Decreased susceptibility to ciprofloxacin in outbreak-associated multiresistant Salmonella typhimurium DT104

Bridging one health and sustainable analysis: enrofloxacin quantification amid combined therapy and its active metabolite in various matrices using green RP-HPLC

Antibiotics play a crucial role in the treatment of infectious diseases in both humans and animals. However, their extensive utilization has caused significant potential harm to both wildlife and humans. Enrofloxacin (ENR) is a common veterinary antibiotic, which is not approved for human use due to associated toxicities. It is often combined with other antibiotics to expand the antibacterial range. It is crucial to monitor and measure the levels of ENR medication in various matrices. RP-HPLC is highly effective for analyzing antibiotics due to its sensitivity, specificity, and ability to handle complex samples. By adopting eco-friendly solvents, decreasing solvent consumption, and limiting waste we developed a method for determination and quantification of ENR, amoxicillin (AMX), and ENR active metabolite in different matrices. The method utilized a reversed stationary phase and a mobile phase composed of phosphate buffer pH 3.0: ethanol (90:10 v/v) pumped at 1.0 mL/min and UV detection at 254.0 nm. Moreover, a comprehensive assessment of the environmental friendliness of the established method was conducted using various tools including the Green Certificate Classification (GCC) and Analytical Greenness AGREE and RGB12. The method was validated for its accuracy and precision in quantifying ENR, demonstrating its potential for the effective monitoring of ENR and contributing to public health protection.

Intramuscular therapeutic doses of enrofloxacin affect microbial community structure but not the relative abundance of fluoroquinolones resistance genes in swine manure

Livestock manure is a major source of veterinary antibiotics and antibiotic resistance genes (ARGs). Elucidation of the residual characteristics of ARGs in livestock manure following the administration of veterinary antibiotics is critical to assess their ecotoxicological effects and environmental contamination risks. Here, we investigated the effects of enrofloxacin (ENR), a fluoroquinolone antibiotic commonly used as a therapeutic drug in animal husbandry, on the characteristics of ARGs, mobile genetic elements, and microbial community structure in swine manure following its intramuscular administration for 3 days and a withdrawal period of 10 days. The results revealed the highest concentrations of ENR and ciprofloxacin (CIP) in swine manure at the end of the administration period, ENR concentrations in swine manure in groups L and H were 88.67 ± 45.46 and 219.75 ± 88.05 mg/kg DM, respectively. Approximately 15 fluoroquinolone resistance genes (FRGs) and 48 fluoroquinolone-related multidrug resistance genes (F-MRGs) were detected in swine manure; the relative abundance of the F-MRGs was considerably higher than that of the FRGs. On day 3, the relative abundance of qacA was significantly higher in group H than in group CK, and no significant differences in the relative abundance of other FRGs, F-MRGs, or MGEs were observed between the three groups on day 3 and day 13. The microbial community structure in swine manure was significantly altered on day 3, and the altered community structure was restored on day 13. The FRGs and F-MRGs with the highest relative abundance were qacA and adeF, respectively, and Clostridium and Lactobacillus were the dominant bacterial genera carrying these genes in swine manure. In summary, a single treatment of intramuscular ENR transiently increased antibiotic concentrations and altered the microbial community structure in swine manure; however, this treatment did not significantly affect the abundance of FRGs and F-MRGs.

Quantitative Risk Assessment of Susceptible and Ciprofloxacin-Resistant Salmonella from Retail Pork in Chiang Mai Province in Northern Thailand

The adverse human health effects as a result of antimicrobial resistance have been recognized worldwide. Salmonella is a leading cause of foodborne illnesses while antimicrobial resistant (AMR) Salmonella has been isolated from foods of animal origin. The quantitative risk assessment (RA) as part of the guidelines for the risk analysis of foodborne antimicrobial resistance was issued by the Codex Alimentarius Commission more than a decade ago. However, only two risk assessments reported the human health effects of AMR Salmonella in dry-cured pork sausage and pork mince. Therefore, the objective of this study was to quantitatively evaluate the adverse health effects attributable to consuming retail pork contaminated with Salmonella using risk assessment models. The sampling frame covered pork at the fresh market (n = 100) and modern trade where pork is refrigerated (n = 50) in Chiang Mai province in northern Thailand. The predictive microbiology models were used in the steps where data were lacking. Susceptible and quinolone-resistant (QR) Salmonella were determined by antimicrobial susceptibility testing and the presence of AMR genes. The probability of mortality conditional to foodborne illness by susceptible Salmonella was modeled as the hazard characterization of susceptible and QR Salmonella. For QR Salmonella, the probabilistic prevalences from the fresh market and modern trade were 28.4 and 1.9%, respectively; the mean concentrations from the fresh market and modern trade were 346 and 0.02 colony forming units/g, respectively. The probability of illness (PI) and probability of mortality given illness (PMI) from QR Salmonella-contaminated pork at retails in Chiang Mai province were in the range of 2.2 × 10-8-3.1 × 10-4 and 3.9 × 10-10-5.4 × 10-6, respectively, while those from susceptible Salmonella contaminated-pork at retails were in the range 1.8 × 10-4-3.2 × 10-4 and 2.3 × 10-7-4.2 × 10-7, respectively. After 1000 iterations of Monte Carlo simulations of the risk assessment models, the annual mortality rates for QR salmonellosis simulated by the risk assessment models were in the range of 0-32, which is in line with the AMR adverse health effects previously reported. Therefore, the risk assessment models used in both exposure assessment and hazard characterization were applicable to evaluate the adverse health effects of AMR Salmonella spp. in Thailand.

Antimicrobial Resistance Development Pathways in Surface Waters and Public Health Implications

Human health is threatened by antibiotic-resistant bacteria and their related infections, which cause thousands of human deaths every year worldwide. Surface waters are vulnerable to human activities and natural processes that facilitate the emergence and spread of antibiotic-resistant bacteria in the environment. This study evaluated the pathways and drivers of antimicrobial resistance (AR) in surface waters. We analyzed antibiotic resistance healthcare-associated infection (HAI) data reported to the CDC's National Healthcare Safety Network to determine the number of antimicrobial-resistant pathogens and their isolates detected in healthcare facilities. Ten pathogens and their isolates associated with HAIs tested resistant to the selected antibiotics, indicating the role of healthcare facilities in antimicrobial resistance in the environment. The analyzed data and literature research revealed that healthcare facilities, wastewater, agricultural settings, food, and wildlife populations serve as the major vehicles for AR in surface waters. Antibiotic residues, heavy metals, natural processes, and climate change were identified as the drivers of antimicrobial resistance in the aquatic environment. Food and animal handlers have a higher risk of exposure to resistant pathogens through ingestion and direct contact compared with the general population. The AR threat to public health may grow as pathogens in aquatic systems adjust to antibiotic residues, contaminants, and climate change effects. The unnecessary use of antibiotics increases the risk of AR, and the public should be encouraged to practice antibiotic stewardship to decrease the risk.

