Global diversity and antimicrobial resistance of typhoid fever pathogens: Insights from a meta-analysis of 13,000 Salmonella Typhi genomes

Background

The Global Typhoid Genomics Consortium was established to bring together the typhoid research community to aggregate and analyse Salmonella enterica serovar Typhi (Typhi) genomic data to inform public health action. This analysis, which marks 22 years since the publication of the first Typhi genome, represents the largest Typhi genome sequence collection to date (n=13,000).

Methods

This is a meta-analysis of global genotype and antimicrobial resistance (AMR) determinants extracted from previously sequenced genome data and analysed using consistent methods implemented in open analysis platforms GenoTyphi and Pathogenwatch.

Results

Compared with previous global snapshots, the data highlight that genotype 4.3.1 (H58) has not spread beyond Asia and Eastern/Southern Africa; in other regions, distinct genotypes dominate and have independently evolved AMR. Data gaps remain in many parts of the world, and we show the potential of travel-associated sequences to provide informal 'sentinel' surveillance for such locations. The data indicate that ciprofloxacin non-susceptibility (>1 resistance determinant) is widespread across geographies and genotypes, with high-level ciprofloxacin resistance (≥3 determinants) reaching 20% prevalence in South Asia. Extensively drug-resistant (XDR) typhoid has become dominant in Pakistan (70% in 2020) but has not yet become established elsewhere. Ceftriaxone resistance has emerged in eight non-XDR genotypes, including a ciprofloxacin-resistant lineage (4.3.1.2.1) in India. Azithromycin resistance mutations were detected at low prevalence in South Asia, including in two common ciprofloxacin-resistant genotypes.

Conclusions

The consortium's aim is to encourage continued data sharing and collaboration to monitor the emergence and global spread of AMR Typhi, and to inform decision-making around the introduction of typhoid conjugate vaccines (TCVs) and other prevention and control strategies.

Funding

No specific funding was awarded for this meta-analysis. Coordinators were supported by fellowships from the European Union (ZAD received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 845681), the Wellcome Trust (SB, Wellcome Trust Senior Fellowship), and the National Health and Medical Research Council (DJI is supported by an NHMRC Investigator Grant [GNT1195210]).

Reoccurring Escherichia coli O157:H7 Strain Linked to Leafy Greens-Associated Outbreaks, 2016-2019

Genomic characterization of an Escherichia coli O157:H7 strain linked to leafy greens-associated outbreaks dates its emergence to late 2015. One clade has notable accessory genomic content and a previously described mutation putatively associated with increased arsenic tolerance. This strain is a reoccurring, emerging, or persistent strain causing illness over an extended period.

First Known Report of mcr-Harboring Enterobacteriaceae in the Dominican Republic

Colistin is a last-resort antibiotic used to treat infections caused by multidrug-resistant Gram-negative bacteria. People with a history of travel to the Dominican Republic have become sick with pathogenic bacteria carrying the mobile colistin resistance gene, mcr-1, during and after traveling. This investigation aimed to identify mcr genes in Enterobacteriaceae isolated from food animal sources in the Dominican Republic. Three hundred and eleven samples were tested, from which 1354 bacterial isolates were obtained. Real-time PCR tests showed that 70.7% (220 out of 311) of the samples and 3.2% (44 out of 1354) of the isolates tested positive for the mcr gene. All RT-PCR presumptive mcr-positive isolates (n = 44) and a subset (n = 133) of RT-PCR presumptive mcr-negative isolates were subjected to whole-genome sequencing. WGS analysis showed that 39 isolates carried the mcr gene, with 37 confirmed as positive through RT-PCR and two as negative. Further, all of the mcr-positive genomes were identified as Escherichia coli and all contained a IncX4 plasmid replicon. Resistant determinants for other antibiotics important for human health were found in almost all isolates carrying mcr genes.

High Throughput Screening of Antimicrobial Resistance Genes in Gram-Negative Seafood Bacteria

From a global view of antimicrobial resistance over different sectors, seafood and the marine environment are often considered as potential reservoirs of antimicrobial resistance genes (ARGs) and mobile genetic elements (MGEs); however, there are few studies and sparse results on this sector. This study aims to provide new data and insights regarding the content of resistance markers in various seafood samples and sources, and therefore the potential exposure to humans in a global One Health approach. An innovative high throughput qPCR screening was developed and validated in order to simultaneously investigate the presence of 41 ARGs and 33 MGEs including plasmid replicons, integrons, and insertion sequences in Gram-negative bacteria. Analysis of 268 seafood isolates from the bacterial microflora of cod (n = 24), shellfish (n = 66), flat fishes (n = 53), shrimp (n = 10), and horse mackerel (n = 115) show the occurrence of sul-1, ant(3″)-Ia, aph(3')-Ia, strA, strB, dfrA1, qnrA, and bla_CTX-M-9 genes in Pseudomonas spp., Providencia spp., Klebsiella spp., Proteus spp., and Shewanella spp. isolates and the presence of MGEs in all bacterial species investigated. We found that the occurrence of MGE may be associated with the seafood type and the environmental, farming, and harvest conditions. Moreover, even if MGE were detected in half of the seafood isolates investigated, association with ARG was only identified for twelve isolates. The results corroborate the hypothesis that the incidence of antimicrobial-resistant bacteria (ARB) and ARG decreases with increasing distance from potential sources of fecal contamination. This unique and original high throughput micro-array designed for the screening of ARG and MGE in Gram-negative bacteria could be easily implementable for monitoring antimicrobial resistance gene markers in diverse contexts.

165. Emergence of Extensively Drug-Resistant Salmonella enterica Serotype Typhi Infections—United States, 2008–2020

Background

Typhoid fever, caused by Salmonella Typhi, is fatal in 12%–30% of patients not treated with appropriate antibiotics. In 2016, a large outbreak of extensively drug-resistant (XDR) Typhi infections began in Pakistan with cases reported globally, including the United States. In 2021, the Centers for Disease Control and Prevention (CDC) issued a health advisory on XDR infections among U.S. residents without international travel. We describe resistance of Typhi infections diagnosed in the United States to help guide treatment decisions.

