Antibiotic Resistance Among Ocular Pathogens in the United States: Five-Year Results From the Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) Surveillance Study.

IMPORTANCE: The Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) study is the only ongoing nationwide antibiotic resistance surveillance program specific to ocular pathogens. OBJECTIVE: To report resistance rates and trends among common ocular isolates collected during the first 5 years of the ARMOR study. DESIGN, SETTING, AND PARTICIPANTS: This antibiotic resistance surveillance study was performed at an independent central laboratory. Clinical centers across the United States were invited to submit ocular isolates of Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa. Isolates were collected from January 1, 2009, through December 31, 2013, and analyzed from January 16 to May 15, 2015. MAIN OUTCOMES AND MEASURES: Minimum inhibitory concentrations for various antibiotic classes were determined by broth microdilution according to the guidelines of the Clinical and Laboratory Standards Institute. Minimum inhibitory concentrations were interpreted as susceptible, intermediate, or resistant based on established break points. RESULTS: A total of 3237 ocular isolates (1169 S aureus, 992 CoNS, 330 S pneumoniae, 357 H influenzae, and 389 P aeruginosa) were collected from 72 centers. Methicillin resistance was found among 493 S aureus isolates (42.2%; 95% CI, 39.3%-45.1%) and 493 CoNS isolates (49.7%; 95% CI, 46.5%-52.9%), and methicillin-resistant (MR) isolates had a high probability of concurrent resistance to fluoroquinolones, aminoglycosides, or macrolides (P < .001). Multidrug resistance to at least 3 additional antibiotic classes was found in 428 MR S aureus isolates (86.8%) and 381 MRCoNS isolates (77.3%). All staphylococcal isolates were susceptible to vancomycin. Resistance among S pneumoniae isolates was highest for azithromycin (113 isolates [34.2%]) whereas resistance among P aeruginosa and H influenzae was low against the antibiotics tested. Staphylococcal isolates from elderly patients were more likely to be MR, as were S aureus isolates obtained from the southern United States (P < .001). Methicillin resistance among staphylococci did not increase during the 5-year study period (P ≤ .22), and small decreases in resistance to ciprofloxacin among CoNS and MRCoNS and to tobramycin among CoNS (P ≤ .03) were found. CONCLUSIONS AND RELEVANCE: Methicillin resistance was prevalent among staphylococcal isolates from ocular infections, with many strains demonstrating multidrug resistance. These findings are consistent with resistance trends reported for nonocular staphylococcal isolates. Overall ocular resistance did not increase during the 5-year study period. Continued surveillance of ocular isolates provides critical information to guide selection of topical antibacterials used for empirical management of ocular infections.

Enterococcal virulence--pathogenicity island of E. Faecalis.

Enterococcal species, though most commonly regarded as members of the microbial flora of the intestinal tract, have recently emerged as human pathogens of significant concern. The rapid spread of antibiotic resistance among enterococci, which has resulted in strains now being routinely isolated that are resistant to all bactericidal regimens, has prompted considerable interest in investigating the pathogenesis of enterococcal infection, with a view toward deriving new, information-based treatment strategies. This review summarizes major findings on the pathogenesis of enterococcal infection, fits them into a model for the dual lifestyle of enterococci as commensal and pathogen, and integrates into that model a recently discovered pathogenicity island of Enterococcus faecalis.

Pseudomonas aeruginosa exotoxin A and keratitis in mice.

PURPOSE: To determine the importance of Pseudomonas aeruginosa exotoxin A (ETA) as a virulence factor in corneal disease. METHODS: Isogenic mutants deficient in ETA were constructed in P. aeruginosa strains PAO1 and ATCC 19660 by allelic exchange and then evaluated for virulence in a mouse model of bacterial keratitis. The effect of ETA on adherence to scarified corneal epithelium was assessed in an in vitro organ culture model. RESULTS: Mutants of either P. aeruginosa PAO1 or 19660, deficient in ETA, adhered to wounded corneal tissue and initiated ocular disease similar to that in wild-type strains. However, in contrast to wild-type strains, ETA mutants were quickly cleared from the eye, inflammation diminished, and the cornea healed. CONCLUSIONS: Although ETA has no effect on the ability of P. aeruginosa to adhere to corneal wounds or to initiate Pseudomonas keratitis, it is crucial for the organism to persist in the eye and ultimately cause disease.

Activities of carbapenem and comparator agents against contemporary US Pseudomonas aeruginosa isolates from the CAPITAL surveillance program.

Antimicrobial susceptibilities of contemporary Pseudomonas aeruginosa clinical isolates were determined from the CAPITAL 2010 surveillance program. Isolates were collected from 100 sites throughout the USA and Puerto Rico, and included isolates representing a range of patient demographics and infection types. A total of 2722 isolates were tested for susceptibility to a broad spectrum of agents, with susceptibilities ranging from 98.8% for colistin to 74% for levofloxacin. Doripenem was the most active carbapenem agent, with 88.6% of isolates susceptible, in comparison with 78.1% and 84.6% for imipenem and meropenem, respectively. Lower respiratory tract isolates and isolates from the intensive care unit setting were the least susceptible overall. Resistance rates were typically highest in lower respiratory tract isolates, with the exception of urinary tract isolates, which displayed the highest resistance for levofloxacin. Overall, multidrug-resistant isolates comprised 14.8% of the total sample population.

Enterococcus faecalis senses target cells and in response expresses cytolysin.

Many virulent strains of Enterococcus faecalis produce a two-subunit toxin, termed cytolysin. Cytolysin expression is regulated by one of the subunits (CylL(S)'') through a quorum-sensing autoinduction mechanism. We found that when target cells are absent, the other subunit (CylL(L)'') forms a complex with CylL(S)'', blocking it from autoinducing the operon. When target cells are present, however, CylL(L)'' binds preferentially to the target, allowing free CylL(S)'' to accumulate above the induction threshold. Thus, enterococci use CylL(L)'' to actively probe the environment for target cells, and when target cells are detected, allows the organism to express high levels of cytolysin in response.