Evolutionary relationships among diverse bacteriophages and prophages: all the world's a phage

We report DNA and predicted protein sequence similarities, implying homology, among genes of double-stranded DNA (dsDNA) bacteriophages and prophages spanning a broad phylogenetic range of host bacteria. The sequence matches reported here establish genetic connections, not always direct, among the lambdoid phages of Escherichia coli, phage phiC31 of Streptomyces, phages of Mycobacterium, a previously unrecognized cryptic prophage, phiflu, in the Haemophilus influenzae genome, and two small prophage-like elements, phiRv1 and phiRv2, in the genome of Mycobacterium tuberculosis. The results imply that these phage genes, and very possibly all of the dsDNA tailed phages, share common ancestry. We propose a model for the genetic structure and dynamics of the global phage population in which all dsDNA phage genomes are mosaics with access, by horizontal exchange, to a large common genetic pool but in which access to the gene pool is not uniform for all phage.

Evaluation of a cocktail of three bacteriophages for biocontrol of Escherichia coli O157:H7

Escherichia coli O157:H7 is an endemic pathogen causing a variety of human diseases including mild diarrhea, hemorrhagic colitis, hemolytic-uremic syndrome, and thrombotic thrombocytopenic purpura. This study concerns the exploitation of bacteriophages as biocontrol agents to eliminate the pathogen E. coli O157:H7. Two distinct lytic phages (e11/2 and e4/1c) isolated against a human strain of E. coli O157:H7, a previously isolated lytic phage (pp01), and a cocktail of all three phages were evaluated for their ability to lyse the bacterium in vivo and in vitro. Phage e11/2, pp01, and the cocktail of all three virulent phages resulted in a 5-log-unit reduction of pathogen numbers in 1 h at 37 degrees C. However, bacteriophage-insensitive mutants (BIMs) emerged following the challenge. All tested BIMs had a growth rate which approximated that of the parental O157 strain, although many of these BIMs had a smaller, more coccoid cellular morphology. The frequency of BIM formation (10(-6) CFU) was similar for e11/2, pp01, and the phage cocktail, while BIMs insensitive to e4/1c occurred at the higher frequency (10(-4) CFU). In addition, BIMs commonly reverted to phage sensitivity within 50 generations. In an initial meat trial experiment, the phage cocktail completely eliminated E. coli O157:H7 from the beef meat surface in seven of nine cases. Given that the frequency of BIM formation is low (10(-6) CFU) for two of the phages, allied to the propensity of these mutants to revert to phage sensitivity, we expect that BIM formation should not hinder the use of these phages as biocontrol agents, particularly since low levels of the pathogen are typically encountered in the environment.

Genotyping male-specific RNA coliphages by hybridization with oligonucleotide probes

F-specific (F+) RNA coliphages are prevalent in sewage and other fecal wastes of humans and animals. There are four antigenically distinct serogroups of F+ RNA coliphages, and those predominating in humans (groups II and III) differ from those predominating in animals (groups I and IV). Hence, it may be possible to distinguish between human and animal wastes by serotyping F+ RNA coliphage isolates. Because serotyping is laborious and requires scarce antiserum reagents, we investigated genotyping using synthetic oligonucleotide probes as an alternative approach to distinguishing the four groups of F+ RNA coliphages. Oligoprobes I, II, III, IV, A, and B were selected to detect group I, II, III, IV, I plus II, and III plus IV phages, respectively. Methods for phage transfer from zones of lysis on a host cell lawn to candidate membrane filters and fixation of genomic nucleic acid on the membranes were optimized. The oligoprobes, which were end labeled with digoxigenin, were applied in DNA-RNA hybridization, and hybrids were observed by colorimetric, immunoenzymatic detection. Of 203 isolates of F+ RNA coliphages from environmental samples of water, wastes, and shellfish, 99.5 and 96.6% could be classified into each group by serotyping and genotyping, respectively. Probes A and B correctly identified 100% of the isolates. On the basis of these results, this method for genotyping F+ RNA coliphages appears to be practical and reliable for typing isolates in field samples.

