Assessment of in vitro activities of novel modified antimicrobial peptides against clarithromycin resistant Mycobacterium abscessus.

Mycobacterium abscessus (Mab) is one of the most drug resistant bacteria with a high treatment failure rate. Antimicrobial peptides (AMPs) are alternative therapeutic agents against this infection. This study was aimed to assess the in vitro activities of thirteen AMPs (S5, S52, S6, S61, S62, S63, KLK, KLK1, KLK2, Pug-1, Pug-2, Pug-3 and Pug-4) that have never been investigated against drug resistant Mab isolates. Only four novel modified AMPs (S61, S62, S63 and KLK1) provided the lowest minimum inhibitory concentration (MIC) values ranging from 200-400 µg/ml against the Mab ATCC19977 strain. These four potential AMPs were further tested with 16 clinical isolates of clarithromycin resistant Mab. The majority of the tested strains (10/16 isolates, 62.5%) showed ~99% kill by all four AMPs within 24 hours with an MIC <50 µg/ml. Only two isolates (12.5%) with acquired clarithromycin resistance, however, exhibited values <50 µg/ml of four potential AMPs, S61, S62, S63 and KLK1 after 3-days-incubation. At the MICs level, S63 showed the lowest toxicity with 1.50% hemolysis and 100% PBMC viability whereas KLK1 showed the highest hemolysis (10.21%) and lowest PBMC viability (93.52%). S61, S62 and S63 were further tested with clarithromycin-AMP interaction assays and found that 5/10 (50%) of selected isolates exhibited a synergistic interaction with 0.02-0.41 FICI values. This present study demonstrated the potential application of novel AMPs as an adjunctive treatment with clarithromycin against drug resistant Mab infection.

Comparison of four agar media for the enumeration of the Mycobacterium abscessus complex.

Background: Traditional culture of nontuberculous mycobacteria (NTMs) has involved egg-based formulations (Lowenstein-Jensen medium) or defined media (Middlebrook formulations), which have disadvantages of composition complexity, availability, and cost. This study quantitatively compared three non-selective, non-blood based basal agars with Columbia blood agar (CBA), to enumerate Mycobacterium abscessus complex organisms in pure culture. Methods: M. abscessus subsp. massiliense, M. abscessus subsp. bolletii, and M. abscessus subsp. abscessus were employed. Inocula of each of these were counted on three basal agar media, including (i) standard plate count agar (SPCA), (ii) tryptone soya agar (TSA), and (iii) Mueller-Hinton agar (MHA) and compared to counts on CBA. Results: All NTM isolates of all subspecies grew successfully on all four media examined. The growth was most profuse on SPCA, with a mean colony diameter of 3 mm, whereas the mean colony diameter on all other media was 1 mm. Statistically, there was no significant difference in counts when comparing CBA with SPCA or MHA (P > 0.05), whereas there was a statistically significant difference between CBA and TSA (P = 0.01). There was no statistically significant difference between SPCA and MHA (P = 0.53). Conclusion: This study indicates that SPCA and MHA are equally effective as CBA, when enumerating of M. abscessus complex organisms. Employment of TSA gave significantly lower counts than CBA (P = 0.01) and therefore should not be employed when enumerating these organisms. SPCA yielded the most profuse growth of all media examined. In addition to these advantages, given that SPCA does (i) not require blood as a medium constituent, (ii) is simple to reconstitute, (iii) is relatively cheap, and (iv) is widely available commercially, this study endorses employment of SPCA for the nonselective culture of M. abscessus complex organisms, including enumeration.

Investigating transmission of Mycobacterium abscessus amongst children in an Australian cystic fibrosis centre.

BACKGROUND: Mycobacterium abscessus is an emerging pathogen in cystic fibrosis (CF) lung disease. Hospital transmission of M. abscessus has been described. This paper details the investigation into possible cross-transmission of M. abscessus locally at our paediatric hospital CF centre, and the subsequent infection control response. METHODS: Whole genome sequencing (WGS) of M. abscessus respiratory isolates with epidemiological linkage analysis using hospital electronic medical records. RESULTS: 6.7% (22/328) of CF patients had M. abscessus isolated from respiratory specimens. WGS revealed a cluster of three patients with genomically related isolates that differed by <7 single nucleotide polymorphisms (SNPs), suggesting a shared recent ancestor and probable cross-transmission. Epidemiological investigation revealed multiple potential crossovers between patients with genomically similar M. abscessus isolates. CONCLUSIONS: Cross-infection of NTM occurs in CF hospital patients. Hospital infection control practices should be upgraded to reflect this. Consensus is needed between centres.

Mandibular Osteomyelitis and Cervical Lymphadenitis Due to Mycobacterium abscessus: Surgical Management of a Pediatric Cohort With a Shared Epidemiologic Exposure.

BACKGROUND: Mycobacterium abscessus has been implicated as the cause of various infections in the setting of healthcare-related "outbreaks." Mandibular osteomyelitis caused by M abscessus is exceedingly rare, with only 1 patient reported in the literature. The authors describe the surgical management of 12 pediatric patients with M abscessus-related mandibular osteomyelitis and cervical lymphadenitis caused by exposure to contaminated water at a regional dental clinic. METHODS: Following institutional review board approval, new suspected patients were reviewed and followed prospectively. A multidisciplinary team coordinated the surgical approach, antibiotic regimen, and follow-up for each patient. RESULTS: Twelve patients (median age 7.5 years) received treatment of M abscessus infection. Eleven had mandibular osteomyelitis and underwent debridement along with extraction of affected teeth. Eight had lymphadenitis and underwent excision of involved nodes. Four patients (in whom surgical debridement was considered inadequate) received antibiotic therapy with a regimen of amikacin, cefoxitin, and azithromycin for 4 months. Nine of 12 patients have been followed for a median of 5 months (range 1-11 months); no patient has evidence of persistent clinical infection. Three of 4 patients treated with amikacin have high-frequency hearing loss. CONCLUSIONS: The authors describe a pediatric cohort with mandibular osteomyelitis and cervical lymphadenitis due to M abscessus following pulpotomy at a single dental clinic. Diagnosis required a high index of suspicion. Patients in our series had resolution of infection even without antibiotic therapy, suggesting that early complete surgical debridement and removal of affected lymph nodes can be sufficient as a sole treatment modality.