Epidemiological data of staphylococcal scalded skin syndrome in France from 1997 to 2007 and microbiological characteristics of Staphylococcus aureus associated strains

Epidemiological data on staphylococcal scalded skin syndromes (SSSS), including bullous impetigo (BI) and generalized exfoliative syndrome (GES), are scarce. To better characterize SSSS and associated Staphylococcus aureus strains, we conducted a retrospective study of 349 cases collected in France between 1997 and 2007 by the National Reference Centre of Staphylococci. Our results showed a stationary evolution of SSSS cases, with a heterogeneous distribution of cases in France. Although notification was not exhaustive, we estimated an incidence of 0.56 cases/year/million inhabitants, in accordance with previous studies conducted in France and Europe, with a median age of 2 years old and sex ratios of 1. A seasonal effect was observed, with a higher GES/BI ratio in autumn compared with other seasons, which could be explained by the impact of viral co-infection. Genetic analysis of S. aureus strains showed that accessory gene regulator (agr) 4, exfoliative toxin A (eta) and B (etb) genes, staphylococcal and enterotoxin-like O (selo) gene and agr4 etb selo profiles were predominantly associated with GES, whereas agr2 eta and agr4 eta selo were more frequently observed with BI. Only one methicillin-resistant strain was found. Protein A (spa) typing identified two main genotypes: spa clonal complex (CC) 159/sequence-type (ST) 121 (75%) and spaCC346/ST15 (18%). spaCC159 was mainly associated with agr4 eta etb selo, agr4 eta selo and agr4 etb selo, and spaCC346 was mainly associated with agr2 eta, suggesting that French SSSS cases are caused by these two main lineages. However, in a multivariate analysis, only etb was independently associated with GES.

Detection of Staphylococcus aureus delta-toxin production by whole-cell MALDI-TOF mass spectrometry

The aim of the present study was to detect the Staphylococcus aureus delta-toxin using Whole-Cell (WC) Matrix Assisted Laser Desorption Ionization-Time-of-Flight (MALDI-TOF) mass spectrometry (MS), correlate delta-toxin expression with accessory gene regulator (agr) status, and assess the prevalence of agr deficiency in clinical isolates with and without resistance to methicillin and glycopeptides. The position of the delta-toxin peak in the mass spectrum was identified using purified delta-toxin and isogenic wild type and mutant strains for agr-rnaIII, which encodes delta-toxin. Correlation between delta-toxin production and agr RNAIII expression was assessed by northern blotting. A series of 168 consecutive clinical isolates and 23 unrelated glycopeptide-intermediate S. aureus strains (GISA/heterogeneous GISA) were then tested by WC-MALDI-TOF MS. The delta-toxin peak was detected at 3005±5 Thomson, as expected for the naturally formylated delta toxin, or at 3035±5 Thomson for its G10S variant. Multivariate analysis showed that chronicity of S. aureus infection and glycopeptide resistance were significantly associated with delta-toxin deficiency (p = 0.048; CI 95%: 1.01-10.24; p = 0.023; CI 95%: 1.20-12.76, respectively). In conclusion, the S. aureus delta-toxin was identified in the WC-MALDI-TOF MS spectrum generated during routine identification procedures. Consequently, agr status can potentially predict infectious complications and rationalise application of novel virulence factor-based therapies.

Reversal of nonstructural protein 3-specific CD4(+) T cell dysfunction in patients with persistent hepatitis C virus infection

Hepatitis C virus (HCV)-specific T cell responses are essential for HCV control, and chronic infection is characterized by functionally altered antigen-specific T cells. It has been proposed that the early inactivation of specific CD4(+) T cell responses may be involved in establishment of HCV persistence. We have investigated whether HCV-specific CD4(+) T cells dysfunction can be reversed in vitro. Nonstructural protein 3 (NS3) and core-specific CD4(+) T cells from eight chronically infected and eight spontaneously resolved HCV individuals were selected through transient CD154 (CD40 ligand) expression, and their functional profile (IFN-γ, IL-2, TNF-α, IL-10 and IL-4 production by enzyme-linked immunospot assay, cytometric bead array and intracellular cytokine staining, and proliferation by carboxy-fluorescein diacetate succinimidyl ester dilution assay) was determined both ex vivo and after in vitro expansion of sorted CD154-expressing cells in the absence of specific antigen in IL-7/IL-15-supplemented medium. Ex vivo bulk CD4(+) T cells from chronic patients expressed CD154 in most cases, albeit at lower frequencies than those of resolved patients (0.11%vs 0.41%; P = 0.01), when stimulated with NS3, but not core, although they had a markedly impaired capacity to produce IL-2 and IFN-γ. Antigen-free in vitro expansion of NS3-specific CD154(+) cells from chronic patients restored IFN-γ and IL-2 production and proliferation to levels similar to those of patients with spontaneously resolved infection. Hence, NS3-specific CD4(+) T cell response can be rescued in most chronic HCV patients by in vitro expansion in the absence of HCV-specific antigen. These results might provide a rationale for adoptive immunotherapy.

