Syphilis outbreak in Walsall, UK: lessons for control and prevention

An assessment of risk-taking behaviour among men who have sex with men (MSM) attending a sauna venue was undertaken, using a standardized questionnaire, after which outreach screening was introduced targeting MSM. The epidemiology of the continuing outbreak of syphilis was reviewed to determine the factors driving the outbreak and assess the benefit of continuing outreach screening. Findings among the 163 respondents at the sauna included a high rate of casual sex and a tendency not to disclose HIV status. Over 12 months, 51 cases of early syphilis were recorded. Our review showed a decline in incidence in MSM after outreach screening, but an increase in heterosexual spread. Given the frequent anonymous nature of syphilis transmission, traditional contact tracing is ineffective. Outreach screening is required at gay venues and other community settings to target at-risk populations.

Isolation and characterization of Staphylococcus aureus strains from a Paso del Norte dairy

The primary purpose of this study was to determine if methicillin-resistant Staphylococcus aureus (MRSA) strains could be identified in the milk of dairy cattle in a Paso del Norte region dairy of the United States. Using physiological and PCR-based identification schemes, a total of 40 Staph. aureus strains were isolated from 29 raw milk samples of 133 total samples analyzed. Pulsed-field gel electrophoresis after digestion with the SmaI enzyme revealed that the 40 confirmed strains were represented by 5 pulsed-field types, which each contained 3 or more strains. Of 7 hospital strains isolated from cows undergoing antibiotic therapy, 3 demonstrated resistance to 3 or more antimicrobial classes and displayed similar pulsed-field gel electrophoresis patterns. A secondary purpose of this study was to elucidate the evolutionary relationships of strains isolated in this study to genomically characterized Staph. aureus strains. Therefore, Roche 454 GS (Roche Diagnostics Corp., Dallas, TX) pyrosequencing was used to produce draft genome sequences of an MRSA raw milk isolate (H29) and a methicillin-susceptible Staph. aureus (PB32). Analysis using the BLASTn database (http://blast.ncbi.nlm.nih.gov/) demonstrated that the H29 draft genome was highly homologous to the human MRSA strain JH1, yet the β-lactamase plasmid carried by H29 was different from that carried by JH1. Genomic analysis of H29 also clearly explained the multidrug resistance phenotype of this raw milk isolate. Analysis of the PB32 draft genome (using BLASTn) demonstrated that this raw milk isolate was most related to human MRSA strain 04-02981. Although PB32 is not a MRSA, the PB32 draft genome did reveal the presence of a unique staphylococcal cassette mec (SCCmec) remnant. In addition, the PB32 draft genome revealed the presence of a novel bovine staphylococcal pathogenicity island, SaPIbovPB32. This study demonstrates the presence of clones closely related to human and (or) bovine Staph. aureus strains circulating in a dairy herd.

Genotyping of Campylobacter coli isolated from humans and retail meats using multilocus sequence typing and pulsed-field gel electrophoresis

AIMS

To determine the antimicrobial resistant profiles and clonality of Campylobacter coli isolated from clinically ill humans and retail meats.

METHODS AND RESULTS

A total of 98 C. coli isolates (20 from humans and 78 from retail meats) were phenotypically characterized. Antimicrobial susceptibility testing was done using agar dilution method for ciprofloxacin, gentamicin, erythromycin and doxycycline. Seventy C. coli isolates including humans (n = 20) and retail meats (n = 50) were genotyped by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Resistance to ciprofloxacin was found in 29% and 15% of isolates from retail meats and humans. We observed 61 PFGE profiles using two enzymes (SmaI, KpnI) with an Index of discrimination of 0.99, whereas MLST generated 37 sequence types. Two clonal complexes were identified with 58 (82%) C. coli isolates clustered in the ST-828 complex.

CONCLUSIONS

Resistance to ciprofloxacin and erythromycin was identified in C. coli obtained from retail meats and ill humans. PFGE typing of C. coli isolates was more discriminatory than MLST. Grouping of C. coli isolates (82%) by MLST in ST-828 clonal complex indicates a common ancestry.

SIGNIFICANCE AND IMPACT OF THE STUDY

A high frequency of resistance found to ciprofloxacin and erythromycin is concerning from food safety perspective. PFGE using single or double restriction enzymes was found to be more discriminatory than MLST for genotyping C. coli. Overall, the C. coli populations recovered from humans and retail meats were genotypically diverse.

Characterization of multidrug resistant Salmonella recovered from diseased animals

Three hundred and eighty Salmonella isolates recovered from animal diagnostic samples obtained from four state veterinary diagnostic laboratories (AZ, NC, MO, and TN) between 2002 and 2003 were tested for antimicrobial susceptibilities and further characterized for bla(CMY) beta-lactamase genes, class 1 integrons and genetic relatedness using PFGE. Forty-seven serovars were identified, the most common being S. Typhimurium (26%), S. Heidelberg (9%), S, Dublin (8%), S. Newport (8%), S. Derby (7%), and S. Choleraesuis (7%). Three hundred and thirteen (82%) isolates were resistant to at least one antimicrobial, and 265 (70%) to three or more antimicrobials. Resistance was most often observed to tetracycline (78%), followed by streptomycin (73%), sulfamethoxazole (68%), and ampicillin (54%), and to a lesser extent chloramphenicol (37%), kanamycin (37%), amoxicillin-clavulanic acid (20%), and ceftiofur (17%). With regards to animal of origin, swine Salmonella isolates displayed the highest rate of resistance, being resistant to at least one antimicrobial (92%), followed by those recovered from turkey (91%), cattle (77%), chicken (68%), and equine (20%). Serovars commonly showing multidrug resistance (MDR) to > or =9 antimicrobials were S. Uganda (100%), S. Agona (79%), and S. Newport (62%), compared to S. Heidelberg (11%) and S. Typhimurium (7%). Class-1 integrons were detected in 43% of all isolates, and were found to contain aadA, aadB, dhfr, cmlA and sat1 gene cassettes alone or in various combinations. All ceftiofur resistant isolates (n=66) carried the bla(CMY) beta-lactamase gene. A total of 230 PFGE patterns were generated among the 380 isolates tested using XbaI, indicating extensive genetic diversity across recovered Salmonella serovars, however, several MDR clones were repeatedly recovered from different diseased animals.

Development of Gibberella Ear Rot on Processing Sweet Corn Hybrids Over an Extended Period of Harvest

Gibberella ear rot, caused by Gibberella zeae, has increased in prevalence recently on lateseason processing sweet corn grown in North America. Little information is available about the development of Gibberella ear rot on processing sweet corn hybrids over extended periods of harvest. In five trials from 2003 to 2005, 12 processing sweet corn hybrids were inoculated with G. zeae and evaluated for severity of Gibberella ear rot on sequential harvest dates from 19 to 27 days after midsilk. Ear rot severity was assessed using a rating scale based on the percentage of kernels with visible symptoms of G. zeae colonization including kernel rot and mycelial growth. Severity ranged from 1.6 to 47.8% over the five trials. None of the hybrids was highly resistant to Gibberella ear rot, although some appeared to be less susceptible. Gibberella ear rot was less severe on three hybrids (GH 2690, GG 147, and Sprint) and more severe on three hybrids (GG 42, GG 145, and Jubilee). Other hybrids had moderate levels of ear rot or responses that varied among years. The relative response of hybrids did not change substantially during the extended period of harvest; however, the rate at which Gibberella ear rot developed on hybrids differed in 2003 and 2005 as reflected by a significant hybrid by harvest interaction. The interaction was primarily the result of Gibberella ear rot developing more severely on susceptible hybrids than on the less susceptible hybrids. The difference in Gibberella development could be exploited to limit losses due to this disease under certain circumstances. If a sweet corn processor had several fields ready to harvest at the same time, and some fields were planted with hybrids that are more susceptible while other fields were planted with hybrids that are less susceptible, losses due to Gibberella ear rot might be minimized by harvesting the most susceptible hybrids first. Other hybrids that might be best suited for early or late harvest can be identified from Gibberella ear rot ratings 28 days after silk channel inoculation at the midsilk growth stage.

