With fluoroquinolone monotherapy, there was significant association between the MIC of the antimicrobial prescribed and the clinical outcome with all bacteria except CNS and Streptococcus spp. The approach used in this study, if used prospectively, could allow topical breakpoint susceptibility concentrations to be determined for individual antimicrobial and bacterial combinations.

Pseudomonas aeruginosa is a common opportunistic bacterial pathogen that causes a variety of infections in humans. Populations of P. aeruginosa are dominated by common clones that can be isolated from diverse clinical and environmental sources. To determine whether specific clones are associated with corneal infection, we used a portable genotyping microarray system to analyze a set of 63 P. aeruginosa isolates from patients with corneal ulcers (keratitis). We then used population analysis to compare the keratitis isolates to a wider collection of P. aeruginosa from various nonocular sources. We identified various markers in a subpopulation of P. aeruginosa associated with keratitis that were in strong disequilibrium with the wider P. aeruginosa population, including oriC, exoU, katN, unmodified flagellin, and the carriage of common genomic islands. The genome sequencing of a keratitis isolate (39016; representing the dominant serotype O11), which was associated with a prolonged clinical healing time, revealed several genomic islands and prophages within the accessory genome. The PCR amplification screening of all 63 keratitis isolates, however, provided little evidence for the shared carriage of specific prophages or genomic islands between serotypes. P. aeruginosa twitching motility, due to type IV pili, is implicated in corneal virulence. We demonstrated that 46% of the O11 keratitis isolates, including 39016, carry a distinctive pilA, encoding the pilin of type IV pili. Thus, the keratitis isolates were associated with specific characteristics, indicating that a subpopulation of P. aeruginosa is adapted to cause corneal infection.Pseudomonas aeruginosa is a common infective cause of corneal ulceration (bacterial keratitis) (14,32,54). P. aeruginosa keratitis is frequently associated with contact lens wear (54), because hypoxia and trauma from the contact lens allows bacterial adhesion, and as the bacterium is a common contaminant of moist areas such as a contact lens case, the exposure of the ocular surface to the bacterium can easily occur. Subsequently, a combination of P. aeruginosa virulence factors and damage to host ocular defenses allows infection to develop. The host immune and inflammatory responses then contribute both to the elimination of the bacteria and to associated damage to tissues (14). P. aeruginosa is an opportunistic pathogen that is capable of causing a range of infections (16, 38), and it carries an impressive array of virulence factors. The virulence factors implicated in keratitis include twitching motility associated with type IV pili (63), flagella (13), a type III secretion system (22), and quorum-sensing regulated exoproducts (58).The genome of P. aeruginosa consists of core genes (approximately 90%) and accessory genes (approximately 10%) (40).The core genome, carried by all strains of P. aeruginosa, includes many of the recognized virulence genes (61). However, some strain-variable virulence-associated genes also occur, often clustered within genomic islands (3,33,47,50,60,61)....

Aim-To determine how long it takes neonatal blood cultures to become positive. Methods-Data were collected retrospectively on 451 positive blood cultures from babies on a tertiary neonatal unit between January 1997 and December 1998. During the study period, the laboratory used the BacT/Alert microbial detection system. Results-Complete information was available on 416 blood cultures. Twelve became positive after 72 hours, none of which were considered to be clinically significant. Of the 404 remaining cultures, 86% were positive at 36 hours, 96% at 48 hours, and 98.5% by 60 hours. If definite bacterial pathogens are considered alone, the time to positivity was 90% by 36 hours, 93% by 48 hours, and 98% by 60 hours. If definite and possible bacterial pathogens are considered (coagulase negative staphylococci taken as possible bacterial pathogens), the time to positivity was 89% at 36 hours and 97% at 48 hours. The negative predictive value, for isolation of any organism before 72 hours, of a negative blood culture was 97% at 36 hours and 99% at 48 hours. The negative predictive value for the isolation of definite bacterial pathogens only was 99.7% at 36 hours and 99.8% at 48 hours. Conclusions-A period of 36 hours is enough to rule out sepsis in the asymptomatic neonate, and a three day incubation period is suYcient to detect all clinically important infections using the BacT/Alert microbial detection system. (Arch Dis Child Fetal Neonatal Ed 2001;85:F182-F186)

Based on systemic breakpoint data, resistance to commonly used antimicrobials was apparent. Meropenem is a potentially effective agent for ophthalmic use, with low MICs throughout all the bacterial subgroups. Tigecycline and linezolid showed good activity against particular groups and may be useful for treating bacterial keratitis resistant to current antimicrobials. Of the fluoroquinolones, moxifloxacin showed the lowest MICs and resistance for both Gram-positive and -negative bacteria.

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