The patterns of in vitro antimicrobial susceptibility and resistance of bacterial keratitis isolates in Glasgow,United Kingdom

Purpose: Trends in antibiotic sensitivity of pathogenic bacteria change with time and the emergence of resistance to commonly used antibiotics is not uncommon. The aim of this study is to identify the antibiotic susceptibility and resistance patterns in a tertiary referral centre that commonly manages corneal infections. Methods: This is a retrospective review of microbiology reports of corneal scrapes in a tertiary care hospital. Results: There were 205 positive corneal scrapes (32 per cent) in 1995 to 1998 and 147 (28 per cent) in 2004 to 2007. There was increased incidence of Staphylococcus aureus (18 to 21 per cent) (p = 0.16), Moraxella catarrhalis (1.5 to 5 per cent) (p = 0.5), pseudomonas species (6 to 14.5 per cent) (p = 0.25) and non‐lactose fermenting coliforms (1.5 to 7 per cent) (p = 0.5). In vitro resistance of gram‐positive bacterial isolates to ciprofloxacin was increased from 5 to 7 per cent (p = 0.5). The in vitro susceptibility of gram‐positive organisms to dual therapy with cefuroxime and gentamicin were 98 per cent in 1995 to 1998, and 94 per cent in 2004 to 2007 (p = 0.1). Pseudomonas species were 100 per cent susceptible to cefuroxime in the first period but developed 100 per cent resistance in the later period (p = 0.0002). However, the susceptibility of gram negative bacterial isolates to dual therapy with cefuroxime and gentamicin (p = 1) and monotherapy with ciprofloxacin (p = 1) was 100 per cent in both periods. The in vitro resistance to chloramphenicol to gram‐positive organisms was reduced to 5 from 12 per cent (p = 0.19) but there was an increase in resistance of gram‐negative organisms from 23 to 36 per cent (p = 0.3). Conclusion: Despite limitations, this study demonstrates that the fortified antibiotics such as 5% cefuroxime 1.5% gentamicin may be the appropriate choices for most episodes of bacterial keratitis, either as an initial therapy or after identification of in vitro susceptibility of bacterial isolates.     

Staphylococcus aureus ocular isolates from symptomatic adverse events: antibiotic resistance and similarity of bacteria causing adverse events

Background: Staphylococcus is the leading cause of microbial keratitis. Staphylococcus aureus isolated from ocular infections with resistance to a wide range of antibiotics, including the commonly prescribed fluoroquinolones, is emerging. The aim of this study was to determine the current antibiotic susceptibilities of ocular S. aureus isolates and also determine whether isolates from different adverse events or those with similar antimicrobial susceptibilities are related. Methods: A collection of 55 S. aureus strains from ocular adverse events were analysed for antibiotic susceptibility using disc diffusion (CDS method) and typed using PCR‐ribotyping and pulsed‐field gel electrophoresis (PFGE). Results: S. aureus isolated from symptomatic ocular adverse events in the USA exhibited greater resistance to antibiotics than did those isolated from symptomatic ocular adverse events in Australia or India (p < 0.05). A larger proportion of ulcerative keratitis isolates was found to be resistant to antibiotics than isolates from conjunctivitis. PFGE analysis separated related isolates determined by ribotype, on the basis of the adverse event caused by the isolate. Isolates were related within geographical regions and adverse event types. Conclusions: Similar isolates within a geographical location cause adverse events but there is a genetic difference between isolates causing corneal adverse events and those causing conjunctivitis. Isolates from corneal adverse events were more resistant to antibiotics, with those from the USA exhibiting the greatest resistance. This suggests that virulence may correlate with increased resistance to antibiotics.     

Pseudomonas aeruginosa in vitro corneal isolate sensitivity to ofloxacin, ciprofloxacin, and trovafloxacin: a comparative study

