Coagulase-negative Staphylococci In Blood Cultures Research Articles

Frequency of Isolation of Coagulase Negative Staphylococcus from Blood Cultures and its Antibiogram

Background: Coagulase-negative Staphylococci are members of stable skin inhabitants. They are frequent contaminants in blood cultures and can lead to unnecessary exposure of patients to antimicrobial drugs and excess hospital costs. This study aims to estimate the frequency of Coagulase-negative Staphylococci in blood cultures and their antibiograms.
 Materials and Methods: This cross-sectional study was performed in a tertiary care hospital over one year from April 2018 to March 2019. Blood cultures received in the laboratory were processed to isolate Coagulase-negative Staphylococci. Susceptibility to various antimicrobial drugs was detected by disc diffusion method and E-strips.
 Results: A total of 13802 blood cultures were processed in one year. 1750 blood cultures yielded bacterial growth and 374 blood cultures were positive for Staphylococci. Out of these 374 blood cultures, 97 were categorized as Staphylococcus aureus and 277 were Coagulase-negative Staphylococci. Out of 13802 total blood cultures performed during study period, 277 blood cultures positive with Coagulase negative Staphylococcus means contamination rate of 2% out of total blood cultures. 277 Coagulase negative Staphylococcus positive cultures out of 1750 positive blood cultures means contamination rate of 15.8% out of positive blood cultures. Among Coagulase-negative Staphylococci, 68.2% isolates were resistant to Cefoxitin, 95.3% to Penicillin, 85.1% to Erythromycin, 37.5% to Ciprofloxacin, 59.6% to Gentamicin, 68.6% to Fusidic acid, 3.6% to Teichoplanin, and 1.4% to Linezolid. All isolates were sensitive to Vancomycin.
 Conclusion: The rate of blood culture contamination was 2% out of total blood cultures and 15.8% out of positive blood cultures.

Clinical significance of coagulase-negative Staphylococci isolated from blood cultures

Objective To analyze clinical characteristics of bloodstream infections caused by coagulase-negative Staphylococci (CNS) and antibiotic resistance of the bacteria, so that to provide basis for the clinical diagnosis and treatment. Methods A retrospective analysis of CNS in blood cultures collected from 108 hospitalized patients in Puai Hospital of Tongji Medical College from January 2016 to December 2017 was performed. The antimicrobial susceptibilities were tested by Kirby-Bauer method and E test method. For measurement variables, normally distributed variables were compared using t test, and non-normal distributed data were compared using Mann-Whitney U test. Categorical variables were compared using χ2 test. Results Of the 108 patients, 66 were male and 42 were female; the age range was 26 to 98 years and the average was 49 years. According to the criteria for bacteremia, 36 of 108 (33.3%) patients with CNS-positive blood cultures were diagnosed with bacteremia and 72 (66.7%) cases were contaminated. CNS bacteremia mainly occurred in the intensive care unit and nephropathy ward. Among them, 23 (62.2%) patients were catheter-related blood stream infections, and 11 (29.7%) patients were dialysis catheter-related bloodstream infections. Fifteen of 36 (41.7%) strains were isolated within 48 hours of admission. The level of serum procalcitonin (PCT) for bacteremia patients was 2.56 (1.44, 7.60) μg/L, and that was 0.13 (0.05, 0.23) μg/L in contaminated patients. The difference was statistically significant (Z=8.097, P 0.05). After antibiotic treatment, 26 of 36 bacteremia patients were survived. The PCT levels before antibiotic treatment were 2.05 (1.42, 4.32) μg/L, and 0.24 (0.07, 0.61) μg/L after antibiotic treatment. Serum PCT was decreased significantly after antibiotic treatment (Z=4.457, P 0.05). No significant difference was found in white blood cell count between survivors and deaths at 28 days (t=0.771, P>0.05). There was no statistical difference of the anti-bacterial drug susceptibility between pathogens and contaminants (P>0.05). All strains were sensitive to vancomycin, teicoplanin and linezolid. Conclusions The incidence of CNS contamination in blood culture is relatively high. It is important to distinguish true bacteraemia from contamination by a review of the clinical and laboratory indicators. PCT is of clinical value to indicate CNS infection and to monitor therapeutic effect. Key words: Bacteremia; Coagulase negative Staphylococci; Procalcitonin

Determination of clinical significance of coagulase-negative staphylococci in blood cultures

The aim of this study was to investigate the criteria used to distinguish coagulase-negative staphylococci (CoNS) bacteremia from contamination. We evaluated 162 adult patients with CoNS-positive blood cultures (BCs). Of the 162 patients, 35 (21.6%) had at least 2 positive BCs and 127 (78.4%) had a single positive BC. According to the Laboratory-Confirmed Bloodstream Infection (LCBI) criteria, 24 (14.8%) patients with the same species of CoNS had true bacteremia, and 138 (85.2%) patients had contaminants. Despite the detection of the same CoNS species, 9 of the 24 patients had different CoNS genotypes. Using clinical assessments, only 20 patients were diagnosed with true bacteremia, 8 of them had a single positive BC. We concluded that only using the LCBI criteria or clinical evaluations of a patient were not sufficient to distinguish CoNS bacteremia from contamination. Molecular identification should also be performed as a diagnostic laboratory parameter for CoNS bacteremia.

