Efficacy of a Salmonella Siderophore Receptor Protein Vaccine on Fecal Shedding and Lymph Node Carriage of Salmonella in Commercial Feedlot Cattle.

The efficacy of a Salmonella vaccine for reducing fecal shedding of Salmonella during the finishing period and lymph node (LN) carriage at harvest was investigated in commercial feedlot cattle. The study was designed as a pen-level randomized complete block with two treatment groups, a Salmonella Newport siderophore receptor and porin proteins-based vaccine (VAC) and a nonvaccinated control (CON). Cattle were randomly allocated into 24 pens within 12 blocks based on the time of allocation. Twenty to 25 fecal pats were collected from each of the study pen floors once a month from June to August 2013. During harvest, a minimum of 25 sub-iliac LN were collected from carcasses within each study pen. Fecal and pulverized LN samples were cultured for Salmonella quantification and detection. Mixed models were used to analyze the effect of vaccination on fecal shedding and LN carriage of Salmonella. Montevideo and Anatum were the predominant Salmonella serotypes among fecal samples and LNs; no Newport isolates were recovered. Vaccination was not significantly associated (p = 0.57) with the prevalence of Salmonella in feces over time; the mean within-pen prevalence was 62.3% and 66.0% among VAC and CON, respectively. Sampling month was significantly associated (p < 0.01) with fecal prevalence; mean prevalence was 71.4% for June, 48.6% for July, and 70.8% for August. Across all pens, the cumulative prevalence of Salmonella in LN was 86.4%. Vaccination resulted in no significant reduction in LN prevalence (p = 0.52); mean prevalence was 85.7% for VAC and 87.4% for CON groups. Although vaccinated cattle had numerically fewer Salmonella LN and fecal positives, there were no statistically significant vaccine effects. Potential reasons for the lack of vaccine efficacy could include an overwhelming Salmonella exposure, a lack of cross-protection against non-Newport serotypes, and insufficient duration of immunity relative to harvest.

Salmonella Prevalence and Antimicrobial Susceptibility Among Dairy Farm Environmental Samples Collected in Texas.

Dairy cattle are a reservoir of several Salmonella serovars that are leading causes of human salmonellosis. The objectives of this study were to estimate the environmental prevalence of Salmonella on dairy farms in Texas and to characterize the antimicrobial susceptibility of the isolates. Eleven dairy farms throughout Texas were sampled from August through October 2013, using a cross-sectional approach. Samples were collected from four locations within each farm (hospital pen, maternity pen, cow housing area, and calf housing area), and feces were collected from cull cows as available. Environmental and fecal samples were processed for Salmonella, and isolates were tested for susceptibility to 15 antimicrobial agents. Serovar characterization was performed on a subset of these isolates. Salmonella was isolated from 67.0% (236/352) of the environmental samples and 64.2% (43/67) of the cull cow fecal samples. Environmental samples from the maternity pen were significantly more likely to be Salmonella positive than samples from the cow and calf housing areas. Multidrug resistance was evident in 11.9% (27/226) of environmental isolates and 19.5% (8/41) of fecal isolates. Salmonella isolates from the calf housing area and maternity pen were significantly more likely to be multidrug resistant (MDR) than isolates from the cow housing area. The most common serovars found among the MDR isolates were Newport, Muenchen, and Typhimurium. These results help provide a focus for efforts to mitigate the burden of antimicrobial-resistant Salmonella at the preharvest level.

Survival and fate of Salmonella enterica serovar Montevideo in adult horn flies (Diptera: Muscidae).

