A virulent nosocomial Klebsiella with a transferable R factor for gentamicin: emergence and suppression

Overcoming Aminoglycoside Enzymatic Resistance: Design of Novel Antibiotics and Inhibitors

Resistance to aminoglycoside antibiotics has had a profound impact on clinical practice. Despite their powerful bactericidal activity, aminoglycosides were one of the first groups of antibiotics to meet the challenge of resistance. The most prevalent source of clinically relevant resistance against these therapeutics is conferred by the enzymatic modification of the antibiotic. Therefore, a deeper knowledge of the aminoglycoside-modifying enzymes and their interactions with the antibiotics and solvent is of paramount importance in order to facilitate the design of more effective and potent inhibitors and/or novel semisynthetic aminoglycosides that are not susceptible to modifying enzymes.

Bloodstream infections caused by carbapenemase-producing Klebsiella pneumoniae: a clinical perspective

Dissemination of carbapenemase-producing Klebsiella pneumoniae (CP-Kp) has caused a public health crisis that can be paralleled with that caused by the spread of MRSA. CP-Kps, being multidrug-resistant, mainly affect patients with severe underlying conditions in the acute-healthcare setting. CP-Kps are responsible for a variety of life-threatening infections including bacteremia and pneumonia. The shortage of therapeutic options has forced clinicians to use colistin as well as tigecycline, a novel bacteriostatic agent. Although both drugs are generally active in vitro against CP-Kps, therapeutic failures, especially in bacteremias, are quite common. The authors suggest here, after reviewing the literature, that use of the latter drugs should be re-assessed and optimized. The authors have also summarized experimental and clinical data indicating that exploitation of the pharmacokinetic/pharmacodynamic features of carbapenems may provide solutions in bloodstream infections caused by CP-Kps with low-level resistance to the latter drugs. Most importantly, there is evidence that monotherapy must be avoided.

Development of immunization trials against Klebsiella pneumoniae

Klebsiella pneumoniae is the most common cause of nosocomial respiratory tract and premature intensive care infections, and the second most frequent cause of Gram-negative bacteraemia and urinary tract infections. Drug resistant isolates remain an important hospital-acquired bacterial pathogen, add significantly to hospital stays, and are especially problematic in high impact medical areas such as intensive care units. Many investigations worldwide proved the increasing resistance of such pathogen, resulting in an average rate of 1.63 outbreak every year. A variety of preventive measures were applied to reduce such incidences. Immunotherapy and passive immunization researches as well found their way to the treatment of Klebsiella. During the last 40 years, many trials for constructing effective vaccines were followed. This up-to-date review classifies such trials and documents them in a progressive way. A following comment discusses each group benefits and defects.

Gentamicin-adenylyltransferase activity as a cause of gentamicin resistance in clinical isolates of Pseudomonas aeruginosa

Gentamicin adenylyltransferase activity was found in extracts of clinical isolates of gentamicin-resistant Pseudomonas aeruginosa. Extracts of one of these isolates, P. aeruginosa POW, inactivated gentamicin in the presence of adenosine 5'-triphosphate. Extracts of strain POW catalyzed the binding of radioactivity from [(14)C]adenine adenosine 5'-triphosphate to gentamicin components, tobramycin, sisomicin, kanamycin A and B and, to a variable degree, streptomycin and spectinomycin. The substrate profile with these agents and other aminocyclitols was similar to that obtained with R factor-mediated gentamicin adenylyltransferase found in Enterobacteriaceae. Adenylylating activity was absent in gentamicin-susceptible mutants of strain POW. Adenylylation may be added to acetylation as an enzymatic mechanism responsible for gentamicin resistance among strains of P. aeruginosa.

Klebsiella spp. as nosocomial pathogens: epidemiology, taxonomy, typing methods, and pathogenicity factors

Bacteria belonging to the genus Klebsiella frequently cause human nosocomial infections. In particular, the medically most important Klebsiella species, Klebsiella pneumoniae, accounts for a significant proportion of hospital-acquired urinary tract infections, pneumonia, septicemias, and soft tissue infections. The principal pathogenic reservoirs for transmission of Klebsiella are the gastrointestinal tract and the hands of hospital personnel. Because of their ability to spread rapidly in the hospital environment, these bacteria tend to cause nosocomial outbreaks. Hospital outbreaks of multidrug-resistant Klebsiella spp., especially those in neonatal wards, are often caused by new types of strains, the so-called extended-spectrum-beta-lactamase (ESBL) producers. The incidence of ESBL-producing strains among clinical Klebsiella isolates has been steadily increasing over the past years. The resulting limitations on the therapeutic options demand new measures for the management of Klebsiella hospital infections. While the different typing methods are useful epidemiological tools for infection control, recent findings about Klebsiella virulence factors have provided new insights into the pathogenic strategies of these bacteria. Klebsiella pathogenicity factors such as capsules or lipopolysaccharides are presently considered to be promising candidates for vaccination efforts that may serve as immunological infection control measures.

