Effects of Ocimum gratissimum L essential oil at subinhibitory concentrations on virulent and multidrug-resistant Shigella strains from Lagos, Nigeria.

Ocimum gratissimum leaf extracts have been extensively demonstrated to be effective against the various aetiologic agents of diarrhoea, including Shigellae. However, the mechanism of the shigellocidal action of this plant remains to be understood. This study investigated the effects of O. gratissimum essential oil (EO) at subinhibitory concentrations of 0.75 and 1.0 microg/ml on virulence and multidrug-resistant strains of 22 Shigella isolates from Nigeria. Compared with untreated Shigella strains, O. gratissimum EO caused significant decreases (p<0.01) in extracellular protease activity, o-lipopolysaccharide rhamnose content and incidence of invasiveness mediated as keratoconjunctivitis in guinea pig. The disparity in extracellular protease activity and o-lipopolysacharide rhamnose between the two treatment groups was also found to be significant (p<0.05), suggesting greater anti-virulent effects of O. gratissimum oil at 1.0 microg/ml. Antibiotic susceptibility testing revealed that the EO of O. gratissimum reduced the MICs of antibiotics to which Shigellae showed resistance by 9.8-53.1% and fluoroquinolones by 18.2-45.5%. The results of this study strongly suggest inhibition of extracellular protease and expression of O-LPS rhamnose in Shigellae by O. gratissimum EO. The future use of O. gratissimum- antibiotic combinations as a therapeutic measure against shigellosis is discussed.

Prevalence of multi-drug resistant Salmonella typhi among clinically diagnosed typhoid fever patients in Lagos, Nigeria.

A total of 635 clinically diagnosed typhoid fever patients were bled from three different health institutions in the metropolis of Lagos, Nigeria over a period of 15 months, May 1997 to July 1998. Out of the total blood cultured, 101 (15.9%) isolates of Salmonella species were isolated of which 68 (67.3%) were S. typhi, 17 (16.8%) and 16 (15.8%) were S. paratyphi A. and S. arizonae respectively. The overall isolation rate of S. typhi among patients is 10.7%, with most isolates 45.9% found among the severely-ill young adults, age group 16-30 years. All isolates were subjected to anti-microbial susceptibility testing using 12 different antibiotics: chloramphenicol, ampicillin, cotrimoxazole, gentamicin, colistin sulfate, nalidixic acid, nitrofurantoin, cefotaxime, tetracycline, streptomycin, ofloxacin and ciprofloxacin. All the S. typhi and S. paratyphi A isolates showed resistance to two or more of the 10 of 12 antibiotics tested particularly the 3-first-line antibiotics commonly used (chloramphenicol, ampicillin and cotrimoxazole) in the treatment of typhoid fever in Nigeria. No isolate showed resistance to ofloxacin and ciprofloxacin, however, nalidixic acid and gentamicin showed a moderate and appreciable inhibition to most of our isolates.