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1.  Genetic Evidence for the Involvement of the S-Layer Protein Gene sap and the Sporulation Genes spo0A, spo0B, and spo0F in Phage AP50c Infection of Bacillus anthracis 
Journal of Bacteriology  2014;196(6):1143-1154.
In order to better characterize the Bacillus anthracis typing phage AP50c, we designed a genetic screen to identify its bacterial receptor. Insertions of the transposon mariner or targeted deletions of the structural gene for the S-layer protein Sap and the sporulation genes spo0A, spo0B, and spo0F in B. anthracis Sterne resulted in phage resistance with concomitant defects in phage adsorption and infectivity. Electron microscopy of bacteria incubated with AP50c revealed phage particles associated with the surface of bacilli of the Sterne strain but not with the surfaces of Δsap, Δspo0A, Δspo0B, or Δspo0F mutants. The amount of Sap in the S layer of each of the spo0 mutant strains was substantially reduced compared to that of the parent strain, and incubation of AP50c with purified recombinant Sap led to a substantial reduction in phage activity. Phylogenetic analysis based on whole-genome sequences of B. cereus sensu lato strains revealed several closely related B. cereus and B. thuringiensis strains that carry sap genes with very high similarities to the sap gene of B. anthracis. Complementation of the Δsap mutant in trans with the wild-type B. anthracis sap or the sap gene from either of two different B. cereus strains that are sensitive to AP50c infection restored phage sensitivity, and electron microscopy confirmed attachment of phage particles to the surface of each of the complemented strains. Based on these data, we postulate that Sap is involved in AP50c infectivity, most likely acting as the phage receptor, and that the spo0 genes may regulate synthesis of Sap and/or formation of the S layer.
PMCID: PMC3957716  PMID: 24363347
4.  Whole genome sequencing and comparative genomic analyses of two Vibrio cholerae O139 Bengal-specific Podoviruses to other N4-like phages reveal extensive genetic diversity 
Virology Journal  2013;10:165.
Vibrio cholerae O139 Bengal is the only serogroup other than O1 implicated in cholera epidemics. We describe the isolation and characterization of an O139 serogroup-specific phage, vB_VchP_VchO139-I (ϕVchO139-I) that has similar host range and virion morphology as phage vB_VchP_JA1 (ϕJA1) described previously. We aimed at a complete molecular characterization of both phages and elucidation of their genetic and structural differences and assessment of their genetic relatedness to the N4-like phage group.
Host-range analysis and plaque morphology screening were done for both ϕJA1 and ϕVchO139-I. Both phage genomes were sequenced by a 454 and Sanger hybrid approach. Genomes were annotated and protein homologies were determined by Blast and HHPred. Restriction profiles, PFGE patterns and data on the physical genome structure were acquired and phylogenetic analyses were performed.
The host specificity of ϕJA1 has been attributed to the unique capsular O-antigen produced by O139 strains. Plaque morphologies of the two phages were different; ϕVchO139-I produced a larger halo around the plaques than ϕJA1. Restriction profiles of ϕJA1 and ϕVchO139-I genomes were also different. The genomes of ϕJA1 and ϕVchO139-I consisted of linear double-stranded DNA of 71,252 and 70,938 base pairs. The presence of direct terminal repeats of around 1974 base pairs was demonstrated. Whole genome comparison revealed single nucleotide polymorphisms, small insertions/deletions and differences in gene content. Both genomes had 79 predicted protein encoding sequences, of which only 59 were identical between the two closely related phages. They also encoded one tRNA-Arg gene, an intein within the large terminase gene, and four homing endonuclease genes. Whole genome phylogenetic analyses of ϕJA1 and ϕVchO139-I against other sequenced N4-like phages delineate three novel subgroups or clades within this phage family.