Contamination of cattle peripheral lymph nodes with Salmonella enterica is proposed to occur via a transdermal route of entry. If so, bacteria may be introduced to cattle by biting arthropods. Biting flies, such as horn flies (Haematobia irritans irritans (L.)) (Diptera: Muscidae), are intriguing candidates for transmitting Salmonella to cattle because they provide a route of entry when they breach the skin barrier during blood feeding. Using a green fluorescent protein-expressing strain of Salmonella Montevideo (S. Montevideo-GFP), the current study demonstrated that horn fly grooming subsequent to tactile exposure to the bacteria resulted in acquisition of the bacteria on mouthparts as well as microbial ingestion. Consumption of a bloodmeal containing approximately 10(2), approximately 10(4), or 10(6) S. Montevideo-GFP resulted in horn fly colonization for up to 72 h postingestion (PI). Epifluorescent microscopy indicated that the bacteria were not localized to the crop but were observed within the endoperitrophic space, suggesting that regurgitation is not a primary route of transmission. S. Montevideo-GFP were cultured from excreta of 100% of flies beginning 6-7 h PI of a medium or high dose meal and > 12 h PI in excreta from 60% of flies fed the low-dose meal. Animal hides and manure pats are sources for horn flies to acquire the Salmonella and mechanically transmit them to an animal while feeding. Mean quantities of 5.65-67.5 x 10(2) CFU per fly were cultured from fly excreta passed within 1 d after feeding, suggesting the excreta can provide an additional microbial source on the animal's hide.

Chemical sensing in mammalian host-bacterial commensal associations.

The mammalian gastrointestinal (GI) tract is colonized by a complex consortium of bacterial species. Bacteria engage in chemical signaling to coordinate population-wide behavior. However, it is unclear if chemical sensing plays a role in establishing mammalian host-bacterial commensal relationships. Enterohemorrhagic Escherichia coli (EHEC) is a deadly human pathogen but is a member of the GI flora in cattle, its main reservoir. EHEC harbors SdiA, a regulator that senses acyl-homoserine lactones (AHLs) produced by other bacteria. Here, we show that SdiA is necessary for EHEC colonization of cattle and that AHLs are prominent within the bovine rumen but absent in other areas of the GI tract. We also assessed the rumen metagenome of heifers, and we show that it is dominated by Clostridia and/or Bacilli but also harbors Bacteroidetes. Of note, some members of the Bacteroidetes phyla have been previously reported to produce AHLs. SdiA-AHL chemical signaling aids EHEC in gauging these GI environments, and promotes adaptation to a commensal lifestyle. We show that chemical sensing in the mammalian GI tract determines the niche specificity for colonization by a commensal bacterium of its natural animal reservoir. Chemical sensing may be a general mechanism used by commensal bacteria to sense and adapt to their mammalian hosts. Additionally, because EHEC is largely prevalent in cattle herds, interference with SdiA-mediated cattle colonization is an exciting alternative to diminish contamination of meat products and cross-contamination of produce crops because of cattle shedding of this human pathogen.

Cross-sectional study examining Salmonella enterica carriage in subiliac lymph nodes of cull and feedlot cattle at harvest.

Bovine peripheral lymph nodes (LNs), including subiliac LNs, have been identified as a potential source of human exposure to Salmonella enterica, when adipose trim containing these nodes is incorporated into ground beef. In order to gain a better understanding of the burden of S. enterica in peripheral LNs of feedlot and cull cattle, a cross-sectional study was undertaken in which 3327 subiliac LNs were collected from cattle at harvest in seven plants, located in three geographically distinct regions of the United States. Samples were collected in three seasons: Fall 2010, Winter/Spring 2011, and Summer/Fall 2011. A convenience sample of 76 LNs per day, 2 days per season (approximately 1 month apart), was collected per plant, from carcasses held in the cooler for no less than 24 h. Every 10(th) carcass half on a rail was sampled, in an attempt to avoid oversampling any single cohort of cattle. Median point estimates of S. enterica contamination were generally low (1.3%); however, median Salmonella prevalence was found to be greater in subiliac LNs of feedlot cattle (11.8%) compared to those of cull cattle (0.65%). Enumeration analysis of a subset of 618 feedlot cattle LNs showed that 67% of those harboring S. enterica (97 of 144) did so at concentrations ranging from <0.1 to 1.8 log10 CFU/g, while 33% carried a higher burden of S. enterica, with levels ranging from 1.9 to >3.8 log10 CFU/g. Serotyping of S. enterica isolated identified 24 serotypes, with the majority being Montevideo (44.0%) and Anatum (24.8%). Antimicrobial susceptibility phenotypes were determined for all isolates, and the majority (86.1%) were pansusceptible; however, multidrug-resistant isolates (8.3%) were also occasionally observed. As Salmonella contained within LNs are protected from carcass interventions, research is needed to define opportunities for mitigating the risk of Salmonella contamination in LNs of apparently healthy cattle.

