**9. Filamentous fungi and yeast**

Bacterial and fungal keratitis often is not clinically distinguishable from monomicrobial infections, because they override the pathognomonic picture typical of bacterial or fungal keratitis [14]. Because of the difficulty of clinical diagnosis, other factors are added; many patients use traditional medicine (with the risk of adding other microorganisms to the infection) or initiate topical medication without a medical prescription. These therapeutic

Bacteria and fungus coinfection can be incidental in the first instance. However, this condition favors the development in the participating pathogens of adaptive mechanisms that strengthen their protection versus the immune system host or the antimicrobial drug. This phenomenon is explained by the ability of fungi and bacteria to form biofilms. Studies recently showed that 99 % of microorganisms can form biofilms; only 10 % live as planktonic cells (unicellular cells)

The characteristic that best distinguishes chronic infections from acute infections is the response to treatment with antibiotics. While acute infections can be removed after a short treatment with antibiotics, the biofilm in keratitis coinfections normally fails to be completely eliminated, produces recurrent episodes, and often must be solved with keratoplasty. The etiologic agents form biofilms that can be up to 1,000 times more resistant to antibiotics [17,

Several reports in the literature have described this coinfection. Fröhlich *et. al*. studied patients with and without clinical history of contact lens use and showed that 51 of the 275 samples (18.5 %) from patients with bacteria keratitis were coinfections. The most common pathogens isolated were *Staphylococcus epidermidis* (44 %), *Staphylococcus aureus* (18 %), *Streptococcus* spp. (10 %), *Propionibacterium acnes* (7 %), and *Pseudomonas aeruginosa* (6 %) [20]. Yeh *et. al*. presented a study of 307 samples, of which 21 % were keratitis bacteria-bacteria coinfections with similar bacterial genera [21]. Jones reported coinfections between *Streptococcus pneumoniae* with *Corynebacterium* spp. or *Staphylococcus epidermidis* and isolated three microorganisms from one case, *Staphylococcus aureus* and *Streptococcus pneumoniae*, *Corynebacterium* spp., and *Micrococ‐ cus* spp., and, finally, *Streptococcus equinus* and *Haemophilus influenzae* from another patient.

Coinfections that involve *Candida* spp. or a filamentous fungus are usually difficult to treat, and the prognosis is poor. A coinfection of *Stenotrophomonas maltophilia* (Gram (-) bacteria) and a yeast has been documented. The corneal injury presented as an ulcer that quickly progressed despite treatment with proven sensitivity. The case was treated with penetrat‐

18, 19]. The issue of biofilms will be fully explained in the following section.

interventions delay the specific treatment, and the prognosis of infection is poor [14].

[15, 16, 17].

126 Advances in Common Eye Infections

**7. Bacteria and bacteria**

**8. Bacteria and yeast**

ing keratoplasty [22].

In a case with clinically distinguishable corneal infiltrates, *Exserohilum mcginnisii* and *Candida parapsilosis*, an unusual coinfection, were isolated. The infection showed torpid evolution with severe damage in the visual area [23]. Katragkou *et. al.* conducted a review that showed *Exserohilum* spp. produces a wide spectrum of diseases, including atopic, cutaneous, subcu‐ taneous, systemic, and corneal infections; the most common factor was immunocompromised status [24]. In addition, *Candida* spp. is an opportunistic pathogen that affects immunocom‐ promised and immunocompetent patients. This genus generates biofilms responsible for resistance to a wide range of antifungal drugs and often affects the cornea [25, 26]. *Exserohi‐ lum* spp. and *Candida* spp. can acquire a filamentous form that invades the stroma or produces endophthalmitis and has the capability of assembling biofilms.
