Molecular analysis of multiple isolates of the major serotypes of group B streptococci

Perinatal Streptococcus agalactiae Epidemiology and Surveillance Targets

Streptococcus agalactiae, or group B streptococcus (GBS), is a major neonatal pathogen. Recent data have elucidated the global prevalence of maternal and neonatal colonization, but gaps still remain in the epidemiology of this species. A number of phenotypic and genotypic classifications can be used to identify the diversity of GBS strains, and some are more discriminatory than others. This review explores the main schemes used for GBS epidemiology and further details the targets for epidemiological surveillance. Current screening practices across the world provide a unique opportunity to gain detailed information on maternal colonizing strains and neonatal disease-causing strains, which is vital for monitoring and therapeutics, if sufficient detail can be extracted. Deciphering which isolates are circulating within specific populations and recording targets within invasive strains are crucial steps in monitoring the implementation of therapeutics, such as vaccines, as well as developing novel therapies against prevalent GBS strains. Having a detailed understanding of global GBS epidemiology will prove invaluable for understanding the pathogenesis of this organism and equipping future prevention strategies for success.

Genetic diversity and antimicrobial resistance in Streptococcus agalactiae strains recovered from female carriers in the Bucharest area

For the first time, we used multilocus sequence typing (MLST) to understand how Romanian group B streptococcus (GBS) strains fit into the global GBS population structure. Colonising isolates recovered from adult human females were tested for antibiotic resistance, were molecularly serotyped based on the capsular polysaccharide synthesis (cps) gene cluster and further characterised using a set of molecular markers (surface protein genes, pilus-encoded islands and mobile genetic elements inserted in the scpB-lmb intergenic region). Pulsed-field gel electrophoresis was used to complement the MLST clonal distribution pattern of selected strains. Among the 55 strains assigned to six cps types (Ia, Ib, II-V), 18 sequence types (STs) were identified by MLST. Five STs represented new entries to the MLST database. The prevalent STs were ST-1, ST-17, ST-19 and ST-28. Twenty molecular marker profiles were identified. The most common profiles (rib+GBSi1+PI-1, rib+GBSi1+PI-1, PI-2b and alp2/3+PI-1, PI-2a) were associated with the cps III/ST-17 and cps V/ST-1 strains. A cluster of fluoroquinolone-resistant strains was detected among the cps V/ST-19 members; these strains shared alp1 and IS1548 and carried PI-1, PI-2a or both. Our results support the usefulness of implementing an integrated genotyping system at the reference laboratory level to obtain the reliable data required to make comparisons between countries.

Protein degradation in bovine milk caused byStreptococcus agalactiae

Streptococcus(Str.)agalactiaeis a contagious mastitis bacterium, often associated with cases of subclinical mastitis. Different mastitis bacteria have been evaluated previously from a diagnostic point of view, but there is a lack of knowledge concerning their effect on milk composition. Protein composition is important in achieving optimal yield and texture when milk is processed to fermented products, such as cheese and yoghurt, and is thus of great economic value. The aim of thisin vitrostudy was to evaluate protein degradation mainly caused by exogenous proteases originating from naturally occurringStr. agalactiae. The samples were incubated at 37°C to imitate degradation caused by the bacteria in the udder. Protein degradation caused by different strains ofStr. agalactiaewas also investigated. Protein degradation was observed to occur whenStr. agalactiaewas added to milk, but there were variations between strains of the bacteria. Caseins, the most economically important proteins in milk, were degraded up to 75% in milk inoculated withStr. agalactiaein relation to sterile ultra-high temperature (UHT) milk, used as control milk. The major whey proteins, α-lactalbumin and β-lactoglobulin, were degraded up to 21% in relation to the sterile control milk. These results suggest that different mastitis bacteria but also different strains of mastitis bacteria should be evaluated from a milk quality perspective to gain knowledge about their ability to degrade the economically important proteins in milk.

Group B Streptococcal sepsis: an old or ongoing threat?

BACKGROUND

Group B Streptococcus (GBS) is a major cause of severe infections in newborns. Early-onset disease (EOD) occurs within the first week of life, and it is usually vertically transmitted. In late-onset disease (LOD), pathogens may also come from nosocomial sources. We report 3 cases of GBS infection in very low birth weight infants hospitalized by a neonatal intensive care unit (NICU) in Italy.

METHODS

The cluster was identified thanks to an active surveillance program; an epidemiologic investigation took place. Pulsed-field gel electrophoresis (PFGE) was used to assess the clonal relatedness of strains. An audit to stress the adherence to isolation precautions and hand hygiene was organized.

RESULTS

During a 16-day period, 2 preterm newborns developed GBS LOD; an earlier case of GBS EOD occurred in a baby hospitalized by the same ward. The 3 GBS strains had the same antibiotic susceptibility pattern. The PFGE profiles of the 2 cases of LOD are indistinguishable from each other and closely related with the case of EOD. Strict infection control measures were adopted.

CONCLUSION

The implementation of additional infection control measures was able to stop the diffusion of infection; however, clusters like this should remind us the ongoing threat of GBS for the small NICU patients.

