Antimicrobial use and microbiological testing in district general hospital ICUs of the Veneto region of north-east Italy.

International - predominantly American - studies undertaken in the ICUs of teaching centres show that inadequate antibiotic therapy increases mortality and length of stay. We sought to ascertain whether this also pertains to smaller ICUs in the Veneto region of north-east Italy. To the best of our knowledge, this is the first such survey in the Veneto area or in Italy as a whole. A retrospective, observational study was performed across five general-hospital ICUs to examine appropriateness of microbiological sampling, empirical antibiotic adequacy, and outcomes. Among 911 patients (mean age, 65.8 years ± 16.2 SD; median ICU stay, 17.0 days [IQR, 8.0-29.0]), 757 (83.1 %) were given empirical antibiotics. Treatment adequacy could be fully assessed in only 212 patients (28.0 %), who received empirical treatment and who had a relevant clinical sample collected at the initiation of this antibiotic (T0). Many other patients only had delayed microbiological investigation of their infections between day 1 and day 10 of therapy. Mortality was significantly higher among the 34.9 % of patients receiving inadequate treatment (48.6 % vs 18.80 %; p < 0.001). Only 32.5 % of combination regimens comprised a broad-spectrum Gram-negative ß-lactam plus an anti-MRSA agent, and many combinations were irrational. Inadequate treatment was frequent and was strongly associated with mortality; moreover, there was delayed microbiological investigation of many infections, precluding appropriate treatment modification and de-escalation. Improvements in these aspects and in antibiotic stewardship are being sought.

The impact of resistance on the management of urinary tract infections.

Urinary tract infections requiring treatment are extremely common. It is estimated that between 20 and 50% of adult women will have had at least one symptomatic urinary tract infection. When considering the optimal therapy of any infection, patient factors, organism factors, drug factors (e.g. pharmacokinetics), side-effects and cost as well as antimicrobial resistance all need to be considered. This paper deals with the impact of increasing antibiotic resistance on the management of urinary tract infections.

Macrolides and changes in the oral flora.

Macrolides have been used in dental practice for many years, and may have a role in treating periodontal disease. Increased numbers of antibiotic-resistant oral streptococci have been reported after administration of both penicillins and macrolides. We confirm these findings for erythromycin, josamycin and azithromycin, and show that small numbers of macrolide-resistant streptococci are part of the normal oral flora at baseline. Resistant organisms fill the vacuum created by the removal of sensitive strains by antibiotic treatment. Following treatment with azithromycin, periodontal bacterial pathogens such as black pigmented anaerobes and spirochaetes decrease, whereas numbers of oral streptococci increase. These changes in the oral flora indicate a return to a healthier oral environment. In our studies, no clinical problems resulted from the transient increase in macrolide-resistant streptococci.

Comparative in-vitro activity of penicillin alone and combined with gentamicin against clinical isolates of Streptococcus pneumoniae with decreased susceptibility to penicillin.

The worldwide emergence of Streptococcus pneumoniae with decreased susceptibility to penicillin has led to the suggestion that drug combinations might be used. The aim of this study was to determine possible synergy using a combination of penicillin with sub-inhibitory doses of gentamicin against 26 clinical isolates of S. pneumoniae with decreased susceptibility to penicillin, using half-chequerboards and killing curves. Synergy was demonstrated for ten of the 26 isolates with the combination of penicillin with gentamicin at 1 mg/l and for 22 isolates with penicillin and gentamicin at 2 mg/l. Killing curves on three isolates showed synergy and confirmed the chequerboard results. Further synergy studies using penicillin or cefotaxime/ceftriaxone, plus low dose gentamicin against penicillin-resistant pneumococci are indicated.

Imipenem for the treatment of melioidosis.