Pharmacokinetic profile of enrofloxacin and its metabolite ciprofloxacin in Asian house geckos (Hemidactylus frenatus) after single-dose oral administration of enrofloxacin

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxacin were determined following oral administration in 21 Asian house geckos (Hemidactylus frenatus) at a dose of 10 mg/kg. Changes in enrofloxacin and ciprofloxacin plasma concentrations were quantified at regular intervals over 72 h (1, 2, 6, 12, 24, 48, and 72 h). Samples were analysed by high-pressure liquid chromatography (HPLC) and the enrofloxacin pharmacokinetic data underwent a two-compartment analysis. Due to the limited ciprofloxacin plasma concentrations above the lower limit of quantification (LLOQ), the ciprofloxacin data underwent non-compartment analysis and the half-life was determined by the Lineweaver-Burke plot and analysis. The enrofloxacin and ciprofloxacin mean half-lives (t _½) were 0.95 h (α) / 24.36 h (β), and 11.06 h respectively, area under the curve (AUC_0-24h) were 60.56 and 3.14 µg/mL*h, respectively, maximum concentrations (C _max) were 12.31 and 0.24 µg/mL, respectively, and time required to reach the C _max (T _max) were 1 and 2 h respectively. Enrofloxacin was minimally converted to the active metabolite ciprofloxacin, with ciprofloxacin concentrations contributing only 4.91% of the total fluoroquinolone concentrations (AUC_0-24h). Based on the pharmacokinetic indices when using susceptibility breakpoints when determined at mammalian body temperature it is predicted that single oral administration of enrofloxacin (10 mg/kg) would result in plasma concentrations effective against susceptible bacterial species inhibited by an enrofloxacin MIC ≤ 0.5 µg/mL in vitro, but additional studies will be required to determine its efficacy in vivo.

Salmonella enterica serovar Typhimurium skills to succeed in the host: virulence and regulation

Salmonella enterica serovar Typhimurium is a primary enteric pathogen infecting both humans and animals. Infection begins with the ingestion of contaminated food or water so that salmonellae reach the intestinal epithelium and trigger gastrointestinal disease. In some patients the infection spreads upon invasion of the intestinal epithelium, internalization within phagocytes, and subsequent dissemination. In that case, antimicrobial therapy, based on fluoroquinolones and expanded-spectrum cephalosporins as the current drugs of choice, is indicated. To accomplish the pathogenic process, the Salmonella chromosome comprises several virulence mechanisms. The most important virulence genes are those located within the so-called Salmonella pathogenicity islands (SPIs). Thus far, five SPIs have been reported to have a major contribution to pathogenesis. Nonetheless, further virulence traits, such as the pSLT virulence plasmid, adhesins, flagella, and biofilm-related proteins, also contribute to success within the host. Several regulatory mechanisms which synchronize all these elements in order to guarantee bacterial survival have been described. These mechanisms govern the transitions from the different pathogenic stages and drive the pathogen to achieve maximal efficiency inside the host. This review focuses primarily on the virulence armamentarium of this pathogen and the extremely complicated regulatory network controlling its success.

Antibiotic-resistant bacteria: a challenge for the food industry

Antibiotic-resistant bacteria were first described in the 1940s, but whereas new antibiotics were being discovered at a steady rate, the consequences of this phenomenon were slow to be appreciated. At present, the paucity of new antimicrobials coming into the market has led to the problem of antibiotic resistance fast escalating into a global health crisis. Although the selective pressure exerted by the use of antibiotics (particularly overuse or misuse) has been deemed the major factor in the emergence of bacterial resistance to these antimicrobials, concerns about the role of the food industry have been growing in recent years and have been raised at both national and international levels. The selective pressure exerted by the use of antibiotics (primary production) and biocides (e.g., disinfectants, food and feed preservatives, or decontaminants) is the main driving force behind the selection and spread of antimicrobial resistance throughout the food chain. Genetically modified (GM) crops with antibiotic resistance marker genes, microorganisms added intentionally to the food chain (probiotic or technological) with potentially transferable antimicrobial resistance genes, and food processing technologies used at sub-lethal doses (e.g., alternative non-thermal treatments) are also issues for concern. This paper presents the main trends in antibiotic resistance and antibiotic development in recent decades, as well as their economic and health consequences, current knowledge concerning the generation, dissemination, and mechanisms of antibacterial resistance, progress to date on the possible routes for emergence of resistance throughout the food chain and the role of foods as a vehicle for antibiotic-resistant bacteria. The main approaches to prevention and control of the development, selection, and spread of antibacterial resistance in the food industry are also addressed.

Outbreak investigation and case-control study: penta-resistant Salmonella Typhimurium DT104 associated with biltong in London in 2008

In August 2008 an outbreak of Salmonella Typhimurium DT104 occurred in South West London. Sixteen cases were identified with a particular multilocus variable number tandem repeat analysis (MLVA) pattern. In a matched case-control study 14 primary cases were included. These were defined as individuals with gastrointestinal symptoms and Salmonella Typhimurium DT104 isolated from a stool specimen, with a characteristic antibiotic resistance profile and MLVA pattern, and diagnosed in a local laboratory. Four controls per case were matched on age, gender and area of residence. Cases were 26 times more likely than controls to have eaten beef biltong, a South African speciality meat product (odds ratio 25·83, 95% confidence interval 4·92–135·59, P < 0·01). Although environmental investigation failed to identify Salmonella in the food product we conclude that beef biltong consumption led to this outbreak. This conclusion has importance in informing the ongoing risk assessment relating to uncontrolled foodstuffs.

Prevalence and antimicrobial resistance of Salmonella serotypes in chickens from retail markets in Yaounde (Cameroon)

From February 2006 to January 2007, 150 chickens were collected from eight retail markets in Yaounde, and 90 (60%) tested positive for Salmonella. Seventy-nine chickens were contaminated with only one Salmonella serotype, 10 with two different serotypes, and 1 with four serotypes. The most prevalent serotypes were Enteritidis (47 strains) and Hadar (29 strains). The isolates were tested for their susceptibilities to amoxicillin, amoxicillin/clavulanic acid, cefoxitin, cefotaxime, gentamicin, streptomycin, tetracycline, chloramphenicol, sulfonamides, nalidixic acid, ciprofloxacin, and trimethoprim/sulfamethazole by disk diffusion assay. Minimum inhibitory concentrations of ampicillin, streptomycin, tetracycline, sulfonamides, and nalidixic acid were determined for the resistant strains by agar dilution method. Eleven isolates (10.7%) of the 103 tested were susceptible to all antimicrobials. Resistance was most observed to tetracycline (84.5%), streptomycin (44.7%), and nalidixic acid (34%). Forty-one isolates (39.8%) were multidrug resistant (resistant to three or more antimicrobials from different classes), of which 68.3% were Hadar and 21.9% Enteritidis. The most frequent resistant pattern in Hadar was streptomycin-tetracycline-nalidixic acid. These results highlight once more the need for surveillance of Salmonella contamination in poultry.

