Variation and persistence of methicillin-resistant Staphylococcus aureus strains among individual patients over extended periods of time

Outcomes and Treatment of Chronic Methicillin-Resistant Staphylococcus aureus Differs by Staphylococcal Cassette Chromosome mec (SCCmec) Type in Children With Cystic Fibrosis

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infects ∼25% of patients with cystic fibrosis (CF) in the United States. We hypothesized that health-related outcomes differed between healthcare-associated (staphylococcal cassette chromosome mec [SCCmec] II) vs community-associated (SCCmec IV) MRSA strains in patients chronically infected with CF.

METHODS

At 7 CF centers, MRSA isolates were prospectively obtained from patients ≤18 years old with 2 or more positive MRSA cultures within 1 year. Isolates were classified by SCCmec type and Panton-Valentine-leukocidin (PVL) status at a core laboratory, and sites remained blinded to SCCmec type and PVL results. Prospective clinical data including antibiotic use, respiratory symptoms, and pulmonary exacerbations were obtained.

RESULTS

Among the 295 cohort participants with typeable MRSA isolates, 69.5% had SCCmec II PVL(-), 13.2% had SCCmec IV PVL(-), and 17.3% had SCCmec IV PVL(+) strains. During follow-up of 287 patients with prospective data after enrollment, the risk for pulmonary exacerbations was significantly higher among participants with SCCmec II than SCCmec IV strains (risk ratio [RR] = 1.13; P = .03) and higher in those with SCCmec IV PVL(-) than SCCmec IV PVL(+) strains (RR = 1.62; P < .0001). Neither decline in lung function nor changes in nutritional outcomes differed by SCCmec type or PVL status during the study period.

CONCLUSIONS

Participants harboring chronic SCCmec II MRSA received more antibiotics and may have more lung disease than those with SCCmec IV; PVL(+) isolates were not associated with more advanced disease.

Improving transformation of Staphylococcus aureus belonging to the CC1, CC5 and CC8 clonal complexes

Methicillin resistant Staphylococcus aureus (MRSA) is an opportunistic pathogen found in hospital and community environments that can cause serious infections. A major barrier to genetic manipulations of clinical isolates has been the considerable difficulty in transforming these strains with foreign plasmids, such as those from E. coli, in part due to the type I and IV Restriction Modification (R-M) barriers. Here we combine a Plasmid Artificial Modification (PAM) system with DC10B E. coli cells (dcm mutants) to bypass the barriers of both type I and IV R-M of S. aureus, thus allowing E. coli plasmid DNA to be transformed directly into clinical MRSA strains MW2, N315 and LAC, representing three of the most common clonal complexes. Successful transformation of clinical S. aureus isolates with E. coli-derived plasmids should greatly increase the ability to genetically modify relevant S. aureus strains and advance our understanding of S. aureus pathogenesis.

Molecular Epidemiology of Methicillin–ResistantStaphylococcus Aureusin a Veterans Administration Medical Center

Objectives:

To determine whether patients who were colonized or infected with methicillin-resistantStaphylococcus aureus(MRSA) persistently carried the same strain and to identify the extent of strain variation within a population of patients.

Design:

Molecular typing by pulsed-field gel electrophoresis (PFGE) of stored MRSA isolates.

Setting:

A Veterans Administration Medical Center with 288 hospital, 45 intermediate-care, and 75 extended-care beds.

Isolates:

Between January 1991 and March 1993, 91 patients had MRSA identified in routine cultures. One hundred isolates from 57 patients (63%) were available for typing.

Results:

Before 1988, only occasional MRSA isolates were identified. By 1993, 50% ofS. aureusisolates from unique patients were resistant to methicillin. PFGE identified 7 MRSA strains, 3 of which were identified in specimens from 1 patient each. The most common strains were SD4 (20 patients), SD1 (12 patients), SD2 (12 patients), and SD5a (5 patients). Twenty patients had 2 or more isolates obtained at least 1 week apart (mean, 30.7 weeks; range, 1 to 102 weeks). Of these patients, 12 were colonized or infected with only one strain (mean time observed, 25.1 weeks; range, 1 to 82 weeks). Eight patients had at least 2 different strains (mean time observed, 39 weeks; range, 2 to 102 weeks).

