Antibiotic-resistant Staphylococcus aureus

The Role of Nitroreductases in Resistance to Nitroimidazoles

Antimicrobial resistance is a major challenge facing modern medicine, with an estimated 700,000 people dying annually and a global cost in excess of $100 trillion. This has led to an increased need to develop new, effective treatments. This review focuses on nitroimidazoles, which have seen a resurgence in interest due to their broad spectrum of activity against anaerobic Gram-negative and Gram-positive bacteria. The role of nitroreductases is to activate the antimicrobial by reducing the nitro group. A decrease in the activity of nitroreductases is associated with resistance. This review will discuss the resistance mechanisms of different disease organisms, including Mycobacterium tuberculosis, Helicobacter pylori and Staphylococcus aureus, and how these impact the effectiveness of specific nitroimidazoles. Perspectives in the field of nitroimidazole drug development are also summarised.

Building a genomic framework for prospective MRSA surveillance in the United Kingdom and the Republic of Ireland

The correct interpretation of microbial sequencing data applied to surveillance and outbreak investigation depends on accessible genomic databases to provide vital genetic context. Our aim was to construct and describe a United Kingdom MRSA database containing over 1000 methicillin-resistant Staphylococcus aureus (MRSA) genomes drawn from England, Northern Ireland, Wales, Scotland, and the Republic of Ireland over a decade. We sequenced 1013 MRSA submitted to the British Society for Antimicrobial Chemotherapy by 46 laboratories between 2001 and 2010. Each isolate was assigned to a regional healthcare referral network in England and was otherwise grouped based on country of origin. Phylogenetic reconstructions were used to contextualize MRSA outbreak investigations and to detect the spread of resistance. The majority of isolates (n = 783, 77%) belonged to CC22, which contains the dominant United Kingdom epidemic clone (EMRSA-15). There was marked geographic structuring of EMRSA-15, consistent with widespread dissemination prior to the sampling decade followed by local diversification. The addition of MRSA genomes from two outbreaks and one pseudo-outbreak demonstrated the certainty with which outbreaks could be confirmed or refuted. We identified local and regional differences in antibiotic resistance profiles, with examples of local expansion, as well as widespread circulation of mobile genetic elements across the bacterial population. We have generated a resource for the future surveillance and outbreak investigation of MRSA in the United Kingdom and Ireland and have shown the value of this during outbreak investigation and tracking of antimicrobial resistance.

Methicillin-resistant Staphylococcus aureus (MRSA) is increasing in Norway: a time series analysis of reported MRSA and methicillin-sensitive S. aureus cases, 1997-2010

BACKGROUND

Accurate estimates of the incidence and prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections are needed to inform public health policies. In Norway, where both MRSA infection and carriage are notifiable conditions, the reported incidence of MRSA is slowly increasing. However, the proportion of MRSA in relation to all S. aureus isolates is unknown, making it difficult to determine if the rising incidence is real or an artifact of an increasing number of tests performed.

AIM

To characterize recent trends in MRSA infections and obtain a more complete understanding of the MRSA level in Norway.

METHODS

All reported cases of MRSA and methicillin-sensitive S. aureus (MSSA) from Oslo County (1997-2010) and Health Region East (2008-2008), representing approximately 11% and 36% of the Norwegian population, respectively, were analyzed using a stochastic time series analysis to characterize trends.

RESULTS

In Oslo County, the proportion of methicillin-resistant cases increased from 0.73% to 3.78% during the study period and was well modeled by an exponential growth with a doubling constant of 5.7 years (95% CI 4.5-7.4 years). In Health Region East, the proportion of MRSA cases increased from 0.4% to 2.1% from 2002 to 2008, with a best-fitting linear increase of 0.26% (95% CI 0.21-0.30%) per year. In both cases, the choice of a linear or exponential model for the time trend produced only marginally different model fits. We found no significant changes due to revised national MRSA guidelines published in June 2009. Significant variations in the increasing time trend were observed in the five hospitals within the region. The yearly reported incidence of MSSA was relatively stable in both study areas although we found seasonal patterns with peaks in August.

