Cultivation of 146 Clinical Strains of Nocardia species
Nocardia species generally grow well on culture media in contrast to limited metabolic activities. Yet there are rare studies that have examined systematically the effect of culture media on the clinical recovery of these Gram-positive branching bacilli, particularly in relation to many recently described or revised Nocardia species. We analyzed 146 clinical Nocardia strains, of 24 species, recovered at the University of Texas M. D. Anderson Cancer Center from 2002-2018 for their growth on culture media. Among media setups to culture routine bacteria, fungi, and acid-fast bacilli (AFB), the AFB media alone recovered 35 strains as did fungal media with 26 strains and routine media with 10 strains. Seventy five strains were recovered on two and three media setups. On AFB media most Nocardia nova strains (24 of 29) grew, significantly more than all other strains did. Likewise, all four strains of Nocardia mikamii were cultivated solely on AFB media. Fungal media yielded all six strains of Nocardia wallacei that were resistant to tobramycin and/or amikacin; this growth could be explained by the presence of gentamycin in one fungal medium. Specimen source also affected the recovery: more Nocardia strains grew on every media setup from normally sterile specimens than from nonsterile specimens. These results suggest that diverse culture media support the growth of many Nocardia species. The better recoveries of these organisms from AFB media and fungal media are likely attributable to decontamination of specimens on AFB culture, incorporation of selective antimicrobial agents into the media, and prolonged incubation.