Infection and antibiotic-associated changes in the fecal microbiota of C. rodentium ϕstx2dact-infected C57BL/6 mice

Enterohemorrhagic Escherichia coli causes watery to bloody diarrhea, which may progress to hemorrhagic colitis and hemolytic-uremic syndrome. While early studies suggested that antibiotic treatment may worsen the pathology of an enterohemorrhagic Escherichia coli (EHEC) infection, recent work has shown that certain non-Shiga toxin-inducing antibiotics avert disease progression. Unfortunately, both intestinal bacterial infections and antibiotic treatment are associated with dysbiosis. This can alleviate colonization resistance, facilitate secondary infections, and potentially lead to more severe illness. To address the consequences in the context of an EHEC infection, we used the established mouse infection model organism Citrobacter rodentium ϕstx2dact and monitored changes in fecal microbiota composition during infection and antibiotic treatment. C. rodentium ϕstx2dact infection resulted in minor changes compared to antibiotic treatment. The infection caused clear alterations in the microbial community, leading mainly to a reduction of Muribaculaceae and a transient increase in Enterobacteriaceae distinct from Citrobacter. Antibiotic treatments of the infection resulted in marked and distinct variations in microbiota composition, diversity, and dispersion. Enrofloxacin and trimethoprim/sulfamethoxazole, which did not prevent Shiga toxin-mediated organ damage, had the least disruptive effects on the intestinal microbiota, while kanamycin and tetracycline, which rapidly cleared the infection without causing organ damage, caused a severe reduction in diversity. Kanamycin treatment resulted in the depletion of all but Bacteroidetes genera, whereas tetracycline effects on Clostridia were less severe. Together, these data highlight the need to address the impact of individual antibiotics in the clinical care of life-threatening infections and consider microbiota-regenerating therapies.IMPORTANCEUnderstanding the impact of antibiotic treatment on EHEC infections is crucial for appropriate clinical care. While discouraged by early studies, recent findings suggest certain antibiotics can impede disease progression. Here, we investigated the impact of individual antibiotics on the fecal microbiota in the context of an established EHEC mouse model using C. rodentium ϕstx2dact. The infection caused significant variations in the microbiota, leading to a transient increase in Enterobacteriaceae distinct from Citrobacter. However, these effects were minor compared to those observed for antibiotic treatments. Indeed, antibiotics that most efficiently cleared the infection also had the most detrimental effect on the fecal microbiota, causing a substantial reduction in microbial diversity. Conversely, antibiotics showing adverse effects or incomplete bacterial clearance had a reduced impact on microbiota composition and diversity. Taken together, our findings emphasize the delicate balance required to weigh the harmful effects of infection and antibiosis in treatment.

Intramammary preparation of enrofloxacin hydrochloride-dihydrate for bovine mastitis (biofilm-forming Staphylococcus aureus)

BACKGROUND

Chronic bovine mastitis is linked to biofilm-producing Staphylococcus aureus (bp-Sa) or Staphylococcus coagulase-negative (bp-Scn).

OBJECTIVES

Bp-Sa and bp-Scn were treated with intramammary preparations of either enrofloxacin HCl·2H2O-dimethyl-sulfoxide-chitosan (enro-C/DMSO/chitosan) or enro-C alone. Their potential to inhibit and degrade biofilm formation in vitro was also assessed.

METHODS

Milk samples were obtained from the affected quarters in a herd. Phenotypical and genotypical identifications as biofilm-producing Staphylococcus species were carried out. Enro-C/DMSO/chitosan and enro-C alone were assessed to determine their in vitro efficacy in interfering with biofilm formation and their bactericidal effects. A prolonged eight-day treatment with a twice-daily intramammary insertion of 10 mL of enro-C/DMSO/chitosan or enro-C alone was set to evaluate the clinical and bacteriological cures on day 10 in 15 cows per group and the biofilm-inhibiting ability.

RESULTS

Fifty-seven percent of the isolates were identified as Staphylococcus spp., of which 50% were bp-Sa, 46% bp-Scn, and 4% Staphylococcus pseudintermedius. One hundred percent of the S. aureus isolated and 77% of Staphylococcus coagulase-negative were biofilm producers. In both groups, the icaA and icaD biofilm-producing genes were identified. The experimental preparation could inhibit biofilm formation, degrade mature biofilms, and have well-defined microbicidal effects on planktonic and biofilm bacteria. The respective clinical and bacteriological cure rates were 100% and 80% for enro-C/DMSO/chitosan and 41.7% and 25% for enro-C alone.

