Outbreak of group A streptococci in a burn center: use of pheno- and genotypic procedures for strain tracking

A report on the first outbreak of emm89 group A streptococcus invasive infections in a burns unit in Tunisia

Four group A streptococcus (GAS) bacteraemia occurred in a small burn unit within 2 weeks. The GAS patient isolates, characterized as emm89, shared the same PFGE pulsotype with two other strains isolated 2 months later. The outbreak investigation revealed that a nurse was the most likely source of GAS transmission, as she was confirmed to carry the same outbreak strain in her throat and had direct and regular contact with the six outbreak patients in the unit. The outbreak was controlled after the nurse had undergone eradication treatment. This report highlights the emergence of the emm89 clone and its capacity to elicit invasive GAS outbreaks.

Outbreak of Streptococcus pyogenes emm type 58 in a high dependency unit of a level-1 trauma center of India

Background and Aims:

Group A Streptococcus (GAS) can cause illnesses ranging from self-limited to severe, life-threatening, invasive infections. The objective of the following study was to investigate a suspected Streptococcus pyogenes outbreak in a high dependency unit (HDU) of our trauma center.

Materials and Methods:

All the isolates of beta hemolytic Streptococci were identified by standard microbiological methods, Vitek 2 system and latex agglutination tests. Antimicrobial susceptibility testing was performed as recommended by Clinical Laboratory Standards Institute. Exotoxin genes, including speA, speB, speC, speF, smeZ, ssa, speG, speH, speJ, speL, speM and speI were detected by polymerase chain reaction (PCR). The emm types of isolates of S. pyogenes were determined by sequencing the variable 5’ end of emm gene after amplification by PCR.

Results:

In a 28 bedded poly-trauma ward with a four bedded HDU three out of four patients developed S. pyogenes emm type 58 infection. The strain was macrolide and tetracycline resistant and produced the Streptococcal pyrogenic exotoxins speB, speC, speG, speF and smeZ. Surveillance sampling was done for investigation from patients, health-care workers and environmental samples.

Conclusion:

An outbreak of GAS infections was established caused by the uncommonly reported emm type 58. The outbreak was controlled by prompt treatment, intensive surveillance, feedback and training.

Infection control in the burn unit

The survival rates for burn patients have improved substantially in the past few decades due to advances in modern medical care in specialized burn centers. Burn wound infections are one of the most important and potentially serious complications that occur in the acute period following injury. In addition to the nature and extent of the thermal injury influencing infections, the type and quantity of microorganisms that colonize the burn wound appear to influence the future risk of invasive wound infection. The focus of medical care needs to be to prevent infection. The value of infection prevention has been acknowledged in organized burn care since its establishment and is of crucial importance. This review focuses on modern aspects of the epidemiology, diagnosis, management, and prevention of burn wound infections and sepsis.

Molecular typing of Aspergillus species

Aspergillus species are widely distributed fungi that release large amounts of airborne conidia, which are dispersed in the environment. Several Aspergillus species have been described as human pathogens. Molecular techniques have been developed to investigate the epidemiological relation between environmental and clinical isolates. Several typing methods have been described for Aspergillus species, most of them with reference to Aspergillus fumigatus. Here, we summarise all the different available molecular typing techniques for Aspergillus. The performance of these techniques is evaluated with respect to their practical feasibility, and their interpretation and discriminatory power assessed. For A. fumigatus isolates, a large extent of genetic variability is demonstrated and therefore fingerprinting techniques with high discriminatory power and high reproducibility are required for this species. Afut1-restriction fragment length polymorphism and microsatellite typing showed the highest discriminatory power. In addition, the microsatellites show excellent reproducibility. Other typing techniques are still useful for smaller epidemiological problems and for less well-equipped laboratories.

Feasibility and clinical applicability of polihexanide for treatment of second-degree burn wounds

OBJECTIVES

Due to a partial rejection of mesh split-thickness skin grafts (mesh grafts) after application of povidone-iodine and silver nitrate and due to its better in vitro tolerance, polihexanide was investigated as an alternative and its applicability in the treatment of second-degree burn wounds.

