Tiruvoor G. Nagaraja

Background: Necrotic laryngitis is an important cause of respiratory distress and economic loss in feedlot cattle. Hypothesis/Objectives: Describe the clinical presentation, pathologic lesions, and microbiologic findings associated with necrotic laryngitis in feedlot steers. Animals: Four 20-month-old feedlot steers diagnosed with necrotic laryngitis. Clinically affected steers exhibited inspiratory stridor, increased respiratory effort, and flared nares, indicative of upper airway obstruction. Methods: Samples from inflamed nasopharyngeal tissues were collected endoscopically using guarded cytology swabs and submitted for culture, with concurrent blood collection for CBC and plasma and serum biochemistry analyses. Results: Endoscopic examinations identified laryngeal chondritis, mucopurulent diphtheritic membranes, and necrotic inflammation of the vocal folds. Aerobic cultures were negative, but anaerobic cultures yielded Fusobacterium necrophorum subsp. necrophorum and or F. necrophorum subsp. funduliforme. Hematologic evaluation indicated leukocytosis and increased plasma fibrinogen concentration, whereas serum biochemistry disclosed marked hyperglycemia and mild increases in hepatic enzyme activities, consistent with stress-related metabolic alterations. Antimicrobial susceptibility testing showed that F. necrophorum isolates were susceptible to β-lactams, tetracyclines, florfenicol, tiamulin, and trimethoprim/sulfamethoxazole, and resistant to aminoglycosides, fluoroquinolones, and with respect to macrolides, 4 strains were susceptible and 1 strain was resistant to tylosin, tilmicosin, and tulathromycin. Conclusions and clinical importance: These findings indicate involvement of either F. necrophorum subsp. necrophorum or subsp. funduliforme in necrotic laryngitis of feedlot cattle. Observed antimicrobial susceptibility patterns indicate ongoing susceptibility to β-lactams and tetracyclines, supporting their continued use as first-line therapeutic options.

Our objective was to assess liver abscess (LA) prevalence in beef × dairy heifers subjected to individual intraruminal bacterial inoculations of F. necrophorum subsp. necrophorum, subsp. funduliforme, Trueperella pyogenes, or Salmonella enterica serotype Lubbock to further understand their etiological roles in LA formation. Beef × dairy heifers (n = 40, initial BW = 126 ± 1.1 kg) were assigned randomly to 1 of 4 treatments: FN = F. necrophorum subsp. necrophorum alone; FF = F. necrophorum subsp. funduliforme alone; TP = T. pyogenes alone; or SL = S. enterica serotype Lubbock alone. Heifers received two doses of 100 mL inoculum consisting of ∼1.0 × 109 CFU/g mL each. Heifer was the experimental unit. Feed disappearance and hematology measurements were analyzed as repeated measures. The model included fixed effects of treatment, sampling day, and treatment × sampling day interaction, with heifer nested within treatment as the subject of the repeated measure. Differences in the percentage prevalence of gross pathology scores among treatments were analyzed as binomial proportions with treatment as a fixed effect. Prevalence of LA was 10, 0, 0, and 0% for FN, FF, TP, and SL, respectively, and did not differ among treatments (P = 1.00). No differences among treatments were observed for rumenitis, lungs, colon, or ileal scores (P ≥ 0.38). While no difference among treatments was observed (P = 0.95), an abundance of LA scars across treatments were recorded (38%). While prevalence was lower than expected, FN was the only treatment to present with an active LA at harvest. The abundance of LA scars across treatments warrants further investigation as timeframe for LA formation and resolution are not fully understood.

