Successful treatment of a localised CDC Group EF-4a infection in a cat

Abstract

Organisms classified within the Center for Disease Control (CDC) Group eugonic fermenter (EF)-4a are facultative anaerobic, Gram-negative coccobacilli, thought to be of the family Neisseriaceae. CDC Group EF-4a is considered a component of normal oral flora in cats and dogs and is most commonly isolated from bite injuries of human patients. Most previously reported cases in cats have involved fatal necrotising pneumonia. We report a localised infection of the retropharyngeal/mandibular tissues in a cat, which responded to surgical drainage and a 5-week course of amoxycillin clavulanate. There are no prior reports of successfully treated EF-4a infections in cats in the literature.

A 3-year-old castrated Russian Blue cat was presented for a swollen jaw of 1-day duration and for inappetence of 3-days duration. Physical findings included pyrexia (39.8°C) and a 3.5 cm mass ventral to the right ramus of the mandible. The soft tissues of the ipsilateral jaw were swollen. No puncture wounds were evident after clipping of the overlying hair. The cat had moderate periodontal disease. Attempted needle aspiration of the mass did not produce appreciable amounts of material. Haematology revealed mild monocytosis (0.8×10⁹/l; reference range (RR): <0.7×10⁹) and serum biochemistry demonstrated only mild hyperglycaemia (9.1 mmol/l; RR: 4.2–8.1 mmol/l) likely attributable to stress; urinalysis was unremarkable.

The mass was initially assessed as being most likely either an enlarged right mandibular lymph node or a retropharyngeal abscess. Specific diagnostic possibilities included lymphadenitis, lymphoid hyperplasia secondary to a primary disease process elsewhere (eg, in the mouth), neoplasia (eg, lymphoma), foreign body granuloma or retropharyngeal infection.

The mass was explored surgically under general anaesthesia. It was situated beneath the masseter muscle and not well demarcated from adjacent tissues. It was not possible to determine by inspection whether the mass was a lymph node or surrounding tissue.

A small amount of pus, of which a representative specimen was collected for cytological evaluation and culture, was found centrally within the lesion. A portion of the mass was excised and bisected; half was placed in buffered formalin, the remainder was kept moist in a saline-soaked gauze swab. The specimens were submitted to the laboratory for histopathological and microbiological assessment, respectively. The wound was debrided and flushed with copious volumes of saline before the dead space and the skin incision were sutured in turn. The right lower canine tooth, right lower fourth premolar and left lower molar were extracted due to the presence of odontoclastic resorptive lesions. The cat was given amoxycillin clavulanate (122.5 mg subcutaneously) at the completion of the procedure and meloxicam (2.2 mg subcutaneously) after recovery from anaesthesia. Amoxycillin clavulanate (125 mg twice daily) was continued orally.

Histopathological examination revealed widespread necrosis and a marked mixed inflammatory response consisting mostly of neutrophils but also including large numbers of plasma cells and aggregates of lymphocytes. Fibroplasia was also prominent (Fig. 1A). It was not possible to determine microscopically if the sample had originally been a lymph node with the tissue architecture effaced by the severe inflammatory response, or whether it represented retropharyngeal tissue adjacent to the lymph node (Fig. 1B). No aetiological agents were identified in 5 μm sections stained with haematoxylin and eosin, periodic acid–Schiff, Ziehl–Neelsen, Giemsa, or Warthin Starry silver method.

Fig 1

Haematoxylin and eosin-stained histological section of the tissue resected from the swollen submandibular tissues. Note the fibroblastic response and mixed inflammatory infiltrate consisting of neutrophils, plasma cells and lymphocytes (A). In B, note also the aggregation of lymphocytes (arrow), which may be part of the inflammatory response or the remnants of the submandibular lymph node.

The titrated biopsy material was cultured aerobically and anaerobically on blood agar and aerobically in brain heart infusion broth. A light pure growth of a small, Gram-negative coccobacillus was observed after 3 days of aerobic incubation on blood agar. The organism grew anaerobically on subculture. The colonies at this time were 2 mm diameter, dull, dry, yellow, crinkled and non-haemolytic on blood agar.

The bacterium was non-motile, strongly oxidase positive, catalase positive, reduced nitrate to nitrogen gas, arginine dihydrolase positive and produced acid fermentatively from glucose. It was identified as CDC Group EF-4a by gas chromatography flame ionisation detection (GC-FID) using the Sherlock Microbial identification System Version 4.0 (MIDI Incorporated, Newark, Delaware, USA) at a reference laboratory (Centre for Infectious Diseases and Microbiology Laboratory Services, Westmead Hospital).

The isolate was susceptible to penicillin, ampicillin, first generation cephalosporins, doxycycline, gentamicin, enrofloxacin, ciprofloxacin, sulphonamides, erythromycin, clarithromycin and amoxycillin clavulanate but resistant to trimethoprim.

