Gram-negative bacilli in burns

The Characteristic of Virulence, Biofilm and Antibiotic Resistance of Klebsiella pneumoniae

Klebsiella pneumoniae is an important gram-negative opportunistic pathogen that causes a variety of infectious diseases, including urinary tract infections, bacteremia, pneumonia, and liver abscesses. With the emergence of multidrug-resistant (MDR) and hypervirulent K. pneumoniae (hvKP) strains, the rapid spread of these clinical strains in geography is particularly worrying. However, the detailed mechanisms of virulence and antibiotic resistance in K. pneumoniae are still not very clear. Therefore, studying and elucidating the pathogenic mechanisms and drug resistance mechanism of K. pneumoniae infection are important parts of current medical research. In this paper, we systematically summarized the virulence, biofilm, and antibiotic tolerance mechanisms of K. pneumoniae, and explored the application of whole genome sequencing and global proteomics, which will provide new clues for clinical treatment of K. pneumoniae.

Klebsiella pneumoniae: a major worldwide source and shuttle for antibiotic resistance

Klebsiella pneumoniae is an important multidrug-resistant (MDR) pathogen affecting humans and a major source for hospital infections associated with high morbidity and mortality due to limited treatment options. We summarize the wide resistome of this pathogen, which encompasses plentiful chromosomal and plasmid-encoded antibiotic resistance genes (ARGs). Under antibiotic selective pressure, K. pneumoniae continuously accumulates ARGs, by de novo mutations, and via acquisition of plasmids and transferable genetic elements, leading to extremely drug resistant (XDR) strains harboring a 'super resistome'. In the last two decades, numerous high-risk (HiR) MDR and XDR K. pneumoniae sequence types have emerged showing superior ability to cause multicontinent outbreaks, and continuous global dissemination. The data highlight the complex evolution of MDR and XDR K. pneumoniae, involving transfer and spread of ARGs, and epidemic plasmids in highly disseminating successful clones. With the worldwide catastrophe of antibiotic resistance and the urgent need to identify the main pathogens that pose a threat on the future of infectious diseases, further studies are warranted to determine the epidemic traits and plasmid acquisition in K. pneumoniae. There is a need for future genomic and translational studies to decipher specific targets in HiR clones to design targeted prevention and treatment.

The epidemiology of burn wound infections: then and now

Burn wound infections are a serious complication of thermal injury. Although pneumonia is now the most important infection in patients with burns, burn wound infection remains a serious complication unique to the burn recipient. The methods for managing thermal injury have evolved during the past 50 years. This evolution has been accompanied by changes in the etiology, epidemiology, and approach to prevention of burn wound infections. In the 1950s, 1960s, and 1970s and into the mid-1980s, burn wounds were treated by the exposure method, with application of topical antimicrobials to the burn wound surface and gradual debridement with immersion hydrotherapy. As early burn wound excision and wound closure became the focal point of burn wound management, accompanied by a change from immersion hydrotherapy to showering hydrotherapy, the rate of burn wound infection appeared to decrease. Few epidemiologic studies have been done since this change in the approach to management of thermal injury. There are few data on the epidemiology of burn wound infections from the era of early excision and closure. Data are needed on infection rates for excised and closed burn wounds, the etiologies of these infections, and the epidemiology and the prevention of such infections. Additional studies are needed on the indications for topical and antimicrobial prophylaxis and selective decontamination of the digestive tract.

Immunoprotective extracellular polysaccharides of Klebsiella aerogenes capsular type K1, expressed in Escherichia coli

A gene library of genomic DNA Klebsiella aerogenes of capsular serotype K1 was constructed in E. coli LE392 using the cosmid pMMB33. Culture filtrates of E. coli recombinants were screened by ELISA for extracellular polysaccharides specific for K. aerogenes K1. Extracellular polysaccharide extracts from K. aerogenes K1 and 3% of the E. coli recombinants contained immunoprotective extracellular polysaccharides (IEP) with similar chemical and immunological properties as shown by gel filtration through Sephacryl 1000, double immunodiffusion and mouse protection tests. IEPs contained no detectable protein, had molecular weights of several hundred million and protected mice against lethal autologous K. aerogenes K1 challenge at a dosage of 10 nanograms per mouse.