CONCLUSION

The level of MRSA is increasing in Norway, and the proportion of methicillin resistance in all S. aureus isolates are higher than the reported proportion of MRSA in invasive infections.

Community-acquired methicillin-resistant Staphylococcus aureus: the new face of an old foe?

The burden of infections caused by community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is increasing among different patient populations globally. As CA-MRSA has become established in healthcare facilities, the range of infections caused by them has also increased. Molecular characterization of CA-MRSA isolates obtained from different centers has revealed significant diversity in their genetic backgrounds. Although many CA-MRSA strains are still susceptible to non-β-lactam antibiotics, multiresistance to non-β-lactam agents has emerged in some clones, posing substantial problems for empirical and directed therapy of infections caused by these strains. Some CA-MRSA clones have acquired the capacity to spread locally and internationally. CA-MRSA belonging to ST80-MRSA-IV and ST30-MRSA-IV appear to be the dominant clones in the countries of the Gulf Cooperation Council (GCC). The emergence of pandemic CA-MRSA clones not only limits therapeutic options but also presents significant challenges for infection control. Continued monitoring of global epidemiology and emerging drug resistance data is critical for the effective management of these infections.

Genetics of antimicrobial resistance in Staphylococcus aureus

Strains of Staphylococcus aureus that are resistant to multiple antimicrobial compounds, including most available classes of antibiotics and some antiseptics, are a major threat to patient care owing to their stubborn intransigence to chemotherapy and disinfection. This reality has stimulated extensive efforts to understand the genetic nature of the determinants encoding antimicrobial resistance, together with the mechanisms by which these determinants evolve over time and are spread within bacterial populations. Such studies have benefited from the application of molecular genetics and in recent years, the sequencing of over a dozen complete staphylococcal genomes. It is now evident that the evolution of multiresistance is driven by the acquisition of discrete preformed antimicrobial resistance genes that are exchanged between organisms via horizontal gene transfer. Nonetheless, chromosomal mutation is the catalyst of novel resistance determinants and is likely to have an enhanced influence with the ongoing introduction of synthetic antibiotics.

Surveillance and epidemiology of MRSA bacteraemia in the UK

Surveillance of bacteraemia caused by methicillin-resistant Staphylococcus aureus (MRSA) in the UK has involved collection of data from hospital microbiology laboratories via several mechanisms, including a voluntary reporting scheme that has been operational in England and Wales since 1989 and mandatory reporting schemes that have been running independently in England, Wales, Scotland and Northern Ireland since 2001. In addition, surveillance schemes involving panels of participating sentinel laboratories that submit isolates for centralized susceptibility testing, such as the Bacteraemia Resistance Surveillance Programme run by the BSAC, have also been established. Each of these data sources have particular advantages, but they also have their individual limitations, with the result that they each give an incomplete picture if considered in isolation. However, by pooling the findings from these different but complementary surveillance programmes, a much more comprehensive and credible picture of the problem posed by MRSA is produced. These schemes have shown both a dramatic rise in the total numbers of cases of S. aureus bacteraemia reported annually and an increase in the proportion of such cases that involve MRSA (from 2% in 1990 to >40% in the early 2000s), although the most recent data indicate a slight reversal of these trends. Characterization of isolates of MRSA shows a marked temporal relationship between the rise in MRSA bacteraemias and the emergence and spread of two strains of epidemic MRSA, EMRSA-15 and EMRSA-16. Surveillance and control of MRSA infection continue to be high profile and further developments to the mandatory surveillance system in England are likely in the near future.

MRSA at an English children's hospital from 1998 to 2003

AIMS

To investigate the epidemiological and clinical aspects of MRSA among inpatients and outpatients presenting to hospital.

METHODS

Analysis of demographic, epidemiological, and clinical data collected on 385 children first identified as having MRSA between January 1998 and December 2003 in a 250 bed English children's hospital.