A USA300 variant and other human-related methicillin-resistant Staphylococcus aureus strains infecting cats and dogs in France

OBJECTIVES

To characterize methicillin-resistant Staphylococcus aureus (MRSA) clinical strains from cats and dogs in France, and to compare the clones identified with the distribution of French human MRSA.

METHODS

Susceptibilities to antimicrobials were assessed by disc diffusion. Resistance and virulence genes were screened using a microarray-based assay. Isolates were additionally characterized by SmaI macrorestriction analysis and spa typing.

RESULTS

From 2006 to 2010, the proportion of MRSA infections in pets in France was low (1.8%), but most isolates (87.0%, 20/23) belonged to human clones. The most common clones were the Lyon clone (69.6%, 16/23), the livestock-associated CC398 (13.0%, 3/23) and the Geraldine clone (8.7%, 2/23). Interestingly, we report the first USA300 clone infecting a European dog, which was probably imported by a US patient.

CONCLUSIONS

Over a 5 year period, the proportion of MRSA infections in pets appears low (<2%) in France, but the distribution of the clones mostly mirrors the epidemiology of human invasive clones. These data highlight the role of pets as both victims and reservoirs of endemic, epidemic and/or invasive MRSA.

High prevalence of methicillin-resistant Staphylococcus aureus clone ST80-IV in hospital and community settings in Algiers

USA300 is an epidemic community-acquired methicillin-resistant Staphylococcus aureus (C-MRSA) clone in the USA, whereas the European C-MRSA clone ST80-IV has mainly a sporadic diffusion in Europe. The prevalence of European clone ST80-IV in Algeria is poorly documented. We prospectively studied S. aureus infections at Mustapha Bacha hospital in Algiers over a 20-month period. S. aureus nasal colonization was studied during a further 6-month period. The European clone ST80-IV was responsible for more than one-third of both community infections (35.7%) and hospital infections (35.8%). Panton-Valentine leukocidin (PVL)-positive MRSA isolated from hospital inpatients were resistant to multiple antibiotics, including fluoroquinolones in 44.9% of cases. The PVL-positive MRSA nasal carriage rate was high among patients and staff in the dermatology unit (8.7% and 18.5%, respectively), but low (2.7%) among patients attending the outpatient clinic. The European PVL-positive C-MRSA clone ST80-IV is widespread in the Algiers hospital and community settings.

Panton-Valentine leukocidin-positive Staphylococcus aureus strains are associated with follicular skin infections

BACKGROUND/AIMS

Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus have been associated with suppurative infections; however, their precise role in skin infections has not been elucidated. We studied the rate of PVL-positive S. aureus in the different types of skin infections and compared follicular to nonfollicular skin infections.

METHODS

In our institution, patients with a skin infection caused by S. aureus were enrolled in a prospective, observational cohort study (from July 1, 2003 to June 30, 2010). We studied the rate of PVL-positive S. aureus in the different clinical types of skin infections and compared the rate of PVL-positive S. aureus in follicular infections to that in nonfollicular infections.

RESULTS

A total 229 skin infections were included: 97 (42.5%) were caused by PVL-positive strains. Thirty-nine of the 53 (74%) follicular infections [8 of the 17 (47%) with folliculitis, 30 of the 35 (85.5%) with furuncles and 1 with a carbuncle (100%)] were caused by PVL-positive S. aureus, compared to 16 of the 131 (12%) nonfollicular infections (p < 0.001).

CONCLUSION

PVL-positive S. aureus strains are mainly associated with follicular skin infections.

Are host genetics the predominant determinant of persistent nasal Staphylococcus aureus carriage in humans?

BACKGROUND

Staphylococcus aureus nasal carriage is influenced by multifactorial interactions which are difficult to study in open populations. Therefore, we concomitantly assessed the epidemiological, microbiological, and human-genetic carriage-related factors in a nearly closed population.

