Microbial colonization of soft contact lenses over time

PURPOSE

To compare the bacterial colonization of soft contact lenses in subjects for successively increasing periods, up to 13 nights of wear. The aim of this study was to determine whether increasing the length of lens wear predisposed subjects to high levels of microbial colonization of lenses.

METHODS

Subjects (N = 20) were divided into those with a prior history of adverse events (N = 6), gram-negative bacterial carriers (N = 6), and those with no previous history (N = 8).

RESULTS

There were no temporal changes in microbial colonization of lenses. Lenses from all wearers were colonized at least once during the study by gram-positive bacteria at low numbers (<10 cfu/ml). Gram-negative bacteria colonized lenses at least once in 80% of all wearers. Lenses from gram-negative bacterial carriers were more frequently colonized by Staphylococcus aureus and Pseudomonas sp. compared with subjects with no previous history and subjects with a prior history of adverse events, respectively. Lenses from gram-negative bacterial carriers were less frequently colonized by a range of gram-positive bacteria compared with subjects with a prior history of adverse events.

CONCLUSIONS

Increasing the length of lens wear up to 13 nights did not result in a predictable increase in bacterial colonization of contact lenses. Gram-positive bacteria were isolated frequently but in low numbers, whereas gram-negative bacteria were present sporadically.

Incidence of contamination of preserved saline solutions during normal use

PURPOSE

To ascertain the incidence of microbial contamination of preserved contact lens saline solutions with normal patient use.

METHODS

Eight different brands of preserved saline were dispensed to 40 patients attending optometric practices in the Sydney area. After specific periods of time (7 to 28 days), the samples were collected and the solution bottle nozzles and contents underwent microbial analysis.

RESULTS

The overall contamination rate was approximately 26% for contents only and 55% for nozzles of preserved saline solutions. This rate remained constant for all periods of use. Coagulase-negative Staphylococci were most frequently isolated. No Acanthamoebae were isolated. Saline preserved with ethylene-diamine-tetraacetic acid (EDTA) in conjunction with sorbic acid showed the highest percentage of sterility.

CONCLUSIONS

The results of this study show that preserved saline became contaminated with gram-positive bacteria. This is in contrast to our previously published paper using unpreserved saline, where contamination was predominantly with gram-negative bacteria. The overall contamination rates with preserved saline were lower than for unpreserved saline.

Potential sources of bacteria that are isolated from contact lenses during wear

PURPOSE

The aim of this paper was to determine the possible contamination sources of contact lenses during wear.

METHODS

Potential sources of the microbiota that colonized hydrogel contact lenses during wear were examined. The microorganisms that colonize contact lenses were grown, identified, and compared to those microorganisms that colonized the lower lid margins, upper bulbar conjunctiva, hands, and contact lens cases of contact lens wearers. In addition, the incidence of contamination of the domestic water supply in the Sydney area was obtained, and this was compared to the incidence of colonization of contact lenses by microorganisms in general and gram-negative bacteria in particular.

RESULTS

There was a wide diversity of bacteria that were isolated from each site sampled. Coagulase-negative staphylococci and Propionibacterium spp. were the most common isolates from all ocular sites examined, and constituted the normal ocular microbiota. Other bacteria, including members of the families Enterobacteriaceae and Pseudomonadaceae, were isolated infrequently from all sites, but most frequently from contact lens cases. Statistical analysis revealed that there was a correlation between the isolation of bacteria from the contact lens and the lower lid margin (p < 0.001). Analysis of this correlation revealed that this was true for the normal microbiota. A correlation was also noted between the colonization of contact lenses by gram-negative bacteria and contamination of the domestic water supply.

DISCUSSION

This study has demonstrated that the likely route for the normal ocular microbiota colonizing contact lenses is via the lid margins, whereas colonization by gram-negative bacteria, including potential agents of microbial keratitis, is likely to be from the domestic water supply.

Normal superoxide dismutase (SOD) gene in pregnancy-induced hypertension: is the decreased SOD activity a secondary phenomenon?

Reactive oxygen species (ROS) have been implicated in the pathogenesis of pregnancy-induced hypertension (PIH). A genetic factor is also thought to be associated with the disease. The aim of the present study was to investigate whether decreased superoxide dismutase (SOD) activity in PIH resulted from gene abnormalities. Fourteen patients with PIH were enrolled in the study. Normal pregnant women and normal nonpregnant women served as controls. Genomic DNA and mRNA were isolated from white cells and subjected to Southern and Northern blot analysis with a 600 bp CuZn-SOD probe. SOD activity was also determined in the white blood cells and red blood cells. The results showed that SOD activity was significantly reduced in patients with PIH compared to both control groups. There were no significant differences in the size of the CuZn-SOD gene and its expression between the patients with PIH and the controls. This study confirmed that there was a decreased SOD activity in PIH but revealed neither major structural changes in the genomic DNA nor mRNA size of CuZn-SOD. Our results suggest that the decreased SOD levels in PIH are not due to abnormalities in the CuZn-SOD gene and are an acquired phenomenon which occurs during the development of the disease.

Detection of bacteremia by Difco ESP blood culture system

In a multicenter study, the Difco ESP blood culture system (Difco Laboratories, Detroit, Mich.) was compared with the BACTEC NR660 system (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.). The ESP system monitors each blood culture bottle every 12 to 24 min to detect changes in oxygen consumption and gas production by microbes. Equal volumes of blood were inoculated into aerobic ESP-80A and BACTEC 6A, 16A, or PEDS Plus broths and anaerobic ESP-80N and BACTEC 7A or 17A broths and were incubated for up to 7 days. ESP bottles contain supplemented tryptic soy broth without antimicrobial agent-adsorbing resins. From 7,532 aerobic compliant sets, the ESP system detected 356 clinically significant positive cultures and the BACTEC NR660 system detected 329. From 6,007 anaerobic cultures, the ESP system detected 234 clinically significant positive cultures and the BACTEC NR660 system detected 198. In aerobic broths, 292 organisms were isolated from both systems and 78 organisms were isolated from the ESP system alone, whereas 54 organisms were isolated from the BACTEC NR660 system alone (P < 0.05). Among individual organisms, pneumococci were isolated significantly more often in ESP aerobic broths. In anaerobic broths, 180 organisms were isolated from both systems and 68 organisms were isolated from the ESP system alone, whereas 35 organisms were isolated from the BACTEC NR660 system alone (P < 0.05). Aerobic gram-positive organisms as a group and Candida spp. were isolated significantly more often in ESP anaerobic broths. Both systems detected 207 clinically significant bacteremic episodes and the ESP system alone detected 63, whereas the BACTEC NR660 system alone detected 32 (P < 0.05). Significantly more episodes of bacteremia caused by Staphylococcus epidermidis and anaerobes were detected by the ESP system. The differences in the numbers of organisms detected >6h earlier in ESP broths compared with BACTNEC NR660 broths were significant, as were earlier times to detection. Although the total number of organisms detected was not significantly different, the ESP system alone detected more organisms in a shorter time than did the BACTEC NR660 system alone. The continuous monitoring capability of the ESP system makes it an attractive alternative to the BACTEC NR660 system.