JAC Advance Access originally published online on July 23, 2007
Journal of Antimicrobial Chemotherapy 2007 60(4):906-908; doi:10.1093/jac/dkm277
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Correspondence |
High prevalence of CTX-M-15 extended-spectrum ß-lactamase among contacts of patients with shigellosis due to Shigella flexneri carrying CTX-M-15
1 Clinical Microbiology, Lab Plus, Auckland City Hospital, Auckland, New Zealand 2 Population Protection Group, Auckland Regional Public Health Service, Auckland, New Zealand 3 Clinical Microbiology, Middlemore Hospital, Auckland, New Zealand 4 Antibiotic Reference Laboratory, Institute of Environmental Science and Research, Wellington, New Zealand
* Corresponding author. Tel: +64-9-307-4949 ext. 6411; Fax: +64-9-307-4939; E-mail: arlou{at}adhb.govt.nz
Keywords: Escherichia coli , antibiotic resistance , community
Extended-spectrum ß-lactamases (ESBLs) are plasmid-mediated bacterial enzymes that hydrolyse extended-spectrum cephalosporins, conferring resistance to penicillins, cephalosporins and aztreonam. In New Zealand, ESBL-producing organisms are relatively uncommon. We report here on the epidemiological and microbiological investigation of four cases of shigellosis due to Shigella flexneri with CTX-M-15 ESBL.
On 2 October 2006, a 36-year-old woman (case 1) was admitted to Auckland City Hospital with a 1-day history of dysentery, abdominal pain and fever. S. flexneri was isolated from her faeces, and the isolate was confirmed as producing an ESBL by the CLSI combination disc test.1 Two further cases with ESBL-producing S. flexneri were subsequently identified: a 31-year-old woman, sister of case 1 (case 2), and a 5-year-old boy (case 3). Both had been assessed at a nearby hospital during the preceding 3 weeks. Public health investigation revealed that case 1 and case 2 lived in the same household (family A), whereas case 3 lived in a related household (family B). Both cases 1 and 2 lived with and cared for case 1’s 4-year-old son who had developed a gastrointestinal illness on 18 September 2006. This boy did not have microbiological investigation until 3 November 2006, by which time no Shigella was isolated from his faeces. However, given his history and the relationship with the cases, he was considered to be a probable case (probable case 4).
Twenty contacts, sharing household toilet facilities used by cases during the symptomatic phase of their illness, from three different households were identified. These contacts included 4 household contacts of case 1, case 2 and probable case 4 (family A), 11 household contacts of case 3 (family B and family C) and 5 contacts in a third household (family D) (Figure 1). All contacts were closely related through family and cultural ties. Seven contacts, three from family B (brother and parents of case 3) and four from family C, had recently spent 6 weeks in Central Asia and had returned to New Zealand on 14 August 2006. None of the cases had recently travelled overseas. Two contacts, both children who had travelled to Central Asia, had developed an illness consistent with shigellosis while overseas. One of these contacts had Salmonella Enteritidis isolated from a faeces specimen in November 2006.
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Eighteen of the 20 contacts submitted faeces specimens that were cultured for ESBL-producing Enterobacteriaceae. Faeces were inoculated onto two MacConkey agar plates: one containing ceftazidime 1 mg/L and the other containing cefotaxime 1 mg/L. Oxidase-negative colonies were identified by routine phenotypic tests. Isolates that grew on either ceftriaxone 1 mg/L or ceftazidime 1 mg/L Mueller–Hinton agar dilution breakpoint plates were confirmed as ESBL producers using the CLSI combination disc test.1 PCR, using consensus primers for blaTEM, blaSHV and blaCTX-M,2–4 and sequencing of PCR products were used to identify the specific ESBL gene.
No Shigella were isolated from the contacts. Seventeen ESBL-producing Escherichia coli were isolated from the faeces of case 3, probable case 4 and 12 contacts, including all 7 contacts who had travelled to Central Asia (Figure 1). The ESBL in the S. flexneri isolates from the three cases and the 17 E. coli isolates was identified as CTX-M-15.
The relatedness of the three S. flexneri isolates and the 17 ESBL-producing E. coli isolates was determined by PFGE after digestion with XbaI restriction enzyme. The three S. flexneri isolates were indistinguishable. Among the 17 ESBL-producing E. coli, there were 10 distinct strains, with 1 strain isolated from seven people and another strain from two people. The other eight strains were each isolated from only one person. Three people had two strains of ESBL-producing E. coli. None of the 10 strains had previously been identified among ESBL-producing E. coli in New Zealand (H. Heffernan, Institute of Environmental Science and Research).
With the exception of one female adult contact who had a single-day maternity-related visit to Auckland City Hospital, none of contacts had been admitted to hospital either in New Zealand or overseas in the year prior to this outbreak. Seven of the 16 people with an ESBL-producing organism had received oral antibiotics in the previous 12 months.
Infections due to ESBL-producing organisms are predominantly hospital-acquired, although ESBL-producing organisms have recently been isolated from people in the community. The majority of these people have a chronic medical condition, a history of recent antibiotic use and/or healthcare contact.5–8 Genuine community-acquired ESBLs among patients without known risk factors are not well described. ESBL production has been infrequently reported in Shigella species.9,10
Our results show a high rate of carriage of the CTX-M-15 gene among members of three households in a community setting with minimal risk factors for carriage of multiresistant organisms. Bacteria with this gene were isolated from 67% of people examined. Further information on the prevalence of ESBL carriage in the community would be useful and may impact future infection control strategies.
No funding was received for this study.
None to declare.
Acknowledgements
We would like to acknowledge the assistance of Dr David Karthak.
References
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Kim S, Kim J, Kang Y, et al. Occurrence of extended-spectrum ß-lactamases in members of the genus Shigella in the Republic of Korea. J Clin Microbiol (2004) 42:5264–9.
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