**4. Antibiotic resistance** *Salmonella*

The first reports on antibiotic resistant *Salmonella* had been indicated since 1960s and describe mainly case with monoresistance strain (Helmuth, 2000). In the late 1980s, the appearance multiple resistances against ampicillin, chloramphenicol, streptomycin, sulfonamides and tetracycline were found in serovar *Thyphimurium* definitive type 104 (DT 104) (Montville & Matthews, 2005). The main mechanism of bacteria exhibit resistance to antimicrobial agents can be due to many factors including drug inactivation, reduced drug accumulation, alteration of metabolic pathway and target site (Barbosa & Levy, 2000; Schwarz & Chaslus-Dancla, 2001). Much of the resistance to penicillins and cephalosporins by *Salmonella* spp. is attributable to the acquired ability of the strains to produce β-lactamase that can degrade the chemical structure of the antimicrobial agents (Bush, 2003).

In recent years, the prevalence of multidrug resistant *Salmonella* in foods has been reported in many parts of the world. Several clinical treatment failures with fluoroquinolones (such as ciprofloxacin) in cases of *S. typhi* showed in Europe, Asia, and Africa (Butt et al., 2003; Nkemngu et al., 2005). Shirakawa et al. (2006) claims that the resistance to nalidixic acid and decreased susceptibility to fluoroquinolone in the *S. enterica* serovar *Typhi* isolated in Katmandu, Nepal, in 2003 were completely correlated to the mutation at codon 83 of gyrA. Most antimicrobial-resistant *Salmonella* infections are acquired from eating contaminated foods of animal origin. During 2000-2006 in Taiwan, it was found that 30.5% of the raw chicken meat was contaminated with multidrug resistant *S. enterica* serovar *Schwarzengrund* (Chen et al., 2011). Among the 88 *Salmonella* isolated from 300 meat products (raw beef, chicken meat and street foods) in Kuala Lumpur, the highest resistance was to tetracycline (73.8%), followed by sulfonamide (63.6%), streptomycin (57.9%), nalidixic acid (44.3%), trimethoprim sulfamethoxazole (19.3%), ampicillin (17.0%), chloramphenicol (10.2%) (Thong & Modarressi, 2011). The most antimicrobial resistance *S. enteritidis* isolates from South of Brazil reported by de Oliveir et al. (2005) was found in poultry related samples, where all strains were resistant to at least one antimicrobial agent.

The prevalence of extraintestinal *salmonella* infections caused by antibiotic resistant *Salmonella* spp. in several geographic areas of the world is increasing. Pokharel et al. (2006) demonstrated a 5% prevalence of multidrug resistance among *S. enterica* at a tertiary care hospital in Kathmandu, Nepal, with a higher rate of multidrug resistance among *S. paratyphi A* (7%) compared to *S. typhi* (3%). Rotimi et al. (2008) reported the serious problem of drug resistance in *Salmonella* spp. in Kuwait and United Arab Emirates that the non-typhoidal *Salmonella* spp. isolates from fecal samples of patients had 5-fold rise in resistant to cefotaxime and ceftriaxone compared with reported earlier.
