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Microbial flora of odontogenic abscesses in pet guinea pigs
  1. A. Minarikova, DVM, PhD,
  2. K. Hauptman, DVM, PhD,
  3. Z. Knotek, Univ Prof., DVM, PhD, DipECZM (Herpetology) and
  4. V. Jekl, Assoc. Prof., DVM, PhD, DipECZM (Small Mammal)
  1. Avian and Exotic Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Palackého tř. 1946/1, Brno 61242, Czech Republic
  1. E-mail for correspondence: jeklv{at}vfu.cz, VladimirJekl{at}gmail.com

Abstract

Abscesses of odontogenic origin in guinea pigs pose a serious health problem and need to be treated with a combination of surgical and medical therapy. The aim of this prospective study was to describe the microbial flora of odontogenic abscesses associated with osteomyelitis in 24 pet guinea pigs, to perform antibiotic sensitivity testing, and to make recommendations for practitioners on the antibiotics of first choice. Inclusion criteria for the study included the animal being diagnosed with an odontogenic abscess which underwent surgery and was not pre-treated with an antibiotic. Inclusion criteria matched for 24 guinea pigs. Samples (pus, capsule and affected tooth/bone) for bacteriological examination were collected under sterile conditions during the surgical procedure. The most commonly isolated bacteria from abscesses of odontogenic origin were Bacteroides fragilis in 12.8 per cent (6/47) of cases, Pasteurella multocida in 10.6 per cent (5/47) and Peptostreptococcus anaerobius in 8.5 per cent (4/47). Aerobic bacterial species only were isolated in 29.2 per cent (7/24) of cases, anaerobic bacteria only were isolated in 33.3 per cent (8/24), and mixed infection with anaerobic and aerobic bacterial species was seen in 37.5 per cent (9/24). Aerobes (n=20) were sensitive to enrofloxacin and marbofloxacin in 100 per cent of samples, benzylpenicillin potassium (penicillin G, PNCG) in 90 per cent, cephalotin in 85 per cent, amoxicillin-clavulanate in 75 per cent, doxycycline in 70 per cent, gentamicin in 65 per cent and trimethoprim-sulfamethoxazole in 55 per cent. Anaerobes (n=27) were sensitive to amoxicillin-clavulanate in 100 per cent of cases, clindamycin in 96.3 per cent, metronidazole in 92.6 per cent, PNCG in 92.6 per cent and cephalotin in 74.1 per cent. As guinea pigs are strictly herbivorous animals, based on the results of this study the recommended antibiotic treatment for odontogenic abscesses is a combination of fluoroquinolones and metronidazole.

  • Guinea pigs
  • Bacterial diseases
  • Dentistry
  • Rodents
  • osteomyelitis
  • abscess
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Introduction

A recent retrospective study reviewed the disease prevalence in 1000 pet guinea pigs presented to a single university exotic animal clinic over a five-and-a-half-year period (Minarikova and others 2015). Dental disease was the most common condition, seen in 36.3 per cent of cases. Odontogenic abscesses, which were always diagnosed along with dental disease, were seen in 31 out of 1000 cases (Minarikova and others 2015). The incidence of odontogenic abscesses in guinea pigs (6.7 per cent) is much lower than in rabbits (22.7 per cent) (Jekl and others 2008), but this condition is always associated with moderate to very extensive life-threatening osteomyelitis (Harcout-Brown 2009, Capello and Lennox 2012). Abscesses of odontogenic origin in guinea pigs pose a serious health problem and may manifest as facial masses, respiratory disease and/or exophthalmos (retrobulbar mass) depending on the affected jaw (Mayer and Donelly 2013, Minarikova and others 2015). Treatment consists of extraction of the affected tooth/teeth, removal of the affected bone, thorough wound debridement, supportive care, analgesia and antibiotic administration. The use of antibiotics should be based on bacterial culture and antibiotic sensitivity testing (Capello 2008). However, information about microbial flora of odontogenic abscesses in guinea pigs is limited; therefore interpretation of the results of bacteriology may be challenging. Information about antibiotic therapy of facial abscesses in domestic guinea pigs is reported only as a summary about the treatment of facial abscesses in rodents or in individual clinical cases (Souza and others 2006, Capello and Lennox 2012).