METHODS

In 4 patients with poorly healing decubitus ulcers the mesh grafts were each divided into three areas which were pre-treated with either undiluted povidone-iodine solution, 1% silver nitrate solution or 0.04% polihexanide solution. After 7 days of application the wound areas were compared clinically and histologically. Thereafter 14 patients (average extent of burns 28% TBSA) were treated in the same way.

RESULTS

Clinically and histologically the mesh grafts treated with polihexanide showed by far the best re-epithelialization compared with the deep tissue necrosis and marked fibrin discharge observed for application of povidone-iodine and silver nitrate. The second-degree burn wounds treated with polihexanide epithelialized without any further débridement after an average of 10 days with remarkable freedom from pain. Compared with silver nitrate treatment, no fibrin film was observed on the wound.

CONCLUSION

Polihexanide proved clinically and histologically superior to povidone-iodine and silver nitrate. For the treatment of second-degree burns, which cannot primarily be covered by plastic surgery, polihexanide is suitable because in addition to its antiseptic efficacy it does not inhibit the re-epithelialization process.

Molecular characterization of Streptococcus pyogenes isolates to investigate an outbreak of puerperal sepsis

OBJECTIVE

To describe microbiological characteristics and epidemiologic features of an outbreak of postpartum endometritis.

METHODS

Various markers were investigated in five patients and three throat carriage isolates of Streptococcus pyogenes obtained during an outbreak of endometritis occurring in a 13-week period. Molecular characterization included biotyping, T-serotyping, emm gene sequence and restriction, pulsed-field gel electrophoresis (PFGE), and random amplified polymorphic DNA (RAPD) analysis.

RESULTS

Biotype, T-serotype, and genotypic data (emm analysis, PFGE, and RAPD analysis) revealed a close relationship among the isolates from three patients, suggesting that cross-contamination had occurred. These isolates were biotype 1, T type 28, and emm type 28. The isolates from one patient and one carrier differed from those of the index patient by minor variations of the emm amplicon restriction pattern, PFGE pattern, or RAPD pattern. The remaining isolates were phenotypically and genetically different.

CONCLUSION

Identification of different isolates demonstrated that different strains may circulate simultaneously during a true outbreak and that the predominant strain might persist for several months.

Hospital-acquired invasive group a streptococcal infections in Ontario, Canada, 1992-2000

BACKGROUND

A significant proportion of invasive group A streptococcal infections are hospital acquired. No large, prospective studies have characterized this subgroup of cases and evaluated the risk of transmission in hospitals.

METHODS

We conducted prospective, population-based surveillance of invasive group A streptococcal infections in Ontario, Canada, from 1992 to 2000. Epidemiologic and microbiologic investigations were conducted to identify cross-transmission.

RESULTS

We identified 291 hospital-acquired cases (12.4%) among 2351 cases of invasive group A streptococcal disease. Hospital-acquired invasive group A streptococcal infections are heterogeneous, including surgical site (96 cases), postpartum (86 cases), and nonsurgical, nonobstetrical infections (109 cases). Surgical site infections affected 1 of 100,000 surgical procedures and involved all organ systems. Postpartum infections occurred at a rate of 0.7 cases per 10,000 live births and exhibited an excellent prognosis. Nonsurgical, nonobstetrical infections encompassed a broad range of infectious syndromes (case-fatality rate, 37%). Nine percent of cases were associated with in-hospital transmission. Transmission occurred from 3 of 142 patients with community-acquired cases of necrotizing fasciitis requiring intensive care unit (ICU) admission, compared with 1 of 367 patients with community-acquired cases without necrotizing fasciitis admitted to the ICU and 1 of 1551 patients with other cases (P<.001). Fifteen outbreaks were identified; 9 (60%) involved only 2 cases. Hospital staff were infected in 1 of 15 outbreaks, but colonized staff were identified in 6 (60%) of 10 investigations in which staff were screened.

