Comparative In Vitro Killing by Pradofloxacin in Comparison to Ceftiofur, Enrofloxacin, Florfenicol, Marbofloxacin, Tildipirosin, Tilmicosin and Tulathromycin against Bovine Respiratory Bacterial Pathogens.

Pradofloxacin is the newest of the veterinary fluoroquinolones to be approved for use in animals-initially companion animals and most recently food animals. It has a broad spectrum of in vitro activity, working actively against Gram-positive/negative, atypical and some anaerobic microorganisms. It simultaneously targets DNA gyrase (topoisomerase type II) and topoisomerase type IV, suggesting a lower propensity to select for antimicrobial resistance. The purpose of this study was to determine the rate and extent of bacterial killing by pradofloxacin against bovine strains of Mannheimia haemolytica and Pasteurella multocida, in comparison with several other agents (ceftiofur, enrofloxacin, florfenicol, marbofloxacin, tildipirosin, tilmicosin and tulathromycin) using four clinically relevant drug concentrations: minimum inhibitory and mutant prevention drug concentration, maximum serum and maximum tissue drug concentrations. At the maximum serum and tissue drug concentrations, pradofloxacin killed 99.99% of M. haemolytica cells following 5 min of drug exposure (versus growth to 76% kill rate for the other agents) and 94.1-98.6% of P. multocida following 60-120 min of drug exposure (versus growth to 98.6% kill rate for the other agents). Statistically significant differences in kill rates were seen between the various drugs tested depending on drug concentration and time of sampling after drug exposure.

Comparative Minimum Inhibitory and Mutant Prevention Drug Concentrations for Pradofloxacin and Seven Other Antimicrobial Agents Tested against Bovine Isolates of Mannheimia haemolytica and Pasteurella multocida.

Pradofloxacin-a dual-targeting fluoroquinolone-is the most recent approved for use in food animals. Minimum inhibitory and mutant prevention concentration values were determined for pradofloxacin, ceftiofur, enrofloxacin, florfenicol, marbofloxacin, tildipirosin, tilmicosin, and tulathromycin. For M. haemolytica strains, MIC50/90/100 values were ≤0.016/≤0.016/≤0.016 and MPC50/90/100 values were 0.031/0.063/0.063; for P. multocida strains, the MIC50/90/100 values ≤0.016/≤0.016/0.031 and MPC50/90/100 ≤ 0.016/0.031/0.063 for pradofloxacin. The pradofloxacin Cmax/MIC90 and Cmax/MPC90 values for M. haemolytica and P. multocida strains, respectively, were 212.5 and 53.9 and 212.5 and 109.7. Similarly, AUC24/MIC90 and AUC24/MPC90 for M. haemolytica were 825 and 209.5, and for P. multocida, they were 825 and 425.8. Pradofloxacin would exceed the mutant selection window for >12-16 h. Pradofloxacin appears to have a low likelihood for resistance selection against key bovine respiratory disease bacterial pathogens based on low MIC and MPC values.

In vitro killing of drug susceptible and multidrug resistant bacteria by amikacin considering pulmonary drug concentrations based on an inhaled formulation.

Nosocomial infections with drug resistant bacteria impact morbidity and mortality, length of therapy and stay and the overall cost of treatment. Key pathogens with ventilator associated pneumonia may be drug-susceptible or multi-drug resistant and inhaled amikacin has been investigated as an adjunctive therapy option. High pulmonary drug concentrations (epithelial lining fluid [ELF]) along with minimal systemic toxicity is seen as an advantage to inhaled formulations. In vitro killing of bacteria using clinically relevant drug concentrations provide insight on bug-drug interactions. The aim of this study was to measure killing of clinical isolates of Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus and methicillin-susceptible S. aureus using the minimum inhibitory concentration (MIC), mutant prevention concentration (MPC) and median (976 µg/ml) ELF drug concentration for amikacin. Overall killing took longer at the MIC drug concentration and was inconsistent amongst the pathogens tested with the percentage of bacteria killed following 180 min of drug exposure ranging from growth in the presence of the drug to 95% kill. At the MPC drug concentrations, killing ranged from 55-88% for all pathogens following 30 min of drug exposure and increased to 99-100% following 180 min of drug exposure. At the ELF amikacin tested, killing was 81-100% following 20 min and 94-100% by 30 min of drug exposure. Rapid killing against MDR respiratory pathogens by amikacin ELF drug concentrations is encouraging.

A nested cohort 5-year Canadian surveillance of Gram-negative antimicrobial resistance for optimized antimicrobial therapy.