Clonal analysis of colonizing group B Streptococcus, serotype IV, an emerging pathogen in the United States

Colonizing group B Streptococcus (GBS) capsular polysaccharide (CPS) type IV isolates were recovered from vaginal and rectal samples obtained from 97 (8.4%) nonpregnant women of 1,160 women enrolled in a U.S. multicenter GBS vaccine study from 2004 to 2008. Since this rate was much higher than the rate of prevalence of 0.4 to 0.6% that we found in previous studies, the isolates were analyzed by using surface protein profile identification, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST) to characterize them and identify trends in DNA clonality and divergence. Of the 101 type IV isolates studied, 53 expressed alpha and group B protective surface (BPS) proteins, 27 expressed BPS only, 20 expressed alpha only, and 1 had no detectable surface proteins. The isolates spanned three PFGE macrorestriction profile groups, groups 37, 38, and 39, of which group 37 was predominant. The isolates in group 37 expressed the alpha and BPS proteins, while those in groups 38 and 39 expressed the alpha protein only, with two exceptions. MLST studies of selective isolates from the four protein profile groups showed that isolates expressing alpha,BPS or BPS only were of a new sequence type, sequence type 452, while those expressing alpha only or no proteins were mainly of a new sequence type, sequence type 459. Overall, our study revealed a limited diversity in surface proteins, MLST types, and DNA macrorestriction profiles for type IV GBS. There appeared to be an association between the MLST types and protein expression profiles. The increased prevalence of type IV GBS colonization suggested the possibility that this serotype may emerge as a GBS pathogen.

Genotyping of Streptococcus agalactiae (group B streptococci) isolated from vaginal and rectal swabs of women at 35-37 weeks of pregnancy

BACKGROUND

Group B streptococci (GBS), or Streptococcus agalactiae, are the leading bacterial cause of meningitis and bacterial sepsis in newborns. Here we compared different culture media for GBS detection and we compared the occurrence of different genotypes and serotypes of GBS isolates from the vagina and rectum.

METHODS

Streptococcus agalactiae was cultured separately from both rectum and vagina, for a total of 150 pregnant women, i) directly onto Columbia CNA agar, or indirectly onto ii) Granada agar resp. iii) Columbia CNA agar, after overnight incubation in Lim broth.

RESULTS

Thirty six women (24%) were colonized by GBS. Of these, 19 harbored GBS in both rectum and vagina, 9 only in the vagina and 8 exclusively in the rectum. The combination of Lim broth and subculture on Granada agar was the only culture method that detected all GBS positive women. Using RAPD-analysis, a total of 66 genotypes could be established among the 118 isolates from 32 women for which fingerprinting was carried out. Up to 4 different genotypes in total (rectal + vaginal) were found for 4 women, one woman carried 3 different genotypes vaginally and 14 women carried two 2 different genotypes vaginally. Only two subjects were found to carry strains with the same genotype, although the serotype of both of these strains was different.Eighteen of the 19 subjects with GBS at both sites had at least one vaginal and one rectal isolate with the same genotype.We report the presence of two to four different genotypes in 22 (61%) of the 36 GBS positive women and the presence of identical genotypes in both sites for all women but one.

CONCLUSION

The combination of Lim broth and subculture on Granada medium provide high sensitivity for GBS detection from vaginal and rectal swabs from pregnant women. We established a higher genotypic diversity per individual than other studies, with up to four different genotypes among a maximum of 6 isolates per individual picked. Still, 18 of the 19 women with GBS from both rectum and vagina had at least one isolate from each sampling site with the same genotype.

Molecular investigation of Streptococcus agalactiae isolates from environmental samples and fish specimens during a massive fish kill in Kuwait Bay

This study was undertaken to identify and characterize bacterial isolates obtained simultaneously from dead fish samples during a massive fish kill in Kuwait Bay and sewage-water samples running into Kuwait Bay using conventional and molecular techniques. Of the 71 bacterial isolates studied; 66 were recovered from 7 different fish species and 5 strains were isolated from sewage samples. The species-specific identity of the isolates was established by phenotypic characteristics and by PCR amplification of 16S rRNA by using Streptococcus agalactiae-specific primers. The genotyping of 12 isolates from fish samples and all 5 isolates from sewage samples was performed by random amplification of polymorphic DNA (RAPD) analysis. Culture methods identified 44 of 66 (67%) and 4 of 5 (80%) isolates obtained from fish and sewage samples, respectively, as S. agalactiae. The PCR amplification of 16S rRNA not only confirmed the results of conventional methods but also resulted in additional identification of 14 of 66 (21%) isolates obtained from fish samples and the remaining isolate recovered from sewage sample, as S. agalactiae. A total of 9 RAPD patterns were observed among the 17 isolates studied; these RAPD patterns were grouped into three clusters. Interestingly, four of the isolates recovered from sewage samples produced nearly identical RAPD band patterns (85-100% similarity) with some of the S. agalactiae strains isolated from Mullet kidney and brain indicting the possibility of sewage being the source of infection.

