Salmonellosis in Trinidad: evidence for transovarian transmission of Salmonella in farm eggs

This paper describes the second part of a longtime-study, started in 1987. Serologic investigations for detecting antibodies against Maedi Visna-virus (MVV) were performed, involving an institute own sheep flock. The method used was the immunodiffusiontest. The flock consisted of different breeds and their offsprings. So far, the virus seems to persist in the herd. This work also shows the importance of the central role of the does for spreading the virus. Seroconversion was detected in a sheep at the age of 32 months. The mother of this sheep was a thoroughbred and MVV-negative mountain sheep. After removal of the animals with high antibody (ab)-titers, until the end of 1991, the percentage of seronegative sheep increased. Then seropositive sheep didn't show high ab-titers anymore. Since 1990 only offsprings increased the size of the herd. The health status of the flock was clinically inconspicuous. It can be concluded that in spite of good food quality, good hygiene, without culling positive animals and just giving away accidentally some sheep, no elimination of MVV was registered in the flock over a period of more than six years. There was only seen a reduction of seropositive animals. Single results of serological tests, without knowing the sheep and the serological status of the herd, could pretend a false negative status.     

Gene transfer between related bacteria by electrotransformation: mapping Salmonella typhi genes in Salmonella typhimurium

Transfer of newly isolated mutations into a fresh background is an essential step of genetic analysis and strain construction. Gene transfer is hampered in Salmonella typhi and in other pathogenic bacteria by the lack of a generalized transduction system. We show here that this problem can be partially circumvented by using electrotransformation as a means for delivering S. typhi DNA into suitable S. typhi or Salmonella typhimurium recipients. Transferred DNA can recombine with the homologous region in the host chromosome. In one application of the method, mutations isolated in S. typhi were genetically mapped in S. typhimurium.     

Simulation of the transmission of Salmonella enteritidis phage type 4 in a flock of laying hens

Simulation of disease transmission in laying flocks infected with Salmonella enteritidis phage type 4 over a 48-week egg-production period indicated that the maximum weekly incidence risk could range from 0.05 to 0.28, and the maximum proportion of culture-positive birds could range from 0.20 to 0.77 of the flock, depending on the effective contact rate. If the egg contamination proportion were 0.08, contaminated egg production could vary from a weekly maximum of 0.42 per cent to 2.24 per cent depending on the effective contact rate, but the actual rate of contamination was more important in determining the numbers of infected eggs produced. The results from previous studies suggest that this proportion could range from 0.075 to 0.25. The model produced levels of infected and immune birds similar to those reported in the literature, suggesting effective contact rates of between 2 and 4.5. There is insufficient information on transmission cycles to validate the model, but it does provide a mechanism for consolidating research findings, reviewing areas for further research, and aiding more effective planning for disease control.     

Interaction of Salmonella typhi strains with cultured human monocyte-derived macrophages

Human monocyte-derived macrophages (MDM) provided this laboratory with a tool to develop a primary-cell assay for evaluating the relative virulence of newly constructed Salmonella typhi carrier strains. In this study, the interaction with and survival within MDM were compared for delta aroA143-attenuated strains, wild-type virulent strains, and the current oral-vaccine strain, Ty21a.     

Chromosomal rearrangements in Salmonella enterica serotype typhi affecting molecular typing in outbreak investigations

Salmonella enterica serotype Typhi strains belonging to eight different outbreaks of typhoid fever that occurred in Spain between 1989 and 1994 were analyzed by ribotyping and pulsed-field gel electrophoresis. For three outbreaks, two different patterns were detected for each outbreak. The partial digestion analysis by the intron-encoded endonuclease I-CeuI of the two different strains from each outbreak provided an excellent tool for examining the organization of the genomes of epidemiologically related strains. S. enterica serotype Typhi seems to be more susceptible than other serotypes to genetic rearrangements produced by homologous recombinations between rrn operons; these rearrangements do not substantially alter the stability or survival of the bacterium. We conclude that genetic rearrangements can occur during the emergence of an outbreak.     

Typing of freshly isolated strains of Salmonella typhi using bacteriophages and colicins

The effect of ketamine administered to 20 rabbits in a single dose and in fractionated doses on the blood clotting system was studied. The following blood clotting indices were determined: thrombelastography (TEG), plasma thrombin time, platelet count, euglobulin lysis time. No statistically significant differences were observed in the activity of clotting and fibrinolysis systems in the group of animals receiving a single dose of ketamine and in the group receiving fractionated doses. The obtained results suggest that ketamine as an agent used for dissociative anaesthesia can be administered safely in serious conditions associated with disturbances in the haemostasis system.     