Conclusion:

Numerous MRSA strains circulated in tiiis endemic setting; 40% of patients observed over time were colonized or infected witii more than one strain. Molecular typing was an essential tool for evaluating the epidemiology of MRSA in this setting.

Risk factors for development of methicillin-resistant Staphylococcus aureus-positive clinical culture in nasal carriers after decolonization treatment

BACKGROUND

Active surveillance systems are effective in reducing health care-associated infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Nonetheless, some patients develop MRSA infection despite control measures. We tried to identify risk factors related to the appearance of MRSA at sites other than the nasal fossa in patients who were nasal carriers of MRSA.

METHODS

A retrospective case-control study was conducted in an active surveillance program for MRSA between January 2009 and December 2010 at a Spanish teaching hospital. Cases were patients with MRSA in the anterior nares and a length of stay of at least 5 days who developed MRSA-positive clinical culture after decolonization treatment had started. Controls were patients with the same characteristics as the case group, except that they did not develop MRSA-positive clinical culture as verified by negative clinical cultures.

RESULTS

After intrinsic and extrinsic risk factors were analyzed, the emergence of mupirocin-resistant MRSA clones after decolonization treatment, and residence in a nursing home were marginally significant in the univariate analysis. The detection of the emergence of mupirocin-resistant MRSA clones was independently associated with the detection of MRSA in other clinical locations.

CONCLUSIONS

In an active surveillance program for MRSA it is important to determine the mupirocin susceptibility of the isolates to determine appropriate treatment and to verify negativity after decolonizing treatment has been completed.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus isolates from patients newly identified as nasal carriers

We aimed to determine whether additional molecular and microbiological evaluations of methicillin-resistant Staphylococcus aureus (MRSA) isolated from patients newly identified as nasal carriers were useful for control strategies and whether longitudinal testing during the same or repeat hospitalization changed MRSA status. Nasal swabs from patients positive by Xpert MRSA PCR and not known to be colonized in the previous year were cultured for S. aureus. Isolates were tested for resistance to a variety of antibiotics, including high-level mupirocin resistance (HLMR) and low-level mupirocin resistance (LLMR) and the presence of genes mecA and mupA and those for Panton-Valentine leukocidin (PVL), USA300, and USA400. Repeat nasal screens during the 6-month study were tested for continued presence of MRSA. Among 130 patients, cultures revealed MRSA in 85 (65.4%), methicillin-susceptible S. aureus in 19 (14.6%), and no growth in 26 (20%). MRSA isolates were USA300 positive in 13/85 (15.3%) and LLMR in 8/85 (9.4%) patients. No isolates were HLMR or mupA positive. mecA dropout was detected in 9/130 (6.9%) patients. The rate of subsequent MRSA infections in USA300-positive versus -negative patients was not different. MRSA nasal status remained concordant in 69/70 (98.6%) patients who had follow-up testing. The findings do not support expanding MRSA surveillance to include routine detection of genes for USA300, PVL, or mupA, all of which were either of low frequency or not significantly associated with MRSA infection risk in our population of newly identified nasal carriers. Repeat nasal screening for MRSA during the same or subsequent hospitalizations over 6 months could also be deferred, reducing costs associated with screening.

A type III-like restriction endonuclease functions as a major barrier to horizontal gene transfer in clinical Staphylococcus aureus strains

Staphylococcus aureus is an versatile pathogen that can cause life-threatening infections. Depending on the clinical setting, up to 50% of S. aureus infections are caused by methicillin-resistant strains (MRSA) that in most cases are resistant to many other antibiotics, making treatment difficult. The emergence of community-acquired MRSA drastically changed the picture by increasing the risk of MRSA infections. Horizontal transfer of genes encoding for antibiotic resistance or virulence factors is a major concern of multidrug-resistant S. aureus infections and epidemiology. We identified and characterized a type III-like restriction system present in clinical S. aureus strains that prevents transformation with DNA from other bacterial species. Interestingly, our analysis revealed that some clinical MRSA strains are deficient in this restriction system, and thus are hypersusceptible to the horizontal transfer of DNA from other species, such as Escherichia coli, and could easily acquire a vancomycin-resistance gene from enterococci. Inactivation of this restriction system dramatically increases the transformation efficiency of clinical S. aureus strains, opening the field of molecular genetic manipulation of these strains using DNA of exogenous origin.