Laboratory markers to determine clinical significance of coagulase-negative staphylococci in blood cultures

Laboratory markers to determine clinical significance of coagulase-negative staphylococci in blood cultures

Evaluation of the LightCycler Staphylococcus M GRADE Kits on Positive Blood Cultures That Contained Gram-Positive Cocci in Clusters

We evaluated the Roche LightCycler Staphylococcus M(GRADE) kits to differentiate between Staphylococcus aureus and coagulase-negative staphylococci in blood cultures growing clusters of gram-positive cocci. Testing 100 bottles (36 containing S. aureus), the assay was 100% sensitive and 98.44% specific for S. aureus and 100% sensitive and specific for coagulase-negative staphylococci.

Rapid identification of Staphylococcus aureus and coagulase-negative Staphylococci by fluorescent in situ hybridization

目的 建立一种新的荧光原位杂交法,快速鉴定血培养中的金黄色葡萄球菌(金葡菌)和凝固酶阴性葡萄球菌.方法将荧光同位素标记的针对金葡菌和凝固酶阴性葡萄球菌的核糖体16SrRNA序列的互补的DNA寡核苷酸探针,在同一张玻片上50℃杂交1 h,用杂交缓冲液50℃洗涤10min,干燥后置荧光显微镜下观察,全过程大约2 h.结果探针的特异性经标准菌株和临床分离菌株证实.将259份临床标本测试与培养法比较,金葡菌的特异性和敏感性均为100%,CoNs的特异性和敏感性分别为100%和95.5%,荧光原位杂交法的最低检出限为103 CFU/ml.结论本方法适用于血培养中的金葡菌和凝固酶阴性葡萄球菌的快速鉴定。

Relevance of the number of positive bottles in determining clinical significance of coagulase-negative staphylococci in blood cultures.

Coagulase-negative staphylococci (CNS) are the most commonly isolated contaminants from blood cultures, yet they frequently cause true infections. Determining the clinical significance of CNS is difficult, and clinicians often consider the number of positive bottles within a set of blood culture bottles in their assessment. Therefore, in three separate studies, we counted the number of positive bottles within blood culture sets comprising two, three, or four bottles in order to predict whether or not CNS were clinically significant isolates (CSI) in adult patients with suspected sepsis. Each culture was evaluated by independent, published clinical criteria to determine its clinical importance. Of 486 positive sets that included two adequately filled bottles, 127 (26%) CNS were CSI, 329 (67%) were contaminants, and 30 (6%) were indeterminate as a cause of sepsis. Among CSI, 39 and 61% were isolated from one and two bottles, respectively. The positive predictive value for sepsis was 18% when one bottle was positive and 37% when both bottles were positive. Of 235 positive sets that included three adequately filled bottles, 81 (34%) were CSI, 109 (46%) were contaminants, and 45 (19%) were indeterminate as a cause of sepsis. Of CSI, 43, 38, and 19% were found in one, two, and three bottles, respectively. The positive predictive value for sepsis was 28, 52, and 30% when one, two and three bottles were positive. Of 303 positive blood culture sets that included four adequately filled bottles, 64 (21%) were considered CSI, 197 (65%) were contaminants, and 42 (14%) were indeterminate as a cause of sepsis. Of CSI, 27, 28, 19, and 27% were found in one, two, three, and four bottles, respectively. The positive predictive value for sepsis was 11, 30, 34, and 37% when one, two, three, and four bottles were positive. We conclude that the number of culture bottles positive in a given culture set cannot reliably predict the clinical significance of the CNS isolated and, therefore, should not be used as a criterion for determining whether or not an isolate represents true infection or contamination.

