Clinical significance of methicillin-resistant coagulase-negative staphylococci obtained from sterile specimens

Evaluation of in-house cefoxitin screening broth to determine methicillin-resistant staphylococci

Methicillin-resistant staphylococci (MRS), including methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative staphylococci (MRCoNS), have a global impact as a public health threat contributing significantly to morbidity, mortality, and socio-economic costs. Accurate and rapid detection of MRS results in effective antimicrobial therapy, immediate patient isolation, dissemination control, and appropriate disinfection measures. Herein, we developed an in-house cefoxitin screening broth and compared it to the cefoxitin disk diffusion method and polymerase chain reaction (PCR) for the detection of MRS. Verification of this screening broth on 52 MRSA, 37 MRCoNS, 44 methicillin-susceptible S. aureus (MSSA), and 11 MSCoNS revealed greater validity for MRSA/MSSA than for MRCoNS/MSCoNS. The kappa coefficient of 0.87 was superior for determination of MRSA and MSSA, whereas it was 0.54, which was considered poor, for determination of MRCoNS and MSCoNS. Application of this assay to screen MRSA should be useful in clinical laboratories and hospital infection-control units.

The species distribution, antimicrobial resistance and risk factors for poor outcome of coagulase-negative staphylococci bacteraemia in China

Objective

Coagulase-negative staphylococci (CoNS) are one of the major opportunistic pathogens and the incidence of CoNS bacteraemia is increasing. However, most of the CoNS-positive blood cultures are contaminants rather than true CoNS bacteraemia. In order to minimize contamination, we defined true CoNS bacteraemia as the patient that has two or more identical CoNS-positive blood cultures drawn within 48 h in this study and the objective of this study was to analyse the species distribution and antibiotic resistance and to identify risk factors for 30-day mortality of the true CoNS-bacteraemia.

Method

By reviewing the electronic medical database, this study retrospectively analysed patients diagnosed as CoNS bacteraemia by blood cultures in a comprehensive tertiary care hospital in China from January 1, 2014, to December 31, 2017.

Result

A total of 1241 patients with 1562 episodes of CoNS-positive blood cultures were recorded in the database but only 157 patients were finally diagnosed as true CoNS bacteraemia after contaminants were excluded. All these 157 patients (12.7%, 157/1241) had bacteraemia-related clinical symptoms. Among the 157 patients, the most common species were Staphylococcus hominis (40.8%), Staphylococcus epidermidis (36.3%) and Staphylococcus capitis (11.5%). The antimicrobial susceptibility tests showed that all CoNS had a high rate of resistance to penicillin (94.9%), oxacillin (93.6%) and erythromycin (92.4%). Resistance to gentamicin (22.3%) and rifampicin (10.8%) was low, and none of the bacteria were resistant to vancomycin or linezolid. The 30-day mortality of patients with CoNS bacteraemia was up to 12.7% (20/157), and the multivariate logistics regression analysis showed that chronic renal failure (OR 5.9, 95% CI 1.6–21.5, p = 0.007) and chronic liver failure (OR 4.0, 95% CI 1.2–13.1, p = 0.024) were both the significant independent risk factors for the 30-day mortality of CoNS bacteraemia.

Conclusion

Staphylococcus hominis and Staphylococcus epidermidis were the most common species in CoNS bacteraemia. All CoNS had high multi-drug resistance, but gentamicin and rifampicin had a relatively lower resistance and could be considered as alternative antibiotics for anti-CoNS bacteraemia in addition to vancomycin and linezolid. Additionally, patients with chronic renal failure or chronic liver failure have a higher 30-day mortality after the onset of CoNS bacteraemia.

Clinical features, outcomes, and molecular characteristics of an outbreak of Staphylococcus haemolyticus infection, among a mass-burn casualty patient group, in a tertiary center in northern Taiwan

BACKGROUND/PURPOSE

We reported an outbreak of Staphylococcus haemolyticus (SH) infection in a group of young patients (mean age 21.6) simultaneously hospitalized due to a mass-burn incident. This study analyzed the clinical features of these patients and the microbiological characteristics of the outbreak.

METHODS

All 50 patients hospitalized for burns were enrolled, and their clinical differences were analyzed based on culture results. A drug sensitivity test and pulsed-field gel electrophoresis (PFGE) were conducted to analyze the microbiological difference between SH isolates from the mass-burn casualty patients (the study group) and SH isolates from other patients hospitalized during the same period (the control group) with the intention of identifying the strain of SH outbreak.

RESULTS

Patients with isolated SH (N = 36) had a significantly higher disease severity (higher revised Baux score, APACHE II score, and concurrent bacteremia rate), and a significantly poorer clinical outcome (longer ICU and hospital stay, and longer MV usage). Significant differences in the phenotype (antibiotics drug sensitivity test) and genotype (PFGE typing) were observed between the study and control groups. The dominant PFGE type C identified among the study group was related to poorer outcomes in a subgroup analysis.

CONCLUSION

A dominant PFGE type of SH infection was found in these mass-burn casualty patients. Pathogenesis or virulence factors may have contributed to our results. Further study of isolated SH should be conducted.

