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Isolation, Identification and Characterization of Salmonella Serovars from Diarrhoeic Stool Samples of Human

M. K Nesa
Department of Microbiology and Hygiene, Bangladesh Agricultural University, Mymensingh

M. S. R. Khan
Department of Microbiology and Hygiene, Bangladesh Agricultural University, Mymensingh

M. Alam
International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka

Abstract/ Executive Summary:

The present study aimed at isolation and identification of Salmonella serovars from human stool and characterization of the isolated serovars using biochemical, serological, molecular and antimicrobial sensitivity techniques. A total of 25 samples were collected of which 16% were positive to Salmonella serovars. All the culturally positive isolates fermented dextrose, maltose and mannitol with the peoduction of acid and gas but not fermented sucrose and lactose. The same isolates showed Indole and V-P tests negative but M-R test positive. All the culturally and biochemically positive Salmonella serovars showed agglutination with poly ‘O’ and poly ‘H’ antisera. The antimicrobial susceptibility testing showed that the isolated Salmonella serovars were highly sensitive to ciprofloxacin and moderately sensitive to chloramphenicol, kanamycin, cotrimoxazol and nalidixic acid. However, the positive isolates were resistant to erythromycin. The present study indicates that ciprofloxacin can be used as a first line therapy for the treatment of Salmonella gastroenteritis.

Keywords: Isolation, characterization, sensitivity, Salmonella

Location: Mymensingh.

Start Date: 01-06-2009

End Date: 31-05-2010

Program Area: Socio-economic and Policy

Commodity:

Objectives:

The present study was undertaken with the following objectives of (i) to isolate and identify Salmonella serovars from human stool, (ii) to characterize the isolated Salmonella serovars using cultural, biochemical and serological techniques and (iii) to study the antibacterial sensitivity of the isolated Salmonella serovars.

Methodology:

The present research was conducted during the period of June 2009 to May 2010 in the Bacteriology Laboratory of the Department of Microbiology and Hygiene, BAU, Mymensingh. A total of 25 diarrhoeic stool samples were collected for the study. Among the samples 9 were from BAU Diabetic Center (BDC) and the rest 16 were from Mymensingh Medical College Hospital (MMCH). The entire study was divided into two major steps. The first step included selection of sources, collection of samples, transportation to the laboratory, isolation and identification of Salmonellae on the basis of their colony morphology, staining property, motility and biochemical and serological characteristics. In the second step, the current statuses of drugs sensitivity and resistance patterns of isolated bacteria were determined. After collection, each sample was inoculated into freshly prepared Nutrient broth (NB), identified into tube properly and incubated at 37⁰C for 24 hours aerobically in bacteriological incubator. Then, a loop full of bacterial culture from incubated tubes were streaked separately into the Salmonella-Shigella agar (SSA), McConkey agar (MCA), Eosin methylene blue agar (EMBA) and Brilliant green agar (BGA) plates. The plates were examined and studied carefully for the presence of characteristic colonies of Salmonellae. Nailidixic acid (NA) medium was used to grow the organisms from the collected samples. The representative Salmonella colonies were characterized morphologically using Gram’s staining method according to the method described by Merchant and Packer (1967). For carbohydrate fermentation tests, triple sugar iron agar (TSIA) slant reaction, methyl red-Voges-Proskauer (MR-VP) and Indole reaction tests were carried out for identification of suspected Salmonella according to the methods described by Douglas et al. (1998) and OIE (2000). The carbohydrate fermentation test was performed by inoculating a loop full of NB culture of the organisms into the tubes containing different sugar media. Acid production was indicated by the color change reddish to yellow in the medium and the gas production was noted by the appearance of gas bubbles in the inverted Durham’s tube. The TSIA slant was used to detect the lactose fermenters and the saccharose and dextrose fermenters. The medium also helped to determine the ability of the organisms to produce H₂S. Pinkish slant and yellow butt or black slant and yellow butt were recorded as the positive reaction for Salmonella.

Source of Information: Bangl. J. Vet. Med. (2011). 9(1): 85 – 93

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

All culturally and biochemically positive Salmonella serovars showed agglutination with poly ‘O’ and in case of poly ‘H’ all showed positive reaction. From the antibiotic sensitivity study, it was exhibited that all isolates were highly sensitive to ciprofloxacin, kanamycin and chloramphenicol; moderately sensitive to cotrimazole and nalidixic acid; and less sensitive to cephalixin. The antibacterial resistance observed here in the isolated Salmonellae might be due to routine indiscriminate use of those antibacterial agents in field condition in study areas and/or rapid chromosomal mutation and presence of specific plasmid DNA. This provided the guideline to the veterinarians and physicians to select appropriate antibiotics to reduce economic loss through selecting the sensitive antibiotics. The development and use of antibiotic has been one of the most important steps towards controlling of infectious bacterial diseases in 21st century. However, the subsequent appearance and spread of antibiotic resistance in pathogenic organisms have made many currently available antibiotics ineffective. To successfully fight the increasing number of drug resistant and multi drug resistance bacteria, extensive knowledge of the molecular mechanisms of acquiring antibiotic resistance and updated information is required. From the present study, it could be concluded that public health awareness should be developed to reduce the incidence of Salmonellosis among the people in order to avoid food borne illness. Proper treatment should be done with strict sanitary measures.

Knowledge Management: Journal