F-specific RNA bacteriophages and sensitive host strains in faeces and wastewater of human and animal origin

Faeces of humans, pigs, cattle and chickens were investigated for the presence of somatic coliphages, F-specific bacteriophages and Escherichia coli strains sensitive to infection by F-specific phages. Attention was given to the possible effect of age and use of antibiotics on the prevalence of the FRNA phages and sensitive E. coli strains. Somatic coliphages were often detected in high numbers in all types of faeces. In contrast, FRNA phages were rarely detected in faeces from humans and cattle but more often in faeces from pigs and adult chickens. Samples from young chickens (with or without antibiotics) were consistently positive for FRNA phages (up to 3 x 10(6) pfu/g). F-specific RNA phages were found in substantial numbers (greater than 10(3) pfu/ml) in a variety of wastewaters: domestic, hospital, slaughterhouses and occasionally in 'grey water'. Their origin in wastewater was not clear. Strains from faeces usually belonged to serogroups I and IV. These types were also found in wastewater, as were group II and III strains. Serogroup II phages were abundant in wastewater of human origin but rare in faeces. Escherichia coli strains sensitive to infection by F-specific phages were common in faeces (overall 290/1081: 27%). No strains with fully depressed F-pilus synthesis were detected among the sensitive strains. It is concluded that the occurrence of F-specific RNA bacteriophages in water points to sewage pollution rather than faecal pollution; the mechanism of replication of these organisms in wastewater is not understood.

Characterization of a Shiga toxin-encoding temperate bacteriophage of Shigella sonnei

A Shiga toxin (Stx)-encoding temperate bacteriophage of Shigella sonnei strain CB7888 was investigated for its morphology, DNA similarity, host range, and lysogenization in Shigella and Escherichia coli strains. Phage 7888 formed plaques on a broad spectrum of Shigella strains belonging to different species and serotypes, including Stx-producing Shigella dysenteriae type 1. With E. coli, only strains with rough lipopolysaccharide were sensitive to this phage. The phage integrated into the genome of nontoxigenic S. sonnei and laboratory E. coli K-12 strains, which became Stx positive upon lysogenization. Moreover, phage 7888 is capable of transducing chromosomal genes in E. coli K-12. The relationships of phage 7888 with the E. coli Stx1-producing phage H-19B and the E. coli Stx2-producing phage 933W were investigated by DNA cross-hybridization of phage genomes and by nucleotide sequencing of an 8,053-bp DNA region of the phage 7888 genome flanking the stx genes. By these methods, a high similarity was found between phages 7888 and 933W. Much less similarity was found between phages H-19B and 7888. As in the other Stx phages, a regulatory region involved in Q-dependent expression is found upstream of stxA and stxB (stx gene) in phage 7888. The morphology of phage 7888 was similar to that of phage 933W, which shows a hexagonal head and a short tail. Our findings demonstrate that stx genes are naturally transferable and are expressed in strains of S. sonnei, which points to the continuous evolution of human-pathogenic Shigella by horizontal gene transfer.

Morphological, host range, and genetic characterization of two coliphages

Two coliphages, AR1 and LG1, were characterized based on their morphological, host range, and genetic properties. Transmission electron microscopy showed that both phages belonged to the Myoviridae; phage particles of LG1 were smaller than those of AR1 and had an isometric head 68 nm in diameter and a complex contractile tail 111 nm in length. Transmission electron micrographs of AR1 showed phage particles consisting of an elongated isometric head of 103 by 74 nm and a complex contractile tail 116 nm in length. Both phages were extensively tested on many strains of Escherichia coli and other enterobacteria. The results showed that both phages could infect many serotypes of E. coli. Among the enterobacteria, Proteus mirabilis, Shigella dysenteriae, and two Salmonella strains were lysed by the phages. The genetic material of AR1 and LG1 was characterized. Phage LG1 had a genome size of 49.5 kb compared to 150 kb for AR1. Restriction endonuclease analysis showed that several restriction enzymes could degrade DNA from both phages. The morphological, genome size, and restriction endonuclease similarities between AR1 and phage T4 were striking. Southern hybridizations showed that AR1 and T4 are genetically related. The wide host ranges of phages AR1 and LG1 suggest that they may be useful as biocontrol, therapeutic, or diagnostic agents to control and detect the prevalence of E. coli in animals and food.

