Single-site sampling versus multi-site sampling for blood cultures; A retrospective clinical study

Objectives The performance of blood cultures (BC) relies on optimal sampling. Sepsis guidelines do not specify which sampling protocol to use, but recommend two sets of BC bottles, each set containing one aerobic and one anaerobic bottle. For the single-site sampling (SSS) protocol, only one venipuncture is performed for all four bottles. The predominating multi-site sampling (MSS) protocol implies that BC bottles are collected from two separate venipuncture sites. The aim of this study was to compare SSS and MSS. Primary outcomes were number of BC sets collected, sample volume and diagnostic performance. Methods This was a retrospective clinical study comparing BC results in an emergency department before and after changing the sampling protocol to SSS from MSS. All BC samples were incubated in the BacT/ALERT BC system. Results The analysis included 5,248 patients before and 5,364 patients after the implementation of SSS. There was a significantly higher proportion of positive BCs sampled with SSS compared to MSS, 1,049/5,364 (19.56%) and 932/5,248 (17.76%) respectively ( P =0.018). This difference was due to a higher proportion of solitary BC sets (two BC bottles) in MSS. Analyzing only patients with the recommended four BC bottles, there was no difference in positivity. SSS had a higher proportion of BC bottles with the recommended sample volumes of 8-12 ml than MSS ( P <0.001). Conclusions Changing the sampling protocol to SSS from MSS resulted in higher positivity rates, higher sample volume and fewer solitary BC sets. These advantages of SSS should be considered in future sepsis guidelines.

The Addition of Anaerobic Blood Cultures for Pediatric Patients with Concerns for Bloodstream Infections: Prevalence and Time to Positive Cultures

ABSTRACT Anaerobes are an important but uncommon cause of bloodstream infections (BSIs). For pediatric patients, routine inclusion of an anaerobic blood culture alongside the aerobic remains controversial. We implemented automatic anaerobic blood culture alongside aerobic blood cultures in a pediatric emergency department (ED) and sought to determine changes in recovery of obligate and facultative anaerobes. This was a cohort study in a pediatric ED (August 2015 to July 2018) that began in February 2017. Blood culture positivity results for true pathogens and contaminants were assessed, along with a secondary outcome of time to positivity (TTP) of blood culture. A total of 14,180 blood cultures (5,202 preimplementation and 8,978 postimplementation) were collected, with 8.8% (456) and 7.1% (635) positive cultures in the pre- and postimplementation phases, respectively. Of 635 positive cultures in the postimplementation phase, aerobic blood cultures recovered 7.6% (349/4,615), whereas anaerobic blood cultures recovered 6.6% (286/4,363). In 211/421 (50.0%) paired blood cultures, an organism was recovered in both cultures. The number of cases where organisms were only recovered from an aerobic or an anaerobic bottle in the paired cultures were 126 (30.0%) and 84 (20.0%), respectively. The TTP was comparable regardless of bottle type. Recovery of true pathogens from blood cultures was approximately 7 h faster than recovery of contaminants. Although inclusion of anaerobic blood cultures only recovered 2 (0.69%) obligate anaerobes, it did allow for recovery of clinically significant pathogens that were negative in aerobic blood cultures and supports the routine collection of both bottles in pediatric patients with a concern of bloodstream infections.

A dog’s dinner: an interesting case presenting as gastroenteritis

We report a case of a 60-year-old Caucasian man with a history of alcohol excess who presented to the emergency department with a 72-hour history of abdominal pain, profuse diarrhoea and vomiting. He was admitted to the intensive care unit (ICU) 12 hours later in extremis with severe sepsis and multiorgan failure. Collateral history from the patient on admission to ICU identified that he had been bitten by a dog 3 days prior to his symptom onset. Provisional microscopy and Gram staining from peripheral blood cultures taken on admission revealed the presence of long, thin Gram-negative bacilli in the anaerobic bottle only. This was later identified asCapnocytophaga canimorsus. The patient survived the septic episode and was discharged to level 2 care 9 days later under the care of the renal physicians for ongoing renal dialysis.

The Study of Residual Oil Gasification into Methane

The residual oil in situ microbial gasification technology is a new method to extend the life of oil reservoir, which means using the microbial to transform petroleum hydrocarbons into methane under anaerobic conditions, then the oil reservoir can be exploited or stored in situ. 50ml samples were added to 120ml sterile anaerobic bottle, at the same time, residual oxygen was removed under a gentle stream of high purity nitrogen by Hungate, then the bottle was filled tightly with rubber stoppers to remain strictly anaerobic state. These samples were placed in the incubator in dark condition. 100 days later, methane was detected by gas chromatography analyzing headspace gas, so it is used as inoculum for enrichment culture. 5ml inoculum above mentioned was added to the oil reservoir conditions simulated reactors. The ones with 10ml crude oil sample is (Y), the ones without crude oil sample is (N), at the same time, 10ml inorganic salt culture medium was added to each reactor.

Rapid identification of Candida glabrata in Candida bloodstream infections

Candida species are the fourth most common cause of bloodstream infection (BSI) in the hospitalized patient. Candida glabrata is the most common non-Candida albicans Candida species in England and Wales with an attributed mortality of 48 %. C. glabrata is known to demonstrate reduced susceptibility to fluconazole, resulting in treatment failures when employing this agent for empirical treatment of Candida BSI. The first part of this study demonstrated a technique utilizing a blood culture system commonly used by many laboratories (BACTEC 9240 automated detection system) that reduced the time to identification of this potentially resistant organism by up to 72 h. A presumptive identification was achieved by observing a difference in the duration of incubation required before growth was detected automatically between Lytic Anaerobic and Plus Aerobic culture bottles. Secondly, experiments exploring the growth characteristics of C. glabrata in BACTEC blood culture bottles containing various media were carried out to explore possible reasons underpinning this clinical observation. The detection of yeast in the anaerobic bottle of a blood culture pair consisting of Lytic Anaerobic and Plus Aerobic in a BACTEC 9240 system was found to be highly predictive of the isolation of C. glabrata (positive predictive value 93.3 %, negative predictive value 98.3 %). The reason for this appeared to be a component of the Lytic Anaerobic blood culture medium enhancing the growth of C. glabrata in that medium.

Predictive value of isolating Pseudomonas aeruginosa from aerobic and anaerobic blood culture bottles

Pseudomonas aeruginosa is a particularly virulent pathogen when it causes bacteraemia and early diagnosis is essential to reduce morbidity and mortality. It is an aerobe and is thought by many to be almost exclusively isolated from the aerobic blood culture bottle in cases of bacteraemia. This study analysed 277 Gram-negative bacteraemic episodes over 1 year at a single institution in order to assess the predictive value of this finding. In 39 of 44 episodes of P. aeruginosa bacteraemia, the organism was isolated from the aerobic bottle only, which gave a sensitivity of 88.6 % for this ‘test’ and a specificity of 73.8 %. However, for all episodes of Gram-negative bacteraemia, the likelihood of a Gram-negative bacillus occurring in the aerobic bottle first being P. aeruginosa was only 39 %. The converse finding of a Gram-negative bacillus isolated first in the anaerobic bottle or from both bottles together was clinically helpful, having a negative predictive value of 97.2 % (i.e. that the organism was not P. aeruginosa).