Acinetobacter baumannii is a non-fermenting gram-negative bacillus that is widely found in nature and is a conditionally pathogenic bacterium. It is an important pathogen of hospital infections, mainly causing respiratory tract infections, but also bacteremia, urinary tract infections, secondary meningitis, surgical site infections, ventilator-associated pneumonia, etc. The rate of resistance to commonly used antibiotics has been increasing year by year and has caused serious concern among clinicians and microbiologists. Jie Shenghua, Department of Infection, Wuhan Union Medical College Hospital
The data show that A. baumannii accounts for more than 70% of the clinical isolates of A. baumannii. The resistance rate of A. baumannii to the third and fourth generation cephalosporins has reached 63.0%-89.9%. The resistance rate to four aminoglycosides (amikacin, gentamicin, netilmicin, tobramycin) and ciprofloxacin reached 96.3%. The majority of our current strains remain sensitive to imipenem, meropenem, cefapenem/sulbactam and polymyxin B, but are less effective in the treatment of respiratory tract infections.
Distribution
Acinetobacter baumannii is the most common Gram-negative bacillus in the genus Acinetobacter and is widely found in water and soil in nature, in the hospital environment and in the human skin, respiratory tract, gastrointestinal tract and genitourinary tract as a conditional pathogen. It is widely distributed in the hospital environment and can survive for a long time. It is very easy to cause infection in critical patients, so it is often isolated from specimens such as blood, urine, pus and respiratory secretions of infected patients, and is second only to Pseudomonas aeruginosa among non-fermentative bacteria. The results of this survey showed that 138 strains of Acinetobacter baumannii were most frequently detected in sputum and bronchial aspirate specimens, followed by pus and secretions.
The departmental distribution was most frequent in ICU, followed by patients in respiratory medicine. Infected patients are mostly elderly patients, patients with critical diseases and weak organism resistance, and patients treated with various invasive operations and long-term use of broad-spectrum antibiotics. Because the bacterium is highly resistant to moist heat ultraviolet light and chemical disinfectants, conventional disinfection can only inhibit its growth but not kill it, and patients with weak resistance or trauma may have more chances to be infected by bacteria carried from medical staff’s hands or incompletely disinfected medical devices.
From the origin of 72 strains of A. baumannii, their infection sites are widely distributed, such as the respiratory system, urinary system, wounds, abdominal cavity and nervous system. Among them, respiratory system infections accounted for the majority (54.2%). Bacillus is a genus with a high rate of hospital-acquired infections in recent years, among which infections caused by Acinetobacter baumannii should be taken seriously.
Pathogen
The genus Acinetobacter (Acinetobacter spp.) is divided into six species, namely, Acinetobacter calcoaceticus (A. calcoaceticus), Acinetobacter lwoffi (A. lwoffi), Acinetobacter baumanii (A. baumanii), Acinetobacter haemolytius (A. haemolytius), Acinetobacter agalactiae (A. junii) and A. johnsonii.
Epidemiology
A. immobilis is widely distributed in the external environment, mainly in water bodies and soil, and easily survives in moist environments, such as bath tubs and soap boxes. The bacterium is extremely adherent and easily adheres to all types of medical materials, and may become a source of storage. In addition, the bacterium also exists in the skin (25%), pharynx (7%), also in the conjunctiva, saliva, gastrointestinal tract and vaginal secretions of healthy people.
The source of infection can be the patient himself (endogenous infection) or a person infected with B. immortalis or a carrier, especially medical personnel with bacteria on their hands. Transmission can occur by contact and airborne transmission. In hospitals, contaminated medical equipment and staff hands are important vectors of transmission. Susceptible individuals are elderly patients, premature and newborn infants, those with surgical trauma, severe burns, tracheotomy or intubation, use of artificial ventilators, intravenous catheters and peritoneal dialysis, and those on broad-spectrum antibacterial drugs or immunosuppressive agents. The incidence of pneumonia is about 3-5% in those who use ventilators.
Clinical manifestations
1. Pulmonary infection As far as the source of infection is concerned, there are both exogenous and endogenous infections. Inhalation of oropharyngeal organisms is likely to be the main pathogenesis of endogenous infections. Fever, cough, chest pain, shortness of breath and bloody sputum are often present. The lungs may be characterized by fine woven 7-tailed pit emaciated 3-hand pneumonia, or large lobar or lamellar infiltrative shadows, occasionally with lung abscess and exudative pleurisy manifestations.