Still Something to Discover: Novel Insights intoEscherichia coli Phage Diversity and Taxonomy

The aim of this study was to gain further insight into the diversity of Escherichia coli phagesfollowed by enhanced work on taxonomic issues in that field. Therefore, we present the genomiccharacterization and taxonomic classification of 50 bacteriophages against E. coli isolated fromvarious sources, such as manure or sewage. All phages were examined for their host range on a setof different E. coli strains, originating, e.g., from human diagnostic laboratories or poultry farms.Transmission electron microscopy revealed a diversity of morphotypes (70% Myo-, 22% Sipho-, and8% Podoviruses), and genome sequencing resulted in genomes sizes from ~44 to ~370 kb.Annotation and comparison with databases showed similarities in particular to T4- and T5-likephages, but also to less-known groups. Though various phages against E. coli are already describedin literature and databases, we still isolated phages that showed no or only few similarities to otherphages, namely phages Goslar, PTXU04, and KWBSE43-6. Genome-based phylogeny andclassification of the newly isolated phages using VICTOR resulted in the proposal of new generaand led to an enhanced taxonomic classification of E. coli phages.

Shiga Toxin-Producing Escherichia coli O157, England and Wales, 1983-2012

Although incidence remained constant, outbreaks from contaminated meat and milk declined and those from petting farms and schools and nurseries increased.

We evaluated clinical Shiga toxin–producing Escherichia coli O157 infections in England and Wales during 1983–2012 to describe changes in microbiological and surveillance methods. A strain replacement event was captured; phage type (PT) 2 decreased to account for just 3% of cases by 2012, whereas PT8 and PT21/28 strains concurrently emerged, constituting almost two thirds of cases by 2012. Despite interventions to control and reduce transmission, incidence remained constant. However, sources of infection changed over time; outbreaks caused by contaminated meat and milk declined, suggesting that interventions aimed at reducing meat cross-contamination were effective. Petting farm and school and nursery outbreaks increased, suggesting the emergence of other modes of transmission and potentially contributing to the sustained incidence over time. Studies assessing interventions and consideration of policies and guidance should be undertaken to reduce Shiga toxin–producing E. coli O157 infections in England and Wales in line with the latest epidemiologic findings.

Molecular detection and genotyping of male-specific coliphages by reverse transcription-PCR and reverse line blot hybridization

In recent years, there has been increased interest in the use of male-specific or F+ coliphages as indicators of microbial inputs to source waters. Sero- or genotyping of these coliphages can also be used for microbial source tracking (MST). Among the male-specific coliphages, the F+ RNA (FRNA) viruses are well studied, while little is known about the F+ DNA (FDNA) viruses. We have developed a reverse line blot hybridization (RLB) assay which allows for the simultaneous detection and genotyping of both FRNA as well as FDNA coliphages. These assays included a novel generic duplex reverse transcription-PCR (RT-PCR) assay for FRNA viruses as well as a generic PCR for FDNA viruses. The RT-PCR assays were validated by using 190 field and prototype strains. Subsequent DNA sequencing and phylogenetic analyses of RT-PCR products revealed the classification of six different FRNA clusters, including the well-established subgroups I through IV, and three different FDNA clusters, including one (CH) not previously described. Within the leviviruses, a potentially new subgroup (called JS) including strains having more than 40% nucleotide sequence diversity with the known levivirus subgroups (MS2 and GA) was identified. We designed subgroup-specific oligonucleotides that were able to genotype all nine (six FRNA, three FDNA) different clusters. Application of the method to a panel of 351 enriched phage samples from animal feces and wastewater, including known prototype strains (MS2, GA, Q beta, M11, FI, and SP for FRNA and M13, f1, and fd for FDNA), resulted in successful genotyping of 348 (99%) of the samples. In summary, we developed a novel method for standardized genotyping of F+ coliphages as a useful tool for large-scale MST studies.

