Prior antimicrobial agent use increases the risk of sporadic infections with multidrug-resistant Salmonella enterica serotype Typhimurium: a FoodNet case-control study, 1996-1997

Pleural empyema due to Salmonella in a patient with bronchogenic carcinoma: the first case report from a cancer hospital in Egypt

Background

Salmonella species are motile, Gram-negative facultative anaerobic bacilli, which belong to the family Enterobacteriaceae. The most common clinical presentations of Salmonella infection are gastroenteritis and enteric fever. Detection of Salmonella organisms in empyema is very rare.

Case presentation

We report the case of a 66-year-old female patient with bronchogenic carcinoma who developed empyema, and Salmonella was identified from the culture of pleural fluid. After antimicrobial therapy and other therapeutic measures, including the insertion of an intercostal tube, oxygen supplementation, frequent suction of respiratory secretions, and chest physiotherapy, the patient's condition improved. To the best of our knowledge, this is the first case to be reported in Egypt.

Conclusions

Our case sheds light on the role of Salmonella in immunocompromised patients in general and cancer patients in specific. We recommend further study of this role, since it may lead to a better understanding of the pathogenicity of this organism in these patients.

A farm-to-fork quantitative risk assessment model for Salmonella Heidelberg resistant to third-generation cephalosporins in broiler chickens in Canada

Salmonella Heidelberg resistant to ceftiofur (a third-generation cephalosporin antimicrobial agent) in broiler chicken products pose a risk to public health in Canada. The objective of this study was to assess the extent of that risk and to evaluate the effect of intervention measures along the agri-food chain. A stochastic farm-to-fork quantitative microbial risk assessment model was developed following the Codex Alimentarius Guidelines for Risk Analysis of Foodborne Antimicrobial Resistance. Different scenarios were analyzed to assess the individual relative effects of 18 possible interventions in comparison to a baseline scenario. The baseline scenario represented the first year of on-farm antimicrobial use surveillance in the Canadian broiler industry and the year before an industry-imposed ban on the preventive use of antimicrobials of very high importance to human health (2013), where 31.3% of broiler flocks consisted of birds to which ceftiofur was administered. The baseline scenario predicted an average probability of illness of 1.1 per 100,000 servings (SE: 0.064 per 100,000), corresponding to an average of 22,000 human infections (SE: 1900) with ceftiofur-resistant S. Heidelberg per year, which is likely an overestimation. This risk was reduced by 90% or 20% when two separate scenarios designed to capture the effect of withdrawing preventive ceftiofur use from poultry production were simulated using different approaches; data used for the former scenario were confounded by other potential concomitant control measures (e.g. Salmonella vaccination programme), so the true effect likely lies somewhere between the two estimates. A theoretical 'worst case' scenario where all flocks had birds exposed to ceftiofur increased the risk by 107%. A 50% reduction in the probability of human prior exposure to antimicrobials, which has a selective and competitive effect for Salmonella spp. following ingestion of contaminated products, reduced the risk by 65%. Other promising measures that could be considered for further risk management included improved cleaning and disinfection between broiler flocks on farm (risk reduction by 26%), exclusive use of air chilling (risk reduction by 34%), and the improvement of meat storage and preparation conditions, e.g., no temperature abuse at retail (risk reduction by 88%). These findings showed the importance of a structured approach to assessing and potentially implementing effective interventions to reduce the risk associated with ceftiofur-resistant S. Heidelberg at different steps along the agri-food chain. Major data gaps included information on concentrations of resistant bacteria, cross contamination at processing and how ceftiofur-resistant S. Heidelberg behave in comparison with susceptible ones, e.g., in terms of growth and survival ability, as well as pathogenicity and virulence.

National Antimicrobial Resistance Monitoring System: Two Decades of Advancing Public Health Through Integrated Surveillance of Antimicrobial Resistance

Drug-resistant bacterial infections pose a serious and growing public health threat globally. In this review, we describe the role of the National Antimicrobial Resistance Monitoring System (NARMS) in providing data that help address the resistance problem and show how such a program can have broad positive impacts on public health. NARMS was formed two decades ago to help assess the consequences to human health arising from the use of antimicrobial drugs in food animal production in the United States. A collaboration among the Centers for Disease Control and Prevention, the U.S. Food and Drug Administration, the United States Department of Agriculture, and state and local health departments, NARMS uses an integrated "One Health" approach to monitor antimicrobial resistance in enteric bacteria from humans, retail meat, and food animals. NARMS has adapted to changing needs and threats by expanding surveillance catchment areas, examining new isolate sources, adding bacteria, adjusting sampling schemes, and modifying antimicrobial agents tested. NARMS data are not only essential for ensuring that antimicrobial drugs approved for food animals are used in ways that are safe for human health but they also help address broader food safety priorities. NARMS surveillance, applied research studies, and outbreak isolate testing provide data on the emergence of drug-resistant enteric bacteria; genetic mechanisms underlying resistance; movement of bacterial populations among humans, food, and food animals; and sources and outcomes of resistant and susceptible infections. These data can be used to guide and evaluate the impact of science-based policies, regulatory actions, antimicrobial stewardship initiatives, and other public health efforts aimed at preserving drug effectiveness, improving patient outcomes, and preventing infections. Many improvements have been made to NARMS over time and the program will continue to adapt to address emerging resistance threats, changes in clinical diagnostic practices, and new technologies, such as whole genome sequencing.