Methods

Typhoid fever is a nationally notifiable disease. Health departments report cases to CDC through the National Typhoid and Paratyphoid Fever Surveillance system. Isolates are submitted to the National Antimicrobial Resistance Monitoring System for antimicrobial susceptibility testing (AST) using broth microdilution. AST results are categorized by Clinical and Laboratory Standards Institute criteria. We defined XDR as resistant to ceftriaxone, ampicillin, chloramphenicol, and co-trimoxazole, and nonsusceptible to ciprofloxacin.

Results

During 2008–2019, of 4,637 Typhi isolates, 52 (1%) were ceftriaxone resistant (axo-R); 71% were ciprofloxacin nonsusceptible, 1 azithromycin resistant (azm-R), and none meropenem resistant. XDR was first detected in 2018, in 2% of 474 isolates and increased to 7% of 535 in 2019. Of the 52 axo-R isolates, 46 were XDR, of which 45 were from travelers to Pakistan, and one from a non-traveler; 6 were not XDR, of which 4 were linked to travel to Iraq. In preliminary 2020 reports, 23 isolates were XDR; 14 were from travelers to Pakistan, 8 from non-travelers, and 1 from someone with unknown travel status. Among those with XDR infection, median age was 11 years (range 1–62), 54% were female, and 62% were from 6 states.

Conclusion

Ceftriaxone-resistant Typhi infections, mostly XDR, are increasing. Clinicians should ask patients with suspected Typhi infections about travel and adjust treatment based on susceptibility results. Carbapenem, azithromycin, or both may be considered for empiric therapy of typhoid fever among travelers to Pakistan or Iraq and in uncommon instances when persons report no international travel. Ceftriaxone is an empiric therapy option for travelers to countries other than Pakistan and Iraq.

Disclosures

All Authors: No reported disclosures

COPLA, a taxonomic classifier of plasmids

Background

Plasmids are mobile genetic elements, key in the dissemination of antibiotic resistance, virulence determinants and other adaptive traits in bacteria. Obtaining a robust method for plasmid classification is necessary to better understand the genetics and epidemiology of many pathogens. Until now, plasmid classification systems focused on specific traits, which limited their precision and universality. The definition of plasmid taxonomic units (PTUs), based on average nucleotide identity metrics, allows the generation of a universal plasmid classification scheme, applicable to all bacterial taxa. Here we present COPLA, a software able to assign plasmids to known and novel PTUs, based on their genomic sequence.

Results

We implemented an automated pipeline able to assign a given plasmid DNA sequence to its cognate PTU, and assessed its performance using a sample of 1000 unclassified plasmids. Overall, 41% of the samples could be assigned to a previously defined PTU, a number that reached 63% in well-known taxa such as the Enterobacterales order. The remaining plasmids represent novel PTUs, indicating that a large fraction of plasmid backbones is still uncharacterized.

Conclusions

COPLA is a bioinformatic tool for universal, species-independent, plasmid classification. Offered both as an automatable pipeline and an open web service, COPLA will help bacterial geneticists and clinical microbiologists to quickly classify plasmids.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-021-04299-x.

731. The Emergence of Mobile Colistin Resistance (mcr) Genes among Enteric Pathogens in the United States — 2008–2019

Background

Colistin, once seldom used clinically, has resurged as a “last resort antibiotic” for multidrug-resistant infections and is still used in animal agriculture in countries outside the United States. During 2015–2018, 8 plasmid-mediated, mobile colistin resistance genes (mcr-1 to mcr-8) were each found in one or more clinical, animal, food, and environmental bacterial sources. We describe the epidemiology of mcr genes in enteric pathogens from US patients.

Methods

State public health laboratories have performed whole-genome sequencing on enteric bacterial pathogens since 2015, and some have sequenced older isolates. We screened sequences of isolates collected through 2019 for mcr genes using a workflow based on ResFinder 3.0. State health officials interviewed patients for clinical and epidemiologic information, including demographics, hospitalization, and travel history.

Results

We identified 41 patient isolates with mcr genes collected from stool, urine, and blood during 2008–2019. These included 37 nontyphoidal Salmonella (31 mcr-1, 6 mcr-3), 2 Vibrio (both mcr-4), and 2 Shiga toxin-producing E. coli (both mcr-1). The median patient age was 34 years (interquartile range: 24–54) and 54% were female. Of 23 patients with comorbidity data, 2 (9%) had immunodeficiency, 2 (9%) had past abdominal surgeries, and 1 (4%) had cancer. Patients sought care at doctor’s offices (46%), emergency rooms (35%), and urgent care clinics (19%); 24% were hospitalized for the enteric illness. None died. Among 36 with information, 35 (97%) travelled internationally in the 12 months before illness; 30 (94%) of 32 traveled in the 7 days before. Only 4 (15%) of 27 had contact with a healthcare setting during their trip; common destinations were the Dominican Republic (35%), Vietnam (24%), Thailand (15%), and China (12%).

Conclusion

The data strongly suggest that many patients acquired infection abroad. Nearly one in four were hospitalized, raising concerns that plasmids carrying mcr genes could spread among patients hospitalized with infections caused by multidrug-resistant pathogens for which colistin is the only available treatment. The acquisition of mcr genes by US travelers highlights the need for a global approach to antimicrobial stewardship.

Disclosures

All Authors: No reported disclosures

130. increase in Multidrug Resistance (2011–2018) and the Emergence of Extensive Drug Resistance (2020) in shigella Sonnei in the United States

Background

Multidrug-resistant (MDR) Shigella sonnei infections are a serious public health threat, and outbreaks are common among men who have sex with men (MSM). In February 2020, Australia’s Department of Health notified CDC of extensively drug-resistant (XDR) S. sonnei in 2 Australian residents linked to a cruise that departed from Florida. We describe an international outbreak of XDR S. sonnei and report on trends in MDR among S. sonnei in the United States.

Methods

Health departments (HDs) submit every 20th Shigella isolate to CDC’s National Antimicrobial Resistance Monitoring System (NARMS) laboratory for susceptibility testing. We defined MDR as decreased susceptibility to azithromycin (MIC ≥32 µg/mL) with resistance to ampicillin, ciprofloxacin, and cotrimoxazole, and XDR as MDR with additional resistance to ceftriaxone. We used PulseNet, the national subtyping network for enteric disease surveillance, to identify US isolates related to the Australian XDR isolates by short-read whole genome sequencing. We screened these isolates for resistance determinants (ResFinder v3.0) and plasmid replicons (PlasmidFinder) and obtained patient histories from HDs. We used long-read sequencing to generate closed plasmid sequences for 2 XDR isolates.