2, wound and skin infections surgical incisions, burns and traumatic wounds are susceptible to secondary inactivated bacillus skin infections, or mixed infections with other bacteria. Clinical features are not significantly different from other bacterial infections. Mostly no fever. Occasionally, it can be manifested as cellulitis.
3, genitourinary system infection Bacteroides immobilis can cause pyelonephritis, cystitis, urethritis, vaginitis, etc. It can also present asymptomatic bacteriuria, but clinically it can not be distinguished from other bacterial infections, the cause is mostly indwelling catheterization, cystostomy.
4, bacteraemia Bacteraemia is the most serious clinical type of Bacillus immobilis infection, the morbidity and mortality rate of more than 30%. Mostly secondary to other sites of infection or after intravenous catheterization, a few primary after infusion, including infusion of antibiotics, corticosteroids, anti-tumor drugs, etc.. There are fever, systemic toxicity, skin petechiae or petechiae, and hepatosplenomegaly, and in severe cases, infectious shock. A few can form plural bacteriophage bacteremia with other bacteria.
5, meningitis Meningitis mostly occurs after cranial surgery. There are manifestations of septic meningitis such as fever, headache, vomiting, neck tonicity, positive Kellogg’s sign. Laboratory:Normal or increased total white blood cell count and increased neutrophil count. Sputum specimens obtained by anti-pollution sampling techniques have greater diagnostic value. Sputum smear finding gram-negative cocci can be an important clue for diagnosis.
Strain identification
Biochemical identification was performed mainly based on the API-20NE system, supplemented by the necessary five tests. The results showed that all four immobile bacilli conformed to the general traits of the genus Immobileobacterium: oxidase negative, catalase positive, non-motile, indole negative, non-fermenting sugars, and non-nitrate reducing. In the API-20NE system, the percent identification (%id) of 72 strains of A. baumannii was ≥99.0%; the %id of 15 strains of Calcium acetate was ≥99.0%; the %id of 3 strains of Agrobacterium was between 95.0% and 99.9%, with an average of 98.3%; the %id of 6 strains of A. loftii was between 97.0% and 99.9%, with an average of 99.4%.
Treatment
The treatment of A. baumannii infection has been a great clinical problem because A. baumannii is highly resistant to various disinfectants and antimicrobial drugs, which is a great threat to patients in intensive care and ICU wards, etc. The widespread spread of MDR-AB (multi-drug resistant A. baumannii), PDR-AB (pan-drug resistant A. baumannii), CRAB (carbapenem-resistant A. baumannii), etc. has become a major problem for doctors and patients. Widespread transmission has become a nightmare for physicians and patients.
Among nosocomial infections, a high proportion of infections of the genus Immunobacterium are found, and the majority of strains of the genus Immunobacterium extracted in the hospital are A. baumannii. A. baumannii is a Gram-negative bacterium, so it has inherent resistance to vancomycin, etc. It also maintains a high rate of resistance to penicillin G, ampicillin, amoxicillin, chloramphenicol, tetracycline, and first and second generation cephalosporins. Usually, the drugs with strong effects on A. baumannii mainly include penicillins against P. aeruginosa, third and fourth generation cephalosporins (mainly ceftazidime, cefepime, etc.), carbapenems, β-lactam antibiotic combinations (cefoperazone/sulbactam, piperacillin/tazobactam, etc.), fluoroquinolones, aminoglycosides, tigecycline, polymyxin, sulbactam, etc. However, because of the abuse of antimicrobial drugs in recent years, the resistance rate of A. baumannii to the above drugs is also increasing, and the resistance rate of fluoroquinolones and aminoglycosides is very high, and the resistance rate of carbapenems has also increased.
Considering that A. baumannii is highly susceptible to antibacterial drug resistance, the combination of drugs should be used. Commonly used regimens are β-lactams + fluoroquinolones, β-lactams + aminoglycosides, etc. My personal preferred regimen is cefoperazone/sulbactam + fosfomycin (time difference attack therapy), and also ampicillin/sulbactam + ciprofloxacin, etc.).