METHODS

In 2006 and 2008, we collected nasal S. aureus strains, human DNA, and epidemiological data from 154 adult Wayampi Amerindians living in an isolated village in the Amazonian forest. The genetics of the strains (multilocus sequence type, spa type, and toxin-content type), epidemiological risk factors, antibiotic exposure, and allelic polymorphism of human genes putatively involved in carriage of the persistent carriers were compared with those of other volunteers.

RESULTS

Overall carriage prevalence was 41.7% in 2006 and 57.8% in 2008, but the overall prevalence of persistent carriage was only 26%. The rare and phylogenetically distant multilocus sequence type ST1223 was present in 18.5% of the carriers in 2006 and 34.8% in 2008. No epidemiological factors or antibiotic exposure were significantly associated with persistent carriage, but single nucleotide polymorphism distribution in C-reactive proteins C2042T and C1184T and interleukin-4 C524T genes was significantly associated (P=.02, by global test).

CONCLUSION

Host genetic factors appeared to be the predominant determinant for S. aureus persistent nasal carriage in humans.

Clinical manifestations and outcome of skin infections caused by the community-acquired methicillin-resistant Staphylococcus aureus clone ST80-IV

BACKGROUND

Several Panton-Valentin leukocidin-positive clones of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are spreading worldwide. The European clone ST80-IV is the main CA-MRSA clone in Europe. There is no reported study of the specific clinical manifestations and outcome of skin infections caused by the clone ST80-IV, using strict definitions of skin diseases.

METHODS

Single-centre observational prospective cohort of S. aureus skin infections caused by the clone ST80-IV.

RESULTS

From November 1999 to October 2009, we diagnosed skin infections due to the clone ST80-IV in 20 patients (median age 28 years, median 27; range 1-66). All the isolates had all the following characteristics: lukPV, etd and edin gene-positive, agr 3 allele, spa-type t044 and ST80. All the isolates were resistant to beta-lactam agents, kanamycin, tetracycline and fusidic acid. During the study period, the 20 patients had the following manifestations: 19 primary abscesses (18 single abscess and one patient with two), eight furuncles, four folliculitis, one case of cellulitis, one wound infection and one felon. Surgical treatment and drainage was required for all the primary abscesses. The infections occurred mainly in the perineal area (50%). No secondary infections occurred in family members. Despite strict hygiene measures, systemic antibiotics and nasal mupirocine, four patients (20%) had recurrent skin infections over a period of a few months to 6 years.

CONCLUSIONS

The CA-MRSA clone ST80-IV is responsible for suppurative skin infections such as furuncles and abscesses, which can recur over a period of several years.

Primary skin abscesses are mainly caused by Panton-Valentine leukocidin-positive Staphylococcus aureus strains

BACKGROUND

The role of Panton-Valentine leukocidin (PVL) in skin and soft-tissue infections is not clear.

OBJECTIVE

Our purpose was to determine the prevalence of PVL gene carriage among Staphylococcus aureus strains isolated from primary and secondary skin abscesses.

METHODS

A prospective study was conducted. From July 2003 to June 2008, S. aureus isolates from skin abscesses were screened for the PVL genes. The abscesses were considered primary if they occurred on previously healthy skin and secondary in all other cases.

RESULTS

Fifty-seven patients presenting with S. aureus skin abscesses were included in the study. The PVL genes were detected in 40 (70%) of the 57 S. aureus isolates. Thirty-eight (92.7%) of the 41 primary skin abscesses were due to PVL-positive strains, compared to only 2 (12.5%) of the 16 secondary skin abscesses (p < 0.001).

CONCLUSIONS

Primary skin abscesses are mainly caused by PVL-positive S. aureus strains.

Distribution of the exfoliative toxin D gene in clinical Staphylococcus aureus isolates in France

Exfoliative toxin D (ETD) was identified recently as a new exfoliative toxin serotype. Like other exfoliative toxins, ETD induces intra-epidermal cleavage through the granular layer of the epidermis of neonatal mice. The distribution of ETD production was investigated in Staphylococcus aureus isolates from infected and colonised patients in France. The etd gene was found in 55 (10.5%) of 522 isolates tested. Isolates responsible for bullous impetigo and generalised staphylococcal scalded skin syndrome did not harbour etd, but etd was significantly more frequent in isolates causing cutaneous abscesses and furuncles. Most etd- and Panton-Valentine leukocidin-positive strains belonged to the clone of community-acquired methicillin-resistant S. aureus spreading currently throughout France.