Results

NARMS tested 2,781 S. sonnei surveillance isolates during 2011–2018; 80 (2.9%) were MDR, including 1 (0.04%) that was XDR. MDR isolates were from men (87%), women (9%), and children (4%). MDR increased from 0% in 2011 to 15.3% in 2018 (Figure). In 2020, we identified XDR isolates from 3 US residents on the same cruise as the Australians. The US residents were 41–42 year-old men; 2 with available information were MSM. The US and Australian isolates were highly related (0–1 alleles). Short-read sequence data from all 3 US isolates mapped to the bla_CTX-M-27 harboring IncFII plasmids from the 2 Australian isolates with >99% nucleotide identity. bla_CTX-M-27 genes confer ceftriaxone resistance.

Increase in Percentage of Shigella sonnei Isolates with Multidrug Resistance* in the United States, 2011–2018†

Conclusion

MDR S. sonnei is increasing and is most often identified among men. XDR S. sonnei infections are emerging and are resistant to all recommended antibiotics, making them difficult to treat without IV antibiotics. This outbreak illustrates the alarming capacity for XDR S. sonnei to disseminate globally among at-risk populations, such as MSM.

Disclosures

All Authors: No reported disclosures

Salmonella in Peripheral Lymph Nodes of Healthy Cattle at Slaughter

To more fully characterize the burden of Salmonella enterica in bovine peripheral lymph nodes (PLN), PLN (n = 5,450) were collected from healthy cattle at slaughter in 12 commercial abattoirs that slaughtered feedlot-fattened (FF) cattle exclusively (n = 7), cattle removed (or culled) from breeding herds (n = 3), or both FF and cull cattle (n = 2). Qualitative and quantitative methods were used to estimate prevalence and concentration of Salmonella in PLN. Isolates were subjected to a variety of phenotypic, serological, and molecular assays. Overall, Salmonella prevalence in PLN from FF and cull cattle was 7.1 and 1.8%. However, burden varied by season in that observed prevalence in PLN collected in cooler or warmer seasons was 2.4 and 8.2%, respectively. Prevalence in PLN from cull cattle in the southwest region of the US was 2.1 and 1.1% for cool and warm seasons, respectively; however, prevalence in FF PLN was far greater in that it was 6.5 and 31.1%, respectively. Salmonella was recovered from 289 (5.6%) PLN and 2.9% (n = 160) of all PLN tested had quantifiable concentrations that varied from 1.6 to 4.9 log₁₀ colony forming units/PLN. The most common serotypes isolated from PLN were Montevideo (26.9%), Lille (14.9%), Cerro (13.0%), Anatum (12.8%), and Dublin (6.9%). In all, 376 unique isolates were collected from the 289 Salmonella-positive PLN. Antimicrobial susceptibility testing revealed the majority (80.6%) of these isolates were pansusceptible; however, 10.7% of isolates were found to be resistant to two or more antimicrobial classes. We were able to document an observed increased in prevalence of Salmonella in PLN during the warmer season, particularly in FF cattle from the southwest region of the US. The mechanisms underlying the observed association between season, region, and production source have yet to be elucidated. Nevertheless, these findings increase our understanding of the sources of contamination of beef products and shed light on transmission dynamics that may be useful in targeting these sources.

Illustrative examples of probable transfer of resistance determinants from food animals to humans: Streptothricins, glycopeptides, and colistin

Use, overuse, and misuse of antimicrobials contributes to selection and dissemination of bacterial resistance determinants that may be transferred to humans and constitute a global public health concern. Because of the continued emergence and expansion of antimicrobial resistance, combined with the lack of novel antimicrobial agents, efforts are underway to preserve the efficacy of current available life-saving antimicrobials in humans. As a result, uses of medically important antimicrobials in food animal production have generated debate and led to calls to reduce both antimicrobial use and the need for use. This manuscript, commissioned by the World Health Organization (WHO) to help inform the development of the WHO guidelines on the use of medically important antimicrobials in food animals, includes three illustrations of antimicrobial use in food animal production that has contributed to the selection-and subsequent transfer-of resistance determinants from food animals to humans. Herein, antimicrobial use and the epidemiology of bacterial resistance are described for streptothricins, glycopeptides, and colistin. Taken together, these historical and current narratives reinforce the need for actions that will preserve the efficacy of antimicrobials.

The Mobilome; A Major Contributor to Escherichia coli stx2-Positive O26:H11 Strains Intra-Serotype Diversity

Shiga toxin-producing Escherichia coli of serotype O26:H11/H- constitute a diverse group of strains and several clones with distinct genetic characteristics have been identified and characterized. Whole genome sequencing was performed using Illumina and PacBio technologies on eight stx2-positive O26:H11 strains circulating in France. Comparative analyses of the whole genome of the stx2-positive O26:H11 strains indicate that several clones of EHEC O26:H11 are co-circulating in France. Phylogenetic analysis of the French strains together with stx2-positive and stx-negative E. coli O26:H11 genomes obtained from Genbank indicates the existence of four clonal complexes (SNP-CCs) separated in two distinct lineages, one of which comprises the "new French clone" (SNP-CC1) that appears genetically closely related to stx-negative attaching and effacing E. coli (AEEC) strains. Interestingly, the whole genome SNP (wgSNP) phylogeny is summarized in the cas gene phylogeny, and a simple qPCR assay targeting the CRISPR array specific to SNP-CC1 (SP_O26-E) can distinguish between the two main lineages. The PacBio sequencing allowed a detailed analysis of the mobile genetic elements (MGEs) of the strains. Numerous MGEs were identified in each strain, including a large number of prophages and up to four large plasmids, representing overall 8.7-19.8% of the total genome size. Analysis of the prophage pool of the strains shows a considerable diversity with a complex history of recombination. Each clonal complex (SNP-CC) is characterized by a unique set of plasmids and phages, including stx-prophages, suggesting evolution through separate acquisition events. Overall, the MGEs appear to play a major role in O26:H11 intra-serotype clonal diversification.

