Relationship between molecular epidemiology and antibiotic susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) in a French teaching hospital

Frequent occurrence of trimethoprim-sulfamethoxazole hetero-resistant Staphylococcus aureus isolates in different African countries

High rates of trimethoprim/sulfamethoxazole (SXT) resistance, a combination of two antifolate antibiotics trimethoprim (TMP) and sulfamethoxazole (SMZ), have been reported among Staphylococcus aureus isolates in Portuguese-speaking African countries. Our study aimed to evaluate the occurrence of TMP resistance markers in major SXT^R methicillin-resistant S. aureus (MRSA) clones from these countries. We accessed also different fitness traits that could explain the success of these isolates over the Brazilian MRSA (the most successful SXT^R MRSA clone worldwide but never identified in these countries). Minimum inhibitory concentrations for SXT, TMP and SMZ were determined, and genes encoding TMP resistance (dfrG, dfrA, dfrK and dfrB) were searched. Representatives of the Brazilian clone and of the major MRSA African clones were evaluated for their fitness by individual growth curves, competition assays, survival under desiccation, autolytic activity, resistance to oxidative stress, and also growth at high osmolarity and in acid and alkaline environments. Although all African isolates showed high-level resistance to TMP, the majority presented hetero-resistance to SXT. TMP resistance was linked to the presence of dfrG (78%), dfrA (19%) or both (3%) genes. Compared to the Brazilian clone, the African isolates showed higher growth rates and autolytic activity, and better survival to desiccation and alkaline conditions. Since isolates exhibiting SXT hetero-resistance are frequent in Africa, the implementation of standardized guidelines to detect this phenomenon is of major interest. The predominant MRSA clones in Portuguese-speaking African countries likely possess significant advantages over other clones, such as the Brazilian MRSA, that may explain their epidemiological success.

Turning the tide or riding the waves? Impacts of antibiotic stewardship and infection control on MRSA strain dynamics in a Scottish region over 16 years: non-linear time series analysis

OBJECTIVES

To explore temporal associations between planned antibiotic stewardship and infection control interventions and the molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA).

DESIGN

Retrospective ecological study and time-series analysis integrating typing data from the Scottish MRSA reference laboratory.

SETTING

Regional hospital and primary care in a Scottish Health Board.

PARTICIPANTS

General adult (N=1,051,993) or intensive care (18,235) admissions and primary care registrations (460,000 inhabitants) between January 1997 and December 2012.

INTERVENTIONS

Hand-hygiene campaign; MRSA admission screening; antibiotic stewardship limiting use of macrolides and '4Cs' (cephalosporins, coamoxiclav, clindamycin and fluoroquinolones).

OUTCOME MEASURES

Prevalence density of MRSA clonal complexes CC22, CC30 and CC5/Other in hospital (isolates/1000 occupied bed days, OBDs) and community (isolates/10,000 inhabitant-days).

RESULTS

67% of all clinical MRSA isolates (10,707/15,947) were typed. Regional MRSA population structure was dominated by hospital epidemic strains CC30, CC22 and CC45. Following declines in overall MRSA prevalence density, CC5 and other strains of community origin became increasingly important. Reductions in use of '4Cs' and macrolides anticipated declines in sublineages with higher levels of associated resistances. In multivariate time-series models (R(2)=0.63-0.94) introduction of the hand-hygiene campaign, reductions in mean length of stay (when >4 days) and bed occupancy (when >74 to 78%) predicted declines in CC22 and CC30, but not CC5/other strains. Lower importation pressures, expanded MRSA admission screening, and reductions in macrolide and third generation cephalosporin use (thresholds for association: 135-141, and 48-81 defined daily doses/1000 OBDs, respectively) were followed by declines in all clonal complexes. Strain-specific associations with fluoroquinolones and clindamycin reflected resistance phenotypes of clonal complexes.

CONCLUSIONS

Infection control measures and changes in population antibiotic use were important predictors of MRSA strain dynamics in our region. Strategies to control MRSA should consider thresholds for effects and strain-specific impacts.

Epidemic MRSA clone ST22-IV is more resistant to multiple host- and environment-related stresses compared with ST228-I

BACKGROUND

ST22-IV is a successful hospital-associated MRSA clone. Due to its known ability to replace other MRSA clones in hospitals, it became a dominant clone in Europe and beyond. So far, there are no studies investigating the relationship between the epidemiological success of MRSA clones and their capacity to withstand commonly encountered stresses.