Changing molecular epidemiology of methicillin-resistant Staphylococcus aureus in a small geographic area over an eight-year period

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) at an international level shows that most MRSA strains belong to a few pandemic clones. At the local level, a predominance of one or two clones was generally reported. However, the situation is evolving and new clones are emerging worldwide, some of them with specific biological characteristics, such as the presence of Panton-Valentine leucocidin (PVL). Understanding these changes at the local and international levels is of great importance. Our objective was to analyze the evolution of MRSA epidemiology at multiple sites on a local level (Western Switzerland) over a period of 8 years. Data were based on MRSA reports from seven sentinel laboratories and infection control programs covering different areas. Pulsed-field gel electrophoresis was used to type MRSA isolates. From 1997 to 2004, a total of 2,256 patients with MRSA were reported. Results showed the presence of four predominant clones (accounting for 86% of patients), which could be related to known international clones (Berlin, New York/Japan, Southern Germany, and Iberian clones). Within the small geographic region, the 8-year follow-up period in the different areas showed spacio-temporal differences in the relative proportions of the four clones. Other international MRSA clones, as well as clones showing genetic characteristics identical to those of community-acquired MRSA (SCCmec type IV and the presence of PVL genes), were also identified but presumably did not disseminate. Despite the worldwide predominance of a few MRSA clones, our data showed that at a local level, the epidemiology of MRSA might be different from one hospital to another. Moreover, MRSA clones were replaced by other emerging clones, suggesting a rapid change.

Methicillin-susceptible, doxycycline-resistant Staphylococcus aureus, Côte d'Ivoire

We report 2 outbreaks of Panton-Valentine leukocidin-positive, doxycycline-resistant, methicillin-susceptible Staphylococcus aureus infections in French soldiers operating in Côte d'Ivoire. In a transssectional survey, nasal carriage of this strain was found in 2.9% of 273 soldiers about to be sent to Côte d'Ivoire and was associated with prior malaria prophylaxis with doxycycline.

Molecular characterization of methicillin-resistant Staphylococcus aureus isolates collected in Asunción, Paraguay

We characterized 34 methicillin-resistant Staphylococcus aureus strains isolated in Paraguay in 2005. The strains belonged to two clones. The major clone (sequence type 5 [ST5] or ST221, spa type t149, staphylococcal cassette chromosome mec [SCCmec] type I) was similar to the Cordobes/Chilean clone spreading through South America, and the minor clone (ST239 or ST889, spa type t037, SCCmec type IIIA) was related to the Brazilian clone.

Toxin gene content of the Lyon methicillin-resistant Staphylococcus aureus clone compared with that of other pandemic clones

The methicillin-resistant Staphylococcus aureus (MRSA) Lyon clone, detected throughout France, contains the enterotoxin A gene (sea), like other pandemic clones of clonal complex 8 (CC8). The egc locus was detected in MRSA pandemic clones of CC5, CC22, and CC45, occasionally with the toxic shock syndrome toxin 1 gene. The representative strain of the EMRSA-16 clone (CC30) harbored both sea and the egc locus.

Detection of new methicillin-resistant Staphylococcus aureus clones containing the toxic shock syndrome toxin 1 gene responsible for hospital- and community-acquired infections in France

Methicillin-resistant Staphylococcus aureus (MRSA) clones harboring the toxic shock syndrome toxin 1 (tst) gene have been detected in France and in Switzerland since 2002. During a passive survey conducted between 2002 and 2003, we collected 103 tst-positive S. aureus isolates from 42 towns in France, of which 27 were resistant to methicillin. The tst-positive MRSA belonged to two clones: a major clone comprising 25 isolates of sequence type (ST) 5 and agr group 2 and a minor clone comprising two isolates of ST30 and agr3. The tst-positive MRSA clones were associated with both hospital-acquired (12 cases) and community-acquired (8 cases) infections. The MRSA clones were mainly isolated from children (overall median age, 3 years). They caused a variety of clinical syndromes, including toxic shock syndrome and suppurative infections. Both clones were found to harbor a type IV staphylococcal chromosomal cassette mec (SCCmec) and to have similar antibiotic resistance profiles (usually resistant to oxacillin, kanamycin, and tobramycin and with intermediate resistance to fusidic acid). The origin of these clones is unclear. The tst-positive agr2 MRSA clone has the same sequence type (ST5) of two pandemic nosocomial MRSA clones, namely, the Pediatric clone and the New York/Japan clone. These findings suggest that all these clones are phylogenetically related. The pulsotype of the tst-positive MRSA clones differed from that of methicillin-sensitive S. aureus (MSSA) clones by a single band involving the SCCmec element. These findings suggest that the tst-positive MRSA clones may have emerged from their respective MSSA counterparts.

