Β-lactam Antimicrobial Drugs Research Articles

Teaching a New Dog Old Tricks: Ultrafast Liquid Chromatography/Tandem-Mass Spectrometry Analysis of Nine ß-Lactam Antibiotics for Improved Therapeutic Drug Monitoring.

Therapeutic drug monitoring (TDM) of β-lactam antibiotics provides critical knowledge in hospital intensive care unit environments to support dosing within the narrow window between therapeutic failure and toxicity. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the most suitable analytical technique for these drugs; however, clinicians, patients, and laboratories would benefit from shortening the timeframe between the collection of samples and reporting of results. The authors developed a very rapid LC-MS/MS method for 9 β-lactam antimicrobial drugs on a commercial core-shell reverse-phase LC column by exploiting the performance of such stationary phase materials at a high mobile-phase linear velocity and using a simple flow split to optimize ionization conditions in the mass spectrometer ion source. The method's performance was assessed using a currently validated routine LC-MS/MS assay performed on the same instrument. Routine ß-lactam assays were reduced from >6 minutes per sample to less than 2 minutes with improved chromatographic resolution, while still maintaining acceptable analytical performance (average correlation coefficient: 0.99670, interday imprecision: 2.0%-10.8%, and bias: -1.68%), hence generating results in agreement with an existing validated method for patient and quality assurance program samples. Time-critical results, such as those for β-lactam antimicrobials, may be reported by the TDM laboratory several hours earlier than current methods allow, providing improved patient care and generating capacity on LC-MS/MS instruments for larger batch sizes and/or additional assays. The simple-to-implement technique demonstrated in this study may be applicable to other TDM assays or any LC-MS/MS method where faster turnaround times are desirable.

Knowledge, Awareness and Practice towards New Generation Cephalosporin among Dental Students

Dentists all over the world prescribe antibiotics therapeutically and prophylactically to manage oral and dental infections more commonly orofacial infections. The prescribing of antibiotics by dental practitioners has become an important aspect of dental practice as most human orofacial infections originate from odontogenic infections. The cephalosporins are a large family of broad-spectrum β-lactam antimicrobial drugs. Cephalosporins are now used as first-line agents in the treatment of many infections, including pneumonia, meningitis, and gonorrhea. The aim of this study was to assess knowledge awareness and Practice towards New Generation Cephalosporin among dental students. A questionnaire consisting of 10 questions were prepared and distributed to 100 dental students, the questionnaire was prepared online and the link was distributed to the dental students. The results were tabulated and statistical analysis was done using SPSS software. From this survey, it is seen that most of the students were not well aware of the new generation cephalosporins. 63% of the dental students were aware that cephalosporins are broad-spectrum antibiotics. 74% of the students were aware of cephalosporin drugs, 88% of the respondents do not use cephalosporins in their practice, among the entire population only 32% were aware regarding the new generation cephalosporin and only 33% of the students were aware regarding its action against MRSA. 17% of the dental students were aware that 5 generations of cephalosporins are available Most of the dental students who attempted this questionnaire did not have complete knowledge regarding the new generations of cephalosporins rather they were aware of the 3rd and 4th generation cephalosporins. Furthermore, knowledge regarding the pharmacological aspects of new generation cephalosporins is necessary so that they can apply it to their practice.

Community-Associated Methicillin-Resistant Staphylococcus aureus: An Enemy amidst Us.

