Hanna N. Canawati

Optimization of ascitic fluid culture technique

The conventional method of ascitic fluid culture detects bacteria in only 42%-65% of patients who have neutrocytic ascites and suspected spontaneous bacterial peritonitis. In this study ascitic fluid was cultured by the conventional method as well as by a new method consisting of bedside inoculation of blood culture bottles with ascites. The conventional cultures grew bacteria in only 13 (43%) of 30 episodes of neutrocytic ascites, whereas the blood culture bottles grew bacteria in 28 (93%); this difference was significant (p less than 0.0001). The blood culture bottle method also resulted in more rapid detection of bacterial growth. The median concentration of bacteria in infected ascites was one organism per milliliter. Bedside inoculation of blood culture bottles with ascitic fluid is more sensitive than the conventional method in detecting bacterial peritonitis. The insensitivity of the conventional method is probably due to the low concentration of bacteria in infected ascites and the small volume of ascites cultured by this method.

Quantitative microbiology of pressure sores in different stages of healing

The quantitative microbiology of 25 pressure sores in different stages of healing was examined in 25 patients with spinal cord injury. When grossly necrotic tissue was present (stage 1), 5.8 isolates per patient with a density of 6.4 log10/g was recovered, with comparable findings for aerobes and anaerobes. In the absence of necrotic tissue but with the presence of undermining (stage 2), 1.5 aerobic and 0.2 anaerobic isolates were recovered per patient with a mean density of 2.7 and 0.1 log10/g of tissue for aerobic and anaerobic isolates, respectively. The lesions were almost sterile in patients with no necrotic tissue and no undermining (stage 3). Foul smell was always associated with the presence of anaerobes in deep tissue cultures, however, six patients with nonfoul-smelling lesions yielded anaerobes. A 75% quantitative concordance was seen between swab and biopsy culture results. The quantitative concordance between peripheral and central biopsy culture results was 63%, showing variability in results from different sampling areas. No relationship was observed between the density of microorganisms and the eventual outcome of the myocutaneous flap procedure.

Prevalence of Corynebacteria in Diabetic Foot Infections

OBJECTIVE Microbiological flora of diabetic foot infections are usually polymicrobial and frequently include bacteria of the Corynebacterium sp. (diphtheroids). The purpose of this study was to determine the prevalence of these bacteria in both deep and superficial cultures in diabetic patients with foot infections. RESEARCH DESIGN AND METHODS The charts of 50 patients of successive admissions to the Orthopedic-Diabetes Service at our hospital were reviewed to obtain the following data: age, sex, ethnic origin, method of treatment of diabetes, blood glucose level, prior antibiotics, and reports of cultures taken from bedside and intraoperative sites. Data were analyzed to compare the prevalence of diphtheroids in reliable versus nonreliable cultures and the influence of other parameters on the presence of these organisms. RESULTS Fourteen of 19 (74%) of the intraoperative specimens grew diphtheroids compared with 25 of 65 (39%) of the bedside cultures, a highly significant difference. In addition, there was a somewhat greater occurrence of diphtheroids in women compared with men. The likelihood that contamination is the cause for the presence of diphtheroids is highly unlikely, because one arm of the study included cultures derived from deep tissue at the time of the surgical procedure (i.e., the intraoperative cultures). Cultures always grew at least one other organism in addition to the diphtheroid. CONCLUSIONS Corynebacteria, commonly known as diphtheroids, are present as a part of the polymicrobial flora in a large percentage of diabetic patients with foot infections. Because the diphtheroids were identified in culture material taken in the operating room or at the time of incision and drainage in a higher percentage of patients than in specimens from superficial cultures, it is highly unlikely that they are contaminants.

LY146032, alone and in combination with gentamicin, for the treatment of enterococcal pyelonephritis in the rat model.

The in vivo and in vitro activity of LY146032 against Streptococcus faecalis GK was examined. The following MICs and MBCs in micrograms per milliliter were obtained: ampicillin, 0.8 and 1.5; vancomycin, 0.8 and 50; gentamicin, 12 and 25; and LY146032, 0.8 and 6. A time-kill-curve study involving approximately 10(6) organisms per ml showed a drop in the number of organisms of almost 2 log10 in the tube containing LY146032 (2 micrograms/ml) plus gentamicin (4 micrograms/ml) compared with bacterial numbers for the control at 4 h of incubation. However, regrowth was observed at 24 and 48 h, and no in vitro synergism was observed with the combination. A sample (1 ml) of overnight growth of this enterococcal strain at a concentration of 10(7) was then injected intravenously into 184 male Wistar rats weighing about 100 g each. After 12 days, 10 rats were sacrificed and the remaining ones were randomized into four treatment groups: (i) untreated control, (ii) LY146032 (3 mg) given subcutaneously, (iii) gentamicin (0.8 mg) given intramuscularly, and (iv) LY146032 plus gentamicin at the same dosages as when the drugs were used singly. The rats received antibiotics for 4 weeks twice daily, and approximately 10 rats in each group were sacrificed for quantitative kidney cultures at 1, 2, 4, and 6 weeks after the start of therapy. At the end of the 4- and 6-week periods, significantly better results were obtained with the combination of LY146032 plus gentamicin than with no treatment or treatment with single antibiotics.