Altered growth, pigmentation, and antimicrobial susceptibility properties of Staphylococcus aureus due to loss of the major cold shock gene cspB

An insertional mutation made in the major cold shock gene cspB in Staphylococcus aureus strain COL, a methicillin-resistant clinical isolate, yielded a mutant that displayed a reduced capacity to respond to cold shock and many phenotypic characteristics of S. aureus small-colony variants: a growth defect at 37 degrees C, a reduction in pigmentation, and altered levels of susceptibility to many antimicrobials. In particular, a cspB null mutant displayed increased resistance to aminoglycosides, trimethoprim-sulfamethoxazole, and paraquat and increased susceptibility to daptomycin, teicoplanin, and methicillin. With the exception of the increased susceptibility to methicillin, which was due to a complete loss of the type I staphylococcal cassette chromosome mec element, these properties were restored to wild-type levels by complementation when cspB was expressed in trans. Taken together, our results link a stress response protein (CspB) of S. aureus to important phenotypic properties that include resistance to certain antimicrobials.

Staphylococcus aureus isolates from blood and anterior nares induce similar innate immune responses in endothelial cells

To evaluate the possibility to distinguish virulent from non-virulent isolates, gene expression in human umbilical vein endothelial cells (HUVEC) induced by invasive and colonizing isolates of Staphylococcus aureus was compared. Gene expression in HUVEC was analyzed by microarray analysis after 4 h of infection with Staphylococcus aureus, isolated from healthy nasal carriers (n = 5) and from blood of septic patients (n = 5), to explore possible differences between the groups of bacteria in interaction with HUVEC. All isolates were spa-typed to disclose strain relatedness. Moreover, the isolates were characterized with DNA microarray to determine the presence of virulence genes and to investigate the potential genes of importance in HUVEC interaction. The expression of 41 genes was up-regulated, and four were down-regulated in HUVEC by all isolates. Most of the up-regulated genes encode cytokines, chemokines, interferon-induced proteins, proteins regulating apoptosis and cell proliferation. There was no difference in the gene expression pattern between HUVEC infected with invasive or colonizing isolates. Furthermore, there was no difference in the presence of bacterial virulence genes between the two groups. In conclusion, our data indicate that S. aureus isolates induce comparable expression patterns in HUVEC, irrespective of invasiveness or presence of virulence genes.

Methicillin-resistant Staphylococcus aureus in orthopaedic trauma

We have conducted a case-control study over a period of ten years comparing both deep infection with methicillin-resistant staphylococcus aureus (MRSA) and colonised cases with a control group.

Risk factors associated with deep infection were vascular diseases, chronic obstructive pulmonary disease, admission to a high-dependency or an intensive-care unit and open wounds. Those for colonisation were institutional care, vascular diseases and dementia. Older age was a risk factor for any MRSA infection. The length of hospital stay was dramatically increased by deep infection.

These risk factors are useful in identifying higher-risk patients who may be more susceptible to MRSA infection. A strategy of early identification and isolation may help to control its spread in trauma units.

Risk of infection and death due to methicillin-resistant Staphylococcus aureus in long-term carriers

BACKGROUND

Patients with newly acquired methicillin-resistant Staphylococcus aureus (MRSA) have significant risks of short-term morbidity and mortality due to this pathogen. We were interested in assessing whether long-term carriers have persistent risks of disease and whether all carriers, regardless of the duration of carriage, should be considered to be reasonable candidates for interventions to reduce the risk of infection.

METHODS

We conducted a single-center retrospective cohort study to evaluate the risk of subsequent MRSA infection and death among patients known to have harbored MRSA for at least 1 year (i.e., prevalent carriers).