Salmonella diversity and burden in cows on and culled from dairy farms in the Texas High Plains.

The objective of this study was to characterize the epidemiology of Salmonella carried by dairy cows culled from herds in the Texas High Plains. Feces were collected from a convenience sample of 706 animals culled from nine dairy farms. In addition, individually paired fecal and hide samples were collected from 70 healthy milking cows on three of the dairies. Samples were cultured for Salmonella using routine methods; isolates were serotyped and subjected to a panel of antimicrobial drugs to determine susceptibility. Salmonella was recovered from 32.6% of culled cows. Whole-herd use of a vaccine containing siderophore receptors and porin proteins was associated (p=0.05) with reduced Salmonella prevalence in that the prevalence among herds that practiced whole-herd vaccination was 8.0% compared to 36.8% among herds that did not use this vaccine. The majority (88.6%) of isolates were pansusceptible or resistant to one drug. Of the 3.1% of isolates resistant to more than four drugs, all were Salmonella Newport and were recovered from one dairy. Various serotypes were recovered from individual fecal and hide samples. Salmonella Montevideo was recovered more frequently (p<0.01) from hide samples, whereas Salmonella Cerro was recovered more frequently (p<0.01) from feces. Salmonella was recovered from at least one cow on all dairies. While our study was not a priori designed to address herd-level factors, we found evidence that the whole-herd use of a siderophore receptor and porin protein-containing vaccine might be a useful aid in the control of Salmonella in groups of cattle. As this is a nonrandomized evaluation of an intervention, other herd-level factors that may be correlated with vaccine use, such as biosecurity, might have been responsible for the observed association.

Kinome Analysis of Cattle Peripheral Lymph Nodes to Elucidate Differential Response to Salmonella spp.

Salmonella spp., contained within the peripheral lymph nodes (PLNs) of cattle, represents a significant source of contamination of ground beef. Herein is the first report where species-specific kinome peptide arrays designed for bovine biology were used to further the understanding of Salmonella spp. within these PLNs. For the purpose of this research, multiple comparisons of sub-iliac lymph nodes were made to include nodes from feedlot cattle that were infected with Salmonella spp. to those that were non-infected; seasonal differences in feedlot cattle harvested in either August or January; cull dairy cows compared to feedlot cattle; and PLNs from cattle experimentally inoculated with Salmonella spp. versus naturally infected animals. The first comparison of Salmonella-positive and -negative PLNs found that considering the kinotypes for these animals, the major distinguishing difference was not the presence or absence of Salmonella spp. in the PLNs but the concentration. Further, the majority of pathways activated were directly related to immune responses including innate immunity, thus Salmonella spp. within the PLNs activates the immune system in that node. Results from the comparison of feedlot cattle and cull dairy cows suggests that a Salmonella spp.-negative animal, regardless of type, has a more consistent kinome profile than that of a Salmonella spp.-positive animal and that the differences between feedlot and cull dairy cattle are only pronounced when the PLNs are Salmonella spp. positive. PLNs collected in the winter showed a much more consistent kinome profile, regardless of Salmonella status, suggesting that in the winter these cattle are similar, and this is not affected by the presence of Salmonella spp., whereas significant variability among kinotypes was observed for PLNs collected in the summer. The most distinct clustering of kinotypes observed in this study was related to how the animal was infected with Salmonella spp. There were significant differences in the phosphorylation state of the immune response peptides between experimentally and naturally infected animals, suggesting that the immune system is activated in a significantly different manner when comparing these routes of infection. Increasing our understanding of Salmonella spp. within cattle, and specifically within the PLNs, will ultimately help design effective pre-harvest intervention strategies as well as appropriate experimentation to validate those technologies.

