Necrotic pharyngitis associated with Mycoplasma bovis infections in American bison (Bison bison)

Mycoplasma bovis has emerged as a significant and costly infectious disease problem in bison, generally presenting as severe, caseonecrotic pneumonia. Three diagnostic cases in which M. bovis is associated with necrotic pharyngitis in bison are described in the current study. The bacterium was isolated from lesions of the pharynx or lung of 3 American bison ( Bison bison), at 2 different locations in the upper Midwestern United States, with severe, necrotic pharyngeal abscesses. Chronic caseonecrotic inflammation typical of M. bovis infection in bovines was observed microscopically in the pharynxes of affected bison. A mixed population of bacteria was recovered from the pharyngeal lesions, and Trueperella pyogenes, a frequent secondary pathogen in ruminant respiratory disease, was consistently isolated from the affected animals. Distinctive histopathological features of the pharyngeal lesions favor causation by M. bovis, although a role for T. pyogenes in the clinical presentation cannot be excluded. Veterinarians and producers working with bison should be aware that M. bovis may be associated with pharyngitis in bison.

A curated public database for multilocus sequence typing (MLST) and analysis of Haemophilus parasuis based on an optimized typing scheme

Haemophilus parasuis causes Glässer's disease and pneumonia in swine. Serotyping is often used to classify isolates but requires reagents that are costly to produce and not standardized or widely available. Sequence-based methods, such as multilocus sequence typing (MLST), offer many advantages over serotyping. An MLST scheme was previously proposed for H. parasuis but genome sequence data only recently available reveals the primers recommended, based on sequences of related bacteria, are not optimal. Here we report modifications to enhance the original method, including primer redesign to eliminate mismatches with H. parasuis sequences and to avoid regions of high sequence heterogeneity, standardization of primer T(m)s and identification of universal PCR conditions that result in robust and reproducible amplification of all targets. The modified typing method was applied to a collection of 127 isolates from North and South America, Europe and Asia. An alignment of the concatenated sequences obtained from seven target housekeeping genes identified 278 variable nucleotide sites that define 116 unique sequence types. A comparison of the original and modified methods using a subset of 86 isolates indicates little difference in overall locus diversity, discriminatory power or in the clustering of strains within Neighbor-Joining trees. Data from the optimized MLST were used to populate a newly created and publicly available H. parasuis database. An accompanying database designed to capture provenance and epidemiological information for each isolate was also created. The modified MLST scheme is highly discriminatory but more robust, reproducible and user-friendly than the original. The MLST database provides a novel resource for investigation of H. parasuis outbreaks and for tracking strain evolution.

Bordetella bronchiseptica in a paediatric cystic fibrosis patient: possible transmission from a household cat

Bordetella bronchiseptica is a zoonotic respiratory pathogen commonly found in domesticated farm and companion animals, including dogs and cats. Here, we report isolation of B. bronchiseptica from a sputum sample of a cystic fibrosis patient recently exposed to a kitten with an acute respiratory illness. Genetic characterization of the isolate and comparison with other isolates of human or feline origin strongly suggest that the kitten was the source of infection.

Genome sequence of Haemophilus parasuis strain 29755

Haemophilus parasuis is a member of the family Pasteurellaceae and is the etiologic agent of Glässer's disease in pigs, a systemic syndrome associated with only a subset of isolates. The genetic basis for virulence and systemic spread of particular H. parasuis isolates is currently unknown. Strain 29755 is an invasive isolate that has long been used in the study of Glässer's disease. Accordingly, the genome sequence of strain 29755 is of considerable importance to investigators endeavoring to understand the molecular pathogenesis of H. parasuis. Here we describe the features of the 2,224,137 bp draft genome sequence of strain 29755 generated from 454-FLX pyrosequencing. These data comprise the first publicly available genome sequence for this bacterium.

Misidentification of Bordetella bronchiseptica as Bordetella pertussis using a newly described real-time PCR targeting the pertactin gene

Recently, a real-time PCR (RT-PCR) assay based on sequence from the gene for pertactin was proposed for identification of Bordetella pertussis. Here, it is reported that the B. pertussis pertactin gene sequence for the region that encompasses the RT-PCR probe and primers is nearly identical to that of many Bordetella bronchiseptica strains of human and avian origin. Additionally, it is demonstrated that such strains are erroneously identified as B. pertussis using the RT-PCR assay. These data suggest that the use of the assay without confirmatory testing may result in erroneous identification of a significant proportion of human isolates of B. bronchiseptica as B. pertussis.