Genetics of antimicrobial resistance

Antimicrobial resistant strains of bacteria are an increasing threat to animal and human health. Resistance mechanisms to circumvent the toxic action of antimicrobials have been identified and described for all known antimicrobials currently available for clinical use in human and veterinary medicine. Acquired bacterial antibiotic resistance can result from the mutation of normal cellular genes, the acquisition of foreign resistance genes, or a combination of these two mechanisms. The most common resistance mechanisms employed by bacteria include enzymatic degradation or alteration of the antimicrobial, mutation in the antimicrobial target site, decreased cell wall permeability to antimicrobials, and active efflux of the antimicrobial across the cell membrane. The spread of mobile genetic elements such as plasmids, transposons, and integrons has greatly contributed to the rapid dissemination of antimicrobial resistance among several bacterial genera of human and veterinary importance. Antimicrobial resistance genes have been shown to accumulate on mobile elements, leading to a situation where multidrug resistance phenotypes can be transferred to a susceptible recipient via a single genetic event. The increasing prevalence of antimicrobial resistant bacterial pathogens has severe implications for the future treatment and prevention of infectious diseases in both animals and humans. The versatility with which bacteria adapt to their environment and exchange DNA between different genera highlights the need to implement effective antimicrobial stewardship and infection control programs in both human and veterinary medicine.

Comparison of multilocus sequence typing, pulsed-field gel electrophoresis, and antimicrobial susceptibility typing for characterization of Salmonella enterica serotype Newport isolates

In the United States, multidrug-resistant phenotypes of Salmonella enterica serotype Newport (commonly referred to as MDR-AmpC) have emerged in animals and humans and have become a major public health problem. Although pulsed-field gel electrophoresis (PFGE) is the current "gold standard" typing method for Salmonella, multilocus sequence typing (MLST) may be more relevant to investigations exploring evolutionary and population biology relationships. In this study, 81 Salmonella enterica serotype Newport isolates from humans, food animals, and retail foods were examined for antimicrobial susceptibility and characterized using PFGE and MLST of seven genes, aroC, dnaN, hemD, hisD, purE, sucA, and thrA. Forty-nine percent of the isolates were resistant to nine or more of the tested antimicrobials. Salmonella isolates displayed resistance most often to sulfamethoxazole (57%), streptomycin (56%), tetracycline (56%), ampicillin (52%), and ceftiofur (49%) and, to a lesser extent, to kanamycin (19%), trimethoprim-sulfamethoxazole (17%), and gentamicin (11%). A total of 43 PFGE patterns were generated using XbaI, indicating a genetically diverse population. The largest PFGE cluster contained isolates from clinically ill swine, cattle, and humans. MLST resulted in 12 sequence types (STs), with one type encompassing 62% of the strains. Ten new sequence types and one novel allele type were identified. Furthermore, MLST typing showed that strains closely related by PFGE clustered in major STs, whereas more distantly related strains were separated into two clusters by PFGE. The results of this study demonstrated that the MLST scheme employed here clustered S. enterica serovar Newport isolates in distinct molecular populations, and strain discrimination was enhanced by combining PFGE, antimicrobial susceptibility, and MLST results.

Antimicrobial resistance and genetic relatedness among Salmonella from retail foods of animal origin: NARMS retail meat surveillance

Salmonella isolates were recovered from a monthly sampling of chicken breasts, ground turkey, ground beef, and pork chops purchased from selected grocery stores in six participating FoodNet sites (Connecticut, Georgia, Maryland, Minnesota, Oregon, and Tennessee) in 2002 and an additional two sites in 2003 (California and New York). In 2002 and 2003, a total of 6,046 retail meats were examined, including 1,513 chicken breasts, 1,499 ground turkey samples, 1,522 ground beef samples, and 1,502 pork chops. Retail meat samples tested increased to 3,533 in 2003 as compared to 2,513 in 2002. Overall, six percent of 6,046 retail meat samples (n = 365) were contaminated with Salmonella, the bulk recovered from either ground turkey (52%) or chicken breast (39%). Salmonella isolates were serotyped and susceptibility tested using a panel of 16 antimicrobial agents. S. Heidelberg was the predominant serotype identified (23%), followed by S. Saintpaul (12%), S. Typhimurium (11%), and S. Kentucky (10%). Overall, resistance was most often observed to tetracycline (40%), streptomycin (37%), ampicillin (26%), and sulfamethoxazole (25%). Twelve percent of isolates were resistant to cefoxitin and ceftiofur, though only one isolate was resistant to ceftriaxone. All isolates were susceptible to amikacin and ciprofloxacin; however, 3% of isolates were resistant to nalidixic acid and were almost exclusive to ground turkey samples (n = 11/12). All Salmonella isolates were analyzed for genetic relatedness using pulsed-field gel electrophoresis (PFGE) patterns generated by digestion with Xba1 or Xba1 plus Bln1. PFGE fingerprinting profiles showed that Salmonella, in general, were genetically diverse with a total of 175 Xba1 PFGE profiles generated from the 365 isolates. PFGE profiles showed good correlation with serotypes and in some instances, antimicrobial resistance profiles. Results demonstrated a varied spectrum of antimicrobial resistance and PFGE patterns, including several multidrug resistant clonal groups among Salmonella isolates, and signify the importance of sustained surveillance of foodborne pathogens in retail meats.

Characterization of antimicrobial-resistant Salmonella isolated from imported foods

Two-hundred eight Salmonella isolates recovered from over 5,000 imported foods entering the United States in 2001 were tested for antimicrobial susceptibilities and further characterized for quinolone resistance mechanisms, integron carriage, and genetic relatedness. Salmonella Weltevreden (20%), Salmonella Newport (6%), Salmonella Lexington (5%), and Salmonella Thompson (4%) were the four most common serotypes recovered. Twenty-three (11%) isolates were resistant to at least one antimicrobial, and seven (3.4%) to three or more antimicrobials. Resistance was most often observed to tetracycline (9%), followed by sulfamethoxazole (5%), streptomycin (4%), nalidixic acid (3%), and trimethoprim/sulfamethoxazole (2%). One Salmonella Schwarzengrund isolate recovered from squid imported from Taiwan exhibited resistance to eight antimicrobials, including ampicillin, chloramphenicol, gentamicin, kanamycin, nalidixic acid, sulfamethoxazole, tetracycline, and trimethoprim/sulfamethoxazole. Six isolates (Salmonella Bareilly, Salmonella Derby, Salmonella Ohio and three Salmonella Schwarzengrund) contained class 1 integrons, which carried several resistance genes including dhfrI/dhfrXII, aadA, pse-1, and sat1, conferring resistance to trimethoprim/sulfamethoxazole, streptomycin, ampicillin, and streptothricin, respectively. Five of six nalidixic acid-resistant isolates possessed DNA point mutations at either Ser83 or Asp87 in DNA gyrase. One ciprofloxacin-resistant isolate possessed double mutations in DNA gyrase at positions Ser83 and Asp87 as well as a single mutation at Ser80 in parC. The top three serotypes identified, Salmonella Weltevreden (n = 41), Salmonella Newport (n = 13), and Salmonella Lexington (n = 11), were further characterized for genetic relatedness by pulsed-field gel electrophoresis. Fifty-five distinct pulsed-field gel electrophoresis patterns were observed among the 65 isolates, indicating extensive genetic diversity among these Salmonella serotypes contaminating imported foods.

Characterization of Salmonella Typhimurium of Animal Origin Obtained from the National Antimicrobial Resistance Monitoring System

Salmonella Typhimurium remains one of the most common causes of salmonellosis in animals and humans in the United States. The emergence of multi-drug resistant Salmonella reduces the therapeutic options in cases of invasive infections, and has been shown to be associated with an increased burden of illness. In this study, 588 S. Typhimurium (including var. Copenhagen) isolates obtained from either animal diagnostic specimens (n = 199) or food animals after slaughter/processing (n = 389) were examined for antimicrobial susceptibility, presence of class-1 integrons, and characterized using pulsed-field gel electrophoresis and phage typing. Seventy-six percent (448/588) of isolates were resistant to at least one antimicrobial. Salmonella isolates displayed resistance most often to streptomycin (63%), tetracycline (61%), ampicillin (61%), and to a lesser extent, chloramphenicol (36%), ceftiofur (15%), gentamicin (9%), and nalidixic acid (4%), with more resistance observed among diagnostic isolates. Salmonella recovered from turkeys (n = 38) exhibited the highest rates of resistance, with 92% of isolates resistant to least one antimicrobial, and 58% resistant to > or =10 antimicrobials. Class 1 integrons were present in 51% of all isolates. Five integron associated resistance genes (aadA, aadB, pse-1, oxa-2 and dhfr) were identified. A total of 311 PFGE patterns were generated using XbaI, indicating a genetically diverse population. The largest PFGE cluster contained 146 isolates, including DT104 isolates obtained from all seven animal species. Results demonstrated a varied spectrum of antimicrobial resistance, including several multidrug resistant clonal groups, among S. Typhimurium and S. Typhimurium var. Copenhagen isolates recovered from both diagnostic and slaughter/processing samples.