Risk factors for oxacillin/methicillin resistance in coagulase-negative staphylococci

The clinical variables associated with isolation of oxacillin- and methicillin-resistant, coagulase-negative staphylococci (CNS) from blood cultures of hospitalized patients were studied. One hundred CNS strains (49 oxacillin-susceptible; 51 oxacillin-resistant) isolated consecutively from one of two or more sets of blood cultures were collected. Only two variables were independently associated with recovery of oxacillin/methicillin-resistant strains by a multivariate analysis: length of hospital stay >10 days (OR 5·2, 95% CI = 1·7–15·7), and administration of antimicrobial agents in the previous 14 days (OR 4·5, 95% CI = 1·7–11·7). Analysis of the antibiotics administered indicated that only β-lactams were associated with a statistically significant risk of resistance to oxacillin/methicillin (OR of β-lactams vs no antibiotics = 6·94, 95% CI = 1·9–25·3; OR of non-β-lactams vs no antibiotics = 2·64, 95% CI = 0·8–8·3). Length of hospital stay (especially >10 days) and prior administration of antimicrobial agents (mainly β-lactams) independently predicted the presence of oxacillin/methicillin-resistant CNS in blood cultures.

Comparison of blood cultures with corresponding venipuncture site cultures of specimens from hospitalized premature neonates

We compared the presence and identities of isolates from blood culture samples obtained by percutaneous venipuncture with those of commensal skin organisms cultured from respective venipuncture sites after skin cleansing; 677 blood and skin site culture pairs from 488 infants were compared. Organisms grew in 58 blood cultures; nine of these cultures had corresponding venipuncture site cultures that also grew organisms. Forty-two blood culture isolates were coagulase-negative staphylococci; five of these were associated with similar venipuncture site cultures. According to restriction-endonuclease fingerprinting of chromosomal DNA and plasmid analysis, three pairs of blood and venipuncture site cultures were identical and two pairs were different. Thus only 7% (3/42) of coagulase-negative staphylococcal blood isolates were associated with identical contamination at the venipuncture site. We conclude that, if the venipuncture site has been carefully cleansed, the growth of coagulase-negative staphylococci in blood cultures of specimens from premature neonates indicates bacteremia rather than skin contamination in the vast majority of cases.

The laboratory interpretation of coagulase-negative staphylococcal bacteraemia in neonates

In an attempt to detect markers of significance of coagulasenegative staphylococci (CNS) isolated from neonatal blood cultures, epidemiological data and the rate of appearance of positive blood cultures were examined. The main epidemiological factor studied was the relative abundance of the different biotypes of CNS in blood cultures, on neonatal skin and the hands of neonatal unit staff. Our results showed that the relative recovery rates of biotypes found from these sources showed no significant differences. The number of positive blood culture bottles in each set and the number of days taken for growth to appear showed wide variations. A higher proportion of aminoglycoside-resistant strains were found in the group showing both blood culture bottles positive and in the group where isolates were obtained by 24 h of incubation. We conclude that there is no advantage in biotyping CNS in assessing clinical significance, but the association of aminoglycoside resistance with the isolation pattern of CNS in neonatal blood cultures requires further examination.

An estimate for the source of coagulase-negative staphylococci in blood cultures.

An estimate for the source of coagulase-negative staphylococci in blood cultures is presented and its use illustrated in two populations. The method estimates the probability that a positive blood culture is positive due to contamination and the probability of it being positive due to bacteraemia. The effect of changes in efficiency of the blood culture technique on these estimates is demonstrated. One of the illustrative populations consists of 537 sample pairs from 273 patients, taken after open-heart surgery in 1978-80. The other consists of 500 consecutive sample pairs taken in one of two hospitals in 1983-4.

Native valve endocarditis due to coagulase-negative staphylococci: Clinical and microbiologic features

Twenty-one patients with native valve endocarditis caused by coagulase-negative staphylococci were studied; 14 had pre-existing valvular or congenital heart disease. Although commonly subacute in presentation, complications of endocarditis were frequent: arterial emboli in five patients, new electrocardiographic conduction system abnormalities in nine, congestive heart failure in eight, annular or myocardial abscesses in five, and disruption of valve leaflets in three. Cures were achieved in 10 of 12 patients treated medically and seven of nine treated surgically. In microbiologic studies of 16 coagulase-negative staphylococci from patients with endocarditis, only eight were identified as Staphylococcus epidermidis. All isolates were susceptible to vancomycin. Antibiotic resistance (methicillin, four isolates; gentamicin, two isolates; rifampin, one isolate) was usually associated with nosocomial acquisition of endocarditis. Rather than representing contamination, coagulase-negative staphylococci in blood cultures may indicate life-threatening endocarditis. However, with careful attention to the selection of antibiotics for therapy and to the occurrence of heart failure due to intracardiac complications, treatment of this form of endocarditis is frequently successful. Organisms must always be tested for cryptic resistance to beta-lactam antibiotics. Valve replacement may be required frequently.