Epidemiology and successful control of a large outbreak due to Klebsiella pneumoniae producing extended-spectrum beta-lactamases

An outbreak due to extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) was detected from May 1993 to June 1995. A total of 145 patients, particularly patients in intensive care units (ICUs) (107 patients [72%]), were colonized or infected. Infection developed in 92 (63%) patients, and primary bacteremia caused by ESBL-KP was the most frequent infection (40 of 92 patients [43%]). A single clone of ESBL-KP was identified by pulsed-field gel electrophoresis analysis throughout the whole period, and no molecular epidemiological relationship could be found between the epidemic strain and non-ESBL-KP isolates. To determine risk factors for ESBL-KP infection weekly rectal swabs were obtained in three serial incidence surveys (470 patients); the probabilities of carriage of ESBL-KP in the digestive tract were 33% (October and November 1993), 40% (May and June 1994), and 0% (October and November 1995) at 10 days of ICU admission. A logistic regression model identified prior carriage of ESBL-KP in the digestive tract (odds ratio, 3.4; 95% confidence interval 1.1 to 10.4) as an independent variable associated with ESBL-KP infection. A statistically significant correlation was observed between the restricted use of oxyimino-beta-lactams (189 defined daily doses [DDD]/ 1,000 patient-days to 24 DDD/1,000 patient-days) and the trends of ESBL-KP infection (r = 0.7; P = 0.03).

Bacterial resistance to aminoglycoside antibiotics

The aminoglycoside antibiotics are broad-spectrum antibacterial compounds that are used extensively for the treatment of many bacterial infections. In view of the current concerns over the global rise in antibiotic-resistant microorganisms, there has been renewed interest in the mechanisms of resistance to the aminoglycosides, including the superfamily of aminoglycoside-modifying enzymes.

The epidemiology of nosocomial infections caused by Klebsiella pneumoniae

Klebsiella pneumoniae causes serious epidemic and endemic nosocomial infections. We conducted a literature review to characterize the epidemiology of epidemic K. pneumoniae outbreaks. Eighty percent of the outbreaks (20/25) involved infections of the bloodstream or urinary tract. Person-to-person spread was the most common mode of transmission, and nearly 50% of the outbreaks occurred in neonatal intensive care units. No one serotype predominated, and no association was found between serotype and either the site of infection or antimicrobial susceptibility pattern. We used data reported to the Centers for Disease Control (CDC) by hospitals participating in the National Nosocomial Infections Study (NNIS) to describe the epidemiology of endemic K. pneumoniae infections. In the 8-year period from 1975 through 1982 the nosocomial K. pneumoniae infection rate was 16.7 infections per 10,000 patients discharged. The rate of infection at medical school-affiliated hospitals was significantly greater than at nonaffiliated hospitals; furthermore, the rate of infection at large affiliated hospitals was greater than at small affiliated hospitals. The rate of infection varied by service, with the highest rate found on the medicine service. During the 8-year period, 184 deaths were caused by nosocomial K. pneumoniae infections (184 deaths/16,969 infections, case-fatality ratio 1.1%), with higher ratios in pediatrics (5%) where there was a 12% mortality in children infected with an aminoglycoside-resistant strain.

Klebsiella neonatal injections: mechanism of broadening aminoglycoside resistance

Kanamycin resistance in eight strains of Klebsiella pneumoniae isolated during an outbreak of infection in a neonatal intensive care unit was found to be transferable and mediated by neomycin phosphotransferase. After gentamicin was used to control infections caused by kanamycin-resistant organisms, a strain resistant to gentamicin emerged. Gentamicin resistance in this ninth strain was not transferable and was accompanied by resistance to tobramycin, amikacin, and streptomycin. Enzymatic modifications of aminoglycosides other than neomycin and kanamycin could not be demonstrated either by filter binding assays or by electrophoresis of a radioactive aminoglycoside substrate. The strain with broad aminoglycoside resistance contained six plasmid deoxyribonucleic acid bands, none of which appeared to be different in molecular weight from plasmid deoxyribonucleic acid bands in strains isolated before the institution of gentamicin therapy. The broadening of resistance was accompanied by reduced uptake of radioactively labeled streptomycin and gentamicin. The relationship between aminoglycoside resistance and reduced drug transport in the absence of any enzymatic modification is discussed.

