In vitro susceptibilities of Aeromonas hydrophila against new antibiotics

Virulence and antibiotic susceptibility of Aeromonas spp. isolated from drinking water

Aeromonas isolates from tap water, mineral water, and artesian well water were investigated for their ability to produce different potential virulence factors or markers such as hemolysins, cytotoxins, phospholipase, DNase, hydrophobicity and their ability to adhere to epithelial cells and to abiotic surfaces. The susceptibility to antibiotics of Aeromonas isolates was also examined. Majority of the isolates displayed hemolytic activity against sheep erythrocytes, while only 7 of the 23 Aeromonas strains displayed DNase activity and 4 of the 23 Aeromonas strains tested were regarded as positive for phospholipase production. Most of the isolates showed cytotoxic activities in culture filtrate dilutions at titer of 1/8 or lower. No general relation between the strain isolated and the ability to interact with epithelial cells could be established. Using the bacterial adherence to hydrocarbons method, most of the strains were classified as highly hydrophilic. All five Aeromonas jandaei strains isolates, 9 of the 12 Aeromonas sp strains and four of the five Aeromonas hydrophila were multidrug resistant. The most active antimicrobial was ciprofloxacin (susceptible in 100% of the isolates), and the least active antibiotic was ampicillin (resistance in 92% of the isolates). The majority of the isolates tested were not killed by chlorine at 1.2 mg/l. Whether the high tolerance to chlorine of Aeromonas isolates can be linked to greater virulence is not know.

Intraoperative Positive Fluid Balance Improves Tissue Diffusion of Ceftizoxime

AIM OF STUDY

To demonstrate that administration of fluids and the consequent improvement of fluid balance during a surgical procedure can modify the tissue diffusion of ceftizoxime.

METHODS

Twenty-eight patients (30-79 years) undergoing major abdominal surgery of the colon were administered ceftizoxime 30 mg/kg i.v. at induction of anesthesia. A sample of arterial blood was taken before administration of the drug (t0) and then again at the time of vascular occlusion of the colon segment to be removed (t1). A sample of the segment of removed colon was taken. The patients were divided into two groups on the basis of the fluid balance between t0 and t1: group A (n = 17) with a fluid balance <1,000 ml and group B (n = 11) with a fluid balance >1,000 ml. The parameters evaluated in each group were: weight, height and age of the patients, serum and tissue antibiotic concentration, percent ratio of serum and tissue concentration, time elapsed between t0 and t1, volume of administered fluids between t0 and t1, diuresis and hourly diuresis between t0 and t1 and body fluid distribution, obtained using a bioelectrical impedance analyzer. The mean results obtained in the two groups were then compared using Student's t test.

RESULTS

The balance of fluids calculated up to t1 was 675 +/- 308 ml for group A and 1,411 +/- 405 ml for group B (p < 0.01). The means of the recorded values that showed statistically significant differences were: mean percent concentration ratio (43.6 +/- 8.4 vs. 84 +/- 16%; p < 0.05), concentration in the colonic segment (16.3 +/- 7.9 vs. 37.2 +/- 25.9 mg/ml; p < 0.05), urinary volume gathered up to t1 (538 +/- 557 vs. 169 +/- 104 ml; p < 0.05), hourly urinary volume up to t1 (311.1 +/- 296 vs. 97.6 +/- 77.9 ml/h; p < 0.05), percent variation of resistance (95.1 +/- 5.1 vs. 89.7 +/- 8.6; p < 0.05). The other means did not show any significant statistical differences.

CONCLUSIONS

A higher tissue water level seems to facilitate the penetration of the antibiotic into the tissue according to the pharmacokinetic characteristics of ceftizoxime: high amount of free drug (not bound to plasma proteins) and high hydrosolubility.