Necrotizing fasciitis in captive juvenile Crocodylus porosus caused by Streptococcus agalactiae: an outbreak and review of the animal and human literature

We observed an outbreak of necrotizing fasciitis associated with Streptococcus agalactiae infection in a group of juvenile saltwater crocodiles (Crocodylus porosus). We undertook screening of crocodiles and the environment to clarify the source of the outbreak and evaluated the isolates cultured from post-mortem specimens with molecular methods to assess clonality and the presence of known group B streptococcal virulence determinants. The isolates were indistinguishable by pulsed-field gel electrophoresis. They were a typical serotype Ia strain with the Calpha-like protein gene, epsilon (or alp1), the mobile genetic elements IS381 ISSag1 and ISSag2, and belonged to multi-locus sequence type (ST) 23. All of these characteristics suggest they were probably of human origin. We review the medical and veterinary literature relating to S. agalactiae necrotizing fasciitis, epidemiology and virulence determinants.

Identification of novel cps locus polymorphisms in nontypable group B Streptococcus

Group B Streptococcus (GBS) is an important pathogen responsible for a variety of diseases in newborns and the elderly. A clinical GBS isolate is considered nontypable (NT) when serological methods fail to identify it as one of nine known GBS serotypes. Eight clinical isolates (designated A1-A4, B1-B4) showed PFGE profiles similar to that of a GBS serotype V strain expressing R1, R4 surface proteins. These unique isolates were further characterized by immunologic and genetic methods. Rabbit sera to isolates A1 and A2 reacted weakly with concentrated HCl extracts of A1-A4 isolates, but not with those of B1-B4 isolates. In addition, a type V capsular polysaccharide (CPS) inhibition ELISA revealed that cell wall extracts from isolates A1-A4, but not from B1-B4, expressed low but measurable amounts of type V CPS. Molecular serotyping with PCR analysis showed that all eight isolates contained a type V-specific CPS gene (cpsO) and harboured the gene encoding the surface protein Alp3. Multilocus sequence typing identified isolate A1 as belonging to a new sequence type (ST) designated ST-173, whereas the other seven isolates keyed to ST-1. Sequencing of the 18 genes (17 736 bp) in the cps locus showed that each NT isolate harboured one to three unique polymorphisms, and also identified an IS1381 element in cpsE of the B4 isolate. Collectively, genetic and immunologic analyses revealed that these NT isolates expressing R1, R4 proteins have a genetic profile consistent with that of type V, an emergent, antigenically diverse and increasingly prevalent GBS serotype.

Molecular characterization of nontypeable group B streptococcus

Traditionally, the capsular polysaccharide (CPS) antigen has been used to distinguish between the nine known serotypes of group B streptococcus (GBS) by classical antibody-antigen reactions. In this study, we used PCR for all CPSs and selected protein antigens, multilocus sequencing typing (MLST), and pulsed-field gel electrophoresis (PFGE) to molecularly characterize 92 clinical isolates identified as nontypeable (NT) by CPS-specific antibody-antigen reactivity. The PCR and MLST were performed on blinded, randomly numbered isolates. All isolates contained the cfb gene coding for CAMP factor. While most (56.5%) contained a single CPS-specific gene, 40 isolates contained either two or three CPS-specific genes. Type V CPS-specific gene was present in 66% of the isolates, and all serotypes except types IV, VII, and VIII were represented. Most (44.5%) of the isolates contained a single protein antigen gene (bca, bac, rib, alp1, or alp3), and the remaining isolates had multiple protein antigen genes. Of the 61 isolates that had the V CPS-specific gene, 48 (78.6%) had the alp3 gene. PFGE analysis classified the isolates into 21 profile groups, while MLST analysis divided the isolates into 16 sequence types. Forty-two (69%) of 61 isolates with the V CPS-specific gene were in PFGE profile group 4; 41 of these 42 were sequence type 1 by MLST. These data shed new light on the antigenic complexity of NT GBS isolates, information that can be valuable in the formulation of an effective GBS vaccine.

Prevalence of erythromycin and clindamycin resistance among Streptococcus agalactiae isolates in Germany

The antimicrobial susceptibilities of 338 clinical Streptococcus agalactiae isolates from two geographical regions in Germany were determined by agar dilution. All isolates were susceptible to penicillin, cefotaxime and vancomycin. The overall frequencies of erythromycin and clindamycin resistance were 11% and 4.7%, respectively. Determination of resistance phenotypes among the 37 erythromycin-resistant isolates revealed constitutive and inducible MLS(B) resistance in 40.6% and 37.8% of isolates, respectively, and susceptibility to clindamycin in 21.6% of isolates. Only 14.3% of isolates with inducible MLS(B) resistance were identified as clindamycin-resistant by determination of clindamycin MICs. Pulsed-field gel electrophoresis suggested a clonal distribution pattern among the erythromycin-resistant isolates.

Group B streptococcal soft tissue infections in non-pregnant adults

Skin and soft tissue infections are the most common presentations of invasive Streptococcus agalactiae infections. This study reviewed 71 patients in a medical centre in southern Taiwan with S. agalactiae soft tissue infections. The mortality rate was 7%, and 11% of patients lost their extremities following extensive tissue necrosis. Critical illness and the presence of cutaneous ulceration heralded a fatal prognosis. Risk-factors for amputation of limbs included advanced age, cutaneous ulceration and polymicrobial infection. It was concluded that invasive S. agalactiae soft tissue infections, as with infections caused by Streptococcus pyogenes, can also lead to substantial morbidity and mortality in non-pregnant adults.