RESULTS

There were 267 inpatients and 118 outpatients. The number of new cases of MRSA declined from 72 in 1998 to 52 in 2003, whereas hospital activity increased. Ninety nine (37.1%) inpatients acquired MRSA outside the hospital; a further 90 occurred among 31 clusters of cases. One hundred and seventy eight (66.7%) inpatients were aged <2 years; cardiac services and paediatric & neonatal surgery accounted for 59.6% of cases. Dermatology and A&E accounted for 51.7% of outpatients; 73.8% of outpatients had recently previously attended the hospital. A total of 13.9% of inpatients with MRSA developed bacteraemia; MRSA accounted for 15% of Staphylococcus aureus bacteraemias. The risk of MRSA bacteraemia in colonised patients, and the proportion of S aureus bacteraemias that were MRSA, varied between specialties. Intravascular devices were the most common source of MRSA bacteraemia (63.4% of cases). The mortality rate was 7.3%.

CONCLUSIONS

Enhanced surveillance of MRSA can identify at-risk patient groups, thus facilitating targeting of control measures. The absence of a link between numbers of cases of acquisition of MRSA and bacteraemia suggests that the rise in MRSA bacteraemia may not solely reflect an increase in MRSA prevalence in children in the UK. The need for larger epidemiological studies is emphasised.

High levels of fusidic acid-resistant Staphylococcus aureus in dermatology patients

BACKGROUND

Antibiotic resistance is a significant problem both in hospitals and the community. Topical antibiotics are widely used for dermatological problems and this may be leading to the emergence of resistant bacteria.

OBJECTIVE

To assess the level of fusidic acid-resistant Staphylococcus aureus inpatients with dermatological problems.

METHODS

All microbiology samples over a 4-month period were tested for antibiotic sensitivities. Patients with cultures positive for S. aureus were studied.

RESULTS

The study shows 50% of S. aureus isolates from dermatology patients were resistant to fusidic acid. This figure rose to 78% inpatients with atopic eczema. Of patients with fusidic acid-resistant S. aureus isolates, 96% had used a fusidic acid-containing preparation within the previous 6 months. The level of fusidic acid resistance in S. aureus samples cultured from nondermatology patients was only 9.6%, a level significantly below that for dermatology patients (P < 0.001).

CONCLUSIONS

High levels of fusidic acid-resistant S. aureus are found in dermatology patients. Inappropriate use of topical antibiotics in dermatology patients leading to fusidic acid resistance may threaten the efficacy of systemic fusidic acid for the treatment of serious S. aureus infections. Education of health professionals and restriction of the use of fusidic acid is needed.

Analysis of a mini-outbreak of methicillin-resistant Staphylococcus aureus in a surgical ward by using arbitrarily primed-polymerase chain reaction

In November 1995, an increase was noticed in the number of methicillin-resistant Staphylococcus aureus (MRSA) isolates from a surgical ward at Hacettepe University Hospital. All MRSA isolates obtained from clinical specimens in this ward (14 MRSA isolates from wound cultures of 10 patients) were collected prospectively for 10 weeks. Surveillance cultures were taken from ward personnel (nose cultures from 4 physicians, 7 nurses, 1 secretary, 1 waiter), 2 surgical dressing containers and 1 nebulizer. MRSA was isolated from one of the surgical dressing containers, the nebulizer and nose cultures of 3 physicians, 3 nurses and the ward secretary. Arbitrarily primed polymerase chain reaction (AP-PCR) analysis showed that most MRSA isolates belonged to 2 major clones (pattern A, pattern B). Pattern A was the most frequent one and was present in 4 clinical isolates, surgical dressing container-1. Pattern B was identified in 3 clinical isolates and nose culture of physician-3. AP-PCR analysis revealed that this mini-MRSA outbreak was caused by contamination of surgical dressing container with MRSA and nasal MRSA carriage in ward staff. AP-PCR seems to be a valuable typing method for analysis of nosocomial MRSA outbreaks because of its simplicity and rapidity.

