Search

Ampicillin-resistant (Ampr) Salmonella enterica isolates (n = 344) representing 32 serotypes isolated from retail meats from 2002 to 2006 were tested for susceptibility to 21 other antimicrobial agents and screened for the presence of five beta-lactamase gene families (blaCMY, blaTEM, blaSHV, blaOXA, and blaCTX-M) and class 1 integrons. Among the Ampr isolates, 66.9% were resistant to five or more antimicrobials and 4.9% were resistant to 10 or more antimicrobials. Coresistance to other β-lactams was noted for amoxicillin-clavulanic acid (55.5%), ceftiofur (50%), cefoxitin (50%), and ceftazidime (24.7%), whereas less than 5% of isolates were resistant to piperacillin-tazobactam (4.9%), cefotaxime (3.5%), ceftriaxone (2%), and aztreonam (1.2%). All isolates were susceptible to cefepime, imipenem, and cefquinome. No Salmonella producing extended-spectrum beta-lactamases was found in this study. Approximately 7% of the isolates displayed a typical multidrug-resistant (MDR)-AmpC phenotype, with resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, tetracycline, plus resistance to amoxicillin-clavulanic acid, cefoxitin, and ceftiofur and with decreased susceptibility to ceftriaxone (MIC 4 μg/ml). Pulsed-field gel electrophoresis results showed that several MDR clones were geographically dispersed in different types of meats throughout the five sampling years. Additionally, 50% of the isolates contained blaCMY, 47% carried blaTEM-1, and 2.6% carried both genes. Only 15% of the isolates harbored class I integrons carrying various combinations of aadA, aadB, and dfrA gene cassettes. The blaCMY, blaTEM, and class 1 integrons were transferable through conjugation and/or transformation. Our findings indicate that a varied spectrum of coresistance traits is present in Ampr Salmonella strains in the meat supply of the United States, with a continued predominance of blaCMY and blaTEM genes in β-lactam-resistant isolates. [ABSTRACT FROM AUTHOR]

The spirochetes inhabiting the large intestines of humans and animals consist of a diverse group of related organisms. Intestinal spirochetosis caused by Serpulina pilosicoli is a newly recognized enteric disease of human beings and animals with potential public health significance. The purpose of this study was to determine the species identity of canine intestinal spirochetes by comparing 30 isolates obtained from dogs in Australia (n = 25) and the United States (n = 5) with reference strains representing Serpulina species and Brachyspira aalborgi, by phenotypic and genetically based typing methods. All of the canine isolates were indole negative and produced a weak beta-hemolysis when cultured anaerobically on agar medium containing blood. Four isolates were identified as S. pilosicoli by 16S rRNA-specific PCR assays, rRNA gene restriction fragment length polymorphism or ribotyping, and multilocus enzyme electrophoresis. The remaining 26 isolates formed a cluster related to porcine Serpulina innocens as determined by multilocus enzyme electrophoresis but had a unique ribotype pattern. The data suggested the existence of a novel Serpulina species, provisionally designated "Serpulina canis," colonizing the intestines of dogs.

We compared four phenotypic and six genotypic methods for distinguishing Campylobacter jejuni strains from animals and humans involved in four epidemics. Based on a comparison with epidemiologic data, the methods that correctly identified all strains in three milkborne outbreaks and one waterborne outbreak were heat-stable and heat-labile serotyping; multilocus enzyme electrophoresis (MEE); DNA restriction endonuclease analysis with BglII, XhoI, PvuII, or PstI; and Southern blot and hybridization of PvuII- and PstI-digested DNA with Escherichia coli 16S and 23S rRNA (ribotyping). Biotyping, phage typing, plasmid analysis, and probing of BglII and XhoI DNA digests with C. jejuni 16S rRNA genes failed to correctly separate one or more strains. MEE, restriction endonuclease analysis, and ribotyping were the most sensitive methods and identified nine types among the 22 strains. These methods were also capable of further distinguishing strains within the same serotype. Data from MEE were also analyzed to calculate genetic relatedness among strains. Serotyping was the most discriminating phenotypic method, with eight and seven types distinguished by the heat-stable and heat-labile methods, respectively. MEE and ribotyping had several advantages over the other methods because they measure relatively stable and significant chromosomal differences and are applicable to other species and genera. These methods, however, are complex and not easily quantified; they are currently limited to specialized laboratories. When antisera are available, serotyping appears to be an effective and more practical approach to the identification of epidemic-related strains.