Evaluation of two commercially-available Salmonella vaccines on Salmonella in the peripheral lymph nodes of experimentally-infected cattle.

BACKGROUND: Salmonella is a common inhabitant of the ruminant gastrointestinal tract, where it often resides asymptomatically and may be shed into the feces. More recently it was discovered that Salmonella may be contained within the peripheral, non-mesenteric lymph nodes, where it is impervious to in-plant pathogen control interventions and may serve as a source of Salmonella-contamination of ground beef. Over the past 10 years considerable research effort has been expended at understanding how this pathogen gets to these lymph nodes, the duration of infection, and, most importantly, screening and developing potential intervention strategies that may be employed on farm prior to the animal being presented for slaughter. METHODS: Utilizing an experimental model of Salmonella inoculation of bovine peripheral lymph nodes (PLNs), two pilot vaccine experiments were conducted to evaluate two Salmonella vaccines: Salmonella Newport Bacterial Extract (Experiment I) and Endovac-Bovi® (Experiment II) on preventing Salmonella acquisition by these nodes. In Experiment I, 4 months following the booster vaccination, 30 steers were inoculated with three Salmonella serotypes intradermally: Newport, Montevideo, and Anatum administered to the right legs, left legs, and to the caudal thorax and abdomen, respectively. Cattle were inoculated every other day over the course of five days (three total inoculation events) and 6 and 12 days following the final Salmonella inoculation, 16 and 14 head in each treatment were euthanized, respectively. In Experiment II, 12 head of Holstein steers were utilized. Seven days following the booster and weekly thereafter for 3 weeks (four total inoculation events), cattle were inoculated as above and euthanized 7 days following final inoculation. Right and left sub-iliac, popliteal and pre-scapular lymph nodes were collected in each experiment, weighed and cultured for Salmonella. RESULTS: In Experiment I, no treatment differences were observed in Salmonella prevalence 6 days post-inoculation (necropsy 1). However, in vaccinated cattle at the second necropsy, a reduction (p = 0.05) in Salmonella prevalence was observed in the sub-iliac and pre-scapular lymph nodes as well as when all nodes were evaluated collectively (p = 0.04). In Experiment II, the vaccine reduced (p = 0.03) Salmonella prevalence in the right popliteal and tended (p = 0.09) to decrease prevalence in both popliteal lymph nodes. CONCLUSION: Under these experimental conditions, the data generated provide evidence of a partial vaccine effect on Salmonella within PLNs and indicate that further research may be warranted.

Effect of nitroethane and nitroethanol on the production of indole and 3-methylindole (skatole) from bacteria in swine feces by gas chromatography.

Indole and 3-methylindole (skatole) are odor pollutants in livestock waste, and skatole is a major component of boar taint. Skatole causes pulmonary edema and emphysema in ruminants and causes damage to lung Clara cells in animals and humans. A gas chromatographic method that originally used a nitrogen-phosphorus detector to increase sensitivity was modified resulting in an improved flame ionization detection response for indole and skatole of 236% and 207%, respectively. The improved method eliminates the large amount of indole decomposition in the injector. A 10 micro g mL(-1) spike of indole and skatole in water and swine fecal slurries resulted in recovery of 78.5% and 96% in water and 76.1% and 85.8% in fecal slurries, respectively. The effect of the addition of nitroethane and nitroethanol at 21.8 mM in swine fecal slurries was studied on the microbial production of indole and skatole. Nitroethane and nitroethanol decreased the production of skatole in swine fecal slurries at 24 h. The nitroethane effect on l-tryptophan-supplemented fecal slurries after 6 and 24 h incubation resulted in a decrease of 69.0% (P = 0.02) and 23.5% skatole production, respectively, and a decrease of 14.9% indole at 6 h, but an increase in indole production of 81.1% at 24 h.