Liver abscesses (LA) in cattle are commonly categorized as mild or severe, based on the size and number of abscesses, and only the latter has significant economic impact. Fusobacterium necrophorum subsp. necrophorum, F. necrophorum subsp. funduliforme, Trueperella pyogenes, and Salmonella enterica are implicated in LA. Our objectives were to compare the prevalence and concentrations of these bacterial pathogens in purulent materials of mild (n = 134) or severe (n = 140) LA, and in matched ruminal (n = 94 and n = 88) and colonic (n = 52 and n = 69) epithelial tissues of feedlot cattle collected at slaughter in three independent studies. Samples were homogenized, and methods of detection included culture and quantitative PCR (qPCR) to determine prevalence and concentrations. Data were analyzed using a generalized linear mixed-effects model with severity, mild or severe, as a fixed effect, and the feedlot study as a random effect. Nearly all LA (90.9 to 98.9%) contained either or both subspecies of F. necrophorum and the prevalence was greater (P = 0.04) in severe LA (96.7%) compared to mild LA (90.9%) with qPCR and tended to be greater (P = 0.09) with the culture method (97% vs. 92.7%). The subsp. funduliforme, not associated with subsp. necrophorum, was prevalent in 15 to 21% of LA and did not differ (P > 0.4) in prevalence between mild and severe LA. Concentrations of F. necrophorum were in the range of 6.9 to 7.3 log₁₀ CFU per g of purulent material and were not different (P > 0.14) between mild or severe abscesses. The prevalence of T. pyogenes, detected by the culture method, was greater (P < 0.01) in severe (42.1%) compared to mild (26.1%) abscesses, but the prevalence based on qPCR only tended to be greater (P = 0.06) in severe LA (32.5%) compared to mild abscesses (22.2%). The prevalence and concentration of S. enterica were not affected (P > 0.13) by LA severity. The co-occurrences of the subsp. necrophorum and T. pyogenes and subsp. necrophorum and S. enterica were greater (P = 0.03) in severe compared to mild LA. Prevalence and concentrations of the four bacterial pathogens in ruminal and colonic epithelial tissues were not affected by LA severity. In conclusion, the prevalence of subsp. necrophorum and T. pyogenes were greater in severe compared to mild LA, but the concentrations were not different, and the greater frequency of association of the two species illustrates pathogenic synergy, possibly contributing to the severity of LA. Liver abscesses in cattle often elicit negative economic impacts upon the beef cattle industry because of liver condemnations and reduced cattle performance and carcass yields. Severity of liver abscesses ranges from mild to severe, and only the latter has significant economic impact. In this study, we analyzed and compared prevalence and concentrations of the four major bacterial pathogens, Fusobacterium necrophorum subsp. necrophorum, F. necrophorum subsp. funduliforme, Trueperella pyogenes, and Salmonella enterica, implicated in mild or severe abscesses and ruminal and colonic epithelial tissues collected at slaughter. Samples were analyzed using culture-dependent and culture-independent methods. Prevalence of the subsp. necrophorum, the primary causative agent, was greater in severe compared to mild abscesses. Concentrations of the four pathogens were not different between mild and severe abscesses. A major finding of the study was greater prevalence of T. pyogenes and co-occurrence of F. necrophorum and T. pyogenes in severe than in mild abscesses. Prevalence and concentrations of the four pathogens in ruminal and colonic epithelial tissues were not related to the severity of abscesses. The positive association of F. necrophorum and T. pyogenes with liver abscess severity illustrates pathogenic synergy between the two species, possibly contributing to increased severity.