Methicillin-resistant Staphylococcus aureus: a controversial food-borne pathogen

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of severe healthcare-associated (HA) infections. Although during the last decade the incidence of HA invasive infections has dropped, the incidence of community-associated MRSA (CA-MRSA) infections has risen among the general population. Moreover, CA-MRSA, livestock-associated MRSA (LA-MRSA) and HA-MRSA (HA-MRSA) can be found in foods intended for human consumption. Several studies from different geographical areas have reported the presence of enterotoxin genes in several MRSA food isolates. Molecular typing studies have revealed genetic relatedness of these enterotoxigenic isolates with isolates incriminated in human infections. The contamination sources for foods, especially animal-origin foods, may be livestock as well as humans involved in animal husbandry and food-processing. Under favourable environmental conditions for growth and enterotoxin production, enterotoxigenic S. aureus isolates present in foods can cause staphylococcal food poisoning (SFP), irrespective of the contamination origin. Owing to the typically moderate clinical manifestations of SFP, the S. aureus strains responsible for SFP (cases or outbreaks) are frequently either not identified or not further characterized. Antimicrobial susceptibility testing is rarely performed, because administration of antimicrobial therapy is not required in the vast majority of cases. Staphylococcal food poisoning is the result of consumption of foods with preformed enterotoxins. Hence, similar to methicillin-sensitive enterotoxigenic S. aureus, enterotoxigenic MRSA can also act as food-borne pathogens upon favourable conditions for growth and enterotoxin production. The severity of the intoxication is not related to the antimicrobial resistance profile of the causative S. aureus strain and therefore MRSA food-borne outbreaks are not expected to be more severe.

SIGNIFICANCE AND IMPACT OF THE STUDY

This review evaluates the potential of methicillin-resistant Staphylococcus aureus (MRSA) as food-borne pathogens based on the current knowledge about the epidemiology of MRSA, their prevalence in livestock, foods of animal origin and humans, and their ability to produce enterotoxins.

Acetalated dextran encapsulated AR-12 as a host-directed therapy to control Salmonella infection

AR-12 has been evaluated in clinical trials as an anti-cancer agent but also has demonstrated host-directed, broad-spectrum clearance of bacteria. We have previously shown that AR-12 has activity in vitro against Salmonella enterica serovar Typhimurium and Francisella species by inducing autophagy and other host immune pathways. AR-12 treatment of S. Typhimurium-infected mice resulted in a 10-fold reduction in bacterial load in the liver and spleen and an increased survival time. However, AR-12 treatment did not protect mice from death, likely due poor formulation. In the current study, AR-12 was encapsulated in a microparticulate carrier formulated from the novel degradable biopolymer acetalated dextran (Ace-DEX) and subsequently evaluated for its activity in human monocyte-derived macrophages (hMDMs). Our results show that hMDMs efficiently internalized Ace-DEX microparticles (MPs), and that encapsulation significantly reduced host cell cytotoxicity compared to unencapsulated AR-12. Efficient macrophage internalization of AR-12 loaded MPs (AR-12/MPs) was further demonstrated by autophagosome formation that was comparable to free AR-12 and resulted in enhanced clearance of intracellular Salmonella. Taken together, these studies provide support that Ace-DEX encapsulated AR-12 may be a promising new therapeutic agent to control intracellular bacterial pathogens of macrophages by targeting delivery and reducing drug toxicity.

Risk factors for sporadic Vibrio parahaemolyticus gastroenteritis in east China: a matched case-control study

SUMMARY To determine risk factors for sporadic Vibrio parahaemolyticus gastroenteritis, we conducted a population-based case-control study in sentinel hospital surveillance areas of Shanghai and Jiangsu province, China. Seventy-one patients with diarrhoea and confirmed V. parahaemolyticus infections were enrolled, and they were matched with 142 controls for gender, age and residential area. From the multivariable analysis, V. parahaemolyticus infections were associated with antibiotics taken during the 4 weeks prior to illness [odds ratio (OR) 7·6, 95% confidence interval (CI) 1·1–54·4)], frequent eating out (OR 3·3, 95% CI 1·0–10·4), and shellfish consumption (OR 3·4, 95% CI 1·0–11·1), with population-attributable fractions of 0·09, 0·24, and 0·14, respectively. Protective factors included keeping the aquatic products refrigerated (OR 0·4, 95% CI 0·2–1·0) and pork consumption (OR 0·2, 95% CI 0·1–0·9) [corrected] .

Intestinal alkaline phosphatase prevents antibiotic-induced susceptibility to enteric pathogens

OBJECTIVE

To determine the efficacy of oral supplementation of the gut enzyme intestinal alkaline phosphatase (IAP) in preventing antibiotic-associated infections from Salmonella enterica serovar Typhimurium (S. Typhimurium) and Clostridium difficile.

BACKGROUND

The intestinal microbiota plays a pivotal role in human health and well-being. Antibiotics inherently cause dysbiosis, an imbalance in the number and composition of intestinal commensal bacteria, which leads to susceptibility to opportunistic bacterial infections. Previously, we have shown that IAP preserves the normal homeostasis of intestinal microbiota and that oral supplementation with calf IAP (cIAP) rapidly restores the normal gut flora. We hypothesized that oral IAP supplementation would protect against antibiotic-associated bacterial infections.

METHODS

C57BL/6 mice were treated with antibiotic(s) ± cIAP in the drinking water, followed by oral gavage of S. Typhimurium or C. difficile. Mice were observed for clinical conditions and mortality. After a defined period of time, mice were killed and investigated for hematological, inflammatory, and histological changes.

RESULTS

We observed that oral supplementation with cIAP during antibiotic treatment protects mice from infections with S. Typhimurium as well as with C. difficile. Animals given IAP maintained their weight, had reduced clinical severity and gut inflammation, and showed improved survival.

CONCLUSIONS

Oral IAP supplementation protected mice from antibiotic-associated bacterial infections. We postulate that oral IAP supplementation could represent a novel therapy to protect against antibiotic-associated diarrhea (AAD), C. difficile-associated disease (CDAD), and other enteric infections in humans.