Detection of genes encoding aminoglycoside-modifying enzymes in staphylococci by polymerase chain reaction and dot blot hybridization

Dot blot hybridization and the polymerase chain reaction (PCR) were used to study aminoglycoside-modifying enzymes in aminoglycoside-resistant staphylococci isolated in hospitals in Kuwait. DNA encoding the acetyltransferase (AAC) (6')-phosphotransferase (APH) (2"), nucleotidyltransferase (ANT) (4') and APH (3') enzymes were detected in Staphylococcus aureus and coagulase negative staphylococci. ANT (4') was the most common enzyme detected. The majority of isolates contained genes for all three modifying enzymes, AAC (6')-APH (2"), ANT (4') and APH (3'); only few isolates carried genes for a single modifying enzyme. Genes encoding the AAC (6')-APH (2") were detected in all except two gentamicin-resistant isolates. In these isolates the genes for the AAC (6')-APH (2") enzyme could not be detected by PCR and dot blot hybridization. Whereas antibiotic resistance testing could be used to predict the presence of the AAC (6')-APH (2") enzyme it was not useful in predicting the presence of the ANT (4') or APH (3') enzymes in gentamicin-resistant isolates. Results obtained with dot blot hybridization were comparable to those obtained with PCR. However, PCR was fast and results were obtained within the same day. Therefore PCR would be preferred for the detection and confirmation of the presence of aminoglycoside-modifying enzymes in clinical microbiology laboratories.

Expression of a clone specific DNA sequence from Staphylococcus aureus in Escherichia coli

Staphylococcus aureus produces a large number of factors thought to contribute to virulence, although the precise role of some of these individual factors is not clearly defined. To investigate whether specific virulence factors might be responsible for the selection and dominance of certain genotypes of methicillin- and multiply resistant S. aureus (MRSA), the method of subtractive hybridisation was used to identify conserved DNA sequences associated with the clinical, clonal populations of S. aureus. The findings described in this report indicate that the method of subtractive hybridisation is a valuable tool to identify clone specific virulence factors, which might be of potential as diagnostic markers and as alternative vaccine targets.

Resistance to fusidic acid

Resistance to fusidic acid is determined by a number of mechanisms. The best described are alterations in elongation factor G, which appear in natural mutants that are harboured at low rates in normal populations of staphylococci (10(6) to 10(8)). Altered drug permeability has also been described, and appears to be plasmid-borne. Binding by chloramphenicol acetyltransferase type I and efflux are other described mechanisms of resistance whose prevalence is unclear. A large number of studies have examined rates of fusidic acid resistance in staphylococci. Most show low levels of resistance. Studies where high levels of resistance have been seen are from areas of the hospital where cross infection is common. Rates of resistance have tended to be slightly higher in methicillin-resistant strains of Staphylococcus aureus. Studies on the evolution of resistance have shown no major trends to the emergence of resistance. In one case this is despite increasing use of both systemic and topical fusidic acid over more than 24 years. Selection for resistant variants during treatment was recognised early in vitro and in vivo. However, evidence suggests that it does not occur at high frequency in clinical practice. Nevertheless, accumulated experience is that fusidic acid in combination with other agents results in less resistance emergence.

Antimicrobial resistance in Staphylococcus aureus

Recognized since 1883 as a common cause of infection, Staphylococcus aureus' preantimicrobial-era bacteremia mortality rate was 82%. The mortality of that era threatens to return as evidence of growing vancomycin resistance undermines the utility of vancomycin therapy. Successful treatment of S. aureus infections requires knowledge of its antimicrobial resistance capacity.

