Clones of Streptococcus pneumoniae isolated from nasopharyngeal carriage and invasive disease in young children in central Tennessee

To determine whether nasopharyngeal carriage isolates of Streptococcus pneumoniae are of the same genetic background as isolates that caused invasive disease in one community, IS1167 and boxA genotypes were obtained for 182 pneumococcal isolates from children living in central Tennessee. The isolates represented 70 combined IS1167-boxA genotypes. The genotypic diversity of the invasive isolates was significantly less than that of the total population (P=.003). Most of the carriage isolates belonged to genotypes unique to carriage, whereas most of the invasive isolates belonged to genotypes common to carriage and disease (P=.02). Monte Carlo simulations showed a greater number of genotypes unique to carriage than can be explained by chance (P<.05 in all cases). Two genotypes were identified by multilocus sequence typing as members of globally disseminated clones, and one such genotype that was strictly carriage in this sample caused disease in other studies. Thus, clones can have different propensities for carriage and invasion.     

Molecular characterization of Lyme disease spirochetes (Borrelia burgdorferi sensu lato) isolated in Taiwan by restriction fragment length polymorphism analysis of 5S(rrf)-23S(rrl) intergenic spacer amplicons

We analyzed the 5S (rrf)-23S (rrl) intergenic spacer amplicon gene of Lyme disease spirochetes (Borrelia burgdorferi sensu lato) for the first time in Taiwan. The genetic identities of these Taiwan isolates (TWKM1-7) were clarified by comparing their restriction fragment length polymorphism patterns and sequence similarities of the polymerase chain reaction-amplified intergenic spacer amplicon genes with 3 major genospecies of Lyme disease spirochetes. Amplified-spacer DNAs were purified further and subjected to the cleavage by nuclease DraI or MseI. Differential fragment patterns in relation to different genospecies of Lyme disease spirochetes were observed among tested Borrelia isolates, and all of these Taiwan isolates were closely related to the genospecies of B. burgdorferi sensu stricto. The phylogenetic analysis also revealed that the sequence similarity of polymerase chain reaction-amplified spacer genes of these Taiwan isolates was highly homogeneous (95.7-100%) within the genospecies of B. burgdorferi sensu stricto and can be distinguished clearly from other genospecies of Lyme disease spirochetes with a 4.1% sequence divergence. Based on the differential fragment patterns and sequence similarity among these Taiwan isolates, the genetic identity of these Taiwan isolates should be classified into the genospecies of B. burgdorferi sensu stricto.     

Limited sequence heterogeneity among biologically distinct human immunodeficiency virus type 1 isolates from individuals involved in a clustered infectious outbreak.

Human immunodeficiency virus type 1 isolates were obtained over a 3-year period from blood, brain, and lung of three patients in a clustered infectious outbreak. This included a blood donor who was initially asymptomatic but subsequently developed AIDS-related complex and two neonatal transfusion recipients who developed AIDS. Isolates from brain and lung replicated to greater than 30-fold higher levels in primary monocyte cultures than did those from blood; no growth differences on primary lymphocytes were observed. Thirteen clones were obtained from seven isolates, and env sequences were determined. The predicted amino acid sequences among these clones differed by only 0.01% but differed by 15-27% when compared to previously sequenced isolates from other patients. The level of envelope amino acid sequence divergence noted among these isolates is considerably lower than that previously reported for other human immunodeficiency virus isolates. No differences in the envelope unique to lung or brain isolates compared to blood isolates were noted. This study provides evidence that mutations in the envelope may not be necessary for disease progression and that other portions of the viral genome may contribute to cell-specific tropism.     

2010年福建省手足口病患者中柯萨奇B5病毒的序列分析

摘要：目的 了解福建省手足口病患者中CVB5（Coxsackie virus B5）病毒的变异及进化特征。方法 采集2010年福建省手足口病例呼吸道标本,经RD细胞分离肠道病毒。病毒分离上清用于RNA提取并经RT-PCR法鉴定病毒型别。对鉴定为其他肠道病毒（非EV71或CVA16）的病毒,扩增病毒完整VP1区,扩增产物经克隆、筛选后测序。应用Mega软件对病毒VP1序列进变异比较和种系进化分析。结果 从2010年福建省手足口病患者中扩增得到6份完整的VP1区序列,序列比对证实有4份CVB5病毒。序列差异比较表明,分离自福建省的CVB5病毒一致性程度较高,在种系进化上处于独立的进化分支,而与国内其他省份或其他国家的CVB5病毒分离株比较则有较大差异。结论 2010年福建省手足口病患者中存在CVB5病毒的感染,病毒与既往其它省份分离株有较大差异,提示CVB5病毒在福建省具有独特的传播链。     