The aim of this study was to describe the microbial flora of odontogenic abscesses associated with osteomyelitis in 24 pet guinea pigs, to perform antibiotic sensitivity testing, and to make recommendations for practitioners on the antibiotics of first choice.

Material and Methods

Animals

A prospective study was conducted from April 2010 to April 2015. Seventy-three domestic guinea pigs (Cavia aperea f porcellus, 35 females and 38 males) with private owners were examined at the authors’ clinic and were diagnosed with odontogenic abscess. The guinea pigs were either presented for a medical problem or a regular health check. Their bodyweight ranged from 440 g to 1.29 kg (mean±SD 0.8±0.14 kg) and their age ranged from three months to seven years (2.94±1.22 years).

Inclusion criteria for the study

Inclusion criteria for the study included animals diagnosed with odontogenic abscesses which underwent surgery and had not been pretreated with antibiotics. These criteria matched for 24 guinea pigs.

Odontogenic abscesses were diagnosed based on clinical symptoms, physical examination, stomatoscopy, skull radiography, and/or CT. The surgical treatment consisted of a sterile extraoral approach with extraction of the affected tooth/teeth, removal of the affected bone, thorough wound debridement, eye enucleation (when indicated), and wound marsupialisation.

Sample collection

Samples for bacteriological examination were collected under sterile conditions during the surgical procedure. All the affected tissues, part of the affected tooth, bone and abscess capsule, and pus were placed into Amies transport media (Amies Agar Gel Medium Transport Swab with charcoal; COPAN Italia) and delivered to the accredited bacteriological laboratory (Synlab Czech s.r.o.).

Isolation and identification of bacteria

Bacterial isolation and cultivation followed standard procedures for bacteriological examination of abscesses, which was approved by the Clinical and Laboratory Standards Institute. The examined sample material was put on a glass slide and Gram stained. The material was further inoculated onto both blood agar (Oxoid, Basingstoke, UK) and chromogenic agar. A quarter of CNA medium (colistin-nalidixic acid blood agar; Oxoid) was inoculated with a swab. The material was then further inoculated into a nutrient broth. Inoculated plates were incubated for 18 to 24 hours at 37°C in the incubator with increased carbon dioxide (CO2) pressure (blood agar, CNA) and in a thermostat with a normal atmosphere at 37°C. Subsequently the material was plated onto both blood agar (thermostat with increased tension CO2) and chromogenic agar (thermostat with normal atmosphere), for 18 to 24 hours at 37°C. The first assessment of the solid media was made after 18 to 24 hours of incubation.

Antimicrobial susceptibility testing

Antibiotic sensitivity tests were performed by semiquantitative diffusion assay, by quantitative dilution method and by an E-test (Brown and Brown 1991). Three to five well-isolated colonies of the same morphological type from an agar plate culture were selected and transferred to the tryptic soy broth and then incubated at 35±2°C until it reached a turbidity of 0.5 McFarland standard (usually two to six hours). Within 15 minutes after adjusting the turbidity of the inoculum suspension, the Mueller-Hinton agar was inoculated over the entire sterile agar surface and drug-impregnated discs were applied.

Antimicrobial susceptibility testing included enrofloxacin (drug-impregnated disc, concentration 5 µg), marbofloxacin (5 µg), benzylpenicillin potassium (penicillin G (PNCG), 10 µg), cephalotin (30 µg), amoxicillin-clavulanate (30 µg), trimethoprim-sulfamethoxazole (25 µg), doxycycline (30 µg), metronidazole (80 µg), gentamicin (10 µg) and clindamycin (10 µg).

Each plate was examined after 16 to 18 hours of incubation and then in the next 6 to 8 hours. The antimicrobial agent was assigned as susceptible, intermediate, and resistant. The susceptibility interpretation and disc selection was based on approved methodology by the Clinical and Laboratory Standards Institute (2012a, b, Documents M02-A11 and M11-A8).

Results

Samples from 24 guinea pigs were collected with cultures yielding a total of 20 aerobic (11 species) isolates and 27 anaerobic (15 species) isolates (Table 1). The most commonly encountered bacteria were Bacteroides fragilis (6/47), Pasteurella multocida (5/47) and Peptostreptococcus anaerobius (4/47).