We analyzed 5 years (2016-2020) of nested Canadian data from the Study for Monitoring Antimicrobial Resistance Trends (SMART) to identify pathogen predominance and antimicrobial resistance (AMR) patterns of adult Gram-negative infections in Canadian health care and to complement other public surveillance programs and studies in Canada. A total of 6853 isolates were analyzed from medical (44%), surgical (18%), intensive care (22%) and emergency units (15%) and from respiratory tract (36%), intra-abdominal (25%), urinary tract (24%) and bloodstream (15%) infections. Overall, E. coli (36%), P. aeruginosa (18%) and K. pneumoniae (12%) were the most frequent isolates and P. aeruginosa was the most common respiratory pathogen. 18% of Enterobacterales species were ESBL positive. Collective susceptibility profiles showed that P. aeruginosa isolates were highly susceptible (> 95%) to ceftolozane/tazobactam and colistin, though markedly less susceptible (58-74%) to other antimicrobials tested. Multi-drug resistance (MDR) was present in 10% of P. aeruginosa isolates and was more frequent in those from respiratory infections and from ICU than non-ICU locations. Of P. aeruginosa isolates that were resistant to combinations of ceftazidime, piperacillin/tazobactam and meropenem, 73-96% were susceptible to ceftolozane/tazobactam over the period of the study. These national data can now be combined with clinical prediction rules and genomic data to enable expert antimicrobial stewardship applications and guide treatment policies to optimize adult patient care.

Immunomodulatory Effects of Macrolides Considering Evidence from Human and Veterinary Medicine.

Macrolide antimicrobial agents have been in clinical use for more than 60 years in both human and veterinary medicine. The discovery of the non-antimicrobial properties of macrolides and the effect of immunomodulation of the inflammatory response has benefited patients with chronic airway diseases and impacted morbidity and mortality. This review examines the evidence of antimicrobial and non-antimicrobial properties of macrolides in human and veterinary medicine with a focus toward veterinary macrolides but including important and relevant evidence from the human literature. The complete story for these complex and important molecules is continuing to be written.

Bacteremia and polyarticular septic arthritis secondary to Moraxella bovis in a pregnant patient with HIV who injects drugs.

CASE PRESENTATION: We report a rare case of Moraxella bovis bacteremia and polyarticular septic arthritis in a 37-year-old pregnant woman with HIV who injects drugs. Two sets of blood cultures obtained 5 hours apart were positive for gram-negative bacilli, and purulent fluid was present intra-operatively from both her left knee and her right third MCP joints. DIAGNOSIS: Organism identification using ligation sequencing confirmed both her blood culture and synovial tissue isolates as M. bovis. Her infection was initially treated with third-generation cephalosporins and later changed to moxifloxacin because of a drug reaction; although she defervesced clinically with improvement in her C-reactive protein levels, she died most likely as a result of a non-traumatic fat embolism after an elective cesarean delivery. DISCUSSION: In contrast to Moraxella catarrhalis, other Moraxella species are rarely associated with disease in human hosts. M. bovis is classically associated with infectious bovine keratoconjunctivitis in cattle; interestingly, our patient denied significant animal exposure. To the authors' knowledge, this is the first case describing infection secondary to M. bovis in an adult host.

PRÉSENTATION DU CAS: Les auteurs rendent compte d'un rare cas de bactériémie à Moraxella bovis et d'arthrite septique polyarticulaire chez une femme enceinte de 37 ans atteinte du VIH qui s'injectait des médicaments. Deux séries d'hémocultures obtenues à cinq heures d'intervalle étaient positives aux bacilles Gram négatif, et du liquide purulent a été observé dans le genou gauche et la troisième articulation métacarpophalangienne pendant la période peropératoire. DIAGNOSTIC: La détection des organismes au moyen du séquençage par ligature a confirmé que les isolats des hémocultures et des tissus synoviaux contenaient du M. bovis. L'infection a d'abord été soignée au moyen de céphalosporines de troisième génération, qui ont ensuite été remplacées par de la moxifloxacine en raison d'une réaction au médicament. Même si elle a présenté une défervescence sur le plan clinique et que les taux de protéine C-réactive se sont améliorés, la patiente est décédée, probablement à cause d'une embolie graisseuse d'origine non traumatique après une césarienne non urgente. DISCUSSION: Contrairement au Moraxella catarrhalis, les autres espèces de Moraxella sont rarement associées à des maladies chez les hôtes humains. Le M. bovis est normalement relié à une kératoconjonctivite bovine infectieuse chez le bétail. Fait intéressant, la patiente a nié une exposition importante à des animaux. À la connaissance des auteurs, il s'agit de la première description d'une infection secondaire au M. bovis chez un hôte adulte.