CONCLUSIONS

Enro-C/DMSO/chitosan eliminates bp-Sa and bp-Scn from cases of chronic bovine mastitis.

Antibiotic treatment of Mycoplasma ovipneumoniae in domestic sheep (Ovis aries): Working at the livestock-wildlife interface in Yukon, Canada

Domestic sheep (Ovis aries) can carry the bacterium Mycoplasma ovipneumoniae (M. ovipneumoniae) in their upper respiratory tract, often with little effect on health and productivity. However, for bighorn sheep (Ovis canadensis) populations, there is a link between M. ovipneumoniae infection and pneumonia, poor lamb recruitment, and high fatality rate. Because of these outcomes, preventing transmission of M. ovipneumoniae to free-ranging wild sheep has garnered interest from both the livestock and wildlife sectors. We hypothesized that treatment with intranasal and systemic enrofloxacin would reduce the prevalence of M. ovipneumoniae-positive animals in a flock of domestic sheep. Initially, the prevalence decreased in the treated group; but by 34 d post-treatment, the number of M. ovipneumoniae-positive sheep returned to near pretreatment prevalence. Key clinical message: Test-and-slaughter is a method used to reduce the risk of transmission of pneumonia-causing M. ovipneumoniae from domestic sheep and goats to free-ranging wild sheep. In an effort to find an alternative, we used enrofloxacin to treat a flock of M. ovipneumoniae-positive domestic sheep; however, long-term reduction of M. ovipneumoniae prevalence in the flock was not achieved.

Therapeutic efficacy of enrofloxacin in treatment of Francisella orientalis infections in juvenile Nile tilapia (Oreochromis niloticus L.)

Outbreaks of infections by Francisella orientalis represent one of the main obstacles to Nile tilapia (Oreochromis niloticus L.) farming. It is responsible for acute mortality in fingerlings and juveniles. The main control measure available is oral antibiotic therapy. This study compared the therapeutic efficacy of the antibiotics enrofloxacin and oxytetracycline, the most commonly used antimicrobial, against francisellosis in juvenile Nile tilapia (O. niloticus). Fish were challenged with a virulent isolate of F. orientalis and treated with medicated feed containing one of two doses of oxytetracycline (100 or 300 mg/kg of live weight (LW)) or 10 mg/kg of LW of enrofloxacin. The positive and negative control groups received feed without antibiotics; the negative control group was unchallenged. The results showed that enrofloxacin at a dose of 10 mg/kg of LW is effective against francisellosis in juvenile Nile tilapia (O. niloticus). Treatment with oxytetracycline did not eliminate the pathogen from the infected host, and the surviving fish became carriers. Enrofloxacin was able to cure the fish of infection with F. orientalis. This study suggests that enrofloxacin is a better option for treating francisellosis in Nile tilapia (O. niloticus L.). It controls mortality and avoids the carrier state in the fish, thus reducing the possibility of recurrence in the affected batches.

Comparison between broth microdilution and agar disk diffusion methods for antimicrobial susceptibility testing of bovine mastitis pathogens

In order to counter the antibiotic resistance phenomenon, a prudent and rational use of antimicrobials should be driven by an accurate clinical diagnosis and, when possible, by the isolation of the etiological agent followed by susceptibility testing, with the aim to select the most suitable molecule for therapy. Cow mastitis is considered the main cause of antibiotic use in the cattle breeding sector. The purpose of this study was to compare the broth microdilution (BMD) method performed with Sensititre Custom Plates and the agar disk diffusion (ADD) method in determining antimicrobial susceptibility of 215 isolates from bovine mastitis, including contagious pathogens (Staphylococcus aureus, Streptococcus agalactiae) and environmental (Streptococcus uberis, Streptococcus dysgalactiae, Enterococcus spp., Escherichia coli, Serratia marcescens, Klebsiella pneumoniae). We compared results of the following antimicrobials: amoxicillin/clavulanic acid, ampicillin, cefazolin, ceftiofur, enrofloxacin, erythromycin, kanamycin, oxacillin, penicillin, pirlimycin, rifampicin and trimethoprim/sulphonamides. We applied MIC breakpoints and zone diameter breakpoints as recommended by CLSI and EUCAST. MIC and disk diffusion diameters were compared for 1839 microorganism/antimicrobial combination and discrepancies between the two methods were classified as very major discrepancy (VMD), major discrepancy (MD) and minor discrepancy (MiD). The overall agreement between the two methods was found to be 80.7% with a Cohen's kappa coefficient of 0.397, thus indicating a fair concordance. BMD method and ADD method demonstrated a satisfactory agreement (89 to 100%) for S. aureus and S. marcescens and all antimicrobial agents tested. Low agreement was observed for S. uberis and rifampicin (20%), enrofloxacin (49%), penicillin (51%) and pirlimycin (52%), E. coli and ampicillin (20%), S. dysgalactiae and enrofloxacin (44%), S. agalactiae and rifampicin (25%). A possible explanation for the discrepancies detected could be found in the breakpoints used which, sometimes, are not specific for the tissue-matrix of isolation/animal species/pathogen agent. The majority of the discrepancies found were MiD and MD, revealing a higher restrictiveness of the BMD method, while VMD represented only 0.2% of the total observations, a comforting fact since this type of error may result in treatment failure.