Molecular genetic methods in diagnosis and direct characterization of acute bacterial central nervous system infections

Acute bacterial infection of the central nervous system requires rapid and adequate management. Etiological diagnosis is hence crucial. Moreover, the epidemic threat of certain bacteria necessitates a reliable characterization of the involved bacterial strains to follow the spread of epidemic strains. Conventional identification and characterization of etiological agents are basically based on culture and identification of bacterial markers most frequently by serological assays. Molecular identification and characterization of bacteria have been employed. They provide more reliable analysis of bacterial isolates. Molecular methods for non-culture diagnosis of bacterial infections have recently been developed. In many cases, the molecular assays have decreased the identification time of positive cultures and rescued detection of pathogens in culture-negative clinical samples.

DNA macrorestriction analysis of nontypeable group B streptococcal isolates: clonal evolution of nontypeable and type V isolates

Group B streptococci (GBS) are serotyped according to capsular polysaccharide (CPS) type (Ia to VIII); an isolate is classified as nontypeable (NT) if no detectable CPS is found. Surface-localized protein antigens (alpha, beta, R1, and R4) serve as additional markers to classify GBS isolates, which is particularly useful since NT isolates often express one or more of these proteins. To compare genetic resemblance among isolates with similar protein profiles, we studied 58 NT isolates digested with the SmaI macrorestriction enzyme prior to pulsed-field gel electrophoresis (PFGE). Of these 58, 15.5% expressed alpha only, 20.7% expressed alpha+beta, 15.5% expressed R4, and 25.8% expressed R1,R4, while 22.4% of the isolates expressed no detectable proteins. The largest PFGE profile group, with 48% of the isolates, was group 4, composed primarily of isolates that expressed R1,R4 or no proteins. The second most common profiles were 3 and 32, each with 13.8% of the isolates. Since NT isolates in profile group 4 were highly related to type V isolates, as demonstrated by PFGE profiles, we investigated 45 type V isolates. Two-thirds of the type V isolates within profile group 4 were classified into subgroup 4a, compared to 28.2% of 39 NT isolates. Only 11% of the V/R1,R4 isolates were identical to the prototype group 4 profile, in contrast to 75% of the NT/R1,R4 isolates. A shift of type V isolates into profile 4 subgroups may be indicative of a genetic change over time. PFGE is a valuable approach for comparison of GBS isolate relatedness and for monitoring of NT and typeable GBS isolates for potential clonal divergence.

Phenotypic and molecular characteristics of Streptococcus agalactiae isolates recovered from milk of dairy cows in Brazil

Information on the characteristics of Streptococcus agalactiae obtained from bovine sources in Brazil is still very limited. The aim of this study was to assess the phenotypic and genotypic diversity among S. agalactiae isolates from milk of dairy cows presenting clinical or subclinical mastitis in the southeast region of Brazil. Phenotypic characterization was based on physiological and serological tests. Antimicrobial susceptibility tests were carried out by the disk method. Genetic diversity was evaluated by using random amplified polymorphic DNA-PCR (RAPD-PCR) (by using the primer 1254) and pulsed-field gel electrophoresis (PFGE) (by using SmaI as the restriction enzyme) and by PCRs for detection of genes associated with resistance to erythromycin and tetracycline as well as PCRs for detection of genes coding for cell surface-associated proteins. According to the results of physiologic tests, 45 (52.9%) isolates showed beta-hemolysis and 44 (51.7%) were susceptible to bacitracin. Fourteen different biotypes were detected. The two most frequent biotypes comprised strains that were non-beta-hemolytic; fermented galactose, lactose, and salicin; produced protease; and were negative for DNase production. Serotype III was predominant (66 isolates [77.6%]), followed by serotypes II, Ia, Ib, and VI. Resistance to tetracycline and erythromycin was found in 38 (44.7%) and 9 (10.5%) isolates, respectively, with tet(O) (31.7%) and erm(B) (100%) being the most frequently occurring resistance genes. Three genes coding for surface proteins, bca, lmb, and scpB, were detected in 55 (64.7%), 7 (8.2%), and 43 (50.5%) isolates, respectively. In most cases, isolates from animals in the same herd presented closely related genetic profiles (determined by either RAPD-PCR or PFGE), which were distinct from those of isolates from different herds.

Molecular epidemiology of group B streptococcal infections

Streptococcus agalactiae (GBS) is a causative agent of sepsis and meningitis in newborns and diseases in pregnant women and nonpregnant adults. Various approaches, including both nongenetic and genetic techniques, are currently used for the study of epidemiology of GBS infections. In the present paper the different methods of molecular epidemiology of GBS infections are reviewed, and several novel approaches are introduced. The advantages and disadvantages of molecular methods are discussed and compared with traditional serotyping technique. The possible use of the molecular approaches for identification of different genetic lineages in GBS as well as for identification and control of the epidemiologically actual clones is discussed.