Combined use of topical cyclosporin A and silver sulphadiazine on allografts infected with Pseudomonas in burned rats

In this study, we investigated the effects of a combination of topical Cyclosporin A (CyA) and silver sulphadiazine on infected and normal skin allografts in burned and unburned rats. Buffalo (Buf) allografts on unburned Lewis (Lew) recipients survived 16.8 +/- 0.9 days after a 10-day course of topical CyA and silver sulphadiazine, as compared to 7.4 +/- 1.1 days for untreated allografts and 18.6 +/- 0.9 days for those receiving CyA only for 10 days. Allografts infected with Pseudomonas aeruginosa and placed on burned recipients survived significantly longer (13.7 +/- 1.1 days) when treated with silver sulphadiazine and topical CyA for 7 days compared to a similar group of animals treated with silver sulphadiazine alone (8.4 +/- 1.0 days). The mortality rate for burned, infected and allografted animals receiving no medication or topical CyA was 50 per cent compared with zero in animals treated with silver sulphadiazine only or combined silver sulphadiazine and topical CyA.

Passive immunization of mice against Klebsiella aerogenes

Klebsiella vaccines were isolated by mild diafiltration techniques from culture filtrates of nine capsular types of K. aerogenes (K1, K2, K3, K15, K20, K35, K36, K44 & K63). The bacteria were grown in a chemically defined medium in standardized conditions in a fermenter. The vaccines had a molecular weight of more than 20 000, a carbohydrate content of 40-89%, a protein content of between less than 1 and 16% and small amounts (0.6-1.2%) of lipopolysaccharide. Antisera raised in rabbits to the nine klebsiella vaccines were standardized by passive haemagglutination, immunoglobulin G enzyme-linked immunosorbent assay and by autologous passive protection tests. Each rabbit antiserum when passively transferred to mice showed a variable capacity to passively protect mice against lethal infections by a panel of ten capsular types of K. aerogenes (K1-K10). Seven of the rabbit antisera protected mice against more than half of the challenge strains. A pool of six rabbit antisera (anti-K1, K2, K3, K20, K35 & K44) passively protected mice against lethal infections from strains of bacteria representing each of 77 capsular types of K. aerogenes.

Vaccination against Klebsiella aerogenes

Klebsiella vaccine was prepared from strains of Klebsiella aerogenes with capsular types K1, K36, K44 and K Cross (a type which cross-reacts in vitro with sera from many klebsiella capsular types). The vaccine was extracted by dialysis and ultrafiltration from capsular material released during growth of the bacteria in a five-day batch culture. Mice given one dose of vaccine from K1a (1.0 microgram/mouse) survived lethal intraperitoneal challenge of 11/11 homologous klebsiella strains four days after vaccination; 14 days after vaccination protection against the same challenge strains had declined to 5/11 strains. Vaccines from K1a, b, c, K36, K44 and K Cross induced homologous protection and protected mice against different ranges of heterologous klebsiella capsular types. The protective response of the mice was greatly enhanced by administering three doses of the vaccines. Vaccines from K1, K36, K44 and K Cross protected mice against 14/20, 11/20, 10/20 and 9/20 homologous and heterologous klebsiella challenge strains respectively. None of the klebsiella vaccines was toxic for mice at the immunizing dose (1.0 microgram/mouse). Vaccine from K36 was the most lethal, killing mice at 10(3) immunizing doses. The least toxic vaccine was from K44, which killed mice at 10(4) immunizing doses.

Active and passive immunization against Pseudomonas aeruginosa infection of burned patients

A 16-part polyvalent pseudomonas vaccine, PEV-01 and an immunoglobulin prepared from plasma from human volunteers vaccinated with PEV-01 were tested in a controlled clinical trial in burned patients at Safdarjang hospital, New Delhi. The mortality of the burned patients was reduced four-fold in adults and three-fold in children by the immunological treatments. Both immunoglobulin and vaccine increased the concentration of protective antibody. Patients responded to all 16 components in PEV-01. The vaccine caused no toxic side-effects and enhanced the bactericidal activity of polymorphonuclear leucocytes against Pseudomonas aeruginosa.