This study evaluated the main and interactive effects of dietary starch concentration (49.1% [control] or 64.4% [high starch]) and feeding management regimen (regular [REG] or erratic [ERR]) on prevalence of Fusobacterium necrophorum subsp. necrophorum, F. necrophorum subsp. funduliforme, Trueperella pyogenes, and Salmonella enterica in liver abscesses (LA) and ruminal and colonic tissues of finishing beef steers. Intact LA (n = 132) and sections of ruminal (n = 131) and colonic (n = 120) epithelial tissues were collected from steers at slaughter. Samples were cultured, before and after enrichment, to determine prevalence of four bacterial pathogens and quantitative PCR (qPCR) was used to determine prevalence and concentrations of the two subspecies of F. necrophorum. Subsp. necrophorum was the dominant pathogen in LA, whereas subsp. funduliforme was dominant in ruminal and colonic tissues by both culture and qPCR methods. Steers fed the high-starch diet had greater prevalence (P = 0.01) of subsp. necrophorum, T. pyogenes, and S. enterica in LA compared to steers fed the control diet, indicating the potential impact of dietary starch on promoting bacterial translocation. Of the 132 LA analyzed, culture and qPCR identified 21.7% and 16.4% of LA, respectively, to have subsp. funduliforme, without the subsp. necrophorum, suggesting that subsp. funduliforme without subsp. necrophorum may have caused LA. Concentrations of F. necrophorum in LA were between 7.0 to 7.5 log10 CFU per g, were 2 to 3 log less in ruminal and colonic epithelial tissues, and were not affected by the diet (P ≥ 0.08). The prevalence of S. enterica was greater (P < 0.01) in colonic (71.9%) than ruminal epithelial tissues (48.3%), suggesting that the colon may be the major source of the Salmonella in LA. A total of eight serotypes were identified, and the majority (88.6%) belonged to Kentucky (27.2%), Montevideo (26.2%), Anatum (23.3%), and Lubbock (11.9%). Feeding management regimen had minimal effect, however, diet affected prevalence of the pathogens in LA but not ruminal and colonic epithelial tissues. The prevalence and concentrations of both subspecies of F. necrophorum in colonic epithelial tissue suggest the possibility of the colon being a source of LA pathogens. However, the prevalence and concentration of F. necrophorum in colonic epithelial tissues were much less than that of ruminal tissues, suggesting that the rumen may be the primary reservoir of F. necrophorum in LA.

Liver abscesses (LA) in feedlot cattle are polymicrobial infections, initiated primarily by the translocations of the two subspecies of Fusobacterium necrophorum, necrophorum and funduliforme, and secondarily by Trueperella pyogenes and Salmonella enterica from the rumen into the liver via portal blood. The hindgut has not been investigated as a potential source of LA pathogens. Our objectives were to analyze LA and matched ruminal and colonic epithelial tissues ( n = 96), collected at a commercial beef processor immediately after evisceration, to determine culture-based prevalence of pathogens, specifically, Escherichia coli , Klebsiella pneumoniae , Pseudomonas aeruginosa , and Bacteroides fragilis, which have not been targeted before, in addition to F. necrophorum, T. pyogenes, and S. enterica, and quantitative PCR-based prevalence and concentrations of the F. necrophorum subspecies. The subsp. necrophorum was the most dominant species in LA detected by both methods, and concentrations were in the range of 7.0 log ₁₀ colony forming units (CFU). Fusobacterial concentrations were higher in ruminal epithelial than in colonic epithelial tissues, but colonic epithelial tissues yielded more subsp. necrophorum isolates than ruminal epithelial tissues. Of the targeted bacterial species, E. coli was the most dominant, and none of the tissues was positive for B. fragilis . A majority of the isolations of E. coli were after enrichment, suggesting the concentrations were too low to contribute to the abscess development. The data reaffirm that LA are polymicrobial infections, F. necrophorum, specifically necrophorum, is the most dominant species prevalent, and the hindgut is likely to be a source, in addition to the rumen, of pathogens that cause LA. IMPORTANCE: Liver abscesses (LA) in beef cattle are initiated by entry of bacterial pathogens from the rumen via portal blood. The two most frequently isolated pathogens are the two subspecies of Fusobacterium necrophorum, followed by Trueperella pyogenes and Salmonella enterica . Our objectives were to determine the prevalence of pathogens that have been reported sporadically and have not been targeted before. Liver abscesses and matched ruminal epithelium and colonic epithelial tissues, collected from feedlot cattle at slaughter, were analyzed by culture and PCR methods. The subsp. necrophorum was the most dominant bacterium in liver abscesses. Colonic epithelial tissues yielded more subsp. necrophorum than ruminal epithelial tissues. Although Escherichia coli was the second most prevalent species, a majority of the isolates were obtained after enrichment, indicating low concentrations. Our data reaffirm that F. necrophorum is the dominant species prevalent in LA, and the hindgut is likely to be another source of pathogens that cause LA.