The population dynamics of Salmonella typhi and Tetrahymena pyriformis during joint cultivation

Scientific researches carried out in the area of environmental sanitation are closely related to the principal lines of activity in industry and farming of Ukraine. The main task of research work is establishing principles, criteria and methods of comprehensive assessment of injury to health secondary to environmental contamination. With the purpose of identification of the real physical and chemical environmental factors load that human body experiences, an inventory has been made at the Ukrainian Scientific Research Centre for Hygiene of carcinogen sources, with the concept having been worked out of creation of the integrated system for control of safe NPS operation, and a concept proposed of genetic monitoring, and of state genetic load surveillance service in different regions of Ukraine, taking account of the degree of environmental pollution.     

Surveillance on Vi-II phage typing and antimicrobial susceptibilities of S. typhi strains in Beijing City

From 1973 to 1989, 961 strains of S. typhi collected in Beijing City were tested for their Vi-II phage typing and antimicrobial susceptibilities. The results of phage typing showed that 38 types were found with a high prevalence of types A, D2, E1, K1, D5, D1, O, D4, and L1. The results of antimicrobial susceptibilities showed that all of the 168 local strains were highly susceptible to chloramphenicol, similar to the 96 phage typing standard strains.     

Application of physico-chemical typing methods for the epidemiological analysis of Salmonella enteritidis strains of phage type 25/17

Eighty-nine Salmonella enteritidis phage type 25/17 strains isolated from a localized outbreak in the German state Nordrhein-Westfalen (outbreak NWI) could not be further differentiated by biochemotyping and plasmid pattern analysis. They were submitted to a complex typing system consisting of modern physico-chemical analytical procedures. In lipopolysaccharide pattern analysis the strains proved to be homogeneous. In multilocus enzyme electrophoresis, outer membrane and whole cell protein pattern (WCPP) analysis, and Fourier-transform infrared (FT-IR) spectroscopy (increasing extent of differentiation in the given order) strains deviating from each basal pattern were found. The extent of correspondence in these deviations was satisfactory. Forty-six strains of the same sero- and phage type, however, obtained from different outbreaks, were additionally typed. The results obtained with them indicate that the data of the first group were not restricted to strains from outbreak NWI, but of general validity. It was found that both WCPP and FT-IR represent valuable methods for the sub-grouping of bacteria.     

Cefuroxime axetil in the treatment of Salmonella typhi infection (enteric fever) in adults

A study to evaluate the efficacy and safety of Cefuroxime Axetil in enteric fever was carried out in 30 adult hospitalised patients of either sex. A positive blood culture for S. typhi and sensitivity to cefuroxime axetil were confirmed prior to treatment. On admission, the baseline signs and symptoms were recorded and treatment initiated with cefuroxime axetil in a dose of 500 mg bd; which was continued for 7 days after normalization of temperature. The various clinical parameters were followed up daily during the treatment period and discharge permitted on normalization of temperature. Blood culture for S. typhi was repeated 3 days after stopping treatment. Follow-up Widal, stool and urine cultures were done wherever possible to check for relapse or carrier state. All the patients responded clinically to treatment and had bacteriologically negative blood cultures by the end of 14 days treatment. 87% of the patients responded within 7 days of treatment of which 60% were graded as Excellent responders as they responded within 4 days itself; while 13% took a longer time to respond. There were no relapses or carrier state as indicated by negative follow-up stool cultures. Only one patient reported a side-effect of mild headache confirming the safety of the drug. We conclude that Cefuroxime axetil in a dose of 500 mg bd is an effective and safe drug in the treatment of multi drug resistant enteric fever.     

Slide coagglutination for Salmonella typhi antigens in broths inoculated with feces from typhoid fever patients

Salmonella typhi antigens D, Vi and d were readily detected, by slide coagglutination, in mannitol selenite (MSB) and dulcitol selenite (DSB), Salmonella enrichment broths 4 hours after inoculation with feces from 60 patients with bacteriologically confirmed typhoid fever. Positive coagglutination also occurred using MSB and DSB inoculated with fecal specimens obtained from 16 patients from whom S. typhi was not cultured. Twelve of these later seroconverted to Salmonella O antigen. None of the MSB or DSB inoculated with feces from 50 healthy control subjects, gave a positive coagglutination test. The coagglutination method appears to have potential as a rapid test for the detection of antigens of S. typhi in MSB and DSB broths inoculated with feces from patients with suspected typhoid fever.     