Exogenous Carbohydrate Reduces Cortisol Response from Combined Mental and Physical Stress

Combined mental and physical stress is associated with exacerbated cortisol production which may increase risk for the progression of cardiovascular disease in individuals working in high-stress occupations (e.g., firefighters, military personnel, etc.). Carbohydrate (CHO) ingestion prior to physical stress may attenuate cortisol concentrations. This project was the first to investigate the effect of CHO ingestion on cortisol response from combined mental and physical stress. 16 men 21-30 years old were randomly assigned a 6.6% CHO beverage or non-CHO control 15 min prior to performing a dual-concurrent-stress challenge. This consisted of physical stress (i.e., steady state exercise) combined with computerized mental challenges. Blood was sampled 70, 40, and 15 min before exercise, immediately at onset of exercise, 10, 20, 30, 35 min during exercise, and 15, 30, 45, and 60 min after exercise. There was a significant main effect for treatment regarding mean cortisol concentrations (F=5.30, P=0.0219). The total area under curve for cortisol was less when CHO was ingested (T₇=4.07, P=0.0048). These findings suggest that CHO ingestion immediately prior to combined mental and physical stress may attenuate cortisol responses.

Carbapenem-Resistant Bacteria Recovered from Faeces of Dairy Cattle in the High Plains Region of the USA

Objective

A study was conducted to recover carbapenem-resistant bacteria from the faeces of dairy cattle and identify the underlying genetic mechanisms associated with reduced phenotypic susceptibility to carbapenems.

Methods

One hundred and fifty-nine faecal samples from dairy cattle were screened for carbapenem-resistant bacteria. Phenotypic screening was conducted on two media containing ertapenem. The isolates from the screening step were characterised via disk diffusion, Modified Hodge, and Carba NP assays. Carbapenem-resistant bacteria and carbapenemase-producing isolates were subjected to Gram staining and biochemical testing to include Gram-negative bacilli. Whole genome sequencing was performed on bacteria that exhibited either a carbapenemase-producing phenotype or were not susceptible to ertapenem and were presumptively Enterobacteriaceae.

Results

Of 323 isolates collected from the screening media, 28 were selected for WGS; 21 of which were based on a carbapenemase-producing phenotype and 7 were presumptively Enterobacteriaceae and not susceptible to ertapenem. Based on analysis of WGS data, isolates included: 3 Escherichia coli harbouring bla_CMY-2 and truncated ompF genes; 8 Aeromonas harbouring bla_cphA-like genes; 1 Acinetobacter baumannii harbouring a novel bla_OXA gene (bla_OXA-497); and 6 Pseudomonas with conserved domains of various carbapenemase-producing genes.

Conclusions

Carbapenem resistant bacteria appear to be rare in cattle. Nonetheless, carbapenem-resistant bacteria were detected across various genera and were found to harbour a variety of mechanisms conferring reduced susceptibility. The development and dissemination of carbapenem-resistant bacteria in livestock would have grave implications for therapeutic treatment options in human medicine; thus, continued monitoring of carbapenem susceptibility among enteric bacteria of livestock is warranted.

Revisiting the STEC Testing Approach: Using espK and espV to Make Enterohemorrhagic Escherichia coli (EHEC) Detection More Reliable in Beef

Current methods for screening Enterohemorrhagic Escherichia coli (EHEC) O157 and non-O157 in beef enrichments typically rely on the molecular detection of stx, eae, and serogroup-specific wzx or wzy gene fragments. As these genetic markers can also be found in some non-EHEC strains, a number of "false positive" results are obtained. Here, we explore the suitability of five novel molecular markers, espK, espV, ureD, Z2098, and CRISPRO26:H11 as candidates for a more accurate screening of EHEC strains of greater clinical significance in industrialized countries. Of the 1739 beef enrichments tested, 180 were positive for both stx and eae genes. Ninety (50%) of these tested negative for espK, espV, ureD, and Z2098, but 12 out of these negative samples were positive for the CRISPRO26:H11 gene marker specific for a newly emerging virulent EHEC O26:H11 French clone. We show that screening for stx, eae, espK, and espV, in association with the CRISPRO26:H11 marker is a better approach to narrow down the EHEC screening step in beef enrichments. The number of potentially positive samples was reduced by 48.88% by means of this alternative strategy compared to the European and American reference methods, thus substantially improving the discriminatory power of EHEC screening systems. This approach is in line with the EFSA (European Food Safety Authority) opinion on pathogenic STEC published in 2013.

Genetic Diversity and Pathogenic Potential of Attaching and Effacing Escherichia coli O26:H11 Strains Recovered from Bovine Feces in the United States

Escherichia coli O26 has been identified as the most common non-O157 Shiga toxin-producing E. coli (STEC) serogroup to cause human illnesses in the United States and has been implicated in outbreaks around the world. E. coli has high genomic plasticity, which facilitates the loss or acquisition of virulence genes. Attaching and effacing E. coli (AEEC) O26 strains have frequently been isolated from bovine feces, and there is a need to better characterize the relatedness of these strains to defined molecular pathotypes and to describe the extent of their genetic diversity. High-throughput real-time PCR was used to screen 178 E. coli O26 isolates from a single U.S. cattle feedlot, collected from May to July 2011, for the presence or absence of 25 O26 serogroup-specific and virulence-associated markers. The selected markers were capable of distinguishing these strains into molecularly defined groups (yielding 18 unique marker combinations). Analysis of the clustered regularly interspaced short palindromic repeat 1 (CRISPR1) and CRISPR2a loci further discriminated isolates into 24 CRISPR types. The combination of molecular markers and CRISPR typing provided 20.8% diversity. The recent CRISPR PCR target SP_O26-E, which was previously identified only in stx2-positive O26:H11 human clinical strains, was identified in 96.4% (161/167 [95% confidence interval, 99.2 to 93.6%]) of the stx-negative AEEC O26:H11 bovine fecal strains. This supports that these stx-negative strains may have previously contained a prophage carrying stx or could acquire this prophage, thus possibly giving them the potential to become pathogenic to humans. These results show that investigation of specific genetic markers may further elucidate our understanding of the genetic diversity of AEEC O26 strains in bovine feces.