RESULTS

Among 281 prevalent carriers, 65 (23%) developed a total of 96 discrete and unrelated MRSA infections in the year after their identification as prevalent carriers. The most common infections were pneumonia (accounting for 39% of MRSA infections), soft-tissue infection (14%), and central venous catheter infection (14%). Twenty-four percent of all infections involved bacteremia. Thirty-eight MRSA infections occurred during a new hospitalization, and 32 (84%) of these infections were the reason for admission to the hospital. MRSA contributed to 14 deaths, with 6 of these deaths deemed to be attributable to MRSA. Harboring MRSA for <2 years and MRSA colonization at the time of detection as a prevalent carrier were predictive of subsequent infection with MRSA.

CONCLUSIONS

Individuals who are known to have harbored MRSA for >1 year are at high risk for subsequent MRSA morbidity and mortality and should be considered to be targets for intervention, in addition to individuals who have newly acquired this pathogen.

Strain-relatedness of methicillin-resistant Staphylococcus aureus isolates recovered from patients with repeated infection

Invasive disease following methicillin-resistant Staphylococcus aureus (MRSA) detection is common, regardless of whether initial detection involves colonization or infection. We assessed the genetic relatedness of isolates obtained > or =2 weeks apart representing either repeated infections or colonization-infection sets to determine if infections are likely to be caused by previously harbored strains. We found that MRSA infection following initial colonization or infection is caused by the same strain in most cases, suggesting that a single successful attempt at decolonization may prevent the majority of later infection.

Carriage of multiple subtypes of methicillin-resistant Staphylococcus aureus by intensive care unit patients

OBJECTIVE

To determine how consistently patients are colonized with methicillin-resistant Staphylococcus aureus (MRSA) at various sites and how many subtypes can be carried simultaneously by a single patient.

SETTING

A 28-bed Intensive care unit in a tertiary-care referral hospital.

METHODS

A total of 1,181 patients were screened by culture of swab specimens obtained from the nose, throat, groin, and axilla on admission to the intensive care unit (ICU), twice weekly during their ICU stay, and at discharge.

RESULTS

MRSA was isolated at least once from 224 patients. Of these isolates, 359 were selected from 32 patients to be subtyped using pulsed-field gel electrophoresis. The rate of compliance with collection of swab specimens was 79.9%. The combination of sites colonized varied frequently over time for many patients. Of patients who had swab specimens obtained twice in 1 day, 8.7% had discordant results from the 2 swab sets. No patient had a clinical isolate that was not of an identical subtype to an isolate from an anatomical site that was sampled for screening. Half the patients carried multiple subtypes during their stay, with up to 4 subtypes per patient.

CONCLUSIONS

The findings of this study may indicate that these patients have been colonized with MRSA on more than one occasion, possibly because of multiple breaches in infection control procedure. In MRSA-colonized patients, anatomical sites were intermittently colonized and carriage of multiple subtypes was common. These findings indicate that MRSA carriage is not a fixed state but may vary over time.

Emerging Infections with Community-Associated Methicillin-ResistantStaphylococcus aureusin Outpatients at an Army Community Hospital

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infection typically occurs in chronically ill patients requiring long-term antimicrobial therapy or hospitalization. However, community-associated MRSA (CA-MRSA) necrotizing soft tissue infections seem to be increasing in incidence. Our aim was to describe the incidence and microbiologic characteristics of CA-MRSA isolates collected at an army community hospital.

METHODS

We report a retrospective review of MRSA isolates identified during 1998-2003 at the microbiology laboratory of Moncrief Army Community Hospital that serves a community of approximately 40,000 transient residents yearly in Fort Jackson, South Carolina. We evaluated the incidence of MRSA in our laboratory during 1998-2003. For MRSA isolates from 2003, we evaluated antimicrobial susceptibility patterns. Six selected isolates were evaluated by molecular typing, resistance gene analysis, and toxin analysis.