Plasmid-determined resistance to fosfomycin in Serratia marcescens

Multiple-antibiotic-resistant strains of Serratia marcescens isolated from hospitalized patients were examined for their ability to transfer antibiotic resistance to Escherichia coli by conjugation. Two different patterns of linked transferable resistance were found among the transconjugants. The first comprised resistance to carbenicillin, streptomycin, and fosfomycin; the second, and more common, pattern included resistance to carbenicillin, streptomycin, kanamycin, gentamicin, tetracycline, chloramphenicol, sulfonamide, and fosfomycin. The two types of transconjugant strains carried a single plasmid of either 57 or 97 megadaltons in size. Both of these plasmids are present in parental S. marcescens strains resistant to fosfomycin. The 57-megadalton plasmid was transformed into E. coli.

A transposon, Tn732, encoding gentamicin/tobramycin resistance

Gentamicin and tobramycin are important antibiotics in the treatment of hospital infections because of their activity against a wide range of bacterial genera. With their increasing use, bacteria resistant to these drugs have appeared, the resistance being frequently plasmid determined. The resistance genes determine various enzymes that modify and inactivate the drugs and there is association between particular gentamicin/tobramycin resistance genes and plasmids of particular groups, implying that acquisition of such a gene by any plasmid is a rare event. We now report the identification of a transposon or 'jumping gene' encoding the gentamicin/tobramycin adenylylating enzyme, ANT(2"), on a plasmid of incompatiblity group FII (IncFII).

An investigation into the incidence and sources of klebsiella infections in hospital patients

Coliforms isolated from infections over a period of 22 months were examined and 16% were shown to be klebsiellas. The biochemical reactions and serotypes of these klebsiellas were determined and the relationship between species, serotype and type of infection investigated. Although no obvious outbreaks of infection occurred during this period a number of clusters of isolations of the same serotype of klebsiella were found. Using an enrichment method for the isolation of klebsiellas from faeces, sero and bacteriocin typing, and the examination of ten colonies, it was demonstrated that half of the patients carried a klebsiella of the same type in the bowel as caused the infection.

Nosocomial klebsiellas. I. Colonization of hospitalized patients

The colonization of patients by Klebsiella and several other gram-negative bacteria was studied in a hospital urological ward over a period of six months. Before and during the survey there was no evidence of an outbreak of nosocomial infection and multi-drug resistant strains of Klebsiella were not isolated. Klebsiella were biotyped by nine biochemical tests, which led to the detection of 66 biotypes spread uniformly throughout the survey period. This method of biotyping proved a useful epidemiological tool. The colonization rate of throats, hands, and faeces of patients increased after admission to the ward, especially when antibiotics were used. The effect of systemic antibiotics was greater than that of urinary antibiotics especially on throat and faeces carrier rates. Carrier rates for Klebsiella increased also after catheterization and operation--relationships which could well be multifactorial. During the first two weeks after admission the proportion of antibiotic resistant strains of Klebsiella in carriers increased. The proportion of resistant strains amongst isolations from clinical infections was always greater than among strains isolated routinely from sites of carriage.

Epidemiological patterns of Klebsiella colonization and infection in an intensive care ward

Twenty-four per cent of 2315 patients admitted to the intensive care unit of St Thomas's Hospital in the 4 year period from November 1969 became colonized or infected with Klebsiella species. Capsular typing of 986 klebsiella isolates from 551 patients showed that there were 695 patient-isolates, mostly derived from the respiratory tract. Capsular types 47 and 21 were the commonest types and together accounted for 19.9% of the patient-isolates. The 14 commonest types accounted for 47.3% of all patient-isolates and all these strains showed clustering, strongly suggesting a changing common source, cross infection, or both.

Treatment of hospita-acquired infections with amikacin

Amikacin was used in the treatment of 56 serious gram-negative infections in 54 patients of whom 47 survived. In six of the seven nonsurvivors, the infections were under control at the time of death. The clinical isolates were multiple drug-resistant gram-negative organisms, with Proteus rettgeri being most common. Forty-five (80%) of these infections were nosocomial in origin, and the genitourinary tract was the source in 39 (70%). Complications directly related to amikacin therapy were few and suggested renal or otologic toxicity. In this series of patients, amikacin appeared to be of therapeutic benefit in the treatment of serious gram-negative infections.

