Profiling Branchial Bacteria of Atlantic Salmon (Salmo salar L.) Following Exposure to Antimicrobial Agents

Microbial gill diseases caused by either opportunistic or specific pathogens are an emerging area of concern for aquaculture producers in part due to their sometimes complex and/or cryptic nature. Many antimicrobial treatments used in aquacultural settings are broad spectrum in nature. The effect of such therapeutics upon reduction and recolonization of commensal or pathogenic microbiota post-treatment has received little attention to date. Commensal bacteria are an integral component of the barrier function of mucosal surfaces in animals. This study evaluated the effect of several commercially relevant antimicrobial treatments upon the diversity and composition of branchial bacteria of Atlantic salmon. Here we exposed Atlantic salmon smolt to a number of commercially relevant antimicrobial treatments including chemotherapeutants (chloramine-t and hydrogen peroxide) and antibiotics (oxytetracycline and florfenicol) in vivo. Subsequently we examined the change in bacterial load, 16S rRNA gene expression, and taxonomic diversity post-treatment upon the gills. Results revealed a decrease in cultivable bacterial colonies after antimicrobial treatment, and a downstream decrease in bacterial richness and abundance post-treatment, with colonization of several prominent pathogenic taxa including Vibrio and Tenacibaculum. Temporal tracing over a 14-day period demonstrated that the bacteriome of gill mucus is sensitive to change, and altered by antimicrobial treatment and handling. This study identified candidate antimicrobial treatments which could be implemented in future studies to illustrate the effect of dysbiosis on microbial gill diseases.

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The Effect of Antimicrobial Treatment upon the Gill Bacteriome of Atlantic Salmon (Salmo salar L.) and Progression of Amoebic Gill Disease (AGD) In Vivo

Microorganisms ◽

10.3390/microorganisms9050987 ◽

2021 ◽

Vol 9 (5) ◽

pp. 987

Author(s):

Joel Slinger ◽

Mark B. Adams ◽

Chris N. Stratford ◽

Megan Rigby ◽

James W. Wynne

Keyword(s):

Atlantic Salmon ◽

Salmo Salar ◽

Bacterial Load ◽

Health Condition ◽

Antimicrobial Treatment ◽

Atlantic Salmon Salmo Salar ◽

Chloramine T ◽

Gill Disease ◽

Significant Health

Branchial surfaces of finfish species contain a microbial layer rich in commensal bacteria which can provide protection through competitive colonization and production of antimicrobial products. Upon disturbance or compromise, pathogenic microbiota may opportunistically infiltrate this protective barrier and initiate disease. Amoebic gill disease (AGD) is a globally significant health condition affecting salmonid mariculture. The current study examined whether altering the diversity and/or abundance of branchial bacteria could influence the development of experimentally induced AGD. Here, we challenged Atlantic salmon (Salmo salar) with Neoparamoeba perurans in a number of scenarios where the bacterial community on the gill was altered or in a state of instability. Administration of oxytetracycline (in-feed) and chloramine-T (immersion bath) significantly altered the bacterial load and diversity of bacterial taxa upon the gill surface, and shifted the community profile appreciably. AGD severity was marginally higher in fish previously subjected to chloramine-T treatment following 21 days post-challenge. This research suggests that AGD progression and severity was not clearly linked to specific bacterial taxa present in these systems. However, we identified AGD associated taxa including known pathogenic genus (Aliivibrio, Tenacibaculum and Pseudomonas) which increased in abundance as AGD progressed. Elucidation of a potential role for these bacterial taxa in AGD development is warranted.

