Comparison of small and high volume sample inoculation of fungal media with routine bacterial culture media for improved yield of mold from sputa
Ghazala Jabeen, Salima Rattani, Joveria Farooqi, Kauser Jabeen
Objectives
Patients with productive cough who request sputum cultures frequently have symptoms refractory to empiric therapy with antibiotics and inhaled or systemic steroids. Underlying conditions predispose them to a wide-spectrum of mold infections, usually missed on routine bacterial cultures. Most physicians overlook the importance of requesting additional fungal cultures thus delaying diagnosis. This study was conducted to compare small and high volume sample inoculation of sputa on fungal media with standard bacterial cultures for improved yield of molds.
Methods
Sputum samples from 41 adults submitted to Aga Khan Clinical Laboratories in January 2018 were assessed for quality using gram stain criteria of pus to epithelial cell ratio of >10:1. Those considered representative were processed for routine bacterial culture on Sheep Blood Colistin Nalidixic Agar (BCNA), Chocolate Agar (CHOC) and MacConkey agar. The same samples were processed in parallel for the comparison study: a loopful of the purulent part (small volume) on Sabouraud’s Dextrose Agar (SDA) and Potato Dextrose Agar (PDA), and 1 ml (high volume) on SDA. All culture plates were incubated at 35oC for 5 days for rapidly growing hyaline molds. Patient information collected in the course of clinical reporting of culture, and yield of mold on type of processing was recorded. Frequencies of underlying co-morbids and mold isolation were computed.
Results
Out of 41 specimens assessed, 13 were positive and 5 negative for fungal growth by all three methods. Fifteen specimens yielded fungal growth on both small and high volume fungal cultures, but not routine bacterial. An additional 8 yielded fungal growth only on high volume sample inoculation. The age of the patients ranged from 17-81y, 41.4% being females. Clinical history was available on 26 patients: 46% patients were on systemic or inhaled steroids, 42% on antibiotics and 31% had an underlying lung disease. Sixteen (61.5%) patients presented with symptoms of less than 2 weeks’ duration; all had mold isolated on high volume culture, but only 7 on routine bacterial culture. In patients with symptoms lasting 2 weeks or longer (n=6), mold was isolated from 4 high-volume fungal but only 2 bacterial cultures. In patients with asthma, both high and low volume fungal cultures had a yield of 88%, while only 33% bacterial media grew mold. The predominant molds isolated were Aspergillus flavus (83%), A. niger (64%), Penicillium spp. (8%), A. fumigatus (5.5%). 
Conclusion
High volume sputum inoculation had the highest yield of mold compared to small volume fungal culture and routine bacterial culture, with small volume fungal culture still performing better than routine culture. These results support the recommendation of high volume sample inoculation for improved fungal yield in patients suspected of pulmonary fungal infections.

3 / Comparing small and high volume sample fungal with routine culture for improved yield of mold from sputa