**4. Clinical characteristics**

generated by the production of biofilms, the first indicating that occurs a limited penetration of the drug and the bulk is left on the surface such that the antibiotic never reaches its target. The second refers to the physiological limitation and proposes that some microorganisms within the biofilm can exist in a more recalcitrant phenotypic state. Anderl JN et al [60] in a study of *K. pneumoniae* found that the planktonic form was sensitive to ampicillin and re‐ ported minimum inhibitory concentration (MIC) of 22µg/mL while the same strain that grew as a biofilm presented a survival of 66% increasing the concentration of ampicillin to

**Figure 2.** Resistant mechanism (1) Altered target site of the antibiotic and altered permeability barriers (2) Inactivation of antibiotic by destruction or modification of chemical structure (3) Efflux pumps (4) acquisition of resistance genes

Having recognized the role of biofilm as responsible of infectious diseases, it is necessary the search for new approaches in both the treatment and prevention. A proposal to counteract this resistance factor is the alteration of the surface to inhibit adhesion. In the area of oph‐

by fagos (5) Plasmids (6) Transposons and Integrons (7) modification by mutation of topoisomerase.

5000µg/mL which corresponds to 2500 times the MIC.

94 Common Eye Infections

#### **4.1. Common characteristics**

When developing a bacterial corneal ulcer usually appears chemosis and conjunctival injec‐ tion, eyelid edema, decreased vision, pain, tearing, photophobia, and purulent discharge. Conjunctival reaction is nonspecific, with a predominantly papillary response, is primarily limbal injection. The corneal epithelium and stroma ulcer shows a gray-white infiltrate, may appear necrotic. Infiltration and edema of the cornea can be observed even in areas remote from the ulcer. Appears frequently, an anterior chamber reaction, and in severe cases can be observed fibrin plates on the endothelium and may be a fibrinoid aqueous or hypopyon [61-64].

The hypopyon is produced by the toxic effects of infection on vessels iris and ciliary body, with consequent pouring of fibrin and polymorphonuclear leukocytes. Usually, the hypopy‐ on is sterile as Descemet's membrane is intact. Hypopyon can be seen with any bacterial in‐ fection, most frequently in ulcers caused by *S. pneumoniae* and *Pseudomonas sp.;* not forgetting also can occur in viral and fungal ulcers [64-66].

Signs and symptoms of bacterial corneal ulcers vary depending on the virulence of the or‐ ganism, the previous state of the cornea, the duration of infection, host immune status and prior use of antibiotics and steroids [67-70]. The use of hydrophilic contact lenses can alter the presentation of bacterial ulcers. Infections associated with contact lenses are often multi‐ focal and epithelial and stromal infiltrate is more diffuse. The contact lens wearers present‐ ing with corneal abrasions may have bacterial infections early[71, 72]. Figure 4 are clinical pictures representative in bacterial keratitis.

The aspect sometimes ulcer suggesting the presence of a specific bacterial agent or a group of them. Are indicated below the characteristic signs of infection caused by some agents. However, one must take into account the clinical aspect is never diagnosis, isolation and identification of causative agents is always essential.

#### **4.2.** *Staphylococcus sp.*

*S. aureus* produces coagulase and mannitol fermentation being more aggressive, and *S. epider‐ midis* does not produce coagulase or ferment mannitol. The latter two are usually opportunis‐ tic pathogens that cause infections in compromised corneas, for example, persistent epithelial defects, bullous keratopathy, herpetic epitheliopathy, diabetic epitheliopathy, etcetera. The corneal appearance in *S. aureus*, has a round or oval ulcer, localized, with distinct edges and tends to be deeper, usually accompanied by a creamy white stromal infiltrate and well-de‐ fined gray with overlying epithelial defect and can be multifocal. In severe cases, you can get to see hypopyon and endothelial plaque, staphylococcal blepharitis is common [73-75].