The closely related phages feature significant genetic differences, in spite of being morphologically identical. The phage morphology, genetic organization, genomic content and large terminase protein based phylogeny support the placement of these two phages in the Podoviridae family, more specifically within the N4-like phage group. The physical genome structure of ϕJA1 could be demonstrated experimentally. Our data pave the way for potential use of ϕJA1 and ϕVchO139-I in Vibrio cholerae typing and control.
PMCID: PMC3670811  PMID: 23714204
Vibrio cholerae O139; N4-like virus; Genome comparison; Terminal repeats; Intein; Phylogenetic relationship
5.  Genomic Comparison of Escherichia coli O104:H4 Isolates from 2009 and 2011 Reveals Plasmid, and Prophage Heterogeneity, Including Shiga Toxin Encoding Phage stx2 
PLoS ONE  2012;7(11):e48228.
In May of 2011, an enteroaggregative Escherichia coli O104:H4 strain that had acquired a Shiga toxin 2-converting phage caused a large outbreak of bloody diarrhea in Europe which was notable for its high prevalence of hemolytic uremic syndrome cases. Several studies have described the genomic inventory and phylogenies of strains associated with the outbreak and a collection of historical E. coli O104:H4 isolates using draft genome assemblies. We present the complete, closed genome sequences of an isolate from the 2011 outbreak (2011C–3493) and two isolates from cases of bloody diarrhea that occurred in the Republic of Georgia in 2009 (2009EL–2050 and 2009EL–2071). Comparative genome analysis indicates that, while the Georgian strains are the nearest neighbors to the 2011 outbreak isolates sequenced to date, structural and nucleotide-level differences are evident in the Stx2 phage genomes, the mer/tet antibiotic resistance island, and in the prophage and plasmid profiles of the strains, including a previously undescribed plasmid with homology to the pMT virulence plasmid of Yersinia pestis. In addition, multiphenotype analysis showed that 2009EL–2071 possessed higher resistance to polymyxin and membrane-disrupting agents. Finally, we show evidence by electron microscopy of the presence of a common phage morphotype among the European and Georgian strains and a second phage morphotype among the Georgian strains. The presence of at least two stx2 phage genotypes in host genetic backgrounds that may derive from a recent common ancestor of the 2011 outbreak isolates indicates that the emergence of stx2 phage-containing E. coli O104:H4 strains probably occurred more than once, or that the current outbreak isolates may be the result of a recent transfer of a new stx2 phage element into a pre-existing stx2-positive genetic background.
PMCID: PMC3486847  PMID: 23133618
6.  Development of a high throughput assay for indirectly measuring phage growth using the OmniLogTM system 
Bacteriophage  2012;2(3):159-167.
The conventional and most accepted method of measuring the lytic activity of a phage against its bacterial host is the plaque assay. This method is laborious, time consuming and expensive, especially in high throughput analyses where multiple phage-bacterial interactions are required to be monitored simultaneously. It can also vary considerably with the experimenter and by the growth and plating conditions. Alternatively, the lytic activity can be measured indirectly by following the decrease in optical density of the bacterial cultures owing to lysis. Here we describe an automated, high throughput, indirect liquid lysis assay to evaluate phage growth using the OmniLogTM system. The OmniLogTM system uses redox chemistry, employing cell respiration as a universal reporter. During active growth of bacteria, cellular respiration reduces a tetrazolium dye and produces a color change that is measured in an automated fashion. On the other hand, successful phage infection and subsequent growth of the phage in its host bacterium results in reduced bacterial growth and respiration and a concomitant reduction in color. Here we show that microtiter plate wells inoculated with Bacillus anthracis and phage show decreased or no growth, compared with the wells containing bacteria only or phage resistant bacteria plus phage. Also, we show differences in the kinetics of bacterial growth and the timing of appearance of phage resistant bacteria in the presence of individual phages or a cocktail of B. anthracis specific phages. The results of these experiments indicate that the OmniLogTM system could be used reliably for indirectly measuring phage growth in high throughput host range and phage and antibiotics combination studies.