Evaluation of the bacterial diversity in the feces of cattle using 16S rDNA bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP).

BACKGROUND: The microbiota of an animal's intestinal tract plays important roles in the animal's overall health, productivity and well-being. There is still a scarcity of information on the microbial diversity in the gut of livestock species such as cattle. The primary reason for this lack of data relates to the expense of methods needed to generate such data. Here we have utilized a bacterial tag-encoded FLX 16s rDNA amplicon pyrosequencing (bTEFAP) approach that is able to perform diversity analyses of gastrointestinal populations. bTEFAP is relatively inexpensive in terms of both time and labor due to the implementation of a novel tag priming method and an efficient bioinformatics pipeline. We have evaluated the microbiome from the feces of 20 commercial, lactating dairy cows. RESULTS: Ubiquitous bacteria detected from the cattle feces included Clostridium, Bacteroides, Porpyhyromonas, Ruminococcus, Alistipes, Lachnospiraceae, Prevotella, Lachnospira, Enterococcus, Oscillospira, Cytophage, Anaerotruncus, and Acidaminococcus spp. Foodborne pathogenic bacteria were detected in several of the cattle, a total of 4 cows were found to be positive for Salmonella spp (tentative enterica) and 6 cows were positive for Campylobacter spp. (tentative lanienae). CONCLUSION: Using bTEFAP we have examined the microbiota in the feces of cattle. As these methods continue to mature we will better understand the ecology of the major populations of bacteria the lower intestinal tract. This in turn will allow for a better understanding of ways in which the intestinal microbiome contributes to animal health, productivity and wellbeing.

Effects of select nitrocompounds on in vitro ruminal fermentation during conditions of limiting or excess added reductant.

Ruminal methane (CH(4)) production results in the loss of up to 12% of gross energy intake and contributes nearly 20% of the United States' annual emission of this greenhouse gas. We report the effects of select nitrocompounds on ruminal fermentation after 22 h in vitro incubation (39 degrees C) with or without additions of hydrogen (H(2)), formate or both. In incubations containing no added reductant, CH(4) production was inhibited 41% by 2-nitro-1-propanol (2NPOH) and >97% by 3-nitro-1-propionic acid (3NPA), nitroethane (NE) and 2-nitroethanol (2NEOH) compared to non-treated controls and H(2) did not accumulate. With formate as the sole added reductant, nitro-treatment reduced CH(4) production by >99% and caused 42% to complete inhibition of formate catabolism compared to controls, and the accumulation of H(2) increased slightly. Nitro-treatment decreased CH(4) production 57-98% from that of controls when supplied H(2) or formate plus H(2). Formate catabolism was decreased 42-84% from that in controls by all nitro-treatments except 3NPA with both formate and H(2). Greater than 97% of the added H(2) was catabolized within controls; >84% was catabolized in nitro-treated incubations. Acetate, propionate and butyrate accumulations were unaffected by nitro-treatment irregardless of reductant; however, effects on ammonia and branched chain fatty acid accumulations varied. These results suggest that nitro-treatment inhibited formate dehydrogenase/formate hydrogen lyase and hydrogenase activity.

Effects of nitrate or nitro supplementation, with or without added chlorate, on Salmonella enterica serovar Typhimurium and Escherichia coli in swine feces.

