Coagglutination test for rapid detection of Salmonella enterotoxin

The Bacteriology and Its Virulence Factors in Neonatal Infections: Threats to Child Survival Strategies

BACKGROUND

Neonatal infection refers to the infection of the newborn during the first twenty-eight days of life. It is one of the causes of infant morbidity and mortality worldwide. The aim of the study is to determine the relative contribution of the different pathogens to the overall disease burden. It will also determine the mechanisms of virulence of these pathogens that cause neonatal infections at Chukwuemeka Odumegwu Ojukwu University Teaching Hospital (COOUTH), Awka.

METHODS

Biological samples were collected from 30 neonates admitted at the special care baby unit (SCBU) of COOUTH and cultured using selective media and nutrient agar. The isolates were identified using microbiological and biochemical tests. The antibiogram study was determined using Kirby-Bauer disc diffusion method on Mueller Hinton Agar. Several methods previously reported in literature were used for the characterization of the virulence factors.

RESULTS

From the 30 blood samples collected, Pseudomonas spp. (19.7%), Escherichia coli (23%), Salmonella spp. (24.6%), and Staphylococcus aureus (32.8%) were isolated. Male to female ratio of study population was 1.5: 1. The isolates were 100 % resistant to ticarcillin, cephalothin, ceftazidime, and cefuroxime but appreciably susceptible to only levofloxacin (88.85%). They were moderately susceptible to ceftriaxone/sulbactam (39.05%) and azithromycin (26.46%). Common virulence factors identified among the isolates (up to 90 %) were hemolysin, biofilm formation, and acid resistance. Less common virulence factors were proteases (50 %), deoxyribonucleases (50 %), enterotoxins (63%), and lipopolysaccharide (70%). The virulence factors were found mostly among the S. aureus isolates.

CONCLUSIONS

Pseudomonas spp., Escherichia coli, Salmonella spp., and Staphylococcus aureus were implicated in neonatal infections in the center and most of them were resistant to conventional antibiotics. The organisms showed marked virulence and multidrug resistance properties. Levofloxacin, a fluoroquinolone, had superior activity on the isolates compared to other antibiotics used in the study.

Immunogenicity and antigenic relationship of Salmonella enterotoxin with other enterotoxins

The immunogenicity and antigenic relationship of Salmonella enterotoxin with other enterotoxins were studied. The purified enterotoxin of Salmonella typhimurium strains was immunogenic in rabbits and antiserum produced against it completely neutralized the enterotoxic activity of purified as well as crude enterotoxins. The Salmonella enterotoxin did not cross-react with cholera toxin, heat-labile enterotoxin of Escherichia coli or Shiga toxin. On the other hand, enterotoxins produced by different serotypes of Salmonella were antigenically related. Heat, pH and proteolytic enzymes had not only adversely affected the enterotoxigenicity but also the antigenicity of the Salmonella enterotoxin. However, formalin was found to completely destroy the enterotoxigenicity of enterotoxin without affecting the antigenicity. Formalin-treated enterotoxin may thus be tried as a vaccine to prevent the diarrhoeal syndrome induced by enterotoxigenic salmonellae.

Purification and characterization of enterotoxic moiety present in cell-free culture supernatant of Salmonella typhimurium

The enterotoxic moiety present in the cell-free culture supernatants of Salmonella typhiurium strains (p/536 and p/603) was purified to apparent homogeneity by salt precipitation with ammonium sulphate and successive chromatography through Sephadex G-100 and G-200 columns. It was non-dialysable, heat labile at 90 degrees C and active within pH 6-8. Its activity was completely lost on treatment with trypsin, protease and papain. The enterotoxin appeared to be of high molecular weight (100 kDa) and was highly immunogenic in rabbit. Antigenically, it was not related to cholera toxin, Shiga toxin or the heat labile enterotoxin of Escherichia coli. It did not bind to the GM1 ganglioside. The enterotoxic, delayed permeability and CHO cell elongation activities were attributed to a single protein moiety.