Antimicrobial resistance trends among canine Escherichia coli isolated at a New York veterinary diagnostic laboratory between 2007 and 2020

Dogs are a potential source of drug-resistant Escherichia coli, but very few large-scale antimicrobial resistance surveillance studies have been conducted in the canine population. Here, we assess the antimicrobial susceptibility patterns, identify temporal resistance and minimum inhibitory concentration (MIC) trends, and describe associations between resistance phenotypes among canine clinical E. coli isolates in the northeastern United States. Through a retrospective study design, we collected MICs from 7709 E. coli isolates from canine infections at the Cornell University Animal Health Diagnostic Center between 2007 and 2020. The available clinical data were limited to body site. Isolates were classified as resistant or susceptible to six (urinary) and 22 (non-urinary) antimicrobials based on Clinical and Laboratory Standards Institute breakpoints. We used the Mann-Kendall test (MKT) and Sen's slope to identify the presence of a significant trend in the percent of resistant isolates over the study period. Multivariable logistic regression (MLR) models were built with ceftiofur, enrofloxacin, or trimethoprim-sulfamethoxazole resistance as the outcome and either body site and isolation date, or resistance to other antimicrobials as predictors. MIC trends were characterized with survival analysis models, controlling for body site and year of isolation. Overall, 16.4% of isolates were resistant to enrofloxacin, 14.3% to ceftiofur, and 14% to trimethoprim-sulfamethoxazole. The MKT and Sen's slope revealed a significant decreasing temporal trend for gentamicin and trimethoprim-sulfamethoxazole resistance among non-urinary isolates. No significant temporal resistance trends were detected by MKT for other antimicrobials. However, controlling for body-site in MLR models identified a decrease in resistance rates to enrofloxacin and trimethoprim-sulfamethoxazole after 2010. Similarly, survival analysis data confirmed these findings and showed a decrease in MIC values after 2010 for gentamicin and trimethoprim-sulfamethoxazole, but an increase in cephalosporin MICs. MLR showed that non-urinary isolates were significantly more likely than urinary isolates to demonstrate in vitro resistance to ceftiofur, enrofloxacin, and trimethoprim-sulfamethoxazole after controlling for year of isolation. We identified a higher level of ceftiofur resistance among enrofloxacin resistant isolates from urinary and non-urinary origins. Our findings confirmed that dogs are still a non-negligeable reservoir of drug-resistant E. coli in the northeastern United States. The increase in extended-spectrum cephalosporin MIC values in 2018-2020 compared to 2007-2010 constitutes a particularly worrying issue; the relationship between ceftiofur and enrofloxacin resistance suggests that the use of fluoroquinolones could contribute to this trend. Trimethoprim-sulfamethoxazole may be a good first-line choice for empiric treatment of E. coli infections; it is already recommended for canine urinary tract infections.