Evaluation of Food-Grade Dent Corn Hybrids for Severity of Fusarium Ear Rot and Fumonisin Accumulation in Grain

Fumonisins produced by Fusarium verticillioides (syn = F. moniliforme) and F. proliferatum have been associated with potentially serious toxicoses of animals and humans. Thus, hybrids with low fumonisin accumulation in grain will be valuable for the production of corn-based human food products. We evaluated 68 food-grade dent corn hybrids for severity of Fusarium ear rot and fumonisin accumulation in grain in inoculated trials in Urbana, IL in 2000 and 2001. Our inoculation technique was successful in initiating fumonisin accumulation that allowed discrimination among hybrids. We identified several hybrids that could have acceptable levels (<4 μg/g) of fumonisin accumulation in Illinois in most years. Twenty-six hybrids with low or high fumonisin accumulation in 2000 were reevaluated in noninoculated trials at three locations in Illinois in 2001. Fumonisin concentration in grain at all three locations was relatively low; thus, separation of hybrids was poor. At two locations, those hybrids with the highest fumonisin concentration in grain also had high concentrations following inoculation. However, one hybrid that had relatively low fumonisin concentration following inoculation had unacceptable levels of fumonisin (5 μg/g) in natural conditions. Therefore, hybrids need to be evaluated by inoculation and further evaluated at locations where the environment favors fumonisin accumulation.

Inheritance of resistance to aflatoxin production and Aspergillus ear rot of corn from the cross of inbreds b73 and oh516

ABSTRACT Our objective was to determine the value of corn (Zea mays) inbred Oh516 as a source of resistance to Aspergillus ear rot and aflatoxin accumulation in grain. Types and magnitudes of gene action associated with resistance were determined with generation means analysis. Molecular markers associated with resistance were identified from BCP(1)S(1) families developed from the cross of the susceptible inbred B73 and Oh516. In 2001 and 2002, B73 (P(1)), Oh516 (P(2)), and the F(1), F(2), F(3), BCP(1), BCP(2), and BCP(1)S(1) generations were evaluated for aflatoxin concentration in grain, percent bright greenish yellow fluorescence (BGYF), and severity of Aspergillus ear rot following inoculation in Urbana, IL. BCP(1)S(1) families testcrossed with LH185 also were evaluated at three locations in 2002. Molecular marker-quantitative trait loci (QTL) associations with all traits were determined with single factor analysis of variance. Dominance gene action was associated with aflatoxin concentration in grain and percent BGYF. QTL associated with aflatoxin accumulation in grain were identified on chromosomes 2, 3, and 7 (bins 2.01 to 2.03, 2.08, 3.08, and 7.06). Alleles from inbred Oh516 on chromosomes 2, 3, and 7 should improve resistance of commercially used, B73-type inbreds.

Ability of an ELISA-Based Seed Health Test to Detect Erwinia stewartii in Maize Seed Treated with Fungicides and Insecticides

Two sets of experiments were done to examine whether seed-treatment chemicals affected the ability of an enzyme-linked immunosorbent assay (ELISA)-based seed health test to detect Erwinia stewartii. The chemicals evaluated included Actellic, Apron, Captan, Cruiser, Gaucho, Maxim, Poncho, Thiram, and Vitavax in 11 seed-treatment combinations. In one experiment, seed-treatment chemicals were evaluated quantitatively in a critical region of ELISA absorbance values near 0.5 using maize seed that were spiked with uniform quantities of a liquid suspension of E. stewartii. The number of bacteria in each sample was estimated from ELISA absorbance values using standard curves. Log CFU of E. stewartii per sample were not significantly different among the untreated control and the 11 seed treatments compared with Tukey's Studentized Range Test (P = 0.05). Means of log CFU/ml for all treatments were tightly clustered around 5.70 which corresponded to an absorbance value of 0.440 and a bacterial population of about 500,000 CFU/ml. In a second set of experiments, seed treatment chemicals were evaluated based on qualitative decisions that resulted from the ELISA-based seed health test of seed lots of Jubilee and A632 infected with E. stewartii. The number of negative samples was not substantially greater than expected based on binomial probabilities except for samples of Captan/Vitavax-treated A632, which we considered to be a type I error. The mean absorbance values of positive samples ranged from 1.42 to 1.72 for A632 and from 1.51 to 1.91 for Jubilee and did not differ significantly among the seed treatments. There was no consistent evidence from these experiments that fungicide or insecticide seed treatments interfered with the sensitivity of the ELISA or altered low (e.g., 0.5) or high (e.g. 1.4 to 1.9) absorbance values. The ability of the ELISA-based seed health test to detect E. stewartii in maize seed was not affected by these seed treatments.

Salmonella osteomyelitis of the thoracic spine: an unusual presentation

A case of thoracic vertebral osteomyelitis due to Salmonella enteritidis phage type 2 in an immunocompetent patient is reported. The patient initially presented with abdominal, urinary and chest symptoms, which were followed by a large pleural effusion. The infection was successfully treated with ciprofloxacin. This is the only case of salmonella thoracic vertebral osteomyelitis in an immunocompetent patient reported in the English literature.

Sources of resistance to fumonisin accumulation in grain and fusarium ear and kernel rot of corn

ABSTRACT Fumonisin is a group of homologous mycotoxins produced by several species of Fusarium. Fumonisin has been associated with Fusarium ear and kernel rot of corn (Zea mays) and several toxicoses of animals and humans. Corn inbreds with a high level of resistance to fumonisin production and accumulation in grain have not been identified. The objective of this study was to evaluate a genetically diverse collection of inbreds as potential sources of resistance to fumonisin production and accumulation in grain and Fusarium ear and kernel rot when crossed with a commercial "B73-type" line. F(1) hybrids developed with the inbred FR1064 and 1,589 and 1,030 inbreds were evaluated in inoculated and naturally infected trials, respectively, in 2000. Thirty-five F(1) hybrids with fumonisin concentration in grain of </=5 mug/g in both trials were selected. Inbreds from which these 35 F(1) hybrids were produced included yellow-, white-, and red-kernelled lines; flint and dent lines; and early- through late-maturing lines. In 2001, low fumonisin concentration in grain and low ear rot severity were associated with several of the F(1) hybrids and their distinct F(2), and backcross to FR1064 generations. This suggests that several dominant genes are involved in resistance and that alleles for resistance from these inbreds can be transferred to FR1064.

Characterization of Salmonella enterica serotype newport isolated from humans and food animals

Salmonella enterica serotype Newport isolates resistant to at least nine antimicrobials (including extended-spectrum cephalosporins), known as serotype Newport MDR-AmpC isolates, have been rapidly emerging as pathogens in both animals and humans throughout the United States. Resistance to extended-spectrum cephalosporins is associated with clinical failures, including death, in patients with systemic infections. In this study, 87 Salmonella serotype Newport strains were characterized by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing and examined for the presence of class 1 integrons and bla(CMY) genes. Thirty-five PFGE patterns were observed with XbaI, and three of these patterns were indistinguishable among isolates from humans and animals. Fifty-three (60%) Salmonella serotype Newport isolates were identified as serotype Newport MDR-AmpC, including 16 (53%) of 30 human isolates, 27 (93%) of 29 cattle isolates, 7 (70%) of 10 swine isolates, and 3 (30%) of 10 chicken isolates. However, 28 (32%) Salmonella serotype Newport isolates were susceptible to all 16 antimicrobials tested. The bla(CMY) gene was present in all serotype Newport MDR-AmpC isolates. Furthermore, the plasmid-mediated bla(CMY) gene was transferable via conjugation to an Escherichia coli strain. The transconjugant showed the MDR-AmpC resistance profile. Thirty-five (40%) of the isolates possessed class 1 integrons. Sequence analyses of the integrons showed that they contained aadA, which confers resistance to streptomycin, or aadA and dhfr, which confer resistance to trimethoprim-sulfamethoxazole. One integron from a swine isolate contained the sat-1 gene, which encodes resistance to streptothricin, an antimicrobial agent that has never been approved for use in the United States. In conclusion, Salmonella serotype Newport MDR-AmpC was commonly identified among Salmonella serotype Newport isolates recovered from humans and food animals. These findings support the possibility of transmission of this organism to humans through the food chain.