Salmonella diversity and burden in cows on and culled from dairy farms in the Texas High Plains

The objective of this study was to characterize the epidemiology of Salmonella carried by dairy cows culled from herds in the Texas High Plains. Feces were collected from a convenience sample of 706 animals culled from nine dairy farms. In addition, individually paired fecal and hide samples were collected from 70 healthy milking cows on three of the dairies. Samples were cultured for Salmonella using routine methods; isolates were serotyped and subjected to a panel of antimicrobial drugs to determine susceptibility. Salmonella was recovered from 32.6% of culled cows. Whole-herd use of a vaccine containing siderophore receptors and porin proteins was associated (p=0.05) with reduced Salmonella prevalence in that the prevalence among herds that practiced whole-herd vaccination was 8.0% compared to 36.8% among herds that did not use this vaccine. The majority (88.6%) of isolates were pansusceptible or resistant to one drug. Of the 3.1% of isolates resistant to more than four drugs, all were Salmonella Newport and were recovered from one dairy. Various serotypes were recovered from individual fecal and hide samples. Salmonella Montevideo was recovered more frequently (p<0.01) from hide samples, whereas Salmonella Cerro was recovered more frequently (p<0.01) from feces. Salmonella was recovered from at least one cow on all dairies. While our study was not a priori designed to address herd-level factors, we found evidence that the whole-herd use of a siderophore receptor and porin protein-containing vaccine might be a useful aid in the control of Salmonella in groups of cattle. As this is a nonrandomized evaluation of an intervention, other herd-level factors that may be correlated with vaccine use, such as biosecurity, might have been responsible for the observed association.

Cardiorespiratory Responses of Hi Fit and Low Fit Subjects to Mental Challenge during Exercise

The influence of psychological states on physiological responses during exercise is of considerable importance to individuals for which the efficiency of energy production is critical to occupational performance. Numerous studies have shown that aerobic fitness is associated with enhanced cardiovascular efficiency at rest and that responses to mental stress demonstrate evidence of increased sensitivity (relative increase in HR response) and enhanced efficiency (a decrease in absolute HR). However, the effect of aerobic fitness and its impact on cardiorespiratory (CR) responses to psychological stress during exercise has not been investigated. Therefore, the purpose of this study was three-fold; (1) to examine during exercise, anxiety, effort sense, and CR responses to a mental challenge, (2) to examine anxiety and heart rate (HR) responses from rest to exercise with mental challenge between below average fitness (Low Fit) and well-above average fitness (Hi Fit) individuals (exercising at similar relative intensities), and (3) to examine anxiety, effort sense, and CR responses of Low Fit and Hi Fit individuals to a mental challenge during exercise at a similar relative intensity. Twelve Low Fit and eleven Hi Fit subjects participated in two, 32-minute cycle ergometer rides at 65 % of VO2max. In the mental challenge condition (MCC), subjects rode while participating in mentally challenging tasks (Stroop Color-Word task and mental arithmetic) from min 6 to min 14 of the protocol. In the no mental challenge condition (NMCC), subjects exercised at the same intensity and duration without a stressor. Subjects were counter-balanced between fitness levels and condition. HR, VE, VE/VO2, RR, VO2, RER, effort sense (RPE), and state anxiety (SAI) were assessed at 5, 14, 24, and 30 min. SAI was also assessed at - 5 min before exercise and after 15 min of recovery. In addition, the NASA task load index (NTLX) was used to assess perceived overall workload. SAI increased significantly at 14 min in the MCC. NTLX scores indicated that the MCC was perceived as a greater overall workload. Furthermore, HR, VE, VE/VO2, and RR were significantly elevated during the mental challenge condition at 14 min. The Hi Fit subjects tended to respond to the dual stress of exercise and mental challenge with a relative increase in HR, while absolute HR was similar in both groups. An examination of fitness group differences revealed that SAI and NTLX were similar for Low Fit and Hi Fit subjects when exercising in the MCC, although, Hi Fit subjects demonstrated lower HR responses from 6 min to 14 min. VE, VE/VO2, and RR were similar for Low Fit and Hi Fit subjects. These results suggest that psychological stress during physical activity can exacerbate cardiorespiratory responses and suggests that factors that impact CR adjustment to mental challenge from resting baseline may differ from the factors that impact CR adjustment to mental challenge during exercise. Finally, fitness level attenuates HR and may attenuate additional cardiorespiratory responses while participating in a dual stress condition, of exercise and mental challenge.

Effect of amitriptyline on neurotransmitter levels in adult mice following infection with the avirulent strain of Semliki Forest virus

Infection of adult mice with the avirulent strain of Semliki Forest virus (SFV) led to neurochemical abnormalities, notably depressed levels of catecholamines (CATs) such as noradrenaline (NA), adrenaline (A) and 3-methoxy-4-hydroxyphenylglycol (MHPG) (a metabolite of NA) particularly in the hypothalamus and the inferior colliculus but not in the temporal cortex. In addition, depressed levels of NA and A were also found in the cerebrospinal fluid (CSF) and the serum. Administration of a tricyclic antidepressant drug, amitriptyline, kept the levels of NA, A and MHPG similar to those of the saline-treated control mice in the hypothalamus, inferior colliculus and CSF.

IgG subclass responses in brain and serum in Semliki Forest virus demyelinating encephalitis

The response of IgG subclasses within the central nervous system (CNS) of the mouse to Semliki Forest virus (SFV), an alphavirus associated with meningoencephalitis and primary immune mediated demyelination, has been measured using immunocytochemistry. The subclass response in serum has been assessed using virus specific enzyme linked immunosorbent assays. In the CNS IgG1 was poorly represented throughout the sampling period of 28 days with a maximum of 3% of the total number of positive cells on day 21 after infection. Of the few IgG positive cells present on day 6, 2a and 3 positive cells were dominant. From day 9 onwards the numbers of 2b positive cells rose and by day 28 IgG2a, 2b and 3 subclasses showed roughly equal percentages of total cells counted. By contrast, in serum, anti-SFV IgG 2a and 2b were the first to appear and were dominant on day 12 and 21. Levels of anti-SFV IgG1 did not rise until after day 12 but rose steeply thereafter. IgG3 was weakly positive at days 9 and 12, rising slightly on day 21. Clearly there are differences in the patterns of subclass response between the CNS and the periphery. This may be important in the context of neurotropic viral infection.

Induction of membrane proliferation in mouse CNS by gold sodium thiomalate with reference to increased virulence of the avirulent Semliki Forest virus

Separation of smooth membrane vesicles from whole mouse brain by isopycnic centrifugation in discontinuous sucrose density gradients show an increased membrane proliferation in gold sodium thiomalate (GSTM) treated mice. Induction of membrane proliferation by GSTM seems to be an important factor in converting the avirulent Semliki Forest virus infection into a lethal one.

