Methicillin resistant Staphylococcus aureus (MRSA) isolated in Saudi Arabia: epidemiology and antimicrobial resistance patterns

Methicillin resistant Staphylococcus aureus (MRSA) comprised about 7·5% per annum of all S. aureus isolated in a general hospital in Jeddah, Saudi Arabia during the 3 year period 1990–1992. Most isolates were from wound sites (71%). Resistance to gentamicin (83%) and tetracycline (93%) was frequently observed whilst resistance to ciprofloxacin (1%) and rifampicin (6%) was uncommon. Low levels of mupirocin resistance (MIC 8 mg 1⁻¹), were detected in 3% of all MRSA isolates.     

Risk factors associated with the conversion of meticillin-resistant Staphylococcus aureus colonisation to healthcare-associated infection

The objective of the study was to identify risk factors for healthcare-associated meticillin-resistant Staphylococcus aureus (HA-MRSA) infections in patients with MRSA colonisation over an extended time period. This was a case–control study conducted at a community teaching hospital. Patients included 41 cases and 82 controls, aged ≥18 years, who were nares colonisation culture positive for MRSA and either did or did not develop an HA-MRSA infection within 60 days after index colonisation, respectively. Potential risk factors evaluated included: patient demographics, comorbid conditions, medication use, presence of invasive devices, presence of wounds or other infections, nutritional status, number of hospitalisations and time to infection development. In the univariate analysis, the presence of peripheral vascular disease, three or more comorbidities, a central venous catheter, a Foley catheter, or two or more hospitalisations were significantly associated with increased risk for HA-MRSA infection. Multivariate analysis yielded a model that included presence of a central venous catheter (OR: 8.00; 95% CI: 3.13–20.4) or two or more hospitalisations (OR: 3.37; 95% CI: 1.37–8.26) as independent risk factors for MRSA infection in those with MRSA colonisation. In conclusion, risk factors independently associated with the conversion of MRSA colonisation to HA-MRSA infection include the presence of a central venous catheter or two or more hospitalisations. Strategies involving risk factor minimisation may be helpful in reducing HA-MRSA infections in this patient population.     

c-di-GMP as a vaccine adjuvant enhances protection against systemic methicillin-resistant Staphylococcus aureus (MRSA) infection

Cyclic diguanylate (c-di-GMP) is a novel immunomodulator and immune enhancer that triggers a protective host innate immune response. The protective effect of c-di-GMP as a vaccine adjuvant against Staphylococcus aureus infection was investigated by subcutaneous (s.c.) vaccination with two different S. aureus antigens, clumping factor A (ClfA) and a nontoxic mutant staphylococcal enterotoxin C (mSEC), then intravenous (i.v.) challenge with viable methicillin-resistant S. aureus (MRSA) in a systemic infection model. Mice immunized with c-di-GMP plus mSEC or c-di-GMP plus ClfA vaccines then challenged with MRSA produced strong antigen-specific antibody responses demonstrating immunogenicity of the vaccines. Bacterial counts in the spleen and liver of c-di-GMP plus mSEC and c-di-GMP plus ClfA-immunized mice were significantly lower than those of control mice (P < 0.001). Mice immunized with c-di-GMP plus mSEC or c-di-GMP plus ClfA showed significantly higher survival rates at day 7 (87.5%) than those of the non-immunized control mice (33.3%) (P < 0.05). Furthermore, immunization of mice with c-di-GMP plus mSEC or c-di-GMP plus ClfA induced not only very high titers of immunoglobulin G1 (IgG1), but c-di-GMP plus mSEC also induced significantly higher levels of IgG2a, IgG2b and IgG3 compared to alum adjuvant (P < 0.01 and P < 0.001, respectively) and c-di-GMP plus ClfA induced significantly higher levels of IgG2a, IgG2b and IgG3 compared to alum adjuvant (P < 0.001). Our results show that c-di-GMP should be developed as an adjuvant and immunotherapeutic to provide protection against systemic infection caused by S. aureus (MRSA).     

Detection and molecular characterization of a gentamicin-susceptible, methicillin-resistant Staphylococcus aureus (MRSA) clone in Rio de Janeiro that resembles the New York/Japanese clone

Staphylococcus aureus is the leading cause of hospital-acquired infections in many countries, and multiple factors contribute to the ability of these bacteria to disseminate and spread in hospitals. In Brazil it has been demonstrated that a multiresistant methicillin-resistant S. aureus clone, the so-called Brazilian epidemic clone, is widespread geographically. This clone was first detected in 1992 in Brazil, and recently from many other countries within South America, Europe and Asia. The study describes the detection of a gentamicin-susceptible heterogeneous MRSA clone that resembles another MRSA clone widely spread in US and Japanese hospitals, and supports the premise that the detection of heterogeneous MRSA isolates by some recommended methods is a challenging task that may, occasionally, result in MRSA misidentification.     

Glycopeptide intermediate Staphylococcus aureus and prevalence of the luk-PV gene in clinical isolates,in Northern Lebanon

Objectives

The aim of our study was to confirm the identification of 113 meticillin-resistant Staphylococcus aureus (MRSA) strains by pyrosequencing, to determine the susceptibility of these clinical isolates to various classes of antibiotics, to determine the minimum inhibitory concentration (MIC) to glycopeptides, and to detect mecA and luk-PV genes.