Characterization of Escherichia coli isolates incriminated in colisepticaemia in mink

Colisepticaemia is a major health and economic concern for the mink industry, yet little information is available about the Escherichia coli that cause this disease. In this study, 40 E. coli, isolated from mink clinically diagnosed with colisepticaemia that had been submitted to the North Dakota State University Veterinary Diagnostic Laboratory, were randomly selected for characterization. These isolates were serotyped and screened for resistance to 18 antimicrobials, possession of transmissible R plasmids, and the presence of several virulence traits or genes using bioassays or the polymerase chain reaction. Several serotypes were identified that have previously been associated with septicaemia in other animal species. The majority of the isolates exhibited multiple antimicrobial resistance phenotypes. Common resistance phenotypes observed included those to tetracycline, sulfamethoxazole, streptomycin, ampicillin and kanamycin. Several of the isolates that could be studied by conjugation contained transmissible R plasmids coding for multiple antimicrobial resistance phenotypes. About half of the isolates produced colicin; all produced enterobactin: and all but one-quarter produced aerobactin. None of the isolates tested produced enterohaemolysin, and one-fifth were considered to be beta haemolytic. About half appeared to contain the gene encoding cytotoxic necrotizing factor-1; three contained the gene encoding EAE, but none appeared to contain the genes coding for LT, Sta/b, SLT-I/II or CNF-II toxins or K99 antigen. Approximately one-third of the isolates elaborated capsule. The results show that the E. coli isolates implicated in mink colisepticaemia possess similar virulence traits and antimicrobial resistance phenotypes to those associated with diarrhoeal diseases in food animals.

Antimicrobial susceptibility and genetic relatedness of Salmonella serovars isolated from animal-derived dog treats in the USA

OBJECTIVES

The objectives of this study were to determine the potential risk of dog treats in transmitting Salmonella to humans in the USA, and to characterize genetic relatedness and antimicrobial resistance among the isolates.

METHODS

A total of 158 dog treats derived from pig ears and other animal parts were randomly collected nationwide and assayed for the presence of Salmonella. The Salmonella isolates were characterized using serotyping, pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing.

RESULTS

Forty-one percent (65/158) of samples were positive for Salmonella. Eighty-four Salmonella isolates, comprising 24 serotypes, were recovered from the 65 positive samples. Fourteen samples were contaminated with more than one Salmonella serotype. PFGE analysis of 78 Salmonella isolates yielded 64 patterns. S. Infantis with PFGE patterns indistinguishable from those of strains identified in Canadian outbreaks in 1999 were recovered in several dog treat products. The majority of Salmonella isolates were susceptible to the antimicrobials tested; however, resistance was observed to tetracycline (26%), streptomycin (23%), sulfamethoxazole (19%), chloramphenicol (8%) and ampicillin (8%). Twenty-eight (36%) Salmonella isolates were resistant to at least one antimicrobial and 10 (13%) isolates displayed resistance to four or more antimicrobials. Two isolates were identified as S. Typhimurium DT104 with the characteristic penta-resistance phenotype (ampicillin, chloramphenicol, streptomycin, sulfamethoxazole and tetracycline). One S. Brandenburg isolate was resistant to eight antimicrobials. Seven Salmonella isolates also contained class I integrons encoding resistance genes to aminoglycosides, beta-lactam and streptothricin antimicrobials.

CONCLUSIONS

The study indicates that animal-derived dog treats in the USA could be a potential source of animal and human infections with Salmonella, including multidrug-resistant Salmonella strains.

Evaluation of the MI82 Corn Line as a Source of Resistance to Aflatoxin in Grain and Use of BGYF as a Selection Tool

Our objectives were to determine if the corn (Zea mays) inbred MI82 has alleles for resistance to Aspergillus ear rot (caused by Aspergillus flavus) and aflatoxin accumulation in grain that can be transferred to commercially used inbreds, and to determine the types and magnitudes of gene action, heritabilities, and gain from selection for low levels of bright greenish-yellow fluorescence (BGYF), aflatoxin, and ear rot with MI82. Also, we hoped to determine if selection against BGYF would substantially reduce the concentration of aflatoxin in grain. Primary ears and ground grain from inbred MI82 (P₁), the susceptible inbred B73 (P₂), and the F₁, F₂, F₃, BCP₁S₁, and BCP₂S₁ generations developed from these inbreds were evaluated for BGYF, concentration of aflatoxin in grain, and severity of Aspergillus ear rot in 2000 and 2001. Dominance was the most important gene action associated with low levels of BGYF and a low concentration of aflatoxin in grain. Heritabilities for low levels of BGYF (83.5%), aflatoxin (74.1%), and ear rot (62.8%) were high. Correlation coefficients between aflatoxin and BGYF were high in both years (r = 0.75 and 0.79 for 2000 and 2001, respectively). Unlike aflatoxin, BGYF was not affected by the year in which plants were grown. Selection for low levels of BGYF prior to selection based on aflatoxin concentration is as effective as selection for either factor alone. MI82 has value in programs designed to improve the resistance of commercially used corn inbreds.

Anterior chest wall abscess caused by Salmonella enteritidis in a healthy adult

We report a case of anterior chest wall abscess in an immunocompetent adult by Salmonella enteritidis, whose food was contaminated by bird droppings. The patient did not have any gastrointestinal symptoms. Surgical excision followed by antibiotics (cefuroxime and ciprofloxacin) successfully treated the condition. To our knowledge, this is the first reported case of anterior chest wall abscess caused by S. enteritidis in an immunocompetent adult without any preceding gastrointestinal symptoms. We feel that the contamination of his food with the bird droppings was a risk factor.

Evaluation of Inoculation Techniques for Fusarium Ear Rot and Fumonisin Contamination of Corn

Fumonisins have been associated with potentially serious toxicoses of animals and humans. Prior to initiating a corn (Zea mays) breeding program for resistance to these mycotoxins, an efficient inoculation technique must be developed. Four inoculation techniques were evaluated on 14 commercial corn hybrids in Urbana, IL in 1999 and 2000. The techniques were: injection of inoculum through the ear husk leaves at R2 (blister); silks sprayed with inoculum at R2 and covered with a shoot bag until harvest; silks sprayed with inoculum at R2, covered with a shoot bag, reinoculated 1 week thereafter, and covered with a shoot bag until harvest; and insertion of six Fusarium-colonized toothpicks into the silk channel at R2. Only injection of inoculum through the husk leaves significantly increased the concentration of fumonisin in grain and severity of Fusarium ear rot compared with a control. This technique effectively differentiated hybrids previously identified as resistant or susceptible to Fusarium ear rot. The rank order of hybrids inoculated with this technique did not significantly change in the 2 years of this study. This technique is suitable for efficiently evaluating a large number of corn genotypes for resistance to Fusarium ear rot and fumonisin concentration.

Characterization of antimicrobial resistance among Escherichia coli O111 isolates of animal and human origin

Fifty isolates of Escherichia coli serogroup O111 recovered from humans and various animal species over a 24-year period (1976-1999) were examined for typical virulence-associated factors and susceptibilities to antimicrobials of human and veterinary significance. Nine H (flagellar) types were identified including nonmotile (n = 24), 32 (n = 12), negative (n = 5), and 56 (n = 3). Thirty-five (70%) isolates possessed at least one Shiga-toxin-producing E. coli (STEC)-associated virulence determinants (eae, stxl, stx2, hlyA) via PCR analysis. Of these 35 isolates, 20 possessed eae, stxl, and hlyA genes, whereas three isolates possessed eae, stxl, stx2, and hylA genes. Multiple antibiotic resistance was observed in 70% of the 50 E. coli O111 isolates. The majority of isolates displayed resistance to streptomycin, sulfamethoxazole, tetracycline, and kanamycin. Bacterial resistance to ampicillin, gentamicin, chloramphenicol, trimethoprim and apramycin was also observed. Integrons were identified in 23 (46%) of the E. coli isolates assayed, with a 1-kb amplicon being most frequently observed. DNA sequencing of these integrons revealed the presence of the aadA gene, encoding resistance to streptomycin. Two integrons of 1.5 and 2 kb contained the aadA2 and either dfrI or dfrXII genes, encoding resistance to streptomycin and trimethoprim, respectively. Integrons were also identified from isolates dating back to 1982. Isolates were further genetically characterized via ribotyping, which identified 15 distinct ribogroups, with 62% of isolates clustering into four major ribogroups. Certain riboprint patterns from different animal species, including humans, were observed in isolates spanning the 24-year collection period, suggesting the dissemination of specialized pathogenic O111 clones.

