ANTIBIOTIC SUSCEPTIBILITY PROFILE OF BACTERIAL PATHOGENS ISOLATED FROM MALABOR HOSTEL TAP WATER, CALABAR- NIGERIA

The antibiotic resistance and susceptibility profiles of some bacterial isolates including Listeria monocytogenes, Erwiniastewartii, Legionella pneumophilia, Carnobacteriumgallinarum, Staphylococcus caseolyticus, Enterobacter dissolves, Pseudomonas mallei, Klebsiella pneumonia, Aeromonas media and Lactobacillus sp. were determined using some broad and narrow spectrum antibioticsby the disk diffusion technique. Based on the Clinical and Laboratory Standards Institute (CLSI) interpretive criteria, some isolates were found to be resistant to some of the tested antibiotics but susceptible to others. Among the Gram-positive bacterial isolates, Lactobacillus specie had the highest susceptibility profile with the zone of clearance ranging from 28 30 ± 8 mm in diameter. However, among the Gram-negative bacterial isolates,Pseudomonas mallei, Klebsiellapneumoniae and Aeromonas media were susceptible to all tested antibiotics, with 30mm ± 0 mm zones of clearance.CLSI standards were used to interpret results; while Lactobacillus sp. was the most susceptible isolate, whileErwiniastewartii was resistant to all the test antibiotics except ceporex.


INTRODUCTION
Antibiotics, also known as antibacterials are chemotherapeutic agents that majorly control the growth of bacteria, by bactericidal or bacteriostatic means. They are classified majorly based on their structure, spectrum of activity, route of administration, mode and mechanism of action. Understanding how these antibiotics induce their action is centered on the essential cellular function inhibited when they interact with bacterial cell. These specific antibacterialcellular function interactions are termed drugtarget interactions. Antibiotic susceptibility of bacteria is to a large extent dependent on the spectrum of activity, the mode and mechanism of action of the antibiotics. According to Neonakis . (2003), resistance to aminoglycoside antibiotics such as amikacin by members of the Enterobacteriaceae family is usually due to an aminoglycosidemodifying enzymes-aminoglycoside 6'-Nacetyltransferases which modifies amikacin, tobramycin, kanamycin and netilmicin but not gentamicin. Bacterial spectrum is the number of bacteria a broad-spectrum or narrow-spectrum antibiotic is effective against. Broad-spectrum antibiotics are effective against a broad range of microorganisms (Gram-negative and Gramnegative bacteria), whereas narrow-spectrum antibiotics treat few infections caused especially either by Gram-negative or Gram-negative bacteria. Antibiotics are either bactericidal or bacteriostatic in terms of their mode (how they induce) action. Generally, bactericidal antibiotics completely destroy bacterial cell walls or other cell organelles. Examples may include penicillins, fluoroquinolones, daptomycin, metronidazole, nitrofurantoin and co-trimoxazole. Bacteriostatic antibiotics stop bacterial proliferation and multiplication by interfering with bacterial protein synthesis, DNA replication or any other aspect of bacterial cell metabolism.
Examples may include tetracyclines, macrolides, lincosamides, sulphonamides, trimethoprim, streptomycin and chloramphenicol. Antibiotic activities based on mechanisms of action are group into inhibitors of cell wall synthesis. This group is further divided into inhibitors of peptidoglycan synthesis including bacitracin and cycloserine, and inhibitors of peptidoglycan cross-linking like vancomycin and b-lactams as penicillins and cephalosporins (Joanne ., 2013).

MATERIALS AND METHOD
Antibiotic susceptibility and resistancestudy for Gram-positive and Gram-negative bacterial isolates obtained from Malabor tap water was carried out by the discs diffusion method using Mueller Hinton agar (MHA). The isolates were uniformly streaked on aseptically prepared and solidified MHA on duplicated petri dishes for each identified isolate. The choice of antibiotics was based on the Gram reaction of the isolates and the mechanisms of action of the antibiotics.The antibiotic discs were placed on the duplicate MHA plates for each of the isolates and incubated at 37 o C for 24hours.
By disk diffusion technique, the diameter of the zones of complete inhibition (as judged by the unaided eye), including the diameter of the disk were measured. The Petri plate was held a few inches above a black, nonreflecting background illuminated with reflected light. The zone margins were considered: area showing no obvious, visible growth as detected with the unaided eye. However,faint growth of tiny colonies that can be detectedonly with a magnifying lens at the edge of the zone of inhibited growth were ignored (CLSI, 2016).

RESULTS AND DISCUSSION
The antibiotic susceptibility/resistance for the Gram-positive bacteria was determined usingstreptomycin, ciproflox, gentamicin, amoxil, ampiclox, chloramphenicol, erythromycin, levofloxacin, norfloxacin, rifampicin while that of the Gram-negative bacteria was determined using streptomycin, gentamicin, ciproflox, augmentin, ceporex, nalidixic acid, tarivid, reflacine, ampicillin and septrin. Results were calculated according to the zones of clearing observed in mm ± standard deviation within the antibiotics for the individual bacterial isolates.Tables 1 and 2 below show raw results ± standard deviation.

