A major outbreak involving an Escherichia coli strain that was resistant to expanded-spectrum cephalosporins occurred in Toronto and surrounding regions in 2000 to 2002. We report the complete sequence of a plasmid, pC15-1a, that was found associated with the outbreak strain. Plasmid pC15-1a is a circular molecule of 92,353 bp consisting of two distinct regions. The first is a 64-kb region that is essentially homologous to the non-R-determinant region of plasmid R100 except for several point mutations, a few small insertions and deletions, and the absence of Tn10. The second is a 28.4-kb multidrug resistance region (MDR) that has replaced the R-determinant region of the R100 progenitor and consists mostly of transposons or partial transposons and five copies of the insertion element IS26. All drug resistance genes found in pC15-1a, including the beta-lactamase genes bla CTX-M-15 , bla OXA-1 , and bla TEM-1 , the tetracycline resistance gene tetA, and aminoglycoside resistance genes aac(6)-Ib and aac(3)-II, are located in the MDR. The bla CTX-M-15 gene was found downstream of ISEcp1as part of a transposition unit, as determined from the surrounding sequence. Examination of the plasmids from CTX-M-15-harboring strains isolated from hospitals across Canada showed that pC15-1a was found in several strains isolated from a site in western Canada. Comparison of pC15-1a and pCTX15, found in an E. coli strain isolated in India in 1999, revealed that the plasmids had several features in common, including an R100 backbone and several of the resistance genes, including bla CTX-M-15 , bla TEM-1 , bla OXA-1 , tetA, and aac(6)-Ib.Plasmid-mediated extended-spectrum beta-lactamase (ESBL) enzymes are most commonly of the TEM, SHV, or CTX-M type (8). To date more than 120 TEM enzymes, more than 50 SHV enzymes, and more than 30 CTX-M enzymes have been reported (www.lahey.org/studies/). Members of these groups are class A enzymes and, for the most part, are inhibited by clavulanic acid.The CTX-M-type beta-lactamases are increasingly found in enterobacterial species throughout the world; more than half have been reported within the last 4 years (7, 28). They are generally most active against cefotaxime and show little activity against ceftazidime. Phylogenetically, they are grouped into five clusters based on their amino acid identities: the CTX-M-1 cluster etc.), the CTX-M-2 cluster etc.), the CTX-M-8 cluster (CTX-M-8), the CTX-M-25 cluster , and the CTX-M-9 cluster

Variations in organizational and individual factors can explain much of the variations in self-protective behavior in health care settings. It is likely that these factors were also important determinants during the SARS outbreaks, but they have not been extensively studied.

Failure to implement appropriate barrier precautions is responsible for most nosocomial transmissions. However, the possibility of a gradation of infectious particles generated by aerosolizing procedures suggests that traditional droplet transmission prevention measures may be inadequate in some settings. Further research is needed in this area.

Reverse transcriptase polymerase chain reaction was used to determine the amount of overexpression of the ampC gene in 52 cefoxitin-resistant Escherichia coli clinical isolates that had previously characterized mutations in their ampC promoter/attenuator regions. The results showed that mutations that create a consensus -35 box (TTGACA) are the most important factor in strengthening the ampC promoter, followed by base pair insertions that increase the distance between the -35 and -10 boxes to 17 or 18 bp. Mutations in the -10 box are of lesser importance and those in the attenuator region appear to have little effect on ampC expression. Three strains overexpress ampC due to the effect of insertion elements located in the ampC promoter regions. Further, the data show that there is no correlation between ampC overexpression and the minimum inhibition concentration of cefoxitin in clinical isolates. Overall, the data indicate that a combination of ampC promoter mutations and other strain-specific factors combine to contribute to the magnitude of cefoxitin resistance in E. coli.

A study designed to gain baseline information on strains of Escherichia coli displaying resistance to cefoxitin in Canada is described. A total of 29,323 E. coli isolates were screened at 12 participating hospital sites as part of an extended-spectrum beta-lactamase surveillance initiative. A total of 411 clinically significant, nonrepeat isolates displaying reduced susceptibilities to the NCCLS-recommended beta-lactams were submitted to a central laboratory over a 1-year period ending on 30 September 2000. Two hundred thirty-two isolates were identified as resistant to cefoxitin. All cefoxitin-resistant strains were subtyped by pulsed-field gel electrophoresis, and of these, 182 strains revealed a unique fingerprint and 1 strain was untypeable. PCR and sequence analysis of the ampC promoter region revealed 51 different promoter or attenuator variants and 14 wild-type promoters. Three promoter regions were interrupted by insertion elements, two contained IS10 elements, and one contained an IS911 variant. PCR and sequence analysis for the detection of acquired AmpC resistance (by the acquisition of ACT-1/MIR-1, CMY-2, or FOX) revealed that 25 strains contained CMY-2, including 7 of the strains found to have wild-type promoters. The considerable genetic variability in both the strain fingerprint and the promoter region suggests that AmpC-type resistance may emerge spontaneously by mutation of sensitive strains rather than by the spread of strains or plasmids in the hospital setting.Escherichia coli contains a chromosomal ampC gene which has a weak promoter as well as a transcriptional attenuator (13,14). Strains carrying the wild-type gene produce a low basal amount of AmpC and are susceptible to ampicillin. Analysis of cefoxitin-resistant strains has revealed that the ampC promoter and attenuator regions often carry mutations leading to the overproduction of the enzyme (3,4,5,7,10,14,20,21,22,29). These AmpC-overproducing strains are not only resistant to ampicillin but also usually have reduced susceptibilities to expanded-spectrum cephalosporins. Genetically, the most common mutations are those that create a strong promoter that more closely resembles the E. coli consensus promoter (12) and mutations that destabilize the attenuator.Plasmid-mediated ampC genes were first reported in 1988 (25, 31). The plasmid-mediated ampC genes are derived from inducible chromosomal genes that have become mobilized (11,24,25). The first genetically characterized plasmid-mediated AmpC was MIR-1, which was mobilized from an Enterobacter isolate (23). These plasmid-mediated genes are of special interest because their mobility allows them to emerge in one genus or species and spread to different organisms. The prevalence of plasmid-mediated AmpC-type resistance at the national level in most countries is unknown because studies have not examined the strains at the molecular level of detail required to elucidate the different mechanisms involved. A recent report from the United States, however, showed that among 752 Klebsiella spp. a...