In vitro activity of netilmicin compared with gentamicin, tobramycin, amikacin, and kanamycin

The in vitro activity of netilmicin was compared with that of gentamicin, tobramycin, amikacin, and kanamycin against 636 strains of bacteria recently isolated from clinical sources. Gentamicin was the most active antibiotic, but netilmicin and tobramycin closely paralleled it. Netilmicin was generally four-to eightfold less active than gentamicin against Serratia and group A streptococci, and was twofold less active against Pseudomonas aeruginosa. When effects of inoculum size and concentration of divalent cations in the media were evaluated, netilmicin was shown to be similar to gentamicin in vitro. Minimum inhibitory concentrations for P. aeruginosa were increased as much as 18-fold when the Mg(2+) and Ca(2+) concentrations were increased to physiological levels in Mueller-Hinton broth.

Emergence of gentamicin-resistant Klebsiella in a general hospital

Gentamicin had been in use in a general hospital for over 7 years before any gentamicin-resistant Klebsiella were observed. In 1974 and 1975, nine different gentamicin-resistant serobiotypes of Klebsiella were isolated from 35 patients. The first strain to appear had R-factor-mediated gentamicin resistance, and it infected 19 patients during a period of almost 2 years, spreading largely by case-to-case infection in patients with urinary catheters. It appeared to lose the capacity to transfer its gentamicin resistance after it had infected five of the patients. We had previously isolated on the same ward a gentamicin-susceptible Klebsiella of identical type, and it was found to be capable of acquiring an R-factor for gentamicin resistance. All of the other types of gentamicin-resistant Klebsiella infected few patients and did not persist in the hospital; four of them had R-factor-mediated resistance to gentamicin and all four, as did the original strain, cotransferred kanamycin, neomycin, and tobramycin resistance. Every gentamicin-resistant Klebsiella was susceptible to amikacin and netilmicin.

The emergence of gentamicin-resistant klebsiellae in a large general hospital

Between March and December, 1975, an outbreak of infection with gentamicin-resistant Klebsiella pneumoniae (klebsiella (Gmr)) occurred at the Royal Melbourne Hospital. The klebsiellae were considered to be causing significant infection in 24 of 42 patients harbouring the microorganism. Commonest culture sources were urine and sputum, all but one of the significant urinary infections being associated with indwelling bladder catheters. Antibiotic therapy had been given to 40 patients before the isolation of klebsiella (Gmr), and of these 22 had received gentamicin. Cross infection was a major factor in the outbreak, and control measures (to limit this aspect and curtail the usage of gentamicin) have prevented wider spread within the hospital; at the time of writing the microorganism had been eradicated from all but one of the infected patients. It was shown that klebsiella (Gmr) carry an R-factor capable of transferring gentamicin resistance. Of 22 isolates tested quantitatively, 20 were resistant to 10 mug/ml of gentamicin.

In vitro studies with netilmicin compared with amikacin, gentamicin, and tobramycin

Netilmicin, a new semisynthetic aminoglycoside derived by ethylation of the 1-N position of the deoxystreptamine ring of sisomicin, was tested in vitro with 4,070 strains of gram-negative bacilli isolated at the UCLA Medical Center during 1975 to 1976, using the agar dilution technique and an inoculum of approximately 10(4) organisms. Results were compared with those simultaneously obtained for amikacin, gentamicin, and tobramycin. Using Mueller-Hinton medium, inhibitory concentrations in broth correlated with those obtained by the agar dilution method except for Pseudomonas aeruginosa, where a 2- to 16-fold difference in susceptibility was noted. For most clinically significant Enterobacteriaceae and P. aeruginosa, the activity of netilmicin in vitro was comparable or superior to that of gentamicin, tobramycin, and amikacin with respect to potency by weight and achievable blood levels. Against gentamicin-resistant strains (MIC > 16 mug/ml), the activity of netilmicin paralleled that of amikacin with the exception of Providencia stuartii, which was inhibited by amikacin but not by netilmicin.

A new serotyping method for Klebsiella species: development of the technique

A new serotyping method for Klebsiella species using indirect immunofluorescence is described. Nonspecific fluorescence has been minimized by carrying out the capsular antigen-antibody reaction at pH 9.0. Commercial antisera have been tested with the 72 antigenic types of Klebsiella, and appropriate dilutions of each pool and specific antisera have been proposed for use in routine typing. Dilutions were chosen to allow strong fluorescence with each type and its specific antiserum and minimal fluorescence with cross reacting antisera. Where the pool antisera gave a weak reaction for one or more of the component types, it is recommended that the specific antisera for these types be added to the pool dilution. The few remaining cross reactions, with the pool and specific antisera in test dilution, are listed in a table. The unique cross reacting patterns of particular types have been found to be useful in identification. Typing Klebsiella by the fluorescent antibody technique is easy to perform and interpret; the results are reproducible, and it is less expensive than the existing capsular swelling method as it is more sensitive and requires less concentrated antisera. This new method of typing should facilitate detailed epidemiological studies of the mode of transmission of Klebsiella species in hospitals and thus allow more effective infection control measures to be instituted.