Macrorestriction analysis of Streptococcus agalactiae (group B Streptococcus) isolates from Malaysia

Streptococcus agalactiae or group B streptococci (GBS) often colonize the gastrointestinal and urogenital tracts of women, who may transmit these organisms to their offspring during the birth process. Using PFGE analysis, the genetic diversity of GBS was studied for strains isolated from pregnant women and their newborn infants in a teaching hospital. A total of 48 different PFGE profiles were obtained from 123 strains, with one profile (S1) appearing to be predominant among both groups studied. There was good overall correlation between the profiles obtained for strains from mother-infant pairs and for strains isolated from different body sites in the same individual. Occasional discrepancies seen in related body sites and among mother-infant pairs suggest concurrent carriage of different strains in the same individual as well as the possibility of an environmental source of organism for the neonate. The overall results demonstrated that many variants of GBS strains occur in Malaysia.

Determination of epidemiological relationships of Streptococcus agalactiae isolated from bovine mastitis

In the present study 79 streptococcal cultures isolated from subclinical mastitis of 54 cows from seven dairy farms (A-G) in Hesse, Germany, were comparatively investigated using conventional and molecular methods. The isolates could be identified as Streptococcus agalactiae, belonging to Lancefield's serological group B by determination of cultural, biochemical and serological properties and by polymerase chain reaction (PCR)-mediated amplification of species-specific parts of the 16S ribosomal DNA, the 16S-23S rDNA intergenic spacer region and the CAMP factor gene cfb. The investigated group B streptococci were further characterized serologically for specific polysaccharide and protein antigens. Serotyping the isolates revealed a predominance of surface protein antigen X, either alone or in combination with polysaccharide antigen Ia. This could be observed for 39 isolates of farms A, B and C. Six group B streptococci from farm E displayed the serotype pattern III/Rib, two isolates from farm G showed the serotype pattern Ib/calpha. The remaining cultures from farms D and F (n=32) were non-typable. The occurrence of protein Rib could be confirmed by PCR amplification of the gene rib. The two isolates with serotype pattern Ib/calpha also reacted positively for the cbeta-encoding gene bag. Additional properties which allowed a phenotypic characterization of the S. agalactiae were the degree of pigmentation, growth properties in fluid media and soft agar, the surface hydrophobicity, the ability to hemagglutinate rabbit erythrocytes and their resistance reactions to tetracycline and minocycline. The isolates of the seven farms showed identical or almost identical characteristics. The 79 group B streptococci were additionally investigated by macrorestriction analysis of their chromosomal DNA using the restriction endonucleases SmaI, ApaI and SalI. The restriction patterns obtained by pulsed-field gel electrophoresis displayed identical or closely related patterns for the cultures of the various farms. The pheno- and genotypic characteristics of the 79 group B streptococci of the present study revealed that a single S. agalactiae strain or at least closely related subtypes of this strain were responsible for the mastitis situation of the seven farms.

Can composition and structural features of oligonucleotides contribute to their wide-scale applicability as random PCR primers in mapping bacterial genome diversity?

Among current genotypic methodologies, random amplification of polymorphic DNA (RAPD or AP-PCR) represents a widely employed assay for the evaluation of bacterial genomic diversity. A common bottleneck of this technique, however, is represented by the screening of useful informative primers to discriminate among isolates of a particular bacterial species. In an attempt to simplify this process, we evaluated here the utility of degenerate oligonucleotides to act as informative AP-PCR primers. For this purpose, a number of features (G+C contents, degeneracy rate, modifications at the 5' end) of related degenerate primers was tested for their effects in the generation of informative arrays from a set of bacterial genomes. Our results indicate that a combination of a wide base composition and a common palindromic structure at the 5' end of the sequences that compose the degenerate primers tested here beneficially resulted for the generation of informative arrays aimed to evaluate the bacterial genome heterogeneity.

Improved methods for typing nontypeable isolates of group B streptococci

Group B streptococci (GBS) are classified by capsular polysaccharide (CPS) type and by cell surface-expressed proteins (c and R). Isolates lacking detectable CPS are considered nontypeable (NT) although they frequently express surface proteins. Immunological and genetic methods were used to study 91 NT GBS isolates collected during surveillance studies for invasive disease or colonization in pregnant or non-pregnant women and neonates less than seven days of age. CPS production was upregulated by the addition of glucose and sodium phosphate to Todd-Hewitt broth (THB) and cells were extracted using hot HCl or mutanolysin. Extracts were tested with antisera for specific CPS types Ia, Ib, and II - VIII by double immunodiffusion (DD) in agarose. By mutanolysin extraction, 12 (13.2%) of the 91 isolates were typeable. In contrast, only four of these 12 newly typeable isolates tested positive for CPS with the HCl extracts of cells grown in modified THB. DNA was analyzed by pulsed-field gel electrophoresis (PFGE) using SmaI restriction with NT isolates grouped by protein profile to facilitate analysis. PFGE results of the NT isolates were compared to DNA profiles of typeable isolates and were correlated with the DD results. The DNA profiles of the newly typeable isolates were similar to profiles of isolates with corresponding defined CPS type. Of the remaining 78 NT isolates digested by SmaI, 63 (80.8%) had DNA profiles that resembled those of specific types of GBS. These approaches will be useful for classification of NT isolates in continued epidemiological surveillance associated with GBS vaccine trials.