PURPOSE: To compare sensitivity of Pseudomonas aeruginosa corneal isolates to ofloxacin, ciprofloxacin, and trovafloxacin.METHODS: Sensitivities of P. aeruginosa corneal isolates to each antibiotic from the periods 1985 to 1987 (n = 32) and 1995 to 1999 (n = 85) were evaluated in vitro with E tests (AB Biodisk; Remel, Lenexa, Kansas).RESULTS: Overall, the percent of P. aeruginosa corneal isolates sensitive in vitro to ofloxacin (106/117, 90.6%) was significantly less than to ciprofloxacin (113/117, 96.6%, P = .016) and trovafloxacin (113/117, 96.6%, P = .016). We observed trends of decreasing sensitivity to ciprofloxacin and trovafloxacin, which were not statistically significant. Sensitivity to ofloxacin remained unchanged; however, sensitivity to ofloxacin was always less than sensitivity to ciprofloxacin and trovafloxacin.CONCLUSION: Although in vitro susceptibilities may not correlate with in vivo efficacy, our data suggest that ciprofloxacin and trovafloxacin are superior to ofloxacin in the treatment of P. aeruginosa keratitis.     

Bacteriology of external ocular infections in Aba,South Eastern Nigeria

Background: Bacteria are microbial agents that frequently cause infections of the eye and possible loss of vision. Method: The common isolates were studied in 298 bacterial infections of the anterior eye, consisting of 35 blepharitis, 208 conjunctivitis and 55 keratitis. Isolates were cultured in blood agar and chocolate agar. Each strain's susceptibility to the antibiotics was determined using a standard table of antibiotic susceptibility. Results: In decreasing order of frequency, the implicated bacteria were Staphylococcus aureus 80 (23.7 per cent), Staphylococcus albus 65 (19.2 per cent), Pseudomonas aeruginosa 34 (10.1 per cent), Streptococcus pneumoniae 29 (8.6 per cent), Haemophilus influenzae 26 (7.7 per cent), Streptococcus pyogene 20 (6.2 per cent), Klebsiella pneumoniae 18 (6.2 per cent), Escherichia coli 15 (4.4 per cent), Neisseria gonorrhoeae 13 (3.9 per cent), Streptococcus viridans 11 (3.5 per cent), Moraxella catarrhalis 10 (3.0 per cent), Streptococcus faecalis 5 (1.5 per cent), Proteus mirabilis 5 (1.5 per cent) and Neisseria meningitides 1 (0.3 per cent). Bacteria were isolated most frequently from infections of the conjunctiva (222, 66.7 per cent), then the cornea (65, 20.1 per cent) and least from the eyelids (44, 13.2 per cent). Bacterial isolates varied in their clinical features (p < 0.01). The age distribution showed isolations of 77 (23.2 per cent) and 79 (23.7 per cent) in the age groups of newborn to under three years and three to under 12 years, respectively. This was comparable to 66 (19.8 per cent) for the 12 to under 18 years, 61 (18.3 per cent) for the 18 to under 40 years age group and 50 (15 per cent) for those 40 years and above. Bacterial isolates had no predilection for the age of patients (p < 0.95). Conjunctivitis was diagnosed more in children, 60 (28.8 per cent) in the newborn to under three years and 53 (25.5 per cent) in the three to under 12 years age groups. Blepharitis was diagnosed most frequently (15, 42.8 per cent) in adolescents 12 to under 18 years, while keratitis was more in adults (20, 36.4 per cent) in the 18 to under 40 years and (15, 27.3 per cent) in the 40 years and above. Diagnosis varied among age groups but there was no relationship between sex and diagnosis (p < 0.75). Klebsiella pneumoniae was the most resistant to all the anti‐bacterial preparations. The bacterial isolates were more susceptible to the second generation quinolones than the first. Conclusion: The study recommends that quinolones be available as ophthalmic preparations to be prescribed by the qualified practitioners to avoid development of resistance from indiscriminate use.     

Ciprofloxacin-resistant Pseudomonas keratitis.