Case-control studies of sporadic enteric infections: a review and discussion of studies conducted internationally from 1990 to 2009

Epidemiologists have used case-control studies to investigate enteric disease outbreaks for many decades. Increasingly, case-control studies are also used to investigate risk factors for sporadic (not outbreak-associated) disease. While the same basic approach is used, there are important differences between outbreak and sporadic disease settings that need to be considered in the design and implementation of the case-control study for sporadic disease. Through the International Collaboration on Enteric Disease "Burden of Illness" Studies (the International Collaboration), we reviewed 79 case-control studies of sporadic enteric infections caused by nine pathogens that were conducted in 22 countries and published from 1990 through to 2009. We highlight important methodological and study design issues (including case definition, control selection, and exposure assessment) and discuss how approaches to the study of sporadic enteric disease have changed over the last 20 years (e.g., making use of more sensitive case definitions, databases of controls, and computer-assisted interviewing). As our understanding of sporadic enteric infections grows, methods and topics for case-control studies are expected to continue to evolve; for example, advances in understanding of the role of immunity can be used to improve control selection, the apparent protective effects of certain foods can be further explored, and case-control studies can be used to provide population-based measures of the burden of disease.

Helicobacter and salmonella persistent infection strategies

Some host-adapted bacterial pathogens are capable of causing persistent infections in humans. For example, Helicobacter pylori inhabits the human gastric mucosa and persistence can be lifelong. Salmonella enterica serovar Typhi causes systemic infections that involve colonization of the reticuloendothelial system and some individuals become lifelong carriers. In this review, I compare and contrast the different lifestyles of Helicobacter and Salmonella within the host and the strategies they have evolved to persist in mammalian hosts. Persistently infected carriers serve as the reservoirs for these pathogens, and the carrier state is an essential feature that is required for survival of the bacteria within a restricted host population. Therefore, investigating the chronic carrier state should provide insight into bacterial survival strategies, as well as new therapeutic approaches for treatments.

Peroral ciprofloxacin therapy impairs the generation of a protective immune response in a mouse model for Salmonella enterica serovar Typhimurium diarrhea, while parenteral ceftriaxone therapy does not

Nontyphoidal Salmonella (NTS) species cause self-limiting diarrhea and sometimes severe disease. Antibiotic treatment is considered only in severe cases and immune-compromised patients. The beneficial effects of antibiotic therapy and the consequences for adaptive immune responses are not well understood. We used a mouse model for Salmonella diarrhea to assess the effects of per os treatment with ciprofloxacin (15 mg/kg of body weight intragastrically 2 times/day, 5 days) or parenteral ceftriaxone (50 mg/kg intraperitoneally, 5 days), two common drugs used in human patients. The therapeutic and adverse effects were assessed with respect to generation of a protective adaptive immune response, fecal pathogen excretion, and the emergence of nonsymptomatic excreters. In the mouse model, both therapies reduced disease severity and reduced the level of fecal shedding. In line with clinical data, in most animals, a rebound of pathogen gut colonization/fecal shedding was observed 2 to 12 days after the end of the treatment. Yet, levels of pathogen shedding and frequency of appearance of nonsymptomatic excreters did not differ from those for untreated controls. Moreover, mice treated intraperitoneally with ceftriaxone developed an adaptive immunity protecting the mice from enteropathy in wild-type Salmonella enterica serovar Typhimurium challenge infections. In contrast, the mice treated intragastrically with ciprofloxacin were not protected. Thus, antibiotic treatment regimens can disrupt the adaptive immune response, but treatment regimens may be optimized in order to preserve the generation of protective immunity. It might be of interest to determine whether this also pertains to human patients. In this case, the mouse model might be a tool for further mechanistic studies.

Analysis of risk factors associated with antibiotic-resistant Escherichia coli

Antimicrobial-resistant bacteria represent a major threat to human and animal health. We compared equine fecal samples (n=264) from 138 horses from hospital and nonhospital (livery stable and riding school) premises in North West England to determine the prevalence of Escherichia coli, Salmonella, and Campylobacter and rates of antimicrobial-resistant E. coli strains. Campylobacter jejuni was detected only in hospitalized horses (1.1%), and no Salmonella was identified. Data analysis of the horses' management and veterinary treatments (Tx) identified risk factors associated with shedding of antimicrobial-resistant E. coli. The hospital was the major source of resistant and multi-drug-resistant (MDR) E. coli. Moreover, shedding of antimicrobial-resistant E. coli was associated significantly with hospitalization for a gastrointestinal problem (odds ratio [OR]:±95% confidence intervals=8.50:1.79-40.32), receipt of oral antimicrobial Tx (OR=3.52:1.11-11.10), multiple antimicrobial Tx in hospital (OR/Tx=1.05:1.01-1.09), or geldings (OR=4.62:1.23-17.46). Interestingly, intravenous antimicrobial Tx was negatively associated with shedding of antimicrobial-resistant E. coli (OR=0.18:0.04-0.76). MDR E. coli was associated with hospitalization, antimicrobial Tx in hospital (OR/Tx=3.65:1.54-8.68), and increased age (OR/year=1.11:1.03-1.19). Thus, equine hospitals in this geographic location appear to be an important source of antimicrobial-resistant and MDR E. coli strains, but unlikely reservoirs of Salmonella or Campylobacter. Thus, it is important to moderate antimicrobial Tx given to hospitalized horses to lessen exposure and fecal shedding of resistant pathogens.

Source attribution of human salmonellosis using a meta-analysis of case-control studies of sporadic infections

Salmonella is an important cause of human illness. Disease is frequently associated with foodborne transmission, but other routes of exposure are recognized. Identifying sources of disease is essential for prioritizing public health interventions. Numerous case-control studies of sporadic salmonellosis have been published, often using different methodologies and settings. Systematic reviews consist of a formal process for literature review focused on a research question. With the objective of identifying the most important risk factors for salmonellosis, we performed a systematic review of case-control studies and a meta-analysis of obtained results. Thirty-five Salmonella case-control studies were identified. In the meta-analysis, heterogeneity between studies and possible sources of bias were investigated, and pooled odds ratios estimated. Results suggested that travel, predisposing factors, eating raw eggs, and eating in restaurants were the most important risk factors for salmonellosis. Sub-analyses by serotype were performed when enough studies were available.

