Isolation and identification of Caviibacter abscessus from cervical abscesses in a series of pet guinea pigs (Cavia porcellus)

Abstract

An organism reported in the early literature to be a rare cause of cervical lymphadenitis in guinea pigs, Streptobacillus moniliformis, has been reclassified as Caviibacter abscessus. We describe a series of sequential cases of abscesses in guinea pigs that were presented to our clinic from which the only agent isolated was a unique, serum-requiring bacterium. Discrete colonies were not detected in 6.5% CO2 or anaerobically on routine primary isolation media containing up to 5% whole sheep blood, with and without cysteine, vitamin K, and hemin supplementation after 7 days of incubation at 37°C. Based on subsequently determined growth requirements, the organisms were best described as serum-requiring, aerotolerant anaerobes. Colonies were detectable within 24 h at 37°C in an anaerobic atmosphere on a mycoplasma agar–based medium containing 10% pig serum and reached 3 mm in diameter within 3–5 days. Microscopic appearance consisted of small gram-negative rods and coccobacilli with occasional filaments. However, in direct smears from clinical specimens and from weak or dysgonic growth on plates incubated under suboptimal growth conditions (e.g., in 6.5% CO2), irregular rods with occasional small bulbous forms or numerous long wavy filaments were observed. All of the isolates generated unique spectral profiles similar to that of C. abscessus when examined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Phylogenetic analysis of partial 16S rRNA gene sequences showed that the isolates were identical to each other and shared 99.9% sequence identity with C. abscessus.