Detection of methicillin-resistant Staphylococcus aureus strains resistant to multiple antibiotics and carrying the Panton-Valentine leukocidin genes in an Algiers hospital

Forty-five Panton-Valentine leukocidin (PVL)-positive, methicillin-resistant Staphylococcus aureus strains were isolated in Algeria between 2003 and 2004; 18 isolates were isolated in the community and 27 in a hospital. Five PVL-positive hospital isolates were resistant to multiple antibiotics, including ofloxacin and gentamicin for three isolates.

Comparative Prevalence of Superantigen Genes in Staphylococcus aureus Isolates Causing Sepsis With and Without Septic Shock

BACKGROUND

Staphylococcus aureus superantigens are associated with the pathogenesis of toxic shock syndrome, but their involvement in septic shock is unknown.

METHODS

We compared the distribution of 11 superantigen genes in S. aureus blood culture isolates obtained from patients with sepsis who did and did not have septic shock (19 and 61 patients, respectively), as well as from patients with suppurative infections (101 patients) and patients with colonization (25 patients).

RESULTS

The prevalence of the enterotoxin A gene (sea) increased significantly with the severity of infection (P<.001), whereas the prevalence of the enterotoxin gene cluster (egc) decreased significantly (P=.009).

CONCLUSION

Enterotoxin A (SEA) might play a key role in sea-positive S. aureus sepsis by triggering over-expression of inflammatory mediators associated with shock. Novel treatments targeting superantigens, especially the sea gene, might be beneficial in the treatment of S. aureus sepsis.

Emergence of two populations of methicillin-resistant Staphylococcus aureus with distinct epidemiological, clinical and biological features, isolated from patients with community-acquired skin infections

BACKGROUND

Community-acquired skin and soft-tissue infections due to methicillin-resistant Staphylococcus aureus (MRSA) are an emerging clinical and epidemiological problem.

OBJECTIVES

To characterize community-acquired skin infections caused by S. aureus, and especially MRSA.

METHODS

From November 1999 to December 2003, we conducted in a French hospital a prospective epidemiological, clinical and bacteriological study of skin infections acquired in the community, applying strict criteria for true community-acquired MRSA (CA-MRSA) and health-care-associated MRSA (HCA-MRSA).

RESULTS

One hundred and ninety-seven patients had 207 skin infections (154 primary and 53 secondary infections). Twenty-two (11%) patients had skin infections caused by MRSA. The incidence of MRSA skin infections acquired in the community rose from 4% in 2000 to 17% in 2003, but the increase was not statistically significant. Six patients (3%) were infected by CA-MRSA and 15 (8%) by HCA-MRSA; one patient was lost to follow-up and could not be classified. CA-MRSA and HCA-MRSA had different epidemiological, clinical and biological characteristics. CA-MRSA infections were more severe than HCA-MRSA infections: all the CA-MRSA infections (six of six, 100%) required surgical treatment, compared with only two (15%) of 13 with HCA-MRSA infection (P < 0.001). CA-MRSA all belonged to the same clonal strain, harbouring an agr type 3 allele and the Panton-Valentine leucocidin genes (not detected in HCA-MRSA) and possessing a specific antibiotype.

CONCLUSIONS

Two populations of MRSA causing skin infections are emerging in the French community, with distinct epidemiological, clinical and biological characteristics.

Frequent carriage of Panton-Valentine leucocidin genes by Staphylococcus aureus isolates from surgically drained abscesses

Between 1 February and 15 April 2002, 95 patients were admitted to Gaston Bourret Territorial Hospital (New Caledonia, France) for drainage of community-acquired soft tissue abscesses. Staphylococcus aureus was detected in 68 cases (72%). Two-thirds of the patients with S. aureus infection had furuncles, which were located on the limbs in 82% of cases. The median interval between symptom onset and hospital admission was 5.7 days. Three-quarters of the patients were Melanesians living in tribes. Fifty-four S. aureus isolates were screened for toxin genes. Panton-Valentine leucocidin (PVL) genes were detected in 48 isolates (89%), the exfoliative toxin A gene was detected in 1 isolate, and no toxin genes were detected in 4 isolates. S. aureus nasal carriage was detected in 39.7% of patients with S. aureus infections. Two infecting S. aureus strains and two nasal carriage strains were resistant to methicillin. Comparative pulsed-field gel electrophoresis, performed in 16 cases, showed that five of six patients with PVL-positive nasal carriage strains were infected by the same strains. In contrast, 8 of 10 patients with PVL-negative nasal carriage strains were infected by PVL-positive strains. PVL genes thus appear to be a major virulence factor in both primary and secondary S. aureus skin infections.