Highly different effects of phage therapy and antibiotic therapy on immunological responses of chickens infected with Salmonella enterica serovar Typhimurium

The appearance of bacteria resistant to most or even all known antibiotics has become a serious medical problem. One such promising and effective alternative form of therapy may be the use of phages, the administration of which is considered to be safe and highly effective, especially in animals with drug-resistant infections. Although there have been no reports to date suggesting that bacteriophages can cause any severe complications or adverse effects, we still know little about their interactions with animal organisms, especially in the context of the functioning of the immune system. Therefore, the aim of the present study was to compare the impact of the application of selected bacteriophages and antibiotics (enrofloxacin and colistin), commonly used in veterinary medicine, on immune functions in Salmonella enterica serovar Typhimurium-infected chickens. The birds were infected with S. Typhimurium and then treated with a phage cocktail (14 days), enrofloxacin (5 days), or colistin (5 days). The concentrations of a panel of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, IL-8, and IL-12) and cytokines that reveal anti-inflammatory effects (IL-10 and IL-4), the percentage of lymphocytes, and the level of stress hormones (corticosterone and cortisol), which significantly modulate the immune responses, were determined in different variants of the experiment. The phage cocktail revealed anti-inflammatory effects when administered either 1 day after infection or 2 days after S. Typhimurium detection in feces, as measured by inhibition of the increase in levels of inflammatory response markers (IL-1β, IL-6, IFN-γ, IL-8, and IL-12). This was also confirmed by increased levels of cytokines that exert an anti-inflammatory action (IL-10 and IL-4) following phage therapy. Moreover, phages did not cause a negative effect on the number and activity of lymphocytes’ subpopulations crucial for normal immune system function. These results indicate for the first time that phage therapy not only is effective but also can be used in veterinary medicine without disturbing immune homeostasis, expressed as cytokine imbalance, disturbed percentage of key immune cell subpopulations, and stress axis hyperactivity, which were observed in our experiments as adverse effects accompanying the antibiotic therapy.

Genomic and Therapeutic Analyses of Staphylococcus aureus Isolated from Cattle Reproductive Tract

Staphylococcus aureus is emerging as a ubiquitous multidrug-resistant pathogen circulating among animals, humans, and their environment. The current study focused on molecular epidemiology and evidence-based treatment against S. aureus from bovine endometritis. For this study, n = 304 cattle were screened for endometritis using ultrasonography while presenting case history, and clinical signs were also considered. S. aureus was isolated from endometritis-positive uterine samples which were further put to molecular identification, phylogenetic analysis, susceptibility to antibiotics, and testing of novel drug combinations in both in vitro and field trials. The findings of the study revealed 78.20% of bovine endometritis samples positive for S. aureus, while nuc gene-based genotyping of S. aureus thermal nuclease (SA-1, SA-2, and SA-3) showed close relatedness with S. aureus thermal nuclease of Bos taurus. Drug combinations showed 5.00 to 188.88% rise in zones of inhibitions (ZOI) for drugs used in combination compared to the drugs used alone. Gentamicin in combination with amoxicillin and enrofloxacin with metronidazol showed synergistic interactions in an in vitro trial. Co-amoxiclav with gentamicin, gentamicin with enrofloxacin, and metronidazole with enrofloxacin showed 100%, 80%, and 60% efficacy in treating clinical cases in field trials, respectively. As a result, the study came to the conclusion the higher prevalence of endometritis-based S. aureus, genetic host shifts, narrow options for single drugs, and need for novel drug combinations to treat clinical cases.

Metabolites in Milk after Enrofloxacin Treatment and Their Persistence to Temperature

In this work, metabolomic profile changes in milk from cows affected by mastitis and treated with enrofloxacin (ENR) have been studied using LC-HRMS techniques. Principal component analysis was applied to the obtained results, and the interest was focused on changes affecting compounds without a structural relationship to ENR. Most of the compounds, whose concentrations were modified as a result of the pharmacological treatment and/or the pathological status, were related to amino acids and peptides. Compounds that may become possible biomarkers for either disease or treatment have been detected. Additionally, the alterations caused by thermal processes, such as those applied to milk before consumption, on the identified metabolites have also been considered.