The effects of coincubating the active agent of an experimental chlorate product with nitrate or select nitro compounds, possible inducers and competing substrates for the targeted respiratory nitrate reductase, on concentrations of experimentally inoculated Salmonella enterica serovar Typhimurium and indigenous Escherichia coli were determined. Studies were completed in swine fecal suspensions as a prelude to the administration of these inhibitors to pigs. Results confirmed the bactericidal effect of chlorate (5 to 10 mM) against these fecal enterobacteria, reducing (P < 0.05) concentrations by > 2 log CFU ml(-1) after 3 to 6 h of incubation. An effect (P < 0.05) of pH was observed, with considerable regrowth of Salmonella and E. coli occurring after 24 h of incubation in suspensions buffered to pH 7.1 but not in suspensions buffered to pH 6.5 or 5.6. A 24-h coincubation of fecal suspensions with 5 to 10 mM chlorate and as little as 2.5 mM nitrate or 10 to 20 mM 2-nitro-1-propanol, 2-nitroethanol, and, sometimes, nitroethane decreased (P < 0.05) Salmonella but not necessarily E. coli concentrations. 2-Nitro-1-propanol and 2-nitroethanol exhibited inhibitory activity against Salmonella and E. coli by an undetermined mechanism, even in the absence of added chlorate.

Salmonella in Peripheral Lymph Nodes of Healthy Cattle at Slaughter.

To more fully characterize the burden of Salmonella enterica in bovine peripheral lymph nodes (PLN), PLN (n = 5,450) were collected from healthy cattle at slaughter in 12 commercial abattoirs that slaughtered feedlot-fattened (FF) cattle exclusively (n = 7), cattle removed (or culled) from breeding herds (n = 3), or both FF and cull cattle (n = 2). Qualitative and quantitative methods were used to estimate prevalence and concentration of Salmonella in PLN. Isolates were subjected to a variety of phenotypic, serological, and molecular assays. Overall, Salmonella prevalence in PLN from FF and cull cattle was 7.1 and 1.8%. However, burden varied by season in that observed prevalence in PLN collected in cooler or warmer seasons was 2.4 and 8.2%, respectively. Prevalence in PLN from cull cattle in the southwest region of the US was 2.1 and 1.1% for cool and warm seasons, respectively; however, prevalence in FF PLN was far greater in that it was 6.5 and 31.1%, respectively. Salmonella was recovered from 289 (5.6%) PLN and 2.9% (n = 160) of all PLN tested had quantifiable concentrations that varied from 1.6 to 4.9 log10 colony forming units/PLN. The most common serotypes isolated from PLN were Montevideo (26.9%), Lille (14.9%), Cerro (13.0%), Anatum (12.8%), and Dublin (6.9%). In all, 376 unique isolates were collected from the 289 Salmonella-positive PLN. Antimicrobial susceptibility testing revealed the majority (80.6%) of these isolates were pansusceptible; however, 10.7% of isolates were found to be resistant to two or more antimicrobial classes. We were able to document an observed increased in prevalence of Salmonella in PLN during the warmer season, particularly in FF cattle from the southwest region of the US. The mechanisms underlying the observed association between season, region, and production source have yet to be elucidated. Nevertheless, these findings increase our understanding of the sources of contamination of beef products and shed light on transmission dynamics that may be useful in targeting these sources.

Assessing Transmission of Salmonella to Bovine Peripheral Lymph Nodes upon Horn Fly Feeding.

Biting arthropods are implicated in the transdermal transmission of Salmonella to bovine peripheral lymph nodes, and such contamination can contribute to increased Salmonella prevalence in processed beef. Since horn flies can acquire Salmonella and then excrete the bacteria in their feces, on-animal fly infestations were conducted in this study to assess whether horn flies have a role in this bacterial transmission. Three Salmonella serotypes were used to assess fly acquisition from and excretion onto cattle. The results indicated that flies can acquire Salmonella from the hide, as assessed by recovery from homogenates of surfacesterilized flies, and that Salmonella persists for at least 5 days in the fly. Fly fecal excreta serves as a bacterial contaminant on the hide, and the overall mean probable estimate of the quantity shed was ≈10(5) most probable number per fly cage area. In 5 days, no transmission of the bacteria to bovine peripheral lymph nodes was evident, prompting an assessment of the effects of prolonged horn fly feeding on transmission. Three groups of animals were infested with flies that had consumed a blood meal containing Salmonella Senftenberg. After 5 days, the study was either terminated or the flies were removed and the cages replenished with unfed flies either once or twice over the course of an 11- or 19-day fly exposure period, respectively. A microlancet-inoculated positive-control animal was included in each group for comparison. The impact of prolonged horn fly feeding was evident, as 8% of lymph nodes cultured were positive from the 5-day exposure, whereas 50 and 42% were positive from 11- and 19-day exposures, respectively. Higher concentrations of Salmonella were recovered from fly-infested animals than from the microlancet-inoculated control, likely a result of repeated inoculations over time by flies versus a single introduction. The data described provide new insights into the transmission dynamics of Salmonella in cattle populations, highlighting a role for biting flies as an important reservoir.