PMCID: PMC3530525  PMID: 23275867
Bacillus anthracis; OmniLogTM; bacteriophage; in vitro lytic assay; phage
7.  Sexual Practice and Perception of HIV/AIDS Amongst Men who have Sex with Men in Kolkata 
Background and Objectives:
Men who have Sex with Men (MSM) are a vulnerable population and need special attention in the fight against the global pandemic of HIV/AIDS. A study was conducted in an MSM clinic to find out to their varied socio-demographic characteristics, their knowledge and attitude towards HIV/AIDS, and its association with their different sexual practices.
Materials and Methods:
Descriptive, cross sectional study conducted in an MSM clinic in central Kolkata.
A total of 108 MSM were studied over a period of six months. A majority (25%) were students, followed by drivers (22.2%), with mean age being 22.8 years. About 13.9% of them were illiterate and 30.6% of them married. A majority (75%) of the clients were initiated to first sexual act during adolescence. Most (44%) of them had indulged in sexual acts with two/three partners in the past one month. The most common form of sexual act was receptive anal sex (83.3%). The commonest reasons for indulging into such sexual acts with men were increased pleasure to have sex with men and increased sexual urge (38.9% and 27.8%) while 19.4% performed such acts in an intoxicated state. Only 22.2% ever used condom in the last one month during sexual acts. Their knowledge and positive attitude towards HIV/AIDS increased significantly with increase in literacy status (P less than 0.01). Only 36 (33.3%) knew about HIV transmission through anal route while only 35.2% knew the correct method to use condom. Favorable sexual practices like using a condom or having fewer partners was more among the literates than the illiterates (P less than 0.05). Alarmingly 44.4% felt that one should have sex without a condom if his sex partner was extremely attractive, 88.9% felt that using a condom was not necessary if his partner was clean and hygienic, 69.4% felt that anal sex is for fun, so no condom is required while 43.5% felt getting HIV was a matter of bad luck.
Proper IEC to promote condom use and promotion of safe sexual practice among MSM is the need of the hour.
PMCID: PMC2800899  PMID: 20049297
Anal sex; HIV; MSM; sex partner; sexual practice
9.  Bacteriophage Therapy Rescues Mice Bacteremic from a Clinical Isolate of Vancomycin-Resistant Enterococcus faecium  
Infection and Immunity  2002;70(1):204-210.
Colonization of the gastrointestinal tract with vancomycin-resistant Enterococcus faecium (VRE) has become endemic in many hospitals and nursing homes in the United States. Such colonization predisposes the individual to VRE bacteremia and/or endocarditis, and immunocompromised patients are at particular risk for these conditions. The emergence of antibiotic-resistant bacterial strains requires the exploration of alternative antibacterial therapies, which led our group to study the ability of bacterial viruses (bacteriophages, or phages) to rescue mice with VRE bacteremia. The phage strain used in this study has lytic activity against a wide range of clinical isolates of VRE. One of these VRE strains was used to induce bacteremia in mice by intraperitoneal (i.p.) injection of 109 CFU. The resulting bacteremia was fatal within 48 h. A single i.p. injection of 3 × 108 PFU of the phage strain, administered 45 min after the bacterial challenge, was sufficient to rescue 100% of the animals. Even when treatment was delayed to the point where all animals were moribund, approximately 50% of them were rescued by a single injection of this phage preparation. The ability of this phage to rescue bacteremic mice was demonstrated to be due to the functional capabilities of the phage and not to a nonspecific immune effect. The rescue of bacteremic mice could be effected only by phage strains able to grow in vitro on the bacterial host used to infect the animals, and when such strains are heat inactivated they lose their ability to rescue the infected mice.
PMCID: PMC127648  PMID: 11748184
10.  Molecular Basis for Antigenic Variation of a Protective Strain-Specific Antigen of Ehrlichia risticii 
Infection and Immunity  1998;66(8):3682-3688.