Immune response in mice and swine to DNA vaccines derived from the Pasteurella multocida toxin gene

DNA vaccines were constructed with either a 5'-truncated or full-length, genetically detoxified toxin gene from Pasteurella multocida and two different DNA vaccine vectors, distinguished by the presence or absence of a secretion signal sequence. Optimal PMT-specific antibody responses and spleen cell secretion of interferon-gamma following immunization of mice were achieved with pMM4, the construct containing a signal sequence and encoding the entire toxin. Antibody responses were also induced in pigs immunized with pMM4 and levels increased significantly following booster injections and experimental infection with P. multocida. Significantly increased expression of interferon-gamma was detected in only a small subset of pMM4-immunized pigs. This report documents, for the first time, the ability of a DNA vaccine to elicit immune responses to the P. multocida toxin in both mice and swine.

Expression of the dermonecrotic toxin by Bordetella bronchiseptica is not necessary for predisposing to infection with toxigenic Pasteurella multocida

This experiment was designed to determine whether a Bordetella bronchiseptica mutant that does not produce dermonecrotic toxin (DNT) is still capable of predisposing pigs to infection with toxigenic Pasteurella multocida. Three groups of pigs were initially inoculated intranasally with a wild type B. bronchiseptica that produces DNT, an isogenic mutant of B. bronchiseptica that does not produce DNT, or PBS. All pigs were then challenged intranasally with a toxigenic strain of P. multocida 4 days later. P. multocida was recovered infrequently and in low numbers from pigs initially inoculated with PBS, and no turbinate atrophy was present in these pigs. P. multocida was isolated in similar numbers from the pigs initially inoculated with either the wild type or the DNT mutant of B. bronchiseptica, and turbinate atrophy of a similar magnitude was also seen in pigs from both of these groups. Thus, although the DNT has been shown to be responsible for much of the pathology seen during infection with B. bronchiseptica by itself, infection with non-DNT-producing strains can still predispose to secondary respiratory infections with P. multocida.

Genomic features of Bordetella parapertussis clades with distinct host species specificity

BACKGROUND

The respiratory pathogen Bordetella parapertussis is a valuable model in which to study the complex phenotype of host specificity because of its unique two-species host range. One subset of strains, including the sequenced representative, causes whooping cough in humans, while other strains infect only sheep. The disease process in sheep is not well understood, nor are the genetic and transcriptional differences that might provide the basis for host specificity among ovine and human strains.

RESULTS

We found 40 previously unknown genomic regions in an ovine strain of B. parapertussis using subtractive hybridization, including unique lipopolysaccharide genes. A microarray survey of the gene contents of 71 human and ovine strains revealed further differences, with 47 regions of difference distinguishing the host-restricted subgroups. In addition, sheep and human strains displayed distinct whole-genome transcript abundance profiles. We developed an animal model in which sheep were inoculated with a sheep strain, human strain, or mixture of the two. We found that the ovine strain persisted in the nasal cavity for 12 to 14 days, while the human strain colonized at lower levels and was no longer detected by 7 days post-inoculation. The ovine strain induced less granulocyte infiltration of the nasal mucosa.

CONCLUSION

Several factors may play a role in determining host range of B. parapertussis. Human- and ovine-associated strains have differences in content and sequence of genes encoding proteins that mediate host-pathogen contact, such as lipopolysaccharide and fimbriae, as well as variation in regulation of toxins, type III secretion genes, and other virulence-associated genes.

Prevalence and sequence variants of IS481 in Bordetella bronchiseptica: implications for IS481-based detection of Bordetella pertussis

We report the prevalence in Bordetella bronchiseptica of IS481, a frequent target for diagnosis of Bordetella pertussis, as approximately 5%. However, PCR amplicons of the predicted size were detectable in 78% of IS481-negative strains. Our results suggest that PCR targeting IS481 may not be sufficiently specific for reliable identification of B. pertussis.

