Diagnostic value of pediatric blood culture bottles for acute postoperative endophthalmitis

OBJECTIVE: To report our experience using conventional culture methods (CM) and pediatric blood culture bottles (PBCBs) for vitreous sample culture of acute postoperative endophthalmitis. METHODS: A retrospective study was conducted at the Department of Ophthalmology, Hospital das Clinicas, HCFMUSP, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, BR, from January 2010 to December 2015, and it included 54 patients with clinically suspected acute postoperative endophthalmitis. Vitreous samples were obtained by vitreous tap or vitrectomy. Samples from January 2010 to December 2011 were cultivated in CM, whereas samples from January 2012 to December 2015 were inoculated in PBCBs. The measured outcome was the yield of positive cultures. RESULTS: Twenty cases were included in the CM group, and 34 cases were included in the PBCB group. The yield of positive cultures in PBCBs (64.7%) was significantly higher than that in conventional CM (35%, p=0.034). Staphylococcus epidermidis and Streptococcus viridans were the two most commonly found agents. CONCLUSION: PBCBs can be used successfully in clinically suspected endophthalmitis. The method showed a higher yield of positive cultures than the conventional method. This technique appears to have several advantages over the traditional method: it saves time, as only one medium needs to be inoculated; transportation to a laboratory is easier than in the traditional method, and there is no need to maintain a supply of fresh agar media. The use of PBCBs may be recommended as the primary method for microbiological diagnosis and is especially suitable for office settings and remote clinics.

presentation of endophthalmitis, but bacterial cultures are negative in these cases (5). Identification of the pathogen in cases of endophthalmitis may improve treatment by the early introduction of targeted antibiotics.
Despite advances in molecular assays for detecting pathogens, microbial culture is still the current reference method for the etiological diagnosis of endophthalmitis. Conventional culture methods (CM) use solid or broth media including thioglycolate. However, rates of identification increase when blood culture bottles (BCBs) are used (3,(6)(7)(8)(9).
The present study aimed to report our own experience using pediatric BCBs (PBCBs) and conventional media for vitreous sample culture in acute postoperative endophthalmitis.

■ DISCUSSION
Endophthalmitis is a rare and devastating complication of ocular surgeries. Rapid identification of the pathogen with adequate treatment may impact visual prognosis. Conventional culture uses solid or broth media; however, PBCBs confer several advantages. Therefore, we demonstrate our experience with using PBCBs for endophthalmitis.
Conventional methods include the use of blood agar, chocolate agar, Sabouraud agar and thioglycolate broth. They require immediate incubation (not available at all ophthalmologic centers), and endophthalmitis positivity varies widely in the literature, ranging from 24 to 72% (3,6-8,10-17). These low sensitivities can be explained by various factors such as the small volume of specimens, the use of antibiotics before the collection of clinical material and the presence of fastidious microorganisms causing endophthalmitis (18).
On the other hand, BCBs confer the possibility of storage at room temperature, microorganism growth with small volume samples, ease of inoculation and low risk of contamination during transport. The use of BCBs is a good alternative in cases of endophthalmitis in areas with limited access to a microbiology laboratory. BCBs also allows the growth of fastidious pathogens (which grow better in atmospheres with high CO 2 tension) and contain resin that can adsorb antibiotics if the patient has already received them (19). PBCBs have already been accepted as a diagnostic tool for small samples such as blood in pediatric practice, synovial fluid, pleural fluid and peritoneal fluid (19). Kratz et al. have also used PBCBs to test for infectious keratitis and had promising results. Indeed, in some endophthalmitis studies, PBCBs were used (3). Studies using undiluted vitreous samples and BCBs showed average positivity varying from 61% to 100% (3,(6)(7)(8)(9)(19)(20)(21)(22). In contrast, Rachitskaya et al. (21) had lower positivity (31.7%) than these values when they used BCBs, likely due to the use of diluted vitreous. Chiquet et al. compared diluted with undiluted vitreous samples using conventional culture methods and suggested that diluted samples were as effective as undiluted samples for microbiological diagnosis of endophthalmitis; however, they also commented that the small number of positive cultures could preclude improving the understanding of the impact of dilution on culture sensitivity (23).
Comparative studies of CM and BCB positivities were carried out in six studies (3,(6)(7)(8)(9)22); five of them demonstrated a higher positivity with BCBs than with conventional methods (Figure 1). Yospaiboon et al. had a cohort of 27 patients and reported low growth rates overall, 51.9% positivity in BCBs and 25.9% in the traditional method; as discussed by the authors, these results

Enterococcus faecalis (1)
Serratia marcescens (1) are likely due to the limited volume of samples (0.1-0.2 mL) and previous use of antibiotic therapy (6). Similar to the present study, Kim et al. used (7). In our institution, PBCBs had been used since 2012 for all intraocular samples from patients with endophthalmitis. The present study compared the positivity obtained with the conventional method (previous 2012) and with PBCBs and demonstrated a higher positivity with PBCBs (35% versus 64.7%; p=0.034). These results are in agreement with previous studies and reinforce the advantages of using PBCBs as an alternative to CM for the etiologic diagnosis of acute postoperative endophthalmitis (3,6,9,10). Figure 1 summarizes the main studies using CM and BCB/PBCBs, including the present study.
The low number of samples for each method and the different periods of inclusion are the main limitations of the present study. Additionally, although the use of PBCBs has several advantages over conventional culture, in cases where anaerobic pathogens are suspected, anaerobic BCBs or broth medium (e.g., thioglycolate broth) should be used (21). Nevertheless, these are the first case series of the advantages of PBCBs produced in Brazil and adding to the international literature. The use of PBCBs should be recommended for microbiological diagnosis of endophthalmitis and is especially suitable for office settings and remote clinics.

■ CONCLUSION
PBCBs confer a higher positivity than CM in cultures of vitreous samples of clinically suspected infectious endophthalmitis.

■ ACKNOWLEDGMENTS
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES). Finance Code 001.

■ AUTHOR CONTRIBUTIONS
Tanaka T helped to design the study, collected samples, collected microbiology data, and drafted and reviewed the manuscript. Ferreira BFA, Kato JM and Oliveira LMS collected samples and microbiology data. Gioia TSR, Rossi F, Pimentel SLG and Nakashima Y drafted and reviewed the manuscript. Yamamoto JH and Almeida Junior JN helped to design the study, conducted the statistical analysis, and drafted and reviewed the manuscript.