Characterization of Tn1546 in vancomycin-resistant Enterococcus faecium isolated from canine urinary tract infections: evidence of gene exchange between human and animal enterococci

Thirty-five enterococcal isolates were recovered from dogs diagnosed with urinary tract infections at the Michigan State University Veterinary Teaching Hospital over a 2-year period (1996 to 1998). Isolated species included Enterococcus faecium (n = 13), Enterococcus faecalis (n = 7), Enterococcus gallinarum (n = 11), and Enterococcus casseliflavus (n = 4). Antimicrobial susceptibility testing revealed several different resistance phenotypes, with the majority of the enterococcal isolates exhibiting resistance to three or more antibiotics. One E. faecium isolate, CVM1869, displayed high-level resistance to vancomycin (MIC > 32 micro g/ml) and gentamicin (MIC > 2,048 micro g/ml). Molecular analysis of this isolate revealed the presence of Tn1546 (vanA), responsible for high-level vancomycin resistance, and Tn5281 carrying aac6'-aph2", conferring high-level aminoglycoside resistance. Pulsed-field gel electrophoresis analysis revealed that CVM1869 was a canine E. faecium clone that had acquired Tn1546, perhaps from a human vancomycin-resistant E. faecium. Transposons Tn5281 and Tn1546 were located on two different conjugative plasmids. Sequence analysis revealed that in Tn1546, ORF1 had an 889-bp deletion and an IS1216V insertion at the 5' end and an IS1251 insertion between vanS and vanH. To date, this particular form of Tn1546 has only been described in human clinical vancomycin-resistant enterococcus isolates unique to the United States. Additionally, this is the first report of a vancomycin-resistant E. faecium isolated from a companion animal in the United States.

Prevalence of streptogramin resistance genes among Enterococcus isolates recovered from retail meats in the Greater Washington DC area

The prevalence of streptogramin resistance genes in enterococci recovered from retail poultry in the Greater Washington DC area was examined. Forty-three chicken and 32 turkey retail samples were analysed. Thirty-one non-Enterococcus faecalis enterococcal strains were isolated that displayed MICs of quinupristin-dalfopristin and virginiamycin of > or = 4 mg/L. These included Enterococcus faecium (turkey n = 4, chicken n = 23), Enterococcus gallinarum (turkey n = 2, chicken n = 1) and Enterococcus hirae (chicken n = 1). The presence of streptogramin resistance genes was examined by PCR in all non-E. faecalis isolates. The vat(E) gene was detected in 10/23 chicken E. faecium and from 2/4 turkey E. faecium. No other streptogramin resistance genes were detected by PCR. In addition, erm(B) was detected in all the E. faecium and E. gallinarum found in turkeys and in 7/23 E. faecium found in chickens. The vat(E) gene was transferable by conjugation from only two of the 12 E. faecium isolates (one from chicken and one from turkey). This study suggests that there is a high prevalence of low-level streptogramin resistance among enterococci found in retail poultry and that other, yet to be identified, mechanisms operate in these isolates that confer streptogramin resistance in enterococci.

Identification of vat(E) in Enterococcus faecalis isolates from retail poultry and its transferability to Enterococcus faecium

Sixteen isolates of Enterococcus faecalis were recovered from retail poultry samples (seven chickens and nine turkeys) purchased from grocery stores in the greater Washington, D.C., area. PCR for known streptogramin resistance genes identified vat(E) in five E. faecalis isolates (three isolates from chickens and two isolates from turkeys). The vat(E) gene was transmissible on a ca. 70-kb plasmid, along with resistance to erythromycin, tetracycline, and streptomycin, by conjugation to E. faecalis and Enterococcus faecium recipient strains. DNA sequencing showed little variation between E. faecalis vat(E) genes from the chicken samples; however, one E. faecalis vat(E) gene from a turkey sample possessed 5 nucleotide changes that resulted in four amino acid substitutions. None of these substitutions in the vat(E) allele have previously been described. This is the first report of vat(E) in E. faecalis and its transferability to E. faecium, which indicates that E. faecalis can act as a reservoir for the dissemination of vat(E)-mediated streptogramin resistance to E. faecium.

Rates of Transmitting Erwinia stewartii from Seed to Seedlings of a Sweet Corn Hybrid Susceptible to Stewart's Wilt

Rates of transmitting Erwinia stewartii from seed to seedlings were estimated from field grow-outs of seedlings grown from seed infected with E. stewartii. Infected seed were produced in 1998, 1999, and 2000 on a Stewart's wilt-susceptible sweet corn hybrid, Jubilee. Seedlings were inoculated repeatedly with pinprick inoculators and suspensions of E. stewartii were injected into ear shanks of the primary ears of each adult plant. Seed from inoculated plants were harvested and bulked. Single kernels were assayed for E. stewartii to estimate the proportion of kernels infected with E. stewartii. Estimates of E. stewartii-infection were 15.6 ± 4.3, 49.4 ± 3.9, and 12.5 ± 2.4% for seed produced in 1998, 1999, and 2000, respectively. Approximately 61,800 seedlings were grown in DeKalb, IL in 1999 and 83,400 and 60,000 seedlings were grown in Plover WI in 2000 and 2001, respectively, from infected seed lots produced the previous year. Approximately 10,000, 12,200, and 29,400 seedlings of susceptible sweet corn hybrids also were grown each year from commercial seed produced in Idaho where Stewart's wilt does not occur. Based on estimates of kernel infection in each seed lot and plant populations in each grow-out trial, about 9,600, 41,200, and 7,500 seedlings were grown from infected kernels in 1999, 2000, and 2001, respectively. Seedlings at the two- to three-leaf stage were examined for symptoms of Stewart's wilt. Infected plants were confirmed by microscopic observations of bacterial ooze and by enzyme-linked immunosorbent assay. When data were combined from all three trials, 59 of approximately 58,300 seedlings grown from infected seed were infected with E. stewartii based on symptoms of Stewart's wilt and E. stewartii-positive leaf tissue samples. Of these 59 seedlings, 22 probably were infected from seed-to-seedling transmission of E. stewartii and 37 probably were the result of natural infection due to the presence of flea beetles in DeKalb in 1999. Twenty-two infected seedlings from 58,300 infected kernels corresponds to a seed-to-seedling transmission rate of 0.038%. This rate of seed-to-seedling transmission of E. stewartii is substantially lower than seed transmission rates reported in the first half of the twentieth century; however, it is similar to seed-to-seedling transmission rates reported from other recent research.

The food safety perspective of antibiotic resistance

Bacterial antimicrobial resistance in both the medical and agricultural fields has become a serious problem worldwide. Antibiotic resistant strains of bacteria are an increasing threat to animal and human health, with resistance mechanisms having been identified and described for all known antimicrobials currently available for clinical use. There is currently increased public and scientific interest regarding the administration of therapeutic and sub-therapeutic antimicrobials to animals, due primarily to the emergence and dissemination of multiple antibiotic resistant zoonotic bacterial pathogens. This issue has been the subject of heated debates for many years, however, there is still no complete consensus on the significance of antimicrobial use in animals, or resistance in bacterial isolates from animals, on the development and dissemination of antibiotic resistance among human bacterial pathogens. In fact, the debate regarding antimicrobial use in animals and subsequent human health implications has been going on for over 30 years, beginning with the release of the Swann report in the United Kingdom. The latest report released by the National Research Council (1998) confirmed that there were substantial information gaps that contribute to the difficulty of assessing potential detrimental effects of antimicrobials in food animals on human health. Regardless of the controversy, bacterial pathogens of animal and human origin are becoming increasingly resistant to most frontline antimicrobials, including expanded-spectrum cephalosporins, aminoglycosides, and even fluoroquinolones. The lion's share of these antimicrobial resistant phenotypes is gained from extra-chromosomal genes that may impart resistance to an entire antimicrobial class. In recent years, a number of these resistance genes have been associated with large, transferable, extra-chromosomal DNA elements, called plasmids, on which may be other DNA mobile elements, such as transposons and integrons. These DNA mobile elements have been shown to transmit genetic determinants for several different antimicrobial resistance mechanisms and may account for the rapid dissemination of resistance genes among different bacteria. The increasing incidence of antimicrobial resistant bacterial pathogens has severe implications for the future treatment and prevention of infectious diseases in both animals and humans. Although much scientific information is available on this subject, many aspects of the development of antimicrobial resistance still remain uncertain. The emergence and dissemination of bacterial antimicrobial resistance is the result of numerous complex interactions among antimicrobials, microorganisms, and the surrounding environments. Although research has linked the use of antibiotics in agriculture to the emergence of antibiotic-resistant foodborne pathogens, debate still continues whether this role is significant enough to merit further regulation or restriction.