In vitro susceptibilities of Aeromonas genomic species to 69 antimicrobial agents

A total of 217 strains representing all 14 currently described genomic species in the genus Aeromonas were tested for susceptibility to 69 antimicrobial agents by a microdilution method. All species were susceptible to tetracyclines, quinolones, chloramphenicol, and most of the aminoglycosides and the cephalosporins, but were resistant to lincosamides, vancomycin, teicoplanin and some penicillins. In general, no significant differences were found that correlated with the taxonomic designation or the origin of the isolates tested. The microdilution method proved to be easy to perform allowing susceptibility testing of extensive strain collections for a large number of antimicrobial agents.

Antimicrobial susceptibility patterns of Aeromonas jandaei, A. schubertii, A. trota, and A. veronii biotype veronii

Fifty-six isolates of four Aeromonas species, which have been documented as causative agents of human infections or isolated from human clinical specimens, were subjected to antimicrobial susceptibility testing using a MicroScan WalkAway conventional (overnight incubation) gram-negative panel. The four species tested and the number of isolates of each were as follows: Aeromonas jandaei, 17; A. schubertii, 12; A. trota, 15; and A. veronii biotype veronii, 12. All isolates of A. trota were susceptible to all antimicrobial agents tested, except cefazolin (20% of isolates were resistant) and cefoxitin (13% of isolates were resistant). All isolates of A. schubertii and A. veronii biotype veronii, as well as 88% of A. jandaei isolates, were resistant to ampicillin. Resistance to ampicillin-sulbactam ranged from 25% of A. schubertii strains to 100% of A. veronii biotype veronii strains. Cefazolin resistance ranged from 17% of A. veronii biotype veronii isolates to 59% of A. jandaei isolates. Imipenem resistance was detected in 65% of A. jandaei strains and 67% of A. veronii biotype veronii strains. A. jandaei displayed resistance to piperacillin and ticarcillin in 53 and 71% of the isolates, respectively. A. veronii biotype veronii strains were 100% susceptible to piperacillin and 100% resistant to ticarcillin. These antibiogram data may be useful in establishing the identification of these four species when members of the genus Aeromonas are isolated from human clinical sources.

Resistance to antibiotic and heavy metals of motile aeromonads from Chilean freshwater

In this work the resistance of 172 motile Aeromonas isolates recovered from raw drinking water supplies (56), irrigation waters (60) and runoff waters receiving sewage (56), to some antibiotics and heavy metals was investigated by agar diffusion and agar dilution methods. A high proportion of isolates from all water sources showed resistance to carbenicillin, erythromycin, streptomycin, cephradine and cadmium, and susceptibility to chloramphenicol, kanamycin, gentamicin, tetracycline, nalidixic acid, trimethoprim-sulphametoxazole and chromium. No amikacin-resistant Aeromonas were recovered. No relationship was found between antimicrobial resistance and Aeromonas species, with the exception of cephradine, that exhibited a significantly higher activity against the A. sobria isolates than the other Aeromonas species (P < 0.05). Moderately polluted waters showed lower antibiotic multiresistance and metal susceptibility than unpolluted and highly polluted ones. Although significant differences (P < 0.05), between resistance frequencies to erythromycin, carbenicillin, streptomycin and cephradine were found among isolates from different sources, the antimicrobial resistance patterns of aeromonads could not be related to the level of faecal pollution. These results indicate that aeromonads resistant to antibiotics and heavy metals are easily recovered from water sources in Chile, posing a potential public health risk.

Differential susceptibility of aeromonads and coliforms to cefsulodin

Cefsulodin was evaluated as a potential selective agent for aeromonads. Resistance of Aeromonas and coliform isolates was determined by using a standard disk diffusion technique. A total of 119 Aeromonas and 78 coliform strains were isolated. For 102 of 130 [corrected] Aeromonas isolates (environmental and reference strains), the MIC of cefsulodin was < 8 micrograms/ml. Results of MIC tests by the agar dilution method showed that a concentration of cefsulodin of 10 micrograms/ml or less inhibited the growth of 96% of isolates. In comparison, for 81 of 94 coliform isolates (environmental and reference strains), the MIC of cefsulodin was > 32 micrograms/ml. Because cefsulodin suppresses growth of Aeromonas and other oxidase-positive organisms, total coliform (TC) and Escherichia coli counts on Chromocult Coliform agar (CC agar) without cefsulodin and on CC agar with 10 mg of cefsulodin per liter (CC-CFS) were compared. Variance analysis of data from 14 sewage-polluted irrigation water specimens did not demonstrate any statistically significant difference in the enumeration of E. coli with CC and CC-CFS media. On average, the CC agar recovered 2.46 times as many TCs as CC-CFS. However, Aeromonas colonies made up an average of 58.6% of the TC counts on CC agar. Because no Aeromonas spp. were recovered on CC-CFS, background interference was eliminated and the counts that were obtained reflected more accurately the number of TCs. Results of this study suggest that cefsulodin may be a useful selective agent against Aeromonas spp. which should be included in coliform chromogenic media when high levels of accompanying flora are expected.

