were 2.70-4.99 in 18% of the chickens and 5.00-6.99 in 20%. Campylobacter isolates (425) comprised Campylobacter jejuni (98%) and C. coli (2%) and 98 different sero/phagetypes of these two species were identified. Resistance to at least one antibiotic was found in 73% of the strains and 13% were multiresistant. Thirteen percent of the strains showed lowered susceptibility to ciprofloxacin, while 4.9% were resistant to erythromycin. Vancomycin-resistant enterococci (VRE), able to grow on agar containing 15 mg l(-1) vancomycin (VRE15), were present in 19 chickens. The log10 cfu of VRE15 was 2.90-3.99 in 10 chickens and between 4.00 and 4.99 in two chickens. The data presented here contribute to risk assessment and highlight the need to continue to emphasise the safe handling of raw retail poultry.

Calculating Salmonella inactivation in nonisothermal heat treatments from isothermal nonlinear survival curves.

Salmonella cells in two sugar-rich media were heat treated at various constant temperatures in the range of 55 to 80 degrees C and their survival ratios determined at various time intervals. The resulting nonlinear semilogarithmic survival curves are described by the model log10S(t) = -b(T)tn(T), where S(t) is the momentary survival ratio N(t)/N0, and b(T) and n(T) are coefficients whose temperature dependence is described by two empirical mathematical models. When the temperature profile, T(t), of a nonisothermal heat treatment can also be expressed algebraically, b(T) and n(T) can be transformed into a function of time, i.e., b[T(t)] and n[T(t)]. If the momentary inactivation rate primarily depends on the momentary temperature and survival ratio, then the survival curve under nonisothermal conditions can be constructed by solving a differential equation, previously suggested by Peleg and Penchina, whose coefficients are expressions that contain the corresponding b[T(t)] and n[T(t)] terms. The applicability of the model and its underlying assumptions was tested with a series of eight experiments in which the Salmonella cells, in the same media, were heated at various rates to selected temperatures in the range of 65 to 80 degres C and then cooled. In all the experiments, there was an agreement between the predicted and observed survival curves. This suggests that, at least in the case of Salmonella in the tested media, survival during nonisothermal inactivation can be estimated without assuming any mortality kinetics.

Improving recovery of Salmonella enterica serovar typhimurium DT104 cells injured by heating at different water activity values.

This study describes the evaluation of potentially more sensitive methods for the recovery of Salmonella cells injured by heating (54 to 60 degrees C) at different water activity values (0.65 to 0.90, reduced using equal portions of glucose and fructose). These methods included gradual rehydration, the use of diluting media with added solutes or blood, the addition of blood to plating agar, and the use of different incubation temperatures and times. Gradual rehydration of cells that had been challenged at low water activity (0.65 and 0.70) and high temperature markedly improved recovery, measured as a >50% increase in the time to obtain a 3-log10 reduction in cell numbers, compared to dilution into media with a high water activity. Adding sucrose, glycerol, or blood to the diluting media (maximal recovery diluent) did not improve recovery, but a plating agar containing blood recovered approximately 38% more cells than nutrient agar. Prolonged incubation of agar plates allowed recovery of injured Salmonella cells that presumably had extended lag periods, with significantly higher recovery rates after 48 h incubation at 37 degrees C than after 24 h (P = 0.05). This work highlights that by recovering Salmonella using a method specific to the nature of the injury, a better prediction of food safety and the success of food processing can be made.

An assessment of the microbiological risks involved with egg washing under commercial conditions.

The potential benefits of washing eggs is offset by a historical perception in the European Union that wetted eggs are prone to spoilage and water loss. This study describes the effects of spray jet washing under various processing conditions to shell surface counts of Salmonella and the presence of bacteria in egg contents. Experiments used eggs that were contaminated with Salmonella Enteritidis PT4 or Salmonella Typhimurium DT104 before cuticle hardening. Washing of contaminated eggs under optimum conditions resulted in a more than 5-log reduction of Salmonella counts from the shell surface. Salmonella was not isolated from the yolk or albumen of any egg washed by the optimal protocol, suggesting that when properly controlled, egg washing did not cause Salmonella to enter the contents. However, contamination did arise if strict control was not maintained over the wash and rinse water temperatures. Both Salmonella Enteritidis and Salmonella Typhimurium were shown to enter the egg contents when water temperatures were lowered, indicating that strict temperature control must be maintained in order to prevent the ingress of Salmonella into egg contents. Other washing machine parameters that were investigated did not significantly affect Salmonella entry into the egg contents but influenced shell surface kill levels to varying degrees.