OBJECTIVE: To determine ciprofloxacin resistance of corneal isolates of Pseudomonas and to review the clinical response to topical therapy in cases of ciprofloxacin-resistant Pseudomonas keratitis, where medical therapy was begun with 0.3% ciprofloxacin. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Medical and microbiology records of 141 culture-proven cases of Pseudomonas keratitis, examined between January 1991 and June 1998, were reviewed retrospectively. METHODS: All isolates of the Pseudomonas species from corneal scrapings were tested for their susceptibility to routinely used antibiotics by the Kirby-Bauer disc-diffusion method. The minimum inhibitory concentration of ciprofloxacin was determined by the agar-dilution method for most of the isolates found resistant to ciprofloxacin. Clinical response to initial therapy with 0.3% ciprofloxacin was determined in cases of keratitis caused by ciprofloxacin-resistant Pseudomonas. MAIN OUTCOME MEASURES: Resistance of Pseudomonas isolates to ciprofloxacin and clinical response to initial therapy with 0.3% ciprofloxacin. RESULTS: By use of the in vitro antimicrobial susceptibility test, 22 cases of keratitis caused by ciprofloxacin-resistant Pseudomonas were identified. The minimum inhibitory concentration of ciprofloxacin for these isolates was > or =16 microg/ml (mean = 43 microg/ml). Gentamicin resistance occurred in 63.6% of isolates also, but 90.9% ciprofloxacin-resistant isolates were susceptible to amikacin. Fifteen (76.7%) of 19 patients who initially received ciprofloxacin did not show any clinical improvement even after 3 days of intensive medical therapy. The infiltrate resolved in all 8 cases where the antibiotic therapy was modified on the basis of susceptibility test. Four eyes were subjected to penetrating keratoplasty, and three were eviscerated following failure of treatment with ciprofloxacin. CONCLUSION: True resistance to ciprofloxacin is emerging in ophthalmology even among Pseudomonas isolates; therefore, the empiric treatment of infectious keratitis with ciprofloxacin monotherapy must be critically reviewed at this time.     

Topical 0.3% ciprofloxacin vs topical 0.3% ofloxacin in early treatment of Pseudomonas aeruginosa keratitis in a rabbit model

An in vivo prospective study compared the effectiveness of 0.3% ciprofloxacin to 0.3% ofloxacin against Pseudomonas aeruginosa keratitis in rabbits. Ofloxacin-treated corneas yielded an average amount of colony-forming units (CFUs) of P aeruginosa that was statistically significantly higher than that of ciprofloxacin-treated corneas (4.7×10⁴±2.2×10³ vs 2.5×10³±1.0×10²). Thus, ciprofloxacin was more effective than ofloxacin in the early reduction of CFUs in P aeruginosa keratitis in rabbits.     

Pneumococcal keratitis: a clinical profile

Aim: To study the clinical features of pneumococcal keratitis and response to ciprofloxacin therapy. Methods: A retrospective analysis was undertaken of 58 patients with culture‐proven pneumococcal keratitis seen over a period of 2 years. Results: Pneumococcal keratitis accounted for 33.3% of bacterial keratitis. Most cases presented with non‐severe keratitis (77.5%). Co‐existing sac pathology was more frequent in pneumococcal ulcers as compared to non‐pneumococcal bacterial ulcers (50%vs 9%, P < 0.001). Characteristic clinical features enabling an accurate clinical diagnosis were found in 27.5% and lanceolate diplococci on Gram's stain were identified in 76% of cases. In vitro testing showed a high susceptibility to cephazolin and ciprofloxacin. All patients received ciprofloxacin as first‐line therapy. Eighty per cent responded well with complete healing of the ulcer. A second drug was required in 8.5%. Conclusion: Ciprofloxacin therapy can be effective in the treatment of pneumococcal keratitis.     

Risk factors and causative organisms in microbial keratitis

PURPOSE: To establish the risk factors, causative organisms, levels of antibiotic resistance, patient demographics, clinical presentations, and clinical outcomes of microbial keratitis at a tertiary hospital in Australia. METHODS: Patients who had a corneal scraping for culture over a 5-year period were identified through the local microbiology database, and a retrospective audit of their medical records was carried out. Clinical information was gathered from medical records, and smear, culture, and antibiotic resistance results were from the microbiology database. An index of disease severity was calculated for each patient from scores for the magnitude of the epithelial defect and anterior-chamber reaction and the location of the lesion. Associations between risk factors for keratitis and variables such as patient demographics, causative organism and antibiotic resistance, disease severity, and outcome were analyzed by using analysis of variance and chi tests with appropriate correction for multiple comparisons. RESULTS: Two hundred fifty-three cases of microbial keratitis in 231 patients were included. Sixty percent of patients were men, and there was a bimodal distribution in the age of presentation. Common risk factors for keratitis were contact lens wear (53; 22%), ocular surface disease (45; 18%), ocular trauma (41; 16%), and prior ocular surgery (28; 11%). Gram stains were positive in 33%, with a sensitivity of 53% and specificity of 89%. Cultures of corneal scrapings were positive in 65% of cases, and Pseudomonas aeruginosa (44; 17%), coagulase-negative staphylococci (22; 9%), Staphylococcus aureus (19; 8%), and fungi (7; 3%) were commonly recovered. P. aeruginosa was more common than other culture results in contact lens-related cases (55% vs. 0%-23%; P < 0.001), and S. aureus was more common than other culture results in ocular surgery-related cases (29% vs. 0%-21%; P < 0.001). Patients with keratitis related to prior ocular surface disease had more severe keratitis at the time of scraping (P = 0.037). Cultures positive for Fusarium, P. aeruginosa, and other Gram-negative organisms had statistically significantly more severe keratitis at the time of scraping, whereas patients with negative cultures had milder keratitis (P = 0.030). Only 2% of all bacterial isolates were resistant to ciprofloxacin, 20% of Gram-positive isolates were resistant to cephalothin, and no Gram-negative isolates were resistant to gentamicin. CONCLUSIONS: In this series, the most common risk factor for keratitis was contact lens wear and the most commonly isolated organism was P. aeruginosa.     