Characterization of a ViI-like phage specific to Escherichia coli O157:H7

Phage vB_EcoM_CBA120 (CBA120), isolated against Escherichia coli O157:H7 from a cattle feedlot, is morphologically very similar to the classic phage ViI of Salmonella enterica serovar Typhi. Until recently, little was known genetically or physiologically about the ViI-like phages, and none targeting E. coli have been described in the literature. The genome of CBA120 has been fully sequenced and is highly similar to those of both ViI and the Shigella phage AG3. The core set of structural and replication-related proteins of CBA120 are homologous to those from T-even phages, but generally are more closely related to those from T4-like phages of Vibrio, Aeromonas and cyanobacteria than those of the Enterobacteriaceae. The baseplate and method of adhesion to the host are, however, very different from those of either T4 or the cyanophages. None of the outer baseplate proteins are conserved. Instead of T4's long and short tail fibers, CBA120, like ViI, encodes tail spikes related to those normally seen on podoviruses. The 158 kb genome, like that of T4, is circularly permuted and terminally redundant, but unlike T4 CBA120 does not substitute hmdCyt for cytosine in its DNA. However, in contrast to other coliphages, CBA120 and related coliphages we have isolated cannot incorporate 3H-thymidine (3H-dThd) into their DNA. Protein sequence comparisons cluster the putative "thymidylate synthase" of CBA120, ViI and AG3 much more closely with those of Delftia phage φW-14, Bacillus subtilis phage SPO1, and Pseudomonas phage YuA, all known to produce and incorporate hydroxymethyluracil (hmdUra).

Bacteriophage distribution in human faeces: continuous survey of healthy subjects and patients with internal and leukaemic diseases

In order to elucidate the ecological role of bacteriophages in the human intestine, we analysed the numbers of coliphages and of coliphage strains present in faecal samples collected from healthy individuals and from patients with certain intestinal diseases. The isolated phages were grouped according to their serological properties. The samples with low phage titres, observed in both healthy subjects and patients, contained mainly temperate phages (many were related to phi 80 and lambda), and those with higher titres, observed in patients, contained virulent phages. From successive surveys of coliphages and their host, Escherichia coli, in faecal samples of each subject, it was concluded that temperate phages are maintained in the human intestine through spontaneous induction of lysogenic bacteria. Qualitative and quantitative differences existed between phages isolated from faecal samples from healthy subjects and from patients. Simultaneous changes in the distribution patterns of coliphages and of the clinical symptoms were observed in a continuous survey of a leukaemic patient in a protective environmental ward.

F+ RNA coliphage typing for microbial source tracking in surface waters

AIMS

The utility of coliphages to detect and track faecal pollution was evaluated using South Carolina surface waters that exceeded State faecal coliform standards.

METHODS AND RESULTS

Coliphages were isolated from 117 surface water samples by single agar layer (SAL) and enrichment presence/absence (EP/A) methods. Confirmed F+ RNA coliphages were typed for microbial source tracking using a library-independent approach. Concentrations of somatic coliphages using 37 and 44.5 degrees C incubation temperatures were found to be significantly different and the higher temperature may be more specific for faecal contamination. The EP/A technique detected coliphages infecting Escherichia coli Famp in 38 (66%) of the 58 surface water samples negative for F+ coliphages by the SAL method. However, coliphages isolated by EP/A were found to be less representative of coliphage diversity within a sample. Among the 2939 coliphage isolates tested from surface water and known source samples, 813 (28%) were found to be F+ RNA. The majority (94%) of surface water F+ RNA coliphage isolates typed as group I. Group II and/or III viruses were identified from 14 surface water stations, the majority of which were downstream of wastewater discharges. These sites were likely contaminated by human-source faecal pollution.

