Pathogenic Nocardia: A diverse genus of emerging pathogens or just poorly recognized?

Abstract

Introduction to pathogenic Nocardia, a clinically relevant non-ESKAPE pathogen The clear and present danger posed by the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, and Enterobacter species) and their ability to evade antimicrobials is generally well appreciated [1]. There are, however, a multitude of pathogens, some more rare than others, that can be clinically challenging to diagnose and treat. Nocardia, a genus of aerobic actinomycetes found ubiquitously in soil and water, harbors one such group of pathogens with unique attributes and often complicated properties. Opportunistic infections caused by Nocardia often afflict immunocompromised individuals like cancer patients receiving chemotherapy, individuals with AIDS, and organ transplant recipients. Although commonly considered opportunistic, among 1,000 cases of Nocardia infection published between 1950 and 1991, about one-third occurred in patients with no identifiable underlying predisposing conditions [2], implying that immune status is not the only factor affecting infectivity. Skin and lung are the primary infection sites for these rod shaped, gram-positive bacteria. Nocardia also have the ability to survive as facultative intracellular parasites within macrophages [3,4] and escape killing by human neutrophils and monocytes [5]. Infections can sometimes be largely asymptomatic, which, when coupled with the slow growth rate of Nocardia, makes them difficult to identify in clinical specimens [6]. Dissemination, particularly to the central nervous system (CNS), is relatively common and can be life threatening, with mortality rates as high as 85% in immunocompromised individuals [6-8]. To date, 119 species of Nocardia have been documented (http://www.bacterio.net/ nocardia.html), with more than 40 of them being considered clinically relevant (https://www. cdc.gov/nocardiosis/health-care-workers/index.html).

Isolation and Characterization of Nocardiae Associated with Foaming Coastal Marine Waters

“…This might be due to lack of sensitive identification tests and or the fastidious growth conditions certain species of Nocardia require for cultivation, isolation [ 48 ] and identification [ 49 ] in a clinical laboratory. However, as recently indicated by Mehta and Shamoo [ 22 ] advancements in rapid molecular diagnostic technology will soon place nocardiae in the “extended pantheon of medically important pathogens”. Accordingly, studies like the one presented here will generate further information on the occurrence and diversity of nocardiae in different environments and might have significance in linking the clinical data to the presence of disease causative species in the environment by the public health authorities.…”

“…One of the reasons for this fact might be due to the lack of epidemiological data on the incidence of nocardiosis which may not be truly reflective of the pathogenic potential of Nocardia species. This might be partly due to the fastidious growth patterns of certain species of Nocardia or lack of rapid diagnostic tests required for their detection and subsequent isolation in a clinical laboratory [ 22 ].…”

Granulomatosis in fish aquaculture: a mini review

“…As described above, there are no methods for the early detection or control within infected populations. The genus is still an enigma in several ways; for this reason, Nocardia infections are difficult to identify and treat even in humans, in which most of the research has been focused (Mehta & Shamoo 2020). However, Nocardia sp.…”

“…Most of these species are known to cause nocardiosis in fish and a wide variety of animals including humans (Kandi 2015). Nocardia is considered a genus harbouring a group of pathogens with unique attributes and complicated properties (Mehta & Shamoo 2020). In this regard, Nocardia is clinically challenging to diagnose and treat.…”

Rapid identification of Nocardia cyriacigeorgica from a brain abscess patient using MALDI-TOF-MS

“…The bacterium is primarily found in soil, but can also live in stagnant water and enter the human body through dust respiration and traumatic inoculation. Unfortunately however, the microbiological isolation and identification of Nocardia species from clinical samples within typical hospital laboratories is difficult and time consuming when using conventional diagnostic methods [ 6 ]. One potential candidate method that allows for rapid and accurate identification of bacterial species is matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF).…”