Evaluation of recombinant Salmonella expressing the flagellar protein fliC for persistence and enhanced antibody response in commercial turkeys

Salmonella enterica serovar Enteritidis (SE) is one of the most common causes of human foodborne illness in the United States. Previous research indicates that antibodies against the fliC protein can provide protection against Salmonella challenge in mice. To generate a vaccine that effectively protects poultry against multiple Salmonella serotypes, novel attenuated strains of SE were developed to express a fliC peptide sequence on the outer membrane protein lamB in association with an M2e (marker) epitope. In 3 separate trials, poults were immunized with 10(7) to 10(8) cfu/poult of the appropriate recombinant Salmonella strains (ΔSE-M2e or ΔSE-M2e-fliC) via oral gavage on the day of hatch and again on d 21 posthatch. Liver, spleen, and cecal tonsils were aseptically removed on d 7, 14, 21, 28, 35, and 42 posthatch for detection of Salmonella, and blood samples were obtained at these same time points for determination of an M2e-specific antibody response. In all 3 trials, the ΔSE-M2e-fliC strain exhibited significantly less invasion of the liver and spleen at d 7 and 14 when compared with ΔSE-M2e or SE phage type 13A (P < 0.05). Similarly, colonization of the cecal tonsils was decreased in the poults immunized with the ΔSE-M2e-fliC strain. By d 21, the ΔSE-M2e-fliC strain exhibited a significantly higher M2e-specific antibody response when compared with the negative control and SE phage type 13A groups (P < 0.05). However, no significant differences in M2e-specific antibody responses were observed between the ΔSE candidate vaccine strains throughout the study. Overall, these data suggest that oral live attenuated Salmonella-vectored vaccines expressing a fliC peptide sequence are able to elicit a humoral immune response in commercial poults and may contribute to a reduction in Salmonella organ invasion and colonization.

Antibiotic prophylaxis during chemotherapy-induced neutropenia for patients with acute leukemia

Chemotherapy-induced neutropenia places patients with acute leukemia at high risk for bacterial infections. A number of studies performed over the past 20 years have investigated the utility of prophylactic antimicrobials, including trimethoprim-sulfamethoxazole and fluoroquinolones, to prevent infection in the setting of mucositis and neutropenia. Many of these studies have found a benefit of prophylaxis in terms of the incidence of fever and bacterial infection. Clinical guidelines do not recommend antibacterial prophylaxis, however, in part because of increasing reports of infections due to resistant organisms, including fluoroquinolone-resistant Escherichia coli, fluoroquinolone-insensitive viridans streptococci, and Clostridium difficile. To effectively use prophylaxis and simultaneously limit emerging antibiotic resistance, only patients at high risk for bacterial infections should receive prophylaxis.

DNA microarray analysis of Salmonella serotype Typhimurium strains causing different symptoms of disease

Background

Salmonella enterica subsp. enterica is one of the leading food-borne pathogens in the USA and European countries. Outcome of human Salmonella serotype Typhimurium infections ranges from mild self-limiting diarrhoea to severe diarrhoea that requires hospitalization. Increased knowledge of the mechanisms that are responsible for causing infection and especially the severity of infection is of high interest.

Results

Strains were selected from patients with mild infections (n = 9) and patients with severe infections (n = 9) and clinical data allowed us to correct for known underlying diseases. Additionally, outbreak isolates (n = 3) were selected. Strains were analyzed on a DNA-DNA microarray for presence or absence of 281 genes covering marker groups of genes related to pathogenicity, phages, antimicrobial resistance, fimbriae, mobility, serotype and metabolism. Strains showed highly similar profiles when comparing virulence associated genes, but differences between strains were detected in the prophage marker group. The Salmonella virulence plasmid was present in 72% of the strains, but presence or absence of the virulence plasmid did not correspond to disease symptoms. A dendrogram clustered strains into four groups. Clustering confirmed DT104 as being a clonal phagetype. Clustering of the remaining strains was mainly correlated to presence or absence of the virulence plasmid and mobile elements such as transposons. Each of the four clusters in the tree represented an almost equal amount of strains causing severe or mild symptoms of infection.

Conclusions

We investigated clinical significance of known virulence factors of Salmonella serotype Typhimurium strains causing different disease symptoms, and conclude that the few detected differences in Salmonella serotype Typhimurium do not affect outcome of human disease.

Evolving public health approaches to the global challenge of foodborne infections

The landscape of foodborne infections is in flux. New pathogens emerge, established pathogens may acquire new characteristics and appear in unexpected food vehicles, while many existing problems remain unsolved. Consumers want more fresh foods year round, populations age and migrate, and the technologies and trade practices that produce foods change. Protecting the public health and minimizing the burden of foodborne illness mean expecting the unexpected, and being prepared to understand it when it occurs, so that prevention can be improved. Public health surveillance is also constantly evolving, as new diseases emerge and are judged worthy of notification, as new diagnostic tests change the ease and specificity of routine diagnosis and as social interest in particular issues waxes and wanes. Accurate health information, including reliable estimates of the burden of foodborne disease, can improve foodborne disease prevention, foster global health security, promote economic growth and development and strengthen evidence-based policy making.

Integrated food chain surveillance system for Salmonella spp. in Mexico

This system effectively identified major public health priorities.

Few developing countries have foodborne pathogen surveillance systems, and none of these integrates data from humans, food, and animals. We describe the implementation of a 4-state, integrated food chain surveillance system (IFCS) for Salmonella spp. in Mexico. Significant findings were 1) high rates of meat contamination (21.3%–36.4%), 2) high rates of ceftriaxone-resistant S. Typhimurium in chicken, ill humans, and swine (77.3%, 66.3%, and 40.4% of S. Typhimurium T isolates, respectively), and 3) the emergence of ciprofloxacin resistance in S. Heidelberg (10.4%) and S. Typhimurium (1.7%) from swine. A strong association between Salmonella spp. contamination in beef and asymptomatic Salmonella spp. infection was only observed in the state with the lowest poverty level (Pearson r = 0.91, p<0.001). Pulsed-field gel electrophoresis analysis of 311 S. Typhimurium isolates showed 14 clusters with 102 human, retail meat, and food-animal isolates with indistinguishable patterns. An IFCS is technically and economically feasible in developing countries and can effectively identify major public health priorities.