Methodology

The Staphylococcus species was identified by pyrosequencing of the variable region (V3) of the 16SrRNA. The susceptibility of these 113 strains of MRSA to antibiotics was determined by the disk diffusion method on Mueller-Hinton agar. The MIC of glycopeptides was determined by using the dilution method on solid media. mecA gene and luk-PV gene were detected by PCR.

Results

The disk diffusion method proved full susceptibility to vancomycin, teicoplanin, and linezolid; whereas MIC (dilution method) indicated that 5/113 strains were resistant to teicoplanin, giving a probability of having heterogeneous glycopeptide intermediate S. aureus (hGISA) strains. The mecA gene was detected in all MRSA strains ruling out the probability of having new variants of this gene in the tested strains. The luk-PV gene was detected in 28 out of 113 MRSA strains (24.8%).

Conclusion

The originality of this study was the detection of hGISA strains knowing that they were susceptible to glycopeptides according to the diffusion method. Thus it is necessary to check the level of susceptibility of MRSA clinical isolates to glycopeptides for immunodeficient patients, by determining the MIC.     

Burden of meticillin-resistant Staphylococcus aureus colonization and infection in London acute hospitals: retrospective on a voluntary surveillance programme

Although meticillin-resistant Staphylococcus aureus (MRSA) is recognized as an important cause of hospital and community healthcare-associated morbidity, and colonization as a precursor to infection, few studies have attempted to assess the burden of both colonization and infection across acute healthcare providers within a defined health economy. This study describes the prevalence and incidence of MRSA colonization and infection in acute London hospital Trusts participating in a voluntary surveillance programme in 2000-2001. Hospital infection control staff completed a weekly return including details on incident and prevalent colonizations, bacteraemias and other significant infections due to MRSA. Incidence and prevalence rates were calculated for hospitals with sufficient participation across both years. Colonizations accounted for 79% of incident MRSA cases reported; 4% were bacteraemias, and 17% other significant infections. There was no change in incidence of colonization of hospital patients between 2000 and 2001. By contrast, there was an unexplained 49% increase in prevalence of colonizations over this period. For any given month, prevalent colonizations outnumbered incident colonizations at least twofold. This MRSA surveillance programme was unusual for prospective ascertainment of incident and prevalent cases of both colonization and infection within an English regional health economy. Consistent with other studies, the incidence and prevalence of colonization substantially exceeded infection. Given the small contribution of bacteraemias to the overall MRSA burden, and the surveillance, screening and control interventions of recent years, it may be appropriate to review the present reliance on bacteraemia surveillance.     

Postponing elective hospitalizations for pre-admission MRSA screening and decolonization. A study evaluating eligibility and acceptance among patients of a German university hospital

There is evidence that pre-admission screening and decolonization (PreASD) of MRSA can reduce costs in elective surgical patients. It is not known whether this strategy could also be successfully applied to general medical patients of a tertiary referral hospital with multiple specialties. Our study retrospectively evaluates the eligibility of patients for MRSA-PreASD in a setting of active targeted MRSA surveillance. We carried out a survey among eligible patients to assess acceptance and feasibility of MRSA-PreASD. Of 10,496 admissions to our university hospital 8912 (84.9%) were screened for MRSA-risk factors. In 5382 admissions at risk swabs were taken and analyzed. Using the Appropriateness Evaluation Protocol (AEP) we retrospectively assessed how many of the 5382 admissions at risk could have been postponed for the duration of an MRSA-PreASD. 36 (17%) of 212 admissions with proven MRSA colonization and 2175 (42%) of 5170 patients without detectable MRSA could have been sent home for MRSA-PreASD to be electively admitted later. Of the 36 admissions (35 patients) with proven MRSA eligible for PreASD 23 patients (65%) responded to an interview. 22 of those (95.6%) would have agreed to PreASD. Additional costs for a screening protocol adapted to the needs of MRSA-PreASD of 52,061€ were estimated. Additional hospitalization costs of 6100–9300€ per MRSA case in Germany have been published. In our study population the successful pre-admission decolonization of 22 cases (63% of 35 patients eligible) may therefore have saved about 134,000–205,000€. Thus from an economic point of view our concept should be justified.     