Research progress
With the rapid development of medical technology, the level of treatment of diseases, especially critical diseases, has been improving, and the extensive use of broad-spectrum antibiotics is one of its important tools. However, the abuse of antibiotics in clinical treatment is very common, and under the strong pressure of antibiotics, a large number of drug-resistant strains are inevitably produced, and these drug-resistant strains have become a thorny problem of contemporary hospital infections. The results from our data show that the resistance rate of A. baumannii to subamphetamine and meropenem is relatively low, because of the strong affinity of carbapenems for penicillin-binding protein (PBPS).
However, a small proportion of A. baumannii is still resistant to them, probably because they can produce a β-lactamase ARI-I that can hydrolyze carbapenems, which is certainly a terrible signal. Moreover, it is related to the different chemical structures of cefoperazone/sulbactam or the different forms of expression of multi-drug resistance in Acinetobacter baumannii. And the resistance rate to quinolone antibiotics is more than 60%, which may be due to the widespread use of quinolones in recent years causing antimicrobial drug-mediated resistance gene mutations, and mutations in the gyra or gyrb genes encoding DNA rotamases are thought to be the main cause of bacterial resistance. In addition, the resistance rates of all aminoglycoside antibiotics are high, which may be the result of the resistance that emerged from the common application of this class of antibiotics in our hospital, causing great difficulties in clinical treatment; therefore, attention should be paid to the rational application of all types of antibiotics.
The test results showed that the majority (75.0%) of clinical immobile bacilli infections were Acinetobacter baumannii, followed by Acinetobacter calcoaceticus, Acinetobacter lofebrium and Acinetobacter agalactiae, which were inconsistent with the relevant reports, probably due to the more confusing naming of the genus immobile bacilli and the different classification principles and identification systems. In the identification of four kinds of immobile bacilli, 41 ℃ culture when growing, malate assimilation test positive, can be initially identified as A. baumannii and agrobacterium, the difference between the former benzene acetate assimilation test positive, and oxidation of xylose, while the latter does not oxidize xylose, and benzene acetate assimilation test negative. 41 ℃ culture when not growing, decanoate assimilation test positive, can be initially identified as calcium acetate immobile bacilli The difference between the two was that the former was positive for citrate and phenylacetate assimilation test, while the latter was negative.
From the origin of the 72 strains of A. baumannii, their infection sites were widely distributed, such as the respiratory system, urinary system, wounds, abdominal cavity and nervous system. Among them, respiratory system infection accounted for the majority (54.2%). Immunobacterium is the genus with a high rate of hospital-acquired infections in recent years, among which infections caused by Acinetobacter baumannii should be taken seriously.
Drug susceptibility monitoring of 12 antimicrobial drugs from 2001 to 2005 showed that the resistance rate of 12 drugs to A. baumannii showed an overall increasing trend, and the resistance rate of IMP, which had the lowest resistance rate, increased from 6.5% in 2001 to 31.7% in 2005, and the resistance rate of cephalosporins (CAZ, CFP, FEP) increased from 20.0%, 38.6%, 31.5 The resistance rates of cephalosporins (CAZ, CFP, FEP) increased from 20.0%, 38.6% and 31.5% in 2001 to 66.7%, 72.4% and 67.7% in 2005; the resistance rates of PIP, SXT, ATM, CIP, TZP and LEV also increased from 19.6% to 60.2% in 2001 to 52.2% to 72.1% in 2005; the resistance rates of TOB and GEN decreased, and their resistance rates increased from The resistance rates of TOB and GEN decreased from 62.8% and 63.6% in 2001 to 48.2% and 45.2% in 2005, which may be related to the infrequent use of these drugs in clinical practice. As seen in Table 3, the resistance rates of 12 drugs in ICU were significantly higher than those in non-ICU, and the difference was very significant (P<0.01). The lower resistance rates in ICU were imp and tzp, with resistance rates of 41.7% and 53.3%, respectively, except for the resistance rates of the rest of antibiotics, which were above 70.0%. This is a very serious and multi-drug resistant phenomenon. This is related to the production of multiple enzymes by A. baumannii: resistance to cephalosporins is mainly related to the production of ultra-broad-spectrum β-lactamases; resistance to imipenem is mainly related to the production of metallo-β-lactamases; resistance to quinolones is mainly related to gyra and parc gene mutations. < span="">
In summary, given the trend of further increase in drug resistance of A. baumannii in recent years, this should be of great concern to clinicians and the microbiology community. In order to reduce the occurrence of hospital-acquired infections and the emergence of multi-drug resistant strains of this organism, we should strictly and thoroughly disinfect medical devices and conduct standardized continuous monitoring of A. baumannii to clarify its drug resistance mechanism and monitor its drug resistance status in a timely manner. At the same time, clinicians should pay attention to acquired A. baumannii infections and work closely with clinical microbiology laboratories to strengthen the monitoring of drug resistance to effectively prevent and control infections.