Trends in phage types and antimicrobial resistance of Salmonella enterica serovar Enteritidis isolated from animals in Great Britain from 1990 to 2005

Surveillance data for Salmonella enterica serovar Enteritidis incidents and isolations from food animals in Great Britain from 1990 to 2005 were analysed to detect any trends and provide the basis for a comparison between phage types (pt) and antimicrobial sensitivity patterns in human beings and animals. During 2001 to 2005 there was a decrease in incidents involving most species except ducks. Only the numbers of incidents involving pts 6, 6a, 9b and 14b (in ducks) and pts 6a and 13a (in mammals) increased significantly during this period, whereas there were 93 per cent fewer incidents involving pt 4 than in 1990 to 2000. After adjustment for pt, the isolates from ducks were more resistant to nalidixic acid, tetracyclines and sulfonamides, and were more likely to be multiresistant than isolates from chickens. Isolates from turkeys tended to be more resistant to sulfonamides than isolates from chickens. pts 1, 5a, 6, 6a and 35 had the highest level of resistance after adjusting for species. During 2001 to 2005 there was an increase in resistance among pts 1, 6 and 7, in most cases involving nalidixic acid.

Surveillance and antimicrobial resistance of Salmonella strains isolated from slaughtered pigs in Spain

The prevalence of and the antibiotic resistance shown by Salmonella isolated from pigs in Andalusia (southern Spain) is reported. Salmonella enterica was recovered from 40 (33%) of 121 sampled herds, and a total of 65 isolates were serotyped. The most common Salmonella serotypes were Typhimurium and Rissen (30.7% each); others included Derby (9.2%), Brandenburg (9.2%), Newport (7.7%), Bredeney (4.6%), Anatum (3.0%), Hadar (1.5%), and Goldcoast (1.5%). One strain (1.5%) belonging to the monophasic variant of the Typhimurium serotype (Salmonella 4,5,12:i: -) was also detected. Definitive phage type (DT) 104b was the most common Typhimurium phage type isolated. These Salmonella strains were resistant to various antimicrobial agents, including tetracycline (84.6%), streptomycin (69.2%), neomycin (63.0%), sulfonamides (61.5%), ampicillin (53.8%), and amoxicillin (53.8%). All isolates were fully susceptible to ceftriaxone, ciprofloxacin, and colistin. Thirty-nine strains (64%) resistant to four or more antimicrobial agents were defined as multidrug resistant. Multidrug resistance profiles were observed in Salmonella serotypes Typhimurium, Rissen, Brandenburg, Bredeney, a monophasic variant, Gold-coast, Hadar, and Anatum, with serotypes Typhimurium and Brandenburg showing the most complicated resistance patterns (resistant to > or = 11 drugs).

A longitudinal study of Salmonella shedding and antimicrobial resistance patterns in North Dakota feedlot cattle

Salmonella is one of the most frequent causes of foodborne illness worldwide, and transmission involves foods of animal origin such as beef. The objective of this study was to monitor the prevalence of Salmonella fecal shedding in feedlot cattle during the finishing period and to assess the antimicrobial resistance patterns of the isolated salmonellae. On arrival at the feedlot, 1 (0.7%) of the 144 steers was shedding Salmonella in its feces. After 28 days on feed, shedding was detected in 8 (5.6%) of the 144 steers. At the third sampling, 19 (13%) of 143 steers were shedding, and the number of shedders continued to increase to 89 (62%) of 143 at the last sampling. Salmonella shedding was significantly influenced (P < 0.0001) by sampling time but not by herd of origin. All Salmonella isolates identified belonged to serotype Typhimurium serovar Copenhagen, a type commonly isolated from Salmonella infections in humans. Antimicrobial resistance testing of the isolates revealed five multidrug resistance patterns, two of which accounted for 104 (95.4%) of 109 of the isolates. All the isolates were susceptible to ceftiofur, and all were resistant to spectinomycin, sulfathiazole, tiamulin, florfenicol, ampicillin, penicillin, chlortetracycline, oxytetracycline, and clindamycin. Data from this study indicate that a high prevalence of antimicrobial-resistant Salmonella strains can sometimes be found in feedlot cattle in North Dakota. These data will contribute to risk assessment of Salmonella shedding by cattle in feedlots and highlight the need to continue preharvest monitoring for this organism.

Fluoroquinolone antibiotics in the environment

Fluoroquinolones (FQs) are used in large amounts for human and animal medical care. They are excreted as parent compound, as conjugates, or as oxidation, hydroxylation, dealkylation, or decarboxylation products of the parent compound. A considerable amount of FQs and their metabolites may reach the soil as constituents of urine, feces, or manure. The residues of FQs in foods of animal origin may pose hazards to consumers through emergence of drug-resistant bacteria. FQs bind strongly to topsoil, reducing the threat of surface water and groundwater contamination. The strong binding of FQs to soil and sediments delays their biodegradation and explains the recalcitrance of FQs. Wastewater treatment is an efficient elimination step (79%-87% removal) for FQs before they enter rivers. FQs are susceptible to photodegradation in aqueous medium, involving oxidation, dealkylation, and cleavage of the piperazine ring.

Rapid detection of gyrA and parC mutations in quinolone-resistant Salmonella enterica using Pyrosequencing technology

Fluoroquinolones are broad-spectrum antimicrobials highly effective in the treatment of a wide variety of clinical infections. Salmonella gastroenteritis is usually only treated with fluoroquinolones when the patient is elderly or immunocompromised. Fluoroquinolones are also used for the treatment of systemic Salmonella infection or for long-term salmonella carriage. Resistance to quinolones is commonly mediated by point mutations within the topoisomerase genes gyrA and parC. Pyrosequencing technology is a DNA sequencing method using 'sequencing by synthesis' and is suitable for the rapid detection of single nucleotide polymorphisms (SNPs). One hundred and ten Salmonella enterica isolates, representing 18 different serotypes, were used in this study. One hundred and four isolates had ciprofloxacin MICs of 0.25-32 microg/mL; the remaining six were ciprofloxacin-sensitive (ciprofloxacin MIC<or=0.125 microg/mL). PCR amplification of the quinolone resistance-determining regions of gyrA and parC was performed and the resulting amplicons subjected to a Pyrosequencing protocol using cyclic dispensation of nucleotides. Amino acid substitutions at S83 and D87 were detected in gyrA and at T57 and S80 in parC. Silent mutations were also identified at G81 of gyrA and at V67, H75 and H77 of parC. This is the first report of a Pyrosequencing assay being used to detect mutations in genes conferring quinolone resistance. The Pyrosequencing technology is a rapid and reliable alternative to current methods for identification of gyrA and parC mutations in S. enterica.

