Treatment history and antimicrobial susceptibility results for Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni isolates from bovine respiratory disease cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2013 to 2015.

Bovine respiratory disease is the most costly disease facing the cattle industry. Increasing resistance to antimicrobial treatment has been presented as a significant contributing factor, often through summarized susceptibility testing data. We assessed the relationship between previous antimicrobial treatment and antimicrobial susceptibility results from isolates of Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni cultured from bovine respiratory cases submitted to the Iowa State University Veterinary Diagnostic Laboratory from 2013 to 2015. Antimicrobial susceptibility data from 1,251 bacterial isolates were included for analysis. More bacterial isolates from cattle that received antimicrobial treatment showed resistance compared to isolates from untreated cattle, and the percentage of resistant isolates increased as the number of antimicrobial treatments increased. Resistance to enrofloxacin, spectinomycin, tilmicosin, and tulathromycin was present in >75% of M. haemolytica isolates from cattle that had received 3 or more antimicrobial treatments; resistance to each of those 4 antimicrobials was present in ≤10% of M. haemolytica isolates from untreated cattle. Similar but less dramatic trends were apparent for isolates of P. multocida and H. somni. The percentage of multi-drug resistant bacterial isolates also increased with the number of treatments. Results of our study suggest that previous antimicrobial treatment may have a profound effect on antimicrobial susceptibility testing. Summarized susceptibility results from diagnostic laboratories should not be used to make generalized statements regarding trends in antimicrobial resistance without providing context regarding antimicrobial treatment history.

Benefits of adjunctive moxifloxacin in generalized aggressive periodontitis: a subgroup analyses in Aggregatibacter actinomycetemcomitans-positive/negative patients from a clinical trial.

AIM: The aim of the present study was to evaluate the influence of the baseline detection of Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) on the clinical outcomes of moxifloxacin (MOX) as an adjunct to full-mouth scaling and root planing (SRP) in generalized aggressive periodontitis (GAgP). METHODS: Forty patients were randomly distributed to two therapy protocols: SRP + placebo or SRP combined with MOX. A. actinomycetemcomitans was detected using culture methods. The significance of the treatment option (MOX or SRP + placebo) on the dependent variables (probing depth [PD] and clinical attachment level [CAL]), considering the interaction with the baseline detection of A. actinomycetemcomitans, was estimated. RESULTS: MOX therapy led to a higher significant PD reduction and CAL gain in A. actinomycetemcomitans-positive patients at baseline. In A. actinomycetemcomitans-positive patients, the reduction of sites ≥5 mm was higher in the MOX group. A. actinomycetemcomitans was not present in sites with PD ≥6 mm in the MOX group. The interactions of A. actinomycetemcomitans and MOX were significantly associated with CAL gain and PD reduction at 6 months. CONCLUSIONS: Adjunctive MOX trended toward better clinical responses in A. actinomycetemcomitans-positive patients at baseline. These results suggest that A. actinomycetemcomitans at baseline might modify the effect of adjunctive MOX in GAgP.

Inactivation of Aggregatibacter actinomycetemcomitans by two different modalities of photodynamic therapy using Toluidine blue O or Radachlorin as photosensitizers: an in vitro study.

Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is one of the periodontopathogens strongly associated with aggressive periodontitis. The aim of this investigation was to compare the effect of laser and light-emitting diode on the photodynamic inactivation of A. actinomycetemcomitans. Eighty-four samples of bacterial suspensions (200 µL) were prepared and divided in seven groups: control group (no treatment), laser group (indium-gallium-aluminum-phosphate laser with wavelength of 662 ± 0.1 nm, energy density of 6 j/cm(2), and irradiation time of 34 s), light-emitting diode (LED) group (wavelength 625-635 nm, energy density 6 j/cm(2), time of irradiation 30 s), Toluidine blue O (TBO) group (0.1 mg/mL), Radachlorin group (0.1 %), Radachlorin + laser group (after pre-irradiation time of 10 min, laser was irradiated), and TBO + LED group (after preirradiation time of 10 min, LED was irradiated). Then, 100 µL of each sample was cultured in brain heart infusion (BHI) plates and incubated for 48-72 h in microaerophilic atmosphere for colony counting. Application of Radachlorin + laser resulted in a significant decrease in the concentration of A. actinomycetemcomitans (P values <0.05). Photodynamic therapy with laser + Radachlorin was more effective than that of LED + TBO in suppression of this microorganism (P value <0.05). Within the limits of this study, it can be concluded that photodynamic inactivation using laser and Radachlorin was more effective than that of LED and TBO in eradication of A. actinomycetemcomitans.

Pharmacodynamics of amoxicillin against Mannheimia haemolytica and Pasteurella multocida and pharmacokinetic/pharmacodynamic (PK/PD) correlation in sheep.

Silicone-made tissue cages were implanted in sheep. Blood serum (SBS) and tissue cage fluid (TCF) samples were collected after amoxicillin intravenous and intramuscular administrations, at the dose of 15 mg/kg. Amoxicillin pharmacodynamics were studied in an artificial culture medium, SBS and TCF with use of a Mannheimia haemolytica and a Pasteurella multocida strain. A concentration-independent antimicrobial activity of amoxicillin was confirmed for levels higher than 0.79-1.75×MIC. This result favored the use of the percentage of the 24 h dosing interval during which drug levels remain above MIC as the appropriate pharmacokinetic/pharmacodynamic index. The subsequent correlation revealed that intravenous administration could be considered effective against "deep" infections caused by bacteria with MICs<1 µg/mL or "shallow" infections caused by bacteria with MICs<0.1 µg/mL. Intramuscular administration could be safely considered effective against both "deep" and "shallow" infections when the MICs of the targeted pathogens are lower than 1 µg/mL.