A multi-centre study of nosocomial methicillin-resistant Staphylococcus aureus in Greece. Greek MRSA Study Group

All 105 non-replicate consecutive Staphylococcus aureus strains isolated in 1997 from seven Greek hospitals, were found to be susceptible to vancomycin, teicoplanin and chloramphenicol, but only five (8%) were susceptible to all 16 antibiotics tested. Forty-three (41%) isolates were methicillin-resistant, 58% homogeneously (homMRSA) and 42% heterogeneously (hetMRSA). Resistance of homMRSA strains to other antibiotics was generally high (88-100%), although only one strain was resistant to netilmicin. Resistance in hetMRSA (6-39%) or in MSSA (5-11%) was significantly lower. Consequently, the majority (76%) of homMRSA were multi-drug resistant, while the dominant phenotype of hetMRSA and MSSA was resistance to penicillin (50% and 76%, respectively). Comparison of these strains with isolates from 1994 showed higher resistance rates to erythromycin among MSSA, to erythromycin and amikacin among hetMRSA and to rifampicin among homMRSA strains.

A profile of methicillin resistant Staphylococcus aureus infection in the burn center of the Sultanate of Oman

A retrospective study of patterns of infection in 168 patients admitted during 1995 and 1996 in the burns-unit of Khoula hospital at Muscat, Oman was performed. Out of 819 isolates positive for pathogenic bacterial culture, there were 326 (39.8%) isolates positive for methicillin resistant Staphylococcus aureus (MRSA) infection. Incidence of MRSA infection was marginally more than that of Pseudomonas aeroginosa. The proportion of patients developing MRSA infection sometime or the other during their burns-unit stay ranging from 1 to 112 days rose from 48% in 1995 to 52.7% in 1996. No sophisticated tests were done to identify the MRSA strain but study of the antibiograms of each MRSA positive isolate showed very similar patterns of sensitivity to different antibiotics. This suggests the source of infection to be common and in all probability 'noscomial', since all patients acquired MRSA infection in the hospital. The susceptibility of MRSA to ciprofloxacin, cotrimoxazole and fucidin was 76, 51 and 37% of isolates in 1995, and 59, 44 and 26% in 1996 were susceptible to these drugs. Vancomycin was the antibiotic to which most MRSA cultures were susceptible, but partial resistance was reported due to very low susceptibility observed in 1.4% of the isolates in 1995 and 1.1% of the isolates in 1996. The control measures being practiced in the burns-unit of Khoula Hospital, especially mechanical cleaning and chemical disinfection of all surfaces, are discussed in detail. This paper emphasizes the need for preventive measures against MRSA infection in the burns-unit.

Frequency, clonal heterogeneity and antibiotic resistance of methicillin-resistant Staphylococcus aureus (MRSA) isolated in 1992-1994

Since 1992, the proportion of methicillin-resistant Staphylococcus aureus (MRSA) isolated from patients of the University Hospital of Frankfurt/Main and six community hospitals increased to a level of 11% and has remained constant during the following two years. MRSA and methicillin-sensitive Staphylococcus aureus (MSSA) were distributed equally among almost all specimens except blood. There was evidence of a diminished potency of MRSA to cause bacteremia. All MRSA strains were susceptible to glycopeptides and mupirocin. Resistance rates to other non-beta-lactam antibiotics were low for fusidic acid (7.1%), fosfocin (8.3%), amikacin (11.4%) and cotrimoxazole (18.3%) and high for gentamicin (90.7%), ofloxacin (94.3%) and erythromycin (95.5%). Among 378 MRSA strains originating from 180 individuals, macrorestriction analysis of chromosomal DNA revealed 39 different genotypes. These could be divided into 14 epidemic strains isolated from 155 patients and 25 sporadic strains isolated from single patients. As most of the sporadic strains emerged in close local proximity to epidemic strains, we suppose a horizontal genetic transfer from MRSA to MSSA leading to the appearance of novel MRSA genotypes. Upon repeated isolation of MRSA strains from the same individuals, resistance rates and genotypes remained stable. Resistance patterns of the non-beta-lactams correlated poorly with macrorestriction analysis, whereas several MRSA genotypes could be distinguished by particular MICs of methicillin.

Methicillin-resistant Staphylococcus aureus: do we just have to live with it?

Infection with methicillin-resistant Staphylococcus aureus is a familiar problem in hospital patients and has been a global issue since the 1960s. Control of this organism is expensive both financially and in terms of human resources. This article is an attempt to review the epidemiological evolution and our understanding of the organism and bring together possible solutions.