METHODS

We investigated the fitness of ST22-IV in comparison with the replaced clone ST228-I, evaluating its resistance to oxidative stress, autolytic activity, growth at high osmolarity and in acid and alkaline environments and survival under desiccation and heat shock. We also compared their phenotypic characteristics and examined the impact of antibiotic consumption on epidemiological success.

RESULTS

Here we demonstrate that the dominance of ST22-IV is linked neither to changes in antibiotic consumption nor to acquisition of additional resistances over time. Strong α-haemolysin activity, the production of β-haemolysin and the presence of an active agr could partly explain the virulence of ST22-IV previously observed in a murine model of pneumonia. Most importantly, we show that ST22-IV compared with ST228-I, besides retaining susceptibility to most antibiotics over time, has a superior capacity to survive under all stress conditions tested, which bacteria commonly face during their life cycle.

CONCLUSIONS

Our results support our hypothesis that ST22-IV has a fitness advantage over ST228-I. This fitness advantage could have allowed ST22-IV to displace ST228-I without acquiring additional resistances and could help explain its epidemic success in hospital settings and its spread in Europe and beyond.

Hospital-community interactions foster coexistence between methicillin-resistant strains of Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of morbidity and mortality in both hospitals and the community. Traditionally, MRSA was mainly hospital-associated (HA-MRSA), but in the past decade community-associated strains (CA-MRSA) have spread widely. CA-MRSA strains seem to have significantly lower biological costs of resistance, and hence it has been speculated that they may replace HA-MRSA strains in the hospital. Such a replacement could potentially have major consequences for public health, as there are differences in the resistance spectra of the two strains as well as possible differences in their clinical effects. Here we assess the impact of competition between HA- and CA-MRSA using epidemiological models which integrate realistic data on drug-usage frequencies, resistance profiles, contact, and age structures. By explicitly accounting for the differing antibiotic usage frequencies in the hospital and the community, we find that coexistence between the strains is a possible outcome, as selection favors CA-MRSA in the community, because of its lower cost of resistance, while it favors HA-MRSA in the hospital, because of its broader resistance spectrum. Incorporating realistic degrees of age- and treatment-structure into the model significantly increases the parameter ranges over which coexistence is possible. Thus, our results indicate that the large heterogeneities existing in human populations make coexistence between hospital- and community-associated strains of MRSA a likely outcome.

One of the most notorious cases of antibiotic-resistant bacteria is methicillin-resistant Staphylococcus aureus (MRSA), which causes diseases ranging from skin and soft-tissue infections to pneumonia and septicemia. Traditionally, MRSA was mainly hospital-associated, but in the past decade community-associated strains have spread widely. Typically drug-resistant bacteria have lower reproduction or transmission rates, called a fitness cost. Because this cost is estimated to be significantly lower for community-associated strains, it has been predicted that these will eventually replace the hospital-associated strains. However, hospital-associated strains are resistant against a greater variety of antibiotics, which may compensate for the higher fitness cost. Here, we integrate realistic data on drug-usage, resistance profiles, contact, and age structures into a mathematical model of MRSA transmission to predict the competition between hospital- and community-associated strains. We find that for a realistic degree of population structure it is likely that both strains of MRSA will coexist in the long term. This results from significantly different hospitalization and antibiotic consumption rates between age groups. In particular, elderly individuals have much higher rates of antibiotic usage and hospitalizations than other age groups. This generates a situation where community-associated strains can predominate in the community but are outcompeted in the hospital, resulting in coexistence in the population.

Panton-valentine leukocidin-positive and toxic shock syndrome toxin 1-positive methicillin-resistant Staphylococcus aureus: a French multicenter prospective study in 2008