Global update on the in vitro activity of tigecycline and comparators against isolates of Acinetobacter baumannii and rates of resistant phenotypes (2016-2018).

OBJECTIVES: This study presents 2016-2018 in vitro antimicrobial activity data and rates of resistant phenotypes for clinical isolates of Acinetobacter baumannii from Africa/Middle East, Asia/South Pacific, Europe, Latin America, and North America. METHODS: A total of 4320 A. baumannii isolates were collected across all regions between 2016 and 2018. The in vitro antimicrobial activities of amikacin, colistin, levofloxacin, meropenem, and tigecycline were determined using the broth microdilution methodology of the Clinical and Laboratory Standards Institute. MICs were interpreted using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints (version 11.0). Rates of subsets that were resistant to amikacin, colistin, levofloxacin, and meropenem, according to EUCAST breakpoints, are also presented. RESULTS: In each region, tigecycline and colistin were active against isolates of A. baumannii (MIC90 values, 1 or 2 mg/L) and the lowest rate of resistance was to colistin (1.2%-7.3%). The rates of resistance to the panel of agents were generally lower among A. baumannii from North America (1.3%-42.7%), compared with the other regions. Fewer than 11% of meropenem-resistant A. baumannii were also resistant to colistin. The rates of amikacin-, levofloxacin- and meropenem-resistant A. baumannii were lowest in North America and mostly higher in Africa/Middle East and Latin America. CONCLUSION: In each geographical region, tigecycline and colistin maintained good in vitro antimicrobial activity against isolates of A. baumannii, including antimicrobial-resistant subsets. The higher rates of meropenem-resistant isolates, particularly in Africa/Middle East and Latin America, require continued monitoring because of the scarcity of effective treatment options.

Characterization of Polybacterial versus Monobacterial Conjunctivitis Infections in Pediatric Subjects Across Multiple Studies and Microbiological Outcomes with Besifloxacin Ophthalmic Suspension 0.6.

INTRODUCTION: The choice of empiric therapy for bacterial conjunctivitis should be guided by an awareness of typical causative pathogen distributions. Bacterial conjunctivitis can be polybacterial, although pediatric-specific data are lacking. METHODS: This was a post-hoc analysis of data in pediatric subjects (1-17 years) from five bacterial conjunctivitis trials evaluating besifloxacin ophthalmic solution 0.6%. RESULTS: Of the 730 pediatric subjects with culture-confirmed conjunctivitis, nearly one-fourth (23.6%) had polybacterial infections and three-fourths (76.4%) had monobacterial infections at baseline. In both polybacterial and monobacterial infections, the most prevalent organisms were Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus, and Streptococcus mitis/S. mitis group. In polybacterial versus monobacterial infections, S. mitis/S. mitis group (8.7% vs 4.3%; P=0.032) and Moraxella catarrhalis (4.7% vs 0.5%; P<0.001) were identified more frequently, whereas S. pneumoniae (14.0% vs 28.1%; P<0.001) was identified less frequently, as the dominant infecting species. MICs for individual species were similar for tested antibiotics regardless of polybacterial or monobacterial infection, except Staphylococcus epidermidis for which fluoroquinolone MICs were ≥3 dilutions higher for isolates of this species sourced from polybacterial compared to monobacterial infections. Treatment with besifloxacin resulted in microbial eradication in 79.1% of polybacterial and 92.3% of monobacterial infections (P≤0.005 vs vehicle). DISCUSSION: One in four pediatric bacterial conjunctivitis infections is polybacterial, highlighting the need for a broad-spectrum antibiotic when choosing empiric therapy.

In Vitro Killing of Canine Urinary Tract Infection Pathogens by Ampicillin, Cephalexin, Marbofloxacin, Pradofloxacin, and Trimethoprim/Sulfamethoxazole.

Urinary tract infections are common in dogs, necessitating antimicrobial therapy. We determined the speed and extent of in vitro killing of canine urinary tract infection pathogens by five antimicrobial agents (ampicillin, cephalexin, marbofloxacin, pradofloxacin, and trimethoprim/sulfamethoxazole) following the first 3 h of drug exposure. Minimum inhibitory and mutant prevention drug concentrations were determined for each strain. In vitro killing was determined by exposing bacteria to clinically relevant drug concentrations and recording the log10 reduction and percent kill in viable cells at timed intervals. Marbofloxacin and pradofloxacin killed more bacterial cells, and faster than other agents, depending on the time of sampling and drug concentration. Significant differences were seen between drugs for killing Escherichia coli, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus pseudintermedius strains. At the maximum urine drug concentrations, significantly more E. coli cells were killed by marbofloxacin than by ampicillin (p < 0.0001), cephalexin (p < 0.0001), and TMP/SMX (p < 0.0001) and by pradofloxacin than by cephalexin (p < 0.0001) and TMP/SMX (p < 0.0001), following 5 min of drug exposure. Rapid killing of bacteria should inform thinking on drug selection for short course therapy for uncomplicated UTIs, without compromising patient care, and is consistent with appropriate antimicrobial use and stewardship principles.