Topical levofloxacin 1.5% overcomes in vitro resistance in rabbit keratitis models

Purpose: To determine whether topical levofloxacin 1.5% will successfully treat both levofloxacin‐resistant and susceptible Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) in rabbit keratitis models. Methods: For levofloxacin‐resistant and susceptible SA, respectively, 32 New Zealand White (NZW) rabbits were intrastromally injected with 1000 colony‐forming units (CFU). After 4 hr, the corneas of eight rabbits were homogenized to determine onset CFU/ml. Twenty‐four rabbits were divided into three treatments: levofloxacin, vancomycin (cefazolin for levofloxacin‐susceptible SA) and saline. Twenty‐one drops were administered over 5 hr. One hour post‐treatment, the corneas were homogenized for CFU/ml. For levofloxacin‐resistant and susceptible PA, respectively, 32 NZW rabbits were intrastromally injected with 1000 CFU. After 16 hr, the corneas of eight rabbits were homogenized for CFU/ml. Twenty‐four rabbits were divided into three treatments: levofloxacin, tobramycin (ciprofloxacin for levofloxacin‐susceptible PA) and saline. Nineteen drops were administered over 8 hr. One hour post‐treatment, the corneas were homogenized for CFU/ml. The CFU/ml data were analysed for sterilization and non‐parametrically for reduction. Results: Levofloxacin 1.5% significantly reduced more (p < 0.05) levofloxacin‐resistant SA than vancomycin; was equivalent to cefazolin (p > 0.05) for levofloxacin‐susceptible SA; was equivalent to tobramycin for levofloxacin‐resistant PA; was equivalent to ciprofloxacin for levofloxacin‐susceptible PA; and significantly reduced more SA and PA than saline and onset. Levofloxacin 1.5% sterilized the corneas in the levofloxacin‐resistant and susceptible PA groups (32/32) and levofloxacin‐susceptible SA group (16/16), but not the levofloxacin‐resistant SA group (0/16). Conclusion: Levofloxacin 1.5% was effective for reducing SA and PA in the rabbit keratitis models regardless of in vitro resistance.     

The pathogenesis of bacterial keratitis: studies with Pseudomonas aeruginosa

Bacterial keratitis is a sight‐threatening corneal disease that is most commonly associated with the extended wear of soft contact lenses. Over the past decade, we have investigated the pathogenesis of infectious keratitis involving the opportunistic pathogen Pseudomonas aeruginosa. Our research has focused on understanding the respective roles of bacteria and host in the establishment of this infection. Here, we provide a current perspective on P. aeruginosa keratitis, reviewing some of the research developments that have helped shape our views on the mechanisms by which pathogen and host response cause corneal disease. P. aeruginosa may provide a model for the pathogenesis of bacterial keratitis and help further elucidate the complex array of host factors that normally protect the cornea from infectious agents.     