Melioidosis is a protean disease caused by Burkholderia pseudomallei. It is rare in the UK and is generally only seen in patients with a travel history to endemic areas such as Thailand, Singapore and Malaysia. Cases may present with disseminated bacteraemic, non-disseminated bacteraemic, multi-focal bacteraemic or localized disease. Subclinical infections also occur. Following acquisition of the organism a patient may remain asymptomatic for several years before infection becomes clinically apparent. Factors such as diabetes, renal failure or other causes for a decrease in host immunity may precipitate the appearance of overt disease. The current treatment choice for severe melioidosis is parenteral ceftazidime followed by oral amoxycillin-clavulanic acid or a combination of co-trimoxazole, doxycycline and chloramphenicol. We report a case of melioidosis in a 59-year-old male diabetic from Bangladesh who initially responded to piperacillin-tazobactam but was changed to ceftazidime when a definitive diagnosis was made. His condition deteriorated on the latter antibiotic. He subsequently responded to imipenem. The patient's long-term outcome is still not known.

Selection of resistant variants of respiratory pathogens by quinolones.

Quinolones are widely used in the treatment of respiratory tract infections. However, some disquiet has been expressed over using quinolones for community-acquired pneumonia since their activity is generally rather poor against Streptococcus pneumoniae. In addition, it is known that resistant variants emerge at a fairly high frequency during exposure of Enterobacteriaceae to quinolones; if this also occurred during quinolone treatment of community-acquired pneumonia it could lead to an increased risk of clinical failure. We therefore determined the selection rate of quinolone-resistant variants for six strains of S. pneumoniae, Haemophilus influenzae and Moraxella catarrhalis with nalidixic acid (except for S. pneumoniae), ciprofloxacin, ofloxacin and levofloxacin. We were only able to select resistant variants at low frequency from two of the six strains of S. pneumoniae with ciprofloxacin: no resistant variants were selected by either ofloxacin or levofloxacin. Variants of H. influenzae and M. catarrhalis with decreased susceptibility to quinolones were produced both with more strains and with a greater frequency; however, these variants still remained susceptible according to the NCCLS guidelines. Our study suggests that resistant variants of S. pneumoniae are relatively unlikely to occur in individuals treated with fluoroquinolones especially if they are given quinolones with enhanced anti-gram-positive activity compared to ciprofloxacin.

Failure of two macrolide antibiotics to prevent post-extraction bacteraemia.

Two macrolide antibiotics, erythromycin and josamycin, were compared in a double-blind trial to examine their efficacy in the prevention of post-dental extraction bacteraemia in a group of healthy patients. An in vitro blood culture system was used. Isolates of streptococci were identified to species level. Minimum inhibitory concentrations (MICs) of erythromycin and of josamycin for each isolate were estimated by an agar dilution technique, with controls. Levels of drug in the serum of volunteers and of patients were assayed after oral doses of the macrolide antibiotics. Levels found achieved early peaks and satisfactory concentrations for activity against streptococci. Within the specified parameters, the results demonstrated that the antibiotics failed to prevent survival in blood culture of various strains of streptococci for up to 24 hours following collection of the blood. It is recommended that an alternative antibiotic to either erythromycin or to josamycin be used to achieve prophylaxis against streptococci in infective endocarditis risk patients who are allergic to penicillin.

Comparative efficacy of oral doses of clindamycin and erythromycin in the prevention of bacteraemia.

Two antibiotics, clindamycin and erythromycin, were compared in a double-blind trial to test their efficacy in the prevention of post-dental extraction bacteraemia with streptococci in a group of 40 healthy patients. Tolerance to the oral doses was tested by questionnaire. Levels of drug in the serum were estimated using a microbiological assay. An in-vitro blood culture system was used as an analogy of the persistence of a bacteraemia in the presence of high levels of antibiotic. Isolates of streptococci were identified to species level. Minimum inhibitory concentrations of clindamycin and of erythromycin for each isolate were estimated. Results showed satisfactory levels of antibiotics in the blood for activity against oral streptococci. Clindamycin was slightly more effective than erythromycin in the prevention of post-extraction streptococcal bacteraemia but that efficacy was only 45%. Clindamycin as a single oral dose of 600 mg was well tolerated by patients compared with erythromycin 1.5 g.