Methicillin-resistant Staphylococcus aureus (MRSA), or multidrug-resistant S. aureus, first reported in the early 1960s in the United Kingdom, are strains of S. aureus that through the process of natural selection developed resistance to all available penicillins and other β-lactam antimicrobial drugs [1]. Although the evolution of such resistance does not cause the organism to be more intrinsically virulent, resistance does make MRSA infections more difficult to treat and thus more dangerous, particularly in hospitalized patients and those with weakened immune systems [2]. MRSA can be spread from one person to another through casual contact or through contaminated objects, and a strain acquired in a hospital or health care setting is called health care–associated methicillin-resistant S. aureus (HA-MRSA) [2]. In fact, MRSA has become an important cause of nosocomial infections worldwide and is currently the most commonly identified antibiotic-resistant pathogen in United States hospitals [3–5]. However, although MRSA has been entrenched in hospital settings for several decades, it has undergone rapid evolutionary changes and epidemiologic expansion, spreading beyond the confines of health care facilities, where it is emerging anew as a dominant pathogen known as community associated-MRSA (CA-MRSA) [6]. The rapid dissemination of CA-MRSA strains among general populations in diverse communities has resulted in increasing reports of outbreaks worldwide [1]. In fact, in some regions, CA-MRSA isolates account for 75% of community-associated S. aureus infections in children, creating a public health crisis in the US [1,7]. In this article, we will provide a brief overview of what is known about the epidemiology and pathogenesis of community- associated MRSA and discuss how they differ from the strains originating in health care settings. Further, therapeutic and preventative measures available to combat the rising spread of this revamped pathogen are also discussed.

Detection ofRickettsia sibirica mongolitimonaeby Using Cutaneous Swab Samples and Quantitative PCR

Detection of<i>Rickettsia sibirica mongolitimonae</i>by Using Cutaneous Swab Samples and Quantitative PCR

New Delhi Metallo-β-Lactamase-1 in Carbapenem-ResistantSalmonellaStrain, China

New Delhi Metallo-β-Lactamase-1 in Carbapenem-Resistant<i>Salmonella</i>Strain, China

Methicillin-ResistantStaphylococcus pseudintermediusin Rats

Methicillin-Resistant<i>Staphylococcus pseudintermedius</i>in Rats

New Delhi Metallo-β-Lactamase 4–producingEscherichia coliin Cameroon

New Delhi Metallo-β-Lactamase 4–producing<i>Escherichia coli</i>in Cameroon

BlaNDM-1–positiveKlebsiella pneumoniaefrom Environment, Vietnam

<i>bla</i>_NDM-1–positive<i>Klebsiella pneumoniae</i>from Environment, Vietnam

Clonal Spread ofMycoplasma pneumoniaein Primary School, Bordeaux, France

Clonal Spread of<i>Mycoplasma pneumoniae</i>in Primary School, Bordeaux, France

Granulicatella adiacensand Early-Onset Sepsis in Neonate

<i>Granulicatella adiacens</i>and Early-Onset Sepsis in Neonate

Complete Sequence and Molecular Epidemiology of IncK Epidemic Plasmid EncodingblaCTX-M-14

Antimicrobial drug resistance is a global challenge for the 21st century with the emergence of resistant bacterial strains worldwide. Transferable resistance to β-lactam antimicrobial drugs, mediated by production of extended-spectrum β-lactamases (ESBLs), is of particular concern. In 2004, an ESBL-carrying IncK plasmid (pCT) was isolated from cattle in the United Kingdom. The sequence was a 93,629-bp plasmid encoding a single antimicrobial drug resistance gene, blaCTX-M-14. From this information, PCRs identifying novel features of pCT were designed and applied to isolates from several countries, showing that the plasmid has disseminated worldwide in bacteria from humans and animals. Complete DNA sequences can be used as a platform to develop rapid epidemiologic tools to identify and trace the spread of plasmids in clinically relevant pathogens, thus facilitating a better understanding of their distribution and ability to transfer between bacteria of humans and animals.

Methicillin-ResistantStaphylococcus aureusST398, Italy

To the Editor: It has recently become apparent that livestock can constitute a new methicillin-resistant Staphylococcus aureus (MRSA) reservoir and be a source of a novel and rapidly emerging type of MRSA. These livestock-associated MRSA clones are nontypeable by use of pulsed-field gel electrophoresis with SmaI and belong to sequence type (ST) 398 (1). MRSA ST398 clones account for 20% of all MRSA in the Netherlands (2), but the emergence of such clones has been described worldwide (3). Although ST398 transmission has been reported primarily between animals, persons with occupational exposure to livestock are at higher risk for MRSA carriage than the general population. Even though MRSA ST398 usually causes colonization, several cases of infections of variable clinical relevance, varying from skin and soft tissue infections (4) to endocarditis (5) and pneumonia (6), have been described over the past few years. Most instances of ST398 human carriers have been identified among persons who work at pig farms (7). Data regarding MRSA colonization of dairy farmers are less exhaustive and, to our knowledge, only 1 instance of direct transmission between cattle and humans has been proven. MRSA isolates from cows with subclinical mastitis in 2007 in Hungary were indistinguishable from MRSA isolates from the tonsil swab of a farmer who worked with these animals (8). We report a case of MRSA ST398 invasive disease in a cattle farmer, as well as a case of MRSA ST398 necrotizing fasciitis. In early April 2008, a 52-year-old man was admitted to an intensive care unit in Manerbio, Italy, because of severe sepsis and a large ulcerative and suppurative lesion on the right side of his neck. His medical history was unremarkable. He was a worker at a dairy farm, was obese, and did not report any previous contact with the healthcare system. At the time of hospital admission, he was oriented and cooperative. His temperature was 38.4°C, heart rate was 125 beats per minute, and blood pressure was 165/75 mm Hg. Arterial blood gas analysis showed hypoxemia and mild hypocapnia (PaO2 53 mm Hg and PaCO2 33.8 mm Hg on room air). Leukocyte count was 21,280 cells/μL (81.9% polymorphonuclear cells), and platelet count was 310,000 cells/μL. After blood samples were collected and aggressive surgical debridement of affected tissue was performed, empirical treatment with intravenous teicoplanin and imipenem was started. On the basis of histologic appearance of the intraoperative material and computed tomography scan images, necrotizing fasciitis was diagnosed. Culture of blood and necrotic tissue yielded MRSA. On day 3 after admission, antimicrobial drug therapy was changed to teicoplanin and clindamycin and, on day 7, to linezolid. Fever resolved in 3 days and the patient’s condition progressively improved. The patient was discharged after 31 days of antimicrobial drug therapy. The MRSA isolate was susceptible to all the non–β-lactam antimicrobial drugs tested (excluding tetracycline), carried the staphylococcal cassette chromosome mec type V, and was negative for Panton-Valentine leukocidin (PVL) genes. Multilocus sequence typing and sequence typing of the tandem repeat region of protein A gene (spa typing) showed that the isolate belonged to ST398 and spa type 899, respectively. Some issues are of concern. Although the MRSA isolate was PVL negative, its virulence resembled that of PVL-positive strains. Furthermore, it was resistant to tetracycline, as we expected because oxytetracyclines are the antimicrobial drugs most frequently used in pig and cattle farming (3). The major limitation of our study was that data regarding MRSA colonization of the farm are missing, so cattle-to-human transmission cannot be proven. However, because our patient did not have any other potential risk factor, dairy cows were probably the source of the human infection. In countries where community-acquired MRSA is common, all patients with serious S. aureus infections should be treated for MRSA until antimicrobial susceptibilities are known. Our report suggests that even in countries where community-acquired MRSA is still rare, being a cattle farmer may be considered an indication for early treatment against MRSA. The expanding knowledge of this zoonotic potential may undermine existing nosocomial MRSA control programs. In countries where a search and destroy policy (9) is adopted, such as the Netherlands, pig and cattle farmers may warrant screening and isolation at the time of hospital admission. Nevertheless, the first MRSA ST398 nosocomial outbreak has already been described (10). It is difficult to prevent persons with constant exposure to MRSA in their work or home setting from becoming MRSA carriers. Revisiting policies for the use of antimicrobial drugs on livestock farms, as well as improving hygiene measures, may therefore be necessary in infection control programs. However, before final recommendations can be made, further investigation is needed to determine the prevalence of MRSA among livestock and their handlers.

Increase in Group G Streptococcal Infections in a Community Hospital, New York, USA

To the Editor: Identified in 1935 by Lancefield and Hare, group G streptococci (GGS) are part of the normal flora of the pharynx, gastrointestinal tract, genital tract, and skin (1–3). However, previous case reports have indicated that GGS also could cause complicated infections, including cellulitis, osteomyelitis, septic arthritis, meningitis, endocarditis, and bacteremia (3–6). Since the mid-1980s, several studies worldwide have reported an increasing incidence of GGS bacteremia (1,5–8), but no recent study has been conducted in the United States to determine the incidence of overall GGS infection. We noticed that an increasing number of patients with GGS have been admitted to Long Island College Hospital in Brooklyn, New York, USA, during the past few years. To better understand the trend of GGS infection in our institution, we retrospectively reviewed charts of patients admitted from January 2003 through December 2007 who had microbiologically proven GGS infection. Inclusion criteria were clinically and microbiologically documented GGS infection in patients who received appropriate antimicrobial drugs and were >18 years of age. Lancefield GGS were identified in the laboratory by latex agglutination test; resistance profiles were not done for GGS. A total of 73 persons with GGS were admitted to the hospital during the 5-year study period; the number of patients admitted increased yearly (Figure). Mean age of patients was 53 years; most (77%) were <65 years of age; 52% were women, and most (61%) patients were African American. Thirty (41%) patients had polymicrobial infections; other identified organisms included methicillin-susceptible Staphylococcus aureus (8 [11%]), methicillin-resistant S. aureus (MRSA) (9 [12%]), and gram-negative or anaerobic organisms (13 [18%]). Figure Annual number of patients with group G streptococcal infections admitted to Long Island College Hospital, Brooklyn, New York, USA, 2003–2007. The spectrum of GGS infections ranged from mild skin and soft tissue infection (34 [46%]) to invasive diseases, including urogenital infection (7 [10%]); lower respiratory tract infection (7 [10%]); pharyngitis (6 [8%]); endocarditis and catheter infection (5 [7%]); and others (14 [19%]), such as peritonitis, pelvic abscess, rectal abscess, and septic arthritis. Four of the 6 persons with pharyngitis were assumed to be colonized with the organism. Eight (24%) of 34 skin and soft tissue infections were associated with bacteremia, 5 (15%) with osteomyelitis, and 20 (59%) with polymicrobial infections. Six persons with lower respiratory tract infections and 1 each with endocarditis, genital tract infection, pelvic abscess, and dental abscess also had polymicrobial infections. Eighteen persons had bacteremia, the trend of which also increased yearly. Of these, 8 had skin and soft tissue infections, 4 had endocarditis, 2 had urinary tract infections, 1 had possible spontaneous bacteria peritonitis, and 1 had hemodialysis catheter infection; 2 were of unknown source. Of the patients with endocarditis, 2 had vegetations on the native valves, 1 had a pacemaker infection, and 1 had prosthetic valve vegetation. One case of native valve endocarditis occurred in a tricuspid valve in an injection drug user. Another case occurred in a patient in which an epidural abscess was associated with an aortic valve vegetation. Most of the patients had underlying medical conditions; 34% had diabetes mellitus. In contrast to previous reports, which stated that malignancy was the most common underlying disease (2,3), only 7 (10%) of the patients in our study group had underlying malignancy, of whom 4 had active malignancy and the rest had had previous malignancy. Nine patients with a history of injection drug use and 5 with HIV infection were identified; the patient with bacteremia secondary to hemodialysis catheter infection had a history of both HIV and intravenous drug use. Three (4%) patients died; their deaths were unlikely to be attributable to GGS because all were elderly (78–92 years) and had underlying coexisting conditions and co-infections. All 4 persons with endocarditis and the patient with the catheter infection survived. Five patients who were co-infected with MRSA were treated with vancomycin or daptomycin; the remainder were treated with β-lactam antimicrobial drugs and had the sources of infection (catheter or pacemaker) removed. When infections caused by gram-negative or anaerobe organisms were identified, they were also treated with appropriate antimicrobial drugs. The overall average length of stay for all patients with GGS was 9.4 days, with longer stays for those with underlying diabetes mellitus (14.6 days) than for those without diabetes (6.7 days). GGS was an important etiologic agent for a wide spectrum of infections. Its impressive increase in our institution during the past 5 years raises concerns because other types of β-hemolytic streptococcal infection have increased recently. Group A and B (9,10) increased substantially during the 1980s. A multicenter analysis may confirm GGS as an emerging human pathogen and may help us better understand the reason for this increase.

Role of Ceftiofur in Selection and Dissemination of bla CMY-2 -Mediated Cephalosporin Resistance in Salmonella enterica and Commensal Escherichia coli Isolates from Cattle

Third-generation cephalosporin resistance of Salmonella and commensal Escherichia coli isolates from cattle in the United States is predominantly conferred by the cephamycinase CMY-2, which inactivates beta-lactam antimicrobial drugs used to treat a wide variety of infections, including pediatric salmonellosis. The emergence and dissemination of bla(CMY-2)(-)-bearing plasmids followed and may in part be the result of selection pressure imposed by the widespread utilization of ceftiofur, a third-generation veterinary cephalosporin. This study assessed the potential effects of ceftiofur on bla(CMY-2) transfer and dissemination by (i) an in vivo experimental study in which calves were inoculated with competent bla(CMY-2)-bearing plasmid donors and susceptible recipients and then subjected to ceftiofur selection and (ii) an observational study to determine whether ceftiofur use in dairy herds is associated with the occurrence and frequency of cephalosporin resistance in Salmonella and commensal E. coli. The first study revealed bla(CMY-2) plasmid transfer in both ceftiofur-treated and untreated calves but detected no enhancement of plasmid transfer associated with ceftiofur treatment. The second study detected no association (P = 0.22) between ceftiofur use and either the occurrence of ceftiofur-resistant salmonellosis or the frequency of cephalosporin resistance in commensal E. coli. However, herds with a history of salmonellosis (including both ceftiofur-resistant and ceftiofur-susceptible Salmonella isolates) used more ceftiofur than herds with no history of salmonellosis (P = 0.03) These findings fail to support a major role for ceftiofur use in the maintenance and dissemination of bla(CMY-2)-bearing plasmid mediated cephalosporin resistance in commensal E. coli and in pathogenic Salmonella in these dairy cattle populations.

CTX-M Extended-spectrum β-Lactamases, Washington State

To the Editor: The CTX-M–type β-lactamases are non-TEM and non-SHV plasmid-mediated, class A, extended-spectrum β-lactamases (ESBLs). The CTX-M–type β-lactamases have recently emerged as the most common type of ESBLs, with a global distribution (1). In contrast, the CTX-M–type ESBLs are rarely reported in the United States and have not been identified in pathogens isolated from infected patients with gastroenteritis. We screened 637 Salmonella and 126 Shigella isolates, collected in the state of Washington during 2003–2004, for CTX-M–type β-lactamases. Of these, 60 Salmonella isolates that exhibited an ESBL phenotype were further characterized by PCR for TEV, SHV, CTM-X, and CMY. All were positive for the CMY-2 or TEM-1 β-lactam genes. One Shigella sonnei isolate (WA7593), cultured from a fecal specimen in August 2004, tested positive with an ESBL confirmatory disk diffusion panel (ceftazidime 24 mm, ceftazidime/clavulanate 32 mm, cefotaxime 14 mm, and cefotaxime/clavulanate 34 mm; [2]). The patient had recently traveled to Pakistan and likely became ill there and returned to the United States while still sick. The transfer of extended-spectrum cephalosporin resistance was tested by conjugation to Escherichia coli J53 aziR (3). The MIC for S. sonnei WA7593 and its transconjugant, WA7593TC1, were tested by using the E-test (AB Biodisk, Solna, Sweden). Both strains were resistant to cefotaxime and susceptible to ceftazidime and showed almost the same antimicrobial susceptibility patterns as β-lactam antimicrobial drugs (Table). Table MICs of antimicrobial drugs for Shigella sonnei clinical isolate WA7593 and its transconjugant WA7593TC1 The type of ESBL produced by these strains was determined by using PCR specific for TEM and CTX-M (4,5). Both strains were PCR positive for TEM and CTX-M. The TEM type PCR products were then sequenced and identified as TEM-1; no variation was found on the promoter region of blaTEM-1. The entire sequence of bla CTX-M from WA7593 was then sequenced (1), and the product showed 100% homology with blaCTX-M-15 (GenBank accession no. {type:entrez-nucleotide,attrs:{text:AY960984,term_id:63029819,term_text:AY960984}}AY960984). The mobile element associated with the transfer of blaCTX-M-15 was investigated by sequencing the flanking regions. PCRs were performed with primers from the internal regions of bla CTX-M gene and primers for insertion sequences ISEcp1 and IS903 (4,5). Positive PCR products were obtained with primers ISEcp1F and CTX2 (943 bp); no amplified product was produced with primers CTX1 and IS903R. Sequencing of a 943-bp amplicon showed that blaCTX-M15 was flanked upstream by an ISEcp1-like element. The presence of an integron in S. sonnei WA7593 and WA7593TC1 was investigated by using integron-specific primers hep35 and hep36 (2). Only S. sonnei WA7593 produced a PCR product. This finding suggests that the transmission of blaCTX-M15 is not by integron-mediated transfer. A further 162 Shigella spp. and 260 Salmonella spp. isolated from 2003 through 2005 were also screened for ESBL production; no further isolates were identified. The presence of a CTX-M–type, ESBL-producing isolate is rarely reported in the United States. The only other reference was from a multistate study in 2001–2002 that identified CTX-M type from E. coli isolates from urine, sputum, and blood (6). No further reports about CTX-M–producing organisms have been disseminated. Our investigation suggests that CTX-M–type ESBLs may spread throughout the United States through infected travelers. This finding is notable because S. sonnei is a common enteric pathogen. Our results further emphasize that travelers from others parts of the world can introduce highly mobile and clinically important resistance mechanisms into the community. The spread of CTX-M ESBLs may be faster and more widespread than previously thought; therefore, CTX-M type should be taken seriously as a surveillance target in the United States, especially in patients with a history of travel outside North America.

KPC Type B-Lactamase, Rural Pennsylvania

KPC Type B-Lactamase, Rural Pennsylvania

Extended-spectrum β-Lactamase–producingEnterobacteriaceae, Central African Republic

Extended-spectrum β-Lactamase–producing<i>Enterobacteriaceae</i>, Central African Republic

Contrasting Pediatric and Adult Methicillin-resistantStaphylococcus aureusIsolates

We performed a prospective study of all inpatient and outpatient methicillin-resistant Staphylococcus aureus (MRSA) isolates identified at the University of Chicago Hospitals from November 2003 through November 2004. Differences in resistance to non-beta-lactam antimicrobial drugs were determined after stratification of the 578 MRSA isolates into 4 groups by patient age (pediatric vs. adult) and onset location (community vs. hospital). Non-beta-lactam resistance was significantly greater among the 288 adult than the 177 pediatric community-associated isolates for erythromycin (93.2 vs. 87.0%, p = 0.03), clindamycin (51.8 vs. 7.3%, p<0.001), ciprofloxacin (62.1 vs. 10.7%, p<0.001), gentamicin (11.1 vs. 1.1%, p<0.001), and tetracycline (19.9 vs. 6.4%, p<0.001). In contrast, hospital-associated MRSA isolates from children and adults had similar rates of non-beta-lactam antimicrobial drug resistance. In our region, clindamycin is an appropriate empiric therapy of community-associated MRSA infection in children but should be used with caution in adults.