Some potential pathogenic traits of gram-negative bacteria isolated during ocular inflammation and infections

Background : Bacterial colonisation of contact lenses is believed to be important in the production of microbial keratitis and acute inflammatory reactions. The aim of the current study was to examine strains isolated from ocular infections and non-infectious ocular inflammatory conditions for their ability to adhere to contact lenses and epithelial cells and to stimulate the release of chemotactic substances from epithelial cells. Methods : Bacterial adhesion to contact lenses and bovine corneal or conjunctival cells was studied by adhesion assay. Agglutination of human red blood cells by bacteria was demonstrated by haemagglutination. The chemoattractants released from corneal epithelial cells exposed to bacteria was assessed by polymorphonuclear leukocytes (PMN) chemotaxis. Results : Strains of P. aeruginosa adhered better on the contact lenses than strains of other gram-negative bacteria (p = 0.004). H. influenzae strains isolated from conjunctivitis produced haemagglutination. Leukotriene B₄ was released from corneal epithelial cells after stimulation by the gram-negative bacteria. Conclusion : This study has identified several potential pathogenetic traits of gram-negative bacteria that may contribute to ocular infection and/or inflammation. It has been estimated that 70 per cent of microbial keratitis cases associated with contact lens wear involve P. aeruginosa and this study has shown that this bacterial species adheres in large numbers to contact lenses. This increased adhesion to contact lenses may be one of the reasons for the preponderance of this species in these infections. The finding that strains could stimulate corneal epithelial cells to release chemotactic factors that specifically recruit PMN indicates a mechanism for producing corneal infiltration.     

Microbial keratitis in Waikato, New Zealand

Background: Bacterial keratitis is a potentially sight‐threatening condition. This study is performed to identify the common causative organisms for bacterial keratitis in Waikato region and the antibiotic sensitivities to these organisms. Design: Retrospective, observational, case series. Participants: The microbiology records of all patients with bacterial keratitis who presented to the Ophthalmology department, Waikato Hospital, New Zealand between January 2003 and December 2007. Methods: The corneal scrape results were reviewed. Antibiotic sensitivity for the organism was tested following National Committee for Clinical Laboratory Standards (NCCLS) method. Main Outcome Measures: In vitro laboratory susceptibility testing of ocular isolates to various antibiotics. Results: A total of 265 scrapes were performed. Gram stain was positive in 35 (13.2%) eyes. Positive culture was seen in 174 (65.6%) scrapes; 78.2% were Gram‐positive and 20.2% were Gram‐negative organisms. Most common Gram‐positive organisms were coagulase‐negative Staphylococci (40.8%) and Staphylococcus aureus (11.5%). Most common Gram‐negative organisms were Moraxalla species (8.0%) and Pseudomonas aeroginosa (3.4%). Of the bacterial organisms 99% were sensitive to ciprofloxacin. All Gram‐negative organisms and 95.5% Gram‐positive organisms were sensitive to tobramycin; 96.6% Gram‐positive organisms and 98.3% Gram‐negative organisms were sensitive to cefuroxime. Conclusions: Our results are comparable to other regions in New Zealand but the incidence of coagulase‐negative Staphylococcus is much higher in this region compared with other New Zealand studies. It seems appropriate to start patients with corneal ulcers initially on fluoroquinolone monotherapy while awaiting culture results.     

Antibiotic susceptibility of bacterial isolates from bacterial keratitis cases in a university hospital in Taiwan

PURPOSE: To analyze in vitro antibiotic susceptibility of bacterial isolates from patients with bacterial keratitis at the National Taiwan University Hospital over the past 12 years. DESIGN: Retrospective cross-sectional study. METHODS: Medical records were reviewed for patients with culture-proven bacterial keratitis at the National Taiwan University Hospital from January 1994 to December 2005. Microbial isolation and in vitro antibiotic susceptibility were analyzed. RESULTS: A total of 272 pathogens were isolated from 254 eyes. Pseudomonas species were the most commonly isolated organisms (46.7%), followed by Staphylococcus species (11%), Propionibacterium species (8.1%), Streptococcus species (7.6%), and nontuberculous Mycobacteria (6.6%). There was no significant change in antibiotic susceptibility in the strains of Staphylococcus, Streptococcus, Pseudomonas, or nontuberculous Mycobacteria during the study period. From 1994 to 2005, 81.8% of the gram-negative organisms were susceptible to the combination of cefazolin and gentamicin, whereas 95.8% were susceptible to ciprofloxacin (P < .001). For all bacterial isolates, 83.7% and 89.7% were susceptible to the combination of cefazolin and gentamicin and the combination of cefazolin and ciprofloxacin, respectively (P < .001). CONCLUSION: There was no increase in drug resistance in strains of Pseudomonas, Staphylococcus, Streptococcus, or nontuberculous Mycobacteria from 1994 to 2005. Ciprofloxacin is a more efficacious choice than the combination of cefazolin and gentamicin for gram-negative bacterial keratitis in Taiwan. The combination of cefazolin and ciprofloxacin is an effective empirical therapeutic regimen for bacterial keratitis.     