Increasing antibiotic resistance in clinical isolates of Aeromonas strains in Taiwan

A total of 234 clinical isolates of Aeromonas, primarily A. hydrophila, were collected for the present study. Most were isolates from blood. By the agar dilution method, more than 90% of the Aeromonas strains were found to be susceptible to moxalactam, ceftazidime, cefepime, aztreonam, imipenem, amikacin, and fluoroquinolones, but they were more resistant to tetracycline, trimethoprim-sulfamethoxazole, some extended-spectrum cephalosporins, and aminoglycosides than strains from the United States and Australia.

Aeromonas septicaemia in Hong Kong species distribution and associated disease

During a 5-year study of 2211 patients with clinically significant positive blood cultures in Hong Kong. Aeromonas spp. were isolated in 40 cases. Among 26 episodes in which a single species was isolated. 17 (65.4%) were identified as Aeromonas hydrophila. 8 (30.8%) as A. sobria and one (3.8%) as A. caviae. There were 14 episodes with a mixture of species. Of these, nine (64.3%) were identified as A. hydrophila, two (14.3%) as A. sobria, and two (14.3%) as A. caviae. One (7.1%) was an infection with both A. sobria and A. hydrophila. These polymicrobial infections were usually combined with the presence of Enterobacteriaceae. Hepatobiliary disease was the underlying problem in 24 cases (60.0%) and malignant neoplasia in 14 (35.0%) cases. Most patients presented with fever and leucocytosis. The mortality rate for A. sobria septicaemia was not significantly different from the average rate for all septicaemias. A total of 30 isolates was available for sensitivity testing with 17 antibiotics. More than 86.0% were resistant to ampicillin, and the addition of the beta-lactamase inhibitor sulbactam did not restore its activity. All strains tested were sensitive to cefotaxime, ceftazidime, aztreonam, imipenem, norfloxacin and ciprofloxacin.

In vitro susceptibilities of tropical strains of Aeromonas species from Queensland, Australia, to 22 antimicrobial agents

Greater than 90% of 131 strains of Aeromonas species were susceptible to the aminoglycosides, ureidopenicillins, extended-spectrum cephalosporins, aztreonam, quinolones, tetracycline, and chloramphenicol, and all were uniformly resistant to ampicillin. Except for amoxicillin-clavulanate, sulfonamide, trimethoprim, and trimethoprim-sulfamethoxazole, there was good correlation between the results obtained by the agar dilution and disk diffusion techniques.

Seasonal incidence of and antibiotic resistance among Aeromonas species isolated from domestic wastewater before and after treatment in stabilization ponds

The efficiency of stabilization pond treatment of domestic wastewater in removing culturable cells of motile Aeromonas and its influence on the incidence of resistance to seven antibiotics were investigated in this study. Removal efficiency was higher (P < 0.001) in the warm months (98.8%) than in the cold months (97%). Among the 264 isolates, 163 were Aeromonas caviae, 24 were A. hydrophila, and 54 were A. sobria. Twenty-three isolates could not be identified to the species level. In the influent, A. caviae dominated in both cold and warm months. In the water samples originating from the influent, A. sobria was present at higher percentages in the warm period. All the isolates were resistant to amoxicillin and most of them (73%) exhibited resistance to cephalothin. Of the three species tested, A. sobria was more susceptible to antibiotics than either A. caviae or A. hydrophila. The most striking difference among the species was seen in resistance to cephalothin. There were 91 % of A. caviae strains and 96% of A. hydrophila isolates that were resistant to cephalothin. However, only 9% of A. sobria strains exhibited resistance to this drug. The high incidence of resistance in raw sewage was connected with a high proportion of A. caviae, whereas in the water samples collected from the effluent during the warm months, a high proportion of A. sobria decreased the total amount of multiple-resistant bacteria. Results demonstrated the need for identification to the species level.