Matching criteria in case-control studies in the field of antimicrobial resistance

OBJECTIVE

We evaluated the available evidence from case-control studies in the field of antimicrobial resistance to identify the degree that matching was performed and the criteria used to do so.

METHODS

We performed a systematic search of the PubMed database (articles archived by 08/2006) to identify relevant studies. Studies that used the individual matching technique were further analyzed.

RESULTS

115 case-control studies with a focus on antimicrobial resistance were identified: 28 regarding Acinetobacter baumannii, 25 regarding Pseudomonas aeruginosa, and 62 for other bacteria. Individual matching was performed in 32 (27.8%) out of the 115 studies. Age was the most frequently used matching criterion in 22 of 32 (69%) evaluated matched case-control studies, while sex was used in 11 (34%), presence of underlying illness in 8 (25%), site of infection in 5 (16%), and area of residence in 4 studies (12.5%). Other criteria were used in less than 10% of the studies. Analysis of data for matched pairs was performed in 18 of 32 (56.3%) studies that used a matched case-control design.

DISCUSSION

The available evidence from the analyzed data from case-control studies in the field of antimicrobial resistance shows that individual matching is employed only in a proportion of such studies and only for a few characteristics, when it was used. Also, analysis for matched pairs was not used by almost a half of the relevant studies.

Evaluation of several fluoroquinolones and beta-lactams in terms of their capability to restrict the selection of fluoroquinolone-resistant Salmonella: in vitro models

With a view to understanding the interaction between Salmonella and the drugs used to treat it, our aim was to compare the different capacities of various antibiotics to generate mutants resistant to fluoroquinolones following repeated exposure of the microorganisms to subinhibitory concentrations of these drugs. Mutants were generated by repeated exposure to fluoroquinolones and beta-lactams. In order to compare the different capacity to generate resistant mutants, we studied the minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) of the wild-type strains and of the mutants generated. These data were compared with pharmacokinetic parameters. Mutants generated following repeated exposure to fluoroquinolones exhibit an increased MPC as compared to the wild-type strains, both in strains that are nalidixic acid susceptible and in those that are nalidixic acid resistant, with repeated exposure to ciprofloxacin leading to the smallest increases. This increase in MPC is gradual and depends on the number of exposures the bacteria are subjected to. It results in a decrease in the AUC/MPC ratio, although the absolute values vary. Ciprofloxacin is the most active drug, both against nalidixic acid-susceptible and nalidixic acid-resistant strains, although in late mutants of originally nalidixic acid-resistant strains, the AUC/MPC values are low. Repeated exposure to amoxicillin and cefotaxime also produces an increase in the MPC of fluoroquinolones, with ciprofloxacin being the least affected. Exposure to amoxicillin leads to the greatest increase in the MPC of fluoroquinolones. When the AUC/MPC ratios of these mutants are compared, the values are still seen to be high (between 25 and 75). When we compare the MPC data with the antibiotic levels in humans following administration of the usual doses, it can be seen that ciprofloxacin exhibits the highest AUC/MPC and therefore the lowest risk of therapeutic failures. In addition, administration of subinhibitory concentrations of beta-lactams produces a decrease in fluoroquinolone susceptibility, which may lead to an increase in the risk of therapeutic failure if these compounds are subsequently used.

Host transmission of Salmonella enterica serovar Typhimurium is controlled by virulence factors and indigenous intestinal microbiota

Transmission is an essential stage of a pathogen's life cycle and remains poorly understood. We describe here a model in which persistently infected 129X1/SvJ mice provide a natural model of Salmonella enterica serovar Typhimurium transmission. In this model only a subset of the infected mice, termed supershedders, shed high levels (>10(8) CFU/g) of Salmonella serovar Typhimurium in their feces and, as a result, rapidly transmit infection. While most Salmonella serovar Typhimurium-infected mice show signs of intestinal inflammation, only supershedder mice develop colitis. Development of the supershedder phenotype depends on the virulence determinants Salmonella pathogenicity islands 1 and 2, and it is characterized by mucosal invasion and, importantly, high luminal abundance of Salmonella serovar Typhimurium within the colon. Immunosuppression of infected mice does not induce the supershedder phenotype, demonstrating that the immune response is not the main determinant of Salmonella serovar Typhimurium levels within the colon. In contrast, treatment of mice with antibiotics that alter the health-associated indigenous intestinal microbiota rapidly induces the supershedder phenotype in infected mice and predisposes uninfected mice to the supershedder phenotype for several days. These results demonstrate that the intestinal microbiota plays a critical role in controlling Salmonella serovar Typhimurium infection, disease, and transmissibility. This novel model should facilitate the study of host, pathogen, and intestinal microbiota factors that contribute to infectious disease transmission.

Risk of Recurrent Nontyphoid Salmonella Bacteremia in HIV-Infected Patients in the Era of Highly Active Antiretroviral Therapy and an Increasing Trend of Fluoroquinolone Resistance

BACKGROUND

Risk of recurrent nontyphoid Salmonella (NTS) bacteremia and trends of antimicrobial resistance of NTS remain unknown in human immunodeficiency virus (HIV)-infected patients receiving highly active antiretroviral therapy (HAART).

METHODS

Ninety-three patients who received a diagnosis of NTS bacteremia from June 1994 through June 2006 were prospectively followed up. Incidence of recurrent NTS bacteremia was compared between the pre-HAART era (June 1994-March 1997) and the HAART era (April 1997-June 2006). Prevalence of antimicrobial resistance was compared among the NTS isolates obtained in the pre-HAART era, the early HAART era (April 1997-June 2002), and the late HAART era (July 2002-June 2006).

