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Relationship between gyrA Mutations and Quinolone Resistance in Flavobacterium psychrophilum Isolates. Shotaro Izumi, 2004.Flavobacterium psychrophilum is the causative agent of the fish diseases called bacterial cold-water disease and rainbow trout fry syndrome . It has been reported that some isolates of F . psychrophilum are resistant to quinolones; however, the mechanism of this quinolone resistance has been unexplained . In this study, we examined the quinolone susceptibility patterns of 27 F . psychrophilum strains isolated in Japan and the United States . Out of 27 isolates, 14 were resistant to both nalidixic acid (NA) and oxolinic acid (OXA), and the others were susceptible to NA and OXA . When amino acid sequences deduced from gyrA nucleotide sequences of all isolates tested were analyzed, two amino acid substitutions (a threonine residue replaced by an alanine or isoleucine residue in position 83 of GyrA [Escherichia coli numbering] and an aspartic acid residue replaced by a tyrosine residue in position 87) were observed in the 14 quinolone-resistant isolates . These results strongly suggest that, as in other gram-negative bacteria, DNA gyrase is an important target for quinolones in F . psychrophilum . Purification and Characterization of Streptin, a Type A1 Lantibiotic Produced by Streptococcus pyogenes. Philip A. Wescombe, 2003.Approximately 10% of Streptococcus pyogenes strains inhibit the growth of all nine indicators in a standardized streptococcal bacteriocin typing scheme . The present study has shown that this inhibitory profile, referred to as bacteriocin producer (P)-type 777 activity, is due to the type A1 lantibiotic streptin . Two major forms of streptin were purified to homogeneity from 95% acidified (pH 2) methanol extracts of S . pyogenes M25 cells by using a series of reversed-phase chromatographic separations . The fully processed form of streptin (streptin 1) is a 23-amino-acid peptide with a mass of 2,424 Da . The 2,821-Mr form of the peptide (streptin 2) has three additional amino acids (TPY) at the N terminus . Strain M25 extracts also contained small quantities of the streptin 1 and streptin 2 peptides in various stages of dehydration . Streptin 1 and streptin 2 were each capable of specifically inducing streptin production when added to strain M25 cultures . The streptin gene cluster resembled that of other type A1 lantibiotics but appeared to lack a streptin-specific proteinase gene . Although the streptin structural gene (srtA) was widespread within S . pyogenes, being detected in 40 of 58 strains, each representing a different M serotype, only 10 of these srtA-positive strains produced active streptin . The failure of some strains to express streptin was attributed to an  4.5-kb deletion in their streptin loci, encompassing genes putatively encoding proteins involved in streptin processing (srtB and srtC) and transport (srtT) . In other strains, srtA transcription appeared to be defective . No direct association could be detected between the production of streptin and the production of the lantibiotic-like hemolysin streptolysin S in strain M25 .
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