Epidemiology of bacterial enteric infections under active surveillance in Tennessee and Georgia, 2000-2002.
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Centers for Disease Control and Prevention, U.S.↗
Biomedical subjects
Timothy J Barrett
Publications and source records attributed to Timothy J Barrett.
Emergence of multidrug-resistant Salmonella enterica serotype Newport infections resistant to expanded-spectrum cephalosporins in the United States.
We describe a field investigation in New England that identified the emergence and epidemiology of new strains of multidrug-resistant Salmonella, Newport-MDRAmpC, and summarize the Center for Disease Control and Prevention's surveillance data for these infections. In Massachusetts, the prevalence of Newport-MDRAmpC among Salmonella serotype Newport isolates obtained from humans increased from 0% (0/14) in 1998 to 53% (32/60) in 2001 (P<.001). In a retrospective case-control study, infection with Newport-MDRAmpC was domestically acquired and was associated with exposure to a dairy farm. Isolates from both humans and cattle had indistinguishable or closely related antibiograms and pulsed-field gel electrophoresis patterns. Nationally, the prevalence of ceftriaxone-resistant Salmonella increased from 0.5% in 1998 to 2.4% in 2001; 85% of the isolates in 2001 were Newport-MDRAmpC, and at least 27 states have isolated these strains from humans, cattle, or ground beef. These data document the widespread emergence of Newport-MDRAmpC strains in the United States and show that the 5-fold increase in the prevalence of Salmonella resistant to expanded-spectrum cephalosporins, between 1998 and 2001, is primarily due to the emergence of Newport-MDRAmpC strains.
Adolescent↗
Reevaluating fluoroquinolone breakpoints for Salmonella enterica serotype Typhi and for non-Typhi salmonellae.
Salmonella enterica infections cause considerable morbidity and mortality worldwide. Antimicrobial therapy may be life-saving for patients with extraintestinal infections with S. enterica serotype Typhi or non-Typhi salmonellae. Because antimicrobial resistance to several classes of traditional first-line drugs has emerged in the past several decades, the quinolone antimicrobial agents, particularly the fluoroquinolones, have become the drugs of choice. Recently, resistance to nalidixic acid has emerged among both Typhi and non-Typhi Salmonella serotypes. Such Salmonella isolates typically also have decreased susceptibility to fluoroquinolones, although minimum inhibitory concentrations of the fluoroquinolones usually are within the susceptible range of the interpretive criteria of the NCCLS. A growing body of clinical and microbiological evidence indicates that such nalidixic acid-resistant S. enterica infections also exhibit a decreased clinical response to fluoroquinolones. In this article, we recommend that laboratories test extraintestinal Salmonella isolates for nalidixic acid resistance, we recommend that short-course fluoroquinolone therapy be avoided for infection with nalidixic acid-resistant extraintestinal salmonellae, and we summarize existing data and data needs that would contribute to reevaluation of the current NCCLS fluoroquinolone breakpoints for salmonellae.
Anti-Infective Agents↗
Strains of Escherichia coli O157:H7 differ primarily by insertions or deletions, not single-nucleotide polymorphisms.
Escherichia coli O157:H7 (O157) strains demonstrate varied pulsed-field gel electrophoresis patterns following XbaI digestion, which enable epidemiological surveillance of this important human pathogen. The genetic events underlying PFGE differences between strains, however, are not defined. We investigated the mechanisms for strain variation in O157 by recovering and examining nucleotide sequences flanking each of the XbaI restriction enzyme sites in the genome. Our analysis demonstrated that differences between O157 strains were due to discrete insertions or deletions that contained the XbaI sites polymorphic between strains rather than single-nucleotide polymorphisms in the XbaI sites themselves. These insertions and deletions were found to be uniquely localized within the regions of the genome that are specific to O157 compared to E. coli K-12 (O islands), suggesting that strain-to-strain variation occurs in these O islands. These results may be utilized to devise novel strain-typing tools for this pathogen.
Chromosomes, Bacterial↗
Polymorphic amplified typing sequences provide a novel approach to Escherichia coli O157:H7 strain typing.
Escherichia coli O157:H7 (O157) strains are commonly typed by pulsed-field gel electrophoresis (PFGE) following digestion of genomic DNA with the restriction enzyme XbaI. We have shown that O157 strains differ from each other by a series of discrete insertions or deletions, some of which contain recognition sites for XbaI, suggesting that these insertions and deletions are responsible for the differences in PFGE patterns. We have devised a new O157 strain typing protocol, polymorphic amplified typing sequences (PATS), based on this information. We designed PCR primer pairs to amplify genomic DNA flanking each of 40 individual XbaI sites in the genomes of two O157 reference strains. These primer pairs were tested with 44 O157 isolates, 2 each from 22 different outbreaks of infection. Thirty-two primer pairs amplified identical fragments from all 44 isolates, while eight primer pairs amplified regions that were polymorphic between isolates. The isolates could be differentiated solely on the basis of which of the eight polymorphic amplicons was detected. PATS correctly identified 21 of 22 outbreak pairs as being identical or highly related, whereas PFGE correctly identified 14 of the 22 outbreak pairs as being identical or highly related; PATS was also able to type isolates from three outbreaks that were untypeable by PFGE. However, PATS was less sensitive than PFGE in discriminating between outbreaks. These data suggest that typing by PATS may provide a simple procedure for strain typing of O157 and other bacteria and that further evaluation of the utility of this method for epidemiologic investigations is warranted.
Bacterial Typing Techniques↗
Salmonella enterica serotype Typhimurium DT104 isolated from humans, United States, 1985, 1990, and 1995.
First isolated from an ill person in 1985, multidrug-resistant Salmonella enterica serotype Typhimurium DT104 emerged in the mid-1990s as a strain of Salmonella frequently isolated from humans in the United States. We compared the integron content, plasmid profile, and XbaI pulsed-field gel electrophoresis (PFGE) patterns of multidrug-resistant S. Typhimurium DT104 (MR-DT104) isolated from humans in the United States in 1985, 1990, and 1995. All isolates contained a 60-mDa plasmid and had indistinguishable PFGE and integron profiles, supporting the idea of a clonal relationship between recent and historical isolates. The data suggest that the widespread emergence of MR-DT104 in humans and animals in the 1990s may have been due to the dissemination of a strain already present in the United States rather than the introduction of a new strain.
Drug Resistance, Multiple, Bacterial↗
Surveillance for human Salmonella infections in the United States.
Surveillance for human Salmonella infections plays a critical role in understanding and controlling foodborne illness due to Salmonella. Along with its public health partners, the Centers for Disease Control and Prevention (CDC) has several surveillance systems that collect information on Salmonella infections in the United States. The National Salmonella Surveillance System, begun in 1962, receives reports of laboratory-confirmed Salmonella infections through state public health laboratories. Salmonella outbreaks are reported by state and local health departments through the Foodborne Disease Outbreak Reporting System, which became a Web-based, electronic system (eFORS) in 2001. PulseNet facilitates the detection of clusters of Salmonella infections through standardized molecular subtyping (DNA "fingerprinting") of isolates and maintenance of "fingerprint" databases. The National Antimicrobial Resistance Monitoring System for Enteric Bacteria (NARMS) monitors antimicrobial resistance in Salmonella by susceptibility testing of every 20th Salmonella isolate received by state and local public health laboratories. FootNet is an active surveillance system that monitors Salmonella infections in sentinel areas, providing population-based estimates of infection rates. Efforts are underway to electronically link all of the Salmonella surveillance systems at CDC to facilitate optimum use of available data and minimize duplication.
Animals↗