The epidemiology of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) differs from country to country. We assess the features of the ST80 European clone, which is the most prevalent PVL-positive CA-MRSA clone in Europe, and the TSST-1 ST5 clone that was recently described in France. In 2008, all MRSA strains susceptible to fluoroquinolones and gentamicin and resistant to fusidic acid that were isolated in 104 French laboratories were characterized using agr alleles, spa typing, and the staphylococcal cassette chromosome mec element and PCR profiling of 21 toxin genes. Three phenotypes were defined: (i) kanamycin resistant, associated with the ST80 clone; (ii) kanamycin and tobramycin resistant, associated with the ST5 clone; and (iii) aminoglycoside susceptible, which was less frequently associated with the ST5 clone. Among the 7,253 MRSA strains isolated, 91 (1.3%) were ST80 CA-MRSA (89 phenotype 1) and 190 (2.6%) were ST5 CA-MRSA (146 phenotype 2, 42 phenotype 3). Compared to the latter, ST80 CA-MRSAs were more likely to be community acquired (80% versus 46%) and found in young patients (median age, 26.0 years versus 49.5 years) with deep cutaneous infections (48% versus 6%). They were less likely to be tetracycline susceptible (22% versus 85%) and to be isolated from respiratory infections (6% versus 27%). The TSST-1 ST5 clone has rapidly emerged in France and has become even more prevalent than the ST80 European clone, whose prevalence has remained stable. The epidemiological and clinical patterns of the two clones differ drastically. Given the low prevalence of both among all staphylococcal infections, no modification of antibiotic recommendations is required yet.

Usefulness of antimicrobial resistance pattern for detecting PVL- or TSST-1-producing meticillin-resistant Staphylococcus aureus in a French university hospital

Several recent reports have suggested that community-associated meticillin-resistant Staphylococcus aureus (MRSA) clones, particularly those harbouring genes for Panton-Valentine leukocidin (PVL) or toxic shock syndrome toxin 1 (TSST-1), are increasingly responsible for infections in hospitals. Here, a retrospective study was carried out to investigate whether antimicrobial resistance patterns could be used to detect these pathogens in a French university hospital. Isolates were characterized by antimicrobial susceptibility testing, PCR profiling (PVL genes and tst), PFGE typing and multilocus sequence typing. Demographic and clinical data were collected from all patients. For PVL-positive MRSA, the typical antimicrobial resistance pattern (susceptible to fluoroquinolones, non-susceptible to fusidic acid, kanamycin resistant and susceptible to gentamicin and tobramycin) had a sensitivity of 77.8 % and a positive predictive value (PPV) of 100 %. For tst-positive MRSA, the antimicrobial resistance pattern (susceptible to fluoroquinolones and non-susceptible to fusidic acid) had a sensitivity of 100 % and a PPV of 72.4 %. These results suggest that phenotypic rules based on antimicrobial resistance patterns are potentially useful for the detection of PVL- and tst-positive MRSA isolates.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Spain: a multicentre prevalence study (2002)

A point-prevalence study, performed in 2002 in 143 Spanish hospitals, collected 439 isolates of Staphylococcus aureus. Of these, 134 (30.5%) were resistant to methicillin (i.e., MRSA). Susceptibility testing was performed by a microdilution method, and mecA was detected by PCR. The isolates were characterised by phage typing, pulsed-field gel electrophoresis (PFGE) after SmaI digestion, and SCCmec typing. The 134 MRSA isolates showed resistance to ciprofloxacin (93.3%), tobramycin (88.8%), erythromycin (67.9%), clindamycin (59.7%), gentamicin (42.5%), mupirocin (17.9%), rifampicin (5.2%) and trimethoprim-sulphamethoxazole (5.2%). All of the isolates were susceptible to glycopeptides. Twenty-five resistance patterns were found, of which four accounted for 66% of the isolates. Phage group III was the most frequent (41.1%). PFGE revealed 31 different patterns, with ten major clones (including two predominant clones with variable antibiotypes that accounted for 43.3% of the MRSA isolates) and 21 sporadic patterns. Two isolates belonged to two variants of the Iberian clone (ST247-MRSA-I), one to the Brazilian clone (ST239-MRSA-III), and seven to the EMRSA-16 clone (ST36-MRSA-II). SCCmecIV accounted for 70.2% of the isolates (73.9% were type IVA), while SCCmecI, SCCmecII and SCCmecIII accounted for 22.1%, 6.9% and 0.8% of isolates, respectively, with three non-typeable isolates. Isolates of SCCmecIV and SCCmecIVA were predominantly nosocomial (95.8% and 97.1%, respectively). None of the isolates produced Panton-Valentine leukocidin. Thus, two clones carrying SCCmecIV and SCCmecIVA, respectively, were predominant among nosocomial MRSA isolates throughout Spain.