Publication bias in foodborne outbreaks of infectious intestinal disease and its implications for evidence-based food policy. England and Wales 1992-2003

Systematic national surveillance of outbreaks of infectious intestinal disease (IID) was introduced in England and Wales in 1992 to provide comprehensive information on causative organisms, sources or vehicles of infection and modes of transmission. We compared information from this system with that published in the peer-reviewed literature between 1 January 1992 and 31 January 2003 to assess the potential effect of publication bias on food-safety policy. During the study period 1763 foodborne outbreaks of IID were reported to national surveillance. Fifty-five were published in the peer-reviewed literature. The peer-reviewed literature overestimated the impacts of milk/milk products, miscellaneous foods (e.g. sandwiches) and desserts and underestimated those of poultry, fish and shellfish, red meat/meat products and eggs/egg products. Without systematic surveillance, knowledge of causative organisms, sources or vehicles of infection and modes of transmission, as gleaned from the peer-reviewed literature, would potentially distort food-safety policy.

Trends in antimicrobial resistance phenotypes in non-typhoid Salmonellae from human and poultry origins in France

A total of 1873 strains from human origin and 4283 strains from non-human origin of Salmonella enterica serotypes Typhimurium, Enteritidis, Heidelberg, Hadar and Virchow, collected over three years 1993, 1997 and 2000, were examined in order to determine the rate of antimicrobial resistance to 12 antimicrobial drugs. The objective of the study was to describe and to compare the evolution of the main resistance types in human and non-human isolates, focusing on the poultry sector. The evolution and the rates of antimicrobial resistances for the five serotypes, with the exception of Virchow, were almost comparable in strains isolated from human and non-human sources over the period studied. The most striking result concerning single resistance was the spectacular increase of the resistance frequency to nalidixic acid for the strains belonging to serotypes Hadar and Virchow, especially in the poultry food sector (14% in 1993 vs. 72% in 2000 for Salmonella Virchow, 4% in 1993 vs. 70% in 2000 for Salmonella Hadar) and also in human isolates (24% in 1997 vs. 48% in 2000 for S. Virchow, 31% in 1997 vs. 78% in 2000 for S. Hadar). In addition to the classical resistance to ampicillin, streptomycin, sulphonamide, chloramphenicol and tetracycline (ASSuCT resistance type), which stabilized between 1997 and 2000, the emergence of a new resistance type was observed.

Characterization of isolates of Salmonella enterica serovar typhimurium displaying high-level fluoroquinolone resistance in Japan

Strains of the multidrug-resistant (MDR) Salmonella enterica serovar Typhimurium isolated in Japan were examined for high-level fluoroquinolone resistance. Since the first isolation in 2000 (described in reference 13), we have identified 12 human and 5 nonhuman isolates with high-level fluoroquinolone-resistance (ciprofloxacin MIC of 24 microg/ml or more). Most of these isolates shared some features including definitive phage type (DT 12/193), resistance type (ACSSuTNCp; resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, tetracycline, nalidixic acid, and ciprofloxacin), and genotype on pulsed-field gel electrophoresis that were different from those of the MDR S. enterica Typhimurium DT 104. Mutations in quinolone resistance-determining regions of gyrA and parC were also conserved in almost all of the isolates despite the absence of any apparent epidemiological relationships among cases. This suggests that a specific clonal group of the serovar Typhimurium with high levels of fluoroquinolone resistance is disseminating among animals and humans in Japan.

Mechanisms of quinolone resistance in Escherichia coli and Salmonella: Recent developments

Fluoroquinolones are broad-spectrum antimicrobials highly effective for treatment of a variety of clinical and veterinary infections. Their antibacterial activity is due to inhibition of DNA replication. Usually resistance arises spontaneously due to point mutations that result in amino acid substitutions within the topoisomerase subunits GyrA, GyrB, ParC or ParE, decreased expression of outer membrane porins, or overexpression of multidrug efflux pumps. In addition, the recent discovery of plasmid-mediated quinolone resistance could result in horizontal transfer of fluoroquinolone resistance between strains. Acquisition of high-level resistance appears to be a multifactorial process. Care needs to taken to avoid overuse of this important class of antimicrobial in both human and veterinary medicine to prevent an increase in the occurrence of resistant zoonotic and non-zoonotic bacterial pathogens that could subsequently cause human or animal infections.

Fluorescent amplified fragment length polymorphism subtyping of multiresistant Salmonella enterica serovar Typhimurium DT104

Fluorescent amplified fragment length polymorphism (FAFLP) subtyping analysis was used to genotype multiresistant Salmonella enterica serovar Typhimurium definitive phage type 104. Thirteen distinct FAFLP profiles were found among 85 isolates exhibiting identical pulsed-field gel electrophoresis (PFGE) profiles. A single FAFLP profile was shared by 93% of outbreak-associated isolates and 82% of sporadic isolates. This study demonstrates the value of FAFLP as a high-resolution tool for epidemiological investigation of Salmonella.

AcrAB-TolC directs efflux-mediated multidrug resistance in Salmonella enterica serovar typhimurium DT104

Multidrug-resistant Salmonella enterica serovar Typhimurium definitive phage type 104 (DT104) strains harbor a genomic island, called Salmonella genomic island 1 (SGI1), which contains an antibiotic resistance gene cluster conferring resistance to ampicillin, chloramphenicol, florfenicol, streptomycin, sulfonamides, and tetracyclines. They may be additionally resistant to quinolones. Among the antibiotic resistance genes there are two, i.e., floR and tet(G), which code for efflux pumps of the major facilitator superfamily with 12 transmembrane segments that confer resistance to chloramphenicol-florfenicol and the tetracyclines, respectively. In the present study we determined, by constructing acrB and tolC mutants, the role of the AcrAB-TolC multidrug efflux system in the multidrug resistance of several DT104 strains displaying additional quinolone resistance or not displaying quinolone resistance. This study shows that the quinolone resistance and the decreased fluoroquinolone susceptibilities of the strains are highly dependent on the AcrAB-TolC efflux system and that single mutations in the quinolone resistance-determining region of gyrA are of little relevance in mediating this resistance. Overproduction of the AcrAB efflux pump, as determined by Western blotting with an anti-AcrA polyclonal antibody, appeared to be the major mechanism of resistance to quinolones. Moreover, chloramphenicol-florfenicol and tetracycline resistance also appeared to be highly dependent on the presence of AcrAB-TolC, since the introduction of mutations in the respective acrB and tolC genes resulted in a susceptible or intermediate resistance phenotype, according to clinical MIC breakpoints, despite the presence of the FloR and Tet(G) efflux pumps. Resistance to other antibiotics, ampicillin, streptomycin, and sulfonamides, was not affected in the acrB and tolC mutants of DT104 strains harboring SGI1. Therefore, AcrAB-TolC appears to direct efflux-mediated resistance to quinolones, chloramphenicol-florfenicol, and tetracyclines in multidrug-resistant S. enterica serovar Typhimurium DT104 strains.