Rapid pulsed-field gel electrophoresis method for group B streptococcus isolates

We developed a rapid pulsed-field gel electrophoresis (PFGE) method that required 3 days to complete, an improvement over the standard method that required as many as 8 days. The accuracy and reproducibility of the rapid method were verified by analysis of DNA band sizes of our control group B streptococcus isolate. The rapid method was superior to the standard method, providing more precise molecular sizing and gels of higher image quality. The reproducibility of rapid PFGE substantiated its value and continued use.

Genotyping of the capsule gene cluster (cps) in nontypeable group B streptococci reveals two major cps allelic variants of serotypes III and VII

Forty group B Streptococcus (GBS) isolates obtained from Europe and the United States previously reported to be nontypeable (NT) by capsule serotype determination were subjected to buoyant density gradient centrifugation. From nearly half of the isolates capsule-expressing variants could be selected. For characterization of the remaining NT-GBS isolates, the capsule operon (cps) was amplified by the long-fragment PCR technique and compared by restriction fragment length polymorphism (RFLP) analysis. The patterns from serotype reference isolates (n = 32) were first determined and used as a comparison matrix for the NT-GBS isolates. Using two restriction enzymes, SduI and AvaII, cluster analysis revealed a high degree of similarity within serotypes but less than 88% similarity between serotypes. However, serotypes III and VII were each split in two distant RFLP clusters, which were designated III(1) and III(2) and VII(1) and VII(2), respectively. Among the isolates that remained NT after repeated Percoll gradient selections, two insertional mutants were revealed. Both were found in blood isolates and harbored insertion sequence (IS) elements within cpsD: one harbored IS1548, and the other harbored IS861. All other NT-GBS isolates could, by cluster analysis, be referred to different serotypes by comparison to the RFLP reference matrix. In pulsed-field gel electrophoresis of SmaI-restricted chromosomal DNA, patterns from allelic type 1 and 2 isolates were essentially distributed in separate clusters in serotypes III and VII. A covariation with insertion sequence IS1548 in the hylB gene was suggested for serotype III, since allelic type III(1) harboring IS1548 in hylB, clustered separately. The variation in serotype VII was not dependent on the presence of IS1548, which was not detected at any position in the type VII chromosome.

Characterization of Streptococcus agalactiae isolates of bovine and human origin by randomly amplified polymorphic DNA analysis

Streptococcus agalactiae is considered one of the major causes of bovine intramammary infections. It is also found in the vaginas of women without any apparent clinical symptoms, but reports of neonatal infections, causing significant morbidity, are relatively frequent. The aim of this study was to evaluate the genetic diversity of S. agalactiae strains isolated from bovine milk and from asymptomatic women in Québec, Canada, by randomly amplified polymorphic DNA (RAPD) analysis. A total of 185 bovine isolates and 38 human isolates were first serotyped for capsular polysaccharide by double diffusion in agarose gel (bovine isolates) and coagglutination (human isolates). Strains were then studied by RAPD using 3 primers, designated OPS11, OPB17, and OPB18, which were selected from 12 primers. Thirty-eight percent of bovine isolates and 82% of human isolates could be serotyped. Prevalent serotypes were type III (28%) for bovine isolates and types V (26%) and III (24%) for human isolates. RAPD results showed that, taken together, all isolates (of bovine and human origin) shared 58% similarity. Ninety-four percent of these isolates were clustered in four groups (I, II, III, and IV) with 70% similarity among them. Three clusters, A (48 isolates), B (14 isolates), and C (32 isolates), with 79 to 80% similarity were identified within group IV, whereas the three other groups did not present any clusters. Despite some clustering of human isolates, relatively high diversity was seen among them. Relatively high heterogeneity was observed with the RAPD profiles, not only for field strains belonging to different serotypes but also for those within a given serotype.

Genetic features of Streptococcus agalactiae strains causing severe neonatal infections, as revealed by pulsed-field gel electrophoresis and hylB gene analysis

A collection of 114 independent Streptococcus agalactiae strains, including 54 strains isolated from the cerebrospinal fluid (CSF) samples of neonates and 60 strains from asymptomatic patients, was characterized by pulsed-field gel electrophoresis (PFGE) of DNA restricted with SmaI and by PCR analysis of the hylB gene. All strains were previously studied by multilocus enzyme electrophoresis (MLEE) (R. Quentin, H. Huet, F.-S. Wang, P. Geslin, A. Goudeau, and R. K. Selander, J. Clin. Microbiol. 33:2576-2581, 1995). Among these 114 strains, there were 92 PFGE patterns. Eleven genetic groups (A to K) were identified with 38% divergence. A more homogeneous group (PFGE group A) was defined, consisting of 73% of the strains previously identified as belonging to a particular MLEE phylogenetic group. A 162-kb fragment was identified as a marker of strains that invaded the central nervous system of neonates. It was detected in 69% of the PFGE patterns obtained with CSF isolates and in only 1.8% of the PFGE patterns obtained with carrier strains. The hylB gene encoding hyaluronate lyase was amplified for all strains in our collection. Ten of 15 isolates belonging to an MLEE subgroup, previously described as being likely to cause invasive infection, had an insertion in the hylB gene (IS1548).