Tissue compartmentalization enables Salmonella persistence during chemotherapy

Antimicrobial chemotherapy can fail to eradicate the pathogen, even in the absence of antimicrobial resistance. Persisting pathogens can subsequently cause relapsing diseases. In vitro studies suggest various mechanisms of antibiotic persistence, but their in vivo relevance remains unclear because of the difficulty of studying scarce pathogen survivors in complex host tissues. Here, we localized and characterized rare surviving Salmonella in mouse spleen using high-resolution whole-organ tomography. Chemotherapy cleared >99.5% of the Salmonella but was inefficient against a small Salmonella subset in the white pulp. Previous models could not explain these findings: drug exposure was adequate, Salmonella continued to replicate, and host stresses induced only limited Salmonella drug tolerance. Instead, antimicrobial clearance required support of Salmonella-killing neutrophils and monocytes, and the density of such cells was lower in the white pulp than in other spleen compartments containing higher Salmonella loads. Neutrophil densities declined further during treatment in response to receding Salmonella loads, resulting in insufficient support for Salmonella clearance from the white pulp and eradication failure. However, adjunctive therapies sustaining inflammatory support enabled effective clearance. These results identify uneven Salmonella tissue colonization and spatiotemporal inflammation dynamics as main causes of Salmonella persistence and establish a powerful approach to investigate scarce but impactful pathogen subsets in complex host environments.

Phytobiotics blend as a dietary supplement for Nile tilapia health improvement

Functional additives of natural origin included as dietary supplements have become an alternative to synthetic antibiotics to improve health and resistance to ecologically correct pathogenic diseases in fish farming. We tested whether incorporating a mixture of phytobiotics such as volatile oils of thyme, red thyme and pepper rosemary into the diet improves growth performance, oxidative stress, immune and hematological responses and resistance of juvenile Nile tilapia when subjected to a challenge with Aeromonas hydrophila compared to a synthetic antibiotic (enrofloxacin). The experimental design was completely randomized with three experimental groups: control diet, diets containing a mixture of thyme phytobiotic essential oils, red thyme and pepper rosemary (FTB) and the synthetic antibiotic enrofloxacin (ATB), with four replicates (14 fish per repetition/experimental unit). Plasma glucose levels, leukocyte respiratory activity, serum lysozyme levels, number of circulating erythrocytes and leukocytes, levels of lipid peroxidation (LPO), catalase (CAT) and glutathione S-transferase (GST) activity at the end of 20 days of feeding (phase) were evaluated and 24 h after exposure to bacteria (phase II). The supplementation of FTB and ATB did not change the performance parameters, but it was sufficient to increase lysozyme, leukocytes, neutrophils and monocytes after the bacterial challenge, reduction of CAT and LPO activity and the highest GST activity (P < 0.05). The results of the present study suggest that FTB as a dietary supplement has benefits and can replace synthetic ATB, including supplementation with FTB for 20 days to provide greater antioxidant protection in Nile tilapia, mitigate the impacts of stressors and modulate immunity, providing to fish greater resistance and protection against diseases.

Management of otitis externa with an led-illuminated gel: a randomized controlled clinical trial in dogs

BACKGROUND

Canine otitis externa is a painful condition which can be challenging to treat due to difficulties in the administration of otic medication. This can be due to lack of owner compliance in the application of ear drops or due to the resentment that some dogs demonstrate when attempts are made to administer topical medication into a sensitive ear canal. The aim of the study was to assess the efficacy of a topical LED-illuminated gel (LIG) in canine otitis externa in comparison to standard of care therapy. Dogs with spontaneous otitis externa were randomly allocated in three groups: groups QW received LIG once weekly; BW received LIG twice weekly; group C received enrofloxacin and silver sulfadiazine twice daily. LIG consists of a topical application of a gel containing chromophores that, when illuminated by a LED lamp, re-emit fluorescent light which can stimulate physiological responses, promoting healing and controlling bacteria. The evaluation protocol (T0 to T5) considered clinical assessment (OTIS-3-index-scoring-system; pruritus-severity-scale; pain-severity-score; aural temperature), cytological scoring system, quali-quantitative bacteriologic assessment.

RESULTS

All groups (QW, n = 21; BW, n = 23; C, n = 20) showed improvement during the study (QW: P < 0.02 for cytological and pain scores, P < 0.003 for bacteriologic assessment, P < 10- 4 for pruritus, total OTIS-3 and temperature assessments; BW: P < 10- 4 for all clinical, cytological and bacteriologic assessments; C: P < 0.02 for all clinical and cytological assessments, P < 10- 4 for bacteriologic assessment). The highest clinical score reduction occurred in Group BW (P < 0.014 in T3; P < 0.001 in T4 and P < 10- 4 in T5). BW reached the clinically relevant effect level at T3 (- 3.26 ± 1.21 levels), QW reached it at T4 (- 3.24 ± 0.99), C did not reach it. No differences between groups were seen in the reduction of CFU/mL (T0-T5).