Rapid detection of Panton-Valentine leukocidin from clinical isolates of Staphylococcus aureus strains by real-time PCR

To allow rapid identification of Panton-Valentine leukocidin (PVL)-producing Staphylococcus aureus strains, a real-time PCR assay for detection of PVL was developed. This assay is convenient, since it can be applied directly on bacterial suspensions and does not require previous DNA purification. Furthermore, the assay was found to be highly reproducible, robust and specific, since positive results were generated exclusively with PVL-positive S. aureus strains, and neither with PVL-negative strains nor staphylococci other than S. aureus.

Specific identification of Staphylococcus aureus by Staphychrom II, a rapid chromogenic staphylocoagulase test

We compared the performance of Staphychrom II (International Microbio, Signes, France), a rapid (2-h) chromogenic staphylocoagulase test that uses human prothrombin and protease inhibitors, with those of the reference tube coagulase test (TCT) and the latex agglutination test (LAT) Slidex Staph Plus for the rapid identification of S. aureus. Prospective evaluation with 293 fresh clinical isolates yielded sensitivities, specificities, and predictive and negative predictive values of 98.1, 100, 100, and 95.1%, respectively, for the Staphychrom II test; 98.6, 98.7, 99.6, and 96.3%, respectively, for LAT; and 97.6, 98.7, 99.5, and 93.9%, respectively, for TCT. The perfect specificity of the Staphychrom II test was confirmed by testing 193 collection strains selected because of their potential testing pitfalls. The Staphychrom II test was positive for 90% of the 215 S. aureus strains tested after only 1 h of incubation. The Staphychrom II test was as sensitive as the reference TCT and was 100% specific.

Staphylococcus aureus isolates with reduced susceptibility to glycopeptides belong to accessory gene regulator group I or II

We used multiplex PCR to determine the agr group membership of 18 European glycopeptide heterointermediate and intermediate-resistant Staphylococcus aureus strains. Of the 15 agr group I strains, 13 were resistant and 2 were susceptible to methicillin. The remaining three strains, like the United States and Japanese control strains, belonged to agr group II.

Community-acquired methicillin-resistant Staphylococcus aureus isolated in Switzerland contains the Panton-Valentine leukocidin or exfoliative toxin genes

Among 10 strains of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) isolated in 2002 from patients with skin infections, seven harbored the Panton-Valentine leukocidin gene, two harbored the exfoliative toxin A gene, and one harbored neither of these genes. CA-MRSA isolates producing a variety of exotoxins are currently spreading in the Swiss community.

Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton-Valentine leukocidin genes: worldwide emergence

Infections caused by community-acquired (CA)-methicillin--resistant Staphylococcus aureus (MRSA) have been reported worldwide. We assessed whether any common genetic markers existed among 117 CA-MRSA isolates from the United States, France, Switzerland, Australia, New Zealand, and Western Samoa by performing polymerase chain reaction for 24 virulence factors and the methicillin-resistance determinant. The genetic background of the strain was analyzed by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). The CA-MRSA strains shared a type IV SCCmec cassette and the Panton-Valentine leukocidin locus, whereas the distribution of the other toxin genes was quite specific to the strains from each continent. PFGE and MLST analysis indicated distinct genetic backgrounds associated with each geographic origin, although predominantly restricted to the agr3 background. Within each continent, the genetic background of CA-MRSA strains did not correspond to that of the hospital-acquired MRSA.

Bacterial competition for human nasal cavity colonization: role of Staphylococcal agr alleles

We examined the bacterial aerobic nasal flora of 216 healthy volunteers to identify potential competitive interactions among different species, with special emphasis on the influence of staphylococcal agr alleles. The Staphylococcus aureus colonization rate correlated negatively with the rate of colonization by Corynebacterium spp. and non-aureus staphylococci, especially S. epidermidis, suggesting that both Corynebacterium spp. and S. epidermidis antagonize S. aureus colonization. Most of the S. aureus and S. epidermidis isolates were agr typed by a PCR method. Only one S. aureus agr (agr(Sa)) allele was detected in each carrier. Multiple logistic regression of the two most prevalent agr(Sa) alleles (agr-1(Sa) and agr-2(Sa)) and the three S. epidermidis agr (agr(Se)) alleles showed a specific influence of the agr system. The results of this model did not support conclusions drawn from previous in vitro agr-specific cross-inhibition experiments. Our findings suggest that the agr alleles, which are strongly linked to the bacterial genetic background, may simply be associated with common biological properties--including mediators of bacterial interference--in the strains that bear them.

