Coagulase-negative staphylococci in a major Danish university hospital: diversity in antibiotic susceptibility between wards

Spread of Clones of Multidrug-Resistant, Coagulase-Negative Staphylococci Within a University Hospital

Objective:

To detect putative clonal dissemination of multidrug-resistant, coagulase-negative staphylococci (CNS) in a university hospital in northern Sweden.

Methods:

All consecutive routine clinical samples from our hospital were screened during two periods (November and December 2001 and September and October 2002) for the presence of multidrug-resistant (defined as resistant to oxacillin, clindamycin, co-trimoxazole, gentamicin, and fusidic acid, but susceptible to vancomycin) isolates of CNS. Genetic similarity between isolates was analyzed using pulsed-field gel electrophoresis (PFGE) and a computer program.

Results:

Seventy multidrug-resistant isolates from 62 patients were identified, 28 during the 2001 period and 42 during the 2002 period. All isolates except one, which wasStaphylococcus haemolyticus, were identified asS. epidermidis. Multidrug-resistant CNS were isolated in samples obtained from 24 different wards. Two subgroups (group A and group B) ofS. epidermidisthat differed by approximately 40% in PFGE band similarity were identified. Group A consisted of 44 isolates with a PFGE band similarity of greater than 70% that included 6 subgroups consisting of 3 to 16 isolates that expressed a 100% similarity. These isolates were identified during both sampling periods in cultures performed in 18 different wards. A clonal origin could not be excluded for some of the remaining 26 isolates belonging to group B, but none had identical PFGE patterns, suggesting a more diverse origin.

Conclusion:

The results of this study suggest clonal spread of multidrug-resistant CNS within our hospital and that some clones are endemic in the hospital environment.

Antibiotic use is associated with resistance of environmental organisms in a teaching hospital

An intensive care unit (ICU), acute stroke unit (ASU) and medical day bed unit (MDBU) underwent a standardized four-month environmental screening programme. The aim was to examine environmental organisms from these wards and compare bacterial resistances in association with antimicrobial usage. Hand-touch and other sites were screened using commercial dip-slides, and staff were asked to provide fingertip cultures. Patient blood isolates were retained throughout the study. Organisms were quantitatively and qualitatively assessed including antimicrobial susceptibility testing. Antibiotic consumption data in defined daily doses/1000 patient-days were obtained for each unit for the previous year. Two hundred and seventy-six staphylococci and 67 Gram-negative bacilli were recovered. Antibiotic resistance was significantly associated with individual wards for staphylococci (P<0.0001) and coliforms (P=0.04), and trends were also demonstrated for other Gram-negative organisms (P=0.06) despite fewer numbers. Antibiotic consumption on the ICU was six-fold higher than on the ASU and MDBU. Associations were found between consumption of selected antibiotic groups and corresponding resistances among staphylococci and Gram-negative bacilli. Antibacterial resistance was the only significant difference between environmental bacteria from different wards, and appeared to reflect prescribing pressure. Visual inspection of a ward may not provide a reliable guide regarding the presence of multi-resistant organisms in the hospital environment or the potential risk of infection. These findings have implications for local antibiotic policies, infection control and cleaning schedules.

Fluoroquinolone consumption and resistance in haematology–oncology patients: ecological analysis in two university hospitals 1999–2002

OBJECTIVES

To compare rates of in vitro fluoroquinolone resistance of bacterial isolates obtained from inpatients of two haematology-oncology services with high and low fluoroquinolone consumption.

METHODS

Two hospitals with consistently high (A) and low (B) fluoroquinolone use in their haematology-oncology services between the years 1999 and 2002 were identified in a hospital antibiotic use surveillance project. Rates of in vitro resistance to fluoroquinolones in inpatients of the services were determined for Escherichia coli and coagulase-negative staphylococcal bloodstream isolates, and also for Pseudomonas aeruginosa and Staphylococcus aureus isolates from any site.

RESULTS

Fluoroquinolone resistance of E. coli was significantly higher in hospital A than in hospital B, but there was no such correlation between fluoroquinolone use and resistance rates for P. aeruginosa and staphylococci.

CONCLUSION

The impact of antibiotic consumption on the prevalence of resistance may differ widely between different pathogens. Interventions using ecological analyses of the relationship between hospital antibiotic use and resistance need to consider pathogen-specific dynamics in the emergence and control of bacterial resistance.