Two Draft Genome Sequences of a New Serovar of Salmonella enterica, Serovar Lubbock.

Salmonella enterica is principally a foodborne pathogen that shows considerable serovar diversity. In this report, we present two draft genome sequences of Salmonella enterica subsp. enterica serovar Lubbock, a novel serovar.

Determination of MICs of streptomycin for resistant Salmonella isolates in swine and poultry using a micro-broth dilution system.

The MICs of streptomycin for Salmonella isolates from swine and poultry were determined by a micro-broth dilution technique. The Salmonella isolates were recovered from the lymph nodes and cecal contents of market-age swine and from the cecal contents of poultry at the time of slaughter and were found by disk diffusion to be resistant to 10 microg of streptomycin. MIC testing was carried out with the Sensititre susceptibility system for streptomycin, which uses a microwell concentration gradient of 16 to 800 microg/ml. Results indicated that >80% of the swine isolates had MICs of < or = 64 microg/ml, while 51% of poultry isolates exhibited MICs of > or = 128 microg/ml. The highest MICs observed in swine and poultry were 256 and 800 microg/ml, respectively. Replicate tests performed on 12 of the isolates chosen at random indicated a 100% correlation between runs. Advantages of this system include easily read results and precoated wells. Disadvantages include the cost and the inability to test concentrations of streptomycin other than those in the wells. We found this micro-broth dilution commercial test kit to provide a relatively quick and easy testing procedure for the determination of streptomycin resistance in Salmonella.

Salmonella genotype diversity in nonlactating and lactating dairy cows.

Dairy cows may serve as asymptomatic carriers of Salmonella. The potential for herd carrier status increases with herd size, and Salmonella shedding may be triggered by stresses placed on the animals. The scope of the current study is to determine the effects lactation may have on Salmonella genotypic diversity among detected serotypes. Fecal samples were collected on two sampling dates from 60 nonlactating and 60 lactating Holstein cows. No serotype was predominant over the two collection dates, although Salmonella Albany, Salmonella Anatum, Salmonella Newport, and Salmonella Senftenberg were detected in relatively high numbers. Twenty-three genotypes were detected on the first date and 27 on the second date. The greatest genotypic diversity was seen among Salmonella Newport and Salmonella Senftenberg, with five and nine genotypes, respectively. The presence of multiple serotypes and genotypes in the herd suggests multiple contamination sources. However, there was no conclusive effect of lactation status of the cows on Salmonella genotypic shedding.

Experimental use of 2-nitropropanol for reduction of Salmonella Typhimurium in the ceca of broiler chicks.