TABLE 1:

Aerobic and anaerobic bacteria obtained from facial abscess of odontogenic origin in 24 guinea pigs

Aerobic bacterial species only were isolated in 29.2 per cent (7/24) of cases, while anaerobic bacteria only were isolated in 33.3 per cent (8/24) of cases. Mixed infection with anaerobic and aerobic bacterial species was seen in 37.5 per cent (9/24) of cases. One bacterial species was isolated in 41.7 per cent (10/24) of cases, two bacterial species were isolated in 37.5 per cent (9/24), and three or more species were isolated in 20.8 per cent (5/24).

Aerobic bacteria were sensitive to enrofloxacin and marbofloxacin in 100 per cent (20/20) of samples, doxycycline in 70 per cent (14/20), gentamicin in 65 per cent (13/20) and trimethoprim-sulfamethoxazole in 55 per cent (11/20). Sensitivity to amoxicillin-clavulanate was found in 75 per cent (15/20) of samples, to cephalotin in 85 per cent (17/20) and to PNCG in 90 per cent (18/20).

Anaerobic bacteria were sensitive to amoxicillin-clavulanate in 100 per cent (27/27) of samples, clindamycin in 96.3 per cent (26/27), metronidazole in 92.6 per cent (25/27), PNCG in 92.6 per cent (25/27) and cephalotin in 74.1 per cent (20/27).

The results of bacterial sensitivity to selected antibiotics are summarised in Table 2. The most frequent resistance was detected to clindamycin (nine aerobic and one anaerobic bacterial strains), to trimethoprim-sulfamethoxazole (nine aerobic strains) and to cephalotin (three aerobic and five anaerobic stains). Pseudomonas aeruginosa was resistant to five different types of antibiotics (amoxicillin-clavulanate, gentamicin, doxycycline, cephalosporin, PNCG). P multocida and Streptococcus pneumoniae were resistant to three selected antibiotics. Anaerobe antibiotic resistance was seen in 10 isolates, but the resistance was always detected only to the one antibiotic.

TABLE 2:

Sensitivity of bacteria isolated from odontogenic abscesses in 24 guinea pigs to selected antibiotics

Discussion

Due to an increasing awareness by guinea pig breeders and veterinary professionals, an increasing number of owners require an exact diagnosis and treatment for dental disease (Minarikova and others 2015). The diagnosis is commonly based on results of imaging methods, laboratory analyses and bacteriology (Schweda and others 2014). Baumgartner (2004) argued that culture of the bacteria present in an abscess has a low sensitivity and specificity, due to the polymicrobial nature of the infection. However, for determining optimal antibiotic therapy, it is essential to know which pathogens are present in the disease process (WHO Media Centre 2015). This is done by cultivation of pathogens and by further testing of their sensitivity to different classes of antibiotics (Tyrrell and others 2002, Capello and Lennox 2012, Böhmer 2015).

Purulent material examination and intraoral cavity sampling showed a low recovery of strictly anaerobic bacteria and a low average number of isolates (Lewis and others 1990). In humans, to reduce the risk of contamination with normal oral microflora, the optimal method of sample collection is by aspiration of the purulent content of the odontogenic abscess through the intact mucosa after skin disinfection (Gomes and others 2004, Schweta and Prakash 2013). In the present study, a combination of samples (pus, abscess capsule, bone/tooth) were collected by an aseptic extraoral approach to avoid contamination of the samples by the oral cavity flora.

Disk diffusion testing, like other antimicrobial susceptibility testing assays, is an in vitro determination of antimicrobial susceptibility. These in vitro results may not always correlate with in vivo efficacy, and standardised guidelines should always be used. In the case of optimal dosing intervals for a particular drug, a minimal inhibition concentration needs to be determined (Clinical and Laboratory Standards Institute 2012a, b).

In a study by Tyrrell and others (2002) the most common cause of odontogenic abscesses in rabbits was a mixed infection, particularly with anaerobic Gram-negative rods (predominantly Fusobacterium nucleatum), anaerobic Gram-positive, non-sporulating rods (predominantly Actinomyces species), and aerobic Gram-positive cocci (especially the genus Streptococcus milleri). According to the results of the present study, odontogenic abscesses in guinea pigs are caused by anaerobic bacteria, or by a combination of aerobic and anaerobic bacterial infections, similar to the study performed in rabbits by Tyrrell and others (2002).

