title: A spontaneous 99-kb chromosomal deletion results in multi-antibiotic susceptibility and an attenuation of contact haemolysis in Shigella flexneri 2a.
abstract: A Tn5-generated mutant (strain S2430) of Shigella flexneri 2a (strain YSH6000) exhibited attenuated virulence and, in addition to the Tn5 insertion in the SalI K fragment of its virulence plasmid, had a 99-kb deletion within its chromosome. Unlike its wild-type parent, strain S2430 was susceptible to ampicillin, streptomycin, tetracycline and chloramphenicol. An independent multi-antibiotic susceptible variant of strain YSH6000 had a similar deletion. Southern blot analysis of pulsed field electrophoresis gels enabled the sizing of this deletion and its mapping to a region of the chromosome on NotI fragment D bounded by the S. flexneri homologues of ompA and pyrC. Hybridisation experiments with a probe specific to the multi-antibiotic resistance region indicated that this large deletion was responsible for antibiotic susceptibility. Both strain S2430 and a derivative of the antibiotic-susceptible variant, with a Tn5 insertion in its SalI K fragment, exhibited an equal reduction in contact haemolysis compared with the Tn5-bearing derivative of strain YSH6000. However, strain S2430 alone clearly displayed delayed plaque forming ability in LLC-MK2 monolayers, suggesting that the two examples of this deletion may not be identical.
authors.affiliation: Department of Microbiology, Monash University, Clayton, Victoria, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Rajakumar
authors.forename: C
authors.initials: C
authors.lastname: Sasakawa
authors.forename: B
authors.initials: B
authors.lastname: Adler
mesh_terms: D015139:Blotting, Southern; D002872:Chromosome Deletion; D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry; D018432:Drug Resistance, Multiple / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D006461:Hemolysis / Q000235:genetics*; D011815:R Factors / Q000737:chemistry; D012763:Shigella flexneri / Q000187:drug effects / Q000235:genetics* / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial