Epidemiologic typing of methicillin-resistant Staphylococcus aureus in neonate intensive care units using pulsed-field gel electrophoresis

Identification and functional activity of a staphylocoagulase type XI variant originating from staphylococcal food poisoning isolates

Staphylocoagulase, an extracellular protein secreted by Staphylococcus aureus, has been used as an epidemiological marker. At least 12 serotypes and 24 genotypes subdivided on the basis of nucleotide sequence have been reported to date. In this study, we identified a novel staphylocoagulase nucleotide sequence, coa310, from staphylococcal food poisoning isolates that had the ability to coagulate plasma, but could not be typed using the conventional method. The protein encoded by coa310 contained the six fundamental conserved domains of staphylocoagulase. The full-length nucleotide sequence of coa310 shared the highest similarity (77·5%) with that of staphylocoagulase-type (SCT) XIa. The sequence of the D1 region, which would be responsible for the determination of SCT, shared the highest similarity (91·8%) with that of SCT XIa. These results suggest that coa310 is a novel variant of SCT XI. Moreover, we demonstrated that coa310 encodes a functioning coagulase, by confirming the coagulating activity of the recombinant protein expressed from coa310. This is the first study to directly demonstrate that Coa310, a putative SCT XI, has coagulating activity. These findings may be useful for the improvement of the staphylocoagulase-typing method, including serotyping and genotyping.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to identify a novel variant of staphylocoagulase type XI based on its nucleotide sequence and to demonstrate coagulating activity in the variant using a recombinant protein. Elucidation of the variety of staphylocoagulases will provide suggestions for further improvement of the staphylocoagulase-typing method and contribute to our understanding of the epidemiologic characterization of Staphylococcus aureus.

Molecular Characterization of Methicillin-ResistantStaphylococcus aureusin Hospitals in Niigata, Japan: Divergence and Transmission

The major methicillin-resistant Staphylococcus aureus(MRSA) distributed among hospitals in Japan is New York/Japan clone [multilocus sequence type 5 (ST5), agr type 2 and methicillin resistance locus type (SCC mec) II] which possesses both the toxic shock syndrome toxin 1 gene (tst) and staphylococcal enterotoxin C gene (sec). In this study, we collected 245 MRSA strains from four hospitals during 2001 to 2005 in Niigata, Japan, and analyzed tst and sec genes and SCC mec type among them. A total of 13 strains were further examined for their genotypes, virulence gene patterns and drug resistance. Among the 245 strains four tst sec genes patterns were observed; tst(+) sec(+) strains represented a majority of 86.5% and 9.4% were tst(-) sec(-). SCCmec typing revealed that 91.4% had type II, 4.1% type IV and 4.1% type I. Multilocus sequence typing (MLST) revealed that 10 of the 13 typed strains belonged to clonal complex 5 (7 had ST5 while 3 were single locus variants of ST5) with similar characteristics to the New York/Japan clone and possessed multi-drug resistance with high virulence gene content. The remaining 3 strains were ST8 (n=2) and ST91 (n=1). The ST91 strain had SCC mec IV and seemed to originate in the community, while ST8 strains exhibited SCC mec type I, which is distinct from community type IV. The data suggest that MRSA in hospitals in Niigata now mainly includes the New York/Japan clone (undergoing genomic divergence and clonal expansion) and other minor types (e.g. ST8) as well as the community type.

MRSA enteritis causing a high stoma output in the early postoperative phase after bowel surgery

INTRODUCTION

Nosocomial MRSA infection has become an important healthcare issue. We present 6 cases of MRSA enteritis, acquired following bowel surgery and ileostomy formation.

PATIENTS AND METHODS

The data set was obtained from the experience of one consultant surgeon over 6 years in one medical centre. The clinical features and course of six patients that developed MRSA enteritis postoperatively were obtained through review of case notes and laboratory data.

RESULTS

Four male and two female patients (age range, 22-80 years) developed a clinical syndrome postoperatively requiring treatment within the high dependency unit. Three developed respiratory distress syndrome, and one died from multi-organ failure. Exploratory laparotomy carried out in three patients was negative. All patients were MRSA-negative on admission but had swabs positive for MRSA from ileostomy site postoperatively. All of the three patients who had ileostomy effluent cultured for MRSA had positive results.

DISCUSSION

Fever, abdominal pain, distension and high stoma output in the early postoperative period following bowel surgery should alert the clinician to the possibility of MRSA enteritis. Patients require aggressive resuscitation and culture of ileostomy effluent for MRSA. Exploratory laparotomy has no obvious benefits. As MRSA enteritis has the potential to be a lethally effective disseminator of MRSA, such clinical features should prompt early instigation of appropriate infection control practices.

Molecular epidemiology of enteritis-causing methicillin-resistant Staphylococcus aureus

In the early 1990s, severe enteritis caused by methicillin-resistant Staphylococcus aureus (MRSA enteritis) was prevalent in Japan, but the incidence has since decreased. We compared the genotypes and phenotypes of 12 isolates that caused MRSA enteritis (enteritis isolates), detected between 1990 and 1993, with 186 non-enteritis isolates detected between 1998 and 2002. Organisms were investigated using pulsed-field gel electrophoresis (PFGE), coagulase typing and reverse passive latex agglutination to detect production of staphylococcal enterotoxins (SE) and toxic shock syndrome toxin-1 (TSST-1); and polymerase chain reaction (PCR) for detection of the structural genes entA, entB, entC, entD and tst, which encode proteins SE-A, SE-B, SE-C, SE-D and TSST-1, respectively. The 12 enteritis isolates were classified into four types and four subtypes. Only seven of the 186 non-enteritis isolates had PFGE patterns indistinguishable from the enteritis isolates. Eight of the 12 enteritis isolates had entA, entC and tst, and produced high levels of SE-A and TSST-1, but not SE-C. Of the 186 non-enteritis isolates, 157 produced SE-C and TSST-1, but not SE-A. The seven non-enteritis isolates with a PFGE pattern indistinguishable from the enteritis isolates did not produce SE-A, and showed relatively low levels of TSST-1 production. These isolates may have continued to inhabit our ward since the earlier outbreak, but acquired a different phenotype. In conclusion, the disappearance of MRSA enteritis may have resulted from the decreased incidence of enteritis-causing clones and phenotypical changes.

Establishment of a universal size standard strain for use with the PulseNet standardized pulsed-field gel electrophoresis protocols: converting the national databases to the new size standard

The PulseNet National Database, established by the Centers for Disease Control and Prevention in 1996, consists of pulsed-field gel electrophoresis (PFGE) patterns obtained from isolates of food-borne pathogens (currently Escherichia coli O157:H7, Salmonella, Shigella, and Listeria) and textual information about the isolates. Electronic images and accompanying text are submitted from over 60 U.S. public health and food regulatory agency laboratories. The PFGE patterns are generated according to highly standardized PFGE protocols. Normalization and accurate comparison of gel images require the use of a well-characterized size standard in at least three lanes of each gel. Originally, a well-characterized strain of each organism was chosen as the reference standard for that particular database. The increasing number of databases, difficulty in identifying an organism-specific standard for each database, the increased range of band sizes generated by the use of additional restriction endonucleases, and the maintenance of many different organism-specific strains encouraged us to search for a more versatile and universal DNA size marker. A Salmonella serotype Braenderup strain (H9812) was chosen as the universal size standard. This strain was subjected to rigorous testing in our laboratories to ensure that it met the desired criteria, including coverage of a wide range of DNA fragment sizes, even distribution of bands, and stability of the PFGE pattern. The strategy used to convert and compare data generated by the new and old reference standards is described.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus strains causing neonatal toxic shock syndrome-like exanthematous disease in neonatal and perinatal wards

Neonatal toxic shock syndrome-like exanthematous disease (NTED) is a new neonatal disease caused by toxic shock syndrome toxin 1 (TSST-1). We conducted a prospective surveillance study and characterized the methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from patients with NTED and compared them with the strains from patients with other MRSA infections and asymptomatic carriers. The study was performed in the neonatal intensive care unit and a general neonatal and maternal ward in the Tokyo Women's Medical University Hospital (TWMUH) from September to December 1998. Among 103 patients eligible for the study, MRSA was detected in 62 (60.2%) newborns; of these 62 newborns, 8 (12.9%) developed NTED, 1 (1.6%) had another MRSA infection, and 53 (85.5%) were asymptomatic MRSA carriers. Sixty-nine MRSA strains were obtained from the 62 newborns. DNA fingerprinting by pulsed-field gel electrophoresis showed two clusters: clone A with 8 subtypes and clone B. Sixty-seven of the 69 MRSA strains (97.1%) belonged to clone A, and type A1 was the most predominant (42 of 69 strains; 60.9%) in every neonatal and perinatal ward. All but one of the clone A strains had the TSST-1 and staphylococcal enterotoxin C genes. We also analyzed eight MRSA strains from eight NTED patients in five hospitals in Japan other than TWMUH. All the MRSA strains from NTED patients also belonged to clone A. These results suggest that a single clone that predominated in the neonatal wards of six hospitals might have caused NTED. However, the occurrence of NTED might not be dependent on the presence of an NTED-specific strain.

Molecular epidemiological studies of Staphylococcus aureus in urinary tract infection

In recent years, the increasing incidence of urinary tract infection (UTIs) caused by Staphylococcus aureus has been noted at the urology ward, Okayama University Hospital. We investigated the molecular epidemiological characteristics of 139 UTI isolates, including 45 methicillin-sensitive S. aureus (MSSA) and 94 methicillin-resistant S. aureus (MRSA), collected over a 10-year period from 1990 to 1999. The antibiotic resistance genes ( mecA, aph(3')-III, aac(6')-aph(2"), ant(4')-I) and the toxin genes (tst, sea, seb, and sec) were detected by using multiplex polymerase chain reaction (PCR). Since 1996, the prevalence of the ant(4')-I, tstand secgenes has increased markedly in coagulase type II S. aureus possessing the mecA gene (MRSA). The presence of toxin genes in MRSA was higher than that in MSSA; 66.0% and 26.7% for tst, 7.4% and 4.4% for sea, 24.5% and 8.9% for seb, and 66.0% and 28.9% for sec, respectively. In the review of medical records, it was found that febrile episodes occurred in 12 of 72 patients with monomicrobial UTI caused by S. aureus. For the febrile patients, S. aureus isolates with both the tst and sec genes were found significantly more often (11 of 12; 91.7%) than those without the tst and sec genes ( P = 0.0484). Molecular typing of MRSA isolates, by using random amplified polymorphic DNA analysis and pulsed-field gel electrophoresis analysis, revealed no apparent clonality of these isolates over the 10 years, suggesting that most of the recent MRSA infections are not due to cross-infection in the urology ward.