RESULTS

During 1998-2003, 241 (23%) of 1041 S. aureus isolates identified at the hospital microbiology laboratory were resistant to methicillin. Of these 241 MRSA isolates, 223 were cultured from outpatients. The incidence of MRSA in our population increased from 12% of S. aureus isolates in 1998 to 43% in 2003. In 2003, MRSA was cultured from 76 different patients. Isolates of MRSA were often resistant to erythromycin (91%), although resistance to other agents was less common: Ciprofloxacin (14%), levofloxacin (14%), clindamycin (3%), tetracycline (3%), and trimethoprim sulfamethoxazole (1%). No isolates were resistant to vancomycin, gentamicin, nitrofurantoin, or rifampin. Six CA-MRSA isolates were compared by pulsed-field gel electrophoresis (PFGE). Five were PFGE type USA300, and one was PFGE type USA100, based on the U.S. Centers for Disease Control and Prevention (CDC) classification scheme. The five USA300 isolates carried SCCmec type IV, and the USA100 carried SCCmec II. None of the isolates were positive by PCR for genes encoding enterotoxins A-E and H, or toxic shock syndrome toxin (TSST-1), but the five USA300 isolates carried the gene coding for Panton-Valentine leukocidin toxin.

CONCLUSIONS

The incidence of MRSA at our institution is increasing. Isolates of MRSA show resistance patterns and microbiologic characteristics consistent with CA-MRSA isolates from the United States. Clinicians should consider the possibility of CA-MRSA in patients with soft-tissue infections who do not respond to initial therapy with beta-lactam antimicrobial agents.

Regional audit: perioperative management of MRSA orthopaedic patients in the Oxford region

AIM

Methicillin resistant staphylococcus aureus (MRSA) colonisation or infection is of particular importance in patients undergoing operations involving implantable materials, such as in orthopaedic surgery. An audit of the perioperative management of orthopaedic patients in the Oxford region was carried out to assess the level of clinician awareness and the uniformity of current guidelines between hospitals.

METHODS

A postal questionnaire was designed for asking information on various aspects of perioperative management of MRSA patients and was sent to each hospital.

RESULTS

Responses were obtained from nine of 10 hospitals in the region. The average response rate for each hospital was 75%, and the overall individual response rate was 67.5% (27/40). Seventy-eight per cent of respondents knew that there was a pre-admission screening policy. Fifteen per cent were unaware of any MRSA policy. Forty-four per cent indicated that teicoplanin was used for prophylaxis in implant surgery whilst 44% used vancomycin. Eighteen per cent believed that cefuroxime was used for prophylaxis. Forty-eight per cent of hospitals had an MRSA-free zone for orthopaedic patients.

CONCLUSION

This study indicates a lack of uniformity in the perioperative management of MRSA-positive patients in the region and a lack of awareness of both MRSA guidelines and their implementation. Uniformity of MRSA guidelines is necessary to allow better clinician awareness and compliance, especially in surgical trainees who are travelling between different training hospitals in the region. Implementation of such a policy with re-audit of subsequent awareness and compliance is proposed.

Molecular typing strategies

Nosocomial infections among infants in neonatal intensive care units are an increasing cause of morbidity and mortality. Efforts to rapidly detect, contain and ultimately prevent cross-transmission of these pathogens require constant vigilance by members of the epidemiology team. A vital component of an epidemiological evaluation is the ability to assess the interrelatedness of clinical isolates. This review focuses on the basic principles, strengths and weaknesses of some of the most commonly used molecular-based procedures, which determine clonal identity of outbreak strains in neonatal settings. Published evidence for the cogent selection of the method best suited for studying a particular organism and technological advances that await the new science of Molecular Epidemiology are also presented. The appropriate use of molecular typing technologies should enable reliable tracking of epidemic clones and thereby enhance the effectiveness of infection control strategies.

Polyclonal bacteremia due to gram-negative rods

The frequency of, risk factors for, and outcome of polyclonal gram-negative bacteremia are still unknown. We investigated them in a prospective cohort study of patients for whom a blood culture yielded >/=1 species of gram-negative aerobic rod. For each patient, pulsed field gel electrophoresis (PFGE) was performed on 4 colonies of each morphologic type. Episodes of bacteremia were considered polyclonal if caused by >1 PFGE type of the same species. Ten (6.5%) of 153 investigated patients had polyclonal bacteremia. Bacteremia due to nonfermenting rods was the single significant risk factor for polyclonal bacteremia. Complications were equally frequent in all patient groups. However, patients with polyclonal bacteremia received more extensive antibiotic therapy than did patients with monoclonal bacteremia. Nearly 20% of episodes of bacteremia due to nonfermenting rods were polyclonal, but it remains unclear why nonfermenting rods were more likely to cause polyclonal bacteremia than were other gram-negative rods.

