O'Neill, Colette (2010) Antibiotic-resistant staphylococci in the agricultural environment : reservoirs of resistance and infection. PhD thesis, University of Warwick.

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Abstract

Antibiotic resistance is a serious problem in human and animal infections. Heavy use of
antibiotics in the agricultural environment selects for antibiotic resistance among the
microflora of food animals, providing a reservoir of antibiotic-resistant bacteria. These
may enter the human population through the food chain or by direct contact, as
demonstrated by the recent emergence of livestock-associated MRSA strains. Antibiotic
resistance determinants selected in this environment may also be available for transfer to
human commensals and pathogenic bacteria. Milk from conventional and organic farms
was screened for methicillin-resistant staphylococci to explore the hypothesis that
organic farming methods result in reduced selection for antibiotic resistance. A
significantly greater number isolates from conventionally farmed milk were resistant to
clindamycin, erythromycin, fusidic acid, tetracycline and tobramycin than isolates from
organic milk. Isolates from organic milk mostly belonged to S. fleurettii, which does not
cause any known pathogenesis or contribute to the mobile methicillin resistance
reservoir. Conventional milk harboured a greater number of pathogens, including S.
epidermidis and S. sciuri, both of which carried SCCmec. SCCmec elements were
diverse, some similar to those found in human-associated staphylococci, and some
distinct. The virulence-associated biofilm cluster icaADBC was identified in some S.
epidermidis isolates, indicating increased human pathogenesis. A putative new species,
S. lactis sp. nov. was isolated from a conventionally farmed herd, reflecting the high
diversity of staphylococci in this environment. In pig nasal swabs originating from
Thailand, LA-MRSA was identified for the first time. These isolates belonged to the
ST9/t337 lineage which has been identified previously in Europe, suggesting
importation of colonised pigs as the most likely route of dissemination. These contained
apossible new SCCmecvariant, and harboured toxin genes associated with human
disease. Isolates were resistant to medically important antibiotics including ciprofloxacin
and chloramphenicol. These data support the hypothesis that use of antibiotics in
agricultural practice may select for increased resistance in the microbiome of farm
animals, and that some of these may be able to cause infections in humans. Early
detection of MRSA is the key to effective treatment and control of dissemination; in
food production this would allow early identification of contaminated meat or dairy
products and prevent these from entering the food chain. The novel application of an
isothermal amplification assay, LAMP, was investigated for the sensitive and specific
detection of MRSA. Unfortunately, false negative reactions were common due to high
variability among SCCmec subtypes, and the possession of non-mec SCC elements by
methicillin-sensitive strains precluded this from offering a reliable alternative to existing
methods.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QR Microbiology
Library of Congress Subject Headings (LCSH):	Drug resistance in microorganisms, Milk -- Microbiology, Natural foods, Staphylococcus
Official Date:	November 2010
Dates:	Date Event November 2010 Submitted
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Gaze, William ; Wellington, E. M. H. (Elizabeth M. H.), 1954-
Sponsors:	Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC) ; Lumora Ltd.
Extent:	xiii, 221 leaves : ill., charts
Language:	eng

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