An Epidemiological Study of Antibiotic Resistance of Salmonella typhi and Salmonella paratyphi - A from Clinical Samples in Dhaka City

Aims: Typhoid fever is a serious bacterial disease caused by Salmonella typhi or Salmonella paratyphi. Study Design: The objectives of this study is to determine the prevalence and antibiotic resistance pattern of Salmonella typhi and Salmonella paratyphi isolated from adults and children presenting with symptoms at different hospital in Dhaka from 1 st September-31 st December 2013. Materials and Methods: The antibiotic susceptibility of 106 clinical isolates collected from blood samples was identified. Susceptibility pattern was tested by Kirby-Bauer disc diffusion method using 8 regularly used antibiotics. The patients were categorized in different 9 age groups. Data analysis was performed by using Statistical Package for Social Science (SPSS version 10.0). Results: A total of 1178 blood samples were analyzed in this study. Among which 106 showed positive result, 9% patients were ill, the causative agents- Salmonella typhi was found to be most prevalent (73.58%) followed by Salmonella paratyphi (26.42%). Result of the susceptibility test showed that the isolates were resistant to antibiotics; Nalidixic Acid and Azithromycin (79.49%) and 62(79.49%) for S. typhi isolates, 27(96.43%) and 27(96.43%) for S. paratyphi isolates respectively. Conclusion: Our study revealed high prevalence of and (100%) of MDR Salmonella isolates. This is a serious health problem in the region under study and should be prevented by some effective measure such as eating safely prepared foods and get vaccinated (Ty21a) are recommendable for the treatment of typhoid fever in this community.


INTRODUCTION
Typhoid fever is an epidemic disease in Bangladesh, Indian subcontinent; South and Central America and Africa [1]. Despite the use of newly developed antibacterial drugs, enteric fever such as typhoid and paratyphoid caused by multidrug-resistant bacterial strains are one of major health problems in Bangladesh, especially for the children [2]. On a global scale, at least 16-20 million cases of typhoid fever occur annually, resulting in approximately 600,000 deaths, found in all ages, with the highest incidence in children [3].
Given such a specificity for humans, S. typhi might be younger than the split between humans and higher primates several million years ago and possibly even as young as the expansion of anatomical modern humans from Africa approximately 50,000-100,000 years ago [4]. Preliminary results from recent studies conducted in Bangladesh by the International Centre for Diarrheal Disease Research, Bangladesh revealed an incidence of approximately 2000 per 100 000 people per year [5].
Typhoid fever also has a very high social and economic impact because of the hospitalization of patients with acute disease and the complications and loss of income attributable to the duration of the clinical illness [6].
Since all the signs and symptoms of typhoid fever are nonspecific, a definitive diagnosis of the disease depend on the clinical presentation alone is very difficult. Therefore, laboratorybased investigations are essential for supporting the diagnosis of typhoid fever. The "gold standard" for diagnosis of typhoid fever is the isolation of S. typhi from appropriate samples including blood, bone marrow aspirates, stool, urine and rose spots [7].
A study in Bangladesh reported a gradual change in resistance to ampicillin and cotrimoxazole among S. typhi populations [7]. In the same study, the rate of resistance to cotrimoxazole, ampicillin and chloramphenicol decreased from 59.6 to 5.6% of the organisms over a 3 years period [8]. For this reason, antimicrobial susceptibility test is essential to see the changing trend of antibiogram of circulating strains in the community. Therefore, we performed the present study to investigate the resistance of S. typhi and S. paratyphi samples to commonly used antibiotics in different private hospitals in Bangladesh and to determine the prevalence of typhoid fever among different age groups and sexes.

Isolation and Identification of Salmonella
This hospital-based cross sectional study was performed in Microbiology research laboratory, Primeasia University, Dhaka, Bangladesh. All samples were collected from OPD (Out patients department) and IPD (In patients department) patients of hospital having clinical symptoms of microbial infection both sexes and different age groups. Blood samples were collected from different hospital in Dhaka, during 1 st September-31 st December 2013. With Bactec technique, 5-10 ml blood for adults and 1-4 ml for children were taken and then put into a special bottle (septum of the blood culture bottle) and put in the Bactec machine for incubation at 37° for. The bacterial growth was detected during the incubation: Whenever the bacteria grow, both the machine and the computer will indicate the growth by alarm message on the computer screen [9].

Antibiotic Susceptibility of Salmonella Isolates
Muller Agar plates were inoculated with 0.5 Mc Farland standards of the isolates; antibiotic disks were placed and incubated at 37°C for 24 hrs. Zone of inhibition diameters were measured and interpreted according to the guidelines of the Clinical Laboratory Standard Institute [11].
Resistant isolates to at least one member of three different antimicrobial groups are considered as MDR [12]. The antibiotic susceptibility was performed by disc diffusion method measurement of zone of inhibition using the following antimicrobial discs [13,14].

RESULTS
During the period, total of 1178 typhoid suspected patients were enrolled, covering 722 males and 456 females. Among them, bacterial growth was positive for samples 106(9%) typhoid fever patients. Single colony were isolated from each of the 106 samples, while Salmonella typhi and Salmonella paratyphi were isolated from 78(73.58%) and 28(26.42%) of these samples. 67 male and 39 female blood specimens showed the growth of Salmonella typhi and Salmonella paratyphi.

DISCUSSION
These studies provide valuable data and monitor the status of antimicrobial resistance among typhoid patients to improve efficient empirical treatment. Increasing antimicrobial resistance has been documented globally [15]. A relation between antibiotic use and its resistance in clinical isolates had been proven in many studies. Direct quantitative relationship between the amount of antibiotic used and the frequency of resistance is still lacking [16,17]. In this study, the most affected age group for typhoid fever was 21-30yrs (33.96%) love to eat outside food and in spite of having knowledge about hygiene they can't maintain properly. greater exposure to contaminated food [18,19,20].

CONCLUSION
In this study, the most affected age group for typhoid fever was 21-30 (33.96%). At the end of the study the objectives we carried out were: To identify Salmonella typhi and Salmonella paratyphi by placing the blood samples collected from the patients. Improvement to determine the prevalence of typhoid fever among different ages and sexes. Determination of the antibiotic resistance pattern of Salmonella typhi and Salmonella paratyphi. Typhoid can easily be prevented by some effective measures eat only safely prepared foods, avoid raw meat, eggs, vegetables and fruits, drink clean water and get vaccinated (Ty21a). S. typhi and S. paratyphi showed highest sensitivity to Ceftriaxone, Ciprofloxacin, Cefixime & Levofloxacin that are the drugs of choice for the treatment of typhoid fever.