Bacterial isolates and antimicrobial susceptibilities from odontogenic abscesses in rabbits: 48 cases

Orofacial masses in domestic rabbits: a retrospective review of 120 cases from 2 institutions, 2000-2023

Orofacial masses or swellings are a common presenting complaint in lagomorphs. Similar gross appearances of the masses can complicate clinical interpretation, and histologic review often provides the final diagnosis. Underlying causes vary from infectious to neoplastic. Although inflammatory changes are most commonly reported, various neoplasms occur, although the prevalence of specific tumor types is relatively unknown. We reviewed retrospectively 120 cases (87.5% biopsy, 12.5% autopsy) of neoplastic and non-neoplastic orofacial masses received from January 2000-February 2023 at 2 institutions: University of Guelph, Canada (Animal Health Laboratory and Department of Pathobiology), and Finn Pathologists, United Kingdom. All final diagnoses were achieved through histologic assessment. We included masses or mass-like swellings from the oral cavity, including the mandible and maxilla, and surrounding skin and soft tissues of the oral cavity and jaw. Submissions included pet and commercial (meat and fur) rabbits. Neoplastic lesions were most common (60%), including trichoblastomas, papillomas, melanocytic neoplasms, sarcomas, round-cell tumors, carcinomas (including squamous cell carcinoma), lipomas, odontogenic neoplasms, polyps, osteoma, neuroma, peripheral keratinizing ameloblastoma, and apocrine adenoma. Inflammatory diagnoses (30%) included abscesses, osteomyelitis, dermatitis, and sialadenitis. Other diagnoses (7%) included cysts, as well as hyperplastic skin and proliferative bone lesions. Three cases had no definitive diagnosis. The importance of histologic assessment in diagnosing orofacial "masses" in rabbits is highlighted, given that the most common diagnostic category overall was neoplasia.

Clinical diagnosis and outcome of cervicofacial cellulitis in pyrexic rabbits: six cases (2014-2021)

OBJECTIVES

To assess the signalment, history, exam findings, diagnostics, treatment and outcome of rabbits diagnosed with pyrexia and concurrent cervicofacial cellulitis.

MATERIALS AND METHODS

Retrospective evaluation of medical records of rabbits diagnosed with cervicofacial cellulitis and pyrexia based on physical exam, contrast-enhanced CT, clinicopathology and microbiology findings.

RESULTS

Six out of 1588 rabbits met the study inclusion criteria. Rabbits presented with a median age of 6 years (range, 8 months to 8 years) with a presenting complaint of anorexia or hyporexia. All rabbits had a rectal temperature >40.2°C (104.4°F). Physical exam and contrast-enhanced CT revealed unilateral submandibular and ipsilateral cervical diffuse soft tissue swelling in five of six rabbits. No antemortem evidence of periodontal or dental disease was found on physical exam or CT. Leucopenia was present in five of six rabbits. A left shift with marked toxic changes was present in all four rabbits, for which blood smears were reviewed. Bacterial cultures of the aspirated subcutaneous soft tissue swelling cultured Escherichia coli, Pasteurella multocida, Granulicatella adiacens, Streptococcus species, Haemophilus species and Bacteroides species. Treatment was pursued in five rabbits, where all rabbits received supportive care and four of five rabbits received systemic antibiotics. One rabbit was euthanased following a diagnosis of cervicofacial cellulitis. Three out of five rabbits continued to decline clinically despite medical management, and thus, euthanasia was pursued within 24 hours of starting treatment. Two rabbits responded to initial treatment and developed subsequent multi-focal abscessation. One rabbit was euthanased due to client cost constraints, and one rabbit died shortly after achieving clinical resolution of cervicofacial cellulitis.

CLINICAL SIGNIFICANCE

Cervicofacial cellulitis should be considered a differential diagnosis in pyrexic rabbits with facial or cervical swelling with medical and surgical management pursued for therapy.