Resistance of Salmonella Isolates in Germany

During 2000-2002 the National Veterinary Reference Laboratory for Salmonella (NRL-Salm) in Germany typed 11,911 isolates from animals, food, feed and the environment. All of them were tested for their susceptibility to 17 anti-microbial agents. Sixty-three per cent of all isolates were resistant and 40% were multiresistant (resistant against more than one anti-microbial). This general resistance level was strongly influenced by those specific serotypes which dominate the Salmonella epidemiology in Germany. Salmonella Typhimurium DT104 isolates from pig and cattle, and their resulting food products, were multiresistant in 98 and 94% of the cases respectively. During the period 2000-2003 an increasing quinolone resistance especially in Salmonella isolates from poultry and poultry meat (to 26%) and in S. Paratyphi B D-tartrate positive isolates (to 64%) could be observed. This increase was accompanied by a shift towards higher minimal inhibitory concentrations for ciprofloxacin.

Spread of Resistant Bacteria and Resistance Genes from Animals to Humans - The Public Health Consequences

The paper reviews the lines of evidence which link the use of antimicrobial drugs for food animals with the emergence of antimicrobial drug resistance in bacteria pathogenic to humans, with a particular focus on the public health aspects. Deductions from the epidemiology of food-borne infections, ecological studies, outbreak investigations, typing studies and direct epidemiological observations show that resistant bacteria are transferred from food animals to man. In addition to transfer in the food chain, exchange of mobile genetic elements among commensal and pathogenic bacteria contributes to the emergence of drug resistance. There is growing evidence that this has measurable consequences for human public health. One consequence is increased transmission supported by unrelated use of anti-microbials in humans. Other consequences are related to reduced efficacy of early empirical treatment, limitations in the choices for treatment after confirmed microbiological diagnosis, and finally a possible coselection of virulence traits. Recent epidemiological studies have measured these consequences in terms of excess mortality associated with resistance, increased duration of illness, and increased risk of invasive illness or hospitalization following infections with resistant Salmonella.

Evidence of an Association Between Use of Anti-microbial Agents in Food Animals and Anti-microbial Resistance Among Bacteria Isolated from Humans and the Human Health Consequences of Such Resistance

Several lines of evidence indicate that the use of anti-microbial agents in food animals is associated with anti-microbial resistance among bacteria isolated from humans. The use of anti-microbial agents in food animals is most clearly associated with anti-microbial resistance among Salmonella and Campylobacter isolated from humans, but also appears likely among enterococci, Escherichia coli and other bacteria. Evidence is also accumulating that the anti-microbial resistance among bacteria isolated from humans could be the result of using anti-microbial agents in food animals and is leading to human health consequences. These human health consequences include: (i) infections that would not have otherwise occurred and (ii) increased frequency of treatment failures and increased severity of infection. Increased severity of infection includes longer duration of illness, increased frequency of bloodstream infections, increased hospitalization and increased mortality. Continued work and research efforts will provide more evidence to explain the connection between the use of anti-microbial agents in food animals and anti-microbial-resistant infections in humans. One particular focus, which would solidify this connection, is to understand the factors that dictate spread of resistance determinants, especially resistant genes. With continued efforts on the part of the medical, veterinary and public health community, such research may contribute to more precise guidelines on the use of anti-microbials in food animals.

Evaluation of a scanner-assisted colorimetric MIC method for susceptibility testing of gram-negative fermentative bacteria

We describe the ScanMIC method, a colorimetric MIC method for susceptibility testing of gram-negative fermentative bacteria. The method is a slight modification of the National Committee for Clinical Laboratory Standards (NCCLS) recommended broth microdilution method that uses a redox indicator 2,3,5-triphenyltetrazolium chloride (TTC) to enhance the estimate of bacterial growth inhibition in a microplate and a flatbed scanner to capture the microplate image. In-house software was developed to transform the microplate image into numerical values based on the amount of bacterial growth and to generate the MICs automatically. The choice of indicator was based on its low toxicity and ease of reading by scanner. We compared the ScanMIC method to the NCCLS recommended broth microdilution method with 197 coliform strains against seven antibacterial agents. The interpretative categorical agreement was obtained in 92.4% of the assays, and the agreement for MIC differences (within +/-1 log(2) dilution) was obtained in 96% for ScanMIC versus broth microdilution and 97% for a two-step incubation colorimetric broth microdilution versus the broth microdilution method. The method was found to be labor-saving, not to require any initial investment, and to show reliable results. Thus, the ScanMIC method could be useful for epidemiological surveys that include susceptibility testing of bacteria.

Mutations in topoisomerase genes of fluoroquinolone-resistant salmonellae in Hong Kong

A total of 88 salmonella isolates (72 clinical isolates for which the ciprofloxacin MIC was >0.06 microg/ml, 15 isolates for which the ciprofloxacin MIC was < or =0.06 microg/ml, and Salmonella enterica serotype Typhimurium ATCC 13311) were studied for the presence of genetic alterations in four quinolone resistance genes, gyrA, gyrB, parC, and parE, by multiplex PCR amplimer conformation analysis. The genetic alterations were confirmed by direct nucleotide sequencing. A considerable number of strains had a mutation in parC, the first to be reported in salmonellae. Seven of the isolates sensitive to 0.06 micro g of ciprofloxacin per ml had a novel mutation at codon 57 of parC (Tyr57-->Ser) which was also found in 29 isolates for which ciprofloxacin MICs were >0.06 micro g/ml. Thirty-two isolates had a single gyrA mutation (Ser83-->Phe, Ser83-->Tyr, Asp87-->Asn, Asp87-->Tyr, or Asp87-->Gly), 34 had both a gyrA mutation and a parC mutation (29 isolates with a parC mutation of Tyr57-->Ser and 5 isolates with a parC mutation of Ser80-->Arg). Six isolates which were isolated recently (from 1998 to 2001) were resistant to 4 micro g of ciprofloxacin per ml. Two of these isolates had double gyrA mutations (Ser83-->Phe and Asp87-->Asn) and a parC mutation (Ser80-->Arg) (MICs, 8 to 32 microg/ml), and four of these isolates had double gyrA mutations (Ser83-->Phe and Asp87-->Gly), one parC mutation (Ser80-->Arg), and one parE mutation (Ser458-->Pro) (MICs, 16 to 64 micro g/ml). All six of these isolates and those with a Ser80-->Arg parC mutation were S. enterica serotype Typhimurium. One S. enterica serotype Typhi isolate harbored a single gyrA mutation (Ser83-->Phe), and an S. enterica serotype Paratyphi A isolate harbored a gyrA mutation (Ser83-->Tyr) and a parC mutation (Tyr57-->Ser); both of these isolates had decreased susceptibilities to the fluoroquinolones. The MICs of ciprofloxacin, levofloxacin, and sparfloxacin were in general the lowest of those of the six fluoroquinolones tested. Isolates with a single gyrA mutation were less resistant to fluoroquinolones than those with an additional parC mutation (Tyr57-->Ser or Ser80-->Arg), while those with double gyrA mutations were more resistant.