Analytical verification of a multiplex PCR for identification of Bordetella bronchiseptica and Pasteurella multocida from swine

Bordetella bronchiseptica and Pasteurella multocida are etiologic agents of progressive atrophic rhinitis (PAR) and bronchopneumonia in swine. Only dermonecrotic toxin-producing strains of P. multocida play a role in atrophic rhinitis while both toxigenic and nontoxigenic strains have been associated with pneumonia. Monitoring and investigation of outbreaks involving these bacteria require sensitive and accurate identification and reliable determination of the toxigenic status of P. multocida isolates. In the present study, we report the development, optimization, and performance characteristics of a multiplex PCR assay for simultaneous amplification of up to three different targets, one common to all P. multocida strains, one found only in toxigenic P. multocida strains, and one common to B. bronchiseptica strains. Based on analysis of 94 P. multocida isolates (31 toxigenic) and 126 B. bronchiseptica isolates assay sensitivity is 100% for all amplicons. Evaluation of 22 isolates of other bacterial genera and species commonly found in the swine respiratory tract demonstrated a specificity of 100% for all gene targets. The limit of detection for simultaneous amplification of all targets is 1-10pg of DNA per target, corresponding to a few hundred genomes or less. Amplicon mobility in agarose gels and sequence analysis indicate the amplicons are highly stable. The data presented establish this multiplex PCR as a reliable method for identification of B. bronchiseptica and both toxigenic and nontoxigenic P. multocida that may greatly simplify investigations of swine PAR and bronchopneumonia.

Analytical verification of a PCR assay for identification of Bordetella avium

Bordetella avium is the etiologic agent of turkey coryza or bordetellosis, a respiratory disease responsible for substantial economic losses to the turkey industry. At present, identification of this bacterium relies on isolation and biochemical testing. Although a PCR for the detection of B. avium was proposed a number of years ago, lack of analytical verification precludes its use as a diagnostic tool. Furthermore, a number of details pertaining to the reaction conditions used are missing or unclear. In the present study we have identified an optimal set of PCR conditions for use with the previously described primer pair and determined the limit of detection under these conditions to be approximately 20 pg. Assay sensitivity is 100%, based on an analysis of 72 B. avium isolates from diverse geographic locations and covering a time span of at least 25 years. Evaluation of a separate group of 87 bacterial isolates from poultry, comprising both gram-positive and gram-negative commensals and pathogens representing 11 genera, demonstrated an assay specificity of 98.8%. Reproducibility is 100% using either purified genomic DNA or boiled cell lysates less than 3 days old. Sequence analysis of the B. avium PCR amplicons identified only three occasional sequence polymorphisms. These data indicate the B. avium PCR assay can provide clinically significant results.

Comparative sequence analysis of Bordetella bronchiseptica pertactin gene (prn) repeat region variants in swine vaccines and field isolates

The product of the Bordetella bronchiseptica pertactin gene, prn, has been implicated as an adhesin and a protective immunogen in swine. Recent studies demonstrate prn sequence heterogeneity in swine isolates and vaccine strains within and surrounding the region 1 amino acid repeat GGXXP(n) and the region 2 amino acid repeat PQP(n). However, only a few isolates have been evaluated. Allelic variation between vaccine strains and field isolates may affect vaccine efficacy, since region 2 is known to encode an immunodominant protective epitope. In the present study, the DNA and predicted amino acid sequences of the pertactin repeat regions from a collection of 81 recent swine field isolates and 5 vaccine strains from the United States were determined. Two region 1 variants and four region 2 variants, one of which has not been previously reported, were identified, comprising four pertactin types. Four vaccines are derived from strains with a region 1 variant identical to that found in the majority of field isolates. However, only two vaccines possess the most commonly identified sequence in region 2, while two others contain a variant found in only one other swine isolate. Ribotype analysis demonstrated that although vaccines containing the novel region 2 variant fall within the same major cluster as other common swine ribotypes, they are less closely related. No relationship was observed between pertactin type and ribotype.

Molecular and antigenic characterization of Bordetella bronchiseptica isolated from a wild southern sea otter (Enhydra lutris nereis) with severe suppurative bronchopneumonia

Bordetella bronchiseptica was isolated in pure culture from the lung, abdomen, and intestine of a wild free-ranging southern sea otter (Enhydra lutris nereis) with severe, suppurative bronchopneumonia. Immunohistochemistry, using antiserum raised to B. bronchiseptica, revealed strong positive staining of bacteria attached to bronchial ciliated epithelia as well as scattered positive staining in affected alveoli. Western blot analysis demonstrated that virulence factors, filamentous hemagglutinin, pertactin, and adenylate cyclase toxin are produced by the sea otter B. bronchiseptica isolate. Ribotype analysis using Pvu II restriction digests indicated that this isolate is most similar to strains commonly obtained in domestic dogs and cats.