In vitro and ex vivo antibacterial activity of levofloxacin against Pasteurella multocida and Escherichia coli isolated from rabbits (Oryctolagus cuniculus) - A preliminary study

Levofloxacin veterinary formulations are available in Argentina, China and India for the use in dogs, cattle, pig and sheep, but not currently in the rabbit. Only the extra-label use in rabbits is possible. Levofloxacin is not labelled for veterinary use in the EU or the USA. The activity of levofloxacin against rabbit pathogens Pasteurella multocida (P. multocida) and Escherichia coli (E. coli) was evaluated. Minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined in broth and serum for 10 P. multocida isolates and 5 E. coli isolates from rabbits. One isolate of each bacterial species was used for the time-killing curve study in vitro and ex vivo. In vitro AUC24 /MIC ratios were used for building the inhibitory pharmacodynamic Imax model. The P. multocida MIC were 0.008-0.5 μg/mL, MBC - 0.015-0.5 μg/mL. Escherichia coli MIC was 0.008-0.03 μg/mL and MBC - 0.03-0.25 μg/mL. Bacterial counts were reduced to the limit of detection after 24 h with levofloxacin concentrations of 2 MIC and higher. All serum samples from rabbits treated with levofloxacin eliminated the bacteria within 24 h. AUC24 /MIC ratios for bacteriostatic, bactericidal and bacterial elimination effects for P. multocida and E. coli isolates were 21, 29 and 75 h and 27, 32 and 60 h, respectively. Proposed daily doses against P. multocida (MIC = 0.015 μg/mL) and E. coli (MIC = 0.03 μg/mL) isolates were calculated as ≤0.91 and ≤1.43 mg/kg, respectively. Fluoroquinolones are categorized by WHO as 'highest priority critically important antimicrobials'. Considering the increasing importance of antimicrobial stewardship, antimicrobials from a lower importance category that are active against the isolate of interest should be used in preference to fluoroquinolones. Fluoroquinolone use in veterinary medicine should be based on antimicrobial susceptibility testing in order to mitigate the risk to public health and prevent the spread of bacterial resistance.

Normal bacterial flora of the oral cavity in healthy pet rabbits (Oryctolagus cuniculus)

BACKGROUND

Rabbits often suffer from dental disease, including dental abscesses and periodontal/apical infections. With odontogenic infection and abscessation, a bacterial aetiology can be proven by bacterial culture and identification. Although studies exist on the bacterial flora of dental abscesses, the information available to date on the bacterial flora of the oral cavity in healthy rabbits is limited.

OBJECTIVES

This study aims to evaluate the cultivable bacterial flora in the oral cavity of healthy, young, pet rabbits and to compare this flora with the pathologic flora of odontogenic abscesses described in the literature.

METHODS

Samples were collected from the oral cavity of 33 healthy, young pet rabbits undergoing routine procedures. Oral cavity culture specimens were collected by rolling a sterile flocked paediatric swab in the mouth. Identification was first attempted by morphological assessment, Gram staining and mass spectrometry (MALDI-TOF). Colonies that could not be identified by mass spectrometry were identified by amplification and molecular sequencing of a part of the 16s rRNA gene.

RESULTS

Bacteria were recovered from 100% of oral swabs; 220 isolates of 35 different genera of bacteria were cultured. The most frequently isolated bacteria were Streptococcus sp. (19.8%), Rothia sp. (17.9%), Enterobacter sp. (7%), Staphylococcus sp. (6.6%) and Actinomyces sp. (5.7%). Four phyla are represented: Proteobacteria (38.3%), Firmicutes (30.5%), Actinobacteria (26.9%) and Bacteroidota (4.3%).

CONCLUSIONS

A wide range of commensal bacteria are present in the mouths of rabbits. Bacterial cultures taken from cases of dental abscesses often reveal bacteria. Streptococcus sp., Staphylococcus sp. and Actinomyces sp. are frequently found in cultures from dental abscesses, in contrast to Rothia and Enterobacter species. Our findings enhance the knowledge of rabbit microbial communities throughout oral cavity.

Pharmacokinetic profile and effect on the faecal microbiome of a single dose of pradofloxacin oral suspension in the rabbit (Oryctolagus cuniculus)

Fluoroquinolones are often administered to pet rabbits given their perceived safety and limited effects on anaerobic gut microbiota. However, the pharmacokinetics and relative safety of pradofloxacin, a third-generation veterinary fluoroquinolone with a much broader spectrum of activity, have not been reported in this species. Here, we determined the pharmacokinetic profile of a single dose of oral pradofloxacin in rabbits and evaluated effects on the faecal microbiome. Four mature female rabbits were administered pradofloxacin (25 mg/ml oral suspension), at a dose of 7.5 mg/kg. The pradofloxacin median (range) T_max was 4.50 (2.00-5.00) h, C_max 600.66 (395.85-886.72) ng/ml and t_½ was 1.27 (0.12-1.39) h. These results indicated that oral absorption of pradofloxacin was slower, and elimination faster compared with other fluoroquinolones in healthy rabbits, as well as relative to cats and dogs. Following treatment with pradofloxacin, faecal microbiota profiling showed some compositional differences between treated and control animals. This was the result of a significant decrease in the abundance of Proteobacteria, in particular bacteria belonging to the Pseudomonas, Atopostipes and Parabacteroides genera. The pharmacokinetic profile of pradofloxacin in rabbits should be further studied by increasing the sample size and using multiple-dose protocols (i.e. 7 days) to confirm safety. Further information on the effects of protein binding, higher dosages and disease on pradofloxacin pharmacokinetics in rabbits are needed before an accurate dosing regimen can be recommended.