Trends in antibacterial susceptibility of mastitis pathogens during a seven-year period

Milk samples collected from dairy cattle suspected of having mastitis were submitted to the Microbiology Laboratory of the Animal Health Diagnostic Laboratory, Michigan State University, for bacteriologic culture. A total of 2778 isolates, from the years 1994 to 2000, were isolated, identified, and subjected to in vitro antimicrobial susceptibility testing using the disk diffusion method, in accordance with National Committee on Clinical Laboratory Standards (NCCLS) standards. Isolates included in this study were Streptococcus uberis, Streptococcus dysgalactiae, Streptococcus agalactiae, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Serratia marcesens, and Pseudomonas aeruginosa. The proportion of bacterial isolates determined to be susceptible did not change during the 7-yr period for the majority of bacterial-antibacterial interactions tested. However, analysis for linear trend in proportions determined that there were increases in the proportion of S. aureus isolates that were susceptible to ampicillin, penicillin, and erythromycin. For Strep. uberis, increases in the proportion of susceptible isolates occurred for oxacillin, sulfa-trimethoprim, gentamicin, and pirlimycin, and a decrease in the proportion of susceptible isolates occurred with penicillin. For Strep. dysgalactiae, increases in the proportion of susceptible isolates occurred with erythromycin, gentamicin, sulfa-trimethoprim, and tetracycline. For Strep. agalactiae, increases in the proportion of susceptible isolates occurred with sulfa-trimethoprim. Among E. coli isolates, there was an increase in the proportion that were susceptible to ampicillin and cephalothin. Among K pneumoniae isolates, there was an increase in the proportion that were susceptible to ceftiofur. Overall, there was no indication of increased resistance of mastitis isolates to antibacterials that are commonly used in dairy cattle.

Transmission of Erwinia stewartii from Plants to Kernels and Reactions of Corn Hybrids to Stewart's Wilt

Stewart's wilt reactions of 98 food-grade, white corn hybrids, 3 yellow dent corn hybrids, and 23 sweet corn hybrids and infection of kernels by E. stewartii were evaluated in 1998, 1999, and 2000. Stewart's wilt symptoms were rated from 1 (no appreciable spread of symptoms) to 9 (dead plants) following inoculation. The mean Stewart's wilt ratings for the food-grade, white corn and yellow dent corn hybrids were 1.9, 2.4, and 2.9 in 1998, 1999, and 2000, respectively. The mean Stewart's wilt ratings for the sweet corn hybrids were 3.8, 4.2, and 4.6 in 1998, 1999, and 2000, respectively. Hybrids with ratings less than 3 were classified as resistant. Hybrids with ratings between 3 and 4.5 were classified as moderate. Hybrids with ratings greater than 4.5 were classified as susceptible. Ears harvested from each row in 1998 and 1999 were assayed for E. stewartii using an enzyme-linked immunosorbent assay (ELISA)-based seed health test. Kernels from 16 hybrids were positive for E. stewartii in 1998. Kernels from 11 hybrids were positive for E. stewartii in 1999. Kernel infection by E. stewartii was affected considerably by the level of host resistance (i.e., reactions of seed parent plants). For hybrids classified as resistant, estimates of kernel infection were 0.024 and 0.0007% in 1998 and 1999, respectively. For hybrids with moderate reactions to Stewart's wilt, estimates of kernel infection were 0.19 and 0.07% in 1998 and 1999, respectively. For hybrids with susceptible reactions to Stewart's wilt, estimates of kernel infection were 11.6 and 7.8% in 1998 and 1999, respectively. Based on high levels of Stewart's wilt resistance in food-grade, white corn hybrids, and low rates of kernel infection by E. stewartii in resistant and moderate hybrids, there is an exceedingly low probability of introducing E. stewartii to areas where it does not occur by transmitting the bacterium in grain of the food-grade, white corn hybrids evaluated in this study. Although all of the kernels harvested in these experiments were produced as grain on open-pollinated F1 hybrids, the rates of kernel infection observed for hybrids with resistant, moderate and susceptible reactions to Stewart's wilt are applicable to seed produced on inbred lines with equivalent Stewart's wilt reactions.

Antimicrobial resistance: harmonisation of national antimicrobial resistance monitoring and surveillance programmes in animals and in animal-derived food

A guideline on the harmonisation of national antimicrobial resistance monitoring and surveillance programmes in animals and animal-derived foods has been developed by the Ad hoc Group of experts on antimicrobial resistance of the Office International des Epizooties. The objective of the guideline is to allow the generation of comparable data from various national surveillance and monitoring systems in order to compare the situations in different regions or countries and to consolidate results at the national, regional and international level. Definitions of surveillance and monitoring are provided. National systems should be able to detect the emergence of resistance, and to determine the prevalence of resistant bacteria. The resulting data should be used in the assessment of risks to public health and should contribute to the establishment of a risk management policy. Specific factors identified for harmonisation include the animal species, food commodities, sampling plans, bacterial species, antimicrobials to be tested, laboratory methods, data reporting, database structure and the structure of reports.

Prevalence of Campylobacter spp., Escherichia coli, and Salmonella serovars in retail chicken, turkey, pork, and beef from the Greater Washington, D.C., area

A total of 825 samples of retail raw meats (chicken, turkey, pork, and beef) were examined for the presence of Escherichia coli and Salmonella serovars, and 719 of these samples were also tested for Campylobacter spp. The samples were randomly obtained from 59 stores of four supermarket chains during 107 sampling visits in the Greater Washington, D.C., area from June 1999 to July 2000. The majority (70.7%) of chicken samples (n = 184) were contaminated with Campylobacter, and a large percentage of the stores visited (91%) had Campylobacter-contaminated chickens. Approximately 14% of the 172 turkey samples yielded Campylobacter, whereas fewer pork (1.7%) and beef (0.5%) samples were positive for this pathogen. A total of 722 Campylobacter isolates were obtained from 159 meat samples; 53.6% of these isolates were Campylobacter jejuni, 41.3% were Campylobacter coli, and 5.1% were other species. Of the 212 chicken samples, 82 (38.7%) yielded E. coli, while 19.0% of the beef samples, 16.3% of the pork samples, and 11.9% of the turkey samples were positive for E. coli. However, only 25 (3.0%) of the retail meat samples tested were positive for Salmonella. Significant differences in the bacterial contamination rates were observed for the four supermarket chains. This study revealed that retail raw meats are often contaminated with food-borne pathogens; however, there are marked differences in the prevalence of such pathogens in different meats. Raw retail meats are potential vehicles for transmitting food-borne diseases, and our findings stress the need for increased implementation of hazard analysis of critical control point (HACCP) and consumer food safety education efforts.

Identification and expression of cephamycinase bla(CMY) genes in Escherichia coli and Salmonella isolates from food animals and ground meat

Twenty-one Salmonella and 54 Escherichia coli isolates, recovered from food animals and retail ground meats, that exhibited decreased susceptibilities to ceftiofur and ceftriaxone were shown to possess a bla(CMY) gene. The bla(CMY-4) gene was identified in an E. coli isolate recovered from retail chicken and was further shown to be responsible for resistance to cephalothin, ampicillin, and amoxicillin-clavulanic acid and elevated MICs of ceftriaxone, cefoxitin, and ceftiofur.

Antimicrobial resistance: risk analysis methodology for the potential impact on public health of antimicrobial resistant bacteria of animal origin

The Ad hoc Group of experts on antimicrobial resistance, appointed by the Office International des Epizooties, has developed an objective, transparent and defensible risk analysis process, providing a valid basis for risk management decisions in respect to antimicrobial resistance. The components of risk analysis and of different possible approaches in risk assessment (qualitative, semiquantitative and quantitative) are defined. The Ad hoc Group recommended the following: an independent risk assessment based on scientific data; an iterative risk analysis process; a qualitative risk assessment systematically undertaken before considering a quantitative approach; the establishment of a risk assessment policy; and the availability of technical assistance for developing countries.

Antimicrobial resistance: responsible and prudent use of antimicrobial agents in veterinary medicine

A guideline on the responsible and prudent use of antimicrobials in animal husbandry has been developed by the Ad hoc Group of experts on antimicrobial resistance, created by the Office International des Epizooties. The objectives of responsible use are to maintain antibiotic efficacy, to avoid the dissemination of resistant bacteria or resistance determinants and to avoid the exposure of humans to resistance through food. The guideline attributes a central role to the competent authorities responsible for granting marketing authorizations for antimicrobial substances. Requirements before and after granting of marketing authorizations are defined. Important aspects include the control of the pharmaceutical product quality and the therapeutic efficacy, the assessment of the selection pressure, the protection of the environment, specific and non-specific antimicrobial resistance surveillance. The guideline is also addressed to the veterinary pharmaceutical industry, veterinary practitioners, dispensing pharmacists and farmers. The respective roles and responsibilities of these groups are defined.