Clonal analysis of Hemophilus influenzae isolated from children from Pakistan with lower respiratory tract infections

The clonal diversity of 105 Hemophilus isolates from the blood of children with lower respiratory tract infection in Pakistan was analyzed. Ten isolates were identified as H. parainfluenzae and 95 as H. influenzae. Of the H. influenzae isolates, 61 (64%) were serotype b and 34 (36%) were nontypable; 95% of the type b isolates were members of a single clonal group (as defined by multilocus enzyme electrophoresis, SDS-PAGE outer membrane protein profile, and biotype). This clone is rarely observed among type b strains recovered from patients with invasive type b disease in the USA or Europe. The nontypable isolates in Islamabad also were clonally restricted: 9 clonal groups were found among 34 isolates, with just 5 clonal groups accounting for most (82%) of the strains. Children infected with type b strains were hospitalized more often than those with nontypable H. influenzae disease (64% vs. 41%, P = .06), but no other clinical or demographic features distinguished children infected by type b and nontypable strains.     

Rosette formation in Plasmodium falciparum isolates and anti-rosette activity of sera from Gambians with cerebral or uncomplicated malaria.

The ability of Plasmodium falciparum-infected red blood cells (RBC) to form spontaneous erythrocyte rosettes was studied in 130 fresh isolates from Gambian children with cerebral or uncomplicated malaria from August to November 1990. All isolates (24 of 24) from patients with cerebral malaria formed rosettes, but only 61 of 106 isolates from children with uncomplicated malaria formed rosettes. The mean rate of rosette formation in isolates from children with cerebral malaria (28.3%) was significantly greater than that in isolates from children with uncomplicated malaria (8.5%). Giant rosettes were more frequently formed in isolates from patients with cerebral malaria than in those from patients with uncomplicated malaria. Sera of children with cerebral disease generally lacked anti-rosette activity, while many sera from children with uncomplicated malaria showed strong anti-rosette activity when tested against the patients' ow parasites. Some sera that were devoid of autologous rosette-disrupting activity were able to disrupt rosettes formed in other isolates, indicating the presence of different rosette formation mechanisms. Forty percent (6 of 15) of the sera from patients with cerebral malaria caused microagglutination of the patients' own uninfected and infected RBC, while only 10% (3 of 31) of sera from children with uncomplicated disease caused microagglutination. The ability of infected RBC to bind to melanoma cells grown in vitro did not differ between patients with cerebral or uncomplicated malaria. The results of this study, taken in conjunction with our previous findings, establish a strong association between rosette formation in P. falciparum-infected RBC and cerebral malaria.     

Hospital water as a source of Mycobacterium avium complex isolates in respiratory specimens

The clinical significance of recovery of Mycobacterium avium complex (MAC) organisms from respiratory specimens is poorly understood. One hundred sixty-one respiratory MAC isolates from 131 patients at Grady Memorial Hospital (Atlanta) and 13 MAC isolates from the hospital's hot water system were examined. Of the 131 patients, 35 (27%) had MAC disease, and 96 (73%) did not; 94 (72%) were human immunodeficiency virus infected. Ten different clusters were identified by pulsed-field gel electrophoresis. Patients without MAC disease were significantly more likely to have clustered isolates than were patients with MAC disease. Of 110 MAC isolates recovered from patients without MAC disease, 72 (65%) were part of a single large cluster that contained isolates recovered from the hospital's hot water system; 13 (25%) of 51 isolates from patients with MAC disease were also in this cluster. We conclude that acquisition of MAC from institutional water systems leads to substantial MAC disease but that most patients with MAC recovered from respiratory specimens have only transient colonization by MAC.     

Mycobacteria other than tuberculosis. Pulmonary involvement in patients with acquired immunodeficiency syndrome

A normal host can be colonized by mycobacteria other than tuberculosis (MOTT), resulting in bronchoscopic isolates of no clinical significance. In the acquired immunodeficiency syndrome (AIDS), Mycobacterium avium-intracellulare, Mycobacterium kansasii, and Mycobacterium xenopi have caused widely disseminated infection. To determine the usefulness of fiberoptic bronchoscopy (FB) in evaluating MOTT infection in AIDS, we reviewed MOTT cultures from 36 FBs, correlated these to clinical course, and identified MOTT isolates from cultures of all other sources in these patients. Of ten bronchoscopic MOTT isolates, seven were not related to lung disease or to dissemination within one month of FB. Of the four Mycobacterium fortuitum and seven M avium-intracellulare that did disseminate within one month, only two were reflected in bronchoscopic cultures. In patients with AIDS, bronchopulmonary MOTT colonization does occur. We recommend that standard criteria for pulmonary mycobacterial disease be applied. Negative bronchopulmonary cultures do not seem to exclude dissemination.     