CONCLUSIONS

All treatment groups showed a positive clinical effect. LIG administered twice-a-week was the most favourable protocol of the study. LIG may be considered beneficial in the management of canine otitis externa; it seems to be effective in controlling the clinical condition, including the signs of inflammation and local pain, the bacterial growth, and it may help increasing treatment compliance.

Comparative evaluation of different therapeutic protocols for contagious caprine pleuropneumonia in Himalayan Pashmina goats

Therapeutic management of contagious caprine pleuroneumonia (CCPP) involves mostly the use of oxytetracycline followed by enrofloxacin and rarely tylosin. In many parts of the world including India, the former antibiotics are commonly available than the latter. Therefore, prolonged use of the same leads to the development of antibiotic resistance and decreased efficacy of drug. Besides, inflammatory and allergic pathogenesis of CCPP envisages combination therapy. In this study, we evaluated the effectiveness of the combination therapy using different antibiotics (oxytetracycyline @ 10: group I, enrofloxacin @ 5 group II, and tylosin: group III, @ 10 mg/kg body weight), along with anti-inflammatory (meloxicam @ 0.5 mg/kg) and anti-allergic (pheneramine maleate @ 1.0 mg/kg) drugs. These drugs were given intramuscularly at the interval of 48 h for four times in three test groups (n = 10) of Pashmina goats, viz. groups I, II, and III, respectively, affected with CCPP. Group IV (n = 10) was kept as healthy control when group V (n = 10) treated with oxytetracycline @ 10 mg/kg alone was used as positive control. Clinical signs, clinical parameters, pro-inflammatory cytokine (tumor necrosis factor alpha (TNF-α)), and oxidative stress indices (total oxidant status (TOS), total antioxidant status (TAS)) were evaluated at hours 0, 48, 96, and 144 of experimental trial. Tylosin-based combination therapy resulted in a rapid and favorable recovery resulting in restoration of normal body temperature (102.46 ± 0.31 °F), respiration rate (16.30 ± 0.79 per minute), and heart rate (89.50 ± 2.63 per minute) compared to the oxytetracycline (102.95 ± 0.13, 21.30 ± 1.12, 86.00 ± 2.33, respectively) and enrofloxacin (102.97 ± 0.19, 21.00 ± 1.25, 90.00 ± 2.58, respectively) treated groups. By hour 144, all the groups showed restoration of clinical parameters of normal health and diminishing signs of CCPP, viz. fever, dyspnea, coughing, nasal discharge, weakness, and pleurodynia. Significant (P ≤ 0.05) decrease in levels of TNF-α and non-significant (P > 0.05) decrease in levels of TOS and an increase in levels of TAS were noted from hour 0 to 144 in all the test groups. Within the groups, no significant (P > 0.05) change was noted in TNF-α, TOS, and TAS levels; however, TNF-α levels were comparatively lower in group III. Hematological parameters did not differ significantly (P > 0.05). From these findings, it can be inferred that tylosin-based combination therapy is relatively better for early, rapid, and safe recovery besides minimizing inflammatory and oxidative cascade in CCPP affected Pashmina goats compared to oxytetracycline- and enrofloxacin-based therapies.

Altered Gut Microbiota Activate and Expand Insulin B15-23-Reactive CD8+ T Cells

Insulin is a major autoantigen in type 1 diabetes, targeted by both CD8 and CD4 T cells. We studied an insulin-reactive T-cell receptor (TCR) α-chain transgenic NOD mouse on a TCRCα and proinsulin 2 (PI2)-deficient background, designated as A22Cα^-/-PI2^-/- NOD mice. These mice develop a low incidence of autoimmune diabetes. To test the role of gut microbiota on diabetes development in this model system, we treated the A22Cα^-/-PI2^-/- NOD mice with enrofloxacin, a broad-spectrum antibiotic. The treatment led to male mice developing accelerated diabetes. We found that enrofloxacin increased the frequency of the insulin-reactive CD8+ T cells and activated the cells in the Peyer's patches and pancreatic lymph nodes, together with induction of immunological effects on the antigen-presenting cell populations. The composition of gut microbiota differed between the enrofloxacin-treated and untreated mice and also between the enrofloxacin-treated mice that developed diabetes compared with those that remained normoglycemic. Our results provide evidence that the composition of the gut microbiota is important for determining the expansion and activation of insulin-reactive CD8+ T cells.