Evolution and molecular characterization of methicillin-resistant Staphylococcus aureus epidemic and sporadic clones in Cordoba, Argentina

Since 1999, a new, epidemic, methicillin-resistant Staphylococcus aureus (MRSA) strain, named the "Cordobes clone," has emerged in Argentina and coexists with the pandemic Brazilian clone. The purpose of this study was to determine the stability over time of the new clone and to investigate its evolutionary relationship with epidemic international MRSA lineages and with other MRSA and methicillin-susceptible S. aureus (MSSA) major clones distributed in this region. One hundred three MRSA isolates recovered in 2001 from Cordoba, Argentina, hospitals and 31 MSSA strains collected from 1999 to 2002 were analyzed by their antibiotic resistance patterns, phage typing, and pulsed-field gel electrophoresis. Additionally, representative members of most MRSA defined genotypes (A, B, C, E, K, and I) were characterized by multilocus sequence typing (MLST) and spaA and SCCmec typing. The most prevalent MSSA pulsotypes were also analyzed by MLST. Our results support the displacement of the Brazilian clone (sequence type [ST] 239, spaA type WGKAOMQ, SCCmec type IIIA) by the Cordobes clone (ST5, spaA type TIMEMDMGMGMK, SCCmec type I) in the hospital environment. MRSA and MSSA isolates shared only ST5. The data support the origin of the Cordobes clone as a member of a lineage that includes the pediatric and New York/Japan international clones and that is genetically related to the British EMRSA-3 strain. Interestingly, the pediatric clone, isolated from most community-acquired infections in Cordoba, was characterized by ST100, a single-locus variant of ST5 and a new variant of SCCmec type related to SCCmec type IVc.

Guidelines for the prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the UK

These evidence-based guidelines have been produced after a literature review of the treatment and prophylaxis of methicillin-resistant Staphylococcus aureus (MRSA) infection. The guidelines were further informed by antibiotic susceptibility data on MRSA from the UK. Recommendations are given for the treatment of common infections caused by MRSA, elimination of MRSA from carriage sites and prophylaxis of surgical site infection. There are several antibiotics currently available that are suitable for use in the management of this problem and potentially useful new agents are continuing to emerge.

Use of intranasal mupirocin to prevent methicillin-resistant Staphylococcus aureus infection in intensive care units

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) causes severe morbidity and mortality in intensive care units (ICUs) worldwide. The purpose of this study was to determine whether intranasal mupirocin prophylaxis is useful to prevent ICU-acquired infections with MRSA.

Materials and methods

We conducted a 4-year observational retrospective study in a 15-bed adult medical ICU. During the first 2-year period mupirocin ointment was included in the MRSA control programme; during the second, mupirocin was not used. The main endpoint was the number of endogenous ICU-acquired infections with MRSA.

Results

The number of endogenous acquired infections was significantly higher during the second period than during the first (11 versus 1; P = 0.02), although there was no significant difference in the total number of patients infected with MRSA between the two periods. We also observed that nasal MRSA decolonisation was significantly higher in the mupirocin period than in mupirocin-free period (P = 0.002).

Conclusion

Our findings suggest that intranasal mupirocin can prevent endogenous acquired MRSA infection in an ICU. Further double-blind, randomised, placebo-controlled studies are needed to demonstrate its cost-effectiveness and its impact on resistance.

Surveillance régionale de l'évolution de Staphylococcus aureus résistant à la méticilline (SARM) : quels résultats pour quels enseignements ?

OBJECTIVE

The aim of this study was to describe the evolution of MRSA within hospitals located in Franche-Comté from 1999 to 2003 and to establish the MRSA risk according to the type of hospitalization.

METHODS

Surveillance of multidrug resistant bacteria was carried out according to the French national guidelines for the prevention of nosocomial infections.

RESULTS

The global incidence of MRSA colonized/infected patients (screened by clinical samples) per 1000 patient-days had decreased from 0.73 in 1999 to 0.58 in 2003 (P < 0.004). However, analyzing the results according to each type of hospitalization revealed great heterogeneity. In 2003, the increase of MRSA incidence in short-term public hospitalization was indeed alarming whereas MRSA risk had regularly decreased in the other hospitalization types (rehabilitation and long-term care-facilities) since 1999. The number of potentially serious colonizations/infections caused by MRSA (bacteremia, deep infections, and pulmonary infections) accounted for 12.8% of all colonizations/infections.

CONCLUSION

MRSA, in spite of improved prevention in our region, remains responsible for numerous infections.