Community Case of Methicillin-resistantStaphylococcus aureusInfection

Community Case of Methicillin-resistant<i>Staphylococcus aureus</i>Infection

Methicillin-resistantStaphylococcus aureusNecrotizing Pneumonia

To the Editor: Methicillin-resistant Staphylococcus aureus (MRSA) strains account for >40% of all hospital-acquired S. aureus infections in Italy (1). Although cases of community-acquired MRSA (CA-MRSA) infections have been reported in recent years (2), these isolates have not been characterized for Panton-Valentine leukocidin (PVL) (3); therefore, the presence of isolates with the typical characteristics of CA-MRSA (4) in Italy remains unknown. At the beginning of April 2005, a 37-year-old woman was admitted to the University Hospital Policlinico in Rome because of fever, cough, and headache. Her medical history was unremarkable. She was a teacher in a school for foreign students in Rome, smoked 3 cigarettes per day for 15 years, and reported no recent travel abroad. Her 5-year-old daughter had influenzalike symptoms in the previous week. At hospital admission, her temperature was 39°C, heart rate was108 beats/min, respiratory rate was 32 breaths/min, and blood pressure was 105/70 mmHg. Arterial blood gas analysis showed mild hypoxemia and hypocapnia (PaO2 73 mm Hg and PaCO2 34 mm Hg on room air). Leukocyte count was 24,360 cells/μL (81% polymorphonuclear cells), and platelet count was 506,000/μL. Chest radiograph showed infiltrates in the right upper and lower lobes and left lower lobe. Empiric treatment with clarithromycin and ceftriaxone was started, but the patient's clinical conditions did not improve. Culture of sputum samples obtained at admission yielded growth of MRSA. Computed tomographic scan showed multiple lung cavitary lesions, indicating necrotizing pneumonia. On day 3 of admission, antimicrobial drug therapy was changed to linezolid (600 mg 2 times a day). Fever resolved, and the patient's condition rapidly improved. The patient was discharged after 14 days of linezolid treatment. At discharge, leukocyte count was 6,040 cell/μL (58% polymorphonuclear cells), and arterial blood gas analysis showed PaO2 of 88 mm Hg. The MRSA isolate from sputum was susceptible to all the non–β-lactam antimicrobial drugs tested, including erythromycin, clindamycin, ciprofloxacin, tetracycline, kanamycin, and fusidic acid. With established molecular methods, the isolate was found to harbor SCCmec type IV (5); lukS and lukF, the genes coding for the 2 subunits of the PVL toxin; and hlg, the γ-hemolysin gene (3). The genetic background of the isolate was determined by multilocus sequence typing (MLST) (6) and sequence typing of the tandem repeat region of protein A gene (spa typing) (7). Results showed that the isolate belonged to ST30 according to the MLST database (http://saureus.mlst.net), and spa typing, analyzed by the Ridom Staphtype software (http://www.ridom.de), indicated a novel spa type, to which type 755 was assigned. ST30, 1 of 6 clones more commonly associated with PVL-positive CA-MRSA (4), is designated also the southwest Pacific (SWP) clone, because of the area in which it circulates. Recently, the SWP clone has caused CA-MRSA infections in northern European countries (England, Scotland, the Netherlands, Sweden, and Latvia) (8,9). Molecular analysis suggests that the SWP clone has evolved from a methicillin-susceptible clone of S. aureus, termed phage type 80/81, that was pandemic in the 1950s and considered to be unusually virulent and transmissible (8). In fact, strains belonging to phage type 80/81 carry the PVL gene and appear to have subsequently acquired methicillin resistance through horizontal transfer of SCCmec type IV. The spa type of the Italian isolate comprises 7 nucleotide repeats, indicated by XJ4AKAOM in the alphabetical code. This repeat sequence differs from that of the classical SWP clone, indicated by XKAKAOMQ (8), by only 1 bp in the second repeat and loss of the last Q repeat. In spite of these differences, the spa type is in substantial agreement with the MLST result and indicates that the Italian isolate is either a descendent or a local variant of the SWP clone. The most common clone of CA-MRSA described in Europe is ST80, spa type 44. CA-MRSA belonging to ST80 tend to be more antimicrobial drug resistant than isolates belonging to other clones (4). Resistance to fusidic acid, typical of ST80, has been proposed as a marker for CA-MRSA in Europe (10). In light of our finding, we cannot rely on resistance to fusidic acid to screen for PVL-producing CA-MRSA in our country. To our knowledge, this is the first report from Italy of necrotizing pneumonia caused by PVL-positive CA-MRSA. The presentation was typically that of a severe pneumonia that occurred in a previously healthy, young adult with no risk factors for MRSA acquisition, as described in other cases (11). This is also the first report of a SWP clone isolate in southern Europe; if the strain is circulating in Italy or is occasionally imported from the SWP area, whether our patient acquired it through contact with a foreign contact remains unknown.