Non fermentative Gram negative bacilli infections in a tertiary care rural hospital

The non fermentative Gram negative bacilli (NF GNB) are aerobic and non spore forming microorganisms. They do not utilize carbohydrates or breakdown them through oxidative metabolic pathway. Previously NF GNB were considered to be non pathogenic and of very little significance. Recently, rate of infection by NF GNB is rising, especially in hospitalized and immunocompromised patients. NF GNB infection constitutes about one – fifth of all Gram negative bacilli infections. These organisms can remain viable on medical devices and are resistant to many commonly used antibiotics. Therefore, they play an important role in hospital acquired infection. Although, rate of isolation of NF GNB from clinical specimens is increasing rapidly, very few laboratories in India identify these organisms routinely. Sometimes, NF – GNB is difficult to identify phenotypically. Most of them are multidrug resistant (MDR).1 Malini et al2 from Karnataka, India observed 4.5 % infection rate of NF GNB in their hospital.


Introduction
The non fermentative Gram negative bacilli (NF GNB) are aerobic and non spore forming microorganisms. They do not utilize carbohydrates or breakdown them through oxidative metabolic pathway. Previously NF GNB were considered to be non pathogenic and of very little significance. Recently, rate of infection by NF GNB is rising, especially in hospitalized and immunocompromised patients. NF GNB infection constitutes about one -fifth of all Gram negative bacilli infections. These organisms can remain viable on medical devices and are resistant to many commonly used antibiotics. Therefore, they play an important role in hospital acquired infection. Although, rate of isolation of NF GNB from clinical specimens is increasing rapidly, very few laboratories in India identify these organisms routinely. Sometimes, NF -GNB is difficult to identify phenotypically. Most of them are multidrug resistant (MDR). 1 Malini et al 2 from Karnataka, India observed 4.5 % infection rate of NF GNB in their hospital.
The isolates from patient's specimens were also clinically correlated by discussion with attending physician and by retrospective reference of the patient's records. The symptoms and signs of infections, hematological and radiological findings and repeated isolation of same organisms from patient's specimens were considered in support of clinical significance.

Observations & Results
A total of 1498 specimens, such as, blood, urine, pus etc were processed in the microbiology laboratory over a period of one year. Out of which, 320 (21.36%) NF GNB were isolated and identified up to species level.

4.Discussion
NF GNB is rapidly emerging as important opportunistic pathogen, mainly in immunocompromised or hospitalized patients. These organisms are aerobic, non spore bearing and do not breakdown carbohydrates as a source of energy, other than fermentation. 5 They mainly cause hospital acquired infection. 6 Indiscriminate use of antibiotics play a major role in development of resistance to commonly used antibiotics. 7 Initial identification of NF GNB is done by absence of acid production in triple sugar iron (TSI) agar and no growth on MacConkey's agar. Major laboratory tests to identify NF GNB are -Gram stain, Hugh -Leifson's test, gelatin liquefaction, starch hydrolysis, urease production, nitrate reduction, indole test, hydrogen sulphide production, growth on 6.5% sodium chloride solution, pigment production, lysine decarboxylation and fermentation of glucose, lactose, maltose, Mannitol and xylose. 8,9 Over a period of one year, we isolated 320 (21.36%) NF GNB out of 1498 clinical specimens. The most common isolate was P aeruginosa, i.e., 192 (60%) and P species, 58 (18.12%) followed by A baumannii, 46(14.37%). Siou Cling Su et al 10 in their study, isolated approximately 15% NF GNB out of all Gram negative bacilli isolates. They did oligonucleotide array based test to identify NF GNB from clinical specimens and found that P. aeruginosa was the commonest isolate, followed by Acinetobacter species. Our study was also similar to the study done by Malini et al 2 , i.e., 53.8% P. aeruginosa and 22.2% A. baumannii isolates. Upgade et al 6 isolated 43% Pseudomonas species and 21% Acinetobacter species in their study.
We isolated maximum number of NF GNB from blood, i.e., 90(28.12%). Some other researchers isolated majority of non fermenters from pus and urine samples. 2 IJBR (2013) 04 (02) www.ssjournals.com Multidrug resistance was considered when the organism was resistant to 3 or more classes of antibiotics. 11 Antibiotic susceptibility pattern of NF GNB vary from country to country and from also different places within the same country. 12 All of our NF GNB isolates were MDR. NF GNB has got a tendency for inherent or acquired drug resistance to the commonly used antibiotics. 7 Upgade et al 6 observed 80% resistance of NF GNB to major antibiotics. Nicasio et al 13 reported increasing resistance of NF GNB to commonly used antibiotics, including carbapenems, cephalosporin, penicillin, fluoroquinolones and amino glycosides. They also observed that isolates were mostly sensitive to polymyxin B. Some researchers reported that to treat NF GNB infection, some old antibiotics with more side effects were again in use. 14 All our isolates were sensitive to polymyxin B, colistin and tigecycline. Colistin and polymyxin B has got side effects like renal toxicity (27 -58%). 15 Li et al 16 and Falaqas et al 17 also found usefulness of colistin and polymyxin B against MDR P. aeruginosa, A. baumannii and Klebsiella pneumoniae (K. pneumoniae) due to low resistance rate to this drug. They also advised judicious use of the antibiotics for infection caused by these 3 micro organisms.
Tigecycline (Gar 936) is a new glycopeptides derivative of tetracycline. It has a wide range of antibacterial activity, both against Gram positive and Gram negative bacteria. 18 However, reports regarding resistance to colistin and tigecycline have been observed by some workers. 19,20 NF GNB is ubiquitously distributed in the environment. Their isolation from patient's samples should be clinically correlated to avoid unnecessary administration of antibiotics and thereby preventing the development of MDR strains. We included those cases in our study, in which, there were repeated isolation of same organism from repeat samples. Other inclusion criteria were presence of pus cells along with Gram negative bacilli in the stained smear of the clinical samples, evidence of mono microbial infection from sterile body fluid and radiological or hematological reports supporting infection. Symptoms and signs indicating infection were also taken into consideration.

Conclusion
NF GNB infection is emerging rapidly as major pathogens in health care settings. All infections by NF GNB should be clinically correlated. NF GNB develops resistance to commonly used antibiotics very fast. All our isolates were sensitive to polymyxin B; colistin and tigecycline. Careful administration of antibiotics should be applied, because these organisms have a tendency to develop resistance.