The effect of gold sodium thiomalate and its constituent part, thiomalate, on the virus titres and the lysosomal enzyme activity in peritoneal macrophages of Swiss/A2G mice infected with the avirulent strain of Semliki Forest virus

Treatment of adult mice with gold sodium thiomalate made the normally non-lethal Semliki Forest virus infection lethal. Associated with this was a significant increase in brain virus titre and a depression of peritoneal macrophage lysosomal enzyme activity. In contrast, treatment of adult mice with the constituent part, thiomalate, did not make the non-lethal Semliki Forest virus infection lethal. Brain virus titre and peritoneal macrophage lysosomal enzyme activity were comparable to the controls. The mechanism by which gold sodium thiomalate increases the virulence of Semliki Forest virus is discussed.

Immunoelectron microscopical labelling of a glycolipid in the envelopes of brain cell-derived budding viruses, Semliki Forest, influenza and measles, using a monoclonal antibody directed chiefly against galactocerebroside resulting from Semliki Forest virus infection

Neurotropic RNA budding viruses such as Semliki Forest virus (SFV), influenza and measles were each grown in identical mouse brain cell cultures. Positive immunoelectron microscopical labelling with gold was seen in the envelope of these viruses using an anti-SFV derived glycolipid monoclonal antibody (MAb), 373 shown to be directed chiefly against galactocerebroside. The results indicate that each enveloped virus grown from the same cell type contains the same glycolipid in its envelope. The presence of common glycolipids derived from the host cell in the envelopes of various enveloped budding viruses may play a significant role in the pathogenesis of virus induced, immune mediated CNS autoimmunity and demyelination, particularly in multiple sclerosis (MS).

Identification of immunoglobulin-containing cells in the central nervous system of the mouse following infection with the demyelinating strain of Semliki Forest virus

Cells within the central nervous system were identified as containing immunoglobulin G, A and M using immunocytochemistry in mice previously infected with Semliki Forest virus, a togavirus causing primary immune-mediated demyelination. Cells positive for these immunoglobulins were counted in cerebellar white matter, parenchyma, meninges and choroid plexus/ventricles. No positively staining cells were seen on day 6 after infection although other inflammatory cells were present at this time and virus-specific immunoglobulin was found in serum. Cells positive for IgG appeared in all areas by day 9 and remained dominant in numbers throughout. IgM-secreting cells appeared in small numbers in the parenchyma first on day 9 and subsequently in other areas, their numbers rising to a maximum on day 12 in all areas and falling thereafter. The number of IgA-secreting cells was small. They appeared by PID 12 and continued to rise on successive sampling days. Initially IgG-positive cells were seen in the perivascular cuffs but by day 12 a few had moved away from the cuffs into the adjacent parenchyma. IgG-positive cells were seen both in and away from cuffs within areas of demyelination. IgM and IgA-positive cells tended to follow the distribution of IgG-positive cells, but in fewer numbers.

Enhancement of demyelination in the central nervous system of Semliki Forest virus infected mice after pretreatment with muramyl dipeptide

Semliki Forest virus infections in mice produce an encephalitis with demyelination. If before giving the virus the mice are treated with muramyl dipeptide in Freund's incomplete adjuvant, there is a significant increase in demyelination. If ovalbumin is added to the above and then followed after an interval by a second dose of ovalbumin and finally by the virus, the demyelination is further, but only marginally increased. The addition of ovalbumin without muramyl dipeptide in the schedule appears to increase the number of infiltrating cells and to a lesser extent the perivascular cuffing, but does not increase the demyelination as compared to that obtained when Semliki Forest virus is given on its own.

The pathological effect on the central nervous system of mice following single and repeated infections of the demyelinating A7(74) strain of Semliki Forest virus

The avirulent strain A7(74) of Semliki Forest virus was inoculated intraperitoneally into mice at weekly intervals for 7 weeks. Pathological, virological and serological studies were carried out twice weekly, after each infecting dose. Similar studies were performed on mice that had been given repeated inoculations at 2, 3 or 4 weekly intervals as were a group of control mice given a single dose of SFV. Results showed grossly enhanced central nervous system lesions, in particular the perivascular cuffing and demyelination, after the 2nd and 3rd weekly inoculation. With further injections there was no increase in severity of the lesions and by the eighth inoculation the pathological changes in the brain appeared to have recovered. The maximum and most persistent damage to the brain was seen after the 2nd and 3rd weekly inoculations. As the interval between two SFV inoculations was increased, the lesions in the central nervous system were reduced and protection increased. Virus in the blood was only detectable after the first inoculation and brain virus after the first and second inoculations. Peak IgG antibody levels were seen on day 46 after a single inoculation and day 35 in the multiple inoculations. It was concluded that repeated inoculations of SFV do not produce a relapsing demyelinating disease, but the 7th and 14th day inoculations do enhance the lesions which are seen to persist after the inoculation on the 21st day. In spite of the gross pathological changes inflicted, the brain damage appears to recover.

An electron microscopical study of the replication of avirulent Semliki Forest virus in the retina of mice

Electron microscopical (EM) studies were carried out on the retinas of 2-3-(baby), 12-, 14- and 21-28-day-old (adult) mice infected with avirulent (A774) Semliki Forest virus (SFV). Virions (mature virus), spherules and advanced stages of virus replication, cytopathic vacuoles type II (CPV II), were seen in the retinal neurons of baby mice after intracerebral (i.c.) or intraperitoneal (i.p.) infection. Some virions and spherules were also seen in the retinas of 12- and 14-day-old mice. Virions and advanced stages of virus replication were not seen in adult mice despite high virus titres. Some neurons of the inner nuclear layer and some ganglion cells showed reduced basophilia and appeared pale and occasionally some dense clumps of fine granules (DC) were seen in the neurones of the inner nuclear layer in these mice. A few small spherules were seen in the extracellular spaces. Some infiltrating cells were seen in the retinas in all ages of mice. We suggest that SFV causes retinopathy in baby mice and the neurophysiological changes reported in adult mice may be contributed to by virus replication in the retinal neurones and the presence of infiltrating cells in the retina.