Changing patterns of Pseudomonas aeruginosa antibiotic sensitivity

Using a sample of 71 Pseudomonas aeruginosa infected burns patients admitted to the Burns Injury Unit of the Royal Brisbane Hospital within an 11-year period the pattern of sensitivity of the organism to 18 antibiotics was studied longitudinally looking at first and last cultures (either pus, blood or sputum) separately. Only 5 antibiotics reflected a significant change (towards resistance) in sensitivity patterns (chloramphenicol, gentamycin, kanamycin, tetracycline, achromycin). Six of the other 13 antibiotics showed a trend towards increasing resistance but the changes were not statistically significant (polymyxin B, carbenicillin, sulphanomides, cotrimoxazole, streptomycin, teramycin). The other 7 antibiotics showed no change, all but one (colistin) being resistant throughout.

Controlled trials of a polyvalent pseudomonas vaccine in burns

A polyvalent pseudomonas vaccine has been tested in controlled clinical trials at two burns units, in Birmingham and New Delhi, in children and adults with burns more than 15% full skin thickness. None of the vaccinated patients in either trial showed blood cultures containing Pseudomonas aeruginosa, and vaccinees showed raised titres of protective antibody and increased phagocytic activity against Ps. aeruginosa. In the New Delhi unit, where death from Ps. aeruginosa infection is common, the mortality in adults was reduced from 40.6% (13/32) in the unvaccinated group to 6.6% (2/30) in the vaccinated group, and in children from 20.8% (5/24) in the unvaccinated group to 4.8% (1/21) in the vaccinated group.

Measurement of endotoxins with the limulus test in burned patients

High titres of endotoxin as measured by the Limulus test were usually found in burned patients who had raised body temperatures, and were colonized with gram-negative bacteria; also some infected patients showed raised endotoxin without a raised temperature. Patients vaccinated with an antipseudomonas vaccine rarely showed endotoxin in their plasma but occasional plasma samples from vaccinated patients had a high titre of endotoxin which appeared unrelated to infection or to a raised temperature in the patient.

Antibody responses of burned patients immunized with a polyvalent Pseudomonas vaccine

In two controlled clinical trials of a polyvalent pseudomonas vaccine, vaccinated burned patients showed higher antibody titres to the 16 antigens in the vaccine and higher titres of a passively transferable protective antibody than was found in unvaccinated burned patients.

The NBT test in burned patients

The number of polymorphs which stained with the dye nitro-blue tetrazolium (NBT "Positive") increased sharply during the first week after burning, reaching levels 4--5 times above values for healthy volunteers. In burns of more than 20% of the body surface a second, smaller increase in the number of NBT "positives" occurred 4 to 6 weeks after burning. The high levels of NBT "positive" polymorphs occurred independently of infection on the burns. A burned patient who died from septicaemia had very low numbers of NBT "positive" polymorphs for 3 weeks before death.

Decline of the hospital Staphylococcus? Incidence of multiresistant Staph. aureus in three Birmingham hospitals

The prevalance of antibiotic-resistant strains of Staphylococcus aureus was studied in three Birmingham hospitals. In a general hospital periodic surveys showed a progressive decline in the proportions of patients with Staph. aureus in their noses which were resistant to tetracycline, erythromycin, and kanamycin. This change was associated with a progressive reduction in the use of tetracycline without an overall reduction in the use of antibiotics. There was no similar decline in resistance of staphylococci isolated in a hospital for skin diseases. In a burns unit there was a sudden large reduction during September, 1978, in the proportions of Staph, aureus from burns which were resistant to tetracycline, methicillin, cephaloridine, erythromycin, lincomycin, novobiocin, gentamicin, and kanamycin, and in the proportions of multiresistant strains (resistant to penicillin, tetracycline, erythromycin, kanamycin, methicillin, novobiocin, cephaloridine, and lincomycin). This change was associated with a reduction in the number of patients and in the use of antibiotics; tetracycline was not in use except during one month of the study. Strains of Staph. aureus resistant to these antibiotics became common again in the burns unit when a larger number of patients were admitted and more antibiotics were used in the wards.