Rapid screening and identification of methicillin-resistant Staphylococcus aureus from clinical samples by selective-broth and real-time PCR assay

A screening method for methicillin-resistant Staphylococcus aureus (MRSA) by using selective broth and real-time PCR (broth-PCR) was developed and evaluated. The samples (n = 304) were cultured in the broth overnight, followed by nuc gene detection by real-time PCR. nuc-negative samples were further checked for the presence of nuc amplification inhibitors by a PCR internal inhibitor assay. nuc-positive samples and nuc-negative samples with PCR inhibitors were cultured onto plates and processed further. The diagnostic values for this MRSA screening method were 93.3% sensitivity, 89.6% specificity, 31.8% positive predictive value, and 99.6% negative predictive value. The application of the broth-PCR method will be able to report most of the negative samples (258 of 289 [89.3%]) on the next morning and can save as much as 84.9% (258 of 304) of the labor and cost spent on processing the nuc-negative specimens on plates. In the study, all the samples were processed in parallel by the broth enrichment method and the plating method for comparison. To identify MRSA, the isolated oxacillin-resistant S. aureus strains were tested by a duplex real-time PCR targeting the mecA gene and the nuc gene. A collection of MRSA, methicillin-susceptible Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis, and methicillin-susceptible Staphylococcus epidermidis strains and a panel of standard strains of 11 bacterial species other than S. aureus were also tested by this method, which was proved to be a valuable tool for MRSA identification in a routine microbiological laboratory.

Rapid PCR detection of the methicillin resistance gene, mecA, on the hands of medical and non-medical personnel and healthy children and on surfaces in a neonatal intensive care unit

The hands of medical personnel are the chief vectors for transmission of antibiotic-resistant bacteria and probably serve as an important reservoir for antibiotic resistance genes in hospitals. In this survey we examined different reservoirs of the methicillin resistance gene, mecA, using a simplified PCR method. Samples (n = 151) were taken from the hands of medical and non-medical personnel and healthy children and from surfaces in a neonatal intensive care unit (NICU). We also performed sampling from 4 different body sites in 5 of the medical personnel. Fifteen out of 16 nurses (94%) from the ICU carried the mecA gene on their hands, whereas only 35% of the paediatric nurses were mecA-positive. Of all medical personnel, 44% carried the mecA gene on their hands. There was a significant difference (p < 0.015) between medical and non-medical personnel in terms of the carriage rate of mecA. Four samples from surfaces in a NICU--2 ventilators, 1 bench and 1 telephone--were positive for mecA. Our results are comparable with those from previous studies on reservoirs of methicillin-resistant coagulase-negative staphylococci using conventional culture techniques.

Antibiotic resistance in coagulase-negative staphylococci isolated from Cope's gray treefrogs (Hyla chrysoscelis)

Organisms belonging to the genus Staphylococcus were isolated on mannitol salt agar from the feces of wild caught Cope's gray treefrogs (Hyla chrysoscelis) from east-central Kansas. All 222 presumptive isolates were confirmed as coagulase-negative staphylococci with Staphylococcus sciuri and Staphylococcus xylosus being most prevalent. Antibiotic susceptibility patterns to five different antibiotics were determined and the results indicated 99% of all isolates were resistant to penicillin G and 59% of the isolates were resistant to oxacillin, a clinical substitute for methicillin. Due to the significance of methicillin resistance in the genus Staphylococcus, 10 randomly chosen oxacillin resistant organisms were analyzed for the presence of the mecA gene, which is known to code for methicillin resistance. The gene was detected in four of the 10 organisms examined. These data indicate that gray treefrogs are harboring inordinately large numbers of methicillin resistant staphylococci as part of their normal flora and that the mechanism of methicillin resistance may be independent of mecA.

Survey of methicillin-resistant coagulase-negative staphylococci in the hospitals of central Greece

A sample of 450 consecutive, non-replicated coagulase-negative staphylococci (CoNS), collected from clinical specimens during the period 2000-2001 from the five major hospitals of Thessaly district (Central Greece) were investigated for resistance to methicillin. Most of the isolates had been collected in a sporadic fashion from the intensive care units and the surgical wards of the participating hospitals. The majority of the isolates (76%) were Staphylococcus epidermidis (50%), Staphylococcus haemolyticus (14.8%) and Staphylococcus hominis (11.1%). All 316 isolates (70%) were classified as resistant according to NCCLS breakpoints (MIC > or =0.5 mg/l); 268 (59.5%) of them were mecA-positive in a PCR-based assay. All isolates with MIC > or =8 mg/l carried the gene, while, only 23.8% of isolates with MIC, 0.5-4 mg/l were carriers. Only 9% of the mecA-positive isolates were found to be sensitive to various non-beta-lactams, while 41.8% of the isolates were resistant to more than three antimicrobial groups apart from beta-lactams. Molecular typing by PFGE showed apparent heterogeneity among isolates of each species and the absence of predominant clones.

