Fungal and mycobacterial cultures should not be routinely obtained for diagnostic work-up of patients with suspected periprosthetic joint infections

Aims Fungal and mycobacterial periprosthetic joint infections (PJI) are rare events. Clinicians are wary of missing these diagnoses, often leading to the routine ordering of fungal and mycobacterial cultures on periprosthetic specimens. Our goal was to examine the utility of these cultures and explore a modern bacterial culture technique using bacterial blood culture bottles (BCBs) as an alternative. Methods We performed a retrospective review of patients diagnosed with hip or knee PJI between 1 January 2010 and 31 December 2019, at the Mayo Clinic in Rochester, Minnesota, USA. We included patients aged 18 years or older who had fungal, mycobacterial, or both cultures performed together with bacterial cultures. Cases with positive fungal or mycobacterial cultures were reviewed using the electronic medical record to classify the microbiological findings as representing true infection or not. Results There were 2,067 episodes of PJI diagnosed within the study period. A total of 3,629 fungal cultures and 2,923 mycobacterial cultures were performed, with at least one of these performed in 56% of episodes (n = 1,157). Test positivity rates of fungal and mycobacterial cultures were 5% (n = 179) and 1.2% (n = 34), respectively. After a comprehensive review, there were 40 true fungal and eight true mycobacterial PJIs. BCB were 90% sensitive in diagnosing true fungal PJI and 100% sensitive in detecting rapidly growing mycobacteria (RGM). Fungal stains were performed in 27 true fungal PJI but were only positive in four episodes (14.8% sensitivity). None of the mycobacterial stains was positive. Conclusion Routine fungal and mycobacterial stains and cultures should not be performed as they have little clinical utility in the diagnosis of PJI and are associated with significant costs. Candida species and RGM are readily recovered using BCB. More research is needed to predict rare non- Candida fungal and slowly growing mycobacterial PJI that warrant specialized cultures. Cite this article: Bone Joint J 2022;104-B(1):53–58.

Development of a nucleic acid chromatography assay for the detection of commonly isolated rapidly growing mycobacteria

Introduction. Non-tuberculosis mycobacterium infections are increasing worldwide, including those caused by rapidly growing mycobacteria (RGM). Gap Statement. The identification of the aetiological agent in the context of infections is essential for the adoption of an adequate therapeutic approach. However, the methods for the rapid distinction of different RGM species are less than optimal. Aim. To develop a nucleic acid chromatography kit to identify clinically common RGM. Methodology. We tried to develop a nucleic acid chromatography kit designed to detect four RGM species (including three subspecies) i.e. Mycobacterium abscessus subsp. abscessus , Mycobacterium abscessus subsp. bolletii (detected as M. abscessus/bolletii) Mycobacterium abscessus subsp. massiliense , Mycobacterium fortuitum , Mycobacterium chelonae and Mycobacterium peregrinum . The amplified target genes for each species/subspecies using multiplex PCR were analysed using a nucleic acid chromatography assay. Results. Among the 159 mycobacterial type strains and 70 RGM clinical isolates tested, the developed assay correctly identified all relevant RGM without any cross-reactivity or false-negatives. The limits of detection for each species were approximately 0.2 pg µl-1. Conclusion. The rapid and simple nucleic acid chromatography method developed here, which does not involve heat denaturation, may contribute to the rapid identification and treatment of RGM infections.

