The international spread of methicillin-resistant Staphylococcus aureus

The effects of oral RNA and intraperitoneal nucleoside-nucleotide administration on methicillin-resistant Staphylococcus aureus infection in mice

The effects of oral RNA and intraperitoneal nucleoside-nucleotide mixture administration on methicillin-resistant Staphylococcus aureus (MRSA) strain 8985N infection were studied in mice. BALB/c mice were fed a nucleic acid-free diet or nucleic acid-free diet supplemented with 0.5% or 2.5% ribonucleic acid (RNA) for 30 days. Nucleoside-nucleotide mixture or saline (control) was intraperitoneally administered daily to these rats except for the 2.5% RNA group, which received saline only. On the 10th day of this treatment, the mice were inoculated intravenously with the viable MRSA organisms. Susceptibility to the MRSA was determined by animal survival and recovery of the MRSA from the organs. The survival rates in the three groups that were administered saline were 29%, 35%, and 40% for nucleic acid-free diet, 0.5% RNA, and 2.5% RNA groups, respectively, whereas in the two groups that received the nucleoside-nucleotide mixture the rates were 69% for the nucleic acid-free diet group and 55% for 0.5% RNA group. The susceptibility of the mice to the MRSA challenge was not affected by dietary RNA, which indicates the ineffectiveness of oral RNA. The combined survival rate in the two nucleoside-nucleotide groups (64%) was statistically different (p < .01) from that in the three saline groups (34%). There was a greater reduction in viable organism recovery in the kidney and spleen of the surviving mice that had been administered the nucleoside-nucleotide mixture than in those administered saline.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative in vitro activities of a new quinolone, OPC-17116, possessing potent activity against gram-positive bacteria

The in vitro antibacterial activity of OPC-17116, a new fluoroquinolone, against a wide variety of clinical isolates was evaluated and compared with those of ciprofloxacin, ofloxacin, and norfloxacin. OPC-17116 showed potent broad-spectrum activity against gram-positive and -negative bacteria. The activity of this compound against gram-positive bacteria was higher than those of other quinolones, and its activity against gram-negative and anaerobic bacteria was roughly comparable to those of other quinolones. OPC-17116 had potent activity against important pathogens of respiratory tract infections such as Staphylococcus aureus, Streptococcus pneumoniae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Haemophilus influenzae, and Branhamella catarrhalis. The MICs of this compound against 90% of these organisms, except for methicillin-resistant S. aureus, ranged from less than or equal to 0.006 to 3.13 micrograms/ml. OPC-17116 at more than one-half the MICs was bactericidal against clinical isolates of S. aureus, Escherichia coli, K. pneumoniae, and P. aeruginosa. The activity of OPC-17116 was decreased by several culture conditions such as acidic pH, high concentration of Mg2+ ions, and inoculum size of 10(7) CFU/ml. OPC-17116 inhibited the supercoiling activity of DNA gyrases from E. coli KL-16 and S. aureus SA113 (50% inhibitory concentrations, 0.19 and 23.0 micrograms/ml, respectively). The amount of OPC-17116 accumulation was higher than that of other quinolones in S. aureus.

Typing of methicillin-resistant Staphylococcus aureus with an M13 repeat probe

A bacteriophage M13 tandem repeat has been used to probe EcoRI digested genomic DNA of methicillin-resistant Staphylococcus aureus (MRSA). The patterns generated were found to be useful in typing MRSA and generally confirmed the relationships that had previously been recognized in other studies based on antimicrobial resistance and plasmid profiles. The epidemic MRSA of London hospitals (EMRSA) and the majority of the epidemic MRSA of eastern Australian hospitals (EA MRSA) gave the same pattern. However, two isolates previously classified as EA MRSA gave a different pattern and a third another pattern. One isolate from Dublin, two isolates from Nuneaton and two isolates from Singapore gave the same pattern as the two EA MRSA. With the exception of the early or classic MRSA all the other isolates examined gave their own distinctive patterns. With one exception the classic MRSA belonged to a separate group. The exception was of particular interest because it gave the same pattern as the majority of the EA MRSA. This suggests that there may be an evolutionary relationship between some of the classic MRSA and the EMRSA of London and the EA MRSA of Australia.