Antimicrobial resistance: monitoring the quantities of antimicrobials used in animal husbandry

This guideline, developed by the Office International des Epizooties for the monitoring of the quantities of antimicrobials used in animal husbandry, provides the methodology required to assess the amounts of antimicrobials used, to supply data to be used for risk analysis and to improve guidance on the appropriate use of antimicrobials. Information may be gathered from a number of sources, such as the competent authorities, industry and users. The usefulness of different types of information is discussed and recommendations are given on how to collect detailed information, each year, on the antimicrobial quantities used per class and active substance. Information should also be collected on the route of administration (oral and parenteral) and the animal species.

Antimicrobial resistance: standardisation and harmonisation of laboratory methodologies for the detection and quantification of antimicrobial resistance

The Ad hoc Group of experts on antimicrobial resistance of the Office International des Epizooties has developed a guideline on the standardisation and harmonisation of laboratory methodologies used for the detection and quantification of antimicrobial resistance. The existing methods (disk diffusion [including concentration gradient strips], agar dilution and broth dilution) are reviewed, including a comparison of their advantages and disadvantages. The definitions of resistance characteristics of bacteria (susceptible, intermediate and resistant) are addressed and the criteria for the establishment of breakpoints are discussed. Due consideration has to be given to these aspects in the interpretation and comparison of resistance monitoring or surveillance data. The use of validated laboratory methods and the establishment of quality assurance (internal and external) for microbiological laboratory work and the reporting of quantitative test results is recommended. Equivalence of different methods and laboratory test results is also recommended to be established by external proficiency testing, which should be achieved by the means of a reference laboratory system. This approach allows the comparison of test results obtained using different methods generated by laboratories in different countries.

The isolation of antibiotic-resistant salmonella from retail ground meats

BACKGROUND

Salmonella is a leading cause of foodborne illness. The emergence of antimicrobial-resistant salmonella is associated with the use of antibiotics in animals raised for food; resistant bacteria can be transmitted to humans through foods, particularly those of animal origin. We identified and characterized strains of salmonella isolated from ground meats purchased in the Washington, D.C., area.

METHODS

Salmonella was isolated from samples of ground chicken, beef, turkey, and pork purchased at three supermarkets. The isolates were characterized by serotyping, antimicrobial-susceptibility testing, phage typing, and pulsed-field gel electrophoresis. The polymerase chain reaction and DNA sequencing were used to identify resistance integrons and extended spectrum beta-lactamase genes.

RESULTS

Of 200 meat samples, 41 (20 percent) contained salmonella, with a total of 13 serotypes. Eighty-four percent of the isolates were resistant to at least one antibiotic, and 53 percent were resistant to at least three antibiotics. Sixteen percent of the isolates were resistant to ceftriaxone, the drug of choice for treating salmonellosis in children. Bacteriophage typing identified four isolates of Salmonella enterica serotype typhimurium definitive type 104 (DT104), one of DT104b, and two of DT208. Five isolates of S. enterica serotype agona had resistance to 9 antibiotics, and the two isolates of serotype typhimurium DT208 were resistant to 12 antibiotics. Electrophoretic patterns of DNA that were indistinguishable from one another were repeatedly found in isolates from different meat samples and different stores. Eighteen isolates, representing four serotypes, had integrons with genes conferring resistance to aminoglycosides, sulfonamides, trimethoprim, and beta-lactams.

CONCLUSIONS

Resistant strains of salmonella are common in retail ground meats. These findings provide support for the adoption of guidelines for the prudent use of antibiotics in food animals and for a reduction in the number of pathogens present on farms and in slaughterhouses. National surveillance for antimicrobial-resistant salmonella should be extended to include retail meats.

Characterization of antibiotic-resistant bacteria in rendered animal products

Antibiotics are used in food animal production to treat diseases and also to improve performance. Antibiotics are not used on all farms, and antibiotic resistance is occasionally found on farms that do not use antibiotics. Rendered animal protein products are often included in poultry feeds and could potentially serve as a source of antibiotic-resistant bacteria. One hundred sixty-five rendered animal protein products from cattle, poultry, and fish were aseptically collected from poultry feed mills. Fifty-five percent of the poultry meal samples had detectable levels of gram-negative bacteria ranging from 40 to 10,440 colony-forming units/g of sample. Poultry meal and meat and bone meal had the greatest number of samples with bacteria resistant to five or more antibiotics. A high percentage of feed samples (85%) contained bacteria resistant to amoxicillin, ampicillin, clavulanic acid, or cephalothin, whereas few samples contained bacteria resistant to ciprofloxacin, kanamycin, or trimethoprim/sulfamethoxazole. Acinetobacter calcoaceticus, Citrobacter freundii, and Enterobacter cloacae were the most commonly isolated antibiotic-resistant bacteria. Isolation for Salmonella was also performed, with 14% of the meat and bone meal samples containing Salmonella sp. Only one of the meat and bone meal isolates, Salmonella livingstone, was resistant to five or more antibiotics. Many of the antibiotic-resistant bacteria contained integrons, genetic elements that mediate multiple drug resistance.

Variation within the vat(E) allele of Enterococcus faecium isolates from retail poultry samples

In a survey of retail meat samples, twelve quinupristin-dalfopristin-resistant (MICs, > or =4 mg/liter) Enterococcus faecium isolates that carried a vat(E) gene were recovered. DNA sequence comparison revealed five new variations in the vat(E) allele among 12 isolates, which were designated vat(E-4) through vat(E-8); two isolates had vat(E-1). There was no correlation between the number of base changes and the quinupristin-dalfopristin MIC.

Biocides, drug resistance and microbial evolution

Antimicrobial biocides are widely used in critical human health situations in which rigorous infection control is needed. Increasingly, biocidal agents are being marketed for home use, although there is little evidence that they significantly improve home hygiene. Biocide resistance mechanisms share many themes with antibiotic resistance mechanisms.

Identification and characterization of integron-mediated antibiotic resistance among Shiga toxin-producing Escherichia coli isolates

A total of 50 isolates of Shiga toxin-producing Escherichia coli (STEC), including 29 O157:H7 and 21 non-O157 STEC strains, were analyzed for antimicrobial susceptibilities and the presence of class 1 integrons. Seventy-eight (n = 39) percent of the isolates exhibited resistance to two or more antimicrobial classes. Multiple resistance to streptomycin, sulfamethoxazole, and tetracycline was most often observed. Class 1 integrons were identified among nine STEC isolates, including serotypes O157:H7, O111:H11, O111:H8, O111:NM, O103:H2, O45:H2, O26:H11, and O5:NM. The majority of the amplified integron fragments were 1 kb in size with the exception of one E. coli O111:H8 isolate which possessed a 2-kb amplicon. DNA sequence analysis revealed that the integrons identified within the O111:H11, O111:NM, O45:H2, and O26:H11 isolates contained the aadA gene encoding resistance to streptomycin and spectinomycin. Integrons identified among the O157:H7 and O103:H2 isolates also possessed a similar aadA gene. However, DNA sequencing revealed only 86 and 88% homology, respectively. The 2-kb integron of the E. coli O111:H8 isolate contained three genes, dfrXII, aadA2, and a gene of unknown function, orfF, which were 86, 100, and 100% homologous, respectively, to previously reported gene cassettes identified in integrons found in Citrobacter freundii and Klebsiella pneumoniae. Furthermore, integrons identified among the O157:H7 and O111:NM strains were transferable via conjugation to another strain of E. coli O157:H7 and to several strains of Hafnia alvei. To our knowledge, this is the first report of integrons and antibiotic resistance gene cassettes in STEC, in particular E. coli O157:H7.

Inheritance of Resistance to Aspergillus Ear Rot and Aflatoxin Production of Corn from CI2

This study determined the types and magnitude of gene action, estimated heritabilities, and predicted gain from selection for resistance to Aspergillus ear rot and aflatoxin production in the cross of resistant corn inbred CI2 to susceptible inbred B73 in 1998 and 1999. The warm, dry summer of 1998 favored aflatoxin production, whereas the conditions of 1999 did not. Resistance to ear rot was mainly controlled by additive gene action. Aflatoxin values were analyzed by individual years (environments) because of the highly significant generation × environment interaction. Resistance to aflatoxin production was mainly controlled by epistasis in 1998 and by additive gene action in 1999. Heritabilities for ear rot and aflatoxin production were higher in the F₃ generation than in the BCP₁-selfed generation. In 1998, Spearman's correlation coefficients between Aspergillus ear rot ratings and aflatoxin values for the F₃ and the BCP₁-selfed families were not significant (P > 0.05). In 1999, both were highly significant (P < 0.01), but low at 0.41 and 0.17 for the F₃ and BCP₁-selfed generations, respectively. We found that CI2 is not an acceptable source of resistance due to lower heritabilities and disease resistance compared to other sources of resistance.