Infection control measures to limit antimicrobial resistance

Increasing antimicrobial resistance has resulted in a rapidly decreasing array of therapeutic options for infections in the critical care setting. Reports of reduced susceptibility to vancomycin in Staphylococcus aureus raise the possibility of patients being infected with a virulent pathogen for which most antibiotics are ineffective. Infection control methods to contain resistance, exclusive of antimicrobial restrictions, focus on surveillance to identify carriers of resistant organisms, prevention of nosocomial infections, adequate hand hygiene, isolation of patients who harbor resistant organisms, and the use of barrier techniques such as gowns and gloves. Surveillance using clinical isolates alone is inadequate for the identification of the majority of patients who carry resistant organisms. However, it is unclear what intensity of surveillance is needed to control the spread of these organisms in the intensive care unit in nonoutbreak situations. Attempts at eradicating carriage are often unsuccessful when there is extranasal colonization with methicillin-resistant S. aureus. Transmission of resistant organisms is primarily the result of transient contamination of healthcare workers' hands. Adequate handwashing, isolation of carriers, and barrier techniques are all necessary for containing resistance within the intensive care unit, however, compliance with these measures can be compromised by high staff turnover and heavy workload.

MRSA carriage: the relationship between community and healthcare setting. A study in an Italian hospital

From May 1997 to June 1998, all patients admitted to the study institution were screened at entry for MRSA carriage (both colonization and infection). Eighty-six MRSA carriers were identified; of these, 85 were nasal carriers. Risk factors were compared to those of 86 controls. Although the vast majority of both carriers and controls had at least one previous hospital stay, carriers were less likely than controls to be referred from a community setting, and had resided within the community for a shorter time before the current admission. The number of underlying conditions was comparable in the two groups, but those infected were more likely to have cancer than the controls. While community-acquired MRSA carriage is rare, exposure to a health care setting (particularly if repeated) within six months from the current admission, is a risk factor for MRSA carriage and introduction of the organism into an institution.

Methicillin-resistant Staphylococcus aureus typing methods: which should be the international standard?

Methicillin-resistant Staphylococcus aureus (MRSA) has spread to all parts of the world. Effective control measures are dependent on a thorough knowledge of the organism's epidemiology which requires a typing technique that can be universally applied. Many typing methods have been developed for MRSA but none has been adopted as the internationally recognized standard. This review summarizes the information available on each in order to assess their suitability as a reference procedure. The majority of phenotypic and genotypic techniques are not sufficiently discriminatory, reproducible, stable or useful in an outbreak to be acceptable. The methods which do fulfil these requirements and have a potential for standardization, such as pulsed-field gel electrophoresis, binary typing or a combination of more rapid techniques, require further systematic evaluation.

Oral fusidic acid fails to eradicate methicillin-resistant Staphylococcus aureus colonization and results in emergence of fusidic acid-resistant strains

Carriers of methicillin-resistant Staphylococcus aureus (MRSA) in hospital constitute a reservoir of infections and increase the risk of bacteremia and wound infection. In this prospective randomized trial, we tested the effectiveness of oral fusidic acid for eradication of MRSA colonization. From March 1997 through February 1998, patients with MRSA colonization in medical intensive care units in a large urban teaching hospital were randomly assigned to receive fusidic acid 500 mg q8h orally for 7 days or no anti-staphylococcal treatment. Twenty-three MRSA carriers were found during the study period and 16 were eligible for evaluation; six of them received fusidic acid. MRSA colonization was cleared in only two of the six patients with fusidic acid treatment, and later recurred in one of them. MRSA disappeared for 1, 2, 7, 7, and 8 weeks, respectively, in five of the 10 patients without treatment. MRSA persisted in the other five cases. Although all MRSA isolates found in the initial surveillance culture were susceptible to fusidic acid (MIC </= 2 microg/mL), seven isolates from two patients after fusidic acid treatment demonstrated high fusidic acid resistance (MIC 64 to >/= 256 microg/mL). Pulsed-field gel electrophoresis pattern analysis showed that the resistant strains were genetically identical to the susceptible strains isolated from the same patient before fusidic acid treatment, in both cases. However, genetically distinct strains colonized in the same individual during follow-up were found in four out of 16 cases. We conclude that oral fusidic acid alone is not suitable for eradication of MRSA colonization, and may lead to the emergence of resistant strains.