Effectiveness of traditional Chinese herbal medicine, San-Huang-San, in combination with enrofloxacin to treat AHPND-causing strain of Vibrio parahaemolyticus infection in Litopenaeus vannamei

The effects of oral administration of enrofloxacin (ENR) and San-Huang-San (SHS), singly or in combination, on the survival performance, disease resistance, and immunity of Litopenaeus vannamei were investigated. After challenge with an AHPND-causing strain of Vibrio parahaemolyticus (VP_AHPND), shrimp were immediately fed a drug-free diet, diets containing only ENR (20 mg·kg^-1) or SHS (500 mg·kg^-1) or diets containing low-dose (10 mg·kg^-1 ENR + 250 mg ·kg^-1 SHS), medium-dose (20 mg·kg^-1 ENR + 500 mg ·kg^-1 SHS), and high-dose (40 mg·kg^-1 ENR + 1000 mg ·kg^-1 SHS) drug combinations for 5 days. The cumulative shrimp mortality over 5 days after injection of VP_AHPND in the ENR + SHS combination groups was significantly lower than that in the ENR or SHS alone groups (p < 0.05). Immune parameters, including the vibrio density, total hemocyte counts (THCs), hemocyanin (HEM) concentration, antibacterial activity, activity levels of lysozyme (LZM), acid phosphatase (ACP), alkaline phosphatase (AKP), and phenoloxidase (PO) in cell-free hemolymph, and the expression levels of the immune-related genes anti-lipopolysaccharide factor (ALF), cathepsin B (catB), crustin, lectin (Lec), lysozyme (LZM), and Toll-like receptor (TLR) in hemocytes were determined in the shrimp. The results showed that the shrimp in drug combination groups cleared more VP_AHPND than that in the ENR or SHS group in the same time. The values for other immune parameters in the drug combination groups were higher than those in the ENR or SHS group (p < 0.05). Finally, in the histological examinations, the histological structural alignment and integrity of the hepatopancreatic tubules in the drug combination groups were better than that in the ENR and SHS groups. Under the experimental conditions, compared with ENR or SHS used alone, the combination use of ENR and SHS could improve immunity and disease resistance in shrimp after VP_AHPND infection, and could reduce the use of ENR when the better therapeutic effect was achieved.

Mutant prevention and minimum inhibitory concentration drug values for enrofloxacin, ceftiofur, florfenicol, tilmicosin and tulathromycin tested against swine pathogens Actinobacillus pleuropneumoniae, Pasteurella multocida and Streptococcus suis

Actinobacillus pleuropneumoniae, Pasteurella multocida and Streptococcus suis are prevalent bacterial causes of swine infections. Morbidity, mortality and positively impacting the financial burden of infection occurs with appropriate antimicrobial therapy. Increasing antimicrobial resistance complicates drug therapy and resistance prevention is now a necessity to optimize therapy and prolong drug life. Mutant bacterial cells are said to arise spontaneously in bacterial densities of 107-109 or greater colony forming units/ml. Antibiotic drug concentration inhibiting growth of the least susceptible cell in these high density populations has been termed the mutant prevention concentration (MPC). In this study MPC and minimum inhibitory concentration (MIC) values of ceftiofur, enrofloxacin, florfenicol, tilmicosin and tulathromycin were determined against the swine pathogens A. pleuropneumoniae, P.multocida and S. suis. The following MIC90/MPC90 values (mg/L) for 67 A. pleuropneumoniae and 73 P. multocida strains respectively were as follows: A. pleuropneumoniae 0.031/0.5, ≤0.016/0.5, 0.5/2, 4/32, 2/32; P. multocida 0.004/0.25, 0.016/0.125, 0.5/0.5, 8/16, 0.5/1. For 33 S. suis strains, MIC90 values (mg/L) respectively were as follows: 1, 0.25, 4, ≥8 and ≥8. A total of 16 S. suis strains with MIC values of 0.063-0.5 mg/L to ceftiofur and 0.25-0.5 mg/L to enrofloxacin were tested by MPC; MPC values respectively were 0.5 and 1 mg/L respectively. MPC concentrations provide a dosing target which may serve to reduce amplification of bacterial subpopulations with reduced antimicrobial susceptibility. Drug potency based on MIC90 values was ceftiofur > enrofloxacin >florfenicol = tulathromycin > tilmicosin; based on MPC90 values was enrofloxacin > ceftiofur > tulathromycin > florfenicol ≥ tilmicosin.