Acinetobacter baumannii may be a prelude to a pandemic of “superbugs” in Japan
The multi-drug resistant “superbug” is now showing signs of expanding infection in Japan. Following the incident at the beginning of the month in which the Teikyo University School of Medicine Hospital allegedly underreported a mass infection of “superbugs” among inpatients, a new type of “superbug” was detected at Dokkyo Medical University Hospital in Tochigi Prefecture. The Japanese government decided on the 7th to require all medical institutions nationwide to report cases of infection as soon as they are discovered, and to launch a nationwide investigation into the status of the new “superbug” infection within a week.
The Japanese government has discovered a massive bacterial infection at Teikyo University Medical School Hospital in Tokyo, Japan. The bacterium is called “multi-drug resistant Acinetobacter baumannii”, which does not have much effect on healthy people, but if people with low immunity are infected with this bacterium, it can cause complications such as pneumonia, sepsis, and even death. ” can resist almost all antibiotics.
The first case of infection was reported at Teikyo University Medical School Hospital as early as August last year, however, this hospital reported the infection to the authorities on the 2nd of this month. By the first of this month, the number of infected people had risen to 46, of whom 27 had died, and of the dead, nine were confirmed to have died of infection. In response to the massive bacterial infection at Teikyo University Medical School Hospital, the Japanese Ministry of Health, Labour and Welfare set up a special emergency response team on the 5th and launched an on-site investigation on the 6th into the adequacy of Teikyo University Medical School Hospital’s epidemic prevention system. The investigation found that although the hospital received a notification from the Japanese government in January last year to report cases of infection, all medical staff at the hospital were unaware of it and there were problems with the communication mechanism.
According to the report, eight more cases of infection were reported on the 7th at Arin Hospital in Setagaya-ku, Tokyo, and the cause of death of two of the deceased was suspected to be related to bacterial infection. After investigation, it was found that the first infected patient who appeared at Teikyo University Medical School Hospital last year did not have experience abroad and the route of infection could have come from within the country. As a result, Japanese experts have warned that the spread of A. baumannii may have begun nationwide, possibly as a prelude to a pandemic of the “superbug” in Japan. The government should strengthen its surveillance system and do its best to prevent the spread of infection.
Following the massive bacterial infection at Teikyo University Medical School Hospital, a new type of “superbug” was detected at Dokkyo Medical University Hospital in Tochigi Prefecture on June 6. The bacterium is an E. coli with the NDM-1 gene and is resistant to almost all antibiotics with the NDM-1 gene. If an immunocompromised patient is infected with this bacterium, it may spread throughout the body, resulting in complications such as sepsis and even death. The gene is highly contagious, and because E. coli is widely present in everyday life, it is also highly likely to spread among ordinary healthy people. This is the first time that a “superbug” carrying the NDM-1 gene has been found in Japan.
The emergence of the “superbug” in Japan has caused the government to pay great attention to it. Experts say that because the new “superbug” is highly resistant to drugs and infectious, there is a possibility that the drug-resistant gene will be transferred from E. coli to other types of bacteria, making other bacteria resistant to drugs as well. If the “superbug” gene transfer to Salmonella or dysentery bacillus and other dangerous bacteria, the consequences will be unthinkable.
Japanese Minister of Health, Labour and Welfare Akira Nagatsuma told the media after a cabinet meeting on the 7th that the Japanese government will investigate hospitals nationwide. Although large hospitals in Japan have the ability to analyze bacteria on their own, the Japanese Ministry of Health, Labour and Welfare requires all hospitals nationwide to immediately submit to the National Institute of Infectious Diseases for testing once multi-drug resistant bacteria are found. In addition, the Japanese government will set up a working group composed of infectious disease experts to discuss specific prevention and control measures.