Immunocytochemical evidence for Semliki Forest virus antigen persistence in mouse brain

Semliki Forest virus (SFV) is neurotropic in mice. Mature virulent virus (strain L10) can be identified within the CNS by electron microscopy in adult mice. Inspite of high virus titres, avirulent SFV A7(74) cannot be visualised in the brain of adult mice. Immunocytochemical studies using monoclonal antibodies (MAbs) to A7(74) E1 and E2 proteins and viral envelope glycolipids, showed viral E1 to be labelled in the cerebral capillaries, the E2 and the putative envelope glycolipids were labelled in the cytoplasm of neurons, particularly in the hippocampal areas and glia in the cerebellum. By double labelling the presence of viral antigens in astrocytes and oligodendrocytes was demonstrated. Viral antigens were identified in the brain up to 183 days after infection. Paraffin sections from Bouin-fixed tissue were found to be the most suitable material for immunocytochemistry of SFV. The presence of life-long anti SFV antibody in the sera of animals after SFV infection, could be due to the persistence of viral antigens acting as constant stimuli to the immune system.

CNS pathogenesis following a dual viral infection with Semliki Forest (alphavirus) and Langat (flavivirus)

Mice inoculated intraperitoneally with the alphavirus Semliki Forest were protected against a subsequent challenge with the flavivirus Langat. The protection was seen as a reduction in the Langat virus titres, mortality index and percentage deaths. The severity of the brain pathology was greater in the simultaneously infected mice, or when the time interval between administration of the viruses was 7 days, compared to that seen following a single infection of either Semliki Forest or Langat virus. When the time interval was greater than 14 days the severity of the histopathological lesions were reduced. Two factors were considered to be of possible importance in the protection afforded by the original alphavirus. Either persistence of the alphavirus interfering with the challenge flavivirus or cross-reactive immunity arising from a common host cell membrane derived glycolipid component present in both viral envelopes. This latter phenomenon could be important as anti-glycolipid activity present at 14 days after the first virus increased significantly after challenge with the second virus.

The effect of gold sodium thiomalate in adult Swiss/A2G mice infected with togaviruses and flaviviruses

Treatment of adult mice with gold sodium thiomalate made the normally non-lethal Semliki Forest virus and Sindbis virus infections lethal and increased the virulence of Langat and West Nile viruses. These changes were associated with an enhanced virus invasion of the brain. Depression of the humoral antibody response was not observed.

Persistence of encephalitogenic arboviruses in brain cell culture. Brief report

Virus recovery from brain cultures of mice infected with either Semliki Forest and/or Langat depended on the time interval between inoculation of either virus. Mixed infections may alter the course of a disease.

Do human T-lymphotrophic viruses (HTLVs) and other enveloped viruses induce autoimmunity in multiple sclerosis?

A virally induced autoimmune reaction may be important in the pathogenesis of multiple sclerosis. The role that glycolipids and myelin basic protein presented to the virus may play in this process is considered. The most likely cells to be the source of autoantigens are neurons, myelin and oligodendrocytes. Viral infection of class II-expressing cells and association of the viral envelope autoantigens and the class II molecules could trigger an autoimmune reaction. It is suggested that for MS to develop following a virus infection the virus will need to cause expression of class II antigens on brain cells as well as fulfill the same role as an antigen presenting cell. The part which T-lymphotrophic viruses (HTLVs) and other enveloped viruses may play in this phenomenon is discussed.

The effect of cycloleucine on SFV A7(74) infection in mice

Cycloleucine (CL), a non-metabolizable amino acid analogue, was found to reduce thymus and spleen weights in Semliki Forest virus (SFV) strain A7(74) infected and control mice. The maximum effects were seen when three daily doses of CL were given to mice 24 h after an SFV A7(74) infection. In these mice thymus atrophy led to abolition of thymus dependent immune responses and changes in the pathological features of the viral infection--the most striking feature being prevention of demyelination. In addition virus titres in the brains of CL treated infected mice were increased and prolonged. These results show that demyelination following an SFV A7(74) infection is not a result of direct virus action, but of a T-cell mediated mechanism.

Cyclosporine enhances virally induced T-cell-mediated demyelination. The effect of cyclosporine on a demyelinating virus infection

Semliki Forest virus infection of adult mice results in a demyelinating meningoencephalomyelitis. Demyelination does not result from direct viral damage but from the activity of T lymphocytes. We have studied the effect of the immunosuppressant cyclosporine (Cs) on the outcome of this infection. Cs had no effect when given 5 days after the infection, and little effect when given 4 h after infection. When the Cs was given 48 h before infection there was a prolongation of the blood and brain virus titres, and a reduction in some mice of serum IgG anti-viral antibody synthesis, but an increase in the severity of the CNS inflammatory response and the demyelination. Consideration of these findings along with measurement of Cs levels in the serum and cerebrospinal fluid suggests that this drug does not cross the blood brain barrier.

Semliki Forest virus-induced, immune-mediated demyelination: adoptive transfer studies and viral persistence in nude mice

Adoptive transfer experiments in athymic nude mice demonstrated that the demyelination seen in the central nervous system (CNS) following Semliki Forest virus (SFV) infection was directly dependent upon sensitized T lymphocytes. Antibodies generated during the infection did not seem to be involved in the demyelination, but thymus-dependent antibodies (IgG) were responsible for the reduction of brain virus titres. In the absence of a T cell response and T cell-dependent antibody production, virus persisted in the CNS for several months. Despite persistence of high virus titres for this time, only mice eventually developing a CNS inflammatory response developed lesions of demyelination. In the absence of an inflammatory response no demyelination was apparent even after several months of persistent infection. Administration of anti-SFV hyperimmune serum intracerebrally to both infected and control mice did not produce demyelination but resulted in CNS tissue degeneration with marked pycnosis.

Semliki Forest virus induced, immune mediated demyelination: the effect of irradiation

Intraperitoneal infection with the avirulent A7(74) strain of the alphavirus Semliki Forest virus (SFV) induces an immune mediated demyelinating encephalomyelitis. The blood and brain virus titres, the serum antibody titres and the histopathological changes in the brains of normal mice and mice immunosuppressed with 5.0 or 8.0 Gy total body irradiation (TBX) were determined. SFV infection of immunosuppressed mice resulted in persistently high blood and brain virus titres, neuronal pycnosis, paralysis and death. No demyelination or central nervous system (CNS) inflammatory response occurred in these immunosuppressed mice despite high and persistent brain virus titres. The CNS inflammatory response and associated demyelination could be restored to infected immunosuppressed mice by adoptive transfer of spleen cells, and these changes were brought forward if the donor spleen cells were from mice previously sensitized to SFV. The results indicate that the immune response following SFV A7(74) infection is both protective and pathogenic, and that the demyelination is immune mediated and does not result from direct viral destruction of oligodendrocytes, or any other direct effect of the virus.