Resistance to aflatoxin accumulation in kernels of maize inbreds selected for ear rot resistance in West and Central Africa

Thirty-six inbred lines selected in West and Central Africa for moderate to high resistance to maize ear rot under conditions of severe natural infection were screened for resistance to aflatoxin contamination using the previously established kernel screening assay. Results showed that more than half the inbreds accumulated aflatoxins at levels as low as or lower than the resistant U.S. lines GT-MAS:gk or MI82. In 10 selected aflatoxin-resistant or aflatoxin-susceptible inbreds, Aspergillus flavus growth, which was quantified using an A. flavus transformant containing a GUS-beta-tubulin reporter gene construct, was, in general, positively related to aflatoxin accumulation. However, one aflatoxin-resistant inbred supported a relatively high level of fungal infection, whereas two susceptibles supported relatively low fungal infection. When kernels of the 10 tested lines were profiled for proteins using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, significant variations from protein profiles of U.S. lines were observed. Confirmation of resistance in promising African lines in field trials may significantly broaden the resistant germplasm base available for managing aflatoxin contamination through breeding approaches. Biochemical resistance markers different from those being identified and characterized in U.S. genotypes, such as ones inhibitory to aflatoxin biosynthesis rather than to fungal infection, may also be identified in African lines. These discoveries could significantly enhance the host resistance strategy of pyramiding different traits into agronomically useful maize germplasm to control aflatoxin contamination.

Incidence of class 1 and 2 integrases in clinical and commensal bacteria from livestock, companion animals, and exotics

Many pathogenic and commensal organisms are multidrug resistant due to exposure to various antibiotics. Often, this antimicrobial resistance is encoded by integrons that occur on plasmids or that are integrated into the bacterial chromosome. Integrons are commonly associated with bacterial genera in the family Enterobacteriaceae. We determined that class 1 integrases were present in approximately 46% of the isolates from the family Enterobacteriaceae; class 2 integrases were present only among Escherichia coli and Salmonella isolates. Seven percent of veterinary isolates were positive for class 3 integrase by DNA-DNA hybridization but could not be confirmed to be positive by PCR. None of the veterinary isolates possessed the class 4 integrase gene. The distribution of these integrase genes was variable within the members of the family Enterobacteriaceae when some or all integrase classes were absent from a particular genus. There was also considerable variability in the distribution of these integrases within a species, depending on the animal host. Unlike the class 1 integrases, the other integrase class, intI2, appears to be more restricted in its distribution among the members of the family Enterobacteriaceae. There is also considerable variability in the distribution of the class 1 integrases within E. coli strains isolated from different food animals. The class 1 integrases are the most widely disseminated of the four classes among the members of the family Enterobacteriaceae from both the clinical and normal flora of animals. This is the first report to closely examine the distribution of class 2 integrases in members of the family Enterobacteriaceae isolated in the United States.

Seasonal incidence and antibiotic susceptibility patterns of Pasteurellaceae isolated from American bison (Bison bison)

Ninety pharyngeal tonsils were collected from 2-year-old American bison (Bison bison) bulls and sampled for members of the Pasteurellaceae family. Particular attention was paid to seasonal incidence and antimicrobial resistance in serotypes and biovariants. Multiple strains of Pasteurella haemolytica (39%), P. trehalosi (68%), P. multocida (34%) and Haemophilus somnus (13%) were cultured from 86 out of the 90 (96%) tonsil samples. Pasteurella trehalosi was the most common and evenly distributed of the organisms recovered. Pasteurella haemolytica was found in fewer numbers than P. trehalosi, but showed an increase in number of isolates recovered with each sampling period. Pasteurella multocida, both A and D capsular types, was recovered from all sampling periods. No serotype pattern was observed in any of the animal groups sampled. One hundred twenty-seven of 147 (86%) of the isolates were resistant to at least 1 antibiotic, 95/147 (65%) to at least 2 different antibiotics, and 16/147 (11%) to at least 3 antibiotics. The most common resistance pattern observed was to neomycin and spectinomycin (73/147) (49%).

A soxRS-constitutive mutation contributing to antibiotic resistance in a clinical isolate of Salmonella enterica (Serovar typhimurium)

The soxRS regulon is activated by redox-cycling drugs such as paraquat and by nitric oxide. The >15 genes of this system provide resistance to both oxidants and multiple antibiotics. An association between clinical quinolone resistance and elevated expression of the soxRS regulon has been observed in Escherichia coli, but this association has not been explored for other enteropathogenic bacteria. Here we describe a soxRS-constitutive mutation in a clinical strain of Salmonella enterica (serovar Typhimurium) that arose with the development of resistance to quinolones during treatment. The elevated quinolone resistance in this strain derived from a point mutation in the soxR gene and could be suppressed in trans by multicopy wild-type soxRS. Multiple-antibiotic resistance was also transferred to a laboratory strain of S. enterica by introducing the cloned mutant soxR gene from the clinical strain. The results show that constitutive expression of soxRS can contribute to antibiotic resistance in clinically relevant S. enterica.

Characterization of chloramphenicol and florfenicol resistance in Escherichia coli associated with bovine diarrhea

Florfenicol, a veterinary fluorinated analog of thiamphenicol, is approved for treatment of bovine respiratory pathogens in the United States. However, florfenicol resistance has recently emerged among veterinary Escherichia coli isolates incriminated in bovine diarrhea. The flo gene, which confers resistance to florfenicol and chloramphenicol, has previously been identified in Photobacterium piscicida and Salmonella enterica serovar Typhimurium DT104. The flo gene product is closely related to the CmlA protein identified in Pseudomonas aeruginosa. The cmlA gene confers nonenzymatic chloramphenicol resistance via an efflux mechanism. Forty-eight E. coli isolates recovered from calves with diarrhea, including 41 that were both chloramphenicol and florfenicol resistant, were assayed for the presence of both flo and cmlA genes. Forty-two of the 44 isolates for which florfenicol MICs were > or =16 microg/ml were positive via PCR for the flo gene. All E. coli isolates for which florfenicol MICs were < or =8 microg/ml were negative for the flo gene (n = 4) Twelve E. coli isolates were positive for cmlA, and chloramphenicol MICs for all 12 were > or =32 microg/ml. Additionally, eight isolates were positive for both flo and cmlA, and both florfenicol and chloramphenicol MICs for these isolates were > or =64 microg/ml. DNA sequence analysis of the E. coli flo gene demonstrated 98% identity to the published GenBank sequences of both serovar Typhimurium flo(St) and P. piscicida pp-flo. The flo gene was identified on high-molecular-weight plasmids of approximately 225 kb among the majority of florfenicol-resistant E. coli isolates. However, not all of the florfenicol-resistant E. coli isolates tested contained the large flo-positive plasmids. This suggests that several of the E. coli isolates may possess a chromosomal flo gene. The E. coli flo gene specifies nonenzymatic cross-resistance to both florfenicol and chloramphenicol, and its presence among bovine E. coli isolates of diverse genetic backgrounds indicates a distribution much wider than previously thought.

Evidence for an efflux pump mediating multiple antibiotic resistance in Salmonella enterica serovar Typhimurium

The mechanism of multiple antibiotic resistance in six isolates of Salmonella enterica serovar Typhimurium recovered from a patient treated with ciprofloxacin was studied to investigate the role of efflux in the resistance phenotype. Compared to the patient's pretherapy isolate (L3), five of six isolates accumulated less ciprofloxacin, three of six isolates accumulated less chloramphenicol, and all six accumulated less tetracycline. The accumulation of one or more antibiotics was increased by carbonyl cyanide m-chlorophenylhydrazone to concentrations similar to those accumulated by L3 for all isolates except one, in which accumulation of all three agents remained approximately half that of L3. All isolates had the published wild-type sequences of marO and marR. No increased expression of marA, tolC, or soxS was observed by Northern blotting; however, three isolates showed increased expression of acrB, which was confirmed by quantitative competitive reverse transcription-PCR. However, there were no mutations within acrR or the promoter region of acrAB in any of the isolates.