Antibiotic resistance of Salmonella isolated from hog, beef, and chicken carcass samples from provincially inspected abattoirs in Ontario

The emergence of antimicrobial-resistant Salmonella organisms, especially Salmonella Typhimurium DT104, has been reported in many countries, including the United States and Canada. The purposes of this study were to determine the antimicrobial resistance patterns of Salmonella isolated from hog, beef, and chicken carcasses from provincially inspected abattoirs in Ontario and to determine the agreement between the agar dilution method and the microbroth dilution method for measurement of antimicrobial resistance of the isolates. Antimicrobial resistance of Salmonella isolates from hogs (n = 71), beef (n = 24), and chicken (n = 295) to amikacin, ampicillin, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, streptomycin, sulfamethoxazole, and tetracycline was determined using the two methods. None of the 390 isolates were resistant to ciprofloxacin at levels of 0.125 microg/ml. All chicken and hog isolates were sensitive to amikacin, whereas all beef isolates were sensitive to both amikacin and gentamicin. Multiple antimicrobial resistance (resistance to more than one antimicrobial) was found in 29% of bovine isolates and 42% of porcine isolates using both methods for testing and in 42% by the agar dilution and 33% by the microbroth dilution methods in the chicken isolates. Overall, there was good agreement between the two test methods for resistance to most of the antimicrobials, with disagreement found in the results in 1.3% of the isolates for ampicillin and sulfamethoxazole, 8.2% for streptomycin, 5.6% for cephalothin, and 1.0% of the isolates for tetracycline. The lack of agreement between the two test methods was found mostly among the chicken isolates.

A comparison of antimicrobial susceptibilities in nontyphoidal salmonellas from humans and food animals in England and Wales in 2000

A joint study by the Public Health Laboratory Service and the Veterinary Laboratories Agency of resistance to antimicrobials in isolates of Salmonella enterica serotypes Enteritidis, Typhimurium, Hadar, and Virchow from humans and food-producing animals in England and Wales in 2000 has demonstrated that resistance was most common in Typhimurium, particularly in strains of definitive phage type (DT) 104. However resistance was also common in other phage types, particularly DTs 193 and 208 and phage type U302. Multiresistant strains of DT208 appeared to be predominantly associated with pigs; for the other phage types, the human/food-producing animal relationships of drug-resistant isolates were more complex. For Enteritidis, Virchow, and Hadar, there were substantial differences in the resistance spectra of isolates from humans and food-producing animals, suggesting that food-producing animals bred in England and Wales may not be the primary sources of drug-resistant strains of these serotypes causing infections in humans. Further phenotypic and molecular comparison of drug-resistant isolates of these serotypes may be required to ascertain the sources of strains responsible for infections in humans.

LightCycler gyrA mutation assay (GAMA) identifies heterogeneity in GyrA in Salmonella enterica serotypes Typhi and Paratyphi A with decreased susceptibility to ciprofloxacin

Mutations in gyrA in strains of Salmonella enterica serotypes Typhi and Paratyphi A have been characterised by a LightCycler-based PCR-hybridisation gyrA mutation assay (GAMA) and by DNA sequencing. Four mutations (Ser-83 to Phe, Asp-87 to Asn, Ser-83 to Tyr and Asp-87 to Gly) have been identified in 13 strains of Typhi and three strains of Paratyphi A resistant to nalidixic acid (=nal(r)) and with decreased susceptibility to ciprofloxacin (=Cp(L)), with the mutation Ser-83 to Phe predominating. The results have demonstrated heterogeneity in gyrA in nal(r) Cp(L) strains of Typhi and Paratyphi A and may be useful for epidemiological investigations. No mutations in gyrA were identified in four Cp(L) strains of S. Typhi that were sensitive to nalidixic acid. The mechanism of decreased susceptibility to ciprofloxacin in these strains is under investigation.

Fitness cost of fluoroquinolone resistance in Salmonella enterica serovar Typhimurium

High-level fluoroquinolone (FQ) resistance is still infrequent in salmonellae, compared with other pathogenic enterobacteria. Data provided in this work support the hypothesis that the mechanisms that confer high-level FQ resistance on salmonellae have a prohibitive fitness cost and may thus limit the emergence of highly resistant clones. In vitro mutants that were highly resistant to ciprofloxacin (MIC = 8 and 16 micro g ml(-1)) showed generation times 1.4- and 2-fold longer than their parent strains and were unable to colonize the gut of chickens. Electron microscopy showed an altered morphology for one of these mutants grown to stationary phase. Mutants selected in vivo and exhibiting intermediate resistance to ciprofloxacin (MIC = 2 micro g ml(-1)) also showed growth defects on solid media but had normal generation times in liquid culture and colonized the gut of chickens. After in vitro or in vivo passage in the absence of antibiotic selective pressure, partial reversals of the fitness cost were observed, which were associated with slight decreases in resistance to quinolones and other unrelated antibiotics, but were not linked to the loss of gyrA mutations.

Thermal inactivation of susceptible and multiantimicrobial-resistant salmonella strains grown in the absence or presence of glucose

The heat resistance of susceptible and multiantimicrobial-resistant Salmonella strains grown to stationary phase in glucose-free tryptic soy broth supplemented with 0.6% yeast extract (TSBYE-G; nonadapted), in regular (0.25% glucose) TSBYE, or in TSBYE-G with 1.00% added glucose (TSBYE+G; acid adapted) was determined at 55, 57, 59, and 61 degrees C. Cultures were heated in sterile 0.1% buffered peptone water (50 microl) in heat-sealed capillary tubes immersed in a thermostatically controlled circulating-water bath. Decimal reduction times (D values) were calculated from survival curves having r(2) values of >0.90 as a means of comparing thermal tolerance among variables. D(59 degrees C) values increased (P < 0.05) from 0.50 to 0.58 to 0.66 min for TSBYE-G, TSBYE, and TSBYE+G cultures, respectively. D(61 degrees C) values of antimicrobial-susceptible Salmonella strains increased (P < 0.05) from 0.14 to 0.19 as the glucose concentration increased from 0.00 to 1.00%, respectively, while D(61 degrees C) values of multiantimicrobial-resistant Salmonella strains did not differ (P > 0.05) between TSBYE-G and TSBYE+G cultures. When averaged across glucose levels and temperatures, there were no differences (P > 0.05) between the D values of susceptible and multiantimicrobial-resistant inocula. Collectively, D values ranged from 4.23 to 5.39, 1.47 to 1.81, 0.50 to 0.66, and 0.16 to 0.20 min for Salmonella strains inactivated at 55, 57, 59, and 61 degrees C, respectively. z(D) values were 1.20, 1.48, and 1.49 degrees C for Salmonella strains grown in TSBYE+G, TSBYE, and TSBYE-G, respectively, while the corresponding activation energies of inactivation were 497, 493, and 494 kJ/mol. Study results suggested a cross-protective effect of acid adaptation on thermal inactivation but no association between antimicrobial susceptibility and the ability of salmonellae to survive heat stress.