Characterization of methicillin-resistant Staphylococcus aureus associated with nosocomial infections in the University Hospital, Kuala Lumpur

Methicillin-resistant Staphylococcus aureus (MRSA) as a hospital pathogen has presented many clinical problems in the University Hospital, Kuala Lumpur, Malaysia since 1978. The need for control of spread of these organisms became evident by 1985 when it was noted that the incidence of MRSA among S. aureus isolated from hospital inpatients had increased from 11.5% in 1979 to 18.8% in 1985. The characteristics of 50 MRSA isolates associated with nosocomial infections in the hospital are described here. The predominant strains produced Type IV coagulase and 84% of isolates studied showed moderate to high resistance to methicillin with MIC values of 25 mg l-1 or higher. All the MRSA isolates that could be phagetyped were susceptible to Group III phages, with 76.6% of the isolates being susceptible to phage 85. At least 10 different patterns were distinguishable by plasmid typing, the majority of isolates harbouring up to four small plasmids.

An epidemic methicillin-resistant strain of Staphylococcus aureus in Spain

During 1990, a strain of methicillin-resistant Staphylococcus aureus became epidemic in Spain and spread in a manner analogous to that of EMRSA-1 in England. Isolates of this strain produced little protein A and were resistant to a number of antibiotics including ciprofloxacin. Beta-lactamase production was encoded by a c. 39 kb plasmid, which also conferred resistance to mercury, cadmium, ethidium bromide and propamidine isethionate. Investigation showed that two variants, separable by supplementary and Fisk phage typing, were circulating. The B variant appeared to spread more readily than the A variant. The opportunity was taken to compare the discriminatory power of traditional typing methods with molecular techniques. The discriminatory power of the molecular techniques used only reached the same level as the traditional methods when double enzyme digestion of total cellular DNA by EcoR I and Cla I was performed.

Restriction endonuclease analysis of Staphylococcus aureus plasmid DNA from three continents

Staphylococcus aureus isolates (n = 1201) from 20 centers in Europe, the USA and Brazil were evaluated for the presence of epidemiologic markers. Plasmid typing and restriction endonuclease analysis of plasmid DNA confirmed the presence of an apparently identical plasmid in 13% of clinical isolates. The plasmid was recovered from all 20 hospitals studied, with an overall frequency of greater than 10% on each of the three continents. Since relatively few staphylococcal plasmids may be shared by epidemiologically unrelated strains, there are inherent limitations to this otherwise useful technique. Additionally, these data demonstrate the importance of including unrelated strains of Staphylococcus aureus from the local region as controls when molecular typing methods are performed.

Chlorhexidine resistance in methicillin-resistant Staphylococcus aureus or just an elevated MIC? An in vitro and in vivo assessment

Chlorhexidine (Hibiscrub; ICI) is generally accepted to be effective as an antiseptic hand wash for methicillin-susceptible Staphylococcus aureus (MSSA), but there is dispute whether the chlorhexidine MIC for methicillin-resistant S. aureus (MRSA) strains is higher than that for MSSA strains and, indeed, whether it is relevant. In addition, the link between resistance to chlorhexidine, gentamicin, and "nucleic acid-binding" compounds (NAB; which code, in particular, for propamidine isethionate and ethidium bromide) requires clarification. We performed chlorhexidine MIC and rate of kill tests on a number of MSSA and MRSA isolates. Two gentamicin-resistant MRSA isolates without NAB plasmids were more susceptible (0.25 and 0.5 microgram/ml) than four of eight MSSA that we tested (range, 0.25 to 2 microgram/ml). Chlorhexidine MICs were higher (4 to 8 micrograms/ml) for seven distinct MRSA isolates with plasmids conveying resistance to gentamicin and NAB (GNAB). Curing of the GNAB plasmid from MRSA strains resulted in a fall in the MIC (1 to 3.3 micrograms/ml), but no consistent fall in killing by chlorhexidine was observed. No effect on the chlorhexidine MIC or killing was observed when we cured strains of methicillin resistance. GNAB plasmid transfer resulted in a rise in the chlorhexidine MIC for the strains but not consistent fall in killing by chlorhexidine. Ethical approval was granted for 10 volunteers to each have a methicillin-susceptible, GNAB-resistant, derived transcipient and its GNAB-susceptible isogenic parent applied to separate sites in an in vivo skin test; no significant difference was seen in survival rates after the application of chlorhexidine. These results suggest that chlorhexidine appears to be as effective as a hand-washing agent for MRSA isolates with or with out NAB plasmids as it is for MSSA isolates.