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The Effect of pH on Antibiotic Efficacy against Coxiella burnetii in Axenic Media

Scientific Reports ◽

10.1038/s41598-019-54556-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

Cody B. Smith ◽

Charles Evavold ◽

Gilbert J. Kersh

Keyword(s):

Coxiella Burnetii ◽

Antimicrobial Agents ◽

Q Fever ◽

Antimicrobial Treatment ◽

Etiologic Agent ◽

Growth And Survival ◽

Intracellular Compartments ◽

The Impact

AbstractCoxiella burnetii, the etiologic agent of Q fever, replicates in an intracellular phagolysosome with pH between 4 and 5. The impact of this low pH environment on antimicrobial treatment is not well understood. An in vitro system for testing antibiotic susceptibility of C. burnetii in axenic media was set up to evaluate the impact of pH on C. burnetii growth and survival in the presence and absence of antimicrobial agents. The data show that C. burnetii does not grow in axenic media at pH 6.0 or higher, but the organisms remain viable. At pH of 4.75, 5.25, and 5.75 moxifloxacin, doxycycline, and rifampin are effective at preventing growth of C. burnetii in axenic media, with moxifloxacin and doxycycline being bacteriostatic and rifampin having bactericidal activity. The efficacy of doxycycline and moxifloxacin improved at higher pH, whereas rifampin activity was pH independent. Hydroxychloroquine is thought to inhibit growth of C. burnetii in vivo by raising the pH of typically acidic intracellular compartments. It had no direct bactericidal or bacteriostatic activity on C. burnetii in axenic media, suggesting that raising pH of acidic intracellular compartments is its primary mechanism of action in vivo. The data suggest that doxycycline and hydroxychloroquine are primarily independent bacteriostatic agents.

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Efficacy of enrofloxacin or doxycycline for treatment of Bartonella henselae or Bartonella clarridgeiae infection in cats.

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.41.11.2448 ◽

1997 ◽

Vol 41 (11) ◽

pp. 2448-2455 ◽

Cited By ~ 57

Author(s):

D L Kordick ◽

M G Papich ◽

E B Breitschwerdt

Keyword(s):

Blood Culture ◽

High Performance ◽

Antimicrobial Agents ◽

Bartonella Henselae ◽

Bacterial Load ◽

Treatment Success ◽

In Vitro Susceptibility ◽

Drug Concentrations

Enrofloxacin and doxycycline are antimicrobial agents used to treat bacterial diseases of cats. In vitro susceptibility data indicate that either drug should be effective against Bartonella species. In vivo efficacies of these drugs for eradication of chronic Bartonella henselae or Bartonella clarridgeiae infections were examined in 18 experimentally infected cats and 25 naturally exposed cats treated with enrofloxacin (22.7 mg given orally [PO] every 12 h [q12h] [14 days, n = 10; 28 days, n = 13]) or with doxycycline (25 mg PO q12h [14 days, n = 9; 28 days, n = 8]) or not treated (n = 3). Plasma drug concentrations were determined in experimental cats by high-performance liquid chromatography. Only 23 of 43 cats enrolled ultimately met inclusion criteria. Bacteremia was eliminated for 12 to 25 weeks posttreatment in four of seven cats receiving 14 days of enrofloxacin, five of seven cats receiving 28 days of enrofloxacin, one of six cats receiving 14 days of doxycycline, and one of two cats receiving 28 days of doxycycline. Defining a negative result by blood culture as treatment success may be erroneous; these results may reflect the insensitivity of blood culture or the relapsing nature of Bartonella bacteremia. Our results suggest that MICs obtained with axenic media do not predict antimicrobial activity against intracellular Bartonella, that a long treatment course is required to eliminate infection, and that duration of therapy correlates with pretreatment bacterial load. Given current concern about the development of antimicrobial resistance, we would reserve recommendation for treatment to cats owned by an immunocompromised individual or as an alternative to euthanasia of a pet.