In vitro activity, synergism, and testing parameters of amikacin, with comparisons to other aminoglycoside antibiotics

The activity of the new aminoglycoside antibiotic, amikacin, was evaluated in vitro against 219 clinical bacterial isolates. One hundred eighty-nine of the 219 strains had agar dilution minimal inhibitory concentration values of 8.0 mug/ml or less for amikacin. Comparative agar dilution studies were performed for gentamicin, kanamycin, and tobramycin. Gentamicin was the most active overall, but tobramycin and amikacin also had significant activity against most bacterial groups. The effects of divalent cations on the susceptibility of Pseudomonas aeruginosa to amikacin were evaluated, and the minimal inhibitory concentration values varied sixfold over a range of divalent cation concentrations from 0.2 to 8.75 mg%. The effects of media and inoculum size on disk susceptibility testing with amikacin were also evaluated. In addition, a synergistic interaction between carbenicillin and amikacin against P. aeruginosa was demonstrated. Amikacin appears to be a promising new broad spectrum antimicrobial agent.

R factors in gentamicin-resistant organisms causing hospital infection

An abrupt increase in gentamicin-resistant isolates was noted in the Manhattan Veterans Administration Hospital in 1973 and 1974. Bacteraemic infection occurred in 17 patients, 9 of whom died. R factors mediating gentamicin resistance were demonstrated in 34 of 36 strains. Organisms from 9 of 11 patients transferred a resistance pattern common to all other isolates from that patient, suggesting in-vivo interbacterial spread of the R factor.

Infection caused by Proteus mirabilis strains with transferrable gentamicin-resistance factors

During a period of 10 weeks, four patients in one hospital became infected with gentamicin-resistant Proteus mirabilis. In two of them septicaemia associated with indwelling catheters developed, one had urinary tract and wound infections, and in the fourth patient the organism was isolated from a superficial wound. The P. mirabilis strains showed multiple drug resistance. Strains form the first three patients were apparently identical and were sensitive to tobramycin. Their gentamicin resistance was not transferable to Escherichia coli K12, but could be transferred to another strain of P. mirablilis (PM13-3). The fourth strain was resistant to tobramycin; its gentamicin/tobramycin resistance was transferable to E. coli K12.

Activity of three aminoglycosides and two penicillins against four species of gram-negative bacilli

Three aminoglycoside antibiotics and two penicillins were compared for their in vitro activity against 60 isolates of Serratia, Pseudomonas, Proteus mirabilis, and indole-positive Proteus sp. Testing was done by the agar dilution method using Mueller-Hinton broth solidified with 1.5% agar. The activity of amikacin, aminodeoxybutirosin, and gentamicin against Proteus and Pseudomonas, as related to their peak blood levels, showed no significant differences. Amikacin was the most active against Serratia marcescens. Results using Mueller-Hinton media in broth dilution tests correlated with the agar dilution method except for Pseudomonas aeruginosa. The minimal inhibitory concentration for aminoglycosides in agar was considerably greater than the minimal inhibitory concentration in Mueller-Hinton broth, and the disparity was related to the higher divalent cation concentration of agar. BL-P1654 and carbenicillin were similar except that carbenicillin was much more active against indole-positive Proteus sp. Additionally, the ratio of bactericidal to bacteriostatic concentrations of BL-P1654 was considerably greater than for carbenicillin.

Activity of five aminoglycoside antibiotics in vitro against gram-negative bacilli and Staphylococcus aureus

The in vitro susceptibility to BB-K8, butirosin, gentamicin, sisomicin, and tobramycin of seven groups of clinically significant gram-negative bacilli and Staphylococcus aureus was assessed by using the International Collaborative Study-World Health Organization criteria. The activity of gentamicin, sisomicin, and tobramycin generally paralleled each other. Sisomicin was the most potent compound by weight and usually demonstrated the most rapid rate of killing. BB-K8 and butirosin were less potent, but higher serum levels may be achieved with these agents. BB-K8 generally showed the greatest ratio between achieveable mean peak serum levels and concentrations needed to inhibit [Formula: see text] of each group of organisms tested. Additionally, BB-K8 was active against six of seven highly gentamicin-resistant strains. All of these antibiotics showed diminished activity at pH 6.4 but only gentamicin and sisomicin showed occasionally enhanced activity at pH 8.4.