Virulence in mice of pneumococcal clonal types with known invasive disease potential in humans

Streptococcus pneumoniae isolates of serotypes 1, 4, 6B, 7F, 14, and 19F belonging to clonal types with known invasive disease potential in humans were used to infect C57BL/6 and BALB/c mice. Most isolates were able to colonize the nasopharynx for 7 days. One serotype 19F isolate of the clonal type ST162 had higher bacterial numbers than other isolates and clonal types of the same serotype. Serotype 4 clones caused the most-severe invasive disease, whereas serotype 1 clones caused low-level bacteremia without disease symptoms. BALB/c mice were more likely than C57BL/6 mice to develop meningitis. Disease kinetics varied significantly between clonal types. Although most induced a robust tumor necrosis factor response, some isolates of serotype 1 and 7F did not, suggesting that invasive disease caused by different clonal types may result in different degrees of host response. Capsular serotype, other clonal properties, and host factors are important for the development of pneumococcal disease.     

A genotype of hepatitis D virus that occurs in northern South America.

Hepatitis D virus (HDV) is the cause of an unusually severe form of liver disease with distinct histologic features (morula cell) that occurs throughout northern South America and certain other areas of the world. Clinical studies of HDV disease worldwide indicate that there is, in fact, a wide variation in pathogenesis, and the reasons for these differences are presently unknown. One possible explanation is that factors associated with the viral genotype are determinants of HDV pathogenesis. In this study, nucleic acid sequences were determined for three different northern South American HDV isolates which were obtained from individuals with severe disease or a family history of severe disease, in areas that are hyperendemic for this disease pattern. The sequences of these three isolates are very similar to one another but only distantly related to other published HDV sequences. Comparison of the sequence of a semiconserved region from a total of 14 isolates indicates that there are at least three HDV genotypes. Most published HDV sequences, including those from North America, Europe, the Middle East, the South Pacific, and Asia, belong to a single genotype which may have some geographically based subtypes. A single Japanese isolate is the sole representative of a second HDV genotype. The South American sequences reported here constitute a third genotype. The association of a particular genotype with the severe form of type D hepatitis that occurs in northern South America supports the hypothesis that HDV genetic factors are important determinants in the pathogenesis of type D hepatitis.     

Phylogenetic Analysis of 56-kDa Type-Specific Antigen Gene of Orientia tsutsugamushi Isolates in Taiwan

Scrub typhus is a rickettsial disease transmitted to humans through the bite of chigger mites infected with Orientia tsutsugamushi, and is an endemic disease in Taiwan. To elucidate the molecular epidemiology of O. tsutsugamushi, the complete open reading frame of the 56-kDa type-specific antigen gene sequence of strains isolated from scrub typhus patients were determined and analyzed. A total of 116 isolates of O. tsutsugamushi were successfully isolated from patients infected in diverse geographic origins including Taiwan and three offshore islets, Kinmen, Matsu, and Penghu between May 2006 and December 2007. Sequence analysis revealed that 22 distinct sequence types could be identified that were broadly distributed in different clusters of the phylogenetic tree. Most of the isolates belong to Karp, Kawasaki, and Kuroki genotypes and are closely related to strains from Thailand, Japan, and Korea, whereas unique isolates different from other countries were also found in Taiwan. Distinct seasonal distributions were found in different sequence types. Some sequence types caused disease in the cold season, whereas others caused disease in the warm season.     