CONCLUSIONS

Presentation of hospital-associated invasive group A streptococcal infections is diverse. Cross-transmission is common; illness occurs in patients but rarely in staff. Isolation of new cases of necrotizing fasciitis and intervention after a single nosocomial case may also prevent transmission.

Prophage association of mef(A) elements encoding efflux-mediated erythromycin resistance in Streptococcus pyogenes

OBJECTIVES

To compare different mef(A) elements of Streptococcus pyogenes for a possible chimeric genetic nature, i.e. a transposon inserted into a prophage.

METHODS

Eleven S. pyogenes isolates with efflux-mediated erythromycin resistance were used. The isolates were typed using several genotypic approaches. Gene detection was performed by PCR using specific primer pairs. The mef(A) elements of the test strains were induced with mitomycin C and phage DNA was extracted. Induction was monitored by PCR using primers targeting mef(A).

RESULTS

Six tetracycline-susceptible isolates had PCR evidence of all of the eight open reading frames (ORFs) of the Tn1207.1 element; their mef(A) element was consistent with the Tn1207.3 element in four isolates and with the 58.8 kb chimeric element in two. Five tetracycline-resistant isolates had no PCR evidence of orf1 and orf2 and showed variable patterns as to orf3, orf7, and orf8. Three ORFs placed along the conserved region downstream of Tn1207.1 in the 58.8 kb mef(A) chimeric element were detected in the six tetracycline-susceptible, but not in the five tetracycline-resistant isolates. Induction assays with mitomycin C demonstrated that the mef(A) elements of all strains tested were present in culture supernatants in a DNAse-resistant form, such as a phage capsid.

CONCLUSIONS

All recognized mef(A) elements of S. pyogenes appear to be prophage-associated. Whereas the two elements detected in tetracycline-susceptible isolates (Tn1207.3 and the 58.8 kb one) were apparently inserted into the same prophage, the tet(O)-mef(A) element was inserted into a different prophage. Phage transfer is likely to play a critical role in the dissemination of erythromycin resistance in S. pyogenes populations.

Presence of the tet(O) gene in erythromycin- and tetracycline-resistant strains of Streptococcus pyogenes and linkage with either the mef(A) or the erm(A) gene

Sixty-three recent Italian clinical isolates of Streptococcus pyogenes resistant to both erythromycin (MICs >or=1 microg/ml) and tetracycline (MICs >or= 8 microg/ml) were genotyped for macrolide and tetracycline resistance genes. We found 19 isolates carrying the mef(A) and the tet(O) genes; 25 isolates carrying the erm(A) and tet(O) genes; and 2 isolates carrying the erm(A), tet(M), and tet(O) genes. The resistance of all erm(A)-containing isolates was inducible, but the isolates could be divided into two groups on the basis of erythromycin MICs of either >128 or 1 to 4 microg/ml. The remaining 17 isolates included 15 isolates carrying the erm(B) gene and 2 isolates carrying both the erm(B) and the mef(A) genes, with all 17 carrying the tet(M) gene. Of these, 12 carried Tn916-Tn1545-like conjugative transposons. Conjugal transfer experiments demonstrated that the tet(O) gene moved with and without the erm(A) gene and with the mef(A) gene. These studies, together with the results of pulsed-field gel electrophoresis experiments and hybridization assays with DNA probes specific for the tet(O), erm(A), and mef(A) genes, suggested a linkage of tet(O) with either erm(A) or mef(A) in erythromycin- and tetracycline-resistant S. pyogenes isolates. By amplification and sequencing experiments, we detected the tet(O) gene ca. 5.5 kb upstream from the mef(A) gene. This is the first report demonstrating the presence of the tet(O) gene in S. pyogenes and showing that it may be linked with another gene and can be moved by conjugation from one chromosome to another.