RESULTS

Compared with patients enrolled in the pre-HAART era, patients who received HAART had an incidence of recurrent NTS bacteremia that was significantly reduced by 96%; the incidence of recurrent NTS bacteremia was 2.56 cases per 100 person-years in the HAART era, compared with 70.56 cases per 100 person-years in the pre-HAART era (rate ratio, 0.036; 95% confidence interval, 0.012-0.114; P<.001). In the HAART era, the incidence of recurrent NTS bacteremia did not increase among patients receiving fluoroquinolone prophylaxis for <or=30 days (1.69 cases per 100 person-years), compared with among patients receiving fluoroquinolones for >30 days (3.95 cases per 100 person-years), with a rate ratio of 0.43 (95% confidence interval, 0.07-2.58). Although resistance to ampicillin, cotrimoxazole, and chloramphenicol decreased, the proportion of NTS isolates resistant to fluoroquinolones increased from 0% in the pre-HAART era to 6.2% in the early HAART era and 34.2% in the late HAART era (P=.002).

CONCLUSIONS

The risk of recurrent NTS bacteremia decreased significantly in the HAART era, although NTS isolates obtained from HIV-infected patients were increasingly resistant to fluoroquinolones.

Epidemiology and risk factors for endemic typhoid fever in Uzbekistan

BACKGROUND

To investigate the risk factors for infection with endemic typhoid fever in the Samarkand region of Uzbekistan.

METHODS

Case-control study of culture-confirmed bloodstream infection with Salmonella Typhi. Patients were compared to age-matched community controls. Salmonella Typhi isolates were tested for antimicrobial susceptibility.

RESULTS

We enrolled 97 patients and 192 controls. The median age of patients was 19 years. In a conditional regression model, consumption of unboiled surface water outside the home [adjusted odds ratio (aOR)=3.0, 95% confidence interval (CI)=1.1-8.2], use of antimicrobials in the 2 weeks preceding onset of symptoms (aOR=12.2, 95% CI 4.0-37.0), and being a student (aOR=4.0, 95% CI 1.4-11.3) were independently associated with typhoid fever. Routinely washing vegetables (aOR 0.06, 95% CI 0.02-0.2) and dining at a tea-house (aOR 0.4, 95% CI 0.2-1.0) were associated with protection against illness. Salmonella Typhi resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole was identified in 6 (15%) of 41 isolates tested.

CONCLUSIONS

Endemic typhoid fever in Uzbekistan is transmitted by contaminated water. Recent use of antimicrobials also increased risk of infection. Targeted efforts at improving drinking water quality, especially for students and young adults, are likely to decrease transmission of typhoid fever. Measures to decrease the unnecessary use of antimicrobials would be expected to reduce the risk of typhoid fever and decrease the spread of multiple drug-resistant Salmonella Typhi.

FoodNet: overview of a decade of achievement

The Foodborne Diseases Active Surveillance Network (FoodNet) performs active, population-based laboratory surveillance for nine common foodborne pathogens and one syndrome in a catchment area of 44.5 million persons. FoodNet surveillance data are an important resource for examining trends in specific diseases over time. Population surveys and laboratory surveys have been used to estimate the burden of disease, for example that there are 38.6 cases of Salmonella infection for each reported case. FoodNet case-control studies have identified new risk factors for E. coli O157, Campylobacter, and several Salmonella serotypes. FoodNet sites have demonstrated the value of delivered stool kits for improving the rate of confirming an etiology in foodborne disease outbreaks. FoodNet helps build capacity for foodborne disease surveillance in participating sites and through close collaborations with PulseNet, EHS-Net, Global SalmSurv, and other partners.

Effect of exposure to fluoroquinolones and beta-lactams on the in vitro activity of other groups of antibiotics in Salmonella spp

After designing in vitro models of repeated exposure of Salmonella spp. to various beta-lactams and fluoroquinolones we studied the decrease in susceptibility to other antibiotic families of the mutants generated. There was a decrease in the susceptibility of all the mutants to tetracycline, cotrimoxazole and chloramphenicol. Mutants generated following exposure to fluoroquinolones showed reduced susceptibility to amoxicillin, amoxicillin/clavulanic acid, cefoxitin and cefuroxime, whereas mutants generated following beta-lactam exposure showed reduced susceptibility to nalidixic acid and ciprofloxacin. We observed that the efflux pump systems are activated in the mutants generated and this may therefore be the cause of the decrease in susceptibility. In many cases the decrease is small and is not detected if the CLSI criteria are applied. Nevertheless, more detailed studies should be done to evaluate the importance of this phenomenon and rationalize the use of antibiotics in both humans and animals so as to control the increase in the number of multiresistant strains.

Risk factors for Salmonella Enteritidis and Typhimurium (DT104 and non-DT104) infections in The Netherlands: predominant roles for raw eggs in Enteritidis and sandboxes in Typhimurium infections

Since 1996 Salmonella Typhimurium DT104 salmonellosis has increased in The Netherlands. This prompted a case-control study of risk factors for salmonellosis to inform transmission routes for this phage type. Cases were laboratory-confirmed patients with a Salmonella infection and controls were selected from population registries by frequency matching for age, sex, degree of urbanization and season. Cases and controls received a questionnaire on risk factors. Of the 1171 cases, 573 (49%) responded: 245 S. Enteritidis and 232 S. Typhimurium cases (both DT104 and non-DT104), of which 58 were DT104. Of the 10250 controls, 3409 (33%) responded. Use of H2 antagonists [odds ratio (OR) 4.4, 95% CI 1.6-12.2] and proton pump inhibitors (OR 4.2, 95% CI 2.2-7.9), consumption of raw eggs (OR 3.1, 95% CI 1.3-7.4) and products containing raw eggs (OR 1.8, 95% CI 1.1-3.0) were associated with endemic S. Enteritidis infection. Risk factors for endemic S. Typhimurium infection were use of proton pump inhibitors (OR 8.3, 95% CI 4.3-15.9), occupational exposure to raw meat (OR 3.0, 95% CI 1.1-7.9), playing in a sandbox (for children aged 4-12 years) (OR 2.4, 95% CI 1.6-3.7), consumption of undercooked meat (OR 2.2, 95% CI 1.1-4.1) and use of antibiotics (OR 1.9, 95% CI 1.0-3.4). Use of proton pump inhibitors (OR 11.2, 95% CI 3.9-31.9) and playing in a sandbox (OR 4.4, 95% CI 1.8-10.7) were the only risk factors for S. Typhimurium DT104 salmonellosis. This study confirms known risk factors for salmonellosis. However, playing in a sandbox was a predominant new risk factor for S. Typhimurium salmonellosis in children [population attributable risk (PAR) 14%], and especially for S. Typhimurium DT104 (PAR 32%).

