Antimicrobial susceptibility patterns of bacterial isolates at the American University Medical Center in Lebanon

In Lebanon, knowledge of the prevailing pattern of bacterial resistance to antimicrobial agents has been limited, particularly because of 15 years of civil strife. Thus, the current study was conducted to determine the antimicrobial susceptibility patterns of nonselected bacterial isolates recovered from recent clinical specimens, using the standardized disk agar diffusion technique. A total of 5216 isolates (1443 Gram positive and 3773 Gram negative) were examined. Over 92% of Staphylococcus aureus and coagulase-negative staphylococci (CNS) were resistant to penicillins. Methicillin resistance was more frequently noted among CNS (28%) compared with S. aureus (18%). For the pneumococci, 27% of the isolates were resistant to penicillin G. High but variable rates of multidrug resistance were encountered among Acinetobacter spp., Pseudomonas spp., Serratia spp., Citrobacter spp., and Enterobacter spp. Ampicillin resistance was detected in 65% of Escherichia coli and in 20% of Haemophilus influenzae isolates. Although one resistant Salmonella typhi strain was observed, 17% of other Salmonella spp. and 60% of Shigella spp. proved to be resistant to ampicillin, chloramphenicol, and cotrimoxazole. Among Vibrio cholerae isolates, high resistance to tetracycline (71%) and trimethoprim-sulfamethoxazole (94%) was observed. The overall antimicrobial resistance rates in Lebanon seem to fall between figures reported from the Arabian Gulf countries (higher) and those from medical centers in the United States (lower).

Identification of an epidemic strain of Acinetobacter baumannii using electrophoretic typing methods

Nosocomial infections due to Acinetobacter baumannii dramatically increased in a Lebanese medical center following an outbreak of hostilities in Lebanon in 1984. The incidence of infection caused by this organism has remained high in this institution, thus requiring the implementation of a strain typing system to aid in infection control. Three methods were investigated for their utility in differentiating among a representative group of 36 nosocomial Acinetobacter baumannii isolates obtained over a 10 month period from specimens of hospitalized patients. Isolates were typed by antibiogram analyses, plasmid fingerprinting, and total cell protein profiles. Only three distinct total cell protein profiles were detected, with one pattern accounting for 26 (72.2%) of the isolates. However, eight different plasmid profiles were observed, with 20 (55.5%) isolates having the same profile. Eleven distinct antibiograms were seen with the most prevalent pattern occurring in 21 isolates. Twenty of the 21 (95%) isolates with the common antibiogram also had the same plasmid profile and total protein profile (44.4% of total isolates). The combination of these three typing methods was useful in tracing the spread of these organisms in the medical center. The data obtained suggest the distribution of a common strain among at least six wards of this hospital.

Penetration of intravenous moxalactam into human aqueous humor

Intraocular penetration of moxalactam disodium, a new broad-spectrum oxa-beta-lactam antibiotic, was studied in 18 patients undergoing cataract surgery. The antibiotic was administered in a 2-g single dose by intravenous drip during a 20-minute period. After 40 to 230 minutes, moxalactam aqueous humor concentrations ranged from 1.1 to 5.0 micrograms/mL (mean, 2.3 micrograms/mL). The ratio of aqueous humor concentrations to concomitant serum concentrations ranged from 1.6% to 9.8%. The achievable aqueous moxalactam concentrations were well above the minimum inhibitory concentrations of most Gram-negative enteric bacilli but not of Pseudomonas and staphylococci.

Cloxacillin penetration

We investigated the intraocular penetration of cloxacillin in 14 patients undergoing surgery for senile cataract after intramuscular and subconjunctival injections of the drug. No antibiotic level was detected in the aqueous humor when cloxacillin was administered intramuscularly in a dose that ranged between 1 and 4 g. With subconjunctival injection, therapeutically effective cloxacillin activity was detected in the aqueous humor only after a dose of 250 mg.

Penetration of tobramycin sulfate in the aqueous humor of the rabbit

The intraocular penetration of tobramycin sulfate, a new aminoglycoside antibiotic, was evaluated in rabbits following subconjunctival injection. The mean tobramycin sulfate concentration in the aqueous humor 60 minutes after a single 5-mg dose was 5.5 mug/ml, as compared to a mean concentration of 6.7 mug/ml following a single 10-mg dose. These levels exceed the minimal inhibitory concentration (MIC) for most Pseudomonas species and a variety of other Gram-negative bacilli recovered from clinical infection. No anterior segment changes that may be attributed to the antibiotic could be demonstrated in the injected eye.