CONCLUSIONS

The results suggest that faecal contamination in surface waters can be detected and source identifications aided by coliphage analyses.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study supports the premise that coliphage typing can provide useful, but not absolute, information to distinguish human from animal sources of faecal pollution. Furthermore, the comparison of coliphage isolation methods detailed in this study should provide valuable information to those wishing to incorporate coliphage detection into water quality assessments.

Characterization of coliphage PR772 and evaluation of its use for virus filter performance testing

Virus filtration is a key clearance unit operation in the manufacture of recombinant protein, monoclonal antibody, and plasma-derived biopharmaceuticals. Recently, a consensus has developed among filter manufacturers and end users about the desirability of a common nomenclature and a standardized test for classifying and identifying virus-retentive filters. The Parenteral Drug Association virus filter task force has chosen PR772 as the model bacteriophage to standardize nomenclature for large-pore-size virus-retentive filters (filters designed to retain viruses larger than 50 to 60 nm in size). Previously, the coliphage PR772 (Tectiviridae family) has been used in some filtration studies as a surrogate for mammalian viruses of around 50 to 60 nm. In this report, we describe specific properties of PR772 critical to the support of its use for the standardization of virus filters. The complete genomic sequence of virulent phage PR772 was determined. Its genome contains 14,946 bp with an overall G+C content of 48.3 mol%, and 32 open reading frames of at least 40 codons. Comparison of the PR772 nucleotide sequence with the genome of Tectiviridae family prototype phage PRD1 revealed 97.2% identity at the DNA level. By dynamic light-scattering analysis, its hydrodynamic diameter was measured as 82 +/- 6 nm, consistent with use in testing large-virus-retentive filters. Finally, dynamic light-scattering analysis of PR772 preparations purified on CsCl gradients showed that the phage preparations are largely monodispersed. In summary, PR772 appears to be an appropriate model bacteriophage for standardization of nomenclature for larger-pore-size virus-retentive filters.

The diversity of coliphages and coliforms in horse feces reveals a complex pattern of ecological interactions

The diversity of coliphages and indigenous coliform strains (ICSs) simultaneously present in horse feces was investigated by culture-based and molecular methods. The richness of coliforms (as estimated by the Chao1 method) is about 1,000 individual ICSs distinguishable by genomic fingerprinting present in a single sample of feces. This unexpectedly high value indicates that some factor limits the competition of coliform bacteria in the horse gut microbial system. In contrast, the diversity of phages active against any selected ICS is generally limited to one to three viral genotypes present in the sample. The sensitivities of different ICSs to simultaneously present coliphages overlap only slightly; the phages isolated from the same sample on different ICSs are usually unrelated. As a result, the titers of phages in fecal extract as determined for different Escherichia coli strains and ICSs may differ by several orders of magnitude. Summarizing all the data, we propose that coliphage infection may provide a selection pressure that maintains the high level of coliform diversity, restricting the possibility of a few best competitors outgrowing other ICSs. We also observed high-magnitude temporal variations of coliphage titers as determined using an E. coli C600 test culture in the same animal during a 16-day period of monitoring. No correlation with total coliform count was observed. These results are in good agreement with our hypothesis.