Alterations in thegyrA andparC Genes inSalmonellaspp. FollowingIn VitroExposure to Fluoroquinolones

We characterize alterations in the QRDR fragment of gyrA and parC in Salmonella spp. following repeated exposure to different quinolones in two in vitro models. Mutations in QRDR of gyrA were found in only 25% of the mutants. The most frequent mutations were Asp87(R)Asn and Asp87(R)Tyr. Strains with the former mutation had a higher ciprofloxacin MIC than those with the latter. We did not find mutations in parC. Our data confirm that mutation in the QRDR fragment of gyrA is the mechanism that produces the greatest decrease in fluoroquinolone susceptibility. There is a greater reduction in the ciprofloxacin susceptibility of strains that were originally nalidixic acid-resistant than in that of strains that were originally susceptible, and this confirms that there is a greater likelihood of therapeutic failures with such strains.

Reducing the Carriage of Foodborne Pathogens in Livestock and Poultry

Several foodborne pathogens, including Salmonella species and campylobacters, are common contaminants in poultry and livestock. Typically, these pathogens are carried in the animal's intestinal tract asymptomatically; however, they can be shed in feces in large populations and be transmitted by other vectors from feces to animals, produce, or humans. A wide array of interventions has been developed to reduce the carriage of foodborne pathogens in poultry and livestock, including genetic selection of animals resistant to colonization, treatments to prevent vertical transmission of enteric pathogens, sanitation practices to prevent contamination on the farm and during transportation, elimination of pathogens from feed and water, feed and water additives that create an adverse environment for colonization by the pathogen, and biological treatments that directly or indirectly inactivate the pathogen within the host. To successfully reduce the carriage of foodborne pathogens, it is likely that a combination of intervention strategies will be required.

Common Ground for the Control of Multidrug-Resistant Salmonella in Ground Beef

A strategy to combat multidrug-resistant (MDR) Salmonella in ground beef is urgently needed. A national multi-disciplinary meeting reviewed the epidemiology of MDR Salmonella infection and contamination in humans, animals, and retail meat. In spite of a recent overall decrease in human MDR Salmonella isolates, certain types, such as Salmonella enterica serotype Newport multidrug-resistant-AmpC strain and Salmonella enterica serotype Typhimurium definitive type (DT) 104, have persisted, and several recent large outbreaks of human infection have occurred. Key agencies that contribute to a safe ground beef supply were represented at the meeting and contributed to the discussion of possible control strategies from the farm to the table. Several of the control strategies suggested are unpopular to some, including restricting the use of antimicrobial agents in food animals, designation of multidrug-resistant Salmonella as an adulterant in ground beef, and improving the mechanisms for product trace-back investigations. Nevertheless, enhanced farm-based animal infection control, judicious veterinary and human antibiotic use, regulatory controls, and consumer practices will lead to important industry, veterinary, and public health outcomes.

Emerging microbiological food safety issues related to meat

Avian influenza viruses and antibiotic-resistant pathogens have become topics of current public health interest. This paper will focus on the significance of these pathogens to the meat industry as well as other emerging microbiological food safety topics likely to impact the meat industry. These include surveillance of foodborne pathogens, microbial source tracking, risk assessment, and human populations at increased risk of infection by foodborne microbes. These emerging issues will likely lead to even greater challenges to producing microbiologically safe meat products than the industry has ever experienced. However, accompanying such challenges will be innovative solutions that provide even greater public health protection to meat-containing foods.

Bacteraemia due to ciprofloxacin-resistant Salmonella enterica serotype Choleraesuis in adult patients at a university hospital in Taiwan, 1996-2004

Eighty-one adult patients with Salmonella enterica serotype Choleraesuis (S. Choleraesuis) bacteraemia treated at a university hospital from 1996 to 2004 were evaluated. Multivariate analysis with a logistic regression model was used to characterize risk factors for primary bacteraemia and mycotic aneurysm and to determine the association of clinical characteristics of patients based on ciprofloxacin susceptibility of the causative organism. The incidence per 100,000 discharges was 0.76 in 1996 and 3.9 in 2004. The overall rate of ciprofloxacin resistance among these isolates was 59% (87 isolates) and the annual rate increased with time from 0% prior to 2000 to 80% in 2004. Among these patients, 48 (59%) had primary bacteraemia and 13 (16%) had secondary bacteraemia with mycotic aneurysm. Seventy (86%) patients had fever at presentation, 22 (27%) developed shock during hospitalization, and eight (10%) died of S. Choleraesuis bacteraemia. Patients with immunocompromised conditions had a higher risk of developing primary bacteraemia (OR 18.442, P < 0.001). Hypertension (OR 15.434, P = 0.002) and male gender (OR 7.422, P = 0.039) were associated with mycotic aneurysm. Patients with mycotic aneurysm were more frequently infected with ciprofloxacin-susceptible isolates (P = 0.028) and ciprofloxacin-susceptible isolates were also more frequently associated with recurrent infection than ciprofloxacin-resistant isolates (P = 0.038). The incidence of S. Choleraesuis bacteraemia has increased in the past 8 years, and this increase is associated with the upsurge of ciprofloxacin-resistant isolates.