Methicillin resistance study in clinical isolates of coagulase-negative staphylococci and determination of their susceptibility to alternative antimicrobial agents

AIMS

To achieve reliable detection of methicillin resistance in clinical isolates of coagulase-negative staphylococci.

METHODS AND RESULTS

Strains (105) were evaluated by normatized antimicrobial susceptibility methods, and for the presence of the methicillin resistance-determining mecA gene, using the polymerase chain reaction. Correlation between phenotypic and genotypic methods was obtained in 87.6% of the samples. Six strains, classified as methicillin-susceptible by phenotypic assays, revealed the presence of the mecA gene, indicating that methicillin resistance expression was probably repressed. Another seven isolates failed to show mecA amplification after displaying methicillin resistance in phenotypic evaluations. The susceptibility of the methicillin-resistant isolates to other antimicrobial agents was variable.

CONCLUSION

Genotypic determination of the mecA gene proved to be the most reliable method for detection of methicillin resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

Correct assessment of methicillin resistance, such as that attained through genotyping, is essential for defining therapeutic strategies, particularly when treating severely compromised patients.

Excretion of beta-lactam antibiotics in sweat--a neglected mechanism for development of antibiotic resistance?

The concentrations of beta-lactam antibiotics after standard doses were measured in blood and apocrine (axilla) and eccrine (forearm) sweat from six adult healthy persons. All persons had ceftazidime (axilla, 28.4 microg/ml; forearm, 11 microg/ml) and ceftriaxone (axilla, 8.9 microg/ml; forearm, 2.5 microg/ml) in sweat, and one person had cefuroxime in sweat (axilla, 7.8 microg/ml) (all data are mean peaks). Three persons had benzylpenicillin (axilla, 2.6 to 0.1 microg/ml) and one had phenoxymethylpenicillin (axilla, 0.4 microg/ml) in sweat. Excretion of beta-lactam antibiotics in the sweat may explain why staphylococci so rapidly become resistant to these drugs.

Antibiotic susceptibility of staphylococci isolated in blood cultures in relation to antibiotic consumption in hospital wards

A total of 510 isolates of Micrococcaceae, 500 of staphylococci and 10 micrococci, detected in 485 (3.3%) of 14,860 consecutive blood cultures obtained from patients at a Swedish university hospital and 2 local hospitals were identified to species level and investigated for antibiotic susceptibility. The 5 most frequently isolated species were Staphylococcus epidermidis (54.8%), S. aureus (28.0%), S. hominis (3.4%), S. warneri (3.2%) and S. haemolyticus (2.8%). All isolates of S. aureus were oxacillin sensitive. Great diversity in antibiotic resistance among coagulase negative staphylococci between hospitals and different ward units in the university hospital was observed. The frequency of antimicrobial resistance among S. epidermidis correlated with the antibiotic consumption at different ward units, in particular for ciprofloxacin (p < 0.001) and co-trimoxazole (p < 0.004). The study emphasizes the importance of monitoring antibiotic consumption and resistance patterns of nosocomial staphylococci in order to avoid emergence and spread of multi-resistant bacteria within the hospital environment.

Correlation between consumption of antimicrobials in humans and development of resistance in bacteria

The correlation between consumption of antimicrobials in humans and the emergence of resistance in bacteria is complex and has proved difficult to establish. Besides antimicrobial use, many other distinct contributing factors are also involved in the issue. Despite this complexity, there is a substantial body of evidence that the use of antibiotics in prophylaxis and in therapy is associated with the development of resistance in the hospital and in the community. Some examples are reviewed, including increase of resistance in enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter spp., Streptococcus pneumoniae, Staphylococcus aureus, Coagulase Negative Staphylococci and Streptococcus pyogenes after the use of beta-lactam antibiotics, aminoglycosides, fluoroquinolones and macrolides. Success in reversing the rise of resistant strains has been rarely described. Two examples are highlighted, the reduction in the incidence of nasal carriage of penicillin-resistant pneumococci in Icelandic children, and a significant decline in erythromycin resistance in S. pyogenes after the reduction in the use of macrolides in Finland.