The effect of 2-nitropropanol (2NPOH) administration on Salmonella enterica serovar Typhimurium in experimentally infected chicks was determined. Chicks orally challenged with 10(6) CFU/ml of a novobiocin- and naladixic acid-resistant Salmonella Typhimurium at 6 days of age were divided into three groups receiving 0 (control), 6.5, and 13 mg 2NPOH per bird (experiment 1) or four groups receiving 0 (control), 13, 65, and 130 mg 2NPOH per bird (experiment 2). Treatments were administered orally 1 day post-Salmonella challenge. Cecal contents collected at necropsy 24 and 48 h after treatment were subjected to bacterial and volatile fatty acid (VFA) analysis. In experiment 1, concentrations (mean+/-SD log CFU per g) of Salmonella were reduced (P < 0.05) in the group administered 13 mg 2NPOH per bird at both the 24- and 48-h samplings compared with the controls (2.58+/-2.10 versus 4.64+/-1.79 and 2.88+/-2.78 versus 5.03+/-2.42 at 24 and 48 h, respectively). In experiment 2, mean+/-SD populations of Salmonella were reduced (P < 0.05) in all groups receiving 2NPOH compared with untreated controls (3.65+/-2.01, 3.39+/-2.42, and 3.47+/-1.55 at 13, 65, and 130 mg, respectively, versus 6.09+/-1.02). Propionate concentrations were reduced (P < 0.05) by the 13-mg 2NPOH per bird treatment. Total VFA concentrations from the group treated with 13 mg 2NPOH per bird were lower (P < 0.05) by 48, but not 24, hours posttreatment than those from the group treated with 6.5 mg 2NPOH per bird. These results demonstrate the inhibitory activity of 2NPOH against Salmonella Typhimurium in vivo.

Reduction of Salmonella Typhimurium in experimentally challenged broilers by nitrate adaptation and chlorate supplementation in drinking water.

The effects of two feed supplements on Salmonella Typhimurium in the ceca of market-age broilers were determined. Broilers orally challenged 6 days before slaughter with a novobiocin- and nalidixic acid-resistant strain of Salmonella Typhimurium were divided into one of four groups (20 birds each). The first group (the control group) received no treatment, the second group received sodium nitrate (SN) treatment (574 mg of NaNO3 per kg of feed), the third group received experimental chlorate product (ECP) treatment (15 mM NaClO3 equivalents), and the fourth group received ECP treatment in combination with SN treatment. The SN treatment was administered via feed for 5 days immediately before slaughter, and ECP was provided via ad libitum access to drinking water for the last 2 days before slaughter. Cecal contents were subjected to bacterial analysis. Significant (P < 0.05) Salmonella Typhimurium reductions (ca. 2 log units) relative to levels for untreated control broilers were observed for broilers receiving ECP in combination with SN. The ECP-only treatment resulted in significant (P < 0.05) reductions (ca. 0.8 log) of Salmonella Typhimurium in trial 2. We hypothesize that increasing Salmonella Typhimurium nitrate reductase activity resulted in increased enzymatic reduction of chlorate to chlorite, with a concomitant decrease in cecal Salmonella Typhimurium levels. On the basis of these results, preadaptation with SN followed by ECP supplementation immediately preharvest could be a potential strategy for the reduction of Salmonella Typhimurium in broilers.

Toxicity of fumonisin from Fusarium verticillioides culture material and moniliformin from Fusarium fujikuroi culture material when fed singly and in combination to growing barrows.

The effects of fumonisin B1 (FB1) from Fasarium verticillioides culture material and moniliformin from Fusarum fujikuroi culture material on growing barrows were evaluated. Four groups of six barrows (three replicates of two each; mean body weight, 11.1 kg) were fed diets containing 0 mg of FB1 and 0 mg of moniliformin per kg of feed (control), 100 mg of FB1 per kg of feed, 100 mg of moniliformin per kg of feed, and 100 mg of FB1 plus 100 mg of moniliformin per kg of feed. Barrows were fed these diets for 28 days. Body weight gain, feed efficiency, serum biochemical analytes, and hematological values were adversely affected by the FB1 and the FB1-plus-moniliformin diets. The moniliformin diet decreased body weight gain. Two barrows in the moniliformin diet group died, and two barrows in the FB1-plus-moniliformin diet group died. All deaths occurred during the first 6 days of the study. Mild to moderate lesions were observed microscopically in heart and lung tissues of the groups fed moniliformin and FB1 plus moniliformin and in liver tissues of the groups fed FB1 and FB1 plus moniliformin. Except for the acute mortality associated with the two diets containing moniliformin. clinical disease induced by the combined feeding of these two mycotoxins appears to be additive or less than additive and due primarily to the toxic expression of FB1.