Variability in Antimicrobial Resistance amongSalmonella entericaStrains from Fattening Pigs and Sows

The aim of this study was to determine the prevalence of antibiotic resistance and different resistance patterns for Salmonella isolates collected from Belgian sows and fattening pigs at different ages and at slaughter. The most frequently isolated serotypes were S. Typhimurium (42.3%), S. Derby (25.1%), S. Goldcoast (7.3%), and S. Infantis (4.8%). All 901 isolates were submitted to antimicrobial susceptibility testing for 14 compounds using the disc agar diffusion test. The highest percentage of resistance was found to oxytetracycline (34.2%), streptomycin (32.5%), sulfamethizole (27.6%), and ampicillin (24.9%). Three of the isolates showed resistance to cephalosporins and none to second-generation fluoroquinolones. Multiresistance (resistance to > or =2 antimicrobials) was observed in 33.2% of the strains. Differences in resistance patterns were observed between and within serotypes as well as genotypes. A significant lower proportion (p < 0.01) of resistant strains was recovered in fecal samples from sows (23/56) than from fattening pigs during the weaning (30/30), growing (79/85), and finishing periods (45/52). The proportion of resistant strains recovered from fecal samples taken at the herd (154/167) was higher than in the samples collected at the slaughterhouse (75/140). When designing antimicrobial resistance surveillance programs for Salmonella in pigs, it is important to take multiple samples within each herd from both sows and fattening pigs at different time points.

In vitro generation of Salmonella spp. mutants following repeated exposure to β-lactam antibiotics

Beta-lactams are a group of drugs considered to be the treatment of choice in cases of salmonellosis, although many isolates that are clinically resistant to these compounds have been reported. We developed an in vitro model to determine the dynamics of the generation of resistant mutants following repeated exposure to these drugs. All the isolates exposed repeatedly to amoxicillin and cefotaxime exhibit a decrease in their susceptibility to these compounds and to many other beta-lactam drugs. However, in many cases this reduction in susceptibility is not detected if the CLSI criteria are applied. These mutants with reduced susceptibility may be the reason for therapeutic failures, so this phenomenon should be studied in greater detail by means of in vitro models or clinical studies.

Relation between induction of the mar operon and cyclohexane tolerance and reduction in fluoroquinolone susceptibility in Salmonella spp

The relationship between cyclohexane tolerance and induction of the mar operon and a decrease in susceptibility to ciprofloxacin and moxifloxacin in isolates of Salmonella spp. from food and clinical isolates of Salmonella spp. was studied. We studied the influence of the mar operon using an inductor (acetylsalicylic acid) and we also studied the cyclohexane resistance. Induction was seen to produce an increase in the minimum inhibitory concentration (MIC) of these quinolones, which suggested that there was overexpression of the AcrAB type active efflux systems due to induction of the mar operon. Cyclohexane susceptibility was not shown to be a very sensitive method for studying this process, as only 3% (5/176) of the clinical isolates studied were cyclohexane-resistant; most of these belonged to the Hadar serotype. This study confirmed the participation of active efflux systems in the decrease in fluoroquinolone susceptibility in Salmonella spp. Furthermore, the study has indicated that these mechanisms (i.e., active efflux systems) are present in strains that are susceptible to the fluoroquinolone compounds, so their stimulation may be one of the mechanisms involved in the reduction in fluoroquinolone susceptibility. This suggests that the exposure of Salmonella spp. to antibiotics should be limited in order to prevent these active efflux systems from being activated. Consequently, the use of fluoroquinolones, both in the treatment of humans and in veterinary practice, should be controlled and rationalized in an attempt to curb the increase in the number of strains that are resistant to these compounds.

Antimicrobial-drug susceptibility of human and animal Salmonella typhimurium, Minnesota, 1997-2003

We compared antimicrobial resistance phenotypes and pulsed-field gel electrophoresis (PFGE) subtypes of 1,028 human and 716 animal Salmonella enterica serotype Typhimurium isolates from Minnesota from 1997 to 2003. Overall, 29% of human isolates were multidrug resistant. Predominant phenotypes included resistance to ampicillin, chloramphenicol or kanamycin, streptomycin, sulfisoxazole, and tetracycline (ACSSuT or AKSSuT). Most human multidrug-resistant isolates belonged to PFGE clonal group A, characterized by ACSSuT resistance (64%), or clonal group B, characterized by AKSSuT resistance (19%). Most animal isolates were from cattle (n = 358) or swine (n = 251). Eighty-one percent were multidrug resistant; of these, 54% were at least resistance phenotype ACSSuT, and 43% were at least AKSSuT. More than 80% of multidrug-resistant isolates had a clonal group A or B subtype. Resistance to ceftriaxone and nalidixic acid increased, primarily among clonal group A/ACSSuT isolates. Clonal group B/AKSSuT isolates decreased over time. These data support the hypothesis that food animals are the primary reservoir of multidrug-resistant S. Typhimurium.

Invasive Infection with Multidrug‐ResistantSalmonella entericaSerotype Typhimurium Definitive Type 104 among HIV‐Infected Adults

BACKGROUND

Multidrug-resistant Salmonella enterica serotype Typhimurium definitive type 104 (MRDT104), with resistance to at least ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline (R-type ACSSuT), was first detected in the United States in 1985, and the prevalence increased to account for nearly 7% of Salmonella infections in 1998.

METHODS

A retrospective study of S. Typhimurium infections in an urban health care system assessed whether infection with an antibiotic-resistant strain--and specifically MRDT104--was associated with invasive disease or HIV infection. Sixty cases of S. Typhimurium infection were identified.

RESULTS

Of the 50 isolates available for analysis, 30 (60%) were MRDT104. Pathogens were isolated from blood in 25 (83%) of 30 patients infected with MRDT104, compared with 10 (50%) of 20 patients who were infected with non-MRDT104 strains (P = .01). Among isolates obtained from 32 HIV-infected patients, 19 (95%) of 20 MRDT104 isolates were from blood specimens, compared with 8 (66%) of 12 non-MRDT104 isolates (P = .05).

CONCLUSIONS

MRDT104 accounted for the majority of S. Typhimurium infections in this patient population, and MRDT104 infections were more invasive than non-MRDT104 infections, particularly in HIV-infected persons.

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.