Community-acquired methicillin-resistant Staphylococcus aureus infections in France: emergence of a single clone that produces Panton-Valentine leukocidin

To characterize the clinical and bacteriologic characteristics of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections, we reviewed 14 cases that were diagnosed in previously healthy patients during an 18-month period in France. Eleven patients had skin or soft-tissue infections. Two patients died of CA-MRSA necrotizing pneumonia. A case of pleurisy occurred in a child who acquired CA-MRSA from his mother, who had a breast abscess. The Panton-Valentine leukocidin genes and the lukE-lukD leukocidin genes were detected in all 14 isolates. The clonal origin of all of the isolates was demonstrated on the basis of their pulsotypes and antibiotic resistance profiles. All isolates had an agr3 allele. The combination of the Panton-Valentine leukocidin determinant (which encodes a virulence factor for primary skin infection and pneumonia) with the mecA gene (which confers antibiotic resistance and epidemicity) appears to have created a superadapted S. aureus strain that is spreading in the community.

Population diversity of Staphylococcus intermedius isolates from various host species: typing by 16S-23S intergenic ribosomal DNA spacer polymorphism analysis

Twelve 16S-23S ribosomal DNA intergenic spacer (ITS-PCR) types were identified among 57 Staphylococcus intermedius isolates from humans and other animals. Six ITS-PCR types were host specific, and most human and canine strains belonged to the same types (A and J). Pigeon, horse, and mink strains appeared more heterogeneous.

Association between Staphylococcus aureus strains carrying gene for Panton-Valentine leukocidin and highly lethal necrotising pneumonia in young immunocompetent patients

BACKGROUND

Between 1986 and 1998, eight cases of community-acquired pneumonia due to Staphylococcus aureus strains carrying the gene for the Panton-Valentine leukocidin (PVL) were recorded in France, six of which were fatal. We aimed to assess the clinical features of these eight cases, and those of other cases identified prospectively, and to compare them with the characteristics of patients with pneumonia caused by PVL-negative strains.

METHODS

We compared eight retrospective and eight prospective cases of PVL-positive S aureus pneumonia with 36 cases of PVL-negative S aureus pneumonia. For all patients, we recorded age, length of hospital stay, risk factors for infection, signs and symptoms, laboratory findings, antibiotic treatment, and serial radiological findings.

FINDINGS

Median age was 14.8 years (IQR 5.4-24.0) for the PVL-positive patients and 70.1 years (59.2-81.4) for the others (p=0.001). Influenza-like illness had occurred during the 2 days before admission in 12 of the 16 PVL-positive patients, but in only three of 33 PVL-negative patients (p<0.001). PVL-positive infections were more often marked by: temperature greater than 39 degrees C (p=0.01), heart rate above 140 beats per min (p=0.02), haemoptysis (p=0.005), onset of pleural effusion during hospital stay (p=0.004), and leucopenia (p=0.001). The survival rate 48 h after admission was 63% for the PVL-positive patients and 94% for PVL-negative individuals (p=0.007). Histopathological examination of lungs at necropsy from three cases of necrotising pneumonia associated with PVL-positive S aureus showed extensive necrotic ulcerations of the tracheal and bronchial mucosa and massive haemorrhagic necrosis of interalveolar septa.

INTERPRETATION

PVL-producing S aureus strains cause rapidly progressive, haemorrhagic, necrotising pneumonia, mainly in otherwise healthy children and young adults. The pneumonia is often preceded by influenza-like symptoms and has a high lethality rate.

Role of interdomain salt bridges in the pore-forming ability of the Bacillus thuringiensis toxins Cry1Aa and Cry1Ac

The four salt bridges (Asp(222)-Arg(281), Arg(233)-Glu(288), Arg(234)-Glu(274), and Asp(242)-Arg(265)) linking domains I and II in Cry1Aa were abolished individually in alpha-helix 7 mutants D222A, R233A, R234A, and D242A. Two additional mutants targeting the fourth salt bridge (R265A) and the double mutant (D242A/R265A) were rapidly degraded during trypsin activation. Mutations were also introduced in the corresponding Cry1Ac salt bridge (D242E, D242K, D242N, and D242P), but only D242N and D242P could be produced. All toxins tested, except D242A, were shown by light-scattering experiments to permeabilize Manduca sexta larval midgut brush border membrane vesicles. The three active Cry1Aa mutants at pH 10.5, as well as D222A at pH 7.5, demonstrated a faster rate of pore formation than Cry1Aa, suggesting that increases in molecular flexibility due to the removal of a salt bridge facilitated toxin insertion into the membrane. However, all mutants were considerably less toxic to M. sexta larvae than to the respective parental toxins, suggesting that increased flexibility made the toxins more susceptible to proteolysis in the insect midgut. Interdomain salt bridges, especially the Asp(242)-Arg(265) bridge, therefore contribute greatly to the stability of the protein in the larval midgut, whereas their role in intrinsic pore-forming ability is relatively less important.

