ABSTRACT
Molecular epidemiology of verocytoxigenic Escherichia coli O157:H7 is important to help elucidate reservoirs and modes of transmission, particularly between animals and humans. As the recA gene locus is now beginning to gain application in bacterial genotyping schemes, and as it has not been examined previously in E. coli O157 isolates, this study aims to examine potential polymorphic variation as a possible epidemiological marker for the subspecies characterisation of clinically significant verocytotoxigenic E. coli O157:H7. A novel polymerase chain reaction (PCR) assay was designed to target a 638 bp region of the recA gene in E. coli O157 isolates. The PCR amplification of genomic DNA from extracted organisms was able to generate an amplicon of the expected size (approximately 638 bp) for all E. coli O157:H7 examined (n=80), as well as for other non-O157 E. coli and other members of the Enterobacteriaeceae including Citrobacter, Hafnia, Shigella, Enterobacter and Providencia. Subsequent restriction fragment length polymorphism (RFLP) and single-stranded conformational polymorphism (SSCP) analyses of these recA amplicons were able to differentiate E. coli O157 from the organisms examined, but were unable to distinguish between 79 isolates of wild-type E. coli O157, suggesting a highly conserved recA gene structure within the local population of organisms examined.
Subject(s)
Escherichia coli Infections/epidemiology , Escherichia coli O157/genetics , Genes, Bacterial , Rec A Recombinases/genetics , Animals , DNA Primers , DNA, Bacterial/genetics , Escherichia coli O157/classification , Escherichia coli O157/isolation & purification , Genetic Loci , Humans , Molecular Epidemiology , Northern Ireland/epidemiology , Polymerase Chain Reaction/methods , Polymorphism, Restriction Fragment Length , Polymorphism, Single-Stranded ConformationalABSTRACT
AIMS: To investigate the effect of sub-lethal challenge with tea tree oil (TTO) on the antibiotic resistance profiles of staphylococci. METHODS AND RESULTS: Isolates of methicillin-resistant/-sensitive Staphylococcus aureus (MRSA and MSSA) and coagulase-negative staphylococci (CONS) were habituated to sub-lethal concentrations of TTO (72 h). Following habituation, the minimum inhibitory concentrations (MIC) of antibiotics and TTO were determined. Habituated MRSA/MSSA cultures had higher (P < 0.05) MIC values than control cultures for the examined antibiotics. Habituated MRSA/MSSA cultures also displayed decreased susceptibility to TTO. Although the MIC of habituated MRSA/MSSA for the examined antibiotics reverted to control values after subsequent culture in the absence of TTO, the increased MIC against TTO were maintained. When compared with control cultures, habituated CoNS cultures had higher (P < 0.05) MIC values against three-fifths of the antibiotics examined; no changes in TTO MIC were observed. CONCLUSIONS: TTO habituation 'stress-hardens' MRSA and MSSA, evidenced by transient decreased antibiotic susceptibility and stable decreased TTO susceptibility. Although TTO habituation did not decrease susceptibility of CoNS to TTO, such cultures showed transient decreased antibiotic susceptibility. SIGNIFICANCE AND IMPACT OF THE STUDY: Application of TTO at sub-lethal concentrations may reduce the efficacy of topical antibiotics used with TTO in combination therapies.
Subject(s)
Anti-Bacterial Agents/toxicity , Anti-Infective Agents, Local/toxicity , Drug Resistance, Bacterial/drug effects , Melaleuca/chemistry , Staphylococcus aureus/drug effects , Tea Tree Oil/toxicity , Anti-Infective Agents, Local/pharmacology , Methicillin-Resistant Staphylococcus aureus/drug effects , Microbial Sensitivity Tests , Staphylococcus aureus/metabolism , Tea Tree Oil/pharmacologyABSTRACT
AIMS: To describe the interactions of imposed osmotic and nutritional stress on the morphology of stationary and exponential phase S. Virchow cells. METHODS AND RESULTS: This study examined the morphology and viability of osmotically stressed exponential and stationary phase cultures of Salmonella Virchow under nutritionally deficient and competent conditions. In addition to normal morphology, salt-stressed cultures exhibited filamentous and spherical morphotypes, which were capable of reversion to normal morphology on stress removal. Proportions of atypical morphotypes were influenced by the phase of growth when the stress was applied. Salt-stressed exponential phase populations contained 54% filamentous, 30% spherical forms, salt-stressed stationary phase populations contained 16% filamentous, 79% spherical forms. Proportions of morphotypes were also influenced by the nutrient status of the medium, but not by metabolic by-products. CONCLUSIONS: Development of a range of morphotypes in response to stress (osmotic/nutritional), may offer population level advantages, increasing the survival potential of the population. SIGNIFICANCE AND IMPACT OF STUDY: The application of sublethal concentrations of salt may stimulate S. Virchow morphotype diversity, improving survival and rates of poststress recovery.