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Treatment of a cochlear implant biofilm infection: a potential role for alternative antimicrobial agents

The Journal of Laryngology & Otology ◽

10.1017/s0022215110000319 ◽

2010 ◽

Vol 124 (7) ◽

pp. 729-738 ◽

Cited By ~ 13

Author(s):

A J Brady ◽

T B Farnan ◽

J G Toner ◽

D F Gilpin ◽

M M Tunney

Keyword(s):

Cochlear Implant ◽

Cochlear Implants ◽

Antimicrobial Agents ◽

Antimicrobial Treatment ◽

Novel Agents ◽

Tea Tree Oil ◽

Tea Tree ◽

Microdilution Method ◽

Broth Microdilution Method

AbstractObjective:This study aimed to investigate antimicrobial treatment of an infected cochlear implant, undertaken in an attempt to salvage the infected device.Methods:We used the broth microdilution method to assess the susceptibility of meticillin-sensitive Staphylococcus aureus isolate, cultured from an infected cochlear implant, to common antimicrobial agents as well as to novel agents such as tea tree oil. To better simulate in vivo conditions, where bacteria grow as microcolonies encased in glycocalyx, the bactericidal activity of selected antimicrobial agents against the isolate growing in biofilm were also compared.Results:When grown planktonically, the S aureus isolate was susceptible to 17 of the 18 antimicrobials tested. However, when grown in biofilm, it was resistant to all conventional antimicrobials. In contrast, 5 per cent tea tree oil completely eradicated the biofilm following exposure for 1 hour.Conclusion:Treatment of infected cochlear implants with novel agents such as tea tree oil could significantly improve salvage outcome.

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Antimicrobial treatment of Mycoplasma hyopneumoniae infections.

Mycoplasmas in swine ◽

10.1079/9781789249941.0181 ◽

2021 ◽

pp. 181-205

Author(s):

Anne V. Gautier-Bouchardon

Keyword(s):

Mycoplasma Hyopneumoniae ◽

Resistance Mechanisms ◽

Antimicrobial Treatment ◽

Antimicrobial Treatments

Abstract This chapter reviews the antimicrobials and antimicrobial treatments used to control M. hyopneumoniae infections. It also gives an overview of in vitro and in vivo activities of these antimicrobials and of resistance mechanisms described for M. hyopneumoniae towards these antimicrobials.

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Efficacy of Aerosol MP-376, a Levofloxacin Inhalation Solution, in Models of Mouse Lung Infection Due to Pseudomonas aeruginosa

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00268-09 ◽

2009 ◽

Vol 53 (9) ◽

pp. 3923-3928 ◽

Cited By ~ 32

Author(s):

Mojgan Sabet ◽

Courtney E. Miller ◽

Thomas G. Nolan ◽

Kathy Senekeo-Effenberger ◽

Michael N. Dudley ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Pulmonary Infection ◽

Antimicrobial Agents ◽

Bacterial Load ◽

Lung Infection ◽

In Vivo Studies ◽

Mouse Lung ◽

Bacterial Killing ◽

High Concentrations

ABSTRACT Progressive respiratory failure due to Pseudomonas aeruginosa is the leading cause of morbidity and mortality in patients with cystic fibrosis. The pulmonary delivery of antimicrobial agents provides high concentrations of drug directly to the site of infection and attains pharmacokinetic-pharmacodynamic indices exceeding those which can be achieved with systemic dosing. MP-376 is a new formulation of levofloxacin that enables the safe aerosol delivery of high concentrations of drug to pulmonary tissues. In vivo studies were conducted to demonstrate the efficacy of MP-376 in models of mouse pulmonary infection. The superiority of aerosol dosing over systemic dosing was demonstrated in models of both acute and chronic lung infection. In a model of acute lung infection, aerosol treatment with MP-376 once or twice daily reduced the lung bacterial load to a greater extent than aerosol tobramycin or aztreonam did when they were administered at similar or higher doses. The bacterial killing by aerosol MP-376 observed in the lung in the model of acute pulmonary infection translated to improved survival (P < 0.05). In a model of chronic pulmonary infection, aerosol MP-376 had antimicrobial effects superior to those of aztreonam (P < 0.05) and effects similar to those of tobramycin (P > 0.05). In summary, these data show that aerosol MP-376 has in vivo activity when it is used to treat acute and chronic lung infections caused by P. aeruginosa.

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Improved Stability and Activity of a Marine Peptide-N6NH2 against Edwardsiella tarda and Its Preliminary Application in Fish

Marine Drugs ◽

10.3390/md18120650 ◽

2020 ◽

Vol 18 (12) ◽

pp. 650

Author(s):

Huihui Han ◽

Ting Li ◽

Zhenlong Wang ◽

Da Teng ◽

Ruoyu Mao ◽

...