Unusual case of Aeromonas hydrophila endocarditis

We describe a case of Aeromonas hydrophila endocarditis in a 66-year-old man with myelodysplastic syndrome and non-A, non-B hepatitis, The infection resolved with antibiotic therapy, but the patient succumbed to complications of his underlying illness. This is the second case of Aeromonas endocarditis reported in the world literature.

Susceptibilities of motile Aeromonas sp. to antimicrobial agents

Resistance to antimicrobial agents of 106 isolates of motile Aeromonas sp. was characterized. The results indicated that in vitro susceptibilities among the three species of the motile Aeromonas sp. were similar, and only the distribution of susceptibility to cephalothin was different. The percentage of resistance of A. sobria strains was lower than the percentage of the resistant strains of A. hydrophila and A. caviae. All of the isolates were susceptible to kanamycin, nalidixic acid, tobramycin, amikacin, netilmicin, cefuroxime, ceftriaxone, cefoperazone and cefotaxime. Three of the tested strains (two A. hydrophila and one A. caviae) transferred resistance plasmids to the Aeromonas hydrophila recipient.

In vitro susceptibility of Aeromonas caviae, Aeromonas hydrophila and Aeromonas sobria to fifteen antibacterial agents

In vitro testing of the activity of 15 antibacterial agents against 522 clinical isolates of Aeromonas species demonstrated some species-associated trends. Amoxicillin plus clavulanic acid was effective against approximately 45% of Aeromonas caviae and Aeromonas hydrophila, but all Aeromonas sobria isolates were resistant. Aztreonam, piperacillin and mezlocillin were highly active against all the strains of Aeromonas tested. Ticarcillin was equally effective against Aeromonas caviae and Aeromonas hydrophila, but more than 50% of Aeromonas sobria isolates were resistant. The latter species was more susceptible to cephalosporins than Aeromonas hydrophila and Aeromonas caviae. Chloramphenicol, tetracycline and trimethoprim-sulfamethoxazole were extremely active against all three Aeromonas species, likewise ofloxacin and ciprofloxacin. Aztreonam, third-generation cephalosporins, chloramphenicol and the quinolones can thus be considered for therapy of infections when Aeromonas is implicated.

Aeromonas hydrophila infection complicating digital replantation and revascularization

Two cases of thumb replantation and one of finger revascularization complicated by Aeromonas hydrophila infection are reported. Two digits were lost because of infection in soft tissue and osteomyelitis. One thumb had extensive necrosis. In all cases the infection was difficult to eradicate, probably because of ischemia. All three patients sustained their injuries while cutting meat or fish. These infection sources have not been previously reported. Note is made of Aeromonas hydrophila in medicinal leeches that are used in microvascular surgery and the potential for iatrogenic infection.

Antimicrobial susceptibility of sixty human fecal isolates of Aeromonas species

The MICs of 21 antimicrobial agents were determined for 60 strains of Aeromonas spp. isolated from human feces. All isolates tested were susceptible to aztreonam, tetracycline, imipenem, moxalactam, pipemidic acid, gentamicin, trimethoprim-sulfamethoxazole, pefloxacin and ciprofloxacin. Resistance to erythromycin and streptomycin was observed in all 60 strains. Aeromonas caviae was less susceptible to cefamandole, cefotaxime, norfloxacin, chloramphenicol, tetracycline, sulfamethoxazole and trimethoprim than was either Aeromonas hydrophila or Aeromonas sobria. It was concluded that cotrimoxazole or one of the newer quinolones can be considered for treatment of aeromonas-associated diarrhea.

