Bacteriophage typing of Salmonella weltevreden

Salmonella weltevreden has been found to be one of the commonest Salmonella serotypes isolated from diverse sources in India and has also been isolated in a number of other countries. A phage typing scheme was developed for this serotype using a set of six typing phages. These phages had been selected out of 146 phage strains isolated and purified from stool samples of man, laboratory animals and other animals, sewage and surface water sources, and the lytic mutants of temperate phages from S. weltevreden.The phage typing scheme was applied systematically to type the 946 strains from India isolated during 1958–1974 and 148 strains originating from Australia, Burma, England, Gan Island, Holland, Hong Kong, Malaysia, New Zealand, Papua New Guinea, The Philippines, Thailand, The United States and Vietnam during 1953–1971. The scheme was particularly studied to evaluate its utility in mapping the epidemiologically related strains from various sources.The S. weltevreden strains could be classified into ten phage types. Phage types 2 and 7 were found exclusively amongst Indian strains, type 6 from Vietnam and type 8 from Burma, Thailand and Vietnam. Phage types were found to be stable and consistent with the independent epidemiological data available.     

Host specificity of Salmonella weltevreden typing phages

The host range of the six S. weltevreden typing phages was studied on 1469 strains belonging to 37 different Salmonella serotypes. In addition to S. weltevreden, only S. nchanga, S. give, S. lexington and S. anatum, all belonging to O group E₁, showed varying degrees of susceptibility to the action of some of the typing phages.Typing phage VI lysed only one strain other than S. weltevreden. All serotypes tested other than S. weltevreden were resistant to phages III and IV even at 1000 times the routine test dilution. Thus, typing phages III and IV were specific for S. weltevreden. The sensitivity patterns of S. weltevreden typing phages were not found to bear much correlation with either somatic of flagellar antigens of Salmonellae.     

A new scheme for phage typing Salmonella bareilly and characterization of typing phages

A new phage typing scheme using wild bacteriophages isolated from sewage for phage typing Salmonella bareilly is described. Six hundred and thirty-seven strains of Salm. bareilly could be separated into 11 different phage types using five wild phages. Overall typability was 94˙5%. These phages belonged to two different morphotypes, A1 and B1, and showed varying host range.     

A new scheme for phage typing Salmonella bareilly and characterization of typing phages

A new phage typing scheme using wild bacteriophages isolated from sewage for phage typing Salmonella bareilly is described. Six hundred and thirty-seven strains of Salm. bareilly could be separated into 11 different phage types using five wild phages. Overall typability was 94.5%. These phages belonged to two different morphotypes. A1 and B1, and showed varying host range.     

Plaque morphology and antigenic relationship of the Salmonella weltevreden typing phages

The plaque morphology and antigenic relationship of the six typing phages of Salmonella weltevreden were studied. Under identical conditions of plating, the phages could be classified into three groups based on plaque morphology. Neutralization tests with anti-phage sera showed that typing phages phi I and phi II were antigenically similar. Phages phi III, phi IV and phi VI also showed antigenic similarity. Typing phage phi V was antigenically distinct from all other phages. Thus the phages could be classified into three groups on the basis of both plaque morphology on their respective indicator strains and velocities of neutralization by homologous/heterologous anti-sera.     

A new phage typing scheme forProteus mirabilis andProteus vulgaris strains

A new bacteriophage typing set, composed of 22 phages, was established as a tool for differentiation ofProteus strains. All the phages were tailed and included 4 morphological types (A1, A2, B1 and C1). They were classified into the familiesMyoviridae, Siphoviridae andPodoviridae. From the set, 19 phages had double-stranded DNA and 3 were single-stranded DNA phages.     

Development of a sequence typing scheme for differentiation of Salmonella Enteritidis strains

A DNA sequence typing scheme based on the caiC and SEN0629 loci was developed for differentiation of Salmonella Enteritidis strains and validated using a diverse collection of 102 isolates representing 38 phage types from different sources, year of isolation, geographical locations and epidemiological backgrounds. caiC encodes a probable crotonobetaine/carnitine-CoA ligase, and SEN0629 is a pseudogene. Our system allowed for discrimination of 16 sequence types (STs) among the 102 isolates analysed and intraphage type differentiation. Our findings also suggested that the stability of phage typing may be adversely affected by the occurrence of phage type conversion events. During a confirmatory phage typing analysis performed by a reference laboratory, 13 of 31 S. Enteritidis strains representing nine phage types were assigned phage types that differed from the ones originally determined by the same reference laboratory. It is possible that this phenomenon passes largely unrecognized in reference laboratories performing routine phage typing analyses. Our results demonstrate that phage typing is an unstable system displaying limited reproducibility and that the two-loci sequence typing scheme is highly discriminatory, stable, truly portable and has the potential to become the new gold standard for epidemiological typing of S .?Enteritidis strains.     

Heterogeneity in expression of lipopolysaccharide by strains of Salmonella enterica serotype Typhimurium definitive phage type 104 and related phage types

AIMS: To investigate lipopolysaccharide (LPS) expression in Salmonella enterica serotype Typhimurium definitive phage type 104 (Salmonella Typhimurium DT104) and related phage types. METHODS AND RESULTS: Isolates were examined for the expression of LPS by SDS-PAGE and silver staining and subtyped by Pulsed Field Gel Electrophoresis (PFGE). The 100 isolates expressed one of two LPS profiles designated A (72%) and B (28%). LPS profiling was able to discriminate between isolates of identical PFGE type. Among 10 groups of outbreak isolates examined, each group was of a single LPS profile: A, 8/10 and B, 2/10. All 10 outbreaks were identical by PFGE analysis. CONCLUSIONS: Isolates of Salmonella Typhimurium DT104 and related phage types expressed one of two distinct LPS profiles. The two LPS profiles appear similar but shifted and in phase with one another, suggesting that the heterogeneity is due to changes in the LPS core region rather than among the repeating oligosaccharide units of the long-chain LPS. SIGNIFICANCE AND IMPACT OF THE SUTDY: LPS profiling provides a useful adjunct to PFGE and other molecular methods for the subtyping of this group of bacteria in epidemiological investigations.     

