Antimicrobial susceptibility and pulsed - Field Gel Electrophoretic analysis of Salmonella in a tertiary hospital in northern Malaysia

Abstract

Background and aims: Salmonella infections remain a major public health problem in developing countries. The occurrence of infections caused by antimicrobial-resistant Salmonella has been on the rise complicating the available therapeutic options. The study aimed to determine the antibiograms and genotypes of prevalent Salmonella serotypes. Methods: A retrospective study involving 80 stool and extra-intestinal Salmonella strains collected over a 18-month period (January 2005-June 2006) from a tertiary hospital in Penang, Malaysia was conducted. Isolates were examined for resistance to 14 antimicrobial drugs and the clonality of the strains was determined by PFGE. Results: Twenty-one serotypes were identified, the most common being S. enteritidis (42.5%) followed by S. corvallis (11.25%) and S. braenderup (11.25%). S. enteritidis was significantly more common amongst the extra-intestinal isolates compared to stool isolates (74.2% versus 22.4%, p< 0.0001). Overall, the highest resistance was observed for tetracycline (66.3%), sulphonamides (56.3%), streptomycin (32.5%), trimethoprim (28.8%) and nalidixic acid (27.5%). Amongst the 31 invasive extra-intestinal isolates, resistance towards therapeutically relevant antibiotics was as follows: co-trimoxazole (38.7%), ampicillin (29%) and ceftriaxone (3.2%). Although there was no detectable resistance towards chloramphenicol and ciprofloxacin, 29% strains showed nalidixic acid resistance. About 41% of the 80 isolates were multidrug-resistant. PFGE subtyped the 78 Salmonella isolates to 33 distinct XbaI-pulsotypes. Isolates within the serotypes S. enteritidis, S. corvallis, S. branderup and S. fasta were more homogeneous while S. typhi and S. weltervden were genetically more diverse. Conclusions: The high percentage of multidrug-resistant Salmonella strains is worrying and is of public health concern. PFGE was a useful and discriminative method for assessing the genetic diversity of Salmonellae. © 2011 King Saud Bin Abdulaziz University for Health Sciences.