Surveillance of methicillin-resistant Staphylococcus aureus in England and Wales, 1986-1990

The incidence of methicillin-resistant Staphylococcus aureus in England and Wales was monitored by a weekly reporting scheme from early 1986 to March 1990. Potential coverage was approximately two-thirds of hospital beds. Reporting centres fell from a peak of 210 in 1986 to a low of 101 centres early in 1989 with later recovery. There were 2367 positive reports in 1986, 2174 in 1987, 1700 in 1988, 1701 in 1989 and 632 in the first quarter of 1990. Colonizations outnumbered infections by 2:1. There were marked regional differences: North-East Thames was dominant in 1986 and 1987, and then declined; South-East Thames showed a dramatic increase in 1988 which continued. Other regions showed less significant changes but there were continuing problems in the South-Western Region and in the West Midlands. Some of these changes were related to the decline of EMRSA-1, possibly due to the introduction of effective control measures, and to the emergence of EMRSA-3 in South-East Thames and its spread to Wessex.

Epidemic potential and pathogenicity in outbreaks of infection with EMRSA and EMREC

Multiply antibiotic-resistant Staphylococcus aureus and Escherichia coli have both caused outbreaks in London in recent years, and for this reason have been referred to as E(epidemic)MRSA and EMREC respectively. In each case it has been questioned whether either organism has properties other than antibiotic resistance that distinguish them from other strains. Evidence is adduced to suggest that EMRSA has properties that enable it to spread particularly well, and that EMREC is particularly virulent. Both were introduced into our environment by chance, and were helped by their antibiotic resistance to become involved in a train of events--different in each case--that culminated in severe infection in a small number of patients, and thus to further investigation. The organisms involved in such outbreaks are worthy of investigation and control, if only because of the difficulty of treating clinical infections when they develop.

Typing of methicillin resistant and susceptible Staphylococcus aureus strains by ribosomal RNA gene restriction patterns using a biotinylated probe

Nine methicillin-sensitive (MSSA) and 37 methicillin-resistant (MRSA) Staphylococcus aureus isolates of various phage types and resistotypes from seven countries were investigated. Chromosomal DNA was restricted with HindIII or EcoRI, Southern blotted and hybridised with a cDNA probe to 16S+23S rRNA derived from MRSA NCTC 10442. Resulting rDNA profiles could be differentiated on the basis of 22 patterns which were unaffected by changes in plasmid, transposon, enterotoxin A or phage content. Percentage similarity values were calculated using the Dice coefficient and UPGA clustering. Australian and epidemic (EMRSA-1) isolates from the UK showed a high degree of similarity, but the pattern was not unique and was also found in MSSA and other MRSA, e.g. NCTC 10442. An MSSA of phage group II was the most distinct isolate. The method shows potential as an additional tool in a complex typing system, types non-phage typable strains and may provide clues to the clonal evolution of MRSA and MSSA.

Differing activities of quinolones against ciprofloxacin-susceptible and ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus

The in vitro activities of nine quinolones (seven fluoroquinolones, nalidixic acid, and acrosoxacin) against methicillin-resistant Staphylococcus aureus (MRSA) were compared with those of the glycopeptides teicoplanin and vancomycin. MICs against 160 strains of ciprofloxacin-susceptible (MIC, less than 2.0 micrograms/ml) MRSA and 40 strains of ciprofloxacin-resistant (MIC, greater than or equal to 2.0 micrograms/ml) MRSA were determined. The following MICs for 50% of the strains tested (in micrograms per milliliter) were obtained for ciprofloxacin-susceptible and -resistant strains, respectively: tosufloxacin, 0.06 and 2.0; ofloxacin, 0.25 and 16; ciprofloxacin, 0.5 and 16; pefloxacin, 0.5 and 32; acrosoxacin, 1.0 and greater than 256; enoxacin, 1.0 and 64; fleroxacin, 1.0 and 32; norfloxacin, 2.0 and 64; nalidixic acid, 64 and 512; teicoplanin, 1.0 and 1.0; vancomycin, 2.0 and 2.0. In mutation rate studies using a range of antibiotic concentrations to reflect those achievable in vivo, resistant mutants grew only on plates containing nalidixic acid (rate of mutation to resistance, 10(-7) to 10(-8) and on plates containing low concentrations of ciprofloxacin, enoxacin, and norfloxacin (rate of mutation to resistance, 10(-8) to 10(-9). In time-kill studies, 99.9% killing was found within 8 h for all of the quinolones tested (norfloxacin and nalidixic acid were not tested). Teicoplanin and vancomycin were less rapidly bactericidal. For the clinical isolates of ciprofloxacin-resistant MRSA, different levels and patterns of quinolone resistance were found. Generally, cross-resistance among the fluoroquinolones was complete; however, incomplete cross-resistance did occur with the nonfluorinated quinolone acrosoxacin.

Molecular analysis of a gentamicin resistance transposonlike element on plasmids isolated from North American Staphylococcus aureus strains

Plasmid-encoded resistance to the aminoglycosides gentamicin (Gm), tobramycin (Tm), and kanamycin (Km) (GmTmKmr) in strains of Staphylococcus aureus isolated in Australia and North America appears to be mediated by one resistance determinant. In Australian isolates, this determinant is flanked by inverted copies of a 1.3-kb insertion sequence, IS256, thereby forming a composite transposon, Tn4001. Analysis of two conjugative plasmids and a related nonconjugative plasmid from strains of S. aureus isolated in North America showed that the GmTmKmr determinant on these plasmids is also flanked by inverted repeats. In the nonconjugative plasmid, these repeats include only 425 bp of IS256 immediately adjacent to the GmTmKmr region and identical to that on Tn4001. This truncated Tn4001 element is flanked by copies of the insertion element IS257, and together these elements form a truncated Tn4001-IS257 hybrid transposonlike structure. A third copy of IS257 was located 418 bp from the hybrid structure. The truncated Tn4001 and three repeats of IS257 were present at a conserved site on the plasmids studied. Four additional copies of IS257 were identified on the two conjugative plasmids. These elements flank determinants for resistance to the aminoglycosides neomycin and paromomycin and to ethidium bromide and quaternary ammonium compounds, as well as the region involved in conjugative plasmid transfer.

Endemic methicillin-resistant Staphylococcus aureus in a special care baby unit: a 2 year review

During January 1987, methicillin-resistant Staphylococcus aureus (MRSA) was isolated for the first time from a baby admitted to the special care baby unit of a large metropolitan hospital. Over a 2 year period, of 1574 babies admitted to the unit, at least 573 (36.4%) became colonized with the organism. Only nine (1.6%) developed significant infectious morbidity and one baby died. Minor infections occurred in a further 35 (6.1%). The outbreak remained uncontrolled despite rigid infection control measures. Subsequent emphasis on hand washing, in-service education and provision of weekly review of the MRSA colonization rates have failed to eliminate the organism from the unit.

Numerical analysis of electrophoretic protein patterns of methicillin-resistant strains of Staphylococcus aureus

A total of 50 strains of Staphylococcus aureus, including 41 methicillin-resistant S. aureus (MRSA) strains, were characterized by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins. The protein patterns contained 40-50 discrete bands and were highly reproducible. Partial patterns were used as the basis of a computer-assisted numerical analysis. The MRSA strains clustered into four phenons at the 83% similarity level; and further division of phenon 1, at the 86% similarity level, resulted in a total of six clusters. All of the MRSA isolates from an MRSA epidemic in the United Kingdom were found to cluster in phenon 1 together with 9 of the 12 MRSA isolates from eastern Australia and 3 other MRSA isolates from the United Kingdom. The remaining three eastern Australian isolates clustered separately in phenon 2. Phenon 3 appeared to be exclusive to strains that were both susceptible and resistant to methicillin and that reacted with group V phages, and phenon 4 comprised 11 isolates, all of which were other MRSA isolates from the United Kingdom. We conclude that computer-assisted numerical analysis by high-resolution sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins provides additional criteria for the study of the epidemiology and the evolution of MRSA.