Phenotypes and genotypes of erythromycin-resistant pneumococci in Italy

Of 120 erythromycin-resistant pneumococci isolated in Italian hospitals, 39 (32.5%) were M-type isolates, carrying the mef gene alone. The mef gene was also detected, together with erm(AM), in one constitutively resistant isolate and in five isolates of the partially inducible phenotype. Among the 45 mef-positive isolates, 25 (55.6%) carried mef(A) and 20 (44.4%) carried mef(E) as observed from PCR-restriction fragment length polymorphism analysis of a 1,743-bp amplicon. The same result was obtained by a similar method applied to a more common 348-bp amplicon.

Genetic diversity of Vibrio cholerae O1 in Argentina and emergence of a new variant

The genetic diversity of Vibrio cholerae O1 strains from Argentina was estimated by random amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE). Twenty-nine isolates carrying the virulence genes ctxA, zot, ace, and tcpA appeared to represent a single clone by both typing methods; while 11 strains lacking these virulence genes exhibited several heterogeneous RAPD and PFGE patterns. Among the last group, a set of isolates from the province Tucumán showed a single RAPD pattern and four closely related PFGE profiles. These strains, isolated from patients with diarrhea, did not produce the major V. cholerae O1 virulence determinants, yet cell supernatants of these isolates caused a heat-labile cytotoxic effect on Vero and Y-1 cells and elicited significant variations on the water flux and short-circuit current in human small intestine mounted in an Ussing chamber. All these effects were completely abolished by incubation with a specific antiserum against El Tor hemolysin, suggesting that this virulence factor was responsible for the toxic activity on both the epithelial cells and the small intestine specimens and may hence be involved in the development of diarrhea. We propose "Tucumán variant" as the designation for this new cluster of cholera toxin-negative V. cholerae O1 strains.

A novel efflux system in inducibly erythromycin-resistant strains of Streptococcus pyogenes

Streptococcus pyogenes strains inducibly resistant (iMLS phenotype) to macrolide, lincosamide, and streptogramin B (MLS) antibiotics can be subdivided into three phenotypes: iMLS-A, iMLS-B, and iMLS-C. This study focused on inducibly erythromycin-resistant S. pyogenes strains of the iMLS-B and iMLS-C types, which are very similar and virtually indistinguishable in a number of phenotypic and genotypic features but differ clearly in their degree of resistance to MLS antibiotics (high in the iMLS-B type and low in the iMLS-C type). As expected, the iMLS-B and iMLS-C test strains had the erm(A) methylase gene; the iMLS-A and the constitutively resistant (cMLS) isolates had the erm(B) methylase gene; and a control M isolate had the mef(A) efflux gene. mre(A) and msr(A), i.e., other macrolide efflux genes described in gram-positive cocci, were not detected in any test strain. With a radiolabeled erythromycin method for determination of the intracellular accumulation of the drug in the absence or presence of an efflux pump inhibitor, active efflux of erythromycin was observed in the iMLS-B isolates as well as in the M isolate, whereas no efflux was demonstrated in the iMLS-C isolates. By the triple-disk (erythromycin plus clindamycin and josamycin) test, performed both in normal test medium and in the same medium supplemented with the efflux pump inhibitor, under the latter conditions iMLS-B and iMLS-C strains were no longer distinguishable, all exhibiting an iMLS-C phenotype. In conjugation experiments with an iMLS-B isolate as the donor and a Rif(r) Fus(r) derivative of an iMLS-C isolate as the recipient, transconjugants which shared the iMLS-B type of the donor under all respects, including the presence of an efflux pump, were obtained. These results indicate the existence of a novel, transferable efflux system, not associated with mef(A) or with other known macrolide efflux genes, that is peculiar to iMLS-B strains. Whereas the low-level resistance of iMLS-C strains to MLS antibiotics is apparently due to erm(A)-encoded methylase activity, the high-level resistance of iMLS-B strains appears to depend on the same methylase activity plus the new efflux system.