Aeromonas as a human pathogen

Although the first Aeromonas strain was described by Zimmermann as early as in 1890, it took 60 years until Caselitz established human pathogenicity of strains then called "Vibrio jamaicensis". Since then, and especially in the last 10 years, there have been increasing numbers of reports on different infections caused by members of the genus Aeromonas. These include sepsis; meningitis; cellulitis; necrotizing fasciitis; ecthyma gangrenosum; pneumonia; peritonitis; conjunctivitis; corneal ulcer; endophthalmitis; osteomyelitis; suppurative arthritis; myositis; subphrenic abscess; liver abscess; cholecystitis and/or ascending cholangitis; urinary tract infection; endocarditis; ear, nose, and throat infections; balanitis; etc. The role of Aeromonas in gastrointestinal disease is very controversial. Increasing epidemiological data suggest that these organisms play a major role in enteric infections, but so far enteropathogenicity has not been demonstrable in experiments where volunteers were given high numbers of Aeromonas possessing different virulence factors. Virulence factors include hemolysin(s), enterotoxin(s), hemagglutinins, invasivity, and others; but these are not found more frequently in strains isolated from patients with diarrhea than from healthy controls. Whether there is a correlation between species and disease remains to be elucidated and requires more information about the taxonomy of this genus.

Ceftriaxone. A reappraisal of its antibacterial activity and pharmacokinetic properties, and an update on its therapeutic use with particular reference to once-daily administration

Since ceftriaxone was first reviewed in the Journal, further studies have confirmed its broad antibacterial spectrum in vitro and extended its clinical documentation in comparative studies with other widely used drugs in infections of the urinary and lower respiratory tract, meningitis in infants and children, uncomplicated gonorrhoea, perioperative prophylaxis in patients undergoing surgery, and in several other types of infection. As in earlier studies, which primarily used a twice-daily dosage regimen, few significant differences were found between therapeutic groups in comparative studies and results have demonstrated the efficacy of once-daily ceftriaxone in all but the most serious infections, such as sole antibiotic therapy in pseudomonal infections. Wider clinical experience has established that ceftriaxone is generally well tolerated. Thus, ceftriaxone now has a well-defined place as an appropriate alternative for the parenteral treatment of a variety of infections due to susceptible organisms, as well as for perioperative prophylaxis of surgery, and may offer advantages of greater convenience over other parenteral antibiotics which are administered more frequently.

Bacteriology of the freshwater environment: implications for clinical therapy

Water and animal tissue samples were obtained from sources in Tennessee, California, and Florida. Purified bacterial colonies were isolated and organisms identified. Fifty-eight isolates were recovered. Twenty-seven Gram-negative isolates were identified. Gram-positive organisms were of the coryneform group or Bacillus species. Antibiotic susceptibility testing showed that Aeromonas species were relatively resistant to a wide variety of antimicrobials, which included trimethoprim, cefazolin, and ampicillin. Antibiotics effective against more than 90% of Gram-negative isolates included ciprofloxacin, imipenem, ceftazidime, and trimethoprim-sulfamethoxazole. Freshwater Gram-positive organisms did not display any unexpected susceptibility features. Recommendation for treatment are based on sensitivity in culture and the potentially serious nature of infections caused by Aeromonas species.

Plasmids and resistance to antimicrobial agents in Aeromonas sobria and Aeromonas hydrophila clinical isolates

The antimicrobial susceptibilities of 75 Aeromonas isolates were determined by agar dilution. Differences in resistance patterns were observed between strains isolated from different geographic locations and between A. sobria and A. hydrophila isolates. Multiple resistance was common; however, only one conjugative plasmid was detected. This 110-megadalton plasmid mediated resistance to eight antibiotics.

Antimicrobial susceptibility of Aeromonas species isolated from patients with diarrhea

In vitro susceptibility to 17 antimicrobial agents was determined for Aeromonas caviae, A. hydrophila, and A. sobria isolated from feces of patients with diarrhea. The three Aeromonas species shared a similar susceptibility pattern, except to cephalothin. Of the oral antimicrobial agents, the quinolones, followed by chloramphenicol, were most active; trimethoprim-sulfamethoxazole and tetracycline had good but variable activity.