Epidemiology of Staphylococcus aureus bacteremia in Denmark

The number of Staphylococcus aureus bacteremia cases has increased annually in Denmark during the latest decades. This increase has occurred among older patients with hospital-acquired bacteremia. Methicillin-resistance, which earlier was a property of strains of the 83A phage-complex, has nearly disappeared, while the frequency of penicillin-resistance has increased. Today both the phage-type pattern and antibiotic resistance are nearly similar for strains from hospital-acquired and community-acquired cases. In hospitals the frequency of bacteremia after postoperative wound infections has decreased, while cases associated with intravascular catheters has increased, and these infections are now the most common cause of hospital-acquired S. aureus bacteremia. Endocarditis is most commonly found in community-acquired cases without an identified primary focus in patients between 21-50 years. Also hematogenous osteomyelitis is most common in community-acquired cases, but these infections have changed to having a high predilection for the vertebral column, and the prevalence of chronic cases has decreased.

The threat of multiresistant microorganisms

Enthusiasm about newly developed antimicrobial agents and disappointment because of the development of resistance have been alternating in the decades since the introduction of antibacterial chemotherapy around 1940. During the last few years several mechanisms of bacterial resistance have been elucidated, and new insights into the genetic basis of multiresistance have been gained. The clinical implications of multiresistance depend on timely recognition of the problem, i.e. knowledge of the epidemiology of multiresistant microorganisms and the availability of alternative drugs. A particular problem arises from the fact that infections with multiresistant microorganisms often occur in the most critically ill patients.

The prevalence, antibiotic susceptibility and phage-type of nasally carried Staphylococcus aureus in the Dublin community

A study was undertaken to determine the distribution, antibiotic susceptibility and phage type pattern of nasally-carried Staphylococcus aureus in the community. Coagulase-positive staphylococci were isolated from 180 of 440 individuals. The rate was higher in the inner city and among young adults and middle-aged males. The isolates were examined for phage-type patterns and antibiotic susceptibility. Most (60.6%) of the isolates were typable either at Routine Test Dilution (RTD) or at 100 RTD. Most belonged to phage group I (53.2%) and phage group III (21.1%). Susceptibility to penicillin and ampicillin was low at 12.3 and 15.5% respectively. All were susceptible to vancomycin. Methicillin-resistance was unexpectedly low at 0.6% whereas tetracycline and erythromycin resistance were in line with recent trends at 4.5 and 2.7%. The rate of multiple resistance was low at 2.3%.

Staphylococcus aureus still colonizes the untreated neonatal umbilicus

Two different neonatal umbilical cord treatment regimens were studied prospectively. Although a greater proportion of cords had separated by the seventh day in those babies not treated with topical antiseptics (47% vs. 26%), there was a significant excess (53% vs. 30%) of umbilical colonization by Staphylococcus aureus compared to those neonates whose cords were treated with alcohol wipes and hexachlorophane powder. The main purpose of treating cords is to prevent significant S. aureus colonization, and therefore current proposals to stop antiseptic treatment of umbilical cords should be disregarded.

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.

Comparative sensitivity to antibiotics and biocides of methicillin-resistant Staphylococcus aureus strains isolated from Saudi Arabia and Great Britain

Methicillin-resistant Staphylococcus aureus (MRSA) isolated in Saudi Arabia and Great Britain were examined for susceptibility to antibiotics and biocides. The strains differed in their sensitivity patterns. None of the Saudi strains showed resistance to propamidine isethionate, but most of the British gentamicin methicillin-resistant Staph. aureus (GMRSA) strains were highly resistant to this compound and to some other nucleic acid-binding (NAB) compounds. Both groups showed a low level of resistance towards quaternary ammonium compounds (QACs), but resistance to these compounds was not associated with resistance to gentamicin in the Saudi strains. The aminoglycoside-resistant determinants were non-conjugative in these strains. Natural MRSA strains were good recipients for pWG613, but transferred this plasmid in reciprocal crosses at significantly lower rates.