Keyword(s):

Antimicrobial Agents ◽

Bacterial Load ◽

Organ Injury ◽

Edwardsiella Tarda ◽

Minimal Inhibitory Concentrations ◽

C Terminus ◽

Improved Stability ◽

Marine Peptide

Edwardsiella tarda can cause fatal gastro-/extraintestinal diseases in fish and humans. Overuse of antibiotics has led to antibiotic resistance and contamination in the environment, which highlights the need to find new antimicrobial agents. In this study, the marine peptide-N6 was amidated at its C-terminus to generate N6NH2. The antibacterial activity of N6 and N6NH2 against E. tarda was evaluated in vitro and in vivo; their stability, toxicity and mode of action were also determined. Minimal inhibitory concentrations (MICs) of N6 and N6NH2 against E. tarda were 1.29–3.2 μM. Both N6 and N6NH2 killed bacteria by destroying the cell membrane of E. tarda and binding to lipopolysaccharide (LPS) and genomic DNA. In contrast with N6, N6NH2 improved the stability toward trypsin, reduced hemolysis (by 0.19% at a concentration of 256 μg/mL) and enhanced the ability to penetrate the bacterial outer and inner membrane. In the model of fish peritonitis caused by E. tarda, superior to norfloxacin, N6NH2 improved the survival rate of fish, reduced the bacterial load on the organs, alleviated the organ injury and regulated the immunity of the liver and kidney. These data suggest that the marine peptide N6NH2 may be a candidate for novel antimicrobial agents against E. tarda infections.

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Generation of Bioluminescent Streptococcus mutans and Its Usage in Rapid Analysis of the Efficacy of Antimicrobial Compounds

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.42.8.1906 ◽

1998 ◽

Vol 42 (8) ◽

pp. 1906-1910 ◽

Cited By ~ 48

Author(s):

Vuokko Loimaranta ◽

Jorma Tenovuo ◽

Leeni Koivisto ◽

Matti Karp

Keyword(s):

Streptococcus Mutans ◽

Antimicrobial Agents ◽

Light Emission ◽

Shuttle Vector ◽

Measurement Range ◽

Relative Light Unit ◽

Logarithmic Growth Phase ◽

Light Production ◽

Antimicrobial Treatments

ABSTRACT The oral bacterium Streptococcus mutans was transformed by electroporation with a shuttle vector (pCSS945) containing insect luciferase gene from a click beetle (Pyrophorus plagiophthalamus) resulting in a bioluminescent phenotype. ThisS. mutans strain was used in experiments in which light emission was used as a rapid and, compared to conventional CFU counting, more convenient means of estimating the effects of various antimicrobial treatments. The basic parameters affecting in vivo light production by the strain were studied. It was found that pH 6.0 was optimal for incorporation of the substrate d-luciferin for the luciferase reaction. The optimum concentration ofd-luciferin was approximately 150 μM at room temperature. Under optimum conditions the light emission in vivo increased rapidly to a constant level and thereafter had a decay of 0.6%/min when logarithmic-growth-phase cells were used. The light emission closely paralleled the numbers of CFU, giving a detectable signal from 30,000 cells and having a dynamic measurement range over 4 log CFU/relative light unit. The cells were treated with various antimicrobial agents, and the emitted bioluminescence was measured. With the bioluminescent measurements, the results were obtained within hours compared to the days required for agar plates, and also, the kinetics of the antibacterial actions could be followed. Thus, the light emission was found to be a reliable, sensitive, and real-time indicator of the bacteriostatic actions of the antimicrobial agents tested.