Comparison of macrolide antibiotics.

Macrolides have been in use since the early 1950s. In recent years new macrolides have been developed to try to overcome the problems associated with erythromycin. In general they have fairly similar in-vitro activity, although azithromycin has superior activity against Haemophilus influenzae and some Gram-negative organisms. Clarithromycin shows superior in-vitro activity against Legionella spp. and against the type strain of Chlamydia pneumoniae. The pharmacology of macrolides produces many interpretive problems, and macrolides show marked variation in their pharmacokinetic parameters, tissue affinity and intracellular penetration. Newer macrolides such as clarithromycin, roxithromycin, dirithromycin and azithromycin only need to be taken once or twice a day, which is likely to improve patient compliance. Few objective side-effect studies have been performed with the newer macrolides. Clinical efficacy studies are essential to elucidate the significance of the complex pharmacology of macrolides.

The prevention of antibiotic resistance during treatment.

Prevention of emergence of antibiotic resistance during treatment is an important goal when prescribing antimicrobials. Antibiotic resistant bacteria can emerge in three main ways--by acquisition of new genes via transposons or horizontal gene transfer, by selection of resistant variants and by selection of naturally resistant strains. In order to minimize emergence of antibiotic resistance during therapy it is important to try and avoid antibiotics which encourage the transfer of resistance genes, to avoid selection of resistant variants from susceptible pathogens and to avoid ablation of antibiotic susceptible normal flora. However, implementing these objectives is not always easy. This paper discusses possible ways of limiting the emergence of resistant bacteria during treatment. It does not consider how to prevent the spread of these strains from person to person. The prevalence of antibiotic-resistant bacteria depends upon the selection of antibiotic-resistant strains and spread of these strains from person to person. Prevention therefore consists of two parts--the prevention of acquisition of resistance/selection of antibiotic-resistant variants and interrupting the mechanisms by which person-to-person spread can occur. This paper considers only the first of these two influences on prevalence of resistance.

Mechanism of sulfonamide resistance in clinical isolates of Streptococcus pneumoniae.

The genetic basis of sulfonamide resistance in six clinical isolates of Streptococcus pneumoniae was demonstrated to be 3- or 6-bp duplications within sulA, the chromosomal gene encoding dihydropteroate synthase. The duplications all result in repetition of one or two amino acids in the region from Arg58 to Tyr63, close to but distinct from the sul-d mutation, a duplication previously reported in a resistant laboratory strain (P. Lopez, M. Espinosa, B. Greenberg, and S. A. Lacks, J. Bacteriol. 169:4320-4326, 1987). Six sulfonamide-susceptible clinical isolates lacked such duplications. The role of the duplications in conferring sulfonamide resistance was confirmed by transforming 319- or 322-bp PCR fragments into the chromosome of a susceptible recipient. Two members of a clone of serotype 9V, one susceptible and one resistant to sulfonamide, which are highly related by other criteria, were shown to have sulA sequences that differ in 7.2% of nucleotides in addition to the duplication responsible for resistance. It is postulated that horizontal gene exchange has been involved in the acquisition (or loss) of resistance within this clone. However, five of the six resistant isolates have distinct duplications and other sequence polymorphisms, suggesting that resistance has arisen independently on many occasions.

Multiple mutations modulate the function of dihydrofolate reductase in trimethoprim-resistant Streptococcus pneumoniae.