Aztreonam. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Aztreonam (azthreonam; SQ 26,776) is the first member of a new class of beta-lactam antibiotics, the monobactams. Aztreonam is selectively active against Gram-negative aerobic bacteria and inactive against Gram-positive bacteria. Thus, in vitro, aztreonam is inhibitory at low concentrations (MIC90 less than or equal to 1.6 mg/L) against Enterobacteriaceae except Enterobacter species, and is active against Pseudomonas aeruginosa, 90% of pseudomonads being inhibited by 12 to 32 mg/L. Aztreonam is inactive against Gram-positive aerobic bacteria and anaerobes, including Bacteroides fragilis. Therefore, when administered alone, aztreonam has minimal effect on indigenous faecal anaerobes. Aztreonam must be administered intravenously or intramuscularly when used to treat systemic infections, since absolute bioavailability is very low (about 1%) after oral administration. Since elimination half-life is less than 2 hours, 6- or 8-hourly administration is used in the treatment of moderately severe or severe infections, although 12-hourly injection is adequate in less severe systemic and some urinary tract infections. Therapeutic trials have shown aztreonam to be effective in Gram-negative infections including complicated infections of the urinary tract, in lower respiratory tract infections and in gynaecological and obstetric, intra-abdominal, joint and bone, skin and soft tissue infections, uncomplicated gonorrhoea and septicaemia. In comparisons with other antibiotics, aztreonam has been at least as effective or more effective than cefamandole in urinary tract infections and similar in efficacy to tobramycin or gentamicin. Where necessary, aztreonam and the standard drug have both been combined with another antibiotic active against Gram-positive and/or anaerobic bacteria. Aztreonam has been effective in eradicating pseudomonal infections in most patients (except in patients with cystic fibrosis), but the inevitably limited number of pseudomonal infections available for study prevents any conclusions as to the relative efficacy of aztreonam compared with other appropriate regimens against these infections. Thus, with an antibacterial spectrum which differs from that of other antibiotics, aztreonam should be a useful alternative to aminoglycosides or 'third generation' cephalosporins in patients with proven or suspected serious Gram-negative infections.

Growth of Aeromonas spp. on cefsulodin-Irgasan-novobiocin agar selective for Yersinia enterocolitica

Twenty-eight strains of Aeromonas spp. were analyzed for their ability to grow on two different kinds of cefsulodin-Irgasan (triclosan; Ciba-Geigy AG, Basel, Switzerland)-novobiocin (CIN) agar containing 15 or 4 mg of cefsulodin per ml and on inositol-bile salts-brilliant green (IBB) agar. Relative to blood agar, 68% of the strains were inhibited by more than 2 logs (i.e., less than 1% growth) at 37 degrees C (39% at 25 degrees C) on CIN I (high cefsulodin concentration), 7% were inhibited at either temperature on CIN II (low cefsulodin concentration), 4% were inhibited on IBB agar at 37 degrees C, and none were inhibited on IBB agar at 25 degrees C. These results reflect the MICs of cefsulodin on CIN Base: the MIC for 50% of the strains was 8 mg/liter at 37 and 25 degrees C, and the MICs for 90% of the strains were 16 mg/liter at 37 degrees C and 64 mg/liter at 25 degrees C. The MICs of Irgasan and novobiocin were far beyond the concentrations used in CIN media. We argue that CIN agar containing 4 mg of cefsulodin per ml (CIN II) can be used for the simultaneous detection of Aeromonas spp. and Yersinia spp.

In vitro susceptibilities of Aeromonas hydrophila, Aeromonas sobria, and Aeromonas caviae to 22 antimicrobial agents

MICs of 22 antimicrobial agents for 60 strains of three Aeromonas species were determined by a microdilution method. The newer cephalosporins such as moxalactam, cefotaxime, and cefoperazone, the aminoglycosides, and chloramphenicol, tetracycline, nitrofurantoin, and trimethoprim-sulfamethoxazole inhibited most of the strains studied. Within the genus, A. hydrophila was more resistant than either A. caviae or A. sobria to the antibiotics tested.

