Biomedical subjects

David A McDowell

Publications and source records attributed to David A McDowell.

6 recordsLinked to original sources

PubMed2006

Environmental stress and antibiotic resistance in food-related pathogens.

This study investigated the possibility that sublethal food preservation stresses (high or low temperature and osmotic and pH stress) can lead to changes in the nature and scale of antibiotic resistance (ABR) expressed by three food-related pathogens (Escherichia coli, Salmonella enterica serovar Typhimurium, and Staphylococcus aureus). The study found that some sublethal stresses significantly altered antibiotic resistance. Incubation at sublethal high temperature (45 degrees C) decreased ABR. Incubation under increased salt (>4.5%) or reduced pH (<5.0) conditions increased ABR. Some of the pathogens continued to express higher levels of ABR after removal of stress, suggesting that in some cases the applied sublethal stress had induced stable increases in ABR. These results indicate that increased use of bacteriostatic (sublethal), rather than bactericidal (lethal), food preservation systems may be contributing to the development and dissemination of ABR among important food-borne pathogens.

Adaptation, Physiological↗

PubMed2006

Role of branched-chain fatty acids in pH stress tolerance in Listeria monocytogenes.

In alkaline conditions, Listeria monocytogenes cells develop higher proportions of branched-chain fatty acids (FAs), including more anteiso forms. In acid conditions, the opposite occurs. Reduced growth of pH-sensitive mutants at adverse pH (5.0/9.0) was alleviated by the addition of 2-methylbutyrate (an anteiso-FA precursor), suggesting that anteiso-FAs are important in adaptation to adverse pH. The balance between anteiso- and iso-FAs may be more important than changes in the amounts and/or degrees of saturation of FAs in pH adaptation.

Adaptation, Physiological↗

PubMed2006

Habituation to sub-lethal concentrations of tea tree oil (Melaleuca alternifolia) is associated with reduced susceptibility to antibiotics in human pathogens.

OBJECTIVES: To investigate the effect of sub-lethal challenge with tea tree oil (TTO) on the antibiotic susceptibility profiles of significant human pathogens and commensals. METHODS: The study compared the antibiotic susceptibility (Etest) patterns of Escherichia coli, Staphylococcus aureus/methicillin-resistant S. aureus (MRSA) and Salmonella spp. after broth culture for 72 h in the presence or absence of sub-lethal concentrations of TTO (0.25%, 0.25% and 0.1%). RESULTS: All habituated cultures (exposed to sub-lethal concentrations of TTO) displayed reduced susceptibility to a range of clinically relevant antibiotics compared with non-habituated (control) cultures. CONCLUSIONS: Although TTO may be an effective antimicrobial agent when appropriately used at bactericidal concentrations, its application at sub-lethal concentrations may contribute to the development of antibiotic resistance in human pathogens.

Drug Resistance, Bacterial↗

PubMed2006

The epidemiology of antibiotic resistance in Campylobacter.

Antibiotic resistance, particularly with the fluoroquinolones and macrolide antibiotics, has now emerged globally with thermophilic campylobacters, including Campylobacter jejuni and C. coli, giving rise to concerns about how these organisms have acquired such resistance characteristics, as well as consequences for human and animal treatment. This review examines (i) the clinical epidemiology of antibiotic resistance in human and animal thermophilic campylobacters, (ii) an update on resistance rates globally, (iii) surveillance of antimicrobial resistance in campylobacters originating from animals, particularly poultry, (iv) the role of the environment in the acquisition and transmission of antibiotic-resistant campylobacters, as well as (v) issues of biocide resistance in campylobacters.

Animals↗

PubMed2006

Survival and recovery of Salmonella enterica serovar Typhimurium DT104 at low temperature and water activity in a broth system.

This study investigated the survival of Salmonella enterica serovar Typhimurium DT104 in a broth system under conditions of low temperature (4 degrees C) and low water activity (aw, 0.92 to 0.96). Incubation under these conditions resulted in significant reductions in the viability of stationary phase cells, determined by direct plating on selective XLD medium. Reductions in viable numbers were related to injury associated with initial osmotic shock (hyperosmosis) and further injury associated with longer-term storage under the above conditions. Such injured cells were, however, capable of recovering on a nonselective medium (TSA) and contributing to overall viable cell numbers in nonselective post-storage conditions. Storage at more extreme conditions, at lower aw values, led to cell death at rates influenced by storage temperature. Finally, the data obtained are considered in relation to pathogen survival on the surfaces of beef carcasses during chilling.

Animals↗

PubMedDate not supplied

Campylobacter.

Species within the genus, Campylobacter, have emerged over the last three decades as significant clinical pathogens, particularly of human public health concern, where the majority of acute bacterial enteritis in the Western world is due to these organisms. Of particular concern are the species, C. jejuni and C. coli, which are responsible for most of these gastrointestinal-related infections. Although these organisms have already emerged as causative agents of zoonoses, several aspects of their epidemiology and pathophysiology are only beginning to emerge. Trends in increasing antibiotic resistance are beginning to emerge with oral antibiotics, which may be the drug of choice for when it is necessary to intervene chemotherapeutically. This review wishes to examine (i) emerging clinical aspects of the disease, such as Guillain Barre syndrome (GBS), (ii) the association between these organisms and poultry as a natural host, (iii) environmental aspects of Campylobacter epidemiology, (iv) the emergence of atypical campylobacters (v) emerging trends in antibiotic resistance, (vi) adoption of modern methods for the detection of campylobacters.

Animals↗