Distribution of ribonucleic acid coliphages in south and east Asia

We investigated the distribution of ribonucleic acid (RNA) coliphages in the Philippines, Singapore, Indonesia, India, and Thailand by collecting sewage samples from domestic drainage in November 1976. Of the 221 samples collected from domestic drainage, 50 contained RNA phages (52 strains). By serological analysis, 46 of the 52 strains were found to belong to group III. It can thus be said that the most prevalent RNA phages in Southeast Asia (at least, in the Philippines, Singapore, and Indonesia) were group III phages. Investigations of sewage samples collected from domestic drainage in Japan indicate that the most prevalent RNA phages in mainland Japan (north of Kyushu) are group II phages, whereas group III phages are predominant in the southern part of Japan (south of Amamiohshima Island). We therefore propose a borderline between Kyushu and Amamiohshima Island for the geographical distribution of RNA coliphages in the domestic drainage of South and East Asia. Moreover, one strain (ID2) was inactivated to some extent with the antisera of four groups of RNA phages. This is thought to be significant from the evolutionary viewpoint.

Genomic sequencing and biological characteristics of a novel Escherichia coli bacteriophage 9g, a putative representative of a new Siphoviridae genus

Bacteriophage 9g was isolated from horse feces using Escherichia coli C600 as a host strain. Phage 9g has a slightly elongated capsid 62 × 76 nm in diameter and a non-contractile tail about 185 nm long. The complete genome sequence of this bacteriophage consists of 56,703 bp encoding 70 predicted open reading frames. The closest relative of phage 9g is phage PhiJL001 infecting marine alpha-proteobacterium associated with Ircinia strobilina sponge, sharing with phage 9g 51% of amino acid identity in the main capsid protein sequence. The DNA of 9g is resistant to most restriction endonucleases tested, indicating the presence of hypermodified bases. The gene cluster encoding a biosynthesis pathway similar to biosynthesis of the unusual nucleoside queuosine was detected in the phage 9g genome. The genomic map organization is somewhat similar to the typical temperate phage gene layout but no integrase gene was detected. Phage 9g efficiently forms stable associations with its host that continues to produce the phage over multiple passages, but the phage can be easily eliminated via viricide treatment indicating that no true lysogens are formed. Since the sequence, genomic organization and biological properties of bacteriophage 9g are clearly distinct from other known Enterobacteriaceae phages, we propose to consider it as the representative of a novel genus of the Siphoviridae family.

Epidemiologic evaluation of multiple alternate microbial water quality monitoring indicators at three California beaches

INTRODUCTION

Advances in molecular methods provide new opportunities for directly measuring pathogens or host-associated markers of fecal pollution instead of relying on fecal indicator bacteria (FIB) alone for beach water quality monitoring. Adoption of new indicators depends on identifying relationships between either the presence or concentration of the indicators and illness among swimmers. Here we present results from three epidemiologic studies in which a broad range of bacterial and viral indicators of fecal contamination were measured simultaneously by either culture or molecular methods along with Enterococcus to assess whether they provide better health risk prediction than current microbial indicators of recreational water quality.

METHODS

We conducted prospective cohort studies at three California beaches -- Avalon Bay (Avalon), Doheny State Beach (Doheny), Surfrider State Beach (Malibu) -- during the summers of 2007, 2008 and 2009. The studies enrolled 10,785 swimmers across the beaches and recorded each swimmer's water exposure. Water and sand samples were collected several times per day at multiple locations at each beach and analyzed for up to 41 target indicators using 67 different methodologies. Interviewers contacted participants by phone 10-14 days later and recorded symptoms of gastrointestinal illness occurring after their beach visit. Regression models were used to evaluate the association between water quality indicators and gastrointestinal illness among swimmers at each beach.

RESULTS

F+ coliphage (measured using EPA Method 1602) exhibited a stronger association with GI illness than did EPA Method 1600 at the two beaches where it was measured, while a molecular method, F+ RNA Coliphage Genotype II, was the only indicator significantly associated with GI illness at Malibu. MRSA, a known pathogen, had the strongest association with GI illness of any microbe measured at Avalon. There were two methods targeting human-associated fecal anaerobic bacteria that were more strongly associated with GI illness than EPA Method 1600, but only at Avalon. No indicator combinations consistently had a higher odds ratio than EPA Method 1600, but one composite indicator, based on the number of pathogens detected at a beach, was significantly associated with gastrointestinal illness at both Avalon and Doheny when freshwater flow was high.