Detection of Salmonella typhi in the blood of patients with typhoid fever by polymerase chain reaction

A polymerase chain reaction (PCR)-based test was developed for the detection of Salmonella typhi in the blood specimens from patients with typhoid fever. Two pairs of oligonucleotide primers were designed to amplify a 343-bp fragment of the flagellin gene of S. typhi. Amplified products were analyzed by agarose gel electrophoresis and Southern blot hybridization by using a 32P-labeled 40-base probe internal to the amplified DNA. The nested PCR with two pairs of primers could detect 10 organisms of S. typhi as determined by serial dilutions of DNA from S. typhi. The peripheral mononuclear cells from 11 of 12 patients with typhoid fever confirmed by blood culture were positive for DNA fragment of the flagellin gene of S. typhi, whereas 10 blood specimens of patients with other febrile diseases were negative. With the nested PCR, S. typhi DNAs were detected from blood specimens of four patients with suspected typhoid fever on the basis of clinical features but with negative cultures. We suggest that the PCR technique could be used as a novel diagnostic method of typhoid fever, particularly in culture-negative cases.     

Molecular analysis of and identification of antibiotic resistance genes in clinical isolates of Salmonella typhi from India

A representative sample of 21 Salmonella typhi strains isolated from cultures of blood from patients at the Christian Medical College and Hospital, Vellore, India, were tested for their susceptibilities to various antimicrobial agents. Eleven of the S. typhi strains possessed resistance to chloramphenicol (256 mg/liter), trimethoprim (64 mg/liter), and amoxicillin (>128 mg/liter), while four of the isolates were resistant to each of these agents except for amoxicillin. Six of the isolates were completely sensitive to all of the antimicrobial agents tested. All the S. typhi isolates were susceptible to cephalosporin agents, gentamicin, amoxicillin plus clavulanic acid, and imipenem. The antibiotic resistance determinants in each S. typhi isolate were encoded by one of four plasmid types. Plasmid-mediated antibiotic resistance genes were identified with specific probes in hybridization experiments; the genes responsible for chloramphenicol, trimethoprim, and ampicillin resistance were chloramphenicol acetyltransferase type I, dihydrofolate reductase type VII, and TEM-1 beta-lactamase, respectively. Pulsed-field gel electrophoresis analysis of XbaI-generated genomic restriction fragments identified a single distinct profile (18 DNA fragments) for all of the resistant isolates. In comparison, six profiles, different from each other and from the resistance profile, were recognized among the sensitive isolates. It appears that a single strain containing a plasmid conferring multidrug-resistance has emerged within the S. typhi bacterial population in Vellore and has been able to adapt to and survive the challenge of antibiotics as they are introduced into clinical medicine.     

Evaluation of a UDP-glucose-4-epimeraseless mutant of Salmonella typhi as a liver oral vaccine

A mutant (Ty21a) of Salmonella typhi, which lacks the enzyme uridine 5'-diphosphate-glucose-4-epimerase, was evaluated in volunteers for use as a live attenuated oral typhoid vaccine. Five to eight doses of vaccine (containing 3-10(10) viable organisms per dose) were given to 155 men without significant side effects. The rate of excretion of the vaccine strain in stools was low, and the majority of isolations occurred on day 1 after vaccination. Revertants able to fement galactose were not found in any of 958 stool isolates tested. The mutant, strain Ty21a, grown in brain-heart infusion broth (BHIB) with 0.1% galactose, produces more O side chain than the same vaccine strain cultivated without galactose. Volunteers vaccinated with strain Ty21a grown in galactose and then challenged with 10(5) virulen S. typhi were significantly protected from disease and also had decreased stool carriage of S. typhi as compared with controls. Strain Ty21a grown without galactose did not provide vaccinees significant protection nor decrease fecal excretion of S. typhi as compared with controls. Strain Ty21a, when grown in BHIB with 0.1% galactose, results in a safe, stable and protective oral vaccine that warrants further study in field trials.