The AcrB multidrug transporter plays a major role in high-level fluoroquinolone resistance in Salmonella enterica serovar typhimurium phage type DT204

Salmonella enterica serovar Typhimurium phage type DT204 strains isolated from cattle and animal feed in Belgium were characterized for high-level fluoroquinolone resistance mechanisms [MICs to enrofloxacin (Enr) and ciprofloxacin (Cip), 64 and 32 microg/ml, respectively]. These strains isolated during the periods 1991-1994, and in 2000 were clonally related as shown by pulsed-field gel electrophoresis (PFGE). Selected strains studied carried several mutations in the quinolone target genes, i.e., a double mutation in the quinolone resistance-determining region (QRDR) of gyrA leading to amino acid changes Ser83Ala and Asp87Asn, a single mutation in the QRDR of gyrB leading to amino acid change Ser464Phe, and a single mutation in the QRDR of parC leading to amino acid change Ser80Ile. Moreover, Western blot analysis showed overproduction of the AcrA periplasmic protein belonging to the AcrAB-ToIC efflux system. This suggested active efflux as additional resistance mechanism resulting in a multiple antibiotic resistance (MAR) phenotype, which was measurable by an increased level of resistance to the structurally unrelated antibiotic florfenicol in the absence of the specific floR resistance gene. The importance of the AcrAB-TolC efflux system in high-level fluoroquinolone resistance was further confirmed by inactivating the acrB gene coding for the multidrug transporter. This resulted in a 32-fold reduction of resistance level to Enr (MIC = 2 microg/ml) and actually in a susceptible phenotype according to clinical breakpoints. Thus, AcrB plays a major role in high-level fluoroquinolone resistance, even when multiple target gene mutations are present. The same effect was obtained using the recently identified efflux pump inhibitor (EPI) Phe-Arg-naphthylamide also termed MC207,110. Among several fluoroquinolones tested in combination with EPI, the MIC of Enr was reduced most significantly. Thus, using EPI together with fluoroquinolones such as Enr may be promising in combination therapy against high-level fluoroquinolone-resistant S. enterica serovar Typhimurium.

Phenotypic and genotypic characterization of food animal isolates of Salmonella with reduced sensitivity to ciprofloxacin

Reports of nontyphoidal Salmonella enterica subsp. enterica showing reduced sensitivity to ciprofloxacin (RSC) have increased rapidly during the past decade. Infection in humans with Salmonella possessing RSC may compromise the effectiveness of ciprofloxacin therapy. Nineteen among 4,357 Salmonella strains isolated from food animals in Canada from 1998 to 1999 showed RSC; 17 were from turkeys and 2 from chickens. All were resistant to nalidixic acid and sulfisoxazole and possessed RSC at a level of 0.125-0.5 microg/ml. PCR-RFLP of the gyrA quinolone resistance-determining region (QRDR) with Hinfl revealed that S. Bredeney and S. Heidelberg isolates possessed a mutation in this region. Single-strand conformational polymorphism (SSCP) analysis showed that S. Schwarzengrund and S. Senftenberg isolates also possessed a point mutation in the QRDR. DNA sequencing confirmed the findings and showed that all isolates possessed a base substitution in the gyrA QRDR. Sequencing revealed no mutations in the gyrB and silent wobble mutations in the parC QRDR. Reserpine, a known efflux pump inhibitor, did not effect the MICs for ciprofloxacin, nalidixic acid, and tetracycline. The mar operon could be induced in all isolates at 37 degrees C and in 18 of 19 at 30 degrees C; induction resulted in a two- to four-fold increase in the MIC of ciprofloxacin. In 14 of the 19 isolates, the mutation rate was two-fold or higher than in a ciprofloxacin sensitive S. Bredeney and S. Typhimurium LT2 control strain. Examination of clonal relatedness using pulsed-field gel electrophoresis (PFGE) and plasmid profiles indicated that some degree of clonal dispersion may have occurred, but the majority of isolates may have arisen from de novo mutations.

Development of novel antibacterial peptides that kill resistant isolates

The rapid emergence of bacterial strains that are resistant to current antibiotics requires the development of novel types of antimicrobial compounds. Proline-rich cationic antibacterial peptides such as pyrrhocoricin kill responsive bacteria by binding to the 70 kDa heat shock protein DnaK and inhibiting protein folding. We designed and synthesized multiply protected dimeric analogs of pyrrhocoricin and optimized the in vitro antibacterial efficacy assays for peptide antibiotics. Pyrrhocoricin and the designed dimers killed beta-lactam, tetracycline- or aminoglycoside-resistant strains of Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in the submicromolar or low micromolar concentration range. One of the peptides also killed Pseudomonas aeruginosa. The designed dimers showed improved stability in mammalian sera compared to the native analog. In a murine H. influenzae lung infection model, a single dose of a dimeric pyrrhocoricin analog reduced the bacteria in the bronchoalveolar lavage when delivered intranasally. The solid-phase synthesis was optimized for large-scale laboratory preparations.

Subtyping of Salmonella typhimurium by pulsed-field gel electrophoresis and comparisons with phage types and resistance types

One-hundred and sixty-eight Salmonella enterica subsp. enterica serotype Typhimurium isolates have been analysed by phage typing, by pulsed-field gel electrophoresis and for their antimicrobial susceptibility. Those independent strains, isolated from food animal production including cattle, poultry and pig sectors have been collected by the French non human Salmonella network, during the first semester in 1999. Isolates encompassed 14 phage types. The majority of S. Typhimurium isolates was found to be definitive phage type DT104, representing 39% of all isolates. Other phage types were mainly DT8, PT U302, DT120, DT193 and DT135. Forty-six pulsotypes were obtained using Xbal restriction enzyme, and amongst them, ten were associated to the DT104 phage type. A major pulsotype (px1), was represented by 79% of DT104 isolates and was also found among DT120. Forty-eight percent of isolates showed a classic DT104 resistance profile to ampicillin, streptomycin, chloramphenicol, tetracycline, sulfonamides (ASCTSu). Among this resistance type, 84% were DT104 and 12% were DT120. Some pulsotypes were found associated to this resistant type. The pulsed field gel electrophoresis showed to be a useful typing method for discrimination of S. Typhimurium strains and for tracing clone through different sectors of origin in order to control their spread.

Antimicrobial drug resistance in Salmonella: problems and perspectives in food- and water-borne infections

Strains of Salmonella spp. with resistance to antimicrobial drugs are now widespread in both developed and developing countries. In developed countries it is now increasingly accepted that for the most part such strains are zoonotic in origin and acquire their resistance in the food-animal host before onward transmission to humans through the food chain. Of particular importance since the early 1990s has been a multiresistant strain of Salmonella typhimurium definitive phage type (DT) 104, displaying resistance to up to six commonly used antimicrobials, with about 15% of isolates also exhibiting decreased susceptibility to ciprofloxacin. Mutations in the gyrA gene in such isolates have been characterised by a PCR LightCycler-based gyrA mutation assay, and at least four different mutations have been identified. Multiple resistance (to four or more antimicrobials) is also common in the poultry-associated pathogens Salmonella virchow and Salmonella hadar, with an increasing number of strains of these serotypes exhibiting decreased susceptibility to ciprofloxacin. Multiple resistance is also being found in other serotypes in several other European countries, and has been associated with treatment failures. For Salmonella typhi, multiple drug resistance is now the norm in strains originating in the Indian subcontinent and south-east Asia. Such multiresistant strains have been responsible for several epidemics and some of these have been associated with contaminated water supplies. Furthermore, an increasing number of multiresistant strains of S. typhi are now exhibiting decreased susceptibility to ciprofloxacin, with concomitant treatment failures. In developed countries antimicrobial resistance in zoonotic salmonellas has been attributed to the injudicious use of antimicrobials in food-producing animals. It is hoped that the application of Codes of Practice for the use of such agents, which have been prepared by the pharmaceutical industry in response to widespread international concern about the development of drug resistance in bacterial pathogens, will now result in a widespread reduction in the incidence of drug-resistant salmonellas in food production animals and humans on an international scale.