Endotoxin liberation from Neisseria meningitidis isolated from carriers and clinical cases

Endotoxin liberation was studied in a blinded material of 121 Neisseria meningitidis isolates; from nasopharynx of 58 carriers and from cerebrospinal fluid or blood of 63 cases with meningococcal disease. Endotoxin activity in culture filtrates was determined by a Limulus lysate test. Meningococci isolated from clinical cases were significantly more frequently endotoxin-liberating (E+) (84.1%) than in carriers (25.9%); p less than 0.001. Serogroupable carrier isolates had a significantly higher frequency of E+ meningococci (61.9%) than non-groupable ones (5.4%); p less than 0.002. Serogroup B case isolates, which generally had a larger amount of capsular polysaccharide than B meningococci from carriers, had a significantly higher proportion of E+ meningococci than group B from carriers; p = 0.007. All 7 serogroup C isolates were E+ (5 cases and 2 carriers). No correlation was found between endotoxin liberation and the serotype: subtype 15:P1.16, tested by a selection of monoclonal antibodies, or between endotoxin liberation and sulfonamide resistance, when carrier and case isolates were studied separately. Meningococci isolated from cases had the following mean endotoxin titres: 320.5 in the meningitis group, 408.2 in the septicaemic group, 462.1 in the septicaemic and meningitis group, and 123.7 in the group with other systemic disease. E+ meningococci were isolated from 5/6 fatal cases. Thus, endotoxin liberation from meningococci is strongly, but not completely associated with establishment of meningococcal disease and with the presence of capsular polysaccharide.     

Genetic basis for nongroupable Neisseria meningitidis

Nongroupable Neisseria meningitidis may constitute one-third or more of meningococcal isolates recovered from the nasopharynx of human carriers. The genetic basis for nongroupability was determined in isolates obtained from a population-based study in which 60 (30.9%) of 194 meningococcal isolates from asymptomatic carriers were not groupable. Forty-two percent of nongroupable isolates were related to serogroup Y ET-508/ST-23 clonal complex strains, the most common groupable carrier isolate from the study population. Nongroupable isolates were all rapidly killed by 10% normal human serum. The capsule loci of 6 of the ET-508/ST-23 complex strains and of 25 other genetically diverse nongroupable meningococci were studied in detail. Serogroup A or novel capsule biosynthesis genes were not found. Nongroupable isolates were genetically serogroup Y, B, or C isolates that did not express capsule but were related to groupable isolates found in the population (class I); capsule deficient because of insertion element-associated deletions of capsule biosynthesis genes (class II); or isolates that lacked all capsule genes and formed a distinct genetic cluster not associated with meningococcal disease (class III).     

Bacteriologic epidemiology of Hemophilus influenzae type b strains causing invasive infections in Finland

Consecutive Hemophilus influenzae type b (Hib) isolates (333 total) from children with invasive disease in Finland in 1985-1986 were analyzed. All belonged to the common genetic clusters described in the USA and Europe. However, detailed typing demonstrated some characteristics unique to Hib strains in Finland. Of the isolates, 86% belonged to one of four distinct patterns according to the combination of outer membrane protein subtype, biotype, and lipopolysaccharide serotype: 1-I-1 (25%), 1-II-9 (8%), and 1c-I-1 (18%). Pattern 1-II-9 has not been previously reported; it was most commonly found in the most densely populated area of Finland and among children cared for outside the home. Multilocus enzyme electrophoresis revealed that 87% of isolates with the pattern 1c-I-1 belonged to the electrophoretic type 21.8, which is seldom recovered from patients with invasive Hib disease in other countries.     