Expression of lipopolysaccharide by phage types of Salmonella enteritidis

Examination of 44 type strains of Salmonella enteritidis for the ability to express long-chain lipopolysaccharide showed that strains belonging to phage types (PTs) 7, 23 and 30 were rough variants, a phenotype correlating with avirulence for BALB/c mice. Strains of Salm. enteritidis belonging to PTs 23 and 30 were thought to originate from smooth strains associated with poultry.     

Virulence studies of Salmonella enteritidis phage types

Salmonella enteritidis phage types (PTs) 8, 13a and 24 could be distinguished by their virulence for BALB/c mice, their plasmid content and plasmid fingerprint. Virulent strains expressed long-chain lipopolysaccharide and carried a 38 MDa plasmid indistinguishable from that in Salm. enteritidis PT 4. Avirulent strains were smooth but did not carry the 38 MDa plasmid. Possession of antibiotic resistance factors by some strains of Salm. enteritidis PT 24 did not contribute to the virulence of their host strains.     

Complex typing of Salmonella typhimurium hospital strains

A salmonellosis outbreak, caused by S. typhimurium, was investigated with the use of some microbiological and molecular-biological methods of typing. This investigation revealed that the outbreak was caused by the "outbreak" electrotype of the multi-resistant variant of the infective agent, found to have several plasmidovars. The possibilities and limitations of typing by sensitivity to antibiotics and plasmid DNA profile were shown. These methods of intraspecific typing were regarded as methods making it possible to establish the heterogeneity of S. typhimurium with the use of intraclonal markers.     

Bacteriophage types represented by lactose-fermenting Salmonella agona strains

Bacteriophage typing was performed on 1911 S. agona, lactose-fermenting strains. These strains were isolated from hospitalised newborns and neonates patients. Out of 1911 strains 98.8% were typable by means of phage set prepared for strains differentiation of Salmonella agona showing typical biochemical properties. It was shown that in 16 provinces from which the strains were obtained in 1983-1985 type V (49.5%) and type XI (25.4%) prevailed. Subtypes VA and VB were distinguished within type V. Altogether 20.3% of strains were classified as belonging to these subtypes. Their lytic reaction was weaker with phages 3, 4, and 9 with the characteristic range of phage type V strains. Among tested strains types I, XIII, and XVI were also represented composing 2, 6, 0, 9, and 0.3% of total number of strains respectively. 1.5% of strains were nontypable and 0.2% showed lytic reactions different from that included in up to now used scheme of typing. It can be concluded that lactose-fermenting S. agona strains show susceptibility to lowered number of phages than typical for Salmonella species strains. It seems that differentiation of this atypical biochemical variant of S. agona with, the use of phage set used up to now may be also usefull in practice as it is the case in respect to strains with typical biochemical properties.     

Differentiation of Shigella strains by plasmid profile analysis, serotyping and phage typing

Ninety-one Shigella flexneri and 29 Shigella sonnei strains isolated during 1994 from sporadic cases of shigellosis and healthy carriers were analyzed for plasmid profile in order to compare the discriminating ability of this method with that of serotyping and phage typing. Our study revealed 10 plasmid profiles (PP) among S. sonnei strains. A total of 26 out of 29 (89%) S. sonnei isolates could be placed into two phage types (type 1 and 20) comprising four PP for phage type 1 and seven PP for type 20, respectively. Twenty-three different PP were identified among S. flexneri strains. Each serotype was associated with a specific predominant plasmid profile, except serotype 2a. This serotype, the most frequently isolated in Romania, was still rather homogeneous: 33 out of 39 isolates belonged to phage type 125, 27 of which could be placed into two related PP (F10 and F17). Comparison of plasmid patterns of epidemiologically independent S. flexneri serotype 2a isolates with those exhibited by 45 serotype 2a isolates associated to six independent outbreaks revealed the same homogeneity. Thirty-eight strains, representing 4 of 6 outbreaks, had F10 and F17 plasmid patterns. The discrimination indices (D) for plasmid profile analysis alone (D = 0.890) and for the combination of serotyping and phage typing (D = 0.841) indicate that both typing systems have a nearly similar ability of discriminating among S. flexneri strains. By combining the results of the three typing methods, a total of 42 types are distinguished and the D value is 0.942. Our data suggest that plasmid profile analysis can complement phenotyping methods resulting in a degree of discrimination that cannot be achieved by either system alone.     

Salmonella serotype typhimurium phage typing. A critical evaluation

Of 12,930 Salmonella serotype typhimurium strains, phage typed during 1985-1988, 45.68% were "nontypable" by Anderson's set; the percent of typable strains decreased from 54.17 in 1986 to 30.54 in 1988. Of 90 phage patterns of sensitivity, 22 were currently encountered. Phage types 1, 18 and 104 were most frequent to strain of both human and non-human origin. In food generating S. typhimurium outbreaks, phage types 1 and 36 were prevalent. Except lysotypes 198 and 95, isolated from "single cases" in man only, all other phage types were common in man and animals, too. Introducing other typing methods to serotype typhimurium "nontypable" strains (by Anderson's set) was considered necessary for epidemiological purposes.