Academic journal article Journal of Health Population and Nutrition

Antimicrobial Susceptibility Patterns of Salmonella Enterica Serotype Typhi in Eastern Nepal

Academic journal article Journal of Health Population and Nutrition

Antimicrobial Susceptibility Patterns of Salmonella Enterica Serotype Typhi in Eastern Nepal

Article excerpt

INTRODUCTION

Typhoid fever, a severe systemic illness, caused by Salmonella enterica serotype Typhi, is still an important public-health problem in many developing countries, including Nepal. According to a recently-revised global estimate, it causes 21.6 million illnesses every year, resulting in 216,500 deaths (1).

Multidrug-resistant S. Typhi (MDRST) is epidemiologically defined as strains resistant to any two antimicrobials in vitro even if the antimicrobials tested are known to be clinically ineffective (2). A more useful definition of MDRST is reserved for strains resistant to all three first-line antityphoidal antimicrobial agents, namely ampicillin, chloramphenicol, and trimethoprim-sulphamethoxazole (2).

Typhoid fever, caused by MDRST, has become a significant cause of morbidity and mortality over recent years. These strains have also caused outbreaks throughout the world, especially in South America, Indian subcontinent, Africa, and South-East Asia (3,4). The incidence of MDRST is reported to be as high as 60%, although there are some reports noting its decline (5-8).

With the emergence of MDRST, fluoroquinolones have gained importance for the treatment of enteric fever in recent years. There are reports of prolonged defervescence after ciprofloxacin therapy (9-12). Strains, isolated from these cases, exhibit susceptibility to ciprofloxacin in disc-diffusion testing, but minimum inhibitory concentrations (MICs) for these strains are about 10 times higher than fully-susceptible strains. This reduced susceptibility is probably the cause for poor clinical response to treatment. Isolates of S. Typhi with decreasd susceptibility to ciprofloxacin have been found to be nalidixic acid-resistant. These nalidixic acid-resistant S. Typhi (NARST) require higher concentrations of ciprofloxacin for inhibition (4,9,10).

A considerable variation has been noted in the antimicrobial susceptibility patterns among isolates of S. Typhi as suggested in various studies conducted in different geographical locations (7,11-17). Knowledge of the prevalence of S. Typhi and their antimicrobial susceptibility patterns is of utmost importance in the institution of appropriate antimicrobial therapy. Resistant Salmonellae and failure of ciprofloxacin therapy have been matters of concern in the reports of some studies conducted in central Nepal (8,18-20). Phage type is an important epidemiological marker to study the movement of organisms and their spread from one geographic locale to another. Data on the susceptibility patterns and phage type prevalence of S. Typhi isolates in eastern Nepal are lacking. The present study was, therefore, undertaken to determine the antimicrobial susceptibility patterns of local isolates of S. Typhi with special reference to their multidrug resistance and reduced susceptibility to ciprofloxacin and bacteriophage types.

MATERIALS AND METHODS

Blood samples for culture were obtained from patients who presented to the B.P. Koirala Institute of Health Sciences (BPKIHS) hospital, a tertiary-care teaching hospital in eastern Nepal, with a history of fever of variable duration from January 2000 to December 2004. Brain-heart infusion (BHI) broth, which establishes the growth of all common pathogens causing bacteraemia/septicaemia was used as a culture medium. Collection of blood, incubation, and subculture(s) onto blood agar and MacConkey agar were done as per the standard methods (21). Suspected non-lactose-fermenting colonies were further processed and identified by biochemical reactions and confirmed by group and typespecific Salmonella antisera (Murex Biotech, England) Antimicrobial susceptibility was determined by the Kirby-Bauer disc-diffusion method performed on MullerHinton agar plates against ampicillin (10 [micro]g), ceftriaxone (30 [micro]g), chloramphenicol (30 [micro]g), ciprofloxacin (5 [micro]g), co-trimoxazole (25 [micro]g), gentamicin (10 [micro]g), and nalidixic acid (30 [micro]g) (Hi Media Laboratory Ltd. …

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