Non-tuberculous mycobacteriosis. What has been coming out

Diagnosis of non-tuberculous mycobacteriosis is relatively easy, because of recent technological advances (HRCT, MGIT, PCR, DDH etc). Although many reports of this disease have been published, there are many problems to resolve. (1) Prevalence of non-tuberculous mycobacteriosis: Shigeki SATO (Department of Medical Oncology and Immunology, Nagoya City University Graduate School of Medical Sciences) Questionnaire surveys to determine the prevalence of nontuberculous mycobacterial (NTM) disease were carried out in 2001, 2007, and 2009. The NTM disease rate was estimated at 5.9/100,000, confirming that Japan has one of the world's highest NTM disease rates. Examination of the proportions of M. avium and M. intracellulare disease in Japan by region revealed that the M. avium/M. intracellulare disease ratio increased in different regions since past reports. In the 2007 survey, the M. avium disease rate had increased over the 2001 level. M. kansasii had a high disease rate in the Kinki and Kanto regions. Disease rates tended to be high in regions that have a metropolis. However, the disease rate was low in Aichi Prefecture, so that the presence in a region of a metropolis is probably not of itself a factor causing a high disease rate. The distributions of the bacteria causing NTM thus vary among different countries and regions. (2) Polyclonal infection of Mycobacterium avium using variable numbers of tandem repeats (VNTR) analysis: Tomoshige MATSUMOTO (Department of Clinical Research and Development, Center for Infectious Diseases, Osaka Prefectural Hospital Organization, Osaka Prefectural Medical Center for Respiratory and Allergic Diseases) Mycobacterium avium complex (MAC) is refractory to therapy, containing rifampicin (RFP), ethambutol (EB), and clarithromycin (CAM). It was widely accepted that therapeutic difficulties of pulmonary MAC treatment was caused by highly resistance to antibiotics or repeated re-infection from environment. Variable number of tandem repeats (VNTR) analysis of MAC is available. So, we studied the MAC-VNTR of clinical isolates from 29 patients with pulmonary MAC, refractory to the therapy. Compared the clinical isolates before with after each therapy, clinical isolates derived from the all except one patient showed the same VNTR patterns, before and after. According to MAC-VNTR analysis of the clinical isolates we studied, frequency of polyclonal infection was low (1/29). We concluded that the highly resistance to antibiotics or the repeated same VNTR type infection from environment made refractory pulmonary MAC. (3) An approach to identify susceptibility genes in patients with non-HIV-related pulmonary Mycobaterium avium complex (MAC) infection: Naoto KEICHO (Department of Respiratory Diseases, Research Institute, National Center for Global Health and Medicine) Mycobacterium avium complex causes human pulmonary disease. Th1 T cells play a role in protective immunity from mycobacterial infection. Genetic defect of Interferon-gamma/ Interleukin-12 axis is known to cause familial non-tuberculous mycobacterial infection. On the other hand, non-mendelian type of genetic abnormalities such as polymorphisms of HLA, CFTR and SLC11A1 (NRAMP1) genes has also been investigated as disease susceptibility genes. Recently our group has reported disease association with MHC-class I related chain-A molecule (MICA), comparing 300 sporadic cases with 300 healthy controls. (4) Genetic feature of Mycobacterium avium complex: Taku NAKAGAWA, Kenji OGAWA (Department of Pulmonary Medicine, National Hospital Organization Higashinagoya National Hospital) The bacterial factors contributing to the pathogenesis of M. avium complex infection and diversity of disease progression remain unclear. MATR-VNTR typing is inexpensive and easy to perform and has an excellent discriminatory power compared with MIRU-VNTR and IS1245-RFLP typing. MATR-VNTR typing revealed that M. avium isolates from HIV-positive patients are analogous to the isolates from pig enterically-transmitted rather than those from HIV-negative patients with pulmonary diseases. M. avium comprises four subspecies. We performed genetic analysis by using Insertion Sequence (IS) for 114 clinical isolates of M. avium. All clinical isolates were identified as M. avium subsp. hominissuis by sequence analysis of hsp65. PCR detection rate of IS901 was about 70%, while detection rate in Europe and America was 0-8%. Compared with the original IS901, 60 point mutations were found in the sequence of the insertion sequence detected from all PCR-positive clinical isolates. This new insertion sequence was designated ISMav6. It became clear that M. avium strains in Japan are distinct from strains in Western countries in terms of the prevalence of ISMav6. We conducted genetic analysis for M. avium isolates collected from 11 hospitals all over Japan, but MATR-VNTR typing failed to show that distinct clusters correlate with disease progression or region. Genetic typing for M. intracellulare using VNTR has not yet been developed. We identified VNTR loci in the genome of M. intracellulare ATCC1395 and applied them as a molecular epidemiological tool to clinical isolates. (5) Infection source of pulmonary Mycobactrium avium complex (MAC) disease: Yukiko NISHIUCHI (Toneyama Institute for Tuberculosis Research Osaka City University Medical School), Ryoji MAEKURA (National Hospital Organization Toneyama National Hospital) Pulmonary MAC disease is characterized as the polyclonal infection and the recurrence, which suggest the presence of polyclonal niche of MAC in environment surrounding patients. We revealed that MAC was recovered from bathrooms but not from other sites of residences. The bathtub inlet was the niche with polyclonal colonization of MAC in the bathrooms of MAC patients. The identical/related genotypic profiles with isolates from patients were revealed by pulsed field gel electrophoresis. These results implied that the residential bathroom might be one of the infectious sources of pulmonary MAC disease.     

Use of DNA probes to detect Mycobacterium intracellulare and "X" mycobacteria among clinical isolates of Mycobacterium avium complex.