In Vitro Time-Kill of Common Ocular Pathogens with Besifloxacin Alone and in Combination with Benzalkonium Chloride.

BACKGROUND: Besifloxacin ophthalmic suspension 0.6% (w/v%) contains benzalkonium chloride (BAK) as a preservative. We evaluated the in vitro time-kill activity of besifloxacin, alone and in combination with BAK, against common bacteria implicated in ophthalmic infections. METHODS: The activity of besifloxacin (100 µg/mL), BAK (10, 15, 20, and 100 µg/mL), and combinations of besifloxacin and BAK were evaluated against isolates of Staphylococcus epidermidis (n = 4), Staphylococcus aureus (n = 3), Haemophilus influenzae (n = 2), and Pseudomonas aeruginosa (n = 2) in time-kill experiments of 180 min duration. With the exception of one S. aureus isolate, all of the staphylococcal isolates were methicillin- and/or ciprofloxacin-resistant; one P. aeruginosa isolate was ciprofloxacin-resistant. The reductions in the viable colony counts (log10 CFU/mL) were plotted against time, and the differences among the time-kill curves were evaluated using an analysis of variance. Areas-under-the-killing-curve (AUKCs) were also computed. RESULTS: Besifloxacin alone demonstrated ≥3-log killing of P. aeruginosa (<5 min) and H. influenzae (<120 min), and approached 3-log kills of S. aureus. BAK alone demonstrated concentration-dependent killing of S. epidermidis, S. aureus and H. influenzae, and at 100 µg/mL produced ≥3-log kills in <5 min against these species. The addition of BAK (10, 15, and 20 µg/mL) to besifloxacin increased the rate of killing compared to besifloxacin alone, with earlier 3-log kills of all species except P. aeruginosa and a variable impact on S. aureus. The greatest reductions in AUKC were observed among H. influenzae (8-fold) and S. epidermidis (≥5-fold). Similar results were found when the isolates were evaluated individually by their resistance phenotype. CONCLUSIONS: In addition to confirming the activity of 100 µg/mL BAK as a preservative in the bottle, these data suggest that BAK may help besifloxacin to achieve faster time-kills on-eye in the immediate timeframe post-instillation before extensive dilution against bacterial species implicated in ophthalmic infections, including drug-resistant S. epidermidis. Greater killing activity may help prevent resistance development and/or help treat resistant organisms.

Clinical microbiology laboratories and COVID-19: an interview with Joseph Blondeau.

This interview was conducted by Atiya Henry, Commissioning Editor of Future Microbiology. Joseph M Blondeau, MSc, PhD, RSM(CCM), SM(AAM), SM(ASCP), FCCP is a Clinical Microbiologist and Head of Clinical Microbiology at Royal University Hospital (Saskatoon Health Region) and the University of Saskatchewan in Saskatoon, Canada. He is also the Provincial Clinical Lead for Microbiology in Saskatchewan, Canada. He holds a Masters of Sciences in Microbiology from Dalhousie University (1985) and a Doctor of Philosophy in Medical Microbiology from the University of Manitoba (1989). Following completion of his PhD, he completed an 1-month post-doctoral training in an infectious diseases research laboratory at Dalhousie University and following which he completed a 2-year post-doctoral residency training program in Clinical Microbiology, also at Dalhousie University. He holds appointments as a Clinical Associate Professor of Pathology, Adjunct Professor of Microbiology and Immunology and Clinical Associate Professor of Ophthalmology. He teaches to undergraduate and graduate students in the areas of microbiology, infectious diseases, antimicrobial agents and pharmacology. Dr Blondeau's main research interests are in the area of antimicrobial agents and antimicrobial resistance, clinical microbiology and clinical outcomes associated with antimicrobial therapy in both human and veterinary medicine.

Diagnostic clinical microbiology.

