The possibility that the strains included within the Mycobacterium avium complex (MAC), but not belonging either to M. avium or to Mycobacterium intracellulare, may be members of undescribed taxa, has already been questioned by several taxonomists. A very homogeneous cluster of 12 strains characterized by identical nucleotide sequences both in the 16S rDNA and in the 16S–23S internal transcribed spacer was investigated. Similar strains, previously reported in the literature, had been assigned either to the species M. intracellulare on the basis of the 16S rDNA similarity or to the group of MAC intermediates. However, several phenotypical and epidemiological characteristics seem to distinguish these strains from all other MAC organisms. The unique mycolic acid pattern obtained by HPLC is striking as it is characterized by two clusters of peaks, instead of the three presented by all other MAC organisms. All of the strains have been isolated from humans and all but one came from the respiratory tract of elderly people. The clinical significance of these strains, ascertained for seven patients, seems to suggest an unusually high virulence. The characteristics of all the strains reported in the literature, genotypically identical to the ones described here, seem to confirm our data, without reports of isolations from animals or the environment or, among humans, from AIDS patients. Therefore, an elevation of the MAC variant was proposed and characterized here, with the name Mycobacterium chimaera sp. nov.; this increases the number of species included in the M. avium complex. The type strain is FI-01069T (=CIP 107892T=DSM 44623T).

The Italian burden of disease associated with infections due to antibiotic-resistant bacteria has been very high, largely attributed to Carbapenem-Resistant Klebsiella pneumoniae (CR-Kp). The implementation of infection control measures and antimicrobial stewardship programs (ASP) has been shown to reduce healthcare-related infections caused by multidrug resistance (MDR) germs. Since 2016, in our teaching hospital of Terni, an ASP has been implemented in an intensive care unit (ICU) setting, with the “daily-ICU round strategy” and particular attention to infection control measures. We performed active surveillance for search patients colonized by Carbapenem-Resistant Enterobacteriaceae (CRE). In March 2020, coronavirus disease 2019 (COVID-19) arrived and the same ICU was reserved only for COVID-19 patients. In our retrospective observational study, we analyzed the bimonthly incidence of CRE colonization patients and the incidence of CRE acquisition in our ICU during the period of January 2019 to June 2020. In consideration of the great attention and training of all staff on infection control measures in the COVID-19 era, we would have expected a clear reduction in CRE acquisition, but this did not happen. In fact, the incidence of CRE acquisition went from 6.7% in 2019 to 50% in March–April 2020. We noted that 67% of patients that had been changed in posture with prone position were colonized by CRE, while only 37% of patients that had not been changed in posture were colonized by CRE. In our opinion, the high intensity of care, the prone position requiring 4–5 healthcare workers (HCWs), equipped with personal protective equipment (PPE) in a high risk area, with extended and prolonged contact with the patient, and the presence of 32 new HCWs from other departments and without work experience in the ICU setting, contributed to the spread of CR-Kp in our ICU, determining an increase in CRE acquisition colonization.

INNO-LiPA MYCOBACTERIA (Innogenetics, Ghent, Belgium) is a reverse hybridization DNA probe assay that has been recently improved by increasing the number of identifiable mycobacterial species to 16. Our assessment, performed with 197 mycobacteria belonging to 81 taxa, revealed 100% specificity and sensitivity for 20 out of 23 probes. The probes specific for Mycobacterium fortuitum complex, for the Mycobacterium aviumintracellulare-scrofulaceum group, and for Mycobacterium intracellulare type 2 cross-reacted with several mycobacteria rarely isolated from clinical specimens. The overall sensitivity was 100%, and the overall specificity was 94.4%.

A thorough phenotypic and genotypic analysis of 150 strains belonging to the Mycobacterium terrae complex resulted in the identification of a number of previously unreported sequevars (sqvs) within the species known to belong to the complex. For the species Mycobacterium arupense , three sqvs were detected in the 16S rRNA gene, six sqvs in the hsp65 gene and 15 sqvs in the rpoB gene; in Mycobacterium senuense two sqvs were present in each of the three genetic regions; in Mycobacterium kumamotonense four, two and nine sqvs were found, respectively, and in M. terrae three, four and six sqvs were found, respectively. The inappropriate inclusion of Mycobacterium triviale within the M. terrae complex was confirmed. The limited utility of biochemical tests and of mycolic acid analyses for the differentiation of the members of M. terrae complex was also confirmed. The survey allowed the recognition of three previously undescribed species that were characterized by unique sequences in the 16S rRNA, hsp65 and rpoB genes. Mycobacterium engbaekii sp. nov. (proposed previously 40 years ago but never validly published) was characterized by pink photochromogenic pigmentation and rapid growth; phylogenetically it was related to Mycobacterium hiberniae . The type strain of this species, of which eight strains were investigated, is ATCC 27353T ( = DSM 45694T). A cluster of 24 strains was the basis for the description of Mycobacterium heraklionense sp. nov., which has an intermediate growth rate and is unpigmented; nitrate reductase activity is typically strong. Closely related to M. arupense with respect to the 16S rRNA gene, M. heraklionense sp. nov. could be clearly differentiated from the latter species in the other genetic regions investigated. The type strain is NCTC 13432T ( = LMG 24735T = CECT 7509T). Mycobacterium longobardum sp. nov., represented in the study by seven strains, was characterized by a unique phylogenetic location within the M. terrae complex, clearly divergent from any other species. The type strain is DSM 45394T ( = CCUG 58460T).

Four bacterial strains were isolated from independent clinical specimens in different countries and their genotypic and phenotypic characters support their classification in a novel species within the genus Mycobacterium. One strain was clearly responsible for a severe, post-traumatic wound infection in a healthy boy. The novel species, for which the name Mycobacterium monacense sp. nov. is proposed, is yellow-pigmented, non-photochromogenic and grows in less than a week on solid medium. Based on phenotypic investigations alone, distinction of these four strains from known scotochromogenic rapidly growing strains is problematic. However, the novel strains differ from any other mycobacterium in each of the molecular species markers investigated: the 16S rRNA gene, the 16S-23S rRNA gene internal transcribed spacer and the hsp65 gene. Of the strains investigated, two different sequevars were detected for the hsp65 region. Phylogenetic analysis revealed that these four strains were most closely related to Mycobacterium doricum. The type strain of Mycobacterium monacense sp. nov. is B9-21-178 T (=DSM 44395 T =CIP 109237 T ).