Trends in resistance to ciprofloxacin, cefazolin, and gentamicin in the treatment of bacterial keratitis.

PURPOSE: The aim of this study was to evaluate the microbial profile, resistance patterns, and antibiotic sensitivity of bacterial keratitis to three commonly used ocular antibiotics. METHODS: All cases of bacterial keratitis referred to the Massachusetts Eye and Ear Infirmary Microbiology Laboratory from two consecutive annual 10-month periods were reviewed. The bacterial profile and resistance to ciprofloxacin, cefazolin, and gentamicin was evaluated within the two intervals. RESULTS: Of the 485 cultures analyzed, 66.4% (322) were positive for bacterial isolates. Of these, 19.2% were polymicrobial, 87.5% were gram-positive, and 12.5% were gram-negative. The most prevalent isolate was coagulase-negative Staphylococcus (45.5%), followed by S. aureus (15.2%). The resistance patterns for gram-positive bacteria for ciprofloxacin for the first versus second time interval were 12% and 22% (P = 0.04) respectively, for cefazolin 13% and 23% (P = 0.04), and for gentamicin 4% and 7% (P = 0.36). The resistance patterns for gram-negative bacteria for ciprofloxacin, cefazolin, and gentamicin were not significantly different in the two tested time periods (all P > 0.05). CONCLUSIONS: There was increased resistance of gram-positive organisms to ciprofloxacin and cefazolin, but not gentamicin, in the two examined time periods. Increased resistance to these commonly used antibiotics emphasizes the need for close follow-up after initial empiric treatment, and maintaining a low threshold for selecting alternative therapy.     

An in vitro resistance study of levofloxacin, ciprofloxacin, and ofloxacin using keratitis isolates of Staphylococcus aureus and Pseudomonas aeruginosa

PURPOSE: We compared levofloxacin with ciprofloxacin and ofloxacin using the in vitro susceptibilities of Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) keratitis isolates. DESIGN: Retrospective, clinical laboratory study of antibiotic susceptibility among keratitis isolates. PARTICIPANTS: Keratitis isolates from 200 patients with either SA or PA keratitis. METHODS: Minimum inhibitory concentrations (MICs) were determined for levofloxacin, ofloxacin, and ciprofloxacin for 93 SA keratitis isolates (68 fluoroquinolone-resistant and 25 susceptible, as determined by disk diffusion) and 107 PA keratitis isolates (13 fluoroquinolone-resistant and 94 susceptible). National Committee for Clinical Laboratory Standards susceptibilities were determined and analyzed statistically. Time kill studies were determined for fluoroquinolone-susceptible and -resistant isolates to all antibiotics at 8 microg/ml. The killing rates were determined by regression, and the colony count decreases were analyzed. MAIN OUTCOME MEASURES: The susceptibilities and potencies of levofloxacin, ciprofloxacin, and ofloxacin to SA and PA were determined from the MICs. Time kill studies determined the killing rates and decreases in colony counts. RESULTS: The fluoroquinolone-resistant SA susceptibilities to levofloxacin, ofloxacin, and ciprofloxacin were only 22%, 10%, and 3%, respectively. The fluoroquinolone-susceptible SA were 100% susceptible to all antibiotics, with levofloxacin demonstrating the best potency. The fluoroquinolone-resistant PA were resistant to all antibiotics. The fluoroquinolone-susceptible PA isolates were highly susceptible to levofloxacin, ofloxacin, and ciprofloxacin, with ciprofloxacin demonstrating the highest potency. For fluoroquinolone-susceptible SA and PA, the time kill studies determined that the killing rates and decreases in colony counts were equivalent for all three antibiotics tested. The time kill studies demonstrated no colony count decreases for the fluoroquinolone-resistant SA and PA. CONCLUSIONS: Taken together, our susceptibility and time kill data failed to demonstrate convincing differences in the susceptibility of SA and PA keratitis isolates to levofloxacin, ciprofloxacin, and ofloxacin. In general, bacterial isolates that were resistant to ciprofloxacin and ofloxacin were also resistant to levofloxacin.     