Ceftizoxime. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ceftizoxime is a 'third generation' cephalosporin administered intravenously or intramuscularly. Like other third generation cephalosporins it has a wide spectrum of in vitro activity against Gram-positive and Gram-negative bacteria, is particularly active against Enterobacteriaceae (including beta-lactamase-positive strains), and is resistant to hydrolysis by beta-lactamases. However, the third generation cephalosporins are less active than earlier cephalosporins against staphylococci and so could not be considered the drugs of choice. Like many currently available third generation cephalosporins, ceftizoxime has limited activity against Pseudomonas aeruginosa, and thus cannot be recommended as sole treatment of known or suspected non-urinary tract pseudomonal infections. Similarly, although favourable clinical results have been obtained in patients treated with ceftizoxime for infections caused by mixed aerobic/anaerobic organisms (such as intra-abdominal, and obstetric and gynaecological infections), the relatively low in vitro activity of ceftizoxime (in common with most other third generation cephalosporins) against Bacteroides fragilis and enterococci may restrict its usage in situations where these organisms are the suspected or proven pathogens. Ceftizoxime appears to be similar in efficacy to several other cephalosporins in lower respiratory tract infections in elderly and/or debilitated patients, and in chronic and/or complicated urinary tract infections, 2 clinical situations in which third generation cephalosporins may have a major role. Ceftizoxime is also effective clinically and bacteriologically in skin, soft tissue, bone and joint infections, septicaemia/bacteraemia, meningitis and neonatal infections. However, a few large, well designed clinical comparisons of efficacy with aminoglycosides are needed before ceftizoxime can be recommended as an alternative in patients in whom potential aminoglycoside toxicity is a concern. Single intramuscular doses of ceftizoxime appear similar in efficacy to aqueous procaine penicillin G in gonorrhoeae due to nonpenicillinase-producing Neisseria gonorrhoea, and ceftizoxime is also highly effective against penicillinase-producing strains. Although only a few infections have been treated to date, ceftizoxime may be useful in the treatment of gonorrhoea in places where penicillinase-producing strains are common. Thus, ceftizoxime appears to be an effective addition to the growing number of third generation cephalosporins. However, further studies are needed to confirm its relative efficacy compared with other new cephalosporins, in particular cefotaxime.(ABSTRACT TRUNCATED AT 400 WORDS)

Resistance patterns of nonfermentative gram-negative rods and aeromonads to beta-lactam antibiotics: a diagnostic aid

Consistent resistance to certain antimicrobial agents has in the past been of help in the diagnosis of nonfermentative gram-negative rods. In order to establish patterns of consistent resistance to 15 mostly newer betalactam antibiotics, 561 strains of such organisms plus Aeromonas and Plesiomonas were tested with the Kirby-Bauer method and also against the selective agent C-390 in three concentrations in Mueller-Hinton agar. No species-specific patterns emerged but the resistance data can be used to exclude certain species. C-390 was almost specifically selective for Pseudomonas aeruginosa.