Gentamicin- and silver-resistant pseudomonas in a burns unit

In 1977-8 gentamicin-resistant strains of Pseudomonas aeruginosa became very common in a burns unit, over 90% being resistant at the peak of the outbreak. Some strains were also resistant to silver nitrate, though silver resistance was not found in any other strains of Ps aeruginosa isolated. Unlike the gentamicin resistance, the silver resistance was unstable, and strains became sensitive on repeated subculture. All the gentamicin-resistant strains of Ps aeruginosa were of the same serotype (O:11, H:2,5). Though gentamicin resistance could be transferred in vitro from resistant strains of Ps aeruginosa to one sensitive strain of Ps aeruginosa, there was no evidence of in-vivo transfer of gentamicin resistance between strains of pseudomonas in the patients' burns, nor was there evidence of transfer of gentamicin resistance between Ps aeruginosa and enterobacteria. Carbenicillin-resistant and gentamicin-resistant Ps aeruginosa were sometimes found in the same burns, but no gentamicin-carbenicillin (doubly) resistant strains were found among the 986 strains tested during the outbreak. The outbreak of gentamicin-resistant Ps aeruginosa from burns was not reduced by stopping treatment with gentamicin and its analogues but only by segregating all patients with Ps aeruginosa in one of the two wards of the unit and admitting new patients only to the other ward.

Low mortality in burned patients in a Pseudomonas vaccine trial

In a controlled clinical trial of a polyvalent pseudomonas vaccine in burned patients infected with Pseudomonas aeruginosa all 18 vaccinated patients survived, whereas 8 of 20 unvaccinated patients died.

Distribution of R plasmids among the O-antigen types of Escherichia coli isolated from human and animal sources

The O-antigen types of 600 independently isolated Escherichia coli strains from human feces have been determined, and the types have been related to the antibiotic resistance patterns of the strains. The relative abundance of each O-antigen type differed in the susceptible and resistant series of strains. The majority (86%) of the resistant strains carried R plasmids. Resistant E. coli (20.3%) were found associated with O-antigen types 8, 9 and 101, whereas the susceptible strains covered a wide range of O-antigen types. Examination of 174 resistant strains isolated from calf feces also showed a prevalence of O-antigen types 8, 9, 101 (24.1%), and it seems probable that strains expressing these three O-antigen types commonly carry R plasmids in the alimentary tracts of man and calves. The number of strains not typeable with the O sera available were similar in the human (12.5%) and the calf (11.5%) series. There are no grounds for distinguishing "human" from "calf" E. coli on the basis of their O-antigen reactions.

Detection of endotoxins with the Limulus test in burned and unburned mice infected with different species of gram-negative bacteria

The Limulus test detected endotoxins in the plasma of burned and unburned mice infected with different species of gram-negative bacteria produced different amounts of endotoxin in the plasma of infected mice. Plasma from mice given lethal infections showed very high concentrations of endotoxin. Low concentrations of endotoxin in the plasma were tolerated by mice but high concentrations were invariably fatal. A polyvalent pseudomonas vaccine reduced endotoxin in the plasma of mice given lethal infections of Pseudomonas aeruginosa.

Properties of silver sulfadiazine-resistant Enterobacter cloacae

Two silver sulfadiazine-resistant isolates of Enterobacter cloacae obtained in a burns unit where the drug was in use were studied. These strains were resistant to elevated levels of the drug, and they were cross-resistant to silver benzoate, but not to silver nitrate. Growth of the strains in nutritionally poor defined media sensitized them to the inhibitory action of the drug. Exposure of the bacteria to penicillins rendered them susceptible to silver sulfadiazine. The resistant bacteria harbored episomes for resistance to carbenicillin and kanamycin; however, resistance to silver sulfadiazine could not be transferred by these episomes. Twenty-three strains of E. cloacae isolated in a general hospital were sensitive to much lower levels of the drug (</=50 mug/ml).

Silver sulfadiazine: in vitro antibacterial activity

Isolates (657) representing 22 bacterial species were tested for susceptibility to silver sulfadiazine. All of the strains tested were inhibited by concentration levels of the drug which are easily achieved topically. It is suggested that silver sulfadiazine may be useful as a broad-spectrum antimicrobial substance for the prevention and treatment of infections of burns and wounds.