Trimethoprim resistance in Streptococcus pneumoniae can be conferred by a single amino acid substitution (I100-L) in dihydrofolate reductase (DHFR), but resistant clinical isolates usually carry multiple DHFR mutations. DHFR genes from five trimethoprim-resistant isolates from the United Kingdom were compared to susceptible isolates and used to transform a susceptible control strain (CP1015). All trimethoprim-resistant isolates and transformants contained the I100-L mutation. The properties of DHFRs from transformants with different combinations of mutations were compared. In a transformant with only the I100-L mutation (R12/T2) and a D92-A mutation also found in the DHFRs of susceptible isolates, the enzyme was much more resistant to trimethoprim inhibition (50% inhibitory concentration [IC50], 4.2 microM) than was the DHFR from strain CP1015 (IC50, 0.09 microM). However, Km values indicated a lower affinity for the enzyme's natural substrates (Km for dihydrofolate [DHF], 3.1 microM for CP1015 and 27.5 microM for R12/T2) and a twofold decrease in the specificity constant. In transformants with additional mutations in the C-terminal portion of the enzyme, Km values for DHF were reduced (9.2 to 15.2 microM), indicating compensation for the lower affinity generated by I100-L. Additional mutations in the N-terminal portion of the enzyme were associated with up to threefold-increased resistance to trimethoprim (IC50 of up to 13.7 microM). It is postulated that carriage of the mutation M53-I-which, like I100-L, corresponds to a trimethoprim binding site in the Escherichia coli DHFR-is responsible for this increase. This study demonstrates that although the I100-L mutation alone may give rise to trimethoprim resistance, additional mutations serve to enhance resistance and modulate the effects of existing mutations on the affinity of DHFR for its natural substrates.

Comparative in-vitro activity of azithromycin and erythromycin against Gram-positive cocci, Haemophilus influenzae and anaerobes.

The in-vitro activities of azithromycin and erythromycin were compared against 689 clinical isolates, including Gram-positive cocci, Haemophilus influenzae, and anaerobes. Of the 100 methicillin-susceptible isolates of Staphylococcus aureus tested, 77% were susceptible to 1 mg/l azithromycin and 0.5 mg/l erythromycin, whereas 22% were resistant to 32 mg/l of both compounds. All methicillin-resistant S. aureus isolates were highly resistant to both macrolides (MIC greater than 64 mg/l). Coagulase-negative staphylococci showed a wide range of susceptibilities to both compounds; MIC50 values for azithromycin and erythromycin for all isolates were 0.5 and 0.25 mg/l, respectively. With the exception of enterococci, both macrolides showed similar activity against streptococci; MIC90 values for both group A and group B streptococci were 0.03 and 0.06 mg/l for erythromycin and azithromycin, respectively. Azithromycin was less active than erythromycin against enterococci, with mode MICs of 4.0 and 1.0 mg/l, respectively; about 20% of isolates were highly resistant to both compounds. Azithromycin was substantially more active than erythromycin against H. influenzae; 41% of isolates were inhibited by 0.5 mg/l azithromycin and all isolates were inhibited by 2 mg/l. The MIC90 for erythromycin was 8 mg/l; 36% of isolates required concentrations of greater than or equal to 4 mg/l for inhibition. The anaerobic bacteria tested showed similar susceptibility to both azithromycin and erythromycin.

Successful treatment of concomitant pulmonary nocardiosis and aspergillosis in an immunocompromised renal patient.

A case is reported of rapid onset concomitant pulmonary infection with Nocardia and Aspergillus fumigatus in a patient six weeks after the institution of immunosuppressive therapy for renal vasculitis. Pulmonary lesions completely resolved on treatment with a combination of imipenem, cotrimoxazole and a prolonged course of itraconazole.

Comparative in-vitro activity of erythromycin, vancomycin and pristinamycin.