Use of plasmid analysis and determination of aminoglycoside-modifying enzymes to characterize isolates from an outbreak of methicillin-resistant Staphylococcus aureus

We compared disk susceptibility, plasmid analysis, aminoglycoside resistance patterns, and DNA hybridization for their usefulness in characterizing isolates from a hospital outbreak of methicillin-resistant Staphylococcus aureus. Fifteen isolates were susceptible (group 1) and 28 were resistant (group 2) to gentamicin. A total of 15 of 15 (100%) group 1 and 22 of 28 (79%) group 2 isolates carried a 21.5-megadalton plasmid. All group 2 isolates and none of the group 1 isolates possessed a 33-megadalton plasmid. Aminoglycoside resistance pattern determinations revealed the presence of the ANT(4')-I enzyme (aminoglycoside 4' adenyltransferase) in all group 1 isolates but was unable to demonstrate presence of this enzyme in group 2 organisms. The APH(2") + AAC(6')-II enzyme (aminoglycoside 2" phosphotransferase plus 6' acetyltransferase) was found in all of the group 2 isolates but in none of the group 1 isolates. Use of DNA hybridization revealed the presence of the ANT(4')-I enzyme in both groups (group 1, 14 of 15; group 2, 26 of 28). In this hospital outbreak, we found good correlation between disk susceptibility, plasmid profile, aminoglycoside resistance patterns, and DNA hybridization results. It was difficult to predict the presence of the ANT(4')-I enzyme in the presence of the bifunctional [APH(2") + AAC(6')-II] enzyme by the aminoglycoside resistance pattern method because of overlap of the substrate profile.

Resistance to dicloxacillin, methicillin and oxacillin in methicillin-susceptible and methicillin-resistant Staphylococcus aureus detected by dilution and diffusion methods

A total of 54 Staphylococcus aureus strains of varying methicillin resistance were investigated for their resistance to methicillin, oxacillin and dicloxacillin by different diffusion tests. Inhibition zones were measured around locally prepared paperdiscs with 10 micrograms methicillin, 5 and 10 micrograms oxacillin, 5 and 10 micrograms dicloxacillin, PDM paperdiscs with 10 micrograms methicillin or oxacillin and Neo-sensitabs tablets with methicillin or oxacillin. All diffusion tests were performed both with Mueller-Hinton agar and Danish Blood agar as well as at 37 degrees C and 30 degrees C and read after overnight incubation. Differences in zone diameter under different conditions were found to be independent of the susceptibility level of the strains. Seventeen of the strains were detected as methicillin-resistant (MRSA) by two methods including high inoculum and prolonged incubation at 30 degrees C. The minimum inhibitory concentration (MIC) of the 54 strains was determined by a plate dilution method at 30 degrees C and 37 degrees C. A 10 micrograms locally prepared methicillin disc detected all MRSA strains with no false reactions either at 37 degrees C or 30 degrees C on Mueller-Hinton agar. Investigations with oxacillin discs had to be performed at 30 degrees C or with a 5 microgram disc in order to detect correctly. PDM paperdiscs gave reactions identical to the corresponding locally prepared discs. Methicillin Neo-sensitabs detected all MRSA strains but also included a few susceptible strains among the resistant ones. Addition of blood increased the number of not-detected MRSA strains. All 17 MRSA strains were susceptible to dicloxacillin by the dilution method, and the disc diffusion test showed similar results. Dicloxacillin discs therefore did not detect the presence of MRSA strains. The implications of replacement of the methicillin/oxacillin disc by a dicloxacillin disc are discussed.

