Sirajul Islam Khan

Distribution of Plesiomonas shigelloides in various components of pond ecosystems in Dhaka, Bangladesh.

Plesiomonas shigelloides is considered to be a waterborne agent of human gastroenteritis. An ecological study was carried out in five ponds in Dhaka city over a period of one year to elucidate the distribution and seasonality of this organism in various components of pond ecosystems. Samples were collected from hydrophytes, water, phytoplankton and sediment every 15 days over 12 months and cultured for P. shigelloides. P. shigelloides was isolated from a total of 120 samples including 25 (20.8%), 16 (13.3%), 22 (18.3%) and 35 (29.2%) of hydrophytes, water, phytoplankton and sediment samples, respectively. Distinct seasonal patterns of isolation of P. shigelloides were observed in the four components with two distinct peaks. The highest peaks were observed in hydrophytes and water samples in May and in phytoplankton and sediment in November. P. shigelloides was isolated from all components from all ponds during the study period. These results suggest that P. shigelloides is an autochthonous member in the freshwater pond ecosystems in Dhaka, Bangladesh.

Occurrence and distribution of culturable Vibrio cholerae 01 in aquatic environments of Bangladesh

Cholera epidemics occur twice a year in Bangladesh during which Vibrio cholerae 01 can be isolated from the aquatic environment. The reservoirs or sites of survival and multiplication of the bacteria between epidemics remain obscure. An investigation was carried out over 12 months to investigate the occurrence and distribution of Vibrio cholerae 01 in various components of 5 ponds in Dhaka. Samples were collected bimonthly with a total of 600 samples which included surface water, plants, phytoplankton, zooplankton and sediment and cultured for Vibrio cholerae 01 following an enrichment technique. Identification was carried out by following standard procedures. The highest isolation was from water (2.5%), followed by plants (1.67%) and phytoplankton (1.67%). The lowest and highest pH and salinity were recorded in pond 1 and 5, respectively. A total of 9 V. cholerae 01 biotype E1 Tor and serotype Inaba were isolated from water, plants, phytoplankton, zooplankton and sediment samples. This study demonstrated...

Faecal pollution of freshwater environments in Bangladesh

The sanitary quality of any water source is conventionally measured by estimating the concentration of faecal coliform bacteria. An investigation was carried out over 12 months to determine the faecal pollution of 5 ponds in and around Dhaka city from May 1988 to April 1989. The results showed that four of the 5 studied ponds, were heavily polluted by faecal matter. These data suggested that these ponds are potential sources of health hazards which is important from a public health point of view.

Prevalence and distribution of different diarrhoeagenic Escherichia coli virulotypes in major water bodies in Bangladesh.

Escherichia coli, a prominent waterborne pathogen, causes a variety of gastrointestinal and extraintestinal infections that depend on virulence determinants. To monitor natural aquatic systems for virulence-associated genes of E. coli, multiplex PCR was used in a survey covering 46 major natural water bodies in Bangladesh. DNA was extracted directly from water samples as well as from pre-enriched and enriched cultures during three successive seasons and assessed for E. coli virulotype distribution. From the five virulotypes, genes from the enterotoxigenic (ETEC), enteropathogenic (EPEC), and enterohaemorrhagic (EHEC) virulotypes were detected consistently, but genes from the enteroinvasive (EIEC) and enteroaggregative (EAEC) virulotypes were traced only occasionally. ETEC was the most prevalent virulotype, followed by EPEC. However, EIEC and EAEC virulotypes could not be detected in winter or the rainy season, respectively. Specific regional distribution patterns of different E. coli virulotypes and their temporal fluctuations were identified. These observations may assist with assessing seasonal risk and identifying vulnerable areas of the country prone to E. coli-associated outbreaks.

The emerging strains of Shigella dysenteriae type 2 in bangladesh are clonal

A total of 113 strains of Shigella dysenteriae type 2 isolated from patients attending the Dhaka diarrhoea treatment centre of ICDDR,B: Centre for Health and Population Research during the period 1999-2004 were studied. Serotype of the isolates was confirmed using commercially available antisera. Except for arabinose fermentation, all the strains had similar biochemical reactions. More than 60% of the strains were sensitive to commonly used antibiotics; only 6% (n=7) of the strains were resistant to nalidixic acid, and none of the strains were resistant to mecillinam and ciprofloxacin. All strains were invasive as demonstrated by the presence of a 140 MDa plasmid, ial, sen and ipaH genes, Congo Red absorption ability and by the Sereny test performed on representative strains. Plasmid patterns were heterogeneous but more than 50% of strains were confined to a single pattern. All strains possessed a 1.6 MDa plasmid and 87% of the strains contained a 4 MDa plasmid. Middle-range plasmids (90 MDa to 30 MDa) present in 36% of the strains were not associated with antibiotic resistance. All the strains were clustered within a single type with four subtypes by pulsed-field gel electrophoresis while ribotyping patterns of all the strains were identical.