The most commonly isolated anaerobic bacteria from odontogenic abscesses in guinea pigs were B fragilis (5/47) and P anaerobius (4/47). B fragilis is an obligate anaerobic, rod shaped Gram-negative bacteria. It is a part of normal guinea pig and human intestinal microflora (Hildebrand and others 2012). In combination with other strictly anaerobic bacteria, B fragilis can cause localised abscesses on the skull, chest, peritoneum, liver, or on the genital organs (Ryan 2004), as well as causing bacteraemia (Kasper and Onderdonk 1982). P anaerobius is an anaerobic, Gram-positive, non-sporulating slow growing bacteria with increasing resistance to antibiotics (Higaki and others 2004). It is one of the aetiological factors of gingivitis and periodontitis in humans (Moore and others 1987). According to the present study it also found in guinea pigs.

The most common isolated aerobic bacterium from odontogenic abscesses in guinea pigs was P multocida. P multocida is a pathogenic, highly contagious bacterium that causes respiratory diseases in guinea pigs (Yarto-Jaramillo 2011). P multocida was isolated from odontogenic abscesses in five cases, which in comparison with rabbits (Taylor and others 2010, Jekl and others 2012) is a surprisingly more frequent finding.

Bacteria isolated from odontogenic abscesses from rabbits (Tyrrell and others 2002, Jekl and others 2012, Gardhouse and others 2015) and guinea pigs (present study) are sensitive to penicillins and clindamycin; however, these drugs can cause clostridial infections and toxaemia, and cannot be used in guinea pigs. Odontogenic abscesses in guinea pigs were, apart from surgical debridement, treated medically with marbofloxacin (Capello and Lennox 2012), enrofloxacin or metronidazole (Souza and others 2006). Due to frequent mixed aerobic and anaerobic infection, the severity of the life-threatening condition and the possible presence of resistant strains of bacteria, it is generally recommended to use a combination of antibiotics (Madison and others 2008). Based on results of the present study we recommend a combination of fluoroquinolones (enrofloxacin, marbofloxacin) with nitroimidazole antibiotics (metronidazole).

An alternative therapy for odontogenic abscesses is the application of topical antibiotics in the form of antibiotic-impregnated poly-methyl methacrylate (AIPMMA) beads. These enable high levels of antibiotic to be achieved at the site of infection with low systemic absorption (Tobias and others 1996, Meredith 2007, Taylor and others 2010). For the safe use of clindamycin, or other orally contraindicated AIPMMA beads, it is necessary to ensure that there is no communication between the wound and the oral cavity (and sometimes also no direct communication to the bloodstream). This prevents accidental ingestion of the AIPMMA beads. If left in place, AIPMMA beads mostly do not dissolve and once no longer releasing antibiotics they can cause a foreign body nidus and site for reinfection. Only two cases of a multiple-resistant (to five kinds of antibiotics) strain of P aeruginosa were isolated from guinea pig abscesses. This is important as P aeruginosa is a potential nosocomial pathogen (Lister and others 2009). As some of the other bacteria (Bacteroides species, Prevotella oris, Fusobacterium species) isolated in the present study may have zoonotic potential and can cause respiratory, skin, brain or mouth cavity infections (Kasper and Onderdonk 1982; Coggin 2006), it is necessary to use personal protective equipment during surgery. Thorough disinfection of the hospital environment where the sick guinea pigs are kept (cage/box) is also essential. Clients should be informed about any possible zoonotic potential of isolated bacteria from odontogenic abscesses in guinea pigs.

In conclusion, the most commonly isolated bacteria from abscesses of odontogenic origin in guinea pigs were B fragilis (12.8 per cent), Pasteurella multocida (10.6 per cent) and P anaerobius (8.5 per cent). Based on the results of the present study and due to the animals’ sensitivity to the antibiotic classes and resulting possible side effects, the authors recommend a combination of fluoroquinolones (enrofloxacin or marbofloxacin) with nitroimidazole antibiotics (metronidazole) as a first choice for the treatment of oral abscesses in guinea pigs. The primary cause of the disease should be addressed surgically (affected tooth and bone removal), as medical therapy alone is not sufficient (Capello and Lennox 2012, Jekl and others 2013). As these odontogenic abscesses are commonly associated with cheek teeth malocclusion, this condition should also be addressed.

Acknowledgments

This study was supported by grant project – IGA 28/2011/FVL.

References

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Footnotes

  • Provenance Not commissioned; externally peer reviewed.

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