1392. Nontuberculous Mycobacteria Isolated from Wisconsin Residents, 2010-2018

Background Wisconsin is one of a handful of states in which laboratory identification of nontuberculous mycobacteria (NTM) from clinical samples is reportable to public health. The aims of this study were to characterize the demographic features of Wisconsin adults with NTM, assess the relative abundance of NTM species recovered, and describe trends in NTM isolation over the study period. Methods We conducted a retrospective cohort study of Wisconsin residents 18 years of age and older from whom NTM isolates were recovered and reported to the Wisconsin Electronic Disease Surveillance System (WEDSS) between 2010 and 2018. Isolates of M. gordonae were excluded. For the analysis of NTM frequency, multiple reports from the same individual were enumerated as separate isolates when non-identical or collected from different sites. Because NTM were usually reported into WEDSS without clinical data, this study couldn’t discern the clinical significance of the isolates. Results A total of 9,032 NTM isolates from 7,722 adults were analyzed. The average annual number of reported NTM cases was 950 (21.7/100,000 adults) during 2011-2018. Table 1 shows the demographic characteristics of individuals with NTM isolates, stratified by specimen collection site and NTM species. M. avium complex (MAC) accounted for 75.7% of respiratory isolates. An important pathogenic NTM, M. xenopi, accounted for 8.9% of non-MAC respiratory isolates. As shown in Table 2, M. chelonae, a rapidly growing mycobacteria (RGM), was the most common species isolated from skin and soft tissue, head, ears, nose and throat, and eye specimens. MAC was the most common isolate from other tissue sites. Table 1. Demographic characteristics of individuals with NTM isolates. Categorization was based upon the initially recovered sample when multiple samples were obtained from a given individual. “Respiratory” samples included sputum, bronchoalveolar lavage, and tracheal aspirate specimens. IQR, interquartile range. RGM, rapidly growing mycobacteria (M. chelonae and the M. abscessus, M. chelonae-abscessus, and M. fortuitum groups). SST, skin and soft tissue. Table 2. Most common NTM species isolated from non-respiratory sites. *’Respiratory specimens’ was inclusive of sputum, bronchoalveolar lavage, and tracheal aspirate specimens. CNS, central nervous system. HENT, head, ears, nose, or throat. SST, skin and soft tissue. Conclusion Consistent with prior studies, MAC is the predominant NTM isolated from respiratory specimens in Wisconsin. RGM are important minority respiratory pathogens, and predominate as skin and soft tissue NTMs. We highlight M. xenopi as an important pathogen in Wisconsin compared to other parts of the United States. In contrast to recent reports of increasing incidence of NTM disease, we found a stable annual incidence of NTM isolation between 2010 and 2018. Disclosures All Authors: No reported disclosures

Antimicrobial resistance spectrum conferred by pRErm46 of emerging macrolide (multidrug)-resistant Rhodococcus equi

Clonal multidrug resistance recently emerged in Rhodococcus equi , complicating the therapeutic management of this difficult-to-treat animal and human pathogenic actinomycete. The currently spreading multidrug-resistant (MDR) “2287” clone arose in equine farms upon acquisition, and co-selection by mass macrolide-rifampin therapy, of the pRErm46 plasmid carrying the erm (46) macrolides-lincosamides-streptogramins resistance determinant, and an rpoB S531F mutation. Here, we screened a collection of susceptible and macrolide-rifampin-resistant R. equi from equine clinical cases using a panel of 15 antimicrobials against rapidly growing mycobacteria (RGM), nocardiae and other aerobic actinomycetes (NAA). R. equi –including MDR isolates– was generally susceptible to linezolid, minocycline, tigecycline, amikacin and tobramycin according to Staphylococcus aureus interpretive criteria, plus imipenem, cefoxitin and ceftriaxone based on Clinical & Laboratory Standards Institute (CLSI) guidelines for RGM/NAA. Ciprofloxacin and moxifloxacin were in the borderline category according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. Molecular analyses linked pRErm46 to significantly increased MICs for trimethoprim-sulfamethoxazole and doxycycline in addition to clarithromycin within the RGM/NAA panel, and to streptomycin, spectinomycin and tetracycline resistance. pRErm46 variants with spontaneous deletions in the class 1 integron (C1I) region, observed in ≈30% of erm (46)-positive isolates, indicated that the newly identified resistances were attributable to C1I’s sulfonamide ( sul1 ) and aminoglycoside ( aaA9 ) resistance cassettes and adjacent tetRA (33) determinant. Most MDR isolates carried the rpoB S531F mutation of the 2287 clone, while different rpoB mutations (S531L, S531Y) detected in two cases suggest the emergence of novel MDR R. equi strains.

Disseminated Cutaneous Mycobacterium Fortuitum-Chelonae Complex Infection in a Young, Immunocompetent Patient: A Case Report

Mycobacteria fortuitum and chelonae are a group of Rapidly Growing Mycobacteria (RGM) that can cause skin infections, most commonly in immunocompromised patients. RGM can also infect immunocompetent patients, but the disease is usually localized. Immunocompetent patients infected by RGM usually had a predisposing condition leading to the skin infection. We present a case of an immunocompetent patient with no predisposing factors, who presented with a chronic lesion on his neck that disseminated to his axilla. Culture and species identification from the skin biopsy revealed Mycobacterium fortuitum-chelonae complex. The patient was treated with a combination of surgery and multi-drug therapy. This case report highlights the rarity of cutaneous RGM infections encountered in ENT setting and the diagnostic dilemma due to the non-typical characteristics of skin lesion in RGM infections.

