October Q&A: Readers’ questions answered

Sept. 21, 2022

Can fluid samples for culture be submitted in heparin or potassium ethylenediaminetetraacetic acid (EDTA)?

There are a variety of different media designed to support the transport needs of a diverse range of microorganisms; however, heparin and EDTA tubes have not been formulated to maintain microorganism viability during transport to the lab and therefore should not be used. In some cases, EDTA can even actively damage the cell walls of some bacteria preventing effective culture. Examples of commonly used transport media include Amies media, which can support the transport of a wide range of bacteria; Stuarts media, often used when gonococcus is suspected; Cary Blair for stool samples; anaerobic transport medium for when anaerobic bacteria are suspected; and viral transport medium for viral pathogens.

Should urine cultures be finalized in 24 hours or 48 hours?

Although practices vary, most laboratories consider a urine culture as ‘negative’ if no significant growth is found on the plates after 18–24 hours; however, with advances in microbiology laboratory automation, some labs are reporting further reductions in duration of urine culture. Occasionally, cultures may be prolonged to look for unusual organisms such as Oligella urolytica, a slow-growing, Gram-negative, and rare UTI-causing organism that has been reported to have an incubation of over 48 hours.

Should Gardnerella vaginalis be identified from a urine culture?

Gardnerella vaginalis is a common commensal organism of the vaginal microbiome and its overgrowth is also associated with bacterial vaginosis. The role of this organism as a cause or contributor to various disorders of the urinary tract is still unfolding; however, it has been associated with urinary tract infections, and therefore, is often reported when found in urine cultures.

With the emergence of Candida auris, should the recovery of any yeast be identified to the genus and species level? (Our facility has a MALDI that can identify C. auris.)

Candida auris infection is a nationally notifiable condition. As such, the Centers for Disease Control and Prevention (CDC) has provided guidance on when laboratories should identify a candida isolate to the species level. This includes all isolates from normally sterile body sites, as well as non-sterile sites in certain circumstances. More information can be found at https://www.cdc.gov/fungal/candida-auris/c-auris-surveillance.html. Laboratories that identify cases of C. auris should report cases immediately to the state or local health department and to CDC at [email protected]

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