Mupirocin resistance in

Two thousand seven hundred eighty single-patient, methicillin-resistant Staphylococcus aureus (MRSA) isolates collected between January 1995 and December 1999 at 17 tertiary care hospital sites across Canada were characterized by phenotypic and genotypic techniques. Six clonal types, as defined by pulsed-field gel electrophoresis, comprised 87% of all isolates and were labeled Canadian (C) MRSA-1 through -6. CMRSA-1 was the most prevalent clonal type, representing 45% of all MRSA. CMRSA-2 was indistinguishable from the New York clone and was more likely to be associated with community acquisition. CMRSA-3 was more likely to cause an infection, compared with the other CMRSA types. CMRSA-4 was indistinguishable from epidemic (E) MRSA-16 from the United Kingdom. Both CMRSA-5 and -6 occurred primarily in single-site, multiyear outbreaks. This study confirms that the epidemiology of MRSA in Canada is evolving, but most isolates at this time appear to belong to one of a small number of epidemic clones.

This report describes a study carried out to gain baseline information on the molecular characteristics of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella spp. in Canada. A total of 29,323 E. coli and 5,156 Klebsiella sp. isolates were screened at 12 participating sites. Of these, 505 clinically significant, nonrepeat isolates displaying reduced susceptibility to the NCCLS-recommended beta-lactams were submitted to a central laboratory over a 1-year period ending on 30 September 2000. A total of 116 isolates were confirmed to be ESBL producers. PCR and sequence analysis revealed the presence of TEM-11 (n ‫؍‬ 1), TEM-12 (n ‫؍‬ 1), TEM-29 (n ‫؍‬ 1), TEM-52 (n ‫؍‬ 4), CTX-M-13 (n ‫؍‬ 1), CTX-M-14 (n ‫؍‬ 15), CTX-M-15 (n ‫؍‬ 11), SHV-2 (n ‫؍‬ 2), SHV-2a (n ‫؍‬ 12), SHV-5 (n ‫؍‬ 6), SHV-12 (n ‫؍‬ 45), and SHV-30 (n ‫؍‬ 2). Five novel beta-lactamases were identified and designated TEM-115 (n ‫؍‬ 2), TEM-120 (n ‫؍‬ 1), SHV-40 (n ‫؍‬ 2), SHV-41 (n ‫؍‬ 4), and SHV-42 (n ‫؍‬ 1). In addition, no molecular mechanism was identified for five isolates displaying an ESBL phenotype. Macrorestriction analysis of all ESBL isolates was conducted, as was restriction fragment length polymorphism analysis of plasmids harboring ESBLs. Although a "clonal" distribution of isolates was observed at some individual sites, there was very little evidence suggesting intrahospital spread. In addition, examples of identical or closely related plasmids that were identified at geographically distinct sites across Canada are given. However, there was considerable diversity with respect to plasmid types observed.Infections caused by aerobic gram-negative bacilli are common in hospitalized patients and result in serious infections, such as bacteremia and the majority of cases of nosocomial pneumonia (8, 32). These infections also are associated with high rates of mortality; for example, sepsis is one of the most common causes of death in intensive-care-unit patients (32,35). The emergence of gram-negative bacilli that contain extended-spectrum beta-lactamases (ESBLs) and AmpC cephalosporinases has compounded this problem and has become a worldwide concern (7).The first ESBL was identified in Germany in 1983; since then, over 200 variants of the clavulanic acid-inhibited form of the enzyme have been described worldwide. The most common extended-spectrum phenotypes arise from point mutations in the bla TEM , bla SHV , or bla CTX gene resulting in alterations of the primary amino acid sequence of the enzyme (7). Since these genes are generally found on plasmids, many of the organisms that harbor ESBLs also are resistant to other classes of antibiotics, such as aminoglycosides, fluoroquinolones, tetracyclines, chloramphenicol, and sulfonamides (24).In this study, we examined the molecular characteristics of ESBLs isolated over a 1-year period in 12 Canadian hospitals. MATERIALS AND METHODSSurveillance network. Established in 1995, The Canadian Nosocomial Infection Surveillance Program (CNISP) is a collaborative effort in...