**EF-4a (Neisseriaceae spp) bacterial infections in cats**

'EF' stands for 'Eugonic fermenter', where eugonic means luxuriant growth. The formal name of the bacteria is CDC Group EF-4a and it is a facultative anaerobic, Gram-negative coccibacillus thought to belong to the family Neisseriaceae. EF-4a is thought to be part of the normal flora of the oral cavity of cats and dogs. Most reports of this organism relate to cat bite wounds to humans and otitis media subsequent to a dog licking its owner's ears.

Pathology

The most commonly recognised disease cause by EF-4a in cats is severe necrotising pneumonia resulting in death. Since first being recognised in 1973, it has been reported in cats, a tiger cub, a lion and two Chinese leopard cats. A further cat also had pyothorax. These cats all had acute signs (all starting a few days before death) but the histology was suggestive of a chronic infection. One report tabulates localised infections in various cats including keratitis, otitis, retrobulbar abscess, sinusitis and the author has recently reported the successful treatment of a cat with mandibular infection. These localised infections have also shown chronic inflammation with a large amount of fibrous tissue.

These two syndromes (fatal pneumonia and localised infection) most likely represent different stages of infection depending on how long infection has been present and therefore how many organisms are present. EF-4 has been shown to have inherently low virulence since experimental inoculation of guinea pigs with low numbers of organisms did not cause any discernible change, however inoculation with large numbers of organisms resulted in death within 18 hours. This indicates that it is not merely the presence of the organism that results in death but the presence of large numbers as contributory to death.

The precise pathogenesis has not been elucidated but is likely to begin with translocation of the bacteria from the oral cavity to a site favourable for replication, such as a local lymph node. If the organism replicates beyond a threshold number, this can result in bacteraemia that is likely to be subclinical since the organism is of inherently low pathogenicity. The bacteraemia, however, allows haematogenous dissemination to the lungs, resulting in systemic disease and a high likelihood of death.

Diagnosis

Diagnosis requires recognising the organism from cytological or histological preparations and/or successful culture and identification of the organism. Successful culture requires identification of EF-4a using normal culture plates. Each colony on an agar plate has an initial 'crinkled' appearance or has concentric circles like a ripple or pond. This crinkling is lost after several days and may be missed. The EF-4a bacteria are biochemically unreactive, so requires sophisticated methods of identification such as gas chromatography flame ionisation detection (GC-FID) or PCR that can only be performed at specialist laboratories. These difficulties means that precise diagnosis will only occur with a strong index of suspicion on the part of the clinician and laboratory.

Treatment

Reported susceptibilities include penicillin, ampicillin,, cephalosporins, doxycycline, gentamicin, enrofloxacin, ciprofloxacin, sulphonamides, erythromycin, clarithromycin and clavulox.