Molecular characterization of the R factors implicated in the carbenicillin resistance of a sequence of Pseudomonas aeruginosa strains isolated from burns

An outbreak of R-factor-mediated carbenicillin resistance in Pseudomonas aeruginosa in burned patients in March 1969 was followed by a second outbreak 6 months later. No R-factor-carrying P. aeruginosa strains were detected in the intervening period but R-factor-determined lactamase was commonly encountered, particularly in Klebsiella aerogenes strains. A comparison of the molecular properties of the R factors in pseudomonads from the first and second phases with those in the Klebsiella strains from the intervening period showed them to be very closely related. A single R-factor type therefore may have been maintained in the Burns Unit between the two Pseudomonas outbreaks as a plasmid conferring resistance to ampicillin in K. aerogenes.

Changes in antibiotic sensitivity patterns of Gram-negative bacilli in burns

Sensitivity tests with 12 antibiotics on 1,018 strains of Gram-negative bacilli isolated in a burns unit between 1969 and 1971 showed some important differences from results in similar tests on a series of strains isolated between 1965 and 1967. These changes included the emergence of a large proportion of kanamycin-resistant strains of Klebsiella aerogenes, Proteus mirabilis, and Escherichia coli and of smaller proportions of trimethoprim- and gentamicin-resistant strains; also the complete replacement of Proteus mirabilis with dissociated resistance to ampicillin by strains showing linked resistance to ampicillin and carbenicillin. The probable relationship of these changes to the emergence of an R factor determining resistance to tetracycline, kanamycin, carbenicillin, ampicillin, and cephaloridine in Enterobacteria and Pseudomonas aeruginosa is discussed.

Protective isolation in a burns unit: the use of plastic isolators and air curtains

The use of plastic isolators and of an ;air curtain' isolator for protection of patients against infection was studied in a burns unit.Preliminary bacteriological tests showed that very few airborne bacteria gained access to a plastic ventilated isolator; even when the filter and pre-filter were removed from the air inflow, settle-plate counts inside the isolator were much lower than those in the open ward, but the difference was smaller in tests made with an Anderson air sampler, which showed also that fewer large bacteria-carrying particles appeared inside the isolator than outside it. An open-topped isolator allowed virtually free access of bacteria from ambient air. The numbers of airborne bacteria inside an air curtain were appreciably lower than the counts of airborne bacteria in the open ward, but not as low as those in the plastic ventilated isolator.Controlled trials of isolators were made on patients with fresh burns of 4-30% of the body surface; the patients were given no topical chemoprophylaxis against Staphylococcus aureus or Gram-negative bacilli. Patients treated in plastic isolators showed a significantly lower incidence of infection with Pseudomonas aeruginosa than those treated in the open ward; this protective effect was shown by isolators with or without filters or with an open top. Ventilated isolators, which protected patients against personal contact and airborne infection, gave a limited protection against multi-resistant ;hospital' strains of Staph. aureus, but no such protection was given by an open-topped isolator, which protected only against personal contact infection, or by air curtains, which protected only against airborne infection; the air curtain gave no protection against Ps. aeruginosa, and there was no evidence of protection by any isolator against Proteus spp. and coliform bacilli.Both the controlled trials and evidence from the bacteriology of air, hands, fomites and rectal and nasal swabs taken on admission and later, supported the view that Ps. aeruginosa is transferred mainly by personal contact, Staph. aureus probably by air as well as by contact and coliform bacilli mainly by self infection with faecal flora, many of which are first acquired from the hospital environment in food or on fomites.The use of plastic isolators is cumbersome, and of limited value except in the control of infection with Ps. aeruginosa. For this reason and because of the effectiveness of topical chemoprophylaxis such isolators are unlikely to have more than an occasional use in the treatment of burns. Though air curtains greatly reduce airborne contamination, their use in a burns unit does not appear to protect patients against infection when the alternative (and, for Ps. aeruginosa, more important) routes of contamination by personal contact and fomites are left open.