Dissemination of CTX-M type extended-spectrum beta-lactamase
(ESBL)-producing Escherichia coli (E. coli) is a serious health issue in Hong Kong.
However, research knowledge concerning its dissemination mechanism and plasmid
characteristics over time in health care setting is still limited.
This study was conducted to characterize ESBL-producing E. coli from blood
culture isolates and the epidemiology of the plasmids harboring CTX-M-14 collected
from a healthcare region in Hong Kong from two periods of time.
A total of 167 ESBL-producing E. coli in blood culture specimens were retrieved
from period 1 (1996 - 1999, n = 50) and period 2 (2007 - 2008, n = 117).
Antimicrobial susceptibilities were defined by disk diffusion method according to
CLSI. Phylogenetic groups and CTX-M enzymes were detected among all the
ESBL-producers. Clonal relatedness of the hosts was analyzed by pulsed-field gel
electrophoresis and multi-locus sequence typing. A subset of 65
CTX-M-14-producing isolates was undergone for further plasmid characterization.
Conjugation, PCR-based replicon typing, S1-PFGE, southern-blot hybridization, and
genetic environment PCRs were performed. Plasmid PCR-restriction fragment length
polymorphism (pRFLP), F-allele replicon sequence typing and variable region PCRs
were studied in 54 F-plasmids obtained.
Results showed that over half of the ESBL-positive isolates were non-susceptible
to ciprofloxacin, cotrimoxazole and gentamicin. A surprisingly high number of
CTX-M-type ESBL was carried by 98.2% (164/167) of the isolates. CTX-M-9 group
(89.8%, 150/167) and CTX-M-14 (103/109) were predominantly found among both
periods. Overall, nearly half (41.3%, 69/167) of the isolates belonged to 5 major
clones. Clonal types undetermined-ST68 (n = 18) and O102-ST405 (n = 15) were
dominant in period 1 while clonal types O25b-ST131 (n = 30), O15-ST69 (n = 5) and
O12-ST12 (n = 3) emerged in period 2.
Among a subset of 65 CTX-M-14 plasmids, most of them were transferable
(84.6%, 55/65) with high frequency, similar plasmid sizes and genetic environment
ISEcp1-blaCTX-M-14-IS903 (90.8%, 59/65). Replicon types of the CTX-M-14 encoding
plasmids were FII (n = 48) or FII ± FIA/FIB types (n = 6), I1-I (n = 3), B/O (n = 2),
K (n = 1) and undetermined (n = 4). Subtyping of 54 IncF plasmids by replicon
sequence typing, pRFLP and PCR for marker genes (yac, malB, eitA, eitC and parAB)
showed that 79.6% (43/54) of the plasmid subset exhibited identical or highly similar
results with the completely sequenced plasmid, pHK01 (E. coli isolated from urine
sample of a patient in Hong Kong, 2004). These 43 plasmids were originated from
both period 1 (n = 11) and period 2 (n = 32). These pHK01-like plasmids were found
to have spread to the major clones (ST68, ST405 and ST131) and multiple singleton
isolates of all four phylogenetic groups.
In conclusion, this study demonstrated the widespread dissemination of
pHK01-like CTX-M-14 encoding plasmids among isolates of diverse genetic lineages
over a decade. The dissemination was probably due to both clonal expansion and
horizontal gene transfer of pHK01-like IncF plasmid. / published_or_final_version / Microbiology / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/174386 |
| Date | January 2011 |
| Creators | Yeung, Man-kiu., 楊敏翹. |
| Contributors | Ho, PL, Tse, H |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47326232 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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