Microbiological Laboratory Diagnosis of Human Brucellosis: An Overview

Abstract

Brucella spp. are Gram-negative, non-motile, non-spore-forming, slow-growing, facultative intracellular bacteria causing brucellosis. Brucellosis is an endemic of specific geographic areas and, although underreported, represents the most common zoonotic infection, with an annual global incidence of 500,000 cases among humans. Humans represent an occasional host where the infection is mainly caused by B. melitensis, which is the most virulent; B. abortus; B. suis; and B. canis. A microbiological analysis is crucial to identifying human cases because clinical symptoms of human brucellosis are variable and aspecific. The laboratory diagnosis is based on three different microbiological approaches: (i) direct diagnosis by culture, (ii) indirect diagnosis by serological tests, and (iii) direct rapid diagnosis by molecular PCR-based methods. Despite the established experience with serological tests and highly sensitive nucleic acid amplification tests (NAATs), a culture is still considered the “gold standard” in the laboratory diagnosis of brucellosis due to its clinical and epidemiological relevance. Moreover, the automated BC systems now available have increased the sensitivity of BCs and shortened the time to detection of Brucella species. The main limitations of serological tests are the lack of common interpretative criteria, the suboptimal specificity due to interspecies cross-reactivity, and the low sensitivity during the early stage of disease. Despite that, serological tests remain the main diagnostic tool, especially in endemic areas because they are inexpensive, user friendly, and have high negative predictive value. Promising serological tests based on new synthetic antigens have been recently developed together with novel point-of-care tests without the need for dedicated equipment and expertise. NAATs are rapid tests that can help diagnose brucellosis in a few hours with high sensitivity and specificity. Nevertheless, the interpretation of NAAT-positive results requires attention because it may not necessarily indicate an active infection but rather a low bacterial inoculum, DNA from dead bacteria, or a patient that has recovered. Refined NAATs should be developed, and their performances should be compared with those of commercial and home-made molecular tests before being commercialized for the diagnosis of brucellosis. Here, we review and report the most common and updated microbiological diagnostic methods currently available for the laboratory diagnosis of brucellosis.

Spatio-Temporal Distribution of Brucellosis in European Terrestrial and Marine Wildlife Species and Its Regional Implications

“…On the other hand, canine brucellosis cannot be detected with the smooth LPS antigens used for the diagnosis of livestock brucellosis and needs antigens prepared from the rough LPS of B. canis [ 101 ]. Cytoplasmic proteins, however, could be of diagnostic importance in this scenario [ 108 , 109 ].…”

A Case of Coincidentally Diagnosed Brucellosis in a Patient with COVID-19

“…Especially in our case, reproduction was registered in the blood culture of a patient without clinical suspicion of Brucellosis. [10][11][12] Respiratory system involvement is an unexpected finding in Brucella cases and is usually seen in COVID-19 cases. 13 However, it has been shown in the literature that Brucella can be transmitted through the respiratory tract and can cause respiratory system symptoms, although it is rare.…”

Milk Borne Brucellosis

“…Antibodies against Brucella were assessed using a series of serological tests to confirm the presence of infection with this bacterium [32][33][34].…”