DISCUSSION

While EPA Method1600 performed adequately at two beaches based on its consistency of association with gastrointestinal illness and the precision of its estimated associations, F+ coliphage measured by EPA Method 1602 had a stronger association with GI illness under high risk conditions at the two beaches where it was measured. One indicator, F+ Coliphage Genotype II was the only indicator significantly associated with GI illness at Malibu. Several indicators, particularly those targeting human associated bacteria, exhibited relationships with GI illness that were equal to or greater than that of EPA Method 1600 at Avalon, which has a focused human fecal source. Our results suggest that site-specific conditions at each beach determine which indicator or indicators best predict GI illness.

Distribution of ribonucleic acid coliphages in raw sewage from treatment plants in Japan

To determine the transmission cycle of ribonucleic acid (RNA) coliphages in their natural habitats, we investigated the distribution patterns of RNA phages in raw sewage collected from treatment plants in various localities in Japan. Most of the sewage samples contained group II and III phages. Samples from treatment plants in Sapporo, Tokyo, and Toyama contained appreciable amounts of group I phages in addition to the group II and III phages. As a whole, raw sewage from treatment plants in Japan contained RNA phages of the three groups in the ratio 1:2:5, group I/II/III. Based on the distribution patterns of RNA phages in sewage from domestic drainage in Japan proper (group II/III, 3:1), in animal feces and sewage from slaughter houses (mostly group I), and in human feces (group II/III, 1:1), it can be reasonably said that group I phages tend to be introduced from animal sources and group II and III phages tend to be introduced from human sources. Raw sewage from treatment plants in Japan consists mainly of human feces, sewage from domestic drainage, and industrial wastewater, and, in part, from slaughter houses. In fact, sewage from slaughter houses together with that from human sources flowed into the treatment plants of Tokyo as far as we could confirm.

Phage types and genotypes of shiga toxin-producing Escherichia coli O157:H7 isolates from humans and animals in spain: identification and characterization of two predominating phage types (PT2 and PT8)

Phage typing and DNA macrorestriction fragment analysis by pulsed-field electrophoresis (PFGE) were used for the epidemiological subtyping of a collection of Shiga toxin-producing Escherichia coli (STEC) O157:H7 strains isolated in Spain between 1980 and 1999. Phage typing distinguished a total of 18 phage types among 171 strains isolated from different sources (67 humans, 82 bovines, 12 ovines, and 10 beef products). However, five phage types, phage type 2 (PT2; 42 strains), PT8 (33 strains), PT14 (14 strains), PT21/28 (11 strains), and PT54 (16 strains), accounted for 68% of the study isolates. PT2 and PT8 were the most frequently found among strains from both humans (51%) and bovines (46%). Interestingly, we detected a significant association between PT2 and PT14 and the presence of acute pathologies. A group of 108 of the 171 strains were analyzed by PFGE, and 53 distinct XbaI macrorestriction patterns were identified, with 38 strains exhibiting unique PFGE patterns. In contrast, phage typing identified 15 different phage types. A total of 66 phage type-PFGE subtype combinations were identified among the 108 strains. PFGE subtyping differentiated between unrelated strains that exhibited the same phage type. The most common phage type-PFGE pattern combinations were PT2-PFGE type 1 (1 human and 11 bovine strains), PT8-PFGE type 8 (2 human, 6 bovine, and 1 beef product strains), PT2-PFGE subtype 4A (1 human, 3 bovine, and 1 beef product strains). Nine (29%) of 31 human strains showed phage type-PFGE pattern combinations that were detected among the bovine strains included in this study, and 26 (38%) of 68 bovine strains produced phage type-PFGE pattern combinations observed among human strains included in this study, confirming that cattle are a major reservoir of strains pathogenic for humans. PT2 and PT8 strains formed two groups which differed from each other in their motilities, stx genotypes, PFGE patterns, and the severity of the illnesses that they caused.