Nationwide surveillance of antimicrobial susceptibility of 509 rapidly growing mycobacteria strains isolated from clinical specimens in Japan

This study aimed to identify effective treatments against rapidly growing mycobacteria (RGM) infections by investigating the minimum inhibitory concentrations (MIC) of 24 antimicrobial agents and their molecular mechanisms of resistance. In total, 509 clinical RGM isolates were identified by analyzing the sequences of three housekeeping genes (hsp65, rpoB, and sodA), and their susceptibilities to 24 antimicrobial agents were tested. We also performed sequencing analysis of antimicrobial resistance genes (rrl, rrs, gyrA, and gyrB). To identify Mycobacteroides abscessus group subspecies, we performed PCR-based typing and determined the sequevar of erm(41). We identified 15 RGM species, most of which were susceptible to amikacin and linezolid. Among these species, arbekacin and sitafloxacin had the lowest MIC among the same class of antimicrobials. The MIC of rifabutin for M. abscessus subsp. abscessus (MAB) was lower than that for M. abscessus subsp. massiliense (MMA). The proportion of MAB isolates with MIC ≤ 2 mg/L for rifabutin was significantly higher than that of MMA [MAB: 50/178 (28.1%) vs. MMA: 23/130 (17.7%); p = 0.041]. In summary, our study revealed the antimicrobial susceptibility profile of 15 RGM species isolated in Japan and indicated that arbekacin, sitafloxacin, and rifabutin may be possible therapeutic options for RGM infections.

Comparison of In Vitro Susceptibility of Delafloxacin with Ciprofloxacin, Moxifloxacin, and other Comparator Antimicrobials Against Isolates of Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTM) infections are increasing globally. Mycobacterium avium complex (MAC) and M. abscessus complex are the most commonly reported NTM. Oral treatment options are limited, especially for the M. abscessus. We tested delafloxacin, a new oral fluoroquinolone, against 131 isolates of NTM. Delafloxacin microdilution MICs were performed as recommended by the Clinical and Laboratory Standards Institute using cation adjusted Mueller Hinton broth. The rapidly growing mycobacteria tested included: M. abscessus subsp. abscessus (16) and subsp. massiliense (5), M. chelonae (11), M. immunogenum (5), M. fortuitum group (13), M. porcinum (7), M. senegalense (7), M. mucogenicum group (5), and M. goodii (1). For the slowly growing NTM (SGM), M. avium (16), M. intracellulare (13), M. chimaera (9), M. arupense (5), M. simiae (5), M. lentiflavum (4), M. kansasii (6), and M. marinum (3) were tested. Delafloxacin was most active in vitro against M. fortuitum and M. mucogenicum groups and M. kansasii with MIC50 values of 0.12-0.5 μg/mL (MIC range 0.001-4 μg/mL) compared to ≤0.06->4 μg/mL for ciprofloxacin and ≤0.06->8 μg/mL for moxifloxacin. For other SGM (including MAC), and the M. abscessus/chelonae, the delafloxacin MIC range was 8->16 μg/mL compared to ciprofloxacin and moxifloxacin of 0.5->4 μg/mL and ≤0.06-8 μg/mL, respectively. To our knowledge, this is the first MIC study with delafloxacin to use Clinical and Laboratory Standards Institute (CLSI) recommended methods. This study illustrates the potential utility of delafloxacin in treatment of infections due to some NTM.

Nationwide surveillance of antimicrobial susceptibility of 509 rapidly growing mycobacteria strains isolated from clinical specimens in Japan

This study aimed to identify effective treatments against rapidly growing mycobacteria (RGM) infections by investigating the minimum inhibitory concentrations (MIC) of 24 antimicrobial agents and their molecular mechanisms of resistance. In total, 509 clinical RGM isolates were identified by analyzing the sequences of three housekeeping genes (hsp65, rpoB, and sodA), and their susceptibilities to 24 antimicrobial agents were tested. We also performed sequencing analysis of antimicrobial resistance genes (rrl, rrs, gyrA, gyrB). To identify Mycobacteroides abscessus group subspecies, we performed PCR-based typing and determined the sequevar of erm(41). We identified 15 RGM species, most of which were susceptible to amikacin and linezolid. Among these species, arbekacin and sitafloxacin had the lowest MIC among the same class of antibiotics. The MIC of rifabutin for M. abscessus subsp. abscessus (MAB) was lower than that for M. abscessus subsp. massiliense (MMA). The number of MAB isolates with MIC ≤ 2 mg/L for rifabutin was significantly higher than that of MMA [MAB: 50/178 (28.1%) vs. MMA: 23/130 (17.7%); p = 0.041]. In summary, our study revealed the antimicrobial susceptibility profile of 15 RGM species isolated in Japan and indicated that arbekacin, sitafloxacin, and rifabutin may be possible therapeutic options for RGM infections.