Liver abscesses (LA) in cattle are a polymicrobial infection, and the major bacterial pathogens associated are as follows: Fusobacterium necrophorum subsp. necrophorum (FNN), F. necrophorum subsp. funduliforme (FNF), Trueperella pyogenes (TP), and Salmonella enterica (SE). In polymicrobial infections, the contributions of individual species are difficult to assess. We hypothesized that species abundance in abscesses may be indicative of their contributions. Therefore, the objective was to develop a 4-plex quantitative PCR (qPCR) assay to determine prevalence and concentrations of the pathogens in LA ( n = 384) and matched ruminal (RT; n = 374) and colonic epithelial (CT; n = 256) tissues. Fusobacterium necrophorum , either FNN or FNF, was detected in 85.9% of LA by qPCR, which was slightly lower than the culture-based prevalence (89.1%). Only 16.9% of LA were positive for FNF with no FNN. The concentrations of FNN or FNF were 7 to 7.5 log ₁₀ CFU/g. The qPCR assay identified more ( P < 0.01) samples (29.2%) as positive for TP than the culture method (16.7%). The mean concentration of TP was 5.9 log ₁₀ CFU/g. None of the LA was positive for SE by the qPCR assay. The prevalence of FN was greater ( P < 0.01) in RT than CT (73.2% vs. 16%). The concentrations were in the 4 to 5 log ₁₀ CFU/g. The low concentrations of TP suggest that it is unlikely to be the primary etiologic agent. Although SE was detected by culture method, it was not quantifiable, which suggests that the species does not contribute to the development of LA. IMPORTANCE: Liver abscesses (LA) in cattle are a polymicrobial infection, and four bacterial pathogens are implicated: Fusobacterium necrophorum subsp. necrophorum (FNN) and subsp. funduliforme (FNF), Trueperella pyogenes (TP), and Salmonella enterica (SE). In mixed infections, the species abundance may be indicative of their contributions. Our objective was to develop a quantitative PCR assay to determine prevalence and concentrations of the pathogens in LA ( n = 384) and matched ruminal (RT; n = 374) and colonic tissues (CT; n = 256). The dominant species in LA was FNN with a mean concentration of 7.0 log ₁₀ CFU/g. The subsp. FNF without FNN was prevalent in a small number of LA, with a mean concentration of 7.0 log ₁₀ CFU. The concentration of TP was 5.0 log₁₀ CFU, which suggests that it is unlikely to be the primary etiologic agent. Although S. enterica was prevalent in LA, none was quantifiable, which suggests that it is not contributing to LA.

Colibacillosis in nursery pigs, caused by Escherichia coli (ETEC, EPEC, and STEC pathotypes), remains a major economic concern in the swine industry. This study evaluated the effects of in-feed or in-water chlortetracycline (CTC) administration on the fecal prevalence of virulence genes and pathotypes associated with colibacillosis. A total of 1296 weaned piglets (21 days old) were allocated to 48 pens (16 pens/treatment; 27 piglets/pen) and assigned randomly to no CTC, in-feed CTC, or in-water CTC groups. CTC was administered from days 0 to 14. Fecal samples from five piglets per pen on days 0, 14, and 28 were enriched, screened by 11-plex PCR, cultured for pathotypes, and tested for CTC susceptibility and tetracycline resistance genes. None of the 360 fecal samples or 3267 E. coli isolates were positive for bfpA or aggA. Prevalence of estB (96.9%) and astA (92.8%) was highest. ETEC was the dominant pathotype (41.2%), with astA (29%) and estB (21.9%) as predominant enterotoxin genes. CTC administration had no significant effect on fecal prevalence of virulence genes or pathotypes (p > 0.05). stx2 and STEC were detected only at day 28, all harboring stx2e. All pathotypes were CTC-resistant, with tetA as the predominant resistance gene.