Comparison of ribotyping and restriction enzyme analysis for inter- and intraspecies discrimination of Bordetella avium and Bordetella hinzii

Bordetella avium is an avian respiratory disease pathogen responsible for substantial economic losses to the turkey industry. The inability to distinguish isolates has hampered outbreak investigations and prevents a complete understanding of transmission mechanisms. Isolates of Bordetella hinzii, often referred to as B. avium-like or as Alcaligenes faecalis type II prior to 1995, have also been acquired from the respiratory tracts of diseased poultry but are not believed to be pathogenic for birds. Therefore, differentiating between B. avium and B. hinzii is of importance for veterinary diagnostic laboratories. It was recently reported that both PvuII ribotyping and HinfI/DdeI restriction endonuclease analysis (REA) show promise for distinguishing isolates of B. avium and B. hinzii. Here we compare the ability of these techniques to discern inter- and intraspecies differences. While both approaches distinguished numerous types within a species, only REA was sufficiently discriminatory for routine use as an epidemiologic tool. Both techniques clearly distinguish between B. avium and B. hinzii, although the results of ribotyping are more easily interpreted. Ribotyping and REA identified numerous, previously unrecognized B. hinzii strains from a collection of bordetella isolates, including one acquired from a rabbit. This is the first report of B. hinzii isolation from a nonhuman mammalian species. At least some of the newly recognized B. hinzii isolates have been previously reported to cause disease in poults, suggesting that the pathogenicity of this agent for poultry should be more rigorously examined.

Role of the dermonecrotic toxin of Bordetella bronchiseptica in the pathogenesis of respiratory disease in swine

Bordetella bronchiseptica is one of the etiologic agents causing atrophic rhinitis and pneumonia in swine. It produces several purported virulence factors, including the dermonecrotic toxin (DNT), which has been implicated in the turbinate atrophy seen in cases of atrophic rhinitis. The purpose of these experiments was to clarify the role of this toxin in respiratory disease by comparing the pathogenicity in swine of two isogenic dnt mutants to their virulent DNT(+) parent strains. Two separate experiments were performed, one with each of the mutant-parent pairs. One-week-old cesarean-derived, colostrum-deprived pigs were inoculated intranasally with the parent strain, the dnt mutant strain, or phosphate-buffered saline. Weekly nasal washes were performed to monitor colonization of the nasal cavity, and the pigs were euthanized 4 weeks after inoculation to determine colonization of tissues and to examine the respiratory tract for pathology. There was evidence that colonization of the upper respiratory tract, but not the lower respiratory tract, was slightly greater for the parent strains than for the dnt mutants. Moderate turbinate atrophy and bronchopneumonia were found in most pigs given the parent strains, while there was no turbinate atrophy or pneumonia in pigs challenged with the dnt mutant strains. Therefore, production of DNT by B. bronchiseptica is necessary to produce the lesions of turbinate atrophy and bronchopneumonia in pigs infected with this organism.

Prevalence of Bordetella avium infection in selected wild and domesticated birds in the eastern USA

Bordetella avium is the etiologic agent of bordetellosis, a highly contagious upper respiratory disease of young poultry. Its prevalence among domesticated turkeys is well-known, but information on prevalence of this bacterium in other birds is limited. A survey of the prevalence of B. avium in wild and domesticated birds was conducted from June 1998 to January 2000, using tracheal cultures and serology. Of 237 blood samples from 61 species, 100 individuals from 41 species had antibodies against B. avium as determined with a microtiter agglutination test. Nine isolates of B. avium were cultured from 128 tracheal samples. Ribotype analysis of seven isolates from mallards (Anas platyrhynchos), one from a wild turkey (Meleagris gallopavo), and one from a Canada goose (Branta canadensis) indicated that they represent three strains, two of which were indistinguishable from clinical isolates from domesticated turkeys. Bordetella avium is present in wild bird populations of multiple species. Transmission from free-living avian populations to domesticated poultry populations may be possible and should be examined.