Bacteremia in Diabetic Patients with Infected Lower Extremities

Eleven cases of bacteremia in diabetic patients with infected lower extremities at Rancho Los Amigos Hospital (RLAH) were observed over a 34-mo period. The yearly incidence was 0.6% of admissions to the Ortho-Diabetes service. Aerobic bacteria were recovered in six cases and anaerobic bacteria in five. Bacteroides fragilis was isolated four times, Staphylococcus aureus three times, and nonfragilis Bacteroides sp., Escherichia coli, group B streptococcus, and viridans streptococcus were each seen once. Ten of the 11 patients were febrile at the time of bacteremia. Clinical, laboratory, radiologic, and ultrasonographic parameters were comparable in patients with aerobic and anaerobic bacteremia, and between bacteremi patients and nonbacteremic controls. Fever, however, was significantly more frequent in bacteremic patients. Foul-smelling lesions were seen in two of the five patients with anaerobic bacteremia, and in none of the patients with aerobic bacteremia. Postoperative B. fragilis bacteremia was observed to be transient and resolved without definitive therapy in one patient. Appropriate antibiotic therapy in 10 patients together with surgical intervention in eight cases resulted in resolution of the infection in the remaining patients.

Methicillin-resistant Staphylococcus aureus bacteriuria

Methicillin-resistant Staphylococcus aureus (MRSA) bacteriuria was detected in 11 of 41 patients colonized or infected with MRSA. The patients with bacteriuria generally were older than 40 years of age, five were diabetic, seven had prior indwelling urethral catheters, two had undergone other urologic manipulations, and only one was clinically symptomatic. Eight patients received variable combinations of antibiotic therapy prior to the diagnosis of MRSA bacteriuria, and seven were still on antibiotic therapy at the time the bacteriuria was detected. Bacteriuria lasted four days to 14 weeks, and was eradicated promptly with cephalosporin therapy in five of six patients. Bacteriuria in the untreated patients cleared spontaneously in one month. A single MRSA serotype (83A) predominated. The MRSA isolates were resistant in vitro to most antibiotics except vancomycin. Resistant colonies were observed within cephalothin disc zones of inhibition at 30C (resistance was confirmed by microtube-dilution sensitivity testing). MRSA disc sensitivity testing for cephalothin may be unreliable when performed at 35C. (Am J Med Sci 281(2):101–109.)

Ciprofloxacin-resistant Escherichia coli emerging in a rehabilitation medical center

A retrospective review of laboratory records from 1988 to 1996 has shown an increased rate of ciprofloxacin-resistant (cip(r)) Escherichia coli in our rehabilitation center. Resistance increased from 0.6% in 1989 to 5.9% in 1996. Of 7870 E. coli strains isolated during this period, 257 cip(r)-E. coli were recovered from 257 patients. The majority (96%) of these resistant strains were isolated from the urine samples. One hundred and twenty strains of cip(r)-E. coli were also resistant to four other fluoroquinolones. MICs ranging from 64 to 512 micrograms/mL were observed in 75% of the strains and > or = 1028 micrograms/mL in 6.4% of the strains. Resistance to ciprofloxacin was due to possible mutations in topoisomerase gyrA.

Comparative in vitro activity of cefoxitin, cefotaxime alone, and in combination with desacetylcefotaxime against the Bacteroides species

The agar dilution method was used to determine the inhibitory activity of cefotaxime (CTX) alone, desacetylcefotaxime (dCTX) alone, CTX plus dCTX, and cefoxitin against 74 clinical isolates of the Bacteroides species recovered from diabetic patients with foot ulcers. The study concluded that the addition of dCTX to CTX increased the inhibitory activity from 45% to 73% for all strains tested and from 50% to 81% among the 32 strains of Bacteroides fragilis. This synergistic interaction against B. fragilis resulted in a four- to nine-fold reduction in the MIC of seven strains (64-128 micrograms/ml, resistant category MICs). While the lowest CTX MIC for B. fragilis was 2 micrograms/ml (four strains), the addition of dCTX also produced a remarkable reduction in susceptible range CTX MICs to 0.05-2 micrograms/ml in 16 strains (50%). The overall susceptibility to cefoxitin and CTX plus dCTX was as follows: 100% and 100% for Bacteroides vulgatus, 50% and 66% for Bacteroides thetaiotaomicron, 100% and 33% for Bacteroides ovatus, and 83% and 82% for Bacteroides species other than the B. fragilis group.

In vitro susceptibility of methicillin-resistant and methicillin-susceptible Staphylococcus aureus strains to N-formimidoyl thienamycin.

A total of 82 clinical isolates of methicillin-resistant Staphylococcus aureus and 21 isolates of methicillin-susceptible S. aureus were studied for in vitro susceptibility to N-forminidoyl thienamycin at incubation temperatures of 30 and 35 degrees C. The disk diffusion test results were correlated with the macrobroth dilution test by means of the error rate-bounded method of analysis. Both methicillin-susceptible and (to a lesser degree) methicillin-resistant strains were generally susceptible to the antibiotic as judged from their minimum inhibitory concentrations. The discrepancy between in vitro results obtained at 30 and at 35 degrees C was not very remarkable. However, tolerance of N-formimidoyl thienamycin was observed in 37% of methicillin-resistant strains and 24% of methicillin-susceptible strains at an incubation temperature of 30 degrees C; at 35 degrees C, the values were 54% (methicillin-resistant strains) and 14% (methicillin-susceptible strains).

Temperature Effect on the Susceptibility of Methicillin-Resistant Staphylococcus aureus to Four Different Cephalosporins

Forty isolates of methicillin-resistant Staphylococcus aureus were tested for in vitro susceptibility to cephalothin, cefamandole, cefotaxime, and moxalactam, using the disk diffusion and microbroth dilution methods at incubation temperatures of 30 and 35°C. Resistance to all four antibiotics was more clearly evident at an incubation temperature of 30°C.