Immunological relationship between a demyelinating RNA enveloped budding virus (Semliki Forest) and brain glycolipids

A monoclonal antibody (MAb) raised against central nervous system (CNS) myelin (212) and a MAb (308) raised against brain with Semliki Forest virus (SFV) were both found to react against the same CNS glycolipids. Both these MAbs were also found to react strongly with SFV and against certain brain glycolipid fractions in an immunosorbent assay (ELISA). This demonstrates the presence of common glycolipid antigens in the viral envelope and CNS myelin. MAb 212 had no SFV neutralising capacity and that of MAb 308 was not significant. However, MAb 212 inhibited the neutralisation of the virus by the MAbs (302, 307) specific to SFV proteins. The implications of these findings in relation to the viral induced CNS autoimmunity and persistence of virus in the CNS is discussed.

Use of N-acetylethyleneimine [AEI] for the inactivation of Semliki Forest virus in vitro

N-Acetylethyleneimine (AEI) was used to inactivate the avirulent Togavirus Semliki Forest virus (A774 strain) grown in chick embryo, Vero, and brain cell cultures. The purity of the virus preparation affected the kinetics of inactivation. The rate of inactivation increased with a rise in temperature from 5 to 40 degrees C and in concentration of AEI from 0.025 to 0.1%. The resultant vaccine was inoculated into adult mice to test its antigenicity and into suckling mice to test for the presence of infective virus. Semliki Forest virus-specific IgG was produced equal to that of mice given live virus, and mice were protected against the lethal SFV L10 strain. No suckling mice died, and the brains of the adult mice showed no pathology.

Immunoelectron-microscopical labelling of glycolipids in the envelope of a demyelinating brain-derived RNA virus (Semliki Forest) by anti-glycolipid sera

Immunoelectron-microscopical techniques using gold-labelled antibodies were used to localize the glycolipids ganglioside, glucocerebroside and galactocerebroside, and spike glycoprotein antigens, in the envelope of the RNA virus Semliki Forest which had replicated in mouse brain cell cultures. The demonstration of host cell membrane glycolipid antigens in viruses is discussed in relation to the possibility of an autoimmune reaction to central nervous system cells.

Comparison of protein A-gold and ferritin immunoelectron microscopy of Semliki Forest virus in mouse brain using a rapid processing technique

Processing tissue for transmission electron microscopy by standard laboratory methods can take two to three days. This makes the development of new techniques time consuming and generally restricts the use of the electron microscope in routine diagnostic work. The possibility of viewing tissue with the electron microscope five hours after sampling using rapid processing techniques is presented. The morphology of the tissue appears undamaged with cell and organelle ultrastructures being readily recognized, as is the presence of virus and its replicating stages. When combined with immunoelectron microscopy a rapid labeling protocol is possible. We have used the technique to develop protein A-gold (6 and 16 nm particles) and ferritin immunoelectron microscopic techniques to demonstrate viral antigens in brain cell cultures and brain tissue from mice infected with Semliki Forest virus.

Immunological reaction of the demyelinating Semliki Forest virus with immune serum to glycolipids and its possible importance to central nervous system viral auto-immune disease

The avirulent demyelinating strain A7(74) of Semliki Forest virus after passage through mouse brain in vivo and mouse brain cell cultures has been shown to react immunologically with immune sera against galactocerebroside, glucocerebroside, total ganglioside and GT1b ganglioside but not against myelin or sulphatide . Semliki Forest virus is known to take host membrane glycolipid into its coat. The importance of the findings is discussed in relation to the production of a possible anti-brain cell auto-immune phenomenon and its implication in a disease such as multiple sclerosis.

Can viral envelope glycolipids produce auto-immunity, with reference to the CNS and multiple sclerosis?

Many viruses, with lipid envelopes derived from the host cell membranes, have been implicated in the aetiology of multiple sclerosis (MS), and epidemiological studies support an infectious agent. Alternatively the disease is thought by other workers to be auto-immune in nature, and recently much attention has been focused on immunological sensitivity to glycolipids in MS patients. In this paper it is proposed that CNS demyelination could arise in susceptible individuals (HLA type) from an immune response to glycolipids, triggered by the carrier effect of one or more enveloped neurotropic viruses.

Effect of myocrisin (sodium auro-thio-malate) on the morphogenesis of avirulent Semliki Forest virus in mouse brain: an electron microscopical study

Adult mice, infected intracerebrally or intraperitoneally with avirulent Semliki Forest virus, do not show mature virus or advanced stages of viral replication in the brain. If myocrisin is given intraperitoneally 3 h before the virus there is enhancement of all stages of viral replication and budding of virus and mature virions are seen. Compared with controls many intracytoplasmic smooth membrane vesicles were seen in the parenchymal cells of the brain treated with myocrisin or with myocrisin and virus. Myocrisin was visible in the brain and has a membrane proliferating effect which may enhance viral synthesis in the early stages of replication, as well as help in the assembly and budding of mature virus. Increased numbers of infiltrating cells were observed in myocrisin treated mice infected with SFV. The formation of mature virus, and its virulence, appears to be related to the degree of membrane proliferation of the brain cells. The inflammation associated with the increased number of infiltrating cells is secondary to this, the whole process promoting the death of the animals rather than survival.

Reconstitution of Semliki forest virus infected mice, induces immune mediated pathological changes in the CNS

Reconstitution of Semliki forest virus infected nude mice with spleen cells from their immunocompetent nu/+ litter mates resulted in an abolition of the otherwise persistent brain virus, production of anti-SFV IgG, and development of normally absent brain pathology. The brain pathological changes, including demyelination, seem to be mediated by T cells, and are maximum 14 days after sensitization of the reconstituting spleen cells. Sensitization of the spleen cells 7 days before transfer to the nude mice results in pathological changes advanced by about 8 days, compared to reconstitution with unsensitized cells. The involvement of T cells in the virus-induced pathology is discussed.