Respiratory Disorders in Rabbits

Respiratory disorders are very common in rabbits. Rabbits are obligate nasal breathers, so "simple" rhinitis can cause severe respiratory distress and patient collapse. Causes of dyspnea could be of primary origin or secondary, whereby diseases primarily affecting other organs can result in respiratory embarrassment even if the respiratory system is healthy (eg, anemia, cardiac disease). Diagnosis is based on radiography, ultrasonography, endoscopy, computed tomography, and/or pathogen isolation. Once the diagnosis has been completed, treatment options should be discussed with the owner. The article describes the anatomy of the respiratory tract, diagnostics, and therapy for selected respiratory disorders in rabbits.

Identification of uncultured bacteria from abscesses of exotic pet animals using broad-range nested 16S rRNA polymerase chain reaction and Sanger sequencing

Background:

The Sanger sequencing technique has been questioned and challenged by advanced high-throughput sequencing approaches. Sanger sequencing seems to be an obsolete technology. However, there are still research problems that could be answered using the Sanger sequencing technology. Fastidious obligate anaerobic bacteria are mostly associated with abscesses in animals. These bacteria are difficult to isolate from abscesses and are frequently excluded due to the bias of conventional bacterial culturing.

Aim:

This study demonstrated the usefulness of a broad-range polymerase chain reaction (PCR) with Sanger sequencing to identify the majority population of bacteria in abscesses from exotic pet animals.

Materials and Methods:

This study performed a pilot investigation of abscesses from 20 clinical cases (17 rabbits, 2 hedgehogs, and 1 sugar glider) using standard culture methods for both aerobes and anaerobes and broad-range nested PCR targeting the 16S rRNA gene followed by the Sanger sequencing technique.

Results:

The standard culture and PCR techniques detected bacteria in 9 and 17 of 20 samples, respectively. From the 17 sequencings of the 16S rRNA, 10 PCR products were found to be closely related with obligate anaerobes including Bacteroides spp., Fusobacterium spp., Prevotella spp. Phylogenetic analysis using the rpoB gene revealed that the species for the Bacteroides was thetaiotaomicron and for the Fusobacterium was varium and nucleatum. However, the amplification of the rpoB gene for the Prevotella spp. was unsuccessful. Correlations between the standard culture and PCR techniques were found in 9 (6 positive and 3 negative samples) of 20 samples. Eleven samples were discordant between the standard culture and PCR techniques which were composed of eight samples negative by culture but positive by PCR and three samples had different bacteria by the culture and PCR techniques.

Conclusion:

According to this study, broad-range PCR combined with Sanger sequencing might be useful for the detection of dominant anaerobic bacteria in abscesses that were overlooked based on conventional bacterial culture.

Aortocavitary fistula secondary to vegetative endocarditis in a rabbit

A 4-year-old intact male mini lop rabbit (Oryctolagus cuniculus) was presented with a 2-week history of severe progressive lethargy. A right parasternal continuous heart murmur and an irregular rhythm were detected on physical examination. Echocardiography identified vegetative aortic and tricuspid valve (TV) endocarditis. There was an aortocavitary fistula between the right sinus of Valsalva into the right ventricle, creating a left-to-right intracardiac shunt. Based on the echocardiographic findings, it was suspected that the infection originated in the aortic valve, eroded through the periannular tissue, and secondarily infected the TV. Pleural and peritoneal effusion secondary to right-sided congestive heart failure was also found during the echocardiogram. Atrial fibrillation, conducted with a left bundle branch block morphology, was identified using electrocardiography. Necropsy findings directly correlated with the echocardiographic diagnosis; marked periodontal disease was also identified. Aerobic culture of the aortic and tricuspid vegetations resulted in significant growth of Haemophilus parainfluenzae. Haemophilus spp. belong to a group of similar gram-negative coccobacillus bacteria (HACEK group), which can act as an uncommon cause of endocarditis in humans. HACEK endocarditis is most commonly associated with oral infection and/or dental procedures in people. This is the first case report of a rabbit with periannular complications of infective endocarditis. It remains unknown whether dental disease resulted in endocarditis in this patient.