Performance of the chromogenic medium CHROMagar Staph Aureus and the Staphychrom coagulase test in the detection and identification of Staphylococcus aureus in clinical specimens

CHROMagar Staph aureus (CSAM) (CHROMagar Microbiology, Paris, France) is a new chromogenic medium designed to enable detection of colonies of Staphylococcus aureus by their pink color. A total of 775 specimens were cultured in parallel on CHROMagar Staph aureus and conventional media. Among the 267 S. aureus strains recovered on at least one medium, 263 were isolated on CSAM medium (sensitivity, 98.5%), and 245 (sensitivity, 91.8%) were isolated on conventional media. The specificity of presumptive identification of S. aureus on the basis of pink colony color on CSAM medium was 97% (493 of 508). This specificity increased to 100% when coagulase detection with the Staphychrom coagulase test was added and to 98.8% when S. aureus surface components were detected by agglutination in the Pastorex Staph Plus test. Susceptibility testing of 67 S. aureus strains, performed in parallel on pink CSAM colonies and on colonies grown on blood agar, gave similar results. Thus, rapid and accurate recognition and identification of S. aureus isolates were achieved with CSAM as the primary isolation medium, followed by the staphylocoagulase Staphychrom test. Antimicrobial susceptibility testing (disk-diffusion method or ATB STAPH System) can be performed directly on pink CSAM colonies.

International multicenter evaluation of latex agglutination tests for identification of Staphylococcus aureus

A newly marketed rapid agglutination kit for the identification of Staphylococcus aureus, Slidex Staph Plus (bioMérieux), was compared to Staphaurex Plus (Murex Diagnostics) and Pastorex Staph-Plus (Sanofi Diagnostics Pasteur). The study took place in three clinical microbiology laboratories in three different European countries. A total of 892 staphylococcal isolates, including 278 methicillin-sensitive S. aureus (MSSA) isolates, 171 methicillin-resistant S. aureus (MRSA) isolates, and 443 coagulase-negative staphylococcal isolates, were analyzed. The sensitivities (MSSA/MRSA) and specificities, respectively, were 98. 2% (98.9%/97.1%) and 98.9% for Slidex Staph Plus, 98.2% (98.2%/98. 2%) and 96.2% for Staphaurex Plus, and 98.7% (98.6%/98.8%) and 95.7% for Pastorex Staph Plus. The specificity of the Slidex Staph Plus kit was statistically significantly higher than the specificities of Staphaurex Plus and Pastorex Staph-Plus. The Slidex Staph Plus is a very reliable test for the identification of S. aureus.

Molecular techniques open up new vistas for typing of coagulase-negative staphylococci

Several methods were used to type 64 clinical isolates of coagulase-negative staphylococci (CNS) derived from hospitals in Morocco. The clinical isolates originated principally from blood cultures and wound sources. These isolates provided the opportunity to substantially compare the proficiency of developing molecular techniques with conventional phenotypic tests for use in the identification of clinical staphylococci. The following molecular methods were examined: Utility ribotyping analysis (Ribotyping); PCR analysis performed with 16S-23S ribosomal-DNA intergenic spacer (ITS-PCR); PCR-based random amplified polymorphic DNA (RAPD). The results obtained by the molecular techniques were contrasted to those of conventional phenotypic tests. Conventional phenotypic tests allowed the outright recognition of the majority of isolates (50/64). These 50 isolates were subdivided into 33 novobiocin-susceptible and 17 novobiocin-resistant strains of CNS. However, 2 other novobiocin-susceptible and 12 other novobiocin-resistant isolates remained unclassified by these tests. There was a good agreement between the conventional phenotypic tests and RAPD for the 33 novobiocin-susceptible isolates. But, the RAPD technique permitted the assignment of the two unidentified novobiocin-susceptible isolates to the Staphylococcus hominis species. A complete correlation was obtained between the three molecular tools for recognition of the 12 novobiocin-resistant isolates that were not identified by phenotypic typing; these were in fact identified as 5 Staphylococcus cohnii and 4 Staphylococcus equorum. Three isolates remained unidentified by all three systems of molecular techniques.