**6. Keratitis due to coinfections**

#### **6.1. Bacteria and fungus**

Bacteria and fungus represent the most frequent type of coinfection in the eye (Table 1]. The main microorganisms that produce coinfections are bacteria, such as *Staphylococcus* spp., *Streptococcus* spp., *Pseudomonas* spp., *Haemophilus* spp., *Klebsiella* spp., *Bacillus* spp., and *Corynebacterium* spp. The fungi genera microorganisms include *Aspergillus* spp., *Fusarium* spp., *Curvularia* spp., *Cladosporium* spp., *Bipolaris* spp., *Alternaria* spp., and the yeast *Candida* spp. Most of these microorganisms are normal microbiota in the conjunctival sac or the lids [8]. Their presence depends on the geographic area. However, bacteria and fungus coinfections that have been reported more frequently in a large series of cases are the genera *Staphylococ‐ cus* spp. with *Aspergillus* spp. or *Fusarium* spp., [3, 9, 10, 11, 12, 13].



**Table 1.** Main reports of human eye coinfections.

One risk factor for coinfection of fungus and bacteria is trauma. Dry eye also seems to be a risk

The most frequently reported risk factor is the use of contact lenses, especially soft lenses. Coinfection with *Acanthamoeba* spp. *and Pseudomonas* spp. has been reported in contact lensassociated keratitis. Poor response to treatment has been observed in young people with

The most important challenge in the emergence of this clinical entity is the identification of a new form of presentation of eye infections. The standard method of causality associates the disease with a single causative agent. However, in this new scenario, more than one causal agent is observed. The new entity must be monitored and addressed as a new disease, which

Bacteria and fungus represent the most frequent type of coinfection in the eye (Table 1]. The main microorganisms that produce coinfections are bacteria, such as *Staphylococcus* spp., *Streptococcus* spp., *Pseudomonas* spp., *Haemophilus* spp., *Klebsiella* spp., *Bacillus* spp., and *Corynebacterium* spp. The fungi genera microorganisms include *Aspergillus* spp., *Fusarium* spp., *Curvularia* spp., *Cladosporium* spp., *Bipolaris* spp., *Alternaria* spp., and the yeast *Candida* spp. Most of these microorganisms are normal microbiota in the conjunctival sac or the lids [8]. Their presence depends on the geographic area. However, bacteria and fungus coinfections that have been reported more frequently in a large series of cases are the genera *Staphylococ‐*

> Transversal Keratitis Gopinathan *et. al*. 2009 Transversal Keratitis Basak *et. al.* 2005 Transversal Keratitis Pate *et. al*. 2006 Transversal Keratitis Bharathi *et. al*. 2002

Transversal Keratitis Fröhlich *et. al*. 1999 Transversal Keratitis Yeh *et. al*. 2006 Case Keratitis Jones 1981

requires a new diagnostic approach, prognosis, and treatment.

*cus* spp. with *Aspergillus* spp. or *Fusarium* spp., [3, 9, 10, 11, 12, 13].

**Organisms Study type Infection caused Reference**

factor.

greater frequency in women.

124 Advances in Common Eye Infections

**6. Keratitis due to coinfections**

**6.1. Bacteria and fungus**

**Bacteria and fungus**

**Bacteria and bacteria**

**5. Challenges**

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

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) [15, 16, 17].

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