Coagulase-negative Staphylococci Blood Culture Research Articles

A case of histopathologically confirmed infective endocarditis with no vegetations observed during preoperative diagnosis.

An 81-year-old woman on maintenance hemodialysis (HD) was admitted to the hospital with fever and repeated positive blood cultures for coagulase-negative staphylococci. The patient had a history of aortic valve replacement for aortic valve stenosis (AS). Although one major criterion and two minor criteria from the Duke criteria were met and therefore infective endocarditis (IE) was suspected for this case, no definitive diagnosis was made. Vegetations were not observed on the transesophageal echocardiography, but AS was prominent. The patient was refractory to antibiotic therapy using vancomycin, and blood cultures did not convert to negative. To treat the suspected IE and AS, aortic valve replacement was performed. Although vegetations were not observed in the resected valve, gram-positive cocci were found in clusters, and a histopathological diagnosis of IE was made. The postoperative blood culture converted from positive to negative, and the patient was subsequently discharged from the hospital. While relative risk of IE is high in HD patients, a definitive diagnosis of IE may be difficult due to calcification of the valve and valve replacement. In HD patients with bacteremia, suspicion of IE should be aggressively pursued if other sources of infections are negative, and if the patient is refractory to medical treatment, surgical treatment may be necessary.

Clonal Diversity in Episodes with Multiple Coagulase-Negative Staphylococcus Bloodstream Isolates Suggesting Frequent Contamination

Coagulase-negative Staphylococci (CoNS) are frequently recovered from blood cultures, which may indicate contamination or true bacteremia. CoNS isolates recovered from patients with episodes of two or more blood cultures positive for CoNS within 24 h were typed by both pulsed-field gel electrophoresis (PFGE) and speciation. PFGE typing of 94 CoNS isolates recovered from episodes with two or more positive blood cultures for CoNS within 24 h discriminated 35 strain clusters. The CoNS isolates were unrelated in 15 (39%) of 38 episodes, suggesting contamination. Sensitivity and specificity of CoNS speciation compared to PFGE was 96% and 67%, respectively. Clonal and species diversity differed between hospital areas. Contamination may frequently be present even in the setting of the recovery of CoNS from two or more blood culture sets within 24 h. Speciation of CoNS bloodstream isolates is rapid and may improve patient care as well as reduce unnecessary antibiotic use.

Positive blood cultures for coagulase-negative staphylococci in neonates: does highly selective vancomycin usage affect outcome?

The implication of highly-selective vancomycin usage on the outcome for infants with positive blood cultures for coagulase-negative staphylococci (CONS) was assessed retrospectively. The analysis was performed on partly prospective collected data from infants under 3 months of age with a least one CONS-positive blood culture in the neonatal intensive care unit at the Soroka University Medical Center between 1990 and 1996. During the study period, 239 episodes of CONS-positive blood cultures were identified from among 64,226 live births (3.7 per 1,000). Vancomycin was administered in 22 (9%) episodes, in all cases only after identification of the bacteria. The remaining 217 episodes were managed either without antibiotics or with continuation or initiation of empiric antibiotic therapy (usually ceftazidime +/- ampicillin) for suspected sepsis. Severity of the initial illness, subsequent morbidity and mortality were low regardless of the treatment administered. Only a single case of a blood-borne vancomycin resistant gram-positive organism was observed during the study period. The approach to CONS-positive blood cultures in neonates used here was associated with low morbidity and mortality. These findings support a policy of highly selective vancomycin usage in an era of emerging vancomycin resistance.

Significância clínica, epidemiologia e microbiologia das bacteremias por estafilococos coagulase-negativos em Hospital de Ensino

Coagulase-negative staphylococci (CNS) are an important cause of nosocomial bacteremia and they are frequently considered as contaminants of blood-cultures. From October 1990 to September 1992, 300 positive blood-cultures for CNS at the Hospital São Paulo were studied and 141 CNS bacteremias were characterized as nosocomial bacteremias. Clinical and microbiological criteria were defined to differentiate between true CNS bacteremia and contaminated cultures. Only 20.6% of the CNS nosocomial bacteremia were considered as true bacteremia. Most of the CNS true nosocomial bacteremia were detected among newborns admitted to the neonatal intensive care unit; the presence of intravascular catheter and parenteral nutrition were significant findings. We did not detect significant difference between true nosocomial bacteremia and contaminated cultures regarding to resistance to oxacillin and SLIME production. The clinical criteria and the positivity of the blood-cultures up to 48 hours after incubation, utilized in our definitions, were useful parameters to characterize the CNS true nosocomial bacteremia.