Evaluation of an in vitro model with a novel statistical approach to measure differences in bacterial survival of extended-spectrum ß-lactamase-producing Escherichia coli on an inanimate surface.

Background: The role of environmental contamination in the transmission of Enterobacteriaceae is increasingly recognized. However, factors influencing the duration of survival in the environment have not yet been extensively studied. In this study, we developed and evaluated an in vitro model with a novel statistical approach to accurately measure differences in bacterial survival, that can be used to model the effects of multiple factors/conditions in future experiments. Methods: Two extended-spectrum ß-lactamase (ESBL)-producing Escherichia coli (E. coli) isolates were used for this in vitro experiment: a CTX-M-15-producing E. coli sequence type (ST) 131 and a CTX-M-1-producing E. coli ST10 isolate. Each strain was 1:1 diluted in sterile water, sterile saline or sheep blood. Cover glasses (18 × 18 mm) were inoculated with the dilution and subsequently kept at room temperature. Bacterial survival on the glasses was determined hourly during the first day, once daily during the following 6 days, and from day 7 on, once weekly up to 100 days. The experiment was repeated six times for each strain, per suspension fluid. Results: Viable bacteria could be detected up to 70 days. A biphasic survival curve for all suspension fluids was observed, whereby there was a rapid decrease in the number of viable bacteria in the first 7 h, followed by a much slower decrease in the subsequent days. Conclusions: We found a difference in survival probability between E. coli ST10 and ST131, with a higher proportion of viable bacteria remaining after 7 h for ST131, particularly in sheep blood.

Dynamics and determinants of Staphylococcus aureus carriage in livestock veterinarians: a prospective cohort study.

BACKGROUND: Since 2003, a new clade of methicillin-resistant Staphylococcus aureus (MRSA) belonging to clonal complex (CC) 398 and associated with animal husbandry has emerged in the Netherlands. The purpose of this study was to determine the dynamics of carriage in persons with direct contact to livestock. METHODS: A 2-year prospective cohort study was performed in which the anterior nares and oropharynx of 137 livestock veterinarians were sampled for the presence of S. aureus every 4 months during the first year and again 1 year later. All S. aureus isolates were genotyped by staphylococcal protein A (spa) typing and with multilocus variable-number tandem repeat analysis (MLVA). RESULTS: The mean prevalence of MRSA CC398 carriage was 44% (range, 42%-46%), and for S. aureus the prevalence was 72% (range, 69%-75%). Thirty-two veterinarians (23%) were always carrying MRSA CC398 and 18 of those (56%, 13% of all veterinarians) had identical MLVA types at all sampling moments. CONCLUSIONS: A high proportion of veterinarians had persistent MRSA CC398 carriage during the 2-year study period, indicating that this variant may colonize humans for prolonged periods. Furthermore, prevalence of S. aureus carriage was extremely high, indicating that MRSA CC398 is not replacing the susceptible strains, but comes on top of it.