The cat was rechecked weekly. The swelling was reduced at each visit until it was no longer apparent. The mandibular lymph node on the affected side was palpably normal 3 weeks after surgical drainage. Amoxycillin clavulanate (125 mg orally twice daily) was continued for 2 weeks beyond clinical resolution (5 weeks total duration of therapy). The cat remains clinically well 8 months after treatment was completed.

Discussion

We report for the first time the successful treatment of a localised CDC EF-4a infection in a cat. CDC Group EF-4 is the designation given by the CDC for an as-yet unclassified, facultative anaerobic, Gram-negative coccobacillus, thought to be of the family Neisseriaceae. Two biovars are recognised: EF-4a biovars ferment glucose to produce acid and possess arginine dihydrolase activity, whereas EF-4b biovars do not. Both are considered as part of the normal oral flora of the dog and cat and have been recovered from the oral cavity of 30–82% of normal dogs (Saphir and Carter 1976, Bailie et al 1978); no specific studies appear to have been undertaken in cats but they are thought to be normal flora in this species also (Weaver et al 1985).

CDC Group EF-4 has most commonly been recovered from bite wounds to people caused by dogs and cats (Peel and Holmes 1980, Holmes et al 1990) and, on one occasion, a tiger (Isotalo et al 2000). Endophthalmitis with EF-4 infection in a child has been reported as a result of a cat scratch (Vartian and Septimus 1989). One report of EF-4 isolation from a human limb wound was allegedly caused by a wood splinter (Chatelain et al 1980), while in the only two reports of EF-4 bacteraemia in human patients, prior animal bites were denied by the patients (Dul et al 1983, Gonzalez et al 2001). The organism has also been isolated from the lung, spleen and kidney of a badger (Corboz et al 1993), multiple external abscesses in a mouse, the mandible of a wallaby and a human vagina (Holmes et al 1990). These disparate infections not obviously related to the oral cavity of dogs or cats may suggest alternative ecological niches for this organism.

Most prior reports of pathogenic infections in felidae have involved fatal necrotising pneumonia, the multifocal distribution of which suggests haematogenous dissemination. This has been reported in 16 cats (Jang et al 1973, McParland et al 1982, Drolet et al 1986, Ceyssens et al 1989, Corboz et al 1993, Weyant et al 1994, MacDonald et al 2003), as well as a tiger cub (Lloyd and Allen 1980), a lion (Fenwick et al 1983) and two Chinese leopard cats (Perry and Schlingman 1988). A further cat also had pyothorax (Guérin-Faublée et al 1995). The organism has also been recovered on pure culture from the liver of a cat with a chronic wasting disease that progressed to death (Holmes et al 1990). Other lesions tabulated for cats are keratitis, retrobulbar abscessation, otitis, sinusitis and an infected fracture; the treatment and fate of these cats, however, were not documented (Corboz et al 1993).

The precise pathogenesis of EF-4a infection in cats is not well understood. All prior cases have clinically appeared acute but with necropsy and histological findings indicative of chronicity. EF-4 has been shown to have inherently low virulence as experimental inoculation of guinea pigs with low numbers of bacteria did not result in any discernible change but inoculation with larger numbers resulted in death within 18h (Lloyd and Allen 1980). It has been postulated that prolonged infection overwhelms the host's defences resulting in periodic subclinical bacteraemias with haematogenous dissemination to the lungs and an eventual acute on chronic terminal exacerbation (Fenwick et al 1983). Thus, the eventual outcome for the patient almost certainly depends on whether the organism spreads to locations that favour survival and replication.

The localised infection in the case of this report most likely followed the organism translocating from the oral cavity to the mandibular lymph node and/or adjacent tissues, possibly subsequent to penetrating injury; the concurrent dental disease was not considered severe enough to result in the clinical signs seen. The peripheral monocytosis suggests chronicity, as does the nature of the histological findings, especially the pronounced fibroblastic response. A long clinical course may have enabled healing of an initial penetrating wound from inside the mouth due to, for example, a fish bone. Likewise, evidence of external penetrating injury (eg, from a cat fight) may no longer have been evident. Although there was no clinical evidence of dissemination to the lungs, this possibility could not be excluded, as thoracic radiographs were not taken.

The widespread susceptibility to antimicrobials of the EF-4a isolate reported here is consistent with prior reports (Lion et al 1992). The treatment course was extended to 2 weeks beyond apparent resolution because of the apparent chronicity and the recorded potentially dramatic consequences of an unchecked infection.

It has been suggested that infection with CDC Group EF-4 has been under-reported due to the organism's relative obscurity. Because of its small size and Gram reaction, the organism is difficult to visualise in cytological and histological preparations necessitating culture of specimens to recognise infection, as in the current report. Identification of the organism by standard culture methods is also difficult as it shares several morphological characteristics with closely related organisms such as Neisseria and Pasteurella species (Lloyd and Allen 1980, Fenwick et al 1983). Furthermore, because of its relative biochemical unreactivity, more sophisticated methods of identification, such as the use of GC-FID or molecular techniques are often required to confirm its identity. This report highlights the need for clinicians to be aware of CDC Group EF-4a.