Poststreptococcal acute disseminated encephalomyelitis with basal ganglia involvement and auto-reactive antibasal ganglia antibodies

Antibasal ganglia antibodies (ABGA) are associated with Sydenham's chorea and pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections. We present 10 patients with acute disseminated encephalomyelitis (ADEM) associated with Group A beta hemolytic streptococcal infection. The clinical phenotype was novel, with 50% having a dystonic extrapyramidal movement disorder, and 70% a behavioral syndrome. None of the patients had rheumatic fever or Sydenham's chorea. Enzyme-linked immunosorbent assay, Western immunoblotting, and immunohistochemistry were used to detect ABGA. Neurological (n = 40) and streptococcal (n = 40) controls were used for comparison. Enzyme-linked immunosorbent assay results showed significantly elevated ABGA in the patients with poststreptococcal ADEM. Western immunoblotting demonstrated ABGA reactivity to three dominant protein bands of 60, 67, or 80 kDa; a finding not reproduced in controls. Fluorescent immunohistochemistry demonstrated specific binding to large striatal neurones, which was not seen in controls. Streptococcal serology was also significantly elevated in the poststreptococcal ADEM group compared with neurological controls. Magnetic resonance imaging studies showed hyperintense basal ganglia in 80% of patients with poststreptococcal ADEM, compared to 18% of patients with nonstreptococcal ADEM. These findings support a new subgroup of postinfectious autoimmune inflammatory disorders associated with Group A beta hemolytic streptococcus, abnormal basal ganglia imaging, and elevated ABGA.

Enterobacterial repetitive intergenic consensus sequence-based PCR (ERIC-PCR); its ability to differentiate Streptococcus pyogenes strains and applicability to the study of outbreaks of streptococcal infection

We evaluated the ability of enterobacterial repetitive intergenic consensus sequence-based PCR (ERIC-PCR) to differentiate 95 Streptococcus pyogenes strains with M or T serotypes isolated from sporadic streptococcal infections as compared with M or T serotypings and pulsed-field gel electrophoresis (PFGE). Although the ERIC-PCR had less discriminatory power, defined as the ability to divide the strains with the same serotypes into the different sub-types, than PFGE, it consistently classified the strains into 16 patterns with a high correlation with M or T serotyping. The PCR method further discriminated 4 M or T serotypes into sub-types. The application of ERIC-PCR to 5 outbreaks of streptococcal infection produced the results that agreed closely with those of T serotyping and PFGE. ERIC-PCR has sufficient discriminatory power and is a quick and relatively easy technique, making it useful for routine epidemiological investigations.

Outbreak of scarlet fever at a hospital day care centre: analysis of strain relatedness with phenotypic and genotypic characteristics

An outbreak of scarlet fever involving 12 children occurred at a hospital day care centre from February to March 1996. Twenty-five throat isolates of Streptococcus pyogenes (GAS, group A streptococcus) available from 24 children, including 10 children with scarlet fever and 14 asymptomatic carriers, and one asymptomatic staff member were studied for the presence of genes encoding streptococcal pyrogenic exotoxin types A (speA), B (speB), and C (speC) and for protease activity. Antimicrobial susceptibilities using the E-test, cluster analysis by cellular fatty acid composition and random amplified polymorphic DNA (RAPD) patterns by means of arbitrarily-primed polymerase chain reaction (APPCR) of the isolates were performed to investigate the outbreak. Only one isolate from an asymptomatic child possessed the speA gene. All isolates possessed the speB gene and 24 (96%) isolates were positive for the speC gene. There was no difference in protease activity between isolates from children with scarlet fever and from asymptomatic carriers. Thirteen isolates (10 recovered from children with scarlet fever, two from asymptomatic children, and one from the staff member) were considered to be the same strain according to the identical antimicrobial susceptibility profile and RAPD patterns and were also considered to be similar by cluster analysis of fatty acid composition. These findings suggest that the outbreak was caused by a unique clone of GAS. We conclude that RAPD typing and cluster analysis by cellular fatty acids composition both provide a powerful tool for epidemiological investigation of GAS infections.