We have studied the in-vitro activity of erythromycin, vancomycin and pristinamycin against 1,006 clinical isolates comprising streptococci, staphylococci, Neisseria gonorrhoeae, Haemophilus influenzae and anaerobes. In-vitro studies show pristinamycin to inhibit staphylococci and streptococci, including erythromycin highly-resistant organisms, at a concentration of less than or equal to 0.78 mg/l. Although pristinamycin's mean MIC for streptococci is higher than that of erythromycin, pristinamycin is bactericidal, whereas erythromycin is bacteristatic against Streptococcus agalactiae and oral streptococci. Enterococci were less uniformly susceptible to pristinamycin: 58 of the 94 Enterococcus faecalis tested were resistant (MIC greater than or equal to 3.12 mg/l). 14 of the 15 isolates of Enterococcus faecium were inhibited by less than or equal to 1.56 mg/l pristinamycin. Pristinamycin showed poor activity against Haemophilus influenzae (mode MIC 1.56 and MIC90 of 3.12 mg/l) but all except two of the 100 Neisseria gonorrhoeae tested were inhibited by less than or equal to 0.78 mg/l pristinamycin. Pristinamycin inhibited all nine Clostridium spp. at less than or equal to 0.39 mg/l and 38 of 40 strains of anaerobic gram-positive cocci at less than or equal to 0.78 mg/l. It was less effective against the Bacteroides fragilis group: (MIC90 3.12 mg/l). Pristinamycin had poor bactericidal activity against the anaerobes tested.

The in-vitro activity of trovafloxacin, a new fluoroquinolone, against Gram-positive bacteria.

The in-vitro activity of trovafloxacin, a new quinolone, was compared with that of ciprofloxacin, erythromycin, various beta-lactam antibiotics and, where appropriate, clindamycin and vancomycin against a range of Gram-positive bacteria including staphylococci (n = 201), Streptococcus pneumoniae (n = 83), beta-haemolytic streptococci (n = 46), viridans group streptococci (n = 100), Streptococcus milleri (n = 18) and enterococci (n = 161) by an agar dilution technique. In addition, time-kill studies were performed to estimate the bactericidal activity of trovafloxacin against S. milleri and viridans group streptococci. Trovafloxacin was the most active agent tested against staphylococci. It also showed good activity, at least four-fold and usually eight- to 16-fold that of ciprofloxacin, against all the streptococci. Trovafloxacin showed good activity against vancomycin-sensitive Enterococcus faecalis and Enterococcus faecium, but was less active against the 11 isolates of vancomycin-resistant enterococci. Trovafloxacin showed comparable or superior bactericidal activity to amoxycillin against the S. milleri and viridans group streptococci tested.

Comparative in-vitro activity of CP-99219, a new quinolone, against respiratory pathogens.

The comparative in-vitro activity of CP-99219, a new quinolone, against Haemophilus influenzae (150 isolates), Moraxella catarrhalis (100), Streptococcus pneumoniae (80) and Group A beta-haemolytic streptococci (40) was determined using an agar dilution technique. CP-99219 was the most active compound tested against M. catarrhalis (MIC50 = 0.015 mg/L, MIC90 = 0.03 mg/L). Ceftriaxone, CP-99219 and ciprofloxacin were the three most active agents tested against H.influenzae. CP-99219 showed good activity, 16-fold greater than that of ciprofloxacin, against S.pneumoniae (MIC50 = 0.12 mg/L; MIC90 = 0.25 mg/L) and was also active against Group A streptococci. Clinical studies regarding the use of CP-99219 in respiratory tract infections seem indicated.

Comparative pharmacokinetic study between lenampicillin, bacampicillin and amoxycillin.

A cross-over study was performed comparing serum kinetics and urinary excretion in six healthy, fasting volunteers after ingestion of comparable amounts of lenampicillin, bacampicillin and amoxycillin. Venous blood samples and urine samples were taken at intervals for 6 and 12 h respectively post-tablet ingestion and assayed for free ampicillin or amoxycillin concentration with Bacillus subtilis as indicator organism. The most rapid Tmax and the highest Cmax were achieved with lenampicillin. The AUC was similar for lenampicillin, bacampicillin and amoxycillin as was the total percentage urinary recovery of antibiotic. Potential pharmacokinetic advantage of orally administered lenampicillin and bacampicillin compared to comparable doses of amoxycillin are higher peak serum concentrations (12.0 mg/l lenampicillin; 9.7 mg/l bacampicillin; 7.6 mg/l amoxycillin) and more rapid time to peak concentration (0.6 h lenampicillin; 0.7 h bacampicillin and 1.4 h amoxycillin).