Identification and antibiotic susceptibility of coagulase negative staphylococci isolated in corneal/external infections

AIMS: To identify and determine antibiotic susceptibility of coagulase negative staphylococci (CoNS) isolated from patients with chronic blepharitis, purulent conjunctivitis, and suppurative keratitis. METHODS: A retrospective review of all culture positive cases of chronic blepharitis, purulent conjunctivitis, and suppurative keratitis between July 1995 and December 1996 was performed. Cases in which CoNS were the sole isolates were analysed. Species identification was performed by using a commercially available standardised biochemical test system. Antibiotic susceptibility to penicillin, gentamicin, tetracycline, erythromycin, ciprofloxacin, and teicoplanin was determined by agar disc diffusion (Kirby-Bauer method). Teicoplanin resistance was confirmed by agar dilution. RESULTS: 42 Staphylococcus epidermidis, four S warneri, three S capitis, two S hominis, one each of S xylosus, S simulans, S equorum, and S lugdunensis were identified. 37 CoNS were penicillin resistant, 12 gentamicin resistant, 28 tetracycline resistant, 18 erythromycin resistant, four ciprofloxacin resistant, and one teicoplanin resistant (MIC, 32 microg/ml). In total, 16 strains were resistant to three or more antibiotics. CONCLUSION: Species of CoNS apart from S epidermidis may be isolated from patients with corneal and external infection. Antibiotic susceptibility of CoNS is unpredictable and multiresistant strains are common. As a result, antibiotic susceptibility testing should be performed in all cases of clinically significant ocular infections caused by CoNS.     

Contact lens-related corneal infection: Intrinsic resistance and its compromise

Contact lenses represent a widely utilized form of vision correction with more than 140 million wearers worldwide. Although generally well-tolerated, contact lenses can cause corneal infection (microbial keratitis), with an approximate annualized incidence ranging from ~2 to ~20 cases per 10,000 wearers, and sometimes resulting in permanent vision loss. Research suggests that the pathogenesis of contact lens-associated microbial keratitis is complex and multifactorial, likely requiring multiple conspiring factors that compromise the intrinsic resistance of a healthy cornea to infection. Here, we outline our perspective of the mechanisms by which contact lens wear sometimes renders the cornea susceptible to infection, focusing primarily on our own research efforts during the past three decades. This has included studies of host factors underlying the constitutive barrier function of the healthy cornea, its response to bacterial challenge when intrinsic resistance is not compromised, pathogen virulence mechanisms, and the effects of contact lens wear that alter the outcome of host-microbe interactions. For almost all of this work, we have utilized the bacterium Pseudomonas aeruginosa because it is the leading cause of lens-related microbial keratitis. While not yet common among corneal isolates, clinical isolates of P. aeruginosa have emerged that are resistant to virtually all currently available antibiotics, leading the United States CDC (Centers for Disease Control) to add P. aeruginosa to its list of most serious threats. Compounding this concern, the development of advanced contact lenses for biosensing and augmented reality, together with the escalating incidence of myopia, could portent an epidemic of vision-threatening corneal infections in the future. Thankfully, technological advances in genomics, proteomics, metabolomics and imaging combined with emerging models of contact lens-associated P. aeruginosa infection hold promise for solving the problem - and possibly life-threatening infections impacting other tissues.     

Emerging ciprofloxacin-resistant Pseudomonas aeruginosa

PURPOSE: To report a clinical series of ciprofloxacin-resistant ocular isolates of Pseudomonas aeruginosa from a tertiary care ophthalmic center. METHODS: Review of in vitro sensitivities of all ocular isolates of P. aeruginosa be tween July 1991 and September 1998. In vitro resistance was defined as a minimum inhibitory concentration of 4 or more microg per ml. RESULTS: Nine of 423 ocular isolates of P. aeruginosa showed in vitro resistance to ciprofloxacin. From 1991 to 1994, 0.44% (1/227) of ocular isolates were resistant to ciprofloxacin, whereas from 1995 to 1998, 4.1% (8/ 196) of ocular isolates showed in vitro resistance (P = .014). CONCLUSIONS: Ciprofloxacin-resistant P. aeruginosa has been identified in recent clinical ocular specimens. Ciprofloxacin resistance among ocular isolates of P. aeruginosa is a local and worldwide concern.