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.

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.

Control of epidemic methicillin-resistant Staphylococcus aureus in a Dutch university hospital

Between 1986 and 1989 a single strain of a methicillin- and multiply-resistant Staphylococcus aureus caused three distinct outbreaks at Utrecht University Hospital, involving 11, 19 and 32 patients, respectively. In all three episodes, members of staff were screened for MRSA carriage, and 58 persons were found to have positive nose cultures. In each outbreak it became necessary to isolate colonized and infected patients on a separate isolation ward. Staff carriers were also treated. Over the 18 months since the last outbreak, no new acquisitions of this epidemic MRSA strain have occurred. Between 1986 and 1989, the strain which caused the three outbreaks was not the only MRSA strain which was introduced into the hospital. Six other strains, which differed from the epidemic strain as shown by phage typing and antimicrobial susceptibility pattern, were found in single patients. The experience at Utrecht University Hospital illustrates the need for strict measures to eradicate epidemic strains of MRSA as well as the differences in "epidemicity" among various strains of MRSA.

Increasing Prevalence of Methicillin-Resistant Staphylococcus aureus in the United States

In the period 1975 to 1981, methicillin-resistant Staphylococcus aureus (MRSA) emerged as an important nosocomial pathogen in tertiary care centers in the United States. To determine if the prevalence of this organism has continued to increase, a questionnaire was sent to hospital epidemiologists in 360 acute care hospitals. A total of 256 (71%) of the 360 individuals responded. Overall, 97% (246/256) of responding hospitals reported having patients with MRSA in the period 1987 through 1989. Respondents in 217 hospitals provided estimates of the number of cases seen in 1987, 1988 and 1989. The percentage of respondents reporting one or more patients with MRSA increased from 88% in 1987 to 96.3% in 1989 (p = .0008). The percent of respondents reporting large numbers (≥50) of cases per year increased from 18% in 1987 to 32% in 1989 (p = .0006). Increasing frequency of large outbreaks was observed in community, community-teaching, federal, municipal and university hospitals.

Nasal carriage of Staphylococcus aureus and its influence on hospital infections caused by methicillin-resistant strains

A short review of the literature on the actual epidemiological situation related to nosocomial infections caused by methicillin-resistant Staphylococcus aureus and the importance of the nasal carriage of this pathogen is given together with selected data derived from our own studies on these problems.

Outbreaks of infection with methicillin-resistant Staphylococcus aureus on neonatal and burns units of a new hospital

Multiple introductions of methicillin-resistant Staphylococcus aureus (MRSA) strains occurred to a new hospital in Hong Kong. Two years of clinical microbiological surveillance of the resulting outbreaks was combined with laboratory investigation by phage and antibiogram typing, and plasmid profiling. The outbreaks on the special care baby (SCBU) and burns (BU) units were studied in detail, and colonization of staff and contamination of the environment were investigated. MRSA were spread by the hands of staff on the SCBU, where long-term colonization of dermatitis was important, but were probably transmitted on the BU by a combination of the airborne, transient hand-borne and environmental routes. Simple control measures to restrict hand-borne spread on the SCBU were highly effective, but control was not successful on the BU.

A survey of methicillin-resistant Staphylococcus aureus affecting patients in England and Wales

For a six-month period between October 1987 and March 1988, 660 isolates of methicillin-resistant Staphylococcus aureus (MRSA) from 570 patients were sent to the Staphylococcus Reference Laboratory at Colindale to supplement the National reporting survey of MRSA in England and Wales. The isolates were characterized by phage typing, antibiotic susceptibility and by selected biochemical tests. Patient details were also surveyed. Fourteen strains affected more than one hospital and were called multi-hospital epidemic strains. One strain, EMRSA-1, accounted for more than 40% of isolates and of patients. Other epidemic strains were defined. Ten additional strains were restricted to single hospitals. Only 25 primary isolates were non-typable but 67 sporadic typable strains occurred. The patients affected were approximately equally either infected or colonized. The sexes were represented equally. Orthopaedic and geriatric wards were over-represented. Epidemic strains were clumping factor positive while some sporadic strains were weak producers. Urea alkalinization and protein A production could supplement phage typing and antibiotic resistance in strain recognition.