A bundle of care to reduce colorectal surgical infections: an Australian experience

Staphylococcus aureus carriage increases the risk of infection. Demographic and microbiological data from adult patients with nasal S. aureus carriage were analysed in order to define effect modifiers of this association. Predictors for growth of S. aureus from clinical cultures were identified in a case-control study using bivariate and multi-variate logistic regression analysis. Between 1 January 2005 and 1 April 2009, 645 patients with nasal S. aureus colonization and documented follow-up of ≥90 days were identified; 159 (25%) patients were found to carry meticillin-resistant S.?aureus (MRSA). The median age of patients was 58 years, and 421 (65%) were male. During the subsequent 90 days, one or more clinical cultures were positive for S. aureus in 131 patients (20%). Multi-variate analysis identified a prior history of any S. aureus positive culture [adjusted odds ratio (aOR) 2.4, 95% confidence interval (CI) 1.5-3.8; P=0.0005) as an independent predictor of subsequent S. aureus infection. MRSA colonization was a predictor of infection in patients aged >40 years (aOR 2.5, 95% CI 1.4-4.1; P=0.0004), and even more so in patients aged ≤40 years (aOR 12.4, 95% CI 3.0-51; P=0.0005). Age >40 years was an additional independent risk?factor for meticillin-susceptible S. aureus carriers (aOR 3.0, 95% CI 1.2-7.8; P=0.02) but not for MRSA carriers. Preferential screening of patients at high risk for MRSA carriage and subsequent infection, as well as the absence of a universal policy for the use of decolonization regimens, may partly explain the relatively high risk of S. aureus infection in the patient population. MRSA carriers and older patients with recurrent S. aureus positive cultures may gain the greatest benefit from routine decolonization measures.     

Unexpected absence of meticillin-resistant Staphylococcus aureus nasal carriage by healthcare workers in a tertiary hospital in Kenya

Healthcare workers (HCWs) are a major reservoir of meticillin-resistant Staphylococcus aureus (MRSA). A cross-sectional study was conducted between July and December 2010 to determine the prevalence of nasal carriage of MRSA at the Aga Khan University Hospital Nairobi. Nasal swabs were taken from 246 randomly selected HCWs. MRSA was identified using both phenotypic and genotypic methods. The prevalence of MRSA carriage was 0% [95% confidence interval (CI): 0-1.5%] whereas that of meticillin-susceptible Staphylococcus aureus was 18.3% (95% CI: 14.0-23.6%). Given the absence of MRSA in our hospital, screening HCWs should be limited to an outbreak setting.     

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.     

Staphylococcal cassette chromosome mec in MRSA, Taiwan

To determine the predominant staphylococcal cassette chromosome (SCC) mec element in methicillin-resistant Staphylococcus aureus, we typed 190 isolates from a hospital in Taiwan. We found a shift from type IV to type III SCCmec element during 1992-2003, perhaps caused by selective pressure from indiscriminate use of antimicrobial drugs.     

Contributions of capsule, lipoproteins and duration of colonisation towards the protective immunity of prior Streptococcus pneumoniae nasopharyngeal colonisation

Live attenuated vaccines have been proposed as a strategy to induce protective immunity against infectious diseases. Recent data have demonstrated that nasopharyngeal colonisation with Streptococcus pneumoniae induces protective immunity against subsequent invasive infection, suggesting nasal vaccination with live attenuated bacteria could be a preventative strategy. However the bacterial factors affecting the strength of this adaptive immune response remain unclear. In a direct comparison with the parent wild-type strain, we found that colonisation with bacteria lacking either capsule or surface lipoproteins led to significantly diminished protection. Immunity after colonisation was not dependent on serum IgG to capsular antigens. Colonisation density and duration was reduced for all the non-protective strains, suggesting that protective immunity maybe related to the extent of nasopharyngeal bacterial exposure. To investigate this hypothesis, we utilised an auxotrophic bacterial Δpab strain where duration of colonisation could be controlled by supply and removal of para-amino-benzoic acid (PABA) to mouse drinking water. Supporting colonisation with the Δpab strain for 5 days with PABA led to a faster serum antibody response compared to colonisation for less than 48 h. This enhanced immunogenicity was associated with a trend towards protection. The data presented here aid our understanding of why only certain live attenuated strains are able to function as effective vaccines, and may be valuable in informing the constituents of future live attenuated vaccines.     

Low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission in the Netherlands: the value of search and destroy and restrictive antibiotic use

In the Netherlands, less than 1% of clinical isolates of Staphylococcus aureus are methicillin-resistant (MRSA). A national search and destroy policy prevents MRSA from becoming endemic. Some MRSA outbreaks cannot be related to patients at risk for MRSA carriage. This study was designed to measure the prevalence of MRSA among patients without risk factors for MRSA carriage at the time of admission to the hospital. In four Dutch hospitals, patients admitted to non-surgical departments in the period 1999-2000 were screened for MRSA nasal carriage. Nasal swabs were streaked on 5% sheep blood agar (BA), submerged in a selective broth, and incubated for two to three days at 35 degrees C. Colonies suspected of being S. aureus were identified with an agglutination test. Susceptibility testing was performed by an automated system and additional oxacillin disk diffusion. Methicillin resistance was confirmed by a DNA hybridization test and mecA PCR. MRSA strains were genotyped by pulsed-field gel electrophoresis (PFGE). Twenty-four percent (2332/9859) of the patients were S. aureus nasal carriers. Only three (0.03%) patients were MRSA carriers. These patients were not repatriated, nor known to be MRSA carriers before screening. Genotyping revealed that the strains were not clonally related and were not related to MRSA outbreaks in the hospital where the patients were admitted. We conclude that at routine admission to a Dutch hospital (excluding high-risk foreign admissions) the MRSA prevalence is low (0.03%), due to the Dutch search and destroy policy and restrictive antibiotic prescribing.