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Milk microbiome in dairy cattle and the challenges of low microbial biomass and exogenous contamination

Animal Microbiome ◽

10.1186/s42523-021-00144-x ◽

2021 ◽

Vol 3 (1) ◽

Author(s):

Jolinda Pollock ◽

Susannah J. Salter ◽

Rebecca Nixon ◽

Michael R. Hutchings

Keyword(s):

Dairy Cattle ◽

Antimicrobial Agents ◽

Bacterial Load ◽

Treatment Protocol ◽

Rrna Gene ◽

Microbiota Composition ◽

Milk Samples ◽

Antimicrobial Usage ◽

Significant Difference ◽

Contamination Effects

Abstract Background The blanket usage of antimicrobials at the end of lactation (or “drying off”) in dairy cattle is under increasing scrutiny due to concerns about antimicrobial resistance. To lower antimicrobial usage in dairy farming, farmers are now encouraged to use “selective dry cow therapy” whereby only cows viewed as at high risk of mastitis are administered antimicrobial agents. It is important to gain a better understanding of how this practice affects the udder-associated microbiota and the potential knock-on effects on antimicrobial-resistant bacterial populations circulating on the farm. However, there are challenges associated with studying low biomass environments such as milk, due to known contamination effects on microbiome datasets. Here, we obtained milk samples from cattle at drying off and at calving to measure potential shifts in bacterial load and microbiota composition, with a critical assessment of contamination effects. Results Several samples had no detectable 16S rRNA gene copies and crucially, exogenous contamination was detected in the initial microbiome dataset. The affected samples were removed from the final microbiome analysis, which compromised the experimental design and statistical analysis. There was no significant difference in bacterial load between treatments (P > 0.05), but load was lower at calving than at drying off (P = 0.039). Escherichia coli counts by both sequence and culture data increased significantly in the presence of reduced bacterial load and a decreasing trend of microbiome richness and diversity. The milk samples revealed diverse microbiomes not reflecting a typical infection profile and were largely comprised of gut- and skin-associated taxa, with the former decreasing somewhat after prolonged sealing of the teats. Conclusions The drying off period had a key influence on microbiota composition and bacterial load, which appeared to be independent of antimicrobial usage. The interactions between drying off treatment protocol and milk microbiome dynamics are clearly complex, and our evaluations of these interactions were restricted by low biomass samples and contamination effects. Therefore, our analysis will inform the design of future studies to establish whether different selection protocols could be implemented to further minimise antimicrobial usage.

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From Evidence to Clinical Guidelines in Antibiotic Treatment in Acute Otitis Media in Children

Antibiotics ◽

10.3390/antibiotics10010052 ◽

2021 ◽

Vol 10 (1) ◽

pp. 52

Author(s):

Elena Lia Spoială ◽

Gabriela Dumitrita Stanciu ◽

Veronica Bild ◽

Daniela Carmen Ababei ◽

Cristina Gavrilovici

Keyword(s):

Otitis Media ◽

Antibiotic Treatment ◽

Antimicrobial Agents ◽

Acute Otitis Media ◽

Antimicrobial Treatment ◽

Health Concern ◽

First Line ◽

Amoxicillin Clavulanate ◽

Third Line ◽

Antimicrobial Treatments

Acute otitis media (AOM) in children represents a public health concern, being one of the leading causes of health care visits and antibiotic prescriptions worldwide. The overall aim of this paper is to unravel the major current insights into the antibiotic treatment of AOM in children. Our approach is three-fold: 1. a preclinical evaluation of antibiotics in animal models of AOM stressing on the advantages of different species when testing for different schemes of antibiotics; 2. an overview on the new antimicrobial agents whose efficacy has been demonstrated in refractory cases of AOM in children; and 3. an analysis of the different guidelines stressing on the differences and similarities between the various schemes of antibiotic treatment. The preferred therapeutic agents remain amoxicillin and the amoxicillin-clavulanate combination for AOM caused by Streptococcus pneumoniae, whereas oral cephalosporin is preferred in AOM due to Moraxella catarrhalis and Haemophilus influenzae. As for the second and third line antimicrobial treatments, there is a wide variety of suggested antibiotic classes with variations in duration and posology. The decision to prescribe antimicrobial treatment as a first-line choice is based on the severity of the symptoms in 16 of the guidelines included in this review.

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