In vitro inhibition of S. pneumoniae, nontypable H. influenzae and M. catharralis by alpha-hemolytic streptococci from healthy children

The present study aimed to investigate the inhibitory activity of the normal epipharyngeal flora against the three most common acute otitis media (AOM) pathogens in healthy children, and to study if the inhibitory activity differs between alpha-hemolytic streptococci (AHS) sampled from the tubal orifice and from those sampled from the adenoid. A total number of ten isolates of AHS were collected from the tubal orifice and the adenoid, respectively, in ten children undergoing adenoidectomy or tonsillectomy. None of the children had a history of otitis media, neither secretory otitis media (SOM) nor AOM. The method used to test the bacterial interference in vitro was a modified agar overlay method. The results showed that the AHS from nasopharynx were able to inhibit the majority of the S. pneumoniae, nontypable Haemophilus influenzae and Moraxella catharralis isolates tested. The AHS isolates from the tubal orifice inhibited growth of 93% of S. pneumoniae, 79% of H. influenzae and 84% of M. catharralis isolates. The corresponding figures among isolates from the adenoid were 76, 48 and 62%. This difference in the inhibitory capacity between the AHS isolates collected from the adenoid, compared with the AHS collected from the tubal orifice, is statistically significant (P<0.01) and implies that it is important to know the exact sampling locality before conclusions are made concerning the significance of bacterial interference in the upper airways.

Cloning of the glutamine synthetase gene from group B streptococci

The glnA gene from the human pathogen Streptococcus agalactiae was cloned from a genomic library prepared with the lambda phage vector lambdaDASHII. A 4.6-kb DNA fragment of one of the recombinant phages was subcloned in pUC18. This Escherichia coli clone expressed a 52-kDa protein encoded by a 1,341-bp open reading frame. The nucleotide sequence of the open reading frame and the deduced amino acid sequence shared a significant degree of homology with the sequences of other glutamine synthetases (GS). The highest homology was between our deduced protein and GS of gram-positive bacteria such as Bacillus subtilis, Bacillus cereus, and Staphylococcus aureus. Plasmids with the cloned streptococcal glnA were able to complement E. coli glnA mutants grown on minimal media. Rabbit antisera to streptococcal GS recombinant protein recognized not only the recombinant protein but also a similar-sized band in mutanolysin extracts of all group B streptococcal strains tested, regardless of polysaccharide type or surface protein profile. The amino acid sequence of the deduced protein had similarities to other streptococcal cell-surface-bound proteins. The possible functional role of the immunological features of streptococcal GS is discussed.

Epidemiological aspects of group B streptococci of bovine and human origin

Restriction fragment length polymorphism of the gene encoding rRNA (ribotyping) was used in combination with conventional epidemiological markers to study phenotypic variations among Streptococcus agalactiae of bovine origin and the possible epidemiological interrelationship between the bovine and human reservoirs of Streptococcus agalactiae. The bovine material constituted 53 strains (9 antigen combinations) isolated from 11 herds. Herds with a uniform as well as heterogenic antigenic pattern were included. Furthermore, strains isolated in the course of time from the same persistently infected quarters were examined. The human material constituted 16 strains, 4 each of 4 serotypes, isolated from healthy carriers. Finally, nine serotype- and the group reference strains were examined. All strains were serotyped by double diffusion in agarose gel, biotyped (lactose +/-), and ribotyped using two restriction enzymes, Hind III and HhaI. All isolates could be typed by ribotyping and seven ribotypes were identified among the reference strains. The restriction enzymes used alone or in combination gave typing results that allowed discrimination between and within serotype. Combined use of serotype, Hind III and HhaI ribotypes produced 11 types among the 16 human strains. Ribotype analysis discriminated between herds infected with the same serotype. Strains of varying antigenic patterns from the same herd had the same ribotype. Phenotypic variations in serotype observed in persistent intramammary infection were not related to genetic changes as monitored by ribotype. Two ribotypes were represented among both bovine and human strains. The discriminating capability of lactose fermentation was of limited value.

Group B streptococci escape host immunity by deletion of tandem repeat elements of the alpha C protein

Group B streptococci (GBS) are the most common cause of neonatal sepsis, pneumonia, and meningitis. The alpha C protein is a surface-associated antigen; the gene (bca) for this protein contains a series of tandem repeats (each encoding 82 aa) that are identical at the nucleotide level and express a protective epitope. We previously reported that GBS isolates from two of 14 human maternal and neonatal pairs differed in the number of repeats contained in their alpha C protein; in both pairs, the alpha C protein of the neonatal isolate was smaller in molecular size. We now demonstrate by PCR that the neonatal isolates contain fewer tandem repeats. Maternal isolates were susceptible to opsonophagocytic killing in the presence of alpha C protein-specific antiserum, whereas the discrepant neonatal isolates proliferated. An animal model was developed to further study this phenomenon. Adult mice passively immunized with antiserum to the alpha C protein were challenged with an alpha C protein-expressing strain of GBS. Splenic isolates of GBS from these mice showed a high frequency of mutation in bca--most commonly a decrease in repeat number. Isolates from non-immune mice were not altered. Spontaneous deletions in the repeat region were observed at a much lower frequency (6 x 10(-4)); thus, deletions in that region are selected for under specific antibody pressure and appear to lower the organism's susceptibility to killing by antibody specific to the alpha C protein. This mechanism of antigenic variation may provide a means whereby GBS evade host immunity.