Methicillin-resistant Staphylococcus aureus from China characterized by digestion of total DNA with restriction enzymes

A series of clinical isolates of methicillin resistant Staphylococcus aureus (MRSA) from two hospitals in China was examined. Fragment patterns obtained by digestion of total cellular DNA with restriction enzymes were used to characterize the isolates, in combination with phage-typing, antibiotic resistance profile, and plasmid profile. Digestion of total cellular DNA with restriction enzymes was most useful in discriminating between isolates and yielded additional information on the relatedness of non-identical isolates. In one hospital a single strain, resistant to a large number of antibiotics, had apparently become endemic. In the second hospital a number of distinct but related strains were present. The isolates were also related but not identical to the strain of MRSA endemic at the London Hospital.

Staff carriage of epidemic methicillin-resistant Staphylococcus aureus

Twenty-six nurses were repeatedly screened for carriage of epidemic methicillin-resistant Staphylococcus aureus (EMRSA) immediately before and after duty periods in which they solely attended six patients widely colonized with two EMRSA strains distinguishable by plasmid analysis. EMRSA carriage was detected in 13 nurses. Three EMRSA carriage patterns emerged: transient carriage in 12 nurses, when the EMRSA was isolated from noses or fingers of nurses after duty but was gone before their next day's duty; short-term nasal carriage, seen on occasion in 4 of these 12 nurses, when EMRSA carriage was detected on two consecutive screens; and persistent nasal carriage, seen in 1 nurse only, when the EMRSA was seen on more than two consecutive occasions. All but one of these incidents of carriage could be explained by close patient, rather than environmental, exposure and occurred despite an intensive control programme. Transient or short-term carriage in nurses probably resulted in transfer of the EMRSA between patients. Staff decontamination should be considered following a period of cohort nursing of EMRSA patients, especially if staff members are shortly to nurse unaffected patients. Our findings may explain some of the difficulties in controlling EMRSA.

Transmissible mupirocin resistance in Staphylococcus aureus

The spread of two strains of Staphylococcus aureus with high level resistance to mupirocin is described. The resistance proved to be easily transferred to other S. aureus strains by filter mating experiments and on the skin of mice. No plasmid band corresponding to the resistance could be demonstrated by agarose gel electrophoresis or by caesium chloride gradient centrifugation but cleavage of 'chromosomal' DNA from resistant recipients showed bright bands of DNA absent from sensitive controls.

Plasmid analysis of 219 methicillin-resistant Staphylococcus aureus strains with uncommon profiles isolated in Lisbon

During the years 1986 and 1987, 219 methicillin-resistant Staphylococcus aureus (MRSA) strains were isolated in a Lisbon hospital. Antimicrobial susceptibilities and genetic analysis showed that resistance to penicillin, methicillin, erythromycin (inducible phenotype), tetracycline, gentamicin, tobramycin, kanamycin, streptomycin, neomycin and trimethoprim were chromosomally encoded. Plasmid DNA was absent from 38.8% of the isolates. Constitutive erythromycin resistance was coded by three plasmids of c. 2.3 Md, c. 2.0 Md and c. 1.6 Md. Chloramphenicol resistance was mediated by two plasmids of c. 2.9 Md and c. 1.8 Md. Small cryptic plasmids of c. 1.65 Md, c. 1.2 Md and c. 1.0 Md were also detected. The majority of the strains revealed antigen 17, were lysed by phages 75, 89 and/or 85, and were either devoid of plasmid DNA, or possessed a c. 1.6 Md plasmid coding for constitutive erythromycin resistance or a c. 1.0 Md cryptic plasmid. These observations cannot rule out that the MRSA Lisbon isolates are a homogeneous group of strains that might have a common origin, and seem to be different from MRSA recently isolated in other countries.

Pattern of antibiotic and heavy-metal ion resistance in recent hospital isolates of Staphylococcus aureus

Two hundred and one strains of Staphylococcus aureus isolated from in-patients and out-patients were examined for sensitivity to antibiotics, heavy-metal ions and ethidium bromide and for phage-typing pattern. Heavy-metal ion resistance was less frequent than reported in previous studies and was as frequent in penicillinase non-producing as producing strains. 'Methicillin-resistant' strains were resistance to ethidium bromide and mercury. Resistance to heavy-metal ions, including cadmium, may be becoming less common amongst clinical isolates of S. aureus.