Genetic diversity and relationships among 42 strains of Citrobacter diversus recovered from the cerebrospinal fluid of human infants with meningitis and from other clinical sources in the United States were estimated on the basis of electrophoretically detectable allelic variation in 20 genes encoding metabolic enzymes. Sixteen distinctive multilocus enzyme genotypes were identified, among which the mean genetic diversity per locus was 0.244. The recovery of isolates of the same genotype in several regions of the United States and over periods as long as 20 years indicates that the population structure of C. diversus is clonal. There was little association between multilocus enzyme genotype and biotype, piliation, or presence of a 32-kilodalton outer membrane protein. The observation that the 32-kilodalton outer membrane protein, which is expressed predominantly by strains recovered from infants with meningitis, occurs in a variety of genotypically diverse clones belonging to several phylogenetic lineages supports the hypothesis that this protein confers virulence.

Pulsed-field gel electrophoresis techniques were used to examine the chromosomes of Pneumocystis carinii isolated from laboratory rats and two human subjects. P. carinii organisms isolated from each of four rat colonies and from two patients each produced a distinct band pattern, but in all cases the bands ranged in size from 300 to 700 kilobase pairs. P. carinii from three rat colonies produced patterns containing 15 prominent bands. Of these 15 bands, 2 stained more intensely than would be expected of bands of their size, suggesting that the P. carinii haploid genome contains 17 to 19 chromosomes. Summing the molecular sizes of the bands and accounting for staining intensities suggested that the haploid genome of rat-derived P. carinii contains on the order of 10(7) base pairs. Human-derived P. carinii produced patterns containing 10 to 12 bands which appeared to be similar to the 15-band patterns seen in rat-derived P. carinii with respect to the size range of the bands. P. carinii from the fourth rat colony produced a more complex band pattern containing approximately 22 bands, most of which appeared to comigrate with the bands present in one of the 15-band P. carinii patterns, suggesting that these animals were simultaneously infected by two different varieties of P. carinii. Hybridization experiments using oligonucleotide probes specific for the P. carinii 18S rRNA gene supported this possibility. The band pattern of P. carinii derived from a given rat colony was generally stable over time. P. carinii band patterns were not strictly rat strain specific and appeared to be transferrable between animals housed in the same room.

To investigate the microbiology and epidemiology of the 1,700 sporadic cases of listeriosis that occur annually in the United States, we developed a multilocus enzyme electrophoresis (MEE) typing system for Listeria monocytogenes. We studied 390 isolates by MEE. Eighty-two electrophoretic types (ETs) were defined. Two distinct clusters of ETs, ET group A (ETGA) and ET group B (ETGB), separated at a genetic distance of 0.440, were identified. Strains of ETGB were associated with perinatal listeriosis (P = 0.03). All strains of H antigen type a were in ETGA, while all strains of H antigen type b were in ETGB. Among 328 clinical isolates from cases of literiosis, 55 ETs of L. monocytogenes were defined. Thirty-four ETs were identified among 62 isolates from food products. The mean number of strains per ET (5.2) was significantly higher among clinical isolates than among food-borne isolates. Examination of isolates from outbreaks further documented the link between cases and contaminated food products. In one investigation, we found 11 different ETs, ruling out a single common source as a cause of that outbreak. By examining a large number of isolates collected over a specified time in diverse geographic locations in the United States, we have begun to establish a baseline for the study of the epidemiology of listeriosis by MEE.