**Figure 4.** Representative Clinical pictures of patients with Bacterial Keratitis infection..

#### **4.3.** *Pseudomonas sp.*

The aspect sometimes ulcer suggesting the presence of a specific bacterial agent or a group of them. Are indicated below the characteristic signs of infection caused by some agents. However, one must take into account the clinical aspect is never diagnosis, isolation and

*S. aureus* produces coagulase and mannitol fermentation being more aggressive, and *S. epider‐ midis* does not produce coagulase or ferment mannitol. The latter two are usually opportunis‐ tic pathogens that cause infections in compromised corneas, for example, persistent epithelial defects, bullous keratopathy, herpetic epitheliopathy, diabetic epitheliopathy, etcetera. The corneal appearance in *S. aureus*, has a round or oval ulcer, localized, with distinct edges and tends to be deeper, usually accompanied by a creamy white stromal infiltrate and well-de‐ fined gray with overlying epithelial defect and can be multifocal. In severe cases, you can get to see hypopyon and endothelial plaque, staphylococcal blepharitis is common [73-75].

identification of causative agents is always essential.

**Figure 4.** Representative Clinical pictures of patients with Bacterial Keratitis infection..

**4.2.** *Staphylococcus sp.*

96 Common Eye Infections

*Pseudomonas sp.* is a Gram(-) often associated with contact lens use, which adheres to the damaged epithelium and stromal cause rapid invasion, the ulcer has a deep peripheral ex‐ tension in hours (can reach twice its size in 24 hrs.) peripheral infiltration with diffuse gray, yellow-green discharge, severe reaction and hypopyon in the anterior chamber, which may extend to sclera and cause necrotizing scleritis and/or perforation in 2-5 days. You can also get to see a multifocal pattern that is more associated with use of soft contact lens [67, 76].

#### **4.4.** *Streptococcus sp.*

*S. pneumoniae* isolates in the upper respiratory tract half of the population, their proximity to the eye may explain the frequency of problems associated with it. *Streptococcus sp.* generates hemolysis of erythrocytes, being in full by the *S. pyogenes*, and partially by the alpha hemo‐ lytic as *S. viridans* and *S. pneumoniae*. The infection usually arises after corneal trauma and is often associated with chronic dacryocystitis. We present a deep stromal abscess with fibrin deposition, plaque formation, severe anterior chamber reaction, hypopyon, synechiae iridi‐ anas, if left untreated can lead to perforation. *S. viridans* has a less aggressive course and is responsible for cristalinean keratopathy, also related to the indiscriminate use of topical an‐ esthetic, use of contact lenses and chemical burns [77-79].

#### **4.5.** *Bacillus sp.*

*Bacillus cereus* are bacilli anaerobic Gram + in soil, water and vegetation. The infection usual‐ ly occurs within 24 hours after penetrating trauma in the presence of chemosis, severe eyelid edema, proptosis, edema peripheral microcystic with a ring followed by a circumferential corneal abscess may lead to drilling in hours [80-82].

#### **4.6. Less common infectious agents**

#### *4.6.1. Corynebacterium diphtheriae*

*Corynebacterium diphtheriae* are bacilli Gram + that rarely causes corneal disease but does re‐ mark commonly as a cause of pseudomembranous conjunctivitis with preauricular lympha‐ denopathy resulting in corneal epithelial opacity diffuse stromal necrosis and thinning [83-87].

#### *4.6.2. Listeria monocytogenes*

*Listeria monocytogenes* is a facultative anaerobe that causes infection in people who are dedi‐ cated to animal care. It is colonizing persistent epithelial defects and keratitis developed a type of necrotizing ulcer-shaped ring with large anterior chamber reaction, fibrinoid exuda‐ tion and hypopyon [87-89].

#### *4.6.3. Propionibacterium acnes*

*Propionibacterium acnes* are bacilli anaerobic Gram + rod that is part of normal flora, so the infection occurs before a surgical trauma, contact lens use, chronic use of steroids or other associated corneal disease. It takes the form of corneal stromal abscess with intact epitheli‐ um [90-93].