A mycobacterial DNA probe (designated X) was recently developed to help identify Mycobacterium avium complex (MAC) isolates that are nonreactive with probes specific for M. avium or Mycobacterium intracellulare. The prevalence of X probe-positive mycobacteria in clinical specimens and their role in causing disease is unknown. Using a DNA probe kit that includes the X probe, we characterized 100 consecutive clinical MAC isolates as M. avium, M. intracellulare, or X. Lysates from 81 of the isolates reacted with the M. avium probe, 13 with the M. intracellulare probe, 3 with the X probe, and 3 failed to hybridize with any of the probes. All three X-positive isolates were recovered from sputa of patients who were recent immigrants to the United States and who presented with hemoptysis. One isolate was from a Hispanic man infected with human immunodeficiency virus type 1 (HIV-1) and the other 2 were from Filipino patients with no HIV-1 risk factors. This study also showed a higher than expected number of M. intracellulare isolates from blood and cerebrospinal fluid of HIV-1-infected patients.     

Clonal relationships between invasive and carriage Streptococcus pneumoniae and serotype- and clone-specific differences in invasive disease potential

By use of multilocus sequence typing, Streptococcus pneumoniae isolates causing invasive disease (n=150) were compared with those from nasopharyngeal carriage (n=351) among children in Oxford. The prevalence of individual clones (sequence types) and serotypes among isolates from invasive disease was related to their prevalence in carriage, and an odds ratio (OR) for invasive disease was calculated for the major clones and serotypes. All major carried clones and serotypes caused invasive disease, although their ability to do so varied greatly. Thus, 2 serotype 14 clones were approximately 10-fold overrepresented among disease isolates, compared with carriage isolates, whereas a serotype 3 clone was approximately 10-fold underrepresented. The lack of heterogeneity between the ORs of different clones of the same serotype, and analysis of isolates of the same genotype, but different serotype, suggested that capsular serotype may be more important than genotype in the ability of pneumococci to cause invasive disease.     

Characterization of Trypanosoma cruzi from Argentina by electrophoretic zymograms.

Polyacrylamide gel electrophoretic patterns for six enzymes in 73 isolates and 38 clones of Trypanosoma cruzi from different areas of Argentina were classified into 12 zymodemes. The isolates were obtained from human patients with acute, chronic or congenital Chagas' disease, vector insects, domestic and sylvatic animals. Two out of 8 isolates cloned were shown to be heterogeneous. Zymodemes 1 and 12 exhibit widespread geographic distribution; isolates belonging to both zymodemes account for 55% of the total analyzed. The other zymodemes are not widely geographically dispersed. Although there is a clear predominance of zymodeme 1 among asymptomatic patients, the data do not show a clear relationship between particular zymodemes and the clinical picture. The results suggest that the sylvatic and domestic transmission cycles overlap. This remarkable heterogeneity of T. cruzi in Argentina supports the possible multiclonal origin of these parasite populations.     

Viral determinants of FeLV infection and pathogenesis: lessons learned from analysis of a natural cohort

Detailed analysis has been performed over many years of a geographic and temporal cohort of cats naturally infected with feline leukemia virus (FeLV). Molecular analysis of FeLV present in the diseased tissues and application of those viruses to experimental systems has revealed unique isolates with distinctive disease potential, previously uncharacterized virus-receptor interactions, information about the role of recombinant viruses in disease induction, and novel viral and cellular oncogenes implicated in pathogenesis, among other findings. The studies have contributed to an understanding of the selective forces that lead to predominance of distinctive FeLV isolates and disease outcomes in a natural population.     

Streptococcus pyogenes causing toxic-shock-like syndrome and other invasive diseases: clonal diversity and pyrogenic exotoxin expression.

Genetic diversity and relationships among 108 isolates of the bacterium Streptococcus pyogenes recently recovered from patients in the United States with toxic-shock-like syndrome or other invasive diseases were estimated by multilocus enzyme electrophoresis. Thirty-three electrophoretic types (ETs), representing distinctive multilocus clonal genotypes, were identified, but nearly half the disease episodes, including more than two-thirds of the cases of toxic-shock-like syndrome, were caused by strains of two related clones (ET 1 and ET 2). These two clones were also represented by recent pathogenic European isolates. A previous report of a relatively high frequency of expression of exotoxin A among isolates recovered from toxic-shock-like syndrome patients in the United States was confirmed; and the demonstration of this association both within clones and among distantly related clones supports the hypothesis that exotoxin A is a causal factor in pathogenesis of this disease. Near identity of the nucleotide sequences of the exotoxin A structural gene of six isolates of five ETs in diverse phylogenetic lineages was interpreted as evidence that the gene has been horizontally distributed among clones, presumably by bacteriophage-mediated transfer.