Technological advancements have changed the way clinical microbiology laboratories are detecting and identifying bacterial, viral, parasitic, and yeast/fungal pathogens. Such advancements have improved sensitivity and specificity and reduce turnaround time to reporting of clinically important results. This article discusses and reviews some traditional methodologies along with some of the technological innovations introduced into diagnostic microbiology laboratories. Some insight to what might be available in the coming years is also discussed.

Recovery of borderline oxacillin-resistant Staphylococcus pseudintermedius (BORSP) from bone and soft tissue of a rheumatoid arthritis patient with severe osteoporosis: transmission from the family dog.

We report a case of borderline oxacillin-resistant S. pseudintermedius (BORSP) in a rheumatoid arthritis patient with severe osteoporosis. The organism is also resistant to erythromycin and clindamycin. We also present clear evidence on transmission from the family dog.

Characterization of baseline polybacterial versus monobacterial infections in three randomized controlled bacterial conjunctivitis trials and microbial outcomes with besifloxacin ophthalmic suspension 0.6.

BACKGROUND/PURPOSE: To date, studies examining polymicrobial infections in ocular disease have mostly been limited to keratitis or endophthalmitis. We characterized polybacterial infections compared to monobacterial infections in prior clinical studies evaluating besifloxacin ophthalmic suspension 0.6% for the treatment of bacterial conjunctivitis and report on associated microbiological outcomes. METHODS: In this post-hoc analysis, microbiological data for subjects with conjunctivitis due to one or more than one bacterial species in three previous studies (two vehicle-, one active-controlled) of besifloxacin were extracted. Bacterial species identified at baseline were deemed causative if their colony count equaled or exceeded species-specific prespecified threshold criteria. In subjects with polybacterial infections, the fold-increase over threshold was used to rank order the contribution of individual species. Baseline pathogens and their minimum inhibitory concentrations (MICs) for common ophthalmic antibiotics were compared by infection type, as were microbial eradication rates following treatment with besifloxacin. RESULTS: Of 1041 subjects with culture-confirmed conjunctivitis, 17% had polybacterial and 83% had monobacterial conjunctivitis at baseline. In polybacterial compared to monobacterial infections, Haemophilus influenzae and Streptococcus pneumoniae were identified less frequently as the dominant infecting species (P = 0.042 and P<0.001, respectively), whereas Streptococcus mitis/S. mitis group was identified more frequently as dominant (P<0.001). Viral coinfection was also identified more frequently in polybacterial infections (P<0.001). Staphylococcus aureus was the most common coinfecting species in polybacterial infections and the second most common dominant species in such infections. With few exceptions, MICs for individual species were comparable regardless of infection type. Clinical microbial eradication rates with besifloxacin were high regardless of infection type (P≤0.016 vs vehicle at follow-up visits). CONCLUSIONS: Approximately one in five subjects with bacterial conjunctivitis are infected with more than one bacterial species underscoring the need for a broad-spectrum antibiotic for such infections. Besifloxacin treatment resulted in robust eradication rates of these infections comparable to monobacterial infections. TRIAL REGISTRATION: NCT000622908, NCT00347932, NCT00348348.

Bacteremia with Staphylococcus pseudintermedius in a 4 month old pediatric oncology patient.

Staphylococcus pseudintermedius colonizes and is a pathogen of dogs and is being increasingly recognized from specimens from humans with various infections. We describe a case of S. pseudintermedius bacteremia in a 4 month old pediatric oncology patient with clear evidence of transmission from the family pet.

Methicillin-resistant Staphylococcus aureus replication in the presence of high (≥32 µg/ml) drug concentration of vancomycin as seen by electron microscopy.

Methicillin-resistant Staphylococcus aureus (MRSA) has unfortunately become a common pathogen in many healthcare facilities. In many institutions, vancomycin remains the preferred agent for treating serious MRSA infections including bacteraemia with or without endocarditis. The mutant prevention concentration (MPC) testing ≥109 colony forming units of bacteria, describes the antimicrobial drug concentration blocking the growth of the least susceptible cell from high density bacterial populations. With blood culture isolates of MRSA, we discovered strains with MPC values ≥32 µg/ml and viable cells could be readily recovered from agar plates containing 32 µg/ml of vancomycin. To investigate MRSA strains surviving in high concentrations of vancomycin on drug containing agar plates, we utilized electron microscopy to measure cell wall thickness as this has been previously reported as a potential mechanism of resistance1 along with septum thickening. Our data shows MRSA replication from high density bacterial populations in the presence of ≥32 µg/ml of vancomycin. Such observations may explain vancomycin failure in some patients and/or persistent bacteraemia and could potentially question the use of this drug in some critically ill patients in favour of an alternative agent.