Fluoroquinolone resistance in Salmonella serovars isolated from humans and food animals

Quinolone-resistant Salmonella enterica usually contain a mutation in gyrA within the region encoding the quinolone resistance determining region of the A subunit of DNA gyrase. These mutations confer substitutions analogous to Escherichia coli Ser83-->Phe and Asp87-->Gly or Tyr, or a novel mutation resulting in Ala119-->Glu or Val. Mutations in gyrB are rare, and no mutations in parC or parE have been described. Quinolone-resistant Salmonella can also be cross-resistant to other agents including chloramphenicol and tetracycline. Increased efflux has been demonstrated and for some strains this has been associated with increased expression of acrB. Mutation in soxR has also been shown for one isolate. Detection of low level resistance (minimum inhibitory concentrations <0.5 microg ml(-1)) to fluoroquinolones is proving an increasing problem in the treatment of invasive Salmonella infections.

Prevalence and antibiotic susceptibility of Salmonella isolated from beef animal hides and carcasses

This study determined the prevalence of Salmonella on beef animal hides and carcasses and antimicrobial susceptibility profiles against a panel of 13 antibiotics. In each of the eight commercial packing facilities, of which five processed primarily heifers and steers and the remaining three processed primarily cows and bulls, hide and carcass sponge swab samples were obtained immediately before hide removal and before carcass chilling, respectively. Overall, prevalence of Salmonella on external surfaces (hides) of cattle was 15.4% (49 of 319), whereas prevalence after dehiding and other slaughtering/dressing processes, including the application of decontamination treatments, was, as expected, reduced (P < 0.05) to 1.3% (4 of 320) on carcass surfaces. From 53 total Salmonella-positive hide and carcass samples, 526 biochemically confirmed isolates were obtained to determine antimicrobial susceptibility profiles. Of 53 Salmonella-positive samples, individually, 24 (45.3%), 17 (32.1%), 17 (32.1%), 11 (20.8%), 8 (15.1%), 8 (15.1%), 8 (15.1%), 4 (7.5%), and 2 (3.8%) samples yielded at least one isolate resistant to amoxicillin/clavulanic acid, tetracycline, streptomycin, sulfonamides, ampicillin, ampicillin/sulbactam, chloramphenicol, gentamicin, and trimethoprim/sulfamethoxazole, respectively. None of the Salmonella-positive samples yielded an isolate resistant to ceftriaxone, ciprofloxacin, enrofloxacin, or levofloxacin. Although none of the samples yielded an isolate simultaneously resistant to three or four antimicrobials, a total of eight samples yielded at least one isolate resistant to five or more antimicrobials tested. Included among the 18 group B-positive samples were three samples that, individually, yielded at least one Salmonella Typhimurium var. Copenhagen DT104 isolate resistant to at least six antimicrobials tested. Results from this study support current prudent therapeutic and subtherapeutic antimicrobial use recommendations.

Antimicrobial drug resistance in non-typhoidal salmonellas from humans in England and Wales in 1999: decrease in multiple resistance in Salmonella enterica serotypes Typhimurium, Virchow, and Hadar

In 1999 the incidence of multiple drug resistance (to four or more antimicrobials) in non-typhoidal salmonellas from humans in England and Wales fell in isolations of Salmonella enterica serotypes Typhimurium, Virchow, and Hadar. This fall has been most noticeable in S. Typhimurium, where 59% of isolates were multiresistant compared to 81% in 1996. The main reason for this has been a 75% decline in isolations of multiply-resistant S. Typhimurium definitive phage type (DT) 104 (MR DT104) since 1996. Nevertheless MR DT104 remains second to S. Enteritidis phage type 4 as the most common strain in cases of human salmonellosis in England and Wales. Multiple resistance has also remained high in S. Hadar, with 49% of isolates resistant to four drugs or more compared to 56% in 1996. Isolates with decreased sensitivity to ciprofloxacin (minimal inhibitory concentration: 0.25-1.0 mg/L) have increased in incidence in S. Enteritidis, S. Virchow, and S. Hadar; in S. Hadar 70% of isolates were resistant to ciprofloxacin at this level. It is hoped that Codes of Practice introduced by some pharmaceutical companies, governments, professional organisations, and others to combat the unnecessary prophylactic use of fluoroquinolones in animal husbandry will not result in a reduction in the incidence of resistance to ciprofloxacin in salmonella organisms causing infections in humans.

Use of a LightCycler gyrA mutation assay for rapid identification of mutations conferring decreased susceptibility to ciprofloxacin in multiresistant Salmonella enterica serotype Typhimurium DT104 isolates

A LightCycler-based PCR-hybridization gyrA mutation assay (GAMA) was developed to rapidly detect gyrA point mutations in multiresistant (MR) Salmonella enterica serotype Typhimurium DT104 with decreased susceptibility to ciprofloxacin (MIC, 0.25 to 1.0 mg/liter). Ninety-two isolates (49 human, 43 animal) were tested with three individual oligonucleotide probes directed against an Asp-87-to-Asn (GAC-->AAC) mutation, an Asp-87-to-Gly (GAC-->GGC) mutation, and a Ser-83-to-Phe (TCC-->TTC) mutation. Strains homologous to the probes could be distinguished from strains that had different mutations by their probe-target melting temperatures. Thirty-seven human and 30 animal isolates had an Asp-87-to-Asn substitution, 6 human and 6 animal isolates had a Ser-83-to-Phe substitution, and 5 human and 2 animal isolates had an Asp-87-to-Gly substitution. The remaining six strains all had mismatches with the three probes and therefore different gyrA mutations. The sequencing of gyrA from these six isolates showed that one human strain and two animal strains had an Asp-87-to-Tyr (GAC-->TAC) substitution and two animal strains had a Ser-83-to-Tyr (TCC-->TAC) substitution. One animal strain had no gyrA mutation, suggesting that this isolate had a different mechanism of resistance. Fifty-eight of the strains tested were indistinguishable by several different typing methods including antibiograms, pulsed-field gel gel electrophoresis, and plasmid profiling, although they could be further subdivided according to gyrA mutation. This study confirmed that MR DT104 with decreased susceptibility to ciprofloxacin from humans and food animals in England and Wales may have arisen independently against a background of clonal spread of MR DT104.