Reduced virulence of a Bordetella bronchiseptica siderophore mutant in neonatal swine

One means by which Bordetella bronchiseptica scavenges iron is through production of the siderophore alcaligin. A nonrevertible alcaligin mutant derived from the virulent strain 4609, designated DBB25, was constructed by insertion of a kanamycin resistance gene into alcA, one of the genes essential for alcaligin biosynthesis. The virulence of the alcA mutant in colostrum-deprived, caesarean-delivered piglets was compared with that of the parent strain in two experiments. At 1 week of age, piglets were inoculated with phosphate-buffered saline, 4609, or DBB25. Two piglets in each group were euthanatized on day 10 postinfection. The remainder were euthanatized at 21 days postinfection. Clinical signs, including fever, coughing, and sneezing, were present in both groups. Nasal washes performed 7, 14, and 21 days postinoculation demonstrated that strain DBB25 colonized the nasal cavity but did so at levels that were significantly less than those achieved by strain 4609. Analysis of colonization based on the number of CFU per gram of tissue recovered from the turbinate, trachea, and lung also demonstrated significant differences between DBB25 and 4609, at both day 10 and day 21 postinfection. Mild to moderate turbinate atrophy was apparent in pigs inoculated with strain 4609, while turbinates of those infected with strain DBB25 developed no or mild atrophy. We conclude from these results that siderophore production by B. bronchiseptica is not essential for colonization of swine but is required for maximal virulence. B. bronchiseptica mutants with nonrevertible defects in genes required for alcaligin synthesis may be candidates for evaluation as attenuated, live vaccine strains in conventionally reared pigs.

Novel genetic and phenotypic heterogeneity in Bordetella bronchiseptica pertactin

The Bordetella bronchiseptica outer membrane protein pertactin is believed to function as an adhesin and is an important protective immunogen. Previous sequence analysis of the pertactin gene identified two regions predicted to encode amino acid repeat motifs. Recent studies have documented DNA sequence heterogeneity in both regions. The present study describes additional variants in these regions, which form the basis for six novel pertactin types. Immunoblotting demonstrated phenotypic heterogeneity in pertactin consistent with the predicted combined sizes of the repeat regions. A revised system for classifying B. bronchiseptica pertactin variants is proposed.

Restriction endonuclease analysis discriminates Bordetella bronchiseptica isolates

One hundred ninety-five Bordetella bronchiseptica isolates from 12 different host species worldwide were characterized by restriction enzyme analysis (REA). These isolates had previously been categorized into 19 PvuII ribotypes. Twenty restriction endonucleases were evaluated for use in REA. Digestion of chromosomal DNA with HinfI, followed by submarine electrophoresis in agarose gels and staining with ethidium bromide, produced DNA fragments in the 4.0- to 10-kb range, which readily discriminated B. bronchiseptica isolates, resulting in 48 fingerprint patterns. Moreover, AluI digestion of chromosomal DNA produced 39 distinct fingerprint profiles with DNA fragments ranging from 6.0 to 20.0 kb. While REA frequently provided more discriminatory power than ribotyping, there were examples where the use of ribotyping was more discriminatory than REA. Passage of selected isolates up to passage 25 did not change the REA profile. Moreover, the Bvg phase did not alter the fingerprint profile of chromosomal DNA from B. bronchiseptica strains digested with HinfI or AluI. Based on the results presented herein, the combination of REA and ribotyping should provide valuable information in understanding the molecular epidemiology of B. bronchiseptica infections.

Ribotyping and restriction endonuclease analysis reveal a novel clone of Bordetella bronchiseptica in seals

The goal of the present study was to characterize, by ribotyping and restriction endonuclease analysis (REA), 35 phocine Bordetella bronchiseptica isolates and to ascertain their relationship to one another and to isolates acquired from other host species. Thirty-four isolates were obtained in Scotland during a 10-year period encompassing the 1988 epizootic; the remaining isolate was obtained independently in Denmark. All phocine isolates had an identical Pvu II ribotype unique from the 18 ribotypes previously detected in strains from heterologous hosts. Alternative restriction enzymes, useful for subgrouping strains within Pvu II ribotypes, also failed to discriminate among isolates from seals. The exclusive occurrence of a single ribotype of B. bronchiseptica in a particular host species has not been previously observed. Similarly, REA based on either HinfI or Dde I profiles did not reveal detectable polymorphisms, although unique patterns were readily distinguished among a limited number of isolates from other host species. This is the first report demonstrating the utility of REA using frequently cutting enzymes for discrimination of B. bronchiseptica strains. These data suggest that B. bronchiseptica-induced respiratory disease in seals along the Scottish shore may be due to the circulation of a single, unique clone.

