Acridine orange stain in the early detection of bacteria in blood cultures

Fluorescence Microscopy: Determination of Meropenem Activity against Klebsiella pneumoniae

The development and implementation of diagnostic methods that allow rapid assessment of antibiotic activity against pathogenic microorganisms is an important step towards antibiotic therapy optimization and increase in the likelihood of successful treatment outcome. To determine whether fluorescence microscopy with acridine orange can be used for rapid assessment (≤8 h) of the meropenem activity against Klebsiella pneumoniae, six isolates including three OXA-48-carbapenemase-producers were exposed to meropenem at different levels of its concentration (0.5 × MIC, 1 × MIC, 8 or 16 µg/mL) and the changes in the viable counts within 24 h were evaluated using fluorescence microscopy and a control culture method. The approach was to capture the regrowth of bacteria as early as possible. Within the first 8 h fluorescence microscopy allowed to categorize 5 out of 6 K. pneumoniae strains by their meropenem susceptibility (based on the MIC breakpoint of 8 mg/L), but meropenem activity against three isolates, two of which were OXA-48-producers, could not be accurately determined at 8 h. The method proposed in our study requires improvement in terms of accelerating the bacterial growth and regrowth for early meropenem MIC determination. Volume-dependent elevation in meropenem MICs against OXA-48-producers was found and this phenomenon should be studied further.

Effect of novel therapeutic medicine swertiamarin from Enicostema axillare in zebrafish infected with Salmonella typhi

Herbal treatments have been practiced by humans over centuries and therefore possess time-proven safety. However, it is crucial to evaluate the toxic effects of herbal medicine to confirm their safety, particularly when developing therapeutic drugs. Use of laboratory animals such as mice, rat, and rabbits was considered as gold standard in herbal toxicity assessments. However, in the last few decades, the ethical consideration of using higher vertebrates for toxicity testing has become more controversial. As a possible alternative model involving lower vertebrates such as zebra fish were introduced. Hence in the present study, swertiamain compound isolated from E. axillare was assessed for it antimicrobial activity in zebra fish larvae againt S. typhi. The cumulative mortality rate and bacterial localization in zebra fish larvae were studied. Biochemical markers assays were performed to find the preventive role of the compound during the typhoid infection. The results showed that zebra fish can be successfully used as a model to study typhoid infection and the anti-bacterial compound swertiamarin used in this study clears the bacterial load and pathogenic symptoms to a great extent.

Comparison of acridine orange fluorescent microscopy and gram stain light microscopy for the rapid detection of bacteria in cerebrospinal fluid

OBJECTIVE

Bacterial meningitis is a life threatening condition that requires prompt recognition and treatment. Currently, Gram stain is widely used for the microscopic detection of bacterial pathogens in cerebrospinal fluid (CSF). In Nepal, fluorescent microscopes have been installed in laboratories as a part of the National tuberculosis control program. However, information on the utility of the acridine orange (AO) stain for the direct detection of bacteria in CSF samples in Nepal is not available. Therefore, this study aims to compare Gram stain and AO stain for the rapid detection of bacterial pathogens in CSF of clinically suspected meningitis cases in Kathmandu, Nepal.

RESULTS

Bacterial pathogens were detected in 9.30% (36/387) by either of the three tests, 9.04% (35/387) by AO stain, 8.27% (32/387) by culture and 6.46% (25/387) by Gram's stain. Considering culture as a gold standard, the sensitivity of AO stain was higher than Gram stain. The specificity of AO stain was 98.87%. Detection and differentiation of the bacteria was much clear in AO staining than Gram staining. AO is a better alternative to Gram stain in the rapid detection of bacterial pathogens in CSF in the setting where fluorescent microscope is available.

Subcultures of BACTEC-positive but gram or acridine orange stain-negative NR 6A and 7A blood culture bottles are unnecessary

A prospective study was done to assess the comparative use of acridine orange and Gram stains for detecting false-positive BACTEC blood culture bottles, thereby eliminating unnecessary subcultures. A total of 1049 NR 6A and 7A bottles that were instrument-positive in the BACTEC 660 nonradiometric system, but were Gram stain-negative, had aerobic and anaerobic subcultures as well as an acridine orange stain performed. Only five of 1049 (0.5%) instrument-positive, Gram stain-negative bottles grew microorganisms on subculture. Of these five microorganisms, acridine orange stain detected two. All five microorganisms were assessed not to be clinically significant based on review of the patients' charts. Our data showed that the Gram stain and the acridine orange stain are comparable for detecting false-positive NR 6A and 7A bottles. We conclude that subculture of BACTEC-positive, Gram stain-negative NR 6A and 7A bottles is not necessary.

Clinical evaluation of diagnostic hemoperfusion for in vivo enrichment of bacteria and fungi in comparison with a conventional blood culture technique

The hemoperfusion module, a newly developed technique for recovering pathogenic microorganisms from patients suffering from septicemia, was compared with conventional blood cultures. The module was interconnected with the extracorporeal circulation of 92 predominantly hemodialyzed patients. Nearly 12 liters of flowing blood (up to 200 ml min-1; mean running time, 60 min) came in contact with the coated charcoal. Of 99 modules examined, 44 (44.7%) yielded positive cultures and contained 54 potentially pathogenic bacteria or fungi (22 species). Only 32 of 190 (16.8%) conventional blood cultures were positive and contained 37 microorganisms (10 species). Even when patients were receiving antibiotic treatment, the frequency of isolation was significantly higher in hemoperfusion (21 of 44 modules positive, 47.7%) than in conventional blood cultures (10 of 88 cultures positive, 11.4%). In contrast, 23 of 55 modules (41.8%) and 22 of 102 conventional blood cultures (21.6%) were positive when patients were not treated with antibiotics prior to blood sampling. Altogether, hemoperfusion modules appeared to be superior to and more sensitive than the conventional blood cultures used and seemed to be a valuable tool for detecting septicemia.

Serratia bacteremia

During a 6-yr period, 146 patients at our institution had Serratia bacteremia (3.8% of the total number of episodes of bacteremia), with an incidence of 1.24/1000 admitted patients. We chose a random group of 50 cases for clinical analysis in the present study. The disease was community-acquired in 8% of the cases and nosocomially-acquired in the remaining 92%. The bacteremia was unimicrobial in 84% and part of a polymicrobial bacteremia in 16% of the episodes. The most frequently isolated species of the Serratia genus was S. marcescens. Portals of entry, in decreasing order of frequency, were: urinary, unknown, respiratory, and surgical wound infections. Clinically, the most frequent finding was fever (100%). Shock occurred in 28% of the patients, and none of our cases showed evidence of disseminated intravascular coagulation. We found 62% of Serratia isolates resistant to gentamicin. Overall mortality was 38% and factors associated with a poor prognosis were: severity of the underlying disease, critical clinical situation at onset of bacteremia, presence in the intensive care unit (I.C.U.), occurrence of shock or polymicrobial bacteremia, portal of entry in the respiratory tract, and inadequate treatment.