Ehrlichia risticii, the causative agent of Potomac horse fever, has recently been isolated from many vaccinated horses with typical clinical signs of the disease. The heterogeneity of the E. risticii isolates obtained from the vaccinated horses necessitates the identification of the molecular basis of strain variations to elucidate the vaccine failure and to aid in the development of an efficient vaccine against this disease. As an attempt, two major cross-reacting surface antigen genes of 50- and 85-kDa antigens, present separately in strains 25-D (isolated in 1984) and 90-12 (isolated in 1990 from a vaccinated horse), respectively, were cloned and sequenced. A comparative sequence analysis revealed differences and similarities between these two antigens with strain-specific sizes (SSA). The 2.5- and 1.6-kb genes coding for the 85- and 50-kDa proteins, respectively, contained many different tandem repeats. The identical repeat motifs were more frequent in the middle of both genes, but the numbers and positions of the repeats were altogether different in the genes. Many of these direct repeats of both genes had exact sequence homology and coded for the same amino acids. The homology of the 5′- and 3′-flanking regions of the two genes was greater than that of the regions in the central part of the genes. A comparative analysis of the deduced amino acid sequences of these two antigen genes indicated eight common domains, which were designated identical domains. Although the sequence homologies of these identical domains were the same, the positions of the domains in their respective strains were completely different. This finding might be one of the bases of antigenic variation between the strains. In addition, there were a few unique regions in both antigen genes where no sequence homology existed. These specific regions were designated unique domains. The 50-kDa protein had two such unique domains, and the 85-kDa protein had six such unique domains. The presence of such unique domains contributed to the large size variation of these SSA. The cross-reactivity of recombinant proteins confirmed the presence of conserved epitopes between these two antigens. The SSA have been determined to be apparent protective antigens of E. risticii.
PMCID: PMC108402  PMID: 9673249
11.  Association of Deficiency in Antibody Response to Vaccine and Heterogeneity of Ehrlichia risticii Strains with Potomac Horse Fever Vaccine Failure in Horses 
Journal of Clinical Microbiology  1998;36(2):506-512.
Ehrlichia risticii is the causative agent of Potomac horse fever (PHF), which continues to be an important disease of horses. Commercial inactivated whole-cell vaccines are regularly used for immunization of horses against the disease. However, PHF is occurring in large numbers of horses in spite of vaccination. In a limited study, 43 confirmed cases of PHF occurred between the 1994 and 1996 seasons; of these, 38 (89%) were in horses that had been vaccinated for the respective season, thereby clearly indicating vaccine failure. A field study of horses vaccinated with two PHF vaccines indicated a poor antibody response, as determined by immunofluorescence assay (IFA) titers. In a majority of horses, the final antibody titer ranged between 40 and 1,280, in spite of repeated vaccinations. None of the vaccinated horses developed in vitro neutralizing antibody in their sera. Similarly, one horse experimentally vaccinated three times with one of the vaccines showed a poor antibody response, with final IFA titers between 80 and 160. The horse did not develop in vitro neutralizing antibody or antibody against the 50/85-kDa strain-specific antigen (SSA), which is the protective antigen of the original strain, 25-D, and the variant strain of our laboratory, strain 90-12. Upon challenge infection with the 90-12 strain, the horse showed clinical signs of the disease. The horse developed neutralizing antibody and antibody to the 50/85-kDa SSA following the infection. Studies of the new E. risticii isolates from the field cases indicated that they were heterogeneous among themselves and showed differences from the 25-D and 90-12 strains as determined by IFA reactivity pattern, DNA amplification finger printing profile, and in vitro neutralization activity. Most importantly, the molecular sizes of the SSA of these isolates varied, ranging from 48 to 85 kDa. These studies suggest that the deficiency in the antibody response to the PHF vaccines and the heterogeneity of E. risticii isolates may be associated with the vaccine failure.
PMCID: PMC104568  PMID: 9466767

Results 1-11 (11)