Defining Reference Sequences for Nocardia Species by Similarity and Clustering Analyses of 16S rRNA Gene Sequence Data

International audienceBACKGROUND: The intra- and inter-species genetic diversity of bacteria and the absence of 'reference', or the most representative, sequences of individual species present a significant challenge for sequence-based identification. The aims of this study were to determine the utility, and compare the performance of several clustering and classification algorithms to identify the species of 364 sequences of 16S rRNA gene with a defined species in GenBank, and 110 sequences of 16S rRNA gene with no defined species, all within the genus Nocardia. METHODS: A total of 364 16S rRNA gene sequences of Nocardia species were studied. In addition, 110 16S rRNA gene sequences assigned only to the Nocardia genus level at the time of submission to GenBank were used for machine learning classification experiments. Different clustering algorithms were compared with a novel algorithm or the linear mapping (LM) of the distance matrix. Principal Components Analysis was used for the dimensionality reduction and visualization. RESULTS: The LM algorithm achieved the highest performance and classified the set of 364 16S rRNA sequences into 80 clusters, the majority of which (83.52%) corresponded with the original species. The most representative 16S rRNA sequences for individual Nocardia species have been identified as 'centroids' in respective clusters from which the distances to all other sequences were minimized; 110 16S rRNA gene sequences with identifications recorded only at the genus level were classified using machine learning methods. Simple kNN machine learning demonstrated the highest performance and classified Nocardia species sequences with an accuracy of 92.7% and a mean frequency of 0.578. CONCLUSION: The identification of centroids of 16S rRNA gene sequence clusters using novel distance matrix clustering enables the identification of the most representative sequences for each individual species of Nocardia and allows the quantitation of inter- and intra-species variability

Genotype Prevalence and Risk Factors for Severe Clinical Adenovirus Infection, United States 2004-2006

Recently, epidemiological and clinical data have revealed important changes with regard to clinical adenovirus infection, including alterations in antigenic presentation, geographical distribution, and virulence of the virus

Transmission of Coccidioidomycosis to a Human via a Cat Bite ▿

We report an unusual case of coccidioidomycosis in the arm of a veterinary assistant without pulmonary symptoms. The patient had been bitten on the hand by a cat which was later diagnosed with disseminated disease. The patient responded to fluconazole therapy and remained asymptomatic at 2 months after cessation of therapy

Mycobacterium haemophilum as a Novel Etiology of Cervical Lymphadenitis in an Otherwise Healthy Adult Patient▿

We describe a case and summarize six additional cases of cervical lymphadenitis in otherwise healthy adults caused by Mycobacterium haemophilum. The organism causes cervicofacial lymphadenitis in healthy children and severe disease in immunocompromised patients but has not been previously reported to cause cervical lymphadenitis in nonimmunocompromised, healthy adults

Multicenter Evaluation of the BD Phoenix Automated Microbiology System for Antimicrobial Susceptibility Testing of Streptococcus Species▿

This multicenter study evaluated the BD Phoenix Automated Microbiology System STREP panel (BD Diagnostic Systems). Antimicrobial susceptibility testing (AST) with 13 agents was performed on 2,013 streptococci (938 Streptococcus pneumoniae isolates; 396 group B streptococci [GBS]; 369 viridans group streptococci [VGS]; 290 beta-hemolytic streptococcus groups A, C, and G; and 20 other streptococci) with the Phoenix system and a broth microdilution reference method. Clinical and challenge isolates were tested against cefepime, cefotaxime (CTX), ceftriaxone (CTR), clindamycin (CLI), erythromycin (ERY), gatifloxacin, levofloxacin, linezolid, meropenem, penicillin (PEN), tetracycline (TET), trimethoprim-sulfamethoxazole, and vancomycin. Clinical isolates with major errors or very major errors (VMEs) were retested in duplicate by both methods. The final results for clinical isolates showed the following trends. For all of the organism-antimicrobial agent combinations tested, categorical agreement (CA) was 92 to 100%, with one exception—VGS-PEN (87% CA; all errors were minor). For S. pneumoniae, there was one major error with CLI (0.1%) and one or two VMEs with CTX (4%), CTR (4.5%), ERY (0.9%), and TET (0.7%). For groups A, C, and G, the CA was 97 to 100% and the only VMEs were resolved by additional reference laboratory testing. For GBS, there was only one VME (TET, 0.3%) and D-zone testing of 23 isolates with CLI major errors (one isolate unavailable) revealed inducible CLI resistance. For VGS, the major error rates were 0 to 3% and VMEs occurred with seven agents (3.5 to 7.1%). The mean times required for organism groups to generate results ranged from 8.4 to 9.4 h. The Phoenix system provided reliable and rapid AST results for most of the organism-antimicrobial agent combinations tested