Gram-positive Antibiotic Susceptibility and Resistance
In terms of Gram-positive bacterial isolates, there was significant difference in the mean antibiotic susceptibility within Grampositive bacterial isolates, at 95% confidence interval, hence Fcal. (9.7) is greater than Fcrit. (3.6). Similarly, there was a significant difference in the mean antibiotic sensitivity of test antibiotics at 95% confidence interval with Fcal. (4.7) being greater than Fcrit. (2.6). Interpreting, using the Clinical and Laboratory Standards Institute (CLSI, 2016), all the Gram-positive bacterial isolates were susceptible to levofloxacin, a narrow-spectrum Grampositive antibiotic while majority of the isolates were resistant to streptomycin-a broad-spectrum antibiotic. Results also show that Lactobacillus specie isolated from Hall9 tap water in the Malabor hostel was susceptible to almost all the tested broadspectrum and Gram-positive antibiotics.

Gram-negative Antibiotic Susceptibility and Resistance
There was significant difference in the mean antibiotic susceptibility within  According to WHO (2006), the spectrum of organisms detected by HPC testing includes organisms sensitive to disinfection processes, such as coliform bacteria; organisms resistant to disinfection, such as spore formers; and organisms that rapidly

Zone of Clarence (mm)
proliferate in treated water in the absence of residual disinfectants.Some drinking-water treatment processes, such as coagulation and sedimentation, reduce the number of HPC organisms in water. However, the numbers of HPC organisms are reduced significantly by disinfection practices, such as chlorination, ozonation and UV light irradiation. In practice, none of the disinfection processes sterilizes water while under suitable conditions such as the absence of disinfectant residuals, HPC organisms can grow rapidly. In distribution systems, a high HPC number can indicate deterioration in cleanliness, possibly stagnation and the potential development of biofilms (WHO, 2006). Moreover, new macrolide antibiotics, such as clarithromycin and azithromycin, show more effective in-vitro activity and have better intracellular and tissue penetration than erythromycin, as do the quinolones. Table 3 below shows CLSI standards for antibiotic susceptibility test.

Resistant
All Gram positive isolates were susceptive to levofloxacin even though it does not sustain a CSLI standard, but the zone of inhibition is quit fascinating. Lactobacillussp was susceptible to all the test antibiotics but not streptomycin. Staphylococcus spp. may develop resistance during prolonged therapy with quinolones. Therefore, isolates that are initially susceptible may become resistant within three to four days after initiation of therapy. Testing of repeat isolates may be warranted (CLSI, 2011). Majority of the gram negative bacterial isolatesiincludingLegionella, Enterobacter, Pseudomonas, Klebsiella and Aeromonas spp. were susceptible to ciproflox and streptomycin, while Erwinia sp. is resistant all the relative test antibiotics. Also, ampicilin is not a drug of of choice for the gram negative spp especially members of the Enterobacteriaceae family. According to CLSI (2011), members of the family Enterobacteriaceae are susceptible to trimethoprim, a sulphonamide and ceftolozane, a cephalosporin and blactamase-inhibitor combination. This is evident in the like Klebsiellasp, Pseudomonas sp, Enterobactersp, Erwiniasp. Usually, quinolones (like ciproflox) are synergistic with β-lactams (like ampicilin) and aminoglycosides (Catherine et al., 2002). Similarly, urinary tract infections are often treated with different broad-spectrum antibiotics even when one with a narrow spectrum of activity may be appropriate because of concerns about infection with resistant organisms (Yakubuet al., 2010). Fluoroquinolones are preferred as initial agents for empiric therapy of UTI in areas where resistance is likely to be of concern (Biswaset al., 2006;Schaeffer, 2002) this is evident in all Gram negative isolates except for Legionella and Erwinia spp. This is because they have high bacteriological and clinical cure rates, as well as low rates of resistance among most common uropathogens (Tankhiwaleet al., 2004). Antibiotics have proven an effective weapon against bacterial contamination and infection. However, the presence of multiple drug resistant microorganisms will compromise our ability in treating infections caused by such pathogens. Thus, the isolation of Erwiniasp from the tap water stands as a major public health threat to people using the water as drinking water source. This corroborates the report by Bashir et al. (2014) thatmultiple antibiotic resistant bacteria living in various drinkingwater sources suggests that contaminated water may be a primary source of severe infectious diseases and according to Mmuoegbulamet al. (2016), enteopathogenic bacteria when not treated, are not only enterotoxigenic but also induce some histological changes.The emergence of bacteria resistant to most of the commonly used antibiotics is of considerable medical significance, because of public health implications; hence the prevalence of drug resistant organisms poses a great challenge to clinicians and the consumption of water containing these antibiotic resistant organisms mayprolong the treatment of water borne pathogens, thus bringing about the need for a new and more expensive antibiotics (Tagoeet al.(2011).

CONCLUSION
There is need to treat the Malabor tap water so as to reduce the coliform count to zero (0) as required by the water quality standards. However, such pathogens when present (even after water treatment) are susceptible to some broad and narrow spectrum antibiotics except for Erwiniastewartii which was susceptible to ceporex alone.

NOTE:
The "resistant" category of antibiotics confirms that isolates are not inhibited by the usually achievable concentrations of the agent with normal dosage schedules, and/or that demonstrate MICs or zone diameters that fall in the range where specific microbial resistance mechanisms (eg, β-lactamases) are likely, and clinical efficacy of the agent against the isolate has not been reliably shown in treatment studies.