Virulence Properties of Rough and Smooth Strains of Vibrio cholerae O1

A comparative study was carried out to see the differences in pathogenicity of rough and smooth strains. A total of 10 strains including 5 each of rough and smooth strains of Vibrio cholerae O1 were tested and found positive for toxin production by enzyme‐linked immunosorbent assay (ELISA) in Richardsons and AKI media. All the smooth and rough strains, except one, showed a titre of 1:10 and 1:100 in Richardsons and AKI media, respectively. Both types of strains produced enterotoxin in rabbit ileal loop (RIL). The differences in multiplication abilities of smooth and rough strains in RIL were statistically significant (P<0.05). However, these differences in multiplying abilities did not influence the adherence potential or enterotoxin production as there was no significant difference (P>0.05) between these properties. This study demonstrated that the rough strains are equally pathogenic and as important as smooth strains.

Microbiology of pond ecosystems in rural Bangladesh: its public health implications

In rural Bangladesh various components of four ponds, including aquatic plants, snails, water, oysters, and sediment were studied for faecal contamination for three years, from July 1994, to June 1997. Faecal coliform counts ranged from 2.80–5.45, 2.95–5.64, 1.49–2.05, 2.51–4.60 and 1.30–3.15 log10cfu/gm or ml in plant, snail, water, oyster and sediment samples respectively during the study period. Snail and sediment samples showed highest and lowest counts, respectively. All components of the studied ponds included in this study yielded coliform counts higher than the accepted limit for potability and domestic use, as recommended by the WHO. Therefore these ponds have a high potential for transmission of diarrhoeal and other water‐borne diseases.

Serological Cross-Reactivity of Environmental Isolates of Enterobacter, Escherichia, Stenotrophomonas, and Aerococcus with Shigella spp.-Specific Antisera

Using protocols designed for the isolation of Shigella from environmental freshwater samples from different regions of Bangladesh, 11 bacterial strains giving rise to Shigella-like colonies on selective agar plates and showing serological cross-reaction with Shigella-specific antisera were isolated. Phylogenetic analyses revealed that three of the isolates were most closely related to Escherichia coli, four to Enterobacter sp., two to Stenotrophomonas, and two isolates belonged to the Gram-positive genus Aerococcus. The isolates cross-reacted with six different serotypes of Shigella and were, in each case, highly type-specific. Two of the isolates belonging to the Enterobacter and Escherichia genera gave extremely strong cross-reactivity with Shigella dysenteriae and Shigella boydii antisera, respectively. The Aerococcus isolates gave relatively weak but significant cross-reactions with S. dysenteriae. Western blot analysis revealed that a number of antigens from the isolates cross-react with Shigella spp. The results indicate that important Shigella spp. surface antigens are shared by a number of environmental bacteria, which have implications for the use of serological methods in attempts for the detection and recovery of Shigella from aquatic environments.

Evidence of interspecies O antigen gene cluster transfer between Shigella boydii 15 and Escherichia fergusonii.

An environmental bacterial isolate, Iso10, previously found to show serological cross‐reactivity with type‐specific Shigella boydii 15 antisera was subjected to further molecular and serological analyses that revealed interspecies transfer of the O antigen gene cluster. Western blot analysis of Iso10 cell surface extracts and purified lipopolysaccharides demonstrated strong cross‐reactivity with S. boydii 15‐specific monovalent antisera and a lipopolysaccharide gel banding profile similar to that of S. boydii 15. Biochemical and phylogenetic analyses identified the Iso10 isolate as Escherichia fergusonii. O antigen gene cluster analyses of Iso10, carried out by restriction fragment length analysis of the amplified ~10‐kb O antigen‐encoding gene cluster, revealed a profile highly similar to that of S. boydii 15, confirming the presence of the S. boydii 15 somatic antigen in Iso10. To the best of our knowledge, this is the first report of interspecies transfer of O antigen‐encoding genes between S. boydii and E. fergusonii, and it has implications for our understanding of the role of lateral gene transfer in the emergence of novel Shigella serotypes.

Organization of the CTX Prophage in Environmental Isolates of Vibrio mimicus

The organization of the CTX prophage in environmental strains of Vibrio mimicus was investigated. Sixteen hundred non‐sucrose fermenting vibrios were examined for ctx gene by hybridization. Out of 1,600 isolates, 6 V. mimicus isolates contained ctxA gene. The organization of CTX prophage was determined by RFLP using ctxA probe. The CTX prophage integrated at a single site in V. mimicus genome which was present as a single copy flanked by at least a single RS element. Ribotype pattern revealed that a particular clone of V. mimicus acquired the CTXφ in the aquatic environment. This study demonstrated that V. mimicus could act as a reservoir of CTXφ in the aquatic environment.