Stomatococcus mucilaginosus septicemia in leukemic patients

OBJECTIVE: To report an unexpectedly high number of cases of septicemia with Stomatococcus mucilaginosus, and try to identify predisposing factors. METHODS: All blood cultures obtained during 1991--93 from patients treated at the hematologic ward were bacteriologically identified. The medical records of patients with S. mucilaginosus-positive blood cultures were retrospectively reviewed and evaluated. The antibiotic susceptibility pattern and restriction fragment length polymorphism (RFLP) of S. mucilaginosus were tested. RESULTS: S. mucilaginosus blood isolates from patients with hematologic malignancies were found to be as common as isolates of Staphylococcus aureus. Eleven patients with myelogenous leukemia and isolation of S. mucilaginosus from the blood are reported on. One patient had concomitant meningitis. All patients were neutropenic and most had oral mucositis and had been given ciprofloxacin prophylaxis. S. mucilaginosus isolates from these patients were resistant to ciprofloxacin in contrast to isolates from patients who had received other prophylactic regimens and seven isolates found in healthy individuals not recently treated with antibiotics. The resistant S. mucilaginosus were found to be of diverse genetic origin as determined by RFLP. CONCLUSIONS: The appearance of resistant strains during ciprofloxacin prophylaxis may be a predisposing factor for S. mucilaginosus septicemia. There was no evidence of a nosocomial spread of S. mucilaginosus strains.

Molecular epidemiology of Xanthomonas maltophilia colonization and infection in the hospital environment

Between April 1992 and December 1993, 80 Xanthomonas maltophilia isolates were collected from 63 patients in three acute-care hospitals in Calgary, Alberta, Canada. On the basis of Centers for Disease Control and Prevention definitions, 48 patients had nosocomial and 15 had community-acquired X. maltophilia. Thirty-eight of the patients were colonized and 25 were infected. Sixty-four percent of patients who acquired X. maltophilia in the intensive care unit (ICU) became infected, whereas 32% of patients in a non-ICU setting became infected. ICU patients tended to be hospitalized for a shorter period of time than non-ICU patients before the onset of X. maltophilia infection. Regardless of being colonized or infected, all patients had debilitating conditions, with respiratory disease being the most common underlying illness (35%). Forty-two patients (88%) with hospital-acquired X. maltophilia received prior antibiotic therapy which included gentamicin, tobramycin, ceftazidime, piperacillin, and imipenem. Agar dilution MICs showed that patient isolates were resistant to these antimicrobial agents that patients had received. Pulsed-field gel electrophoresis of SpeI-digested genomic DNA revealed that six epidemiologically linked patient isolates from the ICU of one acute-care hospital had identical DNA profiles. In contrast, isolates from patients from the other two hospitals had unique genotype profiles (n = 57) regardless of the presence or absence of an epidemiologic association. In these patients there was genetic evidence against the acquisition of a resident hospital clone. These results indicate that pulsed-field gel electrophoresis can resolve genotypically distinct strains of X. maltophilia and, consequently, is a useful tool for evaluating nosocomial infections caused by X. maltophilia.

Epidemiologic analysis of sporadic Salmonella typhi isolates and those from outbreaks by pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) was used to compare and analyze 158 isolates of Salmonella typhi from five well-defined outbreaks of typhoid fever in Malaysia and also isolates involved in sporadic cases of typhoid fever occurring during the same period. Digestion of chromosomal DNAs from these S. typhi isolates with the restriction endonucleases XbaI (5'-TCTAGA-3'), SpeI (5'-ACTAGT-3'), and AvrII (5'-CCTAGG-3') and then PFGE produced restriction endonuclease analysis (REA) patterns consisting of 11 to 24 DNA fragments ranging in size from 20 to 630 kbp. Analysis of the REA patterns generated by PFGE after digestion with XbaI and SpeI indicated that the S. typhi isolates obtained from sporadic cases of infection were much more heterogeneous (at least 13 different REA patterns were detected; Dice coefficient, between 0.73 and 1.0) than those obtained during outbreaks of typhoid fever. The clonal nature and the close genetic identities of isolates from outbreaks in Alor Setar, Penang, Kota Kinabalu, Johor Bahru, and Kota Bahru were suggested by the fact that only a limited number of REA patterns, which mostly differed by only a single band, were detected (one to four patterns; Dice coefficient, between 0.82 and 1.0), although a different pattern was associated with each of these outbreaks. Comparison of REA patterns with ribotyping for 18 S. typhi isolates involved in sporadic cases of infection showed a good correlation, in that 72% of the isolates were in the same group. There was no clear correlation of phage types with a specific REA pattern. We conclude that PFGE of s. typhi chromosomal DNA digested with infrequently cutting restriction endonucleases is a useful method for comparing and differentiating S. typhi isolates for epidemiological purposes.