Effect of temperature modulation and bvg mutation of Bordetella bronchiseptica on adhesion, intracellular survival and cytotoxicity for swine alveolar macrophages

Bordetella bronchiseptica causes respiratory disease in swine, yet there are no studies examining the interaction of B. bronchiseptica with swine alveolar macrophages. A swine isolate of B. bronchiseptica was able to adhere to, and survive intracellularly in, swine alveolar macrophages, but the relative ability of the bacteria to accomplish these functions was dependent on its phenotypic phase and culture conditions. More bacteria were observed extracellularly as well as intracellularly by immunofluorescent staining when B. bronchiseptica was cultured at 23 degrees C as compared to 37 degrees C. However, more bacteria cultured at 37 degrees C were found surviving intracellularly after the macrophages were cultured with polymyxin B to kill extracellular bacteria. Similar results were seen in experiments performed with an isogenic Bvg(-) phase-locked mutant of B. bronchiseptica cultured at 37 or 23 degrees C, indicating that another temperature dependent mechanism in addition to bvg may play a role in adhesion and intracellular survival. B. bronchiseptica was cytotoxic for swine alveolar macrophages in the Bvg(+) phase only. The cytotoxicity of B. bronchiseptica for alveolar macrophages, and its ability to survive phagocytosis, are no doubt important to escape from immune clearance mechanisms and establish infection, and could leave the host susceptible to secondary respiratory pathogens.

Restriction enzyme analysis and ribotyping distinguish Bordetella avium and Bordetella hinzii isolates

Fifty-seven bacterial isolates previously identified as Bordetella avium or B. hinzii were characterized by restriction enzyme analysis (REA) and/or ribotyping. Twenty restriction endonucleases were evaluated for REA. Digestion of chromosomal DNA from the 42 B. avium and 15 B. hinzii isolates with HinfI produced 8 and 7 distinct fingerprint profiles, respectively. Digestion with DdeI further discriminated these Bordetella species and produced 12 fingerprint profiles for B. avium and 4 profiles of B. hinzii. In addition, B. avium isolates were clearly distinguishable from B. hinzii isolates by ribotyping with the restriction endonuclease PvuII. The ribotype patterns of these two species of Bordetella were unique when compared to previously reported ribotype patterns for B. bronchiseptica isolates. Since it was possible to discern differences among isolates within each Bordetella species by REA analysis, we suggest that REA could be used in developing a typing system based on the fingerprint profiles generated.

Optimized ribotyping protocol applied to Hungarian Bordetella bronchiseptica isolates: identification of two novel ribotypes

We reported previously that ribotype patterns generated with PvuII and a probe derived from the Escherichia coli rrnB gene could be used to differentiate isolates of Bordetella bronchiseptica. In the present study we report modifications made to the original ribotyping procedure that permit detection in the formerly characterized isolates of an additional 8 fragments with homology to rrnB. Ribotypes were redefined to include these fragments. Although this modification did not permit the detection of novel ribotypes from the previously characterized isolates, it did result in a more accurate reclassification of five of these isolates to other existing ribotypes. It was hypothesized that the additional fragments could form the basis for novel ribotypes in future analyses, and this was supported by the subsequent evaluation of 101 previously uncharacterized pig, rabbit, and dog B. bronchiseptica isolates from Hungary. A total of six different patterns were detected from this group, including two previously not identified that were designated ribotypes 17 and 18. The profile of ribotype 17 includes a novel fragment not associated with any other ribotype. A subset of the fragments constituting ribotype 18, essential for its differentiation from other ribotypes, is only detectable under the modified conditions reported here. Hungarian swine isolates are highly clonal, since 98.2% were identified as ribotype 3. Similarly, 83.7% of rabbit isolates from Hungary are also ribotype 3. Cluster analysis revealed that despite the existence of numerous ribotypes, B. bronchiseptica isolates display limited heterogeneity. The ability to detect additional ribotypes under the modified conditions described in this study strengthens the usefulness of ribotyping as an epidemiologic tool.