Piperacillin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Piperacillin is one of the new generation of semisynthetic penicillins which can be administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria. Although piperacillin has shown greater activity against beta-lactamase-producing organisms than the other penicillins, it is hydrolysed by the plasmid-mediated beta-lactamases (TEM-1). Activity against Pseudomonas aeruginosa is better than that of ticarcillin, carbenicillin and mezlocillin. Although only limited controlled studies have been reported, in those which have been conducted and in a larger number of open studies piperacillin was effective in the treatment of complicated urinary tract infections and lower respiratory tract infections, particularly pneumonia, caused by Gram-negative bacilli. Favourable clinical results have been obtained in patients with infections caused by mixed aerobic/anaerobic organisms (such as intra-abdominal infections) but the relatively average in vitro activity of piperacillin against Bacteroides fragilis may not indicate its usage in situations where this organism is the suspected or proven pathogen. Piperacillin in combination with an aminoglycoside or a 'third generation' cephalosporin gave encouraging results in the treatment of infections in immunocompromised patients, whilst its penetration into the diseased central nervous system and lack of toxicity indicate a potential value in the treatment of neonatal Gram-negative bacillary meningitis, particularly where the causative organism is Pseudomonas aeruginosa. Whether piperacillin alone is appropriate therapy for conditions usually treated with aminoglycosides (other than pseudomonal infections) needs additional clarification, but if established as equally effective in such conditions it has the advantages of its apparent lack of serious adverse effects and freedom from the need to undertake plasma concentration monitoring. These advantages would not, however, apply when considering one of the new (third generation) cephalosporins as alternative therapy in non-pseudomonal infections. Generally, however, it is still considered necessary to treat serious and complicated infections with combination therapy, either a cephalosporin, or in cases of resistance to P. aeruginosa an aminoglycoside.

Isolation of enterotoxigenic, hemolytic, and antibiotic-resistant Aeromonas hydrophila strains from infected fish in Bangladesh

Strains of Aeromonas hydrophila isolated from skin infections of common freshwater fish in Bangladesh were tested for enterotoxin production, hemolysin production, and any correlation between these two activities. We also tested the resistance patterns of A. hydrophila to different drugs, especially in relation to ampicillin. The A. hydrophila strains produced an enterotoxin that was related to their beta-hemolytic activities. Production of beta-hemolysin may thus be an indicator of enterotoxicity. As 50% of the strains of A. hydrophila were found to be susceptible to 12.5 micrograms of ampicillin per ml, media containing this antibiotic may not be suitable for their isolation.

Ceftriaxone. A review of its antibacterial activity, pharmacological properties and therapeutic use

Ceftriaxone is a new 'third generation' semisynthetic cephalosporin with a long half-life which has resulted in a recommended once daily administration schedule. It is administered intravenously or intramuscularly and has a broad spectrum of activity against Gram-positive and Gram-negative aerobic, and some anaerobic, bacteria. The activity of ceftriaxone is generally greater than that of the 'first' and 'second generation' cephalosporins against Gram-negative bacteria, but less than that of the earlier generations of cephalosporins against many Gram-positive bacteria. Although ceftriaxone has some activity against Pseudomonas aeruginosa, on the basis of present evidence it cannot be recommended as sole antibiotic therapy in pseudomonal infections. Ceftriaxone has been effective in treating infections due to other 'difficult' organisms such as multidrug-resistant Enterobacteriaceae. Ceftriaxone was effective in complicated and uncomplicated urinary tract infections, lower respiratory tract infections, skin, soft tissue, bone and joint infections, bacteraemia/septicaemia, and paediatric meningitis due to susceptible organisms. In most of these types of infections once-daily administration appears efficacious. Results were also encouraging in a few patients with ear, nose and throat, intra-abdominal, obstetric and gynaecological infections, and adult meningitis, but conclusions are not yet possible as to the efficacy of the drug in these indications due to limited experience. A single intramuscular dose of ceftriaxone has been compared with standard therapy for gonorrhoea due to non-penicillinase-producing and penicillinase-producing strains of Neisseria gonorrhoeae and shown to be highly effective. In a few small trials the comparative efficacy of ceftriaxone and other antibacterials has been assessed in other types of infections and in perioperative prophylaxis in patients undergoing surgery. Few significant differences in response rates were found between therapeutic groups in these comparative studies, but larger well-designed studies are needed to more clearly assess the comparative efficacy of ceftriaxone and other antimicrobials, especially the aminoglycosides and other 'third generation' cephalosporins, and to confirm the apparent lack of serious side effects with ceftriaxone. If more widespread use confirms the safety and efficacy of ceftriaxone, it will offer an important alternative, particularly for the treatment of serious infections due to multidrug-resistant Gram-negative bacteria and in situations where the long half-life of the drug could result in worthwhile convenience and cost benefits.