Hong Kong strains of methicillin-resistant and methicillin-sensitive Staphylococcus aureus have similar virulence

While most authorities agree that methicillin-resistant Staphylococcus aureus (MRSA) are as pathogenic as methicillin-sensitive strains (MSSA), some believe that MRSA are relatively avirulent opportunists, and that their importance has been exaggerated. We present evidence that Hong Kong strains of MRSA and MSSA are equally pathogenic: they have similar virulence in animal models; they are isolated in similar proportions from both deep and superficial clinical sites including blood; in patients with hospital-acquired bacteraemias mortality rates are similar when adjusted for clinical factors; and in both animals and patients with systemic MRSA infection, mortality rates are significantly reduced by vancomycin therapy. Efforts to control the spread of MRSA are justified, and in invasive sepsis early treatment with vancomycin may be life-saving.

Antibiotic susceptibility and phage-type pattern of Staphylococcus aureus strains isolated from patients in general practice compared to strains from hospitalized patients

Phage-type patterns and antibiotic susceptibility have been examined in 904 Staphylococcus aureus strains from general practice in the Copenhagen municipality, in 1107 strains from hospitals in the Copenhagen municipality and in 18,028 strains isolated in 1988 from inpatients all over Denmark. The phage-type patterns of the 3 materials were very similar except for a slightly higher frequency of group II strains among isolates from general practice (24% compared to 19%). Penicillin resistance was high (86-87%) in all materials. Resistance to tetracycline and erythromycin was more frequent in strains from general practice (8.6% and 3.8%) than in strains both from hospitals in the same area (3.6% an 2.2%) and in all Danish hospitals (5.3% and 2.4%). This indicates that the restrictive use of antibiotics in hospitals seems to have eliminated the previous preponderance of multiresistant staphylococci in hospitals compared to community acquired staphylococci. It even seems as if the less restrictive use of tetracycline and erythromycin in general practice has now inversed the situation.

Methicillin-resistant Staphylococcus aureus: a ten-year survey in a Dublin hospital

We undertook a retrospective, longitudinal survey to monitor the changing incidence, phage types and patterns of antibiotic resistance of methicillin-resistant Staphylococcus aureus (MRSA) in St Laurence's Hospital (SLH), Dublin over the last 10 years. Following a peak in 1979, the incidence of MRSA has gradually decreased to around 17% of S. aureus isolates in 1986, almost identical to its incidence 10 years before. However, the spectrum of antibiotic resistance among these organisms remains broad and this seems to be at least partially related to antibiotic usage. Many strains could not be phage typed and others were typable only by the additional phage 90. This has severely limited the usefulness of phage typing in the tracing of sources of outbreaks. Thus, there is a need for a more specific method of typing as well as a rational antibiotic policy, to successfully monitor and curtail the hospital spread of MRSA.

The changing pattern of severe neonatal staphylococcal infection: a 10-year study

Forty-two cases of severe staphylococcal infection occurring over a 10-year period in the neonatal unit at Queen Mary Hospital are described. There was a 4.5-fold increase in incidence in the latter half of the study period, when methicillin-resistant Staphylococcus aureus (MRSA) emerged. The isolated MRSA were also resistant to gentamicin, but sensitive to vancomycin, fusidic acid, co-trimoxazole and amikacin. Comparison between MRSA and methicillin-sensitive cases showed that the former was associated with a longer hospital stay after diagnosis. Overall mortality was 9.5%. Two cases with meningitis died. MRSA is at least as virulent as its methicillin-sensitive counterparts. The treatment implications of severe neonatal staphylococcal infection are discussed.

Antimicrobial resistance of Staphylococcus aureus: genetic basis

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