Characterization of IS1245 for strain typing of Mycobacterium avium

IS1245 is an insertion element widely prevalent among isolates of Mycobacterium avium. We used PvuII Southern blots to analyze IS1245 polymorphisms among 159 M. avium isolates (141 clinical isolates from 40 human immunodeficiency virus-infected patients plus 18 epidemiologically related environmental isolates) that represented 40 distinct M. avium strains, as resolved by previous studies by pulsed-field gel electrophoresis (PFGE). All 40 strains carried DNA homologous to IS1245 and thus were typeable. Twenty-five (63%) strains had > or = 10 copies of the element, 6 (15%) had 4 to 9 copies, and 9 (23%) had only 1 to 3 copies. Among the last group of nine strains (each of which was distinct by PFGE analysis), IS1245 typing resolved only four patterns and thus provided poor discriminatory power. To evaluate the in vivo stability of IS1245, we analyzed 32 strains for which sets of 2 to 19 epidemiologically related isolates were available. For 19 (59%) of these sets, all isolates representing the same strain had indistinguishable IS1245 patterns. Within eight (25%) sets, one or more isolates had IS1245 patterns that differed by one or two fragments from the modal pattern for the isolates of that strain. Five (16%) sets included isolates whose patterns differed by three or more fragments; on the basis of IS1245 typing those isolates would have been designated distinct strains. IS1245 was stable during in vitro passage, suggesting that the variations observed represented natural translocations of the element. IS1245 provides a useful tool for molecular strain typing of M. avium but may have limitations for analyzing strains with low copy numbers or for resolving extended epidemiologic relationships.

Randomly amplified polymorphic DNA PCR analysis of bovine Cryptosporidium parvum strains isolated from the watershed of the Red River of the North

Cryptosporidium parvum is a protozoan parasite that causes the disease cryptosporidiosis in a variety of mammals, including neonatal calves and humans. Millions of oocysts are shed during acute cryptosporidiosis, and zoonotic transmission is inferred, though not proven, to be a general phenomenon. Very little is known about the degree of strain variation exhibited by bovine and human isolates, though such knowledge would enable the amount of bovine-to-human transmission to be more precisely analyzed. This research was initiated to determine whether variations exist among bovine strains isolated from a localized geographic area, the watershed of the Red River of the North. Sixteen strains were isolated and compared to each other and to two human and two calf strains from Australia by randomly amplified polymorphic DNA PCR. A statistical analysis of the data indicated that the isolates belonged to four different groups of strains.

Sensitivity and specificity of an improved rapid latex agglutination test for identification of methicillin-sensitive and -resistant Staphylococcus aureus isolates

The performance of a second-generation rapid agglutination kit, Slidex Staph Plus (SSP; bioMérieux), was compared to those of the Slidex Staph (SS; bioMérieux), Staphaurex (SRX; Murex Diagnostics), and BBL Staphyloslide (BBL; Becton Dickinson) kits by using 508 clinical isolates composed of 150 methicillin-sensitive Staphylococcus aureus (MSSA) organisms, 154 methicillin-resistant S. aureus (MRSA) organisms, and 204 non-S. aureus Staphylococcus spp. Of the 508 isolates tested, 75% were fresh clinical isolates, with the remainder taken from five different freezer collections. All four agglutination tests had comparable sensitivities for MSSA and MRSA. However, the SS kit was significantly less specific (93.1%) than the three other tests (P > 0.05, McNemar test). These results demonstrate that the new rapid latex agglutination kit, SSP, was more specific for the identification of S. aureus than the previous version and performed comparably to the SRX and BBL kits.