Molecular investigation of staphylococcal cassette chromosome mec types and genotypic relations of methicillin-resistant staphylococci isolated from before and after hospital exposed students

Background

Reservoir of methicillin resistance genes called staphylococcal cassette chromosome mec (SCCmec), plasmids and genomic characterisations of isolates have been widely investigated in epidemiologic research. However, the extent to which these organisms are transported by patients or hospital staff is not entirely clear.

Aim

This study aims to investigate the molecular relatedness and plasmid profiles of MR staphylococci isolated from nursing students before and after hospital training, to find out the possible source.

Materials and Methods

This study examined 39 methicillin-resistant (MR) staphylococci and 2 inducible clindamycin-resistant, methicillin-susceptible Staphylococcus aureus. Specimens were collected before and after 4 months of hospital training from the hands and nares of 75 nursing students. A polymerase chain reaction technique was used to confirm the existence of mecA gene and identify SCCmec types; total DNA was digested by SmaI endonuclease restriction to monitorise clonal relatedness by pulsed-field gel electrophoresis (PFGE); plasmid profiles were monitorised on agarose gel.

Results

All 39 isolates tested positive for mecA; SCCmec type III was observed most frequently. Interestingly, in one isolate of Staphylococcus epidermidis, four different types of SCCmec elements were observed. There were 23 different types of plasmids, whose sizes ranged from 1.4 to 46.0 kb. After PFGE dendogram analysis, two strains were classified as indistinguishable; six were closely related. Most of the isolates obtained after hospital training showed clonal similarity and seven had multiple SCCmec elements require further investigation for the possible mechanism.

Conclusion

Most of the isolates obtained after hospital training showed clonal similarity and seven had multiple SCCmec elements require further investigation for the possible mechanism.

Pathogen or contaminant? Distinguishing true infection from synovial fluid culture contamination in patients with suspected septic arthritis

BACKGROUND

Isolation of bacteria from synovial fluid (SF) is the gold standard for diagnosis of septic arthritis (SA). Contamination results in misdiagnosis and mismanagement. This study identifies clinical characteristics, microbiology, and outcomes of patients with contaminated SF and compares them with patients with true SA.

METHODS

We conducted a retrospective study including all patients aged 18 and older admitted to a single, tertiary-care hospital between 1998 and 2015 with suspected SA and positive SF cultures. Contamination cases were determined by infectious disease specialists involved in the patients' care and a clinical course inconsistent with SA.

RESULTS

398 patients with true SA and 22 with contaminated SF were identified. The SA group was younger (60.9 vs. 75.6 years; p < 0.01), had higher peripheral polymorphonuclear lymphocytes (78.0 vs. 69.4%; p < 0.01) and SF white blood cell count (91.7 vs. 25.6K/mL; p = 0.02), and longer mean length of stay (10.9 vs. 6.7 days; p = 0.02). The average time to positive culture was longer in the contaminated group (3.62 vs. 1.4 days; p < 0.01). The SA group was less likely to receive a new rheumatologic diagnosis within 1 year (3.0 vs. 36.4%; p < 0.01).

CONCLUSION

This is the first study of its kind looking at clinical features and outcomes of patients with contaminated SF. These patients present with less severe disease, have better outcomes, and receive new rheumatologic diagnoses in more than a third of cases within 1 year. We recommend a conservative approach for patients with suspected contaminated SF, mild symptoms, and no bacterial growth within the first 48 h.

Clinical significance of coagulase-negative staphylococci isolates from nosocomial bloodstream infections

BACKGROUND

Identification of coagulase-negative staphylococci (CoNS) as nosocomial pathogens or contaminants is significant for microbiologists and clinicians. This study aimed to determine the frequency of isolation and antimicrobial resistance patterns of CoNS isolates from nosocomial bloodstream infections (BSIs) and to identify risk factors associated with true bacteremia caused by these emerging pathogens in a Saudi tertiary care hospital.

METHODS

All CoNS-positive cultures from inpatients were identified using the standard methods during a 10-month period. Antimicrobial susceptibility testing was done using the reference broth microdilution method.

RESULTS

A total of 208 isolates were identified; of these 75 (32.2%) were considered infection associated, and 133 (67.8%) were considered contamination. S. epidermidis accounted for 34.7% of bacteremia cases, followed by S. hominis (21.3%), S. haemolyticus (16%), and S. saprophyticus (12%). Central venous catheters (p ≤ 0.0001), prior antibiotic therapy (p ≤ 0.0001), the occurrence of more than one positive blood culture (p ≤ 0.0001), and intensive care unit (ICU) admission (p = 0.007) were all independently associated with CoNS bacteremia. Overall, all isolates were highly resistant to penicillin (94.7%), oxacillin (90.7%), and erythromycin (85.3%). The rates of susceptibility to vancomycin, daptomycin, and teicoplanin were 98.7%, 98.7%, and 93.3%, respectively.

CONCLUSIONS

Our results further highlight that accurate identification and susceptibility testing of CoNS isolates from nosocomial BSIs are crucial to minimize excessive antibiotic use and unnecessary catheter removal. In addition, daptomycin may be an efficient alternative therapeutic option for CoNS resistant to oxacillin and other commonly used antibiotics.